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
117 Support masking of GPEs numbered from 0x00 to 0x7f.
119 acpi_no_auto_serialize [HW,ACPI]
120 Disable auto-serialization of AML methods
121 AML control methods that contain the opcodes to create
122 named objects will be marked as "Serialized" by the
123 auto-serialization feature.
124 This feature is enabled by default.
125 This option allows to turn off the feature.
127 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
130 acpi_no_static_ssdt [HW,ACPI]
131 Disable installation of static SSDTs at early boot time
132 By default, SSDTs contained in the RSDT/XSDT will be
133 installed automatically and they will appear under
134 /sys/firmware/acpi/tables.
135 This option turns off this feature.
136 Note that specifying this option does not affect
137 dynamic table installation which will install SSDT
138 tables to /sys/firmware/acpi/tables/dynamic.
140 acpi_rsdp= [ACPI,EFI,KEXEC]
141 Pass the RSDP address to the kernel, mostly used
142 on machines running EFI runtime service to boot the
143 second kernel for kdump.
145 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
146 Format: To spoof as Windows 98: ="Microsoft Windows"
148 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
149 of 2 which is mandated by ACPI 6) as the supported ACPI
150 specification revision (when using this switch, it may
151 be necessary to carry out a cold reboot _twice_ in a
152 row to make it take effect on the platform firmware).
154 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
155 acpi_osi="string1" # add string1
156 acpi_osi="!string2" # remove string2
157 acpi_osi=!* # remove all strings
158 acpi_osi=! # disable all built-in OS vendor
160 acpi_osi=!! # enable all built-in OS vendor
162 acpi_osi= # disable all strings
164 'acpi_osi=!' can be used in combination with single or
165 multiple 'acpi_osi="string1"' to support specific OS
166 vendor string(s). Note that such command can only
167 affect the default state of the OS vendor strings, thus
168 it cannot affect the default state of the feature group
169 strings and the current state of the OS vendor strings,
170 specifying it multiple times through kernel command line
171 is meaningless. This command is useful when one do not
172 care about the state of the feature group strings which
173 should be controlled by the OSPM.
175 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
176 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
177 can make '_OSI("Windows 2000")' TRUE.
179 'acpi_osi=' cannot be used in combination with other
180 'acpi_osi=' command lines, the _OSI method will not
181 exist in the ACPI namespace. NOTE that such command can
182 only affect the _OSI support state, thus specifying it
183 multiple times through kernel command line is also
186 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
189 'acpi_osi=!*' can be used in combination with single or
190 multiple 'acpi_osi="string1"' to support specific
191 string(s). Note that such command can affect the
192 current state of both the OS vendor strings and the
193 feature group strings, thus specifying it multiple times
194 through kernel command line is meaningful. But it may
195 still not able to affect the final state of a string if
196 there are quirks related to this string. This command
197 is useful when one want to control the state of the
198 feature group strings to debug BIOS issues related to
201 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
202 '_OSI("Module Device")' FALSE.
203 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
204 '_OSI("Module Device")' TRUE.
205 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
207 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
209 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
210 they all will make '_OSI("Windows 2000")' TRUE.
213 Override the pmtimer bug detection: force the kernel
214 to assume that this machine's pmtimer latches its value
215 and always returns good values.
217 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
218 Format: { level | edge | high | low }
220 acpi_skip_timer_override [HW,ACPI]
221 Recognize and ignore IRQ0/pin2 Interrupt Override.
222 For broken nForce2 BIOS resulting in XT-PIC timer.
224 acpi_sleep= [HW,ACPI] Sleep options
225 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
226 old_ordering, nonvs, sci_force_enable }
227 See Documentation/power/video.txt for information on
229 s3_beep is for debugging; it makes the PC's speaker beep
230 as soon as the kernel's real-mode entry point is called.
231 s4_nohwsig prevents ACPI hardware signature from being
232 used during resume from hibernation.
233 old_ordering causes the ACPI 1.0 ordering of the _PTS
234 control method, with respect to putting devices into
235 low power states, to be enforced (the ACPI 2.0 ordering
236 of _PTS is used by default).
237 nonvs prevents the kernel from saving/restoring the
238 ACPI NVS memory during suspend/hibernation and resume.
239 sci_force_enable causes the kernel to set SCI_EN directly
240 on resume from S1/S3 (which is against the ACPI spec,
241 but some broken systems don't work without it).
243 acpi_use_timer_override [HW,ACPI]
244 Use timer override. For some broken Nvidia NF5 boards
245 that require a timer override, but don't have HPET
247 add_efi_memmap [EFI; X86] Include EFI memory map in
248 kernel's map of available physical RAM.
251 { off | try_unsupported }
252 off: disable AGP support
253 try_unsupported: try to drive unsupported chipsets
254 (may crash computer or cause data corruption)
257 See Documentation/sound/alsa/alsa-parameters.txt
260 Allow the default userspace alignment fault handler
261 behaviour to be specified. Bit 0 enables warnings,
262 bit 1 enables fixups, and bit 2 sends a segfault.
264 align_va_addr= [X86-64]
265 Align virtual addresses by clearing slice [14:12] when
266 allocating a VMA at process creation time. This option
267 gives you up to 3% performance improvement on AMD F15h
268 machines (where it is enabled by default) for a
269 CPU-intensive style benchmark, and it can vary highly in
270 a microbenchmark depending on workload and compiler.
272 32: only for 32-bit processes
273 64: only for 64-bit processes
274 on: enable for both 32- and 64-bit processes
275 off: disable for both 32- and 64-bit processes
277 alloc_snapshot [FTRACE]
278 Allocate the ftrace snapshot buffer on boot up when the
279 main buffer is allocated. This is handy if debugging
280 and you need to use tracing_snapshot() on boot up, and
281 do not want to use tracing_snapshot_alloc() as it needs
282 to be done where GFP_KERNEL allocations are allowed.
284 amd_iommu= [HW,X86-64]
285 Pass parameters to the AMD IOMMU driver in the system.
287 fullflush - enable flushing of IO/TLB entries when
288 they are unmapped. Otherwise they are
289 flushed before they will be reused, which
291 off - do not initialize any AMD IOMMU found in
293 force_isolation - Force device isolation for all
294 devices. The IOMMU driver is not
295 allowed anymore to lift isolation
296 requirements as needed. This option
297 does not override iommu=pt
299 amd_iommu_dump= [HW,X86-64]
300 Enable AMD IOMMU driver option to dump the ACPI table
301 for AMD IOMMU. With this option enabled, AMD IOMMU
302 driver will print ACPI tables for AMD IOMMU during
303 IOMMU initialization.
305 amd_iommu_intr= [HW,X86-64]
306 Specifies one of the following AMD IOMMU interrupt
308 legacy - Use legacy interrupt remapping mode.
309 vapic - Use virtual APIC mode, which allows IOMMU
310 to inject interrupts directly into guest.
311 This mode requires kvm-amd.avic=1.
312 (Default when IOMMU HW support is present.)
314 amijoy.map= [HW,JOY] Amiga joystick support
315 Map of devices attached to JOY0DAT and JOY1DAT
317 See also Documentation/input/joystick.txt
319 analog.map= [HW,JOY] Analog joystick and gamepad support
320 Specifies type or capabilities of an analog joystick
321 connected to one of 16 gameports
322 Format: <type1>,<type2>,..<type16>
325 Power management functions (SPARCstation-4/5 + deriv.)
327 Disable APC CPU standby support. SPARCstation-Fox does
328 not play well with APC CPU idle - disable it if you have
329 APC and your system crashes randomly.
331 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
332 Change the output verbosity whilst booting
333 Format: { quiet (default) | verbose | debug }
334 Change the amount of debugging information output
335 when initialising the APIC and IO-APIC components.
337 apic_extnmi= [APIC,X86] External NMI delivery setting
338 Format: { bsp (default) | all | none }
339 bsp: External NMI is delivered only to CPU 0
340 all: External NMIs are broadcast to all CPUs as a
342 none: External NMI is masked for all CPUs. This is
343 useful so that a dump capture kernel won't be
347 See Documentation/networking/ipv6.txt.
349 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
350 Limit apic dumping. The parameter defines the maximal
351 number of local apics being dumped. Also it is possible
352 to set it to "all" by meaning -- no limit here.
353 Format: { 1 (default) | 2 | ... | all }.
354 The parameter valid if only apic=debug or
355 apic=verbose is specified.
356 Example: apic=debug show_lapic=all
358 apm= [APM] Advanced Power Management
359 See header of arch/x86/kernel/apm_32.c.
361 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
362 Format: <io>,<irq>,<nodeID>
366 atarimouse= [HW,MOUSE] Atari Mouse
368 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
369 EzKey and similar keyboards
371 atkbd.reset= [HW] Reset keyboard during initialization
373 atkbd.set= [HW] Select keyboard code set
374 Format: <int> (2 = AT (default), 3 = PS/2)
376 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
379 atkbd.softraw= [HW] Choose between synthetic and real raw mode
380 Format: <bool> (0 = real, 1 = synthetic (default))
382 atkbd.softrepeat= [HW]
383 Use software keyboard repeat
385 audit= [KNL] Enable the audit sub-system
386 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
387 0 - kernel audit is disabled and can not be enabled
388 until the next reboot
389 unset - kernel audit is initialized but disabled and
390 will be fully enabled by the userspace auditd.
391 1 - kernel audit is initialized and partially enabled,
392 storing at most audit_backlog_limit messages in
393 RAM until it is fully enabled by the userspace
397 audit_backlog_limit= [KNL] Set the audit queue size limit.
398 Format: <int> (must be >=0)
401 bau= [X86_UV] Enable the BAU on SGI UV. The default
402 behavior is to disable the BAU (i.e. bau=0).
403 Format: { "0" | "1" }
406 unset - Disable the BAU.
408 baycom_epp= [HW,AX25]
411 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
413 See header of drivers/net/hamradio/baycom_par.c.
415 baycom_ser_fdx= [HW,AX25]
416 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
417 Format: <io>,<irq>,<mode>[,<baud>]
418 See header of drivers/net/hamradio/baycom_ser_fdx.c.
420 baycom_ser_hdx= [HW,AX25]
421 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
422 Format: <io>,<irq>,<mode>
423 See header of drivers/net/hamradio/baycom_ser_hdx.c.
425 blkdevparts= Manual partition parsing of block device(s) for
426 embedded devices based on command line input.
427 See Documentation/block/cmdline-partition.txt
429 boot_delay= Milliseconds to delay each printk during boot.
430 Values larger than 10 seconds (10000) are changed to
434 bootmem_debug [KNL] Enable bootmem allocator debug messages.
437 Disable BERT OS support on buggy BIOSes.
439 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
440 bttv.radio= Most important insmod options are available as
442 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
445 bulk_remove=off [PPC] This parameter disables the use of the pSeries
446 firmware feature for flushing multiple hpte entries
449 c101= [NET] Moxa C101 synchronous serial card
451 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
452 Sometimes CPU hardware bugs make them report the cache
453 size incorrectly. The kernel will attempt work arounds
454 to fix known problems, but for some CPUs it is not
455 possible to determine what the correct size should be.
456 This option provides an override for these situations.
458 ca_keys= [KEYS] This parameter identifies a specific key(s) on
459 the system trusted keyring to be used for certificate
461 format: { id:<keyid> | builtin }
463 cca= [MIPS] Override the kernel pages' cache coherency
464 algorithm. Accepted values range from 0 to 7
465 inclusive. See arch/mips/include/asm/pgtable-bits.h
466 for platform specific values (SB1, Loongson3 and
469 ccw_timeout_log [S390]
470 See Documentation/s390/CommonIO for details.
472 cgroup_disable= [KNL] Disable a particular controller
473 Format: {name of the controller(s) to disable}
474 The effects of cgroup_disable=foo are:
475 - foo isn't auto-mounted if you mount all cgroups in
477 - foo isn't visible as an individually mountable
479 {Currently only "memory" controller deal with this and
480 cut the overhead, others just disable the usage. So
481 only cgroup_disable=memory is actually worthy}
483 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
484 Format: { controller[,controller...] | "all" }
485 Like cgroup_disable, but only applies to cgroup v1;
486 the blacklisted controllers remain available in cgroup2.
488 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
490 nosocket -- Disable socket memory accounting.
491 nokmem -- Disable kernel memory accounting.
493 checkreqprot [SELINUX] Set initial checkreqprot flag value.
494 Format: { "0" | "1" }
495 See security/selinux/Kconfig help text.
496 0 -- check protection applied by kernel (includes
497 any implied execute protection).
498 1 -- check protection requested by application.
499 Default value is set via a kernel config option.
500 Value can be changed at runtime via
501 /selinux/checkreqprot.
504 See Documentation/s390/CommonIO for details.
507 Prevents the clock framework from automatically gating
508 clocks that have not been explicitly enabled by a Linux
509 device driver but are enabled in hardware at reset or
510 by the bootloader/firmware. Note that this does not
511 force such clocks to be always-on nor does it reserve
512 those clocks in any way. This parameter is useful for
513 debug and development, but should not be needed on a
514 platform with proper driver support. For more
515 information, see Documentation/clk.txt.
517 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
519 Forces specified clocksource (if available) to be used
520 when calculating gettimeofday(). If specified
521 clocksource is not available, it defaults to PIT.
522 Format: { pit | tsc | cyclone | pmtmr }
524 clocksource= Override the default clocksource
526 Override the default clocksource and use the clocksource
527 with the name specified.
528 Some clocksource names to choose from, depending on
530 [all] jiffies (this is the base, fallback clocksource)
532 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
533 pxa_timer,timer3,32k_counter,timer0_1
534 [X86-32] pit,hpet,tsc;
535 scx200_hrt on Geode; cyclone on IBM x440
543 clocksource.arm_arch_timer.evtstrm=
546 Enable/disable the eventstream feature of the ARM
547 architected timer so that code using WFE-based polling
548 loops can be debugged more effectively on production
551 clearcpuid=BITNUM [X86]
552 Disable CPUID feature X for the kernel. See
553 arch/x86/include/asm/cpufeatures.h for the valid bit
554 numbers. Note the Linux specific bits are not necessarily
555 stable over kernel options, but the vendor specific
557 Also note that user programs calling CPUID directly
558 or using the feature without checking anything
559 will still see it. This just prevents it from
560 being used by the kernel or shown in /proc/cpuinfo.
561 Also note the kernel might malfunction if you disable
564 cma=nn[MG]@[start[MG][-end[MG]]]
566 Sets the size of kernel global memory area for
567 contiguous memory allocations and optionally the
568 placement constraint by the physical address range of
569 memory allocations. A value of 0 disables CMA
570 altogether. For more information, see
571 include/linux/dma-contiguous.h
573 cmo_free_hint= [PPC] Format: { yes | no }
574 Specify whether pages are marked as being inactive
575 when they are freed. This is used in CMO environments
576 to determine OS memory pressure for page stealing by
580 coherent_pool=nn[KMG] [ARM,KNL]
581 Sets the size of memory pool for coherent, atomic dma
582 allocations, by default set to 256K.
584 code_bytes [X86] How many bytes of object code to print
589 com20020= [HW,NET] ARCnet - COM20020 chipset
591 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
593 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
597 ARCnet - COM90xx chipset (memory-mapped buffers)
598 Format: <io>[,<irq>[,<memstart>]]
600 condev= [HW,S390] console device
603 console= [KNL] Output console device and options.
605 tty<n> Use the virtual console device <n>.
609 Use the specified serial port. The options are of
610 the form "bbbbpnf", where "bbbb" is the baud rate,
611 "p" is parity ("n", "o", or "e"), "n" is number of
612 bits, and "f" is flow control ("r" for RTS or
613 omit it). Default is "9600n8".
615 See Documentation/admin-guide/serial-console.rst for more
617 Documentation/networking/netconsole.txt for an
620 uart[8250],io,<addr>[,options]
621 uart[8250],mmio,<addr>[,options]
622 uart[8250],mmio16,<addr>[,options]
623 uart[8250],mmio32,<addr>[,options]
624 uart[8250],0x<addr>[,options]
625 Start an early, polled-mode console on the 8250/16550
626 UART at the specified I/O port or MMIO address,
627 switching to the matching ttyS device later.
628 MMIO inter-register address stride is either 8-bit
629 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
630 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
631 to be equivalent to 'mmio'. 'options' are specified in
632 the same format described for ttyS above; if unspecified,
633 the h/w is not re-initialized.
635 hvc<n> Use the hypervisor console device <n>. This is for
636 both Xen and PowerPC hypervisors.
638 If the device connected to the port is not a TTY but a braille
639 device, prepend "brl," before the device type, for instance
641 For now, only VisioBraille is supported.
643 consoleblank= [KNL] The console blank (screen saver) timeout in
644 seconds. Defaults to 10*60 = 10mins. A value of 0
645 disables the blank timer.
648 [KNL] Change the default value for
649 /proc/<pid>/coredump_filter.
650 See also Documentation/filesystems/proc.txt.
652 cpuidle.off=1 [CPU_IDLE]
653 disable the cpuidle sub-system
655 cpufreq.off=1 [CPU_FREQ]
656 disable the cpufreq sub-system
659 [X86] Delay for N microsec between assert and de-assert
660 of APIC INIT to start processors. This delay occurs
661 on every CPU online, such as boot, and resume from suspend.
664 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
666 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
668 crashkernel=size[KMG][@offset[KMG]]
669 [KNL] Using kexec, Linux can switch to a 'crash kernel'
670 upon panic. This parameter reserves the physical
671 memory region [offset, offset + size] for that kernel
672 image. If '@offset' is omitted, then a suitable offset
673 is selected automatically. Check
674 Documentation/kdump/kdump.txt for further details.
676 crashkernel=range1:size1[,range2:size2,...][@offset]
677 [KNL] Same as above, but depends on the memory
678 in the running system. The syntax of range is
679 start-[end] where start and end are both
680 a memory unit (amount[KMG]). See also
681 Documentation/kdump/kdump.txt for an example.
683 crashkernel=size[KMG],high
684 [KNL, x86_64] range could be above 4G. Allow kernel
685 to allocate physical memory region from top, so could
686 be above 4G if system have more than 4G ram installed.
687 Otherwise memory region will be allocated below 4G, if
689 It will be ignored if crashkernel=X is specified.
690 crashkernel=size[KMG],low
691 [KNL, x86_64] range under 4G. When crashkernel=X,high
692 is passed, kernel could allocate physical memory region
693 above 4G, that cause second kernel crash on system
694 that require some amount of low memory, e.g. swiotlb
695 requires at least 64M+32K low memory, also enough extra
696 low memory is needed to make sure DMA buffers for 32-bit
697 devices won't run out. Kernel would try to allocate at
698 at least 256M below 4G automatically.
699 This one let user to specify own low range under 4G
700 for second kernel instead.
701 0: to disable low allocation.
702 It will be ignored when crashkernel=X,high is not used
703 or memory reserved is below 4G.
706 [KNL] Disable crypto self-tests
711 cs89x0_media= [HW,NET]
712 Format: { rj45 | aui | bnc }
715 See header of drivers/s390/block/dasd_devmap.c.
717 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
718 (one device per port)
719 Format: <port#>,<type>
720 See also Documentation/input/joystick-parport.txt
722 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
723 time. See Documentation/dynamic-debug-howto.txt for
724 details. Deprecated, see dyndbg.
726 debug [KNL] Enable kernel debugging (events log level).
729 [KNL] verbose self-tests
731 Print debugging info while doing the locking API
733 We default to 0 (no extra messages), setting it to
734 1 will print _a lot_ more information - normally
735 only useful to kernel developers.
737 debug_objects [KNL] Enable object debugging
740 [KNL] Disable object debugging
742 debug_guardpage_minorder=
743 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
744 parameter allows control of the order of pages that will
745 be intentionally kept free (and hence protected) by the
746 buddy allocator. Bigger value increase the probability
747 of catching random memory corruption, but reduce the
748 amount of memory for normal system use. The maximum
749 possible value is MAX_ORDER/2. Setting this parameter
750 to 1 or 2 should be enough to identify most random
751 memory corruption problems caused by bugs in kernel or
752 driver code when a CPU writes to (or reads from) a
753 random memory location. Note that there exists a class
754 of memory corruptions problems caused by buggy H/W or
755 F/W or by drivers badly programing DMA (basically when
756 memory is written at bus level and the CPU MMU is
757 bypassed) which are not detectable by
758 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
759 tracking down these problems.
762 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
763 parameter enables the feature at boot time. In
764 default, it is disabled. We can avoid allocating huge
765 chunk of memory for debug pagealloc if we don't enable
766 it at boot time and the system will work mostly same
767 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
768 on: enable the feature
770 debugpat [X86] Enable PAT debugging
772 decnet.addr= [HW,NET]
773 Format: <area>[,<node>]
774 See also Documentation/networking/decnet.txt.
777 [same as hugepagesz=] The size of the default
778 HugeTLB page size. This is the size represented by
779 the legacy /proc/ hugepages APIs, used for SHM, and
780 default size when mounting hugetlbfs filesystems.
781 Defaults to the default architecture's huge page size
785 Set number of hash buckets for dentry cache.
787 disable_1tb_segments [PPC]
788 Disables the use of 1TB hash page table segments. This
789 causes the kernel to fall back to 256MB segments which
790 can be useful when debugging issues that require an SLB
794 See Documentation/networking/ipv6.txt.
797 Disable RADIX MMU mode on POWER9
799 disable_cpu_apicid= [X86,APIC,SMP]
801 The number of initial APIC ID for the
802 corresponding CPU to be disabled at boot,
803 mostly used for the kdump 2nd kernel to
804 disable BSP to wake up multiple CPUs without
805 causing system reset or hang due to sending
808 disable_ddw [PPC/PSERIES]
809 Disable Dynamic DMA Window support. Use this if
810 to workaround buggy firmware.
813 See Documentation/networking/ipv6.txt.
815 disable_mtrr_cleanup [X86]
816 The kernel tries to adjust MTRR layout from continuous
817 to discrete, to make X server driver able to add WB
818 entry later. This parameter disables that.
820 disable_mtrr_trim [X86, Intel and AMD only]
821 By default the kernel will trim any uncacheable
822 memory out of your available memory pool based on
823 MTRR settings. This parameter disables that behavior,
824 possibly causing your machine to run very slowly.
826 disable_timer_pin_1 [X86]
827 Disable PIN 1 of APIC timer
828 Can be useful to work around chipset bugs.
830 dis_ucode_ldr [X86] Disable the microcode loader.
832 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
833 this option disables the debugging code at boot.
835 dma_debug_entries=<number>
836 This option allows to tune the number of preallocated
837 entries for DMA-API debugging code. One entry is
838 required per DMA-API allocation. Use this if the
839 DMA-API debugging code disables itself because the
840 architectural default is too low.
842 dma_debug_driver=<driver_name>
843 With this option the DMA-API debugging driver
844 filter feature can be enabled at boot time. Just
845 pass the driver to filter for as the parameter.
846 The filter can be disabled or changed to another
847 driver later using sysfs.
849 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
850 Broken monitors, graphic adapters, KVMs and EDIDless
851 panels may send no or incorrect EDID data sets.
852 This parameter allows to specify an EDID data sets
853 in the /lib/firmware directory that are used instead.
854 Generic built-in EDID data sets are used, if one of
855 edid/1024x768.bin, edid/1280x1024.bin,
856 edid/1680x1050.bin, or edid/1920x1080.bin is given
857 and no file with the same name exists. Details and
858 instructions how to build your own EDID data are
859 available in Documentation/EDID/HOWTO.txt. An EDID
860 data set will only be used for a particular connector,
861 if its name and a colon are prepended to the EDID
862 name. Each connector may use a unique EDID data
863 set by separating the files with a comma. An EDID
864 data set with no connector name will be used for
865 any connectors not explicitly specified.
869 dump_apple_properties [X86]
870 Dump name and content of EFI device properties on
871 x86 Macs. Useful for driver authors to determine
872 what data is available or for reverse-engineering.
874 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
875 module.dyndbg[="val"]
876 Enable debug messages at boot time. See
877 Documentation/dynamic-debug-howto.txt for details.
879 nompx [X86] Disables Intel Memory Protection Extensions.
880 See Documentation/x86/intel_mpx.txt for more
881 information about the feature.
883 nopku [X86] Disable Memory Protection Keys CPU feature found
886 module.async_probe [KNL]
887 Enable asynchronous probe on this module.
889 early_ioremap_debug [KNL]
890 Enable debug messages in early_ioremap support. This
891 is useful for tracking down temporary early mappings
892 which are not unmapped.
894 earlycon= [KNL] Output early console device and options.
896 When used with no options, the early console is
897 determined by the stdout-path property in device
900 cdns,<addr>[,options]
901 Start an early, polled-mode console on a Cadence
902 (xuartps) serial port at the specified address. Only
903 supported option is baud rate. If baud rate is not
904 specified, the serial port must already be setup and
907 uart[8250],io,<addr>[,options]
908 uart[8250],mmio,<addr>[,options]
909 uart[8250],mmio32,<addr>[,options]
910 uart[8250],mmio32be,<addr>[,options]
911 uart[8250],0x<addr>[,options]
912 Start an early, polled-mode console on the 8250/16550
913 UART at the specified I/O port or MMIO address.
914 MMIO inter-register address stride is either 8-bit
915 (mmio) or 32-bit (mmio32 or mmio32be).
916 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
917 to be equivalent to 'mmio'. 'options' are specified
918 in the same format described for "console=ttyS<n>"; if
919 unspecified, the h/w is not initialized.
923 Start an early, polled-mode console on a pl011 serial
924 port at the specified address. The pl011 serial port
925 must already be setup and configured. Options are not
926 yet supported. If 'mmio32' is specified, then only
927 the driver will use only 32-bit accessors to read/write
928 the device registers.
931 Start an early, polled-mode console on a meson serial
932 port at the specified address. The serial port must
933 already be setup and configured. Options are not yet
937 Start an early, polled-mode console on an msm serial
938 port at the specified address. The serial port
939 must already be setup and configured. Options are not
943 Start an early, polled-mode console on an msm serial
944 dm port at the specified address. The serial port
945 must already be setup and configured. Options are not
948 smh Use ARM semihosting calls for early console.
956 Use early console provided by serial driver available
957 on Samsung SoCs, requires selecting proper type and
958 a correct base address of the selected UART port. The
959 serial port must already be setup and configured.
960 Options are not yet supported.
963 Start an early, polled-mode console on a lantiq serial
964 (lqasc) port at the specified address. The serial port
965 must already be setup and configured. Options are not
970 Use early console provided by Freescale LP UART driver
971 found on Freescale Vybrid and QorIQ LS1021A processors.
972 A valid base address must be provided, and the serial
973 port must already be setup and configured.
975 armada3700_uart,<addr>
976 Start an early, polled-mode console on the
977 Armada 3700 serial port at the specified
978 address. The serial port must already be setup
979 and configured. Options are not yet supported.
981 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
986 earlyprintk=serial[,ttySn[,baudrate]]
987 earlyprintk=serial[,0x...[,baudrate]]
988 earlyprintk=ttySn[,baudrate]
989 earlyprintk=dbgp[debugController#]
990 earlyprintk=pciserial,bus:device.function[,baudrate]
991 earlyprintk=xdbc[xhciController#]
993 earlyprintk is useful when the kernel crashes before
994 the normal console is initialized. It is not enabled by
995 default because it has some cosmetic problems.
997 Append ",keep" to not disable it when the real console
1000 Only one of vga, efi, serial, or usb debug port can
1003 Currently only ttyS0 and ttyS1 may be specified by
1004 name. Other I/O ports may be explicitly specified
1005 on some architectures (x86 and arm at least) by
1006 replacing ttySn with an I/O port address, like this:
1007 earlyprintk=serial,0x1008,115200
1008 You can find the port for a given device in
1009 /proc/tty/driver/serial:
1010 2: uart:ST16650V2 port:00001008 irq:18 ...
1012 Interaction with the standard serial driver is not
1015 The VGA and EFI output is eventually overwritten by
1018 The xen output can only be used by Xen PV guests.
1020 The sclp output can only be used on s390.
1022 edac_report= [HW,EDAC] Control how to report EDAC event
1023 Format: {"on" | "off" | "force"}
1024 on: enable EDAC to report H/W event. May be overridden
1025 by other higher priority error reporting module.
1026 off: disable H/W event reporting through EDAC.
1027 force: enforce the use of EDAC to report H/W event.
1030 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1033 This is designed to be used in conjunction with
1034 the boot argument: earlyprintk=vga
1037 Format: {"off" | "on" | "skip[mbr]"}
1040 Format: { "old_map", "nochunk", "noruntime", "debug" }
1041 old_map [X86-64]: switch to the old ioremap-based EFI
1042 runtime services mapping. 32-bit still uses this one by
1044 nochunk: disable reading files in "chunks" in the EFI
1045 boot stub, as chunking can cause problems with some
1046 firmware implementations.
1047 noruntime : disable EFI runtime services support
1048 debug: enable misc debug output
1050 efi_no_storage_paranoia [EFI; X86]
1051 Using this parameter you can use more than 50% of
1052 your efi variable storage. Use this parameter only if
1053 you are really sure that your UEFI does sane gc and
1054 fulfills the spec otherwise your board may brick.
1056 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1057 Add arbitrary attribute to specific memory range by
1058 updating original EFI memory map.
1059 Region of memory which aa attribute is added to is
1061 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1062 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1063 attribute is added to range 0x100000000-0x180000000 and
1064 0x10a0000000-0x1120000000.
1066 Using this parameter you can do debugging of EFI memmap
1067 related feature. For example, you can do debugging of
1068 Address Range Mirroring feature even if your box
1071 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1072 that is to be dynamically loaded by Linux. If there are
1073 multiple variables with the same name but with different
1074 vendor GUIDs, all of them will be loaded. See
1075 Documentation/acpi/ssdt-overlays.txt for details.
1078 eisa_irq_edge= [PARISC,HW]
1079 See header of drivers/parisc/eisa.c.
1082 See comment before function elanfreq_setup() in
1083 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1086 Format: {"cfq" | "deadline" | "noop"}
1087 See Documentation/block/cfq-iosched.txt and
1088 Documentation/block/deadline-iosched.txt for details.
1090 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1091 Specifies physical address of start of kernel core
1092 image elf header and optionally the size. Generally
1093 kexec loader will pass this option to capture kernel.
1094 See Documentation/kdump/kdump.txt for details.
1096 enable_mtrr_cleanup [X86]
1097 The kernel tries to adjust MTRR layout from continuous
1098 to discrete, to make X server driver able to add WB
1099 entry later. This parameter enables that.
1101 enable_timer_pin_1 [X86]
1102 Enable PIN 1 of APIC timer
1103 Can be useful to work around chipset bugs
1104 (in particular on some ATI chipsets).
1105 The kernel tries to set a reasonable default.
1107 enforcing [SELINUX] Set initial enforcing status.
1109 See security/selinux/Kconfig help text.
1110 0 -- permissive (log only, no denials).
1111 1 -- enforcing (deny and log).
1113 Value can be changed at runtime via /selinux/enforce.
1116 Disable Error Record Serialization Table (ERST)
1119 ether= [HW,NET] Ethernet cards parameters
1120 This option is obsoleted by the "netdev=" option, which
1121 has equivalent usage. See its documentation for details.
1125 Permit 'security.evm' to be updated regardless of
1126 current integrity status.
1130 fail_make_request=[KNL]
1131 General fault injection mechanism.
1132 Format: <interval>,<probability>,<space>,<times>
1133 See also Documentation/fault-injection/.
1136 See Documentation/blockdev/floppy.txt.
1138 force_pal_cache_flush
1139 [IA-64] Avoid check_sal_cache_flush which may hang on
1140 buggy SAL_CACHE_FLUSH implementations. Using this
1141 parameter will force ia64_sal_cache_flush to call
1142 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1145 Forcefully enable Physical Address Extension (PAE).
1146 Many Pentium M systems disable PAE but may have a
1147 functionally usable PAE implementation.
1148 Warning: use of this parameter will taint the kernel
1149 and may cause unknown problems.
1152 [FTRACE] will set and start the specified tracer
1153 as early as possible in order to facilitate early
1156 ftrace_dump_on_oops[=orig_cpu]
1157 [FTRACE] will dump the trace buffers on oops.
1158 If no parameter is passed, ftrace will dump
1159 buffers of all CPUs, but if you pass orig_cpu, it will
1160 dump only the buffer of the CPU that triggered the
1163 ftrace_filter=[function-list]
1164 [FTRACE] Limit the functions traced by the function
1165 tracer at boot up. function-list is a comma separated
1166 list of functions. This list can be changed at run
1167 time by the set_ftrace_filter file in the debugfs
1170 ftrace_notrace=[function-list]
1171 [FTRACE] Do not trace the functions specified in
1172 function-list. This list can be changed at run time
1173 by the set_ftrace_notrace file in the debugfs
1176 ftrace_graph_filter=[function-list]
1177 [FTRACE] Limit the top level callers functions traced
1178 by the function graph tracer at boot up.
1179 function-list is a comma separated list of functions
1180 that can be changed at run time by the
1181 set_graph_function file in the debugfs tracing directory.
1183 ftrace_graph_notrace=[function-list]
1184 [FTRACE] Do not trace from the functions specified in
1185 function-list. This list is a comma separated list of
1186 functions that can be changed at run time by the
1187 set_graph_notrace file in the debugfs tracing directory.
1189 ftrace_graph_max_depth=<uint>
1190 [FTRACE] Used with the function graph tracer. This is
1191 the max depth it will trace into a function. This value
1192 can be changed at run time by the max_graph_depth file
1193 in the tracefs tracing directory. default: 0 (no limit)
1196 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1197 support via parallel port (up to 5 devices per port)
1198 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1199 See also Documentation/input/joystick-parport.txt
1203 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1207 gcov_persist= [GCOV] When non-zero (default), profiling data for
1208 kernel modules is saved and remains accessible via
1209 debugfs, even when the module is unloaded/reloaded.
1210 When zero, profiling data is discarded and associated
1211 debugfs files are removed at module unload time.
1213 goldfish [X86] Enable the goldfish android emulator platform.
1214 Don't use this when you are not running on the
1217 gpt [EFI] Forces disk with valid GPT signature but
1218 invalid Protective MBR to be treated as GPT. If the
1219 primary GPT is corrupted, it enables the backup/alternate
1220 GPT to be used instead.
1222 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1223 the "Enable 0" bit of the configuration register.
1226 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1227 the "Enable 0" bit of the configuration register.
1230 grcan.select= [HW] Select which physical interface to use.
1233 grcan.txsize= [HW] Sets the size of the tx buffer.
1234 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1236 grcan.rxsize= [HW] Sets the size of the rx buffer.
1237 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1240 gpio-mockup.gpio_mockup_ranges
1241 [HW] Sets the ranges of gpiochip of for this device.
1242 Format: <start1>,<end1>,<start2>,<end2>...
1244 hardlockup_all_cpu_backtrace=
1245 [KNL] Should the hard-lockup detector generate
1246 backtraces on all cpus.
1249 hashdist= [KNL,NUMA] Large hashes allocated during boot
1250 are distributed across NUMA nodes. Defaults on
1251 for 64-bit NUMA, off otherwise.
1252 Format: 0 | 1 (for off | on)
1254 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1256 hd= [EIDE] (E)IDE hard drive subsystem geometry
1257 Format: <cyl>,<head>,<sect>
1260 Disable Hardware Error Source Table (HEST) support;
1261 corresponding firmware-first mode error processing
1262 logic will be disabled.
1264 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1265 size of <nn>. This works even on boxes that have no
1266 highmem otherwise. This also works to reduce highmem
1267 size on bigger boxes.
1269 highres= [KNL] Enable/disable high resolution timer mode.
1270 Valid parameters: "on", "off"
1274 See Documentation/isdn/README.HiSax.
1278 hpet= [X86-32,HPET] option to control HPET usage
1279 Format: { enable (default) | disable | force |
1281 disable: disable HPET and use PIT instead
1282 force: allow force enabled of undocumented chips (ICH4,
1284 verbose: show contents of HPET registers during setup
1286 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1287 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1289 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1290 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1291 On x86-64 and powerpc, this option can be specified
1292 multiple times interleaved with hugepages= to reserve
1293 huge pages of different sizes. Valid pages sizes on
1294 x86-64 are 2M (when the CPU supports "pse") and 1G
1295 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1297 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1298 terminal devices. Valid values: 0..8
1299 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1300 If specified, z/VM IUCV HVC accepts connections
1301 from listed z/VM user IDs only.
1303 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1304 hardware thread id mappings.
1305 Format: <cpu>:<hwthread>
1308 Do not unregister boot console at start. This is only
1309 useful for debugging when something happens in the window
1310 between unregistering the boot console and initializing
1313 i2c_bus= [HW] Override the default board specific I2C bus speed
1314 or register an additional I2C bus that is not
1315 registered from board initialization code.
1319 i8042.debug [HW] Toggle i8042 debug mode
1320 i8042.unmask_kbd_data
1321 [HW] Enable printing of interrupt data from the KBD port
1322 (disabled by default, and as a pre-condition
1323 requires that i8042.debug=1 be enabled)
1324 i8042.direct [HW] Put keyboard port into non-translated mode
1325 i8042.dumbkbd [HW] Pretend that controller can only read data from
1326 keyboard and cannot control its state
1327 (Don't attempt to blink the leds)
1328 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1329 i8042.nokbd [HW] Don't check/create keyboard port
1330 i8042.noloop [HW] Disable the AUX Loopback command while probing
1332 i8042.nomux [HW] Don't check presence of an active multiplexing
1334 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1336 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1337 i8042.reset [HW] Reset the controller during init, cleanup and
1338 suspend-to-ram transitions, only during s2r
1339 transitions, or never reset
1340 Format: { 1 | Y | y | 0 | N | n }
1341 1, Y, y: always reset controller
1342 0, N, n: don't ever reset controller
1343 Default: only on s2r transitions on x86; most other
1344 architectures force reset to be always executed
1345 i8042.unlock [HW] Unlock (ignore) the keylock
1346 i8042.kbdreset [HW] Reset device connected to KBD port
1350 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1351 indicates that the driver is running on unsupported
1353 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1354 does not match list of supported models.
1356 [HW] Report power status in /proc/i8k
1357 (disabled by default)
1358 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1361 i915.invert_brightness=
1362 [DRM] Invert the sense of the variable that is used to
1363 set the brightness of the panel backlight. Normally a
1364 brightness value of 0 indicates backlight switched off,
1365 and the maximum of the brightness value sets the backlight
1366 to maximum brightness. If this parameter is set to 0
1367 (default) and the machine requires it, or this parameter
1368 is set to 1, a brightness value of 0 sets the backlight
1369 to maximum brightness, and the maximum of the brightness
1370 value switches the backlight off.
1371 -1 -- never invert brightness
1372 0 -- machine default
1373 1 -- force brightness inversion
1376 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1378 ide-core.nodma= [HW] (E)IDE subsystem
1379 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1380 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1381 .cdrom .chs .ignore_cable are additional options
1382 See Documentation/ide/ide.txt.
1384 ide-generic.probe-mask= [HW] (E)IDE subsystem
1386 Probe mask for legacy ISA IDE ports. Depending on
1387 platform up to 6 ports are supported, enabled by
1388 setting corresponding bits in the mask to 1. The
1389 default value is 0x0, which has a special meaning.
1390 On systems that have PCI, it triggers scanning the
1391 PCI bus for the first and the second port, which
1392 are then probed. On systems without PCI the value
1393 of 0x0 enables probing the two first ports as if it
1396 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1397 Claim all unknown PCI IDE storage controllers.
1400 Format: idle=poll, idle=halt, idle=nomwait
1401 Poll forces a polling idle loop that can slightly
1402 improve the performance of waking up a idle CPU, but
1403 will use a lot of power and make the system run hot.
1405 idle=halt: Halt is forced to be used for CPU idle.
1406 In such case C2/C3 won't be used again.
1407 idle=nomwait: Disable mwait for CPU C-states
1409 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1410 Format: { strict | legacy | 2008 | relaxed }
1413 Choose which programs will be accepted for execution
1414 based on the IEEE 754 NaN encoding(s) supported by
1415 the FPU and the NaN encoding requested with the value
1416 of an ELF file header flag individually set by each
1417 binary. Hardware implementations are permitted to
1418 support either or both of the legacy and the 2008 NaN
1421 Available settings are as follows:
1422 strict accept binaries that request a NaN encoding
1423 supported by the FPU
1424 legacy only accept legacy-NaN binaries, if supported
1426 2008 only accept 2008-NaN binaries, if supported
1428 relaxed accept any binaries regardless of whether
1429 supported by the FPU
1431 The FPU emulator is always able to support both NaN
1432 encodings, so if no FPU hardware is present or it has
1433 been disabled with 'nofpu', then the settings of
1434 'legacy' and '2008' strap the emulator accordingly,
1435 'relaxed' straps the emulator for both legacy-NaN and
1436 2008-NaN, whereas 'strict' enables legacy-NaN only on
1437 legacy processors and both NaN encodings on MIPS32 or
1440 The setting for ABS.fmt/NEG.fmt instruction execution
1441 mode generally follows that for the NaN encoding,
1442 except where unsupported by hardware.
1444 ignore_loglevel [KNL]
1445 Ignore loglevel setting - this will print /all/
1446 kernel messages to the console. Useful for debugging.
1447 We also add it as printk module parameter, so users
1448 could change it dynamically, usually by
1449 /sys/module/printk/parameters/ignore_loglevel.
1452 Ignore RLIMIT_DATA setting for data mappings,
1453 print warning at first misuse. Can be changed via
1454 /sys/module/kernel/parameters/ignore_rlimit_data.
1456 ihash_entries= [KNL]
1457 Set number of hash buckets for inode cache.
1459 ima_appraise= [IMA] appraise integrity measurements
1460 Format: { "off" | "enforce" | "fix" | "log" }
1463 ima_appraise_tcb [IMA]
1464 The builtin appraise policy appraises all files
1467 ima_canonical_fmt [IMA]
1468 Use the canonical format for the binary runtime
1469 measurements, instead of host native format.
1472 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1476 The list of supported hash algorithms is defined
1477 in crypto/hash_info.h.
1480 The builtin measurement policy to load during IMA
1481 setup. Specyfing "tcb" as the value, measures all
1482 programs exec'd, files mmap'd for exec, and all files
1483 opened with the read mode bit set by either the
1484 effective uid (euid=0) or uid=0.
1487 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1488 Load a policy which meets the needs of the Trusted
1489 Computing Base. This means IMA will measure all
1490 programs exec'd, files mmap'd for exec, and all files
1491 opened for read by uid=0.
1494 Select one of defined IMA measurements template formats.
1495 Formats: { "ima" | "ima-ng" | "ima-sig" }
1499 [IMA] Define a custom template format.
1500 Format: { "field1|...|fieldN" }
1502 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1503 Format: <min_file_size>
1504 Set the minimal file size for using asynchronous hash.
1505 If left unspecified, ahash usage is disabled.
1507 ahash performance varies for different data sizes on
1508 different crypto accelerators. This option can be used
1509 to achieve the best performance for a particular HW.
1511 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1513 Set hashing buffer size. Default: 4k.
1515 ahash performance varies for different chunk sizes on
1516 different crypto accelerators. This option can be used
1517 to achieve best performance for particular HW.
1521 Run specified binary instead of /sbin/init as init
1524 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1525 for working out where the kernel is dying during
1528 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1529 initcall functions. Useful for debugging built-in
1530 modules and initcalls.
1532 initrd= [BOOT] Specify the location of the initial ramdisk
1534 init_pkru= [x86] Specify the default memory protection keys rights
1535 register contents for all processes. 0x55555554 by
1536 default (disallow access to all but pkey 0). Can
1537 override in debugfs after boot.
1539 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1542 int_pln_enable [x86] Enable power limit notification interrupt
1544 integrity_audit=[IMA]
1545 Format: { "0" | "1" }
1546 0 -- basic integrity auditing messages. (Default)
1547 1 -- additional integrity auditing messages.
1549 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1551 Enable intel iommu driver.
1553 Disable intel iommu driver.
1554 igfx_off [Default Off]
1555 By default, gfx is mapped as normal device. If a gfx
1556 device has a dedicated DMAR unit, the DMAR unit is
1557 bypassed by not enabling DMAR with this option. In
1558 this case, gfx device will use physical address for
1561 With this option iommu will not optimize to look
1562 for io virtual address below 32-bit forcing dual
1563 address cycle on pci bus for cards supporting greater
1564 than 32-bit addressing. The default is to look
1565 for translation below 32-bit and if not available
1566 then look in the higher range.
1567 strict [Default Off]
1568 With this option on every unmap_single operation will
1569 result in a hardware IOTLB flush operation as opposed
1570 to batching them for performance.
1571 sp_off [Default Off]
1572 By default, super page will be supported if Intel IOMMU
1573 has the capability. With this option, super page will
1575 ecs_off [Default Off]
1576 By default, extended context tables will be supported if
1577 the hardware advertises that it has support both for the
1578 extended tables themselves, and also PASID support. With
1579 this option set, extended tables will not be used even
1580 on hardware which claims to support them.
1581 tboot_noforce [Default Off]
1582 Do not force the Intel IOMMU enabled under tboot.
1583 By default, tboot will force Intel IOMMU on, which
1584 could harm performance of some high-throughput
1585 devices like 40GBit network cards, even if identity
1587 Note that using this option lowers the security
1588 provided by tboot because it makes the system
1589 vulnerable to DMA attacks.
1591 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1592 0 disables intel_idle and fall back on acpi_idle.
1593 1 to 9 specify maximum depth of C-state.
1597 Do not enable intel_pstate as the default
1598 scaling driver for the supported processors
1600 Use intel_pstate as a scaling driver, but configure it
1601 to work with generic cpufreq governors (instead of
1602 enabling its internal governor). This mode cannot be
1603 used along with the hardware-managed P-states (HWP)
1606 Enable intel_pstate on systems that prohibit it by default
1607 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1608 instead of acpi-cpufreq may disable platform features, such
1609 as thermal controls and power capping, that rely on ACPI
1610 P-States information being indicated to OSPM and therefore
1611 should be used with caution. This option does not work with
1612 processors that aren't supported by the intel_pstate driver
1613 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1615 Do not enable hardware P state control (HWP)
1618 Only load intel_pstate on systems which support
1619 hardware P state control (HWP) if available.
1621 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1622 Description Table, specifies preferred power management
1623 profile as "Enterprise Server" or "Performance Server",
1624 then this feature is turned on by default.
1626 Allow per-logical-CPU P-State performance control limits using
1627 cpufreq sysfs interface
1629 intremap= [X86-64, Intel-IOMMU]
1630 on enable Interrupt Remapping (default)
1631 off disable Interrupt Remapping
1632 nosid disable Source ID checking
1634 BIOS x2APIC opt-out request will be ignored
1635 nopost disable Interrupt Posting
1637 iomem= Disable strict checking of access to MMIO memory
1638 strict regions from userspace.
1653 nobypass [PPC/POWERNV]
1654 Disable IOMMU bypass, using IOMMU for PCI devices.
1657 [ARM64] Configure DMA to bypass the IOMMU by default.
1658 Format: { "0" | "1" }
1659 0 - Use IOMMU translation for DMA.
1660 1 - Bypass the IOMMU for DMA.
1661 unset - Use IOMMU translation for DMA.
1663 io7= [HW] IO7 for Marvel based alpha systems
1664 See comment before marvel_specify_io7 in
1665 arch/alpha/kernel/core_marvel.c.
1667 io_delay= [X86] I/O delay method
1669 Standard port 0x80 based delay
1671 Alternate port 0xed based delay (needed on some systems)
1673 Simple two microseconds delay
1678 See Documentation/filesystems/nfs/nfsroot.txt.
1680 irqaffinity= [SMP] Set the default irq affinity mask
1681 The argument is a cpu list, as described above.
1684 When an interrupt is not handled search all handlers
1685 for it. Intended to get systems with badly broken
1689 When an interrupt is not handled search all handlers
1690 for it. Also check all handlers each timer
1691 interrupt. Intended to get systems with badly broken
1695 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1697 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1698 The argument is a cpu list, as described above.
1700 This option can be used to specify one or more CPUs
1701 to isolate from the general SMP balancing and scheduling
1702 algorithms. You can move a process onto or off an
1703 "isolated" CPU via the CPU affinity syscalls or cpuset.
1704 <cpu number> begins at 0 and the maximum value is
1705 "number of CPUs in system - 1".
1707 This option is the preferred way to isolate CPUs. The
1708 alternative -- manually setting the CPU mask of all
1709 tasks in the system -- can cause problems and
1710 suboptimal load balancer performance.
1714 ivrs_ioapic [HW,X86_64]
1715 Provide an override to the IOAPIC-ID<->DEVICE-ID
1716 mapping provided in the IVRS ACPI table. For
1717 example, to map IOAPIC-ID decimal 10 to
1718 PCI device 00:14.0 write the parameter as:
1719 ivrs_ioapic[10]=00:14.0
1721 ivrs_hpet [HW,X86_64]
1722 Provide an override to the HPET-ID<->DEVICE-ID
1723 mapping provided in the IVRS ACPI table. For
1724 example, to map HPET-ID decimal 0 to
1725 PCI device 00:14.0 write the parameter as:
1726 ivrs_hpet[0]=00:14.0
1728 ivrs_acpihid [HW,X86_64]
1729 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1730 mapping provided in the IVRS ACPI table. For
1731 example, to map UART-HID:UID AMD0020:0 to
1732 PCI device 00:14.5 write the parameter as:
1733 ivrs_acpihid[00:14.5]=AMD0020:0
1735 js= [HW,JOY] Analog joystick
1736 See Documentation/input/joystick.txt.
1739 When CONFIG_RANDOMIZE_BASE is set, this disables
1740 kernel and module base offset ASLR (Address Space
1741 Layout Randomization).
1744 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1745 report on every invalid memory access. Without this
1746 parameter KASAN will print report only for the first
1751 kernelcore= [KNL,X86,IA-64,PPC]
1752 Format: nn[KMGTPE] | "mirror"
1754 specifies the amount of memory usable by the kernel
1755 for non-movable allocations. The requested amount is
1756 spread evenly throughout all nodes in the system. The
1757 remaining memory in each node is used for Movable
1758 pages. In the event, a node is too small to have both
1759 kernelcore and Movable pages, kernelcore pages will
1760 take priority and other nodes will have a larger number
1761 of Movable pages. The Movable zone is used for the
1762 allocation of pages that may be reclaimed or moved
1763 by the page migration subsystem. This means that
1764 HugeTLB pages may not be allocated from this zone.
1765 Note that allocations like PTEs-from-HighMem still
1766 use the HighMem zone if it exists, and the Normal
1767 zone if it does not.
1769 Instead of specifying the amount of memory (nn[KMGTPE]),
1770 you can specify "mirror" option. In case "mirror"
1771 option is specified, mirrored (reliable) memory is used
1772 for non-movable allocations and remaining memory is used
1773 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1774 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1777 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1778 Format: <Controller#>[,poll interval]
1779 The controller # is the number of the ehci usb debug
1780 port as it is probed via PCI. The poll interval is
1781 optional and is the number seconds in between
1782 each poll cycle to the debug port in case you need
1783 the functionality for interrupting the kernel with
1784 gdb or control-c on the dbgp connection. When
1785 not using this parameter you use sysrq-g to break into
1786 the kernel debugger.
1788 kgdboc= [KGDB,HW] kgdb over consoles.
1789 Requires a tty driver that supports console polling,
1790 or a supported polling keyboard driver (non-usb).
1791 Serial only format: <serial_device>[,baud]
1792 keyboard only format: kbd
1793 keyboard and serial format: kbd,<serial_device>[,baud]
1794 Optional Kernel mode setting:
1795 kms, kbd format: kms,kbd
1796 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1798 kgdbwait [KGDB] Stop kernel execution and enter the
1799 kernel debugger at the earliest opportunity.
1801 kmac= [MIPS] korina ethernet MAC address.
1802 Configure the RouterBoard 532 series on-chip
1803 Ethernet adapter MAC address.
1805 kmemleak= [KNL] Boot-time kmemleak enable/disable
1806 Valid arguments: on, off
1808 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1811 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1812 Valid arguments: 0, 1, 2
1813 kmemcheck=0 (disabled)
1814 kmemcheck=1 (enabled)
1815 kmemcheck=2 (one-shot mode)
1816 Default: 2 (one-shot mode)
1818 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1819 Default is 0 (don't ignore, but inject #GP)
1821 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1825 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1826 Default is 1 (enabled)
1828 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1830 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1832 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1833 (virtualized MMU) support on capable Intel chips.
1834 Default is 1 (enabled)
1836 kvm-intel.emulate_invalid_guest_state=
1837 [KVM,Intel] Enable emulation of invalid guest states
1838 Default is 0 (disabled)
1840 kvm-intel.flexpriority=
1841 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1842 Default is 1 (enabled)
1845 [KVM,Intel] Enable VMX nesting (nVMX).
1846 Default is 0 (disabled)
1848 kvm-intel.unrestricted_guest=
1849 [KVM,Intel] Disable unrestricted guest feature
1850 (virtualized real and unpaged mode) on capable
1851 Intel chips. Default is 1 (enabled)
1853 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1854 feature (tagged TLBs) on capable Intel chips.
1855 Default is 1 (enabled)
1861 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1864 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1865 value for LAPIC timer one-shot implementation. Default
1866 back to the programmable timer unit in the LAPIC.
1868 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1871 libata.dma= [LIBATA] DMA control
1872 libata.dma=0 Disable all PATA and SATA DMA
1873 libata.dma=1 PATA and SATA Disk DMA only
1874 libata.dma=2 ATAPI (CDROM) DMA only
1875 libata.dma=4 Compact Flash DMA only
1876 Combinations also work, so libata.dma=3 enables DMA
1877 for disks and CDROMs, but not CFs.
1879 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1880 libata.ignore_hpa=0 keep BIOS limits (default)
1881 libata.ignore_hpa=1 ignore limits, using full disk
1883 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1887 libata.force= [LIBATA] Force configurations. The format is comma
1888 separated list of "[ID:]VAL" where ID is
1889 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1890 matching port, link or device. Basically, it matches
1891 the ATA ID string printed on console by libata. If
1892 the whole ID part is omitted, the last PORT and DEVICE
1893 values are used. If ID hasn't been specified yet, the
1894 configuration applies to all ports, links and devices.
1896 If only DEVICE is omitted, the parameter applies to
1897 the port and all links and devices behind it. DEVICE
1898 number of 0 either selects the first device or the
1899 first fan-out link behind PMP device. It does not
1900 select the host link. DEVICE number of 15 selects the
1901 host link and device attached to it.
1903 The VAL specifies the configuration to force. As long
1904 as there's no ambiguity shortcut notation is allowed.
1905 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1906 The following configurations can be forced.
1908 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1909 Any ID with matching PORT is used.
1911 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1913 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1914 udma[/][16,25,33,44,66,100,133] notation is also
1917 * [no]ncq: Turn on or off NCQ.
1919 * [no]ncqtrim: Turn off queued DSM TRIM.
1921 * nohrst, nosrst, norst: suppress hard, soft
1924 * rstonce: only attempt one reset during
1925 hot-unplug link recovery
1927 * dump_id: dump IDENTIFY data.
1929 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1931 * disable: Disable this device.
1933 If there are multiple matching configurations changing
1934 the same attribute, the last one is used.
1936 memblock=debug [KNL] Enable memblock debug messages.
1938 load_ramdisk= [RAM] List of ramdisks to load from floppy
1939 See Documentation/blockdev/ramdisk.txt.
1941 lockd.nlm_grace_period=P [NFS] Assign grace period.
1944 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1947 lockd.nlm_timeout=T [NFS] Assign timeout value.
1950 lockd.nlm_udpport=M [NFS] Assign UDP port.
1953 locktorture.nreaders_stress= [KNL]
1954 Set the number of locking read-acquisition kthreads.
1955 Defaults to being automatically set based on the
1956 number of online CPUs.
1958 locktorture.nwriters_stress= [KNL]
1959 Set the number of locking write-acquisition kthreads.
1961 locktorture.onoff_holdoff= [KNL]
1962 Set time (s) after boot for CPU-hotplug testing.
1964 locktorture.onoff_interval= [KNL]
1965 Set time (s) between CPU-hotplug operations, or
1966 zero to disable CPU-hotplug testing.
1968 locktorture.shuffle_interval= [KNL]
1969 Set task-shuffle interval (jiffies). Shuffling
1970 tasks allows some CPUs to go into dyntick-idle
1971 mode during the locktorture test.
1973 locktorture.shutdown_secs= [KNL]
1974 Set time (s) after boot system shutdown. This
1975 is useful for hands-off automated testing.
1977 locktorture.stat_interval= [KNL]
1978 Time (s) between statistics printk()s.
1980 locktorture.stutter= [KNL]
1981 Time (s) to stutter testing, for example,
1982 specifying five seconds causes the test to run for
1983 five seconds, wait for five seconds, and so on.
1984 This tests the locking primitive's ability to
1985 transition abruptly to and from idle.
1987 locktorture.torture_runnable= [BOOT]
1988 Start locktorture running at boot time.
1990 locktorture.torture_type= [KNL]
1991 Specify the locking implementation to test.
1993 locktorture.verbose= [KNL]
1994 Enable additional printk() statements.
1996 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1999 loglevel= All Kernel Messages with a loglevel smaller than the
2000 console loglevel will be printed to the console. It can
2001 also be changed with klogd or other programs. The
2002 loglevels are defined as follows:
2004 0 (KERN_EMERG) system is unusable
2005 1 (KERN_ALERT) action must be taken immediately
2006 2 (KERN_CRIT) critical conditions
2007 3 (KERN_ERR) error conditions
2008 4 (KERN_WARNING) warning conditions
2009 5 (KERN_NOTICE) normal but significant condition
2010 6 (KERN_INFO) informational
2011 7 (KERN_DEBUG) debug-level messages
2013 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2014 in bytes. n must be a power of two and greater
2015 than the minimal size. The minimal size is defined
2016 by LOG_BUF_SHIFT kernel config parameter. There is
2017 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2018 that allows to increase the default size depending on
2019 the number of CPUs. See init/Kconfig for more details.
2021 logo.nologo [FB] Disables display of the built-in Linux logo.
2022 This may be used to provide more screen space for
2023 kernel log messages and is useful when debugging
2024 kernel boot problems.
2026 lp=0 [LP] Specify parallel ports to use, e.g,
2027 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2028 lp=reset first parallel port). 'lp=0' disables the
2029 lp=auto printer driver. 'lp=reset' (which can be
2030 specified in addition to the ports) causes
2031 attached printers to be reset. Using
2032 lp=port1,port2,... specifies the parallel ports
2033 to associate lp devices with, starting with
2034 lp0. A port specification may be 'none' to skip
2035 that lp device, or a parport name such as
2036 'parport0'. Specifying 'lp=auto' instead of a
2037 port specification list means that device IDs
2038 from each port should be examined, to see if
2039 an IEEE 1284-compliant printer is attached; if
2040 so, the driver will manage that printer.
2041 See also header of drivers/char/lp.c.
2044 Sets loops_per_jiffy to given constant, thus avoiding
2045 time-consuming boot-time autodetection (up to 250 ms per
2046 CPU). 0 enables autodetection (default). To determine
2047 the correct value for your kernel, boot with normal
2048 autodetection and see what value is printed. Note that
2049 on SMP systems the preset will be applied to all CPUs,
2050 which is likely to cause problems if your CPUs need
2051 significantly divergent settings. An incorrect value
2052 will cause delays in the kernel to be wrong, leading to
2053 unpredictable I/O errors and other breakage. Although
2054 unlikely, in the extreme case this might damage your
2058 Format: <io>,<irq>,<dma>
2060 machvec= [IA-64] Force the use of a particular machine-vector
2061 (machvec) in a generic kernel.
2062 Example: machvec=hpzx1_swiotlb
2064 machtype= [Loongson] Share the same kernel image file between different
2066 Example: machtype=lemote-yeeloong-2f-7inch
2068 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2069 than or equal to this physical address is ignored.
2071 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2072 will bring up during bootup. maxcpus=n : n >= 0 limits
2073 the kernel to bring up 'n' processors. Surely after
2074 bootup you can bring up the other plugged cpu by executing
2075 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2076 only takes effect during system bootup.
2077 While n=0 is a special case, it is equivalent to "nosmp",
2078 which also disables the IO APIC.
2080 max_loop= [LOOP] The number of loop block devices that get
2081 (loop.max_loop) unconditionally pre-created at init time. The default
2082 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2083 of statically allocating a predefined number, loop
2084 devices can be requested on-demand with the
2085 /dev/loop-control interface.
2087 mce [X86-32] Machine Check Exception
2089 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2091 md= [HW] RAID subsystems devices and level
2092 See Documentation/admin-guide/md.rst.
2095 Format: <first>,<last>
2096 Specifies range of consoles to be captured by the MDA.
2098 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2099 Amount of memory to be used when the kernel is not able
2100 to see the whole system memory or for test.
2101 [X86] Work as limiting max address. Use together
2102 with memmap= to avoid physical address space collisions.
2103 Without memmap= PCI devices could be placed at addresses
2104 belonging to unused RAM.
2106 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2110 [KNL,SH] Allow user to override the default size for
2111 per-device physically contiguous DMA buffers.
2113 memhp_default_state=online/offline
2114 [KNL] Set the initial state for the memory hotplug
2115 onlining policy. If not specified, the default value is
2116 set according to the
2117 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2119 See Documentation/memory-hotplug.txt.
2121 memmap=exactmap [KNL,X86] Enable setting of an exact
2122 E820 memory map, as specified by the user.
2123 Such memmap=exactmap lines can be constructed based on
2124 BIOS output or other requirements. See the memmap=nn@ss
2127 memmap=nn[KMG]@ss[KMG]
2128 [KNL] Force usage of a specific region of memory.
2129 Region of memory to be used is from ss to ss+nn.
2131 memmap=nn[KMG]#ss[KMG]
2132 [KNL,ACPI] Mark specific memory as ACPI data.
2133 Region of memory to be marked is from ss to ss+nn.
2135 memmap=nn[KMG]$ss[KMG]
2136 [KNL,ACPI] Mark specific memory as reserved.
2137 Region of memory to be reserved is from ss to ss+nn.
2138 Example: Exclude memory from 0x18690000-0x1869ffff
2139 memmap=64K$0x18690000
2141 memmap=0x10000$0x18690000
2143 memmap=nn[KMG]!ss[KMG]
2144 [KNL,X86] Mark specific memory as protected.
2145 Region of memory to be used, from ss to ss+nn.
2146 The memory region may be marked as e820 type 12 (0xc)
2147 and is NVDIMM or ADR memory.
2149 memory_corruption_check=0/1 [X86]
2150 Some BIOSes seem to corrupt the first 64k of
2151 memory when doing things like suspend/resume.
2152 Setting this option will scan the memory
2153 looking for corruption. Enabling this will
2154 both detect corruption and prevent the kernel
2155 from using the memory being corrupted.
2156 However, its intended as a diagnostic tool; if
2157 repeatable BIOS-originated corruption always
2158 affects the same memory, you can use memmap=
2159 to prevent the kernel from using that memory.
2161 memory_corruption_check_size=size [X86]
2162 By default it checks for corruption in the low
2163 64k, making this memory unavailable for normal
2164 use. Use this parameter to scan for
2165 corruption in more or less memory.
2167 memory_corruption_check_period=seconds [X86]
2168 By default it checks for corruption every 60
2169 seconds. Use this parameter to check at some
2170 other rate. 0 disables periodic checking.
2172 memtest= [KNL,X86,ARM] Enable memtest
2174 default : 0 <disable>
2175 Specifies the number of memtest passes to be
2176 performed. Each pass selects another test
2177 pattern from a given set of patterns. Memtest
2178 fills the memory with this pattern, validates
2179 memory contents and reserves bad memory
2180 regions that are detected.
2182 mem_sleep_default= [SUSPEND] Default system suspend mode:
2183 s2idle - Suspend-To-Idle
2184 shallow - Power-On Suspend or equivalent (if supported)
2185 deep - Suspend-To-RAM or equivalent (if supported)
2186 See Documentation/power/states.txt.
2188 meye.*= [HW] Set MotionEye Camera parameters
2189 See Documentation/video4linux/meye.txt.
2191 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2192 Multi-Function General Purpose Timers on AMD Geode
2195 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2196 the BIOS has incorrectly applied a workaround. TinyBIOS
2197 version 0.98 is known to be affected, 0.99 fixes the
2198 problem by letting the user disable the workaround.
2202 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2203 physical address is ignored.
2205 mini2440= [ARM,HW,KNL]
2206 Format:[0..2][b][c][t]
2208 MINI2440 configuration specification:
2209 0 - The attached screen is the 3.5" TFT
2210 1 - The attached screen is the 7" TFT
2211 2 - The VGA Shield is attached (1024x768)
2212 Leaving out the screen size parameter will not load
2213 the TFT driver, and the framebuffer will be left
2215 b - Enable backlight. The TFT backlight pin will be
2216 linked to the kernel VESA blanking code and a GPIO
2217 LED. This parameter is not necessary when using the
2219 c - Enable the s3c camera interface.
2220 t - Reserved for enabling touchscreen support. The
2221 touchscreen support is not enabled in the mainstream
2222 kernel as of 2.6.30, a preliminary port can be found
2223 in the "bleeding edge" mini2440 support kernel at
2224 http://repo.or.cz/w/linux-2.6/mini2440.git
2227 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2228 parameter allows control of the logging verbosity for
2229 the additional memory initialisation checks. A value
2230 of 0 disables mminit logging and a level of 4 will
2231 log everything. Information is printed at KERN_DEBUG
2232 so loglevel=8 may also need to be specified.
2235 [KNL] When CONFIG_MODULE_SIG is set, this means that
2236 modules without (valid) signatures will fail to load.
2237 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2238 is always true, so this option does nothing.
2240 module_blacklist= [KNL] Do not load a comma-separated list of
2241 modules. Useful for debugging problem modules.
2244 [MOUSE] Maximum time between finger touching and
2245 leaving touchpad surface for touch to be considered
2246 a tap and be reported as a left button click (for
2247 touchpads working in absolute mode only).
2249 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2250 reporting absolute coordinates, such as tablets
2251 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2252 reporting absolute coordinates, such as tablets
2254 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2255 is similar to kernelcore except it specifies the
2256 amount of memory used for migratable allocations.
2257 If both kernelcore and movablecore is specified,
2258 then kernelcore will be at *least* the specified
2259 value but may be more. If movablecore on its own
2260 is specified, the administrator must be careful
2261 that the amount of memory usable for all allocations
2264 movable_node [KNL] Boot-time switch to enable the effects
2265 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2267 MTD_Partition= [MTD]
2268 Format: <name>,<region-number>,<size>,<offset>
2270 MTD_Region= [MTD] Format:
2271 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2274 See drivers/mtd/cmdlinepart.c.
2276 multitce=off [PPC] This parameter disables the use of the pSeries
2277 firmware feature for updating multiple TCE entries
2280 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2282 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2284 boundary - index of last SLC block on Flex-OneNAND.
2285 The remaining blocks are configured as MLC blocks.
2286 lock - Configure if Flex-OneNAND boundary should be locked.
2287 Once locked, the boundary cannot be changed.
2288 1 indicates lock status, 0 indicates unlock status.
2291 ARM/S3C2412 JIVE boot control
2293 See arch/arm/mach-s3c2412/mach-jive.c
2295 mtouchusb.raw_coordinates=
2296 [HW] Make the MicroTouch USB driver use raw coordinates
2297 ('y', default) or cooked coordinates ('n')
2299 mtrr_chunk_size=nn[KMG] [X86]
2300 used for mtrr cleanup. It is largest continuous chunk
2301 that could hold holes aka. UC entries.
2303 mtrr_gran_size=nn[KMG] [X86]
2304 Used for mtrr cleanup. It is granularity of mtrr block.
2306 Large value could prevent small alignment from
2309 mtrr_spare_reg_nr=n [X86]
2311 Range: 0,7 : spare reg number
2313 Used for mtrr cleanup. It is spare mtrr entries number.
2314 Set to 2 or more if your graphical card needs more.
2316 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2318 netdev= [NET] Network devices parameters
2319 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2320 Note that mem_start is often overloaded to mean
2321 something different and driver-specific.
2322 This usage is only documented in each driver source
2326 [NETFILTER] Enable connection tracking flow accounting
2327 0 to disable accounting
2328 1 to enable accounting
2331 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2332 See Documentation/filesystems/nfs/nfsroot.txt.
2334 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2335 See Documentation/filesystems/nfs/nfsroot.txt.
2337 nfsrootdebug [NFS] enable nfsroot debugging messages.
2338 See Documentation/filesystems/nfs/nfsroot.txt.
2340 nfs.callback_nr_threads=
2341 [NFSv4] set the total number of threads that the
2342 NFS client will assign to service NFSv4 callback
2345 nfs.callback_tcpport=
2346 [NFS] set the TCP port on which the NFSv4 callback
2347 channel should listen.
2350 [NFS] sets the pathname to the program which is used
2351 to update the NFS client cache entries.
2353 nfs.cache_getent_timeout=
2354 [NFS] sets the timeout after which an attempt to
2355 update a cache entry is deemed to have failed.
2357 nfs.idmap_cache_timeout=
2358 [NFS] set the maximum lifetime for idmapper cache
2362 [NFS] enable 64-bit inode numbers.
2363 If zero, the NFS client will fake up a 32-bit inode
2364 number for the readdir() and stat() syscalls instead
2365 of returning the full 64-bit number.
2366 The default is to return 64-bit inode numbers.
2368 nfs.max_session_cb_slots=
2369 [NFSv4.1] Sets the maximum number of session
2370 slots the client will assign to the callback
2371 channel. This determines the maximum number of
2372 callbacks the client will process in parallel for
2373 a particular server.
2375 nfs.max_session_slots=
2376 [NFSv4.1] Sets the maximum number of session slots
2377 the client will attempt to negotiate with the server.
2378 This limits the number of simultaneous RPC requests
2379 that the client can send to the NFSv4.1 server.
2380 Note that there is little point in setting this
2381 value higher than the max_tcp_slot_table_limit.
2383 nfs.nfs4_disable_idmapping=
2384 [NFSv4] When set to the default of '1', this option
2385 ensures that both the RPC level authentication
2386 scheme and the NFS level operations agree to use
2387 numeric uids/gids if the mount is using the
2388 'sec=sys' security flavour. In effect it is
2389 disabling idmapping, which can make migration from
2390 legacy NFSv2/v3 systems to NFSv4 easier.
2391 Servers that do not support this mode of operation
2392 will be autodetected by the client, and it will fall
2393 back to using the idmapper.
2394 To turn off this behaviour, set the value to '0'.
2396 [NFS4] Specify an additional fixed unique ident-
2397 ification string that NFSv4 clients can insert into
2398 their nfs_client_id4 string. This is typically a
2399 UUID that is generated at system install time.
2401 nfs.send_implementation_id =
2402 [NFSv4.1] Send client implementation identification
2403 information in exchange_id requests.
2404 If zero, no implementation identification information
2406 The default is to send the implementation identification
2409 nfs.recover_lost_locks =
2410 [NFSv4] Attempt to recover locks that were lost due
2411 to a lease timeout on the server. Please note that
2412 doing this risks data corruption, since there are
2413 no guarantees that the file will remain unchanged
2414 after the locks are lost.
2415 If you want to enable the kernel legacy behaviour of
2416 attempting to recover these locks, then set this
2418 The default parameter value of '0' causes the kernel
2419 not to attempt recovery of lost locks.
2421 nfs4.layoutstats_timer =
2422 [NFSv4.2] Change the rate at which the kernel sends
2423 layoutstats to the pNFS metadata server.
2425 Setting this to value to 0 causes the kernel to use
2426 whatever value is the default set by the layout
2427 driver. A non-zero value sets the minimum interval
2428 in seconds between layoutstats transmissions.
2430 nfsd.nfs4_disable_idmapping=
2431 [NFSv4] When set to the default of '1', the NFSv4
2432 server will return only numeric uids and gids to
2433 clients using auth_sys, and will accept numeric uids
2434 and gids from such clients. This is intended to ease
2435 migration from NFSv2/v3.
2437 nmi_debug= [KNL,SH] Specify one or more actions to take
2438 when a NMI is triggered.
2439 Format: [state][,regs][,debounce][,die]
2441 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2442 Format: [panic,][nopanic,][num]
2444 0 - turn hardlockup detector in nmi_watchdog off
2445 1 - turn hardlockup detector in nmi_watchdog on
2446 When panic is specified, panic when an NMI watchdog
2447 timeout occurs (or 'nopanic' to override the opposite
2448 default). To disable both hard and soft lockup detectors,
2449 please see 'nowatchdog'.
2450 This is useful when you use a panic=... timeout and
2451 need the box quickly up again.
2453 netpoll.carrier_timeout=
2454 [NET] Specifies amount of time (in seconds) that
2455 netpoll should wait for a carrier. By default netpoll
2458 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2459 emulation library even if a 387 maths coprocessor
2463 [HW] Never suspend the console
2464 Disable suspending of consoles during suspend and
2465 hibernate operations. Once disabled, debugging
2466 messages can reach various consoles while the rest
2467 of the system is being put to sleep (ie, while
2468 debugging driver suspend/resume hooks). This may
2469 not work reliably with all consoles, but is known
2470 to work with serial and VGA consoles.
2471 To facilitate more flexible debugging, we also add
2472 console_suspend, a printk module parameter to control
2473 it. Users could use console_suspend (usually
2474 /sys/module/printk/parameters/console_suspend) to
2475 turn on/off it dynamically.
2477 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2478 caches in the slab allocator. Saves per-node memory,
2479 but will impact performance.
2483 noapic [SMP,APIC] Tells the kernel to not make use of any
2484 IOAPICs that may be present in the system.
2486 noautogroup Disable scheduler automatic task group creation.
2488 nobats [PPC] Do not use BATs for mapping kernel lowmem
2489 on "Classic" PPC cores.
2493 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2495 nodelayacct [KNL] Disable per-task delay accounting
2497 nodsp [SH] Disable hardware DSP at boot time.
2499 noefi Disable EFI runtime services support.
2504 On X86-32 available only on PAE configured kernels.
2505 noexec=on: enable non-executable mappings (default)
2506 noexec=off: disable non-executable mappings
2509 Disable SMAP (Supervisor Mode Access Prevention)
2510 even if it is supported by processor.
git.samba.org / sfrench / cifs-2.6.git / blob