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 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" | "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.
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/driver-api/clk.rst.
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 com20020= [HW,NET] ARCnet - COM20020 chipset
592 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
594 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
598 ARCnet - COM90xx chipset (memory-mapped buffers)
599 Format: <io>[,<irq>[,<memstart>]]
601 condev= [HW,S390] console device
604 console= [KNL] Output console device and options.
606 tty<n> Use the virtual console device <n>.
610 Use the specified serial port. The options are of
611 the form "bbbbpnf", where "bbbb" is the baud rate,
612 "p" is parity ("n", "o", or "e"), "n" is number of
613 bits, and "f" is flow control ("r" for RTS or
614 omit it). Default is "9600n8".
616 See Documentation/admin-guide/serial-console.rst for more
618 Documentation/networking/netconsole.txt for an
621 uart[8250],io,<addr>[,options]
622 uart[8250],mmio,<addr>[,options]
623 uart[8250],mmio16,<addr>[,options]
624 uart[8250],mmio32,<addr>[,options]
625 uart[8250],0x<addr>[,options]
626 Start an early, polled-mode console on the 8250/16550
627 UART at the specified I/O port or MMIO address,
628 switching to the matching ttyS device later.
629 MMIO inter-register address stride is either 8-bit
630 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
631 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
632 to be equivalent to 'mmio'. 'options' are specified in
633 the same format described for ttyS above; if unspecified,
634 the h/w is not re-initialized.
636 hvc<n> Use the hypervisor console device <n>. This is for
637 both Xen and PowerPC hypervisors.
639 If the device connected to the port is not a TTY but a braille
640 device, prepend "brl," before the device type, for instance
642 For now, only VisioBraille is supported.
645 [KNL] Change console messages format
647 By default we print messages on consoles in
648 "[time stamp] text\n" format (time stamp may not be
649 printed, depending on CONFIG_PRINTK_TIME or
650 `printk_time' param).
652 Switch to syslog format: "<%u>[time stamp] text\n"
653 IOW, each message will have a facility and loglevel
654 prefix. The format is similar to one used by syslog()
655 syscall, or to executing "dmesg -S --raw" or to reading
658 consoleblank= [KNL] The console blank (screen saver) timeout in
659 seconds. A value of 0 disables the blank timer.
663 [KNL] Change the default value for
664 /proc/<pid>/coredump_filter.
665 See also Documentation/filesystems/proc.txt.
667 coresight_cpu_debug.enable
670 Enable/disable the CPU sampling based debugging.
671 0: default value, disable debugging
672 1: enable debugging at boot time
674 cpuidle.off=1 [CPU_IDLE]
675 disable the cpuidle sub-system
677 cpufreq.off=1 [CPU_FREQ]
678 disable the cpufreq sub-system
681 [X86] Delay for N microsec between assert and de-assert
682 of APIC INIT to start processors. This delay occurs
683 on every CPU online, such as boot, and resume from suspend.
686 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
688 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
690 crashkernel=size[KMG][@offset[KMG]]
691 [KNL] Using kexec, Linux can switch to a 'crash kernel'
692 upon panic. This parameter reserves the physical
693 memory region [offset, offset + size] for that kernel
694 image. If '@offset' is omitted, then a suitable offset
695 is selected automatically. Check
696 Documentation/kdump/kdump.txt for further details.
698 crashkernel=range1:size1[,range2:size2,...][@offset]
699 [KNL] Same as above, but depends on the memory
700 in the running system. The syntax of range is
701 start-[end] where start and end are both
702 a memory unit (amount[KMG]). See also
703 Documentation/kdump/kdump.txt for an example.
705 crashkernel=size[KMG],high
706 [KNL, x86_64] range could be above 4G. Allow kernel
707 to allocate physical memory region from top, so could
708 be above 4G if system have more than 4G ram installed.
709 Otherwise memory region will be allocated below 4G, if
711 It will be ignored if crashkernel=X is specified.
712 crashkernel=size[KMG],low
713 [KNL, x86_64] range under 4G. When crashkernel=X,high
714 is passed, kernel could allocate physical memory region
715 above 4G, that cause second kernel crash on system
716 that require some amount of low memory, e.g. swiotlb
717 requires at least 64M+32K low memory, also enough extra
718 low memory is needed to make sure DMA buffers for 32-bit
719 devices won't run out. Kernel would try to allocate at
720 at least 256M below 4G automatically.
721 This one let user to specify own low range under 4G
722 for second kernel instead.
723 0: to disable low allocation.
724 It will be ignored when crashkernel=X,high is not used
725 or memory reserved is below 4G.
728 [KNL] Disable crypto self-tests
733 cs89x0_media= [HW,NET]
734 Format: { rj45 | aui | bnc }
737 See header of drivers/s390/block/dasd_devmap.c.
739 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
740 (one device per port)
741 Format: <port#>,<type>
742 See also Documentation/input/devices/joystick-parport.rst
744 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
746 Documentation/admin-guide/dynamic-debug-howto.rst for
747 details. Deprecated, see dyndbg.
749 debug [KNL] Enable kernel debugging (events log level).
752 [KNL] verbose self-tests
754 Print debugging info while doing the locking API
756 We default to 0 (no extra messages), setting it to
757 1 will print _a lot_ more information - normally
758 only useful to kernel developers.
760 debug_objects [KNL] Enable object debugging
763 [KNL] Disable object debugging
765 debug_guardpage_minorder=
766 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
767 parameter allows control of the order of pages that will
768 be intentionally kept free (and hence protected) by the
769 buddy allocator. Bigger value increase the probability
770 of catching random memory corruption, but reduce the
771 amount of memory for normal system use. The maximum
772 possible value is MAX_ORDER/2. Setting this parameter
773 to 1 or 2 should be enough to identify most random
774 memory corruption problems caused by bugs in kernel or
775 driver code when a CPU writes to (or reads from) a
776 random memory location. Note that there exists a class
777 of memory corruptions problems caused by buggy H/W or
778 F/W or by drivers badly programing DMA (basically when
779 memory is written at bus level and the CPU MMU is
780 bypassed) which are not detectable by
781 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
782 tracking down these problems.
785 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
786 parameter enables the feature at boot time. In
787 default, it is disabled. We can avoid allocating huge
788 chunk of memory for debug pagealloc if we don't enable
789 it at boot time and the system will work mostly same
790 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
791 on: enable the feature
793 debugpat [X86] Enable PAT debugging
795 decnet.addr= [HW,NET]
796 Format: <area>[,<node>]
797 See also Documentation/networking/decnet.txt.
800 [same as hugepagesz=] The size of the default
801 HugeTLB page size. This is the size represented by
802 the legacy /proc/ hugepages APIs, used for SHM, and
803 default size when mounting hugetlbfs filesystems.
804 Defaults to the default architecture's huge page size
808 Set number of hash buckets for dentry cache.
810 disable_1tb_segments [PPC]
811 Disables the use of 1TB hash page table segments. This
812 causes the kernel to fall back to 256MB segments which
813 can be useful when debugging issues that require an SLB
817 See Documentation/networking/ipv6.txt.
820 Disable RADIX MMU mode on POWER9
822 disable_cpu_apicid= [X86,APIC,SMP]
824 The number of initial APIC ID for the
825 corresponding CPU to be disabled at boot,
826 mostly used for the kdump 2nd kernel to
827 disable BSP to wake up multiple CPUs without
828 causing system reset or hang due to sending
831 disable_ddw [PPC/PSERIES]
832 Disable Dynamic DMA Window support. Use this if
833 to workaround buggy firmware.
836 See Documentation/networking/ipv6.txt.
838 disable_mtrr_cleanup [X86]
839 The kernel tries to adjust MTRR layout from continuous
840 to discrete, to make X server driver able to add WB
841 entry later. This parameter disables that.
843 disable_mtrr_trim [X86, Intel and AMD only]
844 By default the kernel will trim any uncacheable
845 memory out of your available memory pool based on
846 MTRR settings. This parameter disables that behavior,
847 possibly causing your machine to run very slowly.
849 disable_timer_pin_1 [X86]
850 Disable PIN 1 of APIC timer
851 Can be useful to work around chipset bugs.
853 dis_ucode_ldr [X86] Disable the microcode loader.
855 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
856 this option disables the debugging code at boot.
858 dma_debug_entries=<number>
859 This option allows to tune the number of preallocated
860 entries for DMA-API debugging code. One entry is
861 required per DMA-API allocation. Use this if the
862 DMA-API debugging code disables itself because the
863 architectural default is too low.
865 dma_debug_driver=<driver_name>
866 With this option the DMA-API debugging driver
867 filter feature can be enabled at boot time. Just
868 pass the driver to filter for as the parameter.
869 The filter can be disabled or changed to another
870 driver later using sysfs.
872 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
873 Broken monitors, graphic adapters, KVMs and EDIDless
874 panels may send no or incorrect EDID data sets.
875 This parameter allows to specify an EDID data sets
876 in the /lib/firmware directory that are used instead.
877 Generic built-in EDID data sets are used, if one of
878 edid/1024x768.bin, edid/1280x1024.bin,
879 edid/1680x1050.bin, or edid/1920x1080.bin is given
880 and no file with the same name exists. Details and
881 instructions how to build your own EDID data are
882 available in Documentation/EDID/HOWTO.txt. An EDID
883 data set will only be used for a particular connector,
884 if its name and a colon are prepended to the EDID
885 name. Each connector may use a unique EDID data
886 set by separating the files with a comma. An EDID
887 data set with no connector name will be used for
888 any connectors not explicitly specified.
893 Format: {"off" | "known"}
894 Control how the dt_cpu_ftrs device-tree binding is
895 used for CPU feature discovery and setup (if it
897 off: Do not use it, fall back to legacy cpu table.
898 known: Do not pass through unknown features to guests
899 or userspace, only those that the kernel is aware of.
901 dump_apple_properties [X86]
902 Dump name and content of EFI device properties on
903 x86 Macs. Useful for driver authors to determine
904 what data is available or for reverse-engineering.
906 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
907 module.dyndbg[="val"]
908 Enable debug messages at boot time. See
909 Documentation/admin-guide/dynamic-debug-howto.rst
912 nompx [X86] Disables Intel Memory Protection Extensions.
913 See Documentation/x86/intel_mpx.txt for more
914 information about the feature.
916 nopku [X86] Disable Memory Protection Keys CPU feature found
919 module.async_probe [KNL]
920 Enable asynchronous probe on this module.
922 early_ioremap_debug [KNL]
923 Enable debug messages in early_ioremap support. This
924 is useful for tracking down temporary early mappings
925 which are not unmapped.
927 earlycon= [KNL] Output early console device and options.
929 [ARM64] The early console is determined by the
930 stdout-path property in device tree's chosen node,
931 or determined by the ACPI SPCR table.
933 [X86] When used with no options the early console is
934 determined by the ACPI SPCR table.
936 cdns,<addr>[,options]
937 Start an early, polled-mode console on a Cadence
938 (xuartps) serial port at the specified address. Only
939 supported option is baud rate. If baud rate is not
940 specified, the serial port must already be setup and
943 uart[8250],io,<addr>[,options]
944 uart[8250],mmio,<addr>[,options]
945 uart[8250],mmio32,<addr>[,options]
946 uart[8250],mmio32be,<addr>[,options]
947 uart[8250],0x<addr>[,options]
948 Start an early, polled-mode console on the 8250/16550
949 UART at the specified I/O port or MMIO address.
950 MMIO inter-register address stride is either 8-bit
951 (mmio) or 32-bit (mmio32 or mmio32be).
952 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
953 to be equivalent to 'mmio'. 'options' are specified
954 in the same format described for "console=ttyS<n>"; if
955 unspecified, the h/w is not initialized.
959 Start an early, polled-mode console on a pl011 serial
960 port at the specified address. The pl011 serial port
961 must already be setup and configured. Options are not
962 yet supported. If 'mmio32' is specified, then only
963 the driver will use only 32-bit accessors to read/write
964 the device registers.
967 Start an early, polled-mode console on a meson serial
968 port at the specified address. The serial port must
969 already be setup and configured. Options are not yet
973 Start an early, polled-mode console on an msm serial
974 port at the specified address. The serial port
975 must already be setup and configured. Options are not
979 Start an early, polled-mode console on an msm serial
980 dm port at the specified address. The serial port
981 must already be setup and configured. Options are not
985 Start an early, polled-mode console on a serial port
986 of an Actions Semi SoC, such as S500 or S900, at the
987 specified address. The serial port must already be
988 setup and configured. Options are not yet supported.
990 smh Use ARM semihosting calls for early console.
998 Use early console provided by serial driver available
999 on Samsung SoCs, requires selecting proper type and
1000 a correct base address of the selected UART port. The
1001 serial port must already be setup and configured.
1002 Options are not yet supported.
1005 Start an early, polled-mode console on a lantiq serial
1006 (lqasc) port at the specified address. The serial port
1007 must already be setup and configured. Options are not
1012 Use early console provided by Freescale LP UART driver
1013 found on Freescale Vybrid and QorIQ LS1021A processors.
1014 A valid base address must be provided, and the serial
1015 port must already be setup and configured.
1018 Start an early, polled-mode console on the
1019 Armada 3700 serial port at the specified
1020 address. The serial port must already be setup
1021 and configured. Options are not yet supported.
1024 Start an early, polled-mode console on a Qualcomm
1025 Generic Interface (GENI) based serial port at the
1026 specified address. The serial port must already be
1027 setup and configured. Options are not yet supported.
1029 earlyprintk= [X86,SH,ARM,M68k,S390]
1034 earlyprintk=serial[,ttySn[,baudrate]]
1035 earlyprintk=serial[,0x...[,baudrate]]
1036 earlyprintk=ttySn[,baudrate]
1037 earlyprintk=dbgp[debugController#]
1038 earlyprintk=pciserial,bus:device.function[,baudrate]
1039 earlyprintk=xdbc[xhciController#]
1041 earlyprintk is useful when the kernel crashes before
1042 the normal console is initialized. It is not enabled by
1043 default because it has some cosmetic problems.
1045 Append ",keep" to not disable it when the real console
1048 Only one of vga, efi, serial, or usb debug port can
1051 Currently only ttyS0 and ttyS1 may be specified by
1052 name. Other I/O ports may be explicitly specified
1053 on some architectures (x86 and arm at least) by
1054 replacing ttySn with an I/O port address, like this:
1055 earlyprintk=serial,0x1008,115200
1056 You can find the port for a given device in
1057 /proc/tty/driver/serial:
1058 2: uart:ST16650V2 port:00001008 irq:18 ...
1060 Interaction with the standard serial driver is not
1063 The VGA and EFI output is eventually overwritten by
1066 The xen output can only be used by Xen PV guests.
1068 The sclp output can only be used on s390.
1070 edac_report= [HW,EDAC] Control how to report EDAC event
1071 Format: {"on" | "off" | "force"}
1072 on: enable EDAC to report H/W event. May be overridden
1073 by other higher priority error reporting module.
1074 off: disable H/W event reporting through EDAC.
1075 force: enforce the use of EDAC to report H/W event.
1078 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1081 This is designed to be used in conjunction with
1082 the boot argument: earlyprintk=vga
1085 Format: {"off" | "on" | "skip[mbr]"}
1088 Format: { "old_map", "nochunk", "noruntime", "debug" }
1089 old_map [X86-64]: switch to the old ioremap-based EFI
1090 runtime services mapping. 32-bit still uses this one by
1092 nochunk: disable reading files in "chunks" in the EFI
1093 boot stub, as chunking can cause problems with some
1094 firmware implementations.
1095 noruntime : disable EFI runtime services support
1096 debug: enable misc debug output
1098 efi_no_storage_paranoia [EFI; X86]
1099 Using this parameter you can use more than 50% of
1100 your efi variable storage. Use this parameter only if
1101 you are really sure that your UEFI does sane gc and
1102 fulfills the spec otherwise your board may brick.
1104 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1105 Add arbitrary attribute to specific memory range by
1106 updating original EFI memory map.
1107 Region of memory which aa attribute is added to is
1109 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1110 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1111 attribute is added to range 0x100000000-0x180000000 and
1112 0x10a0000000-0x1120000000.
1114 Using this parameter you can do debugging of EFI memmap
1115 related feature. For example, you can do debugging of
1116 Address Range Mirroring feature even if your box
1119 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1120 that is to be dynamically loaded by Linux. If there are
1121 multiple variables with the same name but with different
1122 vendor GUIDs, all of them will be loaded. See
1123 Documentation/acpi/ssdt-overlays.txt for details.
1126 eisa_irq_edge= [PARISC,HW]
1127 See header of drivers/parisc/eisa.c.
1130 See comment before function elanfreq_setup() in
1131 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1134 Format: {"cfq" | "deadline" | "noop"}
1135 See Documentation/block/cfq-iosched.txt and
1136 Documentation/block/deadline-iosched.txt for details.
1138 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1139 Specifies physical address of start of kernel core
1140 image elf header and optionally the size. Generally
1141 kexec loader will pass this option to capture kernel.
1142 See Documentation/kdump/kdump.txt for details.
1144 enable_mtrr_cleanup [X86]
1145 The kernel tries to adjust MTRR layout from continuous
1146 to discrete, to make X server driver able to add WB
1147 entry later. This parameter enables that.
1149 enable_timer_pin_1 [X86]
1150 Enable PIN 1 of APIC timer
1151 Can be useful to work around chipset bugs
1152 (in particular on some ATI chipsets).
1153 The kernel tries to set a reasonable default.
1155 enforcing [SELINUX] Set initial enforcing status.
1157 See security/selinux/Kconfig help text.
1158 0 -- permissive (log only, no denials).
1159 1 -- enforcing (deny and log).
1161 Value can be changed at runtime via /selinux/enforce.
1164 Disable Error Record Serialization Table (ERST)
1167 ether= [HW,NET] Ethernet cards parameters
1168 This option is obsoleted by the "netdev=" option, which
1169 has equivalent usage. See its documentation for details.
1173 Permit 'security.evm' to be updated regardless of
1174 current integrity status.
1178 fail_make_request=[KNL]
1179 General fault injection mechanism.
1180 Format: <interval>,<probability>,<space>,<times>
1181 See also Documentation/fault-injection/.
1184 See Documentation/blockdev/floppy.txt.
1186 force_pal_cache_flush
1187 [IA-64] Avoid check_sal_cache_flush which may hang on
1188 buggy SAL_CACHE_FLUSH implementations. Using this
1189 parameter will force ia64_sal_cache_flush to call
1190 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1193 Forcefully enable Physical Address Extension (PAE).
1194 Many Pentium M systems disable PAE but may have a
1195 functionally usable PAE implementation.
1196 Warning: use of this parameter will taint the kernel
1197 and may cause unknown problems.
1200 [FTRACE] will set and start the specified tracer
1201 as early as possible in order to facilitate early
1204 ftrace_dump_on_oops[=orig_cpu]
1205 [FTRACE] will dump the trace buffers on oops.
1206 If no parameter is passed, ftrace will dump
1207 buffers of all CPUs, but if you pass orig_cpu, it will
1208 dump only the buffer of the CPU that triggered the
1211 ftrace_filter=[function-list]
1212 [FTRACE] Limit the functions traced by the function
1213 tracer at boot up. function-list is a comma separated
1214 list of functions. This list can be changed at run
1215 time by the set_ftrace_filter file in the debugfs
1218 ftrace_notrace=[function-list]
1219 [FTRACE] Do not trace the functions specified in
1220 function-list. This list can be changed at run time
1221 by the set_ftrace_notrace file in the debugfs
1224 ftrace_graph_filter=[function-list]
1225 [FTRACE] Limit the top level callers functions traced
1226 by the function graph tracer at boot up.
1227 function-list is a comma separated list of functions
1228 that can be changed at run time by the
1229 set_graph_function file in the debugfs tracing directory.
1231 ftrace_graph_notrace=[function-list]
1232 [FTRACE] Do not trace from the functions specified in
1233 function-list. This list is a comma separated list of
1234 functions that can be changed at run time by the
1235 set_graph_notrace file in the debugfs tracing directory.
1237 ftrace_graph_max_depth=<uint>
1238 [FTRACE] Used with the function graph tracer. This is
1239 the max depth it will trace into a function. This value
1240 can be changed at run time by the max_graph_depth file
1241 in the tracefs tracing directory. default: 0 (no limit)
1244 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1245 support via parallel port (up to 5 devices per port)
1246 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1247 See also Documentation/input/devices/joystick-parport.rst
1251 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1255 gcov_persist= [GCOV] When non-zero (default), profiling data for
1256 kernel modules is saved and remains accessible via
1257 debugfs, even when the module is unloaded/reloaded.
1258 When zero, profiling data is discarded and associated
1259 debugfs files are removed at module unload time.
1261 goldfish [X86] Enable the goldfish android emulator platform.
1262 Don't use this when you are not running on the
1265 gpt [EFI] Forces disk with valid GPT signature but
1266 invalid Protective MBR to be treated as GPT. If the
1267 primary GPT is corrupted, it enables the backup/alternate
1268 GPT to be used instead.
1270 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1271 the "Enable 0" bit of the configuration register.
1274 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1275 the "Enable 0" bit of the configuration register.
1278 grcan.select= [HW] Select which physical interface to use.
1281 grcan.txsize= [HW] Sets the size of the tx buffer.
1282 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1284 grcan.rxsize= [HW] Sets the size of the rx buffer.
1285 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1288 gpio-mockup.gpio_mockup_ranges
1289 [HW] Sets the ranges of gpiochip of for this device.
1290 Format: <start1>,<end1>,<start2>,<end2>...
1292 hardlockup_all_cpu_backtrace=
1293 [KNL] Should the hard-lockup detector generate
1294 backtraces on all cpus.
1297 hashdist= [KNL,NUMA] Large hashes allocated during boot
1298 are distributed across NUMA nodes. Defaults on
1299 for 64-bit NUMA, off otherwise.
1300 Format: 0 | 1 (for off | on)
1302 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1304 hd= [EIDE] (E)IDE hard drive subsystem geometry
1305 Format: <cyl>,<head>,<sect>
1308 Disable Hardware Error Source Table (HEST) support;
1309 corresponding firmware-first mode error processing
1310 logic will be disabled.
1312 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1313 size of <nn>. This works even on boxes that have no
1314 highmem otherwise. This also works to reduce highmem
1315 size on bigger boxes.
1317 highres= [KNL] Enable/disable high resolution timer mode.
1318 Valid parameters: "on", "off"
1322 See Documentation/isdn/README.HiSax.
1326 hpet= [X86-32,HPET] option to control HPET usage
1327 Format: { enable (default) | disable | force |
1329 disable: disable HPET and use PIT instead
1330 force: allow force enabled of undocumented chips (ICH4,
1332 verbose: show contents of HPET registers during setup
1334 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1335 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1337 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1338 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1339 On x86-64 and powerpc, this option can be specified
1340 multiple times interleaved with hugepages= to reserve
1341 huge pages of different sizes. Valid pages sizes on
1342 x86-64 are 2M (when the CPU supports "pse") and 1G
1343 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1346 [KNL] Should the hung task detector generate panics.
1349 A nonzero value instructs the kernel to panic when a
1350 hung task is detected. The default value is controlled
1351 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1352 option. The value selected by this boot parameter can
1353 be changed later by the kernel.hung_task_panic sysctl.
1355 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1356 terminal devices. Valid values: 0..8
1357 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1358 If specified, z/VM IUCV HVC accepts connections
1359 from listed z/VM user IDs only.
1361 Do not unregister boot console at start. This is only
1362 useful for debugging when something happens in the window
1363 between unregistering the boot console and initializing
1366 i2c_bus= [HW] Override the default board specific I2C bus speed
1367 or register an additional I2C bus that is not
1368 registered from board initialization code.
1372 i8042.debug [HW] Toggle i8042 debug mode
1373 i8042.unmask_kbd_data
1374 [HW] Enable printing of interrupt data from the KBD port
1375 (disabled by default, and as a pre-condition
1376 requires that i8042.debug=1 be enabled)
1377 i8042.direct [HW] Put keyboard port into non-translated mode
1378 i8042.dumbkbd [HW] Pretend that controller can only read data from
1379 keyboard and cannot control its state
1380 (Don't attempt to blink the leds)
1381 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1382 i8042.nokbd [HW] Don't check/create keyboard port
1383 i8042.noloop [HW] Disable the AUX Loopback command while probing
1385 i8042.nomux [HW] Don't check presence of an active multiplexing
1387 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1389 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1390 i8042.reset [HW] Reset the controller during init, cleanup and
1391 suspend-to-ram transitions, only during s2r
1392 transitions, or never reset
1393 Format: { 1 | Y | y | 0 | N | n }
1394 1, Y, y: always reset controller
1395 0, N, n: don't ever reset controller
1396 Default: only on s2r transitions on x86; most other
1397 architectures force reset to be always executed
1398 i8042.unlock [HW] Unlock (ignore) the keylock
1399 i8042.kbdreset [HW] Reset device connected to KBD port
1403 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1404 indicates that the driver is running on unsupported
1406 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1407 does not match list of supported models.
1409 [HW] Report power status in /proc/i8k
1410 (disabled by default)
1411 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1414 i915.invert_brightness=
1415 [DRM] Invert the sense of the variable that is used to
1416 set the brightness of the panel backlight. Normally a
1417 brightness value of 0 indicates backlight switched off,
1418 and the maximum of the brightness value sets the backlight
1419 to maximum brightness. If this parameter is set to 0
1420 (default) and the machine requires it, or this parameter
1421 is set to 1, a brightness value of 0 sets the backlight
1422 to maximum brightness, and the maximum of the brightness
1423 value switches the backlight off.
1424 -1 -- never invert brightness
1425 0 -- machine default
1426 1 -- force brightness inversion
1429 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1431 ide-core.nodma= [HW] (E)IDE subsystem
1432 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1433 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1434 .cdrom .chs .ignore_cable are additional options
1435 See Documentation/ide/ide.txt.
1437 ide-generic.probe-mask= [HW] (E)IDE subsystem
1439 Probe mask for legacy ISA IDE ports. Depending on
1440 platform up to 6 ports are supported, enabled by
1441 setting corresponding bits in the mask to 1. The
1442 default value is 0x0, which has a special meaning.
1443 On systems that have PCI, it triggers scanning the
1444 PCI bus for the first and the second port, which
1445 are then probed. On systems without PCI the value
1446 of 0x0 enables probing the two first ports as if it
1449 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1450 Claim all unknown PCI IDE storage controllers.
1453 Format: idle=poll, idle=halt, idle=nomwait
1454 Poll forces a polling idle loop that can slightly
1455 improve the performance of waking up a idle CPU, but
1456 will use a lot of power and make the system run hot.
1458 idle=halt: Halt is forced to be used for CPU idle.
1459 In such case C2/C3 won't be used again.
1460 idle=nomwait: Disable mwait for CPU C-states
1462 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1463 Format: { strict | legacy | 2008 | relaxed }
1466 Choose which programs will be accepted for execution
1467 based on the IEEE 754 NaN encoding(s) supported by
1468 the FPU and the NaN encoding requested with the value
1469 of an ELF file header flag individually set by each
1470 binary. Hardware implementations are permitted to
1471 support either or both of the legacy and the 2008 NaN
1474 Available settings are as follows:
1475 strict accept binaries that request a NaN encoding
1476 supported by the FPU
1477 legacy only accept legacy-NaN binaries, if supported
1479 2008 only accept 2008-NaN binaries, if supported
1481 relaxed accept any binaries regardless of whether
1482 supported by the FPU
1484 The FPU emulator is always able to support both NaN
1485 encodings, so if no FPU hardware is present or it has
1486 been disabled with 'nofpu', then the settings of
1487 'legacy' and '2008' strap the emulator accordingly,
1488 'relaxed' straps the emulator for both legacy-NaN and
1489 2008-NaN, whereas 'strict' enables legacy-NaN only on
1490 legacy processors and both NaN encodings on MIPS32 or
1493 The setting for ABS.fmt/NEG.fmt instruction execution
1494 mode generally follows that for the NaN encoding,
1495 except where unsupported by hardware.
1497 ignore_loglevel [KNL]
1498 Ignore loglevel setting - this will print /all/
1499 kernel messages to the console. Useful for debugging.
1500 We also add it as printk module parameter, so users
1501 could change it dynamically, usually by
1502 /sys/module/printk/parameters/ignore_loglevel.
1505 Ignore RLIMIT_DATA setting for data mappings,
1506 print warning at first misuse. Can be changed via
1507 /sys/module/kernel/parameters/ignore_rlimit_data.
1509 ihash_entries= [KNL]
1510 Set number of hash buckets for inode cache.
1512 ima_appraise= [IMA] appraise integrity measurements
1513 Format: { "off" | "enforce" | "fix" | "log" }
1516 ima_appraise_tcb [IMA]
1517 The builtin appraise policy appraises all files
1520 ima_canonical_fmt [IMA]
1521 Use the canonical format for the binary runtime
1522 measurements, instead of host native format.
1525 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1529 The list of supported hash algorithms is defined
1530 in crypto/hash_info.h.
1533 The builtin policies to load during IMA setup.
1534 Format: "tcb | appraise_tcb | secure_boot |
1537 The "tcb" policy measures all programs exec'd, files
1538 mmap'd for exec, and all files opened with the read
1539 mode bit set by either the effective uid (euid=0) or
1542 The "appraise_tcb" policy appraises the integrity of
1543 all files owned by root. (This is the equivalent
1544 of ima_appraise_tcb.)
1546 The "secure_boot" policy appraises the integrity
1547 of files (eg. kexec kernel image, kernel modules,
1548 firmware, policy, etc) based on file signatures.
1550 The "fail_securely" policy forces file signature
1551 verification failure also on privileged mounted
1552 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1555 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1556 Load a policy which meets the needs of the Trusted
1557 Computing Base. This means IMA will measure all
1558 programs exec'd, files mmap'd for exec, and all files
1559 opened for read by uid=0.
1562 Select one of defined IMA measurements template formats.
1563 Formats: { "ima" | "ima-ng" | "ima-sig" }
1567 [IMA] Define a custom template format.
1568 Format: { "field1|...|fieldN" }
1570 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1571 Format: <min_file_size>
1572 Set the minimal file size for using asynchronous hash.
1573 If left unspecified, ahash usage is disabled.
1575 ahash performance varies for different data sizes on
1576 different crypto accelerators. This option can be used
1577 to achieve the best performance for a particular HW.
1579 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1581 Set hashing buffer size. Default: 4k.
1583 ahash performance varies for different chunk sizes on
1584 different crypto accelerators. This option can be used
1585 to achieve best performance for particular HW.
1589 Run specified binary instead of /sbin/init as init
1592 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1593 for working out where the kernel is dying during
1596 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1597 initcall functions. Useful for debugging built-in
1598 modules and initcalls.
1600 initrd= [BOOT] Specify the location of the initial ramdisk
1602 init_pkru= [x86] Specify the default memory protection keys rights
1603 register contents for all processes. 0x55555554 by
1604 default (disallow access to all but pkey 0). Can
1605 override in debugfs after boot.
1607 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1610 int_pln_enable [x86] Enable power limit notification interrupt
1612 integrity_audit=[IMA]
1613 Format: { "0" | "1" }
1614 0 -- basic integrity auditing messages. (Default)
1615 1 -- additional integrity auditing messages.
1617 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1619 Enable intel iommu driver.
1621 Disable intel iommu driver.
1622 igfx_off [Default Off]
1623 By default, gfx is mapped as normal device. If a gfx
1624 device has a dedicated DMAR unit, the DMAR unit is
1625 bypassed by not enabling DMAR with this option. In
1626 this case, gfx device will use physical address for
1629 With this option iommu will not optimize to look
1630 for io virtual address below 32-bit forcing dual
1631 address cycle on pci bus for cards supporting greater
1632 than 32-bit addressing. The default is to look
1633 for translation below 32-bit and if not available
1634 then look in the higher range.
1635 strict [Default Off]
1636 With this option on every unmap_single operation will
1637 result in a hardware IOTLB flush operation as opposed
1638 to batching them for performance.
1639 sp_off [Default Off]
1640 By default, super page will be supported if Intel IOMMU
1641 has the capability. With this option, super page will
1643 ecs_off [Default Off]
1644 By default, extended context tables will be supported if
1645 the hardware advertises that it has support both for the
1646 extended tables themselves, and also PASID support. With
1647 this option set, extended tables will not be used even
1648 on hardware which claims to support them.
1649 tboot_noforce [Default Off]
1650 Do not force the Intel IOMMU enabled under tboot.
1651 By default, tboot will force Intel IOMMU on, which
1652 could harm performance of some high-throughput
1653 devices like 40GBit network cards, even if identity
1655 Note that using this option lowers the security
1656 provided by tboot because it makes the system
1657 vulnerable to DMA attacks.
1659 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1660 0 disables intel_idle and fall back on acpi_idle.
1661 1 to 9 specify maximum depth of C-state.
1665 Do not enable intel_pstate as the default
1666 scaling driver for the supported processors
1668 Use intel_pstate as a scaling driver, but configure it
1669 to work with generic cpufreq governors (instead of
1670 enabling its internal governor). This mode cannot be
1671 used along with the hardware-managed P-states (HWP)
1674 Enable intel_pstate on systems that prohibit it by default
1675 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1676 instead of acpi-cpufreq may disable platform features, such
1677 as thermal controls and power capping, that rely on ACPI
1678 P-States information being indicated to OSPM and therefore
1679 should be used with caution. This option does not work with
1680 processors that aren't supported by the intel_pstate driver
1681 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1683 Do not enable hardware P state control (HWP)
1686 Only load intel_pstate on systems which support
1687 hardware P state control (HWP) if available.
1689 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1690 Description Table, specifies preferred power management
1691 profile as "Enterprise Server" or "Performance Server",
1692 then this feature is turned on by default.
1694 Allow per-logical-CPU P-State performance control limits using
1695 cpufreq sysfs interface
1697 intremap= [X86-64, Intel-IOMMU]
1698 on enable Interrupt Remapping (default)
1699 off disable Interrupt Remapping
1700 nosid disable Source ID checking
1702 BIOS x2APIC opt-out request will be ignored
1703 nopost disable Interrupt Posting
1705 iomem= Disable strict checking of access to MMIO memory
1706 strict regions from userspace.
1720 nobypass [PPC/POWERNV]
1721 Disable IOMMU bypass, using IOMMU for PCI devices.
1724 [ARM64] Configure DMA to bypass the IOMMU by default.
1725 Format: { "0" | "1" }
1726 0 - Use IOMMU translation for DMA.
1727 1 - Bypass the IOMMU for DMA.
1728 unset - Use IOMMU translation for DMA.
1730 io7= [HW] IO7 for Marvel based alpha systems
1731 See comment before marvel_specify_io7 in
1732 arch/alpha/kernel/core_marvel.c.
1734 io_delay= [X86] I/O delay method
1736 Standard port 0x80 based delay
1738 Alternate port 0xed based delay (needed on some systems)
1740 Simple two microseconds delay
1745 See Documentation/filesystems/nfs/nfsroot.txt.
1747 irqaffinity= [SMP] Set the default irq affinity mask
1748 The argument is a cpu list, as described above.
1750 irqchip.gicv2_force_probe=
1753 Force the kernel to look for the second 4kB page
1754 of a GICv2 controller even if the memory range
1755 exposed by the device tree is too small.
1757 irqchip.gicv3_nolpi=
1759 Force the kernel to ignore the availability of
1760 LPIs (and by consequence ITSs). Intended for system
1761 that use the kernel as a bootloader, and thus want
1762 to let secondary kernels in charge of setting up
1766 When an interrupt is not handled search all handlers
1767 for it. Intended to get systems with badly broken
1771 When an interrupt is not handled search all handlers
1772 for it. Also check all handlers each timer
1773 interrupt. Intended to get systems with badly broken
1777 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1779 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1780 [Deprecated - use cpusets instead]
1781 Format: [flag-list,]<cpu-list>
1783 Specify one or more CPUs to isolate from disturbances
1784 specified in the flag list (default: domain):
1787 Disable the tick when a single task runs.
1789 A residual 1Hz tick is offloaded to workqueues, which you
1790 need to affine to housekeeping through the global
1791 workqueue's affinity configured via the
1792 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1793 by using the 'domain' flag described below.
1795 NOTE: by default the global workqueue runs on all CPUs,
1796 so to protect individual CPUs the 'cpumask' file has to
1797 be configured manually after bootup.
1800 Isolate from the general SMP balancing and scheduling
1801 algorithms. Note that performing domain isolation this way
1802 is irreversible: it's not possible to bring back a CPU to
1803 the domains once isolated through isolcpus. It's strongly
1804 advised to use cpusets instead to disable scheduler load
1805 balancing through the "cpuset.sched_load_balance" file.
1806 It offers a much more flexible interface where CPUs can
1807 move in and out of an isolated set anytime.
1809 You can move a process onto or off an "isolated" CPU via
1810 the CPU affinity syscalls or cpuset.
1811 <cpu number> begins at 0 and the maximum value is
1812 "number of CPUs in system - 1".
1814 The format of <cpu-list> is described above.
1820 ivrs_ioapic [HW,X86_64]
1821 Provide an override to the IOAPIC-ID<->DEVICE-ID
1822 mapping provided in the IVRS ACPI table. For
1823 example, to map IOAPIC-ID decimal 10 to
1824 PCI device 00:14.0 write the parameter as:
1825 ivrs_ioapic[10]=00:14.0
1827 ivrs_hpet [HW,X86_64]
1828 Provide an override to the HPET-ID<->DEVICE-ID
1829 mapping provided in the IVRS ACPI table. For
1830 example, to map HPET-ID decimal 0 to
1831 PCI device 00:14.0 write the parameter as:
1832 ivrs_hpet[0]=00:14.0
1834 ivrs_acpihid [HW,X86_64]
1835 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1836 mapping provided in the IVRS ACPI table. For
1837 example, to map UART-HID:UID AMD0020:0 to
1838 PCI device 00:14.5 write the parameter as:
1839 ivrs_acpihid[00:14.5]=AMD0020:0
1841 js= [HW,JOY] Analog joystick
1842 See Documentation/input/joydev/joystick.rst.
1845 When CONFIG_RANDOMIZE_BASE is set, this disables
1846 kernel and module base offset ASLR (Address Space
1847 Layout Randomization).
1850 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1851 report on every invalid memory access. Without this
1852 parameter KASAN will print report only for the first
1857 kernelcore= [KNL,X86,IA-64,PPC]
1858 Format: nn[KMGTPE] | nn% | "mirror"
1859 This parameter specifies the amount of memory usable by
1860 the kernel for non-movable allocations. The requested
1861 amount is spread evenly throughout all nodes in the
1862 system as ZONE_NORMAL. The remaining memory is used for
1863 movable memory in its own zone, ZONE_MOVABLE. In the
1864 event, a node is too small to have both ZONE_NORMAL and
1865 ZONE_MOVABLE, kernelcore memory will take priority and
1866 other nodes will have a larger ZONE_MOVABLE.
1868 ZONE_MOVABLE is used for the allocation of pages that
1869 may be reclaimed or moved by the page migration
1870 subsystem. Note that allocations like PTEs-from-HighMem
1871 still use the HighMem zone if it exists, and the Normal
1872 zone if it does not.
1874 It is possible to specify the exact amount of memory in
1875 the form of "nn[KMGTPE]", a percentage of total system
1876 memory in the form of "nn%", or "mirror". If "mirror"
1877 option is specified, mirrored (reliable) memory is used
1878 for non-movable allocations and remaining memory is used
1879 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1880 are exclusive, so you cannot specify multiple forms.
1882 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1883 Format: <Controller#>[,poll interval]
1884 The controller # is the number of the ehci usb debug
1885 port as it is probed via PCI. The poll interval is
1886 optional and is the number seconds in between
1887 each poll cycle to the debug port in case you need
1888 the functionality for interrupting the kernel with
1889 gdb or control-c on the dbgp connection. When
1890 not using this parameter you use sysrq-g to break into
1891 the kernel debugger.
1893 kgdboc= [KGDB,HW] kgdb over consoles.
1894 Requires a tty driver that supports console polling,
1895 or a supported polling keyboard driver (non-usb).
1896 Serial only format: <serial_device>[,baud]
1897 keyboard only format: kbd
1898 keyboard and serial format: kbd,<serial_device>[,baud]
1899 Optional Kernel mode setting:
1900 kms, kbd format: kms,kbd
1901 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1903 kgdbwait [KGDB] Stop kernel execution and enter the
1904 kernel debugger at the earliest opportunity.
1906 kmac= [MIPS] korina ethernet MAC address.
1907 Configure the RouterBoard 532 series on-chip
1908 Ethernet adapter MAC address.
1910 kmemleak= [KNL] Boot-time kmemleak enable/disable
1911 Valid arguments: on, off
1913 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1916 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1917 Default is 0 (don't ignore, but inject #GP)
1919 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
1920 Default is false (don't support).
1922 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1926 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1927 Default is 1 (enabled)
1929 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1931 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1933 kvm-arm.vgic_v3_group0_trap=
1934 [KVM,ARM] Trap guest accesses to GICv3 group-0
1937 kvm-arm.vgic_v3_group1_trap=
1938 [KVM,ARM] Trap guest accesses to GICv3 group-1
1941 kvm-arm.vgic_v3_common_trap=
1942 [KVM,ARM] Trap guest accesses to GICv3 common
1945 kvm-arm.vgic_v4_enable=
1946 [KVM,ARM] Allow use of GICv4 for direct injection of
1949 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1950 (virtualized MMU) support on capable Intel chips.
1951 Default is 1 (enabled)
1953 kvm-intel.emulate_invalid_guest_state=
1954 [KVM,Intel] Enable emulation of invalid guest states
1955 Default is 0 (disabled)
1957 kvm-intel.flexpriority=
1958 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1959 Default is 1 (enabled)
1962 [KVM,Intel] Enable VMX nesting (nVMX).
1963 Default is 0 (disabled)
1965 kvm-intel.unrestricted_guest=
1966 [KVM,Intel] Disable unrestricted guest feature
1967 (virtualized real and unpaged mode) on capable
1968 Intel chips. Default is 1 (enabled)
1970 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1971 feature (tagged TLBs) on capable Intel chips.
1972 Default is 1 (enabled)
1978 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1981 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1982 value for LAPIC timer one-shot implementation. Default
1983 back to the programmable timer unit in the LAPIC.
1985 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1988 libata.dma= [LIBATA] DMA control
1989 libata.dma=0 Disable all PATA and SATA DMA
1990 libata.dma=1 PATA and SATA Disk DMA only
1991 libata.dma=2 ATAPI (CDROM) DMA only
1992 libata.dma=4 Compact Flash DMA only
1993 Combinations also work, so libata.dma=3 enables DMA
1994 for disks and CDROMs, but not CFs.
1996 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1997 libata.ignore_hpa=0 keep BIOS limits (default)
1998 libata.ignore_hpa=1 ignore limits, using full disk
2000 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2004 libata.force= [LIBATA] Force configurations. The format is comma
2005 separated list of "[ID:]VAL" where ID is
2006 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2007 matching port, link or device. Basically, it matches
2008 the ATA ID string printed on console by libata. If
2009 the whole ID part is omitted, the last PORT and DEVICE
2010 values are used. If ID hasn't been specified yet, the
2011 configuration applies to all ports, links and devices.
2013 If only DEVICE is omitted, the parameter applies to
2014 the port and all links and devices behind it. DEVICE
2015 number of 0 either selects the first device or the
2016 first fan-out link behind PMP device. It does not
2017 select the host link. DEVICE number of 15 selects the
2018 host link and device attached to it.
2020 The VAL specifies the configuration to force. As long
2021 as there's no ambiguity shortcut notation is allowed.
2022 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2023 The following configurations can be forced.
2025 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2026 Any ID with matching PORT is used.
2028 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2030 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2031 udma[/][16,25,33,44,66,100,133] notation is also
2034 * [no]ncq: Turn on or off NCQ.
2036 * [no]ncqtrim: Turn off queued DSM TRIM.
2038 * nohrst, nosrst, norst: suppress hard, soft
2041 * rstonce: only attempt one reset during
2042 hot-unplug link recovery
2044 * dump_id: dump IDENTIFY data.
2046 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2048 * disable: Disable this device.
2050 If there are multiple matching configurations changing
2051 the same attribute, the last one is used.
2053 memblock=debug [KNL] Enable memblock debug messages.
2055 load_ramdisk= [RAM] List of ramdisks to load from floppy
2056 See Documentation/blockdev/ramdisk.txt.
2058 lockd.nlm_grace_period=P [NFS] Assign grace period.
2061 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2064 lockd.nlm_timeout=T [NFS] Assign timeout value.
2067 lockd.nlm_udpport=M [NFS] Assign UDP port.
2070 locktorture.nreaders_stress= [KNL]
2071 Set the number of locking read-acquisition kthreads.
2072 Defaults to being automatically set based on the
2073 number of online CPUs.
2075 locktorture.nwriters_stress= [KNL]
2076 Set the number of locking write-acquisition kthreads.
2078 locktorture.onoff_holdoff= [KNL]
2079 Set time (s) after boot for CPU-hotplug testing.
2081 locktorture.onoff_interval= [KNL]
2082 Set time (s) between CPU-hotplug operations, or
2083 zero to disable CPU-hotplug testing.
2085 locktorture.shuffle_interval= [KNL]
2086 Set task-shuffle interval (jiffies). Shuffling
2087 tasks allows some CPUs to go into dyntick-idle
2088 mode during the locktorture test.
2090 locktorture.shutdown_secs= [KNL]
2091 Set time (s) after boot system shutdown. This
2092 is useful for hands-off automated testing.
2094 locktorture.stat_interval= [KNL]
2095 Time (s) between statistics printk()s.
2097 locktorture.stutter= [KNL]
2098 Time (s) to stutter testing, for example,
2099 specifying five seconds causes the test to run for
2100 five seconds, wait for five seconds, and so on.
2101 This tests the locking primitive's ability to
2102 transition abruptly to and from idle.
2104 locktorture.torture_type= [KNL]
2105 Specify the locking implementation to test.
2107 locktorture.verbose= [KNL]
2108 Enable additional printk() statements.
2110 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2113 loglevel= All Kernel Messages with a loglevel smaller than the
2114 console loglevel will be printed to the console. It can
2115 also be changed with klogd or other programs. The
2116 loglevels are defined as follows:
2118 0 (KERN_EMERG) system is unusable
2119 1 (KERN_ALERT) action must be taken immediately
2120 2 (KERN_CRIT) critical conditions
2121 3 (KERN_ERR) error conditions
2122 4 (KERN_WARNING) warning conditions
2123 5 (KERN_NOTICE) normal but significant condition
2124 6 (KERN_INFO) informational
2125 7 (KERN_DEBUG) debug-level messages
2127 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2128 in bytes. n must be a power of two and greater
2129 than the minimal size. The minimal size is defined
2130 by LOG_BUF_SHIFT kernel config parameter. There is
2131 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2132 that allows to increase the default size depending on
2133 the number of CPUs. See init/Kconfig for more details.
2135 logo.nologo [FB] Disables display of the built-in Linux logo.
2136 This may be used to provide more screen space for
2137 kernel log messages and is useful when debugging
2138 kernel boot problems.
2140 lp=0 [LP] Specify parallel ports to use, e.g,
2141 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2142 lp=reset first parallel port). 'lp=0' disables the
2143 lp=auto printer driver. 'lp=reset' (which can be
2144 specified in addition to the ports) causes
2145 attached printers to be reset. Using
2146 lp=port1,port2,... specifies the parallel ports
2147 to associate lp devices with, starting with
2148 lp0. A port specification may be 'none' to skip
2149 that lp device, or a parport name such as
2150 'parport0'. Specifying 'lp=auto' instead of a
2151 port specification list means that device IDs
2152 from each port should be examined, to see if
2153 an IEEE 1284-compliant printer is attached; if
2154 so, the driver will manage that printer.
2155 See also header of drivers/char/lp.c.
2158 Sets loops_per_jiffy to given constant, thus avoiding
2159 time-consuming boot-time autodetection (up to 250 ms per
2160 CPU). 0 enables autodetection (default). To determine
2161 the correct value for your kernel, boot with normal
2162 autodetection and see what value is printed. Note that
2163 on SMP systems the preset will be applied to all CPUs,
2164 which is likely to cause problems if your CPUs need
2165 significantly divergent settings. An incorrect value
2166 will cause delays in the kernel to be wrong, leading to
2167 unpredictable I/O errors and other breakage. Although
2168 unlikely, in the extreme case this might damage your
2172 Format: <io>,<irq>,<dma>
2174 machvec= [IA-64] Force the use of a particular machine-vector
2175 (machvec) in a generic kernel.
2176 Example: machvec=hpzx1_swiotlb
2178 machtype= [Loongson] Share the same kernel image file between different
2180 Example: machtype=lemote-yeeloong-2f-7inch
2182 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2183 than or equal to this physical address is ignored.
2185 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2186 will bring up during bootup. maxcpus=n : n >= 0 limits
2187 the kernel to bring up 'n' processors. Surely after
2188 bootup you can bring up the other plugged cpu by executing
2189 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2190 only takes effect during system bootup.
2191 While n=0 is a special case, it is equivalent to "nosmp",
2192 which also disables the IO APIC.
2194 max_loop= [LOOP] The number of loop block devices that get
2195 (loop.max_loop) unconditionally pre-created at init time. The default
2196 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2197 of statically allocating a predefined number, loop
2198 devices can be requested on-demand with the
2199 /dev/loop-control interface.
2201 mce [X86-32] Machine Check Exception
2203 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2205 md= [HW] RAID subsystems devices and level
2206 See Documentation/admin-guide/md.rst.
2209 Format: <first>,<last>
2210 Specifies range of consoles to be captured by the MDA.
2212 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2213 Amount of memory to be used when the kernel is not able
2214 to see the whole system memory or for test.
2215 [X86] Work as limiting max address. Use together
2216 with memmap= to avoid physical address space collisions.
2217 Without memmap= PCI devices could be placed at addresses
2218 belonging to unused RAM.
2220 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2224 [KNL,SH] Allow user to override the default size for
2225 per-device physically contiguous DMA buffers.
2227 memhp_default_state=online/offline
2228 [KNL] Set the initial state for the memory hotplug
2229 onlining policy. If not specified, the default value is
2230 set according to the
2231 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2233 See Documentation/memory-hotplug.txt.
2235 memmap=exactmap [KNL,X86] Enable setting of an exact
2236 E820 memory map, as specified by the user.
2237 Such memmap=exactmap lines can be constructed based on
2238 BIOS output or other requirements. See the memmap=nn@ss
2241 memmap=nn[KMG]@ss[KMG]
2242 [KNL] Force usage of a specific region of memory.
2243 Region of memory to be used is from ss to ss+nn.
2244 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2245 which limits max address to nn[KMG].
2246 Multiple different regions can be specified,
2249 memmap=100M@2G,100M#3G,1G!1024G
2251 memmap=nn[KMG]#ss[KMG]
2252 [KNL,ACPI] Mark specific memory as ACPI data.
2253 Region of memory to be marked is from ss to ss+nn.
2255 memmap=nn[KMG]$ss[KMG]
2256 [KNL,ACPI] Mark specific memory as reserved.
2257 Region of memory to be reserved is from ss to ss+nn.
2258 Example: Exclude memory from 0x18690000-0x1869ffff
2259 memmap=64K$0x18690000
2261 memmap=0x10000$0x18690000
2262 Some bootloaders may need an escape character before '$',
2263 like Grub2, otherwise '$' and the following number
2266 memmap=nn[KMG]!ss[KMG]
2267 [KNL,X86] Mark specific memory as protected.
2268 Region of memory to be used, from ss to ss+nn.
2269 The memory region may be marked as e820 type 12 (0xc)
2270 and is NVDIMM or ADR memory.
2272 memmap=<size>%<offset>-<oldtype>+<newtype>
2273 [KNL,ACPI] Convert memory within the specified region
2274 from <oldtype> to <newtype>. If "-<oldtype>" is left
2275 out, the whole region will be marked as <newtype>,
2276 even if previously unavailable. If "+<newtype>" is left
2277 out, matching memory will be removed. Types are
2278 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2279 3 = ACPI, 12 = PRAM.
2281 memory_corruption_check=0/1 [X86]
2282 Some BIOSes seem to corrupt the first 64k of
2283 memory when doing things like suspend/resume.
2284 Setting this option will scan the memory
2285 looking for corruption. Enabling this will
2286 both detect corruption and prevent the kernel
2287 from using the memory being corrupted.
2288 However, its intended as a diagnostic tool; if
2289 repeatable BIOS-originated corruption always
2290 affects the same memory, you can use memmap=
2291 to prevent the kernel from using that memory.
2293 memory_corruption_check_size=size [X86]
2294 By default it checks for corruption in the low
2295 64k, making this memory unavailable for normal
2296 use. Use this parameter to scan for
2297 corruption in more or less memory.
2299 memory_corruption_check_period=seconds [X86]
2300 By default it checks for corruption every 60
2301 seconds. Use this parameter to check at some
2302 other rate. 0 disables periodic checking.
2304 memtest= [KNL,X86,ARM] Enable memtest
2306 default : 0 <disable>
2307 Specifies the number of memtest passes to be
2308 performed. Each pass selects another test
2309 pattern from a given set of patterns. Memtest
2310 fills the memory with this pattern, validates
2311 memory contents and reserves bad memory
2312 regions that are detected.
2314 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2315 Valid arguments: on, off
2316 Default (depends on kernel configuration option):
2317 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2318 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2319 mem_encrypt=on: Activate SME
2320 mem_encrypt=off: Do not activate SME
2322 Refer to Documentation/x86/amd-memory-encryption.txt
2323 for details on when memory encryption can be activated.
2325 mem_sleep_default= [SUSPEND] Default system suspend mode:
2326 s2idle - Suspend-To-Idle
2327 shallow - Power-On Suspend or equivalent (if supported)
2328 deep - Suspend-To-RAM or equivalent (if supported)
2329 See Documentation/admin-guide/pm/sleep-states.rst.
2331 meye.*= [HW] Set MotionEye Camera parameters
2332 See Documentation/media/v4l-drivers/meye.rst.
2334 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2335 Multi-Function General Purpose Timers on AMD Geode
2338 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2339 the BIOS has incorrectly applied a workaround. TinyBIOS
2340 version 0.98 is known to be affected, 0.99 fixes the
2341 problem by letting the user disable the workaround.
2345 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2346 physical address is ignored.
2348 mini2440= [ARM,HW,KNL]
2349 Format:[0..2][b][c][t]
2351 MINI2440 configuration specification:
2352 0 - The attached screen is the 3.5" TFT
2353 1 - The attached screen is the 7" TFT
2354 2 - The VGA Shield is attached (1024x768)
2355 Leaving out the screen size parameter will not load
2356 the TFT driver, and the framebuffer will be left
2358 b - Enable backlight. The TFT backlight pin will be
2359 linked to the kernel VESA blanking code and a GPIO
2360 LED. This parameter is not necessary when using the
2362 c - Enable the s3c camera interface.
2363 t - Reserved for enabling touchscreen support. The
2364 touchscreen support is not enabled in the mainstream
2365 kernel as of 2.6.30, a preliminary port can be found
2366 in the "bleeding edge" mini2440 support kernel at
2367 http://repo.or.cz/w/linux-2.6/mini2440.git
2370 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2371 parameter allows control of the logging verbosity for
2372 the additional memory initialisation checks. A value
2373 of 0 disables mminit logging and a level of 4 will
2374 log everything. Information is printed at KERN_DEBUG
2375 so loglevel=8 may also need to be specified.
2378 [KNL] When CONFIG_MODULE_SIG is set, this means that
2379 modules without (valid) signatures will fail to load.
2380 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2381 is always true, so this option does nothing.
2383 module_blacklist= [KNL] Do not load a comma-separated list of
2384 modules. Useful for debugging problem modules.
2387 [MOUSE] Maximum time between finger touching and
2388 leaving touchpad surface for touch to be considered
2389 a tap and be reported as a left button click (for
2390 touchpads working in absolute mode only).
2392 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2393 reporting absolute coordinates, such as tablets
2394 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2395 reporting absolute coordinates, such as tablets
2397 movablecore= [KNL,X86,IA-64,PPC]
2398 Format: nn[KMGTPE] | nn%
2399 This parameter is the complement to kernelcore=, it
2400 specifies the amount of memory used for migratable
2401 allocations. If both kernelcore and movablecore is
2402 specified, then kernelcore will be at *least* the
2403 specified value but may be more. If movablecore on its
2404 own is specified, the administrator must be careful
2405 that the amount of memory usable for all allocations
2408 movable_node [KNL] Boot-time switch to make hotplugable memory
2409 NUMA nodes to be movable. This means that the memory
2410 of such nodes will be usable only for movable
2411 allocations which rules out almost all kernel
2412 allocations. Use with caution!
2414 MTD_Partition= [MTD]
2415 Format: <name>,<region-number>,<size>,<offset>
2417 MTD_Region= [MTD] Format:
2418 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2421 See drivers/mtd/cmdlinepart.c.
2423 multitce=off [PPC] This parameter disables the use of the pSeries
2424 firmware feature for updating multiple TCE entries
2427 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2429 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2431 boundary - index of last SLC block on Flex-OneNAND.
2432 The remaining blocks are configured as MLC blocks.
2433 lock - Configure if Flex-OneNAND boundary should be locked.
2434 Once locked, the boundary cannot be changed.
2435 1 indicates lock status, 0 indicates unlock status.
2438 ARM/S3C2412 JIVE boot control
2440 See arch/arm/mach-s3c2412/mach-jive.c
2442 mtouchusb.raw_coordinates=
2443 [HW] Make the MicroTouch USB driver use raw coordinates
2444 ('y', default) or cooked coordinates ('n')
2446 mtrr_chunk_size=nn[KMG] [X86]
2447 used for mtrr cleanup. It is largest continuous chunk
2448 that could hold holes aka. UC entries.
2450 mtrr_gran_size=nn[KMG] [X86]
2451 Used for mtrr cleanup. It is granularity of mtrr block.
2453 Large value could prevent small alignment from
2456 mtrr_spare_reg_nr=n [X86]
2458 Range: 0,7 : spare reg number
2460 Used for mtrr cleanup. It is spare mtrr entries number.
2461 Set to 2 or more if your graphical card needs more.
2463 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2465 netdev= [NET] Network devices parameters
2466 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2467 Note that mem_start is often overloaded to mean
2468 something different and driver-specific.
2469 This usage is only documented in each driver source
2473 [NETFILTER] Enable connection tracking flow accounting
2474 0 to disable accounting
2475 1 to enable accounting
2478 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2479 See Documentation/filesystems/nfs/nfsroot.txt.
2481 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2482 See Documentation/filesystems/nfs/nfsroot.txt.
2484 nfsrootdebug [NFS] enable nfsroot debugging messages.
2485 See Documentation/filesystems/nfs/nfsroot.txt.
2487 nfs.callback_nr_threads=
2488 [NFSv4] set the total number of threads that the
2489 NFS client will assign to service NFSv4 callback
2492 nfs.callback_tcpport=
2493 [NFS] set the TCP port on which the NFSv4 callback
2494 channel should listen.
2497 [NFS] sets the pathname to the program which is used
2498 to update the NFS client cache entries.
2500 nfs.cache_getent_timeout=
2501 [NFS] sets the timeout after which an attempt to
2502 update a cache entry is deemed to have failed.
2504 nfs.idmap_cache_timeout=
2505 [NFS] set the maximum lifetime for idmapper cache
2509 [NFS] enable 64-bit inode numbers.
2510 If zero, the NFS client will fake up a 32-bit inode
2511 number for the readdir() and stat() syscalls instead
2512 of returning the full 64-bit number.
2513 The default is to return 64-bit inode numbers.
2515 nfs.max_session_cb_slots=
2516 [NFSv4.1] Sets the maximum number of session
2517 slots the client will assign to the callback
2518 channel. This determines the maximum number of
2519 callbacks the client will process in parallel for
2520 a particular server.
2522 nfs.max_session_slots=
2523 [NFSv4.1] Sets the maximum number of session slots
2524 the client will attempt to negotiate with the server.
2525 This limits the number of simultaneous RPC requests
2526 that the client can send to the NFSv4.1 server.
2527 Note that there is little point in setting this
2528 value higher than the max_tcp_slot_table_limit.
2530 nfs.nfs4_disable_idmapping=
2531 [NFSv4] When set to the default of '1', this option
2532 ensures that both the RPC level authentication
2533 scheme and the NFS level operations agree to use
2534 numeric uids/gids if the mount is using the
2535 'sec=sys' security flavour. In effect it is
2536 disabling idmapping, which can make migration from
2537 legacy NFSv2/v3 systems to NFSv4 easier.
2538 Servers that do not support this mode of operation
2539 will be autodetected by the client, and it will fall
2540 back to using the idmapper.
2541 To turn off this behaviour, set the value to '0'.
2543 [NFS4] Specify an additional fixed unique ident-
2544 ification string that NFSv4 clients can insert into
2545 their nfs_client_id4 string. This is typically a
2546 UUID that is generated at system install time.
2548 nfs.send_implementation_id =
2549 [NFSv4.1] Send client implementation identification
2550 information in exchange_id requests.
2551 If zero, no implementation identification information
2553 The default is to send the implementation identification
2556 nfs.recover_lost_locks =
2557 [NFSv4] Attempt to recover locks that were lost due
2558 to a lease timeout on the server. Please note that
2559 doing this risks data corruption, since there are
2560 no guarantees that the file will remain unchanged
2561 after the locks are lost.
2562 If you want to enable the kernel legacy behaviour of
2563 attempting to recover these locks, then set this
2565 The default parameter value of '0' causes the kernel
2566 not to attempt recovery of lost locks.
2568 nfs4.layoutstats_timer =
2569 [NFSv4.2] Change the rate at which the kernel sends
2570 layoutstats to the pNFS metadata server.
2572 Setting this to value to 0 causes the kernel to use
2573 whatever value is the default set by the layout
2574 driver. A non-zero value sets the minimum interval
2575 in seconds between layoutstats transmissions.
2577 nfsd.nfs4_disable_idmapping=
2578 [NFSv4] When set to the default of '1', the NFSv4
2579 server will return only numeric uids and gids to
2580 clients using auth_sys, and will accept numeric uids
2581 and gids from such clients. This is intended to ease
2582 migration from NFSv2/v3.
2584 nmi_debug= [KNL,SH] Specify one or more actions to take
2585 when a NMI is triggered.
2586 Format: [state][,regs][,debounce][,die]
2588 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2589 Format: [panic,][nopanic,][num]
2591 0 - turn hardlockup detector in nmi_watchdog off
2592 1 - turn hardlockup detector in nmi_watchdog on
2593 When panic is specified, panic when an NMI watchdog
2594 timeout occurs (or 'nopanic' to override the opposite
2595 default). To disable both hard and soft lockup detectors,
2596 please see 'nowatchdog'.
2597 This is useful when you use a panic=... timeout and
2598 need the box quickly up again.
2600 These settings can be accessed at runtime via
2601 the nmi_watchdog and hardlockup_panic sysctls.
2603 netpoll.carrier_timeout=
2604 [NET] Specifies amount of time (in seconds) that
2605 netpoll should wait for a carrier. By default netpoll
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