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.
377 amijoy.map= [HW,JOY] Amiga joystick support
378 Map of devices attached to JOY0DAT and JOY1DAT
380 See also Documentation/input/joydev/joystick.rst
382 analog.map= [HW,JOY] Analog joystick and gamepad support
383 Specifies type or capabilities of an analog joystick
384 connected to one of 16 gameports
385 Format: <type1>,<type2>,..<type16>
388 Power management functions (SPARCstation-4/5 + deriv.)
390 Disable APC CPU standby support. SPARCstation-Fox does
391 not play well with APC CPU idle - disable it if you have
392 APC and your system crashes randomly.
394 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller
395 Change the output verbosity while booting
396 Format: { quiet (default) | verbose | debug }
397 Change the amount of debugging information output
398 when initialising the APIC and IO-APIC components.
399 For X86-32, this can also be used to specify an APIC
401 Format: apic=driver_name
402 Examples: apic=bigsmp
404 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting
405 Format: { bsp (default) | all | none }
406 bsp: External NMI is delivered only to CPU 0
407 all: External NMIs are broadcast to all CPUs as a
409 none: External NMI is masked for all CPUs. This is
410 useful so that a dump capture kernel won't be
414 See Documentation/networking/ipv6.rst.
416 apm= [APM] Advanced Power Management
417 See header of arch/x86/kernel/apm_32.c.
419 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
420 Format: { "0" | "1" }
421 See security/apparmor/Kconfig help text
424 Default value is set via kernel config option.
426 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
427 Format: <io>,<irq>,<nodeID>
429 arm64.nobti [ARM64] Unconditionally disable Branch Target
430 Identification support
432 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory
433 Set instructions support
435 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension
438 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
441 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix
444 arm64.nosve [ARM64] Unconditionally disable Scalable Vector
449 atarimouse= [HW,MOUSE] Atari Mouse
451 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
452 EzKey and similar keyboards
454 atkbd.reset= [HW] Reset keyboard during initialization
456 atkbd.set= [HW] Select keyboard code set
457 Format: <int> (2 = AT (default), 3 = PS/2)
459 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
462 atkbd.softraw= [HW] Choose between synthetic and real raw mode
463 Format: <bool> (0 = real, 1 = synthetic (default))
465 atkbd.softrepeat= [HW]
466 Use software keyboard repeat
468 audit= [KNL] Enable the audit sub-system
469 Format: { "0" | "1" | "off" | "on" }
470 0 | off - kernel audit is disabled and can not be
471 enabled until the next reboot
472 unset - kernel audit is initialized but disabled and
473 will be fully enabled by the userspace auditd.
474 1 | on - kernel audit is initialized and partially
475 enabled, storing at most audit_backlog_limit
476 messages in RAM until it is fully enabled by the
480 audit_backlog_limit= [KNL] Set the audit queue size limit.
481 Format: <int> (must be >=0)
484 bau= [X86_UV] Enable the BAU on SGI UV. The default
485 behavior is to disable the BAU (i.e. bau=0).
486 Format: { "0" | "1" }
489 unset - Disable the BAU.
491 baycom_epp= [HW,AX25]
494 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
496 See header of drivers/net/hamradio/baycom_par.c.
498 baycom_ser_fdx= [HW,AX25]
499 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
500 Format: <io>,<irq>,<mode>[,<baud>]
501 See header of drivers/net/hamradio/baycom_ser_fdx.c.
503 baycom_ser_hdx= [HW,AX25]
504 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
505 Format: <io>,<irq>,<mode>
506 See header of drivers/net/hamradio/baycom_ser_hdx.c.
509 Disable BERT OS support on buggy BIOSes.
511 bgrt_disable [ACPI,X86,EARLY]
512 Disable BGRT to avoid flickering OEM logo.
514 blkdevparts= Manual partition parsing of block device(s) for
515 embedded devices based on command line input.
516 See Documentation/block/cmdline-partition.rst
518 boot_delay= [KNL,EARLY]
519 Milliseconds to delay each printk during boot.
520 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled,
521 and you may also have to specify "lpj=". Boot_delay
522 values larger than 10 seconds (10000) are assumed
523 erroneous and ignored.
526 bootconfig [KNL,EARLY]
527 Extended command line options can be added to an initrd
528 and this will cause the kernel to look for it.
530 See Documentation/admin-guide/bootconfig.rst
532 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
533 bttv.radio= Most important insmod options are available as
535 bttv.pll= See Documentation/admin-guide/media/bttv.rst
538 bulk_remove=off [PPC] This parameter disables the use of the pSeries
539 firmware feature for flushing multiple hpte entries
542 c101= [NET] Moxa C101 synchronous serial card
544 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
545 Sometimes CPU hardware bugs make them report the cache
546 size incorrectly. The kernel will attempt work arounds
547 to fix known problems, but for some CPUs it is not
548 possible to determine what the correct size should be.
549 This option provides an override for these situations.
552 [NET] Specifies amount of time (in seconds) that
553 the kernel should wait for a network carrier. By default
554 it waits 120 seconds.
556 ca_keys= [KEYS] This parameter identifies a specific key(s) on
557 the system trusted keyring to be used for certificate
559 format: { id:<keyid> | builtin }
561 cca= [MIPS,EARLY] Override the kernel pages' cache coherency
562 algorithm. Accepted values range from 0 to 7
563 inclusive. See arch/mips/include/asm/pgtable-bits.h
564 for platform specific values (SB1, Loongson3 and
567 ccw_timeout_log [S390]
568 See Documentation/arch/s390/common_io.rst for details.
570 cgroup_disable= [KNL] Disable a particular controller or optional feature
571 Format: {name of the controller(s) or feature(s) to disable}
572 The effects of cgroup_disable=foo are:
573 - foo isn't auto-mounted if you mount all cgroups in
575 - foo isn't visible as an individually mountable
577 - if foo is an optional feature then the feature is
578 disabled and corresponding cgroup files are not
580 {Currently only "memory" controller deal with this and
581 cut the overhead, others just disable the usage. So
582 only cgroup_disable=memory is actually worthy}
583 Specifying "pressure" disables per-cgroup pressure
584 stall information accounting feature
586 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
587 Format: { { controller | "all" | "named" }
588 [,{ controller | "all" | "named" }...] }
589 Like cgroup_disable, but only applies to cgroup v1;
590 the blacklisted controllers remain available in cgroup2.
591 "all" blacklists all controllers and "named" disables
592 named mounts. Specifying both "all" and "named" disables
595 cgroup_favordynmods= [KNL] Enable or Disable favordynmods.
596 Format: { "true" | "false" }
597 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS.
599 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
601 nosocket -- Disable socket memory accounting.
602 nokmem -- Disable kernel memory accounting.
603 nobpf -- Disable BPF memory accounting.
605 checkreqprot= [SELINUX] Set initial checkreqprot flag value.
606 Format: { "0" | "1" }
607 See security/selinux/Kconfig help text.
608 0 -- check protection applied by kernel (includes
609 any implied execute protection).
610 1 -- check protection requested by application.
611 Default value is set via a kernel config option.
612 Value can be changed at runtime via
613 /sys/fs/selinux/checkreqprot.
614 Setting checkreqprot to 1 is deprecated.
617 See Documentation/arch/s390/common_io.rst for details.
619 clearcpuid=X[,X...] [X86]
620 Disable CPUID feature X for the kernel. See
621 arch/x86/include/asm/cpufeatures.h for the valid bit
622 numbers X. Note the Linux-specific bits are not necessarily
623 stable over kernel options, but the vendor-specific
625 X can also be a string as appearing in the flags: line
626 in /proc/cpuinfo which does not have the above
627 instability issue. However, not all features have names
629 Note that using this option will taint your kernel.
630 Also note that user programs calling CPUID directly
631 or using the feature without checking anything
632 will still see it. This just prevents it from
633 being used by the kernel or shown in /proc/cpuinfo.
634 Also note the kernel might malfunction if you disable
639 Prevents the clock framework from automatically gating
640 clocks that have not been explicitly enabled by a Linux
641 device driver but are enabled in hardware at reset or
642 by the bootloader/firmware. Note that this does not
643 force such clocks to be always-on nor does it reserve
644 those clocks in any way. This parameter is useful for
645 debug and development, but should not be needed on a
646 platform with proper driver support. For more
647 information, see Documentation/driver-api/clk.rst.
649 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
651 Forces specified clocksource (if available) to be used
652 when calculating gettimeofday(). If specified
653 clocksource is not available, it defaults to PIT.
654 Format: { pit | tsc | cyclone | pmtmr }
656 clocksource= Override the default clocksource
658 Override the default clocksource and use the clocksource
659 with the name specified.
660 Some clocksource names to choose from, depending on
662 [all] jiffies (this is the base, fallback clocksource)
664 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
665 pxa_timer,timer3,32k_counter,timer0_1
666 [X86-32] pit,hpet,tsc;
667 scx200_hrt on Geode; cyclone on IBM x440
675 clocksource.arm_arch_timer.evtstrm=
678 Enable/disable the eventstream feature of the ARM
679 architected timer so that code using WFE-based polling
680 loops can be debugged more effectively on production
683 clocksource.verify_n_cpus= [KNL]
684 Limit the number of CPUs checked for clocksources
685 marked with CLOCK_SOURCE_VERIFY_PERCPU that
686 are marked unstable due to excessive skew.
687 A negative value says to check all CPUs, while
688 zero says not to check any. Values larger than
689 nr_cpu_ids are silently truncated to nr_cpu_ids.
690 The actual CPUs are chosen randomly, with
691 no replacement if the same CPU is chosen twice.
693 clocksource-wdtest.holdoff= [KNL]
694 Set the time in seconds that the clocksource
695 watchdog test waits before commencing its tests.
696 Defaults to zero when built as a module and to
697 10 seconds when built into the kernel.
699 cma=nn[MG]@[start[MG][-end[MG]]]
701 Sets the size of kernel global memory area for
702 contiguous memory allocations and optionally the
703 placement constraint by the physical address range of
704 memory allocations. A value of 0 disables CMA
705 altogether. For more information, see
706 kernel/dma/contiguous.c
710 Sets the size of kernel per-numa memory area for
711 contiguous memory allocations. A value of 0 disables
712 per-numa CMA altogether. And If this option is not
713 specified, the default value is 0.
714 With per-numa CMA enabled, DMA users on node nid will
715 first try to allocate buffer from the pernuma area
716 which is located in node nid, if the allocation fails,
717 they will fallback to the global default memory area.
719 numa_cma=<node>:nn[MG][,<node>:nn[MG]]
721 Sets the size of kernel numa memory area for
722 contiguous memory allocations. It will reserve CMA
723 area for the specified node.
725 With numa CMA enabled, DMA users on node nid will
726 first try to allocate buffer from the numa area
727 which is located in node nid, if the allocation fails,
728 they will fallback to the global default memory area.
730 cmo_free_hint= [PPC] Format: { yes | no }
731 Specify whether pages are marked as being inactive
732 when they are freed. This is used in CMO environments
733 to determine OS memory pressure for page stealing by
737 coherent_pool=nn[KMG] [ARM,KNL,EARLY]
738 Sets the size of memory pool for coherent, atomic dma
739 allocations, by default set to 256K.
741 com20020= [HW,NET] ARCnet - COM20020 chipset
743 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
745 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
749 ARCnet - COM90xx chipset (memory-mapped buffers)
750 Format: <io>[,<irq>[,<memstart>]]
752 condev= [HW,S390] console device
755 con3215_drop= [S390,EARLY] 3215 console drop mode.
757 When set to true, drop data on the 3215 console when
758 the console buffer is full. In this case the
759 operator using a 3270 terminal emulator (for example
760 x3270) does not have to enter the clear key for the
761 console output to advance and the kernel to continue.
762 This leads to a much faster boot time when a 3270
763 terminal emulator is active. If no 3270 terminal
764 emulator is used, this parameter has no effect.
766 console= [KNL] Output console device and options.
768 tty<n> Use the virtual console device <n>.
772 Use the specified serial port. The options are of
773 the form "bbbbpnf", where "bbbb" is the baud rate,
774 "p" is parity ("n", "o", or "e"), "n" is number of
775 bits, and "f" is flow control ("r" for RTS or
776 omit it). Default is "9600n8".
778 See Documentation/admin-guide/serial-console.rst for more
780 Documentation/networking/netconsole.rst for an
783 uart[8250],io,<addr>[,options]
784 uart[8250],mmio,<addr>[,options]
785 uart[8250],mmio16,<addr>[,options]
786 uart[8250],mmio32,<addr>[,options]
787 uart[8250],0x<addr>[,options]
788 Start an early, polled-mode console on the 8250/16550
789 UART at the specified I/O port or MMIO address,
790 switching to the matching ttyS device later.
791 MMIO inter-register address stride is either 8-bit
792 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
793 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
794 to be equivalent to 'mmio'. 'options' are specified in
795 the same format described for ttyS above; if unspecified,
796 the h/w is not re-initialized.
798 hvc<n> Use the hypervisor console device <n>. This is for
799 both Xen and PowerPC hypervisors.
802 Use to disable console output, i.e., to have kernel
803 console messages discarded.
804 This must be the only console= parameter used on the
807 If the device connected to the port is not a TTY but a braille
808 device, prepend "brl," before the device type, for instance
810 For now, only VisioBraille is supported.
813 [KNL] Change console messages format
815 By default we print messages on consoles in
816 "[time stamp] text\n" format (time stamp may not be
817 printed, depending on CONFIG_PRINTK_TIME or
818 `printk_time' param).
820 Switch to syslog format: "<%u>[time stamp] text\n"
821 IOW, each message will have a facility and loglevel
822 prefix. The format is similar to one used by syslog()
823 syscall, or to executing "dmesg -S --raw" or to reading
826 consoleblank= [KNL] The console blank (screen saver) timeout in
827 seconds. A value of 0 disables the blank timer.
831 [KNL] Change the default value for
832 /proc/<pid>/coredump_filter.
833 See also Documentation/filesystems/proc.rst.
835 coresight_cpu_debug.enable
838 Enable/disable the CPU sampling based debugging.
839 0: default value, disable debugging
840 1: enable debugging at boot time
842 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
844 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
846 cpuidle.off=1 [CPU_IDLE]
847 disable the cpuidle sub-system
850 [CPU_IDLE] Name of the cpuidle governor to use.
852 cpufreq.off=1 [CPU_FREQ]
853 disable the cpufreq sub-system
855 cpufreq.default_governor=
856 [CPU_FREQ] Name of the default cpufreq governor or
857 policy to use. This governor must be registered in the
858 kernel before the cpufreq driver probes.
861 [X86,EARLY] Delay for N microsec between assert and de-assert
862 of APIC INIT to start processors. This delay occurs
863 on every CPU online, such as boot, and resume from suspend.
867 [SMP] Enable/disable parallel bringup of secondary CPUs
869 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise
870 the parameter has no effect.
872 crash_kexec_post_notifiers
873 Run kdump after running panic-notifiers and dumping
874 kmsg. This only for the users who doubt kdump always
875 succeeds in any situation.
876 Note that this also increases risks of kdump failure,
877 because some panic notifiers can make the crashed
878 kernel more unstable.
880 crashkernel=size[KMG][@offset[KMG]]
881 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel'
882 upon panic. This parameter reserves the physical
883 memory region [offset, offset + size] for that kernel
884 image. If '@offset' is omitted, then a suitable offset
885 is selected automatically.
886 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region
887 under 4G first, and fall back to reserve region above
888 4G when '@offset' hasn't been specified.
889 See Documentation/admin-guide/kdump/kdump.rst for further details.
891 crashkernel=range1:size1[,range2:size2,...][@offset]
892 [KNL] Same as above, but depends on the memory
893 in the running system. The syntax of range is
894 start-[end] where start and end are both
895 a memory unit (amount[KMG]). See also
896 Documentation/admin-guide/kdump/kdump.rst for an example.
898 crashkernel=size[KMG],high
899 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be
901 Allow kernel to allocate physical memory region from top,
902 so could be above 4G if system have more than 4G ram
903 installed. Otherwise memory region will be allocated
904 below 4G, if available.
905 It will be ignored if crashkernel=X is specified.
906 crashkernel=size[KMG],low
907 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G.
908 When crashkernel=X,high is passed, kernel could allocate
909 physical memory region above 4G, that cause second kernel
910 crash on system that require some amount of low memory,
911 e.g. swiotlb requires at least 64M+32K low memory, also
912 enough extra low memory is needed to make sure DMA buffers
913 for 32-bit devices won't run out. Kernel would try to allocate
914 default size of memory below 4G automatically. The default
915 size is platform dependent.
916 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB)
919 --> loongarch: 128MiB
920 This one lets the user specify own low range under 4G
921 for second kernel instead.
922 0: to disable low allocation.
923 It will be ignored when crashkernel=X,high is not used
924 or memory reserved is below 4G.
927 [KNL] Disable crypto self-tests
932 cs89x0_media= [HW,NET]
933 Format: { rj45 | aui | bnc }
935 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU
936 function call handling. When switched on,
937 additional debug data is printed to the console
938 in case a hanging CPU is detected, and that
939 CPU is pinged again in order to try to resolve
940 the hang situation. The default value of this
941 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT
945 See header of drivers/s390/block/dasd_devmap.c.
947 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
948 (one device per port)
949 Format: <port#>,<type>
950 See also Documentation/input/devices/joystick-parport.rst
952 debug [KNL,EARLY] Enable kernel debugging (events log level).
955 [KNL,EARLY] Enable printing [hashed] pointers early in the
956 boot sequence. If enabled, we use a weak hash instead
957 of siphash to hash pointers. Use this option if you are
958 seeing instances of '(___ptrval___)') and need to see a
959 value (hashed pointer) instead. Cryptographically
960 insecure, please do not use on production kernels.
963 [KNL] verbose locking self-tests
965 Print debugging info while doing the locking API
967 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
968 (no extra messages), setting it to -1 (all bits set)
969 will print _a_lot_ more information - normally only
970 useful to lockdep developers.
972 debug_objects [KNL,EARLY] Enable object debugging
974 debug_guardpage_minorder=
975 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this
976 parameter allows control of the order of pages that will
977 be intentionally kept free (and hence protected) by the
978 buddy allocator. Bigger value increase the probability
979 of catching random memory corruption, but reduce the
980 amount of memory for normal system use. The maximum
981 possible value is MAX_PAGE_ORDER/2. Setting this
982 parameter to 1 or 2 should be enough to identify most
983 random memory corruption problems caused by bugs in
984 kernel or driver code when a CPU writes to (or reads
985 from) a random memory location. Note that there exists
986 a class of memory corruptions problems caused by buggy
987 H/W or F/W or by drivers badly programming DMA
988 (basically when memory is written at bus level and the
989 CPU MMU is bypassed) which are not detectable by
990 CONFIG_DEBUG_PAGEALLOC, hence this option will not
991 help tracking down these problems.
994 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
995 enables the feature at boot time. By default, it is
996 disabled and the system will work mostly the same as a
997 kernel built without CONFIG_DEBUG_PAGEALLOC.
998 Note: to get most of debug_pagealloc error reports, it's
999 useful to also enable the page_owner functionality.
1000 on: enable the feature
1002 debugfs= [KNL,EARLY] This parameter enables what is exposed to
1003 userspace and debugfs internal clients.
1004 Format: { on, no-mount, off }
1005 on: All functions are enabled.
1007 Filesystem is not registered but kernel clients can
1008 access APIs and a crashkernel can be used to read
1009 its content. There is nothing to mount.
1010 off: Filesystem is not registered and clients
1011 get a -EPERM as result when trying to register files
1012 or directories within debugfs.
1013 This is equivalent of the runtime functionality if
1014 debugfs was not enabled in the kernel at all.
1015 Default value is set in build-time with a kernel configuration.
1017 debugpat [X86] Enable PAT debugging
1020 [HW] The size of the default HugeTLB page. This is
1021 the size represented by the legacy /proc/ hugepages
1022 APIs. In addition, this is the default hugetlb size
1023 used for shmget(), mmap() and mounting hugetlbfs
1024 filesystems. If not specified, defaults to the
1025 architecture's default huge page size. Huge page
1026 sizes are architecture dependent. See also
1027 Documentation/admin-guide/mm/hugetlbpage.rst.
1030 deferred_probe_timeout=
1031 [KNL] Debugging option to set a timeout in seconds for
1032 deferred probe to give up waiting on dependencies to
1033 probe. Only specific dependencies (subsystems or
1034 drivers) that have opted in will be ignored. A timeout
1035 of 0 will timeout at the end of initcalls. If the time
1036 out hasn't expired, it'll be restarted by each
1037 successful driver registration. This option will also
1038 dump out devices still on the deferred probe list after
1041 delayacct [KNL] Enable per-task delay accounting
1043 dell_smm_hwmon.ignore_dmi=
1044 [HW] Continue probing hardware even if DMI data
1045 indicates that the driver is running on unsupported
1048 dell_smm_hwmon.force=
1049 [HW] Activate driver even if SMM BIOS signature does
1050 not match list of supported models and enable otherwise
1051 blacklisted features.
1053 dell_smm_hwmon.power_status=
1054 [HW] Report power status in /proc/i8k
1055 (disabled by default).
1057 dell_smm_hwmon.restricted=
1058 [HW] Allow controlling fans only if SYS_ADMIN
1061 dell_smm_hwmon.fan_mult=
1062 [HW] Factor to multiply fan speed with.
1064 dell_smm_hwmon.fan_max=
1065 [HW] Maximum configurable fan speed.
1068 Format: { on | off | def_only | inf_only | always }
1069 on: s390 zlib hardware support for compression on
1070 level 1 and decompression (default)
1071 off: No s390 zlib hardware support
1072 def_only: s390 zlib hardware support for deflate
1073 only (compression on level 1)
1074 inf_only: s390 zlib hardware support for inflate
1075 only (decompression)
1076 always: Same as 'on' but ignores the selected compression
1077 level always using hardware support (used for debugging)
1079 dhash_entries= [KNL]
1080 Set number of hash buckets for dentry cache.
1082 disable_1tb_segments [PPC,EARLY]
1083 Disables the use of 1TB hash page table segments. This
1084 causes the kernel to fall back to 256MB segments which
1085 can be useful when debugging issues that require an SLB
1089 See Documentation/networking/ipv6.rst.
1091 disable_radix [PPC,EARLY]
1092 Disable RADIX MMU mode on POWER9
1095 Disable TLBIE instruction. Currently does not work
1096 with KVM, with HASH MMU, or with coherent accelerators.
1098 disable_ddw [PPC/PSERIES,EARLY]
1099 Disable Dynamic DMA Window support. Use this
1100 to workaround buggy firmware.
1102 disable_ipv6= [IPV6]
1103 See Documentation/networking/ipv6.rst.
1105 disable_mtrr_cleanup [X86,EARLY]
1106 The kernel tries to adjust MTRR layout from continuous
1107 to discrete, to make X server driver able to add WB
1108 entry later. This parameter disables that.
1110 disable_mtrr_trim [X86, Intel and AMD only,EARLY]
1111 By default the kernel will trim any uncacheable
1112 memory out of your available memory pool based on
1113 MTRR settings. This parameter disables that behavior,
1114 possibly causing your machine to run very slowly.
1116 disable_timer_pin_1 [X86,EARLY]
1117 Disable PIN 1 of APIC timer
1118 Can be useful to work around chipset bugs.
1120 dis_ucode_ldr [X86] Disable the microcode loader.
1122 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1123 this option disables the debugging code at boot.
1125 dma_debug_entries=<number>
1126 This option allows to tune the number of preallocated
1127 entries for DMA-API debugging code. One entry is
1128 required per DMA-API allocation. Use this if the
1129 DMA-API debugging code disables itself because the
1130 architectural default is too low.
1132 dma_debug_driver=<driver_name>
1133 With this option the DMA-API debugging driver
1134 filter feature can be enabled at boot time. Just
1135 pass the driver to filter for as the parameter.
1136 The filter can be disabled or changed to another
1137 driver later using sysfs.
1139 reg_file_data_sampling=
1140 [X86] Controls mitigation for Register File Data
1141 Sampling (RFDS) vulnerability. RFDS is a CPU
1142 vulnerability which may allow userspace to infer
1143 kernel data values previously stored in floating point
1144 registers, vector registers, or integer registers.
1145 RFDS only affects Intel Atom processors.
1147 on: Turns ON the mitigation.
1148 off: Turns OFF the mitigation.
1150 This parameter overrides the compile time default set
1151 by CONFIG_MITIGATION_RFDS. Mitigation cannot be
1152 disabled when other VERW based mitigations (like MDS)
1153 are enabled. In order to disable RFDS mitigation all
1154 VERW based mitigations need to be disabled.
1157 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
1159 driver_async_probe= [KNL]
1160 List of driver names to be probed asynchronously. *
1161 matches with all driver names. If * is specified, the
1162 rest of the listed driver names are those that will NOT
1164 Format: <driver_name1>,<driver_name2>...
1166 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1167 Broken monitors, graphic adapters, KVMs and EDIDless
1168 panels may send no or incorrect EDID data sets.
1169 This parameter allows to specify an EDID data sets
1170 in the /lib/firmware directory that are used instead.
1171 Generic built-in EDID data sets are used, if one of
1172 edid/1024x768.bin, edid/1280x1024.bin,
1173 edid/1680x1050.bin, or edid/1920x1080.bin is given
1174 and no file with the same name exists. Details and
1175 instructions how to build your own EDID data are
1176 available in Documentation/admin-guide/edid.rst. An EDID
1177 data set will only be used for a particular connector,
1178 if its name and a colon are prepended to the EDID
1179 name. Each connector may use a unique EDID data
1180 set by separating the files with a comma. An EDID
1181 data set with no connector name will be used for
1182 any connectors not explicitly specified.
1186 dt_cpu_ftrs= [PPC,EARLY]
1187 Format: {"off" | "known"}
1188 Control how the dt_cpu_ftrs device-tree binding is
1189 used for CPU feature discovery and setup (if it
1191 off: Do not use it, fall back to legacy cpu table.
1192 known: Do not pass through unknown features to guests
1193 or userspace, only those that the kernel is aware of.
1195 dump_apple_properties [X86]
1196 Dump name and content of EFI device properties on
1197 x86 Macs. Useful for driver authors to determine
1198 what data is available or for reverse-engineering.
1200 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1201 <module>.dyndbg[="val"]
1202 Enable debug messages at boot time. See
1203 Documentation/admin-guide/dynamic-debug-howto.rst
1206 early_ioremap_debug [KNL,EARLY]
1207 Enable debug messages in early_ioremap support. This
1208 is useful for tracking down temporary early mappings
1209 which are not unmapped.
1211 earlycon= [KNL,EARLY] Output early console device and options.
1213 When used with no options, the early console is
1214 determined by stdout-path property in device tree's
1215 chosen node or the ACPI SPCR table if supported by
1218 cdns,<addr>[,options]
1219 Start an early, polled-mode console on a Cadence
1220 (xuartps) serial port at the specified address. Only
1221 supported option is baud rate. If baud rate is not
1222 specified, the serial port must already be setup and
1225 uart[8250],io,<addr>[,options[,uartclk]]
1226 uart[8250],mmio,<addr>[,options[,uartclk]]
1227 uart[8250],mmio32,<addr>[,options[,uartclk]]
1228 uart[8250],mmio32be,<addr>[,options[,uartclk]]
1229 uart[8250],0x<addr>[,options]
1230 Start an early, polled-mode console on the 8250/16550
1231 UART at the specified I/O port or MMIO address.
1232 MMIO inter-register address stride is either 8-bit
1233 (mmio) or 32-bit (mmio32 or mmio32be).
1234 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1235 to be equivalent to 'mmio'. 'options' are specified
1236 in the same format described for "console=ttyS<n>"; if
1237 unspecified, the h/w is not initialized. 'uartclk' is
1238 the uart clock frequency; if unspecified, it is set
1239 to 'BASE_BAUD' * 16.
1243 Start an early, polled-mode console on a pl011 serial
1244 port at the specified address. The pl011 serial port
1245 must already be setup and configured. Options are not
1246 yet supported. If 'mmio32' is specified, then only
1247 the driver will use only 32-bit accessors to read/write
1248 the device registers.
1251 Start an early console on a litex serial port at the
1252 specified address. The serial port must already be
1253 setup and configured. Options are not yet supported.
1256 Start an early, polled-mode console on a meson serial
1257 port at the specified address. The serial port must
1258 already be setup and configured. Options are not yet
1262 Start an early, polled-mode console on an msm serial
1263 port at the specified address. The serial port
1264 must already be setup and configured. Options are not
1267 msm_serial_dm,<addr>
1268 Start an early, polled-mode console on an msm serial
1269 dm port at the specified address. The serial port
1270 must already be setup and configured. Options are not
1274 Start an early, polled-mode console on a serial port
1275 of an Actions Semi SoC, such as S500 or S900, at the
1276 specified address. The serial port must already be
1277 setup and configured. Options are not yet supported.
1280 Start an early, polled-mode console on a serial port
1281 of an RDA Micro SoC, such as RDA8810PL, at the
1282 specified address. The serial port must already be
1283 setup and configured. Options are not yet supported.
1286 Use RISC-V SBI (Supervisor Binary Interface) for early
1289 smh Use ARM semihosting calls for early console.
1297 Use early console provided by serial driver available
1298 on Samsung SoCs, requires selecting proper type and
1299 a correct base address of the selected UART port. The
1300 serial port must already be setup and configured.
1301 Options are not yet supported.
1304 Start an early, polled-mode console on a lantiq serial
1305 (lqasc) port at the specified address. The serial port
1306 must already be setup and configured. Options are not
1311 Use early console provided by Freescale LP UART driver
1312 found on Freescale Vybrid and QorIQ LS1021A processors.
1313 A valid base address must be provided, and the serial
1314 port must already be setup and configured.
1318 Start an early, polled-mode, output-only console on the
1319 Freescale i.MX UART at the specified address. The UART
1320 must already be setup and configured.
1323 Start an early, polled-mode console on the
1324 Armada 3700 serial port at the specified
1325 address. The serial port must already be setup
1326 and configured. Options are not yet supported.
1329 Start an early, polled-mode console on a Qualcomm
1330 Generic Interface (GENI) based serial port at the
1331 specified address. The serial port must already be
1332 setup and configured. Options are not yet supported.
1335 Start an early, unaccelerated console on the EFI
1336 memory mapped framebuffer (if available). On cache
1337 coherent non-x86 systems that use system memory for
1338 the framebuffer, pass the 'ram' option so that it is
1339 mapped with the correct attributes.
1342 Use early console provided by Freescale LINFlexD UART
1343 serial driver for NXP S32V234 SoCs. A valid base
1344 address must be provided, and the serial port must
1345 already be setup and configured.
1347 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY]
1351 earlyprintk=serial[,ttySn[,baudrate]]
1352 earlyprintk=serial[,0x...[,baudrate]]
1353 earlyprintk=ttySn[,baudrate]
1354 earlyprintk=dbgp[debugController#]
1355 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1356 earlyprintk=xdbc[xhciController#]
1359 earlyprintk is useful when the kernel crashes before
1360 the normal console is initialized. It is not enabled by
1361 default because it has some cosmetic problems.
1363 Append ",keep" to not disable it when the real console
1366 Only one of vga, serial, or usb debug port can
1369 Currently only ttyS0 and ttyS1 may be specified by
1370 name. Other I/O ports may be explicitly specified
1371 on some architectures (x86 and arm at least) by
1372 replacing ttySn with an I/O port address, like this:
1373 earlyprintk=serial,0x1008,115200
1374 You can find the port for a given device in
1375 /proc/tty/driver/serial:
1376 2: uart:ST16650V2 port:00001008 irq:18 ...
1378 Interaction with the standard serial driver is not
1381 The VGA output is eventually overwritten by
1384 The xen option can only be used in Xen domains.
1386 The sclp output can only be used on s390.
1388 The bios output can only be used on SuperH.
1390 The optional "force" to "pciserial" enables use of a
1391 PCI device even when its classcode is not of the
1394 edac_report= [HW,EDAC] Control how to report EDAC event
1395 Format: {"on" | "off" | "force"}
1396 on: enable EDAC to report H/W event. May be overridden
1397 by other higher priority error reporting module.
1398 off: disable H/W event reporting through EDAC.
1399 force: enforce the use of EDAC to report H/W event.
1403 Format: {"off" | "on" | "skip[mbr]"}
1406 Format: { "debug", "disable_early_pci_dma",
1407 "nochunk", "noruntime", "nosoftreserve",
1408 "novamap", "no_disable_early_pci_dma" }
1409 debug: enable misc debug output.
1410 disable_early_pci_dma: disable the busmaster bit on all
1411 PCI bridges while in the EFI boot stub.
1412 nochunk: disable reading files in "chunks" in the EFI
1413 boot stub, as chunking can cause problems with some
1414 firmware implementations.
1415 noruntime : disable EFI runtime services support
1416 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1417 attribute may cause the kernel to reserve the
1418 memory range for a memory mapping driver to
1419 claim. Specify efi=nosoftreserve to disable this
1420 reservation and treat the memory by its base type
1421 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1422 novamap: do not call SetVirtualAddressMap().
1423 no_disable_early_pci_dma: Leave the busmaster bit set
1424 on all PCI bridges while in the EFI boot stub
1426 efi_no_storage_paranoia [EFI,X86,EARLY]
1427 Using this parameter you can use more than 50% of
1428 your efi variable storage. Use this parameter only if
1429 you are really sure that your UEFI does sane gc and
1430 fulfills the spec otherwise your board may brick.
1432 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI,X86,EARLY]
1433 Add arbitrary attribute to specific memory range by
1434 updating original EFI memory map.
1435 Region of memory which aa attribute is added to is
1438 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1439 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1440 attribute is added to range 0x100000000-0x180000000 and
1441 0x10a0000000-0x1120000000.
1443 If efi_fake_mem=8G@9G:0x40000 is specified, the
1444 EFI_MEMORY_SP(0x40000) attribute is added to
1445 range 0x240000000-0x43fffffff.
1447 Using this parameter you can do debugging of EFI memmap
1448 related features. For example, you can do debugging of
1449 Address Range Mirroring feature even if your box
1450 doesn't support it, or mark specific memory as
1453 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1454 that is to be dynamically loaded by Linux. If there are
1455 multiple variables with the same name but with different
1456 vendor GUIDs, all of them will be loaded. See
1457 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1460 eisa_irq_edge= [PARISC,HW]
1461 See header of drivers/parisc/eisa.c.
1463 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging
1466 This is designed to be used in conjunction with
1467 the boot argument: earlyprintk=vga
1469 This parameter works in place of the kgdboc parameter
1470 but can only be used if the backing tty is available
1471 very early in the boot process. For early debugging
1472 via a serial port see kgdboc_earlycon instead.
1475 See comment before function elanfreq_setup() in
1476 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1478 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY]
1479 Specifies physical address of start of kernel core
1480 image elf header and optionally the size. Generally
1481 kexec loader will pass this option to capture kernel.
1482 See Documentation/admin-guide/kdump/kdump.rst for details.
1484 enable_mtrr_cleanup [X86,EARLY]
1485 The kernel tries to adjust MTRR layout from continuous
1486 to discrete, to make X server driver able to add WB
1487 entry later. This parameter enables that.
1489 enable_timer_pin_1 [X86]
1490 Enable PIN 1 of APIC timer
1491 Can be useful to work around chipset bugs
1492 (in particular on some ATI chipsets).
1493 The kernel tries to set a reasonable default.
1495 enforcing= [SELINUX] Set initial enforcing status.
1497 See security/selinux/Kconfig help text.
1498 0 -- permissive (log only, no denials).
1499 1 -- enforcing (deny and log).
1501 Value can be changed at runtime via
1502 /sys/fs/selinux/enforce.
1505 Disable Error Record Serialization Table (ERST)
1508 ether= [HW,NET] Ethernet cards parameters
1509 This option is obsoleted by the "netdev=" option, which
1510 has equivalent usage. See its documentation for details.
1514 Permit 'security.evm' to be updated regardless of
1515 current integrity status.
1517 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier
1518 stages so cover more early boot allocations.
1519 Please note that as side effect some optimizations
1520 might be disabled to achieve that (e.g. parallelized
1521 memory initialization is disabled) so the boot process
1522 might take longer, especially on systems with a lot of
1523 memory. Available with CONFIG_PAGE_EXTENSION=y.
1528 fail_make_request=[KNL]
1529 General fault injection mechanism.
1530 Format: <interval>,<probability>,<space>,<times>
1531 See also Documentation/fault-injection/.
1534 Format: { initns | none }
1535 See Documentation/admin-guide/sysctl/net.rst for
1536 fb_tunnels_only_for_init_ns
1539 See Documentation/admin-guide/blockdev/floppy.rst.
1542 Forcefully enable Physical Address Extension (PAE).
1543 Many Pentium M systems disable PAE but may have a
1544 functionally usable PAE implementation.
1545 Warning: use of this parameter will taint the kernel
1546 and may cause unknown problems.
1549 Enable/disable Flexible Return and Event Delivery.
1550 Format: { on | off }
1551 on: enable FRED when it's present.
1552 off: disable FRED, the default setting.
1555 [FTRACE] will set and start the specified tracer
1556 as early as possible in order to facilitate early
1559 ftrace_boot_snapshot
1560 [FTRACE] On boot up, a snapshot will be taken of the
1561 ftrace ring buffer that can be read at:
1562 /sys/kernel/tracing/snapshot.
1563 This is useful if you need tracing information from kernel
1564 boot up that is likely to be overridden by user space
1565 start up functionality.
1567 Optionally, the snapshot can also be defined for a tracing
1568 instance that was created by the trace_instance= command
1571 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo
1573 The above will cause the "foo" tracing instance to trigger
1574 a snapshot at the end of boot up.
1576 ftrace_dump_on_oops[=orig_cpu]
1577 [FTRACE] will dump the trace buffers on oops.
1578 If no parameter is passed, ftrace will dump
1579 buffers of all CPUs, but if you pass orig_cpu, it will
1580 dump only the buffer of the CPU that triggered the
1583 ftrace_filter=[function-list]
1584 [FTRACE] Limit the functions traced by the function
1585 tracer at boot up. function-list is a comma-separated
1586 list of functions. This list can be changed at run
1587 time by the set_ftrace_filter file in the debugfs
1590 ftrace_notrace=[function-list]
1591 [FTRACE] Do not trace the functions specified in
1592 function-list. This list can be changed at run time
1593 by the set_ftrace_notrace file in the debugfs
1596 ftrace_graph_filter=[function-list]
1597 [FTRACE] Limit the top level callers functions traced
1598 by the function graph tracer at boot up.
1599 function-list is a comma-separated list of functions
1600 that can be changed at run time by the
1601 set_graph_function file in the debugfs tracing directory.
1603 ftrace_graph_notrace=[function-list]
1604 [FTRACE] Do not trace from the functions specified in
1605 function-list. This list is a comma-separated list of
1606 functions that can be changed at run time by the
1607 set_graph_notrace file in the debugfs tracing directory.
1609 ftrace_graph_max_depth=<uint>
1610 [FTRACE] Used with the function graph tracer. This is
1611 the max depth it will trace into a function. This value
1612 can be changed at run time by the max_graph_depth file
1613 in the tracefs tracing directory. default: 0 (no limit)
1615 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier
1616 devices by scanning the firmware to infer the
1617 consumer/supplier relationships. This feature is
1618 especially useful when drivers are loaded as modules as
1619 it ensures proper ordering of tasks like device probing
1620 (suppliers first, then consumers), supplier boot state
1621 clean up (only after all consumers have probed),
1622 suspend/resume & runtime PM (consumers first, then
1624 Format: { off | permissive | on | rpm }
1625 off -- Don't create device links from firmware info.
1626 permissive -- Create device links from firmware info
1627 but use it only for ordering boot state clean
1628 up (sync_state() calls).
1629 on -- Create device links from firmware info and use it
1630 to enforce probe and suspend/resume ordering.
1631 rpm -- Like "on", but also use to order runtime PM.
1633 fw_devlink.strict=<bool>
1634 [KNL,EARLY] Treat all inferred dependencies as mandatory
1635 dependencies. This only applies for fw_devlink=on|rpm.
1638 fw_devlink.sync_state =
1639 [KNL,EARLY] When all devices that could probe have finished
1640 probing, this parameter controls what to do with
1641 devices that haven't yet received their sync_state()
1643 Format: { strict | timeout }
1644 strict -- Default. Continue waiting on consumers to
1646 timeout -- Give up waiting on consumers and call
1647 sync_state() on any devices that haven't yet
1648 received their sync_state() calls after
1649 deferred_probe_timeout has expired or by
1650 late_initcall() if !CONFIG_MODULES.
1653 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1654 support via parallel port (up to 5 devices per port)
1655 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1656 See also Documentation/input/devices/joystick-parport.rst
1660 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART
1664 gather_data_sampling=
1665 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS)
1668 Gather Data Sampling is a hardware vulnerability which
1669 allows unprivileged speculative access to data which was
1670 previously stored in vector registers.
1672 This issue is mitigated by default in updated microcode.
1673 The mitigation may have a performance impact but can be
1674 disabled. On systems without the microcode mitigation
1675 disabling AVX serves as a mitigation.
1677 force: Disable AVX to mitigate systems without
1678 microcode mitigation. No effect if the microcode
1679 mitigation is present. Known to cause crashes in
1680 userspace with buggy AVX enumeration.
1682 off: Disable GDS mitigation.
1684 gcov_persist= [GCOV] When non-zero (default), profiling data for
1685 kernel modules is saved and remains accessible via
1686 debugfs, even when the module is unloaded/reloaded.
1687 When zero, profiling data is discarded and associated
1688 debugfs files are removed at module unload time.
1690 goldfish [X86] Enable the goldfish android emulator platform.
1691 Don't use this when you are not running on the
1694 gpio-mockup.gpio_mockup_ranges
1695 [HW] Sets the ranges of gpiochip of for this device.
1696 Format: <start1>,<end1>,<start2>,<end2>...
1697 gpio-mockup.gpio_mockup_named_lines
1698 [HW] Let the driver know GPIO lines should be named.
1700 gpt [EFI] Forces disk with valid GPT signature but
1701 invalid Protective MBR to be treated as GPT. If the
1702 primary GPT is corrupted, it enables the backup/alternate
1703 GPT to be used instead.
1705 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1706 the "Enable 0" bit of the configuration register.
1709 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1710 the "Enable 0" bit of the configuration register.
1713 grcan.select= [HW] Select which physical interface to use.
1716 grcan.txsize= [HW] Sets the size of the tx buffer.
1717 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1719 grcan.rxsize= [HW] Sets the size of the rx buffer.
1720 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1724 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
1725 hardening is enabled for this boot. Hardened
1726 usercopy checking is used to protect the kernel
1727 from reading or writing beyond known memory
1728 allocation boundaries as a proactive defense
1729 against bounds-checking flaws in the kernel's
1730 copy_to_user()/copy_from_user() interface.
1731 on Perform hardened usercopy checks (default).
1732 off Disable hardened usercopy checks.
1734 hardlockup_all_cpu_backtrace=
1735 [KNL] Should the hard-lockup detector generate
1736 backtraces on all cpus.
1739 hashdist= [KNL,NUMA] Large hashes allocated during boot
1740 are distributed across NUMA nodes. Defaults on
1741 for 64-bit NUMA, off otherwise.
1742 Format: 0 | 1 (for off | on)
1744 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1746 hd= [EIDE] (E)IDE hard drive subsystem geometry
1747 Format: <cyl>,<head>,<sect>
1750 Disable Hardware Error Source Table (HEST) support;
1751 corresponding firmware-first mode error processing
1752 logic will be disabled.
1754 hibernate= [HIBERNATION]
1755 noresume Don't check if there's a hibernation image
1756 present during boot.
1757 nocompress Don't compress/decompress hibernation images.
1758 no Disable hibernation and resume.
1759 protect_image Turn on image protection during restoration
1760 (that will set all pages holding image data
1761 during restoration read-only).
1763 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact
1764 size of <nn>. This works even on boxes that have no
1765 highmem otherwise. This also works to reduce highmem
1766 size on bigger boxes.
1768 highres= [KNL] Enable/disable high resolution timer mode.
1769 Valid parameters: "on", "off"
1774 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename).
1776 This allows setting the system's hostname during early
1777 startup. This sets the name returned by gethostname.
1778 Using this parameter to set the hostname makes it
1779 possible to ensure the hostname is correctly set before
1780 any userspace processes run, avoiding the possibility
1781 that a process may call gethostname before the hostname
1782 has been explicitly set, resulting in the calling
1783 process getting an incorrect result. The string must
1784 not exceed the maximum allowed hostname length (usually
1785 64 characters) and will be truncated otherwise.
1787 hpet= [X86-32,HPET] option to control HPET usage
1788 Format: { enable (default) | disable | force |
1790 disable: disable HPET and use PIT instead
1791 force: allow force enabled of undocumented chips (ICH4,
1793 verbose: show contents of HPET registers during setup
1795 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1796 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1798 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1799 If this follows hugepagesz (below), it specifies
1800 the number of pages of hugepagesz to be allocated.
1801 If this is the first HugeTLB parameter on the command
1802 line, it specifies the number of pages to allocate for
1803 the default huge page size. If using node format, the
1804 number of pages to allocate per-node can be specified.
1805 See also Documentation/admin-guide/mm/hugetlbpage.rst.
1806 Format: <integer> or (node format)
1807 <node>:<integer>[,<node>:<integer>]
1810 [HW] The size of the HugeTLB pages. This is used in
1811 conjunction with hugepages (above) to allocate huge
1812 pages of a specific size at boot. The pair
1813 hugepagesz=X hugepages=Y can be specified once for
1814 each supported huge page size. Huge page sizes are
1815 architecture dependent. See also
1816 Documentation/admin-guide/mm/hugetlbpage.rst.
1819 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation
1820 of gigantic hugepages. Or using node format, the size
1821 of a CMA area per node can be specified.
1822 Format: nn[KMGTPE] or (node format)
1823 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
1825 Reserve a CMA area of given size and allocate gigantic
1826 hugepages using the CMA allocator. If enabled, the
1827 boot-time allocation of gigantic hugepages is skipped.
1829 hugetlb_free_vmemmap=
1830 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
1832 Control if HugeTLB Vmemmap Optimization (HVO) is enabled.
1833 Allows heavy hugetlb users to free up some more
1834 memory (7 * PAGE_SIZE for each 2MB hugetlb page).
1835 Format: { on | off (default) }
1840 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
1843 Note that the vmemmap pages may be allocated from the added
1844 memory block itself when memory_hotplug.memmap_on_memory is
1845 enabled, those vmemmap pages cannot be optimized even if this
1846 feature is enabled. Other vmemmap pages not allocated from
1847 the added memory block itself do not be affected.
1850 [KNL] Should the hung task detector generate panics.
1853 A value of 1 instructs the kernel to panic when a
1854 hung task is detected. The default value is controlled
1855 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1856 option. The value selected by this boot parameter can
1857 be changed later by the kernel.hung_task_panic sysctl.
1859 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1860 terminal devices. Valid values: 0..8
1861 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1862 If specified, z/VM IUCV HVC accepts connections
1863 from listed z/VM user IDs only.
1865 hv_nopvspin [X86,HYPER_V,EARLY]
1866 Disables the paravirt spinlock optimizations
1867 which allow the hypervisor to 'idle' the guest
1870 i2c_bus= [HW] Override the default board specific I2C bus speed
1871 or register an additional I2C bus that is not
1872 registered from board initialization code.
1876 i8042.debug [HW] Toggle i8042 debug mode
1877 i8042.unmask_kbd_data
1878 [HW] Enable printing of interrupt data from the KBD port
1879 (disabled by default, and as a pre-condition
1880 requires that i8042.debug=1 be enabled)
1881 i8042.direct [HW] Put keyboard port into non-translated mode
1882 i8042.dumbkbd [HW] Pretend that controller can only read data from
1883 keyboard and cannot control its state
1884 (Don't attempt to blink the leds)
1885 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1886 i8042.nokbd [HW] Don't check/create keyboard port
1887 i8042.noloop [HW] Disable the AUX Loopback command while probing
1889 i8042.nomux [HW] Don't check presence of an active multiplexing
1891 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1893 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1894 i8042.reset [HW] Reset the controller during init, cleanup and
1895 suspend-to-ram transitions, only during s2r
1896 transitions, or never reset
1897 Format: { 1 | Y | y | 0 | N | n }
1898 1, Y, y: always reset controller
1899 0, N, n: don't ever reset controller
1900 Default: only on s2r transitions on x86; most other
1901 architectures force reset to be always executed
1902 i8042.unlock [HW] Unlock (ignore) the keylock
1903 i8042.kbdreset [HW] Reset device connected to KBD port
1905 [HW] Allow deferred probing upon i8042 probe errors
1909 i915.invert_brightness=
1910 [DRM] Invert the sense of the variable that is used to
1911 set the brightness of the panel backlight. Normally a
1912 brightness value of 0 indicates backlight switched off,
1913 and the maximum of the brightness value sets the backlight
1914 to maximum brightness. If this parameter is set to 0
1915 (default) and the machine requires it, or this parameter
1916 is set to 1, a brightness value of 0 sets the backlight
1917 to maximum brightness, and the maximum of the brightness
1918 value switches the backlight off.
1919 -1 -- never invert brightness
1920 0 -- machine default
1921 1 -- force brightness inversion
1923 ia32_emulation= [X86-64]
1925 When true, allows loading 32-bit programs and executing 32-bit
1926 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at
1927 boot time. When false, unconditionally disables IA32 emulation.
1930 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1934 Format: idle=poll, idle=halt, idle=nomwait
1935 Poll forces a polling idle loop that can slightly
1936 improve the performance of waking up a idle CPU, but
1937 will use a lot of power and make the system run hot.
1939 idle=halt: Halt is forced to be used for CPU idle.
1940 In such case C2/C3 won't be used again.
1941 idle=nomwait: Disable mwait for CPU C-states
1945 Allow force disabling of Shared Virtual Memory (SVA)
1946 support for the idxd driver. By default it is set to
1949 idxd.tc_override= [HW]
1951 Allow override of default traffic class configuration
1952 for the device. By default it is set to false (0).
1954 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1955 Format: { strict | legacy | 2008 | relaxed }
1958 Choose which programs will be accepted for execution
1959 based on the IEEE 754 NaN encoding(s) supported by
1960 the FPU and the NaN encoding requested with the value
1961 of an ELF file header flag individually set by each
1962 binary. Hardware implementations are permitted to
1963 support either or both of the legacy and the 2008 NaN
1966 Available settings are as follows:
1967 strict accept binaries that request a NaN encoding
1968 supported by the FPU
1969 legacy only accept legacy-NaN binaries, if supported
1971 2008 only accept 2008-NaN binaries, if supported
1973 relaxed accept any binaries regardless of whether
1974 supported by the FPU
1976 The FPU emulator is always able to support both NaN
1977 encodings, so if no FPU hardware is present or it has
1978 been disabled with 'nofpu', then the settings of
1979 'legacy' and '2008' strap the emulator accordingly,
1980 'relaxed' straps the emulator for both legacy-NaN and
1981 2008-NaN, whereas 'strict' enables legacy-NaN only on
1982 legacy processors and both NaN encodings on MIPS32 or
1985 The setting for ABS.fmt/NEG.fmt instruction execution
1986 mode generally follows that for the NaN encoding,
1987 except where unsupported by hardware.
1989 ignore_loglevel [KNL,EARLY]
1990 Ignore loglevel setting - this will print /all/
1991 kernel messages to the console. Useful for debugging.
1992 We also add it as printk module parameter, so users
1993 could change it dynamically, usually by
1994 /sys/module/printk/parameters/ignore_loglevel.
1997 Ignore RLIMIT_DATA setting for data mappings,
1998 print warning at first misuse. Can be changed via
1999 /sys/module/kernel/parameters/ignore_rlimit_data.
2001 ihash_entries= [KNL]
2002 Set number of hash buckets for inode cache.
2004 ima_appraise= [IMA] appraise integrity measurements
2005 Format: { "off" | "enforce" | "fix" | "log" }
2008 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
2009 The builtin appraise policy appraises all files
2012 ima_canonical_fmt [IMA]
2013 Use the canonical format for the binary runtime
2014 measurements, instead of host native format.
2017 Format: { md5 | sha1 | rmd160 | sha256 | sha384
2021 The list of supported hash algorithms is defined
2022 in crypto/hash_info.h.
2025 The builtin policies to load during IMA setup.
2026 Format: "tcb | appraise_tcb | secure_boot |
2027 fail_securely | critical_data"
2029 The "tcb" policy measures all programs exec'd, files
2030 mmap'd for exec, and all files opened with the read
2031 mode bit set by either the effective uid (euid=0) or
2034 The "appraise_tcb" policy appraises the integrity of
2035 all files owned by root.
2037 The "secure_boot" policy appraises the integrity
2038 of files (eg. kexec kernel image, kernel modules,
2039 firmware, policy, etc) based on file signatures.
2041 The "fail_securely" policy forces file signature
2042 verification failure also on privileged mounted
2043 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
2046 The "critical_data" policy measures kernel integrity
2049 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
2050 Load a policy which meets the needs of the Trusted
2051 Computing Base. This means IMA will measure all
2052 programs exec'd, files mmap'd for exec, and all files
2053 opened for read by uid=0.
2056 Select one of defined IMA measurements template formats.
2057 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" |
2062 [IMA] Define a custom template format.
2063 Format: { "field1|...|fieldN" }
2065 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
2066 Format: <min_file_size>
2067 Set the minimal file size for using asynchronous hash.
2068 If left unspecified, ahash usage is disabled.
2070 ahash performance varies for different data sizes on
2071 different crypto accelerators. This option can be used
2072 to achieve the best performance for a particular HW.
2074 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
2076 Set hashing buffer size. Default: 4k.
2078 ahash performance varies for different chunk sizes on
2079 different crypto accelerators. This option can be used
2080 to achieve best performance for particular HW.
2084 Run specified binary instead of /sbin/init as init
2087 initcall_debug [KNL] Trace initcalls as they are executed. Useful
2088 for working out where the kernel is dying during
2091 initcall_blacklist= [KNL] Do not execute a comma-separated list of
2092 initcall functions. Useful for debugging built-in
2093 modules and initcalls.
2095 initramfs_async= [KNL]
2098 This parameter controls whether the initramfs
2099 image is unpacked asynchronously, concurrently
2100 with devices being probed and
2101 initialized. This should normally just work,
2102 but as a debugging aid, one can get the
2103 historical behaviour of the initramfs
2104 unpacking being completed before device_ and
2107 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk
2109 initrdmem= [KNL,EARLY] Specify a physical address and size from which to
2110 load the initrd. If an initrd is compiled in or
2111 specified in the bootparams, it takes priority over this
2113 Format: ss[KMG],nn[KMG]
2116 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with
2119 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
2121 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes.
2123 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
2125 init_pkru= [X86] Specify the default memory protection keys rights
2126 register contents for all processes. 0x55555554 by
2127 default (disallow access to all but pkey 0). Can
2128 override in debugfs after boot.
2130 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
2133 int_pln_enable [X86] Enable power limit notification interrupt
2135 integrity_audit=[IMA]
2136 Format: { "0" | "1" }
2137 0 -- basic integrity auditing messages. (Default)
2138 1 -- additional integrity auditing messages.
2140 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
2142 Enable intel iommu driver.
2144 Disable intel iommu driver.
2145 igfx_off [Default Off]
2146 By default, gfx is mapped as normal device. If a gfx
2147 device has a dedicated DMAR unit, the DMAR unit is
2148 bypassed by not enabling DMAR with this option. In
2149 this case, gfx device will use physical address for
2151 strict [Default Off]
2152 Deprecated, equivalent to iommu.strict=1.
2153 sp_off [Default Off]
2154 By default, super page will be supported if Intel IOMMU
2155 has the capability. With this option, super page will
2158 Enable the Intel IOMMU scalable mode if the hardware
2159 advertises that it has support for the scalable mode
2162 Disallow use of the Intel IOMMU scalable mode.
2163 tboot_noforce [Default Off]
2164 Do not force the Intel IOMMU enabled under tboot.
2165 By default, tboot will force Intel IOMMU on, which
2166 could harm performance of some high-throughput
2167 devices like 40GBit network cards, even if identity
2169 Note that using this option lowers the security
2170 provided by tboot because it makes the system
2171 vulnerable to DMA attacks.
2173 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
2174 0 disables intel_idle and fall back on acpi_idle.
2175 1 to 9 specify maximum depth of C-state.
2177 intel_pstate= [X86,EARLY]
2179 Do not enable intel_pstate as the default
2180 scaling driver for the supported processors
2182 Use intel_pstate driver to bypass the scaling
2183 governors layer of cpufreq and provides it own
2184 algorithms for p-state selection. There are two
2185 P-state selection algorithms provided by
2186 intel_pstate in the active mode: powersave and
2187 performance. The way they both operate depends
2188 on whether or not the hardware managed P-states
2189 (HWP) feature has been enabled in the processor
2190 and possibly on the processor model.
2192 Use intel_pstate as a scaling driver, but configure it
2193 to work with generic cpufreq governors (instead of
2194 enabling its internal governor). This mode cannot be
2195 used along with the hardware-managed P-states (HWP)
2198 Enable intel_pstate on systems that prohibit it by default
2199 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2200 instead of acpi-cpufreq may disable platform features, such
2201 as thermal controls and power capping, that rely on ACPI
2202 P-States information being indicated to OSPM and therefore
2203 should be used with caution. This option does not work with
2204 processors that aren't supported by the intel_pstate driver
2205 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2207 Do not enable hardware P state control (HWP)
2210 Only load intel_pstate on systems which support
2211 hardware P state control (HWP) if available.
2213 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2214 Description Table, specifies preferred power management
2215 profile as "Enterprise Server" or "Performance Server",
2216 then this feature is turned on by default.
2218 Allow per-logical-CPU P-State performance control limits using
2219 cpufreq sysfs interface
2221 intremap= [X86-64,Intel-IOMMU,EARLY]
2222 on enable Interrupt Remapping (default)
2223 off disable Interrupt Remapping
2224 nosid disable Source ID checking
2226 BIOS x2APIC opt-out request will be ignored
2227 nopost disable Interrupt Posting
2229 iomem= Disable strict checking of access to MMIO memory
2230 strict regions from userspace.
2245 nobypass [PPC/POWERNV]
2246 Disable IOMMU bypass, using IOMMU for PCI devices.
2248 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices.
2249 Format: { "0" | "1" }
2250 0 - Try to allocate a 32-bit DMA address first, before
2251 falling back to the full range if needed.
2252 1 - Allocate directly from the full usable range,
2253 forcing Dual Address Cycle for PCI cards supporting
2254 greater than 32-bit addressing.
2256 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour
2257 Format: { "0" | "1" }
2259 Request that DMA unmap operations use deferred
2260 invalidation of hardware TLBs, for increased
2261 throughput at the cost of reduced device isolation.
2262 Will fall back to strict mode if not supported by
2263 the relevant IOMMU driver.
2265 DMA unmap operations invalidate IOMMU hardware TLBs
2267 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2268 Note: on x86, strict mode specified via one of the
2269 legacy driver-specific options takes precedence.
2272 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default.
2273 Format: { "0" | "1" }
2274 0 - Use IOMMU translation for DMA.
2275 1 - Bypass the IOMMU for DMA.
2276 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2278 io7= [HW] IO7 for Marvel-based Alpha systems
2279 See comment before marvel_specify_io7 in
2280 arch/alpha/kernel/core_marvel.c.
2282 io_delay= [X86,EARLY] I/O delay method
2284 Standard port 0x80 based delay
2286 Alternate port 0xed based delay (needed on some systems)
2288 Simple two microseconds delay
2293 See Documentation/admin-guide/nfs/nfsroot.rst.
2295 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V
2296 IPC identifiers from 32,768 to 16,777,216.
2298 irqaffinity= [SMP] Set the default irq affinity mask
2299 The argument is a cpu list, as described above.
2301 irqchip.gicv2_force_probe=
2304 Force the kernel to look for the second 4kB page
2305 of a GICv2 controller even if the memory range
2306 exposed by the device tree is too small.
2308 irqchip.gicv3_nolpi=
2310 Force the kernel to ignore the availability of
2311 LPIs (and by consequence ITSs). Intended for system
2312 that use the kernel as a bootloader, and thus want
2313 to let secondary kernels in charge of setting up
2316 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY]
2317 Enables support for pseudo-NMIs in the kernel. This
2318 requires the kernel to be built with
2319 CONFIG_ARM64_PSEUDO_NMI.
2322 When an interrupt is not handled search all handlers
2323 for it. Intended to get systems with badly broken
2327 When an interrupt is not handled search all handlers
2328 for it. Also check all handlers each timer
2329 interrupt. Intended to get systems with badly broken
2333 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2335 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2336 [Deprecated - use cpusets instead]
2337 Format: [flag-list,]<cpu-list>
2339 Specify one or more CPUs to isolate from disturbances
2340 specified in the flag list (default: domain):
2343 Disable the tick when a single task runs.
2345 A residual 1Hz tick is offloaded to workqueues, which you
2346 need to affine to housekeeping through the global
2347 workqueue's affinity configured via the
2348 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2349 by using the 'domain' flag described below.
2351 NOTE: by default the global workqueue runs on all CPUs,
2352 so to protect individual CPUs the 'cpumask' file has to
2353 be configured manually after bootup.
2356 Isolate from the general SMP balancing and scheduling
2357 algorithms. Note that performing domain isolation this way
2358 is irreversible: it's not possible to bring back a CPU to
2359 the domains once isolated through isolcpus. It's strongly
2360 advised to use cpusets instead to disable scheduler load
2361 balancing through the "cpuset.sched_load_balance" file.
2362 It offers a much more flexible interface where CPUs can
2363 move in and out of an isolated set anytime.
2365 You can move a process onto or off an "isolated" CPU via
2366 the CPU affinity syscalls or cpuset.
2367 <cpu number> begins at 0 and the maximum value is
2368 "number of CPUs in system - 1".
2372 Isolate from being targeted by managed interrupts
2373 which have an interrupt mask containing isolated
2374 CPUs. The affinity of managed interrupts is
2375 handled by the kernel and cannot be changed via
2376 the /proc/irq/* interfaces.
2378 This isolation is best effort and only effective
2379 if the automatically assigned interrupt mask of a
2380 device queue contains isolated and housekeeping
2381 CPUs. If housekeeping CPUs are online then such
2382 interrupts are directed to the housekeeping CPU
2383 so that IO submitted on the housekeeping CPU
2384 cannot disturb the isolated CPU.
2386 If a queue's affinity mask contains only isolated
2387 CPUs then this parameter has no effect on the
2388 interrupt routing decision, though interrupts are
2389 only delivered when tasks running on those
2390 isolated CPUs submit IO. IO submitted on
2391 housekeeping CPUs has no influence on those
2394 The format of <cpu-list> is described above.
2398 ivrs_ioapic [HW,X86-64]
2399 Provide an override to the IOAPIC-ID<->DEVICE-ID
2400 mapping provided in the IVRS ACPI table.
2401 By default, PCI segment is 0, and can be omitted.
2403 For example, to map IOAPIC-ID decimal 10 to
2404 PCI segment 0x1 and PCI device 00:14.0,
2405 write the parameter as:
2406 ivrs_ioapic=10@0001:00:14.0
2409 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0
2410 write the parameter as:
2411 ivrs_ioapic[10]=00:14.0
2412 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and
2413 PCI device 00:14.0 write the parameter as:
2414 ivrs_ioapic[10]=0001:00:14.0
2416 ivrs_hpet [HW,X86-64]
2417 Provide an override to the HPET-ID<->DEVICE-ID
2418 mapping provided in the IVRS ACPI table.
2419 By default, PCI segment is 0, and can be omitted.
2421 For example, to map HPET-ID decimal 10 to
2422 PCI segment 0x1 and PCI device 00:14.0,
2423 write the parameter as:
2424 ivrs_hpet=10@0001:00:14.0
2427 * To map HPET-ID decimal 0 to PCI device 00:14.0
2428 write the parameter as:
2429 ivrs_hpet[0]=00:14.0
2430 * To map HPET-ID decimal 10 to PCI segment 0x1 and
2431 PCI device 00:14.0 write the parameter as:
2432 ivrs_ioapic[10]=0001:00:14.0
2434 ivrs_acpihid [HW,X86-64]
2435 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2436 mapping provided in the IVRS ACPI table.
2437 By default, PCI segment is 0, and can be omitted.
2439 For example, to map UART-HID:UID AMD0020:0 to
2440 PCI segment 0x1 and PCI device ID 00:14.5,
2441 write the parameter as:
2442 ivrs_acpihid=AMD0020:0@0001:00:14.5
2445 * To map UART-HID:UID AMD0020:0 to PCI segment is 0,
2446 PCI device ID 00:14.5, write the parameter as:
2447 ivrs_acpihid[00:14.5]=AMD0020:0
2448 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and
2449 PCI device ID 00:14.5, write the parameter as:
2450 ivrs_acpihid[0001:00:14.5]=AMD0020:0
2452 js= [HW,JOY] Analog joystick
2453 See Documentation/input/joydev/joystick.rst.
2456 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2457 report on every invalid memory access. Without this
2458 parameter KASAN will print report only for the first
2461 keep_bootcon [KNL,EARLY]
2462 Do not unregister boot console at start. This is only
2463 useful for debugging when something happens in the window
2464 between unregistering the boot console and initializing
2467 keepinitrd [HW,ARM] See retain_initrd.
2469 kernelcore= [KNL,X86,IA-64,PPC,EARLY]
2470 Format: nn[KMGTPE] | nn% | "mirror"
2471 This parameter specifies the amount of memory usable by
2472 the kernel for non-movable allocations. The requested
2473 amount is spread evenly throughout all nodes in the
2474 system as ZONE_NORMAL. The remaining memory is used for
2475 movable memory in its own zone, ZONE_MOVABLE. In the
2476 event, a node is too small to have both ZONE_NORMAL and
2477 ZONE_MOVABLE, kernelcore memory will take priority and
2478 other nodes will have a larger ZONE_MOVABLE.
2480 ZONE_MOVABLE is used for the allocation of pages that
2481 may be reclaimed or moved by the page migration
2482 subsystem. Note that allocations like PTEs-from-HighMem
2483 still use the HighMem zone if it exists, and the Normal
2484 zone if it does not.
2486 It is possible to specify the exact amount of memory in
2487 the form of "nn[KMGTPE]", a percentage of total system
2488 memory in the form of "nn%", or "mirror". If "mirror"
2489 option is specified, mirrored (reliable) memory is used
2490 for non-movable allocations and remaining memory is used
2491 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2492 are exclusive, so you cannot specify multiple forms.
2494 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port.
2495 Format: <Controller#>[,poll interval]
2496 The controller # is the number of the ehci usb debug
2497 port as it is probed via PCI. The poll interval is
2498 optional and is the number seconds in between
2499 each poll cycle to the debug port in case you need
2500 the functionality for interrupting the kernel with
2501 gdb or control-c on the dbgp connection. When
2502 not using this parameter you use sysrq-g to break into
2503 the kernel debugger.
2505 kgdboc= [KGDB,HW] kgdb over consoles.
2506 Requires a tty driver that supports console polling,
2507 or a supported polling keyboard driver (non-usb).
2508 Serial only format: <serial_device>[,baud]
2509 keyboard only format: kbd
2510 keyboard and serial format: kbd,<serial_device>[,baud]
2511 Optional Kernel mode setting:
2512 kms, kbd format: kms,kbd
2513 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2515 kgdboc_earlycon= [KGDB,HW,EARLY]
2516 If the boot console provides the ability to read
2517 characters and can work in polling mode, you can use
2518 this parameter to tell kgdb to use it as a backend
2519 until the normal console is registered. Intended to
2520 be used together with the kgdboc parameter which
2521 specifies the normal console to transition to.
2523 The name of the early console should be specified
2524 as the value of this parameter. Note that the name of
2525 the early console might be different than the tty
2526 name passed to kgdboc. It's OK to leave the value
2527 blank and the first boot console that implements
2528 read() will be picked.
2530 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the
2531 kernel debugger at the earliest opportunity.
2533 kmac= [MIPS] Korina ethernet MAC address.
2534 Configure the RouterBoard 532 series on-chip
2535 Ethernet adapter MAC address.
2537 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable
2538 Valid arguments: on, off
2540 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2543 kprobe_event=[probe-list]
2544 [FTRACE] Add kprobe events and enable at boot time.
2545 The probe-list is a semicolon delimited list of probe
2546 definitions. Each definition is same as kprobe_events
2547 interface, but the parameters are comma delimited.
2548 For example, to add a kprobe event on vfs_read with
2549 arg1 and arg2, add to the command line;
2551 kprobe_event=p,vfs_read,$arg1,$arg2
2553 See also Documentation/trace/kprobetrace.rst "Kernel
2554 Boot Parameter" section.
2556 kpti= [ARM64,EARLY] Control page table isolation of
2557 user and kernel address spaces.
2558 Default: enabled on cores which need mitigation.
2562 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires
2563 CONFIG_KUNIT to be set to be fully enabled. The
2564 default value can be overridden via
2565 KUNIT_DEFAULT_ENABLED.
2566 Default is 1 (enabled)
2568 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2569 Default is 0 (don't ignore, but inject #GP)
2571 kvm.eager_page_split=
2572 [KVM,X86] Controls whether or not KVM will try to
2573 proactively split all huge pages during dirty logging.
2574 Eager page splitting reduces interruptions to vCPU
2575 execution by eliminating the write-protection faults
2576 and MMU lock contention that would otherwise be
2577 required to split huge pages lazily.
2579 VM workloads that rarely perform writes or that write
2580 only to a small region of VM memory may benefit from
2581 disabling eager page splitting to allow huge pages to
2582 still be used for reads.
2584 The behavior of eager page splitting depends on whether
2585 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If
2586 disabled, all huge pages in a memslot will be eagerly
2587 split when dirty logging is enabled on that memslot. If
2588 enabled, eager page splitting will be performed during
2589 the KVM_CLEAR_DIRTY ioctl, and only for the pages being
2592 Eager page splitting is only supported when kvm.tdp_mmu=Y.
2596 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2597 Default is false (don't support).
2600 [KVM] Controls the software workaround for the
2601 X86_BUG_ITLB_MULTIHIT bug.
2602 force : Always deploy workaround.
2603 off : Never deploy workaround.
2604 auto : Deploy workaround based on the presence of
2605 X86_BUG_ITLB_MULTIHIT.
2609 If the software workaround is enabled for the host,
2610 guests do need not to enable it for nested guests.
2612 kvm.nx_huge_pages_recovery_ratio=
2613 [KVM] Controls how many 4KiB pages are periodically zapped
2614 back to huge pages. 0 disables the recovery, otherwise if
2615 the value is N KVM will zap 1/Nth of the 4KiB pages every
2616 period (see below). The default is 60.
2618 kvm.nx_huge_pages_recovery_period_ms=
2619 [KVM] Controls the time period at which KVM zaps 4KiB pages
2620 back to huge pages. If the value is a non-zero N, KVM will
2621 zap a portion (see ratio above) of the pages every N msecs.
2622 If the value is 0 (the default), KVM will pick a period based
2623 on the ratio, such that a page is zapped after 1 hour on average.
2625 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in
2626 KVM/SVM. Default is 1 (enabled).
2628 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables,
2629 a.k.a. Two-Dimensional Page Tables. Default is 1
2630 (enabled). Disable by KVM if hardware lacks support
2634 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of
2637 none: Forcefully disable KVM.
2639 nvhe: Standard nVHE-based mode, without support for
2642 protected: nVHE-based mode with support for guests whose
2643 state is kept private from the host.
2645 nested: VHE-based mode with support for nested
2646 virtualization. Requires at least ARMv8.3
2649 Defaults to VHE/nVHE based on hardware support. Setting
2650 mode to "protected" will disable kexec and hibernation
2651 for the host. "nested" is experimental and should be
2652 used with extreme caution.
2654 kvm-arm.vgic_v3_group0_trap=
2655 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0
2658 kvm-arm.vgic_v3_group1_trap=
2659 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1
2662 kvm-arm.vgic_v3_common_trap=
2663 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common
2666 kvm-arm.vgic_v4_enable=
2667 [KVM,ARM,EARLY] Allow use of GICv4 for direct
2670 kvm_cma_resv_ratio=n [PPC,EARLY]
2671 Reserves given percentage from system memory area for
2672 contiguous memory allocation for KVM hash pagetable
2674 By default it reserves 5% of total system memory.
2678 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables,
2679 a.k.a. Two-Dimensional Page Tables. Default is 1
2680 (enabled). Disable by KVM if hardware lacks support
2683 kvm-intel.emulate_invalid_guest_state=
2684 [KVM,Intel] Control whether to emulate invalid guest
2685 state. Ignored if kvm-intel.enable_unrestricted_guest=1,
2686 as guest state is never invalid for unrestricted
2687 guests. This param doesn't apply to nested guests (L2),
2688 as KVM never emulates invalid L2 guest state.
2689 Default is 1 (enabled).
2691 kvm-intel.flexpriority=
2692 [KVM,Intel] Control KVM's use of FlexPriority feature
2693 (TPR shadow). Default is 1 (enabled). Disable by KVM if
2694 hardware lacks support for it.
2697 [KVM,Intel] Control nested virtualization feature in
2698 KVM/VMX. Default is 1 (enabled).
2700 kvm-intel.unrestricted_guest=
2701 [KVM,Intel] Control KVM's use of unrestricted guest
2702 feature (virtualized real and unpaged mode). Default
2703 is 1 (enabled). Disable by KVM if EPT is disabled or
2704 hardware lacks support for it.
2706 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2709 Valid arguments: never, cond, always
2711 always: L1D cache flush on every VMENTER.
2712 cond: Flush L1D on VMENTER only when the code between
2713 VMEXIT and VMENTER can leak host memory.
2714 never: Disables the mitigation
2716 Default is cond (do L1 cache flush in specific instances)
2718 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor
2719 Identification feature (tagged TLBs). Default is 1
2720 (enabled). Disable by KVM if hardware lacks support
2723 l1d_flush= [X86,INTEL,EARLY]
2724 Control mitigation for L1D based snooping vulnerability.
2726 Certain CPUs are vulnerable to an exploit against CPU
2727 internal buffers which can forward information to a
2728 disclosure gadget under certain conditions.
2730 In vulnerable processors, the speculatively
2731 forwarded data can be used in a cache side channel
2732 attack, to access data to which the attacker does
2733 not have direct access.
2735 This parameter controls the mitigation. The
2738 on - enable the interface for the mitigation
2740 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on
2743 The kernel PTE inversion protection is unconditionally
2744 enabled and cannot be disabled.
2747 Provides all available mitigations for the
2748 L1TF vulnerability. Disables SMT and
2749 enables all mitigations in the
2750 hypervisors, i.e. unconditional L1D flush.
2752 SMT control and L1D flush control via the
2753 sysfs interface is still possible after
2754 boot. Hypervisors will issue a warning
2755 when the first VM is started in a
2756 potentially insecure configuration,
2757 i.e. SMT enabled or L1D flush disabled.
2760 Same as 'full', but disables SMT and L1D
2761 flush runtime control. Implies the
2762 'nosmt=force' command line option.
2763 (i.e. sysfs control of SMT is disabled.)
2766 Leaves SMT enabled and enables the default
2767 hypervisor mitigation, i.e. conditional
2770 SMT control and L1D flush control via the
2771 sysfs interface is still possible after
2772 boot. Hypervisors will issue a warning
2773 when the first VM is started in a
2774 potentially insecure configuration,
2775 i.e. SMT enabled or L1D flush disabled.
2779 Disables SMT and enables the default
2780 hypervisor mitigation.
2782 SMT control and L1D flush control via the
2783 sysfs interface is still possible after
2784 boot. Hypervisors will issue a warning
2785 when the first VM is started in a
2786 potentially insecure configuration,
2787 i.e. SMT enabled or L1D flush disabled.
2790 Same as 'flush', but hypervisors will not
2791 warn when a VM is started in a potentially
2792 insecure configuration.
2795 Disables hypervisor mitigations and doesn't
2797 It also drops the swap size and available
2798 RAM limit restriction on both hypervisor and
2803 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2809 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS
2812 lapic= [X86,APIC] Do not use TSC deadline
2813 value for LAPIC timer one-shot implementation. Default
2814 back to the programmable timer unit in the LAPIC.
2815 Format: notscdeadline
2817 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer
2820 libata.dma= [LIBATA] DMA control
2821 libata.dma=0 Disable all PATA and SATA DMA
2822 libata.dma=1 PATA and SATA Disk DMA only
2823 libata.dma=2 ATAPI (CDROM) DMA only
2824 libata.dma=4 Compact Flash DMA only
2825 Combinations also work, so libata.dma=3 enables DMA
2826 for disks and CDROMs, but not CFs.
2828 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2829 libata.ignore_hpa=0 keep BIOS limits (default)
2830 libata.ignore_hpa=1 ignore limits, using full disk
2832 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2836 libata.force= [LIBATA] Force configurations. The format is a comma-
2837 separated list of "[ID:]VAL" where ID is PORT[.DEVICE].
2838 PORT and DEVICE are decimal numbers matching port, link
2839 or device. Basically, it matches the ATA ID string
2840 printed on console by libata. If the whole ID part is
2841 omitted, the last PORT and DEVICE values are used. If
2842 ID hasn't been specified yet, the configuration applies
2843 to all ports, links and devices.
2845 If only DEVICE is omitted, the parameter applies to
2846 the port and all links and devices behind it. DEVICE
2847 number of 0 either selects the first device or the
2848 first fan-out link behind PMP device. It does not
2849 select the host link. DEVICE number of 15 selects the
2850 host link and device attached to it.
2852 The VAL specifies the configuration to force. As long
2853 as there is no ambiguity, shortcut notation is allowed.
2854 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2855 The following configurations can be forced.
2857 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2858 Any ID with matching PORT is used.
2860 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2862 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2863 udma[/][16,25,33,44,66,100,133] notation is also
2866 * nohrst, nosrst, norst: suppress hard, soft and both
2869 * rstonce: only attempt one reset during hot-unplug
2872 * [no]dbdelay: Enable or disable the extra 200ms delay
2873 before debouncing a link PHY and device presence
2876 * [no]ncq: Turn on or off NCQ.
2878 * [no]ncqtrim: Enable or disable queued DSM TRIM.
2880 * [no]ncqati: Enable or disable NCQ trim on ATI chipset.
2882 * [no]trim: Enable or disable (unqueued) TRIM.
2884 * trim_zero: Indicate that TRIM command zeroes data.
2886 * max_trim_128m: Set 128M maximum trim size limit.
2888 * [no]dma: Turn on or off DMA transfers.
2890 * atapi_dmadir: Enable ATAPI DMADIR bridge support.
2892 * atapi_mod16_dma: Enable the use of ATAPI DMA for
2893 commands that are not a multiple of 16 bytes.
2895 * [no]dmalog: Enable or disable the use of the
2896 READ LOG DMA EXT command to access logs.
2898 * [no]iddevlog: Enable or disable access to the
2899 identify device data log.
2901 * [no]logdir: Enable or disable access to the general
2902 purpose log directory.
2904 * max_sec_128: Set transfer size limit to 128 sectors.
2906 * max_sec_1024: Set or clear transfer size limit to
2909 * max_sec_lba48: Set or clear transfer size limit to
2912 * [no]lpm: Enable or disable link power management.
2914 * [no]setxfer: Indicate if transfer speed mode setting
2917 * [no]fua: Disable or enable FUA (Force Unit Access)
2918 support for devices supporting this feature.
2920 * dump_id: Dump IDENTIFY data.
2922 * disable: Disable this device.
2924 If there are multiple matching configurations changing
2925 the same attribute, the last one is used.
2927 load_ramdisk= [RAM] [Deprecated]
2929 lockd.nlm_grace_period=P [NFS] Assign grace period.
2932 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2935 lockd.nlm_timeout=T [NFS] Assign timeout value.
2938 lockd.nlm_udpport=M [NFS] Assign UDP port.
2941 lockdown= [SECURITY,EARLY]
2942 { integrity | confidentiality }
2943 Enable the kernel lockdown feature. If set to
2944 integrity, kernel features that allow userland to
2945 modify the running kernel are disabled. If set to
2946 confidentiality, kernel features that allow userland
2947 to extract confidential information from the kernel
2950 locktorture.acq_writer_lim= [KNL]
2951 Set the time limit in jiffies for a lock
2952 acquisition. Acquisitions exceeding this limit
2953 will result in a splat once they do complete.
2955 locktorture.bind_readers= [KNL]
2956 Specify the list of CPUs to which the readers are
2959 locktorture.bind_writers= [KNL]
2960 Specify the list of CPUs to which the writers are
2963 locktorture.call_rcu_chains= [KNL]
2964 Specify the number of self-propagating call_rcu()
2965 chains to set up. These are used to ensure that
2966 there is a high probability of an RCU grace period
2967 in progress at any given time. Defaults to 0,
2968 which disables these call_rcu() chains.
2970 locktorture.long_hold= [KNL]
2971 Specify the duration in milliseconds for the
2972 occasional long-duration lock hold time. Defaults
2973 to 100 milliseconds. Select 0 to disable.
2975 locktorture.nested_locks= [KNL]
2976 Specify the maximum lock nesting depth that
2977 locktorture is to exercise, up to a limit of 8
2978 (MAX_NESTED_LOCKS). Specify zero to disable.
2979 Note that this parameter is ineffective on types
2980 of locks that do not support nested acquisition.
2982 locktorture.nreaders_stress= [KNL]
2983 Set the number of locking read-acquisition kthreads.
2984 Defaults to being automatically set based on the
2985 number of online CPUs.
2987 locktorture.nwriters_stress= [KNL]
2988 Set the number of locking write-acquisition kthreads.
2990 locktorture.onoff_holdoff= [KNL]
2991 Set time (s) after boot for CPU-hotplug testing.
2993 locktorture.onoff_interval= [KNL]
2994 Set time (s) between CPU-hotplug operations, or
2995 zero to disable CPU-hotplug testing.
2997 locktorture.rt_boost= [KNL]
2998 Do periodic testing of real-time lock priority
2999 boosting. Select 0 to disable, 1 to boost
3000 only rt_mutex, and 2 to boost unconditionally.
3001 Defaults to 2, which might seem to be an
3002 odd choice, but which should be harmless for
3003 non-real-time spinlocks, due to their disabling
3004 of preemption. Note that non-realtime mutexes
3007 locktorture.rt_boost_factor= [KNL]
3008 Number that determines how often and for how
3009 long priority boosting is exercised. This is
3010 scaled down by the number of writers, so that the
3011 number of boosts per unit time remains roughly
3012 constant as the number of writers increases.
3013 On the other hand, the duration of each boost
3014 increases with the number of writers.
3016 locktorture.shuffle_interval= [KNL]
3017 Set task-shuffle interval (jiffies). Shuffling
3018 tasks allows some CPUs to go into dyntick-idle
3019 mode during the locktorture test.
3021 locktorture.shutdown_secs= [KNL]
3022 Set time (s) after boot system shutdown. This
3023 is useful for hands-off automated testing.
3025 locktorture.stat_interval= [KNL]
3026 Time (s) between statistics printk()s.
3028 locktorture.stutter= [KNL]
3029 Time (s) to stutter testing, for example,
3030 specifying five seconds causes the test to run for
3031 five seconds, wait for five seconds, and so on.
3032 This tests the locking primitive's ability to
3033 transition abruptly to and from idle.
3035 locktorture.torture_type= [KNL]
3036 Specify the locking implementation to test.
3038 locktorture.verbose= [KNL]
3039 Enable additional printk() statements.
3041 locktorture.writer_fifo= [KNL]
3042 Run the write-side locktorture kthreads at
3043 sched_set_fifo() real-time priority.
3045 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
3048 loglevel= [KNL,EARLY]
3049 All Kernel Messages with a loglevel smaller than the
3050 console loglevel will be printed to the console. It can
3051 also be changed with klogd or other programs. The
3052 loglevels are defined as follows:
3054 0 (KERN_EMERG) system is unusable
3055 1 (KERN_ALERT) action must be taken immediately
3056 2 (KERN_CRIT) critical conditions
3057 3 (KERN_ERR) error conditions
3058 4 (KERN_WARNING) warning conditions
3059 5 (KERN_NOTICE) normal but significant condition
3060 6 (KERN_INFO) informational
3061 7 (KERN_DEBUG) debug-level messages
3063 log_buf_len=n[KMG] [KNL,EARLY]
3064 Sets the size of the printk ring buffer, in bytes.
3065 n must be a power of two and greater than the
3066 minimal size. The minimal size is defined by
3067 LOG_BUF_SHIFT kernel config parameter. There
3068 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config
3069 parameter that allows to increase the default size
3070 depending on the number of CPUs. See init/Kconfig
3073 logo.nologo [FB] Disables display of the built-in Linux logo.
3074 This may be used to provide more screen space for
3075 kernel log messages and is useful when debugging
3076 kernel boot problems.
3078 lp=0 [LP] Specify parallel ports to use, e.g,
3079 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
3080 lp=reset first parallel port). 'lp=0' disables the
3081 lp=auto printer driver. 'lp=reset' (which can be
3082 specified in addition to the ports) causes
3083 attached printers to be reset. Using
3084 lp=port1,port2,... specifies the parallel ports
3085 to associate lp devices with, starting with
3086 lp0. A port specification may be 'none' to skip
3087 that lp device, or a parport name such as
3088 'parport0'. Specifying 'lp=auto' instead of a
3089 port specification list means that device IDs
3090 from each port should be examined, to see if
3091 an IEEE 1284-compliant printer is attached; if
3092 so, the driver will manage that printer.
3093 See also header of drivers/char/lp.c.
3096 Sets loops_per_jiffy to given constant, thus avoiding
3097 time-consuming boot-time autodetection (up to 250 ms per
3098 CPU). 0 enables autodetection (default). To determine
3099 the correct value for your kernel, boot with normal
3100 autodetection and see what value is printed. Note that
3101 on SMP systems the preset will be applied to all CPUs,
3102 which is likely to cause problems if your CPUs need
3103 significantly divergent settings. An incorrect value
3104 will cause delays in the kernel to be wrong, leading to
3105 unpredictable I/O errors and other breakage. Although
3106 unlikely, in the extreme case this might damage your
3110 Format: <io>,<irq>,<dma>
3112 lsm.debug [SECURITY] Enable LSM initialization debugging output.
3115 [SECURITY] Choose order of LSM initialization. This
3116 overrides CONFIG_LSM, and the "security=" parameter.
3118 machvec= [IA-64] Force the use of a particular machine-vector
3119 (machvec) in a generic kernel.
3120 Example: machvec=hpzx1
3122 machtype= [Loongson] Share the same kernel image file between
3123 different yeeloong laptops.
3124 Example: machtype=lemote-yeeloong-2f-7inch
3126 max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater
3127 than or equal to this physical address is ignored.
3129 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
3130 will bring up during bootup. maxcpus=n : n >= 0 limits
3131 the kernel to bring up 'n' processors. Surely after
3132 bootup you can bring up the other plugged cpu by executing
3133 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
3134 only takes effect during system bootup.
3135 While n=0 is a special case, it is equivalent to "nosmp",
3136 which also disables the IO APIC.
3138 max_loop= [LOOP] The number of loop block devices that get
3139 (loop.max_loop) unconditionally pre-created at init time. The default
3140 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
3141 of statically allocating a predefined number, loop
3142 devices can be requested on-demand with the
3143 /dev/loop-control interface.
3145 mce [X86-32] Machine Check Exception
3147 mce=option [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst
3149 md= [HW] RAID subsystems devices and level
3150 See Documentation/admin-guide/md.rst.
3153 Format: <first>,<last>
3154 Specifies range of consoles to be captured by the MDA.
3156 mds= [X86,INTEL,EARLY]
3157 Control mitigation for the Micro-architectural Data
3158 Sampling (MDS) vulnerability.
3160 Certain CPUs are vulnerable to an exploit against CPU
3161 internal buffers which can forward information to a
3162 disclosure gadget under certain conditions.
3164 In vulnerable processors, the speculatively
3165 forwarded data can be used in a cache side channel
3166 attack, to access data to which the attacker does
3167 not have direct access.
3169 This parameter controls the MDS mitigation. The
3172 full - Enable MDS mitigation on vulnerable CPUs
3173 full,nosmt - Enable MDS mitigation and disable
3174 SMT on vulnerable CPUs
3175 off - Unconditionally disable MDS mitigation
3177 On TAA-affected machines, mds=off can be prevented by
3178 an active TAA mitigation as both vulnerabilities are
3179 mitigated with the same mechanism so in order to disable
3180 this mitigation, you need to specify tsx_async_abort=off
3183 Not specifying this option is equivalent to
3186 For details see: Documentation/admin-guide/hw-vuln/mds.rst
3188 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size.
3189 Must be specified, otherwise memory size will be 0.
3191 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount
3192 of memory Amount of memory to be used in cases
3196 2 when the kernel is not able to see the whole system memory;
3197 3 memory that lies after 'mem=' boundary is excluded from
3198 the hypervisor, then assigned to KVM guests.
3199 4 to limit the memory available for kdump kernel.
3201 [ARC,MICROBLAZE] - the limit applies only to low memory,
3202 high memory is not affected.
3204 [ARM64] - only limits memory covered by the linear
3205 mapping. The NOMAP regions are not affected.
3207 [X86] Work as limiting max address. Use together
3208 with memmap= to avoid physical address space collisions.
3209 Without memmap= PCI devices could be placed at addresses
3210 belonging to unused RAM.
3212 Note that this only takes effects during boot time since
3213 in above case 3, memory may need be hot added after boot
3214 if system memory of hypervisor is not sufficient.
3217 [ARM,MIPS,EARLY] - override the memory layout
3218 reported by firmware.
3219 Define a memory region of size nn[KMG] starting at
3221 Multiple different regions can be specified with
3222 multiple mem= parameters on the command line.
3224 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
3227 memblock=debug [KNL,EARLY] Enable memblock debug messages.
3230 [KNL,SH] Allow user to override the default size for
3231 per-device physically contiguous DMA buffers.
3233 memhp_default_state=online/offline/online_kernel/online_movable
3234 [KNL] Set the initial state for the memory hotplug
3235 onlining policy. If not specified, the default value is
3236 set according to the
3237 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
3239 See Documentation/admin-guide/mm/memory-hotplug.rst.
3241 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact
3242 E820 memory map, as specified by the user.
3243 Such memmap=exactmap lines can be constructed based on
3244 BIOS output or other requirements. See the memmap=nn@ss
3247 memmap=nn[KMG]@ss[KMG]
3248 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory.
3249 Region of memory to be used is from ss to ss+nn.
3250 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
3251 which limits max address to nn[KMG].
3252 Multiple different regions can be specified,
3255 memmap=100M@2G,100M#3G,1G!1024G
3257 memmap=nn[KMG]#ss[KMG]
3258 [KNL,ACPI,EARLY] Mark specific memory as ACPI data.
3259 Region of memory to be marked is from ss to ss+nn.
3261 memmap=nn[KMG]$ss[KMG]
3262 [KNL,ACPI,EARLY] Mark specific memory as reserved.
3263 Region of memory to be reserved is from ss to ss+nn.
3264 Example: Exclude memory from 0x18690000-0x1869ffff
3265 memmap=64K$0x18690000
3267 memmap=0x10000$0x18690000
3268 Some bootloaders may need an escape character before '$',
3269 like Grub2, otherwise '$' and the following number
3272 memmap=nn[KMG]!ss[KMG,EARLY]
3273 [KNL,X86] Mark specific memory as protected.
3274 Region of memory to be used, from ss to ss+nn.
3275 The memory region may be marked as e820 type 12 (0xc)
3276 and is NVDIMM or ADR memory.
3278 memmap=<size>%<offset>-<oldtype>+<newtype>
3279 [KNL,ACPI,EARLY] Convert memory within the specified region
3280 from <oldtype> to <newtype>. If "-<oldtype>" is left
3281 out, the whole region will be marked as <newtype>,
3282 even if previously unavailable. If "+<newtype>" is left
3283 out, matching memory will be removed. Types are
3284 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
3285 3 = ACPI, 12 = PRAM.
3287 memory_corruption_check=0/1 [X86,EARLY]
3288 Some BIOSes seem to corrupt the first 64k of
3289 memory when doing things like suspend/resume.
3290 Setting this option will scan the memory
3291 looking for corruption. Enabling this will
3292 both detect corruption and prevent the kernel
3293 from using the memory being corrupted.
3294 However, its intended as a diagnostic tool; if
3295 repeatable BIOS-originated corruption always
3296 affects the same memory, you can use memmap=
3297 to prevent the kernel from using that memory.
3299 memory_corruption_check_size=size [X86,EARLY]
3300 By default it checks for corruption in the low
3301 64k, making this memory unavailable for normal
3302 use. Use this parameter to scan for
3303 corruption in more or less memory.
3305 memory_corruption_check_period=seconds [X86,EARLY]
3306 By default it checks for corruption every 60
3307 seconds. Use this parameter to check at some
3308 other rate. 0 disables periodic checking.
3310 memory_hotplug.memmap_on_memory
3311 [KNL,X86,ARM] Boolean flag to enable this feature.
3312 Format: {on | off (default)}
3313 When enabled, runtime hotplugged memory will
3314 allocate its internal metadata (struct pages,
3315 those vmemmap pages cannot be optimized even
3316 if hugetlb_free_vmemmap is enabled) from the
3317 hotadded memory which will allow to hotadd a
3318 lot of memory without requiring additional
3320 This feature is disabled by default because it
3321 has some implication on large (e.g. GB)
3322 allocations in some configurations (e.g. small
3324 The state of the flag can be read in
3325 /sys/module/memory_hotplug/parameters/memmap_on_memory.
3326 Note that even when enabled, there are a few cases where
3327 the feature is not effective.
3329 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest
3331 default : 0 <disable>
3332 Specifies the number of memtest passes to be
3333 performed. Each pass selects another test
3334 pattern from a given set of patterns. Memtest
3335 fills the memory with this pattern, validates
3336 memory contents and reserves bad memory
3337 regions that are detected.
3339 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
3340 Valid arguments: on, off
3342 mem_encrypt=on: Activate SME
3343 mem_encrypt=off: Do not activate SME
3345 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst
3346 for details on when memory encryption can be activated.
3348 mem_sleep_default= [SUSPEND] Default system suspend mode:
3349 s2idle - Suspend-To-Idle
3350 shallow - Power-On Suspend or equivalent (if supported)
3351 deep - Suspend-To-RAM or equivalent (if supported)
3352 See Documentation/admin-guide/pm/sleep-states.rst.
3354 mfgpt_irq= [IA-32] Specify the IRQ to use for the
3355 Multi-Function General Purpose Timers on AMD Geode
3358 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
3359 the BIOS has incorrectly applied a workaround. TinyBIOS
3360 version 0.98 is known to be affected, 0.99 fixes the
3361 problem by letting the user disable the workaround.
3365 microcode.force_minrev= [X86]
3367 Enable or disable the microcode minimal revision
3368 enforcement for the runtime microcode loader.
3370 min_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory below this
3371 physical address is ignored.
3373 mini2440= [ARM,HW,KNL]
3374 Format:[0..2][b][c][t]
3376 MINI2440 configuration specification:
3377 0 - The attached screen is the 3.5" TFT
3378 1 - The attached screen is the 7" TFT
3379 2 - The VGA Shield is attached (1024x768)
3380 Leaving out the screen size parameter will not load
3381 the TFT driver, and the framebuffer will be left
3383 b - Enable backlight. The TFT backlight pin will be
3384 linked to the kernel VESA blanking code and a GPIO
3385 LED. This parameter is not necessary when using the
3387 c - Enable the s3c camera interface.
3388 t - Reserved for enabling touchscreen support. The
3389 touchscreen support is not enabled in the mainstream
3390 kernel as of 2.6.30, a preliminary port can be found
3391 in the "bleeding edge" mini2440 support kernel at
3392 https://repo.or.cz/w/linux-2.6/mini2440.git
3395 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for
3396 CPU vulnerabilities. This is a set of curated,
3397 arch-independent options, each of which is an
3398 aggregation of existing arch-specific options.
3401 Disable all optional CPU mitigations. This
3402 improves system performance, but it may also
3403 expose users to several CPU vulnerabilities.
3404 Equivalent to: if nokaslr then kpti=0 [ARM64]
3405 gather_data_sampling=off [X86]
3406 kvm.nx_huge_pages=off [X86]
3409 mmio_stale_data=off [X86]
3410 no_entry_flush [PPC]
3411 no_uaccess_flush [PPC]
3414 nospectre_bhb [ARM64]
3415 nospectre_v1 [X86,PPC]
3416 nospectre_v2 [X86,PPC,S390,ARM64]
3417 reg_file_data_sampling=off [X86]
3419 spec_rstack_overflow=off [X86]
3420 spec_store_bypass_disable=off [X86,PPC]
3421 spectre_v2_user=off [X86]
3422 srbds=off [X86,INTEL]
3423 ssbd=force-off [ARM64]
3424 tsx_async_abort=off [X86]
3427 This does not have any effect on
3428 kvm.nx_huge_pages when
3429 kvm.nx_huge_pages=force.
3432 Mitigate all CPU vulnerabilities, but leave SMT
3433 enabled, even if it's vulnerable. This is for
3434 users who don't want to be surprised by SMT
3435 getting disabled across kernel upgrades, or who
3436 have other ways of avoiding SMT-based attacks.
3437 Equivalent to: (default behavior)
3440 Mitigate all CPU vulnerabilities, disabling SMT
3441 if needed. This is for users who always want to
3442 be fully mitigated, even if it means losing SMT.
3443 Equivalent to: l1tf=flush,nosmt [X86]
3444 mds=full,nosmt [X86]
3445 tsx_async_abort=full,nosmt [X86]
3446 mmio_stale_data=full,nosmt [X86]
3447 retbleed=auto,nosmt [X86]
3450 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this
3451 parameter allows control of the logging verbosity for
3452 the additional memory initialisation checks. A value
3453 of 0 disables mminit logging and a level of 4 will
3454 log everything. Information is printed at KERN_DEBUG
3455 so loglevel=8 may also need to be specified.
3458 [X86,INTEL,EARLY] Control mitigation for the Processor
3459 MMIO Stale Data vulnerabilities.
3461 Processor MMIO Stale Data is a class of
3462 vulnerabilities that may expose data after an MMIO
3463 operation. Exposed data could originate or end in
3464 the same CPU buffers as affected by MDS and TAA.
3465 Therefore, similar to MDS and TAA, the mitigation
3466 is to clear the affected CPU buffers.
3468 This parameter controls the mitigation. The
3471 full - Enable mitigation on vulnerable CPUs
3473 full,nosmt - Enable mitigation and disable SMT on
3476 off - Unconditionally disable mitigation
3478 On MDS or TAA affected machines,
3479 mmio_stale_data=off can be prevented by an active
3480 MDS or TAA mitigation as these vulnerabilities are
3481 mitigated with the same mechanism so in order to
3482 disable this mitigation, you need to specify
3483 mds=off and tsx_async_abort=off too.
3485 Not specifying this option is equivalent to
3486 mmio_stale_data=full.
3489 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
3491 <module>.async_probe[=<bool>] [KNL]
3492 If no <bool> value is specified or if the value
3493 specified is not a valid <bool>, enable asynchronous
3494 probe on this module. Otherwise, enable/disable
3495 asynchronous probe on this module as indicated by the
3496 <bool> value. See also: module.async_probe
3498 module.async_probe=<bool>
3499 [KNL] When set to true, modules will use async probing
3500 by default. To enable/disable async probing for a
3501 specific module, use the module specific control that
3502 is documented under <module>.async_probe. When both
3503 module.async_probe and <module>.async_probe are
3504 specified, <module>.async_probe takes precedence for
3505 the specific module.
3507 module.enable_dups_trace
3508 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set,
3509 this means that duplicate request_module() calls will
3510 trigger a WARN_ON() instead of a pr_warn(). Note that
3511 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s
3512 will always be issued and this option does nothing.
3514 [KNL] When CONFIG_MODULE_SIG is set, this means that
3515 modules without (valid) signatures will fail to load.
3516 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3517 is always true, so this option does nothing.
3519 module_blacklist= [KNL] Do not load a comma-separated list of
3520 modules. Useful for debugging problem modules.
3523 [MOUSE] Maximum time between finger touching and
3524 leaving touchpad surface for touch to be considered
3525 a tap and be reported as a left button click (for
3526 touchpads working in absolute mode only).
3528 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3529 reporting absolute coordinates, such as tablets
3530 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3531 reporting absolute coordinates, such as tablets
3533 movablecore= [KNL,X86,IA-64,PPC,EARLY]
3534 Format: nn[KMGTPE] | nn%
3535 This parameter is the complement to kernelcore=, it
3536 specifies the amount of memory used for migratable
3537 allocations. If both kernelcore and movablecore is
3538 specified, then kernelcore will be at *least* the
3539 specified value but may be more. If movablecore on its
3540 own is specified, the administrator must be careful
3541 that the amount of memory usable for all allocations
3544 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory
3545 NUMA nodes to be movable. This means that the memory
3546 of such nodes will be usable only for movable
3547 allocations which rules out almost all kernel
3548 allocations. Use with caution!
3550 MTD_Partition= [MTD]
3551 Format: <name>,<region-number>,<size>,<offset>
3553 MTD_Region= [MTD] Format:
3554 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3557 See drivers/mtd/parsers/cmdlinepart.c
3560 ARM/S3C2412 JIVE boot control
3562 See arch/arm/mach-s3c/mach-jive.c
3564 mtouchusb.raw_coordinates=
3565 [HW] Make the MicroTouch USB driver use raw coordinates
3566 ('y', default) or cooked coordinates ('n')
3568 mtrr=debug [X86,EARLY]
3569 Enable printing debug information related to MTRR
3570 registers at boot time.
3572 mtrr_chunk_size=nn[KMG,X86,EARLY]
3573 used for mtrr cleanup. It is largest continuous chunk
3574 that could hold holes aka. UC entries.
3576 mtrr_gran_size=nn[KMG,X86,EARLY]
3577 Used for mtrr cleanup. It is granularity of mtrr block.
3579 Large value could prevent small alignment from
3582 mtrr_spare_reg_nr=n [X86,EARLY]
3584 Range: 0,7 : spare reg number
3586 Used for mtrr cleanup. It is spare mtrr entries number.
3587 Set to 2 or more if your graphical card needs more.
3589 multitce=off [PPC] This parameter disables the use of the pSeries
3590 firmware feature for updating multiple TCE entries
3593 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3595 netdev= [NET] Network devices parameters
3596 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3597 Note that mem_start is often overloaded to mean
3598 something different and driver-specific.
3599 This usage is only documented in each driver source
3602 netpoll.carrier_timeout=
3603 [NET] Specifies amount of time (in seconds) that
3604 netpoll should wait for a carrier. By default netpoll
3608 [NETFILTER] Enable connection tracking flow accounting
3609 0 to disable accounting
3610 1 to enable accounting
3614 [NFS] sets the pathname to the program which is used
3615 to update the NFS client cache entries.
3617 nfs.cache_getent_timeout=
3618 [NFS] sets the timeout after which an attempt to
3619 update a cache entry is deemed to have failed.
3621 nfs.callback_nr_threads=
3622 [NFSv4] set the total number of threads that the
3623 NFS client will assign to service NFSv4 callback
3626 nfs.callback_tcpport=
3627 [NFS] set the TCP port on which the NFSv4 callback
3628 channel should listen.
3631 [NFS] specifies the number of times the NFSv4 client
3632 retries the request before returning an EAGAIN error,
3633 after a reply of NFS4ERR_DELAY from the server.
3634 Only applies if the softerr mount option is enabled,
3635 and the specified value is >= 0.
3638 [NFS] enable 64-bit inode numbers.
3639 If zero, the NFS client will fake up a 32-bit inode
3640 number for the readdir() and stat() syscalls instead
3641 of returning the full 64-bit number.
3642 The default is to return 64-bit inode numbers.
3644 nfs.idmap_cache_timeout=
3645 [NFS] set the maximum lifetime for idmapper cache
3648 nfs.max_session_cb_slots=
3649 [NFSv4.1] Sets the maximum number of session
3650 slots the client will assign to the callback
3651 channel. This determines the maximum number of
3652 callbacks the client will process in parallel for
3653 a particular server.
3655 nfs.max_session_slots=
3656 [NFSv4.1] Sets the maximum number of session slots
3657 the client will attempt to negotiate with the server.
3658 This limits the number of simultaneous RPC requests
3659 that the client can send to the NFSv4.1 server.
3660 Note that there is little point in setting this
3661 value higher than the max_tcp_slot_table_limit.
3663 nfs.nfs4_disable_idmapping=
3664 [NFSv4] When set to the default of '1', this option
3665 ensures that both the RPC level authentication
3666 scheme and the NFS level operations agree to use
3667 numeric uids/gids if the mount is using the
3668 'sec=sys' security flavour. In effect it is
3669 disabling idmapping, which can make migration from
3670 legacy NFSv2/v3 systems to NFSv4 easier.
3671 Servers that do not support this mode of operation
3672 will be autodetected by the client, and it will fall
3673 back to using the idmapper.
3674 To turn off this behaviour, set the value to '0'.
3677 [NFS4] Specify an additional fixed unique ident-
3678 ification string that NFSv4 clients can insert into
3679 their nfs_client_id4 string. This is typically a
3680 UUID that is generated at system install time.
3682 nfs.recover_lost_locks=
3683 [NFSv4] Attempt to recover locks that were lost due
3684 to a lease timeout on the server. Please note that
3685 doing this risks data corruption, since there are
3686 no guarantees that the file will remain unchanged
3687 after the locks are lost.
3688 If you want to enable the kernel legacy behaviour of
3689 attempting to recover these locks, then set this
3691 The default parameter value of '0' causes the kernel
3692 not to attempt recovery of lost locks.
3694 nfs.send_implementation_id=
3695 [NFSv4.1] Send client implementation identification
3696 information in exchange_id requests.
3697 If zero, no implementation identification information
3699 The default is to send the implementation identification
3702 nfs4.layoutstats_timer=
3703 [NFSv4.2] Change the rate at which the kernel sends
3704 layoutstats to the pNFS metadata server.
3706 Setting this to value to 0 causes the kernel to use
3707 whatever value is the default set by the layout
3708 driver. A non-zero value sets the minimum interval
3709 in seconds between layoutstats transmissions.
3711 nfsd.inter_copy_offload_enable=
3712 [NFSv4.2] When set to 1, the server will support
3713 server-to-server copies for which this server is
3714 the destination of the copy.
3716 nfsd.nfs4_disable_idmapping=
3717 [NFSv4] When set to the default of '1', the NFSv4
3718 server will return only numeric uids and gids to
3719 clients using auth_sys, and will accept numeric uids
3720 and gids from such clients. This is intended to ease
3721 migration from NFSv2/v3.
3723 nfsd.nfsd4_ssc_umount_timeout=
3724 [NFSv4.2] When used as the destination of a
3725 server-to-server copy, knfsd temporarily mounts
3726 the source server. It caches the mount in case
3727 it will be needed again, and discards it if not
3728 used for the number of milliseconds specified by
3731 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3732 See Documentation/admin-guide/nfs/nfsroot.rst.
3734 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3735 See Documentation/admin-guide/nfs/nfsroot.rst.
3737 nfsrootdebug [NFS] enable nfsroot debugging messages.
3738 See Documentation/admin-guide/nfs/nfsroot.rst.
3740 nmi_backtrace.backtrace_idle [KNL]
3741 Dump stacks even of idle CPUs in response to an
3742 NMI stack-backtrace request.
3744 nmi_debug= [KNL,SH] Specify one or more actions to take
3745 when a NMI is triggered.
3746 Format: [state][,regs][,debounce][,die]
3748 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3749 Format: [panic,][nopanic,][num]
3751 0 - turn hardlockup detector in nmi_watchdog off
3752 1 - turn hardlockup detector in nmi_watchdog on
3753 When panic is specified, panic when an NMI watchdog
3754 timeout occurs (or 'nopanic' to not panic on an NMI
3755 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3756 To disable both hard and soft lockup detectors,
3757 please see 'nowatchdog'.
3758 This is useful when you use a panic=... timeout and
3759 need the box quickly up again.
3761 These settings can be accessed at runtime via
3762 the nmi_watchdog and hardlockup_panic sysctls.
3764 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3765 emulation library even if a 387 maths coprocessor
3768 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes.
3769 Forces kernel to use 3-level paging instead.
3771 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces
3772 kernel to use 4-level paging instead.
3774 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3775 caches in the slab allocator. Saves per-node memory,
3776 but will impact performance.
3780 noaltinstr [S390,EARLY] Disables alternative instructions
3781 patching (CPU alternatives feature).
3783 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any
3784 IOAPICs that may be present in the system.
3786 noautogroup Disable scheduler automatic task group creation.
3791 [HW] Never suspend the console
3792 Disable suspending of consoles during suspend and
3793 hibernate operations. Once disabled, debugging
3794 messages can reach various consoles while the rest
3795 of the system is being put to sleep (ie, while
3796 debugging driver suspend/resume hooks). This may
3797 not work reliably with all consoles, but is known
3798 to work with serial and VGA consoles.
3799 To facilitate more flexible debugging, we also add
3800 console_suspend, a printk module parameter to control
3801 it. Users could use console_suspend (usually
3802 /sys/module/printk/parameters/console_suspend) to
3803 turn on/off it dynamically.
3806 [KNL,EARLY] Disable object debugging
3808 nodsp [SH] Disable hardware DSP at boot time.
3810 noefi [EFI,EARLY] Disable EFI runtime services support.
3812 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel.
3817 This affects only 32-bit executables.
3818 noexec32=on: enable non-executable mappings (default)
3819 read doesn't imply executable mappings
3820 noexec32=off: disable non-executable mappings
3821 read implies executable mappings
3823 no_file_caps Tells the kernel not to honor file capabilities. The
3824 only way then for a file to be executed with privilege
3825 is to be setuid root or executed by root.
3827 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3829 nofsgsbase [X86] Disables FSGSBASE instructions.
3831 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3832 register save and restore. The kernel will only save
3833 legacy floating-point registers on task switch.
3835 nohalt [IA-64] Tells the kernel not to use the power saving
3836 function PAL_HALT_LIGHT when idle. This increases
3837 power-consumption. On the positive side, it reduces
3838 interrupt wake-up latency, which may improve performance
3839 in certain environments such as networked servers or
3844 Force pointers printed to the console or buffers to be
3845 unhashed. By default, when a pointer is printed via %p
3846 format string, that pointer is "hashed", i.e. obscured
3847 by hashing the pointer value. This is a security feature
3848 that hides actual kernel addresses from unprivileged
3849 users, but it also makes debugging the kernel more
3850 difficult since unequal pointers can no longer be
3851 compared. However, if this command-line option is
3852 specified, then all normal pointers will have their true
3853 value printed. This option should only be specified when
3854 debugging the kernel. Please do not use on production
3857 nohibernate [HIBERNATION] Disable hibernation and resume.
3859 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,SH] Forces the kernel to
3860 busy wait in do_idle() and not use the arch_cpu_idle()
3861 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3862 to be effective. This is useful on platforms where the
3863 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3864 correctly or when doing power measurements to evaluate
3865 the impact of the sleep instructions. This is also
3866 useful when using JTAG debugger.
3868 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings.
3870 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings.
3872 nohz= [KNL] Boottime enable/disable dynamic ticks
3873 Valid arguments: on, off
3876 nohz_full= [KNL,BOOT,SMP,ISOL]
3877 The argument is a cpu list, as described above.
3878 In kernels built with CONFIG_NO_HZ_FULL=y, set
3879 the specified list of CPUs whose tick will be stopped
3880 whenever possible. The boot CPU will be forced outside
3881 the range to maintain the timekeeping. Any CPUs
3882 in this list will have their RCU callbacks offloaded,
3883 just as if they had also been called out in the
3884 rcu_nocbs= boot parameter.
3886 Note that this argument takes precedence over
3887 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
3889 noinitrd [RAM] Tells the kernel not to load any configured
3892 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt
3894 [Deprecated - use intremap=off]
3898 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature.
3900 noiotrap [SH] Disables trapped I/O port accesses.
3902 noirqdebug [X86-32] Disables the code which attempts to detect and
3903 disable unhandled interrupt sources.
3905 noisapnp [ISAPNP] Disables ISA PnP code.
3907 nojitter [IA-64] Disables jitter checking for ITC timers.
3910 When CONFIG_RANDOMIZE_BASE is set, this disables
3911 kernel and module base offset ASLR (Address Space
3912 Layout Randomization).
3914 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page
3917 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver
3919 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC.
3921 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer.
3923 nomca [IA-64] Disable machine check abort handling
3925 nomce [X86-32] Disable Machine Check Exception
3927 nomfgpt [X86-32] Disable Multi-Function General Purpose
3928 Timer usage (for AMD Geode machines).
3930 nomodeset Disable kernel modesetting. Most systems' firmware
3931 sets up a display mode and provides framebuffer memory
3932 for output. With nomodeset, DRM and fbdev drivers will
3933 not load if they could possibly displace the pre-
3934 initialized output. Only the system framebuffer will
3935 be available for use. The respective drivers will not
3936 perform display-mode changes or accelerated rendering.
3938 Useful as error fallback, or for testing and debugging.
3940 nomodule Disable module load
3942 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3943 shutdown the other cpus. Instead use the REBOOT_VECTOR
3946 nopat [X86,EARLY] Disable PAT (page attribute table extension of
3947 pagetables) support.
3949 nopcid [X86-64,EARLY] Disable the PCID cpu feature.
3951 nopku [X86] Disable Memory Protection Keys CPU feature found
3954 nopti [X86-64,EARLY]
3955 Equivalent to pti=off
3957 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY]
3958 Disables the PV optimizations forcing the guest to run
3959 as generic guest with no PV drivers. Currently support
3960 XEN HVM, KVM, HYPER_V and VMWARE guest.
3962 nopvspin [X86,XEN,KVM,EARLY]
3963 Disables the qspinlock slow path using PV optimizations
3964 which allow the hypervisor to 'idle' the guest on lock
3967 norandmaps Don't use address space randomization. Equivalent to
3968 echo 0 > /proc/sys/kernel/randomize_va_space
3970 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3971 with UP alternatives
3973 noresume [SWSUSP] Disables resume and restores original swap
3978 no-scroll [VGA] Disables scrollback.
3979 This is required for the Braillex ib80-piezo Braille
3980 reader made by F.H. Papenmeier (Germany).
3982 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support.
3985 Disable SMAP (Supervisor Mode Access Prevention)
3986 even if it is supported by processor.
3988 nosmep [PPC64s,EARLY]
3989 Disable SMEP (Supervisor Mode Execution Prevention)
3990 even if it is supported by processor.
3992 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel,
3993 and disable the IO APIC. legacy for "maxcpus=0".
3995 nosmt [KNL,MIPS,PPC,S390,EARLY] Disable symmetric multithreading (SMT).
3996 Equivalent to smt=1.
3998 [KNL,X86,PPC] Disable symmetric multithreading (SMT).
3999 nosmt=force: Force disable SMT, cannot be undone
4000 via the sysfs control file.
4002 nosoftlockup [KNL] Disable the soft-lockup detector.
4004 nospec_store_bypass_disable
4005 [HW,EARLY] Disable all mitigations for the Speculative
4006 Store Bypass vulnerability
4008 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch
4009 history injection) vulnerability. System may allow data leaks
4012 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1
4013 (bounds check bypass). With this option data leaks are
4014 possible in the system.
4016 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations
4017 for the Spectre variant 2 (indirect branch
4018 prediction) vulnerability. System may allow data
4019 leaks with this option.
4021 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,EARLY] Disable
4022 paravirtualized steal time accounting. steal time is
4023 computed, but won't influence scheduler behaviour
4025 nosync [HW,M68K] Disables sync negotiation for all devices.
4027 no_timer_check [X86,APIC] Disables the code which tests for
4028 broken timer IRQ sources.
4031 [PPC,EARLY] Don't flush the L1-D cache after accessing user data.
4033 novmcoredd [KNL,KDUMP]
4034 Disable device dump. Device dump allows drivers to
4035 append dump data to vmcore so you can collect driver
4036 specified debug info. Drivers can append the data
4037 without any limit and this data is stored in memory,
4038 so this may cause significant memory stress. Disabling
4039 device dump can help save memory but the driver debug
4040 data will be no longer available. This parameter
4041 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
4045 [X86,PV_OPS,EARLY] Disable paravirtualized VMware
4046 scheduler clock and use the default one.
4048 nowatchdog [KNL] Disable both lockup detectors, i.e.
4049 soft-lockup and NMI watchdog (hard-lockup).
4053 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode.
4055 NOTE: this parameter will be ignored on systems with the
4056 LEGACY_XAPIC_DISABLED bit set in the
4057 IA32_XAPIC_DISABLE_STATUS MSR.
4059 noxsave [BUGS=X86] Disables x86 extended register state save
4060 and restore using xsave. The kernel will fallback to
4061 enabling legacy floating-point and sse state.
4063 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
4064 register states. The kernel will fall back to use
4065 xsave to save the states. By using this parameter,
4066 performance of saving the states is degraded because
4067 xsave doesn't support modified optimization while
4068 xsaveopt supports it on xsaveopt enabled systems.
4070 noxsaves [X86] Disables xsaves and xrstors used in saving and
4071 restoring x86 extended register state in compacted
4072 form of xsave area. The kernel will fall back to use
4073 xsaveopt and xrstor to save and restore the states
4074 in standard form of xsave area. By using this
4075 parameter, xsave area per process might occupy more
4076 memory on xsaves enabled systems.
4078 nps_mtm_hs_ctr= [KNL,ARC]
4079 This parameter sets the maximum duration, in
4080 cycles, each HW thread of the CTOP can run
4081 without interruptions, before HW switches it.
4082 The actual maximum duration is 16 times this
4084 Format: integer between 1 and 255
4087 nptcg= [IA-64] Override max number of concurrent global TLB
4088 purges which is reported from either PAL_VM_SUMMARY or
4091 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
4092 could support. nr_cpus=n : n >= 1 limits the kernel to
4093 support 'n' processors. It could be larger than the
4094 number of already plugged CPU during bootup, later in
4095 runtime you can physically add extra cpu until it reaches
4096 n. So during boot up some boot time memory for per-cpu
4097 variables need be pre-allocated for later physical cpu
4100 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
4102 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY]
4103 Disable NUMA, Only set up a single NUMA node
4104 spanning all memory.
4106 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
4108 Allowed values are enable and disable
4110 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
4111 'node', 'default' can be specified
4112 This can be set from sysctl after boot.
4113 See Documentation/admin-guide/sysctl/vm.rst for details.
4115 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver.
4116 See Documentation/core-api/debugging-via-ohci1394.rst for more
4119 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
4120 Rather than timing out after 20 ms if an EC
4121 command is not properly ACKed, override the length
4122 of the timeout. We have interrupts disabled while
4123 waiting for the ACK, so if this is set too high
4124 interrupts *may* be lost!
4126 omap_mux= [OMAP] Override bootloader pin multiplexing.
4127 Format: <mux_mode0.mode_name=value>...
4128 For example, to override I2C bus2:
4129 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
4131 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
4133 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
4135 boundary - index of last SLC block on Flex-OneNAND.
4136 The remaining blocks are configured as MLC blocks.
4137 lock - Configure if Flex-OneNAND boundary should be locked.
4138 Once locked, the boundary cannot be changed.
4139 1 indicates lock status, 0 indicates unlock status.
4141 oops=panic [KNL,EARLY]
4142 Always panic on oopses. Default is to just kill the
4143 process, but there is a small probability of
4144 deadlocking the machine.
4145 This will also cause panics on machine check exceptions.
4146 Useful together with panic=30 to trigger a reboot.
4149 [KNL] Boolean flag to control whether the page allocator
4150 should randomize its free lists. The randomization may
4151 be automatically enabled if the kernel detects it is
4152 running on a platform with a direct-mapped memory-side
4153 cache, and this parameter can be used to
4154 override/disable that behavior. The state of the flag
4155 can be read from sysfs at:
4156 /sys/module/page_alloc/parameters/shuffle.
4158 page_owner= [KNL,EARLY] Boot-time page_owner enabling option.
4159 Storage of the information about who allocated
4160 each page is disabled in default. With this switch,
4162 on: enable the feature
4164 page_poison= [KNL,EARLY] Boot-time parameter changing the state of
4165 poisoning on the buddy allocator, available with
4166 CONFIG_PAGE_POISONING=y.
4167 off: turn off poisoning (default)
4168 on: turn on poisoning
4170 page_reporting.page_reporting_order=
4171 [KNL] Minimal page reporting order
4173 Adjust the minimal page reporting order. The page
4174 reporting is disabled when it exceeds MAX_PAGE_ORDER.
4176 panic= [KNL] Kernel behaviour on panic: delay <timeout>
4177 timeout > 0: seconds before rebooting
4178 timeout = 0: wait forever
4179 timeout < 0: reboot immediately
4182 panic_on_taint= [KNL,EARLY]
4183 Bitmask for conditionally calling panic() in add_taint()
4184 Format: <hex>[,nousertaint]
4185 Hexadecimal bitmask representing the set of TAINT flags
4186 that will cause the kernel to panic when add_taint() is
4187 called with any of the flags in this set.
4188 The optional switch "nousertaint" can be utilized to
4189 prevent userspace forced crashes by writing to sysctl
4190 /proc/sys/kernel/tainted any flagset matching with the
4191 bitmask set on panic_on_taint.
4192 See Documentation/admin-guide/tainted-kernels.rst for
4193 extra details on the taint flags that users can pick
4194 to compose the bitmask to assign to panic_on_taint.
4196 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump
4199 panic_print= Bitmask for printing system info when panic happens.
4200 User can chose combination of the following bits:
4201 bit 0: print all tasks info
4202 bit 1: print system memory info
4203 bit 2: print timer info
4204 bit 3: print locks info if CONFIG_LOCKDEP is on
4205 bit 4: print ftrace buffer
4206 bit 5: print all printk messages in buffer
4207 bit 6: print all CPUs backtrace (if available in the arch)
4208 *Be aware* that this option may print a _lot_ of lines,
4209 so there are risks of losing older messages in the log.
4210 Use this option carefully, maybe worth to setup a
4211 bigger log buffer with "log_buf_len" along with this.
4213 parkbd.port= [HW] Parallel port number the keyboard adapter is
4214 connected to, default is 0.
4216 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
4217 0 for XT, 1 for AT (default is AT).
4220 parport= [HW,PPT] Specify parallel ports. 0 disables.
4221 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
4222 Use 'auto' to force the driver to use any
4223 IRQ/DMA settings detected (the default is to
4224 ignore detected IRQ/DMA settings because of
4225 possible conflicts). You can specify the base
4226 address, IRQ, and DMA settings; IRQ and DMA
4227 should be numbers, or 'auto' (for using detected
4228 settings on that particular port), or 'nofifo'
4229 (to avoid using a FIFO even if it is detected).
4230 Parallel ports are assigned in the order they
4231 are specified on the command line, starting
4234 parport_init_mode= [HW,PPT]
4235 Configure VIA parallel port to operate in
4236 a specific mode. This is necessary on Pegasos
4237 computer where firmware has no options for setting
4238 up parallel port mode and sets it to spp.
4239 Currently this function knows 686a and 8231 chips.
4240 Format: [spp|ps2|epp|ecp|ecpepp]
4242 pata_legacy.all= [HW,LIBATA]
4244 Set to non-zero to probe primary and secondary ISA
4245 port ranges on PCI systems where no PCI PATA device
4246 has been found at either range. Disabled by default.
4248 pata_legacy.autospeed= [HW,LIBATA]
4250 Set to non-zero if a chip is present that snoops speed
4251 changes. Disabled by default.
4253 pata_legacy.ht6560a= [HW,LIBATA]
4255 Set to 1, 2, or 3 for HT 6560A on the primary channel,
4256 the secondary channel, or both channels respectively.
4257 Disabled by default.
4259 pata_legacy.ht6560b= [HW,LIBATA]
4261 Set to 1, 2, or 3 for HT 6560B on the primary channel,
4262 the secondary channel, or both channels respectively.
4263 Disabled by default.
4265 pata_legacy.iordy_mask= [HW,LIBATA]
4267 IORDY enable mask. Set individual bits to allow IORDY
4268 for the respective channel. Bit 0 is for the first
4269 legacy channel handled by this driver, bit 1 is for
4270 the second channel, and so on. The sequence will often
4271 correspond to the primary legacy channel, the secondary
4272 legacy channel, and so on, but the handling of a PCI
4273 bus and the use of other driver options may interfere
4274 with the sequence. By default IORDY is allowed across
4277 pata_legacy.opti82c46x= [HW,LIBATA]
4279 Set to 1, 2, or 3 for Opti 82c611A on the primary
4280 channel, the secondary channel, or both channels
4281 respectively. Disabled by default.
4283 pata_legacy.opti82c611a= [HW,LIBATA]
4285 Set to 1, 2, or 3 for Opti 82c465MV on the primary
4286 channel, the secondary channel, or both channels
4287 respectively. Disabled by default.
4289 pata_legacy.pio_mask= [HW,LIBATA]
4291 PIO mode mask for autospeed devices. Set individual
4292 bits to allow the use of the respective PIO modes.
4293 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
4294 All modes allowed by default.
4296 pata_legacy.probe_all= [HW,LIBATA]
4298 Set to non-zero to probe tertiary and further ISA
4299 port ranges on PCI systems. Disabled by default.
4301 pata_legacy.probe_mask= [HW,LIBATA]
4303 Probe mask for legacy ISA PATA ports. Depending on
4304 platform configuration and the use of other driver
4305 options up to 6 legacy ports are supported: 0x1f0,
4306 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
4307 of individual ports can be disabled by setting the
4308 corresponding bits in the mask to 1. Bit 0 is for
4309 the first port in the list above (0x1f0), and so on.
4310 By default all supported ports are probed.
4312 pata_legacy.qdi= [HW,LIBATA]
4314 Set to non-zero to probe QDI controllers. By default
4315 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
4317 pata_legacy.winbond= [HW,LIBATA]
4319 Set to non-zero to probe Winbond controllers. Use
4320 the standard I/O port (0x130) if 1, otherwise the
4321 value given is the I/O port to use (typically 0x1b0).
4322 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
4325 pata_platform.pio_mask= [HW,LIBATA]
4327 Supported PIO mode mask. Set individual bits to allow
4328 the use of the respective PIO modes. Bit 0 is for
4329 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
4333 Halt all CPUs after the first oops has been printed for
4334 the specified number of seconds. This is to be used if
4335 your oopses keep scrolling off the screen.
4339 pci=option[,option...] [PCI,EARLY] various PCI subsystem options.
4341 Some options herein operate on a specific device
4342 or a set of devices (<pci_dev>). These are
4343 specified in one of the following formats:
4345 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
4346 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
4348 Note: the first format specifies a PCI
4349 bus/device/function address which may change
4350 if new hardware is inserted, if motherboard
4351 firmware changes, or due to changes caused
4352 by other kernel parameters. If the
4353 domain is left unspecified, it is
4354 taken to be zero. Optionally, a path
4355 to a device through multiple device/function
4356 addresses can be specified after the base
4357 address (this is more robust against
4358 renumbering issues). The second format
4359 selects devices using IDs from the
4360 configuration space which may match multiple
4361 devices in the system.
4363 earlydump dump PCI config space before the kernel
4365 off [X86] don't probe for the PCI bus
4366 bios [X86-32] force use of PCI BIOS, don't access
4367 the hardware directly. Use this if your machine
4368 has a non-standard PCI host bridge.
4369 nobios [X86-32] disallow use of PCI BIOS, only direct
4370 hardware access methods are allowed. Use this
4371 if you experience crashes upon bootup and you
4372 suspect they are caused by the BIOS.
4373 conf1 [X86] Force use of PCI Configuration Access
4374 Mechanism 1 (config address in IO port 0xCF8,
4375 data in IO port 0xCFC, both 32-bit).
4376 conf2 [X86] Force use of PCI Configuration Access
4377 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
4378 the function, IO port 0xCFA, also 8-bit, sets
4379 bus number. The config space is then accessed
4380 through ports 0xC000-0xCFFF).
4381 See http://wiki.osdev.org/PCI for more info
4382 on the configuration access mechanisms.
4383 noaer [PCIE] If the PCIEAER kernel config parameter is
4384 enabled, this kernel boot option can be used to
4385 disable the use of PCIE advanced error reporting.
4386 nodomains [PCI] Disable support for multiple PCI
4387 root domains (aka PCI segments, in ACPI-speak).
4388 nommconf [X86] Disable use of MMCONFIG for PCI
4390 check_enable_amd_mmconf [X86] check for and enable
4391 properly configured MMIO access to PCI
4392 config space on AMD family 10h CPU
4393 nomsi [MSI] If the PCI_MSI kernel config parameter is
4394 enabled, this kernel boot option can be used to
4395 disable the use of MSI interrupts system-wide.
4396 noioapicquirk [APIC] Disable all boot interrupt quirks.
4397 Safety option to keep boot IRQs enabled. This
4398 should never be necessary.
4399 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
4400 primary IO-APIC for bridges that cannot disable
4401 boot IRQs. This fixes a source of spurious IRQs
4402 when the system masks IRQs.
4403 noioapicreroute [APIC] Disable workaround that uses the
4404 boot IRQ equivalent of an IRQ that connects to
4405 a chipset where boot IRQs cannot be disabled.
4406 The opposite of ioapicreroute.
4407 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
4408 routing table. These calls are known to be buggy
4409 on several machines and they hang the machine
4410 when used, but on other computers it's the only
4411 way to get the interrupt routing table. Try
4412 this option if the kernel is unable to allocate
4413 IRQs or discover secondary PCI buses on your
4415 rom [X86] Assign address space to expansion ROMs.
4416 Use with caution as certain devices share
4417 address decoders between ROMs and other
4419 norom [X86] Do not assign address space to
4420 expansion ROMs that do not already have
4421 BIOS assigned address ranges.
4422 nobar [X86] Do not assign address space to the
4423 BARs that weren't assigned by the BIOS.
4424 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
4425 assigned automatically to PCI devices. You can
4426 make the kernel exclude IRQs of your ISA cards
4428 pirqaddr=0xAAAAA [X86] Specify the physical address
4429 of the PIRQ table (normally generated
4430 by the BIOS) if it is outside the
4431 F0000h-100000h range.
4432 lastbus=N [X86] Scan all buses thru bus #N. Can be
4433 useful if the kernel is unable to find your
4434 secondary buses and you want to tell it
4435 explicitly which ones they are.
4436 assign-busses [X86] Always assign all PCI bus
4437 numbers ourselves, overriding
4438 whatever the firmware may have done.
4439 usepirqmask [X86] Honor the possible IRQ mask stored
4440 in the BIOS $PIR table. This is needed on
4441 some systems with broken BIOSes, notably
4442 some HP Pavilion N5400 and Omnibook XE3
4443 notebooks. This will have no effect if ACPI
4444 IRQ routing is enabled.
4445 noacpi [X86] Do not use ACPI for IRQ routing
4446 or for PCI scanning.
4447 use_crs [X86] Use PCI host bridge window information
4448 from ACPI. On BIOSes from 2008 or later, this
4449 is enabled by default. If you need to use this,
4450 please report a bug.
4451 nocrs [X86] Ignore PCI host bridge windows from ACPI.
4452 If you need to use this, please report a bug.
4453 use_e820 [X86] Use E820 reservations to exclude parts of
4454 PCI host bridge windows. This is a workaround
4455 for BIOS defects in host bridge _CRS methods.
4456 If you need to use this, please report a bug to
4457 <linux-pci@vger.kernel.org>.
4458 no_e820 [X86] Ignore E820 reservations for PCI host
4459 bridge windows. This is the default on modern
4460 hardware. If you need to use this, please report
4461 a bug to <linux-pci@vger.kernel.org>.
4462 routeirq Do IRQ routing for all PCI devices.
4463 This is normally done in pci_enable_device(),
4464 so this option is a temporary workaround
4465 for broken drivers that don't call it.
4466 skip_isa_align [X86] do not align io start addr, so can
4467 handle more pci cards
4468 noearly [X86] Don't do any early type 1 scanning.
4469 This might help on some broken boards which
4470 machine check when some devices' config space
4471 is read. But various workarounds are disabled
4472 and some IOMMU drivers will not work.
4473 bfsort Sort PCI devices into breadth-first order.
4474 This sorting is done to get a device
4475 order compatible with older (<= 2.4) kernels.
4476 nobfsort Don't sort PCI devices into breadth-first order.
4477 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
4478 tuning and use the BIOS-configured MPS defaults.
4479 pcie_bus_safe Set every device's MPS to the largest value
4480 supported by all devices below the root complex.
4481 pcie_bus_perf Set device MPS to the largest allowable MPS
4482 based on its parent bus. Also set MRRS (Max
4483 Read Request Size) to the largest supported
4484 value (no larger than the MPS that the device
4485 or bus can support) for best performance.
4486 pcie_bus_peer2peer Set every device's MPS to 128B, which
4487 every device is guaranteed to support. This
4488 configuration allows peer-to-peer DMA between
4489 any pair of devices, possibly at the cost of
4490 reduced performance. This also guarantees
4491 that hot-added devices will work.
4492 cbiosize=nn[KMG] The fixed amount of bus space which is
4493 reserved for the CardBus bridge's IO window.
4494 The default value is 256 bytes.
4495 cbmemsize=nn[KMG] The fixed amount of bus space which is
4496 reserved for the CardBus bridge's memory
4497 window. The default value is 64 megabytes.
4500 [<order of align>@]<pci_dev>[; ...]
4501 Specifies alignment and device to reassign
4502 aligned memory resources. How to
4503 specify the device is described above.
4504 If <order of align> is not specified,
4505 PAGE_SIZE is used as alignment.
4506 A PCI-PCI bridge can be specified if resource
4507 windows need to be expanded.
4508 To specify the alignment for several
4509 instances of a device, the PCI vendor,
4510 device, subvendor, and subdevice may be
4511 specified, e.g., 12@pci:8086:9c22:103c:198f
4512 for 4096-byte alignment.
4513 ecrc= Enable/disable PCIe ECRC (transaction layer
4514 end-to-end CRC checking). Only effective if
4515 OS has native AER control (either granted by
4516 ACPI _OSC or forced via "pcie_ports=native")
4517 bios: Use BIOS/firmware settings. This is the
4521 hpiosize=nn[KMG] The fixed amount of bus space which is
4522 reserved for hotplug bridge's IO window.
4523 Default size is 256 bytes.
4524 hpmmiosize=nn[KMG] The fixed amount of bus space which is
4525 reserved for hotplug bridge's MMIO window.
4526 Default size is 2 megabytes.
4527 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
4528 reserved for hotplug bridge's MMIO_PREF window.
4529 Default size is 2 megabytes.
4530 hpmemsize=nn[KMG] The fixed amount of bus space which is
4531 reserved for hotplug bridge's MMIO and
4533 Default size is 2 megabytes.
4534 hpbussize=nn The minimum amount of additional bus numbers
4535 reserved for buses below a hotplug bridge.
4537 realloc= Enable/disable reallocating PCI bridge resources
4538 if allocations done by BIOS are too small to
4539 accommodate resources required by all child
4541 off: Turn realloc off
4543 realloc same as realloc=on
4544 noari do not use PCIe ARI.
4545 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4546 do not use PCIe ATS (and IOMMU device IOTLB).
4547 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4548 only look for one device below a PCIe downstream
4550 big_root_window Try to add a big 64bit memory window to the PCIe
4551 root complex on AMD CPUs. Some GFX hardware
4552 can resize a BAR to allow access to all VRAM.
4553 Adding the window is slightly risky (it may
4554 conflict with unreported devices), so this
4556 disable_acs_redir=<pci_dev>[; ...]
4557 Specify one or more PCI devices (in the format
4558 specified above) separated by semicolons.
4559 Each device specified will have the PCI ACS
4560 redirect capabilities forced off which will
4561 allow P2P traffic between devices through
4562 bridges without forcing it upstream. Note:
4563 this removes isolation between devices and
4564 may put more devices in an IOMMU group.
4565 force_floating [S390] Force usage of floating interrupts.
4566 nomio [S390] Do not use MIO instructions.
4567 norid [S390] ignore the RID field and force use of
4568 one PCI domain per PCI function
4570 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
4573 force Enable ASPM even on devices that claim not to support it.
4574 WARNING: Forcing ASPM on may cause system lockups.
4576 pcie_ports= [PCIE] PCIe port services handling:
4577 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4578 even if the platform doesn't give the OS permission to
4579 use them. This may cause conflicts if the platform
4580 also tries to use these services.
4581 dpc-native Use native PCIe service for DPC only. May
4582 cause conflicts if firmware uses AER or DPC.
4583 compat Disable native PCIe services (PME, AER, DPC, PCIe
4586 pcie_port_pm= [PCIE] PCIe port power management handling:
4587 off Disable power management of all PCIe ports
4588 force Forcibly enable power management of all PCIe ports
4590 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4591 nomsi Do not use MSI for native PCIe PME signaling (this makes
4592 all PCIe root ports use INTx for all services).
4594 pcmv= [HW,PCMCIA] BadgePAD 4
4598 Keep all power-domains already enabled by bootloader on,
4599 even if no driver has claimed them. This is useful
4600 for debug and development, but should not be
4601 needed on a platform with proper driver support.
4603 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4606 See arch/parisc/kernel/pdc_chassis.c
4608 percpu_alloc= [MM,EARLY]
4609 Select which percpu first chunk allocator to use.
4610 Currently supported values are "embed" and "page".
4611 Archs may support subset or none of the selections.
4612 See comments in mm/percpu.c for details on each
4613 allocator. This parameter is primarily for debugging
4614 and performance comparison.
4616 pirq= [SMP,APIC] Manual mp-table setup
4617 See Documentation/arch/x86/i386/IO-APIC.rst.
4619 plip= [PPT,NET] Parallel port network link
4620 Format: { parport<nr> | timid | 0 }
4621 See also Documentation/admin-guide/parport.rst.
4623 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4624 Override pmtimer IOPort with a hex value.
4627 pmu_override= [PPC] Override the PMU.
4628 This option takes over the PMU facility, so it is no
4629 longer usable by perf. Setting this option starts the
4630 PMU counters by setting MMCR0 to 0 (the FC bit is
4631 cleared). If a number is given, then MMCR1 is set to
4632 that number, otherwise (e.g., 'pmu_override=on'), MMCR1
4635 pm_debug_messages [SUSPEND,KNL]
4636 Enable suspend/resume debug messages during boot up.
4639 Enable PNP debug messages (depends on the
4640 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4641 via /sys/module/pnp/parameters/debug. We always show
4642 current resource usage; turning this on also shows
4643 possible settings and some assignment information.
4649 { on | off | curr | res | no-curr | no-res }
4652 [ISAPNP] Exclude IRQs for the autoconfiguration
4655 [ISAPNP] Exclude DMAs for the autoconfiguration
4657 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4658 Ranges are in pairs (I/O port base and size).
4661 [ISAPNP] Exclude memory regions for the
4663 Ranges are in pairs (memory base and size).
4665 ports= [IP_VS_FTP] IPVS ftp helper module
4667 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4669 Format: <port>,<port>....
4671 possible_cpus= [SMP,S390,X86]
4672 Format: <unsigned int>
4673 Set the number of possible CPUs, overriding the
4674 regular discovery mechanisms (such as ACPI/FW, etc).
4676 powersave=off [PPC] This option disables power saving features.
4677 It specifically disables cpuidle and sets the
4678 platform machine description specific power_save
4679 function to NULL. On Idle the CPU just reduces
4682 ppc_strict_facility_enable
4683 [PPC,ENABLE] This option catches any kernel floating point,
4684 Altivec, VSX and SPE outside of regions specifically
4685 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4686 There is some performance impact when enabling this.
4690 Disable Hardware Transactional Memory
4693 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4694 none - Limited to cond_resched() calls
4695 voluntary - Limited to cond_resched() and might_sleep() calls
4696 full - Any section that isn't explicitly preempt disabled
4697 can be preempted anytime.
4699 print-fatal-signals=
4700 [KNL] debug: print fatal signals
4702 If enabled, warn about various signal handling
4703 related application anomalies: too many signals,
4704 too many POSIX.1 timers, fatal signals causing a
4707 If you hit the warning due to signal overflow,
4708 you might want to try "ulimit -i unlimited".
4712 printk.always_kmsg_dump=
4713 Trigger kmsg_dump for cases other than kernel oops or
4715 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4718 printk.console_no_auto_verbose=
4719 Disable console loglevel raise on oops, panic
4720 or lockdep-detected issues (only if lock debug is on).
4721 With an exception to setups with low baudrate on
4722 serial console, keeping this 0 is a good choice
4723 in order to provide more debug information.
4725 default: 0 (auto_verbose is enabled)
4727 printk.devkmsg={on,off,ratelimit}
4728 Control writing to /dev/kmsg.
4729 on - unlimited logging to /dev/kmsg from userspace
4730 off - logging to /dev/kmsg disabled
4731 ratelimit - ratelimit the logging
4734 printk.time= Show timing data prefixed to each printk message line
4735 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4737 processor.max_cstate= [HW,ACPI]
4738 Limit processor to maximum C-state
4739 max_cstate=9 overrides any DMI blacklist limit.
4741 processor.nocst [HW,ACPI]
4742 Ignore the _CST method to determine C-states,
4743 instead using the legacy FADT method
4745 profile= [KNL] Enable kernel profiling via /proc/profile
4746 Format: [<profiletype>,]<number>
4747 Param: <profiletype>: "schedule", "sleep", or "kvm"
4748 [defaults to kernel profiling]
4749 Param: "schedule" - profile schedule points.
4750 Param: "sleep" - profile D-state sleeping (millisecs).
4751 Requires CONFIG_SCHEDSTATS
4752 Param: "kvm" - profile VM exits.
4753 Param: <number> - step/bucket size as a power of 2 for
4754 statistical time based profiling.
4756 prompt_ramdisk= [RAM] [Deprecated]
4758 prot_virt= [S390] enable hosting protected virtual machines
4759 isolated from the hypervisor (if hardware supports
4763 psi= [KNL] Enable or disable pressure stall information
4767 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4768 probe for; one of (bare|imps|exps|lifebook|any).
4769 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4771 psmouse.resetafter= [HW,MOUSE]
4772 Try to reset the device after so many bad packets
4775 [HW,MOUSE] Set desired mouse resolution, in dpi.
4776 psmouse.smartscroll=
4777 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4778 0 = disabled, 1 = enabled (default).
4780 pstore.backend= Specify the name of the pstore backend to use
4782 pti= [X86-64] Control Page Table Isolation of user and
4783 kernel address spaces. Disabling this feature
4784 removes hardening, but improves performance of
4785 system calls and interrupts.
4787 on - unconditionally enable
4788 off - unconditionally disable
4789 auto - kernel detects whether your CPU model is
4790 vulnerable to issues that PTI mitigates
4792 Not specifying this option is equivalent to pti=auto.
4795 [KNL] Number of legacy pty's. Overwrites compiled-in
4798 quiet [KNL,EARLY] Disable most log messages
4802 radix_hcall_invalidate=on [PPC/PSERIES]
4803 Disable RADIX GTSE feature and use hcall for TLB
4807 See Documentation/admin-guide/md.rst.
4809 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4810 See Documentation/admin-guide/blockdev/ramdisk.rst.
4812 ramdisk_start= [RAM] RAM disk image start address
4814 random.trust_cpu=off
4815 [KNL,EARLY] Disable trusting the use of the CPU's
4816 random number generator (if available) to
4817 initialize the kernel's RNG.
4819 random.trust_bootloader=off
4820 [KNL,EARLY] Disable trusting the use of the a seed
4821 passed by the bootloader (if available) to
4822 initialize the kernel's RNG.
4824 randomize_kstack_offset=
4825 [KNL,EARLY] Enable or disable kernel stack offset
4826 randomization, which provides roughly 5 bits of
4827 entropy, frustrating memory corruption attacks
4828 that depend on stack address determinism or
4829 cross-syscall address exposures. This is only
4830 available on architectures that have defined
4831 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4832 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4833 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4835 ras=option[,option,...] [KNL] RAS-specific options
4838 Disable the Correctable Errors Collector,
4839 see CONFIG_RAS_CEC help text.
4841 rcu_nocbs[=cpu-list]
4842 [KNL] The optional argument is a cpu list,
4845 In kernels built with CONFIG_RCU_NOCB_CPU=y,
4846 enable the no-callback CPU mode, which prevents
4847 such CPUs' callbacks from being invoked in
4848 softirq context. Invocation of such CPUs' RCU
4849 callbacks will instead be offloaded to "rcuox/N"
4850 kthreads created for that purpose, where "x" is
4851 "p" for RCU-preempt, "s" for RCU-sched, and "g"
4852 for the kthreads that mediate grace periods; and
4853 "N" is the CPU number. This reduces OS jitter on
4854 the offloaded CPUs, which can be useful for HPC
4855 and real-time workloads. It can also improve
4856 energy efficiency for asymmetric multiprocessors.
4858 If a cpulist is passed as an argument, the specified
4859 list of CPUs is set to no-callback mode from boot.
4861 Otherwise, if the '=' sign and the cpulist
4862 arguments are omitted, no CPU will be set to
4863 no-callback mode from boot but the mode may be
4864 toggled at runtime via cpusets.
4866 Note that this argument takes precedence over
4867 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
4870 Rather than requiring that offloaded CPUs
4871 (specified by rcu_nocbs= above) explicitly
4872 awaken the corresponding "rcuoN" kthreads,
4873 make these kthreads poll for callbacks.
4874 This improves the real-time response for the
4875 offloaded CPUs by relieving them of the need to
4876 wake up the corresponding kthread, but degrades
4877 energy efficiency by requiring that the kthreads
4878 periodically wake up to do the polling.
4880 rcutree.blimit= [KNL]
4881 Set maximum number of finished RCU callbacks to
4882 process in one batch.
4884 rcutree.do_rcu_barrier= [KNL]
4885 Request a call to rcu_barrier(). This is
4886 throttled so that userspace tests can safely
4887 hammer on the sysfs variable if they so choose.
4888 If triggered before the RCU grace-period machinery
4889 is fully active, this will error out with EAGAIN.
4891 rcutree.dump_tree= [KNL]
4892 Dump the structure of the rcu_node combining tree
4893 out at early boot. This is used for diagnostic
4894 purposes, to verify correct tree setup.
4896 rcutree.gp_cleanup_delay= [KNL]
4897 Set the number of jiffies to delay each step of
4898 RCU grace-period cleanup.
4900 rcutree.gp_init_delay= [KNL]
4901 Set the number of jiffies to delay each step of
4902 RCU grace-period initialization.
4904 rcutree.gp_preinit_delay= [KNL]
4905 Set the number of jiffies to delay each step of
4906 RCU grace-period pre-initialization, that is,
4907 the propagation of recent CPU-hotplug changes up
4908 the rcu_node combining tree.
4910 rcutree.jiffies_till_first_fqs= [KNL]
4911 Set delay from grace-period initialization to
4912 first attempt to force quiescent states.
4913 Units are jiffies, minimum value is zero,
4914 and maximum value is HZ.
4916 rcutree.jiffies_till_next_fqs= [KNL]
4917 Set delay between subsequent attempts to force
4918 quiescent states. Units are jiffies, minimum
4919 value is one, and maximum value is HZ.
4921 rcutree.jiffies_till_sched_qs= [KNL]
4922 Set required age in jiffies for a
4923 given grace period before RCU starts
4924 soliciting quiescent-state help from
4925 rcu_note_context_switch() and cond_resched().
4926 If not specified, the kernel will calculate
4927 a value based on the most recent settings
4928 of rcutree.jiffies_till_first_fqs
4929 and rcutree.jiffies_till_next_fqs.
4930 This calculated value may be viewed in
4931 rcutree.jiffies_to_sched_qs. Any attempt to set
4932 rcutree.jiffies_to_sched_qs will be cheerfully
4935 rcutree.kthread_prio= [KNL,BOOT]
4936 Set the SCHED_FIFO priority of the RCU per-CPU
4937 kthreads (rcuc/N). This value is also used for
4938 the priority of the RCU boost threads (rcub/N)
4939 and for the RCU grace-period kthreads (rcu_bh,
4940 rcu_preempt, and rcu_sched). If RCU_BOOST is
4941 set, valid values are 1-99 and the default is 1
4942 (the least-favored priority). Otherwise, when
4943 RCU_BOOST is not set, valid values are 0-99 and
4944 the default is zero (non-realtime operation).
4945 When RCU_NOCB_CPU is set, also adjust the
4946 priority of NOCB callback kthreads.
4948 rcutree.nocb_nobypass_lim_per_jiffy= [KNL]
4949 On callback-offloaded (rcu_nocbs) CPUs,
4950 RCU reduces the lock contention that would
4951 otherwise be caused by callback floods through
4952 use of the ->nocb_bypass list. However, in the
4953 common non-flooded case, RCU queues directly to
4954 the main ->cblist in order to avoid the extra
4955 overhead of the ->nocb_bypass list and its lock.
4956 But if there are too many callbacks queued during
4957 a single jiffy, RCU pre-queues the callbacks into
4958 the ->nocb_bypass queue. The definition of "too
4959 many" is supplied by this kernel boot parameter.
4961 rcutree.qhimark= [KNL]
4962 Set threshold of queued RCU callbacks beyond which
4963 batch limiting is disabled.
4965 rcutree.qlowmark= [KNL]
4966 Set threshold of queued RCU callbacks below which
4967 batch limiting is re-enabled.
4969 rcutree.qovld= [KNL]
4970 Set threshold of queued RCU callbacks beyond which
4971 RCU's force-quiescent-state scan will aggressively
4972 enlist help from cond_resched() and sched IPIs to
4973 help CPUs more quickly reach quiescent states.
4974 Set to less than zero to make this be set based
4975 on rcutree.qhimark at boot time and to zero to
4976 disable more aggressive help enlistment.
4978 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
4979 Set the page-cache refill delay (in milliseconds)
4980 in response to low-memory conditions. The range
4981 of permitted values is in the range 0:100000.
4983 rcutree.rcu_divisor= [KNL]
4984 Set the shift-right count to use to compute
4985 the callback-invocation batch limit bl from
4986 the number of callbacks queued on this CPU.
4987 The result will be bounded below by the value of
4988 the rcutree.blimit kernel parameter. Every bl
4989 callbacks, the softirq handler will exit in
4990 order to allow the CPU to do other work.
4992 Please note that this callback-invocation batch
4993 limit applies only to non-offloaded callback
4994 invocation. Offloaded callbacks are instead
4995 invoked in the context of an rcuoc kthread, which
4996 scheduler will preempt as it does any other task.
4998 rcutree.rcu_fanout_exact= [KNL]
4999 Disable autobalancing of the rcu_node combining
5000 tree. This is used by rcutorture, and might
5001 possibly be useful for architectures having high
5002 cache-to-cache transfer latencies.
5004 rcutree.rcu_fanout_leaf= [KNL]
5005 Change the number of CPUs assigned to each
5006 leaf rcu_node structure. Useful for very
5007 large systems, which will choose the value 64,
5008 and for NUMA systems with large remote-access
5009 latencies, which will choose a value aligned
5010 with the appropriate hardware boundaries.
5012 rcutree.rcu_min_cached_objs= [KNL]
5013 Minimum number of objects which are cached and
5014 maintained per one CPU. Object size is equal
5015 to PAGE_SIZE. The cache allows to reduce the
5016 pressure to page allocator, also it makes the
5017 whole algorithm to behave better in low memory
5020 rcutree.rcu_nocb_gp_stride= [KNL]
5021 Set the number of NOCB callback kthreads in
5022 each group, which defaults to the square root
5023 of the number of CPUs. Larger numbers reduce
5024 the wakeup overhead on the global grace-period
5025 kthread, but increases that same overhead on
5026 each group's NOCB grace-period kthread.
5028 rcutree.rcu_kick_kthreads= [KNL]
5029 Cause the grace-period kthread to get an extra
5030 wake_up() if it sleeps three times longer than
5031 it should at force-quiescent-state time.
5032 This wake_up() will be accompanied by a
5033 WARN_ONCE() splat and an ftrace_dump().
5035 rcutree.rcu_resched_ns= [KNL]
5036 Limit the time spend invoking a batch of RCU
5037 callbacks to the specified number of nanoseconds.
5038 By default, this limit is checked only once
5039 every 32 callbacks in order to limit the pain
5040 inflicted by local_clock() overhead.
5042 rcutree.rcu_unlock_delay= [KNL]
5043 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
5044 this specifies an rcu_read_unlock()-time delay
5045 in microseconds. This defaults to zero.
5046 Larger delays increase the probability of
5047 catching RCU pointer leaks, that is, buggy use
5048 of RCU-protected pointers after the relevant
5049 rcu_read_unlock() has completed.
5051 rcutree.sysrq_rcu= [KNL]
5052 Commandeer a sysrq key to dump out Tree RCU's
5053 rcu_node tree with an eye towards determining
5054 why a new grace period has not yet started.
5056 rcutree.use_softirq= [KNL]
5057 If set to zero, move all RCU_SOFTIRQ processing to
5058 per-CPU rcuc kthreads. Defaults to a non-zero
5059 value, meaning that RCU_SOFTIRQ is used by default.
5060 Specify rcutree.use_softirq=0 to use rcuc kthreads.
5062 But note that CONFIG_PREEMPT_RT=y kernels disable
5063 this kernel boot parameter, forcibly setting it
5066 rcutree.enable_rcu_lazy= [KNL]
5067 To save power, batch RCU callbacks and flush after
5068 delay, memory pressure or callback list growing too
5071 rcuscale.gp_async= [KNL]
5072 Measure performance of asynchronous
5073 grace-period primitives such as call_rcu().
5075 rcuscale.gp_async_max= [KNL]
5076 Specify the maximum number of outstanding
5077 callbacks per writer thread. When a writer
5078 thread exceeds this limit, it invokes the
5079 corresponding flavor of rcu_barrier() to allow
5080 previously posted callbacks to drain.
5082 rcuscale.gp_exp= [KNL]
5083 Measure performance of expedited synchronous
5084 grace-period primitives.
5086 rcuscale.holdoff= [KNL]
5087 Set test-start holdoff period. The purpose of
5088 this parameter is to delay the start of the
5089 test until boot completes in order to avoid
5092 rcuscale.kfree_by_call_rcu= [KNL]
5093 In kernels built with CONFIG_RCU_LAZY=y, test
5094 call_rcu() instead of kfree_rcu().
5096 rcuscale.kfree_mult= [KNL]
5097 Instead of allocating an object of size kfree_obj,
5098 allocate one of kfree_mult * sizeof(kfree_obj).
5101 rcuscale.kfree_rcu_test= [KNL]
5102 Set to measure performance of kfree_rcu() flooding.
5104 rcuscale.kfree_rcu_test_double= [KNL]
5105 Test the double-argument variant of kfree_rcu().
5106 If this parameter has the same value as
5107 rcuscale.kfree_rcu_test_single, both the single-
5108 and double-argument variants are tested.
5110 rcuscale.kfree_rcu_test_single= [KNL]
5111 Test the single-argument variant of kfree_rcu().
5112 If this parameter has the same value as
5113 rcuscale.kfree_rcu_test_double, both the single-
5114 and double-argument variants are tested.
5116 rcuscale.kfree_nthreads= [KNL]
5117 The number of threads running loops of kfree_rcu().
5119 rcuscale.kfree_alloc_num= [KNL]
5120 Number of allocations and frees done in an iteration.
5122 rcuscale.kfree_loops= [KNL]
5123 Number of loops doing rcuscale.kfree_alloc_num number
5124 of allocations and frees.
5126 rcuscale.minruntime= [KNL]
5127 Set the minimum test run time in seconds. This
5128 does not affect the data-collection interval,
5129 but instead allows better measurement of things
5130 like CPU consumption.
5132 rcuscale.nreaders= [KNL]
5133 Set number of RCU readers. The value -1 selects
5134 N, where N is the number of CPUs. A value
5135 "n" less than -1 selects N-n+1, where N is again
5136 the number of CPUs. For example, -2 selects N
5137 (the number of CPUs), -3 selects N+1, and so on.
5138 A value of "n" less than or equal to -N selects
5141 rcuscale.nwriters= [KNL]
5142 Set number of RCU writers. The values operate
5143 the same as for rcuscale.nreaders.
5144 N, where N is the number of CPUs
5146 rcuscale.scale_type= [KNL]
5147 Specify the RCU implementation to test.
5149 rcuscale.shutdown= [KNL]
5150 Shut the system down after performance tests
5151 complete. This is useful for hands-off automated
5154 rcuscale.verbose= [KNL]
5155 Enable additional printk() statements.
5157 rcuscale.writer_holdoff= [KNL]
5158 Write-side holdoff between grace periods,
5159 in microseconds. The default of zero says
5162 rcuscale.writer_holdoff_jiffies= [KNL]
5163 Additional write-side holdoff between grace
5164 periods, but in jiffies. The default of zero
5167 rcutorture.fqs_duration= [KNL]
5168 Set duration of force_quiescent_state bursts
5171 rcutorture.fqs_holdoff= [KNL]
5172 Set holdoff time within force_quiescent_state bursts
5175 rcutorture.fqs_stutter= [KNL]
5176 Set wait time between force_quiescent_state bursts
5179 rcutorture.fwd_progress= [KNL]
5180 Specifies the number of kthreads to be used
5181 for RCU grace-period forward-progress testing
5182 for the types of RCU supporting this notion.
5183 Defaults to 1 kthread, values less than zero or
5184 greater than the number of CPUs cause the number
5187 rcutorture.fwd_progress_div= [KNL]
5188 Specify the fraction of a CPU-stall-warning
5189 period to do tight-loop forward-progress testing.
5191 rcutorture.fwd_progress_holdoff= [KNL]
5192 Number of seconds to wait between successive
5193 forward-progress tests.
5195 rcutorture.fwd_progress_need_resched= [KNL]
5196 Enclose cond_resched() calls within checks for
5197 need_resched() during tight-loop forward-progress
5200 rcutorture.gp_cond= [KNL]
5201 Use conditional/asynchronous update-side
5202 primitives, if available.
5204 rcutorture.gp_exp= [KNL]
5205 Use expedited update-side primitives, if available.
5207 rcutorture.gp_normal= [KNL]
5208 Use normal (non-expedited) asynchronous
5209 update-side primitives, if available.
5211 rcutorture.gp_sync= [KNL]
5212 Use normal (non-expedited) synchronous
5213 update-side primitives, if available. If all
5214 of rcutorture.gp_cond=, rcutorture.gp_exp=,
5215 rcutorture.gp_normal=, and rcutorture.gp_sync=
5216 are zero, rcutorture acts as if is interpreted
5217 they are all non-zero.
5219 rcutorture.irqreader= [KNL]
5220 Run RCU readers from irq handlers, or, more
5221 accurately, from a timer handler. Not all RCU
5222 flavors take kindly to this sort of thing.
5224 rcutorture.leakpointer= [KNL]
5225 Leak an RCU-protected pointer out of the reader.
5226 This can of course result in splats, and is
5227 intended to test the ability of things like
5228 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
5231 rcutorture.n_barrier_cbs= [KNL]
5232 Set callbacks/threads for rcu_barrier() testing.
5234 rcutorture.nfakewriters= [KNL]
5235 Set number of concurrent RCU writers. These just
5236 stress RCU, they don't participate in the actual
5237 test, hence the "fake".
5239 rcutorture.nocbs_nthreads= [KNL]
5240 Set number of RCU callback-offload togglers.
5241 Zero (the default) disables toggling.
5243 rcutorture.nocbs_toggle= [KNL]
5244 Set the delay in milliseconds between successive
5245 callback-offload toggling attempts.
5247 rcutorture.nreaders= [KNL]
5248 Set number of RCU readers. The value -1 selects
5249 N-1, where N is the number of CPUs. A value
5250 "n" less than -1 selects N-n-2, where N is again
5251 the number of CPUs. For example, -2 selects N
5252 (the number of CPUs), -3 selects N+1, and so on.
5254 rcutorture.object_debug= [KNL]
5255 Enable debug-object double-call_rcu() testing.
5257 rcutorture.onoff_holdoff= [KNL]
5258 Set time (s) after boot for CPU-hotplug testing.
5260 rcutorture.onoff_interval= [KNL]
5261 Set time (jiffies) between CPU-hotplug operations,
5262 or zero to disable CPU-hotplug testing.
5264 rcutorture.read_exit= [KNL]
5265 Set the number of read-then-exit kthreads used
5266 to test the interaction of RCU updaters and
5267 task-exit processing.
5269 rcutorture.read_exit_burst= [KNL]
5270 The number of times in a given read-then-exit
5271 episode that a set of read-then-exit kthreads
5274 rcutorture.read_exit_delay= [KNL]
5275 The delay, in seconds, between successive
5276 read-then-exit testing episodes.
5278 rcutorture.shuffle_interval= [KNL]
5279 Set task-shuffle interval (s). Shuffling tasks
5280 allows some CPUs to go into dyntick-idle mode
5281 during the rcutorture test.
5283 rcutorture.shutdown_secs= [KNL]
5284 Set time (s) after boot system shutdown. This
5285 is useful for hands-off automated testing.
5287 rcutorture.stall_cpu= [KNL]
5288 Duration of CPU stall (s) to test RCU CPU stall
5289 warnings, zero to disable.
5291 rcutorture.stall_cpu_block= [KNL]
5292 Sleep while stalling if set. This will result
5293 in warnings from preemptible RCU in addition to
5294 any other stall-related activity. Note that
5295 in kernels built with CONFIG_PREEMPTION=n and
5296 CONFIG_PREEMPT_COUNT=y, this parameter will
5297 cause the CPU to pass through a quiescent state.
5298 Given CONFIG_PREEMPTION=n, this will suppress
5299 RCU CPU stall warnings, but will instead result
5300 in scheduling-while-atomic splats.
5302 Use of this module parameter results in splats.
5305 rcutorture.stall_cpu_holdoff= [KNL]
5306 Time to wait (s) after boot before inducing stall.
5308 rcutorture.stall_cpu_irqsoff= [KNL]
5309 Disable interrupts while stalling if set.
5311 rcutorture.stall_gp_kthread= [KNL]
5312 Duration (s) of forced sleep within RCU
5313 grace-period kthread to test RCU CPU stall
5314 warnings, zero to disable. If both stall_cpu
5315 and stall_gp_kthread are specified, the
5316 kthread is starved first, then the CPU.
5318 rcutorture.stat_interval= [KNL]
5319 Time (s) between statistics printk()s.
5321 rcutorture.stutter= [KNL]
5322 Time (s) to stutter testing, for example, specifying
5323 five seconds causes the test to run for five seconds,
5324 wait for five seconds, and so on. This tests RCU's
5325 ability to transition abruptly to and from idle.
5327 rcutorture.test_boost= [KNL]
5328 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
5329 "Maybe" means test if the RCU implementation
5330 under test support RCU priority boosting.
5332 rcutorture.test_boost_duration= [KNL]
5333 Duration (s) of each individual boost test.
5335 rcutorture.test_boost_interval= [KNL]
5336 Interval (s) between each boost test.
5338 rcutorture.test_no_idle_hz= [KNL]
5339 Test RCU's dyntick-idle handling. See also the
5340 rcutorture.shuffle_interval parameter.
5342 rcutorture.torture_type= [KNL]
5343 Specify the RCU implementation to test.
5345 rcutorture.verbose= [KNL]
5346 Enable additional printk() statements.
5348 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
5349 Dump ftrace buffer after reporting RCU CPU
5352 rcupdate.rcu_cpu_stall_notifiers= [KNL]
5353 Provide RCU CPU stall notifiers, but see the
5354 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig
5355 option's help text. TL;DR: You almost certainly
5356 do not want rcupdate.rcu_cpu_stall_notifiers.
5358 rcupdate.rcu_cpu_stall_suppress= [KNL]
5359 Suppress RCU CPU stall warning messages.
5361 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
5362 Suppress RCU CPU stall warning messages and
5363 rcutorture writer stall warnings that occur
5364 during early boot, that is, during the time
5365 before the init task is spawned.
5367 rcupdate.rcu_cpu_stall_timeout= [KNL]
5368 Set timeout for RCU CPU stall warning messages.
5369 The value is in seconds and the maximum allowed
5370 value is 300 seconds.
5372 rcupdate.rcu_exp_cpu_stall_timeout= [KNL]
5373 Set timeout for expedited RCU CPU stall warning
5374 messages. The value is in milliseconds
5375 and the maximum allowed value is 21000
5376 milliseconds. Please note that this value is
5377 adjusted to an arch timer tick resolution.
5378 Setting this to zero causes the value from
5379 rcupdate.rcu_cpu_stall_timeout to be used (after
5380 conversion from seconds to milliseconds).
5382 rcupdate.rcu_cpu_stall_cputime= [KNL]
5383 Provide statistics on the cputime and count of
5384 interrupts and tasks during the sampling period. For
5385 multiple continuous RCU stalls, all sampling periods
5386 begin at half of the first RCU stall timeout.
5388 rcupdate.rcu_exp_stall_task_details= [KNL]
5389 Print stack dumps of any tasks blocking the
5390 current expedited RCU grace period during an
5391 expedited RCU CPU stall warning.
5393 rcupdate.rcu_expedited= [KNL]
5394 Use expedited grace-period primitives, for
5395 example, synchronize_rcu_expedited() instead
5396 of synchronize_rcu(). This reduces latency,
5397 but can increase CPU utilization, degrade
5398 real-time latency, and degrade energy efficiency.
5399 No effect on CONFIG_TINY_RCU kernels.
5401 rcupdate.rcu_normal= [KNL]
5402 Use only normal grace-period primitives,
5403 for example, synchronize_rcu() instead of
5404 synchronize_rcu_expedited(). This improves
5405 real-time latency, CPU utilization, and
5406 energy efficiency, but can expose users to
5407 increased grace-period latency. This parameter
5408 overrides rcupdate.rcu_expedited. No effect on
5409 CONFIG_TINY_RCU kernels.
5411 rcupdate.rcu_normal_after_boot= [KNL]
5412 Once boot has completed (that is, after
5413 rcu_end_inkernel_boot() has been invoked), use
5414 only normal grace-period primitives. No effect
5415 on CONFIG_TINY_RCU kernels.
5417 But note that CONFIG_PREEMPT_RT=y kernels enables
5418 this kernel boot parameter, forcibly setting
5419 it to the value one, that is, converting any
5420 post-boot attempt at an expedited RCU grace
5421 period to instead use normal non-expedited
5422 grace-period processing.
5424 rcupdate.rcu_task_collapse_lim= [KNL]
5425 Set the maximum number of callbacks present
5426 at the beginning of a grace period that allows
5427 the RCU Tasks flavors to collapse back to using
5428 a single callback queue. This switching only
5429 occurs when rcupdate.rcu_task_enqueue_lim is
5430 set to the default value of -1.
5432 rcupdate.rcu_task_contend_lim= [KNL]
5433 Set the minimum number of callback-queuing-time
5434 lock-contention events per jiffy required to
5435 cause the RCU Tasks flavors to switch to per-CPU
5436 callback queuing. This switching only occurs
5437 when rcupdate.rcu_task_enqueue_lim is set to
5438 the default value of -1.
5440 rcupdate.rcu_task_enqueue_lim= [KNL]
5441 Set the number of callback queues to use for the
5442 RCU Tasks family of RCU flavors. The default
5443 of -1 allows this to be automatically (and
5444 dynamically) adjusted. This parameter is intended
5447 rcupdate.rcu_task_ipi_delay= [KNL]
5448 Set time in jiffies during which RCU tasks will
5449 avoid sending IPIs, starting with the beginning
5450 of a given grace period. Setting a large
5451 number avoids disturbing real-time workloads,
5452 but lengthens grace periods.
5454 rcupdate.rcu_task_lazy_lim= [KNL]
5455 Number of callbacks on a given CPU that will
5456 cancel laziness on that CPU. Use -1 to disable
5457 cancellation of laziness, but be advised that
5458 doing so increases the danger of OOM due to
5461 rcupdate.rcu_task_stall_info= [KNL]
5462 Set initial timeout in jiffies for RCU task stall
5463 informational messages, which give some indication
5464 of the problem for those not patient enough to
5465 wait for ten minutes. Informational messages are
5466 only printed prior to the stall-warning message
5467 for a given grace period. Disable with a value
5468 less than or equal to zero. Defaults to ten
5469 seconds. A change in value does not take effect
5470 until the beginning of the next grace period.
5472 rcupdate.rcu_task_stall_info_mult= [KNL]
5473 Multiplier for time interval between successive
5474 RCU task stall informational messages for a given
5475 RCU tasks grace period. This value is clamped
5476 to one through ten, inclusive. It defaults to
5477 the value three, so that the first informational
5478 message is printed 10 seconds into the grace
5479 period, the second at 40 seconds, the third at
5480 160 seconds, and then the stall warning at 600
5481 seconds would prevent a fourth at 640 seconds.
5483 rcupdate.rcu_task_stall_timeout= [KNL]
5484 Set timeout in jiffies for RCU task stall
5485 warning messages. Disable with a value less
5486 than or equal to zero. Defaults to ten minutes.
5487 A change in value does not take effect until
5488 the beginning of the next grace period.
5490 rcupdate.rcu_tasks_lazy_ms= [KNL]
5491 Set timeout in milliseconds RCU Tasks asynchronous
5492 callback batching for call_rcu_tasks().
5493 A negative value will take the default. A value
5494 of zero will disable batching. Batching is
5495 always disabled for synchronize_rcu_tasks().
5497 rcupdate.rcu_tasks_rude_lazy_ms= [KNL]
5498 Set timeout in milliseconds RCU Tasks
5499 Rude asynchronous callback batching for
5500 call_rcu_tasks_rude(). A negative value
5501 will take the default. A value of zero will
5502 disable batching. Batching is always disabled
5503 for synchronize_rcu_tasks_rude().
5505 rcupdate.rcu_tasks_trace_lazy_ms= [KNL]
5506 Set timeout in milliseconds RCU Tasks
5507 Trace asynchronous callback batching for
5508 call_rcu_tasks_trace(). A negative value
5509 will take the default. A value of zero will
5510 disable batching. Batching is always disabled
5511 for synchronize_rcu_tasks_trace().
5513 rcupdate.rcu_self_test= [KNL]
5514 Run the RCU early boot self tests
5518 Run specified binary instead of /init from the ramdisk,
5519 used for early userspace startup. See initrd.
5522 force - Override the decision by the kernel to hide the
5523 advertisement of RDRAND support (this affects
5524 certain AMD processors because of buggy BIOS
5525 support, specifically around the suspend/resume
5529 Turn on/off individual RDT features. List is:
5530 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
5532 E.g. to turn on cmt and turn off mba use:
5536 Format (x86 or x86_64):
5537 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
5539 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
5541 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
5542 (prefix with 'panic_' to set mode for panic
5544 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
5545 reboot_force is either force or not specified,
5546 reboot_cpu is s[mp]#### with #### being the processor
5547 to be used for rebooting.
5549 refscale.holdoff= [KNL]
5550 Set test-start holdoff period. The purpose of
5551 this parameter is to delay the start of the
5552 test until boot completes in order to avoid
5555 refscale.lookup_instances= [KNL]
5556 Number of data elements to use for the forms of
5557 SLAB_TYPESAFE_BY_RCU testing. A negative number
5558 is negated and multiplied by nr_cpu_ids, while
5559 zero specifies nr_cpu_ids.
5561 refscale.loops= [KNL]
5562 Set the number of loops over the synchronization
5563 primitive under test. Increasing this number
5564 reduces noise due to loop start/end overhead,
5565 but the default has already reduced the per-pass
5566 noise to a handful of picoseconds on ca. 2020
5569 refscale.nreaders= [KNL]
5570 Set number of readers. The default value of -1
5571 selects N, where N is roughly 75% of the number
5572 of CPUs. A value of zero is an interesting choice.
5574 refscale.nruns= [KNL]
5575 Set number of runs, each of which is dumped onto
5578 refscale.readdelay= [KNL]
5579 Set the read-side critical-section duration,
5580 measured in microseconds.
5582 refscale.scale_type= [KNL]
5583 Specify the read-protection implementation to test.
5585 refscale.shutdown= [KNL]
5586 Shut down the system at the end of the performance
5587 test. This defaults to 1 (shut it down) when
5588 refscale is built into the kernel and to 0 (leave
5589 it running) when refscale is built as a module.
5591 refscale.verbose= [KNL]
5592 Enable additional printk() statements.
5594 refscale.verbose_batched= [KNL]
5595 Batch the additional printk() statements. If zero
5596 (the default) or negative, print everything. Otherwise,
5597 print every Nth verbose statement, where N is the value
5600 regulator_ignore_unused
5602 Prevents regulator framework from disabling regulators
5603 that are unused, due no driver claiming them. This may
5604 be useful for debug and development, but should not be
5605 needed on a platform with proper driver support.
5608 [KNL, SMP] Set scheduler's default relax_domain_level.
5609 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
5611 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
5612 Format: <base1>,<size1>[,<base2>,<size2>,...]
5613 Reserve I/O ports or memory so the kernel won't use
5614 them. If <base> is less than 0x10000, the region
5615 is assumed to be I/O ports; otherwise it is memory.
5617 reservetop= [X86-32,EARLY]
5619 Reserves a hole at the top of the kernel virtual
5622 reset_devices [KNL] Force drivers to reset the underlying device
5623 during initialization.
5626 Specify the partition device for software suspend
5628 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
5630 resume_offset= [SWSUSP]
5631 Specify the offset from the beginning of the partition
5632 given by "resume=" at which the swap header is located,
5633 in <PAGE_SIZE> units (needed only for swap files).
5634 See Documentation/power/swsusp-and-swap-files.rst
5636 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
5637 read the resume files
5639 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
5640 Useful for devices that are detected asynchronously
5641 (e.g. USB and MMC devices).
5643 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will
5644 be accessible via /sys/firmware/initrd.
5646 retbleed= [X86] Control mitigation of RETBleed (Arbitrary
5647 Speculative Code Execution with Return Instructions)
5650 AMD-based UNRET and IBPB mitigations alone do not stop
5651 sibling threads from influencing the predictions of other
5652 sibling threads. For that reason, STIBP is used on pro-
5653 cessors that support it, and mitigate SMT on processors
5657 auto - automatically select a migitation
5658 auto,nosmt - automatically select a mitigation,
5659 disabling SMT if necessary for
5660 the full mitigation (only on Zen1
5661 and older without STIBP).
5662 ibpb - On AMD, mitigate short speculation
5663 windows on basic block boundaries too.
5664 Safe, highest perf impact. It also
5665 enables STIBP if present. Not suitable
5667 ibpb,nosmt - Like "ibpb" above but will disable SMT
5668 when STIBP is not available. This is
5669 the alternative for systems which do not
5671 unret - Force enable untrained return thunks,
5672 only effective on AMD f15h-f17h based
5674 unret,nosmt - Like unret, but will disable SMT when STIBP
5675 is not available. This is the alternative for
5676 systems which do not have STIBP.
5678 Selecting 'auto' will choose a mitigation method at run
5679 time according to the CPU.
5681 Not specifying this option is equivalent to retbleed=auto.
5683 rfkill.default_state=
5684 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
5685 etc. communication is blocked by default.
5688 rfkill.master_switch_mode=
5689 0 The "airplane mode" button does nothing.
5690 1 The "airplane mode" button toggles between everything
5691 blocked and the previous configuration.
5692 2 The "airplane mode" button toggles between everything
5693 blocked and everything unblocked.
5695 rhash_entries= [KNL,NET]
5696 Set number of hash buckets for route cache
5699 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
5702 riscv_isa_fallback [RISCV,EARLY]
5703 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit
5704 falling back to detecting extension support by parsing
5705 "riscv,isa" property on devicetree systems when the
5706 replacement properties are not found. See the Kconfig
5707 entry for RISCV_ISA_FALLBACK.
5709 ro [KNL] Mount root device read-only on boot
5712 on Mark read-only kernel memory as read-only (default).
5713 off Leave read-only kernel memory writable for debugging.
5714 full Mark read-only kernel memory and aliases as read-only
5719 Enable the uart passthrough on the designated usb port
5720 on Rockchip SoCs. When active, the signals of the
5721 debug-uart get routed to the D+ and D- pins of the usb
5722 port and the regular usb controller gets disabled.
5724 root= [KNL] Root filesystem
5725 Usually this a a block device specifier of some kind,
5726 see the early_lookup_bdev comment in
5727 block/early-lookup.c for details.
5728 Alternatively this can be "ram" for the legacy initial
5729 ramdisk, "nfs" and "cifs" for root on a network file
5730 system, or "mtd" and "ubi" for mounting from raw flash.
5732 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
5733 mount the root filesystem
5735 rootflags= [KNL] Set root filesystem mount option string
5737 rootfstype= [KNL] Set root filesystem type
5739 rootwait [KNL] Wait (indefinitely) for root device to show up.
5740 Useful for devices that are detected asynchronously
5741 (e.g. USB and MMC devices).
5743 rootwait= [KNL] Maximum time (in seconds) to wait for root device
5744 to show up before attempting to mount the root
5747 rproc_mem=nn[KMG][@address]
5748 [KNL,ARM,CMA] Remoteproc physical memory block.
5749 Memory area to be used by remote processor image,
5752 rw [KNL] Mount root device read-write on boot
5754 S [KNL] Run init in single mode
5756 s390_iommu= [HW,S390]
5757 Set s390 IOTLB flushing mode
5759 With strict flushing every unmap operation will result
5760 in an IOTLB flush. Default is lazy flushing before
5761 reuse, which is faster. Deprecated, equivalent to
5764 s390_iommu_aperture= [KNL,S390]
5765 Specifies the size of the per device DMA address space
5766 accessible through the DMA and IOMMU APIs as a decimal
5767 factor of the size of main memory.
5768 The default is 1 meaning that one can concurrently use
5769 as many DMA addresses as physical memory is installed,
5770 if supported by hardware, and thus map all of memory
5771 once. With a value of 2 one can map all of memory twice
5772 and so on. As a special case a factor of 0 imposes no
5773 restrictions other than those given by hardware at the
5774 cost of significant additional memory use for tables.
5777 See drivers/net/irda/sa1100_ir.c.
5779 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages.
5781 schedstats= [KNL,X86] Enable or disable scheduled statistics.
5782 Allowed values are enable and disable. This feature
5783 incurs a small amount of overhead in the scheduler
5784 but is useful for debugging and performance tuning.
5786 sched_thermal_decay_shift=
5787 [KNL, SMP] Set a decay shift for scheduler thermal
5788 pressure signal. Thermal pressure signal follows the
5789 default decay period of other scheduler pelt
5790 signals(usually 32 ms but configurable). Setting
5791 sched_thermal_decay_shift will left shift the decay
5792 period for the thermal pressure signal by the shift
5794 i.e. with the default pelt decay period of 32 ms
5795 sched_thermal_decay_shift thermal pressure decay pr
5799 Format: integer between 0 and 10
5802 scftorture.holdoff= [KNL]
5803 Number of seconds to hold off before starting
5804 test. Defaults to zero for module insertion and
5805 to 10 seconds for built-in smp_call_function()
5808 scftorture.longwait= [KNL]
5809 Request ridiculously long waits randomly selected
5810 up to the chosen limit in seconds. Zero (the
5811 default) disables this feature. Please note
5812 that requesting even small non-zero numbers of
5813 seconds can result in RCU CPU stall warnings,
5814 softlockup complaints, and so on.
5816 scftorture.nthreads= [KNL]
5817 Number of kthreads to spawn to invoke the
5818 smp_call_function() family of functions.
5819 The default of -1 specifies a number of kthreads
5820 equal to the number of CPUs.
5822 scftorture.onoff_holdoff= [KNL]
5823 Number seconds to wait after the start of the
5824 test before initiating CPU-hotplug operations.
5826 scftorture.onoff_interval= [KNL]
5827 Number seconds to wait between successive
5828 CPU-hotplug operations. Specifying zero (which
5829 is the default) disables CPU-hotplug operations.
5831 scftorture.shutdown_secs= [KNL]
5832 The number of seconds following the start of the
5833 test after which to shut down the system. The
5834 default of zero avoids shutting down the system.
5835 Non-zero values are useful for automated tests.
5837 scftorture.stat_interval= [KNL]
5838 The number of seconds between outputting the
5839 current test statistics to the console. A value
5840 of zero disables statistics output.
5842 scftorture.stutter_cpus= [KNL]
5843 The number of jiffies to wait between each change
5844 to the set of CPUs under test.
5846 scftorture.use_cpus_read_lock= [KNL]
5847 Use use_cpus_read_lock() instead of the default
5848 preempt_disable() to disable CPU hotplug
5849 while invoking one of the smp_call_function*()
5852 scftorture.verbose= [KNL]
5853 Enable additional printk() statements.
5855 scftorture.weight_single= [KNL]
5856 The probability weighting to use for the
5857 smp_call_function_single() function with a zero
5858 "wait" parameter. A value of -1 selects the
5859 default if all other weights are -1. However,
5860 if at least one weight has some other value, a
5861 value of -1 will instead select a weight of zero.
5863 scftorture.weight_single_wait= [KNL]
5864 The probability weighting to use for the
5865 smp_call_function_single() function with a
5866 non-zero "wait" parameter. See weight_single.
5868 scftorture.weight_many= [KNL]
5869 The probability weighting to use for the
5870 smp_call_function_many() function with a zero
5871 "wait" parameter. See weight_single.
5872 Note well that setting a high probability for
5873 this weighting can place serious IPI load
5876 scftorture.weight_many_wait= [KNL]
5877 The probability weighting to use for the
5878 smp_call_function_many() function with a
5879 non-zero "wait" parameter. See weight_single
5882 scftorture.weight_all= [KNL]
5883 The probability weighting to use for the
5884 smp_call_function_all() function with a zero
5885 "wait" parameter. See weight_single and
5888 scftorture.weight_all_wait= [KNL]
5889 The probability weighting to use for the
5890 smp_call_function_all() function with a
5891 non-zero "wait" parameter. See weight_single
5894 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate
5895 xtime_lock contention on larger systems, and/or RCU lock
5896 contention on all systems with CONFIG_MAXSMP set.
5897 Format: { "0" | "1" }
5898 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
5900 Note: increases power consumption, thus should only be
5901 enabled if running jitter sensitive (HPC/RT) workloads.
5903 security= [SECURITY] Choose a legacy "major" security module to
5904 enable at boot. This has been deprecated by the
5907 selinux= [SELINUX] Disable or enable SELinux at boot time.
5908 Format: { "0" | "1" }
5909 See security/selinux/Kconfig help text.
5914 serialnumber [BUGS=X86-32]
5916 sev=option[,option...] [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst
5919 Maximal number of shapers.
5921 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
5922 Limit apic dumping. The parameter defines the maximal
5923 number of local apics being dumped. Also it is possible
5924 to set it to "all" by meaning -- no limit here.
5925 Format: { 1 (default) | 2 | ... | all }.
5926 The parameter valid if only apic=debug or
5927 apic=verbose is specified.
5928 Example: apic=debug show_lapic=all
5936 Enable merging of slabs with similar size when the
5937 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
5940 Disable merging of slabs with similar size. May be
5941 necessary if there is some reason to distinguish
5942 allocs to different slabs, especially in hardened
5943 environments where the risk of heap overflows and
5944 layout control by attackers can usually be
5945 frustrated by disabling merging. This will reduce
5946 most of the exposure of a heap attack to a single
5947 cache (risks via metadata attacks are mostly
5948 unchanged). Debug options disable merging on their
5950 For more information see Documentation/mm/slub.rst.
5952 slab_max_order= [MM, SLAB]
5953 Determines the maximum allowed order for slabs.
5954 A high setting may cause OOMs due to memory
5955 fragmentation. Defaults to 1 for systems with
5956 more than 32MB of RAM, 0 otherwise.
5958 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
5959 Enabling slub_debug allows one to determine the
5960 culprit if slab objects become corrupted. Enabling
5961 slub_debug can create guard zones around objects and
5962 may poison objects when not in use. Also tracks the
5963 last alloc / free. For more information see
5964 Documentation/mm/slub.rst.
5966 slub_max_order= [MM, SLUB]
5967 Determines the maximum allowed order for slabs.
5968 A high setting may cause OOMs due to memory
5969 fragmentation. For more information see
5970 Documentation/mm/slub.rst.
5972 slub_min_objects= [MM, SLUB]
5973 The minimum number of objects per slab. SLUB will
5974 increase the slab order up to slub_max_order to
5975 generate a sufficiently large slab able to contain
5976 the number of objects indicated. The higher the number
5977 of objects the smaller the overhead of tracking slabs
5978 and the less frequently locks need to be acquired.
5979 For more information see Documentation/mm/slub.rst.
5981 slub_min_order= [MM, SLUB]
5982 Determines the minimum page order for slabs. Must be
5983 lower than slub_max_order.
5984 For more information see Documentation/mm/slub.rst.
5986 slub_merge [MM, SLUB]
5987 Same with slab_merge.
5989 slub_nomerge [MM, SLUB]
5990 Same with slab_nomerge. This is supported for legacy.
5991 See slab_nomerge for more information.
5994 Format: <io1>[,<io2>[,...,<io8>]]
5996 smp.csd_lock_timeout= [KNL]
5997 Specify the period of time in milliseconds
5998 that smp_call_function() and friends will wait
5999 for a CPU to release the CSD lock. This is
6000 useful when diagnosing bugs involving CPUs
6001 disabling interrupts for extended periods
6002 of time. Defaults to 5,000 milliseconds, and
6003 setting a value of zero disables this feature.
6004 This feature may be more efficiently disabled
6005 using the csdlock_debug- kernel parameter.
6007 smp.panic_on_ipistall= [KNL]
6008 If a csd_lock_timeout extends for more than
6009 the specified number of milliseconds, panic the
6010 system. By default, let CSD-lock acquisition
6011 take as long as they take. Specifying 300,000
6012 for this value provides a 5-minute timeout.
6014 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
6015 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
6016 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
6017 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
6018 smsc-ircc2.ircc_irq= [HW] IRQ line
6019 smsc-ircc2.ircc_dma= [HW] DMA channel
6020 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
6021 0: Toshiba Satellite 1800 (GP data pin select)
6022 1: Fast pin select (default)
6025 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads
6026 (logical CPUs) to use per physical CPU on systems
6027 capable of symmetric multithreading (SMT). Will
6028 be capped to the actual hardware limit.
6030 Default: -1 (no limit)
6033 [KNL] Should the soft-lockup detector generate panics.
6036 A value of 1 instructs the soft-lockup detector
6037 to panic the machine when a soft-lockup occurs. It is
6038 also controlled by the kernel.softlockup_panic sysctl
6039 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
6040 respective build-time switch to that functionality.
6042 softlockup_all_cpu_backtrace=
6043 [KNL] Should the soft-lockup detector generate
6044 backtraces on all cpus.
6047 sonypi.*= [HW] Sony Programmable I/O Control Device driver
6048 See Documentation/admin-guide/laptops/sonypi.rst
6050 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2
6051 (indirect branch speculation) vulnerability.
6052 The default operation protects the kernel from
6055 on - unconditionally enable, implies
6057 off - unconditionally disable, implies
6059 auto - kernel detects whether your CPU model is
6062 Selecting 'on' will, and 'auto' may, choose a
6063 mitigation method at run time according to the
6064 CPU, the available microcode, the setting of the
6065 CONFIG_MITIGATION_RETPOLINE configuration option,
6066 and the compiler with which the kernel was built.
6068 Selecting 'on' will also enable the mitigation
6069 against user space to user space task attacks.
6071 Selecting 'off' will disable both the kernel and
6072 the user space protections.
6074 Specific mitigations can also be selected manually:
6076 retpoline - replace indirect branches
6077 retpoline,generic - Retpolines
6078 retpoline,lfence - LFENCE; indirect branch
6079 retpoline,amd - alias for retpoline,lfence
6080 eibrs - Enhanced/Auto IBRS
6081 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines
6082 eibrs,lfence - Enhanced/Auto IBRS + LFENCE
6083 ibrs - use IBRS to protect kernel
6085 Not specifying this option is equivalent to
6089 [X86] Control mitigation of Spectre variant 2
6090 (indirect branch speculation) vulnerability between
6093 on - Unconditionally enable mitigations. Is
6094 enforced by spectre_v2=on
6096 off - Unconditionally disable mitigations. Is
6097 enforced by spectre_v2=off
6099 prctl - Indirect branch speculation is enabled,
6100 but mitigation can be enabled via prctl
6101 per thread. The mitigation control state
6102 is inherited on fork.
6105 - Like "prctl" above, but only STIBP is
6106 controlled per thread. IBPB is issued
6107 always when switching between different user
6111 - Same as "prctl" above, but all seccomp
6112 threads will enable the mitigation unless
6113 they explicitly opt out.
6116 - Like "seccomp" above, but only STIBP is
6117 controlled per thread. IBPB is issued
6118 always when switching between different
6119 user space processes.
6121 auto - Kernel selects the mitigation depending on
6122 the available CPU features and vulnerability.
6124 Default mitigation: "prctl"
6126 Not specifying this option is equivalent to
6127 spectre_v2_user=auto.
6129 spec_rstack_overflow=
6130 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs
6132 off - Disable mitigation
6133 microcode - Enable microcode mitigation only
6134 safe-ret - Enable sw-only safe RET mitigation (default)
6135 ibpb - Enable mitigation by issuing IBPB on
6137 ibpb-vmexit - Issue IBPB only on VMEXIT
6138 (cloud-specific mitigation)
6140 spec_store_bypass_disable=
6141 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation
6142 (Speculative Store Bypass vulnerability)
6144 Certain CPUs are vulnerable to an exploit against a
6145 a common industry wide performance optimization known
6146 as "Speculative Store Bypass" in which recent stores
6147 to the same memory location may not be observed by
6148 later loads during speculative execution. The idea
6149 is that such stores are unlikely and that they can
6150 be detected prior to instruction retirement at the
6151 end of a particular speculation execution window.
6153 In vulnerable processors, the speculatively forwarded
6154 store can be used in a cache side channel attack, for
6155 example to read memory to which the attacker does not
6156 directly have access (e.g. inside sandboxed code).
6158 This parameter controls whether the Speculative Store
6159 Bypass optimization is used.
6161 On x86 the options are:
6163 on - Unconditionally disable Speculative Store Bypass
6164 off - Unconditionally enable Speculative Store Bypass
6165 auto - Kernel detects whether the CPU model contains an
6166 implementation of Speculative Store Bypass and
6167 picks the most appropriate mitigation. If the
6168 CPU is not vulnerable, "off" is selected. If the
6169 CPU is vulnerable the default mitigation is
6170 architecture and Kconfig dependent. See below.
6171 prctl - Control Speculative Store Bypass per thread
6172 via prctl. Speculative Store Bypass is enabled
6173 for a process by default. The state of the control
6174 is inherited on fork.
6175 seccomp - Same as "prctl" above, but all seccomp threads
6176 will disable SSB unless they explicitly opt out.
6178 Default mitigations:
6181 On powerpc the options are:
6183 on,auto - On Power8 and Power9 insert a store-forwarding
6184 barrier on kernel entry and exit. On Power7
6185 perform a software flush on kernel entry and
6189 Not specifying this option is equivalent to
6190 spec_store_bypass_disable=auto.
6192 spia_io_base= [HW,MTD]
6198 [X86] Enable split lock detection or bus lock detection
6200 When enabled (and if hardware support is present), atomic
6201 instructions that access data across cache line
6202 boundaries will result in an alignment check exception
6203 for split lock detection or a debug exception for
6208 warn - the kernel will emit rate-limited warnings
6209 about applications triggering the #AC
6210 exception or the #DB exception. This mode is
6211 the default on CPUs that support split lock
6212 detection or bus lock detection. Default
6213 behavior is by #AC if both features are
6214 enabled in hardware.
6216 fatal - the kernel will send SIGBUS to applications
6217 that trigger the #AC exception or the #DB
6218 exception. Default behavior is by #AC if
6219 both features are enabled in hardware.
6222 Set system wide rate limit to N bus locks
6223 per second for bus lock detection.
6226 N/A for split lock detection.
6229 If an #AC exception is hit in the kernel or in
6230 firmware (i.e. not while executing in user mode)
6231 the kernel will oops in either "warn" or "fatal"
6234 #DB exception for bus lock is triggered only when
6237 srbds= [X86,INTEL,EARLY]
6238 Control the Special Register Buffer Data Sampling
6241 Certain CPUs are vulnerable to an MDS-like
6242 exploit which can leak bits from the random
6245 By default, this issue is mitigated by
6246 microcode. However, the microcode fix can cause
6247 the RDRAND and RDSEED instructions to become
6248 much slower. Among other effects, this will
6249 result in reduced throughput from /dev/urandom.
6251 The microcode mitigation can be disabled with
6252 the following option:
6254 off: Disable mitigation and remove
6255 performance impact to RDRAND and RDSEED
6257 srcutree.big_cpu_lim [KNL]
6258 Specifies the number of CPUs constituting a
6259 large system, such that srcu_struct structures
6260 should immediately allocate an srcu_node array.
6261 This kernel-boot parameter defaults to 128,
6262 but takes effect only when the low-order four
6263 bits of srcutree.convert_to_big is equal to 3
6266 srcutree.convert_to_big [KNL]
6267 Specifies under what conditions an SRCU tree
6268 srcu_struct structure will be converted to big
6269 form, that is, with an rcu_node tree:
6272 1: At init_srcu_struct() time.
6273 2: When rcutorture decides to.
6274 3: Decide at boot time (default).
6275 0x1X: Above plus if high contention.
6277 Either way, the srcu_node tree will be sized based
6278 on the actual runtime number of CPUs (nr_cpu_ids)
6279 instead of the compile-time CONFIG_NR_CPUS.
6281 srcutree.counter_wrap_check [KNL]
6282 Specifies how frequently to check for
6283 grace-period sequence counter wrap for the
6284 srcu_data structure's ->srcu_gp_seq_needed field.
6285 The greater the number of bits set in this kernel
6286 parameter, the less frequently counter wrap will
6287 be checked for. Note that the bottom two bits
6290 srcutree.exp_holdoff [KNL]
6291 Specifies how many nanoseconds must elapse
6292 since the end of the last SRCU grace period for
6293 a given srcu_struct until the next normal SRCU
6294 grace period will be considered for automatic
6295 expediting. Set to zero to disable automatic
6298 srcutree.srcu_max_nodelay [KNL]
6299 Specifies the number of no-delay instances
6300 per jiffy for which the SRCU grace period
6301 worker thread will be rescheduled with zero
6302 delay. Beyond this limit, worker thread will
6303 be rescheduled with a sleep delay of one jiffy.
6305 srcutree.srcu_max_nodelay_phase [KNL]
6306 Specifies the per-grace-period phase, number of
6307 non-sleeping polls of readers. Beyond this limit,
6308 grace period worker thread will be rescheduled
6309 with a sleep delay of one jiffy, between each
6310 rescan of the readers, for a grace period phase.
6312 srcutree.srcu_retry_check_delay [KNL]
6313 Specifies number of microseconds of non-sleeping
6314 delay between each non-sleeping poll of readers.
6316 srcutree.small_contention_lim [KNL]
6317 Specifies the number of update-side contention
6318 events per jiffy will be tolerated before
6319 initiating a conversion of an srcu_struct
6320 structure to big form. Note that the value of
6321 srcutree.convert_to_big must have the 0x10 bit
6322 set for contention-based conversions to occur.
6324 ssbd= [ARM64,HW,EARLY]
6325 Speculative Store Bypass Disable control
6327 On CPUs that are vulnerable to the Speculative
6328 Store Bypass vulnerability and offer a
6329 firmware based mitigation, this parameter
6330 indicates how the mitigation should be used:
6332 force-on: Unconditionally enable mitigation for
6333 for both kernel and userspace
6334 force-off: Unconditionally disable mitigation for
6335 for both kernel and userspace
6336 kernel: Always enable mitigation in the
6337 kernel, and offer a prctl interface
6338 to allow userspace to register its
6339 interest in being mitigated too.
6341 stack_guard_gap= [MM]
6342 override the default stack gap protection. The value
6343 is in page units and it defines how many pages prior
6344 to (for stacks growing down) resp. after (for stacks
6345 growing up) the main stack are reserved for no other
6346 mapping. Default value is 256 pages.
6348 stack_depot_disable= [KNL,EARLY]
6349 Setting this to true through kernel command line will
6350 disable the stack depot thereby saving the static memory
6351 consumed by the stack hash table. By default this is set
6355 Enabled the stack tracer on boot up.
6357 stacktrace_filter=[function-list]
6358 [FTRACE] Limit the functions that the stack tracer
6359 will trace at boot up. function-list is a comma-separated
6360 list of functions. This list can be changed at run
6361 time by the stack_trace_filter file in the debugfs
6362 tracing directory. Note, this enables stack tracing
6363 and the stacktrace above is not needed.
6367 Set the STI (builtin display/keyboard on the HP-PARISC
6368 machines) console (graphic card) which should be used
6369 as the initial boot-console.
6370 See also comment in drivers/video/console/sticore.c.
6373 See comment in drivers/video/console/sticore.c.
6376 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
6381 Enable or disable strict sigaltstack size checks
6382 against the required signal frame size which
6383 depends on the supported FPU features. This can
6384 be used to filter out binaries which have
6385 not yet been made aware of AT_MINSIGSTKSZ.
6387 stress_hpt [PPC,EARLY]
6388 Limits the number of kernel HPT entries in the hash
6389 page table to increase the rate of hash page table
6390 faults on kernel addresses.
6392 stress_slb [PPC,EARLY]
6393 Limits the number of kernel SLB entries, and flushes
6394 them frequently to increase the rate of SLB faults
6395 on kernel addresses.
6397 sunrpc.min_resvport=
6398 sunrpc.max_resvport=
6400 SunRPC servers often require that client requests
6401 originate from a privileged port (i.e. a port in the
6402 range 0 < portnr < 1024).
6403 An administrator who wishes to reserve some of these
6404 ports for other uses may adjust the range that the
6405 kernel's sunrpc client considers to be privileged
6406 using these two parameters to set the minimum and
6407 maximum port values.
6409 sunrpc.svc_rpc_per_connection_limit=
6411 Limit the number of requests that the server will
6412 process in parallel from a single connection.
6413 The default value is 0 (no limit).
6417 Control how the NFS server code allocates CPUs to
6418 service thread pools. Depending on how many NICs
6419 you have and where their interrupts are bound, this
6420 option will affect which CPUs will do NFS serving.
6421 Note: this parameter cannot be changed while the
6422 NFS server is running.
6424 auto the server chooses an appropriate mode
6425 automatically using heuristics
6426 global a single global pool contains all CPUs
6427 percpu one pool for each CPU
6428 pernode one pool for each NUMA node (equivalent
6429 to global on non-NUMA machines)
6431 sunrpc.tcp_slot_table_entries=
6432 sunrpc.udp_slot_table_entries=
6434 Sets the upper limit on the number of simultaneous
6435 RPC calls that can be sent from the client to a
6436 server. Increasing these values may allow you to
6437 improve throughput, but will also increase the
6438 amount of memory reserved for use by the client.
6440 suspend.pm_test_delay=
6442 Sets the number of seconds to remain in a suspend test
6443 mode before resuming the system (see
6444 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
6445 is set. Default value is 5.
6448 Format: { on | off | y | n | 1 | 0 }
6449 This parameter controls use of the Protected
6450 Execution Facility on pSeries.
6452 swiotlb= [ARM,IA-64,PPC,MIPS,X86,EARLY]
6453 Format: { <int> [,<int>] | force | noforce }
6454 <int> -- Number of I/O TLB slabs
6455 <int> -- Second integer after comma. Number of swiotlb
6456 areas with their own lock. Will be rounded up
6458 force -- force using of bounce buffers even if they
6459 wouldn't be automatically used by the kernel
6460 noforce -- Never use bounce buffers (for debugging)
6462 switches= [HW,M68k,EARLY]
6465 Set a sysctl parameter, right before loading the init
6466 process, as if the value was written to the respective
6467 /proc/sys/... file. Both '.' and '/' are recognized as
6468 separators. Unrecognized parameters and invalid values
6469 are reported in the kernel log. Sysctls registered
6470 later by a loaded module cannot be set this way.
6471 Example: sysctl.vm.swappiness=40
6473 sysrq_always_enabled
6475 Ignore sysrq setting - this boot parameter will
6476 neutralize any effect of /proc/sys/kernel/sysrq.
6477 Useful for debugging.
6479 tcpmhash_entries= [KNL,NET]
6480 Set the number of tcp_metrics_hash slots.
6481 Default value is 8192 or 16384 depending on total
6482 ram pages. This is used to specify the TCP metrics
6483 cache size. See Documentation/networking/ip-sysctl.rst
6484 "tcp_no_metrics_save" section for more details.
6488 test_suspend= [SUSPEND]
6489 Format: { "mem" | "standby" | "freeze" }[,N]
6490 Specify "mem" (for Suspend-to-RAM) or "standby" (for
6491 standby suspend) or "freeze" (for suspend type freeze)
6492 as the system sleep state during system startup with
6493 the optional capability to repeat N number of times.
6494 The system is woken from this state using a
6495 wakeup-capable RTC alarm.
6497 thash_entries= [KNL,NET]
6498 Set number of hash buckets for TCP connection
6500 thermal.act= [HW,ACPI]
6501 -1: disable all active trip points in all thermal zones
6502 <degrees C>: override all lowest active trip points
6504 thermal.crt= [HW,ACPI]
6505 -1: disable all critical trip points in all thermal zones
6506 <degrees C>: override all critical trip points
6508 thermal.off= [HW,ACPI]
6509 1: disable ACPI thermal control
6511 thermal.psv= [HW,ACPI]
6512 -1: disable all passive trip points
6513 <degrees C>: override all passive trip points to this
6516 thermal.tzp= [HW,ACPI]
6517 Specify global default ACPI thermal zone polling rate
6518 <deci-seconds>: poll all this frequency
6519 0: no polling (default)
6521 threadirqs [KNL,EARLY]
6522 Force threading of all interrupt handlers except those
6523 marked explicitly IRQF_NO_THREAD.
6525 topology= [S390,EARLY]
6527 Specify if the kernel should make use of the cpu
6528 topology information if the hardware supports this.
6529 The scheduler will make use of this information and
6530 e.g. base its process migration decisions on it.
6533 topology_updates= [KNL, PPC, NUMA]
6535 Specify if the kernel should ignore (off)
6536 topology updates sent by the hypervisor to this
6539 torture.disable_onoff_at_boot= [KNL]
6540 Prevent the CPU-hotplug component of torturing
6541 until after init has spawned.
6543 torture.ftrace_dump_at_shutdown= [KNL]
6544 Dump the ftrace buffer at torture-test shutdown,
6545 even if there were no errors. This can be a
6546 very costly operation when many torture tests
6547 are running concurrently, especially on systems
6548 with rotating-rust storage.
6550 torture.verbose_sleep_frequency= [KNL]
6551 Specifies how many verbose printk()s should be
6552 emitted between each sleep. The default of zero
6553 disables verbose-printk() sleeping.
6555 torture.verbose_sleep_duration= [KNL]
6556 Duration of each verbose-printk() sleep in jiffies.
6560 tpm_suspend_pcr=[HW,TPM]
6561 Format: integer pcr id
6562 Specify that at suspend time, the tpm driver
6563 should extend the specified pcr with zeros,
6564 as a workaround for some chips which fail to
6565 flush the last written pcr on TPM_SaveState.
6566 This will guarantee that all the other pcrs
6569 tpm_tis.interrupts= [HW,TPM]
6570 Enable interrupts for the MMIO based physical layer
6571 for the FIFO interface. By default it is set to false
6572 (0). For more information about TPM hardware interfaces
6573 defined by Trusted Computing Group (TCG) see
6574 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
6577 Have the tracepoints sent to printk as well as the
6578 tracing ring buffer. This is useful for early boot up
6579 where the system hangs or reboots and does not give the
6580 option for reading the tracing buffer or performing a
6581 ftrace_dump_on_oops.
6583 To turn off having tracepoints sent to printk,
6584 echo 0 > /proc/sys/kernel/tracepoint_printk
6585 Note, echoing 1 into this file without the
6586 tracepoint_printk kernel cmdline option has no effect.
6588 The tp_printk_stop_on_boot (see below) can also be used
6589 to stop the printing of events to console at
6594 Having tracepoints sent to printk() and activating high
6595 frequency tracepoints such as irq or sched, can cause
6596 the system to live lock.
6598 tp_printk_stop_on_boot [FTRACE]
6599 When tp_printk (above) is set, it can cause a lot of noise
6600 on the console. It may be useful to only include the
6601 printing of events during boot up, as user space may
6602 make the system inoperable.
6604 This command line option will stop the printing of events
6605 to console at the late_initcall_sync() time frame.
6607 trace_buf_size=nn[KMG]
6608 [FTRACE] will set tracing buffer size on each cpu.
6610 trace_clock= [FTRACE] Set the clock used for tracing events
6612 local - Use the per CPU time stamp counter
6613 (converted into nanoseconds). Fast, but
6614 depending on the architecture, may not be
6615 in sync between CPUs.
6616 global - Event time stamps are synchronize across
6617 CPUs. May be slower than the local clock,
6618 but better for some race conditions.
6619 counter - Simple counting of events (1, 2, ..)
6620 note, some counts may be skipped due to the
6621 infrastructure grabbing the clock more than
6623 uptime - Use jiffies as the time stamp.
6624 perf - Use the same clock that perf uses.
6625 mono - Use ktime_get_mono_fast_ns() for time stamps.
6626 mono_raw - Use ktime_get_raw_fast_ns() for time
6628 boot - Use ktime_get_boot_fast_ns() for time stamps.
6629 Architectures may add more clocks. See
6630 Documentation/trace/ftrace.rst for more details.
6632 trace_event=[event-list]
6633 [FTRACE] Set and start specified trace events in order
6634 to facilitate early boot debugging. The event-list is a
6635 comma-separated list of trace events to enable. See
6636 also Documentation/trace/events.rst
6638 trace_instance=[instance-info]
6639 [FTRACE] Create a ring buffer instance early in boot up.
6640 This will be listed in:
6642 /sys/kernel/tracing/instances
6644 Events can be enabled at the time the instance is created
6647 trace_instance=<name>,<system1>:<event1>,<system2>:<event2>
6649 Note, the "<system*>:" portion is optional if the event is
6652 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall
6654 will enable the "sched_switch" event (note, the "sched:" is optional, and
6655 the same thing would happen if it was left off). The irq_handler_entry
6656 event, and all events under the "initcall" system.
6658 trace_options=[option-list]
6659 [FTRACE] Enable or disable tracer options at boot.
6660 The option-list is a comma delimited list of options
6661 that can be enabled or disabled just as if you were
6662 to echo the option name into
6664 /sys/kernel/tracing/trace_options
6666 For example, to enable stacktrace option (to dump the
6667 stack trace of each event), add to the command line:
6669 trace_options=stacktrace
6671 See also Documentation/trace/ftrace.rst "trace options"
6674 trace_trigger=[trigger-list]
6675 [FTRACE] Add a event trigger on specific events.
6676 Set a trigger on top of a specific event, with an optional
6679 The format is is "trace_trigger=<event>.<trigger>[ if <filter>],..."
6680 Where more than one trigger may be specified that are comma deliminated.
6684 trace_trigger="sched_switch.stacktrace if prev_state == 2"
6686 The above will enable the "stacktrace" trigger on the "sched_switch"
6687 event but only trigger it if the "prev_state" of the "sched_switch"
6688 event is "2" (TASK_UNINTERUPTIBLE).
6690 See also "Event triggers" in Documentation/trace/events.rst
6694 [FTRACE] enable this option to disable tracing when a
6695 warning is hit. This turns off "tracing_on". Tracing can
6696 be enabled again by echoing '1' into the "tracing_on"
6697 file located in /sys/kernel/tracing/
6699 This option is useful, as it disables the trace before
6700 the WARNING dump is called, which prevents the trace to
6701 be filled with content caused by the warning output.
6703 This option can also be set at run time via the sysctl
6704 option: kernel/traceoff_on_warning
6706 transparent_hugepage=
6708 Format: [always|madvise|never]
6709 Can be used to control the default behavior of the system
6710 with respect to transparent hugepages.
6711 See Documentation/admin-guide/mm/transhuge.rst
6714 trusted.source= [KEYS]
6716 This parameter identifies the trust source as a backend
6717 for trusted keys implementation. Supported trust
6722 If not specified then it defaults to iterating through
6723 the trust source list starting with TPM and assigns the
6724 first trust source as a backend which is initialized
6725 successfully during iteration.
6729 The RNG used to generate key material for trusted keys.
6732 - the same value as trusted.source: "tpm" or "tee"
6734 If not specified, "default" is used. In this case,
6735 the RNG's choice is left to each individual trust source.
6737 tsc= Disable clocksource stability checks for TSC.
6739 [x86] reliable: mark tsc clocksource as reliable, this
6740 disables clocksource verification at runtime, as well
6741 as the stability checks done at bootup. Used to enable
6742 high-resolution timer mode on older hardware, and in
6743 virtualized environment.
6744 [x86] noirqtime: Do not use TSC to do irq accounting.
6745 Used to run time disable IRQ_TIME_ACCOUNTING on any
6746 platforms where RDTSC is slow and this accounting
6748 [x86] unstable: mark the TSC clocksource as unstable, this
6749 marks the TSC unconditionally unstable at bootup and
6750 avoids any further wobbles once the TSC watchdog notices.
6751 [x86] nowatchdog: disable clocksource watchdog. Used
6752 in situations with strict latency requirements (where
6753 interruptions from clocksource watchdog are not
6755 [x86] recalibrate: force recalibration against a HW timer
6756 (HPET or PM timer) on systems whose TSC frequency was
6757 obtained from HW or FW using either an MSR or CPUID(0x15).
6758 Warn if the difference is more than 500 ppm.
6759 [x86] watchdog: Use TSC as the watchdog clocksource with
6760 which to check other HW timers (HPET or PM timer), but
6761 only on systems where TSC has been deemed trustworthy.
6762 This will be suppressed by an earlier tsc=nowatchdog and
6763 can be overridden by a later tsc=nowatchdog. A console
6764 message will flag any such suppression or overriding.
6766 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given
6767 value instead. Useful when the early TSC frequency discovery
6768 procedure is not reliable, such as on overclocked systems
6769 with CPUID.16h support and partial CPUID.15h support.
6770 Format: <unsigned int>
6772 tsx= [X86] Control Transactional Synchronization
6773 Extensions (TSX) feature in Intel processors that
6774 support TSX control.
6776 This parameter controls the TSX feature. The options are:
6778 on - Enable TSX on the system. Although there are
6779 mitigations for all known security vulnerabilities,
6780 TSX has been known to be an accelerator for
6781 several previous speculation-related CVEs, and
6782 so there may be unknown security risks associated
6783 with leaving it enabled.
6785 off - Disable TSX on the system. (Note that this
6786 option takes effect only on newer CPUs which are
6787 not vulnerable to MDS, i.e., have
6788 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
6789 the new IA32_TSX_CTRL MSR through a microcode
6790 update. This new MSR allows for the reliable
6791 deactivation of the TSX functionality.)
6793 auto - Disable TSX if X86_BUG_TAA is present,
6794 otherwise enable TSX on the system.
6796 Not specifying this option is equivalent to tsx=off.
6798 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6801 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async
6802 Abort (TAA) vulnerability.
6804 Similar to Micro-architectural Data Sampling (MDS)
6805 certain CPUs that support Transactional
6806 Synchronization Extensions (TSX) are vulnerable to an
6807 exploit against CPU internal buffers which can forward
6808 information to a disclosure gadget under certain
6811 In vulnerable processors, the speculatively forwarded
6812 data can be used in a cache side channel attack, to
6813 access data to which the attacker does not have direct
6816 This parameter controls the TAA mitigation. The
6819 full - Enable TAA mitigation on vulnerable CPUs
6822 full,nosmt - Enable TAA mitigation and disable SMT on
6823 vulnerable CPUs. If TSX is disabled, SMT
6824 is not disabled because CPU is not
6825 vulnerable to cross-thread TAA attacks.
6826 off - Unconditionally disable TAA mitigation
6828 On MDS-affected machines, tsx_async_abort=off can be
6829 prevented by an active MDS mitigation as both vulnerabilities
6830 are mitigated with the same mechanism so in order to disable
6831 this mitigation, you need to specify mds=off too.
6833 Not specifying this option is equivalent to
6834 tsx_async_abort=full. On CPUs which are MDS affected
6835 and deploy MDS mitigation, TAA mitigation is not
6836 required and doesn't provide any additional
6840 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6842 turbografx.map[2|3]= [HW,JOY]
6843 TurboGraFX parallel port interface
6845 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
6846 See also Documentation/input/devices/joystick-parport.rst
6848 udbg-immortal [PPC] When debugging early kernel crashes that
6849 happen after console_init() and before a proper
6850 console driver takes over, this boot options might
6851 help "seeing" what's going on.
6853 uhash_entries= [KNL,NET]
6854 Set number of hash buckets for UDP/UDP-Lite connections
6857 [USB] Ignore overcurrent events (default N).
6858 Some badly-designed motherboards generate lots of
6859 bogus events, for ports that aren't wired to
6860 anything. Set this parameter to avoid log spamming.
6861 Note that genuine overcurrent events won't be
6865 [X86] Cause panic on unknown NMI.
6867 unwind_debug [X86-64,EARLY]
6868 Enable unwinder debug output. This can be
6869 useful for debugging certain unwinder error
6870 conditions, including corrupt stacks and
6871 bad/missing unwinder metadata.
6873 usbcore.authorized_default=
6874 [USB] Default USB device authorization:
6875 (default -1 = authorized (same as 1),
6876 0 = not authorized, 1 = authorized, 2 = authorized
6877 if device connected to internal port)
6879 usbcore.autosuspend=
6880 [USB] The autosuspend time delay (in seconds) used
6881 for newly-detected USB devices (default 2). This
6882 is the time required before an idle device will be
6883 autosuspended. Devices for which the delay is set
6884 to a negative value won't be autosuspended at all.
6886 usbcore.usbfs_snoop=
6887 [USB] Set to log all usbfs traffic (default 0 = off).
6889 usbcore.usbfs_snoop_max=
6890 [USB] Maximum number of bytes to snoop in each URB
6893 usbcore.blinkenlights=
6894 [USB] Set to cycle leds on hubs (default 0 = off).
6896 usbcore.old_scheme_first=
6897 [USB] Start with the old device initialization
6898 scheme (default 0 = off).
6900 usbcore.usbfs_memory_mb=
6901 [USB] Memory limit (in MB) for buffers allocated by
6902 usbfs (default = 16, 0 = max = 2047).
6904 usbcore.use_both_schemes=
6905 [USB] Try the other device initialization scheme
6906 if the first one fails (default 1 = enabled).
6908 usbcore.initial_descriptor_timeout=
6909 [USB] Specifies timeout for the initial 64-byte
6910 USB_REQ_GET_DESCRIPTOR request in milliseconds
6911 (default 5000 = 5.0 seconds).
6913 usbcore.nousb [USB] Disable the USB subsystem
6916 [USB] A list of quirk entries to augment the built-in
6917 usb core quirk list. List entries are separated by
6918 commas. Each entry has the form
6919 VendorID:ProductID:Flags. The IDs are 4-digit hex
6920 numbers and Flags is a set of letters. Each letter
6921 will change the built-in quirk; setting it if it is
6922 clear and clearing it if it is set. The letters have
6923 the following meanings:
6924 a = USB_QUIRK_STRING_FETCH_255 (string
6925 descriptors must not be fetched using
6927 b = USB_QUIRK_RESET_RESUME (device can't resume
6928 correctly so reset it instead);
6929 c = USB_QUIRK_NO_SET_INTF (device can't handle
6930 Set-Interface requests);
6931 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
6932 handle its Configuration or Interface
6934 e = USB_QUIRK_RESET (device can't be reset
6935 (e.g morph devices), don't use reset);
6936 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
6937 more interface descriptions than the
6938 bNumInterfaces count, and can't handle
6939 talking to these interfaces);
6940 g = USB_QUIRK_DELAY_INIT (device needs a pause
6941 during initialization, after we read
6942 the device descriptor);
6943 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
6944 high speed and super speed interrupt
6945 endpoints, the USB 2.0 and USB 3.0 spec
6946 require the interval in microframes (1
6947 microframe = 125 microseconds) to be
6948 calculated as interval = 2 ^
6950 Devices with this quirk report their
6951 bInterval as the result of this
6952 calculation instead of the exponent
6953 variable used in the calculation);
6954 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
6955 handle device_qualifier descriptor
6957 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
6958 generates spurious wakeup, ignore
6959 remote wakeup capability);
6960 k = USB_QUIRK_NO_LPM (device can't handle Link
6962 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
6963 (Device reports its bInterval as linear
6964 frames instead of the USB 2.0
6966 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
6967 to be disconnected before suspend to
6968 prevent spurious wakeup);
6969 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
6970 pause after every control message);
6971 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
6972 delay after resetting its port);
6973 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT
6974 (Reduce timeout of the SET_ADDRESS
6975 request from 5000 ms to 500 ms);
6976 Example: quirks=0781:5580:bk,0a5c:5834:gij
6979 [USBHID] The interval which mice are to be polled at.
6982 [USBHID] The interval which joysticks are to be polled at.
6985 [USBHID] The interval which keyboards are to be polled at.
6987 usb-storage.delay_use=
6988 [UMS] The delay in seconds before a new device is
6989 scanned for Logical Units (default 1).
6992 [UMS] A list of quirks entries to supplement or
6993 override the built-in unusual_devs list. List
6994 entries are separated by commas. Each entry has
6995 the form VID:PID:Flags where VID and PID are Vendor
6996 and Product ID values (4-digit hex numbers) and
6997 Flags is a set of characters, each corresponding
6998 to a common usb-storage quirk flag as follows:
6999 a = SANE_SENSE (collect more than 18 bytes
7000 of sense data, not on uas);
7001 b = BAD_SENSE (don't collect more than 18
7002 bytes of sense data, not on uas);
7003 c = FIX_CAPACITY (decrease the reported
7004 device capacity by one sector);
7005 d = NO_READ_DISC_INFO (don't use
7006 READ_DISC_INFO command, not on uas);
7007 e = NO_READ_CAPACITY_16 (don't use
7008 READ_CAPACITY_16 command);
7009 f = NO_REPORT_OPCODES (don't use report opcodes
7011 g = MAX_SECTORS_240 (don't transfer more than
7012 240 sectors at a time, uas only);
7013 h = CAPACITY_HEURISTICS (decrease the
7014 reported device capacity by one
7015 sector if the number is odd);
7016 i = IGNORE_DEVICE (don't bind to this
7018 j = NO_REPORT_LUNS (don't use report luns
7020 k = NO_SAME (do not use WRITE_SAME, uas only)
7021 l = NOT_LOCKABLE (don't try to lock and
7022 unlock ejectable media, not on uas);
7023 m = MAX_SECTORS_64 (don't transfer more
7024 than 64 sectors = 32 KB at a time,
7026 n = INITIAL_READ10 (force a retry of the
7027 initial READ(10) command, not on uas);
7028 o = CAPACITY_OK (accept the capacity
7029 reported by the device, not on uas);
7030 p = WRITE_CACHE (the device cache is ON
7031 by default, not on uas);
7032 r = IGNORE_RESIDUE (the device reports
7033 bogus residue values, not on uas);
7034 s = SINGLE_LUN (the device has only one
7036 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
7037 commands, uas only);
7038 u = IGNORE_UAS (don't bind to the uas driver);
7039 w = NO_WP_DETECT (don't test whether the
7040 medium is write-protected).
7041 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
7042 even if the device claims no cache,
7044 Example: quirks=0419:aaf5:rl,0421:0433:rc
7046 user_debug= [KNL,ARM]
7048 See arch/arm/Kconfig.debug help text.
7049 1 - undefined instruction events
7051 4 - invalid data aborts
7054 Example: user_debug=31
7057 [X86,EARLY] Flags controlling user PTE allocations.
7059 nohigh = do not allocate PTE pages in
7060 HIGHMEM regardless of setting
7063 vdso= [X86,SH,SPARC]
7064 On X86_32, this is an alias for vdso32=. Otherwise:
7066 vdso=1: enable VDSO (the default)
7067 vdso=0: disable VDSO mapping
7069 vdso32= [X86] Control the 32-bit vDSO
7070 vdso32=1: enable 32-bit VDSO
7071 vdso32=0 or vdso32=2: disable 32-bit VDSO
7073 See the help text for CONFIG_COMPAT_VDSO for more
7074 details. If CONFIG_COMPAT_VDSO is set, the default is
7075 vdso32=0; otherwise, the default is vdso32=1.
7077 For compatibility with older kernels, vdso32=2 is an
7080 Try vdso32=0 if you encounter an error that says:
7081 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
7084 vector=percpu: enable percpu vector domain
7086 video= [FB,EARLY] Frame buffer configuration
7087 See Documentation/fb/modedb.rst.
7089 video.brightness_switch_enabled= [ACPI]
7091 If set to 1, on receiving an ACPI notify event
7092 generated by hotkey, video driver will adjust brightness
7093 level and then send out the event to user space through
7094 the allocated input device. If set to 0, video driver
7095 will only send out the event without touching backlight
7100 [VMMIO] Memory mapped virtio (platform) device.
7102 <size>@<baseaddr>:<irq>[:<id>]
7104 <size> := size (can use standard suffixes
7106 <baseaddr> := physical base address
7107 <irq> := interrupt number (as passed to
7109 <id> := (optional) platform device id
7111 virtio_mmio.device=1K@0x100b0000:48:7
7113 Can be used multiple times for multiple devices.
7115 vga= [BOOT,X86-32] Select a particular video mode
7116 See Documentation/arch/x86/boot.rst and
7117 Documentation/admin-guide/svga.rst.
7118 Use vga=ask for menu.
7119 This is actually a boot loader parameter; the value is
7120 passed to the kernel using a special protocol.
7122 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
7123 May slow down system boot speed, especially when
7124 enabled on systems with a large amount of memory.
7125 All options are enabled by default, and this
7126 interface is meant to allow for selectively
7127 enabling or disabling specific virtual memory
7130 Available options are:
7131 P Enable page structure init time poisoning
7132 - Disable all of the above options
7134 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an
7135 exact size of <nn>. This can be used to increase
7136 the minimum size (128MB on x86). It can also be
7137 used to decrease the size and leave more room
7138 for directly mapped kernel RAM.
7140 vmcp_cma=nn[MG] [KNL,S390,EARLY]
7141 Sets the memory size reserved for contiguous memory
7142 allocations for the vmcp device driver.
7144 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
7147 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
7150 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
7153 vsyscall= [X86-64,EARLY]
7154 Controls the behavior of vsyscalls (i.e. calls to
7155 fixed addresses of 0xffffffffff600x00 from legacy
7156 code). Most statically-linked binaries and older
7157 versions of glibc use these calls. Because these
7158 functions are at fixed addresses, they make nice
7159 targets for exploits that can control RIP.
7161 emulate Vsyscalls turn into traps and are emulated
7162 reasonably safely. The vsyscall page is
7165 xonly [default] Vsyscalls turn into traps and are
7166 emulated reasonably safely. The vsyscall
7167 page is not readable.
7169 none Vsyscalls don't work at all. This makes
7170 them quite hard to use for exploits but
7171 might break your system.
7173 vt.color= [VT] Default text color.
7174 Format: 0xYX, X = foreground, Y = background.
7175 Default: 0x07 = light gray on black.
7177 vt.cur_default= [VT] Default cursor shape.
7178 Format: 0xCCBBAA, where AA, BB, and CC are the same as
7179 the parameters of the <Esc>[?A;B;Cc escape sequence;
7180 see VGA-softcursor.txt. Default: 2 = underline.
7182 vt.default_blu= [VT]
7183 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
7184 Change the default blue palette of the console.
7185 This is a 16-member array composed of values
7188 vt.default_grn= [VT]
7189 Format: <green0>,<green1>,<green2>,...,<green15>
7190 Change the default green palette of the console.
7191 This is a 16-member array composed of values
7194 vt.default_red= [VT]
7195 Format: <red0>,<red1>,<red2>,...,<red15>
7196 Change the default red palette of the console.
7197 This is a 16-member array composed of values
7203 Set system-wide default UTF-8 mode for all tty's.
7204 Default is 1, i.e. UTF-8 mode is enabled for all
7205 newly opened terminals.
7207 vt.global_cursor_default=
7210 Set system-wide default for whether a cursor
7211 is shown on new VTs. Default is -1,
7212 i.e. cursors will be created by default unless
7213 overridden by individual drivers. 0 will hide
7214 cursors, 1 will display them.
7216 vt.italic= [VT] Default color for italic text; 0-15.
7219 vt.underline= [VT] Default color for underlined text; 0-15.
7222 watchdog timers [HW,WDT] For information on watchdog timers,
7223 see Documentation/watchdog/watchdog-parameters.rst
7224 or other driver-specific files in the
7225 Documentation/watchdog/ directory.
7229 Set the hard lockup detector stall duration
7230 threshold in seconds. The soft lockup detector
7231 threshold is set to twice the value. A value of 0
7232 disables both lockup detectors. Default is 10
7235 workqueue.unbound_cpus=
7236 [KNL,SMP] Specify to constrain one or some CPUs
7237 to use in unbound workqueues.
7239 By default, all online CPUs are available for
7242 workqueue.watchdog_thresh=
7243 If CONFIG_WQ_WATCHDOG is configured, workqueue can
7244 warn stall conditions and dump internal state to
7245 help debugging. 0 disables workqueue stall
7246 detection; otherwise, it's the stall threshold
7247 duration in seconds. The default value is 30 and
7248 it can be updated at runtime by writing to the
7249 corresponding sysfs file.
7251 workqueue.cpu_intensive_thresh_us=
7252 Per-cpu work items which run for longer than this
7253 threshold are automatically considered CPU intensive
7254 and excluded from concurrency management to prevent
7255 them from noticeably delaying other per-cpu work
7256 items. Default is 10000 (10ms).
7258 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
7259 will report the work functions which violate this
7260 threshold repeatedly. They are likely good
7261 candidates for using WQ_UNBOUND workqueues instead.
7263 workqueue.cpu_intensive_warning_thresh=<uint>
7264 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
7265 will report the work functions which violate the
7266 intensive_threshold_us repeatedly. In order to prevent
7267 spurious warnings, start printing only after a work
7268 function has violated this threshold number of times.
7270 The default is 4 times. 0 disables the warning.
7272 workqueue.power_efficient
7273 Per-cpu workqueues are generally preferred because
7274 they show better performance thanks to cache
7275 locality; unfortunately, per-cpu workqueues tend to
7276 be more power hungry than unbound workqueues.
7278 Enabling this makes the per-cpu workqueues which
7279 were observed to contribute significantly to power
7280 consumption unbound, leading to measurably lower
7281 power usage at the cost of small performance
7284 The default value of this parameter is determined by
7285 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
7287 workqueue.default_affinity_scope=
7288 Select the default affinity scope to use for unbound
7289 workqueues. Can be one of "cpu", "smt", "cache",
7290 "numa" and "system". Default is "cache". For more
7291 information, see the Affinity Scopes section in
7292 Documentation/core-api/workqueue.rst.
7294 This can be changed after boot by writing to the
7295 matching /sys/module/workqueue/parameters file. All
7296 workqueues with the "default" affinity scope will be
7297 updated accordignly.
7299 workqueue.debug_force_rr_cpu
7300 Workqueue used to implicitly guarantee that work
7301 items queued without explicit CPU specified are put
7302 on the local CPU. This guarantee is no longer true
7303 and while local CPU is still preferred work items
7304 may be put on foreign CPUs. This debug option
7305 forces round-robin CPU selection to flush out
7306 usages which depend on the now broken guarantee.
7307 When enabled, memory and cache locality will be
7310 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access
7311 Type) of ioremap_wc().
7313 on - Enable writecombine, use WUC for ioremap_wc()
7314 off - Disable writecombine, use SUC for ioremap_wc()
7316 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of
7317 default x2apic cluster mode on platforms
7320 xen_512gb_limit [KNL,X86-64,XEN]
7321 Restricts the kernel running paravirtualized under Xen
7322 to use only up to 512 GB of RAM. The reason to do so is
7323 crash analysis tools and Xen tools for doing domain
7324 save/restore/migration must be enabled to handle larger
7327 xen_emul_unplug= [HW,X86,XEN,EARLY]
7328 Unplug Xen emulated devices
7329 Format: [unplug0,][unplug1]
7330 ide-disks -- unplug primary master IDE devices
7331 aux-ide-disks -- unplug non-primary-master IDE devices
7332 nics -- unplug network devices
7333 all -- unplug all emulated devices (NICs and IDE disks)
7334 unnecessary -- unplugging emulated devices is
7335 unnecessary even if the host did not respond to
7337 never -- do not unplug even if version check succeeds
7339 xen_legacy_crash [X86,XEN,EARLY]
7340 Crash from Xen panic notifier, without executing late
7341 panic() code such as dumping handler.
7343 xen_msr_safe= [X86,XEN,EARLY]
7345 Select whether to always use non-faulting (safe) MSR
7346 access functions when running as Xen PV guest. The
7347 default value is controlled by CONFIG_XEN_PV_MSR_SAFE.
7349 xen_nopvspin [X86,XEN,EARLY]
7350 Disables the qspinlock slowpath using Xen PV optimizations.
7351 This parameter is obsoleted by "nopvspin" parameter, which
7352 has equivalent effect for XEN platform.
7355 Disables the PV optimizations forcing the HVM guest to
7356 run as generic HVM guest with no PV drivers.
7357 This option is obsoleted by the "nopv" option, which
7358 has equivalent effect for XEN platform.
7360 xen_no_vector_callback
7361 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen
7362 event channel interrupts.
7364 xen_scrub_pages= [XEN]
7365 Boolean option to control scrubbing pages before giving them back
7366 to Xen, for use by other domains. Can be also changed at runtime
7367 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
7368 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
7370 xen_timer_slop= [X86-64,XEN,EARLY]
7371 Set the timer slop (in nanoseconds) for the virtual Xen
7372 timers (default is 100000). This adjusts the minimum
7373 delta of virtualized Xen timers, where lower values
7374 improve timer resolution at the expense of processing
7375 more timer interrupts.
7377 xen.balloon_boot_timeout= [XEN]
7378 The time (in seconds) to wait before giving up to boot
7379 in case initial ballooning fails to free enough memory.
7380 Applies only when running as HVM or PVH guest and
7381 started with less memory configured than allowed at
7382 max. Default is 180.
7384 xen.event_eoi_delay= [XEN]
7385 How long to delay EOI handling in case of event
7386 storms (jiffies). Default is 10.
7388 xen.event_loop_timeout= [XEN]
7389 After which time (jiffies) the event handling loop
7390 should start to delay EOI handling. Default is 2.
7392 xen.fifo_events= [XEN]
7393 Boolean parameter to disable using fifo event handling
7394 even if available. Normally fifo event handling is
7395 preferred over the 2-level event handling, as it is
7396 fairer and the number of possible event channels is
7397 much higher. Default is on (use fifo events).
7399 xirc2ps_cs= [NET,PCMCIA]
7401 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
7404 By default on POWER9 and above, the kernel will
7405 natively use the XIVE interrupt controller. This option
7406 allows the fallback firmware mode to be used:
7408 off Fallback to firmware control of XIVE interrupt
7409 controller on both pseries and powernv
7410 platforms. Only useful on POWER9 and above.
7412 xive.store-eoi=off [PPC]
7413 By default on POWER10 and above, the kernel will use
7414 stores for EOI handling when the XIVE interrupt mode
7415 is active. This option allows the XIVE driver to use
7416 loads instead, as on POWER9.
7418 xhci-hcd.quirks [USB,KNL]
7419 A hex value specifying bitmask with supplemental xhci
7420 host controller quirks. Meaning of each bit can be
7421 consulted in header drivers/usb/host/xhci.h.
7424 Format: { early | on | rw | ro | off }
7425 Controls if xmon debugger is enabled. Default is off.
7426 Passing only "xmon" is equivalent to "xmon=early".
7427 early Call xmon as early as possible on boot; xmon
7428 debugger is called from setup_arch().
7429 on xmon debugger hooks will be installed so xmon
7430 is only called on a kernel crash. Default mode,
7431 i.e. either "ro" or "rw" mode, is controlled
7432 with CONFIG_XMON_DEFAULT_RO_MODE.
7433 rw xmon debugger hooks will be installed so xmon
7434 is called only on a kernel crash, mode is write,
7435 meaning SPR registers, memory and, other data
7436 can be written using xmon commands.
7437 ro same as "rw" option above but SPR registers,
7438 memory, and other data can't be written using
7440 off xmon is disabled.
git.samba.org / sfrench / cifs-2.6.git / blob