1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
159 acpi_osi=!! # enable all built-in OS vendor
161 acpi_osi= # disable all strings
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
259 See Documentation/sound/alsa-configuration.rst
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
293 off - do not initialize any AMD IOMMU found in
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
319 See also Documentation/input/joydev/joystick.rst
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
327 Power management functions (SPARCstation-4/5 + deriv.)
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity while booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
465 [NET] Specifies amount of time (in seconds) that
466 the kernel should wait for a network carrier. By default
467 it waits 120 seconds.
469 ca_keys= [KEYS] This parameter identifies a specific key(s) on
470 the system trusted keyring to be used for certificate
472 format: { id:<keyid> | builtin }
474 cca= [MIPS] Override the kernel pages' cache coherency
475 algorithm. Accepted values range from 0 to 7
476 inclusive. See arch/mips/include/asm/pgtable-bits.h
477 for platform specific values (SB1, Loongson3 and
480 ccw_timeout_log [S390]
481 See Documentation/s390/CommonIO for details.
483 cgroup_disable= [KNL] Disable a particular controller
484 Format: {name of the controller(s) to disable}
485 The effects of cgroup_disable=foo are:
486 - foo isn't auto-mounted if you mount all cgroups in
488 - foo isn't visible as an individually mountable
490 {Currently only "memory" controller deal with this and
491 cut the overhead, others just disable the usage. So
492 only cgroup_disable=memory is actually worthy}
494 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
495 Format: { { controller | "all" | "named" }
496 [,{ controller | "all" | "named" }...] }
497 Like cgroup_disable, but only applies to cgroup v1;
498 the blacklisted controllers remain available in cgroup2.
499 "all" blacklists all controllers and "named" disables
500 named mounts. Specifying both "all" and "named" disables
503 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
505 nosocket -- Disable socket memory accounting.
506 nokmem -- Disable kernel memory accounting.
508 checkreqprot [SELINUX] Set initial checkreqprot flag value.
509 Format: { "0" | "1" }
510 See security/selinux/Kconfig help text.
511 0 -- check protection applied by kernel (includes
512 any implied execute protection).
513 1 -- check protection requested by application.
514 Default value is set via a kernel config option.
515 Value can be changed at runtime via
516 /selinux/checkreqprot.
519 See Documentation/s390/CommonIO for details.
522 Prevents the clock framework from automatically gating
523 clocks that have not been explicitly enabled by a Linux
524 device driver but are enabled in hardware at reset or
525 by the bootloader/firmware. Note that this does not
526 force such clocks to be always-on nor does it reserve
527 those clocks in any way. This parameter is useful for
528 debug and development, but should not be needed on a
529 platform with proper driver support. For more
530 information, see Documentation/driver-api/clk.rst.
532 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
534 Forces specified clocksource (if available) to be used
535 when calculating gettimeofday(). If specified
536 clocksource is not available, it defaults to PIT.
537 Format: { pit | tsc | cyclone | pmtmr }
539 clocksource= Override the default clocksource
541 Override the default clocksource and use the clocksource
542 with the name specified.
543 Some clocksource names to choose from, depending on
545 [all] jiffies (this is the base, fallback clocksource)
547 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
548 pxa_timer,timer3,32k_counter,timer0_1
549 [X86-32] pit,hpet,tsc;
550 scx200_hrt on Geode; cyclone on IBM x440
558 clocksource.arm_arch_timer.evtstrm=
561 Enable/disable the eventstream feature of the ARM
562 architected timer so that code using WFE-based polling
563 loops can be debugged more effectively on production
566 clearcpuid=BITNUM [X86]
567 Disable CPUID feature X for the kernel. See
568 arch/x86/include/asm/cpufeatures.h for the valid bit
569 numbers. Note the Linux specific bits are not necessarily
570 stable over kernel options, but the vendor specific
572 Also note that user programs calling CPUID directly
573 or using the feature without checking anything
574 will still see it. This just prevents it from
575 being used by the kernel or shown in /proc/cpuinfo.
576 Also note the kernel might malfunction if you disable
579 cma=nn[MG]@[start[MG][-end[MG]]]
581 Sets the size of kernel global memory area for
582 contiguous memory allocations and optionally the
583 placement constraint by the physical address range of
584 memory allocations. A value of 0 disables CMA
585 altogether. For more information, see
586 include/linux/dma-contiguous.h
588 cmo_free_hint= [PPC] Format: { yes | no }
589 Specify whether pages are marked as being inactive
590 when they are freed. This is used in CMO environments
591 to determine OS memory pressure for page stealing by
595 coherent_pool=nn[KMG] [ARM,KNL]
596 Sets the size of memory pool for coherent, atomic dma
597 allocations, by default set to 256K.
599 com20020= [HW,NET] ARCnet - COM20020 chipset
601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
607 ARCnet - COM90xx chipset (memory-mapped buffers)
608 Format: <io>[,<irq>[,<memstart>]]
610 condev= [HW,S390] console device
613 console= [KNL] Output console device and options.
615 tty<n> Use the virtual console device <n>.
619 Use the specified serial port. The options are of
620 the form "bbbbpnf", where "bbbb" is the baud rate,
621 "p" is parity ("n", "o", or "e"), "n" is number of
622 bits, and "f" is flow control ("r" for RTS or
623 omit it). Default is "9600n8".
625 See Documentation/admin-guide/serial-console.rst for more
627 Documentation/networking/netconsole.txt for an
630 uart[8250],io,<addr>[,options]
631 uart[8250],mmio,<addr>[,options]
632 uart[8250],mmio16,<addr>[,options]
633 uart[8250],mmio32,<addr>[,options]
634 uart[8250],0x<addr>[,options]
635 Start an early, polled-mode console on the 8250/16550
636 UART at the specified I/O port or MMIO address,
637 switching to the matching ttyS device later.
638 MMIO inter-register address stride is either 8-bit
639 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
640 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
641 to be equivalent to 'mmio'. 'options' are specified in
642 the same format described for ttyS above; if unspecified,
643 the h/w is not re-initialized.
645 hvc<n> Use the hypervisor console device <n>. This is for
646 both Xen and PowerPC hypervisors.
648 If the device connected to the port is not a TTY but a braille
649 device, prepend "brl," before the device type, for instance
651 For now, only VisioBraille is supported.
654 [KNL] Change console messages format
656 By default we print messages on consoles in
657 "[time stamp] text\n" format (time stamp may not be
658 printed, depending on CONFIG_PRINTK_TIME or
659 `printk_time' param).
661 Switch to syslog format: "<%u>[time stamp] text\n"
662 IOW, each message will have a facility and loglevel
663 prefix. The format is similar to one used by syslog()
664 syscall, or to executing "dmesg -S --raw" or to reading
667 consoleblank= [KNL] The console blank (screen saver) timeout in
668 seconds. A value of 0 disables the blank timer.
672 [KNL] Change the default value for
673 /proc/<pid>/coredump_filter.
674 See also Documentation/filesystems/proc.txt.
676 coresight_cpu_debug.enable
679 Enable/disable the CPU sampling based debugging.
680 0: default value, disable debugging
681 1: enable debugging at boot time
683 cpuidle.off=1 [CPU_IDLE]
684 disable the cpuidle sub-system
687 [CPU_IDLE] Name of the cpuidle governor to use.
689 cpufreq.off=1 [CPU_FREQ]
690 disable the cpufreq sub-system
693 [X86] Delay for N microsec between assert and de-assert
694 of APIC INIT to start processors. This delay occurs
695 on every CPU online, such as boot, and resume from suspend.
698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
700 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
702 crashkernel=size[KMG][@offset[KMG]]
703 [KNL] Using kexec, Linux can switch to a 'crash kernel'
704 upon panic. This parameter reserves the physical
705 memory region [offset, offset + size] for that kernel
706 image. If '@offset' is omitted, then a suitable offset
707 is selected automatically. Check
708 Documentation/kdump/kdump.txt for further details.
710 crashkernel=range1:size1[,range2:size2,...][@offset]
711 [KNL] Same as above, but depends on the memory
712 in the running system. The syntax of range is
713 start-[end] where start and end are both
714 a memory unit (amount[KMG]). See also
715 Documentation/kdump/kdump.txt for an example.
717 crashkernel=size[KMG],high
718 [KNL, x86_64] range could be above 4G. Allow kernel
719 to allocate physical memory region from top, so could
720 be above 4G if system have more than 4G ram installed.
721 Otherwise memory region will be allocated below 4G, if
723 It will be ignored if crashkernel=X is specified.
724 crashkernel=size[KMG],low
725 [KNL, x86_64] range under 4G. When crashkernel=X,high
726 is passed, kernel could allocate physical memory region
727 above 4G, that cause second kernel crash on system
728 that require some amount of low memory, e.g. swiotlb
729 requires at least 64M+32K low memory, also enough extra
730 low memory is needed to make sure DMA buffers for 32-bit
731 devices won't run out. Kernel would try to allocate at
732 at least 256M below 4G automatically.
733 This one let user to specify own low range under 4G
734 for second kernel instead.
735 0: to disable low allocation.
736 It will be ignored when crashkernel=X,high is not used
737 or memory reserved is below 4G.
740 [KNL] Disable crypto self-tests
745 cs89x0_media= [HW,NET]
746 Format: { rj45 | aui | bnc }
749 See header of drivers/s390/block/dasd_devmap.c.
751 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
752 (one device per port)
753 Format: <port#>,<type>
754 See also Documentation/input/devices/joystick-parport.rst
756 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
758 Documentation/admin-guide/dynamic-debug-howto.rst for
759 details. Deprecated, see dyndbg.
761 debug [KNL] Enable kernel debugging (events log level).
764 [KNL] Enable printing [hashed] pointers early in the
765 boot sequence. If enabled, we use a weak hash instead
766 of siphash to hash pointers. Use this option if you are
767 seeing instances of '(___ptrval___)') and need to see a
768 value (hashed pointer) instead. Cryptographically
769 insecure, please do not use on production kernels.
772 [KNL] verbose self-tests
774 Print debugging info while doing the locking API
776 We default to 0 (no extra messages), setting it to
777 1 will print _a lot_ more information - normally
778 only useful to kernel developers.
780 debug_objects [KNL] Enable object debugging
783 [KNL] Disable object debugging
785 debug_guardpage_minorder=
786 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
787 parameter allows control of the order of pages that will
788 be intentionally kept free (and hence protected) by the
789 buddy allocator. Bigger value increase the probability
790 of catching random memory corruption, but reduce the
791 amount of memory for normal system use. The maximum
792 possible value is MAX_ORDER/2. Setting this parameter
793 to 1 or 2 should be enough to identify most random
794 memory corruption problems caused by bugs in kernel or
795 driver code when a CPU writes to (or reads from) a
796 random memory location. Note that there exists a class
797 of memory corruptions problems caused by buggy H/W or
798 F/W or by drivers badly programing DMA (basically when
799 memory is written at bus level and the CPU MMU is
800 bypassed) which are not detectable by
801 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
802 tracking down these problems.
805 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
806 parameter enables the feature at boot time. In
807 default, it is disabled. We can avoid allocating huge
808 chunk of memory for debug pagealloc if we don't enable
809 it at boot time and the system will work mostly same
810 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
811 on: enable the feature
813 debugpat [X86] Enable PAT debugging
815 decnet.addr= [HW,NET]
816 Format: <area>[,<node>]
817 See also Documentation/networking/decnet.txt.
820 [same as hugepagesz=] The size of the default
821 HugeTLB page size. This is the size represented by
822 the legacy /proc/ hugepages APIs, used for SHM, and
823 default size when mounting hugetlbfs filesystems.
824 Defaults to the default architecture's huge page size
827 deferred_probe_timeout=
828 [KNL] Debugging option to set a timeout in seconds for
829 deferred probe to give up waiting on dependencies to
830 probe. Only specific dependencies (subsystems or
831 drivers) that have opted in will be ignored. A timeout of 0
832 will timeout at the end of initcalls. This option will also
833 dump out devices still on the deferred probe list after
837 Set number of hash buckets for dentry cache.
839 disable_1tb_segments [PPC]
840 Disables the use of 1TB hash page table segments. This
841 causes the kernel to fall back to 256MB segments which
842 can be useful when debugging issues that require an SLB
846 See Documentation/networking/ipv6.txt.
849 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
850 hardening is enabled for this boot. Hardened
851 usercopy checking is used to protect the kernel
852 from reading or writing beyond known memory
853 allocation boundaries as a proactive defense
854 against bounds-checking flaws in the kernel's
855 copy_to_user()/copy_from_user() interface.
856 on Perform hardened usercopy checks (default).
857 off Disable hardened usercopy checks.
860 Disable RADIX MMU mode on POWER9
862 disable_cpu_apicid= [X86,APIC,SMP]
864 The number of initial APIC ID for the
865 corresponding CPU to be disabled at boot,
866 mostly used for the kdump 2nd kernel to
867 disable BSP to wake up multiple CPUs without
868 causing system reset or hang due to sending
871 perf_v4_pmi= [X86,INTEL]
873 Disable Intel PMU counter freezing feature.
874 The feature only exists starting from
875 Arch Perfmon v4 (Skylake and newer).
877 disable_ddw [PPC/PSERIES]
878 Disable Dynamic DMA Window support. Use this if
879 to workaround buggy firmware.
882 See Documentation/networking/ipv6.txt.
884 disable_mtrr_cleanup [X86]
885 The kernel tries to adjust MTRR layout from continuous
886 to discrete, to make X server driver able to add WB
887 entry later. This parameter disables that.
889 disable_mtrr_trim [X86, Intel and AMD only]
890 By default the kernel will trim any uncacheable
891 memory out of your available memory pool based on
892 MTRR settings. This parameter disables that behavior,
893 possibly causing your machine to run very slowly.
895 disable_timer_pin_1 [X86]
896 Disable PIN 1 of APIC timer
897 Can be useful to work around chipset bugs.
899 dis_ucode_ldr [X86] Disable the microcode loader.
901 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
902 this option disables the debugging code at boot.
904 dma_debug_entries=<number>
905 This option allows to tune the number of preallocated
906 entries for DMA-API debugging code. One entry is
907 required per DMA-API allocation. Use this if the
908 DMA-API debugging code disables itself because the
909 architectural default is too low.
911 dma_debug_driver=<driver_name>
912 With this option the DMA-API debugging driver
913 filter feature can be enabled at boot time. Just
914 pass the driver to filter for as the parameter.
915 The filter can be disabled or changed to another
916 driver later using sysfs.
918 driver_async_probe= [KNL]
919 List of driver names to be probed asynchronously.
920 Format: <driver_name1>,<driver_name2>...
922 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
923 Broken monitors, graphic adapters, KVMs and EDIDless
924 panels may send no or incorrect EDID data sets.
925 This parameter allows to specify an EDID data sets
926 in the /lib/firmware directory that are used instead.
927 Generic built-in EDID data sets are used, if one of
928 edid/1024x768.bin, edid/1280x1024.bin,
929 edid/1680x1050.bin, or edid/1920x1080.bin is given
930 and no file with the same name exists. Details and
931 instructions how to build your own EDID data are
932 available in Documentation/EDID/HOWTO.txt. An EDID
933 data set will only be used for a particular connector,
934 if its name and a colon are prepended to the EDID
935 name. Each connector may use a unique EDID data
936 set by separating the files with a comma. An EDID
937 data set with no connector name will be used for
938 any connectors not explicitly specified.
943 Format: {"off" | "known"}
944 Control how the dt_cpu_ftrs device-tree binding is
945 used for CPU feature discovery and setup (if it
947 off: Do not use it, fall back to legacy cpu table.
948 known: Do not pass through unknown features to guests
949 or userspace, only those that the kernel is aware of.
951 dump_apple_properties [X86]
952 Dump name and content of EFI device properties on
953 x86 Macs. Useful for driver authors to determine
954 what data is available or for reverse-engineering.
956 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
957 module.dyndbg[="val"]
958 Enable debug messages at boot time. See
959 Documentation/admin-guide/dynamic-debug-howto.rst
962 nompx [X86] Disables Intel Memory Protection Extensions.
963 See Documentation/x86/intel_mpx.txt for more
964 information about the feature.
966 nopku [X86] Disable Memory Protection Keys CPU feature found
969 module.async_probe [KNL]
970 Enable asynchronous probe on this module.
972 early_ioremap_debug [KNL]
973 Enable debug messages in early_ioremap support. This
974 is useful for tracking down temporary early mappings
975 which are not unmapped.
977 earlycon= [KNL] Output early console device and options.
979 [ARM64] The early console is determined by the
980 stdout-path property in device tree's chosen node,
981 or determined by the ACPI SPCR table.
983 [X86] When used with no options the early console is
984 determined by the ACPI SPCR table.
986 cdns,<addr>[,options]
987 Start an early, polled-mode console on a Cadence
988 (xuartps) serial port at the specified address. Only
989 supported option is baud rate. If baud rate is not
990 specified, the serial port must already be setup and
993 uart[8250],io,<addr>[,options]
994 uart[8250],mmio,<addr>[,options]
995 uart[8250],mmio32,<addr>[,options]
996 uart[8250],mmio32be,<addr>[,options]
997 uart[8250],0x<addr>[,options]
998 Start an early, polled-mode console on the 8250/16550
999 UART at the specified I/O port or MMIO address.
1000 MMIO inter-register address stride is either 8-bit
1001 (mmio) or 32-bit (mmio32 or mmio32be).
1002 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1003 to be equivalent to 'mmio'. 'options' are specified
1004 in the same format described for "console=ttyS<n>"; if
1005 unspecified, the h/w is not initialized.
1009 Start an early, polled-mode console on a pl011 serial
1010 port at the specified address. The pl011 serial port
1011 must already be setup and configured. Options are not
1012 yet supported. If 'mmio32' is specified, then only
1013 the driver will use only 32-bit accessors to read/write
1014 the device registers.
1017 Start an early, polled-mode console on a meson serial
1018 port at the specified address. The serial port must
1019 already be setup and configured. Options are not yet
1023 Start an early, polled-mode console on an msm serial
1024 port at the specified address. The serial port
1025 must already be setup and configured. Options are not
1028 msm_serial_dm,<addr>
1029 Start an early, polled-mode console on an msm serial
1030 dm port at the specified address. The serial port
1031 must already be setup and configured. Options are not
1035 Start an early, polled-mode console on a serial port
1036 of an Actions Semi SoC, such as S500 or S900, at the
1037 specified address. The serial port must already be
1038 setup and configured. Options are not yet supported.
1041 Start an early, polled-mode console on a serial port
1042 of an RDA Micro SoC, such as RDA8810PL, at the
1043 specified address. The serial port must already be
1044 setup and configured. Options are not yet supported.
1046 smh Use ARM semihosting calls for early console.
1054 Use early console provided by serial driver available
1055 on Samsung SoCs, requires selecting proper type and
1056 a correct base address of the selected UART port. The
1057 serial port must already be setup and configured.
1058 Options are not yet supported.
1061 Start an early, polled-mode console on a lantiq serial
1062 (lqasc) port at the specified address. The serial port
1063 must already be setup and configured. Options are not
1068 Use early console provided by Freescale LP UART driver
1069 found on Freescale Vybrid and QorIQ LS1021A processors.
1070 A valid base address must be provided, and the serial
1071 port must already be setup and configured.
1074 Start an early, polled-mode console on the
1075 Armada 3700 serial port at the specified
1076 address. The serial port must already be setup
1077 and configured. Options are not yet supported.
1080 Start an early, polled-mode console on a Qualcomm
1081 Generic Interface (GENI) based serial port at the
1082 specified address. The serial port must already be
1083 setup and configured. Options are not yet supported.
1086 Start an early, unaccelerated console on the EFI
1087 memory mapped framebuffer (if available). On cache
1088 coherent non-x86 systems that use system memory for
1089 the framebuffer, pass the 'ram' option so that it is
1090 mapped with the correct attributes.
1092 earlyprintk= [X86,SH,ARM,M68k,S390]
1096 earlyprintk=serial[,ttySn[,baudrate]]
1097 earlyprintk=serial[,0x...[,baudrate]]
1098 earlyprintk=ttySn[,baudrate]
1099 earlyprintk=dbgp[debugController#]
1100 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1101 earlyprintk=xdbc[xhciController#]
1103 earlyprintk is useful when the kernel crashes before
1104 the normal console is initialized. It is not enabled by
1105 default because it has some cosmetic problems.
1107 Append ",keep" to not disable it when the real console
1110 Only one of vga, efi, serial, or usb debug port can
1113 Currently only ttyS0 and ttyS1 may be specified by
1114 name. Other I/O ports may be explicitly specified
1115 on some architectures (x86 and arm at least) by
1116 replacing ttySn with an I/O port address, like this:
1117 earlyprintk=serial,0x1008,115200
1118 You can find the port for a given device in
1119 /proc/tty/driver/serial:
1120 2: uart:ST16650V2 port:00001008 irq:18 ...
1122 Interaction with the standard serial driver is not
1125 The VGA and EFI output is eventually overwritten by
1128 The xen output can only be used by Xen PV guests.
1130 The sclp output can only be used on s390.
1132 The optional "force" to "pciserial" enables use of a
1133 PCI device even when its classcode is not of the
1136 edac_report= [HW,EDAC] Control how to report EDAC event
1137 Format: {"on" | "off" | "force"}
1138 on: enable EDAC to report H/W event. May be overridden
1139 by other higher priority error reporting module.
1140 off: disable H/W event reporting through EDAC.
1141 force: enforce the use of EDAC to report H/W event.
1144 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1147 This is designed to be used in conjunction with
1148 the boot argument: earlyprintk=vga
1151 Format: {"off" | "on" | "skip[mbr]"}
1154 Format: { "old_map", "nochunk", "noruntime", "debug" }
1155 old_map [X86-64]: switch to the old ioremap-based EFI
1156 runtime services mapping. 32-bit still uses this one by
1158 nochunk: disable reading files in "chunks" in the EFI
1159 boot stub, as chunking can cause problems with some
1160 firmware implementations.
1161 noruntime : disable EFI runtime services support
1162 debug: enable misc debug output
1164 efi_no_storage_paranoia [EFI; X86]
1165 Using this parameter you can use more than 50% of
1166 your efi variable storage. Use this parameter only if
1167 you are really sure that your UEFI does sane gc and
1168 fulfills the spec otherwise your board may brick.
1170 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1171 Add arbitrary attribute to specific memory range by
1172 updating original EFI memory map.
1173 Region of memory which aa attribute is added to is
1175 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1176 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1177 attribute is added to range 0x100000000-0x180000000 and
1178 0x10a0000000-0x1120000000.
1180 Using this parameter you can do debugging of EFI memmap
1181 related feature. For example, you can do debugging of
1182 Address Range Mirroring feature even if your box
1185 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1186 that is to be dynamically loaded by Linux. If there are
1187 multiple variables with the same name but with different
1188 vendor GUIDs, all of them will be loaded. See
1189 Documentation/acpi/ssdt-overlays.txt for details.
1192 eisa_irq_edge= [PARISC,HW]
1193 See header of drivers/parisc/eisa.c.
1196 See comment before function elanfreq_setup() in
1197 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1200 Format: { "mq-deadline" | "kyber" | "bfq" }
1201 See Documentation/block/deadline-iosched.txt,
1202 Documentation/block/kyber-iosched.txt and
1203 Documentation/block/bfq-iosched.txt for details.
1205 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1206 Specifies physical address of start of kernel core
1207 image elf header and optionally the size. Generally
1208 kexec loader will pass this option to capture kernel.
1209 See Documentation/kdump/kdump.txt for details.
1211 enable_mtrr_cleanup [X86]
1212 The kernel tries to adjust MTRR layout from continuous
1213 to discrete, to make X server driver able to add WB
1214 entry later. This parameter enables that.
1216 enable_timer_pin_1 [X86]
1217 Enable PIN 1 of APIC timer
1218 Can be useful to work around chipset bugs
1219 (in particular on some ATI chipsets).
1220 The kernel tries to set a reasonable default.
1222 enforcing [SELINUX] Set initial enforcing status.
1224 See security/selinux/Kconfig help text.
1225 0 -- permissive (log only, no denials).
1226 1 -- enforcing (deny and log).
1228 Value can be changed at runtime via /selinux/enforce.
1231 Disable Error Record Serialization Table (ERST)
1234 ether= [HW,NET] Ethernet cards parameters
1235 This option is obsoleted by the "netdev=" option, which
1236 has equivalent usage. See its documentation for details.
1240 Permit 'security.evm' to be updated regardless of
1241 current integrity status.
1245 fail_make_request=[KNL]
1246 General fault injection mechanism.
1247 Format: <interval>,<probability>,<space>,<times>
1248 See also Documentation/fault-injection/.
1251 See Documentation/blockdev/floppy.txt.
1253 force_pal_cache_flush
1254 [IA-64] Avoid check_sal_cache_flush which may hang on
1255 buggy SAL_CACHE_FLUSH implementations. Using this
1256 parameter will force ia64_sal_cache_flush to call
1257 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1260 Forcefully enable Physical Address Extension (PAE).
1261 Many Pentium M systems disable PAE but may have a
1262 functionally usable PAE implementation.
1263 Warning: use of this parameter will taint the kernel
1264 and may cause unknown problems.
1267 [FTRACE] will set and start the specified tracer
1268 as early as possible in order to facilitate early
1271 ftrace_dump_on_oops[=orig_cpu]
1272 [FTRACE] will dump the trace buffers on oops.
1273 If no parameter is passed, ftrace will dump
1274 buffers of all CPUs, but if you pass orig_cpu, it will
1275 dump only the buffer of the CPU that triggered the
1278 ftrace_filter=[function-list]
1279 [FTRACE] Limit the functions traced by the function
1280 tracer at boot up. function-list is a comma separated
1281 list of functions. This list can be changed at run
1282 time by the set_ftrace_filter file in the debugfs
1285 ftrace_notrace=[function-list]
1286 [FTRACE] Do not trace the functions specified in
1287 function-list. This list can be changed at run time
1288 by the set_ftrace_notrace file in the debugfs
1291 ftrace_graph_filter=[function-list]
1292 [FTRACE] Limit the top level callers functions traced
1293 by the function graph tracer at boot up.
1294 function-list is a comma separated list of functions
1295 that can be changed at run time by the
1296 set_graph_function file in the debugfs tracing directory.
1298 ftrace_graph_notrace=[function-list]
1299 [FTRACE] Do not trace from the functions specified in
1300 function-list. This list is a comma separated list of
1301 functions that can be changed at run time by the
1302 set_graph_notrace file in the debugfs tracing directory.
1304 ftrace_graph_max_depth=<uint>
1305 [FTRACE] Used with the function graph tracer. This is
1306 the max depth it will trace into a function. This value
1307 can be changed at run time by the max_graph_depth file
1308 in the tracefs tracing directory. default: 0 (no limit)
1311 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1312 support via parallel port (up to 5 devices per port)
1313 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1314 See also Documentation/input/devices/joystick-parport.rst
1318 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1322 gcov_persist= [GCOV] When non-zero (default), profiling data for
1323 kernel modules is saved and remains accessible via
1324 debugfs, even when the module is unloaded/reloaded.
1325 When zero, profiling data is discarded and associated
1326 debugfs files are removed at module unload time.
1328 goldfish [X86] Enable the goldfish android emulator platform.
1329 Don't use this when you are not running on the
1332 gpt [EFI] Forces disk with valid GPT signature but
1333 invalid Protective MBR to be treated as GPT. If the
1334 primary GPT is corrupted, it enables the backup/alternate
1335 GPT to be used instead.
1337 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1338 the "Enable 0" bit of the configuration register.
1341 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1342 the "Enable 0" bit of the configuration register.
1345 grcan.select= [HW] Select which physical interface to use.
1348 grcan.txsize= [HW] Sets the size of the tx buffer.
1349 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1351 grcan.rxsize= [HW] Sets the size of the rx buffer.
1352 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1355 gpio-mockup.gpio_mockup_ranges
1356 [HW] Sets the ranges of gpiochip of for this device.
1357 Format: <start1>,<end1>,<start2>,<end2>...
1359 hardlockup_all_cpu_backtrace=
1360 [KNL] Should the hard-lockup detector generate
1361 backtraces on all cpus.
1364 hashdist= [KNL,NUMA] Large hashes allocated during boot
1365 are distributed across NUMA nodes. Defaults on
1366 for 64-bit NUMA, off otherwise.
1367 Format: 0 | 1 (for off | on)
1369 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1371 hd= [EIDE] (E)IDE hard drive subsystem geometry
1372 Format: <cyl>,<head>,<sect>
1375 Disable Hardware Error Source Table (HEST) support;
1376 corresponding firmware-first mode error processing
1377 logic will be disabled.
1379 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1380 size of <nn>. This works even on boxes that have no
1381 highmem otherwise. This also works to reduce highmem
1382 size on bigger boxes.
1384 highres= [KNL] Enable/disable high resolution timer mode.
1385 Valid parameters: "on", "off"
1389 See Documentation/isdn/README.HiSax.
1393 hpet= [X86-32,HPET] option to control HPET usage
1394 Format: { enable (default) | disable | force |
1396 disable: disable HPET and use PIT instead
1397 force: allow force enabled of undocumented chips (ICH4,
1399 verbose: show contents of HPET registers during setup
1401 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1402 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1404 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1405 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1406 On x86-64 and powerpc, this option can be specified
1407 multiple times interleaved with hugepages= to reserve
1408 huge pages of different sizes. Valid pages sizes on
1409 x86-64 are 2M (when the CPU supports "pse") and 1G
1410 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1413 [KNL] Should the hung task detector generate panics.
1416 A nonzero value instructs the kernel to panic when a
1417 hung task is detected. The default value is controlled
1418 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1419 option. The value selected by this boot parameter can
1420 be changed later by the kernel.hung_task_panic sysctl.
1422 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1423 terminal devices. Valid values: 0..8
1424 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1425 If specified, z/VM IUCV HVC accepts connections
1426 from listed z/VM user IDs only.
1428 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1429 which allow the hypervisor to 'idle' the
1430 guest on lock contention.
1433 Do not unregister boot console at start. This is only
1434 useful for debugging when something happens in the window
1435 between unregistering the boot console and initializing
1438 i2c_bus= [HW] Override the default board specific I2C bus speed
1439 or register an additional I2C bus that is not
1440 registered from board initialization code.
1444 i8042.debug [HW] Toggle i8042 debug mode
1445 i8042.unmask_kbd_data
1446 [HW] Enable printing of interrupt data from the KBD port
1447 (disabled by default, and as a pre-condition
1448 requires that i8042.debug=1 be enabled)
1449 i8042.direct [HW] Put keyboard port into non-translated mode
1450 i8042.dumbkbd [HW] Pretend that controller can only read data from
1451 keyboard and cannot control its state
1452 (Don't attempt to blink the leds)
1453 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1454 i8042.nokbd [HW] Don't check/create keyboard port
1455 i8042.noloop [HW] Disable the AUX Loopback command while probing
1457 i8042.nomux [HW] Don't check presence of an active multiplexing
1459 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1461 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1462 i8042.reset [HW] Reset the controller during init, cleanup and
1463 suspend-to-ram transitions, only during s2r
1464 transitions, or never reset
1465 Format: { 1 | Y | y | 0 | N | n }
1466 1, Y, y: always reset controller
1467 0, N, n: don't ever reset controller
1468 Default: only on s2r transitions on x86; most other
1469 architectures force reset to be always executed
1470 i8042.unlock [HW] Unlock (ignore) the keylock
1471 i8042.kbdreset [HW] Reset device connected to KBD port
1475 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1476 indicates that the driver is running on unsupported
1478 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1479 does not match list of supported models.
1481 [HW] Report power status in /proc/i8k
1482 (disabled by default)
1483 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1486 i915.invert_brightness=
1487 [DRM] Invert the sense of the variable that is used to
1488 set the brightness of the panel backlight. Normally a
1489 brightness value of 0 indicates backlight switched off,
1490 and the maximum of the brightness value sets the backlight
1491 to maximum brightness. If this parameter is set to 0
1492 (default) and the machine requires it, or this parameter
1493 is set to 1, a brightness value of 0 sets the backlight
1494 to maximum brightness, and the maximum of the brightness
1495 value switches the backlight off.
1496 -1 -- never invert brightness
1497 0 -- machine default
1498 1 -- force brightness inversion
1501 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1503 ide-core.nodma= [HW] (E)IDE subsystem
1504 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1505 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1506 .cdrom .chs .ignore_cable are additional options
1507 See Documentation/ide/ide.txt.
1509 ide-generic.probe-mask= [HW] (E)IDE subsystem
1511 Probe mask for legacy ISA IDE ports. Depending on
1512 platform up to 6 ports are supported, enabled by
1513 setting corresponding bits in the mask to 1. The
1514 default value is 0x0, which has a special meaning.
1515 On systems that have PCI, it triggers scanning the
1516 PCI bus for the first and the second port, which
1517 are then probed. On systems without PCI the value
1518 of 0x0 enables probing the two first ports as if it
1521 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1522 Claim all unknown PCI IDE storage controllers.
1525 Format: idle=poll, idle=halt, idle=nomwait
1526 Poll forces a polling idle loop that can slightly
1527 improve the performance of waking up a idle CPU, but
1528 will use a lot of power and make the system run hot.
1530 idle=halt: Halt is forced to be used for CPU idle.
1531 In such case C2/C3 won't be used again.
1532 idle=nomwait: Disable mwait for CPU C-states
1534 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1535 Format: { strict | legacy | 2008 | relaxed }
1538 Choose which programs will be accepted for execution
1539 based on the IEEE 754 NaN encoding(s) supported by
1540 the FPU and the NaN encoding requested with the value
1541 of an ELF file header flag individually set by each
1542 binary. Hardware implementations are permitted to
1543 support either or both of the legacy and the 2008 NaN
1546 Available settings are as follows:
1547 strict accept binaries that request a NaN encoding
1548 supported by the FPU
1549 legacy only accept legacy-NaN binaries, if supported
1551 2008 only accept 2008-NaN binaries, if supported
1553 relaxed accept any binaries regardless of whether
1554 supported by the FPU
1556 The FPU emulator is always able to support both NaN
1557 encodings, so if no FPU hardware is present or it has
1558 been disabled with 'nofpu', then the settings of
1559 'legacy' and '2008' strap the emulator accordingly,
1560 'relaxed' straps the emulator for both legacy-NaN and
1561 2008-NaN, whereas 'strict' enables legacy-NaN only on
1562 legacy processors and both NaN encodings on MIPS32 or
1565 The setting for ABS.fmt/NEG.fmt instruction execution
1566 mode generally follows that for the NaN encoding,
1567 except where unsupported by hardware.
1569 ignore_loglevel [KNL]
1570 Ignore loglevel setting - this will print /all/
1571 kernel messages to the console. Useful for debugging.
1572 We also add it as printk module parameter, so users
1573 could change it dynamically, usually by
1574 /sys/module/printk/parameters/ignore_loglevel.
1577 Ignore RLIMIT_DATA setting for data mappings,
1578 print warning at first misuse. Can be changed via
1579 /sys/module/kernel/parameters/ignore_rlimit_data.
1581 ihash_entries= [KNL]
1582 Set number of hash buckets for inode cache.
1584 ima_appraise= [IMA] appraise integrity measurements
1585 Format: { "off" | "enforce" | "fix" | "log" }
1588 ima_appraise_tcb [IMA]
1589 The builtin appraise policy appraises all files
1592 ima_canonical_fmt [IMA]
1593 Use the canonical format for the binary runtime
1594 measurements, instead of host native format.
1597 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1601 The list of supported hash algorithms is defined
1602 in crypto/hash_info.h.
1605 The builtin policies to load during IMA setup.
1606 Format: "tcb | appraise_tcb | secure_boot |
1609 The "tcb" policy measures all programs exec'd, files
1610 mmap'd for exec, and all files opened with the read
1611 mode bit set by either the effective uid (euid=0) or
1614 The "appraise_tcb" policy appraises the integrity of
1615 all files owned by root. (This is the equivalent
1616 of ima_appraise_tcb.)
1618 The "secure_boot" policy appraises the integrity
1619 of files (eg. kexec kernel image, kernel modules,
1620 firmware, policy, etc) based on file signatures.
1622 The "fail_securely" policy forces file signature
1623 verification failure also on privileged mounted
1624 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1627 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1628 Load a policy which meets the needs of the Trusted
1629 Computing Base. This means IMA will measure all
1630 programs exec'd, files mmap'd for exec, and all files
1631 opened for read by uid=0.
1634 Select one of defined IMA measurements template formats.
1635 Formats: { "ima" | "ima-ng" | "ima-sig" }
1639 [IMA] Define a custom template format.
1640 Format: { "field1|...|fieldN" }
1642 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1643 Format: <min_file_size>
1644 Set the minimal file size for using asynchronous hash.
1645 If left unspecified, ahash usage is disabled.
1647 ahash performance varies for different data sizes on
1648 different crypto accelerators. This option can be used
1649 to achieve the best performance for a particular HW.
1651 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1653 Set hashing buffer size. Default: 4k.
1655 ahash performance varies for different chunk sizes on
1656 different crypto accelerators. This option can be used
1657 to achieve best performance for particular HW.
1661 Run specified binary instead of /sbin/init as init
1664 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1665 for working out where the kernel is dying during
1668 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1669 initcall functions. Useful for debugging built-in
1670 modules and initcalls.
1672 initrd= [BOOT] Specify the location of the initial ramdisk
1674 init_pkru= [x86] Specify the default memory protection keys rights
1675 register contents for all processes. 0x55555554 by
1676 default (disallow access to all but pkey 0). Can
1677 override in debugfs after boot.
1679 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1682 int_pln_enable [x86] Enable power limit notification interrupt
1684 integrity_audit=[IMA]
1685 Format: { "0" | "1" }
1686 0 -- basic integrity auditing messages. (Default)
1687 1 -- additional integrity auditing messages.
1689 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1691 Enable intel iommu driver.
1693 Disable intel iommu driver.
1694 igfx_off [Default Off]
1695 By default, gfx is mapped as normal device. If a gfx
1696 device has a dedicated DMAR unit, the DMAR unit is
1697 bypassed by not enabling DMAR with this option. In
1698 this case, gfx device will use physical address for
1701 With this option iommu will not optimize to look
1702 for io virtual address below 32-bit forcing dual
1703 address cycle on pci bus for cards supporting greater
1704 than 32-bit addressing. The default is to look
1705 for translation below 32-bit and if not available
1706 then look in the higher range.
1707 strict [Default Off]
1708 With this option on every unmap_single operation will
1709 result in a hardware IOTLB flush operation as opposed
1710 to batching them for performance.
1711 sp_off [Default Off]
1712 By default, super page will be supported if Intel IOMMU
1713 has the capability. With this option, super page will
1716 By default, scalable mode will be disabled even if the
1717 hardware advertises that it has support for the scalable
1718 mode translation. With this option set, scalable mode
1719 will be used on hardware which claims to support it.
1720 tboot_noforce [Default Off]
1721 Do not force the Intel IOMMU enabled under tboot.
1722 By default, tboot will force Intel IOMMU on, which
1723 could harm performance of some high-throughput
1724 devices like 40GBit network cards, even if identity
1726 Note that using this option lowers the security
1727 provided by tboot because it makes the system
1728 vulnerable to DMA attacks.
1730 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1731 0 disables intel_idle and fall back on acpi_idle.
1732 1 to 9 specify maximum depth of C-state.
1736 Do not enable intel_pstate as the default
1737 scaling driver for the supported processors
1739 Use intel_pstate as a scaling driver, but configure it
1740 to work with generic cpufreq governors (instead of
1741 enabling its internal governor). This mode cannot be
1742 used along with the hardware-managed P-states (HWP)
1745 Enable intel_pstate on systems that prohibit it by default
1746 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1747 instead of acpi-cpufreq may disable platform features, such
1748 as thermal controls and power capping, that rely on ACPI
1749 P-States information being indicated to OSPM and therefore
1750 should be used with caution. This option does not work with
1751 processors that aren't supported by the intel_pstate driver
1752 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1754 Do not enable hardware P state control (HWP)
1757 Only load intel_pstate on systems which support
1758 hardware P state control (HWP) if available.
1760 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1761 Description Table, specifies preferred power management
1762 profile as "Enterprise Server" or "Performance Server",
1763 then this feature is turned on by default.
1765 Allow per-logical-CPU P-State performance control limits using
1766 cpufreq sysfs interface
1768 intremap= [X86-64, Intel-IOMMU]
1769 on enable Interrupt Remapping (default)
1770 off disable Interrupt Remapping
1771 nosid disable Source ID checking
1773 BIOS x2APIC opt-out request will be ignored
1774 nopost disable Interrupt Posting
1776 iomem= Disable strict checking of access to MMIO memory
1777 strict regions from userspace.
1792 nobypass [PPC/POWERNV]
1793 Disable IOMMU bypass, using IOMMU for PCI devices.
1795 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1796 Format: { "0" | "1" }
1798 Request that DMA unmap operations use deferred
1799 invalidation of hardware TLBs, for increased
1800 throughput at the cost of reduced device isolation.
1801 Will fall back to strict mode if not supported by
1802 the relevant IOMMU driver.
1803 1 - Strict mode (default).
1804 DMA unmap operations invalidate IOMMU hardware TLBs
1808 [ARM64] Configure DMA to bypass the IOMMU by default.
1809 Format: { "0" | "1" }
1810 0 - Use IOMMU translation for DMA.
1811 1 - Bypass the IOMMU for DMA.
1812 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1814 io7= [HW] IO7 for Marvel based alpha systems
1815 See comment before marvel_specify_io7 in
1816 arch/alpha/kernel/core_marvel.c.
1818 io_delay= [X86] I/O delay method
1820 Standard port 0x80 based delay
1822 Alternate port 0xed based delay (needed on some systems)
1824 Simple two microseconds delay
1829 See Documentation/filesystems/nfs/nfsroot.txt.
1831 irqaffinity= [SMP] Set the default irq affinity mask
1832 The argument is a cpu list, as described above.
1834 irqchip.gicv2_force_probe=
1837 Force the kernel to look for the second 4kB page
1838 of a GICv2 controller even if the memory range
1839 exposed by the device tree is too small.
1841 irqchip.gicv3_nolpi=
1843 Force the kernel to ignore the availability of
1844 LPIs (and by consequence ITSs). Intended for system
1845 that use the kernel as a bootloader, and thus want
1846 to let secondary kernels in charge of setting up
1850 When an interrupt is not handled search all handlers
1851 for it. Intended to get systems with badly broken
1855 When an interrupt is not handled search all handlers
1856 for it. Also check all handlers each timer
1857 interrupt. Intended to get systems with badly broken
1861 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1863 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1864 [Deprecated - use cpusets instead]
1865 Format: [flag-list,]<cpu-list>
1867 Specify one or more CPUs to isolate from disturbances
1868 specified in the flag list (default: domain):
1871 Disable the tick when a single task runs.
1873 A residual 1Hz tick is offloaded to workqueues, which you
1874 need to affine to housekeeping through the global
1875 workqueue's affinity configured via the
1876 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1877 by using the 'domain' flag described below.
1879 NOTE: by default the global workqueue runs on all CPUs,
1880 so to protect individual CPUs the 'cpumask' file has to
1881 be configured manually after bootup.
1884 Isolate from the general SMP balancing and scheduling
1885 algorithms. Note that performing domain isolation this way
1886 is irreversible: it's not possible to bring back a CPU to
1887 the domains once isolated through isolcpus. It's strongly
1888 advised to use cpusets instead to disable scheduler load
1889 balancing through the "cpuset.sched_load_balance" file.
1890 It offers a much more flexible interface where CPUs can
1891 move in and out of an isolated set anytime.
1893 You can move a process onto or off an "isolated" CPU via
1894 the CPU affinity syscalls or cpuset.
1895 <cpu number> begins at 0 and the maximum value is
1896 "number of CPUs in system - 1".
1898 The format of <cpu-list> is described above.
1904 ivrs_ioapic [HW,X86_64]
1905 Provide an override to the IOAPIC-ID<->DEVICE-ID
1906 mapping provided in the IVRS ACPI table. For
1907 example, to map IOAPIC-ID decimal 10 to
1908 PCI device 00:14.0 write the parameter as:
1909 ivrs_ioapic[10]=00:14.0
1911 ivrs_hpet [HW,X86_64]
1912 Provide an override to the HPET-ID<->DEVICE-ID
1913 mapping provided in the IVRS ACPI table. For
1914 example, to map HPET-ID decimal 0 to
1915 PCI device 00:14.0 write the parameter as:
1916 ivrs_hpet[0]=00:14.0
1918 ivrs_acpihid [HW,X86_64]
1919 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1920 mapping provided in the IVRS ACPI table. For
1921 example, to map UART-HID:UID AMD0020:0 to
1922 PCI device 00:14.5 write the parameter as:
1923 ivrs_acpihid[00:14.5]=AMD0020:0
1925 js= [HW,JOY] Analog joystick
1926 See Documentation/input/joydev/joystick.rst.
1929 When CONFIG_RANDOMIZE_BASE is set, this disables
1930 kernel and module base offset ASLR (Address Space
1931 Layout Randomization).
1934 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1935 report on every invalid memory access. Without this
1936 parameter KASAN will print report only for the first
1941 kernelcore= [KNL,X86,IA-64,PPC]
1942 Format: nn[KMGTPE] | nn% | "mirror"
1943 This parameter specifies the amount of memory usable by
1944 the kernel for non-movable allocations. The requested
1945 amount is spread evenly throughout all nodes in the
1946 system as ZONE_NORMAL. The remaining memory is used for
1947 movable memory in its own zone, ZONE_MOVABLE. In the
1948 event, a node is too small to have both ZONE_NORMAL and
1949 ZONE_MOVABLE, kernelcore memory will take priority and
1950 other nodes will have a larger ZONE_MOVABLE.
1952 ZONE_MOVABLE is used for the allocation of pages that
1953 may be reclaimed or moved by the page migration
1954 subsystem. Note that allocations like PTEs-from-HighMem
1955 still use the HighMem zone if it exists, and the Normal
1956 zone if it does not.
1958 It is possible to specify the exact amount of memory in
1959 the form of "nn[KMGTPE]", a percentage of total system
1960 memory in the form of "nn%", or "mirror". If "mirror"
1961 option is specified, mirrored (reliable) memory is used
1962 for non-movable allocations and remaining memory is used
1963 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1964 are exclusive, so you cannot specify multiple forms.
1966 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1967 Format: <Controller#>[,poll interval]
1968 The controller # is the number of the ehci usb debug
1969 port as it is probed via PCI. The poll interval is
1970 optional and is the number seconds in between
1971 each poll cycle to the debug port in case you need
1972 the functionality for interrupting the kernel with
1973 gdb or control-c on the dbgp connection. When
1974 not using this parameter you use sysrq-g to break into
1975 the kernel debugger.
1977 kgdboc= [KGDB,HW] kgdb over consoles.
1978 Requires a tty driver that supports console polling,
1979 or a supported polling keyboard driver (non-usb).
1980 Serial only format: <serial_device>[,baud]
1981 keyboard only format: kbd
1982 keyboard and serial format: kbd,<serial_device>[,baud]
1983 Optional Kernel mode setting:
1984 kms, kbd format: kms,kbd
1985 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1987 kgdbwait [KGDB] Stop kernel execution and enter the
1988 kernel debugger at the earliest opportunity.
1990 kmac= [MIPS] korina ethernet MAC address.
1991 Configure the RouterBoard 532 series on-chip
1992 Ethernet adapter MAC address.
1994 kmemleak= [KNL] Boot-time kmemleak enable/disable
1995 Valid arguments: on, off
1997 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2000 kpti= [ARM64] Control page table isolation of user
2001 and kernel address spaces.
2002 Default: enabled on cores which need mitigation.
2006 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2007 Default is 0 (don't ignore, but inject #GP)
2009 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2010 Default is false (don't support).
2012 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2016 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2017 Default is 1 (enabled)
2019 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2021 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2023 kvm-arm.vgic_v3_group0_trap=
2024 [KVM,ARM] Trap guest accesses to GICv3 group-0
2027 kvm-arm.vgic_v3_group1_trap=
2028 [KVM,ARM] Trap guest accesses to GICv3 group-1
2031 kvm-arm.vgic_v3_common_trap=
2032 [KVM,ARM] Trap guest accesses to GICv3 common
2035 kvm-arm.vgic_v4_enable=
2036 [KVM,ARM] Allow use of GICv4 for direct injection of
2039 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2040 (virtualized MMU) support on capable Intel chips.
2041 Default is 1 (enabled)
2043 kvm-intel.emulate_invalid_guest_state=
2044 [KVM,Intel] Enable emulation of invalid guest states
2045 Default is 0 (disabled)
2047 kvm-intel.flexpriority=
2048 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2049 Default is 1 (enabled)
2052 [KVM,Intel] Enable VMX nesting (nVMX).
2053 Default is 0 (disabled)
2055 kvm-intel.unrestricted_guest=
2056 [KVM,Intel] Disable unrestricted guest feature
2057 (virtualized real and unpaged mode) on capable
2058 Intel chips. Default is 1 (enabled)
2060 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2063 Valid arguments: never, cond, always
2065 always: L1D cache flush on every VMENTER.
2066 cond: Flush L1D on VMENTER only when the code between
2067 VMEXIT and VMENTER can leak host memory.
2068 never: Disables the mitigation
2070 Default is cond (do L1 cache flush in specific instances)
2072 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2073 feature (tagged TLBs) on capable Intel chips.
2074 Default is 1 (enabled)
2076 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2079 The kernel PTE inversion protection is unconditionally
2080 enabled and cannot be disabled.
2083 Provides all available mitigations for the
2084 L1TF vulnerability. Disables SMT and
2085 enables all mitigations in the
2086 hypervisors, i.e. unconditional L1D flush.
2088 SMT control and L1D flush control via the
2089 sysfs interface is still possible after
2090 boot. Hypervisors will issue a warning
2091 when the first VM is started in a
2092 potentially insecure configuration,
2093 i.e. SMT enabled or L1D flush disabled.
2096 Same as 'full', but disables SMT and L1D
2097 flush runtime control. Implies the
2098 'nosmt=force' command line option.
2099 (i.e. sysfs control of SMT is disabled.)
2102 Leaves SMT enabled and enables the default
2103 hypervisor mitigation, i.e. conditional
2106 SMT control and L1D flush control via the
2107 sysfs interface is still possible after
2108 boot. Hypervisors will issue a warning
2109 when the first VM is started in a
2110 potentially insecure configuration,
2111 i.e. SMT enabled or L1D flush disabled.
2115 Disables SMT and enables the default
2116 hypervisor mitigation.
2118 SMT control and L1D flush control via the
2119 sysfs interface is still possible after
2120 boot. Hypervisors will issue a warning
2121 when the first VM is started in a
2122 potentially insecure configuration,
2123 i.e. SMT enabled or L1D flush disabled.
2126 Same as 'flush', but hypervisors will not
2127 warn when a VM is started in a potentially
2128 insecure configuration.
2131 Disables hypervisor mitigations and doesn't
2133 It also drops the swap size and available
2134 RAM limit restriction on both hypervisor and
2139 For details see: Documentation/admin-guide/l1tf.rst
2145 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2148 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2149 value for LAPIC timer one-shot implementation. Default
2150 back to the programmable timer unit in the LAPIC.
2152 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2155 libata.dma= [LIBATA] DMA control
2156 libata.dma=0 Disable all PATA and SATA DMA
2157 libata.dma=1 PATA and SATA Disk DMA only
2158 libata.dma=2 ATAPI (CDROM) DMA only
2159 libata.dma=4 Compact Flash DMA only
2160 Combinations also work, so libata.dma=3 enables DMA
2161 for disks and CDROMs, but not CFs.
2163 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2164 libata.ignore_hpa=0 keep BIOS limits (default)
2165 libata.ignore_hpa=1 ignore limits, using full disk
2167 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2171 libata.force= [LIBATA] Force configurations. The format is comma
2172 separated list of "[ID:]VAL" where ID is
2173 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2174 matching port, link or device. Basically, it matches
2175 the ATA ID string printed on console by libata. If
2176 the whole ID part is omitted, the last PORT and DEVICE
2177 values are used. If ID hasn't been specified yet, the
2178 configuration applies to all ports, links and devices.
2180 If only DEVICE is omitted, the parameter applies to
2181 the port and all links and devices behind it. DEVICE
2182 number of 0 either selects the first device or the
2183 first fan-out link behind PMP device. It does not
2184 select the host link. DEVICE number of 15 selects the
2185 host link and device attached to it.
2187 The VAL specifies the configuration to force. As long
2188 as there's no ambiguity shortcut notation is allowed.
2189 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2190 The following configurations can be forced.
2192 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2193 Any ID with matching PORT is used.
2195 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2197 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2198 udma[/][16,25,33,44,66,100,133] notation is also
2201 * [no]ncq: Turn on or off NCQ.
2203 * [no]ncqtrim: Turn off queued DSM TRIM.
2205 * nohrst, nosrst, norst: suppress hard, soft
2208 * rstonce: only attempt one reset during
2209 hot-unplug link recovery
2211 * dump_id: dump IDENTIFY data.
2213 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2215 * disable: Disable this device.
2217 If there are multiple matching configurations changing
2218 the same attribute, the last one is used.
2220 memblock=debug [KNL] Enable memblock debug messages.
2222 load_ramdisk= [RAM] List of ramdisks to load from floppy
2223 See Documentation/blockdev/ramdisk.txt.
2225 lockd.nlm_grace_period=P [NFS] Assign grace period.
2228 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2231 lockd.nlm_timeout=T [NFS] Assign timeout value.
2234 lockd.nlm_udpport=M [NFS] Assign UDP port.
2237 locktorture.nreaders_stress= [KNL]
2238 Set the number of locking read-acquisition kthreads.
2239 Defaults to being automatically set based on the
2240 number of online CPUs.
2242 locktorture.nwriters_stress= [KNL]
2243 Set the number of locking write-acquisition kthreads.
2245 locktorture.onoff_holdoff= [KNL]
2246 Set time (s) after boot for CPU-hotplug testing.
2248 locktorture.onoff_interval= [KNL]
2249 Set time (s) between CPU-hotplug operations, or
2250 zero to disable CPU-hotplug testing.
2252 locktorture.shuffle_interval= [KNL]
2253 Set task-shuffle interval (jiffies). Shuffling
2254 tasks allows some CPUs to go into dyntick-idle
2255 mode during the locktorture test.
2257 locktorture.shutdown_secs= [KNL]
2258 Set time (s) after boot system shutdown. This
2259 is useful for hands-off automated testing.
2261 locktorture.stat_interval= [KNL]
2262 Time (s) between statistics printk()s.
2264 locktorture.stutter= [KNL]
2265 Time (s) to stutter testing, for example,
2266 specifying five seconds causes the test to run for
2267 five seconds, wait for five seconds, and so on.
2268 This tests the locking primitive's ability to
2269 transition abruptly to and from idle.
2271 locktorture.torture_type= [KNL]
2272 Specify the locking implementation to test.
2274 locktorture.verbose= [KNL]
2275 Enable additional printk() statements.
2277 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2280 loglevel= All Kernel Messages with a loglevel smaller than the
2281 console loglevel will be printed to the console. It can
2282 also be changed with klogd or other programs. The
2283 loglevels are defined as follows:
2285 0 (KERN_EMERG) system is unusable
2286 1 (KERN_ALERT) action must be taken immediately
2287 2 (KERN_CRIT) critical conditions
2288 3 (KERN_ERR) error conditions
2289 4 (KERN_WARNING) warning conditions
2290 5 (KERN_NOTICE) normal but significant condition
2291 6 (KERN_INFO) informational
2292 7 (KERN_DEBUG) debug-level messages
2294 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2295 in bytes. n must be a power of two and greater
2296 than the minimal size. The minimal size is defined
2297 by LOG_BUF_SHIFT kernel config parameter. There is
2298 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2299 that allows to increase the default size depending on
2300 the number of CPUs. See init/Kconfig for more details.
2302 logo.nologo [FB] Disables display of the built-in Linux logo.
2303 This may be used to provide more screen space for
2304 kernel log messages and is useful when debugging
2305 kernel boot problems.
2307 lp=0 [LP] Specify parallel ports to use, e.g,
2308 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2309 lp=reset first parallel port). 'lp=0' disables the
2310 lp=auto printer driver. 'lp=reset' (which can be
2311 specified in addition to the ports) causes
2312 attached printers to be reset. Using
2313 lp=port1,port2,... specifies the parallel ports
2314 to associate lp devices with, starting with
2315 lp0. A port specification may be 'none' to skip
2316 that lp device, or a parport name such as
2317 'parport0'. Specifying 'lp=auto' instead of a
2318 port specification list means that device IDs
2319 from each port should be examined, to see if
2320 an IEEE 1284-compliant printer is attached; if
2321 so, the driver will manage that printer.
2322 See also header of drivers/char/lp.c.
2325 Sets loops_per_jiffy to given constant, thus avoiding
2326 time-consuming boot-time autodetection (up to 250 ms per
2327 CPU). 0 enables autodetection (default). To determine
2328 the correct value for your kernel, boot with normal
2329 autodetection and see what value is printed. Note that
2330 on SMP systems the preset will be applied to all CPUs,
2331 which is likely to cause problems if your CPUs need
2332 significantly divergent settings. An incorrect value
2333 will cause delays in the kernel to be wrong, leading to
2334 unpredictable I/O errors and other breakage. Although
2335 unlikely, in the extreme case this might damage your
2339 Format: <io>,<irq>,<dma>
2341 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2344 [SECURITY] Choose order of LSM initialization. This
2345 overrides CONFIG_LSM, and the "security=" parameter.
2347 machvec= [IA-64] Force the use of a particular machine-vector
2348 (machvec) in a generic kernel.
2349 Example: machvec=hpzx1_swiotlb
2351 machtype= [Loongson] Share the same kernel image file between different
2353 Example: machtype=lemote-yeeloong-2f-7inch
2355 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2356 than or equal to this physical address is ignored.
2358 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2359 will bring up during bootup. maxcpus=n : n >= 0 limits
2360 the kernel to bring up 'n' processors. Surely after
2361 bootup you can bring up the other plugged cpu by executing
2362 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2363 only takes effect during system bootup.
2364 While n=0 is a special case, it is equivalent to "nosmp",
2365 which also disables the IO APIC.
2367 max_loop= [LOOP] The number of loop block devices that get
2368 (loop.max_loop) unconditionally pre-created at init time. The default
2369 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2370 of statically allocating a predefined number, loop
2371 devices can be requested on-demand with the
2372 /dev/loop-control interface.
2374 mce [X86-32] Machine Check Exception
2376 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2378 md= [HW] RAID subsystems devices and level
2379 See Documentation/admin-guide/md.rst.
2382 Format: <first>,<last>
2383 Specifies range of consoles to be captured by the MDA.
2385 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2386 Amount of memory to be used when the kernel is not able
2387 to see the whole system memory or for test.
2388 [X86] Work as limiting max address. Use together
2389 with memmap= to avoid physical address space collisions.
2390 Without memmap= PCI devices could be placed at addresses
2391 belonging to unused RAM.
2393 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2397 [KNL,SH] Allow user to override the default size for
2398 per-device physically contiguous DMA buffers.
2400 memhp_default_state=online/offline
2401 [KNL] Set the initial state for the memory hotplug
2402 onlining policy. If not specified, the default value is
2403 set according to the
2404 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2406 See Documentation/memory-hotplug.txt.
2408 memmap=exactmap [KNL,X86] Enable setting of an exact
2409 E820 memory map, as specified by the user.
2410 Such memmap=exactmap lines can be constructed based on
2411 BIOS output or other requirements. See the memmap=nn@ss
2414 memmap=nn[KMG]@ss[KMG]
2415 [KNL] Force usage of a specific region of memory.
2416 Region of memory to be used is from ss to ss+nn.
2417 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2418 which limits max address to nn[KMG].
2419 Multiple different regions can be specified,
2422 memmap=100M@2G,100M#3G,1G!1024G
2424 memmap=nn[KMG]#ss[KMG]
2425 [KNL,ACPI] Mark specific memory as ACPI data.
2426 Region of memory to be marked is from ss to ss+nn.
2428 memmap=nn[KMG]$ss[KMG]
2429 [KNL,ACPI] Mark specific memory as reserved.
2430 Region of memory to be reserved is from ss to ss+nn.
2431 Example: Exclude memory from 0x18690000-0x1869ffff
2432 memmap=64K$0x18690000
2434 memmap=0x10000$0x18690000
2435 Some bootloaders may need an escape character before '$',
2436 like Grub2, otherwise '$' and the following number
2439 memmap=nn[KMG]!ss[KMG]
2440 [KNL,X86] Mark specific memory as protected.
2441 Region of memory to be used, from ss to ss+nn.
2442 The memory region may be marked as e820 type 12 (0xc)
2443 and is NVDIMM or ADR memory.
2445 memmap=<size>%<offset>-<oldtype>+<newtype>
2446 [KNL,ACPI] Convert memory within the specified region
2447 from <oldtype> to <newtype>. If "-<oldtype>" is left
2448 out, the whole region will be marked as <newtype>,
2449 even if previously unavailable. If "+<newtype>" is left
2450 out, matching memory will be removed. Types are
2451 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2452 3 = ACPI, 12 = PRAM.
2454 memory_corruption_check=0/1 [X86]
2455 Some BIOSes seem to corrupt the first 64k of
2456 memory when doing things like suspend/resume.
2457 Setting this option will scan the memory
2458 looking for corruption. Enabling this will
2459 both detect corruption and prevent the kernel
2460 from using the memory being corrupted.
2461 However, its intended as a diagnostic tool; if
2462 repeatable BIOS-originated corruption always
2463 affects the same memory, you can use memmap=
2464 to prevent the kernel from using that memory.
2466 memory_corruption_check_size=size [X86]
2467 By default it checks for corruption in the low
2468 64k, making this memory unavailable for normal
2469 use. Use this parameter to scan for
2470 corruption in more or less memory.
2472 memory_corruption_check_period=seconds [X86]
2473 By default it checks for corruption every 60
2474 seconds. Use this parameter to check at some
2475 other rate. 0 disables periodic checking.
2477 memtest= [KNL,X86,ARM,PPC] Enable memtest
2479 default : 0 <disable>
2480 Specifies the number of memtest passes to be
2481 performed. Each pass selects another test
2482 pattern from a given set of patterns. Memtest
2483 fills the memory with this pattern, validates
2484 memory contents and reserves bad memory
2485 regions that are detected.
2487 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2488 Valid arguments: on, off
2489 Default (depends on kernel configuration option):
2490 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2491 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2492 mem_encrypt=on: Activate SME
2493 mem_encrypt=off: Do not activate SME
2495 Refer to Documentation/x86/amd-memory-encryption.txt
2496 for details on when memory encryption can be activated.
2498 mem_sleep_default= [SUSPEND] Default system suspend mode:
2499 s2idle - Suspend-To-Idle
2500 shallow - Power-On Suspend or equivalent (if supported)
2501 deep - Suspend-To-RAM or equivalent (if supported)
2502 See Documentation/admin-guide/pm/sleep-states.rst.
2504 meye.*= [HW] Set MotionEye Camera parameters
2505 See Documentation/media/v4l-drivers/meye.rst.
2507 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2508 Multi-Function General Purpose Timers on AMD Geode
2511 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2512 the BIOS has incorrectly applied a workaround. TinyBIOS
2513 version 0.98 is known to be affected, 0.99 fixes the
2514 problem by letting the user disable the workaround.
2518 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2519 physical address is ignored.
2521 mini2440= [ARM,HW,KNL]
2522 Format:[0..2][b][c][t]
2524 MINI2440 configuration specification:
2525 0 - The attached screen is the 3.5" TFT
2526 1 - The attached screen is the 7" TFT
2527 2 - The VGA Shield is attached (1024x768)
2528 Leaving out the screen size parameter will not load
2529 the TFT driver, and the framebuffer will be left
2531 b - Enable backlight. The TFT backlight pin will be
2532 linked to the kernel VESA blanking code and a GPIO
2533 LED. This parameter is not necessary when using the
2535 c - Enable the s3c camera interface.
2536 t - Reserved for enabling touchscreen support. The
2537 touchscreen support is not enabled in the mainstream
2538 kernel as of 2.6.30, a preliminary port can be found
2539 in the "bleeding edge" mini2440 support kernel at
2540 http://repo.or.cz/w/linux-2.6/mini2440.git
2543 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2544 parameter allows control of the logging verbosity for
2545 the additional memory initialisation checks. A value
2546 of 0 disables mminit logging and a level of 4 will
2547 log everything. Information is printed at KERN_DEBUG
2548 so loglevel=8 may also need to be specified.
2551 [KNL] When CONFIG_MODULE_SIG is set, this means that
2552 modules without (valid) signatures will fail to load.
2553 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2554 is always true, so this option does nothing.
2556 module_blacklist= [KNL] Do not load a comma-separated list of
2557 modules. Useful for debugging problem modules.
2560 [MOUSE] Maximum time between finger touching and
2561 leaving touchpad surface for touch to be considered
2562 a tap and be reported as a left button click (for
2563 touchpads working in absolute mode only).
2565 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2566 reporting absolute coordinates, such as tablets
2567 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2568 reporting absolute coordinates, such as tablets
2570 movablecore= [KNL,X86,IA-64,PPC]
2571 Format: nn[KMGTPE] | nn%
2572 This parameter is the complement to kernelcore=, it
2573 specifies the amount of memory used for migratable
2574 allocations. If both kernelcore and movablecore is
2575 specified, then kernelcore will be at *least* the
2576 specified value but may be more. If movablecore on its
2577 own is specified, the administrator must be careful
2578 that the amount of memory usable for all allocations
2581 movable_node [KNL] Boot-time switch to make hotplugable memory
2582 NUMA nodes to be movable. This means that the memory
2583 of such nodes will be usable only for movable
2584 allocations which rules out almost all kernel
2585 allocations. Use with caution!
2587 MTD_Partition= [MTD]
2588 Format: <name>,<region-number>,<size>,<offset>
2590 MTD_Region= [MTD] Format:
2591 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2594 See drivers/mtd/cmdlinepart.c.
2596 multitce=off [PPC] This parameter disables the use of the pSeries
2597 firmware feature for updating multiple TCE entries
2600 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2602 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
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