2 Format: { eager | lazy }
4 By default, unaccepted memory is accepted lazily to
5 avoid prolonged boot times. The lazy option will add
6 some runtime overhead until all memory is eventually
7 accepted. In most cases the overhead is negligible.
8 For some workloads or for debugging purposes
9 accept_memory=eager can be used to accept all memory
12 acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY]
13 Advanced Configuration and Power Interface
14 Format: { force | on | off | strict | noirq | rsdt |
16 force -- enable ACPI if default was off
17 on -- enable ACPI but allow fallback to DT [arm64,riscv64]
18 off -- disable ACPI if default was on
19 noirq -- do not use ACPI for IRQ routing
20 strict -- Be less tolerant of platforms that are not
21 strictly ACPI specification compliant.
22 rsdt -- prefer RSDT over (default) XSDT
23 copy_dsdt -- copy DSDT to memory
24 For ARM64 and RISCV64, ONLY "acpi=off", "acpi=on" or
25 "acpi=force" are available
27 See also Documentation/power/runtime_pm.rst, pci=noacpi
29 acpi_apic_instance= [ACPI,IOAPIC,EARLY]
31 2: use 2nd APIC table, if available
32 1,0: use 1st APIC table
35 acpi_backlight= [HW,ACPI]
36 { vendor | video | native | none }
37 If set to vendor, prefer vendor-specific driver
38 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
39 of the ACPI video.ko driver.
40 If set to video, use the ACPI video.ko driver.
41 If set to native, use the device's native backlight mode.
42 If set to none, disable the ACPI backlight interface.
44 acpi_force_32bit_fadt_addr [ACPI,EARLY]
45 force FADT to use 32 bit addresses rather than the
46 64 bit X_* addresses. Some firmware have broken 64
47 bit addresses for force ACPI ignore these and use
48 the older legacy 32 bit addresses.
50 acpica_no_return_repair [HW, ACPI]
51 Disable AML predefined validation mechanism
52 This mechanism can repair the evaluation result to make
53 the return objects more ACPI specification compliant.
54 This option is useful for developers to identify the
55 root cause of an AML interpreter issue when the issue
56 has something to do with the repair mechanism.
58 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
59 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
61 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
62 debug output. Bits in debug_layer correspond to a
63 _COMPONENT in an ACPI source file, e.g.,
64 #define _COMPONENT ACPI_EVENTS
65 Bits in debug_level correspond to a level in
66 ACPI_DEBUG_PRINT statements, e.g.,
67 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
68 The debug_level mask defaults to "info". See
69 Documentation/firmware-guide/acpi/debug.rst for more information about
70 debug layers and levels.
72 Enable processor driver info messages:
73 acpi.debug_layer=0x20000000
74 Enable AML "Debug" output, i.e., stores to the Debug
75 object while interpreting AML:
76 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
77 Enable all messages related to ACPI hardware:
78 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
80 Some values produce so much output that the system is
81 unusable. The "log_buf_len" parameter may be useful
82 if you need to capture more output.
84 acpi_enforce_resources= [ACPI]
86 Check for resource conflicts between native drivers
87 and ACPI OperationRegions (SystemIO and SystemMemory
88 only). IO ports and memory declared in ACPI might be
89 used by the ACPI subsystem in arbitrary AML code and
90 can interfere with legacy drivers.
91 strict (default): access to resources claimed by ACPI
92 is denied; legacy drivers trying to access reserved
93 resources will fail to bind to device using them.
94 lax: access to resources claimed by ACPI is allowed;
95 legacy drivers trying to access reserved resources
96 will bind successfully but a warning message is logged.
97 no: ACPI OperationRegions are not marked as reserved,
98 no further checks are performed.
100 acpi_force_table_verification [HW,ACPI,EARLY]
101 Enable table checksum verification during early stage.
102 By default, this is disabled due to x86 early mapping
105 acpi_irq_balance [HW,ACPI]
106 ACPI will balance active IRQs
109 acpi_irq_nobalance [HW,ACPI]
110 ACPI will not move active IRQs (default)
113 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
114 Format: <irq>,<irq>...
116 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
118 Format: <irq>,<irq>...
120 acpi_mask_gpe= [HW,ACPI]
121 Due to the existence of _Lxx/_Exx, some GPEs triggered
122 by unsupported hardware/firmware features can result in
123 GPE floodings that cannot be automatically disabled by
125 This facility can be used to prevent such uncontrolled
127 Format: <byte> or <bitmap-list>
129 acpi_no_auto_serialize [HW,ACPI]
130 Disable auto-serialization of AML methods
131 AML control methods that contain the opcodes to create
132 named objects will be marked as "Serialized" by the
133 auto-serialization feature.
134 This feature is enabled by default.
135 This option allows to turn off the feature.
137 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
140 acpi_no_static_ssdt [HW,ACPI,EARLY]
141 Disable installation of static SSDTs at early boot time
142 By default, SSDTs contained in the RSDT/XSDT will be
143 installed automatically and they will appear under
144 /sys/firmware/acpi/tables.
145 This option turns off this feature.
146 Note that specifying this option does not affect
147 dynamic table installation which will install SSDT
148 tables to /sys/firmware/acpi/tables/dynamic.
150 acpi_no_watchdog [HW,ACPI,WDT]
151 Ignore the ACPI-based watchdog interface (WDAT) and let
152 a native driver control the watchdog device instead.
154 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY]
155 Pass the RSDP address to the kernel, mostly used
156 on machines running EFI runtime service to boot the
157 second kernel for kdump.
159 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
160 Format: To spoof as Windows 98: ="Microsoft Windows"
162 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
163 of 2 which is mandated by ACPI 6) as the supported ACPI
164 specification revision (when using this switch, it may
165 be necessary to carry out a cold reboot _twice_ in a
166 row to make it take effect on the platform firmware).
168 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
169 acpi_osi="string1" # add string1
170 acpi_osi="!string2" # remove string2
171 acpi_osi=!* # remove all strings
172 acpi_osi=! # disable all built-in OS vendor
174 acpi_osi=!! # enable all built-in OS vendor
176 acpi_osi= # disable all strings
178 'acpi_osi=!' can be used in combination with single or
179 multiple 'acpi_osi="string1"' to support specific OS
180 vendor string(s). Note that such command can only
181 affect the default state of the OS vendor strings, thus
182 it cannot affect the default state of the feature group
183 strings and the current state of the OS vendor strings,
184 specifying it multiple times through kernel command line
185 is meaningless. This command is useful when one do not
186 care about the state of the feature group strings which
187 should be controlled by the OSPM.
189 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
190 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
191 can make '_OSI("Windows 2000")' TRUE.
193 'acpi_osi=' cannot be used in combination with other
194 'acpi_osi=' command lines, the _OSI method will not
195 exist in the ACPI namespace. NOTE that such command can
196 only affect the _OSI support state, thus specifying it
197 multiple times through kernel command line is also
200 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
203 'acpi_osi=!*' can be used in combination with single or
204 multiple 'acpi_osi="string1"' to support specific
205 string(s). Note that such command can affect the
206 current state of both the OS vendor strings and the
207 feature group strings, thus specifying it multiple times
208 through kernel command line is meaningful. But it may
209 still not able to affect the final state of a string if
210 there are quirks related to this string. This command
211 is useful when one want to control the state of the
212 feature group strings to debug BIOS issues related to
215 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
216 '_OSI("Module Device")' FALSE.
217 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
218 '_OSI("Module Device")' TRUE.
219 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
221 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
223 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
224 they all will make '_OSI("Windows 2000")' TRUE.
227 Override the pmtimer bug detection: force the kernel
228 to assume that this machine's pmtimer latches its value
229 and always returns good values.
231 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode
232 Format: { level | edge | high | low }
234 acpi_skip_timer_override [HW,ACPI,EARLY]
235 Recognize and ignore IRQ0/pin2 Interrupt Override.
236 For broken nForce2 BIOS resulting in XT-PIC timer.
238 acpi_sleep= [HW,ACPI] Sleep options
239 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig,
240 s4_nohwsig, old_ordering, nonvs,
241 sci_force_enable, nobl }
242 See Documentation/power/video.rst for information on
244 s3_beep is for debugging; it makes the PC's speaker beep
245 as soon as the kernel's real-mode entry point is called.
246 s4_hwsig causes the kernel to check the ACPI hardware
247 signature during resume from hibernation, and gracefully
248 refuse to resume if it has changed. This complies with
249 the ACPI specification but not with reality, since
250 Windows does not do this and many laptops do change it
251 on docking. So the default behaviour is to allow resume
252 and simply warn when the signature changes, unless the
253 s4_hwsig option is enabled.
254 s4_nohwsig prevents ACPI hardware signature from being
255 used (or even warned about) during resume.
256 old_ordering causes the ACPI 1.0 ordering of the _PTS
257 control method, with respect to putting devices into
258 low power states, to be enforced (the ACPI 2.0 ordering
259 of _PTS is used by default).
260 nonvs prevents the kernel from saving/restoring the
261 ACPI NVS memory during suspend/hibernation and resume.
262 sci_force_enable causes the kernel to set SCI_EN directly
263 on resume from S1/S3 (which is against the ACPI spec,
264 but some broken systems don't work without it).
265 nobl causes the internal blacklist of systems known to
266 behave incorrectly in some ways with respect to system
267 suspend and resume to be ignored (use wisely).
269 acpi_use_timer_override [HW,ACPI,EARLY]
270 Use timer override. For some broken Nvidia NF5 boards
271 that require a timer override, but don't have HPET
273 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in
274 kernel's map of available physical RAM.
277 { off | try_unsupported }
278 off: disable AGP support
279 try_unsupported: try to drive unsupported chipsets
280 (may crash computer or cause data corruption)
283 See Documentation/sound/alsa-configuration.rst
286 Allow the default userspace alignment fault handler
287 behaviour to be specified. Bit 0 enables warnings,
288 bit 1 enables fixups, and bit 2 sends a segfault.
290 align_va_addr= [X86-64]
291 Align virtual addresses by clearing slice [14:12] when
292 allocating a VMA at process creation time. This option
293 gives you up to 3% performance improvement on AMD F15h
294 machines (where it is enabled by default) for a
295 CPU-intensive style benchmark, and it can vary highly in
296 a microbenchmark depending on workload and compiler.
298 32: only for 32-bit processes
299 64: only for 64-bit processes
300 on: enable for both 32- and 64-bit processes
301 off: disable for both 32- and 64-bit processes
303 alloc_snapshot [FTRACE]
304 Allocate the ftrace snapshot buffer on boot up when the
305 main buffer is allocated. This is handy if debugging
306 and you need to use tracing_snapshot() on boot up, and
307 do not want to use tracing_snapshot_alloc() as it needs
308 to be done where GFP_KERNEL allocations are allowed.
310 allow_mismatched_32bit_el0 [ARM64,EARLY]
311 Allow execve() of 32-bit applications and setting of the
312 PER_LINUX32 personality on systems where only a strict
313 subset of the CPUs support 32-bit EL0. When this
314 parameter is present, the set of CPUs supporting 32-bit
315 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
316 and hot-unplug operations may be restricted.
318 See Documentation/arch/arm64/asymmetric-32bit.rst for more
321 amd_iommu= [HW,X86-64]
322 Pass parameters to the AMD IOMMU driver in the system.
324 fullflush - Deprecated, equivalent to iommu.strict=1
325 off - do not initialize any AMD IOMMU found in
327 force_isolation - Force device isolation for all
328 devices. The IOMMU driver is not
329 allowed anymore to lift isolation
330 requirements as needed. This option
331 does not override iommu=pt
332 force_enable - Force enable the IOMMU on platforms known
333 to be buggy with IOMMU enabled. Use this
335 pgtbl_v1 - Use v1 page table for DMA-API (Default).
336 pgtbl_v2 - Use v2 page table for DMA-API.
337 irtcachedis - Disable Interrupt Remapping Table (IRT) caching.
339 amd_iommu_dump= [HW,X86-64]
340 Enable AMD IOMMU driver option to dump the ACPI table
341 for AMD IOMMU. With this option enabled, AMD IOMMU
342 driver will print ACPI tables for AMD IOMMU during
343 IOMMU initialization.
345 amd_iommu_intr= [HW,X86-64]
346 Specifies one of the following AMD IOMMU interrupt
348 legacy - Use legacy interrupt remapping mode.
349 vapic - Use virtual APIC mode, which allows IOMMU
350 to inject interrupts directly into guest.
351 This mode requires kvm-amd.avic=1.
352 (Default when IOMMU HW support is present.)
354 amd_pstate= [X86,EARLY]
356 Do not enable amd_pstate as the default
357 scaling driver for the supported processors
359 Use amd_pstate with passive mode as a scaling driver.
360 In this mode autonomous selection is disabled.
361 Driver requests a desired performance level and platform
362 tries to match the same performance level if it is
363 satisfied by guaranteed performance level.
365 Use amd_pstate_epp driver instance as the scaling driver,
366 driver provides a hint to the hardware if software wants
367 to bias toward performance (0x0) or energy efficiency (0xff)
368 to the CPPC firmware. then CPPC power algorithm will
369 calculate the runtime workload and adjust the realtime cores
372 Activate guided autonomous mode. Driver requests minimum and
373 maximum performance level and the platform autonomously
374 selects a performance level in this range and appropriate
375 to the current workload.
380 Disable amd-pstate preferred core.
382 amijoy.map= [HW,JOY] Amiga joystick support
383 Map of devices attached to JOY0DAT and JOY1DAT
385 See also Documentation/input/joydev/joystick.rst
387 analog.map= [HW,JOY] Analog joystick and gamepad support
388 Specifies type or capabilities of an analog joystick
389 connected to one of 16 gameports
390 Format: <type1>,<type2>,..<type16>
393 Power management functions (SPARCstation-4/5 + deriv.)
395 Disable APC CPU standby support. SPARCstation-Fox does
396 not play well with APC CPU idle - disable it if you have
397 APC and your system crashes randomly.
399 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller
400 Change the output verbosity while booting
401 Format: { quiet (default) | verbose | debug }
402 Change the amount of debugging information output
403 when initialising the APIC and IO-APIC components.
404 For X86-32, this can also be used to specify an APIC
406 Format: apic=driver_name
407 Examples: apic=bigsmp
409 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting
410 Format: { bsp (default) | all | none }
411 bsp: External NMI is delivered only to CPU 0
412 all: External NMIs are broadcast to all CPUs as a
414 none: External NMI is masked for all CPUs. This is
415 useful so that a dump capture kernel won't be
419 See Documentation/networking/ipv6.rst.
421 apm= [APM] Advanced Power Management
422 See header of arch/x86/kernel/apm_32.c.
424 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
425 Format: { "0" | "1" }
426 See security/apparmor/Kconfig help text
429 Default value is set via kernel config option.
431 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
432 Format: <io>,<irq>,<nodeID>
434 arm64.nobti [ARM64] Unconditionally disable Branch Target
435 Identification support
437 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory
438 Set instructions support
440 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension
443 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
446 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix
449 arm64.nosve [ARM64] Unconditionally disable Scalable Vector
454 atarimouse= [HW,MOUSE] Atari Mouse
456 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
457 EzKey and similar keyboards
459 atkbd.reset= [HW] Reset keyboard during initialization
461 atkbd.set= [HW] Select keyboard code set
462 Format: <int> (2 = AT (default), 3 = PS/2)
464 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
467 atkbd.softraw= [HW] Choose between synthetic and real raw mode
468 Format: <bool> (0 = real, 1 = synthetic (default))
470 atkbd.softrepeat= [HW]
471 Use software keyboard repeat
473 audit= [KNL] Enable the audit sub-system
474 Format: { "0" | "1" | "off" | "on" }
475 0 | off - kernel audit is disabled and can not be
476 enabled until the next reboot
477 unset - kernel audit is initialized but disabled and
478 will be fully enabled by the userspace auditd.
479 1 | on - kernel audit is initialized and partially
480 enabled, storing at most audit_backlog_limit
481 messages in RAM until it is fully enabled by the
485 audit_backlog_limit= [KNL] Set the audit queue size limit.
486 Format: <int> (must be >=0)
489 bau= [X86_UV] Enable the BAU on SGI UV. The default
490 behavior is to disable the BAU (i.e. bau=0).
491 Format: { "0" | "1" }
494 unset - Disable the BAU.
496 baycom_epp= [HW,AX25]
499 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
501 See header of drivers/net/hamradio/baycom_par.c.
503 baycom_ser_fdx= [HW,AX25]
504 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
505 Format: <io>,<irq>,<mode>[,<baud>]
506 See header of drivers/net/hamradio/baycom_ser_fdx.c.
508 baycom_ser_hdx= [HW,AX25]
509 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
510 Format: <io>,<irq>,<mode>
511 See header of drivers/net/hamradio/baycom_ser_hdx.c.
514 Disable BERT OS support on buggy BIOSes.
516 bgrt_disable [ACPI,X86,EARLY]
517 Disable BGRT to avoid flickering OEM logo.
519 blkdevparts= Manual partition parsing of block device(s) for
520 embedded devices based on command line input.
521 See Documentation/block/cmdline-partition.rst
523 boot_delay= [KNL,EARLY]
524 Milliseconds to delay each printk during boot.
525 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled,
526 and you may also have to specify "lpj=". Boot_delay
527 values larger than 10 seconds (10000) are assumed
528 erroneous and ignored.
531 bootconfig [KNL,EARLY]
532 Extended command line options can be added to an initrd
533 and this will cause the kernel to look for it.
535 See Documentation/admin-guide/bootconfig.rst
537 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
538 bttv.radio= Most important insmod options are available as
540 bttv.pll= See Documentation/admin-guide/media/bttv.rst
543 bulk_remove=off [PPC] This parameter disables the use of the pSeries
544 firmware feature for flushing multiple hpte entries
547 c101= [NET] Moxa C101 synchronous serial card
549 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
550 Sometimes CPU hardware bugs make them report the cache
551 size incorrectly. The kernel will attempt work arounds
552 to fix known problems, but for some CPUs it is not
553 possible to determine what the correct size should be.
554 This option provides an override for these situations.
557 [NET] Specifies amount of time (in seconds) that
558 the kernel should wait for a network carrier. By default
559 it waits 120 seconds.
561 ca_keys= [KEYS] This parameter identifies a specific key(s) on
562 the system trusted keyring to be used for certificate
564 format: { id:<keyid> | builtin }
566 cca= [MIPS,EARLY] Override the kernel pages' cache coherency
567 algorithm. Accepted values range from 0 to 7
568 inclusive. See arch/mips/include/asm/pgtable-bits.h
569 for platform specific values (SB1, Loongson3 and
572 ccw_timeout_log [S390]
573 See Documentation/arch/s390/common_io.rst for details.
575 cgroup_disable= [KNL] Disable a particular controller or optional feature
576 Format: {name of the controller(s) or feature(s) to disable}
577 The effects of cgroup_disable=foo are:
578 - foo isn't auto-mounted if you mount all cgroups in
580 - foo isn't visible as an individually mountable
582 - if foo is an optional feature then the feature is
583 disabled and corresponding cgroup files are not
585 {Currently only "memory" controller deal with this and
586 cut the overhead, others just disable the usage. So
587 only cgroup_disable=memory is actually worthy}
588 Specifying "pressure" disables per-cgroup pressure
589 stall information accounting feature
591 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
592 Format: { { controller | "all" | "named" }
593 [,{ controller | "all" | "named" }...] }
594 Like cgroup_disable, but only applies to cgroup v1;
595 the blacklisted controllers remain available in cgroup2.
596 "all" blacklists all controllers and "named" disables
597 named mounts. Specifying both "all" and "named" disables
600 cgroup_favordynmods= [KNL] Enable or Disable favordynmods.
601 Format: { "true" | "false" }
602 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS.
604 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
606 nosocket -- Disable socket memory accounting.
607 nokmem -- Disable kernel memory accounting.
608 nobpf -- Disable BPF memory accounting.
610 checkreqprot= [SELINUX] Set initial checkreqprot flag value.
611 Format: { "0" | "1" }
612 See security/selinux/Kconfig help text.
613 0 -- check protection applied by kernel (includes
614 any implied execute protection).
615 1 -- check protection requested by application.
616 Default value is set via a kernel config option.
617 Value can be changed at runtime via
618 /sys/fs/selinux/checkreqprot.
619 Setting checkreqprot to 1 is deprecated.
622 See Documentation/arch/s390/common_io.rst for details.
624 clearcpuid=X[,X...] [X86]
625 Disable CPUID feature X for the kernel. See
626 arch/x86/include/asm/cpufeatures.h for the valid bit
627 numbers X. Note the Linux-specific bits are not necessarily
628 stable over kernel options, but the vendor-specific
630 X can also be a string as appearing in the flags: line
631 in /proc/cpuinfo which does not have the above
632 instability issue. However, not all features have names
634 Note that using this option will taint your kernel.
635 Also note that user programs calling CPUID directly
636 or using the feature without checking anything
637 will still see it. This just prevents it from
638 being used by the kernel or shown in /proc/cpuinfo.
639 Also note the kernel might malfunction if you disable
644 Prevents the clock framework from automatically gating
645 clocks that have not been explicitly enabled by a Linux
646 device driver but are enabled in hardware at reset or
647 by the bootloader/firmware. Note that this does not
648 force such clocks to be always-on nor does it reserve
649 those clocks in any way. This parameter is useful for
650 debug and development, but should not be needed on a
651 platform with proper driver support. For more
652 information, see Documentation/driver-api/clk.rst.
654 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
656 Forces specified clocksource (if available) to be used
657 when calculating gettimeofday(). If specified
658 clocksource is not available, it defaults to PIT.
659 Format: { pit | tsc | cyclone | pmtmr }
661 clocksource= Override the default clocksource
663 Override the default clocksource and use the clocksource
664 with the name specified.
665 Some clocksource names to choose from, depending on
667 [all] jiffies (this is the base, fallback clocksource)
669 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
670 pxa_timer,timer3,32k_counter,timer0_1
671 [X86-32] pit,hpet,tsc;
672 scx200_hrt on Geode; cyclone on IBM x440
680 clocksource.arm_arch_timer.evtstrm=
683 Enable/disable the eventstream feature of the ARM
684 architected timer so that code using WFE-based polling
685 loops can be debugged more effectively on production
688 clocksource.verify_n_cpus= [KNL]
689 Limit the number of CPUs checked for clocksources
690 marked with CLOCK_SOURCE_VERIFY_PERCPU that
691 are marked unstable due to excessive skew.
692 A negative value says to check all CPUs, while
693 zero says not to check any. Values larger than
694 nr_cpu_ids are silently truncated to nr_cpu_ids.
695 The actual CPUs are chosen randomly, with
696 no replacement if the same CPU is chosen twice.
698 clocksource-wdtest.holdoff= [KNL]
699 Set the time in seconds that the clocksource
700 watchdog test waits before commencing its tests.
701 Defaults to zero when built as a module and to
702 10 seconds when built into the kernel.
704 cma=nn[MG]@[start[MG][-end[MG]]]
706 Sets the size of kernel global memory area for
707 contiguous memory allocations and optionally the
708 placement constraint by the physical address range of
709 memory allocations. A value of 0 disables CMA
710 altogether. For more information, see
711 kernel/dma/contiguous.c
715 Sets the size of kernel per-numa memory area for
716 contiguous memory allocations. A value of 0 disables
717 per-numa CMA altogether. And If this option is not
718 specified, the default value is 0.
719 With per-numa CMA enabled, DMA users on node nid will
720 first try to allocate buffer from the pernuma area
721 which is located in node nid, if the allocation fails,
722 they will fallback to the global default memory area.
724 numa_cma=<node>:nn[MG][,<node>:nn[MG]]
726 Sets the size of kernel numa memory area for
727 contiguous memory allocations. It will reserve CMA
728 area for the specified node.
730 With numa CMA enabled, DMA users on node nid will
731 first try to allocate buffer from the numa area
732 which is located in node nid, if the allocation fails,
733 they will fallback to the global default memory area.
735 cmo_free_hint= [PPC] Format: { yes | no }
736 Specify whether pages are marked as being inactive
737 when they are freed. This is used in CMO environments
738 to determine OS memory pressure for page stealing by
742 coherent_pool=nn[KMG] [ARM,KNL,EARLY]
743 Sets the size of memory pool for coherent, atomic dma
744 allocations, by default set to 256K.
746 com20020= [HW,NET] ARCnet - COM20020 chipset
748 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
750 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
754 ARCnet - COM90xx chipset (memory-mapped buffers)
755 Format: <io>[,<irq>[,<memstart>]]
757 condev= [HW,S390] console device
760 con3215_drop= [S390,EARLY] 3215 console drop mode.
762 When set to true, drop data on the 3215 console when
763 the console buffer is full. In this case the
764 operator using a 3270 terminal emulator (for example
765 x3270) does not have to enter the clear key for the
766 console output to advance and the kernel to continue.
767 This leads to a much faster boot time when a 3270
768 terminal emulator is active. If no 3270 terminal
769 emulator is used, this parameter has no effect.
771 console= [KNL] Output console device and options.
773 tty<n> Use the virtual console device <n>.
777 Use the specified serial port. The options are of
778 the form "bbbbpnf", where "bbbb" is the baud rate,
779 "p" is parity ("n", "o", or "e"), "n" is number of
780 bits, and "f" is flow control ("r" for RTS or
781 omit it). Default is "9600n8".
783 See Documentation/admin-guide/serial-console.rst for more
785 Documentation/networking/netconsole.rst for an
788 uart[8250],io,<addr>[,options]
789 uart[8250],mmio,<addr>[,options]
790 uart[8250],mmio16,<addr>[,options]
791 uart[8250],mmio32,<addr>[,options]
792 uart[8250],0x<addr>[,options]
793 Start an early, polled-mode console on the 8250/16550
794 UART at the specified I/O port or MMIO address,
795 switching to the matching ttyS device later.
796 MMIO inter-register address stride is either 8-bit
797 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
798 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
799 to be equivalent to 'mmio'. 'options' are specified in
800 the same format described for ttyS above; if unspecified,
801 the h/w is not re-initialized.
803 hvc<n> Use the hypervisor console device <n>. This is for
804 both Xen and PowerPC hypervisors.
807 Use to disable console output, i.e., to have kernel
808 console messages discarded.
809 This must be the only console= parameter used on the
812 If the device connected to the port is not a TTY but a braille
813 device, prepend "brl," before the device type, for instance
815 For now, only VisioBraille is supported.
818 [KNL] Change console messages format
820 By default we print messages on consoles in
821 "[time stamp] text\n" format (time stamp may not be
822 printed, depending on CONFIG_PRINTK_TIME or
823 `printk_time' param).
825 Switch to syslog format: "<%u>[time stamp] text\n"
826 IOW, each message will have a facility and loglevel
827 prefix. The format is similar to one used by syslog()
828 syscall, or to executing "dmesg -S --raw" or to reading
831 consoleblank= [KNL] The console blank (screen saver) timeout in
832 seconds. A value of 0 disables the blank timer.
836 [KNL] Change the default value for
837 /proc/<pid>/coredump_filter.
838 See also Documentation/filesystems/proc.rst.
840 coresight_cpu_debug.enable
843 Enable/disable the CPU sampling based debugging.
844 0: default value, disable debugging
845 1: enable debugging at boot time
847 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
849 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
851 cpuidle.off=1 [CPU_IDLE]
852 disable the cpuidle sub-system
855 [CPU_IDLE] Name of the cpuidle governor to use.
857 cpufreq.off=1 [CPU_FREQ]
858 disable the cpufreq sub-system
860 cpufreq.default_governor=
861 [CPU_FREQ] Name of the default cpufreq governor or
862 policy to use. This governor must be registered in the
863 kernel before the cpufreq driver probes.
866 [X86,EARLY] Delay for N microsec between assert and de-assert
867 of APIC INIT to start processors. This delay occurs
868 on every CPU online, such as boot, and resume from suspend.
872 [SMP] Enable/disable parallel bringup of secondary CPUs
874 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise
875 the parameter has no effect.
877 crash_kexec_post_notifiers
878 Run kdump after running panic-notifiers and dumping
879 kmsg. This only for the users who doubt kdump always
880 succeeds in any situation.
881 Note that this also increases risks of kdump failure,
882 because some panic notifiers can make the crashed
883 kernel more unstable.
885 crashkernel=size[KMG][@offset[KMG]]
886 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel'
887 upon panic. This parameter reserves the physical
888 memory region [offset, offset + size] for that kernel
889 image. If '@offset' is omitted, then a suitable offset
890 is selected automatically.
891 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region
892 under 4G first, and fall back to reserve region above
893 4G when '@offset' hasn't been specified.
894 See Documentation/admin-guide/kdump/kdump.rst for further details.
896 crashkernel=range1:size1[,range2:size2,...][@offset]
897 [KNL] Same as above, but depends on the memory
898 in the running system. The syntax of range is
899 start-[end] where start and end are both
900 a memory unit (amount[KMG]). See also
901 Documentation/admin-guide/kdump/kdump.rst for an example.
903 crashkernel=size[KMG],high
904 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be
906 Allow kernel to allocate physical memory region from top,
907 so could be above 4G if system have more than 4G ram
908 installed. Otherwise memory region will be allocated
909 below 4G, if available.
910 It will be ignored if crashkernel=X is specified.
911 crashkernel=size[KMG],low
912 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G.
913 When crashkernel=X,high is passed, kernel could allocate
914 physical memory region above 4G, that cause second kernel
915 crash on system that require some amount of low memory,
916 e.g. swiotlb requires at least 64M+32K low memory, also
917 enough extra low memory is needed to make sure DMA buffers
918 for 32-bit devices won't run out. Kernel would try to allocate
919 default size of memory below 4G automatically. The default
920 size is platform dependent.
921 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB)
924 --> loongarch: 128MiB
925 This one lets the user specify own low range under 4G
926 for second kernel instead.
927 0: to disable low allocation.
928 It will be ignored when crashkernel=X,high is not used
929 or memory reserved is below 4G.
932 [KNL] Disable crypto self-tests
937 cs89x0_media= [HW,NET]
938 Format: { rj45 | aui | bnc }
940 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU
941 function call handling. When switched on,
942 additional debug data is printed to the console
943 in case a hanging CPU is detected, and that
944 CPU is pinged again in order to try to resolve
945 the hang situation. The default value of this
946 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT
950 See header of drivers/s390/block/dasd_devmap.c.
952 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
953 (one device per port)
954 Format: <port#>,<type>
955 See also Documentation/input/devices/joystick-parport.rst
957 debug [KNL,EARLY] Enable kernel debugging (events log level).
960 [KNL,EARLY] Enable printing [hashed] pointers early in the
961 boot sequence. If enabled, we use a weak hash instead
962 of siphash to hash pointers. Use this option if you are
963 seeing instances of '(___ptrval___)') and need to see a
964 value (hashed pointer) instead. Cryptographically
965 insecure, please do not use on production kernels.
968 [KNL] verbose locking self-tests
970 Print debugging info while doing the locking API
972 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
973 (no extra messages), setting it to -1 (all bits set)
974 will print _a_lot_ more information - normally only
975 useful to lockdep developers.
977 debug_objects [KNL,EARLY] Enable object debugging
979 debug_guardpage_minorder=
980 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this
981 parameter allows control of the order of pages that will
982 be intentionally kept free (and hence protected) by the
983 buddy allocator. Bigger value increase the probability
984 of catching random memory corruption, but reduce the
985 amount of memory for normal system use. The maximum
986 possible value is MAX_PAGE_ORDER/2. Setting this
987 parameter to 1 or 2 should be enough to identify most
988 random memory corruption problems caused by bugs in
989 kernel or driver code when a CPU writes to (or reads
990 from) a random memory location. Note that there exists
991 a class of memory corruptions problems caused by buggy
992 H/W or F/W or by drivers badly programming DMA
993 (basically when memory is written at bus level and the
994 CPU MMU is bypassed) which are not detectable by
995 CONFIG_DEBUG_PAGEALLOC, hence this option will not
996 help tracking down these problems.
999 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
1000 enables the feature at boot time. By default, it is
1001 disabled and the system will work mostly the same as a
1002 kernel built without CONFIG_DEBUG_PAGEALLOC.
1003 Note: to get most of debug_pagealloc error reports, it's
1004 useful to also enable the page_owner functionality.
1005 on: enable the feature
1007 debugfs= [KNL,EARLY] This parameter enables what is exposed to
1008 userspace and debugfs internal clients.
1009 Format: { on, no-mount, off }
1010 on: All functions are enabled.
1012 Filesystem is not registered but kernel clients can
1013 access APIs and a crashkernel can be used to read
1014 its content. There is nothing to mount.
1015 off: Filesystem is not registered and clients
1016 get a -EPERM as result when trying to register files
1017 or directories within debugfs.
1018 This is equivalent of the runtime functionality if
1019 debugfs was not enabled in the kernel at all.
1020 Default value is set in build-time with a kernel configuration.
1022 debugpat [X86] Enable PAT debugging
1025 [HW] The size of the default HugeTLB page. This is
1026 the size represented by the legacy /proc/ hugepages
1027 APIs. In addition, this is the default hugetlb size
1028 used for shmget(), mmap() and mounting hugetlbfs
1029 filesystems. If not specified, defaults to the
1030 architecture's default huge page size. Huge page
1031 sizes are architecture dependent. See also
1032 Documentation/admin-guide/mm/hugetlbpage.rst.
1035 deferred_probe_timeout=
1036 [KNL] Debugging option to set a timeout in seconds for
1037 deferred probe to give up waiting on dependencies to
1038 probe. Only specific dependencies (subsystems or
1039 drivers) that have opted in will be ignored. A timeout
1040 of 0 will timeout at the end of initcalls. If the time
1041 out hasn't expired, it'll be restarted by each
1042 successful driver registration. This option will also
1043 dump out devices still on the deferred probe list after
1046 delayacct [KNL] Enable per-task delay accounting
1048 dell_smm_hwmon.ignore_dmi=
1049 [HW] Continue probing hardware even if DMI data
1050 indicates that the driver is running on unsupported
1053 dell_smm_hwmon.force=
1054 [HW] Activate driver even if SMM BIOS signature does
1055 not match list of supported models and enable otherwise
1056 blacklisted features.
1058 dell_smm_hwmon.power_status=
1059 [HW] Report power status in /proc/i8k
1060 (disabled by default).
1062 dell_smm_hwmon.restricted=
1063 [HW] Allow controlling fans only if SYS_ADMIN
1066 dell_smm_hwmon.fan_mult=
1067 [HW] Factor to multiply fan speed with.
1069 dell_smm_hwmon.fan_max=
1070 [HW] Maximum configurable fan speed.
1073 Format: { on | off | def_only | inf_only | always }
1074 on: s390 zlib hardware support for compression on
1075 level 1 and decompression (default)
1076 off: No s390 zlib hardware support
1077 def_only: s390 zlib hardware support for deflate
1078 only (compression on level 1)
1079 inf_only: s390 zlib hardware support for inflate
1080 only (decompression)
1081 always: Same as 'on' but ignores the selected compression
1082 level always using hardware support (used for debugging)
1084 dhash_entries= [KNL]
1085 Set number of hash buckets for dentry cache.
1087 disable_1tb_segments [PPC,EARLY]
1088 Disables the use of 1TB hash page table segments. This
1089 causes the kernel to fall back to 256MB segments which
1090 can be useful when debugging issues that require an SLB
1094 See Documentation/networking/ipv6.rst.
1096 disable_radix [PPC,EARLY]
1097 Disable RADIX MMU mode on POWER9
1100 Disable TLBIE instruction. Currently does not work
1101 with KVM, with HASH MMU, or with coherent accelerators.
1103 disable_ddw [PPC/PSERIES,EARLY]
1104 Disable Dynamic DMA Window support. Use this
1105 to workaround buggy firmware.
1107 disable_ipv6= [IPV6]
1108 See Documentation/networking/ipv6.rst.
1110 disable_mtrr_cleanup [X86,EARLY]
1111 The kernel tries to adjust MTRR layout from continuous
1112 to discrete, to make X server driver able to add WB
1113 entry later. This parameter disables that.
1115 disable_mtrr_trim [X86, Intel and AMD only,EARLY]
1116 By default the kernel will trim any uncacheable
1117 memory out of your available memory pool based on
1118 MTRR settings. This parameter disables that behavior,
1119 possibly causing your machine to run very slowly.
1121 disable_timer_pin_1 [X86,EARLY]
1122 Disable PIN 1 of APIC timer
1123 Can be useful to work around chipset bugs.
1125 dis_ucode_ldr [X86] Disable the microcode loader.
1127 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1128 this option disables the debugging code at boot.
1130 dma_debug_entries=<number>
1131 This option allows to tune the number of preallocated
1132 entries for DMA-API debugging code. One entry is
1133 required per DMA-API allocation. Use this if the
1134 DMA-API debugging code disables itself because the
1135 architectural default is too low.
1137 dma_debug_driver=<driver_name>
1138 With this option the DMA-API debugging driver
1139 filter feature can be enabled at boot time. Just
1140 pass the driver to filter for as the parameter.
1141 The filter can be disabled or changed to another
1142 driver later using sysfs.
1144 reg_file_data_sampling=
1145 [X86] Controls mitigation for Register File Data
1146 Sampling (RFDS) vulnerability. RFDS is a CPU
1147 vulnerability which may allow userspace to infer
1148 kernel data values previously stored in floating point
1149 registers, vector registers, or integer registers.
1150 RFDS only affects Intel Atom processors.
1152 on: Turns ON the mitigation.
1153 off: Turns OFF the mitigation.
1155 This parameter overrides the compile time default set
1156 by CONFIG_MITIGATION_RFDS. Mitigation cannot be
1157 disabled when other VERW based mitigations (like MDS)
1158 are enabled. In order to disable RFDS mitigation all
1159 VERW based mitigations need to be disabled.
1162 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
1164 driver_async_probe= [KNL]
1165 List of driver names to be probed asynchronously. *
1166 matches with all driver names. If * is specified, the
1167 rest of the listed driver names are those that will NOT
1169 Format: <driver_name1>,<driver_name2>...
1171 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1172 Broken monitors, graphic adapters, KVMs and EDIDless
1173 panels may send no or incorrect EDID data sets.
1174 This parameter allows to specify an EDID data sets
1175 in the /lib/firmware directory that are used instead.
1176 An EDID data set will only be used for a particular
1177 connector, if its name and a colon are prepended to
1178 the EDID name. Each connector may use a unique EDID
1179 data set by separating the files with a comma. An EDID
1180 data set with no connector name will be used for
1181 any connectors not explicitly specified.
1185 dt_cpu_ftrs= [PPC,EARLY]
1186 Format: {"off" | "known"}
1187 Control how the dt_cpu_ftrs device-tree binding is
1188 used for CPU feature discovery and setup (if it
1190 off: Do not use it, fall back to legacy cpu table.
1191 known: Do not pass through unknown features to guests
1192 or userspace, only those that the kernel is aware of.
1194 dump_apple_properties [X86]
1195 Dump name and content of EFI device properties on
1196 x86 Macs. Useful for driver authors to determine
1197 what data is available or for reverse-engineering.
1199 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1200 <module>.dyndbg[="val"]
1201 Enable debug messages at boot time. See
1202 Documentation/admin-guide/dynamic-debug-howto.rst
1205 early_ioremap_debug [KNL,EARLY]
1206 Enable debug messages in early_ioremap support. This
1207 is useful for tracking down temporary early mappings
1208 which are not unmapped.
1210 earlycon= [KNL,EARLY] Output early console device and options.
1212 When used with no options, the early console is
1213 determined by stdout-path property in device tree's
1214 chosen node or the ACPI SPCR table if supported by
1217 cdns,<addr>[,options]
1218 Start an early, polled-mode console on a Cadence
1219 (xuartps) serial port at the specified address. Only
1220 supported option is baud rate. If baud rate is not
1221 specified, the serial port must already be setup and
1224 uart[8250],io,<addr>[,options[,uartclk]]
1225 uart[8250],mmio,<addr>[,options[,uartclk]]
1226 uart[8250],mmio32,<addr>[,options[,uartclk]]
1227 uart[8250],mmio32be,<addr>[,options[,uartclk]]
1228 uart[8250],0x<addr>[,options]
1229 Start an early, polled-mode console on the 8250/16550
1230 UART at the specified I/O port or MMIO address.
1231 MMIO inter-register address stride is either 8-bit
1232 (mmio) or 32-bit (mmio32 or mmio32be).
1233 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1234 to be equivalent to 'mmio'. 'options' are specified
1235 in the same format described for "console=ttyS<n>"; if
1236 unspecified, the h/w is not initialized. 'uartclk' is
1237 the uart clock frequency; if unspecified, it is set
1238 to 'BASE_BAUD' * 16.
1242 Start an early, polled-mode console on a pl011 serial
1243 port at the specified address. The pl011 serial port
1244 must already be setup and configured. Options are not
1245 yet supported. If 'mmio32' is specified, then only
1246 the driver will use only 32-bit accessors to read/write
1247 the device registers.
1250 Start an early console on a litex serial port at the
1251 specified address. The serial port must already be
1252 setup and configured. Options are not yet supported.
1255 Start an early, polled-mode console on a meson serial
1256 port at the specified address. The serial port must
1257 already be setup and configured. Options are not yet
1261 Start an early, polled-mode console on an msm serial
1262 port at the specified address. The serial port
1263 must already be setup and configured. Options are not
1266 msm_serial_dm,<addr>
1267 Start an early, polled-mode console on an msm serial
1268 dm port at the specified address. The serial port
1269 must already be setup and configured. Options are not
1273 Start an early, polled-mode console on a serial port
1274 of an Actions Semi SoC, such as S500 or S900, at the
1275 specified address. The serial port must already be
1276 setup and configured. Options are not yet supported.
1279 Start an early, polled-mode console on a serial port
1280 of an RDA Micro SoC, such as RDA8810PL, at the
1281 specified address. The serial port must already be
1282 setup and configured. Options are not yet supported.
1285 Use RISC-V SBI (Supervisor Binary Interface) for early
1288 smh Use ARM semihosting calls for early console.
1296 Use early console provided by serial driver available
1297 on Samsung SoCs, requires selecting proper type and
1298 a correct base address of the selected UART port. The
1299 serial port must already be setup and configured.
1300 Options are not yet supported.
1303 Start an early, polled-mode console on a lantiq serial
1304 (lqasc) port at the specified address. The serial port
1305 must already be setup and configured. Options are not
1310 Use early console provided by Freescale LP UART driver
1311 found on Freescale Vybrid and QorIQ LS1021A processors.
1312 A valid base address must be provided, and the serial
1313 port must already be setup and configured.
1317 Start an early, polled-mode, output-only console on the
1318 Freescale i.MX UART at the specified address. The UART
1319 must already be setup and configured.
1322 Start an early, polled-mode console on the
1323 Armada 3700 serial port at the specified
1324 address. The serial port must already be setup
1325 and configured. Options are not yet supported.
1328 Start an early, polled-mode console on a Qualcomm
1329 Generic Interface (GENI) based serial port at the
1330 specified address. The serial port must already be
1331 setup and configured. Options are not yet supported.
1334 Start an early, unaccelerated console on the EFI
1335 memory mapped framebuffer (if available). On cache
1336 coherent non-x86 systems that use system memory for
1337 the framebuffer, pass the 'ram' option so that it is
1338 mapped with the correct attributes.
1341 Use early console provided by Freescale LINFlexD UART
1342 serial driver for NXP S32V234 SoCs. A valid base
1343 address must be provided, and the serial port must
1344 already be setup and configured.
1346 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY]
1350 earlyprintk=serial[,ttySn[,baudrate]]
1351 earlyprintk=serial[,0x...[,baudrate]]
1352 earlyprintk=ttySn[,baudrate]
1353 earlyprintk=dbgp[debugController#]
1354 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1355 earlyprintk=xdbc[xhciController#]
1358 earlyprintk is useful when the kernel crashes before
1359 the normal console is initialized. It is not enabled by
1360 default because it has some cosmetic problems.
1362 Append ",keep" to not disable it when the real console
1365 Only one of vga, serial, or usb debug port can
1368 Currently only ttyS0 and ttyS1 may be specified by
1369 name. Other I/O ports may be explicitly specified
1370 on some architectures (x86 and arm at least) by
1371 replacing ttySn with an I/O port address, like this:
1372 earlyprintk=serial,0x1008,115200
1373 You can find the port for a given device in
1374 /proc/tty/driver/serial:
1375 2: uart:ST16650V2 port:00001008 irq:18 ...
1377 Interaction with the standard serial driver is not
1380 The VGA output is eventually overwritten by
1383 The xen option can only be used in Xen domains.
1385 The sclp output can only be used on s390.
1387 The bios output can only be used on SuperH.
1389 The optional "force" to "pciserial" enables use of a
1390 PCI device even when its classcode is not of the
1393 edac_report= [HW,EDAC] Control how to report EDAC event
1394 Format: {"on" | "off" | "force"}
1395 on: enable EDAC to report H/W event. May be overridden
1396 by other higher priority error reporting module.
1397 off: disable H/W event reporting through EDAC.
1398 force: enforce the use of EDAC to report H/W event.
1402 Format: {"off" | "on" | "skip[mbr]"}
1405 Format: { "debug", "disable_early_pci_dma",
1406 "nochunk", "noruntime", "nosoftreserve",
1407 "novamap", "no_disable_early_pci_dma" }
1408 debug: enable misc debug output.
1409 disable_early_pci_dma: disable the busmaster bit on all
1410 PCI bridges while in the EFI boot stub.
1411 nochunk: disable reading files in "chunks" in the EFI
1412 boot stub, as chunking can cause problems with some
1413 firmware implementations.
1414 noruntime : disable EFI runtime services support
1415 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1416 attribute may cause the kernel to reserve the
1417 memory range for a memory mapping driver to
1418 claim. Specify efi=nosoftreserve to disable this
1419 reservation and treat the memory by its base type
1420 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1421 novamap: do not call SetVirtualAddressMap().
1422 no_disable_early_pci_dma: Leave the busmaster bit set
1423 on all PCI bridges while in the EFI boot stub
1425 efi_no_storage_paranoia [EFI,X86,EARLY]
1426 Using this parameter you can use more than 50% of
1427 your efi variable storage. Use this parameter only if
1428 you are really sure that your UEFI does sane gc and
1429 fulfills the spec otherwise your board may brick.
1431 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI,X86,EARLY]
1432 Add arbitrary attribute to specific memory range by
1433 updating original EFI memory map.
1434 Region of memory which aa attribute is added to is
1437 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1438 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1439 attribute is added to range 0x100000000-0x180000000 and
1440 0x10a0000000-0x1120000000.
1442 If efi_fake_mem=8G@9G:0x40000 is specified, the
1443 EFI_MEMORY_SP(0x40000) attribute is added to
1444 range 0x240000000-0x43fffffff.
1446 Using this parameter you can do debugging of EFI memmap
1447 related features. For example, you can do debugging of
1448 Address Range Mirroring feature even if your box
1449 doesn't support it, or mark specific memory as
1452 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1453 that is to be dynamically loaded by Linux. If there are
1454 multiple variables with the same name but with different
1455 vendor GUIDs, all of them will be loaded. See
1456 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1459 eisa_irq_edge= [PARISC,HW]
1460 See header of drivers/parisc/eisa.c.
1462 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging
1465 This is designed to be used in conjunction with
1466 the boot argument: earlyprintk=vga
1468 This parameter works in place of the kgdboc parameter
1469 but can only be used if the backing tty is available
1470 very early in the boot process. For early debugging
1471 via a serial port see kgdboc_earlycon instead.
1474 See comment before function elanfreq_setup() in
1475 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1477 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY]
1478 Specifies physical address of start of kernel core
1479 image elf header and optionally the size. Generally
1480 kexec loader will pass this option to capture kernel.
1481 See Documentation/admin-guide/kdump/kdump.rst for details.
1483 enable_mtrr_cleanup [X86,EARLY]
1484 The kernel tries to adjust MTRR layout from continuous
1485 to discrete, to make X server driver able to add WB
1486 entry later. This parameter enables that.
1488 enable_timer_pin_1 [X86]
1489 Enable PIN 1 of APIC timer
1490 Can be useful to work around chipset bugs
1491 (in particular on some ATI chipsets).
1492 The kernel tries to set a reasonable default.
1494 enforcing= [SELINUX] Set initial enforcing status.
1496 See security/selinux/Kconfig help text.
1497 0 -- permissive (log only, no denials).
1498 1 -- enforcing (deny and log).
1500 Value can be changed at runtime via
1501 /sys/fs/selinux/enforce.
1504 Disable Error Record Serialization Table (ERST)
1507 ether= [HW,NET] Ethernet cards parameters
1508 This option is obsoleted by the "netdev=" option, which
1509 has equivalent usage. See its documentation for details.
1513 Permit 'security.evm' to be updated regardless of
1514 current integrity status.
1516 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier
1517 stages so cover more early boot allocations.
1518 Please note that as side effect some optimizations
1519 might be disabled to achieve that (e.g. parallelized
1520 memory initialization is disabled) so the boot process
1521 might take longer, especially on systems with a lot of
1522 memory. Available with CONFIG_PAGE_EXTENSION=y.
1527 fail_make_request=[KNL]
1528 General fault injection mechanism.
1529 Format: <interval>,<probability>,<space>,<times>
1530 See also Documentation/fault-injection/.
1533 Format: { initns | none }
1534 See Documentation/admin-guide/sysctl/net.rst for
1535 fb_tunnels_only_for_init_ns
1538 See Documentation/admin-guide/blockdev/floppy.rst.
1541 Forcefully enable Physical Address Extension (PAE).
1542 Many Pentium M systems disable PAE but may have a
1543 functionally usable PAE implementation.
1544 Warning: use of this parameter will taint the kernel
1545 and may cause unknown problems.
1548 Enable/disable Flexible Return and Event Delivery.
1549 Format: { on | off }
1550 on: enable FRED when it's present.
1551 off: disable FRED, the default setting.
1554 [FTRACE] will set and start the specified tracer
1555 as early as possible in order to facilitate early
1558 ftrace_boot_snapshot
1559 [FTRACE] On boot up, a snapshot will be taken of the
1560 ftrace ring buffer that can be read at:
1561 /sys/kernel/tracing/snapshot.
1562 This is useful if you need tracing information from kernel
1563 boot up that is likely to be overridden by user space
1564 start up functionality.
1566 Optionally, the snapshot can also be defined for a tracing
1567 instance that was created by the trace_instance= command
1570 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo
1572 The above will cause the "foo" tracing instance to trigger
1573 a snapshot at the end of boot up.
1575 ftrace_dump_on_oops[=orig_cpu]
1576 [FTRACE] will dump the trace buffers on oops.
1577 If no parameter is passed, ftrace will dump
1578 buffers of all CPUs, but if you pass orig_cpu, it will
1579 dump only the buffer of the CPU that triggered the
1582 ftrace_filter=[function-list]
1583 [FTRACE] Limit the functions traced by the function
1584 tracer at boot up. function-list is a comma-separated
1585 list of functions. This list can be changed at run
1586 time by the set_ftrace_filter file in the debugfs
1589 ftrace_notrace=[function-list]
1590 [FTRACE] Do not trace the functions specified in
1591 function-list. This list can be changed at run time
1592 by the set_ftrace_notrace file in the debugfs
1595 ftrace_graph_filter=[function-list]
1596 [FTRACE] Limit the top level callers functions traced
1597 by the function graph tracer at boot up.
1598 function-list is a comma-separated list of functions
1599 that can be changed at run time by the
1600 set_graph_function file in the debugfs tracing directory.
1602 ftrace_graph_notrace=[function-list]
1603 [FTRACE] Do not trace from the functions specified in
1604 function-list. This list is a comma-separated list of
1605 functions that can be changed at run time by the
1606 set_graph_notrace file in the debugfs tracing directory.
1608 ftrace_graph_max_depth=<uint>
1609 [FTRACE] Used with the function graph tracer. This is
1610 the max depth it will trace into a function. This value
1611 can be changed at run time by the max_graph_depth file
1612 in the tracefs tracing directory. default: 0 (no limit)
1614 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier
1615 devices by scanning the firmware to infer the
1616 consumer/supplier relationships. This feature is
1617 especially useful when drivers are loaded as modules as
1618 it ensures proper ordering of tasks like device probing
1619 (suppliers first, then consumers), supplier boot state
1620 clean up (only after all consumers have probed),
1621 suspend/resume & runtime PM (consumers first, then
1623 Format: { off | permissive | on | rpm }
1624 off -- Don't create device links from firmware info.
1625 permissive -- Create device links from firmware info
1626 but use it only for ordering boot state clean
1627 up (sync_state() calls).
1628 on -- Create device links from firmware info and use it
1629 to enforce probe and suspend/resume ordering.
1630 rpm -- Like "on", but also use to order runtime PM.
1632 fw_devlink.strict=<bool>
1633 [KNL,EARLY] Treat all inferred dependencies as mandatory
1634 dependencies. This only applies for fw_devlink=on|rpm.
1637 fw_devlink.sync_state =
1638 [KNL,EARLY] When all devices that could probe have finished
1639 probing, this parameter controls what to do with
1640 devices that haven't yet received their sync_state()
1642 Format: { strict | timeout }
1643 strict -- Default. Continue waiting on consumers to
1645 timeout -- Give up waiting on consumers and call
1646 sync_state() on any devices that haven't yet
1647 received their sync_state() calls after
1648 deferred_probe_timeout has expired or by
1649 late_initcall() if !CONFIG_MODULES.
1652 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1653 support via parallel port (up to 5 devices per port)
1654 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1655 See also Documentation/input/devices/joystick-parport.rst
1659 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART
1663 gather_data_sampling=
1664 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS)
1667 Gather Data Sampling is a hardware vulnerability which
1668 allows unprivileged speculative access to data which was
1669 previously stored in vector registers.
1671 This issue is mitigated by default in updated microcode.
1672 The mitigation may have a performance impact but can be
1673 disabled. On systems without the microcode mitigation
1674 disabling AVX serves as a mitigation.
1676 force: Disable AVX to mitigate systems without
1677 microcode mitigation. No effect if the microcode
1678 mitigation is present. Known to cause crashes in
1679 userspace with buggy AVX enumeration.
1681 off: Disable GDS mitigation.
1683 gcov_persist= [GCOV] When non-zero (default), profiling data for
1684 kernel modules is saved and remains accessible via
1685 debugfs, even when the module is unloaded/reloaded.
1686 When zero, profiling data is discarded and associated
1687 debugfs files are removed at module unload time.
1689 goldfish [X86] Enable the goldfish android emulator platform.
1690 Don't use this when you are not running on the
1693 gpio-mockup.gpio_mockup_ranges
1694 [HW] Sets the ranges of gpiochip of for this device.
1695 Format: <start1>,<end1>,<start2>,<end2>...
1696 gpio-mockup.gpio_mockup_named_lines
1697 [HW] Let the driver know GPIO lines should be named.
1699 gpt [EFI] Forces disk with valid GPT signature but
1700 invalid Protective MBR to be treated as GPT. If the
1701 primary GPT is corrupted, it enables the backup/alternate
1702 GPT to be used instead.
1704 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1705 the "Enable 0" bit of the configuration register.
1708 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1709 the "Enable 0" bit of the configuration register.
1712 grcan.select= [HW] Select which physical interface to use.
1715 grcan.txsize= [HW] Sets the size of the tx buffer.
1716 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1718 grcan.rxsize= [HW] Sets the size of the rx buffer.
1719 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1723 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
1724 hardening is enabled for this boot. Hardened
1725 usercopy checking is used to protect the kernel
1726 from reading or writing beyond known memory
1727 allocation boundaries as a proactive defense
1728 against bounds-checking flaws in the kernel's
1729 copy_to_user()/copy_from_user() interface.
1730 on Perform hardened usercopy checks (default).
1731 off Disable hardened usercopy checks.
1733 hardlockup_all_cpu_backtrace=
1734 [KNL] Should the hard-lockup detector generate
1735 backtraces on all cpus.
1738 hashdist= [KNL,NUMA] Large hashes allocated during boot
1739 are distributed across NUMA nodes. Defaults on
1740 for 64-bit NUMA, off otherwise.
1741 Format: 0 | 1 (for off | on)
1743 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1745 hd= [EIDE] (E)IDE hard drive subsystem geometry
1746 Format: <cyl>,<head>,<sect>
1749 Disable Hardware Error Source Table (HEST) support;
1750 corresponding firmware-first mode error processing
1751 logic will be disabled.
1753 hibernate= [HIBERNATION]
1754 noresume Don't check if there's a hibernation image
1755 present during boot.
1756 nocompress Don't compress/decompress hibernation images.
1757 no Disable hibernation and resume.
1758 protect_image Turn on image protection during restoration
1759 (that will set all pages holding image data
1760 during restoration read-only).
1762 hibernate.compressor= [HIBERNATION] Compression algorithm to be
1763 used with hibernation.
1764 Format: { lzo | lz4 }
1767 lzo: Select LZO compression algorithm to
1768 compress/decompress hibernation image.
1770 lz4: Select LZ4 compression algorithm to
1771 compress/decompress hibernation image.
1773 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact
1774 size of <nn>. This works even on boxes that have no
1775 highmem otherwise. This also works to reduce highmem
1776 size on bigger boxes.
1778 highres= [KNL] Enable/disable high resolution timer mode.
1779 Valid parameters: "on", "off"
1784 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename).
1786 This allows setting the system's hostname during early
1787 startup. This sets the name returned by gethostname.
1788 Using this parameter to set the hostname makes it
1789 possible to ensure the hostname is correctly set before
1790 any userspace processes run, avoiding the possibility
1791 that a process may call gethostname before the hostname
1792 has been explicitly set, resulting in the calling
1793 process getting an incorrect result. The string must
1794 not exceed the maximum allowed hostname length (usually
1795 64 characters) and will be truncated otherwise.
1797 hpet= [X86-32,HPET] option to control HPET usage
1798 Format: { enable (default) | disable | force |
1800 disable: disable HPET and use PIT instead
1801 force: allow force enabled of undocumented chips (ICH4,
1803 verbose: show contents of HPET registers during setup
1805 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1806 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1808 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1809 If this follows hugepagesz (below), it specifies
1810 the number of pages of hugepagesz to be allocated.
1811 If this is the first HugeTLB parameter on the command
1812 line, it specifies the number of pages to allocate for
1813 the default huge page size. If using node format, the
1814 number of pages to allocate per-node can be specified.
1815 See also Documentation/admin-guide/mm/hugetlbpage.rst.
1816 Format: <integer> or (node format)
1817 <node>:<integer>[,<node>:<integer>]
1820 [HW] The size of the HugeTLB pages. This is used in
1821 conjunction with hugepages (above) to allocate huge
1822 pages of a specific size at boot. The pair
1823 hugepagesz=X hugepages=Y can be specified once for
1824 each supported huge page size. Huge page sizes are
1825 architecture dependent. See also
1826 Documentation/admin-guide/mm/hugetlbpage.rst.
1829 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation
1830 of gigantic hugepages. Or using node format, the size
1831 of a CMA area per node can be specified.
1832 Format: nn[KMGTPE] or (node format)
1833 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
1835 Reserve a CMA area of given size and allocate gigantic
1836 hugepages using the CMA allocator. If enabled, the
1837 boot-time allocation of gigantic hugepages is skipped.
1839 hugetlb_free_vmemmap=
1840 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
1842 Control if HugeTLB Vmemmap Optimization (HVO) is enabled.
1843 Allows heavy hugetlb users to free up some more
1844 memory (7 * PAGE_SIZE for each 2MB hugetlb page).
1845 Format: { on | off (default) }
1850 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
1853 Note that the vmemmap pages may be allocated from the added
1854 memory block itself when memory_hotplug.memmap_on_memory is
1855 enabled, those vmemmap pages cannot be optimized even if this
1856 feature is enabled. Other vmemmap pages not allocated from
1857 the added memory block itself do not be affected.
1860 [KNL] Should the hung task detector generate panics.
1863 A value of 1 instructs the kernel to panic when a
1864 hung task is detected. The default value is controlled
1865 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1866 option. The value selected by this boot parameter can
1867 be changed later by the kernel.hung_task_panic sysctl.
1869 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1870 terminal devices. Valid values: 0..8
1871 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1872 If specified, z/VM IUCV HVC accepts connections
1873 from listed z/VM user IDs only.
1875 hv_nopvspin [X86,HYPER_V,EARLY]
1876 Disables the paravirt spinlock optimizations
1877 which allow the hypervisor to 'idle' the guest
1880 i2c_bus= [HW] Override the default board specific I2C bus speed
1881 or register an additional I2C bus that is not
1882 registered from board initialization code.
1886 i8042.debug [HW] Toggle i8042 debug mode
1887 i8042.unmask_kbd_data
1888 [HW] Enable printing of interrupt data from the KBD port
1889 (disabled by default, and as a pre-condition
1890 requires that i8042.debug=1 be enabled)
1891 i8042.direct [HW] Put keyboard port into non-translated mode
1892 i8042.dumbkbd [HW] Pretend that controller can only read data from
1893 keyboard and cannot control its state
1894 (Don't attempt to blink the leds)
1895 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1896 i8042.nokbd [HW] Don't check/create keyboard port
1897 i8042.noloop [HW] Disable the AUX Loopback command while probing
1899 i8042.nomux [HW] Don't check presence of an active multiplexing
1901 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1903 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1904 i8042.reset [HW] Reset the controller during init, cleanup and
1905 suspend-to-ram transitions, only during s2r
1906 transitions, or never reset
1907 Format: { 1 | Y | y | 0 | N | n }
1908 1, Y, y: always reset controller
1909 0, N, n: don't ever reset controller
1910 Default: only on s2r transitions on x86; most other
1911 architectures force reset to be always executed
1912 i8042.unlock [HW] Unlock (ignore) the keylock
1913 i8042.kbdreset [HW] Reset device connected to KBD port
1915 [HW] Allow deferred probing upon i8042 probe errors
1919 i915.invert_brightness=
1920 [DRM] Invert the sense of the variable that is used to
1921 set the brightness of the panel backlight. Normally a
1922 brightness value of 0 indicates backlight switched off,
1923 and the maximum of the brightness value sets the backlight
1924 to maximum brightness. If this parameter is set to 0
1925 (default) and the machine requires it, or this parameter
1926 is set to 1, a brightness value of 0 sets the backlight
1927 to maximum brightness, and the maximum of the brightness
1928 value switches the backlight off.
1929 -1 -- never invert brightness
1930 0 -- machine default
1931 1 -- force brightness inversion
1933 ia32_emulation= [X86-64]
1935 When true, allows loading 32-bit programs and executing 32-bit
1936 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at
1937 boot time. When false, unconditionally disables IA32 emulation.
1940 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1944 Format: idle=poll, idle=halt, idle=nomwait
1945 Poll forces a polling idle loop that can slightly
1946 improve the performance of waking up a idle CPU, but
1947 will use a lot of power and make the system run hot.
1949 idle=halt: Halt is forced to be used for CPU idle.
1950 In such case C2/C3 won't be used again.
1951 idle=nomwait: Disable mwait for CPU C-states
1955 Allow force disabling of Shared Virtual Memory (SVA)
1956 support for the idxd driver. By default it is set to
1959 idxd.tc_override= [HW]
1961 Allow override of default traffic class configuration
1962 for the device. By default it is set to false (0).
1964 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1965 Format: { strict | legacy | 2008 | relaxed }
1968 Choose which programs will be accepted for execution
1969 based on the IEEE 754 NaN encoding(s) supported by
1970 the FPU and the NaN encoding requested with the value
1971 of an ELF file header flag individually set by each
1972 binary. Hardware implementations are permitted to
1973 support either or both of the legacy and the 2008 NaN
1976 Available settings are as follows:
1977 strict accept binaries that request a NaN encoding
1978 supported by the FPU
1979 legacy only accept legacy-NaN binaries, if supported
1981 2008 only accept 2008-NaN binaries, if supported
1983 relaxed accept any binaries regardless of whether
1984 supported by the FPU
1986 The FPU emulator is always able to support both NaN
1987 encodings, so if no FPU hardware is present or it has
1988 been disabled with 'nofpu', then the settings of
1989 'legacy' and '2008' strap the emulator accordingly,
1990 'relaxed' straps the emulator for both legacy-NaN and
1991 2008-NaN, whereas 'strict' enables legacy-NaN only on
1992 legacy processors and both NaN encodings on MIPS32 or
1995 The setting for ABS.fmt/NEG.fmt instruction execution
1996 mode generally follows that for the NaN encoding,
1997 except where unsupported by hardware.
1999 ignore_loglevel [KNL,EARLY]
2000 Ignore loglevel setting - this will print /all/
2001 kernel messages to the console. Useful for debugging.
2002 We also add it as printk module parameter, so users
2003 could change it dynamically, usually by
2004 /sys/module/printk/parameters/ignore_loglevel.
2007 Ignore RLIMIT_DATA setting for data mappings,
2008 print warning at first misuse. Can be changed via
2009 /sys/module/kernel/parameters/ignore_rlimit_data.
2011 ihash_entries= [KNL]
2012 Set number of hash buckets for inode cache.
2014 ima_appraise= [IMA] appraise integrity measurements
2015 Format: { "off" | "enforce" | "fix" | "log" }
2018 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
2019 The builtin appraise policy appraises all files
2022 ima_canonical_fmt [IMA]
2023 Use the canonical format for the binary runtime
2024 measurements, instead of host native format.
2027 Format: { md5 | sha1 | rmd160 | sha256 | sha384
2031 The list of supported hash algorithms is defined
2032 in crypto/hash_info.h.
2035 The builtin policies to load during IMA setup.
2036 Format: "tcb | appraise_tcb | secure_boot |
2037 fail_securely | critical_data"
2039 The "tcb" policy measures all programs exec'd, files
2040 mmap'd for exec, and all files opened with the read
2041 mode bit set by either the effective uid (euid=0) or
2044 The "appraise_tcb" policy appraises the integrity of
2045 all files owned by root.
2047 The "secure_boot" policy appraises the integrity
2048 of files (eg. kexec kernel image, kernel modules,
2049 firmware, policy, etc) based on file signatures.
2051 The "fail_securely" policy forces file signature
2052 verification failure also on privileged mounted
2053 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
2056 The "critical_data" policy measures kernel integrity
2059 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
2060 Load a policy which meets the needs of the Trusted
2061 Computing Base. This means IMA will measure all
2062 programs exec'd, files mmap'd for exec, and all files
2063 opened for read by uid=0.
2066 Select one of defined IMA measurements template formats.
2067 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" |
2072 [IMA] Define a custom template format.
2073 Format: { "field1|...|fieldN" }
2075 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
2076 Format: <min_file_size>
2077 Set the minimal file size for using asynchronous hash.
2078 If left unspecified, ahash usage is disabled.
2080 ahash performance varies for different data sizes on
2081 different crypto accelerators. This option can be used
2082 to achieve the best performance for a particular HW.
2084 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
2086 Set hashing buffer size. Default: 4k.
2088 ahash performance varies for different chunk sizes on
2089 different crypto accelerators. This option can be used
2090 to achieve best performance for particular HW.
2094 Run specified binary instead of /sbin/init as init
2097 initcall_debug [KNL] Trace initcalls as they are executed. Useful
2098 for working out where the kernel is dying during
2101 initcall_blacklist= [KNL] Do not execute a comma-separated list of
2102 initcall functions. Useful for debugging built-in
2103 modules and initcalls.
2105 initramfs_async= [KNL]
2108 This parameter controls whether the initramfs
2109 image is unpacked asynchronously, concurrently
2110 with devices being probed and
2111 initialized. This should normally just work,
2112 but as a debugging aid, one can get the
2113 historical behaviour of the initramfs
2114 unpacking being completed before device_ and
2117 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk
2119 initrdmem= [KNL,EARLY] Specify a physical address and size from which to
2120 load the initrd. If an initrd is compiled in or
2121 specified in the bootparams, it takes priority over this
2123 Format: ss[KMG],nn[KMG]
2126 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with
2129 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
2131 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes.
2133 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
2135 init_pkru= [X86] Specify the default memory protection keys rights
2136 register contents for all processes. 0x55555554 by
2137 default (disallow access to all but pkey 0). Can
2138 override in debugfs after boot.
2140 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
2143 int_pln_enable [X86] Enable power limit notification interrupt
2145 integrity_audit=[IMA]
2146 Format: { "0" | "1" }
2147 0 -- basic integrity auditing messages. (Default)
2148 1 -- additional integrity auditing messages.
2150 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
2152 Enable intel iommu driver.
2154 Disable intel iommu driver.
2155 igfx_off [Default Off]
2156 By default, gfx is mapped as normal device. If a gfx
2157 device has a dedicated DMAR unit, the DMAR unit is
2158 bypassed by not enabling DMAR with this option. In
2159 this case, gfx device will use physical address for
2161 strict [Default Off]
2162 Deprecated, equivalent to iommu.strict=1.
2163 sp_off [Default Off]
2164 By default, super page will be supported if Intel IOMMU
2165 has the capability. With this option, super page will
2168 Enable the Intel IOMMU scalable mode if the hardware
2169 advertises that it has support for the scalable mode
2172 Disallow use of the Intel IOMMU scalable mode.
2173 tboot_noforce [Default Off]
2174 Do not force the Intel IOMMU enabled under tboot.
2175 By default, tboot will force Intel IOMMU on, which
2176 could harm performance of some high-throughput
2177 devices like 40GBit network cards, even if identity
2179 Note that using this option lowers the security
2180 provided by tboot because it makes the system
2181 vulnerable to DMA attacks.
2183 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
2184 0 disables intel_idle and fall back on acpi_idle.
2185 1 to 9 specify maximum depth of C-state.
2187 intel_pstate= [X86,EARLY]
2189 Do not enable intel_pstate as the default
2190 scaling driver for the supported processors
2192 Use intel_pstate driver to bypass the scaling
2193 governors layer of cpufreq and provides it own
2194 algorithms for p-state selection. There are two
2195 P-state selection algorithms provided by
2196 intel_pstate in the active mode: powersave and
2197 performance. The way they both operate depends
2198 on whether or not the hardware managed P-states
2199 (HWP) feature has been enabled in the processor
2200 and possibly on the processor model.
2202 Use intel_pstate as a scaling driver, but configure it
2203 to work with generic cpufreq governors (instead of
2204 enabling its internal governor). This mode cannot be
2205 used along with the hardware-managed P-states (HWP)
2208 Enable intel_pstate on systems that prohibit it by default
2209 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2210 instead of acpi-cpufreq may disable platform features, such
2211 as thermal controls and power capping, that rely on ACPI
2212 P-States information being indicated to OSPM and therefore
2213 should be used with caution. This option does not work with
2214 processors that aren't supported by the intel_pstate driver
2215 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2217 Do not enable hardware P state control (HWP)
2220 Only load intel_pstate on systems which support
2221 hardware P state control (HWP) if available.
2223 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2224 Description Table, specifies preferred power management
2225 profile as "Enterprise Server" or "Performance Server",
2226 then this feature is turned on by default.
2228 Allow per-logical-CPU P-State performance control limits using
2229 cpufreq sysfs interface
2231 intremap= [X86-64,Intel-IOMMU,EARLY]
2232 on enable Interrupt Remapping (default)
2233 off disable Interrupt Remapping
2234 nosid disable Source ID checking
2236 BIOS x2APIC opt-out request will be ignored
2237 nopost disable Interrupt Posting
2239 iomem= Disable strict checking of access to MMIO memory
2240 strict regions from userspace.
2255 nobypass [PPC/POWERNV]
2256 Disable IOMMU bypass, using IOMMU for PCI devices.
2258 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices.
2259 Format: { "0" | "1" }
2260 0 - Try to allocate a 32-bit DMA address first, before
2261 falling back to the full range if needed.
2262 1 - Allocate directly from the full usable range,
2263 forcing Dual Address Cycle for PCI cards supporting
2264 greater than 32-bit addressing.
2266 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour
2267 Format: { "0" | "1" }
2269 Request that DMA unmap operations use deferred
2270 invalidation of hardware TLBs, for increased
2271 throughput at the cost of reduced device isolation.
2272 Will fall back to strict mode if not supported by
2273 the relevant IOMMU driver.
2275 DMA unmap operations invalidate IOMMU hardware TLBs
2277 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2278 Note: on x86, strict mode specified via one of the
2279 legacy driver-specific options takes precedence.
2282 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default.
2283 Format: { "0" | "1" }
2284 0 - Use IOMMU translation for DMA.
2285 1 - Bypass the IOMMU for DMA.
2286 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2288 io7= [HW] IO7 for Marvel-based Alpha systems
2289 See comment before marvel_specify_io7 in
2290 arch/alpha/kernel/core_marvel.c.
2292 io_delay= [X86,EARLY] I/O delay method
2294 Standard port 0x80 based delay
2296 Alternate port 0xed based delay (needed on some systems)
2298 Simple two microseconds delay
2303 See Documentation/admin-guide/nfs/nfsroot.rst.
2305 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V
2306 IPC identifiers from 32,768 to 16,777,216.
2308 irqaffinity= [SMP] Set the default irq affinity mask
2309 The argument is a cpu list, as described above.
2311 irqchip.gicv2_force_probe=
2314 Force the kernel to look for the second 4kB page
2315 of a GICv2 controller even if the memory range
2316 exposed by the device tree is too small.
2318 irqchip.gicv3_nolpi=
2320 Force the kernel to ignore the availability of
2321 LPIs (and by consequence ITSs). Intended for system
2322 that use the kernel as a bootloader, and thus want
2323 to let secondary kernels in charge of setting up
2326 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY]
2327 Enables support for pseudo-NMIs in the kernel. This
2328 requires the kernel to be built with
2329 CONFIG_ARM64_PSEUDO_NMI.
2332 When an interrupt is not handled search all handlers
2333 for it. Intended to get systems with badly broken
2337 When an interrupt is not handled search all handlers
2338 for it. Also check all handlers each timer
2339 interrupt. Intended to get systems with badly broken
2343 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2345 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2346 [Deprecated - use cpusets instead]
2347 Format: [flag-list,]<cpu-list>
2349 Specify one or more CPUs to isolate from disturbances
2350 specified in the flag list (default: domain):
2353 Disable the tick when a single task runs.
2355 A residual 1Hz tick is offloaded to workqueues, which you
2356 need to affine to housekeeping through the global
2357 workqueue's affinity configured via the
2358 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2359 by using the 'domain' flag described below.
2361 NOTE: by default the global workqueue runs on all CPUs,
2362 so to protect individual CPUs the 'cpumask' file has to
2363 be configured manually after bootup.
2366 Isolate from the general SMP balancing and scheduling
2367 algorithms. Note that performing domain isolation this way
2368 is irreversible: it's not possible to bring back a CPU to
2369 the domains once isolated through isolcpus. It's strongly
2370 advised to use cpusets instead to disable scheduler load
2371 balancing through the "cpuset.sched_load_balance" file.
2372 It offers a much more flexible interface where CPUs can
2373 move in and out of an isolated set anytime.
2375 You can move a process onto or off an "isolated" CPU via
2376 the CPU affinity syscalls or cpuset.
2377 <cpu number> begins at 0 and the maximum value is
2378 "number of CPUs in system - 1".
2382 Isolate from being targeted by managed interrupts
2383 which have an interrupt mask containing isolated
2384 CPUs. The affinity of managed interrupts is
2385 handled by the kernel and cannot be changed via
2386 the /proc/irq/* interfaces.
2388 This isolation is best effort and only effective
2389 if the automatically assigned interrupt mask of a
2390 device queue contains isolated and housekeeping
2391 CPUs. If housekeeping CPUs are online then such
2392 interrupts are directed to the housekeeping CPU
2393 so that IO submitted on the housekeeping CPU
2394 cannot disturb the isolated CPU.
2396 If a queue's affinity mask contains only isolated
2397 CPUs then this parameter has no effect on the
2398 interrupt routing decision, though interrupts are
2399 only delivered when tasks running on those
2400 isolated CPUs submit IO. IO submitted on
2401 housekeeping CPUs has no influence on those
2404 The format of <cpu-list> is described above.
2408 ivrs_ioapic [HW,X86-64]
2409 Provide an override to the IOAPIC-ID<->DEVICE-ID
2410 mapping provided in the IVRS ACPI table.
2411 By default, PCI segment is 0, and can be omitted.
2413 For example, to map IOAPIC-ID decimal 10 to
2414 PCI segment 0x1 and PCI device 00:14.0,
2415 write the parameter as:
2416 ivrs_ioapic=10@0001:00:14.0
2419 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0
2420 write the parameter as:
2421 ivrs_ioapic[10]=00:14.0
2422 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and
2423 PCI device 00:14.0 write the parameter as:
2424 ivrs_ioapic[10]=0001:00:14.0
2426 ivrs_hpet [HW,X86-64]
2427 Provide an override to the HPET-ID<->DEVICE-ID
2428 mapping provided in the IVRS ACPI table.
2429 By default, PCI segment is 0, and can be omitted.
2431 For example, to map HPET-ID decimal 10 to
2432 PCI segment 0x1 and PCI device 00:14.0,
2433 write the parameter as:
2434 ivrs_hpet=10@0001:00:14.0
2437 * To map HPET-ID decimal 0 to PCI device 00:14.0
2438 write the parameter as:
2439 ivrs_hpet[0]=00:14.0
2440 * To map HPET-ID decimal 10 to PCI segment 0x1 and
2441 PCI device 00:14.0 write the parameter as:
2442 ivrs_ioapic[10]=0001:00:14.0
2444 ivrs_acpihid [HW,X86-64]
2445 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2446 mapping provided in the IVRS ACPI table.
2447 By default, PCI segment is 0, and can be omitted.
2449 For example, to map UART-HID:UID AMD0020:0 to
2450 PCI segment 0x1 and PCI device ID 00:14.5,
2451 write the parameter as:
2452 ivrs_acpihid=AMD0020:0@0001:00:14.5
2455 * To map UART-HID:UID AMD0020:0 to PCI segment is 0,
2456 PCI device ID 00:14.5, write the parameter as:
2457 ivrs_acpihid[00:14.5]=AMD0020:0
2458 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and
2459 PCI device ID 00:14.5, write the parameter as:
2460 ivrs_acpihid[0001:00:14.5]=AMD0020:0
2462 js= [HW,JOY] Analog joystick
2463 See Documentation/input/joydev/joystick.rst.
2466 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2467 report on every invalid memory access. Without this
2468 parameter KASAN will print report only for the first
2471 keep_bootcon [KNL,EARLY]
2472 Do not unregister boot console at start. This is only
2473 useful for debugging when something happens in the window
2474 between unregistering the boot console and initializing
2477 keepinitrd [HW,ARM] See retain_initrd.
2479 kernelcore= [KNL,X86,IA-64,PPC,EARLY]
2480 Format: nn[KMGTPE] | nn% | "mirror"
2481 This parameter specifies the amount of memory usable by
2482 the kernel for non-movable allocations. The requested
2483 amount is spread evenly throughout all nodes in the
2484 system as ZONE_NORMAL. The remaining memory is used for
2485 movable memory in its own zone, ZONE_MOVABLE. In the
2486 event, a node is too small to have both ZONE_NORMAL and
2487 ZONE_MOVABLE, kernelcore memory will take priority and
2488 other nodes will have a larger ZONE_MOVABLE.
2490 ZONE_MOVABLE is used for the allocation of pages that
2491 may be reclaimed or moved by the page migration
2492 subsystem. Note that allocations like PTEs-from-HighMem
2493 still use the HighMem zone if it exists, and the Normal
2494 zone if it does not.
2496 It is possible to specify the exact amount of memory in
2497 the form of "nn[KMGTPE]", a percentage of total system
2498 memory in the form of "nn%", or "mirror". If "mirror"
2499 option is specified, mirrored (reliable) memory is used
2500 for non-movable allocations and remaining memory is used
2501 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2502 are exclusive, so you cannot specify multiple forms.
2504 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port.
2505 Format: <Controller#>[,poll interval]
2506 The controller # is the number of the ehci usb debug
2507 port as it is probed via PCI. The poll interval is
2508 optional and is the number seconds in between
2509 each poll cycle to the debug port in case you need
2510 the functionality for interrupting the kernel with
2511 gdb or control-c on the dbgp connection. When
2512 not using this parameter you use sysrq-g to break into
2513 the kernel debugger.
2515 kgdboc= [KGDB,HW] kgdb over consoles.
2516 Requires a tty driver that supports console polling,
2517 or a supported polling keyboard driver (non-usb).
2518 Serial only format: <serial_device>[,baud]
2519 keyboard only format: kbd
2520 keyboard and serial format: kbd,<serial_device>[,baud]
2521 Optional Kernel mode setting:
2522 kms, kbd format: kms,kbd
2523 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2525 kgdboc_earlycon= [KGDB,HW,EARLY]
2526 If the boot console provides the ability to read
2527 characters and can work in polling mode, you can use
2528 this parameter to tell kgdb to use it as a backend
2529 until the normal console is registered. Intended to
2530 be used together with the kgdboc parameter which
2531 specifies the normal console to transition to.
2533 The name of the early console should be specified
2534 as the value of this parameter. Note that the name of
2535 the early console might be different than the tty
2536 name passed to kgdboc. It's OK to leave the value
2537 blank and the first boot console that implements
2538 read() will be picked.
2540 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the
2541 kernel debugger at the earliest opportunity.
2543 kmac= [MIPS] Korina ethernet MAC address.
2544 Configure the RouterBoard 532 series on-chip
2545 Ethernet adapter MAC address.
2547 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable
2548 Valid arguments: on, off
2550 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2553 kprobe_event=[probe-list]
2554 [FTRACE] Add kprobe events and enable at boot time.
2555 The probe-list is a semicolon delimited list of probe
2556 definitions. Each definition is same as kprobe_events
2557 interface, but the parameters are comma delimited.
2558 For example, to add a kprobe event on vfs_read with
2559 arg1 and arg2, add to the command line;
2561 kprobe_event=p,vfs_read,$arg1,$arg2
2563 See also Documentation/trace/kprobetrace.rst "Kernel
2564 Boot Parameter" section.
2566 kpti= [ARM64,EARLY] Control page table isolation of
2567 user and kernel address spaces.
2568 Default: enabled on cores which need mitigation.
2572 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires
2573 CONFIG_KUNIT to be set to be fully enabled. The
2574 default value can be overridden via
2575 KUNIT_DEFAULT_ENABLED.
2576 Default is 1 (enabled)
2578 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2579 Default is 0 (don't ignore, but inject #GP)
2581 kvm.eager_page_split=
2582 [KVM,X86] Controls whether or not KVM will try to
2583 proactively split all huge pages during dirty logging.
2584 Eager page splitting reduces interruptions to vCPU
2585 execution by eliminating the write-protection faults
2586 and MMU lock contention that would otherwise be
2587 required to split huge pages lazily.
2589 VM workloads that rarely perform writes or that write
2590 only to a small region of VM memory may benefit from
2591 disabling eager page splitting to allow huge pages to
2592 still be used for reads.
2594 The behavior of eager page splitting depends on whether
2595 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If
2596 disabled, all huge pages in a memslot will be eagerly
2597 split when dirty logging is enabled on that memslot. If
2598 enabled, eager page splitting will be performed during
2599 the KVM_CLEAR_DIRTY ioctl, and only for the pages being
2602 Eager page splitting is only supported when kvm.tdp_mmu=Y.
2606 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2607 Default is false (don't support).
2610 [KVM] Controls the software workaround for the
2611 X86_BUG_ITLB_MULTIHIT bug.
2612 force : Always deploy workaround.
2613 off : Never deploy workaround.
2614 auto : Deploy workaround based on the presence of
2615 X86_BUG_ITLB_MULTIHIT.
2619 If the software workaround is enabled for the host,
2620 guests do need not to enable it for nested guests.
2622 kvm.nx_huge_pages_recovery_ratio=
2623 [KVM] Controls how many 4KiB pages are periodically zapped
2624 back to huge pages. 0 disables the recovery, otherwise if
2625 the value is N KVM will zap 1/Nth of the 4KiB pages every
2626 period (see below). The default is 60.
2628 kvm.nx_huge_pages_recovery_period_ms=
2629 [KVM] Controls the time period at which KVM zaps 4KiB pages
2630 back to huge pages. If the value is a non-zero N, KVM will
2631 zap a portion (see ratio above) of the pages every N msecs.
2632 If the value is 0 (the default), KVM will pick a period based
2633 on the ratio, such that a page is zapped after 1 hour on average.
2635 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in
2636 KVM/SVM. Default is 1 (enabled).
2638 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables,
2639 a.k.a. Two-Dimensional Page Tables. Default is 1
2640 (enabled). Disable by KVM if hardware lacks support
2644 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of
2647 none: Forcefully disable KVM.
2649 nvhe: Standard nVHE-based mode, without support for
2652 protected: nVHE-based mode with support for guests whose
2653 state is kept private from the host.
2655 nested: VHE-based mode with support for nested
2656 virtualization. Requires at least ARMv8.3
2659 Defaults to VHE/nVHE based on hardware support. Setting
2660 mode to "protected" will disable kexec and hibernation
2661 for the host. "nested" is experimental and should be
2662 used with extreme caution.
2664 kvm-arm.vgic_v3_group0_trap=
2665 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0
2668 kvm-arm.vgic_v3_group1_trap=
2669 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1
2672 kvm-arm.vgic_v3_common_trap=
2673 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common
2676 kvm-arm.vgic_v4_enable=
2677 [KVM,ARM,EARLY] Allow use of GICv4 for direct
2680 kvm_cma_resv_ratio=n [PPC,EARLY]
2681 Reserves given percentage from system memory area for
2682 contiguous memory allocation for KVM hash pagetable
2684 By default it reserves 5% of total system memory.
2688 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables,
2689 a.k.a. Two-Dimensional Page Tables. Default is 1
2690 (enabled). Disable by KVM if hardware lacks support
2693 kvm-intel.emulate_invalid_guest_state=
2694 [KVM,Intel] Control whether to emulate invalid guest
2695 state. Ignored if kvm-intel.enable_unrestricted_guest=1,
2696 as guest state is never invalid for unrestricted
2697 guests. This param doesn't apply to nested guests (L2),
2698 as KVM never emulates invalid L2 guest state.
2699 Default is 1 (enabled).
2701 kvm-intel.flexpriority=
2702 [KVM,Intel] Control KVM's use of FlexPriority feature
2703 (TPR shadow). Default is 1 (enabled). Disable by KVM if
2704 hardware lacks support for it.
2707 [KVM,Intel] Control nested virtualization feature in
2708 KVM/VMX. Default is 1 (enabled).
2710 kvm-intel.unrestricted_guest=
2711 [KVM,Intel] Control KVM's use of unrestricted guest
2712 feature (virtualized real and unpaged mode). Default
2713 is 1 (enabled). Disable by KVM if EPT is disabled or
2714 hardware lacks support for it.
2716 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2719 Valid arguments: never, cond, always
2721 always: L1D cache flush on every VMENTER.
2722 cond: Flush L1D on VMENTER only when the code between
2723 VMEXIT and VMENTER can leak host memory.
2724 never: Disables the mitigation
2726 Default is cond (do L1 cache flush in specific instances)
2728 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor
2729 Identification feature (tagged TLBs). Default is 1
2730 (enabled). Disable by KVM if hardware lacks support
2733 l1d_flush= [X86,INTEL,EARLY]
2734 Control mitigation for L1D based snooping vulnerability.
2736 Certain CPUs are vulnerable to an exploit against CPU
2737 internal buffers which can forward information to a
2738 disclosure gadget under certain conditions.
2740 In vulnerable processors, the speculatively
2741 forwarded data can be used in a cache side channel
2742 attack, to access data to which the attacker does
2743 not have direct access.
2745 This parameter controls the mitigation. The
2748 on - enable the interface for the mitigation
2750 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on
2753 The kernel PTE inversion protection is unconditionally
2754 enabled and cannot be disabled.
2757 Provides all available mitigations for the
2758 L1TF vulnerability. Disables SMT and
2759 enables all mitigations in the
2760 hypervisors, i.e. unconditional L1D flush.
2762 SMT control and L1D flush control via the
2763 sysfs interface is still possible after
2764 boot. Hypervisors will issue a warning
2765 when the first VM is started in a
2766 potentially insecure configuration,
2767 i.e. SMT enabled or L1D flush disabled.
2770 Same as 'full', but disables SMT and L1D
2771 flush runtime control. Implies the
2772 'nosmt=force' command line option.
2773 (i.e. sysfs control of SMT is disabled.)
2776 Leaves SMT enabled and enables the default
2777 hypervisor mitigation, i.e. conditional
2780 SMT control and L1D flush control via the
2781 sysfs interface is still possible after
2782 boot. Hypervisors will issue a warning
2783 when the first VM is started in a
2784 potentially insecure configuration,
2785 i.e. SMT enabled or L1D flush disabled.
2789 Disables SMT and enables the default
2790 hypervisor mitigation.
2792 SMT control and L1D flush control via the
2793 sysfs interface is still possible after
2794 boot. Hypervisors will issue a warning
2795 when the first VM is started in a
2796 potentially insecure configuration,
2797 i.e. SMT enabled or L1D flush disabled.
2800 Same as 'flush', but hypervisors will not
2801 warn when a VM is started in a potentially
2802 insecure configuration.
2805 Disables hypervisor mitigations and doesn't
2807 It also drops the swap size and available
2808 RAM limit restriction on both hypervisor and
2813 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2819 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS
2822 lapic= [X86,APIC] Do not use TSC deadline
2823 value for LAPIC timer one-shot implementation. Default
2824 back to the programmable timer unit in the LAPIC.
2825 Format: notscdeadline
2827 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer
2830 libata.dma= [LIBATA] DMA control
2831 libata.dma=0 Disable all PATA and SATA DMA
2832 libata.dma=1 PATA and SATA Disk DMA only
2833 libata.dma=2 ATAPI (CDROM) DMA only
2834 libata.dma=4 Compact Flash DMA only
2835 Combinations also work, so libata.dma=3 enables DMA
2836 for disks and CDROMs, but not CFs.
2838 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2839 libata.ignore_hpa=0 keep BIOS limits (default)
2840 libata.ignore_hpa=1 ignore limits, using full disk
2842 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2846 libata.force= [LIBATA] Force configurations. The format is a comma-
2847 separated list of "[ID:]VAL" where ID is PORT[.DEVICE].
2848 PORT and DEVICE are decimal numbers matching port, link
2849 or device. Basically, it matches the ATA ID string
2850 printed on console by libata. If the whole ID part is
2851 omitted, the last PORT and DEVICE values are used. If
2852 ID hasn't been specified yet, the configuration applies
2853 to all ports, links and devices.
2855 If only DEVICE is omitted, the parameter applies to
2856 the port and all links and devices behind it. DEVICE
2857 number of 0 either selects the first device or the
2858 first fan-out link behind PMP device. It does not
2859 select the host link. DEVICE number of 15 selects the
2860 host link and device attached to it.
2862 The VAL specifies the configuration to force. As long
2863 as there is no ambiguity, shortcut notation is allowed.
2864 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2865 The following configurations can be forced.
2867 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2868 Any ID with matching PORT is used.
2870 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2872 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2873 udma[/][16,25,33,44,66,100,133] notation is also
2876 * nohrst, nosrst, norst: suppress hard, soft and both
2879 * rstonce: only attempt one reset during hot-unplug
2882 * [no]dbdelay: Enable or disable the extra 200ms delay
2883 before debouncing a link PHY and device presence
2886 * [no]ncq: Turn on or off NCQ.
2888 * [no]ncqtrim: Enable or disable queued DSM TRIM.
2890 * [no]ncqati: Enable or disable NCQ trim on ATI chipset.
2892 * [no]trim: Enable or disable (unqueued) TRIM.
2894 * trim_zero: Indicate that TRIM command zeroes data.
2896 * max_trim_128m: Set 128M maximum trim size limit.
2898 * [no]dma: Turn on or off DMA transfers.
2900 * atapi_dmadir: Enable ATAPI DMADIR bridge support.
2902 * atapi_mod16_dma: Enable the use of ATAPI DMA for
2903 commands that are not a multiple of 16 bytes.
2905 * [no]dmalog: Enable or disable the use of the
2906 READ LOG DMA EXT command to access logs.
2908 * [no]iddevlog: Enable or disable access to the
2909 identify device data log.
2911 * [no]logdir: Enable or disable access to the general
2912 purpose log directory.
2914 * max_sec_128: Set transfer size limit to 128 sectors.
2916 * max_sec_1024: Set or clear transfer size limit to
2919 * max_sec_lba48: Set or clear transfer size limit to
2922 * [no]lpm: Enable or disable link power management.
2924 * [no]setxfer: Indicate if transfer speed mode setting
2927 * [no]fua: Disable or enable FUA (Force Unit Access)
2928 support for devices supporting this feature.
2930 * dump_id: Dump IDENTIFY data.
2932 * disable: Disable this device.
2934 If there are multiple matching configurations changing
2935 the same attribute, the last one is used.
2937 load_ramdisk= [RAM] [Deprecated]
2939 lockd.nlm_grace_period=P [NFS] Assign grace period.
2942 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2945 lockd.nlm_timeout=T [NFS] Assign timeout value.
2948 lockd.nlm_udpport=M [NFS] Assign UDP port.
2951 lockdown= [SECURITY,EARLY]
2952 { integrity | confidentiality }
2953 Enable the kernel lockdown feature. If set to
2954 integrity, kernel features that allow userland to
2955 modify the running kernel are disabled. If set to
2956 confidentiality, kernel features that allow userland
2957 to extract confidential information from the kernel
2960 locktorture.acq_writer_lim= [KNL]
2961 Set the time limit in jiffies for a lock
2962 acquisition. Acquisitions exceeding this limit
2963 will result in a splat once they do complete.
2965 locktorture.bind_readers= [KNL]
2966 Specify the list of CPUs to which the readers are
2969 locktorture.bind_writers= [KNL]
2970 Specify the list of CPUs to which the writers are
2973 locktorture.call_rcu_chains= [KNL]
2974 Specify the number of self-propagating call_rcu()
2975 chains to set up. These are used to ensure that
2976 there is a high probability of an RCU grace period
2977 in progress at any given time. Defaults to 0,
2978 which disables these call_rcu() chains.
2980 locktorture.long_hold= [KNL]
2981 Specify the duration in milliseconds for the
2982 occasional long-duration lock hold time. Defaults
2983 to 100 milliseconds. Select 0 to disable.
2985 locktorture.nested_locks= [KNL]
2986 Specify the maximum lock nesting depth that
2987 locktorture is to exercise, up to a limit of 8
2988 (MAX_NESTED_LOCKS). Specify zero to disable.
2989 Note that this parameter is ineffective on types
2990 of locks that do not support nested acquisition.
2992 locktorture.nreaders_stress= [KNL]
2993 Set the number of locking read-acquisition kthreads.
2994 Defaults to being automatically set based on the
2995 number of online CPUs.
2997 locktorture.nwriters_stress= [KNL]
2998 Set the number of locking write-acquisition kthreads.
3000 locktorture.onoff_holdoff= [KNL]
3001 Set time (s) after boot for CPU-hotplug testing.
3003 locktorture.onoff_interval= [KNL]
3004 Set time (s) between CPU-hotplug operations, or
3005 zero to disable CPU-hotplug testing.
3007 locktorture.rt_boost= [KNL]
3008 Do periodic testing of real-time lock priority
3009 boosting. Select 0 to disable, 1 to boost
3010 only rt_mutex, and 2 to boost unconditionally.
3011 Defaults to 2, which might seem to be an
3012 odd choice, but which should be harmless for
3013 non-real-time spinlocks, due to their disabling
3014 of preemption. Note that non-realtime mutexes
3017 locktorture.rt_boost_factor= [KNL]
3018 Number that determines how often and for how
3019 long priority boosting is exercised. This is
3020 scaled down by the number of writers, so that the
3021 number of boosts per unit time remains roughly
3022 constant as the number of writers increases.
3023 On the other hand, the duration of each boost
3024 increases with the number of writers.
3026 locktorture.shuffle_interval= [KNL]
3027 Set task-shuffle interval (jiffies). Shuffling
3028 tasks allows some CPUs to go into dyntick-idle
3029 mode during the locktorture test.
3031 locktorture.shutdown_secs= [KNL]
3032 Set time (s) after boot system shutdown. This
3033 is useful for hands-off automated testing.
3035 locktorture.stat_interval= [KNL]
3036 Time (s) between statistics printk()s.
3038 locktorture.stutter= [KNL]
3039 Time (s) to stutter testing, for example,
3040 specifying five seconds causes the test to run for
3041 five seconds, wait for five seconds, and so on.
3042 This tests the locking primitive's ability to
3043 transition abruptly to and from idle.
3045 locktorture.torture_type= [KNL]
3046 Specify the locking implementation to test.
3048 locktorture.verbose= [KNL]
3049 Enable additional printk() statements.
3051 locktorture.writer_fifo= [KNL]
3052 Run the write-side locktorture kthreads at
3053 sched_set_fifo() real-time priority.
3055 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
3058 loglevel= [KNL,EARLY]
3059 All Kernel Messages with a loglevel smaller than the
3060 console loglevel will be printed to the console. It can
3061 also be changed with klogd or other programs. The
3062 loglevels are defined as follows:
3064 0 (KERN_EMERG) system is unusable
3065 1 (KERN_ALERT) action must be taken immediately
3066 2 (KERN_CRIT) critical conditions
3067 3 (KERN_ERR) error conditions
3068 4 (KERN_WARNING) warning conditions
3069 5 (KERN_NOTICE) normal but significant condition
3070 6 (KERN_INFO) informational
3071 7 (KERN_DEBUG) debug-level messages
3073 log_buf_len=n[KMG] [KNL,EARLY]
3074 Sets the size of the printk ring buffer, in bytes.
3075 n must be a power of two and greater than the
3076 minimal size. The minimal size is defined by
3077 LOG_BUF_SHIFT kernel config parameter. There
3078 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config
3079 parameter that allows to increase the default size
3080 depending on the number of CPUs. See init/Kconfig
3083 logo.nologo [FB] Disables display of the built-in Linux logo.
3084 This may be used to provide more screen space for
3085 kernel log messages and is useful when debugging
3086 kernel boot problems.
3088 lp=0 [LP] Specify parallel ports to use, e.g,
3089 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
3090 lp=reset first parallel port). 'lp=0' disables the
3091 lp=auto printer driver. 'lp=reset' (which can be
3092 specified in addition to the ports) causes
3093 attached printers to be reset. Using
3094 lp=port1,port2,... specifies the parallel ports
3095 to associate lp devices with, starting with
3096 lp0. A port specification may be 'none' to skip
3097 that lp device, or a parport name such as
3098 'parport0'. Specifying 'lp=auto' instead of a
3099 port specification list means that device IDs
3100 from each port should be examined, to see if
3101 an IEEE 1284-compliant printer is attached; if
3102 so, the driver will manage that printer.
3103 See also header of drivers/char/lp.c.
3106 Sets loops_per_jiffy to given constant, thus avoiding
3107 time-consuming boot-time autodetection (up to 250 ms per
3108 CPU). 0 enables autodetection (default). To determine
3109 the correct value for your kernel, boot with normal
3110 autodetection and see what value is printed. Note that
3111 on SMP systems the preset will be applied to all CPUs,
3112 which is likely to cause problems if your CPUs need
3113 significantly divergent settings. An incorrect value
3114 will cause delays in the kernel to be wrong, leading to
3115 unpredictable I/O errors and other breakage. Although
3116 unlikely, in the extreme case this might damage your
3120 Format: <io>,<irq>,<dma>
3122 lsm.debug [SECURITY] Enable LSM initialization debugging output.
3125 [SECURITY] Choose order of LSM initialization. This
3126 overrides CONFIG_LSM, and the "security=" parameter.
3128 machvec= [IA-64] Force the use of a particular machine-vector
3129 (machvec) in a generic kernel.
3130 Example: machvec=hpzx1
3132 machtype= [Loongson] Share the same kernel image file between
3133 different yeeloong laptops.
3134 Example: machtype=lemote-yeeloong-2f-7inch
3136 max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater
3137 than or equal to this physical address is ignored.
3139 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
3140 will bring up during bootup. maxcpus=n : n >= 0 limits
3141 the kernel to bring up 'n' processors. Surely after
3142 bootup you can bring up the other plugged cpu by executing
3143 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
3144 only takes effect during system bootup.
3145 While n=0 is a special case, it is equivalent to "nosmp",
3146 which also disables the IO APIC.
3148 max_loop= [LOOP] The number of loop block devices that get
3149 (loop.max_loop) unconditionally pre-created at init time. The default
3150 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
3151 of statically allocating a predefined number, loop
3152 devices can be requested on-demand with the
3153 /dev/loop-control interface.
3155 mce [X86-32] Machine Check Exception
3157 mce=option [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst
3159 md= [HW] RAID subsystems devices and level
3160 See Documentation/admin-guide/md.rst.
3163 Format: <first>,<last>
3164 Specifies range of consoles to be captured by the MDA.
3166 mds= [X86,INTEL,EARLY]
3167 Control mitigation for the Micro-architectural Data
3168 Sampling (MDS) vulnerability.
3170 Certain CPUs are vulnerable to an exploit against CPU
3171 internal buffers which can forward information to a
3172 disclosure gadget under certain conditions.
3174 In vulnerable processors, the speculatively
3175 forwarded data can be used in a cache side channel
3176 attack, to access data to which the attacker does
3177 not have direct access.
3179 This parameter controls the MDS mitigation. The
3182 full - Enable MDS mitigation on vulnerable CPUs
3183 full,nosmt - Enable MDS mitigation and disable
3184 SMT on vulnerable CPUs
3185 off - Unconditionally disable MDS mitigation
3187 On TAA-affected machines, mds=off can be prevented by
3188 an active TAA mitigation as both vulnerabilities are
3189 mitigated with the same mechanism so in order to disable
3190 this mitigation, you need to specify tsx_async_abort=off
3193 Not specifying this option is equivalent to
3196 For details see: Documentation/admin-guide/hw-vuln/mds.rst
3198 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size.
3199 Must be specified, otherwise memory size will be 0.
3201 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount
3202 of memory Amount of memory to be used in cases
3206 2 when the kernel is not able to see the whole system memory;
3207 3 memory that lies after 'mem=' boundary is excluded from
3208 the hypervisor, then assigned to KVM guests.
3209 4 to limit the memory available for kdump kernel.
3211 [ARC,MICROBLAZE] - the limit applies only to low memory,
3212 high memory is not affected.
3214 [ARM64] - only limits memory covered by the linear
3215 mapping. The NOMAP regions are not affected.
3217 [X86] Work as limiting max address. Use together
3218 with memmap= to avoid physical address space collisions.
3219 Without memmap= PCI devices could be placed at addresses
3220 belonging to unused RAM.
3222 Note that this only takes effects during boot time since
3223 in above case 3, memory may need be hot added after boot
3224 if system memory of hypervisor is not sufficient.
3227 [ARM,MIPS,EARLY] - override the memory layout
3228 reported by firmware.
3229 Define a memory region of size nn[KMG] starting at
3231 Multiple different regions can be specified with
3232 multiple mem= parameters on the command line.
3234 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
3237 memblock=debug [KNL,EARLY] Enable memblock debug messages.
3240 [KNL,SH] Allow user to override the default size for
3241 per-device physically contiguous DMA buffers.
3243 memhp_default_state=online/offline/online_kernel/online_movable
3244 [KNL] Set the initial state for the memory hotplug
3245 onlining policy. If not specified, the default value is
3246 set according to the
3247 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
3249 See Documentation/admin-guide/mm/memory-hotplug.rst.
3251 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact
3252 E820 memory map, as specified by the user.
3253 Such memmap=exactmap lines can be constructed based on
3254 BIOS output or other requirements. See the memmap=nn@ss
3257 memmap=nn[KMG]@ss[KMG]
3258 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory.
3259 Region of memory to be used is from ss to ss+nn.
3260 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
3261 which limits max address to nn[KMG].
3262 Multiple different regions can be specified,
3265 memmap=100M@2G,100M#3G,1G!1024G
3267 memmap=nn[KMG]#ss[KMG]
3268 [KNL,ACPI,EARLY] Mark specific memory as ACPI data.
3269 Region of memory to be marked is from ss to ss+nn.
3271 memmap=nn[KMG]$ss[KMG]
3272 [KNL,ACPI,EARLY] Mark specific memory as reserved.
3273 Region of memory to be reserved is from ss to ss+nn.
3274 Example: Exclude memory from 0x18690000-0x1869ffff
3275 memmap=64K$0x18690000
3277 memmap=0x10000$0x18690000
3278 Some bootloaders may need an escape character before '$',
3279 like Grub2, otherwise '$' and the following number
3282 memmap=nn[KMG]!ss[KMG,EARLY]
3283 [KNL,X86] Mark specific memory as protected.
3284 Region of memory to be used, from ss to ss+nn.
3285 The memory region may be marked as e820 type 12 (0xc)
3286 and is NVDIMM or ADR memory.
3288 memmap=<size>%<offset>-<oldtype>+<newtype>
3289 [KNL,ACPI,EARLY] Convert memory within the specified region
3290 from <oldtype> to <newtype>. If "-<oldtype>" is left
3291 out, the whole region will be marked as <newtype>,
3292 even if previously unavailable. If "+<newtype>" is left
3293 out, matching memory will be removed. Types are
3294 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
3295 3 = ACPI, 12 = PRAM.
3297 memory_corruption_check=0/1 [X86,EARLY]
3298 Some BIOSes seem to corrupt the first 64k of
3299 memory when doing things like suspend/resume.
3300 Setting this option will scan the memory
3301 looking for corruption. Enabling this will
3302 both detect corruption and prevent the kernel
3303 from using the memory being corrupted.
3304 However, its intended as a diagnostic tool; if
3305 repeatable BIOS-originated corruption always
3306 affects the same memory, you can use memmap=
3307 to prevent the kernel from using that memory.
3309 memory_corruption_check_size=size [X86,EARLY]
3310 By default it checks for corruption in the low
3311 64k, making this memory unavailable for normal
3312 use. Use this parameter to scan for
3313 corruption in more or less memory.
3315 memory_corruption_check_period=seconds [X86,EARLY]
3316 By default it checks for corruption every 60
3317 seconds. Use this parameter to check at some
3318 other rate. 0 disables periodic checking.
3320 memory_hotplug.memmap_on_memory
3321 [KNL,X86,ARM] Boolean flag to enable this feature.
3322 Format: {on | off (default)}
3323 When enabled, runtime hotplugged memory will
3324 allocate its internal metadata (struct pages,
3325 those vmemmap pages cannot be optimized even
3326 if hugetlb_free_vmemmap is enabled) from the
3327 hotadded memory which will allow to hotadd a
3328 lot of memory without requiring additional
3330 This feature is disabled by default because it
3331 has some implication on large (e.g. GB)
3332 allocations in some configurations (e.g. small
3334 The state of the flag can be read in
3335 /sys/module/memory_hotplug/parameters/memmap_on_memory.
3336 Note that even when enabled, there are a few cases where
3337 the feature is not effective.
3339 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest
3341 default : 0 <disable>
3342 Specifies the number of memtest passes to be
3343 performed. Each pass selects another test
3344 pattern from a given set of patterns. Memtest
3345 fills the memory with this pattern, validates
3346 memory contents and reserves bad memory
3347 regions that are detected.
3349 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
3350 Valid arguments: on, off
3352 mem_encrypt=on: Activate SME
3353 mem_encrypt=off: Do not activate SME
3355 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst
3356 for details on when memory encryption can be activated.
3358 mem_sleep_default= [SUSPEND] Default system suspend mode:
3359 s2idle - Suspend-To-Idle
3360 shallow - Power-On Suspend or equivalent (if supported)
3361 deep - Suspend-To-RAM or equivalent (if supported)
3362 See Documentation/admin-guide/pm/sleep-states.rst.
3364 mfgpt_irq= [IA-32] Specify the IRQ to use for the
3365 Multi-Function General Purpose Timers on AMD Geode
3368 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
3369 the BIOS has incorrectly applied a workaround. TinyBIOS
3370 version 0.98 is known to be affected, 0.99 fixes the
3371 problem by letting the user disable the workaround.
3375 microcode.force_minrev= [X86]
3377 Enable or disable the microcode minimal revision
3378 enforcement for the runtime microcode loader.
3380 min_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory below this
3381 physical address is ignored.
3383 mini2440= [ARM,HW,KNL]
3384 Format:[0..2][b][c][t]
3386 MINI2440 configuration specification:
3387 0 - The attached screen is the 3.5" TFT
3388 1 - The attached screen is the 7" TFT
3389 2 - The VGA Shield is attached (1024x768)
3390 Leaving out the screen size parameter will not load
3391 the TFT driver, and the framebuffer will be left
3393 b - Enable backlight. The TFT backlight pin will be
3394 linked to the kernel VESA blanking code and a GPIO
3395 LED. This parameter is not necessary when using the
3397 c - Enable the s3c camera interface.
3398 t - Reserved for enabling touchscreen support. The
3399 touchscreen support is not enabled in the mainstream
3400 kernel as of 2.6.30, a preliminary port can be found
3401 in the "bleeding edge" mini2440 support kernel at
3402 https://repo.or.cz/w/linux-2.6/mini2440.git
3405 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for
3406 CPU vulnerabilities. This is a set of curated,
3407 arch-independent options, each of which is an
3408 aggregation of existing arch-specific options.
3411 Disable all optional CPU mitigations. This
3412 improves system performance, but it may also
3413 expose users to several CPU vulnerabilities.
3414 Equivalent to: if nokaslr then kpti=0 [ARM64]
3415 gather_data_sampling=off [X86]
3416 kvm.nx_huge_pages=off [X86]
3419 mmio_stale_data=off [X86]
3420 no_entry_flush [PPC]
3421 no_uaccess_flush [PPC]
3424 nospectre_bhb [ARM64]
3425 nospectre_v1 [X86,PPC]
3426 nospectre_v2 [X86,PPC,S390,ARM64]
3427 reg_file_data_sampling=off [X86]
3429 spec_rstack_overflow=off [X86]
3430 spec_store_bypass_disable=off [X86,PPC]
3431 spectre_v2_user=off [X86]
3432 srbds=off [X86,INTEL]
3433 ssbd=force-off [ARM64]
3434 tsx_async_abort=off [X86]
3437 This does not have any effect on
3438 kvm.nx_huge_pages when
3439 kvm.nx_huge_pages=force.
3442 Mitigate all CPU vulnerabilities, but leave SMT
3443 enabled, even if it's vulnerable. This is for
3444 users who don't want to be surprised by SMT
3445 getting disabled across kernel upgrades, or who
3446 have other ways of avoiding SMT-based attacks.
3447 Equivalent to: (default behavior)
3450 Mitigate all CPU vulnerabilities, disabling SMT
3451 if needed. This is for users who always want to
3452 be fully mitigated, even if it means losing SMT.
3453 Equivalent to: l1tf=flush,nosmt [X86]
3454 mds=full,nosmt [X86]
3455 tsx_async_abort=full,nosmt [X86]
3456 mmio_stale_data=full,nosmt [X86]
3457 retbleed=auto,nosmt [X86]
3460 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this
3461 parameter allows control of the logging verbosity for
3462 the additional memory initialisation checks. A value
3463 of 0 disables mminit logging and a level of 4 will
3464 log everything. Information is printed at KERN_DEBUG
3465 so loglevel=8 may also need to be specified.
3468 [X86,INTEL,EARLY] Control mitigation for the Processor
3469 MMIO Stale Data vulnerabilities.
3471 Processor MMIO Stale Data is a class of
3472 vulnerabilities that may expose data after an MMIO
3473 operation. Exposed data could originate or end in
3474 the same CPU buffers as affected by MDS and TAA.
3475 Therefore, similar to MDS and TAA, the mitigation
3476 is to clear the affected CPU buffers.
3478 This parameter controls the mitigation. The
3481 full - Enable mitigation on vulnerable CPUs
3483 full,nosmt - Enable mitigation and disable SMT on
3486 off - Unconditionally disable mitigation
3488 On MDS or TAA affected machines,
3489 mmio_stale_data=off can be prevented by an active
3490 MDS or TAA mitigation as these vulnerabilities are
3491 mitigated with the same mechanism so in order to
3492 disable this mitigation, you need to specify
3493 mds=off and tsx_async_abort=off too.
3495 Not specifying this option is equivalent to
3496 mmio_stale_data=full.
3499 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
3501 <module>.async_probe[=<bool>] [KNL]
3502 If no <bool> value is specified or if the value
3503 specified is not a valid <bool>, enable asynchronous
3504 probe on this module. Otherwise, enable/disable
3505 asynchronous probe on this module as indicated by the
3506 <bool> value. See also: module.async_probe
3508 module.async_probe=<bool>
3509 [KNL] When set to true, modules will use async probing
3510 by default. To enable/disable async probing for a
3511 specific module, use the module specific control that
3512 is documented under <module>.async_probe. When both
3513 module.async_probe and <module>.async_probe are
3514 specified, <module>.async_probe takes precedence for
3515 the specific module.
3517 module.enable_dups_trace
3518 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set,
3519 this means that duplicate request_module() calls will
3520 trigger a WARN_ON() instead of a pr_warn(). Note that
3521 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s
3522 will always be issued and this option does nothing.
3524 [KNL] When CONFIG_MODULE_SIG is set, this means that
3525 modules without (valid) signatures will fail to load.
3526 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3527 is always true, so this option does nothing.
3529 module_blacklist= [KNL] Do not load a comma-separated list of
3530 modules. Useful for debugging problem modules.
3533 [MOUSE] Maximum time between finger touching and
3534 leaving touchpad surface for touch to be considered
3535 a tap and be reported as a left button click (for
3536 touchpads working in absolute mode only).
3538 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3539 reporting absolute coordinates, such as tablets
3540 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3541 reporting absolute coordinates, such as tablets
3543 movablecore= [KNL,X86,IA-64,PPC,EARLY]
3544 Format: nn[KMGTPE] | nn%
3545 This parameter is the complement to kernelcore=, it
3546 specifies the amount of memory used for migratable
3547 allocations. If both kernelcore and movablecore is
3548 specified, then kernelcore will be at *least* the
3549 specified value but may be more. If movablecore on its
3550 own is specified, the administrator must be careful
3551 that the amount of memory usable for all allocations
3554 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory
3555 NUMA nodes to be movable. This means that the memory
3556 of such nodes will be usable only for movable
3557 allocations which rules out almost all kernel
3558 allocations. Use with caution!
3560 MTD_Partition= [MTD]
3561 Format: <name>,<region-number>,<size>,<offset>
3563 MTD_Region= [MTD] Format:
3564 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3567 See drivers/mtd/parsers/cmdlinepart.c
3570 ARM/S3C2412 JIVE boot control
3572 See arch/arm/mach-s3c/mach-jive.c
3574 mtouchusb.raw_coordinates=
3575 [HW] Make the MicroTouch USB driver use raw coordinates
3576 ('y', default) or cooked coordinates ('n')
3578 mtrr=debug [X86,EARLY]
3579 Enable printing debug information related to MTRR
3580 registers at boot time.
3582 mtrr_chunk_size=nn[KMG,X86,EARLY]
3583 used for mtrr cleanup. It is largest continuous chunk
3584 that could hold holes aka. UC entries.
3586 mtrr_gran_size=nn[KMG,X86,EARLY]
3587 Used for mtrr cleanup. It is granularity of mtrr block.
3589 Large value could prevent small alignment from
3592 mtrr_spare_reg_nr=n [X86,EARLY]
3594 Range: 0,7 : spare reg number
3596 Used for mtrr cleanup. It is spare mtrr entries number.
3597 Set to 2 or more if your graphical card needs more.
3599 multitce=off [PPC] This parameter disables the use of the pSeries
3600 firmware feature for updating multiple TCE entries
3603 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3605 netdev= [NET] Network devices parameters
3606 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3607 Note that mem_start is often overloaded to mean
3608 something different and driver-specific.
3609 This usage is only documented in each driver source
3612 netpoll.carrier_timeout=
3613 [NET] Specifies amount of time (in seconds) that
3614 netpoll should wait for a carrier. By default netpoll
3618 [NETFILTER] Enable connection tracking flow accounting
3619 0 to disable accounting
3620 1 to enable accounting
3624 [NFS] sets the pathname to the program which is used
3625 to update the NFS client cache entries.
3627 nfs.cache_getent_timeout=
3628 [NFS] sets the timeout after which an attempt to
3629 update a cache entry is deemed to have failed.
3631 nfs.callback_nr_threads=
3632 [NFSv4] set the total number of threads that the
3633 NFS client will assign to service NFSv4 callback
3636 nfs.callback_tcpport=
3637 [NFS] set the TCP port on which the NFSv4 callback
3638 channel should listen.
3641 [NFS] specifies the number of times the NFSv4 client
3642 retries the request before returning an EAGAIN error,
3643 after a reply of NFS4ERR_DELAY from the server.
3644 Only applies if the softerr mount option is enabled,
3645 and the specified value is >= 0.
3648 [NFS] enable 64-bit inode numbers.
3649 If zero, the NFS client will fake up a 32-bit inode
3650 number for the readdir() and stat() syscalls instead
3651 of returning the full 64-bit number.
3652 The default is to return 64-bit inode numbers.
3654 nfs.idmap_cache_timeout=
3655 [NFS] set the maximum lifetime for idmapper cache
3658 nfs.max_session_cb_slots=
3659 [NFSv4.1] Sets the maximum number of session
3660 slots the client will assign to the callback
3661 channel. This determines the maximum number of
3662 callbacks the client will process in parallel for
3663 a particular server.
3665 nfs.max_session_slots=
3666 [NFSv4.1] Sets the maximum number of session slots
3667 the client will attempt to negotiate with the server.
3668 This limits the number of simultaneous RPC requests
3669 that the client can send to the NFSv4.1 server.
3670 Note that there is little point in setting this
3671 value higher than the max_tcp_slot_table_limit.
3673 nfs.nfs4_disable_idmapping=
3674 [NFSv4] When set to the default of '1', this option
3675 ensures that both the RPC level authentication
3676 scheme and the NFS level operations agree to use
3677 numeric uids/gids if the mount is using the
3678 'sec=sys' security flavour. In effect it is
3679 disabling idmapping, which can make migration from
3680 legacy NFSv2/v3 systems to NFSv4 easier.
3681 Servers that do not support this mode of operation
3682 will be autodetected by the client, and it will fall
3683 back to using the idmapper.
3684 To turn off this behaviour, set the value to '0'.
3687 [NFS4] Specify an additional fixed unique ident-
3688 ification string that NFSv4 clients can insert into
3689 their nfs_client_id4 string. This is typically a
3690 UUID that is generated at system install time.
3692 nfs.recover_lost_locks=
3693 [NFSv4] Attempt to recover locks that were lost due
3694 to a lease timeout on the server. Please note that
3695 doing this risks data corruption, since there are
3696 no guarantees that the file will remain unchanged
3697 after the locks are lost.
3698 If you want to enable the kernel legacy behaviour of
3699 attempting to recover these locks, then set this
3701 The default parameter value of '0' causes the kernel
3702 not to attempt recovery of lost locks.
3704 nfs.send_implementation_id=
3705 [NFSv4.1] Send client implementation identification
3706 information in exchange_id requests.
3707 If zero, no implementation identification information
3709 The default is to send the implementation identification
3712 nfs4.layoutstats_timer=
3713 [NFSv4.2] Change the rate at which the kernel sends
3714 layoutstats to the pNFS metadata server.
3716 Setting this to value to 0 causes the kernel to use
3717 whatever value is the default set by the layout
3718 driver. A non-zero value sets the minimum interval
3719 in seconds between layoutstats transmissions.
3721 nfsd.inter_copy_offload_enable=
3722 [NFSv4.2] When set to 1, the server will support
3723 server-to-server copies for which this server is
3724 the destination of the copy.
3726 nfsd.nfs4_disable_idmapping=
3727 [NFSv4] When set to the default of '1', the NFSv4
3728 server will return only numeric uids and gids to
3729 clients using auth_sys, and will accept numeric uids
3730 and gids from such clients. This is intended to ease
3731 migration from NFSv2/v3.
3733 nfsd.nfsd4_ssc_umount_timeout=
3734 [NFSv4.2] When used as the destination of a
3735 server-to-server copy, knfsd temporarily mounts
3736 the source server. It caches the mount in case
3737 it will be needed again, and discards it if not
3738 used for the number of milliseconds specified by
3741 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3742 See Documentation/admin-guide/nfs/nfsroot.rst.
3744 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3745 See Documentation/admin-guide/nfs/nfsroot.rst.
3747 nfsrootdebug [NFS] enable nfsroot debugging messages.
3748 See Documentation/admin-guide/nfs/nfsroot.rst.
3750 nmi_backtrace.backtrace_idle [KNL]
3751 Dump stacks even of idle CPUs in response to an
3752 NMI stack-backtrace request.
3754 nmi_debug= [KNL,SH] Specify one or more actions to take
3755 when a NMI is triggered.
3756 Format: [state][,regs][,debounce][,die]
3758 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3759 Format: [panic,][nopanic,][num]
3761 0 - turn hardlockup detector in nmi_watchdog off
3762 1 - turn hardlockup detector in nmi_watchdog on
3763 When panic is specified, panic when an NMI watchdog
3764 timeout occurs (or 'nopanic' to not panic on an NMI
3765 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3766 To disable both hard and soft lockup detectors,
3767 please see 'nowatchdog'.
3768 This is useful when you use a panic=... timeout and
3769 need the box quickly up again.
3771 These settings can be accessed at runtime via
3772 the nmi_watchdog and hardlockup_panic sysctls.
3774 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3775 emulation library even if a 387 maths coprocessor
3778 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes.
3779 Forces kernel to use 3-level paging instead.
3781 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces
3782 kernel to use 4-level paging instead.
3786 noaltinstr [S390,EARLY] Disables alternative instructions
3787 patching (CPU alternatives feature).
3789 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any
3790 IOAPICs that may be present in the system.
3792 noautogroup Disable scheduler automatic task group creation.
3797 [HW] Never suspend the console
3798 Disable suspending of consoles during suspend and
3799 hibernate operations. Once disabled, debugging
3800 messages can reach various consoles while the rest
3801 of the system is being put to sleep (ie, while
3802 debugging driver suspend/resume hooks). This may
3803 not work reliably with all consoles, but is known
3804 to work with serial and VGA consoles.
3805 To facilitate more flexible debugging, we also add
3806 console_suspend, a printk module parameter to control
3807 it. Users could use console_suspend (usually
3808 /sys/module/printk/parameters/console_suspend) to
3809 turn on/off it dynamically.
3812 [KNL,EARLY] Disable object debugging
3814 nodsp [SH] Disable hardware DSP at boot time.
3816 noefi [EFI,EARLY] Disable EFI runtime services support.
3818 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel.
3823 This affects only 32-bit executables.
3824 noexec32=on: enable non-executable mappings (default)
3825 read doesn't imply executable mappings
3826 noexec32=off: disable non-executable mappings
3827 read implies executable mappings
3829 no_file_caps Tells the kernel not to honor file capabilities. The
3830 only way then for a file to be executed with privilege
3831 is to be setuid root or executed by root.
3833 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3835 nofsgsbase [X86] Disables FSGSBASE instructions.
3837 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3838 register save and restore. The kernel will only save
3839 legacy floating-point registers on task switch.
3841 nohalt [IA-64] Tells the kernel not to use the power saving
3842 function PAL_HALT_LIGHT when idle. This increases
3843 power-consumption. On the positive side, it reduces
3844 interrupt wake-up latency, which may improve performance
3845 in certain environments such as networked servers or
3850 Force pointers printed to the console or buffers to be
3851 unhashed. By default, when a pointer is printed via %p
3852 format string, that pointer is "hashed", i.e. obscured
3853 by hashing the pointer value. This is a security feature
3854 that hides actual kernel addresses from unprivileged
3855 users, but it also makes debugging the kernel more
3856 difficult since unequal pointers can no longer be
3857 compared. However, if this command-line option is
3858 specified, then all normal pointers will have their true
3859 value printed. This option should only be specified when
3860 debugging the kernel. Please do not use on production
3863 nohibernate [HIBERNATION] Disable hibernation and resume.
3865 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,SH] Forces the kernel to
3866 busy wait in do_idle() and not use the arch_cpu_idle()
3867 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3868 to be effective. This is useful on platforms where the
3869 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3870 correctly or when doing power measurements to evaluate
3871 the impact of the sleep instructions. This is also
3872 useful when using JTAG debugger.
3874 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings.
3876 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings.
3878 nohz= [KNL] Boottime enable/disable dynamic ticks
3879 Valid arguments: on, off
3882 nohz_full= [KNL,BOOT,SMP,ISOL]
3883 The argument is a cpu list, as described above.
3884 In kernels built with CONFIG_NO_HZ_FULL=y, set
3885 the specified list of CPUs whose tick will be stopped
3886 whenever possible. The boot CPU will be forced outside
3887 the range to maintain the timekeeping. Any CPUs
3888 in this list will have their RCU callbacks offloaded,
3889 just as if they had also been called out in the
3890 rcu_nocbs= boot parameter.
3892 Note that this argument takes precedence over
3893 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
3895 noinitrd [RAM] Tells the kernel not to load any configured
3898 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt
3900 [Deprecated - use intremap=off]
3904 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature.
3906 noiotrap [SH] Disables trapped I/O port accesses.
3908 noirqdebug [X86-32] Disables the code which attempts to detect and
3909 disable unhandled interrupt sources.
3911 noisapnp [ISAPNP] Disables ISA PnP code.
3913 nojitter [IA-64] Disables jitter checking for ITC timers.
3916 When CONFIG_RANDOMIZE_BASE is set, this disables
3917 kernel and module base offset ASLR (Address Space
3918 Layout Randomization).
3920 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page
3923 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver
3925 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC.
3927 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer.
3929 nomca [IA-64] Disable machine check abort handling
3931 nomce [X86-32] Disable Machine Check Exception
3933 nomfgpt [X86-32] Disable Multi-Function General Purpose
3934 Timer usage (for AMD Geode machines).
3936 nomodeset Disable kernel modesetting. Most systems' firmware
3937 sets up a display mode and provides framebuffer memory
3938 for output. With nomodeset, DRM and fbdev drivers will
3939 not load if they could possibly displace the pre-
3940 initialized output. Only the system framebuffer will
3941 be available for use. The respective drivers will not
3942 perform display-mode changes or accelerated rendering.
3944 Useful as error fallback, or for testing and debugging.
3946 nomodule Disable module load
3948 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3949 shutdown the other cpus. Instead use the REBOOT_VECTOR
3952 nopat [X86,EARLY] Disable PAT (page attribute table extension of
3953 pagetables) support.
3955 nopcid [X86-64,EARLY] Disable the PCID cpu feature.
3957 nopku [X86] Disable Memory Protection Keys CPU feature found
3960 nopti [X86-64,EARLY]
3961 Equivalent to pti=off
3963 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY]
3964 Disables the PV optimizations forcing the guest to run
3965 as generic guest with no PV drivers. Currently support
3966 XEN HVM, KVM, HYPER_V and VMWARE guest.
3968 nopvspin [X86,XEN,KVM,EARLY]
3969 Disables the qspinlock slow path using PV optimizations
3970 which allow the hypervisor to 'idle' the guest on lock
3973 norandmaps Don't use address space randomization. Equivalent to
3974 echo 0 > /proc/sys/kernel/randomize_va_space
3976 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3977 with UP alternatives
3979 noresume [SWSUSP] Disables resume and restores original swap
3984 no-scroll [VGA] Disables scrollback.
3985 This is required for the Braillex ib80-piezo Braille
3986 reader made by F.H. Papenmeier (Germany).
3988 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support.
3991 Disable SMAP (Supervisor Mode Access Prevention)
3992 even if it is supported by processor.
3994 nosmep [PPC64s,EARLY]
3995 Disable SMEP (Supervisor Mode Execution Prevention)
3996 even if it is supported by processor.
3998 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel,
3999 and disable the IO APIC. legacy for "maxcpus=0".
4001 nosmt [KNL,MIPS,PPC,S390,EARLY] Disable symmetric multithreading (SMT).
4002 Equivalent to smt=1.
4004 [KNL,X86,PPC] Disable symmetric multithreading (SMT).
4005 nosmt=force: Force disable SMT, cannot be undone
4006 via the sysfs control file.
4008 nosoftlockup [KNL] Disable the soft-lockup detector.
4010 nospec_store_bypass_disable
4011 [HW,EARLY] Disable all mitigations for the Speculative
4012 Store Bypass vulnerability
4014 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch
4015 history injection) vulnerability. System may allow data leaks
4018 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1
4019 (bounds check bypass). With this option data leaks are
4020 possible in the system.
4022 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations
4023 for the Spectre variant 2 (indirect branch
4024 prediction) vulnerability. System may allow data
4025 leaks with this option.
4027 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,EARLY] Disable
4028 paravirtualized steal time accounting. steal time is
4029 computed, but won't influence scheduler behaviour
4031 nosync [HW,M68K] Disables sync negotiation for all devices.
4033 no_timer_check [X86,APIC] Disables the code which tests for
4034 broken timer IRQ sources.
4037 [PPC,EARLY] Don't flush the L1-D cache after accessing user data.
4039 novmcoredd [KNL,KDUMP]
4040 Disable device dump. Device dump allows drivers to
4041 append dump data to vmcore so you can collect driver
4042 specified debug info. Drivers can append the data
4043 without any limit and this data is stored in memory,
4044 so this may cause significant memory stress. Disabling
4045 device dump can help save memory but the driver debug
4046 data will be no longer available. This parameter
4047 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
4051 [X86,PV_OPS,EARLY] Disable paravirtualized VMware
4052 scheduler clock and use the default one.
4054 nowatchdog [KNL] Disable both lockup detectors, i.e.
4055 soft-lockup and NMI watchdog (hard-lockup).
4059 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode.
4061 NOTE: this parameter will be ignored on systems with the
4062 LEGACY_XAPIC_DISABLED bit set in the
4063 IA32_XAPIC_DISABLE_STATUS MSR.
4065 noxsave [BUGS=X86] Disables x86 extended register state save
4066 and restore using xsave. The kernel will fallback to
4067 enabling legacy floating-point and sse state.
4069 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
4070 register states. The kernel will fall back to use
4071 xsave to save the states. By using this parameter,
4072 performance of saving the states is degraded because
4073 xsave doesn't support modified optimization while
4074 xsaveopt supports it on xsaveopt enabled systems.
4076 noxsaves [X86] Disables xsaves and xrstors used in saving and
4077 restoring x86 extended register state in compacted
4078 form of xsave area. The kernel will fall back to use
4079 xsaveopt and xrstor to save and restore the states
4080 in standard form of xsave area. By using this
4081 parameter, xsave area per process might occupy more
4082 memory on xsaves enabled systems.
4084 nps_mtm_hs_ctr= [KNL,ARC]
4085 This parameter sets the maximum duration, in
4086 cycles, each HW thread of the CTOP can run
4087 without interruptions, before HW switches it.
4088 The actual maximum duration is 16 times this
4090 Format: integer between 1 and 255
4093 nptcg= [IA-64] Override max number of concurrent global TLB
4094 purges which is reported from either PAL_VM_SUMMARY or
4097 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
4098 could support. nr_cpus=n : n >= 1 limits the kernel to
4099 support 'n' processors. It could be larger than the
4100 number of already plugged CPU during bootup, later in
4101 runtime you can physically add extra cpu until it reaches
4102 n. So during boot up some boot time memory for per-cpu
4103 variables need be pre-allocated for later physical cpu
4106 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
4108 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY]
4109 Disable NUMA, Only set up a single NUMA node
4110 spanning all memory.
4112 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
4114 Allowed values are enable and disable
4116 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
4117 'node', 'default' can be specified
4118 This can be set from sysctl after boot.
4119 See Documentation/admin-guide/sysctl/vm.rst for details.
4121 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver.
4122 See Documentation/core-api/debugging-via-ohci1394.rst for more
4125 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
4126 Rather than timing out after 20 ms if an EC
4127 command is not properly ACKed, override the length
4128 of the timeout. We have interrupts disabled while
4129 waiting for the ACK, so if this is set too high
4130 interrupts *may* be lost!
4132 omap_mux= [OMAP] Override bootloader pin multiplexing.
4133 Format: <mux_mode0.mode_name=value>...
4134 For example, to override I2C bus2:
4135 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
4137 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
4139 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
4141 boundary - index of last SLC block on Flex-OneNAND.
4142 The remaining blocks are configured as MLC blocks.
4143 lock - Configure if Flex-OneNAND boundary should be locked.
4144 Once locked, the boundary cannot be changed.
4145 1 indicates lock status, 0 indicates unlock status.
4147 oops=panic [KNL,EARLY]
4148 Always panic on oopses. Default is to just kill the
4149 process, but there is a small probability of
4150 deadlocking the machine.
4151 This will also cause panics on machine check exceptions.
4152 Useful together with panic=30 to trigger a reboot.
4155 [KNL] Boolean flag to control whether the page allocator
4156 should randomize its free lists. The randomization may
4157 be automatically enabled if the kernel detects it is
4158 running on a platform with a direct-mapped memory-side
4159 cache, and this parameter can be used to
4160 override/disable that behavior. The state of the flag
4161 can be read from sysfs at:
4162 /sys/module/page_alloc/parameters/shuffle.
4164 page_owner= [KNL,EARLY] Boot-time page_owner enabling option.
4165 Storage of the information about who allocated
4166 each page is disabled in default. With this switch,
4168 on: enable the feature
4170 page_poison= [KNL,EARLY] Boot-time parameter changing the state of
4171 poisoning on the buddy allocator, available with
4172 CONFIG_PAGE_POISONING=y.
4173 off: turn off poisoning (default)
4174 on: turn on poisoning
4176 page_reporting.page_reporting_order=
4177 [KNL] Minimal page reporting order
4179 Adjust the minimal page reporting order. The page
4180 reporting is disabled when it exceeds MAX_PAGE_ORDER.
4182 panic= [KNL] Kernel behaviour on panic: delay <timeout>
4183 timeout > 0: seconds before rebooting
4184 timeout = 0: wait forever
4185 timeout < 0: reboot immediately
4188 panic_on_taint= [KNL,EARLY]
4189 Bitmask for conditionally calling panic() in add_taint()
4190 Format: <hex>[,nousertaint]
4191 Hexadecimal bitmask representing the set of TAINT flags
4192 that will cause the kernel to panic when add_taint() is
4193 called with any of the flags in this set.
4194 The optional switch "nousertaint" can be utilized to
4195 prevent userspace forced crashes by writing to sysctl
4196 /proc/sys/kernel/tainted any flagset matching with the
4197 bitmask set on panic_on_taint.
4198 See Documentation/admin-guide/tainted-kernels.rst for
4199 extra details on the taint flags that users can pick
4200 to compose the bitmask to assign to panic_on_taint.
4202 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump
4205 panic_print= Bitmask for printing system info when panic happens.
4206 User can chose combination of the following bits:
4207 bit 0: print all tasks info
4208 bit 1: print system memory info
4209 bit 2: print timer info
4210 bit 3: print locks info if CONFIG_LOCKDEP is on
4211 bit 4: print ftrace buffer
4212 bit 5: print all printk messages in buffer
4213 bit 6: print all CPUs backtrace (if available in the arch)
4214 *Be aware* that this option may print a _lot_ of lines,
4215 so there are risks of losing older messages in the log.
4216 Use this option carefully, maybe worth to setup a
4217 bigger log buffer with "log_buf_len" along with this.
4219 parkbd.port= [HW] Parallel port number the keyboard adapter is
4220 connected to, default is 0.
4222 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
4223 0 for XT, 1 for AT (default is AT).
4226 parport= [HW,PPT] Specify parallel ports. 0 disables.
4227 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
4228 Use 'auto' to force the driver to use any
4229 IRQ/DMA settings detected (the default is to
4230 ignore detected IRQ/DMA settings because of
4231 possible conflicts). You can specify the base
4232 address, IRQ, and DMA settings; IRQ and DMA
4233 should be numbers, or 'auto' (for using detected
4234 settings on that particular port), or 'nofifo'
4235 (to avoid using a FIFO even if it is detected).
4236 Parallel ports are assigned in the order they
4237 are specified on the command line, starting
4240 parport_init_mode= [HW,PPT]
4241 Configure VIA parallel port to operate in
4242 a specific mode. This is necessary on Pegasos
4243 computer where firmware has no options for setting
4244 up parallel port mode and sets it to spp.
4245 Currently this function knows 686a and 8231 chips.
4246 Format: [spp|ps2|epp|ecp|ecpepp]
4248 pata_legacy.all= [HW,LIBATA]
4250 Set to non-zero to probe primary and secondary ISA
4251 port ranges on PCI systems where no PCI PATA device
4252 has been found at either range. Disabled by default.
4254 pata_legacy.autospeed= [HW,LIBATA]
4256 Set to non-zero if a chip is present that snoops speed
4257 changes. Disabled by default.
4259 pata_legacy.ht6560a= [HW,LIBATA]
4261 Set to 1, 2, or 3 for HT 6560A on the primary channel,
4262 the secondary channel, or both channels respectively.
4263 Disabled by default.
4265 pata_legacy.ht6560b= [HW,LIBATA]
4267 Set to 1, 2, or 3 for HT 6560B on the primary channel,
4268 the secondary channel, or both channels respectively.
4269 Disabled by default.
4271 pata_legacy.iordy_mask= [HW,LIBATA]
4273 IORDY enable mask. Set individual bits to allow IORDY
4274 for the respective channel. Bit 0 is for the first
4275 legacy channel handled by this driver, bit 1 is for
4276 the second channel, and so on. The sequence will often
4277 correspond to the primary legacy channel, the secondary
4278 legacy channel, and so on, but the handling of a PCI
4279 bus and the use of other driver options may interfere
4280 with the sequence. By default IORDY is allowed across
4283 pata_legacy.opti82c46x= [HW,LIBATA]
4285 Set to 1, 2, or 3 for Opti 82c611A on the primary
4286 channel, the secondary channel, or both channels
4287 respectively. Disabled by default.
4289 pata_legacy.opti82c611a= [HW,LIBATA]
4291 Set to 1, 2, or 3 for Opti 82c465MV on the primary
4292 channel, the secondary channel, or both channels
4293 respectively. Disabled by default.
4295 pata_legacy.pio_mask= [HW,LIBATA]
4297 PIO mode mask for autospeed devices. Set individual
4298 bits to allow the use of the respective PIO modes.
4299 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
4300 All modes allowed by default.
4302 pata_legacy.probe_all= [HW,LIBATA]
4304 Set to non-zero to probe tertiary and further ISA
4305 port ranges on PCI systems. Disabled by default.
4307 pata_legacy.probe_mask= [HW,LIBATA]
4309 Probe mask for legacy ISA PATA ports. Depending on
4310 platform configuration and the use of other driver
4311 options up to 6 legacy ports are supported: 0x1f0,
4312 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
4313 of individual ports can be disabled by setting the
4314 corresponding bits in the mask to 1. Bit 0 is for
4315 the first port in the list above (0x1f0), and so on.
4316 By default all supported ports are probed.
4318 pata_legacy.qdi= [HW,LIBATA]
4320 Set to non-zero to probe QDI controllers. By default
4321 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
4323 pata_legacy.winbond= [HW,LIBATA]
4325 Set to non-zero to probe Winbond controllers. Use
4326 the standard I/O port (0x130) if 1, otherwise the
4327 value given is the I/O port to use (typically 0x1b0).
4328 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
4331 pata_platform.pio_mask= [HW,LIBATA]
4333 Supported PIO mode mask. Set individual bits to allow
4334 the use of the respective PIO modes. Bit 0 is for
4335 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
4339 Halt all CPUs after the first oops has been printed for
4340 the specified number of seconds. This is to be used if
4341 your oopses keep scrolling off the screen.
4345 pci=option[,option...] [PCI,EARLY] various PCI subsystem options.
4347 Some options herein operate on a specific device
4348 or a set of devices (<pci_dev>). These are
4349 specified in one of the following formats:
4351 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
4352 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
4354 Note: the first format specifies a PCI
4355 bus/device/function address which may change
4356 if new hardware is inserted, if motherboard
4357 firmware changes, or due to changes caused
4358 by other kernel parameters. If the
4359 domain is left unspecified, it is
4360 taken to be zero. Optionally, a path
4361 to a device through multiple device/function
4362 addresses can be specified after the base
4363 address (this is more robust against
4364 renumbering issues). The second format
4365 selects devices using IDs from the
4366 configuration space which may match multiple
4367 devices in the system.
4369 earlydump dump PCI config space before the kernel
4371 off [X86] don't probe for the PCI bus
4372 bios [X86-32] force use of PCI BIOS, don't access
4373 the hardware directly. Use this if your machine
4374 has a non-standard PCI host bridge.
4375 nobios [X86-32] disallow use of PCI BIOS, only direct
4376 hardware access methods are allowed. Use this
4377 if you experience crashes upon bootup and you
4378 suspect they are caused by the BIOS.
4379 conf1 [X86] Force use of PCI Configuration Access
4380 Mechanism 1 (config address in IO port 0xCF8,
4381 data in IO port 0xCFC, both 32-bit).
4382 conf2 [X86] Force use of PCI Configuration Access
4383 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
4384 the function, IO port 0xCFA, also 8-bit, sets
4385 bus number. The config space is then accessed
4386 through ports 0xC000-0xCFFF).
4387 See http://wiki.osdev.org/PCI for more info
4388 on the configuration access mechanisms.
4389 noaer [PCIE] If the PCIEAER kernel config parameter is
4390 enabled, this kernel boot option can be used to
4391 disable the use of PCIE advanced error reporting.
4392 nodomains [PCI] Disable support for multiple PCI
4393 root domains (aka PCI segments, in ACPI-speak).
4394 nommconf [X86] Disable use of MMCONFIG for PCI
4396 check_enable_amd_mmconf [X86] check for and enable
4397 properly configured MMIO access to PCI
4398 config space on AMD family 10h CPU
4399 nomsi [MSI] If the PCI_MSI kernel config parameter is
4400 enabled, this kernel boot option can be used to
4401 disable the use of MSI interrupts system-wide.
4402 noioapicquirk [APIC] Disable all boot interrupt quirks.
4403 Safety option to keep boot IRQs enabled. This
4404 should never be necessary.
4405 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
4406 primary IO-APIC for bridges that cannot disable
4407 boot IRQs. This fixes a source of spurious IRQs
4408 when the system masks IRQs.
4409 noioapicreroute [APIC] Disable workaround that uses the
4410 boot IRQ equivalent of an IRQ that connects to
4411 a chipset where boot IRQs cannot be disabled.
4412 The opposite of ioapicreroute.
4413 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
4414 routing table. These calls are known to be buggy
4415 on several machines and they hang the machine
4416 when used, but on other computers it's the only
4417 way to get the interrupt routing table. Try
4418 this option if the kernel is unable to allocate
4419 IRQs or discover secondary PCI buses on your
4421 rom [X86] Assign address space to expansion ROMs.
4422 Use with caution as certain devices share
4423 address decoders between ROMs and other
4425 norom [X86] Do not assign address space to
4426 expansion ROMs that do not already have
4427 BIOS assigned address ranges.
4428 nobar [X86] Do not assign address space to the
4429 BARs that weren't assigned by the BIOS.
4430 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
4431 assigned automatically to PCI devices. You can
4432 make the kernel exclude IRQs of your ISA cards
4434 pirqaddr=0xAAAAA [X86] Specify the physical address
4435 of the PIRQ table (normally generated
4436 by the BIOS) if it is outside the
4437 F0000h-100000h range.
4438 lastbus=N [X86] Scan all buses thru bus #N. Can be
4439 useful if the kernel is unable to find your
4440 secondary buses and you want to tell it
4441 explicitly which ones they are.
4442 assign-busses [X86] Always assign all PCI bus
4443 numbers ourselves, overriding
4444 whatever the firmware may have done.
4445 usepirqmask [X86] Honor the possible IRQ mask stored
4446 in the BIOS $PIR table. This is needed on
4447 some systems with broken BIOSes, notably
4448 some HP Pavilion N5400 and Omnibook XE3
4449 notebooks. This will have no effect if ACPI
4450 IRQ routing is enabled.
4451 noacpi [X86] Do not use ACPI for IRQ routing
4452 or for PCI scanning.
4453 use_crs [X86] Use PCI host bridge window information
4454 from ACPI. On BIOSes from 2008 or later, this
4455 is enabled by default. If you need to use this,
4456 please report a bug.
4457 nocrs [X86] Ignore PCI host bridge windows from ACPI.
4458 If you need to use this, please report a bug.
4459 use_e820 [X86] Use E820 reservations to exclude parts of
4460 PCI host bridge windows. This is a workaround
4461 for BIOS defects in host bridge _CRS methods.
4462 If you need to use this, please report a bug to
4463 <linux-pci@vger.kernel.org>.
4464 no_e820 [X86] Ignore E820 reservations for PCI host
4465 bridge windows. This is the default on modern
4466 hardware. If you need to use this, please report
4467 a bug to <linux-pci@vger.kernel.org>.
4468 routeirq Do IRQ routing for all PCI devices.
4469 This is normally done in pci_enable_device(),
4470 so this option is a temporary workaround
4471 for broken drivers that don't call it.
4472 skip_isa_align [X86] do not align io start addr, so can
4473 handle more pci cards
4474 noearly [X86] Don't do any early type 1 scanning.
4475 This might help on some broken boards which
4476 machine check when some devices' config space
4477 is read. But various workarounds are disabled
4478 and some IOMMU drivers will not work.
4479 bfsort Sort PCI devices into breadth-first order.
4480 This sorting is done to get a device
4481 order compatible with older (<= 2.4) kernels.
4482 nobfsort Don't sort PCI devices into breadth-first order.
4483 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
4484 tuning and use the BIOS-configured MPS defaults.
4485 pcie_bus_safe Set every device's MPS to the largest value
4486 supported by all devices below the root complex.
4487 pcie_bus_perf Set device MPS to the largest allowable MPS
4488 based on its parent bus. Also set MRRS (Max
4489 Read Request Size) to the largest supported
4490 value (no larger than the MPS that the device
4491 or bus can support) for best performance.
4492 pcie_bus_peer2peer Set every device's MPS to 128B, which
4493 every device is guaranteed to support. This
4494 configuration allows peer-to-peer DMA between
4495 any pair of devices, possibly at the cost of
4496 reduced performance. This also guarantees
4497 that hot-added devices will work.
4498 cbiosize=nn[KMG] The fixed amount of bus space which is
4499 reserved for the CardBus bridge's IO window.
4500 The default value is 256 bytes.
4501 cbmemsize=nn[KMG] The fixed amount of bus space which is
4502 reserved for the CardBus bridge's memory
4503 window. The default value is 64 megabytes.
4506 [<order of align>@]<pci_dev>[; ...]
4507 Specifies alignment and device to reassign
4508 aligned memory resources. How to
4509 specify the device is described above.
4510 If <order of align> is not specified,
4511 PAGE_SIZE is used as alignment.
4512 A PCI-PCI bridge can be specified if resource
4513 windows need to be expanded.
4514 To specify the alignment for several
4515 instances of a device, the PCI vendor,
4516 device, subvendor, and subdevice may be
4517 specified, e.g., 12@pci:8086:9c22:103c:198f
4518 for 4096-byte alignment.
4519 ecrc= Enable/disable PCIe ECRC (transaction layer
4520 end-to-end CRC checking). Only effective if
4521 OS has native AER control (either granted by
4522 ACPI _OSC or forced via "pcie_ports=native")
4523 bios: Use BIOS/firmware settings. This is the
4527 hpiosize=nn[KMG] The fixed amount of bus space which is
4528 reserved for hotplug bridge's IO window.
4529 Default size is 256 bytes.
4530 hpmmiosize=nn[KMG] The fixed amount of bus space which is
4531 reserved for hotplug bridge's MMIO window.
4532 Default size is 2 megabytes.
4533 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
4534 reserved for hotplug bridge's MMIO_PREF window.
4535 Default size is 2 megabytes.
4536 hpmemsize=nn[KMG] The fixed amount of bus space which is
4537 reserved for hotplug bridge's MMIO and
4539 Default size is 2 megabytes.
4540 hpbussize=nn The minimum amount of additional bus numbers
4541 reserved for buses below a hotplug bridge.
4543 realloc= Enable/disable reallocating PCI bridge resources
4544 if allocations done by BIOS are too small to
4545 accommodate resources required by all child
4547 off: Turn realloc off
4549 realloc same as realloc=on
4550 noari do not use PCIe ARI.
4551 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4552 do not use PCIe ATS (and IOMMU device IOTLB).
4553 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4554 only look for one device below a PCIe downstream
4556 big_root_window Try to add a big 64bit memory window to the PCIe
4557 root complex on AMD CPUs. Some GFX hardware
4558 can resize a BAR to allow access to all VRAM.
4559 Adding the window is slightly risky (it may
4560 conflict with unreported devices), so this
4562 disable_acs_redir=<pci_dev>[; ...]
4563 Specify one or more PCI devices (in the format
4564 specified above) separated by semicolons.
4565 Each device specified will have the PCI ACS
4566 redirect capabilities forced off which will
4567 allow P2P traffic between devices through
4568 bridges without forcing it upstream. Note:
4569 this removes isolation between devices and
4570 may put more devices in an IOMMU group.
4571 force_floating [S390] Force usage of floating interrupts.
4572 nomio [S390] Do not use MIO instructions.
4573 norid [S390] ignore the RID field and force use of
4574 one PCI domain per PCI function
4576 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
4579 force Enable ASPM even on devices that claim not to support it.
4580 WARNING: Forcing ASPM on may cause system lockups.
4582 pcie_ports= [PCIE] PCIe port services handling:
4583 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4584 even if the platform doesn't give the OS permission to
4585 use them. This may cause conflicts if the platform
4586 also tries to use these services.
4587 dpc-native Use native PCIe service for DPC only. May
4588 cause conflicts if firmware uses AER or DPC.
4589 compat Disable native PCIe services (PME, AER, DPC, PCIe
4592 pcie_port_pm= [PCIE] PCIe port power management handling:
4593 off Disable power management of all PCIe ports
4594 force Forcibly enable power management of all PCIe ports
4596 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4597 nomsi Do not use MSI for native PCIe PME signaling (this makes
4598 all PCIe root ports use INTx for all services).
4600 pcmv= [HW,PCMCIA] BadgePAD 4
4604 Keep all power-domains already enabled by bootloader on,
4605 even if no driver has claimed them. This is useful
4606 for debug and development, but should not be
4607 needed on a platform with proper driver support.
4609 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4612 See arch/parisc/kernel/pdc_chassis.c
4614 percpu_alloc= [MM,EARLY]
4615 Select which percpu first chunk allocator to use.
4616 Currently supported values are "embed" and "page".
4617 Archs may support subset or none of the selections.
4618 See comments in mm/percpu.c for details on each
4619 allocator. This parameter is primarily for debugging
4620 and performance comparison.
4622 pirq= [SMP,APIC] Manual mp-table setup
4623 See Documentation/arch/x86/i386/IO-APIC.rst.
4625 plip= [PPT,NET] Parallel port network link
4626 Format: { parport<nr> | timid | 0 }
4627 See also Documentation/admin-guide/parport.rst.
4629 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4630 Override pmtimer IOPort with a hex value.
4633 pmu_override= [PPC] Override the PMU.
4634 This option takes over the PMU facility, so it is no
4635 longer usable by perf. Setting this option starts the
4636 PMU counters by setting MMCR0 to 0 (the FC bit is
4637 cleared). If a number is given, then MMCR1 is set to
4638 that number, otherwise (e.g., 'pmu_override=on'), MMCR1
4641 pm_debug_messages [SUSPEND,KNL]
4642 Enable suspend/resume debug messages during boot up.
4645 Enable PNP debug messages (depends on the
4646 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4647 via /sys/module/pnp/parameters/debug. We always show
4648 current resource usage; turning this on also shows
4649 possible settings and some assignment information.
4655 { on | off | curr | res | no-curr | no-res }
4658 [ISAPNP] Exclude IRQs for the autoconfiguration
4661 [ISAPNP] Exclude DMAs for the autoconfiguration
4663 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4664 Ranges are in pairs (I/O port base and size).
4667 [ISAPNP] Exclude memory regions for the
4669 Ranges are in pairs (memory base and size).
4671 ports= [IP_VS_FTP] IPVS ftp helper module
4673 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4675 Format: <port>,<port>....
4677 possible_cpus= [SMP,S390,X86]
4678 Format: <unsigned int>
4679 Set the number of possible CPUs, overriding the
4680 regular discovery mechanisms (such as ACPI/FW, etc).
4682 powersave=off [PPC] This option disables power saving features.
4683 It specifically disables cpuidle and sets the
4684 platform machine description specific power_save
4685 function to NULL. On Idle the CPU just reduces
4688 ppc_strict_facility_enable
4689 [PPC,ENABLE] This option catches any kernel floating point,
4690 Altivec, VSX and SPE outside of regions specifically
4691 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4692 There is some performance impact when enabling this.
4696 Disable Hardware Transactional Memory
4699 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4700 none - Limited to cond_resched() calls
4701 voluntary - Limited to cond_resched() and might_sleep() calls
4702 full - Any section that isn't explicitly preempt disabled
4703 can be preempted anytime.
4705 print-fatal-signals=
4706 [KNL] debug: print fatal signals
4708 If enabled, warn about various signal handling
4709 related application anomalies: too many signals,
4710 too many POSIX.1 timers, fatal signals causing a
4713 If you hit the warning due to signal overflow,
4714 you might want to try "ulimit -i unlimited".
4718 printk.always_kmsg_dump=
4719 Trigger kmsg_dump for cases other than kernel oops or
4721 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4724 printk.console_no_auto_verbose=
4725 Disable console loglevel raise on oops, panic
4726 or lockdep-detected issues (only if lock debug is on).
4727 With an exception to setups with low baudrate on
4728 serial console, keeping this 0 is a good choice
4729 in order to provide more debug information.
4731 default: 0 (auto_verbose is enabled)
4733 printk.devkmsg={on,off,ratelimit}
4734 Control writing to /dev/kmsg.
4735 on - unlimited logging to /dev/kmsg from userspace
4736 off - logging to /dev/kmsg disabled
4737 ratelimit - ratelimit the logging
4740 printk.time= Show timing data prefixed to each printk message line
4741 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4743 processor.max_cstate= [HW,ACPI]
4744 Limit processor to maximum C-state
4745 max_cstate=9 overrides any DMI blacklist limit.
4747 processor.nocst [HW,ACPI]
4748 Ignore the _CST method to determine C-states,
4749 instead using the legacy FADT method
4751 profile= [KNL] Enable kernel profiling via /proc/profile
4752 Format: [<profiletype>,]<number>
4753 Param: <profiletype>: "schedule", "sleep", or "kvm"
4754 [defaults to kernel profiling]
4755 Param: "schedule" - profile schedule points.
4756 Param: "sleep" - profile D-state sleeping (millisecs).
4757 Requires CONFIG_SCHEDSTATS
4758 Param: "kvm" - profile VM exits.
4759 Param: <number> - step/bucket size as a power of 2 for
4760 statistical time based profiling.
4762 prompt_ramdisk= [RAM] [Deprecated]
4764 prot_virt= [S390] enable hosting protected virtual machines
4765 isolated from the hypervisor (if hardware supports
4769 psi= [KNL] Enable or disable pressure stall information
4773 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4774 probe for; one of (bare|imps|exps|lifebook|any).
4775 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4777 psmouse.resetafter= [HW,MOUSE]
4778 Try to reset the device after so many bad packets
4781 [HW,MOUSE] Set desired mouse resolution, in dpi.
4782 psmouse.smartscroll=
4783 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4784 0 = disabled, 1 = enabled (default).
4786 pstore.backend= Specify the name of the pstore backend to use
4788 pti= [X86-64] Control Page Table Isolation of user and
4789 kernel address spaces. Disabling this feature
4790 removes hardening, but improves performance of
4791 system calls and interrupts.
4793 on - unconditionally enable
4794 off - unconditionally disable
4795 auto - kernel detects whether your CPU model is
4796 vulnerable to issues that PTI mitigates
4798 Not specifying this option is equivalent to pti=auto.
4801 [KNL] Number of legacy pty's. Overwrites compiled-in
4804 quiet [KNL,EARLY] Disable most log messages
4808 radix_hcall_invalidate=on [PPC/PSERIES]
4809 Disable RADIX GTSE feature and use hcall for TLB
4813 See Documentation/admin-guide/md.rst.
4815 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4816 See Documentation/admin-guide/blockdev/ramdisk.rst.
4818 ramdisk_start= [RAM] RAM disk image start address
4820 random.trust_cpu=off
4821 [KNL,EARLY] Disable trusting the use of the CPU's
4822 random number generator (if available) to
4823 initialize the kernel's RNG.
4825 random.trust_bootloader=off
4826 [KNL,EARLY] Disable trusting the use of the a seed
4827 passed by the bootloader (if available) to
4828 initialize the kernel's RNG.
4830 randomize_kstack_offset=
4831 [KNL,EARLY] Enable or disable kernel stack offset
4832 randomization, which provides roughly 5 bits of
4833 entropy, frustrating memory corruption attacks
4834 that depend on stack address determinism or
4835 cross-syscall address exposures. This is only
4836 available on architectures that have defined
4837 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4838 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4839 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4841 ras=option[,option,...] [KNL] RAS-specific options
4844 Disable the Correctable Errors Collector,
4845 see CONFIG_RAS_CEC help text.
4847 rcu_nocbs[=cpu-list]
4848 [KNL] The optional argument is a cpu list,
4851 In kernels built with CONFIG_RCU_NOCB_CPU=y,
4852 enable the no-callback CPU mode, which prevents
4853 such CPUs' callbacks from being invoked in
4854 softirq context. Invocation of such CPUs' RCU
4855 callbacks will instead be offloaded to "rcuox/N"
4856 kthreads created for that purpose, where "x" is
4857 "p" for RCU-preempt, "s" for RCU-sched, and "g"
4858 for the kthreads that mediate grace periods; and
4859 "N" is the CPU number. This reduces OS jitter on
4860 the offloaded CPUs, which can be useful for HPC
4861 and real-time workloads. It can also improve
4862 energy efficiency for asymmetric multiprocessors.
4864 If a cpulist is passed as an argument, the specified
4865 list of CPUs is set to no-callback mode from boot.
4867 Otherwise, if the '=' sign and the cpulist
4868 arguments are omitted, no CPU will be set to
4869 no-callback mode from boot but the mode may be
4870 toggled at runtime via cpusets.
4872 Note that this argument takes precedence over
4873 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
4876 Rather than requiring that offloaded CPUs
4877 (specified by rcu_nocbs= above) explicitly
4878 awaken the corresponding "rcuoN" kthreads,
4879 make these kthreads poll for callbacks.
4880 This improves the real-time response for the
4881 offloaded CPUs by relieving them of the need to
4882 wake up the corresponding kthread, but degrades
4883 energy efficiency by requiring that the kthreads
4884 periodically wake up to do the polling.
4886 rcutree.blimit= [KNL]
4887 Set maximum number of finished RCU callbacks to
4888 process in one batch.
4890 rcutree.do_rcu_barrier= [KNL]
4891 Request a call to rcu_barrier(). This is
4892 throttled so that userspace tests can safely
4893 hammer on the sysfs variable if they so choose.
4894 If triggered before the RCU grace-period machinery
4895 is fully active, this will error out with EAGAIN.
4897 rcutree.dump_tree= [KNL]
4898 Dump the structure of the rcu_node combining tree
4899 out at early boot. This is used for diagnostic
4900 purposes, to verify correct tree setup.
4902 rcutree.gp_cleanup_delay= [KNL]
4903 Set the number of jiffies to delay each step of
4904 RCU grace-period cleanup.
4906 rcutree.gp_init_delay= [KNL]
4907 Set the number of jiffies to delay each step of
4908 RCU grace-period initialization.
4910 rcutree.gp_preinit_delay= [KNL]
4911 Set the number of jiffies to delay each step of
4912 RCU grace-period pre-initialization, that is,
4913 the propagation of recent CPU-hotplug changes up
4914 the rcu_node combining tree.
4916 rcutree.jiffies_till_first_fqs= [KNL]
4917 Set delay from grace-period initialization to
4918 first attempt to force quiescent states.
4919 Units are jiffies, minimum value is zero,
4920 and maximum value is HZ.
4922 rcutree.jiffies_till_next_fqs= [KNL]
4923 Set delay between subsequent attempts to force
4924 quiescent states. Units are jiffies, minimum
4925 value is one, and maximum value is HZ.
4927 rcutree.jiffies_till_sched_qs= [KNL]
4928 Set required age in jiffies for a
4929 given grace period before RCU starts
4930 soliciting quiescent-state help from
4931 rcu_note_context_switch() and cond_resched().
4932 If not specified, the kernel will calculate
4933 a value based on the most recent settings
4934 of rcutree.jiffies_till_first_fqs
4935 and rcutree.jiffies_till_next_fqs.
4936 This calculated value may be viewed in
4937 rcutree.jiffies_to_sched_qs. Any attempt to set
4938 rcutree.jiffies_to_sched_qs will be cheerfully
4941 rcutree.kthread_prio= [KNL,BOOT]
4942 Set the SCHED_FIFO priority of the RCU per-CPU
4943 kthreads (rcuc/N). This value is also used for
4944 the priority of the RCU boost threads (rcub/N)
4945 and for the RCU grace-period kthreads (rcu_bh,
4946 rcu_preempt, and rcu_sched). If RCU_BOOST is
4947 set, valid values are 1-99 and the default is 1
4948 (the least-favored priority). Otherwise, when
4949 RCU_BOOST is not set, valid values are 0-99 and
4950 the default is zero (non-realtime operation).
4951 When RCU_NOCB_CPU is set, also adjust the
4952 priority of NOCB callback kthreads.
4954 rcutree.nocb_nobypass_lim_per_jiffy= [KNL]
4955 On callback-offloaded (rcu_nocbs) CPUs,
4956 RCU reduces the lock contention that would
4957 otherwise be caused by callback floods through
4958 use of the ->nocb_bypass list. However, in the
4959 common non-flooded case, RCU queues directly to
4960 the main ->cblist in order to avoid the extra
4961 overhead of the ->nocb_bypass list and its lock.
4962 But if there are too many callbacks queued during
4963 a single jiffy, RCU pre-queues the callbacks into
4964 the ->nocb_bypass queue. The definition of "too
4965 many" is supplied by this kernel boot parameter.
4967 rcutree.qhimark= [KNL]
4968 Set threshold of queued RCU callbacks beyond which
4969 batch limiting is disabled.
4971 rcutree.qlowmark= [KNL]
4972 Set threshold of queued RCU callbacks below which
4973 batch limiting is re-enabled.
4975 rcutree.qovld= [KNL]
4976 Set threshold of queued RCU callbacks beyond which
4977 RCU's force-quiescent-state scan will aggressively
4978 enlist help from cond_resched() and sched IPIs to
4979 help CPUs more quickly reach quiescent states.
4980 Set to less than zero to make this be set based
4981 on rcutree.qhimark at boot time and to zero to
4982 disable more aggressive help enlistment.
4984 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
4985 Set the page-cache refill delay (in milliseconds)
4986 in response to low-memory conditions. The range
4987 of permitted values is in the range 0:100000.
4989 rcutree.rcu_divisor= [KNL]
4990 Set the shift-right count to use to compute
4991 the callback-invocation batch limit bl from
4992 the number of callbacks queued on this CPU.
4993 The result will be bounded below by the value of
4994 the rcutree.blimit kernel parameter. Every bl
4995 callbacks, the softirq handler will exit in
4996 order to allow the CPU to do other work.
4998 Please note that this callback-invocation batch
4999 limit applies only to non-offloaded callback
5000 invocation. Offloaded callbacks are instead
5001 invoked in the context of an rcuoc kthread, which
5002 scheduler will preempt as it does any other task.
5004 rcutree.rcu_fanout_exact= [KNL]
5005 Disable autobalancing of the rcu_node combining
5006 tree. This is used by rcutorture, and might
5007 possibly be useful for architectures having high
5008 cache-to-cache transfer latencies.
5010 rcutree.rcu_fanout_leaf= [KNL]
5011 Change the number of CPUs assigned to each
5012 leaf rcu_node structure. Useful for very
5013 large systems, which will choose the value 64,
5014 and for NUMA systems with large remote-access
5015 latencies, which will choose a value aligned
5016 with the appropriate hardware boundaries.
5018 rcutree.rcu_min_cached_objs= [KNL]
5019 Minimum number of objects which are cached and
5020 maintained per one CPU. Object size is equal
5021 to PAGE_SIZE. The cache allows to reduce the
5022 pressure to page allocator, also it makes the
5023 whole algorithm to behave better in low memory
5026 rcutree.rcu_nocb_gp_stride= [KNL]
5027 Set the number of NOCB callback kthreads in
5028 each group, which defaults to the square root
5029 of the number of CPUs. Larger numbers reduce
5030 the wakeup overhead on the global grace-period
5031 kthread, but increases that same overhead on
5032 each group's NOCB grace-period kthread.
5034 rcutree.rcu_kick_kthreads= [KNL]
5035 Cause the grace-period kthread to get an extra
5036 wake_up() if it sleeps three times longer than
5037 it should at force-quiescent-state time.
5038 This wake_up() will be accompanied by a
5039 WARN_ONCE() splat and an ftrace_dump().
5041 rcutree.rcu_resched_ns= [KNL]
5042 Limit the time spend invoking a batch of RCU
5043 callbacks to the specified number of nanoseconds.
5044 By default, this limit is checked only once
5045 every 32 callbacks in order to limit the pain
5046 inflicted by local_clock() overhead.
5048 rcutree.rcu_unlock_delay= [KNL]
5049 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
5050 this specifies an rcu_read_unlock()-time delay
5051 in microseconds. This defaults to zero.
5052 Larger delays increase the probability of
5053 catching RCU pointer leaks, that is, buggy use
5054 of RCU-protected pointers after the relevant
5055 rcu_read_unlock() has completed.
5057 rcutree.sysrq_rcu= [KNL]
5058 Commandeer a sysrq key to dump out Tree RCU's
5059 rcu_node tree with an eye towards determining
5060 why a new grace period has not yet started.
5062 rcutree.use_softirq= [KNL]
5063 If set to zero, move all RCU_SOFTIRQ processing to
5064 per-CPU rcuc kthreads. Defaults to a non-zero
5065 value, meaning that RCU_SOFTIRQ is used by default.
5066 Specify rcutree.use_softirq=0 to use rcuc kthreads.
5068 But note that CONFIG_PREEMPT_RT=y kernels disable
5069 this kernel boot parameter, forcibly setting it
5072 rcutree.enable_rcu_lazy= [KNL]
5073 To save power, batch RCU callbacks and flush after
5074 delay, memory pressure or callback list growing too
5077 rcuscale.gp_async= [KNL]
5078 Measure performance of asynchronous
5079 grace-period primitives such as call_rcu().
5081 rcuscale.gp_async_max= [KNL]
5082 Specify the maximum number of outstanding
5083 callbacks per writer thread. When a writer
5084 thread exceeds this limit, it invokes the
5085 corresponding flavor of rcu_barrier() to allow
5086 previously posted callbacks to drain.
5088 rcuscale.gp_exp= [KNL]
5089 Measure performance of expedited synchronous
5090 grace-period primitives.
5092 rcuscale.holdoff= [KNL]
5093 Set test-start holdoff period. The purpose of
5094 this parameter is to delay the start of the
5095 test until boot completes in order to avoid
5098 rcuscale.kfree_by_call_rcu= [KNL]
5099 In kernels built with CONFIG_RCU_LAZY=y, test
5100 call_rcu() instead of kfree_rcu().
5102 rcuscale.kfree_mult= [KNL]
5103 Instead of allocating an object of size kfree_obj,
5104 allocate one of kfree_mult * sizeof(kfree_obj).
5107 rcuscale.kfree_rcu_test= [KNL]
5108 Set to measure performance of kfree_rcu() flooding.
5110 rcuscale.kfree_rcu_test_double= [KNL]
5111 Test the double-argument variant of kfree_rcu().
5112 If this parameter has the same value as
5113 rcuscale.kfree_rcu_test_single, both the single-
5114 and double-argument variants are tested.
5116 rcuscale.kfree_rcu_test_single= [KNL]
5117 Test the single-argument variant of kfree_rcu().
5118 If this parameter has the same value as
5119 rcuscale.kfree_rcu_test_double, both the single-
5120 and double-argument variants are tested.
5122 rcuscale.kfree_nthreads= [KNL]
5123 The number of threads running loops of kfree_rcu().
5125 rcuscale.kfree_alloc_num= [KNL]
5126 Number of allocations and frees done in an iteration.
5128 rcuscale.kfree_loops= [KNL]
5129 Number of loops doing rcuscale.kfree_alloc_num number
5130 of allocations and frees.
5132 rcuscale.minruntime= [KNL]
5133 Set the minimum test run time in seconds. This
5134 does not affect the data-collection interval,
5135 but instead allows better measurement of things
5136 like CPU consumption.
5138 rcuscale.nreaders= [KNL]
5139 Set number of RCU readers. The value -1 selects
5140 N, where N is the number of CPUs. A value
5141 "n" less than -1 selects N-n+1, where N is again
5142 the number of CPUs. For example, -2 selects N
5143 (the number of CPUs), -3 selects N+1, and so on.
5144 A value of "n" less than or equal to -N selects
5147 rcuscale.nwriters= [KNL]
5148 Set number of RCU writers. The values operate
5149 the same as for rcuscale.nreaders.
5150 N, where N is the number of CPUs
5152 rcuscale.scale_type= [KNL]
5153 Specify the RCU implementation to test.
5155 rcuscale.shutdown= [KNL]
5156 Shut the system down after performance tests
5157 complete. This is useful for hands-off automated
5160 rcuscale.verbose= [KNL]
5161 Enable additional printk() statements.
5163 rcuscale.writer_holdoff= [KNL]
5164 Write-side holdoff between grace periods,
5165 in microseconds. The default of zero says
5168 rcuscale.writer_holdoff_jiffies= [KNL]
5169 Additional write-side holdoff between grace
5170 periods, but in jiffies. The default of zero
5173 rcutorture.fqs_duration= [KNL]
5174 Set duration of force_quiescent_state bursts
5177 rcutorture.fqs_holdoff= [KNL]
5178 Set holdoff time within force_quiescent_state bursts
5181 rcutorture.fqs_stutter= [KNL]
5182 Set wait time between force_quiescent_state bursts
5185 rcutorture.fwd_progress= [KNL]
5186 Specifies the number of kthreads to be used
5187 for RCU grace-period forward-progress testing
5188 for the types of RCU supporting this notion.
5189 Defaults to 1 kthread, values less than zero or
5190 greater than the number of CPUs cause the number
5193 rcutorture.fwd_progress_div= [KNL]
5194 Specify the fraction of a CPU-stall-warning
5195 period to do tight-loop forward-progress testing.
5197 rcutorture.fwd_progress_holdoff= [KNL]
5198 Number of seconds to wait between successive
5199 forward-progress tests.
5201 rcutorture.fwd_progress_need_resched= [KNL]
5202 Enclose cond_resched() calls within checks for
5203 need_resched() during tight-loop forward-progress
5206 rcutorture.gp_cond= [KNL]
5207 Use conditional/asynchronous update-side
5208 primitives, if available.
5210 rcutorture.gp_exp= [KNL]
5211 Use expedited update-side primitives, if available.
5213 rcutorture.gp_normal= [KNL]
5214 Use normal (non-expedited) asynchronous
5215 update-side primitives, if available.
5217 rcutorture.gp_sync= [KNL]
5218 Use normal (non-expedited) synchronous
5219 update-side primitives, if available. If all
5220 of rcutorture.gp_cond=, rcutorture.gp_exp=,
5221 rcutorture.gp_normal=, and rcutorture.gp_sync=
5222 are zero, rcutorture acts as if is interpreted
5223 they are all non-zero.
5225 rcutorture.irqreader= [KNL]
5226 Run RCU readers from irq handlers, or, more
5227 accurately, from a timer handler. Not all RCU
5228 flavors take kindly to this sort of thing.
5230 rcutorture.leakpointer= [KNL]
5231 Leak an RCU-protected pointer out of the reader.
5232 This can of course result in splats, and is
5233 intended to test the ability of things like
5234 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
5237 rcutorture.n_barrier_cbs= [KNL]
5238 Set callbacks/threads for rcu_barrier() testing.
5240 rcutorture.nfakewriters= [KNL]
5241 Set number of concurrent RCU writers. These just
5242 stress RCU, they don't participate in the actual
5243 test, hence the "fake".
5245 rcutorture.nocbs_nthreads= [KNL]
5246 Set number of RCU callback-offload togglers.
5247 Zero (the default) disables toggling.
5249 rcutorture.nocbs_toggle= [KNL]
5250 Set the delay in milliseconds between successive
5251 callback-offload toggling attempts.
5253 rcutorture.nreaders= [KNL]
5254 Set number of RCU readers. The value -1 selects
5255 N-1, where N is the number of CPUs. A value
5256 "n" less than -1 selects N-n-2, where N is again
5257 the number of CPUs. For example, -2 selects N
5258 (the number of CPUs), -3 selects N+1, and so on.
5260 rcutorture.object_debug= [KNL]
5261 Enable debug-object double-call_rcu() testing.
5263 rcutorture.onoff_holdoff= [KNL]
5264 Set time (s) after boot for CPU-hotplug testing.
5266 rcutorture.onoff_interval= [KNL]
5267 Set time (jiffies) between CPU-hotplug operations,
5268 or zero to disable CPU-hotplug testing.
5270 rcutorture.read_exit= [KNL]
5271 Set the number of read-then-exit kthreads used
5272 to test the interaction of RCU updaters and
5273 task-exit processing.
5275 rcutorture.read_exit_burst= [KNL]
5276 The number of times in a given read-then-exit
5277 episode that a set of read-then-exit kthreads
5280 rcutorture.read_exit_delay= [KNL]
5281 The delay, in seconds, between successive
5282 read-then-exit testing episodes.
5284 rcutorture.shuffle_interval= [KNL]
5285 Set task-shuffle interval (s). Shuffling tasks
5286 allows some CPUs to go into dyntick-idle mode
5287 during the rcutorture test.
5289 rcutorture.shutdown_secs= [KNL]
5290 Set time (s) after boot system shutdown. This
5291 is useful for hands-off automated testing.
5293 rcutorture.stall_cpu= [KNL]
5294 Duration of CPU stall (s) to test RCU CPU stall
5295 warnings, zero to disable.
5297 rcutorture.stall_cpu_block= [KNL]
5298 Sleep while stalling if set. This will result
5299 in warnings from preemptible RCU in addition to
5300 any other stall-related activity. Note that
5301 in kernels built with CONFIG_PREEMPTION=n and
5302 CONFIG_PREEMPT_COUNT=y, this parameter will
5303 cause the CPU to pass through a quiescent state.
5304 Given CONFIG_PREEMPTION=n, this will suppress
5305 RCU CPU stall warnings, but will instead result
5306 in scheduling-while-atomic splats.
5308 Use of this module parameter results in splats.
5311 rcutorture.stall_cpu_holdoff= [KNL]
5312 Time to wait (s) after boot before inducing stall.
5314 rcutorture.stall_cpu_irqsoff= [KNL]
5315 Disable interrupts while stalling if set.
5317 rcutorture.stall_gp_kthread= [KNL]
5318 Duration (s) of forced sleep within RCU
5319 grace-period kthread to test RCU CPU stall
5320 warnings, zero to disable. If both stall_cpu
5321 and stall_gp_kthread are specified, the
5322 kthread is starved first, then the CPU.
5324 rcutorture.stat_interval= [KNL]
5325 Time (s) between statistics printk()s.
5327 rcutorture.stutter= [KNL]
5328 Time (s) to stutter testing, for example, specifying
5329 five seconds causes the test to run for five seconds,
5330 wait for five seconds, and so on. This tests RCU's
5331 ability to transition abruptly to and from idle.
5333 rcutorture.test_boost= [KNL]
5334 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
5335 "Maybe" means test if the RCU implementation
5336 under test support RCU priority boosting.
5338 rcutorture.test_boost_duration= [KNL]
5339 Duration (s) of each individual boost test.
5341 rcutorture.test_boost_interval= [KNL]
5342 Interval (s) between each boost test.
5344 rcutorture.test_no_idle_hz= [KNL]
5345 Test RCU's dyntick-idle handling. See also the
5346 rcutorture.shuffle_interval parameter.
5348 rcutorture.torture_type= [KNL]
5349 Specify the RCU implementation to test.
5351 rcutorture.verbose= [KNL]
5352 Enable additional printk() statements.
5354 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
5355 Dump ftrace buffer after reporting RCU CPU
5358 rcupdate.rcu_cpu_stall_notifiers= [KNL]
5359 Provide RCU CPU stall notifiers, but see the
5360 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig
5361 option's help text. TL;DR: You almost certainly
5362 do not want rcupdate.rcu_cpu_stall_notifiers.
5364 rcupdate.rcu_cpu_stall_suppress= [KNL]
5365 Suppress RCU CPU stall warning messages.
5367 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
5368 Suppress RCU CPU stall warning messages and
5369 rcutorture writer stall warnings that occur
5370 during early boot, that is, during the time
5371 before the init task is spawned.
5373 rcupdate.rcu_cpu_stall_timeout= [KNL]
5374 Set timeout for RCU CPU stall warning messages.
5375 The value is in seconds and the maximum allowed
5376 value is 300 seconds.
5378 rcupdate.rcu_exp_cpu_stall_timeout= [KNL]
5379 Set timeout for expedited RCU CPU stall warning
5380 messages. The value is in milliseconds
5381 and the maximum allowed value is 21000
5382 milliseconds. Please note that this value is
5383 adjusted to an arch timer tick resolution.
5384 Setting this to zero causes the value from
5385 rcupdate.rcu_cpu_stall_timeout to be used (after
5386 conversion from seconds to milliseconds).
5388 rcupdate.rcu_cpu_stall_cputime= [KNL]
5389 Provide statistics on the cputime and count of
5390 interrupts and tasks during the sampling period. For
5391 multiple continuous RCU stalls, all sampling periods
5392 begin at half of the first RCU stall timeout.
5394 rcupdate.rcu_exp_stall_task_details= [KNL]
5395 Print stack dumps of any tasks blocking the
5396 current expedited RCU grace period during an
5397 expedited RCU CPU stall warning.
5399 rcupdate.rcu_expedited= [KNL]
5400 Use expedited grace-period primitives, for
5401 example, synchronize_rcu_expedited() instead
5402 of synchronize_rcu(). This reduces latency,
5403 but can increase CPU utilization, degrade
5404 real-time latency, and degrade energy efficiency.
5405 No effect on CONFIG_TINY_RCU kernels.
5407 rcupdate.rcu_normal= [KNL]
5408 Use only normal grace-period primitives,
5409 for example, synchronize_rcu() instead of
5410 synchronize_rcu_expedited(). This improves
5411 real-time latency, CPU utilization, and
5412 energy efficiency, but can expose users to
5413 increased grace-period latency. This parameter
5414 overrides rcupdate.rcu_expedited. No effect on
5415 CONFIG_TINY_RCU kernels.
5417 rcupdate.rcu_normal_after_boot= [KNL]
5418 Once boot has completed (that is, after
5419 rcu_end_inkernel_boot() has been invoked), use
5420 only normal grace-period primitives. No effect
5421 on CONFIG_TINY_RCU kernels.
5423 But note that CONFIG_PREEMPT_RT=y kernels enables
5424 this kernel boot parameter, forcibly setting
5425 it to the value one, that is, converting any
5426 post-boot attempt at an expedited RCU grace
5427 period to instead use normal non-expedited
5428 grace-period processing.
5430 rcupdate.rcu_task_collapse_lim= [KNL]
5431 Set the maximum number of callbacks present
5432 at the beginning of a grace period that allows
5433 the RCU Tasks flavors to collapse back to using
5434 a single callback queue. This switching only
5435 occurs when rcupdate.rcu_task_enqueue_lim is
5436 set to the default value of -1.
5438 rcupdate.rcu_task_contend_lim= [KNL]
5439 Set the minimum number of callback-queuing-time
5440 lock-contention events per jiffy required to
5441 cause the RCU Tasks flavors to switch to per-CPU
5442 callback queuing. This switching only occurs
5443 when rcupdate.rcu_task_enqueue_lim is set to
5444 the default value of -1.
5446 rcupdate.rcu_task_enqueue_lim= [KNL]
5447 Set the number of callback queues to use for the
5448 RCU Tasks family of RCU flavors. The default
5449 of -1 allows this to be automatically (and
5450 dynamically) adjusted. This parameter is intended
5453 rcupdate.rcu_task_ipi_delay= [KNL]
5454 Set time in jiffies during which RCU tasks will
5455 avoid sending IPIs, starting with the beginning
5456 of a given grace period. Setting a large
5457 number avoids disturbing real-time workloads,
5458 but lengthens grace periods.
5460 rcupdate.rcu_task_lazy_lim= [KNL]
5461 Number of callbacks on a given CPU that will
5462 cancel laziness on that CPU. Use -1 to disable
5463 cancellation of laziness, but be advised that
5464 doing so increases the danger of OOM due to
5467 rcupdate.rcu_task_stall_info= [KNL]
5468 Set initial timeout in jiffies for RCU task stall
5469 informational messages, which give some indication
5470 of the problem for those not patient enough to
5471 wait for ten minutes. Informational messages are
5472 only printed prior to the stall-warning message
5473 for a given grace period. Disable with a value
5474 less than or equal to zero. Defaults to ten
5475 seconds. A change in value does not take effect
5476 until the beginning of the next grace period.
5478 rcupdate.rcu_task_stall_info_mult= [KNL]
5479 Multiplier for time interval between successive
5480 RCU task stall informational messages for a given
5481 RCU tasks grace period. This value is clamped
5482 to one through ten, inclusive. It defaults to
5483 the value three, so that the first informational
5484 message is printed 10 seconds into the grace
5485 period, the second at 40 seconds, the third at
5486 160 seconds, and then the stall warning at 600
5487 seconds would prevent a fourth at 640 seconds.
5489 rcupdate.rcu_task_stall_timeout= [KNL]
5490 Set timeout in jiffies for RCU task stall
5491 warning messages. Disable with a value less
5492 than or equal to zero. Defaults to ten minutes.
5493 A change in value does not take effect until
5494 the beginning of the next grace period.
5496 rcupdate.rcu_tasks_lazy_ms= [KNL]
5497 Set timeout in milliseconds RCU Tasks asynchronous
5498 callback batching for call_rcu_tasks().
5499 A negative value will take the default. A value
5500 of zero will disable batching. Batching is
5501 always disabled for synchronize_rcu_tasks().
5503 rcupdate.rcu_tasks_rude_lazy_ms= [KNL]
5504 Set timeout in milliseconds RCU Tasks
5505 Rude asynchronous callback batching for
5506 call_rcu_tasks_rude(). A negative value
5507 will take the default. A value of zero will
5508 disable batching. Batching is always disabled
5509 for synchronize_rcu_tasks_rude().
5511 rcupdate.rcu_tasks_trace_lazy_ms= [KNL]
5512 Set timeout in milliseconds RCU Tasks
5513 Trace asynchronous callback batching for
5514 call_rcu_tasks_trace(). A negative value
5515 will take the default. A value of zero will
5516 disable batching. Batching is always disabled
5517 for synchronize_rcu_tasks_trace().
5519 rcupdate.rcu_self_test= [KNL]
5520 Run the RCU early boot self tests
5524 Run specified binary instead of /init from the ramdisk,
5525 used for early userspace startup. See initrd.
5528 force - Override the decision by the kernel to hide the
5529 advertisement of RDRAND support (this affects
5530 certain AMD processors because of buggy BIOS
5531 support, specifically around the suspend/resume
5535 Turn on/off individual RDT features. List is:
5536 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
5538 E.g. to turn on cmt and turn off mba use:
5542 Format (x86 or x86_64):
5543 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
5545 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
5547 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
5548 (prefix with 'panic_' to set mode for panic
5550 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
5551 reboot_force is either force or not specified,
5552 reboot_cpu is s[mp]#### with #### being the processor
5553 to be used for rebooting.
5555 refscale.holdoff= [KNL]
5556 Set test-start holdoff period. The purpose of
5557 this parameter is to delay the start of the
5558 test until boot completes in order to avoid
5561 refscale.lookup_instances= [KNL]
5562 Number of data elements to use for the forms of
5563 SLAB_TYPESAFE_BY_RCU testing. A negative number
5564 is negated and multiplied by nr_cpu_ids, while
5565 zero specifies nr_cpu_ids.
5567 refscale.loops= [KNL]
5568 Set the number of loops over the synchronization
5569 primitive under test. Increasing this number
5570 reduces noise due to loop start/end overhead,
5571 but the default has already reduced the per-pass
5572 noise to a handful of picoseconds on ca. 2020
5575 refscale.nreaders= [KNL]
5576 Set number of readers. The default value of -1
5577 selects N, where N is roughly 75% of the number
5578 of CPUs. A value of zero is an interesting choice.
5580 refscale.nruns= [KNL]
5581 Set number of runs, each of which is dumped onto
5584 refscale.readdelay= [KNL]
5585 Set the read-side critical-section duration,
5586 measured in microseconds.
5588 refscale.scale_type= [KNL]
5589 Specify the read-protection implementation to test.
5591 refscale.shutdown= [KNL]
5592 Shut down the system at the end of the performance
5593 test. This defaults to 1 (shut it down) when
5594 refscale is built into the kernel and to 0 (leave
5595 it running) when refscale is built as a module.
5597 refscale.verbose= [KNL]
5598 Enable additional printk() statements.
5600 refscale.verbose_batched= [KNL]
5601 Batch the additional printk() statements. If zero
5602 (the default) or negative, print everything. Otherwise,
5603 print every Nth verbose statement, where N is the value
5606 regulator_ignore_unused
5608 Prevents regulator framework from disabling regulators
5609 that are unused, due no driver claiming them. This may
5610 be useful for debug and development, but should not be
5611 needed on a platform with proper driver support.
5614 [KNL, SMP] Set scheduler's default relax_domain_level.
5615 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
5617 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
5618 Format: <base1>,<size1>[,<base2>,<size2>,...]
5619 Reserve I/O ports or memory so the kernel won't use
5620 them. If <base> is less than 0x10000, the region
5621 is assumed to be I/O ports; otherwise it is memory.
5623 reservetop= [X86-32,EARLY]
5625 Reserves a hole at the top of the kernel virtual
5628 reset_devices [KNL] Force drivers to reset the underlying device
5629 during initialization.
5632 Specify the partition device for software suspend
5634 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
5636 resume_offset= [SWSUSP]
5637 Specify the offset from the beginning of the partition
5638 given by "resume=" at which the swap header is located,
5639 in <PAGE_SIZE> units (needed only for swap files).
5640 See Documentation/power/swsusp-and-swap-files.rst
5642 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
5643 read the resume files
5645 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
5646 Useful for devices that are detected asynchronously
5647 (e.g. USB and MMC devices).
5649 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will
5650 be accessible via /sys/firmware/initrd.
5652 retbleed= [X86] Control mitigation of RETBleed (Arbitrary
5653 Speculative Code Execution with Return Instructions)
5656 AMD-based UNRET and IBPB mitigations alone do not stop
5657 sibling threads from influencing the predictions of other
5658 sibling threads. For that reason, STIBP is used on pro-
5659 cessors that support it, and mitigate SMT on processors
5663 auto - automatically select a migitation
5664 auto,nosmt - automatically select a mitigation,
5665 disabling SMT if necessary for
5666 the full mitigation (only on Zen1
5667 and older without STIBP).
5668 ibpb - On AMD, mitigate short speculation
5669 windows on basic block boundaries too.
5670 Safe, highest perf impact. It also
5671 enables STIBP if present. Not suitable
5673 ibpb,nosmt - Like "ibpb" above but will disable SMT
5674 when STIBP is not available. This is
5675 the alternative for systems which do not
5677 unret - Force enable untrained return thunks,
5678 only effective on AMD f15h-f17h based
5680 unret,nosmt - Like unret, but will disable SMT when STIBP
5681 is not available. This is the alternative for
5682 systems which do not have STIBP.
5684 Selecting 'auto' will choose a mitigation method at run
5685 time according to the CPU.
5687 Not specifying this option is equivalent to retbleed=auto.
5689 rfkill.default_state=
5690 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
5691 etc. communication is blocked by default.
5694 rfkill.master_switch_mode=
5695 0 The "airplane mode" button does nothing.
5696 1 The "airplane mode" button toggles between everything
5697 blocked and the previous configuration.
5698 2 The "airplane mode" button toggles between everything
5699 blocked and everything unblocked.
5701 rhash_entries= [KNL,NET]
5702 Set number of hash buckets for route cache
5705 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
5708 riscv_isa_fallback [RISCV,EARLY]
5709 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit
5710 falling back to detecting extension support by parsing
5711 "riscv,isa" property on devicetree systems when the
5712 replacement properties are not found. See the Kconfig
5713 entry for RISCV_ISA_FALLBACK.
5715 ro [KNL] Mount root device read-only on boot
5718 on Mark read-only kernel memory as read-only (default).
5719 off Leave read-only kernel memory writable for debugging.
5720 full Mark read-only kernel memory and aliases as read-only
5725 Enable the uart passthrough on the designated usb port
5726 on Rockchip SoCs. When active, the signals of the
5727 debug-uart get routed to the D+ and D- pins of the usb
5728 port and the regular usb controller gets disabled.
5730 root= [KNL] Root filesystem
5731 Usually this a a block device specifier of some kind,
5732 see the early_lookup_bdev comment in
5733 block/early-lookup.c for details.
5734 Alternatively this can be "ram" for the legacy initial
5735 ramdisk, "nfs" and "cifs" for root on a network file
5736 system, or "mtd" and "ubi" for mounting from raw flash.
5738 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
5739 mount the root filesystem
5741 rootflags= [KNL] Set root filesystem mount option string
5743 rootfstype= [KNL] Set root filesystem type
5745 rootwait [KNL] Wait (indefinitely) for root device to show up.
5746 Useful for devices that are detected asynchronously
5747 (e.g. USB and MMC devices).
5749 rootwait= [KNL] Maximum time (in seconds) to wait for root device
5750 to show up before attempting to mount the root
5753 rproc_mem=nn[KMG][@address]
5754 [KNL,ARM,CMA] Remoteproc physical memory block.
5755 Memory area to be used by remote processor image,
5758 rw [KNL] Mount root device read-write on boot
5760 S [KNL] Run init in single mode
5762 s390_iommu= [HW,S390]
5763 Set s390 IOTLB flushing mode
5765 With strict flushing every unmap operation will result
5766 in an IOTLB flush. Default is lazy flushing before
5767 reuse, which is faster. Deprecated, equivalent to
5770 s390_iommu_aperture= [KNL,S390]
5771 Specifies the size of the per device DMA address space
5772 accessible through the DMA and IOMMU APIs as a decimal
5773 factor of the size of main memory.
5774 The default is 1 meaning that one can concurrently use
5775 as many DMA addresses as physical memory is installed,
5776 if supported by hardware, and thus map all of memory
5777 once. With a value of 2 one can map all of memory twice
5778 and so on. As a special case a factor of 0 imposes no
5779 restrictions other than those given by hardware at the
5780 cost of significant additional memory use for tables.
5783 See drivers/net/irda/sa1100_ir.c.
5785 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages.
5787 schedstats= [KNL,X86] Enable or disable scheduled statistics.
5788 Allowed values are enable and disable. This feature
5789 incurs a small amount of overhead in the scheduler
5790 but is useful for debugging and performance tuning.
5792 sched_thermal_decay_shift=
5793 [KNL, SMP] Set a decay shift for scheduler thermal
5794 pressure signal. Thermal pressure signal follows the
5795 default decay period of other scheduler pelt
5796 signals(usually 32 ms but configurable). Setting
5797 sched_thermal_decay_shift will left shift the decay
5798 period for the thermal pressure signal by the shift
5800 i.e. with the default pelt decay period of 32 ms
5801 sched_thermal_decay_shift thermal pressure decay pr
5805 Format: integer between 0 and 10
5808 scftorture.holdoff= [KNL]
5809 Number of seconds to hold off before starting
5810 test. Defaults to zero for module insertion and
5811 to 10 seconds for built-in smp_call_function()
5814 scftorture.longwait= [KNL]
5815 Request ridiculously long waits randomly selected
5816 up to the chosen limit in seconds. Zero (the
5817 default) disables this feature. Please note
5818 that requesting even small non-zero numbers of
5819 seconds can result in RCU CPU stall warnings,
5820 softlockup complaints, and so on.
5822 scftorture.nthreads= [KNL]
5823 Number of kthreads to spawn to invoke the
5824 smp_call_function() family of functions.
5825 The default of -1 specifies a number of kthreads
5826 equal to the number of CPUs.
5828 scftorture.onoff_holdoff= [KNL]
5829 Number seconds to wait after the start of the
5830 test before initiating CPU-hotplug operations.
5832 scftorture.onoff_interval= [KNL]
5833 Number seconds to wait between successive
5834 CPU-hotplug operations. Specifying zero (which
5835 is the default) disables CPU-hotplug operations.
5837 scftorture.shutdown_secs= [KNL]
5838 The number of seconds following the start of the
5839 test after which to shut down the system. The
5840 default of zero avoids shutting down the system.
5841 Non-zero values are useful for automated tests.
5843 scftorture.stat_interval= [KNL]
5844 The number of seconds between outputting the
5845 current test statistics to the console. A value
5846 of zero disables statistics output.
5848 scftorture.stutter_cpus= [KNL]
5849 The number of jiffies to wait between each change
5850 to the set of CPUs under test.
5852 scftorture.use_cpus_read_lock= [KNL]
5853 Use use_cpus_read_lock() instead of the default
5854 preempt_disable() to disable CPU hotplug
5855 while invoking one of the smp_call_function*()
5858 scftorture.verbose= [KNL]
5859 Enable additional printk() statements.
5861 scftorture.weight_single= [KNL]
5862 The probability weighting to use for the
5863 smp_call_function_single() function with a zero
5864 "wait" parameter. A value of -1 selects the
5865 default if all other weights are -1. However,
5866 if at least one weight has some other value, a
5867 value of -1 will instead select a weight of zero.
5869 scftorture.weight_single_wait= [KNL]
5870 The probability weighting to use for the
5871 smp_call_function_single() function with a
5872 non-zero "wait" parameter. See weight_single.
5874 scftorture.weight_many= [KNL]
5875 The probability weighting to use for the
5876 smp_call_function_many() function with a zero
5877 "wait" parameter. See weight_single.
5878 Note well that setting a high probability for
5879 this weighting can place serious IPI load
5882 scftorture.weight_many_wait= [KNL]
5883 The probability weighting to use for the
5884 smp_call_function_many() function with a
5885 non-zero "wait" parameter. See weight_single
5888 scftorture.weight_all= [KNL]
5889 The probability weighting to use for the
5890 smp_call_function_all() function with a zero
5891 "wait" parameter. See weight_single and
5894 scftorture.weight_all_wait= [KNL]
5895 The probability weighting to use for the
5896 smp_call_function_all() function with a
5897 non-zero "wait" parameter. See weight_single
5900 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate
5901 xtime_lock contention on larger systems, and/or RCU lock
5902 contention on all systems with CONFIG_MAXSMP set.
5903 Format: { "0" | "1" }
5904 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
5906 Note: increases power consumption, thus should only be
5907 enabled if running jitter sensitive (HPC/RT) workloads.
5909 security= [SECURITY] Choose a legacy "major" security module to
5910 enable at boot. This has been deprecated by the
5913 selinux= [SELINUX] Disable or enable SELinux at boot time.
5914 Format: { "0" | "1" }
5915 See security/selinux/Kconfig help text.
5920 serialnumber [BUGS=X86-32]
5922 sev=option[,option...] [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst
5925 Maximal number of shapers.
5927 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
5928 Limit apic dumping. The parameter defines the maximal
5929 number of local apics being dumped. Also it is possible
5930 to set it to "all" by meaning -- no limit here.
5931 Format: { 1 (default) | 2 | ... | all }.
5932 The parameter valid if only apic=debug or
5933 apic=verbose is specified.
5934 Example: apic=debug show_lapic=all
5939 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM]
5940 Enabling slab_debug allows one to determine the
5941 culprit if slab objects become corrupted. Enabling
5942 slab_debug can create guard zones around objects and
5943 may poison objects when not in use. Also tracks the
5944 last alloc / free. For more information see
5945 Documentation/mm/slub.rst.
5946 (slub_debug legacy name also accepted for now)
5948 slab_max_order= [MM]
5949 Determines the maximum allowed order for slabs.
5950 A high setting may cause OOMs due to memory
5951 fragmentation. For more information see
5952 Documentation/mm/slub.rst.
5953 (slub_max_order legacy name also accepted for now)
5956 Enable merging of slabs with similar size when the
5957 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
5958 (slub_merge legacy name also accepted for now)
5960 slab_min_objects= [MM]
5961 The minimum number of objects per slab. SLUB will
5962 increase the slab order up to slab_max_order to
5963 generate a sufficiently large slab able to contain
5964 the number of objects indicated. The higher the number
5965 of objects the smaller the overhead of tracking slabs
5966 and the less frequently locks need to be acquired.
5967 For more information see Documentation/mm/slub.rst.
5968 (slub_min_objects legacy name also accepted for now)
5970 slab_min_order= [MM]
5971 Determines the minimum page order for slabs. Must be
5972 lower or equal to slab_max_order. For more information see
5973 Documentation/mm/slub.rst.
5974 (slub_min_order legacy name also accepted for now)
5977 Disable merging of slabs with similar size. May be
5978 necessary if there is some reason to distinguish
5979 allocs to different slabs, especially in hardened
5980 environments where the risk of heap overflows and
5981 layout control by attackers can usually be
5982 frustrated by disabling merging. This will reduce
5983 most of the exposure of a heap attack to a single
5984 cache (risks via metadata attacks are mostly
5985 unchanged). Debug options disable merging on their
5987 For more information see Documentation/mm/slub.rst.
5988 (slub_nomerge legacy name also accepted for now)
5993 Format: <io1>[,<io2>[,...,<io8>]]
5995 smp.csd_lock_timeout= [KNL]
5996 Specify the period of time in milliseconds
5997 that smp_call_function() and friends will wait
5998 for a CPU to release the CSD lock. This is
5999 useful when diagnosing bugs involving CPUs
6000 disabling interrupts for extended periods
6001 of time. Defaults to 5,000 milliseconds, and
6002 setting a value of zero disables this feature.
6003 This feature may be more efficiently disabled
6004 using the csdlock_debug- kernel parameter.
6006 smp.panic_on_ipistall= [KNL]
6007 If a csd_lock_timeout extends for more than
6008 the specified number of milliseconds, panic the
6009 system. By default, let CSD-lock acquisition
6010 take as long as they take. Specifying 300,000
6011 for this value provides a 5-minute timeout.
6013 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
6014 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
6015 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
6016 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
6017 smsc-ircc2.ircc_irq= [HW] IRQ line
6018 smsc-ircc2.ircc_dma= [HW] DMA channel
6019 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
6020 0: Toshiba Satellite 1800 (GP data pin select)
6021 1: Fast pin select (default)
6024 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads
6025 (logical CPUs) to use per physical CPU on systems
6026 capable of symmetric multithreading (SMT). Will
6027 be capped to the actual hardware limit.
6029 Default: -1 (no limit)
6032 [KNL] Should the soft-lockup detector generate panics.
6035 A value of 1 instructs the soft-lockup detector
6036 to panic the machine when a soft-lockup occurs. It is
6037 also controlled by the kernel.softlockup_panic sysctl
6038 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
6039 respective build-time switch to that functionality.
6041 softlockup_all_cpu_backtrace=
6042 [KNL] Should the soft-lockup detector generate
6043 backtraces on all cpus.
6046 sonypi.*= [HW] Sony Programmable I/O Control Device driver
6047 See Documentation/admin-guide/laptops/sonypi.rst
6049 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2
6050 (indirect branch speculation) vulnerability.
6051 The default operation protects the kernel from
6054 on - unconditionally enable, implies
6056 off - unconditionally disable, implies
6058 auto - kernel detects whether your CPU model is
6061 Selecting 'on' will, and 'auto' may, choose a
6062 mitigation method at run time according to the
6063 CPU, the available microcode, the setting of the
6064 CONFIG_MITIGATION_RETPOLINE configuration option,
6065 and the compiler with which the kernel was built.
6067 Selecting 'on' will also enable the mitigation
6068 against user space to user space task attacks.
6070 Selecting 'off' will disable both the kernel and
6071 the user space protections.
6073 Specific mitigations can also be selected manually:
6075 retpoline - replace indirect branches
6076 retpoline,generic - Retpolines
6077 retpoline,lfence - LFENCE; indirect branch
6078 retpoline,amd - alias for retpoline,lfence
6079 eibrs - Enhanced/Auto IBRS
6080 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines
6081 eibrs,lfence - Enhanced/Auto IBRS + LFENCE
6082 ibrs - use IBRS to protect kernel
6084 Not specifying this option is equivalent to
6088 [X86] Control mitigation of Spectre variant 2
6089 (indirect branch speculation) vulnerability between
6092 on - Unconditionally enable mitigations. Is
6093 enforced by spectre_v2=on
6095 off - Unconditionally disable mitigations. Is
6096 enforced by spectre_v2=off
6098 prctl - Indirect branch speculation is enabled,
6099 but mitigation can be enabled via prctl
6100 per thread. The mitigation control state
6101 is inherited on fork.
6104 - Like "prctl" above, but only STIBP is
6105 controlled per thread. IBPB is issued
6106 always when switching between different user
6110 - Same as "prctl" above, but all seccomp
6111 threads will enable the mitigation unless
6112 they explicitly opt out.
6115 - Like "seccomp" above, but only STIBP is
6116 controlled per thread. IBPB is issued
6117 always when switching between different
6118 user space processes.
6120 auto - Kernel selects the mitigation depending on
6121 the available CPU features and vulnerability.
6123 Default mitigation: "prctl"
6125 Not specifying this option is equivalent to
6126 spectre_v2_user=auto.
6128 spec_rstack_overflow=
6129 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs
6131 off - Disable mitigation
6132 microcode - Enable microcode mitigation only
6133 safe-ret - Enable sw-only safe RET mitigation (default)
6134 ibpb - Enable mitigation by issuing IBPB on
6136 ibpb-vmexit - Issue IBPB only on VMEXIT
6137 (cloud-specific mitigation)
6139 spec_store_bypass_disable=
6140 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation
6141 (Speculative Store Bypass vulnerability)
6143 Certain CPUs are vulnerable to an exploit against a
6144 a common industry wide performance optimization known
6145 as "Speculative Store Bypass" in which recent stores
6146 to the same memory location may not be observed by
6147 later loads during speculative execution. The idea
6148 is that such stores are unlikely and that they can
6149 be detected prior to instruction retirement at the
6150 end of a particular speculation execution window.
6152 In vulnerable processors, the speculatively forwarded
6153 store can be used in a cache side channel attack, for
6154 example to read memory to which the attacker does not
6155 directly have access (e.g. inside sandboxed code).
6157 This parameter controls whether the Speculative Store
6158 Bypass optimization is used.
6160 On x86 the options are:
6162 on - Unconditionally disable Speculative Store Bypass
6163 off - Unconditionally enable Speculative Store Bypass
6164 auto - Kernel detects whether the CPU model contains an
6165 implementation of Speculative Store Bypass and
6166 picks the most appropriate mitigation. If the
6167 CPU is not vulnerable, "off" is selected. If the
6168 CPU is vulnerable the default mitigation is
6169 architecture and Kconfig dependent. See below.
6170 prctl - Control Speculative Store Bypass per thread
6171 via prctl. Speculative Store Bypass is enabled
6172 for a process by default. The state of the control
6173 is inherited on fork.
6174 seccomp - Same as "prctl" above, but all seccomp threads
6175 will disable SSB unless they explicitly opt out.
6177 Default mitigations:
6180 On powerpc the options are:
6182 on,auto - On Power8 and Power9 insert a store-forwarding
6183 barrier on kernel entry and exit. On Power7
6184 perform a software flush on kernel entry and
6188 Not specifying this option is equivalent to
6189 spec_store_bypass_disable=auto.
6191 spia_io_base= [HW,MTD]
6197 [X86] Enable split lock detection or bus lock detection
6199 When enabled (and if hardware support is present), atomic
6200 instructions that access data across cache line
6201 boundaries will result in an alignment check exception
6202 for split lock detection or a debug exception for
6207 warn - the kernel will emit rate-limited warnings
6208 about applications triggering the #AC
6209 exception or the #DB exception. This mode is
6210 the default on CPUs that support split lock
6211 detection or bus lock detection. Default
6212 behavior is by #AC if both features are
6213 enabled in hardware.
6215 fatal - the kernel will send SIGBUS to applications
6216 that trigger the #AC exception or the #DB
6217 exception. Default behavior is by #AC if
6218 both features are enabled in hardware.
6221 Set system wide rate limit to N bus locks
6222 per second for bus lock detection.
6225 N/A for split lock detection.
6228 If an #AC exception is hit in the kernel or in
6229 firmware (i.e. not while executing in user mode)
6230 the kernel will oops in either "warn" or "fatal"
6233 #DB exception for bus lock is triggered only when
6236 srbds= [X86,INTEL,EARLY]
6237 Control the Special Register Buffer Data Sampling
6240 Certain CPUs are vulnerable to an MDS-like
6241 exploit which can leak bits from the random
6244 By default, this issue is mitigated by
6245 microcode. However, the microcode fix can cause
6246 the RDRAND and RDSEED instructions to become
6247 much slower. Among other effects, this will
6248 result in reduced throughput from /dev/urandom.
6250 The microcode mitigation can be disabled with
6251 the following option:
6253 off: Disable mitigation and remove
6254 performance impact to RDRAND and RDSEED
6256 srcutree.big_cpu_lim [KNL]
6257 Specifies the number of CPUs constituting a
6258 large system, such that srcu_struct structures
6259 should immediately allocate an srcu_node array.
6260 This kernel-boot parameter defaults to 128,
6261 but takes effect only when the low-order four
6262 bits of srcutree.convert_to_big is equal to 3
6265 srcutree.convert_to_big [KNL]
6266 Specifies under what conditions an SRCU tree
6267 srcu_struct structure will be converted to big
6268 form, that is, with an rcu_node tree:
6271 1: At init_srcu_struct() time.
6272 2: When rcutorture decides to.
6273 3: Decide at boot time (default).
6274 0x1X: Above plus if high contention.
6276 Either way, the srcu_node tree will be sized based
6277 on the actual runtime number of CPUs (nr_cpu_ids)
6278 instead of the compile-time CONFIG_NR_CPUS.
6280 srcutree.counter_wrap_check [KNL]
6281 Specifies how frequently to check for
6282 grace-period sequence counter wrap for the
6283 srcu_data structure's ->srcu_gp_seq_needed field.
6284 The greater the number of bits set in this kernel
6285 parameter, the less frequently counter wrap will
6286 be checked for. Note that the bottom two bits
6289 srcutree.exp_holdoff [KNL]
6290 Specifies how many nanoseconds must elapse
6291 since the end of the last SRCU grace period for
6292 a given srcu_struct until the next normal SRCU
6293 grace period will be considered for automatic
6294 expediting. Set to zero to disable automatic
6297 srcutree.srcu_max_nodelay [KNL]
6298 Specifies the number of no-delay instances
6299 per jiffy for which the SRCU grace period
6300 worker thread will be rescheduled with zero
6301 delay. Beyond this limit, worker thread will
6302 be rescheduled with a sleep delay of one jiffy.
6304 srcutree.srcu_max_nodelay_phase [KNL]
6305 Specifies the per-grace-period phase, number of
6306 non-sleeping polls of readers. Beyond this limit,
6307 grace period worker thread will be rescheduled
6308 with a sleep delay of one jiffy, between each
6309 rescan of the readers, for a grace period phase.
6311 srcutree.srcu_retry_check_delay [KNL]
6312 Specifies number of microseconds of non-sleeping
6313 delay between each non-sleeping poll of readers.
6315 srcutree.small_contention_lim [KNL]
6316 Specifies the number of update-side contention
6317 events per jiffy will be tolerated before
6318 initiating a conversion of an srcu_struct
6319 structure to big form. Note that the value of
6320 srcutree.convert_to_big must have the 0x10 bit
6321 set for contention-based conversions to occur.
6323 ssbd= [ARM64,HW,EARLY]
6324 Speculative Store Bypass Disable control
6326 On CPUs that are vulnerable to the Speculative
6327 Store Bypass vulnerability and offer a
6328 firmware based mitigation, this parameter
6329 indicates how the mitigation should be used:
6331 force-on: Unconditionally enable mitigation for
6332 for both kernel and userspace
6333 force-off: Unconditionally disable mitigation for
6334 for both kernel and userspace
6335 kernel: Always enable mitigation in the
6336 kernel, and offer a prctl interface
6337 to allow userspace to register its
6338 interest in being mitigated too.
6340 stack_guard_gap= [MM]
6341 override the default stack gap protection. The value
6342 is in page units and it defines how many pages prior
6343 to (for stacks growing down) resp. after (for stacks
6344 growing up) the main stack are reserved for no other
6345 mapping. Default value is 256 pages.
6347 stack_depot_disable= [KNL,EARLY]
6348 Setting this to true through kernel command line will
6349 disable the stack depot thereby saving the static memory
6350 consumed by the stack hash table. By default this is set
6354 Enabled the stack tracer on boot up.
6356 stacktrace_filter=[function-list]
6357 [FTRACE] Limit the functions that the stack tracer
6358 will trace at boot up. function-list is a comma-separated
6359 list of functions. This list can be changed at run
6360 time by the stack_trace_filter file in the debugfs
6361 tracing directory. Note, this enables stack tracing
6362 and the stacktrace above is not needed.
6366 Set the STI (builtin display/keyboard on the HP-PARISC
6367 machines) console (graphic card) which should be used
6368 as the initial boot-console.
6369 See also comment in drivers/video/console/sticore.c.
6372 See comment in drivers/video/console/sticore.c.
6375 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
6380 Enable or disable strict sigaltstack size checks
6381 against the required signal frame size which
6382 depends on the supported FPU features. This can
6383 be used to filter out binaries which have
6384 not yet been made aware of AT_MINSIGSTKSZ.
6386 stress_hpt [PPC,EARLY]
6387 Limits the number of kernel HPT entries in the hash
6388 page table to increase the rate of hash page table
6389 faults on kernel addresses.
6391 stress_slb [PPC,EARLY]
6392 Limits the number of kernel SLB entries, and flushes
6393 them frequently to increase the rate of SLB faults
6394 on kernel addresses.
6396 sunrpc.min_resvport=
6397 sunrpc.max_resvport=
6399 SunRPC servers often require that client requests
6400 originate from a privileged port (i.e. a port in the
6401 range 0 < portnr < 1024).
6402 An administrator who wishes to reserve some of these
6403 ports for other uses may adjust the range that the
6404 kernel's sunrpc client considers to be privileged
6405 using these two parameters to set the minimum and
6406 maximum port values.
6408 sunrpc.svc_rpc_per_connection_limit=
6410 Limit the number of requests that the server will
6411 process in parallel from a single connection.
6412 The default value is 0 (no limit).
6416 Control how the NFS server code allocates CPUs to
6417 service thread pools. Depending on how many NICs
6418 you have and where their interrupts are bound, this
6419 option will affect which CPUs will do NFS serving.
6420 Note: this parameter cannot be changed while the
6421 NFS server is running.
6423 auto the server chooses an appropriate mode
6424 automatically using heuristics
6425 global a single global pool contains all CPUs
6426 percpu one pool for each CPU
6427 pernode one pool for each NUMA node (equivalent
6428 to global on non-NUMA machines)
6430 sunrpc.tcp_slot_table_entries=
6431 sunrpc.udp_slot_table_entries=
6433 Sets the upper limit on the number of simultaneous
6434 RPC calls that can be sent from the client to a
6435 server. Increasing these values may allow you to
6436 improve throughput, but will also increase the
6437 amount of memory reserved for use by the client.
6439 suspend.pm_test_delay=
6441 Sets the number of seconds to remain in a suspend test
6442 mode before resuming the system (see
6443 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
6444 is set. Default value is 5.
6447 Format: { on | off | y | n | 1 | 0 }
6448 This parameter controls use of the Protected
6449 Execution Facility on pSeries.
6451 swiotlb= [ARM,IA-64,PPC,MIPS,X86,EARLY]
6452 Format: { <int> [,<int>] | force | noforce }
6453 <int> -- Number of I/O TLB slabs
6454 <int> -- Second integer after comma. Number of swiotlb
6455 areas with their own lock. Will be rounded up
6457 force -- force using of bounce buffers even if they
6458 wouldn't be automatically used by the kernel
6459 noforce -- Never use bounce buffers (for debugging)
6461 switches= [HW,M68k,EARLY]
6464 Set a sysctl parameter, right before loading the init
6465 process, as if the value was written to the respective
6466 /proc/sys/... file. Both '.' and '/' are recognized as
6467 separators. Unrecognized parameters and invalid values
6468 are reported in the kernel log. Sysctls registered
6469 later by a loaded module cannot be set this way.
6470 Example: sysctl.vm.swappiness=40
6472 sysrq_always_enabled
6474 Ignore sysrq setting - this boot parameter will
6475 neutralize any effect of /proc/sys/kernel/sysrq.
6476 Useful for debugging.
6478 tcpmhash_entries= [KNL,NET]
6479 Set the number of tcp_metrics_hash slots.
6480 Default value is 8192 or 16384 depending on total
6481 ram pages. This is used to specify the TCP metrics
6482 cache size. See Documentation/networking/ip-sysctl.rst
6483 "tcp_no_metrics_save" section for more details.
6487 test_suspend= [SUSPEND]
6488 Format: { "mem" | "standby" | "freeze" }[,N]
6489 Specify "mem" (for Suspend-to-RAM) or "standby" (for
6490 standby suspend) or "freeze" (for suspend type freeze)
6491 as the system sleep state during system startup with
6492 the optional capability to repeat N number of times.
6493 The system is woken from this state using a
6494 wakeup-capable RTC alarm.
6496 thash_entries= [KNL,NET]
6497 Set number of hash buckets for TCP connection
6499 thermal.act= [HW,ACPI]
6500 -1: disable all active trip points in all thermal zones
6501 <degrees C>: override all lowest active trip points
6503 thermal.crt= [HW,ACPI]
6504 -1: disable all critical trip points in all thermal zones
6505 <degrees C>: override all critical trip points
6507 thermal.off= [HW,ACPI]
6508 1: disable ACPI thermal control
6510 thermal.psv= [HW,ACPI]
6511 -1: disable all passive trip points
6512 <degrees C>: override all passive trip points to this
6515 thermal.tzp= [HW,ACPI]
6516 Specify global default ACPI thermal zone polling rate
6517 <deci-seconds>: poll all this frequency
6518 0: no polling (default)
6520 threadirqs [KNL,EARLY]
6521 Force threading of all interrupt handlers except those
6522 marked explicitly IRQF_NO_THREAD.
6524 topology= [S390,EARLY]
6526 Specify if the kernel should make use of the cpu
6527 topology information if the hardware supports this.
6528 The scheduler will make use of this information and
6529 e.g. base its process migration decisions on it.
6532 topology_updates= [KNL, PPC, NUMA]
6534 Specify if the kernel should ignore (off)
6535 topology updates sent by the hypervisor to this
6538 torture.disable_onoff_at_boot= [KNL]
6539 Prevent the CPU-hotplug component of torturing
6540 until after init has spawned.
6542 torture.ftrace_dump_at_shutdown= [KNL]
6543 Dump the ftrace buffer at torture-test shutdown,
6544 even if there were no errors. This can be a
6545 very costly operation when many torture tests
6546 are running concurrently, especially on systems
6547 with rotating-rust storage.
6549 torture.verbose_sleep_frequency= [KNL]
6550 Specifies how many verbose printk()s should be
6551 emitted between each sleep. The default of zero
6552 disables verbose-printk() sleeping.
6554 torture.verbose_sleep_duration= [KNL]
6555 Duration of each verbose-printk() sleep in jiffies.
6559 tpm_suspend_pcr=[HW,TPM]
6560 Format: integer pcr id
6561 Specify that at suspend time, the tpm driver
6562 should extend the specified pcr with zeros,
6563 as a workaround for some chips which fail to
6564 flush the last written pcr on TPM_SaveState.
6565 This will guarantee that all the other pcrs
6568 tpm_tis.interrupts= [HW,TPM]
6569 Enable interrupts for the MMIO based physical layer
6570 for the FIFO interface. By default it is set to false
6571 (0). For more information about TPM hardware interfaces
6572 defined by Trusted Computing Group (TCG) see
6573 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
6576 Have the tracepoints sent to printk as well as the
6577 tracing ring buffer. This is useful for early boot up
6578 where the system hangs or reboots and does not give the
6579 option for reading the tracing buffer or performing a
6580 ftrace_dump_on_oops.
6582 To turn off having tracepoints sent to printk,
6583 echo 0 > /proc/sys/kernel/tracepoint_printk
6584 Note, echoing 1 into this file without the
6585 tracepoint_printk kernel cmdline option has no effect.
6587 The tp_printk_stop_on_boot (see below) can also be used
6588 to stop the printing of events to console at
6593 Having tracepoints sent to printk() and activating high
6594 frequency tracepoints such as irq or sched, can cause
6595 the system to live lock.
6597 tp_printk_stop_on_boot [FTRACE]
6598 When tp_printk (above) is set, it can cause a lot of noise
6599 on the console. It may be useful to only include the
6600 printing of events during boot up, as user space may
6601 make the system inoperable.
6603 This command line option will stop the printing of events
6604 to console at the late_initcall_sync() time frame.
6606 trace_buf_size=nn[KMG]
6607 [FTRACE] will set tracing buffer size on each cpu.
6609 trace_clock= [FTRACE] Set the clock used for tracing events
6611 local - Use the per CPU time stamp counter
6612 (converted into nanoseconds). Fast, but
6613 depending on the architecture, may not be
6614 in sync between CPUs.
6615 global - Event time stamps are synchronize across
6616 CPUs. May be slower than the local clock,
6617 but better for some race conditions.
6618 counter - Simple counting of events (1, 2, ..)
6619 note, some counts may be skipped due to the
6620 infrastructure grabbing the clock more than
6622 uptime - Use jiffies as the time stamp.
6623 perf - Use the same clock that perf uses.
6624 mono - Use ktime_get_mono_fast_ns() for time stamps.
6625 mono_raw - Use ktime_get_raw_fast_ns() for time
6627 boot - Use ktime_get_boot_fast_ns() for time stamps.
6628 Architectures may add more clocks. See
6629 Documentation/trace/ftrace.rst for more details.
6631 trace_event=[event-list]
6632 [FTRACE] Set and start specified trace events in order
6633 to facilitate early boot debugging. The event-list is a
6634 comma-separated list of trace events to enable. See
6635 also Documentation/trace/events.rst
6637 trace_instance=[instance-info]
6638 [FTRACE] Create a ring buffer instance early in boot up.
6639 This will be listed in:
6641 /sys/kernel/tracing/instances
6643 Events can be enabled at the time the instance is created
6646 trace_instance=<name>,<system1>:<event1>,<system2>:<event2>
6648 Note, the "<system*>:" portion is optional if the event is
6651 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall
6653 will enable the "sched_switch" event (note, the "sched:" is optional, and
6654 the same thing would happen if it was left off). The irq_handler_entry
6655 event, and all events under the "initcall" system.
6657 trace_options=[option-list]
6658 [FTRACE] Enable or disable tracer options at boot.
6659 The option-list is a comma delimited list of options
6660 that can be enabled or disabled just as if you were
6661 to echo the option name into
6663 /sys/kernel/tracing/trace_options
6665 For example, to enable stacktrace option (to dump the
6666 stack trace of each event), add to the command line:
6668 trace_options=stacktrace
6670 See also Documentation/trace/ftrace.rst "trace options"
6673 trace_trigger=[trigger-list]
6674 [FTRACE] Add a event trigger on specific events.
6675 Set a trigger on top of a specific event, with an optional
6678 The format is is "trace_trigger=<event>.<trigger>[ if <filter>],..."
6679 Where more than one trigger may be specified that are comma deliminated.
6683 trace_trigger="sched_switch.stacktrace if prev_state == 2"
6685 The above will enable the "stacktrace" trigger on the "sched_switch"
6686 event but only trigger it if the "prev_state" of the "sched_switch"
6687 event is "2" (TASK_UNINTERUPTIBLE).
6689 See also "Event triggers" in Documentation/trace/events.rst
6693 [FTRACE] enable this option to disable tracing when a
6694 warning is hit. This turns off "tracing_on". Tracing can
6695 be enabled again by echoing '1' into the "tracing_on"
6696 file located in /sys/kernel/tracing/
6698 This option is useful, as it disables the trace before
6699 the WARNING dump is called, which prevents the trace to
6700 be filled with content caused by the warning output.
6702 This option can also be set at run time via the sysctl
6703 option: kernel/traceoff_on_warning
6705 transparent_hugepage=
6707 Format: [always|madvise|never]
6708 Can be used to control the default behavior of the system
6709 with respect to transparent hugepages.
6710 See Documentation/admin-guide/mm/transhuge.rst
6713 trusted.source= [KEYS]
6715 This parameter identifies the trust source as a backend
6716 for trusted keys implementation. Supported trust
6721 If not specified then it defaults to iterating through
6722 the trust source list starting with TPM and assigns the
6723 first trust source as a backend which is initialized
6724 successfully during iteration.
6728 The RNG used to generate key material for trusted keys.
6731 - the same value as trusted.source: "tpm" or "tee"
6733 If not specified, "default" is used. In this case,
6734 the RNG's choice is left to each individual trust source.
6736 tsc= Disable clocksource stability checks for TSC.
6738 [x86] reliable: mark tsc clocksource as reliable, this
6739 disables clocksource verification at runtime, as well
6740 as the stability checks done at bootup. Used to enable
6741 high-resolution timer mode on older hardware, and in
6742 virtualized environment.
6743 [x86] noirqtime: Do not use TSC to do irq accounting.
6744 Used to run time disable IRQ_TIME_ACCOUNTING on any
6745 platforms where RDTSC is slow and this accounting
6747 [x86] unstable: mark the TSC clocksource as unstable, this
6748 marks the TSC unconditionally unstable at bootup and
6749 avoids any further wobbles once the TSC watchdog notices.
6750 [x86] nowatchdog: disable clocksource watchdog. Used
6751 in situations with strict latency requirements (where
6752 interruptions from clocksource watchdog are not
6754 [x86] recalibrate: force recalibration against a HW timer
6755 (HPET or PM timer) on systems whose TSC frequency was
6756 obtained from HW or FW using either an MSR or CPUID(0x15).
6757 Warn if the difference is more than 500 ppm.
6758 [x86] watchdog: Use TSC as the watchdog clocksource with
6759 which to check other HW timers (HPET or PM timer), but
6760 only on systems where TSC has been deemed trustworthy.
6761 This will be suppressed by an earlier tsc=nowatchdog and
6762 can be overridden by a later tsc=nowatchdog. A console
6763 message will flag any such suppression or overriding.
6765 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given
6766 value instead. Useful when the early TSC frequency discovery
6767 procedure is not reliable, such as on overclocked systems
6768 with CPUID.16h support and partial CPUID.15h support.
6769 Format: <unsigned int>
6771 tsx= [X86] Control Transactional Synchronization
6772 Extensions (TSX) feature in Intel processors that
6773 support TSX control.
6775 This parameter controls the TSX feature. The options are:
6777 on - Enable TSX on the system. Although there are
6778 mitigations for all known security vulnerabilities,
6779 TSX has been known to be an accelerator for
6780 several previous speculation-related CVEs, and
6781 so there may be unknown security risks associated
6782 with leaving it enabled.
6784 off - Disable TSX on the system. (Note that this
6785 option takes effect only on newer CPUs which are
6786 not vulnerable to MDS, i.e., have
6787 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
6788 the new IA32_TSX_CTRL MSR through a microcode
6789 update. This new MSR allows for the reliable
6790 deactivation of the TSX functionality.)
6792 auto - Disable TSX if X86_BUG_TAA is present,
6793 otherwise enable TSX on the system.
6795 Not specifying this option is equivalent to tsx=off.
6797 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6800 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async
6801 Abort (TAA) vulnerability.
6803 Similar to Micro-architectural Data Sampling (MDS)
6804 certain CPUs that support Transactional
6805 Synchronization Extensions (TSX) are vulnerable to an
6806 exploit against CPU internal buffers which can forward
6807 information to a disclosure gadget under certain
6810 In vulnerable processors, the speculatively forwarded
6811 data can be used in a cache side channel attack, to
6812 access data to which the attacker does not have direct
6815 This parameter controls the TAA mitigation. The
6818 full - Enable TAA mitigation on vulnerable CPUs
6821 full,nosmt - Enable TAA mitigation and disable SMT on
6822 vulnerable CPUs. If TSX is disabled, SMT
6823 is not disabled because CPU is not
6824 vulnerable to cross-thread TAA attacks.
6825 off - Unconditionally disable TAA mitigation
6827 On MDS-affected machines, tsx_async_abort=off can be
6828 prevented by an active MDS mitigation as both vulnerabilities
6829 are mitigated with the same mechanism so in order to disable
6830 this mitigation, you need to specify mds=off too.
6832 Not specifying this option is equivalent to
6833 tsx_async_abort=full. On CPUs which are MDS affected
6834 and deploy MDS mitigation, TAA mitigation is not
6835 required and doesn't provide any additional
6839 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6841 turbografx.map[2|3]= [HW,JOY]
6842 TurboGraFX parallel port interface
6844 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
6845 See also Documentation/input/devices/joystick-parport.rst
6847 udbg-immortal [PPC] When debugging early kernel crashes that
6848 happen after console_init() and before a proper
6849 console driver takes over, this boot options might
6850 help "seeing" what's going on.
6852 uhash_entries= [KNL,NET]
6853 Set number of hash buckets for UDP/UDP-Lite connections
6856 [USB] Ignore overcurrent events (default N).
6857 Some badly-designed motherboards generate lots of
6858 bogus events, for ports that aren't wired to
6859 anything. Set this parameter to avoid log spamming.
6860 Note that genuine overcurrent events won't be
6864 [X86] Cause panic on unknown NMI.
6866 unwind_debug [X86-64,EARLY]
6867 Enable unwinder debug output. This can be
6868 useful for debugging certain unwinder error
6869 conditions, including corrupt stacks and
6870 bad/missing unwinder metadata.
6872 usbcore.authorized_default=
6873 [USB] Default USB device authorization:
6874 (default -1 = authorized (same as 1),
6875 0 = not authorized, 1 = authorized, 2 = authorized
6876 if device connected to internal port)
6878 usbcore.autosuspend=
6879 [USB] The autosuspend time delay (in seconds) used
6880 for newly-detected USB devices (default 2). This
6881 is the time required before an idle device will be
6882 autosuspended. Devices for which the delay is set
6883 to a negative value won't be autosuspended at all.
6885 usbcore.usbfs_snoop=
6886 [USB] Set to log all usbfs traffic (default 0 = off).
6888 usbcore.usbfs_snoop_max=
6889 [USB] Maximum number of bytes to snoop in each URB
6892 usbcore.blinkenlights=
6893 [USB] Set to cycle leds on hubs (default 0 = off).
6895 usbcore.old_scheme_first=
6896 [USB] Start with the old device initialization
6897 scheme (default 0 = off).
6899 usbcore.usbfs_memory_mb=
6900 [USB] Memory limit (in MB) for buffers allocated by
6901 usbfs (default = 16, 0 = max = 2047).
6903 usbcore.use_both_schemes=
6904 [USB] Try the other device initialization scheme
6905 if the first one fails (default 1 = enabled).
6907 usbcore.initial_descriptor_timeout=
6908 [USB] Specifies timeout for the initial 64-byte
6909 USB_REQ_GET_DESCRIPTOR request in milliseconds
6910 (default 5000 = 5.0 seconds).
6912 usbcore.nousb [USB] Disable the USB subsystem
6915 [USB] A list of quirk entries to augment the built-in
6916 usb core quirk list. List entries are separated by
6917 commas. Each entry has the form
6918 VendorID:ProductID:Flags. The IDs are 4-digit hex
6919 numbers and Flags is a set of letters. Each letter
6920 will change the built-in quirk; setting it if it is
6921 clear and clearing it if it is set. The letters have
6922 the following meanings:
6923 a = USB_QUIRK_STRING_FETCH_255 (string
6924 descriptors must not be fetched using
6926 b = USB_QUIRK_RESET_RESUME (device can't resume
6927 correctly so reset it instead);
6928 c = USB_QUIRK_NO_SET_INTF (device can't handle
6929 Set-Interface requests);
6930 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
6931 handle its Configuration or Interface
6933 e = USB_QUIRK_RESET (device can't be reset
6934 (e.g morph devices), don't use reset);
6935 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
6936 more interface descriptions than the
6937 bNumInterfaces count, and can't handle
6938 talking to these interfaces);
6939 g = USB_QUIRK_DELAY_INIT (device needs a pause
6940 during initialization, after we read
6941 the device descriptor);
6942 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
6943 high speed and super speed interrupt
6944 endpoints, the USB 2.0 and USB 3.0 spec
6945 require the interval in microframes (1
6946 microframe = 125 microseconds) to be
6947 calculated as interval = 2 ^
6949 Devices with this quirk report their
6950 bInterval as the result of this
6951 calculation instead of the exponent
6952 variable used in the calculation);
6953 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
6954 handle device_qualifier descriptor
6956 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
6957 generates spurious wakeup, ignore
6958 remote wakeup capability);
6959 k = USB_QUIRK_NO_LPM (device can't handle Link
6961 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
6962 (Device reports its bInterval as linear
6963 frames instead of the USB 2.0
6965 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
6966 to be disconnected before suspend to
6967 prevent spurious wakeup);
6968 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
6969 pause after every control message);
6970 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
6971 delay after resetting its port);
6972 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT
6973 (Reduce timeout of the SET_ADDRESS
6974 request from 5000 ms to 500 ms);
6975 Example: quirks=0781:5580:bk,0a5c:5834:gij
6978 [USBHID] The interval which mice are to be polled at.
6981 [USBHID] The interval which joysticks are to be polled at.
6984 [USBHID] The interval which keyboards are to be polled at.
6986 usb-storage.delay_use=
6987 [UMS] The delay in seconds before a new device is
6988 scanned for Logical Units (default 1).
6991 [UMS] A list of quirks entries to supplement or
6992 override the built-in unusual_devs list. List
6993 entries are separated by commas. Each entry has
6994 the form VID:PID:Flags where VID and PID are Vendor
6995 and Product ID values (4-digit hex numbers) and
6996 Flags is a set of characters, each corresponding
6997 to a common usb-storage quirk flag as follows:
6998 a = SANE_SENSE (collect more than 18 bytes
6999 of sense data, not on uas);
7000 b = BAD_SENSE (don't collect more than 18
7001 bytes of sense data, not on uas);
7002 c = FIX_CAPACITY (decrease the reported
7003 device capacity by one sector);
7004 d = NO_READ_DISC_INFO (don't use
7005 READ_DISC_INFO command, not on uas);
7006 e = NO_READ_CAPACITY_16 (don't use
7007 READ_CAPACITY_16 command);
7008 f = NO_REPORT_OPCODES (don't use report opcodes
7010 g = MAX_SECTORS_240 (don't transfer more than
7011 240 sectors at a time, uas only);
7012 h = CAPACITY_HEURISTICS (decrease the
7013 reported device capacity by one
7014 sector if the number is odd);
7015 i = IGNORE_DEVICE (don't bind to this
7017 j = NO_REPORT_LUNS (don't use report luns
7019 k = NO_SAME (do not use WRITE_SAME, uas only)
7020 l = NOT_LOCKABLE (don't try to lock and
7021 unlock ejectable media, not on uas);
7022 m = MAX_SECTORS_64 (don't transfer more
7023 than 64 sectors = 32 KB at a time,
7025 n = INITIAL_READ10 (force a retry of the
7026 initial READ(10) command, not on uas);
7027 o = CAPACITY_OK (accept the capacity
7028 reported by the device, not on uas);
7029 p = WRITE_CACHE (the device cache is ON
7030 by default, not on uas);
7031 r = IGNORE_RESIDUE (the device reports
7032 bogus residue values, not on uas);
7033 s = SINGLE_LUN (the device has only one
7035 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
7036 commands, uas only);
7037 u = IGNORE_UAS (don't bind to the uas driver);
7038 w = NO_WP_DETECT (don't test whether the
7039 medium is write-protected).
7040 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
7041 even if the device claims no cache,
7043 Example: quirks=0419:aaf5:rl,0421:0433:rc
7045 user_debug= [KNL,ARM]
7047 See arch/arm/Kconfig.debug help text.
7048 1 - undefined instruction events
7050 4 - invalid data aborts
7053 Example: user_debug=31
7056 [X86,EARLY] Flags controlling user PTE allocations.
7058 nohigh = do not allocate PTE pages in
7059 HIGHMEM regardless of setting
7062 vdso= [X86,SH,SPARC]
7063 On X86_32, this is an alias for vdso32=. Otherwise:
7065 vdso=1: enable VDSO (the default)
7066 vdso=0: disable VDSO mapping
7068 vdso32= [X86] Control the 32-bit vDSO
7069 vdso32=1: enable 32-bit VDSO
7070 vdso32=0 or vdso32=2: disable 32-bit VDSO
7072 See the help text for CONFIG_COMPAT_VDSO for more
7073 details. If CONFIG_COMPAT_VDSO is set, the default is
7074 vdso32=0; otherwise, the default is vdso32=1.
7076 For compatibility with older kernels, vdso32=2 is an
7079 Try vdso32=0 if you encounter an error that says:
7080 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
7083 vector=percpu: enable percpu vector domain
7085 video= [FB,EARLY] Frame buffer configuration
7086 See Documentation/fb/modedb.rst.
7088 video.brightness_switch_enabled= [ACPI]
7090 If set to 1, on receiving an ACPI notify event
7091 generated by hotkey, video driver will adjust brightness
7092 level and then send out the event to user space through
7093 the allocated input device. If set to 0, video driver
7094 will only send out the event without touching backlight
7099 [VMMIO] Memory mapped virtio (platform) device.
7101 <size>@<baseaddr>:<irq>[:<id>]
7103 <size> := size (can use standard suffixes
7105 <baseaddr> := physical base address
7106 <irq> := interrupt number (as passed to
7108 <id> := (optional) platform device id
7110 virtio_mmio.device=1K@0x100b0000:48:7
7112 Can be used multiple times for multiple devices.
7114 vga= [BOOT,X86-32] Select a particular video mode
7115 See Documentation/arch/x86/boot.rst and
7116 Documentation/admin-guide/svga.rst.
7117 Use vga=ask for menu.
7118 This is actually a boot loader parameter; the value is
7119 passed to the kernel using a special protocol.
7121 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
7122 May slow down system boot speed, especially when
7123 enabled on systems with a large amount of memory.
7124 All options are enabled by default, and this
7125 interface is meant to allow for selectively
7126 enabling or disabling specific virtual memory
7129 Available options are:
7130 P Enable page structure init time poisoning
7131 - Disable all of the above options
7133 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an
7134 exact size of <nn>. This can be used to increase
7135 the minimum size (128MB on x86). It can also be
7136 used to decrease the size and leave more room
7137 for directly mapped kernel RAM.
7139 vmcp_cma=nn[MG] [KNL,S390,EARLY]
7140 Sets the memory size reserved for contiguous memory
7141 allocations for the vmcp device driver.
7143 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
7146 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
7149 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
7152 vsyscall= [X86-64,EARLY]
7153 Controls the behavior of vsyscalls (i.e. calls to
7154 fixed addresses of 0xffffffffff600x00 from legacy
7155 code). Most statically-linked binaries and older
7156 versions of glibc use these calls. Because these
7157 functions are at fixed addresses, they make nice
7158 targets for exploits that can control RIP.
7160 emulate Vsyscalls turn into traps and are emulated
7161 reasonably safely. The vsyscall page is
7164 xonly [default] Vsyscalls turn into traps and are
7165 emulated reasonably safely. The vsyscall
7166 page is not readable.
7168 none Vsyscalls don't work at all. This makes
7169 them quite hard to use for exploits but
7170 might break your system.
7172 vt.color= [VT] Default text color.
7173 Format: 0xYX, X = foreground, Y = background.
7174 Default: 0x07 = light gray on black.
7176 vt.cur_default= [VT] Default cursor shape.
7177 Format: 0xCCBBAA, where AA, BB, and CC are the same as
7178 the parameters of the <Esc>[?A;B;Cc escape sequence;
7179 see VGA-softcursor.txt. Default: 2 = underline.
7181 vt.default_blu= [VT]
7182 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
7183 Change the default blue palette of the console.
7184 This is a 16-member array composed of values
7187 vt.default_grn= [VT]
7188 Format: <green0>,<green1>,<green2>,...,<green15>
7189 Change the default green palette of the console.
7190 This is a 16-member array composed of values
7193 vt.default_red= [VT]
7194 Format: <red0>,<red1>,<red2>,...,<red15>
7195 Change the default red palette of the console.
7196 This is a 16-member array composed of values
7202 Set system-wide default UTF-8 mode for all tty's.
7203 Default is 1, i.e. UTF-8 mode is enabled for all
7204 newly opened terminals.
7206 vt.global_cursor_default=
7209 Set system-wide default for whether a cursor
7210 is shown on new VTs. Default is -1,
7211 i.e. cursors will be created by default unless
7212 overridden by individual drivers. 0 will hide
7213 cursors, 1 will display them.
7215 vt.italic= [VT] Default color for italic text; 0-15.
7218 vt.underline= [VT] Default color for underlined text; 0-15.
7221 watchdog timers [HW,WDT] For information on watchdog timers,
7222 see Documentation/watchdog/watchdog-parameters.rst
7223 or other driver-specific files in the
7224 Documentation/watchdog/ directory.
7228 Set the hard lockup detector stall duration
7229 threshold in seconds. The soft lockup detector
7230 threshold is set to twice the value. A value of 0
7231 disables both lockup detectors. Default is 10
7234 workqueue.unbound_cpus=
7235 [KNL,SMP] Specify to constrain one or some CPUs
7236 to use in unbound workqueues.
7238 By default, all online CPUs are available for
7241 workqueue.watchdog_thresh=
7242 If CONFIG_WQ_WATCHDOG is configured, workqueue can
7243 warn stall conditions and dump internal state to
7244 help debugging. 0 disables workqueue stall
7245 detection; otherwise, it's the stall threshold
7246 duration in seconds. The default value is 30 and
7247 it can be updated at runtime by writing to the
7248 corresponding sysfs file.
7250 workqueue.cpu_intensive_thresh_us=
7251 Per-cpu work items which run for longer than this
7252 threshold are automatically considered CPU intensive
7253 and excluded from concurrency management to prevent
7254 them from noticeably delaying other per-cpu work
7255 items. Default is 10000 (10ms).
7257 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
7258 will report the work functions which violate this
7259 threshold repeatedly. They are likely good
7260 candidates for using WQ_UNBOUND workqueues instead.
7262 workqueue.cpu_intensive_warning_thresh=<uint>
7263 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
7264 will report the work functions which violate the
7265 intensive_threshold_us repeatedly. In order to prevent
7266 spurious warnings, start printing only after a work
7267 function has violated this threshold number of times.
7269 The default is 4 times. 0 disables the warning.
7271 workqueue.power_efficient
7272 Per-cpu workqueues are generally preferred because
7273 they show better performance thanks to cache
7274 locality; unfortunately, per-cpu workqueues tend to
7275 be more power hungry than unbound workqueues.
7277 Enabling this makes the per-cpu workqueues which
7278 were observed to contribute significantly to power
7279 consumption unbound, leading to measurably lower
7280 power usage at the cost of small performance
7283 The default value of this parameter is determined by
7284 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
7286 workqueue.default_affinity_scope=
7287 Select the default affinity scope to use for unbound
7288 workqueues. Can be one of "cpu", "smt", "cache",
7289 "numa" and "system". Default is "cache". For more
7290 information, see the Affinity Scopes section in
7291 Documentation/core-api/workqueue.rst.
7293 This can be changed after boot by writing to the
7294 matching /sys/module/workqueue/parameters file. All
7295 workqueues with the "default" affinity scope will be
7296 updated accordignly.
7298 workqueue.debug_force_rr_cpu
7299 Workqueue used to implicitly guarantee that work
7300 items queued without explicit CPU specified are put
7301 on the local CPU. This guarantee is no longer true
7302 and while local CPU is still preferred work items
7303 may be put on foreign CPUs. This debug option
7304 forces round-robin CPU selection to flush out
7305 usages which depend on the now broken guarantee.
7306 When enabled, memory and cache locality will be
7309 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access
7310 Type) of ioremap_wc().
7312 on - Enable writecombine, use WUC for ioremap_wc()
7313 off - Disable writecombine, use SUC for ioremap_wc()
7315 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of
7316 default x2apic cluster mode on platforms
7319 xen_512gb_limit [KNL,X86-64,XEN]
7320 Restricts the kernel running paravirtualized under Xen
7321 to use only up to 512 GB of RAM. The reason to do so is
7322 crash analysis tools and Xen tools for doing domain
7323 save/restore/migration must be enabled to handle larger
7326 xen_emul_unplug= [HW,X86,XEN,EARLY]
7327 Unplug Xen emulated devices
7328 Format: [unplug0,][unplug1]
7329 ide-disks -- unplug primary master IDE devices
7330 aux-ide-disks -- unplug non-primary-master IDE devices
7331 nics -- unplug network devices
7332 all -- unplug all emulated devices (NICs and IDE disks)
7333 unnecessary -- unplugging emulated devices is
7334 unnecessary even if the host did not respond to
7336 never -- do not unplug even if version check succeeds
7338 xen_legacy_crash [X86,XEN,EARLY]
7339 Crash from Xen panic notifier, without executing late
7340 panic() code such as dumping handler.
7342 xen_msr_safe= [X86,XEN,EARLY]
7344 Select whether to always use non-faulting (safe) MSR
7345 access functions when running as Xen PV guest. The
7346 default value is controlled by CONFIG_XEN_PV_MSR_SAFE.
7348 xen_nopvspin [X86,XEN,EARLY]
7349 Disables the qspinlock slowpath using Xen PV optimizations.
7350 This parameter is obsoleted by "nopvspin" parameter, which
7351 has equivalent effect for XEN platform.
7354 Disables the PV optimizations forcing the HVM guest to
7355 run as generic HVM guest with no PV drivers.
7356 This option is obsoleted by the "nopv" option, which
7357 has equivalent effect for XEN platform.
7359 xen_no_vector_callback
7360 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen
7361 event channel interrupts.
7363 xen_scrub_pages= [XEN]
7364 Boolean option to control scrubbing pages before giving them back
7365 to Xen, for use by other domains. Can be also changed at runtime
7366 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
7367 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
7369 xen_timer_slop= [X86-64,XEN,EARLY]
7370 Set the timer slop (in nanoseconds) for the virtual Xen
7371 timers (default is 100000). This adjusts the minimum
7372 delta of virtualized Xen timers, where lower values
7373 improve timer resolution at the expense of processing
7374 more timer interrupts.
7376 xen.balloon_boot_timeout= [XEN]
7377 The time (in seconds) to wait before giving up to boot
7378 in case initial ballooning fails to free enough memory.
7379 Applies only when running as HVM or PVH guest and
7380 started with less memory configured than allowed at
7381 max. Default is 180.
7383 xen.event_eoi_delay= [XEN]
7384 How long to delay EOI handling in case of event
7385 storms (jiffies). Default is 10.
7387 xen.event_loop_timeout= [XEN]
7388 After which time (jiffies) the event handling loop
7389 should start to delay EOI handling. Default is 2.
7391 xen.fifo_events= [XEN]
7392 Boolean parameter to disable using fifo event handling
7393 even if available. Normally fifo event handling is
7394 preferred over the 2-level event handling, as it is
7395 fairer and the number of possible event channels is
7396 much higher. Default is on (use fifo events).
7398 xirc2ps_cs= [NET,PCMCIA]
7400 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
7403 By default on POWER9 and above, the kernel will
7404 natively use the XIVE interrupt controller. This option
7405 allows the fallback firmware mode to be used:
7407 off Fallback to firmware control of XIVE interrupt
7408 controller on both pseries and powernv
7409 platforms. Only useful on POWER9 and above.
7411 xive.store-eoi=off [PPC]
7412 By default on POWER10 and above, the kernel will use
7413 stores for EOI handling when the XIVE interrupt mode
7414 is active. This option allows the XIVE driver to use
7415 loads instead, as on POWER9.
7417 xhci-hcd.quirks [USB,KNL]
7418 A hex value specifying bitmask with supplemental xhci
7419 host controller quirks. Meaning of each bit can be
7420 consulted in header drivers/usb/host/xhci.h.
7423 Format: { early | on | rw | ro | off }
7424 Controls if xmon debugger is enabled. Default is off.
7425 Passing only "xmon" is equivalent to "xmon=early".
7426 early Call xmon as early as possible on boot; xmon
7427 debugger is called from setup_arch().
7428 on xmon debugger hooks will be installed so xmon
7429 is only called on a kernel crash. Default mode,
7430 i.e. either "ro" or "rw" mode, is controlled
7431 with CONFIG_XMON_DEFAULT_RO_MODE.
7432 rw xmon debugger hooks will be installed so xmon
7433 is called only on a kernel crash, mode is write,
7434 meaning SPR registers, memory and, other data
7435 can be written using xmon commands.
7436 ro same as "rw" option above but SPR registers,
7437 memory, and other data can't be written using
7439 off xmon is disabled.
git.samba.org / sfrench / cifs-2.6.git / blob