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/alsa-parameters.txt
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 whilst 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" } (0 = disabled, 1 = enabled)
393 0 - kernel audit is disabled and can not be enabled
394 until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 - kernel audit is initialized and partially enabled,
398 storing at most audit_backlog_limit messages in
399 RAM until it is fully enabled by the userspace
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.
464 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
467 format: { id:<keyid> | builtin }
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
483 - foo isn't visible as an individually mountable
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
510 See Documentation/s390/CommonIO for details.
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/clk.txt.
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
530 clocksource= Override the default clocksource
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
536 [all] jiffies (this is the base, fallback clocksource)
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
549 clocksource.arm_arch_timer.evtstrm=
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
570 cma=nn[MG]@[start[MG][-end[MG]]]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
590 code_bytes [X86] How many bytes of object code to print
595 com20020= [HW,NET] ARCnet - COM20020 chipset
597 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
599 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
603 ARCnet - COM90xx chipset (memory-mapped buffers)
604 Format: <io>[,<irq>[,<memstart>]]
606 condev= [HW,S390] console device
609 console= [KNL] Output console device and options.
611 tty<n> Use the virtual console device <n>.
615 Use the specified serial port. The options are of
616 the form "bbbbpnf", where "bbbb" is the baud rate,
617 "p" is parity ("n", "o", or "e"), "n" is number of
618 bits, and "f" is flow control ("r" for RTS or
619 omit it). Default is "9600n8".
621 See Documentation/admin-guide/serial-console.rst for more
623 Documentation/networking/netconsole.txt for an
626 uart[8250],io,<addr>[,options]
627 uart[8250],mmio,<addr>[,options]
628 uart[8250],mmio16,<addr>[,options]
629 uart[8250],mmio32,<addr>[,options]
630 uart[8250],0x<addr>[,options]
631 Start an early, polled-mode console on the 8250/16550
632 UART at the specified I/O port or MMIO address,
633 switching to the matching ttyS device later.
634 MMIO inter-register address stride is either 8-bit
635 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
636 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
637 to be equivalent to 'mmio'. 'options' are specified in
638 the same format described for ttyS above; if unspecified,
639 the h/w is not re-initialized.
641 hvc<n> Use the hypervisor console device <n>. This is for
642 both Xen and PowerPC hypervisors.
644 If the device connected to the port is not a TTY but a braille
645 device, prepend "brl," before the device type, for instance
647 For now, only VisioBraille is supported.
650 [KNL] Change console messages format
652 By default we print messages on consoles in
653 "[time stamp] text\n" format (time stamp may not be
654 printed, depending on CONFIG_PRINTK_TIME or
655 `printk_time' param).
657 Switch to syslog format: "<%u>[time stamp] text\n"
658 IOW, each message will have a facility and loglevel
659 prefix. The format is similar to one used by syslog()
660 syscall, or to executing "dmesg -S --raw" or to reading
663 consoleblank= [KNL] The console blank (screen saver) timeout in
664 seconds. A value of 0 disables the blank timer.
668 [KNL] Change the default value for
669 /proc/<pid>/coredump_filter.
670 See also Documentation/filesystems/proc.txt.
672 coresight_cpu_debug.enable
675 Enable/disable the CPU sampling based debugging.
676 0: default value, disable debugging
677 1: enable debugging at boot time
679 cpuidle.off=1 [CPU_IDLE]
680 disable the cpuidle sub-system
682 cpufreq.off=1 [CPU_FREQ]
683 disable the cpufreq sub-system
686 [X86] Delay for N microsec between assert and de-assert
687 of APIC INIT to start processors. This delay occurs
688 on every CPU online, such as boot, and resume from suspend.
691 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
693 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
695 crashkernel=size[KMG][@offset[KMG]]
696 [KNL] Using kexec, Linux can switch to a 'crash kernel'
697 upon panic. This parameter reserves the physical
698 memory region [offset, offset + size] for that kernel
699 image. If '@offset' is omitted, then a suitable offset
700 is selected automatically. Check
701 Documentation/kdump/kdump.txt for further details.
703 crashkernel=range1:size1[,range2:size2,...][@offset]
704 [KNL] Same as above, but depends on the memory
705 in the running system. The syntax of range is
706 start-[end] where start and end are both
707 a memory unit (amount[KMG]). See also
708 Documentation/kdump/kdump.txt for an example.
710 crashkernel=size[KMG],high
711 [KNL, x86_64] range could be above 4G. Allow kernel
712 to allocate physical memory region from top, so could
713 be above 4G if system have more than 4G ram installed.
714 Otherwise memory region will be allocated below 4G, if
716 It will be ignored if crashkernel=X is specified.
717 crashkernel=size[KMG],low
718 [KNL, x86_64] range under 4G. When crashkernel=X,high
719 is passed, kernel could allocate physical memory region
720 above 4G, that cause second kernel crash on system
721 that require some amount of low memory, e.g. swiotlb
722 requires at least 64M+32K low memory, also enough extra
723 low memory is needed to make sure DMA buffers for 32-bit
724 devices won't run out. Kernel would try to allocate at
725 at least 256M below 4G automatically.
726 This one let user to specify own low range under 4G
727 for second kernel instead.
728 0: to disable low allocation.
729 It will be ignored when crashkernel=X,high is not used
730 or memory reserved is below 4G.
733 [KNL] Disable crypto self-tests
738 cs89x0_media= [HW,NET]
739 Format: { rj45 | aui | bnc }
742 See header of drivers/s390/block/dasd_devmap.c.
744 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
745 (one device per port)
746 Format: <port#>,<type>
747 See also Documentation/input/devices/joystick-parport.rst
749 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
751 Documentation/admin-guide/dynamic-debug-howto.rst for
752 details. Deprecated, see dyndbg.
754 debug [KNL] Enable kernel debugging (events log level).
757 [KNL] verbose self-tests
759 Print debugging info while doing the locking API
761 We default to 0 (no extra messages), setting it to
762 1 will print _a lot_ more information - normally
763 only useful to kernel developers.
765 debug_objects [KNL] Enable object debugging
768 [KNL] Disable object debugging
770 debug_guardpage_minorder=
771 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
772 parameter allows control of the order of pages that will
773 be intentionally kept free (and hence protected) by the
774 buddy allocator. Bigger value increase the probability
775 of catching random memory corruption, but reduce the
776 amount of memory for normal system use. The maximum
777 possible value is MAX_ORDER/2. Setting this parameter
778 to 1 or 2 should be enough to identify most random
779 memory corruption problems caused by bugs in kernel or
780 driver code when a CPU writes to (or reads from) a
781 random memory location. Note that there exists a class
782 of memory corruptions problems caused by buggy H/W or
783 F/W or by drivers badly programing DMA (basically when
784 memory is written at bus level and the CPU MMU is
785 bypassed) which are not detectable by
786 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
787 tracking down these problems.
790 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
791 parameter enables the feature at boot time. In
792 default, it is disabled. We can avoid allocating huge
793 chunk of memory for debug pagealloc if we don't enable
794 it at boot time and the system will work mostly same
795 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
796 on: enable the feature
798 debugpat [X86] Enable PAT debugging
800 decnet.addr= [HW,NET]
801 Format: <area>[,<node>]
802 See also Documentation/networking/decnet.txt.
805 [same as hugepagesz=] The size of the default
806 HugeTLB page size. This is the size represented by
807 the legacy /proc/ hugepages APIs, used for SHM, and
808 default size when mounting hugetlbfs filesystems.
809 Defaults to the default architecture's huge page size
813 Set number of hash buckets for dentry cache.
815 disable_1tb_segments [PPC]
816 Disables the use of 1TB hash page table segments. This
817 causes the kernel to fall back to 256MB segments which
818 can be useful when debugging issues that require an SLB
822 See Documentation/networking/ipv6.txt.
825 Disable RADIX MMU mode on POWER9
827 disable_cpu_apicid= [X86,APIC,SMP]
829 The number of initial APIC ID for the
830 corresponding CPU to be disabled at boot,
831 mostly used for the kdump 2nd kernel to
832 disable BSP to wake up multiple CPUs without
833 causing system reset or hang due to sending
836 disable_ddw [PPC/PSERIES]
837 Disable Dynamic DMA Window support. Use this if
838 to workaround buggy firmware.
841 See Documentation/networking/ipv6.txt.
843 disable_mtrr_cleanup [X86]
844 The kernel tries to adjust MTRR layout from continuous
845 to discrete, to make X server driver able to add WB
846 entry later. This parameter disables that.
848 disable_mtrr_trim [X86, Intel and AMD only]
849 By default the kernel will trim any uncacheable
850 memory out of your available memory pool based on
851 MTRR settings. This parameter disables that behavior,
852 possibly causing your machine to run very slowly.
854 disable_timer_pin_1 [X86]
855 Disable PIN 1 of APIC timer
856 Can be useful to work around chipset bugs.
858 dis_ucode_ldr [X86] Disable the microcode loader.
860 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
861 this option disables the debugging code at boot.
863 dma_debug_entries=<number>
864 This option allows to tune the number of preallocated
865 entries for DMA-API debugging code. One entry is
866 required per DMA-API allocation. Use this if the
867 DMA-API debugging code disables itself because the
868 architectural default is too low.
870 dma_debug_driver=<driver_name>
871 With this option the DMA-API debugging driver
872 filter feature can be enabled at boot time. Just
873 pass the driver to filter for as the parameter.
874 The filter can be disabled or changed to another
875 driver later using sysfs.
877 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
878 Broken monitors, graphic adapters, KVMs and EDIDless
879 panels may send no or incorrect EDID data sets.
880 This parameter allows to specify an EDID data sets
881 in the /lib/firmware directory that are used instead.
882 Generic built-in EDID data sets are used, if one of
883 edid/1024x768.bin, edid/1280x1024.bin,
884 edid/1680x1050.bin, or edid/1920x1080.bin is given
885 and no file with the same name exists. Details and
886 instructions how to build your own EDID data are
887 available in Documentation/EDID/HOWTO.txt. An EDID
888 data set will only be used for a particular connector,
889 if its name and a colon are prepended to the EDID
890 name. Each connector may use a unique EDID data
891 set by separating the files with a comma. An EDID
892 data set with no connector name will be used for
893 any connectors not explicitly specified.
898 Format: {"off" | "known"}
899 Control how the dt_cpu_ftrs device-tree binding is
900 used for CPU feature discovery and setup (if it
902 off: Do not use it, fall back to legacy cpu table.
903 known: Do not pass through unknown features to guests
904 or userspace, only those that the kernel is aware of.
906 dump_apple_properties [X86]
907 Dump name and content of EFI device properties on
908 x86 Macs. Useful for driver authors to determine
909 what data is available or for reverse-engineering.
911 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
912 module.dyndbg[="val"]
913 Enable debug messages at boot time. See
914 Documentation/admin-guide/dynamic-debug-howto.rst
917 nompx [X86] Disables Intel Memory Protection Extensions.
918 See Documentation/x86/intel_mpx.txt for more
919 information about the feature.
921 nopku [X86] Disable Memory Protection Keys CPU feature found
924 module.async_probe [KNL]
925 Enable asynchronous probe on this module.
927 early_ioremap_debug [KNL]
928 Enable debug messages in early_ioremap support. This
929 is useful for tracking down temporary early mappings
930 which are not unmapped.
932 earlycon= [KNL] Output early console device and options.
934 [ARM64] The early console is determined by the
935 stdout-path property in device tree's chosen node,
936 or determined by the ACPI SPCR table.
938 [X86] When used with no options the early console is
939 determined by the ACPI SPCR table.
941 cdns,<addr>[,options]
942 Start an early, polled-mode console on a Cadence
943 (xuartps) serial port at the specified address. Only
944 supported option is baud rate. If baud rate is not
945 specified, the serial port must already be setup and
948 uart[8250],io,<addr>[,options]
949 uart[8250],mmio,<addr>[,options]
950 uart[8250],mmio32,<addr>[,options]
951 uart[8250],mmio32be,<addr>[,options]
952 uart[8250],0x<addr>[,options]
953 Start an early, polled-mode console on the 8250/16550
954 UART at the specified I/O port or MMIO address.
955 MMIO inter-register address stride is either 8-bit
956 (mmio) or 32-bit (mmio32 or mmio32be).
957 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
958 to be equivalent to 'mmio'. 'options' are specified
959 in the same format described for "console=ttyS<n>"; if
960 unspecified, the h/w is not initialized.
964 Start an early, polled-mode console on a pl011 serial
965 port at the specified address. The pl011 serial port
966 must already be setup and configured. Options are not
967 yet supported. If 'mmio32' is specified, then only
968 the driver will use only 32-bit accessors to read/write
969 the device registers.
972 Start an early, polled-mode console on a meson serial
973 port at the specified address. The serial port must
974 already be setup and configured. Options are not yet
978 Start an early, polled-mode console on an msm serial
979 port at the specified address. The serial port
980 must already be setup and configured. Options are not
984 Start an early, polled-mode console on an msm serial
985 dm port at the specified address. The serial port
986 must already be setup and configured. Options are not
990 Start an early, polled-mode console on a serial port
991 of an Actions Semi SoC, such as S500 or S900, at the
992 specified address. The serial port must already be
993 setup and configured. Options are not yet supported.
995 smh Use ARM semihosting calls for early console.
1003 Use early console provided by serial driver available
1004 on Samsung SoCs, requires selecting proper type and
1005 a correct base address of the selected UART port. The
1006 serial port must already be setup and configured.
1007 Options are not yet supported.
1010 Start an early, polled-mode console on a lantiq serial
1011 (lqasc) port at the specified address. The serial port
1012 must already be setup and configured. Options are not
1017 Use early console provided by Freescale LP UART driver
1018 found on Freescale Vybrid and QorIQ LS1021A processors.
1019 A valid base address must be provided, and the serial
1020 port must already be setup and configured.
1023 Start an early, polled-mode console on the
1024 Armada 3700 serial port at the specified
1025 address. The serial port must already be setup
1026 and configured. Options are not yet supported.
1028 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1033 earlyprintk=serial[,ttySn[,baudrate]]
1034 earlyprintk=serial[,0x...[,baudrate]]
1035 earlyprintk=ttySn[,baudrate]
1036 earlyprintk=dbgp[debugController#]
1037 earlyprintk=pciserial,bus:device.function[,baudrate]
1038 earlyprintk=xdbc[xhciController#]
1040 earlyprintk is useful when the kernel crashes before
1041 the normal console is initialized. It is not enabled by
1042 default because it has some cosmetic problems.
1044 Append ",keep" to not disable it when the real console
1047 Only one of vga, efi, serial, or usb debug port can
1050 Currently only ttyS0 and ttyS1 may be specified by
1051 name. Other I/O ports may be explicitly specified
1052 on some architectures (x86 and arm at least) by
1053 replacing ttySn with an I/O port address, like this:
1054 earlyprintk=serial,0x1008,115200
1055 You can find the port for a given device in
1056 /proc/tty/driver/serial:
1057 2: uart:ST16650V2 port:00001008 irq:18 ...
1059 Interaction with the standard serial driver is not
1062 The VGA and EFI output is eventually overwritten by
1065 The xen output can only be used by Xen PV guests.
1067 The sclp output can only be used on s390.
1069 edac_report= [HW,EDAC] Control how to report EDAC event
1070 Format: {"on" | "off" | "force"}
1071 on: enable EDAC to report H/W event. May be overridden
1072 by other higher priority error reporting module.
1073 off: disable H/W event reporting through EDAC.
1074 force: enforce the use of EDAC to report H/W event.
1077 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1080 This is designed to be used in conjunction with
1081 the boot argument: earlyprintk=vga
1084 Format: {"off" | "on" | "skip[mbr]"}
1087 Format: { "old_map", "nochunk", "noruntime", "debug" }
1088 old_map [X86-64]: switch to the old ioremap-based EFI
1089 runtime services mapping. 32-bit still uses this one by
1091 nochunk: disable reading files in "chunks" in the EFI
1092 boot stub, as chunking can cause problems with some
1093 firmware implementations.
1094 noruntime : disable EFI runtime services support
1095 debug: enable misc debug output
1097 efi_no_storage_paranoia [EFI; X86]
1098 Using this parameter you can use more than 50% of
1099 your efi variable storage. Use this parameter only if
1100 you are really sure that your UEFI does sane gc and
1101 fulfills the spec otherwise your board may brick.
1103 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1104 Add arbitrary attribute to specific memory range by
1105 updating original EFI memory map.
1106 Region of memory which aa attribute is added to is
1108 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1109 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1110 attribute is added to range 0x100000000-0x180000000 and
1111 0x10a0000000-0x1120000000.
1113 Using this parameter you can do debugging of EFI memmap
1114 related feature. For example, you can do debugging of
1115 Address Range Mirroring feature even if your box
1118 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1119 that is to be dynamically loaded by Linux. If there are
1120 multiple variables with the same name but with different
1121 vendor GUIDs, all of them will be loaded. See
1122 Documentation/acpi/ssdt-overlays.txt for details.
1125 eisa_irq_edge= [PARISC,HW]
1126 See header of drivers/parisc/eisa.c.
1129 See comment before function elanfreq_setup() in
1130 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1133 Format: {"cfq" | "deadline" | "noop"}
1134 See Documentation/block/cfq-iosched.txt and
1135 Documentation/block/deadline-iosched.txt for details.
1137 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1138 Specifies physical address of start of kernel core
1139 image elf header and optionally the size. Generally
1140 kexec loader will pass this option to capture kernel.
1141 See Documentation/kdump/kdump.txt for details.
1143 enable_mtrr_cleanup [X86]
1144 The kernel tries to adjust MTRR layout from continuous
1145 to discrete, to make X server driver able to add WB
1146 entry later. This parameter enables that.
1148 enable_timer_pin_1 [X86]
1149 Enable PIN 1 of APIC timer
1150 Can be useful to work around chipset bugs
1151 (in particular on some ATI chipsets).
1152 The kernel tries to set a reasonable default.
1154 enforcing [SELINUX] Set initial enforcing status.
1156 See security/selinux/Kconfig help text.
1157 0 -- permissive (log only, no denials).
1158 1 -- enforcing (deny and log).
1160 Value can be changed at runtime via /selinux/enforce.
1163 Disable Error Record Serialization Table (ERST)
1166 ether= [HW,NET] Ethernet cards parameters
1167 This option is obsoleted by the "netdev=" option, which
1168 has equivalent usage. See its documentation for details.
1172 Permit 'security.evm' to be updated regardless of
1173 current integrity status.
1177 fail_make_request=[KNL]
1178 General fault injection mechanism.
1179 Format: <interval>,<probability>,<space>,<times>
1180 See also Documentation/fault-injection/.
1183 See Documentation/blockdev/floppy.txt.
1185 force_pal_cache_flush
1186 [IA-64] Avoid check_sal_cache_flush which may hang on
1187 buggy SAL_CACHE_FLUSH implementations. Using this
1188 parameter will force ia64_sal_cache_flush to call
1189 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1192 Forcefully enable Physical Address Extension (PAE).
1193 Many Pentium M systems disable PAE but may have a
1194 functionally usable PAE implementation.
1195 Warning: use of this parameter will taint the kernel
1196 and may cause unknown problems.
1199 [FTRACE] will set and start the specified tracer
1200 as early as possible in order to facilitate early
1203 ftrace_dump_on_oops[=orig_cpu]
1204 [FTRACE] will dump the trace buffers on oops.
1205 If no parameter is passed, ftrace will dump
1206 buffers of all CPUs, but if you pass orig_cpu, it will
1207 dump only the buffer of the CPU that triggered the
1210 ftrace_filter=[function-list]
1211 [FTRACE] Limit the functions traced by the function
1212 tracer at boot up. function-list is a comma separated
1213 list of functions. This list can be changed at run
1214 time by the set_ftrace_filter file in the debugfs
1217 ftrace_notrace=[function-list]
1218 [FTRACE] Do not trace the functions specified in
1219 function-list. This list can be changed at run time
1220 by the set_ftrace_notrace file in the debugfs
1223 ftrace_graph_filter=[function-list]
1224 [FTRACE] Limit the top level callers functions traced
1225 by the function graph tracer at boot up.
1226 function-list is a comma separated list of functions
1227 that can be changed at run time by the
1228 set_graph_function file in the debugfs tracing directory.
1230 ftrace_graph_notrace=[function-list]
1231 [FTRACE] Do not trace from the functions specified in
1232 function-list. This list is a comma separated list of
1233 functions that can be changed at run time by the
1234 set_graph_notrace file in the debugfs tracing directory.
1236 ftrace_graph_max_depth=<uint>
1237 [FTRACE] Used with the function graph tracer. This is
1238 the max depth it will trace into a function. This value
1239 can be changed at run time by the max_graph_depth file
1240 in the tracefs tracing directory. default: 0 (no limit)
1243 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1244 support via parallel port (up to 5 devices per port)
1245 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1246 See also Documentation/input/devices/joystick-parport.rst
1250 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1254 gcov_persist= [GCOV] When non-zero (default), profiling data for
1255 kernel modules is saved and remains accessible via
1256 debugfs, even when the module is unloaded/reloaded.
1257 When zero, profiling data is discarded and associated
1258 debugfs files are removed at module unload time.
1260 goldfish [X86] Enable the goldfish android emulator platform.
1261 Don't use this when you are not running on the
1264 gpt [EFI] Forces disk with valid GPT signature but
1265 invalid Protective MBR to be treated as GPT. If the
1266 primary GPT is corrupted, it enables the backup/alternate
1267 GPT to be used instead.
1269 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1270 the "Enable 0" bit of the configuration register.
1273 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1274 the "Enable 0" bit of the configuration register.
1277 grcan.select= [HW] Select which physical interface to use.
1280 grcan.txsize= [HW] Sets the size of the tx buffer.
1281 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1283 grcan.rxsize= [HW] Sets the size of the rx buffer.
1284 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1287 gpio-mockup.gpio_mockup_ranges
1288 [HW] Sets the ranges of gpiochip of for this device.
1289 Format: <start1>,<end1>,<start2>,<end2>...
1291 hardlockup_all_cpu_backtrace=
1292 [KNL] Should the hard-lockup detector generate
1293 backtraces on all cpus.
1296 hashdist= [KNL,NUMA] Large hashes allocated during boot
1297 are distributed across NUMA nodes. Defaults on
1298 for 64-bit NUMA, off otherwise.
1299 Format: 0 | 1 (for off | on)
1301 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1303 hd= [EIDE] (E)IDE hard drive subsystem geometry
1304 Format: <cyl>,<head>,<sect>
1307 Disable Hardware Error Source Table (HEST) support;
1308 corresponding firmware-first mode error processing
1309 logic will be disabled.
1311 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1312 size of <nn>. This works even on boxes that have no
1313 highmem otherwise. This also works to reduce highmem
1314 size on bigger boxes.
1316 highres= [KNL] Enable/disable high resolution timer mode.
1317 Valid parameters: "on", "off"
1321 See Documentation/isdn/README.HiSax.
1325 hpet= [X86-32,HPET] option to control HPET usage
1326 Format: { enable (default) | disable | force |
1328 disable: disable HPET and use PIT instead
1329 force: allow force enabled of undocumented chips (ICH4,
1331 verbose: show contents of HPET registers during setup
1333 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1334 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1336 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1337 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1338 On x86-64 and powerpc, this option can be specified
1339 multiple times interleaved with hugepages= to reserve
1340 huge pages of different sizes. Valid pages sizes on
1341 x86-64 are 2M (when the CPU supports "pse") and 1G
1342 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1344 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1345 terminal devices. Valid values: 0..8
1346 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1347 If specified, z/VM IUCV HVC accepts connections
1348 from listed z/VM user IDs only.
1350 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1351 hardware thread id mappings.
1352 Format: <cpu>:<hwthread>
1355 Do not unregister boot console at start. This is only
1356 useful for debugging when something happens in the window
1357 between unregistering the boot console and initializing
1360 i2c_bus= [HW] Override the default board specific I2C bus speed
1361 or register an additional I2C bus that is not
1362 registered from board initialization code.
1366 i8042.debug [HW] Toggle i8042 debug mode
1367 i8042.unmask_kbd_data
1368 [HW] Enable printing of interrupt data from the KBD port
1369 (disabled by default, and as a pre-condition
1370 requires that i8042.debug=1 be enabled)
1371 i8042.direct [HW] Put keyboard port into non-translated mode
1372 i8042.dumbkbd [HW] Pretend that controller can only read data from
1373 keyboard and cannot control its state
1374 (Don't attempt to blink the leds)
1375 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1376 i8042.nokbd [HW] Don't check/create keyboard port
1377 i8042.noloop [HW] Disable the AUX Loopback command while probing
1379 i8042.nomux [HW] Don't check presence of an active multiplexing
1381 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1383 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1384 i8042.reset [HW] Reset the controller during init, cleanup and
1385 suspend-to-ram transitions, only during s2r
1386 transitions, or never reset
1387 Format: { 1 | Y | y | 0 | N | n }
1388 1, Y, y: always reset controller
1389 0, N, n: don't ever reset controller
1390 Default: only on s2r transitions on x86; most other
1391 architectures force reset to be always executed
1392 i8042.unlock [HW] Unlock (ignore) the keylock
1393 i8042.kbdreset [HW] Reset device connected to KBD port
1397 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1398 indicates that the driver is running on unsupported
1400 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1401 does not match list of supported models.
1403 [HW] Report power status in /proc/i8k
1404 (disabled by default)
1405 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1408 i915.invert_brightness=
1409 [DRM] Invert the sense of the variable that is used to
1410 set the brightness of the panel backlight. Normally a
1411 brightness value of 0 indicates backlight switched off,
1412 and the maximum of the brightness value sets the backlight
1413 to maximum brightness. If this parameter is set to 0
1414 (default) and the machine requires it, or this parameter
1415 is set to 1, a brightness value of 0 sets the backlight
1416 to maximum brightness, and the maximum of the brightness
1417 value switches the backlight off.
1418 -1 -- never invert brightness
1419 0 -- machine default
1420 1 -- force brightness inversion
1423 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1425 ide-core.nodma= [HW] (E)IDE subsystem
1426 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1427 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1428 .cdrom .chs .ignore_cable are additional options
1429 See Documentation/ide/ide.txt.
1431 ide-generic.probe-mask= [HW] (E)IDE subsystem
1433 Probe mask for legacy ISA IDE ports. Depending on
1434 platform up to 6 ports are supported, enabled by
1435 setting corresponding bits in the mask to 1. The
1436 default value is 0x0, which has a special meaning.
1437 On systems that have PCI, it triggers scanning the
1438 PCI bus for the first and the second port, which
1439 are then probed. On systems without PCI the value
1440 of 0x0 enables probing the two first ports as if it
1443 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1444 Claim all unknown PCI IDE storage controllers.
1447 Format: idle=poll, idle=halt, idle=nomwait
1448 Poll forces a polling idle loop that can slightly
1449 improve the performance of waking up a idle CPU, but
1450 will use a lot of power and make the system run hot.
1452 idle=halt: Halt is forced to be used for CPU idle.
1453 In such case C2/C3 won't be used again.
1454 idle=nomwait: Disable mwait for CPU C-states
1456 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1457 Format: { strict | legacy | 2008 | relaxed }
1460 Choose which programs will be accepted for execution
1461 based on the IEEE 754 NaN encoding(s) supported by
1462 the FPU and the NaN encoding requested with the value
1463 of an ELF file header flag individually set by each
1464 binary. Hardware implementations are permitted to
1465 support either or both of the legacy and the 2008 NaN
1468 Available settings are as follows:
1469 strict accept binaries that request a NaN encoding
1470 supported by the FPU
1471 legacy only accept legacy-NaN binaries, if supported
1473 2008 only accept 2008-NaN binaries, if supported
1475 relaxed accept any binaries regardless of whether
1476 supported by the FPU
1478 The FPU emulator is always able to support both NaN
1479 encodings, so if no FPU hardware is present or it has
1480 been disabled with 'nofpu', then the settings of
1481 'legacy' and '2008' strap the emulator accordingly,
1482 'relaxed' straps the emulator for both legacy-NaN and
1483 2008-NaN, whereas 'strict' enables legacy-NaN only on
1484 legacy processors and both NaN encodings on MIPS32 or
1487 The setting for ABS.fmt/NEG.fmt instruction execution
1488 mode generally follows that for the NaN encoding,
1489 except where unsupported by hardware.
1491 ignore_loglevel [KNL]
1492 Ignore loglevel setting - this will print /all/
1493 kernel messages to the console. Useful for debugging.
1494 We also add it as printk module parameter, so users
1495 could change it dynamically, usually by
1496 /sys/module/printk/parameters/ignore_loglevel.
1499 Ignore RLIMIT_DATA setting for data mappings,
1500 print warning at first misuse. Can be changed via
1501 /sys/module/kernel/parameters/ignore_rlimit_data.
1503 ihash_entries= [KNL]
1504 Set number of hash buckets for inode cache.
1506 ima_appraise= [IMA] appraise integrity measurements
1507 Format: { "off" | "enforce" | "fix" | "log" }
1510 ima_appraise_tcb [IMA]
1511 The builtin appraise policy appraises all files
1514 ima_canonical_fmt [IMA]
1515 Use the canonical format for the binary runtime
1516 measurements, instead of host native format.
1519 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1523 The list of supported hash algorithms is defined
1524 in crypto/hash_info.h.
1527 The builtin policies to load during IMA setup.
1528 Format: "tcb | appraise_tcb | secure_boot"
1530 The "tcb" policy measures all programs exec'd, files
1531 mmap'd for exec, and all files opened with the read
1532 mode bit set by either the effective uid (euid=0) or
1535 The "appraise_tcb" policy appraises the integrity of
1536 all files owned by root. (This is the equivalent
1537 of ima_appraise_tcb.)
1539 The "secure_boot" policy appraises the integrity
1540 of files (eg. kexec kernel image, kernel modules,
1541 firmware, policy, etc) based on file signatures.
1543 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1544 Load a policy which meets the needs of the Trusted
1545 Computing Base. This means IMA will measure all
1546 programs exec'd, files mmap'd for exec, and all files
1547 opened for read by uid=0.
1550 Select one of defined IMA measurements template formats.
1551 Formats: { "ima" | "ima-ng" | "ima-sig" }
1555 [IMA] Define a custom template format.
1556 Format: { "field1|...|fieldN" }
1558 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1559 Format: <min_file_size>
1560 Set the minimal file size for using asynchronous hash.
1561 If left unspecified, ahash usage is disabled.
1563 ahash performance varies for different data sizes on
1564 different crypto accelerators. This option can be used
1565 to achieve the best performance for a particular HW.
1567 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1569 Set hashing buffer size. Default: 4k.
1571 ahash performance varies for different chunk sizes on
1572 different crypto accelerators. This option can be used
1573 to achieve best performance for particular HW.
1577 Run specified binary instead of /sbin/init as init
1580 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1581 for working out where the kernel is dying during
1584 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1585 initcall functions. Useful for debugging built-in
1586 modules and initcalls.
1588 initrd= [BOOT] Specify the location of the initial ramdisk
1590 init_pkru= [x86] Specify the default memory protection keys rights
1591 register contents for all processes. 0x55555554 by
1592 default (disallow access to all but pkey 0). Can
1593 override in debugfs after boot.
1595 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1598 int_pln_enable [x86] Enable power limit notification interrupt
1600 integrity_audit=[IMA]
1601 Format: { "0" | "1" }
1602 0 -- basic integrity auditing messages. (Default)
1603 1 -- additional integrity auditing messages.
1605 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1607 Enable intel iommu driver.
1609 Disable intel iommu driver.
1610 igfx_off [Default Off]
1611 By default, gfx is mapped as normal device. If a gfx
1612 device has a dedicated DMAR unit, the DMAR unit is
1613 bypassed by not enabling DMAR with this option. In
1614 this case, gfx device will use physical address for
1617 With this option iommu will not optimize to look
1618 for io virtual address below 32-bit forcing dual
1619 address cycle on pci bus for cards supporting greater
1620 than 32-bit addressing. The default is to look
1621 for translation below 32-bit and if not available
1622 then look in the higher range.
1623 strict [Default Off]
1624 With this option on every unmap_single operation will
1625 result in a hardware IOTLB flush operation as opposed
1626 to batching them for performance.
1627 sp_off [Default Off]
1628 By default, super page will be supported if Intel IOMMU
1629 has the capability. With this option, super page will
1631 ecs_off [Default Off]
1632 By default, extended context tables will be supported if
1633 the hardware advertises that it has support both for the
1634 extended tables themselves, and also PASID support. With
1635 this option set, extended tables will not be used even
1636 on hardware which claims to support them.
1637 tboot_noforce [Default Off]
1638 Do not force the Intel IOMMU enabled under tboot.
1639 By default, tboot will force Intel IOMMU on, which
1640 could harm performance of some high-throughput
1641 devices like 40GBit network cards, even if identity
1643 Note that using this option lowers the security
1644 provided by tboot because it makes the system
1645 vulnerable to DMA attacks.
1647 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1648 0 disables intel_idle and fall back on acpi_idle.
1649 1 to 9 specify maximum depth of C-state.
1653 Do not enable intel_pstate as the default
1654 scaling driver for the supported processors
1656 Use intel_pstate as a scaling driver, but configure it
1657 to work with generic cpufreq governors (instead of
1658 enabling its internal governor). This mode cannot be
1659 used along with the hardware-managed P-states (HWP)
1662 Enable intel_pstate on systems that prohibit it by default
1663 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1664 instead of acpi-cpufreq may disable platform features, such
1665 as thermal controls and power capping, that rely on ACPI
1666 P-States information being indicated to OSPM and therefore
1667 should be used with caution. This option does not work with
1668 processors that aren't supported by the intel_pstate driver
1669 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1671 Do not enable hardware P state control (HWP)
1674 Only load intel_pstate on systems which support
1675 hardware P state control (HWP) if available.
1677 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1678 Description Table, specifies preferred power management
1679 profile as "Enterprise Server" or "Performance Server",
1680 then this feature is turned on by default.
1682 Allow per-logical-CPU P-State performance control limits using
1683 cpufreq sysfs interface
1685 intremap= [X86-64, Intel-IOMMU]
1686 on enable Interrupt Remapping (default)
1687 off disable Interrupt Remapping
1688 nosid disable Source ID checking
1690 BIOS x2APIC opt-out request will be ignored
1691 nopost disable Interrupt Posting
1693 iomem= Disable strict checking of access to MMIO memory
1694 strict regions from userspace.
1709 nobypass [PPC/POWERNV]
1710 Disable IOMMU bypass, using IOMMU for PCI devices.
1713 [ARM64] Configure DMA to bypass the IOMMU by default.
1714 Format: { "0" | "1" }
1715 0 - Use IOMMU translation for DMA.
1716 1 - Bypass the IOMMU for DMA.
1717 unset - Use IOMMU translation for DMA.
1719 io7= [HW] IO7 for Marvel based alpha systems
1720 See comment before marvel_specify_io7 in
1721 arch/alpha/kernel/core_marvel.c.
1723 io_delay= [X86] I/O delay method
1725 Standard port 0x80 based delay
1727 Alternate port 0xed based delay (needed on some systems)
1729 Simple two microseconds delay
1734 See Documentation/filesystems/nfs/nfsroot.txt.
1736 irqaffinity= [SMP] Set the default irq affinity mask
1737 The argument is a cpu list, as described above.
1739 irqchip.gicv2_force_probe=
1742 Force the kernel to look for the second 4kB page
1743 of a GICv2 controller even if the memory range
1744 exposed by the device tree is too small.
1747 When an interrupt is not handled search all handlers
1748 for it. Intended to get systems with badly broken
1752 When an interrupt is not handled search all handlers
1753 for it. Also check all handlers each timer
1754 interrupt. Intended to get systems with badly broken
1758 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1760 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1761 [Deprecated - use cpusets instead]
1762 Format: [flag-list,]<cpu-list>
1764 Specify one or more CPUs to isolate from disturbances
1765 specified in the flag list (default: domain):
1768 Disable the tick when a single task runs.
1770 Isolate from the general SMP balancing and scheduling
1771 algorithms. Note that performing domain isolation this way
1772 is irreversible: it's not possible to bring back a CPU to
1773 the domains once isolated through isolcpus. It's strongly
1774 advised to use cpusets instead to disable scheduler load
1775 balancing through the "cpuset.sched_load_balance" file.
1776 It offers a much more flexible interface where CPUs can
1777 move in and out of an isolated set anytime.
1779 You can move a process onto or off an "isolated" CPU via
1780 the CPU affinity syscalls or cpuset.
1781 <cpu number> begins at 0 and the maximum value is
1782 "number of CPUs in system - 1".
1784 The format of <cpu-list> is described above.
1790 ivrs_ioapic [HW,X86_64]
1791 Provide an override to the IOAPIC-ID<->DEVICE-ID
1792 mapping provided in the IVRS ACPI table. For
1793 example, to map IOAPIC-ID decimal 10 to
1794 PCI device 00:14.0 write the parameter as:
1795 ivrs_ioapic[10]=00:14.0
1797 ivrs_hpet [HW,X86_64]
1798 Provide an override to the HPET-ID<->DEVICE-ID
1799 mapping provided in the IVRS ACPI table. For
1800 example, to map HPET-ID decimal 0 to
1801 PCI device 00:14.0 write the parameter as:
1802 ivrs_hpet[0]=00:14.0
1804 ivrs_acpihid [HW,X86_64]
1805 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1806 mapping provided in the IVRS ACPI table. For
1807 example, to map UART-HID:UID AMD0020:0 to
1808 PCI device 00:14.5 write the parameter as:
1809 ivrs_acpihid[00:14.5]=AMD0020:0
1811 js= [HW,JOY] Analog joystick
1812 See Documentation/input/joydev/joystick.rst.
1815 When CONFIG_RANDOMIZE_BASE is set, this disables
1816 kernel and module base offset ASLR (Address Space
1817 Layout Randomization).
1820 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1821 report on every invalid memory access. Without this
1822 parameter KASAN will print report only for the first
1827 kernelcore= [KNL,X86,IA-64,PPC]
1828 Format: nn[KMGTPE] | "mirror"
1830 specifies the amount of memory usable by the kernel
1831 for non-movable allocations. The requested amount is
1832 spread evenly throughout all nodes in the system. The
1833 remaining memory in each node is used for Movable
1834 pages. In the event, a node is too small to have both
1835 kernelcore and Movable pages, kernelcore pages will
1836 take priority and other nodes will have a larger number
1837 of Movable pages. The Movable zone is used for the
1838 allocation of pages that may be reclaimed or moved
1839 by the page migration subsystem. This means that
1840 HugeTLB pages may not be allocated from this zone.
1841 Note that allocations like PTEs-from-HighMem still
1842 use the HighMem zone if it exists, and the Normal
1843 zone if it does not.
1845 Instead of specifying the amount of memory (nn[KMGTPE]),
1846 you can specify "mirror" option. In case "mirror"
1847 option is specified, mirrored (reliable) memory is used
1848 for non-movable allocations and remaining memory is used
1849 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1850 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1853 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1854 Format: <Controller#>[,poll interval]
1855 The controller # is the number of the ehci usb debug
1856 port as it is probed via PCI. The poll interval is
1857 optional and is the number seconds in between
1858 each poll cycle to the debug port in case you need
1859 the functionality for interrupting the kernel with
1860 gdb or control-c on the dbgp connection. When
1861 not using this parameter you use sysrq-g to break into
1862 the kernel debugger.
1864 kgdboc= [KGDB,HW] kgdb over consoles.
1865 Requires a tty driver that supports console polling,
1866 or a supported polling keyboard driver (non-usb).
1867 Serial only format: <serial_device>[,baud]
1868 keyboard only format: kbd
1869 keyboard and serial format: kbd,<serial_device>[,baud]
1870 Optional Kernel mode setting:
1871 kms, kbd format: kms,kbd
1872 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1874 kgdbwait [KGDB] Stop kernel execution and enter the
1875 kernel debugger at the earliest opportunity.
1877 kmac= [MIPS] korina ethernet MAC address.
1878 Configure the RouterBoard 532 series on-chip
1879 Ethernet adapter MAC address.
1881 kmemleak= [KNL] Boot-time kmemleak enable/disable
1882 Valid arguments: on, off
1884 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1887 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1888 Default is 0 (don't ignore, but inject #GP)
1890 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1894 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1895 Default is 1 (enabled)
1897 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1899 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1901 kvm-arm.vgic_v3_group0_trap=
1902 [KVM,ARM] Trap guest accesses to GICv3 group-0
1905 kvm-arm.vgic_v3_group1_trap=
1906 [KVM,ARM] Trap guest accesses to GICv3 group-1
1909 kvm-arm.vgic_v3_common_trap=
1910 [KVM,ARM] Trap guest accesses to GICv3 common
1913 kvm-arm.vgic_v4_enable=
1914 [KVM,ARM] Allow use of GICv4 for direct injection of
1917 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1918 (virtualized MMU) support on capable Intel chips.
1919 Default is 1 (enabled)
1921 kvm-intel.emulate_invalid_guest_state=
1922 [KVM,Intel] Enable emulation of invalid guest states
1923 Default is 0 (disabled)
1925 kvm-intel.flexpriority=
1926 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1927 Default is 1 (enabled)
1930 [KVM,Intel] Enable VMX nesting (nVMX).
1931 Default is 0 (disabled)
1933 kvm-intel.unrestricted_guest=
1934 [KVM,Intel] Disable unrestricted guest feature
1935 (virtualized real and unpaged mode) on capable
1936 Intel chips. Default is 1 (enabled)
1938 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1939 feature (tagged TLBs) on capable Intel chips.
1940 Default is 1 (enabled)
1946 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1949 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1950 value for LAPIC timer one-shot implementation. Default
1951 back to the programmable timer unit in the LAPIC.
1953 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1956 libata.dma= [LIBATA] DMA control
1957 libata.dma=0 Disable all PATA and SATA DMA
1958 libata.dma=1 PATA and SATA Disk DMA only
1959 libata.dma=2 ATAPI (CDROM) DMA only
1960 libata.dma=4 Compact Flash DMA only
1961 Combinations also work, so libata.dma=3 enables DMA
1962 for disks and CDROMs, but not CFs.
1964 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1965 libata.ignore_hpa=0 keep BIOS limits (default)
1966 libata.ignore_hpa=1 ignore limits, using full disk
1968 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1972 libata.force= [LIBATA] Force configurations. The format is comma
1973 separated list of "[ID:]VAL" where ID is
1974 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1975 matching port, link or device. Basically, it matches
1976 the ATA ID string printed on console by libata. If
1977 the whole ID part is omitted, the last PORT and DEVICE
1978 values are used. If ID hasn't been specified yet, the
1979 configuration applies to all ports, links and devices.
1981 If only DEVICE is omitted, the parameter applies to
1982 the port and all links and devices behind it. DEVICE
1983 number of 0 either selects the first device or the
1984 first fan-out link behind PMP device. It does not
1985 select the host link. DEVICE number of 15 selects the
1986 host link and device attached to it.
1988 The VAL specifies the configuration to force. As long
1989 as there's no ambiguity shortcut notation is allowed.
1990 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1991 The following configurations can be forced.
1993 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1994 Any ID with matching PORT is used.
1996 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1998 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1999 udma[/][16,25,33,44,66,100,133] notation is also
2002 * [no]ncq: Turn on or off NCQ.
2004 * [no]ncqtrim: Turn off queued DSM TRIM.
2006 * nohrst, nosrst, norst: suppress hard, soft
2009 * rstonce: only attempt one reset during
2010 hot-unplug link recovery
2012 * dump_id: dump IDENTIFY data.
2014 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2016 * disable: Disable this device.
2018 If there are multiple matching configurations changing
2019 the same attribute, the last one is used.
2021 memblock=debug [KNL] Enable memblock debug messages.
2023 load_ramdisk= [RAM] List of ramdisks to load from floppy
2024 See Documentation/blockdev/ramdisk.txt.
2026 lockd.nlm_grace_period=P [NFS] Assign grace period.
2029 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2032 lockd.nlm_timeout=T [NFS] Assign timeout value.
2035 lockd.nlm_udpport=M [NFS] Assign UDP port.
2038 locktorture.nreaders_stress= [KNL]
2039 Set the number of locking read-acquisition kthreads.
2040 Defaults to being automatically set based on the
2041 number of online CPUs.
2043 locktorture.nwriters_stress= [KNL]
2044 Set the number of locking write-acquisition kthreads.
2046 locktorture.onoff_holdoff= [KNL]
2047 Set time (s) after boot for CPU-hotplug testing.
2049 locktorture.onoff_interval= [KNL]
2050 Set time (s) between CPU-hotplug operations, or
2051 zero to disable CPU-hotplug testing.
2053 locktorture.shuffle_interval= [KNL]
2054 Set task-shuffle interval (jiffies). Shuffling
2055 tasks allows some CPUs to go into dyntick-idle
2056 mode during the locktorture test.
2058 locktorture.shutdown_secs= [KNL]
2059 Set time (s) after boot system shutdown. This
2060 is useful for hands-off automated testing.
2062 locktorture.stat_interval= [KNL]
2063 Time (s) between statistics printk()s.
2065 locktorture.stutter= [KNL]
2066 Time (s) to stutter testing, for example,
2067 specifying five seconds causes the test to run for
2068 five seconds, wait for five seconds, and so on.
2069 This tests the locking primitive's ability to
2070 transition abruptly to and from idle.
2072 locktorture.torture_type= [KNL]
2073 Specify the locking implementation to test.
2075 locktorture.verbose= [KNL]
2076 Enable additional printk() statements.
2078 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2081 loglevel= All Kernel Messages with a loglevel smaller than the
2082 console loglevel will be printed to the console. It can
2083 also be changed with klogd or other programs. The
2084 loglevels are defined as follows:
2086 0 (KERN_EMERG) system is unusable
2087 1 (KERN_ALERT) action must be taken immediately
2088 2 (KERN_CRIT) critical conditions
2089 3 (KERN_ERR) error conditions
2090 4 (KERN_WARNING) warning conditions
2091 5 (KERN_NOTICE) normal but significant condition
2092 6 (KERN_INFO) informational
2093 7 (KERN_DEBUG) debug-level messages
2095 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2096 in bytes. n must be a power of two and greater
2097 than the minimal size. The minimal size is defined
2098 by LOG_BUF_SHIFT kernel config parameter. There is
2099 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2100 that allows to increase the default size depending on
2101 the number of CPUs. See init/Kconfig for more details.
2103 logo.nologo [FB] Disables display of the built-in Linux logo.
2104 This may be used to provide more screen space for
2105 kernel log messages and is useful when debugging
2106 kernel boot problems.
2108 lp=0 [LP] Specify parallel ports to use, e.g,
2109 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2110 lp=reset first parallel port). 'lp=0' disables the
2111 lp=auto printer driver. 'lp=reset' (which can be
2112 specified in addition to the ports) causes
2113 attached printers to be reset. Using
2114 lp=port1,port2,... specifies the parallel ports
2115 to associate lp devices with, starting with
2116 lp0. A port specification may be 'none' to skip
2117 that lp device, or a parport name such as
2118 'parport0'. Specifying 'lp=auto' instead of a
2119 port specification list means that device IDs
2120 from each port should be examined, to see if
2121 an IEEE 1284-compliant printer is attached; if
2122 so, the driver will manage that printer.
2123 See also header of drivers/char/lp.c.
2126 Sets loops_per_jiffy to given constant, thus avoiding
2127 time-consuming boot-time autodetection (up to 250 ms per
2128 CPU). 0 enables autodetection (default). To determine
2129 the correct value for your kernel, boot with normal
2130 autodetection and see what value is printed. Note that
2131 on SMP systems the preset will be applied to all CPUs,
2132 which is likely to cause problems if your CPUs need
2133 significantly divergent settings. An incorrect value
2134 will cause delays in the kernel to be wrong, leading to
2135 unpredictable I/O errors and other breakage. Although
2136 unlikely, in the extreme case this might damage your
2140 Format: <io>,<irq>,<dma>
2142 machvec= [IA-64] Force the use of a particular machine-vector
2143 (machvec) in a generic kernel.
2144 Example: machvec=hpzx1_swiotlb
2146 machtype= [Loongson] Share the same kernel image file between different
2148 Example: machtype=lemote-yeeloong-2f-7inch
2150 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2151 than or equal to this physical address is ignored.
2153 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2154 will bring up during bootup. maxcpus=n : n >= 0 limits
2155 the kernel to bring up 'n' processors. Surely after
2156 bootup you can bring up the other plugged cpu by executing
2157 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2158 only takes effect during system bootup.
2159 While n=0 is a special case, it is equivalent to "nosmp",
2160 which also disables the IO APIC.
2162 max_loop= [LOOP] The number of loop block devices that get
2163 (loop.max_loop) unconditionally pre-created at init time. The default
2164 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2165 of statically allocating a predefined number, loop
2166 devices can be requested on-demand with the
2167 /dev/loop-control interface.
2169 mce [X86-32] Machine Check Exception
2171 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2173 md= [HW] RAID subsystems devices and level
2174 See Documentation/admin-guide/md.rst.
2177 Format: <first>,<last>
2178 Specifies range of consoles to be captured by the MDA.
2180 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2181 Amount of memory to be used when the kernel is not able
2182 to see the whole system memory or for test.
2183 [X86] Work as limiting max address. Use together
2184 with memmap= to avoid physical address space collisions.
2185 Without memmap= PCI devices could be placed at addresses
2186 belonging to unused RAM.
2188 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2192 [KNL,SH] Allow user to override the default size for
2193 per-device physically contiguous DMA buffers.
2195 memhp_default_state=online/offline
2196 [KNL] Set the initial state for the memory hotplug
2197 onlining policy. If not specified, the default value is
2198 set according to the
2199 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2201 See Documentation/memory-hotplug.txt.
2203 memmap=exactmap [KNL,X86] Enable setting of an exact
2204 E820 memory map, as specified by the user.
2205 Such memmap=exactmap lines can be constructed based on
2206 BIOS output or other requirements. See the memmap=nn@ss
2209 memmap=nn[KMG]@ss[KMG]
2210 [KNL] Force usage of a specific region of memory.
2211 Region of memory to be used is from ss to ss+nn.
2212 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2213 which limits max address to nn[KMG].
2214 Multiple different regions can be specified,
2217 memmap=100M@2G,100M#3G,1G!1024G
2219 memmap=nn[KMG]#ss[KMG]
2220 [KNL,ACPI] Mark specific memory as ACPI data.
2221 Region of memory to be marked is from ss to ss+nn.
2223 memmap=nn[KMG]$ss[KMG]
2224 [KNL,ACPI] Mark specific memory as reserved.
2225 Region of memory to be reserved is from ss to ss+nn.
2226 Example: Exclude memory from 0x18690000-0x1869ffff
2227 memmap=64K$0x18690000
2229 memmap=0x10000$0x18690000
2230 Some bootloaders may need an escape character before '$',
2231 like Grub2, otherwise '$' and the following number
2234 memmap=nn[KMG]!ss[KMG]
2235 [KNL,X86] Mark specific memory as protected.
2236 Region of memory to be used, from ss to ss+nn.
2237 The memory region may be marked as e820 type 12 (0xc)
2238 and is NVDIMM or ADR memory.
2240 memory_corruption_check=0/1 [X86]
2241 Some BIOSes seem to corrupt the first 64k of
2242 memory when doing things like suspend/resume.
2243 Setting this option will scan the memory
2244 looking for corruption. Enabling this will
2245 both detect corruption and prevent the kernel
2246 from using the memory being corrupted.
2247 However, its intended as a diagnostic tool; if
2248 repeatable BIOS-originated corruption always
2249 affects the same memory, you can use memmap=
2250 to prevent the kernel from using that memory.
2252 memory_corruption_check_size=size [X86]
2253 By default it checks for corruption in the low
2254 64k, making this memory unavailable for normal
2255 use. Use this parameter to scan for
2256 corruption in more or less memory.
2258 memory_corruption_check_period=seconds [X86]
2259 By default it checks for corruption every 60
2260 seconds. Use this parameter to check at some
2261 other rate. 0 disables periodic checking.
2263 memtest= [KNL,X86,ARM] Enable memtest
2265 default : 0 <disable>
2266 Specifies the number of memtest passes to be
2267 performed. Each pass selects another test
2268 pattern from a given set of patterns. Memtest
2269 fills the memory with this pattern, validates
2270 memory contents and reserves bad memory
2271 regions that are detected.
2273 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2274 Valid arguments: on, off
2275 Default (depends on kernel configuration option):
2276 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2277 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2278 mem_encrypt=on: Activate SME
2279 mem_encrypt=off: Do not activate SME
2281 Refer to Documentation/x86/amd-memory-encryption.txt
2282 for details on when memory encryption can be activated.
2284 mem_sleep_default= [SUSPEND] Default system suspend mode:
2285 s2idle - Suspend-To-Idle
2286 shallow - Power-On Suspend or equivalent (if supported)
2287 deep - Suspend-To-RAM or equivalent (if supported)
2288 See Documentation/admin-guide/pm/sleep-states.rst.
2290 meye.*= [HW] Set MotionEye Camera parameters
2291 See Documentation/media/v4l-drivers/meye.rst.
2293 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2294 Multi-Function General Purpose Timers on AMD Geode
2297 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2298 the BIOS has incorrectly applied a workaround. TinyBIOS
2299 version 0.98 is known to be affected, 0.99 fixes the
2300 problem by letting the user disable the workaround.
2304 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2305 physical address is ignored.
2307 mini2440= [ARM,HW,KNL]
2308 Format:[0..2][b][c][t]
2310 MINI2440 configuration specification:
2311 0 - The attached screen is the 3.5" TFT
2312 1 - The attached screen is the 7" TFT
2313 2 - The VGA Shield is attached (1024x768)
2314 Leaving out the screen size parameter will not load
2315 the TFT driver, and the framebuffer will be left
2317 b - Enable backlight. The TFT backlight pin will be
2318 linked to the kernel VESA blanking code and a GPIO
2319 LED. This parameter is not necessary when using the
2321 c - Enable the s3c camera interface.
2322 t - Reserved for enabling touchscreen support. The
2323 touchscreen support is not enabled in the mainstream
2324 kernel as of 2.6.30, a preliminary port can be found
2325 in the "bleeding edge" mini2440 support kernel at
2326 http://repo.or.cz/w/linux-2.6/mini2440.git
2329 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2330 parameter allows control of the logging verbosity for
2331 the additional memory initialisation checks. A value
2332 of 0 disables mminit logging and a level of 4 will
2333 log everything. Information is printed at KERN_DEBUG
2334 so loglevel=8 may also need to be specified.
2337 [KNL] When CONFIG_MODULE_SIG is set, this means that
2338 modules without (valid) signatures will fail to load.
2339 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2340 is always true, so this option does nothing.
2342 module_blacklist= [KNL] Do not load a comma-separated list of
2343 modules. Useful for debugging problem modules.
2346 [MOUSE] Maximum time between finger touching and
2347 leaving touchpad surface for touch to be considered
2348 a tap and be reported as a left button click (for
2349 touchpads working in absolute mode only).
2351 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2352 reporting absolute coordinates, such as tablets
2353 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2354 reporting absolute coordinates, such as tablets
2356 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2357 is similar to kernelcore except it specifies the
2358 amount of memory used for migratable allocations.
2359 If both kernelcore and movablecore is specified,
2360 then kernelcore will be at *least* the specified
2361 value but may be more. If movablecore on its own
2362 is specified, the administrator must be careful
2363 that the amount of memory usable for all allocations
2366 movable_node [KNL] Boot-time switch to make hotplugable memory
2367 NUMA nodes to be movable. This means that the memory
2368 of such nodes will be usable only for movable
2369 allocations which rules out almost all kernel
2370 allocations. Use with caution!
2372 MTD_Partition= [MTD]
2373 Format: <name>,<region-number>,<size>,<offset>
2375 MTD_Region= [MTD] Format:
2376 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2379 See drivers/mtd/cmdlinepart.c.
2381 multitce=off [PPC] This parameter disables the use of the pSeries
2382 firmware feature for updating multiple TCE entries
2385 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2387 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2389 boundary - index of last SLC block on Flex-OneNAND.
2390 The remaining blocks are configured as MLC blocks.
2391 lock - Configure if Flex-OneNAND boundary should be locked.
2392 Once locked, the boundary cannot be changed.
2393 1 indicates lock status, 0 indicates unlock status.
2396 ARM/S3C2412 JIVE boot control
2398 See arch/arm/mach-s3c2412/mach-jive.c
2400 mtouchusb.raw_coordinates=
2401 [HW] Make the MicroTouch USB driver use raw coordinates
2402 ('y', default) or cooked coordinates ('n')
2404 mtrr_chunk_size=nn[KMG] [X86]
2405 used for mtrr cleanup. It is largest continuous chunk
2406 that could hold holes aka. UC entries.
2408 mtrr_gran_size=nn[KMG] [X86]
2409 Used for mtrr cleanup. It is granularity of mtrr block.
2411 Large value could prevent small alignment from
2414 mtrr_spare_reg_nr=n [X86]
2416 Range: 0,7 : spare reg number
2418 Used for mtrr cleanup. It is spare mtrr entries number.
2419 Set to 2 or more if your graphical card needs more.
2421 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2423 netdev= [NET] Network devices parameters
2424 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2425 Note that mem_start is often overloaded to mean
2426 something different and driver-specific.
2427 This usage is only documented in each driver source
2431 [NETFILTER] Enable connection tracking flow accounting
2432 0 to disable accounting
2433 1 to enable accounting
2436 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2437 See Documentation/filesystems/nfs/nfsroot.txt.
2439 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2440 See Documentation/filesystems/nfs/nfsroot.txt.
2442 nfsrootdebug [NFS] enable nfsroot debugging messages.
2443 See Documentation/filesystems/nfs/nfsroot.txt.
2445 nfs.callback_nr_threads=
2446 [NFSv4] set the total number of threads that the
2447 NFS client will assign to service NFSv4 callback
2450 nfs.callback_tcpport=
2451 [NFS] set the TCP port on which the NFSv4 callback
2452 channel should listen.
2455 [NFS] sets the pathname to the program which is used
2456 to update the NFS client cache entries.
2458 nfs.cache_getent_timeout=
2459 [NFS] sets the timeout after which an attempt to
2460 update a cache entry is deemed to have failed.
2462 nfs.idmap_cache_timeout=
2463 [NFS] set the maximum lifetime for idmapper cache
2467 [NFS] enable 64-bit inode numbers.
2468 If zero, the NFS client will fake up a 32-bit inode
2469 number for the readdir() and stat() syscalls instead
2470 of returning the full 64-bit number.
2471 The default is to return 64-bit inode numbers.
2473 nfs.max_session_cb_slots=
2474 [NFSv4.1] Sets the maximum number of session
2475 slots the client will assign to the callback
2476 channel. This determines the maximum number of
2477 callbacks the client will process in parallel for
2478 a particular server.
2480 nfs.max_session_slots=
2481 [NFSv4.1] Sets the maximum number of session slots
2482 the client will attempt to negotiate with the server.
2483 This limits the number of simultaneous RPC requests
2484 that the client can send to the NFSv4.1 server.
2485 Note that there is little point in setting this
2486 value higher than the max_tcp_slot_table_limit.
2488 nfs.nfs4_disable_idmapping=
2489 [NFSv4] When set to the default of '1', this option
2490 ensures that both the RPC level authentication
2491 scheme and the NFS level operations agree to use
2492 numeric uids/gids if the mount is using the
2493 'sec=sys' security flavour. In effect it is
2494 disabling idmapping, which can make migration from
2495 legacy NFSv2/v3 systems to NFSv4 easier.
2496 Servers that do not support this mode of operation
2497 will be autodetected by the client, and it will fall
2498 back to using the idmapper.
2499 To turn off this behaviour, set the value to '0'.
2501 [NFS4] Specify an additional fixed unique ident-
2502 ification string that NFSv4 clients can insert into
2503 their nfs_client_id4 string. This is typically a
2504 UUID that is generated at system install time.
2506 nfs.send_implementation_id =
2507 [NFSv4.1] Send client implementation identification
2508 information in exchange_id requests.
2509 If zero, no implementation identification information
2511 The default is to send the implementation identification
2514 nfs.recover_lost_locks =
2515 [NFSv4] Attempt to recover locks that were lost due
2516 to a lease timeout on the server. Please note that
2517 doing this risks data corruption, since there are
2518 no guarantees that the file will remain unchanged
2519 after the locks are lost.
2520 If you want to enable the kernel legacy behaviour of
2521 attempting to recover these locks, then set this
2523 The default parameter value of '0' causes the kernel
2524 not to attempt recovery of lost locks.
2526 nfs4.layoutstats_timer =
2527 [NFSv4.2] Change the rate at which the kernel sends
2528 layoutstats to the pNFS metadata server.
2530 Setting this to value to 0 causes the kernel to use
2531 whatever value is the default set by the layout
2532 driver. A non-zero value sets the minimum interval
2533 in seconds between layoutstats transmissions.
2535 nfsd.nfs4_disable_idmapping=
2536 [NFSv4] When set to the default of '1', the NFSv4
2537 server will return only numeric uids and gids to
2538 clients using auth_sys, and will accept numeric uids
2539 and gids from such clients. This is intended to ease
2540 migration from NFSv2/v3.
2542 nmi_debug= [KNL,SH] Specify one or more actions to take
2543 when a NMI is triggered.
2544 Format: [state][,regs][,debounce][,die]
2546 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2547 Format: [panic,][nopanic,][num]
2549 0 - turn hardlockup detector in nmi_watchdog off
2550 1 - turn hardlockup detector in nmi_watchdog on
2551 When panic is specified, panic when an NMI watchdog
2552 timeout occurs (or 'nopanic' to override the opposite
2553 default). To disable both hard and soft lockup detectors,
2554 please see 'nowatchdog'.
2555 This is useful when you use a panic=... timeout and
2556 need the box quickly up again.
2558 These settings can be accessed at runtime via
2559 the nmi_watchdog and hardlockup_panic sysctls.
2561 netpoll.carrier_timeout=
2562 [NET] Specifies amount of time (in seconds) that
2563 netpoll should wait for a carrier. By default netpoll
2566 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2567 emulation library even if a 387 maths coprocessor
2571 [HW] Never suspend the console
2572 Disable suspending of consoles during suspend and
2573 hibernate operations. Once disabled, debugging
2574 messages can reach various consoles while the rest
2575 of the system is being put to sleep (ie, while
2576 debugging driver suspend/resume hooks). This may
2577 not work reliably with all consoles, but is known
2578 to work with serial and VGA consoles.
2579 To facilitate more flexible debugging, we also add
2580 console_suspend, a printk module parameter to control
2581 it. Users could use console_suspend (usually
2582 /sys/module/printk/parameters/console_suspend) to
2583 turn on/off it dynamically.
2585 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2586 caches in the slab allocator. Saves per-node memory,
2587 but will impact performance.
2591 noaltinstr [S390] Disables alternative instructions patching
2592 (CPU alternatives feature).
2594 noapic [SMP,APIC] Tells the kernel to not make use of any
2595 IOAPICs that may be present in the system.
2597 noautogroup Disable scheduler automatic task group creation.
2599 nobats [PPC] Do not use BATs for mapping kernel lowmem
2600 on "Classic" PPC cores.
2604 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2606 nodelayacct [KNL] Disable per-task delay accounting
2608 nodsp [SH] Disable hardware DSP at boot time.
2610 noefi Disable EFI runtime services support.
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