0001 acpi= [HW,ACPI,X86,ARM64]
0002 Advanced Configuration and Power Interface
0003 Format: { force | on | off | strict | noirq | rsdt |
0004 copy_dsdt }
0005 force -- enable ACPI if default was off
0006 on -- enable ACPI but allow fallback to DT [arm64]
0007 off -- disable ACPI if default was on
0008 noirq -- do not use ACPI for IRQ routing
0009 strict -- Be less tolerant of platforms that are not
0010 strictly ACPI specification compliant.
0011 rsdt -- prefer RSDT over (default) XSDT
0012 copy_dsdt -- copy DSDT to memory
0013 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
0014 are available
0015
0016 See also Documentation/power/runtime_pm.rst, pci=noacpi
0017
0018 acpi_apic_instance= [ACPI, IOAPIC]
0019 Format: <int>
0020 2: use 2nd APIC table, if available
0021 1,0: use 1st APIC table
0022 default: 0
0023
0024 acpi_backlight= [HW,ACPI]
0025 { vendor | video | native | none }
0026 If set to vendor, prefer vendor-specific driver
0027 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
0028 of the ACPI video.ko driver.
0029 If set to video, use the ACPI video.ko driver.
0030 If set to native, use the device's native backlight mode.
0031 If set to none, disable the ACPI backlight interface.
0032
0033 acpi_force_32bit_fadt_addr
0034 force FADT to use 32 bit addresses rather than the
0035 64 bit X_* addresses. Some firmware have broken 64
0036 bit addresses for force ACPI ignore these and use
0037 the older legacy 32 bit addresses.
0038
0039 acpica_no_return_repair [HW, ACPI]
0040 Disable AML predefined validation mechanism
0041 This mechanism can repair the evaluation result to make
0042 the return objects more ACPI specification compliant.
0043 This option is useful for developers to identify the
0044 root cause of an AML interpreter issue when the issue
0045 has something to do with the repair mechanism.
0046
0047 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
0048 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
0049 Format: <int>
0050 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
0051 debug output. Bits in debug_layer correspond to a
0052 _COMPONENT in an ACPI source file, e.g.,
0053 #define _COMPONENT ACPI_EVENTS
0054 Bits in debug_level correspond to a level in
0055 ACPI_DEBUG_PRINT statements, e.g.,
0056 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
0057 The debug_level mask defaults to "info". See
0058 Documentation/firmware-guide/acpi/debug.rst for more information about
0059 debug layers and levels.
0060
0061 Enable processor driver info messages:
0062 acpi.debug_layer=0x20000000
0063 Enable AML "Debug" output, i.e., stores to the Debug
0064 object while interpreting AML:
0065 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
0066 Enable all messages related to ACPI hardware:
0067 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
0068
0069 Some values produce so much output that the system is
0070 unusable. The "log_buf_len" parameter may be useful
0071 if you need to capture more output.
0072
0073 acpi_enforce_resources= [ACPI]
0074 { strict | lax | no }
0075 Check for resource conflicts between native drivers
0076 and ACPI OperationRegions (SystemIO and SystemMemory
0077 only). IO ports and memory declared in ACPI might be
0078 used by the ACPI subsystem in arbitrary AML code and
0079 can interfere with legacy drivers.
0080 strict (default): access to resources claimed by ACPI
0081 is denied; legacy drivers trying to access reserved
0082 resources will fail to bind to device using them.
0083 lax: access to resources claimed by ACPI is allowed;
0084 legacy drivers trying to access reserved resources
0085 will bind successfully but a warning message is logged.
0086 no: ACPI OperationRegions are not marked as reserved,
0087 no further checks are performed.
0088
0089 acpi_force_table_verification [HW,ACPI]
0090 Enable table checksum verification during early stage.
0091 By default, this is disabled due to x86 early mapping
0092 size limitation.
0093
0094 acpi_irq_balance [HW,ACPI]
0095 ACPI will balance active IRQs
0096 default in APIC mode
0097
0098 acpi_irq_nobalance [HW,ACPI]
0099 ACPI will not move active IRQs (default)
0100 default in PIC mode
0101
0102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
0103 Format: <irq>,<irq>...
0104
0105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
0106 use by PCI
0107 Format: <irq>,<irq>...
0108
0109 acpi_mask_gpe= [HW,ACPI]
0110 Due to the existence of _Lxx/_Exx, some GPEs triggered
0111 by unsupported hardware/firmware features can result in
0112 GPE floodings that cannot be automatically disabled by
0113 the GPE dispatcher.
0114 This facility can be used to prevent such uncontrolled
0115 GPE floodings.
0116 Format: <byte> or <bitmap-list>
0117
0118 acpi_no_auto_serialize [HW,ACPI]
0119 Disable auto-serialization of AML methods
0120 AML control methods that contain the opcodes to create
0121 named objects will be marked as "Serialized" by the
0122 auto-serialization feature.
0123 This feature is enabled by default.
0124 This option allows to turn off the feature.
0125
0126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
0127 kernels.
0128
0129 acpi_no_static_ssdt [HW,ACPI]
0130 Disable installation of static SSDTs at early boot time
0131 By default, SSDTs contained in the RSDT/XSDT will be
0132 installed automatically and they will appear under
0133 /sys/firmware/acpi/tables.
0134 This option turns off this feature.
0135 Note that specifying this option does not affect
0136 dynamic table installation which will install SSDT
0137 tables to /sys/firmware/acpi/tables/dynamic.
0138
0139 acpi_no_watchdog [HW,ACPI,WDT]
0140 Ignore the ACPI-based watchdog interface (WDAT) and let
0141 a native driver control the watchdog device instead.
0142
0143 acpi_rsdp= [ACPI,EFI,KEXEC]
0144 Pass the RSDP address to the kernel, mostly used
0145 on machines running EFI runtime service to boot the
0146 second kernel for kdump.
0147
0148 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
0149 Format: To spoof as Windows 98: ="Microsoft Windows"
0150
0151 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
0152 of 2 which is mandated by ACPI 6) as the supported ACPI
0153 specification revision (when using this switch, it may
0154 be necessary to carry out a cold reboot _twice_ in a
0155 row to make it take effect on the platform firmware).
0156
0157 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
0158 acpi_osi="string1" # add string1
0159 acpi_osi="!string2" # remove string2
0160 acpi_osi=!* # remove all strings
0161 acpi_osi=! # disable all built-in OS vendor
0162 strings
0163 acpi_osi=!! # enable all built-in OS vendor
0164 strings
0165 acpi_osi= # disable all strings
0166
0167 'acpi_osi=!' can be used in combination with single or
0168 multiple 'acpi_osi="string1"' to support specific OS
0169 vendor string(s). Note that such command can only
0170 affect the default state of the OS vendor strings, thus
0171 it cannot affect the default state of the feature group
0172 strings and the current state of the OS vendor strings,
0173 specifying it multiple times through kernel command line
0174 is meaningless. This command is useful when one do not
0175 care about the state of the feature group strings which
0176 should be controlled by the OSPM.
0177 Examples:
0178 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
0179 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
0180 can make '_OSI("Windows 2000")' TRUE.
0181
0182 'acpi_osi=' cannot be used in combination with other
0183 'acpi_osi=' command lines, the _OSI method will not
0184 exist in the ACPI namespace. NOTE that such command can
0185 only affect the _OSI support state, thus specifying it
0186 multiple times through kernel command line is also
0187 meaningless.
0188 Examples:
0189 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
0190 FALSE.
0191
0192 'acpi_osi=!*' can be used in combination with single or
0193 multiple 'acpi_osi="string1"' to support specific
0194 string(s). Note that such command can affect the
0195 current state of both the OS vendor strings and the
0196 feature group strings, thus specifying it multiple times
0197 through kernel command line is meaningful. But it may
0198 still not able to affect the final state of a string if
0199 there are quirks related to this string. This command
0200 is useful when one want to control the state of the
0201 feature group strings to debug BIOS issues related to
0202 the OSPM features.
0203 Examples:
0204 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
0205 '_OSI("Module Device")' FALSE.
0206 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
0207 '_OSI("Module Device")' TRUE.
0208 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
0209 equivalent to
0210 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
0211 and
0212 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
0213 they all will make '_OSI("Windows 2000")' TRUE.
0214
0215 acpi_pm_good [X86]
0216 Override the pmtimer bug detection: force the kernel
0217 to assume that this machine's pmtimer latches its value
0218 and always returns good values.
0219
0220 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
0221 Format: { level | edge | high | low }
0222
0223 acpi_skip_timer_override [HW,ACPI]
0224 Recognize and ignore IRQ0/pin2 Interrupt Override.
0225 For broken nForce2 BIOS resulting in XT-PIC timer.
0226
0227 acpi_sleep= [HW,ACPI] Sleep options
0228 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig,
0229 s4_nohwsig, old_ordering, nonvs,
0230 sci_force_enable, nobl }
0231 See Documentation/power/video.rst for information on
0232 s3_bios and s3_mode.
0233 s3_beep is for debugging; it makes the PC's speaker beep
0234 as soon as the kernel's real-mode entry point is called.
0235 s4_hwsig causes the kernel to check the ACPI hardware
0236 signature during resume from hibernation, and gracefully
0237 refuse to resume if it has changed. This complies with
0238 the ACPI specification but not with reality, since
0239 Windows does not do this and many laptops do change it
0240 on docking. So the default behaviour is to allow resume
0241 and simply warn when the signature changes, unless the
0242 s4_hwsig option is enabled.
0243 s4_nohwsig prevents ACPI hardware signature from being
0244 used (or even warned about) during resume.
0245 old_ordering causes the ACPI 1.0 ordering of the _PTS
0246 control method, with respect to putting devices into
0247 low power states, to be enforced (the ACPI 2.0 ordering
0248 of _PTS is used by default).
0249 nonvs prevents the kernel from saving/restoring the
0250 ACPI NVS memory during suspend/hibernation and resume.
0251 sci_force_enable causes the kernel to set SCI_EN directly
0252 on resume from S1/S3 (which is against the ACPI spec,
0253 but some broken systems don't work without it).
0254 nobl causes the internal blacklist of systems known to
0255 behave incorrectly in some ways with respect to system
0256 suspend and resume to be ignored (use wisely).
0257
0258 acpi_use_timer_override [HW,ACPI]
0259 Use timer override. For some broken Nvidia NF5 boards
0260 that require a timer override, but don't have HPET
0261
0262 add_efi_memmap [EFI; X86] Include EFI memory map in
0263 kernel's map of available physical RAM.
0264
0265 agp= [AGP]
0266 { off | try_unsupported }
0267 off: disable AGP support
0268 try_unsupported: try to drive unsupported chipsets
0269 (may crash computer or cause data corruption)
0270
0271 ALSA [HW,ALSA]
0272 See Documentation/sound/alsa-configuration.rst
0273
0274 alignment= [KNL,ARM]
0275 Allow the default userspace alignment fault handler
0276 behaviour to be specified. Bit 0 enables warnings,
0277 bit 1 enables fixups, and bit 2 sends a segfault.
0278
0279 align_va_addr= [X86-64]
0280 Align virtual addresses by clearing slice [14:12] when
0281 allocating a VMA at process creation time. This option
0282 gives you up to 3% performance improvement on AMD F15h
0283 machines (where it is enabled by default) for a
0284 CPU-intensive style benchmark, and it can vary highly in
0285 a microbenchmark depending on workload and compiler.
0286
0287 32: only for 32-bit processes
0288 64: only for 64-bit processes
0289 on: enable for both 32- and 64-bit processes
0290 off: disable for both 32- and 64-bit processes
0291
0292 alloc_snapshot [FTRACE]
0293 Allocate the ftrace snapshot buffer on boot up when the
0294 main buffer is allocated. This is handy if debugging
0295 and you need to use tracing_snapshot() on boot up, and
0296 do not want to use tracing_snapshot_alloc() as it needs
0297 to be done where GFP_KERNEL allocations are allowed.
0298
0299 allow_mismatched_32bit_el0 [ARM64]
0300 Allow execve() of 32-bit applications and setting of the
0301 PER_LINUX32 personality on systems where only a strict
0302 subset of the CPUs support 32-bit EL0. When this
0303 parameter is present, the set of CPUs supporting 32-bit
0304 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
0305 and hot-unplug operations may be restricted.
0306
0307 See Documentation/arm64/asymmetric-32bit.rst for more
0308 information.
0309
0310 amd_iommu= [HW,X86-64]
0311 Pass parameters to the AMD IOMMU driver in the system.
0312 Possible values are:
0313 fullflush - Deprecated, equivalent to iommu.strict=1
0314 off - do not initialize any AMD IOMMU found in
0315 the system
0316 force_isolation - Force device isolation for all
0317 devices. The IOMMU driver is not
0318 allowed anymore to lift isolation
0319 requirements as needed. This option
0320 does not override iommu=pt
0321 force_enable - Force enable the IOMMU on platforms known
0322 to be buggy with IOMMU enabled. Use this
0323 option with care.
0324
0325 amd_iommu_dump= [HW,X86-64]
0326 Enable AMD IOMMU driver option to dump the ACPI table
0327 for AMD IOMMU. With this option enabled, AMD IOMMU
0328 driver will print ACPI tables for AMD IOMMU during
0329 IOMMU initialization.
0330
0331 amd_iommu_intr= [HW,X86-64]
0332 Specifies one of the following AMD IOMMU interrupt
0333 remapping modes:
0334 legacy - Use legacy interrupt remapping mode.
0335 vapic - Use virtual APIC mode, which allows IOMMU
0336 to inject interrupts directly into guest.
0337 This mode requires kvm-amd.avic=1.
0338 (Default when IOMMU HW support is present.)
0339
0340 amijoy.map= [HW,JOY] Amiga joystick support
0341 Map of devices attached to JOY0DAT and JOY1DAT
0342 Format: <a>,<b>
0343 See also Documentation/input/joydev/joystick.rst
0344
0345 analog.map= [HW,JOY] Analog joystick and gamepad support
0346 Specifies type or capabilities of an analog joystick
0347 connected to one of 16 gameports
0348 Format: <type1>,<type2>,..<type16>
0349
0350 apc= [HW,SPARC]
0351 Power management functions (SPARCstation-4/5 + deriv.)
0352 Format: noidle
0353 Disable APC CPU standby support. SPARCstation-Fox does
0354 not play well with APC CPU idle - disable it if you have
0355 APC and your system crashes randomly.
0356
0357 apic= [APIC,X86] Advanced Programmable Interrupt Controller
0358 Change the output verbosity while booting
0359 Format: { quiet (default) | verbose | debug }
0360 Change the amount of debugging information output
0361 when initialising the APIC and IO-APIC components.
0362 For X86-32, this can also be used to specify an APIC
0363 driver name.
0364 Format: apic=driver_name
0365 Examples: apic=bigsmp
0366
0367 apic_extnmi= [APIC,X86] External NMI delivery setting
0368 Format: { bsp (default) | all | none }
0369 bsp: External NMI is delivered only to CPU 0
0370 all: External NMIs are broadcast to all CPUs as a
0371 backup of CPU 0
0372 none: External NMI is masked for all CPUs. This is
0373 useful so that a dump capture kernel won't be
0374 shot down by NMI
0375
0376 autoconf= [IPV6]
0377 See Documentation/networking/ipv6.rst.
0378
0379 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
0380 Limit apic dumping. The parameter defines the maximal
0381 number of local apics being dumped. Also it is possible
0382 to set it to "all" by meaning -- no limit here.
0383 Format: { 1 (default) | 2 | ... | all }.
0384 The parameter valid if only apic=debug or
0385 apic=verbose is specified.
0386 Example: apic=debug show_lapic=all
0387
0388 apm= [APM] Advanced Power Management
0389 See header of arch/x86/kernel/apm_32.c.
0390
0391 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
0392 Format: <io>,<irq>,<nodeID>
0393
0394 arm64.nobti [ARM64] Unconditionally disable Branch Target
0395 Identification support
0396
0397 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
0398 support
0399
0400 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension
0401 support
0402
0403 arm64.nosve [ARM64] Unconditionally disable Scalable Vector
0404 Extension support
0405
0406 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix
0407 Extension support
0408
0409 ataflop= [HW,M68k]
0410
0411 atarimouse= [HW,MOUSE] Atari Mouse
0412
0413 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
0414 EzKey and similar keyboards
0415
0416 atkbd.reset= [HW] Reset keyboard during initialization
0417
0418 atkbd.set= [HW] Select keyboard code set
0419 Format: <int> (2 = AT (default), 3 = PS/2)
0420
0421 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
0422 keyboards
0423
0424 atkbd.softraw= [HW] Choose between synthetic and real raw mode
0425 Format: <bool> (0 = real, 1 = synthetic (default))
0426
0427 atkbd.softrepeat= [HW]
0428 Use software keyboard repeat
0429
0430 audit= [KNL] Enable the audit sub-system
0431 Format: { "0" | "1" | "off" | "on" }
0432 0 | off - kernel audit is disabled and can not be
0433 enabled until the next reboot
0434 unset - kernel audit is initialized but disabled and
0435 will be fully enabled by the userspace auditd.
0436 1 | on - kernel audit is initialized and partially
0437 enabled, storing at most audit_backlog_limit
0438 messages in RAM until it is fully enabled by the
0439 userspace auditd.
0440 Default: unset
0441
0442 audit_backlog_limit= [KNL] Set the audit queue size limit.
0443 Format: <int> (must be >=0)
0444 Default: 64
0445
0446 bau= [X86_UV] Enable the BAU on SGI UV. The default
0447 behavior is to disable the BAU (i.e. bau=0).
0448 Format: { "0" | "1" }
0449 0 - Disable the BAU.
0450 1 - Enable the BAU.
0451 unset - Disable the BAU.
0452
0453 baycom_epp= [HW,AX25]
0454 Format: <io>,<mode>
0455
0456 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
0457 Format: <io>,<mode>
0458 See header of drivers/net/hamradio/baycom_par.c.
0459
0460 baycom_ser_fdx= [HW,AX25]
0461 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
0462 Format: <io>,<irq>,<mode>[,<baud>]
0463 See header of drivers/net/hamradio/baycom_ser_fdx.c.
0464
0465 baycom_ser_hdx= [HW,AX25]
0466 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
0467 Format: <io>,<irq>,<mode>
0468 See header of drivers/net/hamradio/baycom_ser_hdx.c.
0469
0470 bert_disable [ACPI]
0471 Disable BERT OS support on buggy BIOSes.
0472
0473 bgrt_disable [ACPI][X86]
0474 Disable BGRT to avoid flickering OEM logo.
0475
0476 blkdevparts= Manual partition parsing of block device(s) for
0477 embedded devices based on command line input.
0478 See Documentation/block/cmdline-partition.rst
0479
0480 boot_delay= Milliseconds to delay each printk during boot.
0481 Values larger than 10 seconds (10000) are changed to
0482 no delay (0).
0483 Format: integer
0484
0485 bootconfig [KNL]
0486 Extended command line options can be added to an initrd
0487 and this will cause the kernel to look for it.
0488
0489 See Documentation/admin-guide/bootconfig.rst
0490
0491 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
0492 bttv.radio= Most important insmod options are available as
0493 kernel args too.
0494 bttv.pll= See Documentation/admin-guide/media/bttv.rst
0495 bttv.tuner=
0496
0497 bulk_remove=off [PPC] This parameter disables the use of the pSeries
0498 firmware feature for flushing multiple hpte entries
0499 at a time.
0500
0501 c101= [NET] Moxa C101 synchronous serial card
0502
0503 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
0504 Sometimes CPU hardware bugs make them report the cache
0505 size incorrectly. The kernel will attempt work arounds
0506 to fix known problems, but for some CPUs it is not
0507 possible to determine what the correct size should be.
0508 This option provides an override for these situations.
0509
0510 carrier_timeout=
0511 [NET] Specifies amount of time (in seconds) that
0512 the kernel should wait for a network carrier. By default
0513 it waits 120 seconds.
0514
0515 ca_keys= [KEYS] This parameter identifies a specific key(s) on
0516 the system trusted keyring to be used for certificate
0517 trust validation.
0518 format: { id:<keyid> | builtin }
0519
0520 cca= [MIPS] Override the kernel pages' cache coherency
0521 algorithm. Accepted values range from 0 to 7
0522 inclusive. See arch/mips/include/asm/pgtable-bits.h
0523 for platform specific values (SB1, Loongson3 and
0524 others).
0525
0526 ccw_timeout_log [S390]
0527 See Documentation/s390/common_io.rst for details.
0528
0529 cgroup_disable= [KNL] Disable a particular controller or optional feature
0530 Format: {name of the controller(s) or feature(s) to disable}
0531 The effects of cgroup_disable=foo are:
0532 - foo isn't auto-mounted if you mount all cgroups in
0533 a single hierarchy
0534 - foo isn't visible as an individually mountable
0535 subsystem
0536 - if foo is an optional feature then the feature is
0537 disabled and corresponding cgroup files are not
0538 created
0539 {Currently only "memory" controller deal with this and
0540 cut the overhead, others just disable the usage. So
0541 only cgroup_disable=memory is actually worthy}
0542 Specifying "pressure" disables per-cgroup pressure
0543 stall information accounting feature
0544
0545 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
0546 Format: { { controller | "all" | "named" }
0547 [,{ controller | "all" | "named" }...] }
0548 Like cgroup_disable, but only applies to cgroup v1;
0549 the blacklisted controllers remain available in cgroup2.
0550 "all" blacklists all controllers and "named" disables
0551 named mounts. Specifying both "all" and "named" disables
0552 all v1 hierarchies.
0553
0554 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
0555 Format: <string>
0556 nosocket -- Disable socket memory accounting.
0557 nokmem -- Disable kernel memory accounting.
0558
0559 checkreqprot= [SELINUX] Set initial checkreqprot flag value.
0560 Format: { "0" | "1" }
0561 See security/selinux/Kconfig help text.
0562 0 -- check protection applied by kernel (includes
0563 any implied execute protection).
0564 1 -- check protection requested by application.
0565 Default value is set via a kernel config option.
0566 Value can be changed at runtime via
0567 /sys/fs/selinux/checkreqprot.
0568 Setting checkreqprot to 1 is deprecated.
0569
0570 cio_ignore= [S390]
0571 See Documentation/s390/common_io.rst for details.
0572
0573 clearcpuid=X[,X...] [X86]
0574 Disable CPUID feature X for the kernel. See
0575 arch/x86/include/asm/cpufeatures.h for the valid bit
0576 numbers X. Note the Linux-specific bits are not necessarily
0577 stable over kernel options, but the vendor-specific
0578 ones should be.
0579 X can also be a string as appearing in the flags: line
0580 in /proc/cpuinfo which does not have the above
0581 instability issue. However, not all features have names
0582 in /proc/cpuinfo.
0583 Note that using this option will taint your kernel.
0584 Also note that user programs calling CPUID directly
0585 or using the feature without checking anything
0586 will still see it. This just prevents it from
0587 being used by the kernel or shown in /proc/cpuinfo.
0588 Also note the kernel might malfunction if you disable
0589 some critical bits.
0590
0591 clk_ignore_unused
0592 [CLK]
0593 Prevents the clock framework from automatically gating
0594 clocks that have not been explicitly enabled by a Linux
0595 device driver but are enabled in hardware at reset or
0596 by the bootloader/firmware. Note that this does not
0597 force such clocks to be always-on nor does it reserve
0598 those clocks in any way. This parameter is useful for
0599 debug and development, but should not be needed on a
0600 platform with proper driver support. For more
0601 information, see Documentation/driver-api/clk.rst.
0602
0603 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
0604 [Deprecated]
0605 Forces specified clocksource (if available) to be used
0606 when calculating gettimeofday(). If specified
0607 clocksource is not available, it defaults to PIT.
0608 Format: { pit | tsc | cyclone | pmtmr }
0609
0610 clocksource= Override the default clocksource
0611 Format: <string>
0612 Override the default clocksource and use the clocksource
0613 with the name specified.
0614 Some clocksource names to choose from, depending on
0615 the platform:
0616 [all] jiffies (this is the base, fallback clocksource)
0617 [ACPI] acpi_pm
0618 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
0619 pxa_timer,timer3,32k_counter,timer0_1
0620 [X86-32] pit,hpet,tsc;
0621 scx200_hrt on Geode; cyclone on IBM x440
0622 [MIPS] MIPS
0623 [PARISC] cr16
0624 [S390] tod
0625 [SH] SuperH
0626 [SPARC64] tick
0627 [X86-64] hpet,tsc
0628
0629 clocksource.arm_arch_timer.evtstrm=
0630 [ARM,ARM64]
0631 Format: <bool>
0632 Enable/disable the eventstream feature of the ARM
0633 architected timer so that code using WFE-based polling
0634 loops can be debugged more effectively on production
0635 systems.
0636
0637 clocksource.max_cswd_read_retries= [KNL]
0638 Number of clocksource_watchdog() retries due to
0639 external delays before the clock will be marked
0640 unstable. Defaults to two retries, that is,
0641 three attempts to read the clock under test.
0642
0643 clocksource.verify_n_cpus= [KNL]
0644 Limit the number of CPUs checked for clocksources
0645 marked with CLOCK_SOURCE_VERIFY_PERCPU that
0646 are marked unstable due to excessive skew.
0647 A negative value says to check all CPUs, while
0648 zero says not to check any. Values larger than
0649 nr_cpu_ids are silently truncated to nr_cpu_ids.
0650 The actual CPUs are chosen randomly, with
0651 no replacement if the same CPU is chosen twice.
0652
0653 clocksource-wdtest.holdoff= [KNL]
0654 Set the time in seconds that the clocksource
0655 watchdog test waits before commencing its tests.
0656 Defaults to zero when built as a module and to
0657 10 seconds when built into the kernel.
0658
0659 cma=nn[MG]@[start[MG][-end[MG]]]
0660 [KNL,CMA]
0661 Sets the size of kernel global memory area for
0662 contiguous memory allocations and optionally the
0663 placement constraint by the physical address range of
0664 memory allocations. A value of 0 disables CMA
0665 altogether. For more information, see
0666 kernel/dma/contiguous.c
0667
0668 cma_pernuma=nn[MG]
0669 [ARM64,KNL,CMA]
0670 Sets the size of kernel per-numa memory area for
0671 contiguous memory allocations. A value of 0 disables
0672 per-numa CMA altogether. And If this option is not
0673 specificed, the default value is 0.
0674 With per-numa CMA enabled, DMA users on node nid will
0675 first try to allocate buffer from the pernuma area
0676 which is located in node nid, if the allocation fails,
0677 they will fallback to the global default memory area.
0678
0679 cmo_free_hint= [PPC] Format: { yes | no }
0680 Specify whether pages are marked as being inactive
0681 when they are freed. This is used in CMO environments
0682 to determine OS memory pressure for page stealing by
0683 a hypervisor.
0684 Default: yes
0685
0686 coherent_pool=nn[KMG] [ARM,KNL]
0687 Sets the size of memory pool for coherent, atomic dma
0688 allocations, by default set to 256K.
0689
0690 com20020= [HW,NET] ARCnet - COM20020 chipset
0691 Format:
0692 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
0693
0694 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
0695 Format: <io>[,<irq>]
0696
0697 com90xx= [HW,NET]
0698 ARCnet - COM90xx chipset (memory-mapped buffers)
0699 Format: <io>[,<irq>[,<memstart>]]
0700
0701 condev= [HW,S390] console device
0702 conmode=
0703
0704 console= [KNL] Output console device and options.
0705
0706 tty<n> Use the virtual console device <n>.
0707
0708 ttyS<n>[,options]
0709 ttyUSB0[,options]
0710 Use the specified serial port. The options are of
0711 the form "bbbbpnf", where "bbbb" is the baud rate,
0712 "p" is parity ("n", "o", or "e"), "n" is number of
0713 bits, and "f" is flow control ("r" for RTS or
0714 omit it). Default is "9600n8".
0715
0716 See Documentation/admin-guide/serial-console.rst for more
0717 information. See
0718 Documentation/networking/netconsole.rst for an
0719 alternative.
0720
0721 uart[8250],io,<addr>[,options]
0722 uart[8250],mmio,<addr>[,options]
0723 uart[8250],mmio16,<addr>[,options]
0724 uart[8250],mmio32,<addr>[,options]
0725 uart[8250],0x<addr>[,options]
0726 Start an early, polled-mode console on the 8250/16550
0727 UART at the specified I/O port or MMIO address,
0728 switching to the matching ttyS device later.
0729 MMIO inter-register address stride is either 8-bit
0730 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
0731 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
0732 to be equivalent to 'mmio'. 'options' are specified in
0733 the same format described for ttyS above; if unspecified,
0734 the h/w is not re-initialized.
0735
0736 hvc<n> Use the hypervisor console device <n>. This is for
0737 both Xen and PowerPC hypervisors.
0738
0739 { null | "" }
0740 Use to disable console output, i.e., to have kernel
0741 console messages discarded.
0742 This must be the only console= parameter used on the
0743 kernel command line.
0744
0745 If the device connected to the port is not a TTY but a braille
0746 device, prepend "brl," before the device type, for instance
0747 console=brl,ttyS0
0748 For now, only VisioBraille is supported.
0749
0750 console_msg_format=
0751 [KNL] Change console messages format
0752 default
0753 By default we print messages on consoles in
0754 "[time stamp] text\n" format (time stamp may not be
0755 printed, depending on CONFIG_PRINTK_TIME or
0756 `printk_time' param).
0757 syslog
0758 Switch to syslog format: "<%u>[time stamp] text\n"
0759 IOW, each message will have a facility and loglevel
0760 prefix. The format is similar to one used by syslog()
0761 syscall, or to executing "dmesg -S --raw" or to reading
0762 from /proc/kmsg.
0763
0764 consoleblank= [KNL] The console blank (screen saver) timeout in
0765 seconds. A value of 0 disables the blank timer.
0766 Defaults to 0.
0767
0768 coredump_filter=
0769 [KNL] Change the default value for
0770 /proc/<pid>/coredump_filter.
0771 See also Documentation/filesystems/proc.rst.
0772
0773 coresight_cpu_debug.enable
0774 [ARM,ARM64]
0775 Format: <bool>
0776 Enable/disable the CPU sampling based debugging.
0777 0: default value, disable debugging
0778 1: enable debugging at boot time
0779
0780 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
0781 Format:
0782 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
0783
0784 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
0785 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
0786 Some features depend on CPU0. Known dependencies are:
0787 1. Resume from suspend/hibernate depends on CPU0.
0788 Suspend/hibernate will fail if CPU0 is offline and you
0789 need to online CPU0 before suspend/hibernate.
0790 2. PIC interrupts also depend on CPU0. CPU0 can't be
0791 removed if a PIC interrupt is detected.
0792 It's said poweroff/reboot may depend on CPU0 on some
0793 machines although I haven't seen such issues so far
0794 after CPU0 is offline on a few tested machines.
0795 If the dependencies are under your control, you can
0796 turn on cpu0_hotplug.
0797
0798 cpuidle.off=1 [CPU_IDLE]
0799 disable the cpuidle sub-system
0800
0801 cpuidle.governor=
0802 [CPU_IDLE] Name of the cpuidle governor to use.
0803
0804 cpufreq.off=1 [CPU_FREQ]
0805 disable the cpufreq sub-system
0806
0807 cpufreq.default_governor=
0808 [CPU_FREQ] Name of the default cpufreq governor or
0809 policy to use. This governor must be registered in the
0810 kernel before the cpufreq driver probes.
0811
0812 cpu_init_udelay=N
0813 [X86] Delay for N microsec between assert and de-assert
0814 of APIC INIT to start processors. This delay occurs
0815 on every CPU online, such as boot, and resume from suspend.
0816 Default: 10000
0817
0818 crash_kexec_post_notifiers
0819 Run kdump after running panic-notifiers and dumping
0820 kmsg. This only for the users who doubt kdump always
0821 succeeds in any situation.
0822 Note that this also increases risks of kdump failure,
0823 because some panic notifiers can make the crashed
0824 kernel more unstable.
0825
0826 crashkernel=size[KMG][@offset[KMG]]
0827 [KNL] Using kexec, Linux can switch to a 'crash kernel'
0828 upon panic. This parameter reserves the physical
0829 memory region [offset, offset + size] for that kernel
0830 image. If '@offset' is omitted, then a suitable offset
0831 is selected automatically.
0832 [KNL, X86-64] Select a region under 4G first, and
0833 fall back to reserve region above 4G when '@offset'
0834 hasn't been specified.
0835 See Documentation/admin-guide/kdump/kdump.rst for further details.
0836
0837 crashkernel=range1:size1[,range2:size2,...][@offset]
0838 [KNL] Same as above, but depends on the memory
0839 in the running system. The syntax of range is
0840 start-[end] where start and end are both
0841 a memory unit (amount[KMG]). See also
0842 Documentation/admin-guide/kdump/kdump.rst for an example.
0843
0844 crashkernel=size[KMG],high
0845 [KNL, X86-64, ARM64] range could be above 4G. Allow kernel
0846 to allocate physical memory region from top, so could
0847 be above 4G if system have more than 4G ram installed.
0848 Otherwise memory region will be allocated below 4G, if
0849 available.
0850 It will be ignored if crashkernel=X is specified.
0851 crashkernel=size[KMG],low
0852 [KNL, X86-64] range under 4G. When crashkernel=X,high
0853 is passed, kernel could allocate physical memory region
0854 above 4G, that cause second kernel crash on system
0855 that require some amount of low memory, e.g. swiotlb
0856 requires at least 64M+32K low memory, also enough extra
0857 low memory is needed to make sure DMA buffers for 32-bit
0858 devices won't run out. Kernel would try to allocate
0859 at least 256M below 4G automatically.
0860 This one lets the user specify own low range under 4G
0861 for second kernel instead.
0862 0: to disable low allocation.
0863 It will be ignored when crashkernel=X,high is not used
0864 or memory reserved is below 4G.
0865
0866 [KNL, ARM64] range in low memory.
0867 This one lets the user specify a low range in the
0868 DMA zone for the crash dump kernel.
0869 It will be ignored when crashkernel=X,high is not used
0870 or memory reserved is located in the DMA zones.
0871
0872 cryptomgr.notests
0873 [KNL] Disable crypto self-tests
0874
0875 cs89x0_dma= [HW,NET]
0876 Format: <dma>
0877
0878 cs89x0_media= [HW,NET]
0879 Format: { rj45 | aui | bnc }
0880
0881 csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call
0882 handling. When switched on, additional debug data is
0883 printed to the console in case a hanging CPU is
0884 detected, and that CPU is pinged again in order to try
0885 to resolve the hang situation.
0886 0: disable csdlock debugging (default)
0887 1: enable basic csdlock debugging (minor impact)
0888 ext: enable extended csdlock debugging (more impact,
0889 but more data)
0890
0891 dasd= [HW,NET]
0892 See header of drivers/s390/block/dasd_devmap.c.
0893
0894 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
0895 (one device per port)
0896 Format: <port#>,<type>
0897 See also Documentation/input/devices/joystick-parport.rst
0898
0899 debug [KNL] Enable kernel debugging (events log level).
0900
0901 debug_boot_weak_hash
0902 [KNL] Enable printing [hashed] pointers early in the
0903 boot sequence. If enabled, we use a weak hash instead
0904 of siphash to hash pointers. Use this option if you are
0905 seeing instances of '(___ptrval___)') and need to see a
0906 value (hashed pointer) instead. Cryptographically
0907 insecure, please do not use on production kernels.
0908
0909 debug_locks_verbose=
0910 [KNL] verbose locking self-tests
0911 Format: <int>
0912 Print debugging info while doing the locking API
0913 self-tests.
0914 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
0915 (no extra messages), setting it to -1 (all bits set)
0916 will print _a_lot_ more information - normally only
0917 useful to lockdep developers.
0918
0919 debug_objects [KNL] Enable object debugging
0920
0921 no_debug_objects
0922 [KNL] Disable object debugging
0923
0924 debug_guardpage_minorder=
0925 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
0926 parameter allows control of the order of pages that will
0927 be intentionally kept free (and hence protected) by the
0928 buddy allocator. Bigger value increase the probability
0929 of catching random memory corruption, but reduce the
0930 amount of memory for normal system use. The maximum
0931 possible value is MAX_ORDER/2. Setting this parameter
0932 to 1 or 2 should be enough to identify most random
0933 memory corruption problems caused by bugs in kernel or
0934 driver code when a CPU writes to (or reads from) a
0935 random memory location. Note that there exists a class
0936 of memory corruptions problems caused by buggy H/W or
0937 F/W or by drivers badly programing DMA (basically when
0938 memory is written at bus level and the CPU MMU is
0939 bypassed) which are not detectable by
0940 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
0941 tracking down these problems.
0942
0943 debug_pagealloc=
0944 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
0945 enables the feature at boot time. By default, it is
0946 disabled and the system will work mostly the same as a
0947 kernel built without CONFIG_DEBUG_PAGEALLOC.
0948 Note: to get most of debug_pagealloc error reports, it's
0949 useful to also enable the page_owner functionality.
0950 on: enable the feature
0951
0952 debugfs= [KNL] This parameter enables what is exposed to userspace
0953 and debugfs internal clients.
0954 Format: { on, no-mount, off }
0955 on: All functions are enabled.
0956 no-mount:
0957 Filesystem is not registered but kernel clients can
0958 access APIs and a crashkernel can be used to read
0959 its content. There is nothing to mount.
0960 off: Filesystem is not registered and clients
0961 get a -EPERM as result when trying to register files
0962 or directories within debugfs.
0963 This is equivalent of the runtime functionality if
0964 debugfs was not enabled in the kernel at all.
0965 Default value is set in build-time with a kernel configuration.
0966
0967 debugpat [X86] Enable PAT debugging
0968
0969 decnet.addr= [HW,NET]
0970 Format: <area>[,<node>]
0971 See also Documentation/networking/decnet.rst.
0972
0973 default_hugepagesz=
0974 [HW] The size of the default HugeTLB page. This is
0975 the size represented by the legacy /proc/ hugepages
0976 APIs. In addition, this is the default hugetlb size
0977 used for shmget(), mmap() and mounting hugetlbfs
0978 filesystems. If not specified, defaults to the
0979 architecture's default huge page size. Huge page
0980 sizes are architecture dependent. See also
0981 Documentation/admin-guide/mm/hugetlbpage.rst.
0982 Format: size[KMG]
0983
0984 deferred_probe_timeout=
0985 [KNL] Debugging option to set a timeout in seconds for
0986 deferred probe to give up waiting on dependencies to
0987 probe. Only specific dependencies (subsystems or
0988 drivers) that have opted in will be ignored. A timeout
0989 of 0 will timeout at the end of initcalls. If the time
0990 out hasn't expired, it'll be restarted by each
0991 successful driver registration. This option will also
0992 dump out devices still on the deferred probe list after
0993 retrying.
0994
0995 delayacct [KNL] Enable per-task delay accounting
0996
0997 dell_smm_hwmon.ignore_dmi=
0998 [HW] Continue probing hardware even if DMI data
0999 indicates that the driver is running on unsupported
1000 hardware.
1001
1002 dell_smm_hwmon.force=
1003 [HW] Activate driver even if SMM BIOS signature does
1004 not match list of supported models and enable otherwise
1005 blacklisted features.
1006
1007 dell_smm_hwmon.power_status=
1008 [HW] Report power status in /proc/i8k
1009 (disabled by default).
1010
1011 dell_smm_hwmon.restricted=
1012 [HW] Allow controlling fans only if SYS_ADMIN
1013 capability is set.
1014
1015 dell_smm_hwmon.fan_mult=
1016 [HW] Factor to multiply fan speed with.
1017
1018 dell_smm_hwmon.fan_max=
1019 [HW] Maximum configurable fan speed.
1020
1021 dfltcc= [HW,S390]
1022 Format: { on | off | def_only | inf_only | always }
1023 on: s390 zlib hardware support for compression on
1024 level 1 and decompression (default)
1025 off: No s390 zlib hardware support
1026 def_only: s390 zlib hardware support for deflate
1027 only (compression on level 1)
1028 inf_only: s390 zlib hardware support for inflate
1029 only (decompression)
1030 always: Same as 'on' but ignores the selected compression
1031 level always using hardware support (used for debugging)
1032
1033 dhash_entries= [KNL]
1034 Set number of hash buckets for dentry cache.
1035
1036 disable_1tb_segments [PPC]
1037 Disables the use of 1TB hash page table segments. This
1038 causes the kernel to fall back to 256MB segments which
1039 can be useful when debugging issues that require an SLB
1040 miss to occur.
1041
1042 stress_slb [PPC]
1043 Limits the number of kernel SLB entries, and flushes
1044 them frequently to increase the rate of SLB faults
1045 on kernel addresses.
1046
1047 disable= [IPV6]
1048 See Documentation/networking/ipv6.rst.
1049
1050 disable_radix [PPC]
1051 Disable RADIX MMU mode on POWER9
1052
1053 radix_hcall_invalidate=on [PPC/PSERIES]
1054 Disable RADIX GTSE feature and use hcall for TLB
1055 invalidate.
1056
1057 disable_tlbie [PPC]
1058 Disable TLBIE instruction. Currently does not work
1059 with KVM, with HASH MMU, or with coherent accelerators.
1060
1061 disable_cpu_apicid= [X86,APIC,SMP]
1062 Format: <int>
1063 The number of initial APIC ID for the
1064 corresponding CPU to be disabled at boot,
1065 mostly used for the kdump 2nd kernel to
1066 disable BSP to wake up multiple CPUs without
1067 causing system reset or hang due to sending
1068 INIT from AP to BSP.
1069
1070 disable_ddw [PPC/PSERIES]
1071 Disable Dynamic DMA Window support. Use this
1072 to workaround buggy firmware.
1073
1074 disable_ipv6= [IPV6]
1075 See Documentation/networking/ipv6.rst.
1076
1077 disable_mtrr_cleanup [X86]
1078 The kernel tries to adjust MTRR layout from continuous
1079 to discrete, to make X server driver able to add WB
1080 entry later. This parameter disables that.
1081
1082 disable_mtrr_trim [X86, Intel and AMD only]
1083 By default the kernel will trim any uncacheable
1084 memory out of your available memory pool based on
1085 MTRR settings. This parameter disables that behavior,
1086 possibly causing your machine to run very slowly.
1087
1088 disable_timer_pin_1 [X86]
1089 Disable PIN 1 of APIC timer
1090 Can be useful to work around chipset bugs.
1091
1092 dis_ucode_ldr [X86] Disable the microcode loader.
1093
1094 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1095 this option disables the debugging code at boot.
1096
1097 dma_debug_entries=<number>
1098 This option allows to tune the number of preallocated
1099 entries for DMA-API debugging code. One entry is
1100 required per DMA-API allocation. Use this if the
1101 DMA-API debugging code disables itself because the
1102 architectural default is too low.
1103
1104 dma_debug_driver=<driver_name>
1105 With this option the DMA-API debugging driver
1106 filter feature can be enabled at boot time. Just
1107 pass the driver to filter for as the parameter.
1108 The filter can be disabled or changed to another
1109 driver later using sysfs.
1110
1111 driver_async_probe= [KNL]
1112 List of driver names to be probed asynchronously. *
1113 matches with all driver names. If * is specified, the
1114 rest of the listed driver names are those that will NOT
1115 match the *.
1116 Format: <driver_name1>,<driver_name2>...
1117
1118 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1119 Broken monitors, graphic adapters, KVMs and EDIDless
1120 panels may send no or incorrect EDID data sets.
1121 This parameter allows to specify an EDID data sets
1122 in the /lib/firmware directory that are used instead.
1123 Generic built-in EDID data sets are used, if one of
1124 edid/1024x768.bin, edid/1280x1024.bin,
1125 edid/1680x1050.bin, or edid/1920x1080.bin is given
1126 and no file with the same name exists. Details and
1127 instructions how to build your own EDID data are
1128 available in Documentation/admin-guide/edid.rst. An EDID
1129 data set will only be used for a particular connector,
1130 if its name and a colon are prepended to the EDID
1131 name. Each connector may use a unique EDID data
1132 set by separating the files with a comma. An EDID
1133 data set with no connector name will be used for
1134 any connectors not explicitly specified.
1135
1136 dscc4.setup= [NET]
1137
1138 dt_cpu_ftrs= [PPC]
1139 Format: {"off" | "known"}
1140 Control how the dt_cpu_ftrs device-tree binding is
1141 used for CPU feature discovery and setup (if it
1142 exists).
1143 off: Do not use it, fall back to legacy cpu table.
1144 known: Do not pass through unknown features to guests
1145 or userspace, only those that the kernel is aware of.
1146
1147 dump_apple_properties [X86]
1148 Dump name and content of EFI device properties on
1149 x86 Macs. Useful for driver authors to determine
1150 what data is available or for reverse-engineering.
1151
1152 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1153 <module>.dyndbg[="val"]
1154 Enable debug messages at boot time. See
1155 Documentation/admin-guide/dynamic-debug-howto.rst
1156 for details.
1157
1158 nopku [X86] Disable Memory Protection Keys CPU feature found
1159 in some Intel CPUs.
1160
1161 <module>.async_probe[=<bool>] [KNL]
1162 If no <bool> value is specified or if the value
1163 specified is not a valid <bool>, enable asynchronous
1164 probe on this module. Otherwise, enable/disable
1165 asynchronous probe on this module as indicated by the
1166 <bool> value. See also: module.async_probe
1167
1168 early_ioremap_debug [KNL]
1169 Enable debug messages in early_ioremap support. This
1170 is useful for tracking down temporary early mappings
1171 which are not unmapped.
1172
1173 earlycon= [KNL] Output early console device and options.
1174
1175 When used with no options, the early console is
1176 determined by stdout-path property in device tree's
1177 chosen node or the ACPI SPCR table if supported by
1178 the platform.
1179
1180 cdns,<addr>[,options]
1181 Start an early, polled-mode console on a Cadence
1182 (xuartps) serial port at the specified address. Only
1183 supported option is baud rate. If baud rate is not
1184 specified, the serial port must already be setup and
1185 configured.
1186
1187 uart[8250],io,<addr>[,options]
1188 uart[8250],mmio,<addr>[,options]
1189 uart[8250],mmio32,<addr>[,options]
1190 uart[8250],mmio32be,<addr>[,options]
1191 uart[8250],0x<addr>[,options]
1192 Start an early, polled-mode console on the 8250/16550
1193 UART at the specified I/O port or MMIO address.
1194 MMIO inter-register address stride is either 8-bit
1195 (mmio) or 32-bit (mmio32 or mmio32be).
1196 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1197 to be equivalent to 'mmio'. 'options' are specified
1198 in the same format described for "console=ttyS<n>"; if
1199 unspecified, the h/w is not initialized.
1200
1201 pl011,<addr>
1202 pl011,mmio32,<addr>
1203 Start an early, polled-mode console on a pl011 serial
1204 port at the specified address. The pl011 serial port
1205 must already be setup and configured. Options are not
1206 yet supported. If 'mmio32' is specified, then only
1207 the driver will use only 32-bit accessors to read/write
1208 the device registers.
1209
1210 liteuart,<addr>
1211 Start an early console on a litex serial port at the
1212 specified address. The serial port must already be
1213 setup and configured. Options are not yet supported.
1214
1215 meson,<addr>
1216 Start an early, polled-mode console on a meson serial
1217 port at the specified address. The serial port must
1218 already be setup and configured. Options are not yet
1219 supported.
1220
1221 msm_serial,<addr>
1222 Start an early, polled-mode console on an msm serial
1223 port at the specified address. The serial port
1224 must already be setup and configured. Options are not
1225 yet supported.
1226
1227 msm_serial_dm,<addr>
1228 Start an early, polled-mode console on an msm serial
1229 dm port at the specified address. The serial port
1230 must already be setup and configured. Options are not
1231 yet supported.
1232
1233 owl,<addr>
1234 Start an early, polled-mode console on a serial port
1235 of an Actions Semi SoC, such as S500 or S900, at the
1236 specified address. The serial port must already be
1237 setup and configured. Options are not yet supported.
1238
1239 rda,<addr>
1240 Start an early, polled-mode console on a serial port
1241 of an RDA Micro SoC, such as RDA8810PL, at the
1242 specified address. The serial port must already be
1243 setup and configured. Options are not yet supported.
1244
1245 sbi
1246 Use RISC-V SBI (Supervisor Binary Interface) for early
1247 console.
1248
1249 smh Use ARM semihosting calls for early console.
1250
1251 s3c2410,<addr>
1252 s3c2412,<addr>
1253 s3c2440,<addr>
1254 s3c6400,<addr>
1255 s5pv210,<addr>
1256 exynos4210,<addr>
1257 Use early console provided by serial driver available
1258 on Samsung SoCs, requires selecting proper type and
1259 a correct base address of the selected UART port. The
1260 serial port must already be setup and configured.
1261 Options are not yet supported.
1262
1263 lantiq,<addr>
1264 Start an early, polled-mode console on a lantiq serial
1265 (lqasc) port at the specified address. The serial port
1266 must already be setup and configured. Options are not
1267 yet supported.
1268
1269 lpuart,<addr>
1270 lpuart32,<addr>
1271 Use early console provided by Freescale LP UART driver
1272 found on Freescale Vybrid and QorIQ LS1021A processors.
1273 A valid base address must be provided, and the serial
1274 port must already be setup and configured.
1275
1276 ec_imx21,<addr>
1277 ec_imx6q,<addr>
1278 Start an early, polled-mode, output-only console on the
1279 Freescale i.MX UART at the specified address. The UART
1280 must already be setup and configured.
1281
1282 ar3700_uart,<addr>
1283 Start an early, polled-mode console on the
1284 Armada 3700 serial port at the specified
1285 address. The serial port must already be setup
1286 and configured. Options are not yet supported.
1287
1288 qcom_geni,<addr>
1289 Start an early, polled-mode console on a Qualcomm
1290 Generic Interface (GENI) based serial port at the
1291 specified address. The serial port must already be
1292 setup and configured. Options are not yet supported.
1293
1294 efifb,[options]
1295 Start an early, unaccelerated console on the EFI
1296 memory mapped framebuffer (if available). On cache
1297 coherent non-x86 systems that use system memory for
1298 the framebuffer, pass the 'ram' option so that it is
1299 mapped with the correct attributes.
1300
1301 linflex,<addr>
1302 Use early console provided by Freescale LINFlexD UART
1303 serial driver for NXP S32V234 SoCs. A valid base
1304 address must be provided, and the serial port must
1305 already be setup and configured.
1306
1307 earlyprintk= [X86,SH,ARM,M68k,S390]
1308 earlyprintk=vga
1309 earlyprintk=sclp
1310 earlyprintk=xen
1311 earlyprintk=serial[,ttySn[,baudrate]]
1312 earlyprintk=serial[,0x...[,baudrate]]
1313 earlyprintk=ttySn[,baudrate]
1314 earlyprintk=dbgp[debugController#]
1315 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1316 earlyprintk=xdbc[xhciController#]
1317
1318 earlyprintk is useful when the kernel crashes before
1319 the normal console is initialized. It is not enabled by
1320 default because it has some cosmetic problems.
1321
1322 Append ",keep" to not disable it when the real console
1323 takes over.
1324
1325 Only one of vga, serial, or usb debug port can
1326 be used at a time.
1327
1328 Currently only ttyS0 and ttyS1 may be specified by
1329 name. Other I/O ports may be explicitly specified
1330 on some architectures (x86 and arm at least) by
1331 replacing ttySn with an I/O port address, like this:
1332 earlyprintk=serial,0x1008,115200
1333 You can find the port for a given device in
1334 /proc/tty/driver/serial:
1335 2: uart:ST16650V2 port:00001008 irq:18 ...
1336
1337 Interaction with the standard serial driver is not
1338 very good.
1339
1340 The VGA output is eventually overwritten by
1341 the real console.
1342
1343 The xen option can only be used in Xen domains.
1344
1345 The sclp output can only be used on s390.
1346
1347 The optional "force" to "pciserial" enables use of a
1348 PCI device even when its classcode is not of the
1349 UART class.
1350
1351 edac_report= [HW,EDAC] Control how to report EDAC event
1352 Format: {"on" | "off" | "force"}
1353 on: enable EDAC to report H/W event. May be overridden
1354 by other higher priority error reporting module.
1355 off: disable H/W event reporting through EDAC.
1356 force: enforce the use of EDAC to report H/W event.
1357 default: on.
1358
1359 edd= [EDD]
1360 Format: {"off" | "on" | "skip[mbr]"}
1361
1362 efi= [EFI]
1363 Format: { "debug", "disable_early_pci_dma",
1364 "nochunk", "noruntime", "nosoftreserve",
1365 "novamap", "no_disable_early_pci_dma" }
1366 debug: enable misc debug output.
1367 disable_early_pci_dma: disable the busmaster bit on all
1368 PCI bridges while in the EFI boot stub.
1369 nochunk: disable reading files in "chunks" in the EFI
1370 boot stub, as chunking can cause problems with some
1371 firmware implementations.
1372 noruntime : disable EFI runtime services support
1373 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1374 attribute may cause the kernel to reserve the
1375 memory range for a memory mapping driver to
1376 claim. Specify efi=nosoftreserve to disable this
1377 reservation and treat the memory by its base type
1378 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1379 novamap: do not call SetVirtualAddressMap().
1380 no_disable_early_pci_dma: Leave the busmaster bit set
1381 on all PCI bridges while in the EFI boot stub
1382
1383 efi_no_storage_paranoia [EFI; X86]
1384 Using this parameter you can use more than 50% of
1385 your efi variable storage. Use this parameter only if
1386 you are really sure that your UEFI does sane gc and
1387 fulfills the spec otherwise your board may brick.
1388
1389 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1390 Add arbitrary attribute to specific memory range by
1391 updating original EFI memory map.
1392 Region of memory which aa attribute is added to is
1393 from ss to ss+nn.
1394
1395 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1396 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1397 attribute is added to range 0x100000000-0x180000000 and
1398 0x10a0000000-0x1120000000.
1399
1400 If efi_fake_mem=8G@9G:0x40000 is specified, the
1401 EFI_MEMORY_SP(0x40000) attribute is added to
1402 range 0x240000000-0x43fffffff.
1403
1404 Using this parameter you can do debugging of EFI memmap
1405 related features. For example, you can do debugging of
1406 Address Range Mirroring feature even if your box
1407 doesn't support it, or mark specific memory as
1408 "soft reserved".
1409
1410 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1411 that is to be dynamically loaded by Linux. If there are
1412 multiple variables with the same name but with different
1413 vendor GUIDs, all of them will be loaded. See
1414 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1415
1416
1417 eisa_irq_edge= [PARISC,HW]
1418 See header of drivers/parisc/eisa.c.
1419
1420 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1421 Format: ekgdboc=kbd
1422
1423 This is designed to be used in conjunction with
1424 the boot argument: earlyprintk=vga
1425
1426 This parameter works in place of the kgdboc parameter
1427 but can only be used if the backing tty is available
1428 very early in the boot process. For early debugging
1429 via a serial port see kgdboc_earlycon instead.
1430
1431 elanfreq= [X86-32]
1432 See comment before function elanfreq_setup() in
1433 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1434
1435 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1436 Specifies physical address of start of kernel core
1437 image elf header and optionally the size. Generally
1438 kexec loader will pass this option to capture kernel.
1439 See Documentation/admin-guide/kdump/kdump.rst for details.
1440
1441 enable_mtrr_cleanup [X86]
1442 The kernel tries to adjust MTRR layout from continuous
1443 to discrete, to make X server driver able to add WB
1444 entry later. This parameter enables that.
1445
1446 enable_timer_pin_1 [X86]
1447 Enable PIN 1 of APIC timer
1448 Can be useful to work around chipset bugs
1449 (in particular on some ATI chipsets).
1450 The kernel tries to set a reasonable default.
1451
1452 enforcing= [SELINUX] Set initial enforcing status.
1453 Format: {"0" | "1"}
1454 See security/selinux/Kconfig help text.
1455 0 -- permissive (log only, no denials).
1456 1 -- enforcing (deny and log).
1457 Default value is 0.
1458 Value can be changed at runtime via
1459 /sys/fs/selinux/enforce.
1460
1461 erst_disable [ACPI]
1462 Disable Error Record Serialization Table (ERST)
1463 support.
1464
1465 ether= [HW,NET] Ethernet cards parameters
1466 This option is obsoleted by the "netdev=" option, which
1467 has equivalent usage. See its documentation for details.
1468
1469 evm= [EVM]
1470 Format: { "fix" }
1471 Permit 'security.evm' to be updated regardless of
1472 current integrity status.
1473
1474 failslab=
1475 fail_usercopy=
1476 fail_page_alloc=
1477 fail_make_request=[KNL]
1478 General fault injection mechanism.
1479 Format: <interval>,<probability>,<space>,<times>
1480 See also Documentation/fault-injection/.
1481
1482 fb_tunnels= [NET]
1483 Format: { initns | none }
1484 See Documentation/admin-guide/sysctl/net.rst for
1485 fb_tunnels_only_for_init_ns
1486
1487 floppy= [HW]
1488 See Documentation/admin-guide/blockdev/floppy.rst.
1489
1490 force_pal_cache_flush
1491 [IA-64] Avoid check_sal_cache_flush which may hang on
1492 buggy SAL_CACHE_FLUSH implementations. Using this
1493 parameter will force ia64_sal_cache_flush to call
1494 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1495
1496 forcepae [X86-32]
1497 Forcefully enable Physical Address Extension (PAE).
1498 Many Pentium M systems disable PAE but may have a
1499 functionally usable PAE implementation.
1500 Warning: use of this parameter will taint the kernel
1501 and may cause unknown problems.
1502
1503 ftrace=[tracer]
1504 [FTRACE] will set and start the specified tracer
1505 as early as possible in order to facilitate early
1506 boot debugging.
1507
1508 ftrace_boot_snapshot
1509 [FTRACE] On boot up, a snapshot will be taken of the
1510 ftrace ring buffer that can be read at:
1511 /sys/kernel/tracing/snapshot.
1512 This is useful if you need tracing information from kernel
1513 boot up that is likely to be overridden by user space
1514 start up functionality.
1515
1516 ftrace_dump_on_oops[=orig_cpu]
1517 [FTRACE] will dump the trace buffers on oops.
1518 If no parameter is passed, ftrace will dump
1519 buffers of all CPUs, but if you pass orig_cpu, it will
1520 dump only the buffer of the CPU that triggered the
1521 oops.
1522
1523 ftrace_filter=[function-list]
1524 [FTRACE] Limit the functions traced by the function
1525 tracer at boot up. function-list is a comma-separated
1526 list of functions. This list can be changed at run
1527 time by the set_ftrace_filter file in the debugfs
1528 tracing directory.
1529
1530 ftrace_notrace=[function-list]
1531 [FTRACE] Do not trace the functions specified in
1532 function-list. This list can be changed at run time
1533 by the set_ftrace_notrace file in the debugfs
1534 tracing directory.
1535
1536 ftrace_graph_filter=[function-list]
1537 [FTRACE] Limit the top level callers functions traced
1538 by the function graph tracer at boot up.
1539 function-list is a comma-separated list of functions
1540 that can be changed at run time by the
1541 set_graph_function file in the debugfs tracing directory.
1542
1543 ftrace_graph_notrace=[function-list]
1544 [FTRACE] Do not trace from the functions specified in
1545 function-list. This list is a comma-separated list of
1546 functions that can be changed at run time by the
1547 set_graph_notrace file in the debugfs tracing directory.
1548
1549 ftrace_graph_max_depth=<uint>
1550 [FTRACE] Used with the function graph tracer. This is
1551 the max depth it will trace into a function. This value
1552 can be changed at run time by the max_graph_depth file
1553 in the tracefs tracing directory. default: 0 (no limit)
1554
1555 fw_devlink= [KNL] Create device links between consumer and supplier
1556 devices by scanning the firmware to infer the
1557 consumer/supplier relationships. This feature is
1558 especially useful when drivers are loaded as modules as
1559 it ensures proper ordering of tasks like device probing
1560 (suppliers first, then consumers), supplier boot state
1561 clean up (only after all consumers have probed),
1562 suspend/resume & runtime PM (consumers first, then
1563 suppliers).
1564 Format: { off | permissive | on | rpm }
1565 off -- Don't create device links from firmware info.
1566 permissive -- Create device links from firmware info
1567 but use it only for ordering boot state clean
1568 up (sync_state() calls).
1569 on -- Create device links from firmware info and use it
1570 to enforce probe and suspend/resume ordering.
1571 rpm -- Like "on", but also use to order runtime PM.
1572
1573 fw_devlink.strict=<bool>
1574 [KNL] Treat all inferred dependencies as mandatory
1575 dependencies. This only applies for fw_devlink=on|rpm.
1576 Format: <bool>
1577
1578 gamecon.map[2|3]=
1579 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1580 support via parallel port (up to 5 devices per port)
1581 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1582 See also Documentation/input/devices/joystick-parport.rst
1583
1584 gamma= [HW,DRM]
1585
1586 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART
1587 Format: off | on
1588 default: on
1589
1590 gcov_persist= [GCOV] When non-zero (default), profiling data for
1591 kernel modules is saved and remains accessible via
1592 debugfs, even when the module is unloaded/reloaded.
1593 When zero, profiling data is discarded and associated
1594 debugfs files are removed at module unload time.
1595
1596 goldfish [X86] Enable the goldfish android emulator platform.
1597 Don't use this when you are not running on the
1598 android emulator
1599
1600 gpio-mockup.gpio_mockup_ranges
1601 [HW] Sets the ranges of gpiochip of for this device.
1602 Format: <start1>,<end1>,<start2>,<end2>...
1603 gpio-mockup.gpio_mockup_named_lines
1604 [HW] Let the driver know GPIO lines should be named.
1605
1606 gpt [EFI] Forces disk with valid GPT signature but
1607 invalid Protective MBR to be treated as GPT. If the
1608 primary GPT is corrupted, it enables the backup/alternate
1609 GPT to be used instead.
1610
1611 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1612 the "Enable 0" bit of the configuration register.
1613 Format: 0 | 1
1614 Default: 0
1615 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1616 the "Enable 0" bit of the configuration register.
1617 Format: 0 | 1
1618 Default: 0
1619 grcan.select= [HW] Select which physical interface to use.
1620 Format: 0 | 1
1621 Default: 0
1622 grcan.txsize= [HW] Sets the size of the tx buffer.
1623 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1624 Default: 1024
1625 grcan.rxsize= [HW] Sets the size of the rx buffer.
1626 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1627 Default: 1024
1628
1629 hardened_usercopy=
1630 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
1631 hardening is enabled for this boot. Hardened
1632 usercopy checking is used to protect the kernel
1633 from reading or writing beyond known memory
1634 allocation boundaries as a proactive defense
1635 against bounds-checking flaws in the kernel's
1636 copy_to_user()/copy_from_user() interface.
1637 on Perform hardened usercopy checks (default).
1638 off Disable hardened usercopy checks.
1639
1640 hardlockup_all_cpu_backtrace=
1641 [KNL] Should the hard-lockup detector generate
1642 backtraces on all cpus.
1643 Format: 0 | 1
1644
1645 hashdist= [KNL,NUMA] Large hashes allocated during boot
1646 are distributed across NUMA nodes. Defaults on
1647 for 64-bit NUMA, off otherwise.
1648 Format: 0 | 1 (for off | on)
1649
1650 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1651
1652 hd= [EIDE] (E)IDE hard drive subsystem geometry
1653 Format: <cyl>,<head>,<sect>
1654
1655 hest_disable [ACPI]
1656 Disable Hardware Error Source Table (HEST) support;
1657 corresponding firmware-first mode error processing
1658 logic will be disabled.
1659
1660 hibernate= [HIBERNATION]
1661 noresume Don't check if there's a hibernation image
1662 present during boot.
1663 nocompress Don't compress/decompress hibernation images.
1664 no Disable hibernation and resume.
1665 protect_image Turn on image protection during restoration
1666 (that will set all pages holding image data
1667 during restoration read-only).
1668
1669 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1670 size of <nn>. This works even on boxes that have no
1671 highmem otherwise. This also works to reduce highmem
1672 size on bigger boxes.
1673
1674 highres= [KNL] Enable/disable high resolution timer mode.
1675 Valid parameters: "on", "off"
1676 Default: "on"
1677
1678 hlt [BUGS=ARM,SH]
1679
1680 hostname= [KNL] Set the hostname (aka UTS nodename).
1681 Format: <string>
1682 This allows setting the system's hostname during early
1683 startup. This sets the name returned by gethostname.
1684 Using this parameter to set the hostname makes it
1685 possible to ensure the hostname is correctly set before
1686 any userspace processes run, avoiding the possibility
1687 that a process may call gethostname before the hostname
1688 has been explicitly set, resulting in the calling
1689 process getting an incorrect result. The string must
1690 not exceed the maximum allowed hostname length (usually
1691 64 characters) and will be truncated otherwise.
1692
1693 hpet= [X86-32,HPET] option to control HPET usage
1694 Format: { enable (default) | disable | force |
1695 verbose }
1696 disable: disable HPET and use PIT instead
1697 force: allow force enabled of undocumented chips (ICH4,
1698 VIA, nVidia)
1699 verbose: show contents of HPET registers during setup
1700
1701 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1702 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1703
1704 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1705 If this follows hugepagesz (below), it specifies
1706 the number of pages of hugepagesz to be allocated.
1707 If this is the first HugeTLB parameter on the command
1708 line, it specifies the number of pages to allocate for
1709 the default huge page size. If using node format, the
1710 number of pages to allocate per-node can be specified.
1711 See also Documentation/admin-guide/mm/hugetlbpage.rst.
1712 Format: <integer> or (node format)
1713 <node>:<integer>[,<node>:<integer>]
1714
1715 hugepagesz=
1716 [HW] The size of the HugeTLB pages. This is used in
1717 conjunction with hugepages (above) to allocate huge
1718 pages of a specific size at boot. The pair
1719 hugepagesz=X hugepages=Y can be specified once for
1720 each supported huge page size. Huge page sizes are
1721 architecture dependent. See also
1722 Documentation/admin-guide/mm/hugetlbpage.rst.
1723 Format: size[KMG]
1724
1725 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation
1726 of gigantic hugepages. Or using node format, the size
1727 of a CMA area per node can be specified.
1728 Format: nn[KMGTPE] or (node format)
1729 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
1730
1731 Reserve a CMA area of given size and allocate gigantic
1732 hugepages using the CMA allocator. If enabled, the
1733 boot-time allocation of gigantic hugepages is skipped.
1734
1735 hugetlb_free_vmemmap=
1736 [KNL] Reguires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
1737 enabled.
1738 Control if HugeTLB Vmemmap Optimization (HVO) is enabled.
1739 Allows heavy hugetlb users to free up some more
1740 memory (7 * PAGE_SIZE for each 2MB hugetlb page).
1741 Format: { on | off (default) }
1742
1743 on: enable HVO
1744 off: disable HVO
1745
1746 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
1747 the default is on.
1748
1749 Note that the vmemmap pages may be allocated from the added
1750 memory block itself when memory_hotplug.memmap_on_memory is
1751 enabled, those vmemmap pages cannot be optimized even if this
1752 feature is enabled. Other vmemmap pages not allocated from
1753 the added memory block itself do not be affected.
1754
1755 hung_task_panic=
1756 [KNL] Should the hung task detector generate panics.
1757 Format: 0 | 1
1758
1759 A value of 1 instructs the kernel to panic when a
1760 hung task is detected. The default value is controlled
1761 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1762 option. The value selected by this boot parameter can
1763 be changed later by the kernel.hung_task_panic sysctl.
1764
1765 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1766 terminal devices. Valid values: 0..8
1767 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1768 If specified, z/VM IUCV HVC accepts connections
1769 from listed z/VM user IDs only.
1770
1771 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1772 which allow the hypervisor to 'idle' the
1773 guest on lock contention.
1774
1775 keep_bootcon [KNL]
1776 Do not unregister boot console at start. This is only
1777 useful for debugging when something happens in the window
1778 between unregistering the boot console and initializing
1779 the real console.
1780
1781 i2c_bus= [HW] Override the default board specific I2C bus speed
1782 or register an additional I2C bus that is not
1783 registered from board initialization code.
1784 Format:
1785 <bus_id>,<clkrate>
1786
1787 i8042.debug [HW] Toggle i8042 debug mode
1788 i8042.unmask_kbd_data
1789 [HW] Enable printing of interrupt data from the KBD port
1790 (disabled by default, and as a pre-condition
1791 requires that i8042.debug=1 be enabled)
1792 i8042.direct [HW] Put keyboard port into non-translated mode
1793 i8042.dumbkbd [HW] Pretend that controller can only read data from
1794 keyboard and cannot control its state
1795 (Don't attempt to blink the leds)
1796 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1797 i8042.nokbd [HW] Don't check/create keyboard port
1798 i8042.noloop [HW] Disable the AUX Loopback command while probing
1799 for the AUX port
1800 i8042.nomux [HW] Don't check presence of an active multiplexing
1801 controller
1802 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1803 controllers
1804 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1805 i8042.reset [HW] Reset the controller during init, cleanup and
1806 suspend-to-ram transitions, only during s2r
1807 transitions, or never reset
1808 Format: { 1 | Y | y | 0 | N | n }
1809 1, Y, y: always reset controller
1810 0, N, n: don't ever reset controller
1811 Default: only on s2r transitions on x86; most other
1812 architectures force reset to be always executed
1813 i8042.unlock [HW] Unlock (ignore) the keylock
1814 i8042.kbdreset [HW] Reset device connected to KBD port
1815 i8042.probe_defer
1816 [HW] Allow deferred probing upon i8042 probe errors
1817
1818 i810= [HW,DRM]
1819
1820 i915.invert_brightness=
1821 [DRM] Invert the sense of the variable that is used to
1822 set the brightness of the panel backlight. Normally a
1823 brightness value of 0 indicates backlight switched off,
1824 and the maximum of the brightness value sets the backlight
1825 to maximum brightness. If this parameter is set to 0
1826 (default) and the machine requires it, or this parameter
1827 is set to 1, a brightness value of 0 sets the backlight
1828 to maximum brightness, and the maximum of the brightness
1829 value switches the backlight off.
1830 -1 -- never invert brightness
1831 0 -- machine default
1832 1 -- force brightness inversion
1833
1834 icn= [HW,ISDN]
1835 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1836
1837
1838 idle= [X86]
1839 Format: idle=poll, idle=halt, idle=nomwait
1840 Poll forces a polling idle loop that can slightly
1841 improve the performance of waking up a idle CPU, but
1842 will use a lot of power and make the system run hot.
1843 Not recommended.
1844 idle=halt: Halt is forced to be used for CPU idle.
1845 In such case C2/C3 won't be used again.
1846 idle=nomwait: Disable mwait for CPU C-states
1847
1848 idxd.sva= [HW]
1849 Format: <bool>
1850 Allow force disabling of Shared Virtual Memory (SVA)
1851 support for the idxd driver. By default it is set to
1852 true (1).
1853
1854 idxd.tc_override= [HW]
1855 Format: <bool>
1856 Allow override of default traffic class configuration
1857 for the device. By default it is set to false (0).
1858
1859 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1860 Format: { strict | legacy | 2008 | relaxed }
1861 Default: strict
1862
1863 Choose which programs will be accepted for execution
1864 based on the IEEE 754 NaN encoding(s) supported by
1865 the FPU and the NaN encoding requested with the value
1866 of an ELF file header flag individually set by each
1867 binary. Hardware implementations are permitted to
1868 support either or both of the legacy and the 2008 NaN
1869 encoding mode.
1870
1871 Available settings are as follows:
1872 strict accept binaries that request a NaN encoding
1873 supported by the FPU
1874 legacy only accept legacy-NaN binaries, if supported
1875 by the FPU
1876 2008 only accept 2008-NaN binaries, if supported
1877 by the FPU
1878 relaxed accept any binaries regardless of whether
1879 supported by the FPU
1880
1881 The FPU emulator is always able to support both NaN
1882 encodings, so if no FPU hardware is present or it has
1883 been disabled with 'nofpu', then the settings of
1884 'legacy' and '2008' strap the emulator accordingly,
1885 'relaxed' straps the emulator for both legacy-NaN and
1886 2008-NaN, whereas 'strict' enables legacy-NaN only on
1887 legacy processors and both NaN encodings on MIPS32 or
1888 MIPS64 CPUs.
1889
1890 The setting for ABS.fmt/NEG.fmt instruction execution
1891 mode generally follows that for the NaN encoding,
1892 except where unsupported by hardware.
1893
1894 ignore_loglevel [KNL]
1895 Ignore loglevel setting - this will print /all/
1896 kernel messages to the console. Useful for debugging.
1897 We also add it as printk module parameter, so users
1898 could change it dynamically, usually by
1899 /sys/module/printk/parameters/ignore_loglevel.
1900
1901 ignore_rlimit_data
1902 Ignore RLIMIT_DATA setting for data mappings,
1903 print warning at first misuse. Can be changed via
1904 /sys/module/kernel/parameters/ignore_rlimit_data.
1905
1906 ihash_entries= [KNL]
1907 Set number of hash buckets for inode cache.
1908
1909 ima_appraise= [IMA] appraise integrity measurements
1910 Format: { "off" | "enforce" | "fix" | "log" }
1911 default: "enforce"
1912
1913 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1914 The builtin appraise policy appraises all files
1915 owned by uid=0.
1916
1917 ima_canonical_fmt [IMA]
1918 Use the canonical format for the binary runtime
1919 measurements, instead of host native format.
1920
1921 ima_hash= [IMA]
1922 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1923 | sha512 | ... }
1924 default: "sha1"
1925
1926 The list of supported hash algorithms is defined
1927 in crypto/hash_info.h.
1928
1929 ima_policy= [IMA]
1930 The builtin policies to load during IMA setup.
1931 Format: "tcb | appraise_tcb | secure_boot |
1932 fail_securely | critical_data"
1933
1934 The "tcb" policy measures all programs exec'd, files
1935 mmap'd for exec, and all files opened with the read
1936 mode bit set by either the effective uid (euid=0) or
1937 uid=0.
1938
1939 The "appraise_tcb" policy appraises the integrity of
1940 all files owned by root.
1941
1942 The "secure_boot" policy appraises the integrity
1943 of files (eg. kexec kernel image, kernel modules,
1944 firmware, policy, etc) based on file signatures.
1945
1946 The "fail_securely" policy forces file signature
1947 verification failure also on privileged mounted
1948 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1949 flag.
1950
1951 The "critical_data" policy measures kernel integrity
1952 critical data.
1953
1954 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1955 Load a policy which meets the needs of the Trusted
1956 Computing Base. This means IMA will measure all
1957 programs exec'd, files mmap'd for exec, and all files
1958 opened for read by uid=0.
1959
1960 ima_template= [IMA]
1961 Select one of defined IMA measurements template formats.
1962 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" |
1963 "ima-sigv2" }
1964 Default: "ima-ng"
1965
1966 ima_template_fmt=
1967 [IMA] Define a custom template format.
1968 Format: { "field1|...|fieldN" }
1969
1970 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1971 Format: <min_file_size>
1972 Set the minimal file size for using asynchronous hash.
1973 If left unspecified, ahash usage is disabled.
1974
1975 ahash performance varies for different data sizes on
1976 different crypto accelerators. This option can be used
1977 to achieve the best performance for a particular HW.
1978
1979 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1980 Format: <bufsize>
1981 Set hashing buffer size. Default: 4k.
1982
1983 ahash performance varies for different chunk sizes on
1984 different crypto accelerators. This option can be used
1985 to achieve best performance for particular HW.
1986
1987 init= [KNL]
1988 Format: <full_path>
1989 Run specified binary instead of /sbin/init as init
1990 process.
1991
1992 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1993 for working out where the kernel is dying during
1994 startup.
1995
1996 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1997 initcall functions. Useful for debugging built-in
1998 modules and initcalls.
1999
2000 initramfs_async= [KNL]
2001 Format: <bool>
2002 Default: 1
2003 This parameter controls whether the initramfs
2004 image is unpacked asynchronously, concurrently
2005 with devices being probed and
2006 initialized. This should normally just work,
2007 but as a debugging aid, one can get the
2008 historical behaviour of the initramfs
2009 unpacking being completed before device_ and
2010 late_ initcalls.
2011
2012 initrd= [BOOT] Specify the location of the initial ramdisk
2013
2014 initrdmem= [KNL] Specify a physical address and size from which to
2015 load the initrd. If an initrd is compiled in or
2016 specified in the bootparams, it takes priority over this
2017 setting.
2018 Format: ss[KMG],nn[KMG]
2019 Default is 0, 0
2020
2021 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
2022 zeroes.
2023 Format: 0 | 1
2024 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
2025
2026 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
2027 Format: 0 | 1
2028 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
2029
2030 init_pkru= [X86] Specify the default memory protection keys rights
2031 register contents for all processes. 0x55555554 by
2032 default (disallow access to all but pkey 0). Can
2033 override in debugfs after boot.
2034
2035 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
2036 Format: <irq>
2037
2038 int_pln_enable [X86] Enable power limit notification interrupt
2039
2040 integrity_audit=[IMA]
2041 Format: { "0" | "1" }
2042 0 -- basic integrity auditing messages. (Default)
2043 1 -- additional integrity auditing messages.
2044
2045 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
2046 on
2047 Enable intel iommu driver.
2048 off
2049 Disable intel iommu driver.
2050 igfx_off [Default Off]
2051 By default, gfx is mapped as normal device. If a gfx
2052 device has a dedicated DMAR unit, the DMAR unit is
2053 bypassed by not enabling DMAR with this option. In
2054 this case, gfx device will use physical address for
2055 DMA.
2056 strict [Default Off]
2057 Deprecated, equivalent to iommu.strict=1.
2058 sp_off [Default Off]
2059 By default, super page will be supported if Intel IOMMU
2060 has the capability. With this option, super page will
2061 not be supported.
2062 sm_on
2063 Enable the Intel IOMMU scalable mode if the hardware
2064 advertises that it has support for the scalable mode
2065 translation.
2066 sm_off
2067 Disallow use of the Intel IOMMU scalable mode.
2068 tboot_noforce [Default Off]
2069 Do not force the Intel IOMMU enabled under tboot.
2070 By default, tboot will force Intel IOMMU on, which
2071 could harm performance of some high-throughput
2072 devices like 40GBit network cards, even if identity
2073 mapping is enabled.
2074 Note that using this option lowers the security
2075 provided by tboot because it makes the system
2076 vulnerable to DMA attacks.
2077
2078 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
2079 0 disables intel_idle and fall back on acpi_idle.
2080 1 to 9 specify maximum depth of C-state.
2081
2082 intel_pstate= [X86]
2083 disable
2084 Do not enable intel_pstate as the default
2085 scaling driver for the supported processors
2086 passive
2087 Use intel_pstate as a scaling driver, but configure it
2088 to work with generic cpufreq governors (instead of
2089 enabling its internal governor). This mode cannot be
2090 used along with the hardware-managed P-states (HWP)
2091 feature.
2092 force
2093 Enable intel_pstate on systems that prohibit it by default
2094 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2095 instead of acpi-cpufreq may disable platform features, such
2096 as thermal controls and power capping, that rely on ACPI
2097 P-States information being indicated to OSPM and therefore
2098 should be used with caution. This option does not work with
2099 processors that aren't supported by the intel_pstate driver
2100 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2101 no_hwp
2102 Do not enable hardware P state control (HWP)
2103 if available.
2104 hwp_only
2105 Only load intel_pstate on systems which support
2106 hardware P state control (HWP) if available.
2107 support_acpi_ppc
2108 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2109 Description Table, specifies preferred power management
2110 profile as "Enterprise Server" or "Performance Server",
2111 then this feature is turned on by default.
2112 per_cpu_perf_limits
2113 Allow per-logical-CPU P-State performance control limits using
2114 cpufreq sysfs interface
2115
2116 intremap= [X86-64, Intel-IOMMU]
2117 on enable Interrupt Remapping (default)
2118 off disable Interrupt Remapping
2119 nosid disable Source ID checking
2120 no_x2apic_optout
2121 BIOS x2APIC opt-out request will be ignored
2122 nopost disable Interrupt Posting
2123
2124 iomem= Disable strict checking of access to MMIO memory
2125 strict regions from userspace.
2126 relaxed
2127
2128 iommu= [X86]
2129 off
2130 force
2131 noforce
2132 biomerge
2133 panic
2134 nopanic
2135 merge
2136 nomerge
2137 soft
2138 pt [X86]
2139 nopt [X86]
2140 nobypass [PPC/POWERNV]
2141 Disable IOMMU bypass, using IOMMU for PCI devices.
2142
2143 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices.
2144 Format: { "0" | "1" }
2145 0 - Try to allocate a 32-bit DMA address first, before
2146 falling back to the full range if needed.
2147 1 - Allocate directly from the full usable range,
2148 forcing Dual Address Cycle for PCI cards supporting
2149 greater than 32-bit addressing.
2150
2151 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour
2152 Format: { "0" | "1" }
2153 0 - Lazy mode.
2154 Request that DMA unmap operations use deferred
2155 invalidation of hardware TLBs, for increased
2156 throughput at the cost of reduced device isolation.
2157 Will fall back to strict mode if not supported by
2158 the relevant IOMMU driver.
2159 1 - Strict mode.
2160 DMA unmap operations invalidate IOMMU hardware TLBs
2161 synchronously.
2162 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2163 Note: on x86, strict mode specified via one of the
2164 legacy driver-specific options takes precedence.
2165
2166 iommu.passthrough=
2167 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
2168 Format: { "0" | "1" }
2169 0 - Use IOMMU translation for DMA.
2170 1 - Bypass the IOMMU for DMA.
2171 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2172
2173 io7= [HW] IO7 for Marvel-based Alpha systems
2174 See comment before marvel_specify_io7 in
2175 arch/alpha/kernel/core_marvel.c.
2176
2177 io_delay= [X86] I/O delay method
2178 0x80
2179 Standard port 0x80 based delay
2180 0xed
2181 Alternate port 0xed based delay (needed on some systems)
2182 udelay
2183 Simple two microseconds delay
2184 none
2185 No delay
2186
2187 ip= [IP_PNP]
2188 See Documentation/admin-guide/nfs/nfsroot.rst.
2189
2190 ipcmni_extend [KNL] Extend the maximum number of unique System V
2191 IPC identifiers from 32,768 to 16,777,216.
2192
2193 irqaffinity= [SMP] Set the default irq affinity mask
2194 The argument is a cpu list, as described above.
2195
2196 irqchip.gicv2_force_probe=
2197 [ARM, ARM64]
2198 Format: <bool>
2199 Force the kernel to look for the second 4kB page
2200 of a GICv2 controller even if the memory range
2201 exposed by the device tree is too small.
2202
2203 irqchip.gicv3_nolpi=
2204 [ARM, ARM64]
2205 Force the kernel to ignore the availability of
2206 LPIs (and by consequence ITSs). Intended for system
2207 that use the kernel as a bootloader, and thus want
2208 to let secondary kernels in charge of setting up
2209 LPIs.
2210
2211 irqchip.gicv3_pseudo_nmi= [ARM64]
2212 Enables support for pseudo-NMIs in the kernel. This
2213 requires the kernel to be built with
2214 CONFIG_ARM64_PSEUDO_NMI.
2215
2216 irqfixup [HW]
2217 When an interrupt is not handled search all handlers
2218 for it. Intended to get systems with badly broken
2219 firmware running.
2220
2221 irqpoll [HW]
2222 When an interrupt is not handled search all handlers
2223 for it. Also check all handlers each timer
2224 interrupt. Intended to get systems with badly broken
2225 firmware running.
2226
2227 isapnp= [ISAPNP]
2228 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2229
2230 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2231 [Deprecated - use cpusets instead]
2232 Format: [flag-list,]<cpu-list>
2233
2234 Specify one or more CPUs to isolate from disturbances
2235 specified in the flag list (default: domain):
2236
2237 nohz
2238 Disable the tick when a single task runs.
2239
2240 A residual 1Hz tick is offloaded to workqueues, which you
2241 need to affine to housekeeping through the global
2242 workqueue's affinity configured via the
2243 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2244 by using the 'domain' flag described below.
2245
2246 NOTE: by default the global workqueue runs on all CPUs,
2247 so to protect individual CPUs the 'cpumask' file has to
2248 be configured manually after bootup.
2249
2250 domain
2251 Isolate from the general SMP balancing and scheduling
2252 algorithms. Note that performing domain isolation this way
2253 is irreversible: it's not possible to bring back a CPU to
2254 the domains once isolated through isolcpus. It's strongly
2255 advised to use cpusets instead to disable scheduler load
2256 balancing through the "cpuset.sched_load_balance" file.
2257 It offers a much more flexible interface where CPUs can
2258 move in and out of an isolated set anytime.
2259
2260 You can move a process onto or off an "isolated" CPU via
2261 the CPU affinity syscalls or cpuset.
2262 <cpu number> begins at 0 and the maximum value is
2263 "number of CPUs in system - 1".
2264
2265 managed_irq
2266
2267 Isolate from being targeted by managed interrupts
2268 which have an interrupt mask containing isolated
2269 CPUs. The affinity of managed interrupts is
2270 handled by the kernel and cannot be changed via
2271 the /proc/irq/* interfaces.
2272
2273 This isolation is best effort and only effective
2274 if the automatically assigned interrupt mask of a
2275 device queue contains isolated and housekeeping
2276 CPUs. If housekeeping CPUs are online then such
2277 interrupts are directed to the housekeeping CPU
2278 so that IO submitted on the housekeeping CPU
2279 cannot disturb the isolated CPU.
2280
2281 If a queue's affinity mask contains only isolated
2282 CPUs then this parameter has no effect on the
2283 interrupt routing decision, though interrupts are
2284 only delivered when tasks running on those
2285 isolated CPUs submit IO. IO submitted on
2286 housekeeping CPUs has no influence on those
2287 queues.
2288
2289 The format of <cpu-list> is described above.
2290
2291 iucv= [HW,NET]
2292
2293 ivrs_ioapic [HW,X86-64]
2294 Provide an override to the IOAPIC-ID<->DEVICE-ID
2295 mapping provided in the IVRS ACPI table.
2296 By default, PCI segment is 0, and can be omitted.
2297 For example:
2298 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0
2299 write the parameter as:
2300 ivrs_ioapic[10]=00:14.0
2301 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and
2302 PCI device 00:14.0 write the parameter as:
2303 ivrs_ioapic[10]=0001:00:14.0
2304
2305 ivrs_hpet [HW,X86-64]
2306 Provide an override to the HPET-ID<->DEVICE-ID
2307 mapping provided in the IVRS ACPI table.
2308 By default, PCI segment is 0, and can be omitted.
2309 For example:
2310 * To map HPET-ID decimal 0 to PCI device 00:14.0
2311 write the parameter as:
2312 ivrs_hpet[0]=00:14.0
2313 * To map HPET-ID decimal 10 to PCI segment 0x1 and
2314 PCI device 00:14.0 write the parameter as:
2315 ivrs_ioapic[10]=0001:00:14.0
2316
2317 ivrs_acpihid [HW,X86-64]
2318 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2319 mapping provided in the IVRS ACPI table.
2320
2321 For example, to map UART-HID:UID AMD0020:0 to
2322 PCI segment 0x1 and PCI device ID 00:14.5,
2323 write the parameter as:
2324 ivrs_acpihid[0001:00:14.5]=AMD0020:0
2325
2326 By default, PCI segment is 0, and can be omitted.
2327 For example, PCI device 00:14.5 write the parameter as:
2328 ivrs_acpihid[00:14.5]=AMD0020:0
2329
2330 js= [HW,JOY] Analog joystick
2331 See Documentation/input/joydev/joystick.rst.
2332
2333 nokaslr [KNL]
2334 When CONFIG_RANDOMIZE_BASE is set, this disables
2335 kernel and module base offset ASLR (Address Space
2336 Layout Randomization).
2337
2338 kasan_multi_shot
2339 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2340 report on every invalid memory access. Without this
2341 parameter KASAN will print report only for the first
2342 invalid access.
2343
2344 keepinitrd [HW,ARM]
2345
2346 kernelcore= [KNL,X86,IA-64,PPC]
2347 Format: nn[KMGTPE] | nn% | "mirror"
2348 This parameter specifies the amount of memory usable by
2349 the kernel for non-movable allocations. The requested
2350 amount is spread evenly throughout all nodes in the
2351 system as ZONE_NORMAL. The remaining memory is used for
2352 movable memory in its own zone, ZONE_MOVABLE. In the
2353 event, a node is too small to have both ZONE_NORMAL and
2354 ZONE_MOVABLE, kernelcore memory will take priority and
2355 other nodes will have a larger ZONE_MOVABLE.
2356
2357 ZONE_MOVABLE is used for the allocation of pages that
2358 may be reclaimed or moved by the page migration
2359 subsystem. Note that allocations like PTEs-from-HighMem
2360 still use the HighMem zone if it exists, and the Normal
2361 zone if it does not.
2362
2363 It is possible to specify the exact amount of memory in
2364 the form of "nn[KMGTPE]", a percentage of total system
2365 memory in the form of "nn%", or "mirror". If "mirror"
2366 option is specified, mirrored (reliable) memory is used
2367 for non-movable allocations and remaining memory is used
2368 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2369 are exclusive, so you cannot specify multiple forms.
2370
2371 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2372 Format: <Controller#>[,poll interval]
2373 The controller # is the number of the ehci usb debug
2374 port as it is probed via PCI. The poll interval is
2375 optional and is the number seconds in between
2376 each poll cycle to the debug port in case you need
2377 the functionality for interrupting the kernel with
2378 gdb or control-c on the dbgp connection. When
2379 not using this parameter you use sysrq-g to break into
2380 the kernel debugger.
2381
2382 kgdboc= [KGDB,HW] kgdb over consoles.
2383 Requires a tty driver that supports console polling,
2384 or a supported polling keyboard driver (non-usb).
2385 Serial only format: <serial_device>[,baud]
2386 keyboard only format: kbd
2387 keyboard and serial format: kbd,<serial_device>[,baud]
2388 Optional Kernel mode setting:
2389 kms, kbd format: kms,kbd
2390 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2391
2392 kgdboc_earlycon= [KGDB,HW]
2393 If the boot console provides the ability to read
2394 characters and can work in polling mode, you can use
2395 this parameter to tell kgdb to use it as a backend
2396 until the normal console is registered. Intended to
2397 be used together with the kgdboc parameter which
2398 specifies the normal console to transition to.
2399
2400 The name of the early console should be specified
2401 as the value of this parameter. Note that the name of
2402 the early console might be different than the tty
2403 name passed to kgdboc. It's OK to leave the value
2404 blank and the first boot console that implements
2405 read() will be picked.
2406
2407 kgdbwait [KGDB] Stop kernel execution and enter the
2408 kernel debugger at the earliest opportunity.
2409
2410 kmac= [MIPS] Korina ethernet MAC address.
2411 Configure the RouterBoard 532 series on-chip
2412 Ethernet adapter MAC address.
2413
2414 kmemleak= [KNL] Boot-time kmemleak enable/disable
2415 Valid arguments: on, off
2416 Default: on
2417 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2418 the default is off.
2419
2420 kprobe_event=[probe-list]
2421 [FTRACE] Add kprobe events and enable at boot time.
2422 The probe-list is a semicolon delimited list of probe
2423 definitions. Each definition is same as kprobe_events
2424 interface, but the parameters are comma delimited.
2425 For example, to add a kprobe event on vfs_read with
2426 arg1 and arg2, add to the command line;
2427
2428 kprobe_event=p,vfs_read,$arg1,$arg2
2429
2430 See also Documentation/trace/kprobetrace.rst "Kernel
2431 Boot Parameter" section.
2432
2433 kpti= [ARM64] Control page table isolation of user
2434 and kernel address spaces.
2435 Default: enabled on cores which need mitigation.
2436 0: force disabled
2437 1: force enabled
2438
2439 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2440 Default is 0 (don't ignore, but inject #GP)
2441
2442 kvm.eager_page_split=
2443 [KVM,X86] Controls whether or not KVM will try to
2444 proactively split all huge pages during dirty logging.
2445 Eager page splitting reduces interruptions to vCPU
2446 execution by eliminating the write-protection faults
2447 and MMU lock contention that would otherwise be
2448 required to split huge pages lazily.
2449
2450 VM workloads that rarely perform writes or that write
2451 only to a small region of VM memory may benefit from
2452 disabling eager page splitting to allow huge pages to
2453 still be used for reads.
2454
2455 The behavior of eager page splitting depends on whether
2456 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If
2457 disabled, all huge pages in a memslot will be eagerly
2458 split when dirty logging is enabled on that memslot. If
2459 enabled, eager page splitting will be performed during
2460 the KVM_CLEAR_DIRTY ioctl, and only for the pages being
2461 cleared.
2462
2463 Eager page splitting is only supported when kvm.tdp_mmu=Y.
2464
2465 Default is Y (on).
2466
2467 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2468 Default is false (don't support).
2469
2470 kvm.nx_huge_pages=
2471 [KVM] Controls the software workaround for the
2472 X86_BUG_ITLB_MULTIHIT bug.
2473 force : Always deploy workaround.
2474 off : Never deploy workaround.
2475 auto : Deploy workaround based on the presence of
2476 X86_BUG_ITLB_MULTIHIT.
2477
2478 Default is 'auto'.
2479
2480 If the software workaround is enabled for the host,
2481 guests do need not to enable it for nested guests.
2482
2483 kvm.nx_huge_pages_recovery_ratio=
2484 [KVM] Controls how many 4KiB pages are periodically zapped
2485 back to huge pages. 0 disables the recovery, otherwise if
2486 the value is N KVM will zap 1/Nth of the 4KiB pages every
2487 period (see below). The default is 60.
2488
2489 kvm.nx_huge_pages_recovery_period_ms=
2490 [KVM] Controls the time period at which KVM zaps 4KiB pages
2491 back to huge pages. If the value is a non-zero N, KVM will
2492 zap a portion (see ratio above) of the pages every N msecs.
2493 If the value is 0 (the default), KVM will pick a period based
2494 on the ratio, such that a page is zapped after 1 hour on average.
2495
2496 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2497 Default is 1 (enabled)
2498
2499 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2500 for all guests.
2501 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2502
2503 kvm-arm.mode=
2504 [KVM,ARM] Select one of KVM/arm64's modes of operation.
2505
2506 none: Forcefully disable KVM.
2507
2508 nvhe: Standard nVHE-based mode, without support for
2509 protected guests.
2510
2511 protected: nVHE-based mode with support for guests whose
2512 state is kept private from the host.
2513
2514 Defaults to VHE/nVHE based on hardware support. Setting
2515 mode to "protected" will disable kexec and hibernation
2516 for the host.
2517
2518 kvm-arm.vgic_v3_group0_trap=
2519 [KVM,ARM] Trap guest accesses to GICv3 group-0
2520 system registers
2521
2522 kvm-arm.vgic_v3_group1_trap=
2523 [KVM,ARM] Trap guest accesses to GICv3 group-1
2524 system registers
2525
2526 kvm-arm.vgic_v3_common_trap=
2527 [KVM,ARM] Trap guest accesses to GICv3 common
2528 system registers
2529
2530 kvm-arm.vgic_v4_enable=
2531 [KVM,ARM] Allow use of GICv4 for direct injection of
2532 LPIs.
2533
2534 kvm_cma_resv_ratio=n [PPC]
2535 Reserves given percentage from system memory area for
2536 contiguous memory allocation for KVM hash pagetable
2537 allocation.
2538 By default it reserves 5% of total system memory.
2539 Format: <integer>
2540 Default: 5
2541
2542 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2543 (virtualized MMU) support on capable Intel chips.
2544 Default is 1 (enabled)
2545
2546 kvm-intel.emulate_invalid_guest_state=
2547 [KVM,Intel] Disable emulation of invalid guest state.
2548 Ignored if kvm-intel.enable_unrestricted_guest=1, as
2549 guest state is never invalid for unrestricted guests.
2550 This param doesn't apply to nested guests (L2), as KVM
2551 never emulates invalid L2 guest state.
2552 Default is 1 (enabled)
2553
2554 kvm-intel.flexpriority=
2555 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2556 Default is 1 (enabled)
2557
2558 kvm-intel.nested=
2559 [KVM,Intel] Enable VMX nesting (nVMX).
2560 Default is 0 (disabled)
2561
2562 kvm-intel.unrestricted_guest=
2563 [KVM,Intel] Disable unrestricted guest feature
2564 (virtualized real and unpaged mode) on capable
2565 Intel chips. Default is 1 (enabled)
2566
2567 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2568 CVE-2018-3620.
2569
2570 Valid arguments: never, cond, always
2571
2572 always: L1D cache flush on every VMENTER.
2573 cond: Flush L1D on VMENTER only when the code between
2574 VMEXIT and VMENTER can leak host memory.
2575 never: Disables the mitigation
2576
2577 Default is cond (do L1 cache flush in specific instances)
2578
2579 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2580 feature (tagged TLBs) on capable Intel chips.
2581 Default is 1 (enabled)
2582
2583 l1d_flush= [X86,INTEL]
2584 Control mitigation for L1D based snooping vulnerability.
2585
2586 Certain CPUs are vulnerable to an exploit against CPU
2587 internal buffers which can forward information to a
2588 disclosure gadget under certain conditions.
2589
2590 In vulnerable processors, the speculatively
2591 forwarded data can be used in a cache side channel
2592 attack, to access data to which the attacker does
2593 not have direct access.
2594
2595 This parameter controls the mitigation. The
2596 options are:
2597
2598 on - enable the interface for the mitigation
2599
2600 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2601 affected CPUs
2602
2603 The kernel PTE inversion protection is unconditionally
2604 enabled and cannot be disabled.
2605
2606 full
2607 Provides all available mitigations for the
2608 L1TF vulnerability. Disables SMT and
2609 enables all mitigations in the
2610 hypervisors, i.e. unconditional L1D flush.
2611
2612 SMT control and L1D flush control via the
2613 sysfs interface is still possible after
2614 boot. Hypervisors will issue a warning
2615 when the first VM is started in a
2616 potentially insecure configuration,
2617 i.e. SMT enabled or L1D flush disabled.
2618
2619 full,force
2620 Same as 'full', but disables SMT and L1D
2621 flush runtime control. Implies the
2622 'nosmt=force' command line option.
2623 (i.e. sysfs control of SMT is disabled.)
2624
2625 flush
2626 Leaves SMT enabled and enables the default
2627 hypervisor mitigation, i.e. conditional
2628 L1D flush.
2629
2630 SMT control and L1D flush control via the
2631 sysfs interface is still possible after
2632 boot. Hypervisors will issue a warning
2633 when the first VM is started in a
2634 potentially insecure configuration,
2635 i.e. SMT enabled or L1D flush disabled.
2636
2637 flush,nosmt
2638
2639 Disables SMT and enables the default
2640 hypervisor mitigation.
2641
2642 SMT control and L1D flush control via the
2643 sysfs interface is still possible after
2644 boot. Hypervisors will issue a warning
2645 when the first VM is started in a
2646 potentially insecure configuration,
2647 i.e. SMT enabled or L1D flush disabled.
2648
2649 flush,nowarn
2650 Same as 'flush', but hypervisors will not
2651 warn when a VM is started in a potentially
2652 insecure configuration.
2653
2654 off
2655 Disables hypervisor mitigations and doesn't
2656 emit any warnings.
2657 It also drops the swap size and available
2658 RAM limit restriction on both hypervisor and
2659 bare metal.
2660
2661 Default is 'flush'.
2662
2663 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2664
2665 l2cr= [PPC]
2666
2667 l3cr= [PPC]
2668
2669 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2670 disabled it.
2671
2672 lapic= [X86,APIC] Do not use TSC deadline
2673 value for LAPIC timer one-shot implementation. Default
2674 back to the programmable timer unit in the LAPIC.
2675 Format: notscdeadline
2676
2677 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2678 in C2 power state.
2679
2680 libata.dma= [LIBATA] DMA control
2681 libata.dma=0 Disable all PATA and SATA DMA
2682 libata.dma=1 PATA and SATA Disk DMA only
2683 libata.dma=2 ATAPI (CDROM) DMA only
2684 libata.dma=4 Compact Flash DMA only
2685 Combinations also work, so libata.dma=3 enables DMA
2686 for disks and CDROMs, but not CFs.
2687
2688 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2689 libata.ignore_hpa=0 keep BIOS limits (default)
2690 libata.ignore_hpa=1 ignore limits, using full disk
2691
2692 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2693 when set.
2694 Format: <int>
2695
2696 libata.force= [LIBATA] Force configurations. The format is a comma-
2697 separated list of "[ID:]VAL" where ID is PORT[.DEVICE].
2698 PORT and DEVICE are decimal numbers matching port, link
2699 or device. Basically, it matches the ATA ID string
2700 printed on console by libata. If the whole ID part is
2701 omitted, the last PORT and DEVICE values are used. If
2702 ID hasn't been specified yet, the configuration applies
2703 to all ports, links and devices.
2704
2705 If only DEVICE is omitted, the parameter applies to
2706 the port and all links and devices behind it. DEVICE
2707 number of 0 either selects the first device or the
2708 first fan-out link behind PMP device. It does not
2709 select the host link. DEVICE number of 15 selects the
2710 host link and device attached to it.
2711
2712 The VAL specifies the configuration to force. As long
2713 as there is no ambiguity, shortcut notation is allowed.
2714 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2715 The following configurations can be forced.
2716
2717 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2718 Any ID with matching PORT is used.
2719
2720 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2721
2722 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2723 udma[/][16,25,33,44,66,100,133] notation is also
2724 allowed.
2725
2726 * nohrst, nosrst, norst: suppress hard, soft and both
2727 resets.
2728
2729 * rstonce: only attempt one reset during hot-unplug
2730 link recovery.
2731
2732 * [no]dbdelay: Enable or disable the extra 200ms delay
2733 before debouncing a link PHY and device presence
2734 detection.
2735
2736 * [no]ncq: Turn on or off NCQ.
2737
2738 * [no]ncqtrim: Enable or disable queued DSM TRIM.
2739
2740 * [no]ncqati: Enable or disable NCQ trim on ATI chipset.
2741
2742 * [no]trim: Enable or disable (unqueued) TRIM.
2743
2744 * trim_zero: Indicate that TRIM command zeroes data.
2745
2746 * max_trim_128m: Set 128M maximum trim size limit.
2747
2748 * [no]dma: Turn on or off DMA transfers.
2749
2750 * atapi_dmadir: Enable ATAPI DMADIR bridge support.
2751
2752 * atapi_mod16_dma: Enable the use of ATAPI DMA for
2753 commands that are not a multiple of 16 bytes.
2754
2755 * [no]dmalog: Enable or disable the use of the
2756 READ LOG DMA EXT command to access logs.
2757
2758 * [no]iddevlog: Enable or disable access to the
2759 identify device data log.
2760
2761 * [no]logdir: Enable or disable access to the general
2762 purpose log directory.
2763
2764 * max_sec_128: Set transfer size limit to 128 sectors.
2765
2766 * max_sec_1024: Set or clear transfer size limit to
2767 1024 sectors.
2768
2769 * max_sec_lba48: Set or clear transfer size limit to
2770 65535 sectors.
2771
2772 * [no]lpm: Enable or disable link power management.
2773
2774 * [no]setxfer: Indicate if transfer speed mode setting
2775 should be skipped.
2776
2777 * dump_id: Dump IDENTIFY data.
2778
2779 * disable: Disable this device.
2780
2781 If there are multiple matching configurations changing
2782 the same attribute, the last one is used.
2783
2784 load_ramdisk= [RAM] [Deprecated]
2785
2786 lockd.nlm_grace_period=P [NFS] Assign grace period.
2787 Format: <integer>
2788
2789 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2790 Format: <integer>
2791
2792 lockd.nlm_timeout=T [NFS] Assign timeout value.
2793 Format: <integer>
2794
2795 lockd.nlm_udpport=M [NFS] Assign UDP port.
2796 Format: <integer>
2797
2798 lockdown= [SECURITY]
2799 { integrity | confidentiality }
2800 Enable the kernel lockdown feature. If set to
2801 integrity, kernel features that allow userland to
2802 modify the running kernel are disabled. If set to
2803 confidentiality, kernel features that allow userland
2804 to extract confidential information from the kernel
2805 are also disabled.
2806
2807 locktorture.nreaders_stress= [KNL]
2808 Set the number of locking read-acquisition kthreads.
2809 Defaults to being automatically set based on the
2810 number of online CPUs.
2811
2812 locktorture.nwriters_stress= [KNL]
2813 Set the number of locking write-acquisition kthreads.
2814
2815 locktorture.onoff_holdoff= [KNL]
2816 Set time (s) after boot for CPU-hotplug testing.
2817
2818 locktorture.onoff_interval= [KNL]
2819 Set time (s) between CPU-hotplug operations, or
2820 zero to disable CPU-hotplug testing.
2821
2822 locktorture.shuffle_interval= [KNL]
2823 Set task-shuffle interval (jiffies). Shuffling
2824 tasks allows some CPUs to go into dyntick-idle
2825 mode during the locktorture test.
2826
2827 locktorture.shutdown_secs= [KNL]
2828 Set time (s) after boot system shutdown. This
2829 is useful for hands-off automated testing.
2830
2831 locktorture.stat_interval= [KNL]
2832 Time (s) between statistics printk()s.
2833
2834 locktorture.stutter= [KNL]
2835 Time (s) to stutter testing, for example,
2836 specifying five seconds causes the test to run for
2837 five seconds, wait for five seconds, and so on.
2838 This tests the locking primitive's ability to
2839 transition abruptly to and from idle.
2840
2841 locktorture.torture_type= [KNL]
2842 Specify the locking implementation to test.
2843
2844 locktorture.verbose= [KNL]
2845 Enable additional printk() statements.
2846
2847 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2848 Format: <irq>
2849
2850 loglevel= All Kernel Messages with a loglevel smaller than the
2851 console loglevel will be printed to the console. It can
2852 also be changed with klogd or other programs. The
2853 loglevels are defined as follows:
2854
2855 0 (KERN_EMERG) system is unusable
2856 1 (KERN_ALERT) action must be taken immediately
2857 2 (KERN_CRIT) critical conditions
2858 3 (KERN_ERR) error conditions
2859 4 (KERN_WARNING) warning conditions
2860 5 (KERN_NOTICE) normal but significant condition
2861 6 (KERN_INFO) informational
2862 7 (KERN_DEBUG) debug-level messages
2863
2864 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2865 in bytes. n must be a power of two and greater
2866 than the minimal size. The minimal size is defined
2867 by LOG_BUF_SHIFT kernel config parameter. There is
2868 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2869 that allows to increase the default size depending on
2870 the number of CPUs. See init/Kconfig for more details.
2871
2872 logo.nologo [FB] Disables display of the built-in Linux logo.
2873 This may be used to provide more screen space for
2874 kernel log messages and is useful when debugging
2875 kernel boot problems.
2876
2877 lp=0 [LP] Specify parallel ports to use, e.g,
2878 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2879 lp=reset first parallel port). 'lp=0' disables the
2880 lp=auto printer driver. 'lp=reset' (which can be
2881 specified in addition to the ports) causes
2882 attached printers to be reset. Using
2883 lp=port1,port2,... specifies the parallel ports
2884 to associate lp devices with, starting with
2885 lp0. A port specification may be 'none' to skip
2886 that lp device, or a parport name such as
2887 'parport0'. Specifying 'lp=auto' instead of a
2888 port specification list means that device IDs
2889 from each port should be examined, to see if
2890 an IEEE 1284-compliant printer is attached; if
2891 so, the driver will manage that printer.
2892 See also header of drivers/char/lp.c.
2893
2894 lpj=n [KNL]
2895 Sets loops_per_jiffy to given constant, thus avoiding
2896 time-consuming boot-time autodetection (up to 250 ms per
2897 CPU). 0 enables autodetection (default). To determine
2898 the correct value for your kernel, boot with normal
2899 autodetection and see what value is printed. Note that
2900 on SMP systems the preset will be applied to all CPUs,
2901 which is likely to cause problems if your CPUs need
2902 significantly divergent settings. An incorrect value
2903 will cause delays in the kernel to be wrong, leading to
2904 unpredictable I/O errors and other breakage. Although
2905 unlikely, in the extreme case this might damage your
2906 hardware.
2907
2908 ltpc= [NET]
2909 Format: <io>,<irq>,<dma>
2910
2911 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2912
2913 lsm=lsm1,...,lsmN
2914 [SECURITY] Choose order of LSM initialization. This
2915 overrides CONFIG_LSM, and the "security=" parameter.
2916
2917 machvec= [IA-64] Force the use of a particular machine-vector
2918 (machvec) in a generic kernel.
2919 Example: machvec=hpzx1
2920
2921 machtype= [Loongson] Share the same kernel image file between
2922 different yeeloong laptops.
2923 Example: machtype=lemote-yeeloong-2f-7inch
2924
2925 max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater
2926 than or equal to this physical address is ignored.
2927
2928 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2929 will bring up during bootup. maxcpus=n : n >= 0 limits
2930 the kernel to bring up 'n' processors. Surely after
2931 bootup you can bring up the other plugged cpu by executing
2932 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2933 only takes effect during system bootup.
2934 While n=0 is a special case, it is equivalent to "nosmp",
2935 which also disables the IO APIC.
2936
2937 max_loop= [LOOP] The number of loop block devices that get
2938 (loop.max_loop) unconditionally pre-created at init time. The default
2939 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2940 of statically allocating a predefined number, loop
2941 devices can be requested on-demand with the
2942 /dev/loop-control interface.
2943
2944 mce [X86-32] Machine Check Exception
2945
2946 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2947
2948 md= [HW] RAID subsystems devices and level
2949 See Documentation/admin-guide/md.rst.
2950
2951 mdacon= [MDA]
2952 Format: <first>,<last>
2953 Specifies range of consoles to be captured by the MDA.
2954
2955 mds= [X86,INTEL]
2956 Control mitigation for the Micro-architectural Data
2957 Sampling (MDS) vulnerability.
2958
2959 Certain CPUs are vulnerable to an exploit against CPU
2960 internal buffers which can forward information to a
2961 disclosure gadget under certain conditions.
2962
2963 In vulnerable processors, the speculatively
2964 forwarded data can be used in a cache side channel
2965 attack, to access data to which the attacker does
2966 not have direct access.
2967
2968 This parameter controls the MDS mitigation. The
2969 options are:
2970
2971 full - Enable MDS mitigation on vulnerable CPUs
2972 full,nosmt - Enable MDS mitigation and disable
2973 SMT on vulnerable CPUs
2974 off - Unconditionally disable MDS mitigation
2975
2976 On TAA-affected machines, mds=off can be prevented by
2977 an active TAA mitigation as both vulnerabilities are
2978 mitigated with the same mechanism so in order to disable
2979 this mitigation, you need to specify tsx_async_abort=off
2980 too.
2981
2982 Not specifying this option is equivalent to
2983 mds=full.
2984
2985 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2986
2987 mem=nn[KMG] [HEXAGON] Set the memory size.
2988 Must be specified, otherwise memory size will be 0.
2989
2990 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2991 Amount of memory to be used in cases as follows:
2992
2993 1 for test;
2994 2 when the kernel is not able to see the whole system memory;
2995 3 memory that lies after 'mem=' boundary is excluded from
2996 the hypervisor, then assigned to KVM guests.
2997 4 to limit the memory available for kdump kernel.
2998
2999 [ARC,MICROBLAZE] - the limit applies only to low memory,
3000 high memory is not affected.
3001
3002 [ARM64] - only limits memory covered by the linear
3003 mapping. The NOMAP regions are not affected.
3004
3005 [X86] Work as limiting max address. Use together
3006 with memmap= to avoid physical address space collisions.
3007 Without memmap= PCI devices could be placed at addresses
3008 belonging to unused RAM.
3009
3010 Note that this only takes effects during boot time since
3011 in above case 3, memory may need be hot added after boot
3012 if system memory of hypervisor is not sufficient.
3013
3014 mem=nn[KMG]@ss[KMG]
3015 [ARM,MIPS] - override the memory layout reported by
3016 firmware.
3017 Define a memory region of size nn[KMG] starting at
3018 ss[KMG].
3019 Multiple different regions can be specified with
3020 multiple mem= parameters on the command line.
3021
3022 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
3023 memory.
3024
3025 memblock=debug [KNL] Enable memblock debug messages.
3026
3027 memchunk=nn[KMG]
3028 [KNL,SH] Allow user to override the default size for
3029 per-device physically contiguous DMA buffers.
3030
3031 memhp_default_state=online/offline
3032 [KNL] Set the initial state for the memory hotplug
3033 onlining policy. If not specified, the default value is
3034 set according to the
3035 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
3036 option.
3037 See Documentation/admin-guide/mm/memory-hotplug.rst.
3038
3039 memmap=exactmap [KNL,X86] Enable setting of an exact
3040 E820 memory map, as specified by the user.
3041 Such memmap=exactmap lines can be constructed based on
3042 BIOS output or other requirements. See the memmap=nn@ss
3043 option description.
3044
3045 memmap=nn[KMG]@ss[KMG]
3046 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory.
3047 Region of memory to be used is from ss to ss+nn.
3048 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
3049 which limits max address to nn[KMG].
3050 Multiple different regions can be specified,
3051 comma delimited.
3052 Example:
3053 memmap=100M@2G,100M#3G,1G!1024G
3054
3055 memmap=nn[KMG]#ss[KMG]
3056 [KNL,ACPI] Mark specific memory as ACPI data.
3057 Region of memory to be marked is from ss to ss+nn.
3058
3059 memmap=nn[KMG]$ss[KMG]
3060 [KNL,ACPI] Mark specific memory as reserved.
3061 Region of memory to be reserved is from ss to ss+nn.
3062 Example: Exclude memory from 0x18690000-0x1869ffff
3063 memmap=64K$0x18690000
3064 or
3065 memmap=0x10000$0x18690000
3066 Some bootloaders may need an escape character before '$',
3067 like Grub2, otherwise '$' and the following number
3068 will be eaten.
3069
3070 memmap=nn[KMG]!ss[KMG]
3071 [KNL,X86] Mark specific memory as protected.
3072 Region of memory to be used, from ss to ss+nn.
3073 The memory region may be marked as e820 type 12 (0xc)
3074 and is NVDIMM or ADR memory.
3075
3076 memmap=<size>%<offset>-<oldtype>+<newtype>
3077 [KNL,ACPI] Convert memory within the specified region
3078 from <oldtype> to <newtype>. If "-<oldtype>" is left
3079 out, the whole region will be marked as <newtype>,
3080 even if previously unavailable. If "+<newtype>" is left
3081 out, matching memory will be removed. Types are
3082 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
3083 3 = ACPI, 12 = PRAM.
3084
3085 memory_corruption_check=0/1 [X86]
3086 Some BIOSes seem to corrupt the first 64k of
3087 memory when doing things like suspend/resume.
3088 Setting this option will scan the memory
3089 looking for corruption. Enabling this will
3090 both detect corruption and prevent the kernel
3091 from using the memory being corrupted.
3092 However, its intended as a diagnostic tool; if
3093 repeatable BIOS-originated corruption always
3094 affects the same memory, you can use memmap=
3095 to prevent the kernel from using that memory.
3096
3097 memory_corruption_check_size=size [X86]
3098 By default it checks for corruption in the low
3099 64k, making this memory unavailable for normal
3100 use. Use this parameter to scan for
3101 corruption in more or less memory.
3102
3103 memory_corruption_check_period=seconds [X86]
3104 By default it checks for corruption every 60
3105 seconds. Use this parameter to check at some
3106 other rate. 0 disables periodic checking.
3107
3108 memory_hotplug.memmap_on_memory
3109 [KNL,X86,ARM] Boolean flag to enable this feature.
3110 Format: {on | off (default)}
3111 When enabled, runtime hotplugged memory will
3112 allocate its internal metadata (struct pages,
3113 those vmemmap pages cannot be optimized even
3114 if hugetlb_free_vmemmap is enabled) from the
3115 hotadded memory which will allow to hotadd a
3116 lot of memory without requiring additional
3117 memory to do so.
3118 This feature is disabled by default because it
3119 has some implication on large (e.g. GB)
3120 allocations in some configurations (e.g. small
3121 memory blocks).
3122 The state of the flag can be read in
3123 /sys/module/memory_hotplug/parameters/memmap_on_memory.
3124 Note that even when enabled, there are a few cases where
3125 the feature is not effective.
3126
3127 memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
3128 Format: <integer>
3129 default : 0 <disable>
3130 Specifies the number of memtest passes to be
3131 performed. Each pass selects another test
3132 pattern from a given set of patterns. Memtest
3133 fills the memory with this pattern, validates
3134 memory contents and reserves bad memory
3135 regions that are detected.
3136
3137 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
3138 Valid arguments: on, off
3139 Default (depends on kernel configuration option):
3140 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
3141 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
3142 mem_encrypt=on: Activate SME
3143 mem_encrypt=off: Do not activate SME
3144
3145 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst
3146 for details on when memory encryption can be activated.
3147
3148 mem_sleep_default= [SUSPEND] Default system suspend mode:
3149 s2idle - Suspend-To-Idle
3150 shallow - Power-On Suspend or equivalent (if supported)
3151 deep - Suspend-To-RAM or equivalent (if supported)
3152 See Documentation/admin-guide/pm/sleep-states.rst.
3153
3154 meye.*= [HW] Set MotionEye Camera parameters
3155 See Documentation/admin-guide/media/meye.rst.
3156
3157 mfgpt_irq= [IA-32] Specify the IRQ to use for the
3158 Multi-Function General Purpose Timers on AMD Geode
3159 platforms.
3160
3161 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
3162 the BIOS has incorrectly applied a workaround. TinyBIOS
3163 version 0.98 is known to be affected, 0.99 fixes the
3164 problem by letting the user disable the workaround.
3165
3166 mga= [HW,DRM]
3167
3168 min_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory below this
3169 physical address is ignored.
3170
3171 mini2440= [ARM,HW,KNL]
3172 Format:[0..2][b][c][t]
3173 Default: "0tb"
3174 MINI2440 configuration specification:
3175 0 - The attached screen is the 3.5" TFT
3176 1 - The attached screen is the 7" TFT
3177 2 - The VGA Shield is attached (1024x768)
3178 Leaving out the screen size parameter will not load
3179 the TFT driver, and the framebuffer will be left
3180 unconfigured.
3181 b - Enable backlight. The TFT backlight pin will be
3182 linked to the kernel VESA blanking code and a GPIO
3183 LED. This parameter is not necessary when using the
3184 VGA shield.
3185 c - Enable the s3c camera interface.
3186 t - Reserved for enabling touchscreen support. The
3187 touchscreen support is not enabled in the mainstream
3188 kernel as of 2.6.30, a preliminary port can be found
3189 in the "bleeding edge" mini2440 support kernel at
3190 https://repo.or.cz/w/linux-2.6/mini2440.git
3191
3192 mitigations=
3193 [X86,PPC,S390,ARM64] Control optional mitigations for
3194 CPU vulnerabilities. This is a set of curated,
3195 arch-independent options, each of which is an
3196 aggregation of existing arch-specific options.
3197
3198 off
3199 Disable all optional CPU mitigations. This
3200 improves system performance, but it may also
3201 expose users to several CPU vulnerabilities.
3202 Equivalent to: nopti [X86,PPC]
3203 if nokaslr then kpti=0 [ARM64]
3204 nospectre_v1 [X86,PPC]
3205 nobp=0 [S390]
3206 nospectre_v2 [X86,PPC,S390,ARM64]
3207 spectre_v2_user=off [X86]
3208 spec_store_bypass_disable=off [X86,PPC]
3209 ssbd=force-off [ARM64]
3210 l1tf=off [X86]
3211 mds=off [X86]
3212 tsx_async_abort=off [X86]
3213 kvm.nx_huge_pages=off [X86]
3214 srbds=off [X86,INTEL]
3215 no_entry_flush [PPC]
3216 no_uaccess_flush [PPC]
3217 mmio_stale_data=off [X86]
3218 retbleed=off [X86]
3219
3220 Exceptions:
3221 This does not have any effect on
3222 kvm.nx_huge_pages when
3223 kvm.nx_huge_pages=force.
3224
3225 auto (default)
3226 Mitigate all CPU vulnerabilities, but leave SMT
3227 enabled, even if it's vulnerable. This is for
3228 users who don't want to be surprised by SMT
3229 getting disabled across kernel upgrades, or who
3230 have other ways of avoiding SMT-based attacks.
3231 Equivalent to: (default behavior)
3232
3233 auto,nosmt
3234 Mitigate all CPU vulnerabilities, disabling SMT
3235 if needed. This is for users who always want to
3236 be fully mitigated, even if it means losing SMT.
3237 Equivalent to: l1tf=flush,nosmt [X86]
3238 mds=full,nosmt [X86]
3239 tsx_async_abort=full,nosmt [X86]
3240 mmio_stale_data=full,nosmt [X86]
3241 retbleed=auto,nosmt [X86]
3242
3243 mminit_loglevel=
3244 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
3245 parameter allows control of the logging verbosity for
3246 the additional memory initialisation checks. A value
3247 of 0 disables mminit logging and a level of 4 will
3248 log everything. Information is printed at KERN_DEBUG
3249 so loglevel=8 may also need to be specified.
3250
3251 mmio_stale_data=
3252 [X86,INTEL] Control mitigation for the Processor
3253 MMIO Stale Data vulnerabilities.
3254
3255 Processor MMIO Stale Data is a class of
3256 vulnerabilities that may expose data after an MMIO
3257 operation. Exposed data could originate or end in
3258 the same CPU buffers as affected by MDS and TAA.
3259 Therefore, similar to MDS and TAA, the mitigation
3260 is to clear the affected CPU buffers.
3261
3262 This parameter controls the mitigation. The
3263 options are:
3264
3265 full - Enable mitigation on vulnerable CPUs
3266
3267 full,nosmt - Enable mitigation and disable SMT on
3268 vulnerable CPUs.
3269
3270 off - Unconditionally disable mitigation
3271
3272 On MDS or TAA affected machines,
3273 mmio_stale_data=off can be prevented by an active
3274 MDS or TAA mitigation as these vulnerabilities are
3275 mitigated with the same mechanism so in order to
3276 disable this mitigation, you need to specify
3277 mds=off and tsx_async_abort=off too.
3278
3279 Not specifying this option is equivalent to
3280 mmio_stale_data=full.
3281
3282 For details see:
3283 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
3284
3285 module.async_probe=<bool>
3286 [KNL] When set to true, modules will use async probing
3287 by default. To enable/disable async probing for a
3288 specific module, use the module specific control that
3289 is documented under <module>.async_probe. When both
3290 module.async_probe and <module>.async_probe are
3291 specified, <module>.async_probe takes precedence for
3292 the specific module.
3293
3294 module.sig_enforce
3295 [KNL] When CONFIG_MODULE_SIG is set, this means that
3296 modules without (valid) signatures will fail to load.
3297 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3298 is always true, so this option does nothing.
3299
3300 module_blacklist= [KNL] Do not load a comma-separated list of
3301 modules. Useful for debugging problem modules.
3302
3303 mousedev.tap_time=
3304 [MOUSE] Maximum time between finger touching and
3305 leaving touchpad surface for touch to be considered
3306 a tap and be reported as a left button click (for
3307 touchpads working in absolute mode only).
3308 Format: <msecs>
3309 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3310 reporting absolute coordinates, such as tablets
3311 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3312 reporting absolute coordinates, such as tablets
3313
3314 movablecore= [KNL,X86,IA-64,PPC]
3315 Format: nn[KMGTPE] | nn%
3316 This parameter is the complement to kernelcore=, it
3317 specifies the amount of memory used for migratable
3318 allocations. If both kernelcore and movablecore is
3319 specified, then kernelcore will be at *least* the
3320 specified value but may be more. If movablecore on its
3321 own is specified, the administrator must be careful
3322 that the amount of memory usable for all allocations
3323 is not too small.
3324
3325 movable_node [KNL] Boot-time switch to make hotplugable memory
3326 NUMA nodes to be movable. This means that the memory
3327 of such nodes will be usable only for movable
3328 allocations which rules out almost all kernel
3329 allocations. Use with caution!
3330
3331 MTD_Partition= [MTD]
3332 Format: <name>,<region-number>,<size>,<offset>
3333
3334 MTD_Region= [MTD] Format:
3335 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3336
3337 mtdparts= [MTD]
3338 See drivers/mtd/parsers/cmdlinepart.c
3339
3340 mtdset= [ARM]
3341 ARM/S3C2412 JIVE boot control
3342
3343 See arch/arm/mach-s3c/mach-jive.c
3344
3345 mtouchusb.raw_coordinates=
3346 [HW] Make the MicroTouch USB driver use raw coordinates
3347 ('y', default) or cooked coordinates ('n')
3348
3349 mtrr_chunk_size=nn[KMG] [X86]
3350 used for mtrr cleanup. It is largest continuous chunk
3351 that could hold holes aka. UC entries.
3352
3353 mtrr_gran_size=nn[KMG] [X86]
3354 Used for mtrr cleanup. It is granularity of mtrr block.
3355 Default is 1.
3356 Large value could prevent small alignment from
3357 using up MTRRs.
3358
3359 mtrr_spare_reg_nr=n [X86]
3360 Format: <integer>
3361 Range: 0,7 : spare reg number
3362 Default : 1
3363 Used for mtrr cleanup. It is spare mtrr entries number.
3364 Set to 2 or more if your graphical card needs more.
3365
3366 multitce=off [PPC] This parameter disables the use of the pSeries
3367 firmware feature for updating multiple TCE entries
3368 at a time.
3369
3370 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3371
3372 netdev= [NET] Network devices parameters
3373 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3374 Note that mem_start is often overloaded to mean
3375 something different and driver-specific.
3376 This usage is only documented in each driver source
3377 file if at all.
3378
3379 netpoll.carrier_timeout=
3380 [NET] Specifies amount of time (in seconds) that
3381 netpoll should wait for a carrier. By default netpoll
3382 waits 4 seconds.
3383
3384 nf_conntrack.acct=
3385 [NETFILTER] Enable connection tracking flow accounting
3386 0 to disable accounting
3387 1 to enable accounting
3388 Default value is 0.
3389
3390 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3391 See Documentation/admin-guide/nfs/nfsroot.rst.
3392
3393 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3394 See Documentation/admin-guide/nfs/nfsroot.rst.
3395
3396 nfsrootdebug [NFS] enable nfsroot debugging messages.
3397 See Documentation/admin-guide/nfs/nfsroot.rst.
3398
3399 nfs.callback_nr_threads=
3400 [NFSv4] set the total number of threads that the
3401 NFS client will assign to service NFSv4 callback
3402 requests.
3403
3404 nfs.callback_tcpport=
3405 [NFS] set the TCP port on which the NFSv4 callback
3406 channel should listen.
3407
3408 nfs.cache_getent=
3409 [NFS] sets the pathname to the program which is used
3410 to update the NFS client cache entries.
3411
3412 nfs.cache_getent_timeout=
3413 [NFS] sets the timeout after which an attempt to
3414 update a cache entry is deemed to have failed.
3415
3416 nfs.idmap_cache_timeout=
3417 [NFS] set the maximum lifetime for idmapper cache
3418 entries.
3419
3420 nfs.enable_ino64=
3421 [NFS] enable 64-bit inode numbers.
3422 If zero, the NFS client will fake up a 32-bit inode
3423 number for the readdir() and stat() syscalls instead
3424 of returning the full 64-bit number.
3425 The default is to return 64-bit inode numbers.
3426
3427 nfs.max_session_cb_slots=
3428 [NFSv4.1] Sets the maximum number of session
3429 slots the client will assign to the callback
3430 channel. This determines the maximum number of
3431 callbacks the client will process in parallel for
3432 a particular server.
3433
3434 nfs.max_session_slots=
3435 [NFSv4.1] Sets the maximum number of session slots
3436 the client will attempt to negotiate with the server.
3437 This limits the number of simultaneous RPC requests
3438 that the client can send to the NFSv4.1 server.
3439 Note that there is little point in setting this
3440 value higher than the max_tcp_slot_table_limit.
3441
3442 nfs.nfs4_disable_idmapping=
3443 [NFSv4] When set to the default of '1', this option
3444 ensures that both the RPC level authentication
3445 scheme and the NFS level operations agree to use
3446 numeric uids/gids if the mount is using the
3447 'sec=sys' security flavour. In effect it is
3448 disabling idmapping, which can make migration from
3449 legacy NFSv2/v3 systems to NFSv4 easier.
3450 Servers that do not support this mode of operation
3451 will be autodetected by the client, and it will fall
3452 back to using the idmapper.
3453 To turn off this behaviour, set the value to '0'.
3454 nfs.nfs4_unique_id=
3455 [NFS4] Specify an additional fixed unique ident-
3456 ification string that NFSv4 clients can insert into
3457 their nfs_client_id4 string. This is typically a
3458 UUID that is generated at system install time.
3459
3460 nfs.send_implementation_id =
3461 [NFSv4.1] Send client implementation identification
3462 information in exchange_id requests.
3463 If zero, no implementation identification information
3464 will be sent.
3465 The default is to send the implementation identification
3466 information.
3467
3468 nfs.recover_lost_locks =
3469 [NFSv4] Attempt to recover locks that were lost due
3470 to a lease timeout on the server. Please note that
3471 doing this risks data corruption, since there are
3472 no guarantees that the file will remain unchanged
3473 after the locks are lost.
3474 If you want to enable the kernel legacy behaviour of
3475 attempting to recover these locks, then set this
3476 parameter to '1'.
3477 The default parameter value of '0' causes the kernel
3478 not to attempt recovery of lost locks.
3479
3480 nfs4.layoutstats_timer =
3481 [NFSv4.2] Change the rate at which the kernel sends
3482 layoutstats to the pNFS metadata server.
3483
3484 Setting this to value to 0 causes the kernel to use
3485 whatever value is the default set by the layout
3486 driver. A non-zero value sets the minimum interval
3487 in seconds between layoutstats transmissions.
3488
3489 nfsd.inter_copy_offload_enable =
3490 [NFSv4.2] When set to 1, the server will support
3491 server-to-server copies for which this server is
3492 the destination of the copy.
3493
3494 nfsd.nfsd4_ssc_umount_timeout =
3495 [NFSv4.2] When used as the destination of a
3496 server-to-server copy, knfsd temporarily mounts
3497 the source server. It caches the mount in case
3498 it will be needed again, and discards it if not
3499 used for the number of milliseconds specified by
3500 this parameter.
3501
3502 nfsd.nfs4_disable_idmapping=
3503 [NFSv4] When set to the default of '1', the NFSv4
3504 server will return only numeric uids and gids to
3505 clients using auth_sys, and will accept numeric uids
3506 and gids from such clients. This is intended to ease
3507 migration from NFSv2/v3.
3508
3509
3510 nmi_backtrace.backtrace_idle [KNL]
3511 Dump stacks even of idle CPUs in response to an
3512 NMI stack-backtrace request.
3513
3514 nmi_debug= [KNL,SH] Specify one or more actions to take
3515 when a NMI is triggered.
3516 Format: [state][,regs][,debounce][,die]
3517
3518 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3519 Format: [panic,][nopanic,][num]
3520 Valid num: 0 or 1
3521 0 - turn hardlockup detector in nmi_watchdog off
3522 1 - turn hardlockup detector in nmi_watchdog on
3523 When panic is specified, panic when an NMI watchdog
3524 timeout occurs (or 'nopanic' to not panic on an NMI
3525 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3526 To disable both hard and soft lockup detectors,
3527 please see 'nowatchdog'.
3528 This is useful when you use a panic=... timeout and
3529 need the box quickly up again.
3530
3531 These settings can be accessed at runtime via
3532 the nmi_watchdog and hardlockup_panic sysctls.
3533
3534 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3535 emulation library even if a 387 maths coprocessor
3536 is present.
3537
3538 no5lvl [X86-64] Disable 5-level paging mode. Forces
3539 kernel to use 4-level paging instead.
3540
3541 nofsgsbase [X86] Disables FSGSBASE instructions.
3542
3543 no_console_suspend
3544 [HW] Never suspend the console
3545 Disable suspending of consoles during suspend and
3546 hibernate operations. Once disabled, debugging
3547 messages can reach various consoles while the rest
3548 of the system is being put to sleep (ie, while
3549 debugging driver suspend/resume hooks). This may
3550 not work reliably with all consoles, but is known
3551 to work with serial and VGA consoles.
3552 To facilitate more flexible debugging, we also add
3553 console_suspend, a printk module parameter to control
3554 it. Users could use console_suspend (usually
3555 /sys/module/printk/parameters/console_suspend) to
3556 turn on/off it dynamically.
3557
3558 novmcoredd [KNL,KDUMP]
3559 Disable device dump. Device dump allows drivers to
3560 append dump data to vmcore so you can collect driver
3561 specified debug info. Drivers can append the data
3562 without any limit and this data is stored in memory,
3563 so this may cause significant memory stress. Disabling
3564 device dump can help save memory but the driver debug
3565 data will be no longer available. This parameter
3566 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3567 is set.
3568
3569 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3570 caches in the slab allocator. Saves per-node memory,
3571 but will impact performance.
3572
3573 noalign [KNL,ARM]
3574
3575 noaltinstr [S390] Disables alternative instructions patching
3576 (CPU alternatives feature).
3577
3578 noapic [SMP,APIC] Tells the kernel to not make use of any
3579 IOAPICs that may be present in the system.
3580
3581 noautogroup Disable scheduler automatic task group creation.
3582
3583 nocache [ARM]
3584
3585 nodsp [SH] Disable hardware DSP at boot time.
3586
3587 noefi Disable EFI runtime services support.
3588
3589 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
3590
3591 noexec [IA-64]
3592
3593 nosmap [PPC]
3594 Disable SMAP (Supervisor Mode Access Prevention)
3595 even if it is supported by processor.
3596
3597 nosmep [PPC64s]
3598 Disable SMEP (Supervisor Mode Execution Prevention)
3599 even if it is supported by processor.
3600
3601 noexec32 [X86-64]
3602 This affects only 32-bit executables.
3603 noexec32=on: enable non-executable mappings (default)
3604 read doesn't imply executable mappings
3605 noexec32=off: disable non-executable mappings
3606 read implies executable mappings
3607
3608 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3609
3610 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3611 register save and restore. The kernel will only save
3612 legacy floating-point registers on task switch.
3613
3614 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
3615
3616 nohugevmalloc [PPC] Disable kernel huge vmalloc mappings.
3617
3618 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3619 Equivalent to smt=1.
3620
3621 [KNL,X86] Disable symmetric multithreading (SMT).
3622 nosmt=force: Force disable SMT, cannot be undone
3623 via the sysfs control file.
3624
3625 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3626 (bounds check bypass). With this option data leaks are
3627 possible in the system.
3628
3629 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3630 the Spectre variant 2 (indirect branch prediction)
3631 vulnerability. System may allow data leaks with this
3632 option.
3633
3634 nospec_store_bypass_disable
3635 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3636
3637 no_uaccess_flush
3638 [PPC] Don't flush the L1-D cache after accessing user data.
3639
3640 noxsave [BUGS=X86] Disables x86 extended register state save
3641 and restore using xsave. The kernel will fallback to
3642 enabling legacy floating-point and sse state.
3643
3644 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3645 register states. The kernel will fall back to use
3646 xsave to save the states. By using this parameter,
3647 performance of saving the states is degraded because
3648 xsave doesn't support modified optimization while
3649 xsaveopt supports it on xsaveopt enabled systems.
3650
3651 noxsaves [X86] Disables xsaves and xrstors used in saving and
3652 restoring x86 extended register state in compacted
3653 form of xsave area. The kernel will fall back to use
3654 xsaveopt and xrstor to save and restore the states
3655 in standard form of xsave area. By using this
3656 parameter, xsave area per process might occupy more
3657 memory on xsaves enabled systems.
3658
3659 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait
3660 in do_idle() and not use the arch_cpu_idle()
3661 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3662 to be effective. This is useful on platforms where the
3663 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3664 correctly or when doing power measurements to evalute
3665 the impact of the sleep instructions. This is also
3666 useful when using JTAG debugger.
3667
3668 no_file_caps Tells the kernel not to honor file capabilities. The
3669 only way then for a file to be executed with privilege
3670 is to be setuid root or executed by root.
3671
3672 nohalt [IA-64] Tells the kernel not to use the power saving
3673 function PAL_HALT_LIGHT when idle. This increases
3674 power-consumption. On the positive side, it reduces
3675 interrupt wake-up latency, which may improve performance
3676 in certain environments such as networked servers or
3677 real-time systems.
3678
3679 no_hash_pointers
3680 Force pointers printed to the console or buffers to be
3681 unhashed. By default, when a pointer is printed via %p
3682 format string, that pointer is "hashed", i.e. obscured
3683 by hashing the pointer value. This is a security feature
3684 that hides actual kernel addresses from unprivileged
3685 users, but it also makes debugging the kernel more
3686 difficult since unequal pointers can no longer be
3687 compared. However, if this command-line option is
3688 specified, then all normal pointers will have their true
3689 value printed. This option should only be specified when
3690 debugging the kernel. Please do not use on production
3691 kernels.
3692
3693 nohibernate [HIBERNATION] Disable hibernation and resume.
3694
3695 nohz= [KNL] Boottime enable/disable dynamic ticks
3696 Valid arguments: on, off
3697 Default: on
3698
3699 nohz_full= [KNL,BOOT,SMP,ISOL]
3700 The argument is a cpu list, as described above.
3701 In kernels built with CONFIG_NO_HZ_FULL=y, set
3702 the specified list of CPUs whose tick will be stopped
3703 whenever possible. The boot CPU will be forced outside
3704 the range to maintain the timekeeping. Any CPUs
3705 in this list will have their RCU callbacks offloaded,
3706 just as if they had also been called out in the
3707 rcu_nocbs= boot parameter.
3708
3709 Note that this argument takes precedence over
3710 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
3711
3712 noiotrap [SH] Disables trapped I/O port accesses.
3713
3714 noirqdebug [X86-32] Disables the code which attempts to detect and
3715 disable unhandled interrupt sources.
3716
3717 no_timer_check [X86,APIC] Disables the code which tests for
3718 broken timer IRQ sources.
3719
3720 noisapnp [ISAPNP] Disables ISA PnP code.
3721
3722 noinitrd [RAM] Tells the kernel not to load any configured
3723 initial RAM disk.
3724
3725 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3726 remapping.
3727 [Deprecated - use intremap=off]
3728
3729 nointroute [IA-64]
3730
3731 noinvpcid [X86] Disable the INVPCID cpu feature.
3732
3733 nojitter [IA-64] Disables jitter checking for ITC timers.
3734
3735 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3736
3737 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3738 fault handling.
3739
3740 no-vmw-sched-clock
3741 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3742 clock and use the default one.
3743
3744 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
3745 accounting. steal time is computed, but won't
3746 influence scheduler behaviour
3747
3748 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3749
3750 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3751
3752 nomca [IA-64] Disable machine check abort handling
3753
3754 nomce [X86-32] Disable Machine Check Exception
3755
3756 nomfgpt [X86-32] Disable Multi-Function General Purpose
3757 Timer usage (for AMD Geode machines).
3758
3759 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3760 shutdown the other cpus. Instead use the REBOOT_VECTOR
3761 irq.
3762
3763 nomodeset Disable kernel modesetting. DRM drivers will not perform
3764 display-mode changes or accelerated rendering. Only the
3765 system framebuffer will be available for use if this was
3766 set-up by the firmware or boot loader.
3767
3768 Useful as fallback, or for testing and debugging.
3769
3770 nomodule Disable module load
3771
3772 nopat [X86] Disable PAT (page attribute table extension of
3773 pagetables) support.
3774
3775 nopcid [X86-64] Disable the PCID cpu feature.
3776
3777 norandmaps Don't use address space randomization. Equivalent to
3778 echo 0 > /proc/sys/kernel/randomize_va_space
3779
3780 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3781 with UP alternatives
3782
3783 noresume [SWSUSP] Disables resume and restores original swap
3784 space.
3785
3786 no-scroll [VGA] Disables scrollback.
3787 This is required for the Braillex ib80-piezo Braille
3788 reader made by F.H. Papenmeier (Germany).
3789
3790 nosbagart [IA-64]
3791
3792 nosgx [X86-64,SGX] Disables Intel SGX kernel support.
3793
3794 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3795 and disable the IO APIC. legacy for "maxcpus=0".
3796
3797 nosoftlockup [KNL] Disable the soft-lockup detector.
3798
3799 nosync [HW,M68K] Disables sync negotiation for all devices.
3800
3801 nowatchdog [KNL] Disable both lockup detectors, i.e.
3802 soft-lockup and NMI watchdog (hard-lockup).
3803
3804 nowb [ARM]
3805
3806 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3807
3808 nps_mtm_hs_ctr= [KNL,ARC]
3809 This parameter sets the maximum duration, in
3810 cycles, each HW thread of the CTOP can run
3811 without interruptions, before HW switches it.
3812 The actual maximum duration is 16 times this
3813 parameter's value.
3814 Format: integer between 1 and 255
3815 Default: 255
3816
3817 nptcg= [IA-64] Override max number of concurrent global TLB
3818 purges which is reported from either PAL_VM_SUMMARY or
3819 SAL PALO.
3820
3821 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3822 could support. nr_cpus=n : n >= 1 limits the kernel to
3823 support 'n' processors. It could be larger than the
3824 number of already plugged CPU during bootup, later in
3825 runtime you can physically add extra cpu until it reaches
3826 n. So during boot up some boot time memory for per-cpu
3827 variables need be pre-allocated for later physical cpu
3828 hot plugging.
3829
3830 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3831
3832 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only
3833 set up a single NUMA node spanning all memory.
3834
3835 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
3836 NUMA balancing.
3837 Allowed values are enable and disable
3838
3839 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3840 'node', 'default' can be specified
3841 This can be set from sysctl after boot.
3842 See Documentation/admin-guide/sysctl/vm.rst for details.
3843
3844 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3845 See Documentation/core-api/debugging-via-ohci1394.rst for more
3846 info.
3847
3848 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3849 Rather than timing out after 20 ms if an EC
3850 command is not properly ACKed, override the length
3851 of the timeout. We have interrupts disabled while
3852 waiting for the ACK, so if this is set too high
3853 interrupts *may* be lost!
3854
3855 omap_mux= [OMAP] Override bootloader pin multiplexing.
3856 Format: <mux_mode0.mode_name=value>...
3857 For example, to override I2C bus2:
3858 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3859
3860 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
3861
3862 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
3863
3864 boundary - index of last SLC block on Flex-OneNAND.
3865 The remaining blocks are configured as MLC blocks.
3866 lock - Configure if Flex-OneNAND boundary should be locked.
3867 Once locked, the boundary cannot be changed.
3868 1 indicates lock status, 0 indicates unlock status.
3869
3870 oops=panic Always panic on oopses. Default is to just kill the
3871 process, but there is a small probability of
3872 deadlocking the machine.
3873 This will also cause panics on machine check exceptions.
3874 Useful together with panic=30 to trigger a reboot.
3875
3876 page_alloc.shuffle=
3877 [KNL] Boolean flag to control whether the page allocator
3878 should randomize its free lists. The randomization may
3879 be automatically enabled if the kernel detects it is
3880 running on a platform with a direct-mapped memory-side
3881 cache, and this parameter can be used to
3882 override/disable that behavior. The state of the flag
3883 can be read from sysfs at:
3884 /sys/module/page_alloc/parameters/shuffle.
3885
3886 page_owner= [KNL] Boot-time page_owner enabling option.
3887 Storage of the information about who allocated
3888 each page is disabled in default. With this switch,
3889 we can turn it on.
3890 on: enable the feature
3891
3892 page_poison= [KNL] Boot-time parameter changing the state of
3893 poisoning on the buddy allocator, available with
3894 CONFIG_PAGE_POISONING=y.
3895 off: turn off poisoning (default)
3896 on: turn on poisoning
3897
3898 page_reporting.page_reporting_order=
3899 [KNL] Minimal page reporting order
3900 Format: <integer>
3901 Adjust the minimal page reporting order. The page
3902 reporting is disabled when it exceeds (MAX_ORDER-1).
3903
3904 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3905 timeout > 0: seconds before rebooting
3906 timeout = 0: wait forever
3907 timeout < 0: reboot immediately
3908 Format: <timeout>
3909
3910 panic_print= Bitmask for printing system info when panic happens.
3911 User can chose combination of the following bits:
3912 bit 0: print all tasks info
3913 bit 1: print system memory info
3914 bit 2: print timer info
3915 bit 3: print locks info if CONFIG_LOCKDEP is on
3916 bit 4: print ftrace buffer
3917 bit 5: print all printk messages in buffer
3918 bit 6: print all CPUs backtrace (if available in the arch)
3919 *Be aware* that this option may print a _lot_ of lines,
3920 so there are risks of losing older messages in the log.
3921 Use this option carefully, maybe worth to setup a
3922 bigger log buffer with "log_buf_len" along with this.
3923
3924 panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
3925 Format: <hex>[,nousertaint]
3926 Hexadecimal bitmask representing the set of TAINT flags
3927 that will cause the kernel to panic when add_taint() is
3928 called with any of the flags in this set.
3929 The optional switch "nousertaint" can be utilized to
3930 prevent userspace forced crashes by writing to sysctl
3931 /proc/sys/kernel/tainted any flagset matching with the
3932 bitmask set on panic_on_taint.
3933 See Documentation/admin-guide/tainted-kernels.rst for
3934 extra details on the taint flags that users can pick
3935 to compose the bitmask to assign to panic_on_taint.
3936
3937 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3938 on a WARN().
3939
3940 parkbd.port= [HW] Parallel port number the keyboard adapter is
3941 connected to, default is 0.
3942 Format: <parport#>
3943 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3944 0 for XT, 1 for AT (default is AT).
3945 Format: <mode>
3946
3947 parport= [HW,PPT] Specify parallel ports. 0 disables.
3948 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3949 Use 'auto' to force the driver to use any
3950 IRQ/DMA settings detected (the default is to
3951 ignore detected IRQ/DMA settings because of
3952 possible conflicts). You can specify the base
3953 address, IRQ, and DMA settings; IRQ and DMA
3954 should be numbers, or 'auto' (for using detected
3955 settings on that particular port), or 'nofifo'
3956 (to avoid using a FIFO even if it is detected).
3957 Parallel ports are assigned in the order they
3958 are specified on the command line, starting
3959 with parport0.
3960
3961 parport_init_mode= [HW,PPT]
3962 Configure VIA parallel port to operate in
3963 a specific mode. This is necessary on Pegasos
3964 computer where firmware has no options for setting
3965 up parallel port mode and sets it to spp.
3966 Currently this function knows 686a and 8231 chips.
3967 Format: [spp|ps2|epp|ecp|ecpepp]
3968
3969 pata_legacy.all= [HW,LIBATA]
3970 Format: <int>
3971 Set to non-zero to probe primary and secondary ISA
3972 port ranges on PCI systems where no PCI PATA device
3973 has been found at either range. Disabled by default.
3974
3975 pata_legacy.autospeed= [HW,LIBATA]
3976 Format: <int>
3977 Set to non-zero if a chip is present that snoops speed
3978 changes. Disabled by default.
3979
3980 pata_legacy.ht6560a= [HW,LIBATA]
3981 Format: <int>
3982 Set to 1, 2, or 3 for HT 6560A on the primary channel,
3983 the secondary channel, or both channels respectively.
3984 Disabled by default.
3985
3986 pata_legacy.ht6560b= [HW,LIBATA]
3987 Format: <int>
3988 Set to 1, 2, or 3 for HT 6560B on the primary channel,
3989 the secondary channel, or both channels respectively.
3990 Disabled by default.
3991
3992 pata_legacy.iordy_mask= [HW,LIBATA]
3993 Format: <int>
3994 IORDY enable mask. Set individual bits to allow IORDY
3995 for the respective channel. Bit 0 is for the first
3996 legacy channel handled by this driver, bit 1 is for
3997 the second channel, and so on. The sequence will often
3998 correspond to the primary legacy channel, the secondary
3999 legacy channel, and so on, but the handling of a PCI
4000 bus and the use of other driver options may interfere
4001 with the sequence. By default IORDY is allowed across
4002 all channels.
4003
4004 pata_legacy.opti82c46x= [HW,LIBATA]
4005 Format: <int>
4006 Set to 1, 2, or 3 for Opti 82c611A on the primary
4007 channel, the secondary channel, or both channels
4008 respectively. Disabled by default.
4009
4010 pata_legacy.opti82c611a= [HW,LIBATA]
4011 Format: <int>
4012 Set to 1, 2, or 3 for Opti 82c465MV on the primary
4013 channel, the secondary channel, or both channels
4014 respectively. Disabled by default.
4015
4016 pata_legacy.pio_mask= [HW,LIBATA]
4017 Format: <int>
4018 PIO mode mask for autospeed devices. Set individual
4019 bits to allow the use of the respective PIO modes.
4020 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
4021 All modes allowed by default.
4022
4023 pata_legacy.probe_all= [HW,LIBATA]
4024 Format: <int>
4025 Set to non-zero to probe tertiary and further ISA
4026 port ranges on PCI systems. Disabled by default.
4027
4028 pata_legacy.probe_mask= [HW,LIBATA]
4029 Format: <int>
4030 Probe mask for legacy ISA PATA ports. Depending on
4031 platform configuration and the use of other driver
4032 options up to 6 legacy ports are supported: 0x1f0,
4033 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
4034 of individual ports can be disabled by setting the
4035 corresponding bits in the mask to 1. Bit 0 is for
4036 the first port in the list above (0x1f0), and so on.
4037 By default all supported ports are probed.
4038
4039 pata_legacy.qdi= [HW,LIBATA]
4040 Format: <int>
4041 Set to non-zero to probe QDI controllers. By default
4042 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
4043
4044 pata_legacy.winbond= [HW,LIBATA]
4045 Format: <int>
4046 Set to non-zero to probe Winbond controllers. Use
4047 the standard I/O port (0x130) if 1, otherwise the
4048 value given is the I/O port to use (typically 0x1b0).
4049 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
4050 0 otherwise.
4051
4052 pata_platform.pio_mask= [HW,LIBATA]
4053 Format: <int>
4054 Supported PIO mode mask. Set individual bits to allow
4055 the use of the respective PIO modes. Bit 0 is for
4056 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
4057 allowed by default.
4058
4059 pause_on_oops=
4060 Halt all CPUs after the first oops has been printed for
4061 the specified number of seconds. This is to be used if
4062 your oopses keep scrolling off the screen.
4063
4064 pcbit= [HW,ISDN]
4065
4066 pcd. [PARIDE]
4067 See header of drivers/block/paride/pcd.c.
4068 See also Documentation/admin-guide/blockdev/paride.rst.
4069
4070 pci=option[,option...] [PCI] various PCI subsystem options.
4071
4072 Some options herein operate on a specific device
4073 or a set of devices (<pci_dev>). These are
4074 specified in one of the following formats:
4075
4076 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
4077 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
4078
4079 Note: the first format specifies a PCI
4080 bus/device/function address which may change
4081 if new hardware is inserted, if motherboard
4082 firmware changes, or due to changes caused
4083 by other kernel parameters. If the
4084 domain is left unspecified, it is
4085 taken to be zero. Optionally, a path
4086 to a device through multiple device/function
4087 addresses can be specified after the base
4088 address (this is more robust against
4089 renumbering issues). The second format
4090 selects devices using IDs from the
4091 configuration space which may match multiple
4092 devices in the system.
4093
4094 earlydump dump PCI config space before the kernel
4095 changes anything
4096 off [X86] don't probe for the PCI bus
4097 bios [X86-32] force use of PCI BIOS, don't access
4098 the hardware directly. Use this if your machine
4099 has a non-standard PCI host bridge.
4100 nobios [X86-32] disallow use of PCI BIOS, only direct
4101 hardware access methods are allowed. Use this
4102 if you experience crashes upon bootup and you
4103 suspect they are caused by the BIOS.
4104 conf1 [X86] Force use of PCI Configuration Access
4105 Mechanism 1 (config address in IO port 0xCF8,
4106 data in IO port 0xCFC, both 32-bit).
4107 conf2 [X86] Force use of PCI Configuration Access
4108 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
4109 the function, IO port 0xCFA, also 8-bit, sets
4110 bus number. The config space is then accessed
4111 through ports 0xC000-0xCFFF).
4112 See http://wiki.osdev.org/PCI for more info
4113 on the configuration access mechanisms.
4114 noaer [PCIE] If the PCIEAER kernel config parameter is
4115 enabled, this kernel boot option can be used to
4116 disable the use of PCIE advanced error reporting.
4117 nodomains [PCI] Disable support for multiple PCI
4118 root domains (aka PCI segments, in ACPI-speak).
4119 nommconf [X86] Disable use of MMCONFIG for PCI
4120 Configuration
4121 check_enable_amd_mmconf [X86] check for and enable
4122 properly configured MMIO access to PCI
4123 config space on AMD family 10h CPU
4124 nomsi [MSI] If the PCI_MSI kernel config parameter is
4125 enabled, this kernel boot option can be used to
4126 disable the use of MSI interrupts system-wide.
4127 noioapicquirk [APIC] Disable all boot interrupt quirks.
4128 Safety option to keep boot IRQs enabled. This
4129 should never be necessary.
4130 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
4131 primary IO-APIC for bridges that cannot disable
4132 boot IRQs. This fixes a source of spurious IRQs
4133 when the system masks IRQs.
4134 noioapicreroute [APIC] Disable workaround that uses the
4135 boot IRQ equivalent of an IRQ that connects to
4136 a chipset where boot IRQs cannot be disabled.
4137 The opposite of ioapicreroute.
4138 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
4139 routing table. These calls are known to be buggy
4140 on several machines and they hang the machine
4141 when used, but on other computers it's the only
4142 way to get the interrupt routing table. Try
4143 this option if the kernel is unable to allocate
4144 IRQs or discover secondary PCI buses on your
4145 motherboard.
4146 rom [X86] Assign address space to expansion ROMs.
4147 Use with caution as certain devices share
4148 address decoders between ROMs and other
4149 resources.
4150 norom [X86] Do not assign address space to
4151 expansion ROMs that do not already have
4152 BIOS assigned address ranges.
4153 nobar [X86] Do not assign address space to the
4154 BARs that weren't assigned by the BIOS.
4155 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
4156 assigned automatically to PCI devices. You can
4157 make the kernel exclude IRQs of your ISA cards
4158 this way.
4159 pirqaddr=0xAAAAA [X86] Specify the physical address
4160 of the PIRQ table (normally generated
4161 by the BIOS) if it is outside the
4162 F0000h-100000h range.
4163 lastbus=N [X86] Scan all buses thru bus #N. Can be
4164 useful if the kernel is unable to find your
4165 secondary buses and you want to tell it
4166 explicitly which ones they are.
4167 assign-busses [X86] Always assign all PCI bus
4168 numbers ourselves, overriding
4169 whatever the firmware may have done.
4170 usepirqmask [X86] Honor the possible IRQ mask stored
4171 in the BIOS $PIR table. This is needed on
4172 some systems with broken BIOSes, notably
4173 some HP Pavilion N5400 and Omnibook XE3
4174 notebooks. This will have no effect if ACPI
4175 IRQ routing is enabled.
4176 noacpi [X86] Do not use ACPI for IRQ routing
4177 or for PCI scanning.
4178 use_crs [X86] Use PCI host bridge window information
4179 from ACPI. On BIOSes from 2008 or later, this
4180 is enabled by default. If you need to use this,
4181 please report a bug.
4182 nocrs [X86] Ignore PCI host bridge windows from ACPI.
4183 If you need to use this, please report a bug.
4184 use_e820 [X86] Use E820 reservations to exclude parts of
4185 PCI host bridge windows. This is a workaround
4186 for BIOS defects in host bridge _CRS methods.
4187 If you need to use this, please report a bug to
4188 <linux-pci@vger.kernel.org>.
4189 no_e820 [X86] Ignore E820 reservations for PCI host
4190 bridge windows. This is the default on modern
4191 hardware. If you need to use this, please report
4192 a bug to <linux-pci@vger.kernel.org>.
4193 routeirq Do IRQ routing for all PCI devices.
4194 This is normally done in pci_enable_device(),
4195 so this option is a temporary workaround
4196 for broken drivers that don't call it.
4197 skip_isa_align [X86] do not align io start addr, so can
4198 handle more pci cards
4199 noearly [X86] Don't do any early type 1 scanning.
4200 This might help on some broken boards which
4201 machine check when some devices' config space
4202 is read. But various workarounds are disabled
4203 and some IOMMU drivers will not work.
4204 bfsort Sort PCI devices into breadth-first order.
4205 This sorting is done to get a device
4206 order compatible with older (<= 2.4) kernels.
4207 nobfsort Don't sort PCI devices into breadth-first order.
4208 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
4209 tuning and use the BIOS-configured MPS defaults.
4210 pcie_bus_safe Set every device's MPS to the largest value
4211 supported by all devices below the root complex.
4212 pcie_bus_perf Set device MPS to the largest allowable MPS
4213 based on its parent bus. Also set MRRS (Max
4214 Read Request Size) to the largest supported
4215 value (no larger than the MPS that the device
4216 or bus can support) for best performance.
4217 pcie_bus_peer2peer Set every device's MPS to 128B, which
4218 every device is guaranteed to support. This
4219 configuration allows peer-to-peer DMA between
4220 any pair of devices, possibly at the cost of
4221 reduced performance. This also guarantees
4222 that hot-added devices will work.
4223 cbiosize=nn[KMG] The fixed amount of bus space which is
4224 reserved for the CardBus bridge's IO window.
4225 The default value is 256 bytes.
4226 cbmemsize=nn[KMG] The fixed amount of bus space which is
4227 reserved for the CardBus bridge's memory
4228 window. The default value is 64 megabytes.
4229 resource_alignment=
4230 Format:
4231 [<order of align>@]<pci_dev>[; ...]
4232 Specifies alignment and device to reassign
4233 aligned memory resources. How to
4234 specify the device is described above.
4235 If <order of align> is not specified,
4236 PAGE_SIZE is used as alignment.
4237 A PCI-PCI bridge can be specified if resource
4238 windows need to be expanded.
4239 To specify the alignment for several
4240 instances of a device, the PCI vendor,
4241 device, subvendor, and subdevice may be
4242 specified, e.g., 12@pci:8086:9c22:103c:198f
4243 for 4096-byte alignment.
4244 ecrc= Enable/disable PCIe ECRC (transaction layer
4245 end-to-end CRC checking).
4246 bios: Use BIOS/firmware settings. This is the
4247 the default.
4248 off: Turn ECRC off
4249 on: Turn ECRC on.
4250 hpiosize=nn[KMG] The fixed amount of bus space which is
4251 reserved for hotplug bridge's IO window.
4252 Default size is 256 bytes.
4253 hpmmiosize=nn[KMG] The fixed amount of bus space which is
4254 reserved for hotplug bridge's MMIO window.
4255 Default size is 2 megabytes.
4256 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
4257 reserved for hotplug bridge's MMIO_PREF window.
4258 Default size is 2 megabytes.
4259 hpmemsize=nn[KMG] The fixed amount of bus space which is
4260 reserved for hotplug bridge's MMIO and
4261 MMIO_PREF window.
4262 Default size is 2 megabytes.
4263 hpbussize=nn The minimum amount of additional bus numbers
4264 reserved for buses below a hotplug bridge.
4265 Default is 1.
4266 realloc= Enable/disable reallocating PCI bridge resources
4267 if allocations done by BIOS are too small to
4268 accommodate resources required by all child
4269 devices.
4270 off: Turn realloc off
4271 on: Turn realloc on
4272 realloc same as realloc=on
4273 noari do not use PCIe ARI.
4274 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4275 do not use PCIe ATS (and IOMMU device IOTLB).
4276 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4277 only look for one device below a PCIe downstream
4278 port.
4279 big_root_window Try to add a big 64bit memory window to the PCIe
4280 root complex on AMD CPUs. Some GFX hardware
4281 can resize a BAR to allow access to all VRAM.
4282 Adding the window is slightly risky (it may
4283 conflict with unreported devices), so this
4284 taints the kernel.
4285 disable_acs_redir=<pci_dev>[; ...]
4286 Specify one or more PCI devices (in the format
4287 specified above) separated by semicolons.
4288 Each device specified will have the PCI ACS
4289 redirect capabilities forced off which will
4290 allow P2P traffic between devices through
4291 bridges without forcing it upstream. Note:
4292 this removes isolation between devices and
4293 may put more devices in an IOMMU group.
4294 force_floating [S390] Force usage of floating interrupts.
4295 nomio [S390] Do not use MIO instructions.
4296 norid [S390] ignore the RID field and force use of
4297 one PCI domain per PCI function
4298
4299 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
4300 Management.
4301 off Disable ASPM.
4302 force Enable ASPM even on devices that claim not to support it.
4303 WARNING: Forcing ASPM on may cause system lockups.
4304
4305 pcie_ports= [PCIE] PCIe port services handling:
4306 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4307 even if the platform doesn't give the OS permission to
4308 use them. This may cause conflicts if the platform
4309 also tries to use these services.
4310 dpc-native Use native PCIe service for DPC only. May
4311 cause conflicts if firmware uses AER or DPC.
4312 compat Disable native PCIe services (PME, AER, DPC, PCIe
4313 hotplug).
4314
4315 pcie_port_pm= [PCIE] PCIe port power management handling:
4316 off Disable power management of all PCIe ports
4317 force Forcibly enable power management of all PCIe ports
4318
4319 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4320 nomsi Do not use MSI for native PCIe PME signaling (this makes
4321 all PCIe root ports use INTx for all services).
4322
4323 pcmv= [HW,PCMCIA] BadgePAD 4
4324
4325 pd_ignore_unused
4326 [PM]
4327 Keep all power-domains already enabled by bootloader on,
4328 even if no driver has claimed them. This is useful
4329 for debug and development, but should not be
4330 needed on a platform with proper driver support.
4331
4332 pd. [PARIDE]
4333 See Documentation/admin-guide/blockdev/paride.rst.
4334
4335 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4336 boot time.
4337 Format: { 0 | 1 }
4338 See arch/parisc/kernel/pdc_chassis.c
4339
4340 percpu_alloc= Select which percpu first chunk allocator to use.
4341 Currently supported values are "embed" and "page".
4342 Archs may support subset or none of the selections.
4343 See comments in mm/percpu.c for details on each
4344 allocator. This parameter is primarily for debugging
4345 and performance comparison.
4346
4347 pf. [PARIDE]
4348 See Documentation/admin-guide/blockdev/paride.rst.
4349
4350 pg. [PARIDE]
4351 See Documentation/admin-guide/blockdev/paride.rst.
4352
4353 pirq= [SMP,APIC] Manual mp-table setup
4354 See Documentation/x86/i386/IO-APIC.rst.
4355
4356 plip= [PPT,NET] Parallel port network link
4357 Format: { parport<nr> | timid | 0 }
4358 See also Documentation/admin-guide/parport.rst.
4359
4360 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4361 Override pmtimer IOPort with a hex value.
4362 e.g. pmtmr=0x508
4363
4364 pmu_override= [PPC] Override the PMU.
4365 This option takes over the PMU facility, so it is no
4366 longer usable by perf. Setting this option starts the
4367 PMU counters by setting MMCR0 to 0 (the FC bit is
4368 cleared). If a number is given, then MMCR1 is set to
4369 that number, otherwise (e.g., 'pmu_override=on'), MMCR1
4370 remains 0.
4371
4372 pm_debug_messages [SUSPEND,KNL]
4373 Enable suspend/resume debug messages during boot up.
4374
4375 pnp.debug=1 [PNP]
4376 Enable PNP debug messages (depends on the
4377 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4378 via /sys/module/pnp/parameters/debug. We always show
4379 current resource usage; turning this on also shows
4380 possible settings and some assignment information.
4381
4382 pnpacpi= [ACPI]
4383 { off }
4384
4385 pnpbios= [ISAPNP]
4386 { on | off | curr | res | no-curr | no-res }
4387
4388 pnp_reserve_irq=
4389 [ISAPNP] Exclude IRQs for the autoconfiguration
4390
4391 pnp_reserve_dma=
4392 [ISAPNP] Exclude DMAs for the autoconfiguration
4393
4394 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4395 Ranges are in pairs (I/O port base and size).
4396
4397 pnp_reserve_mem=
4398 [ISAPNP] Exclude memory regions for the
4399 autoconfiguration.
4400 Ranges are in pairs (memory base and size).
4401
4402 ports= [IP_VS_FTP] IPVS ftp helper module
4403 Default is 21.
4404 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4405 may be specified.
4406 Format: <port>,<port>....
4407
4408 powersave=off [PPC] This option disables power saving features.
4409 It specifically disables cpuidle and sets the
4410 platform machine description specific power_save
4411 function to NULL. On Idle the CPU just reduces
4412 execution priority.
4413
4414 ppc_strict_facility_enable
4415 [PPC] This option catches any kernel floating point,
4416 Altivec, VSX and SPE outside of regions specifically
4417 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4418 There is some performance impact when enabling this.
4419
4420 ppc_tm= [PPC]
4421 Format: {"off"}
4422 Disable Hardware Transactional Memory
4423
4424 preempt= [KNL]
4425 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4426 none - Limited to cond_resched() calls
4427 voluntary - Limited to cond_resched() and might_sleep() calls
4428 full - Any section that isn't explicitly preempt disabled
4429 can be preempted anytime.
4430
4431 print-fatal-signals=
4432 [KNL] debug: print fatal signals
4433
4434 If enabled, warn about various signal handling
4435 related application anomalies: too many signals,
4436 too many POSIX.1 timers, fatal signals causing a
4437 coredump - etc.
4438
4439 If you hit the warning due to signal overflow,
4440 you might want to try "ulimit -i unlimited".
4441
4442 default: off.
4443
4444 printk.always_kmsg_dump=
4445 Trigger kmsg_dump for cases other than kernel oops or
4446 panics
4447 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4448 default: disabled
4449
4450 printk.console_no_auto_verbose=
4451 Disable console loglevel raise on oops, panic
4452 or lockdep-detected issues (only if lock debug is on).
4453 With an exception to setups with low baudrate on
4454 serial console, keeping this 0 is a good choice
4455 in order to provide more debug information.
4456 Format: <bool>
4457 default: 0 (auto_verbose is enabled)
4458
4459 printk.devkmsg={on,off,ratelimit}
4460 Control writing to /dev/kmsg.
4461 on - unlimited logging to /dev/kmsg from userspace
4462 off - logging to /dev/kmsg disabled
4463 ratelimit - ratelimit the logging
4464 Default: ratelimit
4465
4466 printk.time= Show timing data prefixed to each printk message line
4467 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4468
4469 processor.max_cstate= [HW,ACPI]
4470 Limit processor to maximum C-state
4471 max_cstate=9 overrides any DMI blacklist limit.
4472
4473 processor.nocst [HW,ACPI]
4474 Ignore the _CST method to determine C-states,
4475 instead using the legacy FADT method
4476
4477 profile= [KNL] Enable kernel profiling via /proc/profile
4478 Format: [<profiletype>,]<number>
4479 Param: <profiletype>: "schedule", "sleep", or "kvm"
4480 [defaults to kernel profiling]
4481 Param: "schedule" - profile schedule points.
4482 Param: "sleep" - profile D-state sleeping (millisecs).
4483 Requires CONFIG_SCHEDSTATS
4484 Param: "kvm" - profile VM exits.
4485 Param: <number> - step/bucket size as a power of 2 for
4486 statistical time based profiling.
4487
4488 prompt_ramdisk= [RAM] [Deprecated]
4489
4490 prot_virt= [S390] enable hosting protected virtual machines
4491 isolated from the hypervisor (if hardware supports
4492 that).
4493 Format: <bool>
4494
4495 psi= [KNL] Enable or disable pressure stall information
4496 tracking.
4497 Format: <bool>
4498
4499 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4500 probe for; one of (bare|imps|exps|lifebook|any).
4501 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4502 per second.
4503 psmouse.resetafter= [HW,MOUSE]
4504 Try to reset the device after so many bad packets
4505 (0 = never).
4506 psmouse.resolution=
4507 [HW,MOUSE] Set desired mouse resolution, in dpi.
4508 psmouse.smartscroll=
4509 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4510 0 = disabled, 1 = enabled (default).
4511
4512 pstore.backend= Specify the name of the pstore backend to use
4513
4514 pt. [PARIDE]
4515 See Documentation/admin-guide/blockdev/paride.rst.
4516
4517 pti= [X86-64] Control Page Table Isolation of user and
4518 kernel address spaces. Disabling this feature
4519 removes hardening, but improves performance of
4520 system calls and interrupts.
4521
4522 on - unconditionally enable
4523 off - unconditionally disable
4524 auto - kernel detects whether your CPU model is
4525 vulnerable to issues that PTI mitigates
4526
4527 Not specifying this option is equivalent to pti=auto.
4528
4529 nopti [X86-64]
4530 Equivalent to pti=off
4531
4532 pty.legacy_count=
4533 [KNL] Number of legacy pty's. Overwrites compiled-in
4534 default number.
4535
4536 quiet [KNL] Disable most log messages
4537
4538 r128= [HW,DRM]
4539
4540 raid= [HW,RAID]
4541 See Documentation/admin-guide/md.rst.
4542
4543 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4544 See Documentation/admin-guide/blockdev/ramdisk.rst.
4545
4546 ramdisk_start= [RAM] RAM disk image start address
4547
4548 random.trust_cpu={on,off}
4549 [KNL] Enable or disable trusting the use of the
4550 CPU's random number generator (if available) to
4551 fully seed the kernel's CRNG. Default is controlled
4552 by CONFIG_RANDOM_TRUST_CPU.
4553
4554 random.trust_bootloader={on,off}
4555 [KNL] Enable or disable trusting the use of a
4556 seed passed by the bootloader (if available) to
4557 fully seed the kernel's CRNG. Default is controlled
4558 by CONFIG_RANDOM_TRUST_BOOTLOADER.
4559
4560 randomize_kstack_offset=
4561 [KNL] Enable or disable kernel stack offset
4562 randomization, which provides roughly 5 bits of
4563 entropy, frustrating memory corruption attacks
4564 that depend on stack address determinism or
4565 cross-syscall address exposures. This is only
4566 available on architectures that have defined
4567 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4568 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4569 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4570
4571 ras=option[,option,...] [KNL] RAS-specific options
4572
4573 cec_disable [X86]
4574 Disable the Correctable Errors Collector,
4575 see CONFIG_RAS_CEC help text.
4576
4577 rcu_nocbs[=cpu-list]
4578 [KNL] The optional argument is a cpu list,
4579 as described above.
4580
4581 In kernels built with CONFIG_RCU_NOCB_CPU=y,
4582 enable the no-callback CPU mode, which prevents
4583 such CPUs' callbacks from being invoked in
4584 softirq context. Invocation of such CPUs' RCU
4585 callbacks will instead be offloaded to "rcuox/N"
4586 kthreads created for that purpose, where "x" is
4587 "p" for RCU-preempt, "s" for RCU-sched, and "g"
4588 for the kthreads that mediate grace periods; and
4589 "N" is the CPU number. This reduces OS jitter on
4590 the offloaded CPUs, which can be useful for HPC
4591 and real-time workloads. It can also improve
4592 energy efficiency for asymmetric multiprocessors.
4593
4594 If a cpulist is passed as an argument, the specified
4595 list of CPUs is set to no-callback mode from boot.
4596
4597 Otherwise, if the '=' sign and the cpulist
4598 arguments are omitted, no CPU will be set to
4599 no-callback mode from boot but the mode may be
4600 toggled at runtime via cpusets.
4601
4602 Note that this argument takes precedence over
4603 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
4604
4605 rcu_nocb_poll [KNL]
4606 Rather than requiring that offloaded CPUs
4607 (specified by rcu_nocbs= above) explicitly
4608 awaken the corresponding "rcuoN" kthreads,
4609 make these kthreads poll for callbacks.
4610 This improves the real-time response for the
4611 offloaded CPUs by relieving them of the need to
4612 wake up the corresponding kthread, but degrades
4613 energy efficiency by requiring that the kthreads
4614 periodically wake up to do the polling.
4615
4616 rcutree.blimit= [KNL]
4617 Set maximum number of finished RCU callbacks to
4618 process in one batch.
4619
4620 rcutree.dump_tree= [KNL]
4621 Dump the structure of the rcu_node combining tree
4622 out at early boot. This is used for diagnostic
4623 purposes, to verify correct tree setup.
4624
4625 rcutree.gp_cleanup_delay= [KNL]
4626 Set the number of jiffies to delay each step of
4627 RCU grace-period cleanup.
4628
4629 rcutree.gp_init_delay= [KNL]
4630 Set the number of jiffies to delay each step of
4631 RCU grace-period initialization.
4632
4633 rcutree.gp_preinit_delay= [KNL]
4634 Set the number of jiffies to delay each step of
4635 RCU grace-period pre-initialization, that is,
4636 the propagation of recent CPU-hotplug changes up
4637 the rcu_node combining tree.
4638
4639 rcutree.use_softirq= [KNL]
4640 If set to zero, move all RCU_SOFTIRQ processing to
4641 per-CPU rcuc kthreads. Defaults to a non-zero
4642 value, meaning that RCU_SOFTIRQ is used by default.
4643 Specify rcutree.use_softirq=0 to use rcuc kthreads.
4644
4645 But note that CONFIG_PREEMPT_RT=y kernels disable
4646 this kernel boot parameter, forcibly setting it
4647 to zero.
4648
4649 rcutree.rcu_fanout_exact= [KNL]
4650 Disable autobalancing of the rcu_node combining
4651 tree. This is used by rcutorture, and might
4652 possibly be useful for architectures having high
4653 cache-to-cache transfer latencies.
4654
4655 rcutree.rcu_fanout_leaf= [KNL]
4656 Change the number of CPUs assigned to each
4657 leaf rcu_node structure. Useful for very
4658 large systems, which will choose the value 64,
4659 and for NUMA systems with large remote-access
4660 latencies, which will choose a value aligned
4661 with the appropriate hardware boundaries.
4662
4663 rcutree.rcu_min_cached_objs= [KNL]
4664 Minimum number of objects which are cached and
4665 maintained per one CPU. Object size is equal
4666 to PAGE_SIZE. The cache allows to reduce the
4667 pressure to page allocator, also it makes the
4668 whole algorithm to behave better in low memory
4669 condition.
4670
4671 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
4672 Set the page-cache refill delay (in milliseconds)
4673 in response to low-memory conditions. The range
4674 of permitted values is in the range 0:100000.
4675
4676 rcutree.jiffies_till_first_fqs= [KNL]
4677 Set delay from grace-period initialization to
4678 first attempt to force quiescent states.
4679 Units are jiffies, minimum value is zero,
4680 and maximum value is HZ.
4681
4682 rcutree.jiffies_till_next_fqs= [KNL]
4683 Set delay between subsequent attempts to force
4684 quiescent states. Units are jiffies, minimum
4685 value is one, and maximum value is HZ.
4686
4687 rcutree.jiffies_till_sched_qs= [KNL]
4688 Set required age in jiffies for a
4689 given grace period before RCU starts
4690 soliciting quiescent-state help from
4691 rcu_note_context_switch() and cond_resched().
4692 If not specified, the kernel will calculate
4693 a value based on the most recent settings
4694 of rcutree.jiffies_till_first_fqs
4695 and rcutree.jiffies_till_next_fqs.
4696 This calculated value may be viewed in
4697 rcutree.jiffies_to_sched_qs. Any attempt to set
4698 rcutree.jiffies_to_sched_qs will be cheerfully
4699 overwritten.
4700
4701 rcutree.kthread_prio= [KNL,BOOT]
4702 Set the SCHED_FIFO priority of the RCU per-CPU
4703 kthreads (rcuc/N). This value is also used for
4704 the priority of the RCU boost threads (rcub/N)
4705 and for the RCU grace-period kthreads (rcu_bh,
4706 rcu_preempt, and rcu_sched). If RCU_BOOST is
4707 set, valid values are 1-99 and the default is 1
4708 (the least-favored priority). Otherwise, when
4709 RCU_BOOST is not set, valid values are 0-99 and
4710 the default is zero (non-realtime operation).
4711 When RCU_NOCB_CPU is set, also adjust the
4712 priority of NOCB callback kthreads.
4713
4714 rcutree.rcu_divisor= [KNL]
4715 Set the shift-right count to use to compute
4716 the callback-invocation batch limit bl from
4717 the number of callbacks queued on this CPU.
4718 The result will be bounded below by the value of
4719 the rcutree.blimit kernel parameter. Every bl
4720 callbacks, the softirq handler will exit in
4721 order to allow the CPU to do other work.
4722
4723 Please note that this callback-invocation batch
4724 limit applies only to non-offloaded callback
4725 invocation. Offloaded callbacks are instead
4726 invoked in the context of an rcuoc kthread, which
4727 scheduler will preempt as it does any other task.
4728
4729 rcutree.nocb_nobypass_lim_per_jiffy= [KNL]
4730 On callback-offloaded (rcu_nocbs) CPUs,
4731 RCU reduces the lock contention that would
4732 otherwise be caused by callback floods through
4733 use of the ->nocb_bypass list. However, in the
4734 common non-flooded case, RCU queues directly to
4735 the main ->cblist in order to avoid the extra
4736 overhead of the ->nocb_bypass list and its lock.
4737 But if there are too many callbacks queued during
4738 a single jiffy, RCU pre-queues the callbacks into
4739 the ->nocb_bypass queue. The definition of "too
4740 many" is supplied by this kernel boot parameter.
4741
4742 rcutree.rcu_nocb_gp_stride= [KNL]
4743 Set the number of NOCB callback kthreads in
4744 each group, which defaults to the square root
4745 of the number of CPUs. Larger numbers reduce
4746 the wakeup overhead on the global grace-period
4747 kthread, but increases that same overhead on
4748 each group's NOCB grace-period kthread.
4749
4750 rcutree.qhimark= [KNL]
4751 Set threshold of queued RCU callbacks beyond which
4752 batch limiting is disabled.
4753
4754 rcutree.qlowmark= [KNL]
4755 Set threshold of queued RCU callbacks below which
4756 batch limiting is re-enabled.
4757
4758 rcutree.qovld= [KNL]
4759 Set threshold of queued RCU callbacks beyond which
4760 RCU's force-quiescent-state scan will aggressively
4761 enlist help from cond_resched() and sched IPIs to
4762 help CPUs more quickly reach quiescent states.
4763 Set to less than zero to make this be set based
4764 on rcutree.qhimark at boot time and to zero to
4765 disable more aggressive help enlistment.
4766
4767 rcutree.rcu_kick_kthreads= [KNL]
4768 Cause the grace-period kthread to get an extra
4769 wake_up() if it sleeps three times longer than
4770 it should at force-quiescent-state time.
4771 This wake_up() will be accompanied by a
4772 WARN_ONCE() splat and an ftrace_dump().
4773
4774 rcutree.rcu_unlock_delay= [KNL]
4775 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
4776 this specifies an rcu_read_unlock()-time delay
4777 in microseconds. This defaults to zero.
4778 Larger delays increase the probability of
4779 catching RCU pointer leaks, that is, buggy use
4780 of RCU-protected pointers after the relevant
4781 rcu_read_unlock() has completed.
4782
4783 rcutree.sysrq_rcu= [KNL]
4784 Commandeer a sysrq key to dump out Tree RCU's
4785 rcu_node tree with an eye towards determining
4786 why a new grace period has not yet started.
4787
4788 rcuscale.gp_async= [KNL]
4789 Measure performance of asynchronous
4790 grace-period primitives such as call_rcu().
4791
4792 rcuscale.gp_async_max= [KNL]
4793 Specify the maximum number of outstanding
4794 callbacks per writer thread. When a writer
4795 thread exceeds this limit, it invokes the
4796 corresponding flavor of rcu_barrier() to allow
4797 previously posted callbacks to drain.
4798
4799 rcuscale.gp_exp= [KNL]
4800 Measure performance of expedited synchronous
4801 grace-period primitives.
4802
4803 rcuscale.holdoff= [KNL]
4804 Set test-start holdoff period. The purpose of
4805 this parameter is to delay the start of the
4806 test until boot completes in order to avoid
4807 interference.
4808
4809 rcuscale.kfree_rcu_test= [KNL]
4810 Set to measure performance of kfree_rcu() flooding.
4811
4812 rcuscale.kfree_rcu_test_double= [KNL]
4813 Test the double-argument variant of kfree_rcu().
4814 If this parameter has the same value as
4815 rcuscale.kfree_rcu_test_single, both the single-
4816 and double-argument variants are tested.
4817
4818 rcuscale.kfree_rcu_test_single= [KNL]
4819 Test the single-argument variant of kfree_rcu().
4820 If this parameter has the same value as
4821 rcuscale.kfree_rcu_test_double, both the single-
4822 and double-argument variants are tested.
4823
4824 rcuscale.kfree_nthreads= [KNL]
4825 The number of threads running loops of kfree_rcu().
4826
4827 rcuscale.kfree_alloc_num= [KNL]
4828 Number of allocations and frees done in an iteration.
4829
4830 rcuscale.kfree_loops= [KNL]
4831 Number of loops doing rcuscale.kfree_alloc_num number
4832 of allocations and frees.
4833
4834 rcuscale.nreaders= [KNL]
4835 Set number of RCU readers. The value -1 selects
4836 N, where N is the number of CPUs. A value
4837 "n" less than -1 selects N-n+1, where N is again
4838 the number of CPUs. For example, -2 selects N
4839 (the number of CPUs), -3 selects N+1, and so on.
4840 A value of "n" less than or equal to -N selects
4841 a single reader.
4842
4843 rcuscale.nwriters= [KNL]
4844 Set number of RCU writers. The values operate
4845 the same as for rcuscale.nreaders.
4846 N, where N is the number of CPUs
4847
4848 rcuscale.perf_type= [KNL]
4849 Specify the RCU implementation to test.
4850
4851 rcuscale.shutdown= [KNL]
4852 Shut the system down after performance tests
4853 complete. This is useful for hands-off automated
4854 testing.
4855
4856 rcuscale.verbose= [KNL]
4857 Enable additional printk() statements.
4858
4859 rcuscale.writer_holdoff= [KNL]
4860 Write-side holdoff between grace periods,
4861 in microseconds. The default of zero says
4862 no holdoff.
4863
4864 rcutorture.fqs_duration= [KNL]
4865 Set duration of force_quiescent_state bursts
4866 in microseconds.
4867
4868 rcutorture.fqs_holdoff= [KNL]
4869 Set holdoff time within force_quiescent_state bursts
4870 in microseconds.
4871
4872 rcutorture.fqs_stutter= [KNL]
4873 Set wait time between force_quiescent_state bursts
4874 in seconds.
4875
4876 rcutorture.fwd_progress= [KNL]
4877 Specifies the number of kthreads to be used
4878 for RCU grace-period forward-progress testing
4879 for the types of RCU supporting this notion.
4880 Defaults to 1 kthread, values less than zero or
4881 greater than the number of CPUs cause the number
4882 of CPUs to be used.
4883
4884 rcutorture.fwd_progress_div= [KNL]
4885 Specify the fraction of a CPU-stall-warning
4886 period to do tight-loop forward-progress testing.
4887
4888 rcutorture.fwd_progress_holdoff= [KNL]
4889 Number of seconds to wait between successive
4890 forward-progress tests.
4891
4892 rcutorture.fwd_progress_need_resched= [KNL]
4893 Enclose cond_resched() calls within checks for
4894 need_resched() during tight-loop forward-progress
4895 testing.
4896
4897 rcutorture.gp_cond= [KNL]
4898 Use conditional/asynchronous update-side
4899 primitives, if available.
4900
4901 rcutorture.gp_exp= [KNL]
4902 Use expedited update-side primitives, if available.
4903
4904 rcutorture.gp_normal= [KNL]
4905 Use normal (non-expedited) asynchronous
4906 update-side primitives, if available.
4907
4908 rcutorture.gp_sync= [KNL]
4909 Use normal (non-expedited) synchronous
4910 update-side primitives, if available. If all
4911 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4912 rcutorture.gp_normal=, and rcutorture.gp_sync=
4913 are zero, rcutorture acts as if is interpreted
4914 they are all non-zero.
4915
4916 rcutorture.irqreader= [KNL]
4917 Run RCU readers from irq handlers, or, more
4918 accurately, from a timer handler. Not all RCU
4919 flavors take kindly to this sort of thing.
4920
4921 rcutorture.leakpointer= [KNL]
4922 Leak an RCU-protected pointer out of the reader.
4923 This can of course result in splats, and is
4924 intended to test the ability of things like
4925 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
4926 such leaks.
4927
4928 rcutorture.n_barrier_cbs= [KNL]
4929 Set callbacks/threads for rcu_barrier() testing.
4930
4931 rcutorture.nfakewriters= [KNL]
4932 Set number of concurrent RCU writers. These just
4933 stress RCU, they don't participate in the actual
4934 test, hence the "fake".
4935
4936 rcutorture.nocbs_nthreads= [KNL]
4937 Set number of RCU callback-offload togglers.
4938 Zero (the default) disables toggling.
4939
4940 rcutorture.nocbs_toggle= [KNL]
4941 Set the delay in milliseconds between successive
4942 callback-offload toggling attempts.
4943
4944 rcutorture.nreaders= [KNL]
4945 Set number of RCU readers. The value -1 selects
4946 N-1, where N is the number of CPUs. A value
4947 "n" less than -1 selects N-n-2, where N is again
4948 the number of CPUs. For example, -2 selects N
4949 (the number of CPUs), -3 selects N+1, and so on.
4950
4951 rcutorture.object_debug= [KNL]
4952 Enable debug-object double-call_rcu() testing.
4953
4954 rcutorture.onoff_holdoff= [KNL]
4955 Set time (s) after boot for CPU-hotplug testing.
4956
4957 rcutorture.onoff_interval= [KNL]
4958 Set time (jiffies) between CPU-hotplug operations,
4959 or zero to disable CPU-hotplug testing.
4960
4961 rcutorture.read_exit= [KNL]
4962 Set the number of read-then-exit kthreads used
4963 to test the interaction of RCU updaters and
4964 task-exit processing.
4965
4966 rcutorture.read_exit_burst= [KNL]
4967 The number of times in a given read-then-exit
4968 episode that a set of read-then-exit kthreads
4969 is spawned.
4970
4971 rcutorture.read_exit_delay= [KNL]
4972 The delay, in seconds, between successive
4973 read-then-exit testing episodes.
4974
4975 rcutorture.shuffle_interval= [KNL]
4976 Set task-shuffle interval (s). Shuffling tasks
4977 allows some CPUs to go into dyntick-idle mode
4978 during the rcutorture test.
4979
4980 rcutorture.shutdown_secs= [KNL]
4981 Set time (s) after boot system shutdown. This
4982 is useful for hands-off automated testing.
4983
4984 rcutorture.stall_cpu= [KNL]
4985 Duration of CPU stall (s) to test RCU CPU stall
4986 warnings, zero to disable.
4987
4988 rcutorture.stall_cpu_block= [KNL]
4989 Sleep while stalling if set. This will result
4990 in warnings from preemptible RCU in addition
4991 to any other stall-related activity.
4992
4993 rcutorture.stall_cpu_holdoff= [KNL]
4994 Time to wait (s) after boot before inducing stall.
4995
4996 rcutorture.stall_cpu_irqsoff= [KNL]
4997 Disable interrupts while stalling if set.
4998
4999 rcutorture.stall_gp_kthread= [KNL]
5000 Duration (s) of forced sleep within RCU
5001 grace-period kthread to test RCU CPU stall
5002 warnings, zero to disable. If both stall_cpu
5003 and stall_gp_kthread are specified, the
5004 kthread is starved first, then the CPU.
5005
5006 rcutorture.stat_interval= [KNL]
5007 Time (s) between statistics printk()s.
5008
5009 rcutorture.stutter= [KNL]
5010 Time (s) to stutter testing, for example, specifying
5011 five seconds causes the test to run for five seconds,
5012 wait for five seconds, and so on. This tests RCU's
5013 ability to transition abruptly to and from idle.
5014
5015 rcutorture.test_boost= [KNL]
5016 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
5017 "Maybe" means test if the RCU implementation
5018 under test support RCU priority boosting.
5019
5020 rcutorture.test_boost_duration= [KNL]
5021 Duration (s) of each individual boost test.
5022
5023 rcutorture.test_boost_interval= [KNL]
5024 Interval (s) between each boost test.
5025
5026 rcutorture.test_no_idle_hz= [KNL]
5027 Test RCU's dyntick-idle handling. See also the
5028 rcutorture.shuffle_interval parameter.
5029
5030 rcutorture.torture_type= [KNL]
5031 Specify the RCU implementation to test.
5032
5033 rcutorture.verbose= [KNL]
5034 Enable additional printk() statements.
5035
5036 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
5037 Dump ftrace buffer after reporting RCU CPU
5038 stall warning.
5039
5040 rcupdate.rcu_cpu_stall_suppress= [KNL]
5041 Suppress RCU CPU stall warning messages.
5042
5043 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
5044 Suppress RCU CPU stall warning messages and
5045 rcutorture writer stall warnings that occur
5046 during early boot, that is, during the time
5047 before the init task is spawned.
5048
5049 rcupdate.rcu_cpu_stall_timeout= [KNL]
5050 Set timeout for RCU CPU stall warning messages.
5051 The value is in seconds and the maximum allowed
5052 value is 300 seconds.
5053
5054 rcupdate.rcu_exp_cpu_stall_timeout= [KNL]
5055 Set timeout for expedited RCU CPU stall warning
5056 messages. The value is in milliseconds
5057 and the maximum allowed value is 21000
5058 milliseconds. Please note that this value is
5059 adjusted to an arch timer tick resolution.
5060 Setting this to zero causes the value from
5061 rcupdate.rcu_cpu_stall_timeout to be used (after
5062 conversion from seconds to milliseconds).
5063
5064 rcupdate.rcu_expedited= [KNL]
5065 Use expedited grace-period primitives, for
5066 example, synchronize_rcu_expedited() instead
5067 of synchronize_rcu(). This reduces latency,
5068 but can increase CPU utilization, degrade
5069 real-time latency, and degrade energy efficiency.
5070 No effect on CONFIG_TINY_RCU kernels.
5071
5072 rcupdate.rcu_normal= [KNL]
5073 Use only normal grace-period primitives,
5074 for example, synchronize_rcu() instead of
5075 synchronize_rcu_expedited(). This improves
5076 real-time latency, CPU utilization, and
5077 energy efficiency, but can expose users to
5078 increased grace-period latency. This parameter
5079 overrides rcupdate.rcu_expedited. No effect on
5080 CONFIG_TINY_RCU kernels.
5081
5082 rcupdate.rcu_normal_after_boot= [KNL]
5083 Once boot has completed (that is, after
5084 rcu_end_inkernel_boot() has been invoked), use
5085 only normal grace-period primitives. No effect
5086 on CONFIG_TINY_RCU kernels.
5087
5088 But note that CONFIG_PREEMPT_RT=y kernels enables
5089 this kernel boot parameter, forcibly setting
5090 it to the value one, that is, converting any
5091 post-boot attempt at an expedited RCU grace
5092 period to instead use normal non-expedited
5093 grace-period processing.
5094
5095 rcupdate.rcu_task_collapse_lim= [KNL]
5096 Set the maximum number of callbacks present
5097 at the beginning of a grace period that allows
5098 the RCU Tasks flavors to collapse back to using
5099 a single callback queue. This switching only
5100 occurs when rcupdate.rcu_task_enqueue_lim is
5101 set to the default value of -1.
5102
5103 rcupdate.rcu_task_contend_lim= [KNL]
5104 Set the minimum number of callback-queuing-time
5105 lock-contention events per jiffy required to
5106 cause the RCU Tasks flavors to switch to per-CPU
5107 callback queuing. This switching only occurs
5108 when rcupdate.rcu_task_enqueue_lim is set to
5109 the default value of -1.
5110
5111 rcupdate.rcu_task_enqueue_lim= [KNL]
5112 Set the number of callback queues to use for the
5113 RCU Tasks family of RCU flavors. The default
5114 of -1 allows this to be automatically (and
5115 dynamically) adjusted. This parameter is intended
5116 for use in testing.
5117
5118 rcupdate.rcu_task_ipi_delay= [KNL]
5119 Set time in jiffies during which RCU tasks will
5120 avoid sending IPIs, starting with the beginning
5121 of a given grace period. Setting a large
5122 number avoids disturbing real-time workloads,
5123 but lengthens grace periods.
5124
5125 rcupdate.rcu_task_stall_info= [KNL]
5126 Set initial timeout in jiffies for RCU task stall
5127 informational messages, which give some indication
5128 of the problem for those not patient enough to
5129 wait for ten minutes. Informational messages are
5130 only printed prior to the stall-warning message
5131 for a given grace period. Disable with a value
5132 less than or equal to zero. Defaults to ten
5133 seconds. A change in value does not take effect
5134 until the beginning of the next grace period.
5135
5136 rcupdate.rcu_task_stall_info_mult= [KNL]
5137 Multiplier for time interval between successive
5138 RCU task stall informational messages for a given
5139 RCU tasks grace period. This value is clamped
5140 to one through ten, inclusive. It defaults to
5141 the value three, so that the first informational
5142 message is printed 10 seconds into the grace
5143 period, the second at 40 seconds, the third at
5144 160 seconds, and then the stall warning at 600
5145 seconds would prevent a fourth at 640 seconds.
5146
5147 rcupdate.rcu_task_stall_timeout= [KNL]
5148 Set timeout in jiffies for RCU task stall
5149 warning messages. Disable with a value less
5150 than or equal to zero. Defaults to ten minutes.
5151 A change in value does not take effect until
5152 the beginning of the next grace period.
5153
5154 rcupdate.rcu_self_test= [KNL]
5155 Run the RCU early boot self tests
5156
5157 rdinit= [KNL]
5158 Format: <full_path>
5159 Run specified binary instead of /init from the ramdisk,
5160 used for early userspace startup. See initrd.
5161
5162 rdrand= [X86]
5163 force - Override the decision by the kernel to hide the
5164 advertisement of RDRAND support (this affects
5165 certain AMD processors because of buggy BIOS
5166 support, specifically around the suspend/resume
5167 path).
5168
5169 rdt= [HW,X86,RDT]
5170 Turn on/off individual RDT features. List is:
5171 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
5172 mba.
5173 E.g. to turn on cmt and turn off mba use:
5174 rdt=cmt,!mba
5175
5176 reboot= [KNL]
5177 Format (x86 or x86_64):
5178 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
5179 [[,]s[mp]#### \
5180 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
5181 [[,]f[orce]
5182 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
5183 (prefix with 'panic_' to set mode for panic
5184 reboot only),
5185 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
5186 reboot_force is either force or not specified,
5187 reboot_cpu is s[mp]#### with #### being the processor
5188 to be used for rebooting.
5189
5190 refscale.holdoff= [KNL]
5191 Set test-start holdoff period. The purpose of
5192 this parameter is to delay the start of the
5193 test until boot completes in order to avoid
5194 interference.
5195
5196 refscale.loops= [KNL]
5197 Set the number of loops over the synchronization
5198 primitive under test. Increasing this number
5199 reduces noise due to loop start/end overhead,
5200 but the default has already reduced the per-pass
5201 noise to a handful of picoseconds on ca. 2020
5202 x86 laptops.
5203
5204 refscale.nreaders= [KNL]
5205 Set number of readers. The default value of -1
5206 selects N, where N is roughly 75% of the number
5207 of CPUs. A value of zero is an interesting choice.
5208
5209 refscale.nruns= [KNL]
5210 Set number of runs, each of which is dumped onto
5211 the console log.
5212
5213 refscale.readdelay= [KNL]
5214 Set the read-side critical-section duration,
5215 measured in microseconds.
5216
5217 refscale.scale_type= [KNL]
5218 Specify the read-protection implementation to test.
5219
5220 refscale.shutdown= [KNL]
5221 Shut down the system at the end of the performance
5222 test. This defaults to 1 (shut it down) when
5223 refscale is built into the kernel and to 0 (leave
5224 it running) when refscale is built as a module.
5225
5226 refscale.verbose= [KNL]
5227 Enable additional printk() statements.
5228
5229 refscale.verbose_batched= [KNL]
5230 Batch the additional printk() statements. If zero
5231 (the default) or negative, print everything. Otherwise,
5232 print every Nth verbose statement, where N is the value
5233 specified.
5234
5235 relax_domain_level=
5236 [KNL, SMP] Set scheduler's default relax_domain_level.
5237 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
5238
5239 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
5240 Format: <base1>,<size1>[,<base2>,<size2>,...]
5241 Reserve I/O ports or memory so the kernel won't use
5242 them. If <base> is less than 0x10000, the region
5243 is assumed to be I/O ports; otherwise it is memory.
5244
5245 reservetop= [X86-32]
5246 Format: nn[KMG]
5247 Reserves a hole at the top of the kernel virtual
5248 address space.
5249
5250 reset_devices [KNL] Force drivers to reset the underlying device
5251 during initialization.
5252
5253 resume= [SWSUSP]
5254 Specify the partition device for software suspend
5255 Format:
5256 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
5257
5258 resume_offset= [SWSUSP]
5259 Specify the offset from the beginning of the partition
5260 given by "resume=" at which the swap header is located,
5261 in <PAGE_SIZE> units (needed only for swap files).
5262 See Documentation/power/swsusp-and-swap-files.rst
5263
5264 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
5265 read the resume files
5266
5267 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
5268 Useful for devices that are detected asynchronously
5269 (e.g. USB and MMC devices).
5270
5271 retain_initrd [RAM] Keep initrd memory after extraction
5272
5273 retbleed= [X86] Control mitigation of RETBleed (Arbitrary
5274 Speculative Code Execution with Return Instructions)
5275 vulnerability.
5276
5277 AMD-based UNRET and IBPB mitigations alone do not stop
5278 sibling threads from influencing the predictions of other
5279 sibling threads. For that reason, STIBP is used on pro-
5280 cessors that support it, and mitigate SMT on processors
5281 that don't.
5282
5283 off - no mitigation
5284 auto - automatically select a migitation
5285 auto,nosmt - automatically select a mitigation,
5286 disabling SMT if necessary for
5287 the full mitigation (only on Zen1
5288 and older without STIBP).
5289 ibpb - On AMD, mitigate short speculation
5290 windows on basic block boundaries too.
5291 Safe, highest perf impact. It also
5292 enables STIBP if present. Not suitable
5293 on Intel.
5294 ibpb,nosmt - Like "ibpb" above but will disable SMT
5295 when STIBP is not available. This is
5296 the alternative for systems which do not
5297 have STIBP.
5298 unret - Force enable untrained return thunks,
5299 only effective on AMD f15h-f17h based
5300 systems.
5301 unret,nosmt - Like unret, but will disable SMT when STIBP
5302 is not available. This is the alternative for
5303 systems which do not have STIBP.
5304
5305 Selecting 'auto' will choose a mitigation method at run
5306 time according to the CPU.
5307
5308 Not specifying this option is equivalent to retbleed=auto.
5309
5310 rfkill.default_state=
5311 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
5312 etc. communication is blocked by default.
5313 1 Unblocked.
5314
5315 rfkill.master_switch_mode=
5316 0 The "airplane mode" button does nothing.
5317 1 The "airplane mode" button toggles between everything
5318 blocked and the previous configuration.
5319 2 The "airplane mode" button toggles between everything
5320 blocked and everything unblocked.
5321
5322 rhash_entries= [KNL,NET]
5323 Set number of hash buckets for route cache
5324
5325 ring3mwait=disable
5326 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
5327 CPUs.
5328
5329 ro [KNL] Mount root device read-only on boot
5330
5331 rodata= [KNL]
5332 on Mark read-only kernel memory as read-only (default).
5333 off Leave read-only kernel memory writable for debugging.
5334 full Mark read-only kernel memory and aliases as read-only
5335 [arm64]
5336
5337 rockchip.usb_uart
5338 Enable the uart passthrough on the designated usb port
5339 on Rockchip SoCs. When active, the signals of the
5340 debug-uart get routed to the D+ and D- pins of the usb
5341 port and the regular usb controller gets disabled.
5342
5343 root= [KNL] Root filesystem
5344 See name_to_dev_t comment in init/do_mounts.c.
5345
5346 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
5347 mount the root filesystem
5348
5349 rootflags= [KNL] Set root filesystem mount option string
5350
5351 rootfstype= [KNL] Set root filesystem type
5352
5353 rootwait [KNL] Wait (indefinitely) for root device to show up.
5354 Useful for devices that are detected asynchronously
5355 (e.g. USB and MMC devices).
5356
5357 rproc_mem=nn[KMG][@address]
5358 [KNL,ARM,CMA] Remoteproc physical memory block.
5359 Memory area to be used by remote processor image,
5360 managed by CMA.
5361
5362 rw [KNL] Mount root device read-write on boot
5363
5364 S [KNL] Run init in single mode
5365
5366 s390_iommu= [HW,S390]
5367 Set s390 IOTLB flushing mode
5368 strict
5369 With strict flushing every unmap operation will result in
5370 an IOTLB flush. Default is lazy flushing before reuse,
5371 which is faster.
5372
5373 s390_iommu_aperture= [KNL,S390]
5374 Specifies the size of the per device DMA address space
5375 accessible through the DMA and IOMMU APIs as a decimal
5376 factor of the size of main memory.
5377 The default is 1 meaning that one can concurrently use
5378 as many DMA addresses as physical memory is installed,
5379 if supported by hardware, and thus map all of memory
5380 once. With a value of 2 one can map all of memory twice
5381 and so on. As a special case a factor of 0 imposes no
5382 restrictions other than those given by hardware at the
5383 cost of significant additional memory use for tables.
5384
5385 sa1100ir [NET]
5386 See drivers/net/irda/sa1100_ir.c.
5387
5388 sched_verbose [KNL] Enables verbose scheduler debug messages.
5389
5390 schedstats= [KNL,X86] Enable or disable scheduled statistics.
5391 Allowed values are enable and disable. This feature
5392 incurs a small amount of overhead in the scheduler
5393 but is useful for debugging and performance tuning.
5394
5395 sched_thermal_decay_shift=
5396 [KNL, SMP] Set a decay shift for scheduler thermal
5397 pressure signal. Thermal pressure signal follows the
5398 default decay period of other scheduler pelt
5399 signals(usually 32 ms but configurable). Setting
5400 sched_thermal_decay_shift will left shift the decay
5401 period for the thermal pressure signal by the shift
5402 value.
5403 i.e. with the default pelt decay period of 32 ms
5404 sched_thermal_decay_shift thermal pressure decay pr
5405 1 64 ms
5406 2 128 ms
5407 and so on.
5408 Format: integer between 0 and 10
5409 Default is 0.
5410
5411 scftorture.holdoff= [KNL]
5412 Number of seconds to hold off before starting
5413 test. Defaults to zero for module insertion and
5414 to 10 seconds for built-in smp_call_function()
5415 tests.
5416
5417 scftorture.longwait= [KNL]
5418 Request ridiculously long waits randomly selected
5419 up to the chosen limit in seconds. Zero (the
5420 default) disables this feature. Please note
5421 that requesting even small non-zero numbers of
5422 seconds can result in RCU CPU stall warnings,
5423 softlockup complaints, and so on.
5424
5425 scftorture.nthreads= [KNL]
5426 Number of kthreads to spawn to invoke the
5427 smp_call_function() family of functions.
5428 The default of -1 specifies a number of kthreads
5429 equal to the number of CPUs.
5430
5431 scftorture.onoff_holdoff= [KNL]
5432 Number seconds to wait after the start of the
5433 test before initiating CPU-hotplug operations.
5434
5435 scftorture.onoff_interval= [KNL]
5436 Number seconds to wait between successive
5437 CPU-hotplug operations. Specifying zero (which
5438 is the default) disables CPU-hotplug operations.
5439
5440 scftorture.shutdown_secs= [KNL]
5441 The number of seconds following the start of the
5442 test after which to shut down the system. The
5443 default of zero avoids shutting down the system.
5444 Non-zero values are useful for automated tests.
5445
5446 scftorture.stat_interval= [KNL]
5447 The number of seconds between outputting the
5448 current test statistics to the console. A value
5449 of zero disables statistics output.
5450
5451 scftorture.stutter_cpus= [KNL]
5452 The number of jiffies to wait between each change
5453 to the set of CPUs under test.
5454
5455 scftorture.use_cpus_read_lock= [KNL]
5456 Use use_cpus_read_lock() instead of the default
5457 preempt_disable() to disable CPU hotplug
5458 while invoking one of the smp_call_function*()
5459 functions.
5460
5461 scftorture.verbose= [KNL]
5462 Enable additional printk() statements.
5463
5464 scftorture.weight_single= [KNL]
5465 The probability weighting to use for the
5466 smp_call_function_single() function with a zero
5467 "wait" parameter. A value of -1 selects the
5468 default if all other weights are -1. However,
5469 if at least one weight has some other value, a
5470 value of -1 will instead select a weight of zero.
5471
5472 scftorture.weight_single_wait= [KNL]
5473 The probability weighting to use for the
5474 smp_call_function_single() function with a
5475 non-zero "wait" parameter. See weight_single.
5476
5477 scftorture.weight_many= [KNL]
5478 The probability weighting to use for the
5479 smp_call_function_many() function with a zero
5480 "wait" parameter. See weight_single.
5481 Note well that setting a high probability for
5482 this weighting can place serious IPI load
5483 on the system.
5484
5485 scftorture.weight_many_wait= [KNL]
5486 The probability weighting to use for the
5487 smp_call_function_many() function with a
5488 non-zero "wait" parameter. See weight_single
5489 and weight_many.
5490
5491 scftorture.weight_all= [KNL]
5492 The probability weighting to use for the
5493 smp_call_function_all() function with a zero
5494 "wait" parameter. See weight_single and
5495 weight_many.
5496
5497 scftorture.weight_all_wait= [KNL]
5498 The probability weighting to use for the
5499 smp_call_function_all() function with a
5500 non-zero "wait" parameter. See weight_single
5501 and weight_many.
5502
5503 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
5504 xtime_lock contention on larger systems, and/or RCU lock
5505 contention on all systems with CONFIG_MAXSMP set.
5506 Format: { "0" | "1" }
5507 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
5508 1 -- enable.
5509 Note: increases power consumption, thus should only be
5510 enabled if running jitter sensitive (HPC/RT) workloads.
5511
5512 security= [SECURITY] Choose a legacy "major" security module to
5513 enable at boot. This has been deprecated by the
5514 "lsm=" parameter.
5515
5516 selinux= [SELINUX] Disable or enable SELinux at boot time.
5517 Format: { "0" | "1" }
5518 See security/selinux/Kconfig help text.
5519 0 -- disable.
5520 1 -- enable.
5521 Default value is 1.
5522
5523 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
5524 Format: { "0" | "1" }
5525 See security/apparmor/Kconfig help text
5526 0 -- disable.
5527 1 -- enable.
5528 Default value is set via kernel config option.
5529
5530 serialnumber [BUGS=X86-32]
5531
5532 sev=option[,option...] [X86-64] See Documentation/x86/x86_64/boot-options.rst
5533
5534 shapers= [NET]
5535 Maximal number of shapers.
5536
5537 simeth= [IA-64]
5538 simscsi=
5539
5540 slram= [HW,MTD]
5541
5542 slab_merge [MM]
5543 Enable merging of slabs with similar size when the
5544 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
5545
5546 slab_nomerge [MM]
5547 Disable merging of slabs with similar size. May be
5548 necessary if there is some reason to distinguish
5549 allocs to different slabs, especially in hardened
5550 environments where the risk of heap overflows and
5551 layout control by attackers can usually be
5552 frustrated by disabling merging. This will reduce
5553 most of the exposure of a heap attack to a single
5554 cache (risks via metadata attacks are mostly
5555 unchanged). Debug options disable merging on their
5556 own.
5557 For more information see Documentation/mm/slub.rst.
5558
5559 slab_max_order= [MM, SLAB]
5560 Determines the maximum allowed order for slabs.
5561 A high setting may cause OOMs due to memory
5562 fragmentation. Defaults to 1 for systems with
5563 more than 32MB of RAM, 0 otherwise.
5564
5565 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
5566 Enabling slub_debug allows one to determine the
5567 culprit if slab objects become corrupted. Enabling
5568 slub_debug can create guard zones around objects and
5569 may poison objects when not in use. Also tracks the
5570 last alloc / free. For more information see
5571 Documentation/mm/slub.rst.
5572
5573 slub_max_order= [MM, SLUB]
5574 Determines the maximum allowed order for slabs.
5575 A high setting may cause OOMs due to memory
5576 fragmentation. For more information see
5577 Documentation/mm/slub.rst.
5578
5579 slub_min_objects= [MM, SLUB]
5580 The minimum number of objects per slab. SLUB will
5581 increase the slab order up to slub_max_order to
5582 generate a sufficiently large slab able to contain
5583 the number of objects indicated. The higher the number
5584 of objects the smaller the overhead of tracking slabs
5585 and the less frequently locks need to be acquired.
5586 For more information see Documentation/mm/slub.rst.
5587
5588 slub_min_order= [MM, SLUB]
5589 Determines the minimum page order for slabs. Must be
5590 lower than slub_max_order.
5591 For more information see Documentation/mm/slub.rst.
5592
5593 slub_merge [MM, SLUB]
5594 Same with slab_merge.
5595
5596 slub_nomerge [MM, SLUB]
5597 Same with slab_nomerge. This is supported for legacy.
5598 See slab_nomerge for more information.
5599
5600 smart2= [HW]
5601 Format: <io1>[,<io2>[,...,<io8>]]
5602
5603 smp.csd_lock_timeout= [KNL]
5604 Specify the period of time in milliseconds
5605 that smp_call_function() and friends will wait
5606 for a CPU to release the CSD lock. This is
5607 useful when diagnosing bugs involving CPUs
5608 disabling interrupts for extended periods
5609 of time. Defaults to 5,000 milliseconds, and
5610 setting a value of zero disables this feature.
5611 This feature may be more efficiently disabled
5612 using the csdlock_debug- kernel parameter.
5613
5614 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
5615 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
5616 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
5617 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
5618 smsc-ircc2.ircc_irq= [HW] IRQ line
5619 smsc-ircc2.ircc_dma= [HW] DMA channel
5620 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
5621 0: Toshiba Satellite 1800 (GP data pin select)
5622 1: Fast pin select (default)
5623 2: ATC IRMode
5624
5625 smt= [KNL,S390] Set the maximum number of threads (logical
5626 CPUs) to use per physical CPU on systems capable of
5627 symmetric multithreading (SMT). Will be capped to the
5628 actual hardware limit.
5629 Format: <integer>
5630 Default: -1 (no limit)
5631
5632 softlockup_panic=
5633 [KNL] Should the soft-lockup detector generate panics.
5634 Format: 0 | 1
5635
5636 A value of 1 instructs the soft-lockup detector
5637 to panic the machine when a soft-lockup occurs. It is
5638 also controlled by the kernel.softlockup_panic sysctl
5639 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
5640 respective build-time switch to that functionality.
5641
5642 softlockup_all_cpu_backtrace=
5643 [KNL] Should the soft-lockup detector generate
5644 backtraces on all cpus.
5645 Format: 0 | 1
5646
5647 sonypi.*= [HW] Sony Programmable I/O Control Device driver
5648 See Documentation/admin-guide/laptops/sonypi.rst
5649
5650 spectre_v2= [X86] Control mitigation of Spectre variant 2
5651 (indirect branch speculation) vulnerability.
5652 The default operation protects the kernel from
5653 user space attacks.
5654
5655 on - unconditionally enable, implies
5656 spectre_v2_user=on
5657 off - unconditionally disable, implies
5658 spectre_v2_user=off
5659 auto - kernel detects whether your CPU model is
5660 vulnerable
5661
5662 Selecting 'on' will, and 'auto' may, choose a
5663 mitigation method at run time according to the
5664 CPU, the available microcode, the setting of the
5665 CONFIG_RETPOLINE configuration option, and the
5666 compiler with which the kernel was built.
5667
5668 Selecting 'on' will also enable the mitigation
5669 against user space to user space task attacks.
5670
5671 Selecting 'off' will disable both the kernel and
5672 the user space protections.
5673
5674 Specific mitigations can also be selected manually:
5675
5676 retpoline - replace indirect branches
5677 retpoline,generic - Retpolines
5678 retpoline,lfence - LFENCE; indirect branch
5679 retpoline,amd - alias for retpoline,lfence
5680 eibrs - enhanced IBRS
5681 eibrs,retpoline - enhanced IBRS + Retpolines
5682 eibrs,lfence - enhanced IBRS + LFENCE
5683 ibrs - use IBRS to protect kernel
5684
5685 Not specifying this option is equivalent to
5686 spectre_v2=auto.
5687
5688 spectre_v2_user=
5689 [X86] Control mitigation of Spectre variant 2
5690 (indirect branch speculation) vulnerability between
5691 user space tasks
5692
5693 on - Unconditionally enable mitigations. Is
5694 enforced by spectre_v2=on
5695
5696 off - Unconditionally disable mitigations. Is
5697 enforced by spectre_v2=off
5698
5699 prctl - Indirect branch speculation is enabled,
5700 but mitigation can be enabled via prctl
5701 per thread. The mitigation control state
5702 is inherited on fork.
5703
5704 prctl,ibpb
5705 - Like "prctl" above, but only STIBP is
5706 controlled per thread. IBPB is issued
5707 always when switching between different user
5708 space processes.
5709
5710 seccomp
5711 - Same as "prctl" above, but all seccomp
5712 threads will enable the mitigation unless
5713 they explicitly opt out.
5714
5715 seccomp,ibpb
5716 - Like "seccomp" above, but only STIBP is
5717 controlled per thread. IBPB is issued
5718 always when switching between different
5719 user space processes.
5720
5721 auto - Kernel selects the mitigation depending on
5722 the available CPU features and vulnerability.
5723
5724 Default mitigation: "prctl"
5725
5726 Not specifying this option is equivalent to
5727 spectre_v2_user=auto.
5728
5729 spec_store_bypass_disable=
5730 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
5731 (Speculative Store Bypass vulnerability)
5732
5733 Certain CPUs are vulnerable to an exploit against a
5734 a common industry wide performance optimization known
5735 as "Speculative Store Bypass" in which recent stores
5736 to the same memory location may not be observed by
5737 later loads during speculative execution. The idea
5738 is that such stores are unlikely and that they can
5739 be detected prior to instruction retirement at the
5740 end of a particular speculation execution window.
5741
5742 In vulnerable processors, the speculatively forwarded
5743 store can be used in a cache side channel attack, for
5744 example to read memory to which the attacker does not
5745 directly have access (e.g. inside sandboxed code).
5746
5747 This parameter controls whether the Speculative Store
5748 Bypass optimization is used.
5749
5750 On x86 the options are:
5751
5752 on - Unconditionally disable Speculative Store Bypass
5753 off - Unconditionally enable Speculative Store Bypass
5754 auto - Kernel detects whether the CPU model contains an
5755 implementation of Speculative Store Bypass and
5756 picks the most appropriate mitigation. If the
5757 CPU is not vulnerable, "off" is selected. If the
5758 CPU is vulnerable the default mitigation is
5759 architecture and Kconfig dependent. See below.
5760 prctl - Control Speculative Store Bypass per thread
5761 via prctl. Speculative Store Bypass is enabled
5762 for a process by default. The state of the control
5763 is inherited on fork.
5764 seccomp - Same as "prctl" above, but all seccomp threads
5765 will disable SSB unless they explicitly opt out.
5766
5767 Default mitigations:
5768 X86: "prctl"
5769
5770 On powerpc the options are:
5771
5772 on,auto - On Power8 and Power9 insert a store-forwarding
5773 barrier on kernel entry and exit. On Power7
5774 perform a software flush on kernel entry and
5775 exit.
5776 off - No action.
5777
5778 Not specifying this option is equivalent to
5779 spec_store_bypass_disable=auto.
5780
5781 spia_io_base= [HW,MTD]
5782 spia_fio_base=
5783 spia_pedr=
5784 spia_peddr=
5785
5786 split_lock_detect=
5787 [X86] Enable split lock detection or bus lock detection
5788
5789 When enabled (and if hardware support is present), atomic
5790 instructions that access data across cache line
5791 boundaries will result in an alignment check exception
5792 for split lock detection or a debug exception for
5793 bus lock detection.
5794
5795 off - not enabled
5796
5797 warn - the kernel will emit rate-limited warnings
5798 about applications triggering the #AC
5799 exception or the #DB exception. This mode is
5800 the default on CPUs that support split lock
5801 detection or bus lock detection. Default
5802 behavior is by #AC if both features are
5803 enabled in hardware.
5804
5805 fatal - the kernel will send SIGBUS to applications
5806 that trigger the #AC exception or the #DB
5807 exception. Default behavior is by #AC if
5808 both features are enabled in hardware.
5809
5810 ratelimit:N -
5811 Set system wide rate limit to N bus locks
5812 per second for bus lock detection.
5813 0 < N <= 1000.
5814
5815 N/A for split lock detection.
5816
5817
5818 If an #AC exception is hit in the kernel or in
5819 firmware (i.e. not while executing in user mode)
5820 the kernel will oops in either "warn" or "fatal"
5821 mode.
5822
5823 #DB exception for bus lock is triggered only when
5824 CPL > 0.
5825
5826 srbds= [X86,INTEL]
5827 Control the Special Register Buffer Data Sampling
5828 (SRBDS) mitigation.
5829
5830 Certain CPUs are vulnerable to an MDS-like
5831 exploit which can leak bits from the random
5832 number generator.
5833
5834 By default, this issue is mitigated by
5835 microcode. However, the microcode fix can cause
5836 the RDRAND and RDSEED instructions to become
5837 much slower. Among other effects, this will
5838 result in reduced throughput from /dev/urandom.
5839
5840 The microcode mitigation can be disabled with
5841 the following option:
5842
5843 off: Disable mitigation and remove
5844 performance impact to RDRAND and RDSEED
5845
5846 srcutree.big_cpu_lim [KNL]
5847 Specifies the number of CPUs constituting a
5848 large system, such that srcu_struct structures
5849 should immediately allocate an srcu_node array.
5850 This kernel-boot parameter defaults to 128,
5851 but takes effect only when the low-order four
5852 bits of srcutree.convert_to_big is equal to 3
5853 (decide at boot).
5854
5855 srcutree.convert_to_big [KNL]
5856 Specifies under what conditions an SRCU tree
5857 srcu_struct structure will be converted to big
5858 form, that is, with an rcu_node tree:
5859
5860 0: Never.
5861 1: At init_srcu_struct() time.
5862 2: When rcutorture decides to.
5863 3: Decide at boot time (default).
5864 0x1X: Above plus if high contention.
5865
5866 Either way, the srcu_node tree will be sized based
5867 on the actual runtime number of CPUs (nr_cpu_ids)
5868 instead of the compile-time CONFIG_NR_CPUS.
5869
5870 srcutree.counter_wrap_check [KNL]
5871 Specifies how frequently to check for
5872 grace-period sequence counter wrap for the
5873 srcu_data structure's ->srcu_gp_seq_needed field.
5874 The greater the number of bits set in this kernel
5875 parameter, the less frequently counter wrap will
5876 be checked for. Note that the bottom two bits
5877 are ignored.
5878
5879 srcutree.exp_holdoff [KNL]
5880 Specifies how many nanoseconds must elapse
5881 since the end of the last SRCU grace period for
5882 a given srcu_struct until the next normal SRCU
5883 grace period will be considered for automatic
5884 expediting. Set to zero to disable automatic
5885 expediting.
5886
5887 srcutree.srcu_max_nodelay [KNL]
5888 Specifies the number of no-delay instances
5889 per jiffy for which the SRCU grace period
5890 worker thread will be rescheduled with zero
5891 delay. Beyond this limit, worker thread will
5892 be rescheduled with a sleep delay of one jiffy.
5893
5894 srcutree.srcu_max_nodelay_phase [KNL]
5895 Specifies the per-grace-period phase, number of
5896 non-sleeping polls of readers. Beyond this limit,
5897 grace period worker thread will be rescheduled
5898 with a sleep delay of one jiffy, between each
5899 rescan of the readers, for a grace period phase.
5900
5901 srcutree.srcu_retry_check_delay [KNL]
5902 Specifies number of microseconds of non-sleeping
5903 delay between each non-sleeping poll of readers.
5904
5905 srcutree.small_contention_lim [KNL]
5906 Specifies the number of update-side contention
5907 events per jiffy will be tolerated before
5908 initiating a conversion of an srcu_struct
5909 structure to big form. Note that the value of
5910 srcutree.convert_to_big must have the 0x10 bit
5911 set for contention-based conversions to occur.
5912
5913 ssbd= [ARM64,HW]
5914 Speculative Store Bypass Disable control
5915
5916 On CPUs that are vulnerable to the Speculative
5917 Store Bypass vulnerability and offer a
5918 firmware based mitigation, this parameter
5919 indicates how the mitigation should be used:
5920
5921 force-on: Unconditionally enable mitigation for
5922 for both kernel and userspace
5923 force-off: Unconditionally disable mitigation for
5924 for both kernel and userspace
5925 kernel: Always enable mitigation in the
5926 kernel, and offer a prctl interface
5927 to allow userspace to register its
5928 interest in being mitigated too.
5929
5930 stack_guard_gap= [MM]
5931 override the default stack gap protection. The value
5932 is in page units and it defines how many pages prior
5933 to (for stacks growing down) resp. after (for stacks
5934 growing up) the main stack are reserved for no other
5935 mapping. Default value is 256 pages.
5936
5937 stack_depot_disable= [KNL]
5938 Setting this to true through kernel command line will
5939 disable the stack depot thereby saving the static memory
5940 consumed by the stack hash table. By default this is set
5941 to false.
5942
5943 stacktrace [FTRACE]
5944 Enabled the stack tracer on boot up.
5945
5946 stacktrace_filter=[function-list]
5947 [FTRACE] Limit the functions that the stack tracer
5948 will trace at boot up. function-list is a comma-separated
5949 list of functions. This list can be changed at run
5950 time by the stack_trace_filter file in the debugfs
5951 tracing directory. Note, this enables stack tracing
5952 and the stacktrace above is not needed.
5953
5954 sti= [PARISC,HW]
5955 Format: <num>
5956 Set the STI (builtin display/keyboard on the HP-PARISC
5957 machines) console (graphic card) which should be used
5958 as the initial boot-console.
5959 See also comment in drivers/video/console/sticore.c.
5960
5961 sti_font= [HW]
5962 See comment in drivers/video/console/sticore.c.
5963
5964 stifb= [HW]
5965 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
5966
5967 strict_sas_size=
5968 [X86]
5969 Format: <bool>
5970 Enable or disable strict sigaltstack size checks
5971 against the required signal frame size which
5972 depends on the supported FPU features. This can
5973 be used to filter out binaries which have
5974 not yet been made aware of AT_MINSIGSTKSZ.
5975
5976 sunrpc.min_resvport=
5977 sunrpc.max_resvport=
5978 [NFS,SUNRPC]
5979 SunRPC servers often require that client requests
5980 originate from a privileged port (i.e. a port in the
5981 range 0 < portnr < 1024).
5982 An administrator who wishes to reserve some of these
5983 ports for other uses may adjust the range that the
5984 kernel's sunrpc client considers to be privileged
5985 using these two parameters to set the minimum and
5986 maximum port values.
5987
5988 sunrpc.svc_rpc_per_connection_limit=
5989 [NFS,SUNRPC]
5990 Limit the number of requests that the server will
5991 process in parallel from a single connection.
5992 The default value is 0 (no limit).
5993
5994 sunrpc.pool_mode=
5995 [NFS]
5996 Control how the NFS server code allocates CPUs to
5997 service thread pools. Depending on how many NICs
5998 you have and where their interrupts are bound, this
5999 option will affect which CPUs will do NFS serving.
6000 Note: this parameter cannot be changed while the
6001 NFS server is running.
6002
6003 auto the server chooses an appropriate mode
6004 automatically using heuristics
6005 global a single global pool contains all CPUs
6006 percpu one pool for each CPU
6007 pernode one pool for each NUMA node (equivalent
6008 to global on non-NUMA machines)
6009
6010 sunrpc.tcp_slot_table_entries=
6011 sunrpc.udp_slot_table_entries=
6012 [NFS,SUNRPC]
6013 Sets the upper limit on the number of simultaneous
6014 RPC calls that can be sent from the client to a
6015 server. Increasing these values may allow you to
6016 improve throughput, but will also increase the
6017 amount of memory reserved for use by the client.
6018
6019 suspend.pm_test_delay=
6020 [SUSPEND]
6021 Sets the number of seconds to remain in a suspend test
6022 mode before resuming the system (see
6023 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
6024 is set. Default value is 5.
6025
6026 svm= [PPC]
6027 Format: { on | off | y | n | 1 | 0 }
6028 This parameter controls use of the Protected
6029 Execution Facility on pSeries.
6030
6031 swapaccount= [KNL]
6032 Format: [0|1]
6033 Enable accounting of swap in memory resource
6034 controller if no parameter or 1 is given or disable
6035 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
6036
6037 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
6038 Format: { <int> [,<int>] | force | noforce }
6039 <int> -- Number of I/O TLB slabs
6040 <int> -- Second integer after comma. Number of swiotlb
6041 areas with their own lock. Will be rounded up
6042 to a power of 2.
6043 force -- force using of bounce buffers even if they
6044 wouldn't be automatically used by the kernel
6045 noforce -- Never use bounce buffers (for debugging)
6046
6047 switches= [HW,M68k]
6048
6049 sysctl.*= [KNL]
6050 Set a sysctl parameter, right before loading the init
6051 process, as if the value was written to the respective
6052 /proc/sys/... file. Both '.' and '/' are recognized as
6053 separators. Unrecognized parameters and invalid values
6054 are reported in the kernel log. Sysctls registered
6055 later by a loaded module cannot be set this way.
6056 Example: sysctl.vm.swappiness=40
6057
6058 sysfs.deprecated=0|1 [KNL]
6059 Enable/disable old style sysfs layout for old udev
6060 on older distributions. When this option is enabled
6061 very new udev will not work anymore. When this option
6062 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
6063 in older udev will not work anymore.
6064 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
6065 the kernel configuration.
6066
6067 sysrq_always_enabled
6068 [KNL]
6069 Ignore sysrq setting - this boot parameter will
6070 neutralize any effect of /proc/sys/kernel/sysrq.
6071 Useful for debugging.
6072
6073 tcpmhash_entries= [KNL,NET]
6074 Set the number of tcp_metrics_hash slots.
6075 Default value is 8192 or 16384 depending on total
6076 ram pages. This is used to specify the TCP metrics
6077 cache size. See Documentation/networking/ip-sysctl.rst
6078 "tcp_no_metrics_save" section for more details.
6079
6080 tdfx= [HW,DRM]
6081
6082 test_suspend= [SUSPEND]
6083 Format: { "mem" | "standby" | "freeze" }[,N]
6084 Specify "mem" (for Suspend-to-RAM) or "standby" (for
6085 standby suspend) or "freeze" (for suspend type freeze)
6086 as the system sleep state during system startup with
6087 the optional capability to repeat N number of times.
6088 The system is woken from this state using a
6089 wakeup-capable RTC alarm.
6090
6091 thash_entries= [KNL,NET]
6092 Set number of hash buckets for TCP connection
6093
6094 thermal.act= [HW,ACPI]
6095 -1: disable all active trip points in all thermal zones
6096 <degrees C>: override all lowest active trip points
6097
6098 thermal.crt= [HW,ACPI]
6099 -1: disable all critical trip points in all thermal zones
6100 <degrees C>: override all critical trip points
6101
6102 thermal.nocrt= [HW,ACPI]
6103 Set to disable actions on ACPI thermal zone
6104 critical and hot trip points.
6105
6106 thermal.off= [HW,ACPI]
6107 1: disable ACPI thermal control
6108
6109 thermal.psv= [HW,ACPI]
6110 -1: disable all passive trip points
6111 <degrees C>: override all passive trip points to this
6112 value
6113
6114 thermal.tzp= [HW,ACPI]
6115 Specify global default ACPI thermal zone polling rate
6116 <deci-seconds>: poll all this frequency
6117 0: no polling (default)
6118
6119 threadirqs [KNL]
6120 Force threading of all interrupt handlers except those
6121 marked explicitly IRQF_NO_THREAD.
6122
6123 topology= [S390]
6124 Format: {off | on}
6125 Specify if the kernel should make use of the cpu
6126 topology information if the hardware supports this.
6127 The scheduler will make use of this information and
6128 e.g. base its process migration decisions on it.
6129 Default is on.
6130
6131 topology_updates= [KNL, PPC, NUMA]
6132 Format: {off}
6133 Specify if the kernel should ignore (off)
6134 topology updates sent by the hypervisor to this
6135 LPAR.
6136
6137 torture.disable_onoff_at_boot= [KNL]
6138 Prevent the CPU-hotplug component of torturing
6139 until after init has spawned.
6140
6141 torture.ftrace_dump_at_shutdown= [KNL]
6142 Dump the ftrace buffer at torture-test shutdown,
6143 even if there were no errors. This can be a
6144 very costly operation when many torture tests
6145 are running concurrently, especially on systems
6146 with rotating-rust storage.
6147
6148 torture.verbose_sleep_frequency= [KNL]
6149 Specifies how many verbose printk()s should be
6150 emitted between each sleep. The default of zero
6151 disables verbose-printk() sleeping.
6152
6153 torture.verbose_sleep_duration= [KNL]
6154 Duration of each verbose-printk() sleep in jiffies.
6155
6156 tp720= [HW,PS2]
6157
6158 tpm_suspend_pcr=[HW,TPM]
6159 Format: integer pcr id
6160 Specify that at suspend time, the tpm driver
6161 should extend the specified pcr with zeros,
6162 as a workaround for some chips which fail to
6163 flush the last written pcr on TPM_SaveState.
6164 This will guarantee that all the other pcrs
6165 are saved.
6166
6167 tp_printk [FTRACE]
6168 Have the tracepoints sent to printk as well as the
6169 tracing ring buffer. This is useful for early boot up
6170 where the system hangs or reboots and does not give the
6171 option for reading the tracing buffer or performing a
6172 ftrace_dump_on_oops.
6173
6174 To turn off having tracepoints sent to printk,
6175 echo 0 > /proc/sys/kernel/tracepoint_printk
6176 Note, echoing 1 into this file without the
6177 tracepoint_printk kernel cmdline option has no effect.
6178
6179 The tp_printk_stop_on_boot (see below) can also be used
6180 to stop the printing of events to console at
6181 late_initcall_sync.
6182
6183 ** CAUTION **
6184
6185 Having tracepoints sent to printk() and activating high
6186 frequency tracepoints such as irq or sched, can cause
6187 the system to live lock.
6188
6189 tp_printk_stop_on_boot [FTRACE]
6190 When tp_printk (above) is set, it can cause a lot of noise
6191 on the console. It may be useful to only include the
6192 printing of events during boot up, as user space may
6193 make the system inoperable.
6194
6195 This command line option will stop the printing of events
6196 to console at the late_initcall_sync() time frame.
6197
6198 trace_buf_size=nn[KMG]
6199 [FTRACE] will set tracing buffer size on each cpu.
6200
6201 trace_clock= [FTRACE] Set the clock used for tracing events
6202 at boot up.
6203 local - Use the per CPU time stamp counter
6204 (converted into nanoseconds). Fast, but
6205 depending on the architecture, may not be
6206 in sync between CPUs.
6207 global - Event time stamps are synchronize across
6208 CPUs. May be slower than the local clock,
6209 but better for some race conditions.
6210 counter - Simple counting of events (1, 2, ..)
6211 note, some counts may be skipped due to the
6212 infrastructure grabbing the clock more than
6213 once per event.
6214 uptime - Use jiffies as the time stamp.
6215 perf - Use the same clock that perf uses.
6216 mono - Use ktime_get_mono_fast_ns() for time stamps.
6217 mono_raw - Use ktime_get_raw_fast_ns() for time
6218 stamps.
6219 boot - Use ktime_get_boot_fast_ns() for time stamps.
6220 Architectures may add more clocks. See
6221 Documentation/trace/ftrace.rst for more details.
6222
6223 trace_event=[event-list]
6224 [FTRACE] Set and start specified trace events in order
6225 to facilitate early boot debugging. The event-list is a
6226 comma-separated list of trace events to enable. See
6227 also Documentation/trace/events.rst
6228
6229 trace_options=[option-list]
6230 [FTRACE] Enable or disable tracer options at boot.
6231 The option-list is a comma delimited list of options
6232 that can be enabled or disabled just as if you were
6233 to echo the option name into
6234
6235 /sys/kernel/debug/tracing/trace_options
6236
6237 For example, to enable stacktrace option (to dump the
6238 stack trace of each event), add to the command line:
6239
6240 trace_options=stacktrace
6241
6242 See also Documentation/trace/ftrace.rst "trace options"
6243 section.
6244
6245 traceoff_on_warning
6246 [FTRACE] enable this option to disable tracing when a
6247 warning is hit. This turns off "tracing_on". Tracing can
6248 be enabled again by echoing '1' into the "tracing_on"
6249 file located in /sys/kernel/debug/tracing/
6250
6251 This option is useful, as it disables the trace before
6252 the WARNING dump is called, which prevents the trace to
6253 be filled with content caused by the warning output.
6254
6255 This option can also be set at run time via the sysctl
6256 option: kernel/traceoff_on_warning
6257
6258 transparent_hugepage=
6259 [KNL]
6260 Format: [always|madvise|never]
6261 Can be used to control the default behavior of the system
6262 with respect to transparent hugepages.
6263 See Documentation/admin-guide/mm/transhuge.rst
6264 for more details.
6265
6266 trusted.source= [KEYS]
6267 Format: <string>
6268 This parameter identifies the trust source as a backend
6269 for trusted keys implementation. Supported trust
6270 sources:
6271 - "tpm"
6272 - "tee"
6273 - "caam"
6274 If not specified then it defaults to iterating through
6275 the trust source list starting with TPM and assigns the
6276 first trust source as a backend which is initialized
6277 successfully during iteration.
6278
6279 trusted.rng= [KEYS]
6280 Format: <string>
6281 The RNG used to generate key material for trusted keys.
6282 Can be one of:
6283 - "kernel"
6284 - the same value as trusted.source: "tpm" or "tee"
6285 - "default"
6286 If not specified, "default" is used. In this case,
6287 the RNG's choice is left to each individual trust source.
6288
6289 tsc= Disable clocksource stability checks for TSC.
6290 Format: <string>
6291 [x86] reliable: mark tsc clocksource as reliable, this
6292 disables clocksource verification at runtime, as well
6293 as the stability checks done at bootup. Used to enable
6294 high-resolution timer mode on older hardware, and in
6295 virtualized environment.
6296 [x86] noirqtime: Do not use TSC to do irq accounting.
6297 Used to run time disable IRQ_TIME_ACCOUNTING on any
6298 platforms where RDTSC is slow and this accounting
6299 can add overhead.
6300 [x86] unstable: mark the TSC clocksource as unstable, this
6301 marks the TSC unconditionally unstable at bootup and
6302 avoids any further wobbles once the TSC watchdog notices.
6303 [x86] nowatchdog: disable clocksource watchdog. Used
6304 in situations with strict latency requirements (where
6305 interruptions from clocksource watchdog are not
6306 acceptable).
6307
6308 tsc_early_khz= [X86] Skip early TSC calibration and use the given
6309 value instead. Useful when the early TSC frequency discovery
6310 procedure is not reliable, such as on overclocked systems
6311 with CPUID.16h support and partial CPUID.15h support.
6312 Format: <unsigned int>
6313
6314 tsx= [X86] Control Transactional Synchronization
6315 Extensions (TSX) feature in Intel processors that
6316 support TSX control.
6317
6318 This parameter controls the TSX feature. The options are:
6319
6320 on - Enable TSX on the system. Although there are
6321 mitigations for all known security vulnerabilities,
6322 TSX has been known to be an accelerator for
6323 several previous speculation-related CVEs, and
6324 so there may be unknown security risks associated
6325 with leaving it enabled.
6326
6327 off - Disable TSX on the system. (Note that this
6328 option takes effect only on newer CPUs which are
6329 not vulnerable to MDS, i.e., have
6330 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
6331 the new IA32_TSX_CTRL MSR through a microcode
6332 update. This new MSR allows for the reliable
6333 deactivation of the TSX functionality.)
6334
6335 auto - Disable TSX if X86_BUG_TAA is present,
6336 otherwise enable TSX on the system.
6337
6338 Not specifying this option is equivalent to tsx=off.
6339
6340 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6341 for more details.
6342
6343 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
6344 Abort (TAA) vulnerability.
6345
6346 Similar to Micro-architectural Data Sampling (MDS)
6347 certain CPUs that support Transactional
6348 Synchronization Extensions (TSX) are vulnerable to an
6349 exploit against CPU internal buffers which can forward
6350 information to a disclosure gadget under certain
6351 conditions.
6352
6353 In vulnerable processors, the speculatively forwarded
6354 data can be used in a cache side channel attack, to
6355 access data to which the attacker does not have direct
6356 access.
6357
6358 This parameter controls the TAA mitigation. The
6359 options are:
6360
6361 full - Enable TAA mitigation on vulnerable CPUs
6362 if TSX is enabled.
6363
6364 full,nosmt - Enable TAA mitigation and disable SMT on
6365 vulnerable CPUs. If TSX is disabled, SMT
6366 is not disabled because CPU is not
6367 vulnerable to cross-thread TAA attacks.
6368 off - Unconditionally disable TAA mitigation
6369
6370 On MDS-affected machines, tsx_async_abort=off can be
6371 prevented by an active MDS mitigation as both vulnerabilities
6372 are mitigated with the same mechanism so in order to disable
6373 this mitigation, you need to specify mds=off too.
6374
6375 Not specifying this option is equivalent to
6376 tsx_async_abort=full. On CPUs which are MDS affected
6377 and deploy MDS mitigation, TAA mitigation is not
6378 required and doesn't provide any additional
6379 mitigation.
6380
6381 For details see:
6382 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6383
6384 turbografx.map[2|3]= [HW,JOY]
6385 TurboGraFX parallel port interface
6386 Format:
6387 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
6388 See also Documentation/input/devices/joystick-parport.rst
6389
6390 udbg-immortal [PPC] When debugging early kernel crashes that
6391 happen after console_init() and before a proper
6392 console driver takes over, this boot options might
6393 help "seeing" what's going on.
6394
6395 uhash_entries= [KNL,NET]
6396 Set number of hash buckets for UDP/UDP-Lite connections
6397
6398 uhci-hcd.ignore_oc=
6399 [USB] Ignore overcurrent events (default N).
6400 Some badly-designed motherboards generate lots of
6401 bogus events, for ports that aren't wired to
6402 anything. Set this parameter to avoid log spamming.
6403 Note that genuine overcurrent events won't be
6404 reported either.
6405
6406 unknown_nmi_panic
6407 [X86] Cause panic on unknown NMI.
6408
6409 usbcore.authorized_default=
6410 [USB] Default USB device authorization:
6411 (default -1 = authorized except for wireless USB,
6412 0 = not authorized, 1 = authorized, 2 = authorized
6413 if device connected to internal port)
6414
6415 usbcore.autosuspend=
6416 [USB] The autosuspend time delay (in seconds) used
6417 for newly-detected USB devices (default 2). This
6418 is the time required before an idle device will be
6419 autosuspended. Devices for which the delay is set
6420 to a negative value won't be autosuspended at all.
6421
6422 usbcore.usbfs_snoop=
6423 [USB] Set to log all usbfs traffic (default 0 = off).
6424
6425 usbcore.usbfs_snoop_max=
6426 [USB] Maximum number of bytes to snoop in each URB
6427 (default = 65536).
6428
6429 usbcore.blinkenlights=
6430 [USB] Set to cycle leds on hubs (default 0 = off).
6431
6432 usbcore.old_scheme_first=
6433 [USB] Start with the old device initialization
6434 scheme (default 0 = off).
6435
6436 usbcore.usbfs_memory_mb=
6437 [USB] Memory limit (in MB) for buffers allocated by
6438 usbfs (default = 16, 0 = max = 2047).
6439
6440 usbcore.use_both_schemes=
6441 [USB] Try the other device initialization scheme
6442 if the first one fails (default 1 = enabled).
6443
6444 usbcore.initial_descriptor_timeout=
6445 [USB] Specifies timeout for the initial 64-byte
6446 USB_REQ_GET_DESCRIPTOR request in milliseconds
6447 (default 5000 = 5.0 seconds).
6448
6449 usbcore.nousb [USB] Disable the USB subsystem
6450
6451 usbcore.quirks=
6452 [USB] A list of quirk entries to augment the built-in
6453 usb core quirk list. List entries are separated by
6454 commas. Each entry has the form
6455 VendorID:ProductID:Flags. The IDs are 4-digit hex
6456 numbers and Flags is a set of letters. Each letter
6457 will change the built-in quirk; setting it if it is
6458 clear and clearing it if it is set. The letters have
6459 the following meanings:
6460 a = USB_QUIRK_STRING_FETCH_255 (string
6461 descriptors must not be fetched using
6462 a 255-byte read);
6463 b = USB_QUIRK_RESET_RESUME (device can't resume
6464 correctly so reset it instead);
6465 c = USB_QUIRK_NO_SET_INTF (device can't handle
6466 Set-Interface requests);
6467 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
6468 handle its Configuration or Interface
6469 strings);
6470 e = USB_QUIRK_RESET (device can't be reset
6471 (e.g morph devices), don't use reset);
6472 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
6473 more interface descriptions than the
6474 bNumInterfaces count, and can't handle
6475 talking to these interfaces);
6476 g = USB_QUIRK_DELAY_INIT (device needs a pause
6477 during initialization, after we read
6478 the device descriptor);
6479 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
6480 high speed and super speed interrupt
6481 endpoints, the USB 2.0 and USB 3.0 spec
6482 require the interval in microframes (1
6483 microframe = 125 microseconds) to be
6484 calculated as interval = 2 ^
6485 (bInterval-1).
6486 Devices with this quirk report their
6487 bInterval as the result of this
6488 calculation instead of the exponent
6489 variable used in the calculation);
6490 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
6491 handle device_qualifier descriptor
6492 requests);
6493 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
6494 generates spurious wakeup, ignore
6495 remote wakeup capability);
6496 k = USB_QUIRK_NO_LPM (device can't handle Link
6497 Power Management);
6498 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
6499 (Device reports its bInterval as linear
6500 frames instead of the USB 2.0
6501 calculation);
6502 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
6503 to be disconnected before suspend to
6504 prevent spurious wakeup);
6505 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
6506 pause after every control message);
6507 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
6508 delay after resetting its port);
6509 Example: quirks=0781:5580:bk,0a5c:5834:gij
6510
6511 usbhid.mousepoll=
6512 [USBHID] The interval which mice are to be polled at.
6513
6514 usbhid.jspoll=
6515 [USBHID] The interval which joysticks are to be polled at.
6516
6517 usbhid.kbpoll=
6518 [USBHID] The interval which keyboards are to be polled at.
6519
6520 usb-storage.delay_use=
6521 [UMS] The delay in seconds before a new device is
6522 scanned for Logical Units (default 1).
6523
6524 usb-storage.quirks=
6525 [UMS] A list of quirks entries to supplement or
6526 override the built-in unusual_devs list. List
6527 entries are separated by commas. Each entry has
6528 the form VID:PID:Flags where VID and PID are Vendor
6529 and Product ID values (4-digit hex numbers) and
6530 Flags is a set of characters, each corresponding
6531 to a common usb-storage quirk flag as follows:
6532 a = SANE_SENSE (collect more than 18 bytes
6533 of sense data, not on uas);
6534 b = BAD_SENSE (don't collect more than 18
6535 bytes of sense data, not on uas);
6536 c = FIX_CAPACITY (decrease the reported
6537 device capacity by one sector);
6538 d = NO_READ_DISC_INFO (don't use
6539 READ_DISC_INFO command, not on uas);
6540 e = NO_READ_CAPACITY_16 (don't use
6541 READ_CAPACITY_16 command);
6542 f = NO_REPORT_OPCODES (don't use report opcodes
6543 command, uas only);
6544 g = MAX_SECTORS_240 (don't transfer more than
6545 240 sectors at a time, uas only);
6546 h = CAPACITY_HEURISTICS (decrease the
6547 reported device capacity by one
6548 sector if the number is odd);
6549 i = IGNORE_DEVICE (don't bind to this
6550 device);
6551 j = NO_REPORT_LUNS (don't use report luns
6552 command, uas only);
6553 k = NO_SAME (do not use WRITE_SAME, uas only)
6554 l = NOT_LOCKABLE (don't try to lock and
6555 unlock ejectable media, not on uas);
6556 m = MAX_SECTORS_64 (don't transfer more
6557 than 64 sectors = 32 KB at a time,
6558 not on uas);
6559 n = INITIAL_READ10 (force a retry of the
6560 initial READ(10) command, not on uas);
6561 o = CAPACITY_OK (accept the capacity
6562 reported by the device, not on uas);
6563 p = WRITE_CACHE (the device cache is ON
6564 by default, not on uas);
6565 r = IGNORE_RESIDUE (the device reports
6566 bogus residue values, not on uas);
6567 s = SINGLE_LUN (the device has only one
6568 Logical Unit);
6569 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
6570 commands, uas only);
6571 u = IGNORE_UAS (don't bind to the uas driver);
6572 w = NO_WP_DETECT (don't test whether the
6573 medium is write-protected).
6574 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
6575 even if the device claims no cache,
6576 not on uas)
6577 Example: quirks=0419:aaf5:rl,0421:0433:rc
6578
6579 user_debug= [KNL,ARM]
6580 Format: <int>
6581 See arch/arm/Kconfig.debug help text.
6582 1 - undefined instruction events
6583 2 - system calls
6584 4 - invalid data aborts
6585 8 - SIGSEGV faults
6586 16 - SIGBUS faults
6587 Example: user_debug=31
6588
6589 userpte=
6590 [X86] Flags controlling user PTE allocations.
6591
6592 nohigh = do not allocate PTE pages in
6593 HIGHMEM regardless of setting
6594 of CONFIG_HIGHPTE.
6595
6596 vdso= [X86,SH,SPARC]
6597 On X86_32, this is an alias for vdso32=. Otherwise:
6598
6599 vdso=1: enable VDSO (the default)
6600 vdso=0: disable VDSO mapping
6601
6602 vdso32= [X86] Control the 32-bit vDSO
6603 vdso32=1: enable 32-bit VDSO
6604 vdso32=0 or vdso32=2: disable 32-bit VDSO
6605
6606 See the help text for CONFIG_COMPAT_VDSO for more
6607 details. If CONFIG_COMPAT_VDSO is set, the default is
6608 vdso32=0; otherwise, the default is vdso32=1.
6609
6610 For compatibility with older kernels, vdso32=2 is an
6611 alias for vdso32=0.
6612
6613 Try vdso32=0 if you encounter an error that says:
6614 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
6615
6616 vector= [IA-64,SMP]
6617 vector=percpu: enable percpu vector domain
6618
6619 video= [FB] Frame buffer configuration
6620 See Documentation/fb/modedb.rst.
6621
6622 video.brightness_switch_enabled= [ACPI]
6623 Format: [0|1]
6624 If set to 1, on receiving an ACPI notify event
6625 generated by hotkey, video driver will adjust brightness
6626 level and then send out the event to user space through
6627 the allocated input device. If set to 0, video driver
6628 will only send out the event without touching backlight
6629 brightness level.
6630 default: 1
6631
6632 virtio_mmio.device=
6633 [VMMIO] Memory mapped virtio (platform) device.
6634
6635 <size>@<baseaddr>:<irq>[:<id>]
6636 where:
6637 <size> := size (can use standard suffixes
6638 like K, M and G)
6639 <baseaddr> := physical base address
6640 <irq> := interrupt number (as passed to
6641 request_irq())
6642 <id> := (optional) platform device id
6643 example:
6644 virtio_mmio.device=1K@0x100b0000:48:7
6645
6646 Can be used multiple times for multiple devices.
6647
6648 vga= [BOOT,X86-32] Select a particular video mode
6649 See Documentation/x86/boot.rst and
6650 Documentation/admin-guide/svga.rst.
6651 Use vga=ask for menu.
6652 This is actually a boot loader parameter; the value is
6653 passed to the kernel using a special protocol.
6654
6655 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
6656 May slow down system boot speed, especially when
6657 enabled on systems with a large amount of memory.
6658 All options are enabled by default, and this
6659 interface is meant to allow for selectively
6660 enabling or disabling specific virtual memory
6661 debugging features.
6662
6663 Available options are:
6664 P Enable page structure init time poisoning
6665 - Disable all of the above options
6666
6667 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
6668 size of <nn>. This can be used to increase the
6669 minimum size (128MB on x86). It can also be used to
6670 decrease the size and leave more room for directly
6671 mapped kernel RAM.
6672
6673 vmcp_cma=nn[MG] [KNL,S390]
6674 Sets the memory size reserved for contiguous memory
6675 allocations for the vmcp device driver.
6676
6677 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
6678 Format: <command>
6679
6680 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
6681 Format: <command>
6682
6683 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
6684 Format: <command>
6685
6686 vsyscall= [X86-64]
6687 Controls the behavior of vsyscalls (i.e. calls to
6688 fixed addresses of 0xffffffffff600x00 from legacy
6689 code). Most statically-linked binaries and older
6690 versions of glibc use these calls. Because these
6691 functions are at fixed addresses, they make nice
6692 targets for exploits that can control RIP.
6693
6694 emulate [default] Vsyscalls turn into traps and are
6695 emulated reasonably safely. The vsyscall
6696 page is readable.
6697
6698 xonly Vsyscalls turn into traps and are
6699 emulated reasonably safely. The vsyscall
6700 page is not readable.
6701
6702 none Vsyscalls don't work at all. This makes
6703 them quite hard to use for exploits but
6704 might break your system.
6705
6706 vt.color= [VT] Default text color.
6707 Format: 0xYX, X = foreground, Y = background.
6708 Default: 0x07 = light gray on black.
6709
6710 vt.cur_default= [VT] Default cursor shape.
6711 Format: 0xCCBBAA, where AA, BB, and CC are the same as
6712 the parameters of the <Esc>[?A;B;Cc escape sequence;
6713 see VGA-softcursor.txt. Default: 2 = underline.
6714
6715 vt.default_blu= [VT]
6716 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
6717 Change the default blue palette of the console.
6718 This is a 16-member array composed of values
6719 ranging from 0-255.
6720
6721 vt.default_grn= [VT]
6722 Format: <green0>,<green1>,<green2>,...,<green15>
6723 Change the default green palette of the console.
6724 This is a 16-member array composed of values
6725 ranging from 0-255.
6726
6727 vt.default_red= [VT]
6728 Format: <red0>,<red1>,<red2>,...,<red15>
6729 Change the default red palette of the console.
6730 This is a 16-member array composed of values
6731 ranging from 0-255.
6732
6733 vt.default_utf8=
6734 [VT]
6735 Format=<0|1>
6736 Set system-wide default UTF-8 mode for all tty's.
6737 Default is 1, i.e. UTF-8 mode is enabled for all
6738 newly opened terminals.
6739
6740 vt.global_cursor_default=
6741 [VT]
6742 Format=<-1|0|1>
6743 Set system-wide default for whether a cursor
6744 is shown on new VTs. Default is -1,
6745 i.e. cursors will be created by default unless
6746 overridden by individual drivers. 0 will hide
6747 cursors, 1 will display them.
6748
6749 vt.italic= [VT] Default color for italic text; 0-15.
6750 Default: 2 = green.
6751
6752 vt.underline= [VT] Default color for underlined text; 0-15.
6753 Default: 3 = cyan.
6754
6755 watchdog timers [HW,WDT] For information on watchdog timers,
6756 see Documentation/watchdog/watchdog-parameters.rst
6757 or other driver-specific files in the
6758 Documentation/watchdog/ directory.
6759
6760 watchdog_thresh=
6761 [KNL]
6762 Set the hard lockup detector stall duration
6763 threshold in seconds. The soft lockup detector
6764 threshold is set to twice the value. A value of 0
6765 disables both lockup detectors. Default is 10
6766 seconds.
6767
6768 workqueue.watchdog_thresh=
6769 If CONFIG_WQ_WATCHDOG is configured, workqueue can
6770 warn stall conditions and dump internal state to
6771 help debugging. 0 disables workqueue stall
6772 detection; otherwise, it's the stall threshold
6773 duration in seconds. The default value is 30 and
6774 it can be updated at runtime by writing to the
6775 corresponding sysfs file.
6776
6777 workqueue.disable_numa
6778 By default, all work items queued to unbound
6779 workqueues are affine to the NUMA nodes they're
6780 issued on, which results in better behavior in
6781 general. If NUMA affinity needs to be disabled for
6782 whatever reason, this option can be used. Note
6783 that this also can be controlled per-workqueue for
6784 workqueues visible under /sys/bus/workqueue/.
6785
6786 workqueue.power_efficient
6787 Per-cpu workqueues are generally preferred because
6788 they show better performance thanks to cache
6789 locality; unfortunately, per-cpu workqueues tend to
6790 be more power hungry than unbound workqueues.
6791
6792 Enabling this makes the per-cpu workqueues which
6793 were observed to contribute significantly to power
6794 consumption unbound, leading to measurably lower
6795 power usage at the cost of small performance
6796 overhead.
6797
6798 The default value of this parameter is determined by
6799 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
6800
6801 workqueue.debug_force_rr_cpu
6802 Workqueue used to implicitly guarantee that work
6803 items queued without explicit CPU specified are put
6804 on the local CPU. This guarantee is no longer true
6805 and while local CPU is still preferred work items
6806 may be put on foreign CPUs. This debug option
6807 forces round-robin CPU selection to flush out
6808 usages which depend on the now broken guarantee.
6809 When enabled, memory and cache locality will be
6810 impacted.
6811
6812 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
6813 default x2apic cluster mode on platforms
6814 supporting x2apic.
6815
6816 xen_512gb_limit [KNL,X86-64,XEN]
6817 Restricts the kernel running paravirtualized under Xen
6818 to use only up to 512 GB of RAM. The reason to do so is
6819 crash analysis tools and Xen tools for doing domain
6820 save/restore/migration must be enabled to handle larger
6821 domains.
6822
6823 xen_emul_unplug= [HW,X86,XEN]
6824 Unplug Xen emulated devices
6825 Format: [unplug0,][unplug1]
6826 ide-disks -- unplug primary master IDE devices
6827 aux-ide-disks -- unplug non-primary-master IDE devices
6828 nics -- unplug network devices
6829 all -- unplug all emulated devices (NICs and IDE disks)
6830 unnecessary -- unplugging emulated devices is
6831 unnecessary even if the host did not respond to
6832 the unplug protocol
6833 never -- do not unplug even if version check succeeds
6834
6835 xen_legacy_crash [X86,XEN]
6836 Crash from Xen panic notifier, without executing late
6837 panic() code such as dumping handler.
6838
6839 xen_nopvspin [X86,XEN]
6840 Disables the qspinlock slowpath using Xen PV optimizations.
6841 This parameter is obsoleted by "nopvspin" parameter, which
6842 has equivalent effect for XEN platform.
6843
6844 xen_nopv [X86]
6845 Disables the PV optimizations forcing the HVM guest to
6846 run as generic HVM guest with no PV drivers.
6847 This option is obsoleted by the "nopv" option, which
6848 has equivalent effect for XEN platform.
6849
6850 xen_no_vector_callback
6851 [KNL,X86,XEN] Disable the vector callback for Xen
6852 event channel interrupts.
6853
6854 xen_scrub_pages= [XEN]
6855 Boolean option to control scrubbing pages before giving them back
6856 to Xen, for use by other domains. Can be also changed at runtime
6857 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
6858 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
6859
6860 xen_timer_slop= [X86-64,XEN]
6861 Set the timer slop (in nanoseconds) for the virtual Xen
6862 timers (default is 100000). This adjusts the minimum
6863 delta of virtualized Xen timers, where lower values
6864 improve timer resolution at the expense of processing
6865 more timer interrupts.
6866
6867 xen.balloon_boot_timeout= [XEN]
6868 The time (in seconds) to wait before giving up to boot
6869 in case initial ballooning fails to free enough memory.
6870 Applies only when running as HVM or PVH guest and
6871 started with less memory configured than allowed at
6872 max. Default is 180.
6873
6874 xen.event_eoi_delay= [XEN]
6875 How long to delay EOI handling in case of event
6876 storms (jiffies). Default is 10.
6877
6878 xen.event_loop_timeout= [XEN]
6879 After which time (jiffies) the event handling loop
6880 should start to delay EOI handling. Default is 2.
6881
6882 xen.fifo_events= [XEN]
6883 Boolean parameter to disable using fifo event handling
6884 even if available. Normally fifo event handling is
6885 preferred over the 2-level event handling, as it is
6886 fairer and the number of possible event channels is
6887 much higher. Default is on (use fifo events).
6888
6889 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
6890 Disables the PV optimizations forcing the guest to run
6891 as generic guest with no PV drivers. Currently support
6892 XEN HVM, KVM, HYPER_V and VMWARE guest.
6893
6894 nopvspin [X86,XEN,KVM]
6895 Disables the qspinlock slow path using PV optimizations
6896 which allow the hypervisor to 'idle' the guest on lock
6897 contention.
6898
6899 xirc2ps_cs= [NET,PCMCIA]
6900 Format:
6901 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
6902
6903 xive= [PPC]
6904 By default on POWER9 and above, the kernel will
6905 natively use the XIVE interrupt controller. This option
6906 allows the fallback firmware mode to be used:
6907
6908 off Fallback to firmware control of XIVE interrupt
6909 controller on both pseries and powernv
6910 platforms. Only useful on POWER9 and above.
6911
6912 xive.store-eoi=off [PPC]
6913 By default on POWER10 and above, the kernel will use
6914 stores for EOI handling when the XIVE interrupt mode
6915 is active. This option allows the XIVE driver to use
6916 loads instead, as on POWER9.
6917
6918 xhci-hcd.quirks [USB,KNL]
6919 A hex value specifying bitmask with supplemental xhci
6920 host controller quirks. Meaning of each bit can be
6921 consulted in header drivers/usb/host/xhci.h.
6922
6923 xmon [PPC]
6924 Format: { early | on | rw | ro | off }
6925 Controls if xmon debugger is enabled. Default is off.
6926 Passing only "xmon" is equivalent to "xmon=early".
6927 early Call xmon as early as possible on boot; xmon
6928 debugger is called from setup_arch().
6929 on xmon debugger hooks will be installed so xmon
6930 is only called on a kernel crash. Default mode,
6931 i.e. either "ro" or "rw" mode, is controlled
6932 with CONFIG_XMON_DEFAULT_RO_MODE.
6933 rw xmon debugger hooks will be installed so xmon
6934 is called only on a kernel crash, mode is write,
6935 meaning SPR registers, memory and, other data
6936 can be written using xmon commands.
6937 ro same as "rw" option above but SPR registers,
6938 memory, and other data can't be written using
6939 xmon commands.
6940 off xmon is disabled.
