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/joydev/joystick.rst
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] 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.
336 For X86-32, this can also be used to specify an APIC
338 Format: apic=driver_name
339 Examples: apic=bigsmp
341 apic_extnmi= [APIC,X86] External NMI delivery setting
342 Format: { bsp (default) | all | none }
343 bsp: External NMI is delivered only to CPU 0
344 all: External NMIs are broadcast to all CPUs as a
346 none: External NMI is masked for all CPUs. This is
347 useful so that a dump capture kernel won't be
351 See Documentation/networking/ipv6.txt.
353 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
354 Limit apic dumping. The parameter defines the maximal
355 number of local apics being dumped. Also it is possible
356 to set it to "all" by meaning -- no limit here.
357 Format: { 1 (default) | 2 | ... | all }.
358 The parameter valid if only apic=debug or
359 apic=verbose is specified.
360 Example: apic=debug show_lapic=all
362 apm= [APM] Advanced Power Management
363 See header of arch/x86/kernel/apm_32.c.
365 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
366 Format: <io>,<irq>,<nodeID>
370 atarimouse= [HW,MOUSE] Atari Mouse
372 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
373 EzKey and similar keyboards
375 atkbd.reset= [HW] Reset keyboard during initialization
377 atkbd.set= [HW] Select keyboard code set
378 Format: <int> (2 = AT (default), 3 = PS/2)
380 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
383 atkbd.softraw= [HW] Choose between synthetic and real raw mode
384 Format: <bool> (0 = real, 1 = synthetic (default))
386 atkbd.softrepeat= [HW]
387 Use software keyboard repeat
389 audit= [KNL] Enable the audit sub-system
390 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
391 0 - kernel audit is disabled and can not be enabled
392 until the next reboot
393 unset - kernel audit is initialized but disabled and
394 will be fully enabled by the userspace auditd.
395 1 - kernel audit is initialized and partially enabled,
396 storing at most audit_backlog_limit messages in
397 RAM until it is fully enabled by the userspace
401 audit_backlog_limit= [KNL] Set the audit queue size limit.
402 Format: <int> (must be >=0)
405 bau= [X86_UV] Enable the BAU on SGI UV. The default
406 behavior is to disable the BAU (i.e. bau=0).
407 Format: { "0" | "1" }
410 unset - Disable the BAU.
412 baycom_epp= [HW,AX25]
415 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
417 See header of drivers/net/hamradio/baycom_par.c.
419 baycom_ser_fdx= [HW,AX25]
420 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
421 Format: <io>,<irq>,<mode>[,<baud>]
422 See header of drivers/net/hamradio/baycom_ser_fdx.c.
424 baycom_ser_hdx= [HW,AX25]
425 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
426 Format: <io>,<irq>,<mode>
427 See header of drivers/net/hamradio/baycom_ser_hdx.c.
429 blkdevparts= Manual partition parsing of block device(s) for
430 embedded devices based on command line input.
431 See Documentation/block/cmdline-partition.txt
433 boot_delay= Milliseconds to delay each printk during boot.
434 Values larger than 10 seconds (10000) are changed to
438 bootmem_debug [KNL] Enable bootmem allocator debug messages.
441 Disable BERT OS support on buggy BIOSes.
443 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
444 bttv.radio= Most important insmod options are available as
446 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
449 bulk_remove=off [PPC] This parameter disables the use of the pSeries
450 firmware feature for flushing multiple hpte entries
453 c101= [NET] Moxa C101 synchronous serial card
455 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
456 Sometimes CPU hardware bugs make them report the cache
457 size incorrectly. The kernel will attempt work arounds
458 to fix known problems, but for some CPUs it is not
459 possible to determine what the correct size should be.
460 This option provides an override for these situations.
462 ca_keys= [KEYS] This parameter identifies a specific key(s) on
463 the system trusted keyring to be used for certificate
465 format: { id:<keyid> | builtin }
467 cca= [MIPS] Override the kernel pages' cache coherency
468 algorithm. Accepted values range from 0 to 7
469 inclusive. See arch/mips/include/asm/pgtable-bits.h
470 for platform specific values (SB1, Loongson3 and
473 ccw_timeout_log [S390]
474 See Documentation/s390/CommonIO for details.
476 cgroup_disable= [KNL] Disable a particular controller
477 Format: {name of the controller(s) to disable}
478 The effects of cgroup_disable=foo are:
479 - foo isn't auto-mounted if you mount all cgroups in
481 - foo isn't visible as an individually mountable
483 {Currently only "memory" controller deal with this and
484 cut the overhead, others just disable the usage. So
485 only cgroup_disable=memory is actually worthy}
487 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
488 Format: { controller[,controller...] | "all" }
489 Like cgroup_disable, but only applies to cgroup v1;
490 the blacklisted controllers remain available in cgroup2.
492 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
494 nosocket -- Disable socket memory accounting.
495 nokmem -- Disable kernel memory accounting.
497 checkreqprot [SELINUX] Set initial checkreqprot flag value.
498 Format: { "0" | "1" }
499 See security/selinux/Kconfig help text.
500 0 -- check protection applied by kernel (includes
501 any implied execute protection).
502 1 -- check protection requested by application.
503 Default value is set via a kernel config option.
504 Value can be changed at runtime via
505 /selinux/checkreqprot.
508 See Documentation/s390/CommonIO for details.
511 Prevents the clock framework from automatically gating
512 clocks that have not been explicitly enabled by a Linux
513 device driver but are enabled in hardware at reset or
514 by the bootloader/firmware. Note that this does not
515 force such clocks to be always-on nor does it reserve
516 those clocks in any way. This parameter is useful for
517 debug and development, but should not be needed on a
518 platform with proper driver support. For more
519 information, see Documentation/clk.txt.
521 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
523 Forces specified clocksource (if available) to be used
524 when calculating gettimeofday(). If specified
525 clocksource is not available, it defaults to PIT.
526 Format: { pit | tsc | cyclone | pmtmr }
528 clocksource= Override the default clocksource
530 Override the default clocksource and use the clocksource
531 with the name specified.
532 Some clocksource names to choose from, depending on
534 [all] jiffies (this is the base, fallback clocksource)
536 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
537 pxa_timer,timer3,32k_counter,timer0_1
538 [X86-32] pit,hpet,tsc;
539 scx200_hrt on Geode; cyclone on IBM x440
547 clocksource.arm_arch_timer.evtstrm=
550 Enable/disable the eventstream feature of the ARM
551 architected timer so that code using WFE-based polling
552 loops can be debugged more effectively on production
555 clearcpuid=BITNUM [X86]
556 Disable CPUID feature X for the kernel. See
557 arch/x86/include/asm/cpufeatures.h for the valid bit
558 numbers. Note the Linux specific bits are not necessarily
559 stable over kernel options, but the vendor specific
561 Also note that user programs calling CPUID directly
562 or using the feature without checking anything
563 will still see it. This just prevents it from
564 being used by the kernel or shown in /proc/cpuinfo.
565 Also note the kernel might malfunction if you disable
568 cma=nn[MG]@[start[MG][-end[MG]]]
570 Sets the size of kernel global memory area for
571 contiguous memory allocations and optionally the
572 placement constraint by the physical address range of
573 memory allocations. A value of 0 disables CMA
574 altogether. For more information, see
575 include/linux/dma-contiguous.h
577 cmo_free_hint= [PPC] Format: { yes | no }
578 Specify whether pages are marked as being inactive
579 when they are freed. This is used in CMO environments
580 to determine OS memory pressure for page stealing by
584 coherent_pool=nn[KMG] [ARM,KNL]
585 Sets the size of memory pool for coherent, atomic dma
586 allocations, by default set to 256K.
588 code_bytes [X86] How many bytes of object code to print
593 com20020= [HW,NET] ARCnet - COM20020 chipset
595 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
597 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
601 ARCnet - COM90xx chipset (memory-mapped buffers)
602 Format: <io>[,<irq>[,<memstart>]]
604 condev= [HW,S390] console device
607 console= [KNL] Output console device and options.
609 tty<n> Use the virtual console device <n>.
613 Use the specified serial port. The options are of
614 the form "bbbbpnf", where "bbbb" is the baud rate,
615 "p" is parity ("n", "o", or "e"), "n" is number of
616 bits, and "f" is flow control ("r" for RTS or
617 omit it). Default is "9600n8".
619 See Documentation/admin-guide/serial-console.rst for more
621 Documentation/networking/netconsole.txt for an
624 uart[8250],io,<addr>[,options]
625 uart[8250],mmio,<addr>[,options]
626 uart[8250],mmio16,<addr>[,options]
627 uart[8250],mmio32,<addr>[,options]
628 uart[8250],0x<addr>[,options]
629 Start an early, polled-mode console on the 8250/16550
630 UART at the specified I/O port or MMIO address,
631 switching to the matching ttyS device later.
632 MMIO inter-register address stride is either 8-bit
633 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
634 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
635 to be equivalent to 'mmio'. 'options' are specified in
636 the same format described for ttyS above; if unspecified,
637 the h/w is not re-initialized.
639 hvc<n> Use the hypervisor console device <n>. This is for
640 both Xen and PowerPC hypervisors.
642 If the device connected to the port is not a TTY but a braille
643 device, prepend "brl," before the device type, for instance
645 For now, only VisioBraille is supported.
647 consoleblank= [KNL] The console blank (screen saver) timeout in
648 seconds. A value of 0 disables the blank timer.
652 [KNL] Change the default value for
653 /proc/<pid>/coredump_filter.
654 See also Documentation/filesystems/proc.txt.
656 coresight_cpu_debug.enable
659 Enable/disable the CPU sampling based debugging.
660 0: default value, disable debugging
661 1: enable debugging at boot time
663 cpuidle.off=1 [CPU_IDLE]
664 disable the cpuidle sub-system
666 cpufreq.off=1 [CPU_FREQ]
667 disable the cpufreq sub-system
670 [X86] Delay for N microsec between assert and de-assert
671 of APIC INIT to start processors. This delay occurs
672 on every CPU online, such as boot, and resume from suspend.
675 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
677 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
679 crashkernel=size[KMG][@offset[KMG]]
680 [KNL] Using kexec, Linux can switch to a 'crash kernel'
681 upon panic. This parameter reserves the physical
682 memory region [offset, offset + size] for that kernel
683 image. If '@offset' is omitted, then a suitable offset
684 is selected automatically. Check
685 Documentation/kdump/kdump.txt for further details.
687 crashkernel=range1:size1[,range2:size2,...][@offset]
688 [KNL] Same as above, but depends on the memory
689 in the running system. The syntax of range is
690 start-[end] where start and end are both
691 a memory unit (amount[KMG]). See also
692 Documentation/kdump/kdump.txt for an example.
694 crashkernel=size[KMG],high
695 [KNL, x86_64] range could be above 4G. Allow kernel
696 to allocate physical memory region from top, so could
697 be above 4G if system have more than 4G ram installed.
698 Otherwise memory region will be allocated below 4G, if
700 It will be ignored if crashkernel=X is specified.
701 crashkernel=size[KMG],low
702 [KNL, x86_64] range under 4G. When crashkernel=X,high
703 is passed, kernel could allocate physical memory region
704 above 4G, that cause second kernel crash on system
705 that require some amount of low memory, e.g. swiotlb
706 requires at least 64M+32K low memory, also enough extra
707 low memory is needed to make sure DMA buffers for 32-bit
708 devices won't run out. Kernel would try to allocate at
709 at least 256M below 4G automatically.
710 This one let user to specify own low range under 4G
711 for second kernel instead.
712 0: to disable low allocation.
713 It will be ignored when crashkernel=X,high is not used
714 or memory reserved is below 4G.
716 crossrelease_fullstack
717 [KNL] Allow to record full stack trace in cross-release
720 [KNL] Disable crypto self-tests
725 cs89x0_media= [HW,NET]
726 Format: { rj45 | aui | bnc }
729 See header of drivers/s390/block/dasd_devmap.c.
731 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
732 (one device per port)
733 Format: <port#>,<type>
734 See also Documentation/input/devices/joystick-parport.rst
736 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
738 Documentation/admin-guide/dynamic-debug-howto.rst for
739 details. Deprecated, see dyndbg.
741 debug [KNL] Enable kernel debugging (events log level).
744 [KNL] verbose self-tests
746 Print debugging info while doing the locking API
748 We default to 0 (no extra messages), setting it to
749 1 will print _a lot_ more information - normally
750 only useful to kernel developers.
752 debug_objects [KNL] Enable object debugging
755 [KNL] Disable object debugging
757 debug_guardpage_minorder=
758 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
759 parameter allows control of the order of pages that will
760 be intentionally kept free (and hence protected) by the
761 buddy allocator. Bigger value increase the probability
762 of catching random memory corruption, but reduce the
763 amount of memory for normal system use. The maximum
764 possible value is MAX_ORDER/2. Setting this parameter
765 to 1 or 2 should be enough to identify most random
766 memory corruption problems caused by bugs in kernel or
767 driver code when a CPU writes to (or reads from) a
768 random memory location. Note that there exists a class
769 of memory corruptions problems caused by buggy H/W or
770 F/W or by drivers badly programing DMA (basically when
771 memory is written at bus level and the CPU MMU is
772 bypassed) which are not detectable by
773 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
774 tracking down these problems.
777 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
778 parameter enables the feature at boot time. In
779 default, it is disabled. We can avoid allocating huge
780 chunk of memory for debug pagealloc if we don't enable
781 it at boot time and the system will work mostly same
782 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
783 on: enable the feature
785 debugpat [X86] Enable PAT debugging
787 decnet.addr= [HW,NET]
788 Format: <area>[,<node>]
789 See also Documentation/networking/decnet.txt.
792 [same as hugepagesz=] The size of the default
793 HugeTLB page size. This is the size represented by
794 the legacy /proc/ hugepages APIs, used for SHM, and
795 default size when mounting hugetlbfs filesystems.
796 Defaults to the default architecture's huge page size
800 Set number of hash buckets for dentry cache.
802 disable_1tb_segments [PPC]
803 Disables the use of 1TB hash page table segments. This
804 causes the kernel to fall back to 256MB segments which
805 can be useful when debugging issues that require an SLB
809 See Documentation/networking/ipv6.txt.
812 Disable RADIX MMU mode on POWER9
814 disable_cpu_apicid= [X86,APIC,SMP]
816 The number of initial APIC ID for the
817 corresponding CPU to be disabled at boot,
818 mostly used for the kdump 2nd kernel to
819 disable BSP to wake up multiple CPUs without
820 causing system reset or hang due to sending
823 disable_ddw [PPC/PSERIES]
824 Disable Dynamic DMA Window support. Use this if
825 to workaround buggy firmware.
828 See Documentation/networking/ipv6.txt.
830 disable_mtrr_cleanup [X86]
831 The kernel tries to adjust MTRR layout from continuous
832 to discrete, to make X server driver able to add WB
833 entry later. This parameter disables that.
835 disable_mtrr_trim [X86, Intel and AMD only]
836 By default the kernel will trim any uncacheable
837 memory out of your available memory pool based on
838 MTRR settings. This parameter disables that behavior,
839 possibly causing your machine to run very slowly.
841 disable_timer_pin_1 [X86]
842 Disable PIN 1 of APIC timer
843 Can be useful to work around chipset bugs.
845 dis_ucode_ldr [X86] Disable the microcode loader.
847 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
848 this option disables the debugging code at boot.
850 dma_debug_entries=<number>
851 This option allows to tune the number of preallocated
852 entries for DMA-API debugging code. One entry is
853 required per DMA-API allocation. Use this if the
854 DMA-API debugging code disables itself because the
855 architectural default is too low.
857 dma_debug_driver=<driver_name>
858 With this option the DMA-API debugging driver
859 filter feature can be enabled at boot time. Just
860 pass the driver to filter for as the parameter.
861 The filter can be disabled or changed to another
862 driver later using sysfs.
864 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
865 Broken monitors, graphic adapters, KVMs and EDIDless
866 panels may send no or incorrect EDID data sets.
867 This parameter allows to specify an EDID data sets
868 in the /lib/firmware directory that are used instead.
869 Generic built-in EDID data sets are used, if one of
870 edid/1024x768.bin, edid/1280x1024.bin,
871 edid/1680x1050.bin, or edid/1920x1080.bin is given
872 and no file with the same name exists. Details and
873 instructions how to build your own EDID data are
874 available in Documentation/EDID/HOWTO.txt. An EDID
875 data set will only be used for a particular connector,
876 if its name and a colon are prepended to the EDID
877 name. Each connector may use a unique EDID data
878 set by separating the files with a comma. An EDID
879 data set with no connector name will be used for
880 any connectors not explicitly specified.
885 Format: {"off" | "known"}
886 Control how the dt_cpu_ftrs device-tree binding is
887 used for CPU feature discovery and setup (if it
889 off: Do not use it, fall back to legacy cpu table.
890 known: Do not pass through unknown features to guests
891 or userspace, only those that the kernel is aware of.
893 dump_apple_properties [X86]
894 Dump name and content of EFI device properties on
895 x86 Macs. Useful for driver authors to determine
896 what data is available or for reverse-engineering.
898 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
899 module.dyndbg[="val"]
900 Enable debug messages at boot time. See
901 Documentation/admin-guide/dynamic-debug-howto.rst
904 nompx [X86] Disables Intel Memory Protection Extensions.
905 See Documentation/x86/intel_mpx.txt for more
906 information about the feature.
908 nopku [X86] Disable Memory Protection Keys CPU feature found
911 module.async_probe [KNL]
912 Enable asynchronous probe on this module.
914 early_ioremap_debug [KNL]
915 Enable debug messages in early_ioremap support. This
916 is useful for tracking down temporary early mappings
917 which are not unmapped.
919 earlycon= [KNL] Output early console device and options.
921 When used with no options, the early console is
922 determined by the stdout-path property in device
925 cdns,<addr>[,options]
926 Start an early, polled-mode console on a Cadence
927 (xuartps) serial port at the specified address. Only
928 supported option is baud rate. If baud rate is not
929 specified, the serial port must already be setup and
932 uart[8250],io,<addr>[,options]
933 uart[8250],mmio,<addr>[,options]
934 uart[8250],mmio32,<addr>[,options]
935 uart[8250],mmio32be,<addr>[,options]
936 uart[8250],0x<addr>[,options]
937 Start an early, polled-mode console on the 8250/16550
938 UART at the specified I/O port or MMIO address.
939 MMIO inter-register address stride is either 8-bit
940 (mmio) or 32-bit (mmio32 or mmio32be).
941 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
942 to be equivalent to 'mmio'. 'options' are specified
943 in the same format described for "console=ttyS<n>"; if
944 unspecified, the h/w is not initialized.
948 Start an early, polled-mode console on a pl011 serial
949 port at the specified address. The pl011 serial port
950 must already be setup and configured. Options are not
951 yet supported. If 'mmio32' is specified, then only
952 the driver will use only 32-bit accessors to read/write
953 the device registers.
956 Start an early, polled-mode console on a meson serial
957 port at the specified address. The serial port must
958 already be setup and configured. Options are not yet
962 Start an early, polled-mode console on an msm serial
963 port at the specified address. The serial port
964 must already be setup and configured. Options are not
968 Start an early, polled-mode console on an msm serial
969 dm port at the specified address. The serial port
970 must already be setup and configured. Options are not
974 Start an early, polled-mode console on a serial port
975 of an Actions Semi SoC, such as S500 or S900, at the
976 specified address. The serial port must already be
977 setup and configured. Options are not yet supported.
979 smh Use ARM semihosting calls for early console.
987 Use early console provided by serial driver available
988 on Samsung SoCs, requires selecting proper type and
989 a correct base address of the selected UART port. The
990 serial port must already be setup and configured.
991 Options are not yet supported.
994 Start an early, polled-mode console on a lantiq serial
995 (lqasc) port at the specified address. The serial port
996 must already be setup and configured. Options are not
1001 Use early console provided by Freescale LP UART driver
1002 found on Freescale Vybrid and QorIQ LS1021A processors.
1003 A valid base address must be provided, and the serial
1004 port must already be setup and configured.
1007 Start an early, polled-mode console on the
1008 Armada 3700 serial port at the specified
1009 address. The serial port must already be setup
1010 and configured. Options are not yet supported.
1012 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1017 earlyprintk=serial[,ttySn[,baudrate]]
1018 earlyprintk=serial[,0x...[,baudrate]]
1019 earlyprintk=ttySn[,baudrate]
1020 earlyprintk=dbgp[debugController#]
1021 earlyprintk=pciserial,bus:device.function[,baudrate]
1022 earlyprintk=xdbc[xhciController#]
1024 earlyprintk is useful when the kernel crashes before
1025 the normal console is initialized. It is not enabled by
1026 default because it has some cosmetic problems.
1028 Append ",keep" to not disable it when the real console
1031 Only one of vga, efi, serial, or usb debug port can
1034 Currently only ttyS0 and ttyS1 may be specified by
1035 name. Other I/O ports may be explicitly specified
1036 on some architectures (x86 and arm at least) by
1037 replacing ttySn with an I/O port address, like this:
1038 earlyprintk=serial,0x1008,115200
1039 You can find the port for a given device in
1040 /proc/tty/driver/serial:
1041 2: uart:ST16650V2 port:00001008 irq:18 ...
1043 Interaction with the standard serial driver is not
1046 The VGA and EFI output is eventually overwritten by
1049 The xen output can only be used by Xen PV guests.
1051 The sclp output can only be used on s390.
1053 edac_report= [HW,EDAC] Control how to report EDAC event
1054 Format: {"on" | "off" | "force"}
1055 on: enable EDAC to report H/W event. May be overridden
1056 by other higher priority error reporting module.
1057 off: disable H/W event reporting through EDAC.
1058 force: enforce the use of EDAC to report H/W event.
1061 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1064 This is designed to be used in conjunction with
1065 the boot argument: earlyprintk=vga
1068 Format: {"off" | "on" | "skip[mbr]"}
1071 Format: { "old_map", "nochunk", "noruntime", "debug" }
1072 old_map [X86-64]: switch to the old ioremap-based EFI
1073 runtime services mapping. 32-bit still uses this one by
1075 nochunk: disable reading files in "chunks" in the EFI
1076 boot stub, as chunking can cause problems with some
1077 firmware implementations.
1078 noruntime : disable EFI runtime services support
1079 debug: enable misc debug output
1081 efi_no_storage_paranoia [EFI; X86]
1082 Using this parameter you can use more than 50% of
1083 your efi variable storage. Use this parameter only if
1084 you are really sure that your UEFI does sane gc and
1085 fulfills the spec otherwise your board may brick.
1087 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1088 Add arbitrary attribute to specific memory range by
1089 updating original EFI memory map.
1090 Region of memory which aa attribute is added to is
1092 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1093 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1094 attribute is added to range 0x100000000-0x180000000 and
1095 0x10a0000000-0x1120000000.
1097 Using this parameter you can do debugging of EFI memmap
1098 related feature. For example, you can do debugging of
1099 Address Range Mirroring feature even if your box
1102 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1103 that is to be dynamically loaded by Linux. If there are
1104 multiple variables with the same name but with different
1105 vendor GUIDs, all of them will be loaded. See
1106 Documentation/acpi/ssdt-overlays.txt for details.
1109 eisa_irq_edge= [PARISC,HW]
1110 See header of drivers/parisc/eisa.c.
1113 See comment before function elanfreq_setup() in
1114 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1117 Format: {"cfq" | "deadline" | "noop"}
1118 See Documentation/block/cfq-iosched.txt and
1119 Documentation/block/deadline-iosched.txt for details.
1121 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1122 Specifies physical address of start of kernel core
1123 image elf header and optionally the size. Generally
1124 kexec loader will pass this option to capture kernel.
1125 See Documentation/kdump/kdump.txt for details.
1127 enable_mtrr_cleanup [X86]
1128 The kernel tries to adjust MTRR layout from continuous
1129 to discrete, to make X server driver able to add WB
1130 entry later. This parameter enables that.
1132 enable_timer_pin_1 [X86]
1133 Enable PIN 1 of APIC timer
1134 Can be useful to work around chipset bugs
1135 (in particular on some ATI chipsets).
1136 The kernel tries to set a reasonable default.
1138 enforcing [SELINUX] Set initial enforcing status.
1140 See security/selinux/Kconfig help text.
1141 0 -- permissive (log only, no denials).
1142 1 -- enforcing (deny and log).
1144 Value can be changed at runtime via /selinux/enforce.
1147 Disable Error Record Serialization Table (ERST)
1150 ether= [HW,NET] Ethernet cards parameters
1151 This option is obsoleted by the "netdev=" option, which
1152 has equivalent usage. See its documentation for details.
1156 Permit 'security.evm' to be updated regardless of
1157 current integrity status.
1161 fail_make_request=[KNL]
1162 General fault injection mechanism.
1163 Format: <interval>,<probability>,<space>,<times>
1164 See also Documentation/fault-injection/.
1167 See Documentation/blockdev/floppy.txt.
1169 force_pal_cache_flush
1170 [IA-64] Avoid check_sal_cache_flush which may hang on
1171 buggy SAL_CACHE_FLUSH implementations. Using this
1172 parameter will force ia64_sal_cache_flush to call
1173 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1176 Forcefully enable Physical Address Extension (PAE).
1177 Many Pentium M systems disable PAE but may have a
1178 functionally usable PAE implementation.
1179 Warning: use of this parameter will taint the kernel
1180 and may cause unknown problems.
1183 [FTRACE] will set and start the specified tracer
1184 as early as possible in order to facilitate early
1187 ftrace_dump_on_oops[=orig_cpu]
1188 [FTRACE] will dump the trace buffers on oops.
1189 If no parameter is passed, ftrace will dump
1190 buffers of all CPUs, but if you pass orig_cpu, it will
1191 dump only the buffer of the CPU that triggered the
1194 ftrace_filter=[function-list]
1195 [FTRACE] Limit the functions traced by the function
1196 tracer at boot up. function-list is a comma separated
1197 list of functions. This list can be changed at run
1198 time by the set_ftrace_filter file in the debugfs
1201 ftrace_notrace=[function-list]
1202 [FTRACE] Do not trace the functions specified in
1203 function-list. This list can be changed at run time
1204 by the set_ftrace_notrace file in the debugfs
1207 ftrace_graph_filter=[function-list]
1208 [FTRACE] Limit the top level callers functions traced
1209 by the function graph tracer at boot up.
1210 function-list is a comma separated list of functions
1211 that can be changed at run time by the
1212 set_graph_function file in the debugfs tracing directory.
1214 ftrace_graph_notrace=[function-list]
1215 [FTRACE] Do not trace from the functions specified in
1216 function-list. This list is a comma separated list of
1217 functions that can be changed at run time by the
1218 set_graph_notrace file in the debugfs tracing directory.
1220 ftrace_graph_max_depth=<uint>
1221 [FTRACE] Used with the function graph tracer. This is
1222 the max depth it will trace into a function. This value
1223 can be changed at run time by the max_graph_depth file
1224 in the tracefs tracing directory. default: 0 (no limit)
1227 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1228 support via parallel port (up to 5 devices per port)
1229 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1230 See also Documentation/input/devices/joystick-parport.rst
1234 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1238 gcov_persist= [GCOV] When non-zero (default), profiling data for
1239 kernel modules is saved and remains accessible via
1240 debugfs, even when the module is unloaded/reloaded.
1241 When zero, profiling data is discarded and associated
1242 debugfs files are removed at module unload time.
1244 goldfish [X86] Enable the goldfish android emulator platform.
1245 Don't use this when you are not running on the
1248 gpt [EFI] Forces disk with valid GPT signature but
1249 invalid Protective MBR to be treated as GPT. If the
1250 primary GPT is corrupted, it enables the backup/alternate
1251 GPT to be used instead.
1253 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1254 the "Enable 0" bit of the configuration register.
1257 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1258 the "Enable 0" bit of the configuration register.
1261 grcan.select= [HW] Select which physical interface to use.
1264 grcan.txsize= [HW] Sets the size of the tx buffer.
1265 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1267 grcan.rxsize= [HW] Sets the size of the rx buffer.
1268 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1271 gpio-mockup.gpio_mockup_ranges
1272 [HW] Sets the ranges of gpiochip of for this device.
1273 Format: <start1>,<end1>,<start2>,<end2>...
1275 hardlockup_all_cpu_backtrace=
1276 [KNL] Should the hard-lockup detector generate
1277 backtraces on all cpus.
1280 hashdist= [KNL,NUMA] Large hashes allocated during boot
1281 are distributed across NUMA nodes. Defaults on
1282 for 64-bit NUMA, off otherwise.
1283 Format: 0 | 1 (for off | on)
1285 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1287 hd= [EIDE] (E)IDE hard drive subsystem geometry
1288 Format: <cyl>,<head>,<sect>
1291 Disable Hardware Error Source Table (HEST) support;
1292 corresponding firmware-first mode error processing
1293 logic will be disabled.
1295 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1296 size of <nn>. This works even on boxes that have no
1297 highmem otherwise. This also works to reduce highmem
1298 size on bigger boxes.
1300 highres= [KNL] Enable/disable high resolution timer mode.
1301 Valid parameters: "on", "off"
1305 See Documentation/isdn/README.HiSax.
1309 hpet= [X86-32,HPET] option to control HPET usage
1310 Format: { enable (default) | disable | force |
1312 disable: disable HPET and use PIT instead
1313 force: allow force enabled of undocumented chips (ICH4,
1315 verbose: show contents of HPET registers during setup
1317 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1318 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1320 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1321 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1322 On x86-64 and powerpc, this option can be specified
1323 multiple times interleaved with hugepages= to reserve
1324 huge pages of different sizes. Valid pages sizes on
1325 x86-64 are 2M (when the CPU supports "pse") and 1G
1326 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1328 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1329 terminal devices. Valid values: 0..8
1330 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1331 If specified, z/VM IUCV HVC accepts connections
1332 from listed z/VM user IDs only.
1334 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1335 hardware thread id mappings.
1336 Format: <cpu>:<hwthread>
1339 Do not unregister boot console at start. This is only
1340 useful for debugging when something happens in the window
1341 between unregistering the boot console and initializing
1344 i2c_bus= [HW] Override the default board specific I2C bus speed
1345 or register an additional I2C bus that is not
1346 registered from board initialization code.
1350 i8042.debug [HW] Toggle i8042 debug mode
1351 i8042.unmask_kbd_data
1352 [HW] Enable printing of interrupt data from the KBD port
1353 (disabled by default, and as a pre-condition
1354 requires that i8042.debug=1 be enabled)
1355 i8042.direct [HW] Put keyboard port into non-translated mode
1356 i8042.dumbkbd [HW] Pretend that controller can only read data from
1357 keyboard and cannot control its state
1358 (Don't attempt to blink the leds)
1359 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1360 i8042.nokbd [HW] Don't check/create keyboard port
1361 i8042.noloop [HW] Disable the AUX Loopback command while probing
1363 i8042.nomux [HW] Don't check presence of an active multiplexing
1365 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1367 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1368 i8042.reset [HW] Reset the controller during init, cleanup and
1369 suspend-to-ram transitions, only during s2r
1370 transitions, or never reset
1371 Format: { 1 | Y | y | 0 | N | n }
1372 1, Y, y: always reset controller
1373 0, N, n: don't ever reset controller
1374 Default: only on s2r transitions on x86; most other
1375 architectures force reset to be always executed
1376 i8042.unlock [HW] Unlock (ignore) the keylock
1377 i8042.kbdreset [HW] Reset device connected to KBD port
1381 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1382 indicates that the driver is running on unsupported
1384 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1385 does not match list of supported models.
1387 [HW] Report power status in /proc/i8k
1388 (disabled by default)
1389 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1392 i915.invert_brightness=
1393 [DRM] Invert the sense of the variable that is used to
1394 set the brightness of the panel backlight. Normally a
1395 brightness value of 0 indicates backlight switched off,
1396 and the maximum of the brightness value sets the backlight
1397 to maximum brightness. If this parameter is set to 0
1398 (default) and the machine requires it, or this parameter
1399 is set to 1, a brightness value of 0 sets the backlight
1400 to maximum brightness, and the maximum of the brightness
1401 value switches the backlight off.
1402 -1 -- never invert brightness
1403 0 -- machine default
1404 1 -- force brightness inversion
1407 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1409 ide-core.nodma= [HW] (E)IDE subsystem
1410 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1411 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1412 .cdrom .chs .ignore_cable are additional options
1413 See Documentation/ide/ide.txt.
1415 ide-generic.probe-mask= [HW] (E)IDE subsystem
1417 Probe mask for legacy ISA IDE ports. Depending on
1418 platform up to 6 ports are supported, enabled by
1419 setting corresponding bits in the mask to 1. The
1420 default value is 0x0, which has a special meaning.
1421 On systems that have PCI, it triggers scanning the
1422 PCI bus for the first and the second port, which
1423 are then probed. On systems without PCI the value
1424 of 0x0 enables probing the two first ports as if it
1427 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1428 Claim all unknown PCI IDE storage controllers.
1431 Format: idle=poll, idle=halt, idle=nomwait
1432 Poll forces a polling idle loop that can slightly
1433 improve the performance of waking up a idle CPU, but
1434 will use a lot of power and make the system run hot.
1436 idle=halt: Halt is forced to be used for CPU idle.
1437 In such case C2/C3 won't be used again.
1438 idle=nomwait: Disable mwait for CPU C-states
1440 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1441 Format: { strict | legacy | 2008 | relaxed }
1444 Choose which programs will be accepted for execution
1445 based on the IEEE 754 NaN encoding(s) supported by
1446 the FPU and the NaN encoding requested with the value
1447 of an ELF file header flag individually set by each
1448 binary. Hardware implementations are permitted to
1449 support either or both of the legacy and the 2008 NaN
1452 Available settings are as follows:
1453 strict accept binaries that request a NaN encoding
1454 supported by the FPU
1455 legacy only accept legacy-NaN binaries, if supported
1457 2008 only accept 2008-NaN binaries, if supported
1459 relaxed accept any binaries regardless of whether
1460 supported by the FPU
1462 The FPU emulator is always able to support both NaN
1463 encodings, so if no FPU hardware is present or it has
1464 been disabled with 'nofpu', then the settings of
1465 'legacy' and '2008' strap the emulator accordingly,
1466 'relaxed' straps the emulator for both legacy-NaN and
1467 2008-NaN, whereas 'strict' enables legacy-NaN only on
1468 legacy processors and both NaN encodings on MIPS32 or
1471 The setting for ABS.fmt/NEG.fmt instruction execution
1472 mode generally follows that for the NaN encoding,
1473 except where unsupported by hardware.
1475 ignore_loglevel [KNL]
1476 Ignore loglevel setting - this will print /all/
1477 kernel messages to the console. Useful for debugging.
1478 We also add it as printk module parameter, so users
1479 could change it dynamically, usually by
1480 /sys/module/printk/parameters/ignore_loglevel.
1483 Ignore RLIMIT_DATA setting for data mappings,
1484 print warning at first misuse. Can be changed via
1485 /sys/module/kernel/parameters/ignore_rlimit_data.
1487 ihash_entries= [KNL]
1488 Set number of hash buckets for inode cache.
1490 ima_appraise= [IMA] appraise integrity measurements
1491 Format: { "off" | "enforce" | "fix" | "log" }
1494 ima_appraise_tcb [IMA]
1495 The builtin appraise policy appraises all files
1498 ima_canonical_fmt [IMA]
1499 Use the canonical format for the binary runtime
1500 measurements, instead of host native format.
1503 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1507 The list of supported hash algorithms is defined
1508 in crypto/hash_info.h.
1511 The builtin policies to load during IMA setup.
1512 Format: "tcb | appraise_tcb | secure_boot"
1514 The "tcb" policy measures all programs exec'd, files
1515 mmap'd for exec, and all files opened with the read
1516 mode bit set by either the effective uid (euid=0) or
1519 The "appraise_tcb" policy appraises the integrity of
1520 all files owned by root. (This is the equivalent
1521 of ima_appraise_tcb.)
1523 The "secure_boot" policy appraises the integrity
1524 of files (eg. kexec kernel image, kernel modules,
1525 firmware, policy, etc) based on file signatures.
1527 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1528 Load a policy which meets the needs of the Trusted
1529 Computing Base. This means IMA will measure all
1530 programs exec'd, files mmap'd for exec, and all files
1531 opened for read by uid=0.
1534 Select one of defined IMA measurements template formats.
1535 Formats: { "ima" | "ima-ng" | "ima-sig" }
1539 [IMA] Define a custom template format.
1540 Format: { "field1|...|fieldN" }
1542 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1543 Format: <min_file_size>
1544 Set the minimal file size for using asynchronous hash.
1545 If left unspecified, ahash usage is disabled.
1547 ahash performance varies for different data sizes on
1548 different crypto accelerators. This option can be used
1549 to achieve the best performance for a particular HW.
1551 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1553 Set hashing buffer size. Default: 4k.
1555 ahash performance varies for different chunk sizes on
1556 different crypto accelerators. This option can be used
1557 to achieve best performance for particular HW.
1561 Run specified binary instead of /sbin/init as init
1564 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1565 for working out where the kernel is dying during
1568 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1569 initcall functions. Useful for debugging built-in
1570 modules and initcalls.
1572 initrd= [BOOT] Specify the location of the initial ramdisk
1574 init_pkru= [x86] Specify the default memory protection keys rights
1575 register contents for all processes. 0x55555554 by
1576 default (disallow access to all but pkey 0). Can
1577 override in debugfs after boot.
1579 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1582 int_pln_enable [x86] Enable power limit notification interrupt
1584 integrity_audit=[IMA]
1585 Format: { "0" | "1" }
1586 0 -- basic integrity auditing messages. (Default)
1587 1 -- additional integrity auditing messages.
1589 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1591 Enable intel iommu driver.
1593 Disable intel iommu driver.
1594 igfx_off [Default Off]
1595 By default, gfx is mapped as normal device. If a gfx
1596 device has a dedicated DMAR unit, the DMAR unit is
1597 bypassed by not enabling DMAR with this option. In
1598 this case, gfx device will use physical address for
1601 With this option iommu will not optimize to look
1602 for io virtual address below 32-bit forcing dual
1603 address cycle on pci bus for cards supporting greater
1604 than 32-bit addressing. The default is to look
1605 for translation below 32-bit and if not available
1606 then look in the higher range.
1607 strict [Default Off]
1608 With this option on every unmap_single operation will
1609 result in a hardware IOTLB flush operation as opposed
1610 to batching them for performance.
1611 sp_off [Default Off]
1612 By default, super page will be supported if Intel IOMMU
1613 has the capability. With this option, super page will
1615 ecs_off [Default Off]
1616 By default, extended context tables will be supported if
1617 the hardware advertises that it has support both for the
1618 extended tables themselves, and also PASID support. With
1619 this option set, extended tables will not be used even
1620 on hardware which claims to support them.
1621 tboot_noforce [Default Off]
1622 Do not force the Intel IOMMU enabled under tboot.
1623 By default, tboot will force Intel IOMMU on, which
1624 could harm performance of some high-throughput
1625 devices like 40GBit network cards, even if identity
1627 Note that using this option lowers the security
1628 provided by tboot because it makes the system
1629 vulnerable to DMA attacks.
1631 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1632 0 disables intel_idle and fall back on acpi_idle.
1633 1 to 9 specify maximum depth of C-state.
1637 Do not enable intel_pstate as the default
1638 scaling driver for the supported processors
1640 Use intel_pstate as a scaling driver, but configure it
1641 to work with generic cpufreq governors (instead of
1642 enabling its internal governor). This mode cannot be
1643 used along with the hardware-managed P-states (HWP)
1646 Enable intel_pstate on systems that prohibit it by default
1647 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1648 instead of acpi-cpufreq may disable platform features, such
1649 as thermal controls and power capping, that rely on ACPI
1650 P-States information being indicated to OSPM and therefore
1651 should be used with caution. This option does not work with
1652 processors that aren't supported by the intel_pstate driver
1653 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1655 Do not enable hardware P state control (HWP)
1658 Only load intel_pstate on systems which support
1659 hardware P state control (HWP) if available.
1661 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1662 Description Table, specifies preferred power management
1663 profile as "Enterprise Server" or "Performance Server",
1664 then this feature is turned on by default.
1666 Allow per-logical-CPU P-State performance control limits using
1667 cpufreq sysfs interface
1669 intremap= [X86-64, Intel-IOMMU]
1670 on enable Interrupt Remapping (default)
1671 off disable Interrupt Remapping
1672 nosid disable Source ID checking
1674 BIOS x2APIC opt-out request will be ignored
1675 nopost disable Interrupt Posting
1677 iomem= Disable strict checking of access to MMIO memory
1678 strict regions from userspace.
1693 nobypass [PPC/POWERNV]
1694 Disable IOMMU bypass, using IOMMU for PCI devices.
1697 [ARM64] Configure DMA to bypass the IOMMU by default.
1698 Format: { "0" | "1" }
1699 0 - Use IOMMU translation for DMA.
1700 1 - Bypass the IOMMU for DMA.
1701 unset - Use IOMMU translation for DMA.
1703 io7= [HW] IO7 for Marvel based alpha systems
1704 See comment before marvel_specify_io7 in
1705 arch/alpha/kernel/core_marvel.c.
1707 io_delay= [X86] I/O delay method
1709 Standard port 0x80 based delay
1711 Alternate port 0xed based delay (needed on some systems)
1713 Simple two microseconds delay
1718 See Documentation/filesystems/nfs/nfsroot.txt.
1720 irqaffinity= [SMP] Set the default irq affinity mask
1721 The argument is a cpu list, as described above.
1723 irqchip.gicv2_force_probe=
1726 Force the kernel to look for the second 4kB page
1727 of a GICv2 controller even if the memory range
1728 exposed by the device tree is too small.
1731 When an interrupt is not handled search all handlers
1732 for it. Intended to get systems with badly broken
1736 When an interrupt is not handled search all handlers
1737 for it. Also check all handlers each timer
1738 interrupt. Intended to get systems with badly broken
1742 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1744 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1745 [Deprecated - use cpusets instead]
1746 Format: [flag-list,]<cpu-list>
1748 Specify one or more CPUs to isolate from disturbances
1749 specified in the flag list (default: domain):
1752 Disable the tick when a single task runs.
1754 Isolate from the general SMP balancing and scheduling
1755 algorithms. Note that performing domain isolation this way
1756 is irreversible: it's not possible to bring back a CPU to
1757 the domains once isolated through isolcpus. It's strongly
1758 advised to use cpusets instead to disable scheduler load
1759 balancing through the "cpuset.sched_load_balance" file.
1760 It offers a much more flexible interface where CPUs can
1761 move in and out of an isolated set anytime.
1763 You can move a process onto or off an "isolated" CPU via
1764 the CPU affinity syscalls or cpuset.
1765 <cpu number> begins at 0 and the maximum value is
1766 "number of CPUs in system - 1".
1768 The format of <cpu-list> is described above.
1774 ivrs_ioapic [HW,X86_64]
1775 Provide an override to the IOAPIC-ID<->DEVICE-ID
1776 mapping provided in the IVRS ACPI table. For
1777 example, to map IOAPIC-ID decimal 10 to
1778 PCI device 00:14.0 write the parameter as:
1779 ivrs_ioapic[10]=00:14.0
1781 ivrs_hpet [HW,X86_64]
1782 Provide an override to the HPET-ID<->DEVICE-ID
1783 mapping provided in the IVRS ACPI table. For
1784 example, to map HPET-ID decimal 0 to
1785 PCI device 00:14.0 write the parameter as:
1786 ivrs_hpet[0]=00:14.0
1788 ivrs_acpihid [HW,X86_64]
1789 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1790 mapping provided in the IVRS ACPI table. For
1791 example, to map UART-HID:UID AMD0020:0 to
1792 PCI device 00:14.5 write the parameter as:
1793 ivrs_acpihid[00:14.5]=AMD0020:0
1795 js= [HW,JOY] Analog joystick
1796 See Documentation/input/joydev/joystick.rst.
1799 When CONFIG_RANDOMIZE_BASE is set, this disables
1800 kernel and module base offset ASLR (Address Space
1801 Layout Randomization).
1804 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1805 report on every invalid memory access. Without this
1806 parameter KASAN will print report only for the first
1811 kernelcore= [KNL,X86,IA-64,PPC]
1812 Format: nn[KMGTPE] | "mirror"
1814 specifies the amount of memory usable by the kernel
1815 for non-movable allocations. The requested amount is
1816 spread evenly throughout all nodes in the system. The
1817 remaining memory in each node is used for Movable
1818 pages. In the event, a node is too small to have both
1819 kernelcore and Movable pages, kernelcore pages will
1820 take priority and other nodes will have a larger number
1821 of Movable pages. The Movable zone is used for the
1822 allocation of pages that may be reclaimed or moved
1823 by the page migration subsystem. This means that
1824 HugeTLB pages may not be allocated from this zone.
1825 Note that allocations like PTEs-from-HighMem still
1826 use the HighMem zone if it exists, and the Normal
1827 zone if it does not.
1829 Instead of specifying the amount of memory (nn[KMGTPE]),
1830 you can specify "mirror" option. In case "mirror"
1831 option is specified, mirrored (reliable) memory is used
1832 for non-movable allocations and remaining memory is used
1833 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1834 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1837 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1838 Format: <Controller#>[,poll interval]
1839 The controller # is the number of the ehci usb debug
1840 port as it is probed via PCI. The poll interval is
1841 optional and is the number seconds in between
1842 each poll cycle to the debug port in case you need
1843 the functionality for interrupting the kernel with
1844 gdb or control-c on the dbgp connection. When
1845 not using this parameter you use sysrq-g to break into
1846 the kernel debugger.
1848 kgdboc= [KGDB,HW] kgdb over consoles.
1849 Requires a tty driver that supports console polling,
1850 or a supported polling keyboard driver (non-usb).
1851 Serial only format: <serial_device>[,baud]
1852 keyboard only format: kbd
1853 keyboard and serial format: kbd,<serial_device>[,baud]
1854 Optional Kernel mode setting:
1855 kms, kbd format: kms,kbd
1856 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1858 kgdbwait [KGDB] Stop kernel execution and enter the
1859 kernel debugger at the earliest opportunity.
1861 kmac= [MIPS] korina ethernet MAC address.
1862 Configure the RouterBoard 532 series on-chip
1863 Ethernet adapter MAC address.
1865 kmemleak= [KNL] Boot-time kmemleak enable/disable
1866 Valid arguments: on, off
1868 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1871 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1872 Default is 0 (don't ignore, but inject #GP)
1874 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1878 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1879 Default is 1 (enabled)
1881 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1883 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1885 kvm-arm.vgic_v3_group0_trap=
1886 [KVM,ARM] Trap guest accesses to GICv3 group-0
1889 kvm-arm.vgic_v3_group1_trap=
1890 [KVM,ARM] Trap guest accesses to GICv3 group-1
1893 kvm-arm.vgic_v3_common_trap=
1894 [KVM,ARM] Trap guest accesses to GICv3 common
1897 kvm-arm.vgic_v4_enable=
1898 [KVM,ARM] Allow use of GICv4 for direct injection of
1901 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1902 (virtualized MMU) support on capable Intel chips.
1903 Default is 1 (enabled)
1905 kvm-intel.emulate_invalid_guest_state=
1906 [KVM,Intel] Enable emulation of invalid guest states
1907 Default is 0 (disabled)
1909 kvm-intel.flexpriority=
1910 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1911 Default is 1 (enabled)
1914 [KVM,Intel] Enable VMX nesting (nVMX).
1915 Default is 0 (disabled)
1917 kvm-intel.unrestricted_guest=
1918 [KVM,Intel] Disable unrestricted guest feature
1919 (virtualized real and unpaged mode) on capable
1920 Intel chips. Default is 1 (enabled)
1922 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1923 feature (tagged TLBs) on capable Intel chips.
1924 Default is 1 (enabled)
1930 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1933 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1934 value for LAPIC timer one-shot implementation. Default
1935 back to the programmable timer unit in the LAPIC.
1937 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1940 libata.dma= [LIBATA] DMA control
1941 libata.dma=0 Disable all PATA and SATA DMA
1942 libata.dma=1 PATA and SATA Disk DMA only
1943 libata.dma=2 ATAPI (CDROM) DMA only
1944 libata.dma=4 Compact Flash DMA only
1945 Combinations also work, so libata.dma=3 enables DMA
1946 for disks and CDROMs, but not CFs.
1948 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1949 libata.ignore_hpa=0 keep BIOS limits (default)
1950 libata.ignore_hpa=1 ignore limits, using full disk
1952 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1956 libata.force= [LIBATA] Force configurations. The format is comma
1957 separated list of "[ID:]VAL" where ID is
1958 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1959 matching port, link or device. Basically, it matches
1960 the ATA ID string printed on console by libata. If
1961 the whole ID part is omitted, the last PORT and DEVICE
1962 values are used. If ID hasn't been specified yet, the
1963 configuration applies to all ports, links and devices.
1965 If only DEVICE is omitted, the parameter applies to
1966 the port and all links and devices behind it. DEVICE
1967 number of 0 either selects the first device or the
1968 first fan-out link behind PMP device. It does not
1969 select the host link. DEVICE number of 15 selects the
1970 host link and device attached to it.
1972 The VAL specifies the configuration to force. As long
1973 as there's no ambiguity shortcut notation is allowed.
1974 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1975 The following configurations can be forced.
1977 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1978 Any ID with matching PORT is used.
1980 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1982 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1983 udma[/][16,25,33,44,66,100,133] notation is also
1986 * [no]ncq: Turn on or off NCQ.
1988 * [no]ncqtrim: Turn off queued DSM TRIM.
1990 * nohrst, nosrst, norst: suppress hard, soft
1993 * rstonce: only attempt one reset during
1994 hot-unplug link recovery
1996 * dump_id: dump IDENTIFY data.
1998 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2000 * disable: Disable this device.
2002 If there are multiple matching configurations changing
2003 the same attribute, the last one is used.
2005 memblock=debug [KNL] Enable memblock debug messages.
2007 load_ramdisk= [RAM] List of ramdisks to load from floppy
2008 See Documentation/blockdev/ramdisk.txt.
2010 lockd.nlm_grace_period=P [NFS] Assign grace period.
2013 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2016 lockd.nlm_timeout=T [NFS] Assign timeout value.
2019 lockd.nlm_udpport=M [NFS] Assign UDP port.
2022 locktorture.nreaders_stress= [KNL]
2023 Set the number of locking read-acquisition kthreads.
2024 Defaults to being automatically set based on the
2025 number of online CPUs.
2027 locktorture.nwriters_stress= [KNL]
2028 Set the number of locking write-acquisition kthreads.
2030 locktorture.onoff_holdoff= [KNL]
2031 Set time (s) after boot for CPU-hotplug testing.
2033 locktorture.onoff_interval= [KNL]
2034 Set time (s) between CPU-hotplug operations, or
2035 zero to disable CPU-hotplug testing.
2037 locktorture.shuffle_interval= [KNL]
2038 Set task-shuffle interval (jiffies). Shuffling
2039 tasks allows some CPUs to go into dyntick-idle
2040 mode during the locktorture test.
2042 locktorture.shutdown_secs= [KNL]
2043 Set time (s) after boot system shutdown. This
2044 is useful for hands-off automated testing.
2046 locktorture.stat_interval= [KNL]
2047 Time (s) between statistics printk()s.
2049 locktorture.stutter= [KNL]
2050 Time (s) to stutter testing, for example,
2051 specifying five seconds causes the test to run for
2052 five seconds, wait for five seconds, and so on.
2053 This tests the locking primitive's ability to
2054 transition abruptly to and from idle.
2056 locktorture.torture_runnable= [BOOT]
2057 Start locktorture running at boot time.
2059 locktorture.torture_type= [KNL]
2060 Specify the locking implementation to test.
2062 locktorture.verbose= [KNL]
2063 Enable additional printk() statements.
2065 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2068 loglevel= All Kernel Messages with a loglevel smaller than the
2069 console loglevel will be printed to the console. It can
2070 also be changed with klogd or other programs. The
2071 loglevels are defined as follows:
2073 0 (KERN_EMERG) system is unusable
2074 1 (KERN_ALERT) action must be taken immediately
2075 2 (KERN_CRIT) critical conditions
2076 3 (KERN_ERR) error conditions
2077 4 (KERN_WARNING) warning conditions
2078 5 (KERN_NOTICE) normal but significant condition
2079 6 (KERN_INFO) informational
2080 7 (KERN_DEBUG) debug-level messages
2082 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2083 in bytes. n must be a power of two and greater
2084 than the minimal size. The minimal size is defined
2085 by LOG_BUF_SHIFT kernel config parameter. There is
2086 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2087 that allows to increase the default size depending on
2088 the number of CPUs. See init/Kconfig for more details.
2090 logo.nologo [FB] Disables display of the built-in Linux logo.
2091 This may be used to provide more screen space for
2092 kernel log messages and is useful when debugging
2093 kernel boot problems.
2095 lp=0 [LP] Specify parallel ports to use, e.g,
2096 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2097 lp=reset first parallel port). 'lp=0' disables the
2098 lp=auto printer driver. 'lp=reset' (which can be
2099 specified in addition to the ports) causes
2100 attached printers to be reset. Using
2101 lp=port1,port2,... specifies the parallel ports
2102 to associate lp devices with, starting with
2103 lp0. A port specification may be 'none' to skip
2104 that lp device, or a parport name such as
2105 'parport0'. Specifying 'lp=auto' instead of a
2106 port specification list means that device IDs
2107 from each port should be examined, to see if
2108 an IEEE 1284-compliant printer is attached; if
2109 so, the driver will manage that printer.
2110 See also header of drivers/char/lp.c.
2113 Sets loops_per_jiffy to given constant, thus avoiding
2114 time-consuming boot-time autodetection (up to 250 ms per
2115 CPU). 0 enables autodetection (default). To determine
2116 the correct value for your kernel, boot with normal
2117 autodetection and see what value is printed. Note that
2118 on SMP systems the preset will be applied to all CPUs,
2119 which is likely to cause problems if your CPUs need
2120 significantly divergent settings. An incorrect value
2121 will cause delays in the kernel to be wrong, leading to
2122 unpredictable I/O errors and other breakage. Although
2123 unlikely, in the extreme case this might damage your
2127 Format: <io>,<irq>,<dma>
2129 machvec= [IA-64] Force the use of a particular machine-vector
2130 (machvec) in a generic kernel.
2131 Example: machvec=hpzx1_swiotlb
2133 machtype= [Loongson] Share the same kernel image file between different
2135 Example: machtype=lemote-yeeloong-2f-7inch
2137 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2138 than or equal to this physical address is ignored.
2140 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2141 will bring up during bootup. maxcpus=n : n >= 0 limits
2142 the kernel to bring up 'n' processors. Surely after
2143 bootup you can bring up the other plugged cpu by executing
2144 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2145 only takes effect during system bootup.
2146 While n=0 is a special case, it is equivalent to "nosmp",
2147 which also disables the IO APIC.
2149 max_loop= [LOOP] The number of loop block devices that get
2150 (loop.max_loop) unconditionally pre-created at init time. The default
2151 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2152 of statically allocating a predefined number, loop
2153 devices can be requested on-demand with the
2154 /dev/loop-control interface.
2156 mce [X86-32] Machine Check Exception
2158 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2160 md= [HW] RAID subsystems devices and level
2161 See Documentation/admin-guide/md.rst.
2164 Format: <first>,<last>
2165 Specifies range of consoles to be captured by the MDA.
2167 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2168 Amount of memory to be used when the kernel is not able
2169 to see the whole system memory or for test.
2170 [X86] Work as limiting max address. Use together
2171 with memmap= to avoid physical address space collisions.
2172 Without memmap= PCI devices could be placed at addresses
2173 belonging to unused RAM.
2175 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2179 [KNL,SH] Allow user to override the default size for
2180 per-device physically contiguous DMA buffers.
2182 memhp_default_state=online/offline
2183 [KNL] Set the initial state for the memory hotplug
2184 onlining policy. If not specified, the default value is
2185 set according to the
2186 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2188 See Documentation/memory-hotplug.txt.
2190 memmap=exactmap [KNL,X86] Enable setting of an exact
2191 E820 memory map, as specified by the user.
2192 Such memmap=exactmap lines can be constructed based on
2193 BIOS output or other requirements. See the memmap=nn@ss
2196 memmap=nn[KMG]@ss[KMG]
2197 [KNL] Force usage of a specific region of memory.
2198 Region of memory to be used is from ss to ss+nn.
2199 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2200 which limits max address to nn[KMG].
2201 Multiple different regions can be specified,
2204 memmap=100M@2G,100M#3G,1G!1024G
2206 memmap=nn[KMG]#ss[KMG]
2207 [KNL,ACPI] Mark specific memory as ACPI data.
2208 Region of memory to be marked is from ss to ss+nn.
2210 memmap=nn[KMG]$ss[KMG]
2211 [KNL,ACPI] Mark specific memory as reserved.
2212 Region of memory to be reserved is from ss to ss+nn.
2213 Example: Exclude memory from 0x18690000-0x1869ffff
2214 memmap=64K$0x18690000
2216 memmap=0x10000$0x18690000
2217 Some bootloaders may need an escape character before '$',
2218 like Grub2, otherwise '$' and the following number
2221 memmap=nn[KMG]!ss[KMG]
2222 [KNL,X86] Mark specific memory as protected.
2223 Region of memory to be used, from ss to ss+nn.
2224 The memory region may be marked as e820 type 12 (0xc)
2225 and is NVDIMM or ADR memory.
2227 memory_corruption_check=0/1 [X86]
2228 Some BIOSes seem to corrupt the first 64k of
2229 memory when doing things like suspend/resume.
2230 Setting this option will scan the memory
2231 looking for corruption. Enabling this will
2232 both detect corruption and prevent the kernel
2233 from using the memory being corrupted.
2234 However, its intended as a diagnostic tool; if
2235 repeatable BIOS-originated corruption always
2236 affects the same memory, you can use memmap=
2237 to prevent the kernel from using that memory.
2239 memory_corruption_check_size=size [X86]
2240 By default it checks for corruption in the low
2241 64k, making this memory unavailable for normal
2242 use. Use this parameter to scan for
2243 corruption in more or less memory.
2245 memory_corruption_check_period=seconds [X86]
2246 By default it checks for corruption every 60
2247 seconds. Use this parameter to check at some
2248 other rate. 0 disables periodic checking.
2250 memtest= [KNL,X86,ARM] Enable memtest
2252 default : 0 <disable>
2253 Specifies the number of memtest passes to be
2254 performed. Each pass selects another test
2255 pattern from a given set of patterns. Memtest
2256 fills the memory with this pattern, validates
2257 memory contents and reserves bad memory
2258 regions that are detected.
2260 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2261 Valid arguments: on, off
2262 Default (depends on kernel configuration option):
2263 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2264 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2265 mem_encrypt=on: Activate SME
2266 mem_encrypt=off: Do not activate SME
2268 Refer to Documentation/x86/amd-memory-encryption.txt
2269 for details on when memory encryption can be activated.
2271 mem_sleep_default= [SUSPEND] Default system suspend mode:
2272 s2idle - Suspend-To-Idle
2273 shallow - Power-On Suspend or equivalent (if supported)
2274 deep - Suspend-To-RAM or equivalent (if supported)
2275 See Documentation/admin-guide/pm/sleep-states.rst.
2277 meye.*= [HW] Set MotionEye Camera parameters
2278 See Documentation/media/v4l-drivers/meye.rst.
2280 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2281 Multi-Function General Purpose Timers on AMD Geode
2284 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2285 the BIOS has incorrectly applied a workaround. TinyBIOS
2286 version 0.98 is known to be affected, 0.99 fixes the
2287 problem by letting the user disable the workaround.
2291 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2292 physical address is ignored.
2294 mini2440= [ARM,HW,KNL]
2295 Format:[0..2][b][c][t]
2297 MINI2440 configuration specification:
2298 0 - The attached screen is the 3.5" TFT
2299 1 - The attached screen is the 7" TFT
2300 2 - The VGA Shield is attached (1024x768)
2301 Leaving out the screen size parameter will not load
2302 the TFT driver, and the framebuffer will be left
2304 b - Enable backlight. The TFT backlight pin will be
2305 linked to the kernel VESA blanking code and a GPIO
2306 LED. This parameter is not necessary when using the
2308 c - Enable the s3c camera interface.
2309 t - Reserved for enabling touchscreen support. The
2310 touchscreen support is not enabled in the mainstream
2311 kernel as of 2.6.30, a preliminary port can be found
2312 in the "bleeding edge" mini2440 support kernel at
2313 http://repo.or.cz/w/linux-2.6/mini2440.git
2316 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2317 parameter allows control of the logging verbosity for
2318 the additional memory initialisation checks. A value
2319 of 0 disables mminit logging and a level of 4 will
2320 log everything. Information is printed at KERN_DEBUG
2321 so loglevel=8 may also need to be specified.
2324 [KNL] When CONFIG_MODULE_SIG is set, this means that
2325 modules without (valid) signatures will fail to load.
2326 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2327 is always true, so this option does nothing.
2329 module_blacklist= [KNL] Do not load a comma-separated list of
2330 modules. Useful for debugging problem modules.
2333 [MOUSE] Maximum time between finger touching and
2334 leaving touchpad surface for touch to be considered
2335 a tap and be reported as a left button click (for
2336 touchpads working in absolute mode only).
2338 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2339 reporting absolute coordinates, such as tablets
2340 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2341 reporting absolute coordinates, such as tablets
2343 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2344 is similar to kernelcore except it specifies the
2345 amount of memory used for migratable allocations.
2346 If both kernelcore and movablecore is specified,
2347 then kernelcore will be at *least* the specified
2348 value but may be more. If movablecore on its own
2349 is specified, the administrator must be careful
2350 that the amount of memory usable for all allocations
2353 movable_node [KNL] Boot-time switch to make hotplugable memory
2354 NUMA nodes to be movable. This means that the memory
2355 of such nodes will be usable only for movable
2356 allocations which rules out almost all kernel
2357 allocations. Use with caution!
2359 MTD_Partition= [MTD]
2360 Format: <name>,<region-number>,<size>,<offset>
2362 MTD_Region= [MTD] Format:
2363 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2366 See drivers/mtd/cmdlinepart.c.
2368 multitce=off [PPC] This parameter disables the use of the pSeries
2369 firmware feature for updating multiple TCE entries
2372 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2374 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2376 boundary - index of last SLC block on Flex-OneNAND.
2377 The remaining blocks are configured as MLC blocks.
2378 lock - Configure if Flex-OneNAND boundary should be locked.
2379 Once locked, the boundary cannot be changed.
2380 1 indicates lock status, 0 indicates unlock status.
2383 ARM/S3C2412 JIVE boot control
2385 See arch/arm/mach-s3c2412/mach-jive.c
2387 mtouchusb.raw_coordinates=
2388 [HW] Make the MicroTouch USB driver use raw coordinates
2389 ('y', default) or cooked coordinates ('n')
2391 mtrr_chunk_size=nn[KMG] [X86]
2392 used for mtrr cleanup. It is largest continuous chunk
2393 that could hold holes aka. UC entries.
2395 mtrr_gran_size=nn[KMG] [X86]
2396 Used for mtrr cleanup. It is granularity of mtrr block.
2398 Large value could prevent small alignment from
2401 mtrr_spare_reg_nr=n [X86]
2403 Range: 0,7 : spare reg number
2405 Used for mtrr cleanup. It is spare mtrr entries number.
2406 Set to 2 or more if your graphical card needs more.
2408 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2410 netdev= [NET] Network devices parameters
2411 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2412 Note that mem_start is often overloaded to mean
2413 something different and driver-specific.
2414 This usage is only documented in each driver source
2418 [NETFILTER] Enable connection tracking flow accounting
2419 0 to disable accounting
2420 1 to enable accounting
2423 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2424 See Documentation/filesystems/nfs/nfsroot.txt.
2426 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2427 See Documentation/filesystems/nfs/nfsroot.txt.
2429 nfsrootdebug [NFS] enable nfsroot debugging messages.
2430 See Documentation/filesystems/nfs/nfsroot.txt.
2432 nfs.callback_nr_threads=
2433 [NFSv4] set the total number of threads that the
2434 NFS client will assign to service NFSv4 callback
2437 nfs.callback_tcpport=
2438 [NFS] set the TCP port on which the NFSv4 callback
2439 channel should listen.
2442 [NFS] sets the pathname to the program which is used
2443 to update the NFS client cache entries.
2445 nfs.cache_getent_timeout=
2446 [NFS] sets the timeout after which an attempt to
2447 update a cache entry is deemed to have failed.
2449 nfs.idmap_cache_timeout=
2450 [NFS] set the maximum lifetime for idmapper cache
2454 [NFS] enable 64-bit inode numbers.
2455 If zero, the NFS client will fake up a 32-bit inode
2456 number for the readdir() and stat() syscalls instead
2457 of returning the full 64-bit number.
2458 The default is to return 64-bit inode numbers.
2460 nfs.max_session_cb_slots=
2461 [NFSv4.1] Sets the maximum number of session
2462 slots the client will assign to the callback
2463 channel. This determines the maximum number of
2464 callbacks the client will process in parallel for
2465 a particular server.
2467 nfs.max_session_slots=
2468 [NFSv4.1] Sets the maximum number of session slots
2469 the client will attempt to negotiate with the server.
2470 This limits the number of simultaneous RPC requests
2471 that the client can send to the NFSv4.1 server.
2472 Note that there is little point in setting this
2473 value higher than the max_tcp_slot_table_limit.
2475 nfs.nfs4_disable_idmapping=
2476 [NFSv4] When set to the default of '1', this option
2477 ensures that both the RPC level authentication
2478 scheme and the NFS level operations agree to use
2479 numeric uids/gids if the mount is using the
2480 'sec=sys' security flavour. In effect it is
2481 disabling idmapping, which can make migration from
2482 legacy NFSv2/v3 systems to NFSv4 easier.
2483 Servers that do not support this mode of operation
2484 will be autodetected by the client, and it will fall
2485 back to using the idmapper.
2486 To turn off this behaviour, set the value to '0'.
2488 [NFS4] Specify an additional fixed unique ident-
2489 ification string that NFSv4 clients can insert into
2490 their nfs_client_id4 string. This is typically a
2491 UUID that is generated at system install time.
2493 nfs.send_implementation_id =
2494 [NFSv4.1] Send client implementation identification
2495 information in exchange_id requests.
2496 If zero, no implementation identification information
2498 The default is to send the implementation identification
2501 nfs.recover_lost_locks =
2502 [NFSv4] Attempt to recover locks that were lost due
2503 to a lease timeout on the server. Please note that
2504 doing this risks data corruption, since there are
2505 no guarantees that the file will remain unchanged
2506 after the locks are lost.
2507 If you want to enable the kernel legacy behaviour of
2508 attempting to recover these locks, then set this
2510 The default parameter value of '0' causes the kernel
2511 not to attempt recovery of lost locks.
2513 nfs4.layoutstats_timer =
2514 [NFSv4.2] Change the rate at which the kernel sends
2515 layoutstats to the pNFS metadata server.
2517 Setting this to value to 0 causes the kernel to use
2518 whatever value is the default set by the layout
2519 driver. A non-zero value sets the minimum interval
2520 in seconds between layoutstats transmissions.
2522 nfsd.nfs4_disable_idmapping=
2523 [NFSv4] When set to the default of '1', the NFSv4
2524 server will return only numeric uids and gids to
2525 clients using auth_sys, and will accept numeric uids
2526 and gids from such clients. This is intended to ease
2527 migration from NFSv2/v3.
2529 nmi_debug= [KNL,SH] Specify one or more actions to take
2530 when a NMI is triggered.
2531 Format: [state][,regs][,debounce][,die]
2533 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2534 Format: [panic,][nopanic,][num]
2536 0 - turn hardlockup detector in nmi_watchdog off
2537 1 - turn hardlockup detector in nmi_watchdog on
2538 When panic is specified, panic when an NMI watchdog
2539 timeout occurs (or 'nopanic' to override the opposite
2540 default). To disable both hard and soft lockup detectors,
2541 please see 'nowatchdog'.
2542 This is useful when you use a panic=... timeout and
2543 need the box quickly up again.
2545 netpoll.carrier_timeout=
2546 [NET] Specifies amount of time (in seconds) that
2547 netpoll should wait for a carrier. By default netpoll
2550 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2551 emulation library even if a 387 maths coprocessor
2555 [HW] Never suspend the console
2556 Disable suspending of consoles during suspend and
2557 hibernate operations. Once disabled, debugging
2558 messages can reach various consoles while the rest
2559 of the system is being put to sleep (ie, while
2560 debugging driver suspend/resume hooks). This may
2561 not work reliably with all consoles, but is known
2562 to work with serial and VGA consoles.
2563 To facilitate more flexible debugging, we also add
2564 console_suspend, a printk module parameter to control
2565 it. Users could use console_suspend (usually
2566 /sys/module/printk/parameters/console_suspend) to
2567 turn on/off it dynamically.
2569 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2570 caches in the slab allocator. Saves per-node memory,
2571 but will impact performance.
2575 noaltinstr [S390] Disables alternative instructions patching
2576 (CPU alternatives feature).
2578 noapic [SMP,APIC] Tells the kernel to not make use of any
2579 IOAPICs that may be present in the system.
2581 noautogroup Disable scheduler automatic task group creation.
2583 nobats [PPC] Do not use BATs for mapping kernel lowmem
2584 on "Classic" PPC cores.
2588 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2590 nodelayacct [KNL] Disable per-task delay accounting
2592 nodsp [SH] Disable hardware DSP at boot time.
2594 noefi Disable EFI runtime services support.
2599 On X86-32 available only on PAE configured kernels.
2600 noexec=on: enable non-executable mappings (default)
2601 noexec=off: disable non-executable mappings
2604 Disable SMAP (Supervisor Mode Access Prevention)
2605 even if it is supported by processor.
2608 Disable SMEP (Supervisor Mode Execution Prevention)
2609 even if it is supported by processor.
2612 This affects only 32-bit executables.
2613 noexec32=on: enable non-executable mappings (default)
2614 read doesn't imply executable mappings
2615 noexec32=off: disable non-executable mappings
2616 read implies executable mappings
2618 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2620 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2621 register save and restore. The kernel will only save
2622 legacy floating-point registers on task switch.
2624 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2626 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2627 Equivalent to smt=1.
2629 noxsave [BUGS=X86] Disables x86 extended register state save
2630 and restore using xsave. The kernel will fallback to
2631 enabling legacy floating-point and sse state.
2633 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2634 register states. The kernel will fall back to use
2635 xsave to save the states. By using this parameter,
2636 performance of saving the states is degraded because
2637 xsave doesn't support modified optimization while
2638 xsaveopt supports it on xsaveopt enabled systems.
2640 noxsaves [X86] Disables xsaves and xrstors used in saving and
2641 restoring x86 extended register state in compacted
2642 form of xsave area. The kernel will fall back to use
2643 xsaveopt and xrstor to save and restore the states
2644 in standard form of xsave area. By using this
2645 parameter, xsave area per process might occupy more
2646 memory on xsaves enabled systems.
2648 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2649 wfi(ARM) instruction doesn't work correctly and not to
2650 use it. This is also useful when using JTAG debugger.
2652 no_file_caps Tells the kernel not to honor file capabilities. The
2653 only way then for a file to be executed with privilege
2654 is to be setuid root or executed by root.
2656 nohalt [IA-64] Tells the kernel not to use the power saving
2657 function PAL_HALT_LIGHT when idle. This increases
2658 power-consumption. On the positive side, it reduces
2659 interrupt wake-up latency, which may improve performance
2660 in certain environments such as networked servers or
2663 nohibernate [HIBERNATION] Disable hibernation and resume.
2665 nohz= [KNL] Boottime enable/disable dynamic ticks
2666 Valid arguments: on, off
2669 nohz_full= [KNL,BOOT,SMP,ISOL]
2670 The argument is a cpu list, as described above.
2671 In kernels built with CONFIG_NO_HZ_FULL=y, set
2672 the specified list of CPUs whose tick will be stopped
2673 whenever possible. The boot CPU will be forced outside
2674 the range to maintain the timekeeping. Any CPUs
2675 in this list will have their RCU callbacks offloaded,
2676 just as if they had also been called out in the
2677 rcu_nocbs= boot parameter.
2679 noiotrap [SH] Disables trapped I/O port accesses.
2681 noirqdebug [X86-32] Disables the code which attempts to detect and
2682 disable unhandled interrupt sources.
2684 no_timer_check [X86,APIC] Disables the code which tests for
2685 broken timer IRQ sources.
2687 noisapnp [ISAPNP] Disables ISA PnP code.
2689 noinitrd [RAM] Tells the kernel not to load any configured
2692 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2694 [Deprecated - use intremap=off]
2698 noinvpcid [X86] Disable the INVPCID cpu feature.
2700 nojitter [IA-64] Disables jitter checking for ITC timers.
2702 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2704 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2708 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2709 clock and use the default one.
2711 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2712 steal time is computed, but won't influence scheduler
2715 nopti [X86-64] Disable kernel page table isolation
2717 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2719 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2721 noltlbs [PPC] Do not use large page/tlb entries for kernel
2722 lowmem mapping on PPC40x and PPC8xx
2724 nomca [IA-64] Disable machine check abort handling
2726 nomce [X86-32] Disable Machine Check Exception
2728 nomfgpt [X86-32] Disable Multi-Function General Purpose
2729 Timer usage (for AMD Geode machines).
2731 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2732 shutdown the other cpus. Instead use the REBOOT_VECTOR
2735 nomodule Disable module load
2737 nopat [X86] Disable PAT (page attribute table extension of
2738 pagetables) support.
2740 nopcid [X86-64] Disable the PCID cpu feature.
2742 norandmaps Don't use address space randomization. Equivalent to
2743 echo 0 > /proc/sys/kernel/randomize_va_space
2745 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2747 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2748 with UP alternatives
2750 nordrand [X86] Disable kernel use of the RDRAND and
2751 RDSEED instructions even if they are supported
2752 by the processor. RDRAND and RDSEED are still
2753 available to user space applications.
2755 noresume [SWSUSP] Disables resume and restores original swap
2758 no-scroll [VGA] Disables scrollback.
2759 This is required for the Braillex ib80-piezo Braille
2760 reader made by F.H. Papenmeier (Germany).
2764 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2766 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2767 and disable the IO APIC. legacy for "maxcpus=0".
2769 nosoftlockup [KNL] Disable the soft-lockup detector.
2771 nosync [HW,M68K] Disables sync negotiation for all devices.
2773 notsc [BUGS=X86-32] Disable Time Stamp Counter
2775 nowatchdog [KNL] Disable both lockup detectors, i.e.
2776 soft-lockup and NMI watchdog (hard-lockup).
2780 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2782 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2783 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2784 Some features depend on CPU0. Known dependencies are:
2785 1. Resume from suspend/hibernate depends on CPU0.
2786 Suspend/hibernate will fail if CPU0 is offline and you
2787 need to online CPU0 before suspend/hibernate.
2788 2. PIC interrupts also depend on CPU0. CPU0 can't be
2789 removed if a PIC interrupt is detected.
2790 It's said poweroff/reboot may depend on CPU0 on some
2791 machines although I haven't seen such issues so far
2792 after CPU0 is offline on a few tested machines.
2793 If the dependencies are under your control, you can
2794 turn on cpu0_hotplug.
2796 nps_mtm_hs_ctr= [KNL,ARC]
2797 This parameter sets the maximum duration, in
2798 cycles, each HW thread of the CTOP can run
2799 without interruptions, before HW switches it.
2800 The actual maximum duration is 16 times this
2802 Format: integer between 1 and 255
2805 nptcg= [IA-64] Override max number of concurrent global TLB
2806 purges which is reported from either PAL_VM_SUMMARY or
2809 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2810 could support. nr_cpus=n : n >= 1 limits the kernel to
2811 support 'n' processors. It could be larger than the
2812 number of already plugged CPU during bootup, later in
2813 runtime you can physically add extra cpu until it reaches
2814 n. So during boot up some boot time memory for per-cpu
2815 variables need be pre-allocated for later physical cpu
2818 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2820 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2821 Allowed values are enable and disable
2823 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2824 'node', 'default' can be specified
2825 This can be set from sysctl after boot.
2826 See Documentation/sysctl/vm.txt for details.
2828 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2829 See Documentation/debugging-via-ohci1394.txt for more
2832 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2833 Rather than timing out after 20 ms if an EC
2834 command is not properly ACKed, override the length
2835 of the timeout. We have interrupts disabled while
2836 waiting for the ACK, so if this is set too high
2837 interrupts *may* be lost!
2839 omap_mux= [OMAP] Override bootloader pin multiplexing.
2840 Format: <mux_mode0.mode_name=value>...
2841 For example, to override I2C bus2:
2842 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2844 oprofile.timer= [HW]
2845 Use timer interrupt instead of performance counters
2847 oprofile.cpu_type= Force an oprofile cpu type
2848 This might be useful if you have an older oprofile
2849 userland or if you want common events.
2850 Format: { arch_perfmon }
2851 arch_perfmon: [X86] Force use of architectural
2852 perfmon on Intel CPUs instead of the
2853 CPU specific event set.
2854 timer: [X86] Force use of architectural NMI
2855 timer mode (see also oprofile.timer
2856 for generic hr timer mode)
2858 oops=panic Always panic on oopses. Default is to just kill the
2859 process, but there is a small probability of
2860 deadlocking the machine.
2861 This will also cause panics on machine check exceptions.
2862 Useful together with panic=30 to trigger a reboot.
2865 See Documentation/sound/oss/oss-parameters.txt
2867 page_owner= [KNL] Boot-time page_owner enabling option.
2868 Storage of the information about who allocated
2869 each page is disabled in default. With this switch,
2871 on: enable the feature
2873 page_poison= [KNL] Boot-time parameter changing the state of
2874 poisoning on the buddy allocator.
2875 off: turn off poisoning
2876 on: turn on poisoning
2878 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2879 timeout > 0: seconds before rebooting
2880 timeout = 0: wait forever
2881 timeout < 0: reboot immediately
2884 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2887 crash_kexec_post_notifiers
2888 Run kdump after running panic-notifiers and dumping
2889 kmsg. This only for the users who doubt kdump always
2890 succeeds in any situation.
2891 Note that this also increases risks of kdump failure,
2892 because some panic notifiers can make the crashed
2893 kernel more unstable.
2895 parkbd.port= [HW] Parallel port number the keyboard adapter is
2896 connected to, default is 0.
2898 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2899 0 for XT, 1 for AT (default is AT).
2902 parport= [HW,PPT] Specify parallel ports. 0 disables.
2903 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2904 Use 'auto' to force the driver to use any
2905 IRQ/DMA settings detected (the default is to
2906 ignore detected IRQ/DMA settings because of
2907 possible conflicts). You can specify the base
2908 address, IRQ, and DMA settings; IRQ and DMA
2909 should be numbers, or 'auto' (for using detected
2910 settings on that particular port), or 'nofifo'
2911 (to avoid using a FIFO even if it is detected).
2912 Parallel ports are assigned in the order they
2913 are specified on the command line, starting
2916 parport_init_mode= [HW,PPT]
2917 Configure VIA parallel port to operate in
2918 a specific mode. This is necessary on Pegasos
2919 computer where firmware has no options for setting
2920 up parallel port mode and sets it to spp.
2921 Currently this function knows 686a and 8231 chips.
2922 Format: [spp|ps2|epp|ecp|ecpepp]
2925 Halt all CPUs after the first oops has been printed for
2926 the specified number of seconds. This is to be used if
2927 your oopses keep scrolling off the screen.
2932 See header of drivers/block/paride/pcd.c.
2933 See also Documentation/blockdev/paride.txt.
2935 pci=option[,option...] [PCI] various PCI subsystem options:
2936 earlydump [X86] dump PCI config space before the kernel
2938 off [X86] don't probe for the PCI bus
2939 bios [X86-32] force use of PCI BIOS, don't access
2940 the hardware directly. Use this if your machine
2941 has a non-standard PCI host bridge.
2942 nobios [X86-32] disallow use of PCI BIOS, only direct
2943 hardware access methods are allowed. Use this
2944 if you experience crashes upon bootup and you
2945 suspect they are caused by the BIOS.
2946 conf1 [X86] Force use of PCI Configuration Access
2947 Mechanism 1 (config address in IO port 0xCF8,
2948 data in IO port 0xCFC, both 32-bit).
2949 conf2 [X86] Force use of PCI Configuration Access
2950 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2951 the function, IO port 0xCFA, also 8-bit, sets
2952 bus number. The config space is then accessed
2953 through ports 0xC000-0xCFFF).
2954 See http://wiki.osdev.org/PCI for more info
2955 on the configuration access mechanisms.
2956 noaer [PCIE] If the PCIEAER kernel config parameter is
2957 enabled, this kernel boot option can be used to
2958 disable the use of PCIE advanced error reporting.
2959 nodomains [PCI] Disable support for multiple PCI
2960 root domains (aka PCI segments, in ACPI-speak).
2961 nommconf [X86] Disable use of MMCONFIG for PCI
2963 check_enable_amd_mmconf [X86] check for and enable
2964 properly configured MMIO access to PCI
2965 config space on AMD family 10h CPU
2966 nomsi [MSI] If the PCI_MSI kernel config parameter is
2967 enabled, this kernel boot option can be used to
2968 disable the use of MSI interrupts system-wide.
2969 noioapicquirk [APIC] Disable all boot interrupt quirks.
2970 Safety option to keep boot IRQs enabled. This
2971 should never be necessary.
2972 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2973 primary IO-APIC for bridges that cannot disable
2974 boot IRQs. This fixes a source of spurious IRQs
2975 when the system masks IRQs.
2976 noioapicreroute [APIC] Disable workaround that uses the
2977 boot IRQ equivalent of an IRQ that connects to
2978 a chipset where boot IRQs cannot be disabled.
2979 The opposite of ioapicreroute.
2980 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2981 routing table. These calls are known to be buggy
2982 on several machines and they hang the machine
2983 when used, but on other computers it's the only
2984 way to get the interrupt routing table. Try
2985 this option if the kernel is unable to allocate
2986 IRQs or discover secondary PCI buses on your
2988 rom [X86] Assign address space to expansion ROMs.
2989 Use with caution as certain devices share
2990 address decoders between ROMs and other
2992 norom [X86] Do not assign address space to
2993 expansion ROMs that do not already have
2994 BIOS assigned address ranges.
2995 nobar [X86] Do not assign address space to the
2996 BARs that weren't assigned by the BIOS.
2997 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2998 assigned automatically to PCI devices. You can
2999 make the kernel exclude IRQs of your ISA cards
3001 pirqaddr=0xAAAAA [X86] Specify the physical address
3002 of the PIRQ table (normally generated
3003 by the BIOS) if it is outside the
3004 F0000h-100000h range.
3005 lastbus=N [X86] Scan all buses thru bus #N. Can be
3006 useful if the kernel is unable to find your
3007 secondary buses and you want to tell it
3008 explicitly which ones they are.
3009 assign-busses [X86] Always assign all PCI bus
3010 numbers ourselves, overriding
3011 whatever the firmware may have done.
3012 usepirqmask [X86] Honor the possible IRQ mask stored
3013 in the BIOS $PIR table. This is needed on
3014 some systems with broken BIOSes, notably
3015 some HP Pavilion N5400 and Omnibook XE3
3016 notebooks. This will have no effect if ACPI
3017 IRQ routing is enabled.
3018 noacpi [X86] Do not use ACPI for IRQ routing
3019 or for PCI scanning.
3020 use_crs [X86] Use PCI host bridge window information
3021 from ACPI. On BIOSes from 2008 or later, this
3022 is enabled by default. If you need to use this,
3023 please report a bug.
3024 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3025 If you need to use this, please report a bug.
3026 routeirq Do IRQ routing for all PCI devices.
3027 This is normally done in pci_enable_device(),
3028 so this option is a temporary workaround
3029 for broken drivers that don't call it.
3030 skip_isa_align [X86] do not align io start addr, so can
3031 handle more pci cards
3032 noearly [X86] Don't do any early type 1 scanning.
3033 This might help on some broken boards which
3034 machine check when some devices' config space
3035 is read. But various workarounds are disabled
3036 and some IOMMU drivers will not work.
3037 bfsort Sort PCI devices into breadth-first order.
3038 This sorting is done to get a device
3039 order compatible with older (<= 2.4) kernels.
3040 nobfsort Don't sort PCI devices into breadth-first order.
3041 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3042 tuning and use the BIOS-configured MPS defaults.
3043 pcie_bus_safe Set every device's MPS to the largest value
3044 supported by all devices below the root complex.
3045 pcie_bus_perf Set device MPS to the largest allowable MPS
3046 based on its parent bus. Also set MRRS (Max
3047 Read Request Size) to the largest supported
3048 value (no larger than the MPS that the device
3049 or bus can support) for best performance.
3050 pcie_bus_peer2peer Set every device's MPS to 128B, which
3051 every device is guaranteed to support. This
3052 configuration allows peer-to-peer DMA between
3053 any pair of devices, possibly at the cost of
3054 reduced performance. This also guarantees
3055 that hot-added devices will work.
3056 cbiosize=nn[KMG] The fixed amount of bus space which is
3057 reserved for the CardBus bridge's IO window.
3058 The default value is 256 bytes.
3059 cbmemsize=nn[KMG] The fixed amount of bus space which is
3060 reserved for the CardBus bridge's memory
3061 window. The default value is 64 megabytes.
3064 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3065 [<order of align>@]pci:<vendor>:<device>\
3066 [:<subvendor>:<subdevice>][; ...]
3067 Specifies alignment and device to reassign
3068 aligned memory resources.
3069 If <order of align> is not specified,
3070 PAGE_SIZE is used as alignment.
3071 PCI-PCI bridge can be specified, if resource
3072 windows need to be expanded.
3073 To specify the alignment for several
3074 instances of a device, the PCI vendor,
3075 device, subvendor, and subdevice may be
3076 specified, e.g., 4096@pci:8086:9c22:103c:198f
3077 ecrc= Enable/disable PCIe ECRC (transaction layer
3078 end-to-end CRC checking).
3079 bios: Use BIOS/firmware settings. This is the
3083 hpiosize=nn[KMG] The fixed amount of bus space which is
3084 reserved for hotplug bridge's IO window.
3085 Default size is 256 bytes.
3086 hpmemsize=nn[KMG] The fixed amount of bus space which is
3087 reserved for hotplug bridge's memory window.
3088 Default size is 2 megabytes.
3089 hpbussize=nn The minimum amount of additional bus numbers
3090 reserved for buses below a hotplug bridge.
3092 realloc= Enable/disable reallocating PCI bridge resources
3093 if allocations done by BIOS are too small to
3094 accommodate resources required by all child
3096 off: Turn realloc off
3098 realloc same as realloc=on
3099 noari do not use PCIe ARI.
3100 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3101 only look for one device below a PCIe downstream
3104 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3107 force Enable ASPM even on devices that claim not to support it.
3108 WARNING: Forcing ASPM on may cause system lockups.
3110 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3111 nomsi Do not use MSI for PCI Express Native Hotplug (this
3112 makes all PCIe ports use INTx for hotplug services).
3114 pcie_ports= [PCIE] PCIe ports handling:
3115 auto Ask the BIOS whether or not to use native PCIe services
3116 associated with PCIe ports (PME, hot-plug, AER). Use
3117 them only if that is allowed by the BIOS.
3118 native Use native PCIe services associated with PCIe ports
3120 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3123 pcie_port_pm= [PCIE] PCIe port power management handling:
3124 off Disable power management of all PCIe ports
3125 force Forcibly enable power management of all PCIe ports
3127 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3128 nomsi Do not use MSI for native PCIe PME signaling (this makes
3129 all PCIe root ports use INTx for all services).
3131 pcmv= [HW,PCMCIA] BadgePAD 4
3135 Keep all power-domains already enabled by bootloader on,
3136 even if no driver has claimed them. This is useful
3137 for debug and development, but should not be
3138 needed on a platform with proper driver support.
3141 See Documentation/blockdev/paride.txt.
3143 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3146 See arch/parisc/kernel/pdc_chassis.c
3148 percpu_alloc= Select which percpu first chunk allocator to use.
3149 Currently supported values are "embed" and "page".
3150 Archs may support subset or none of the selections.
3151 See comments in mm/percpu.c for details on each
3152 allocator. This parameter is primarily for debugging
3153 and performance comparison.
3156 See Documentation/blockdev/paride.txt.
3159 See Documentation/blockdev/paride.txt.
3161 pirq= [SMP,APIC] Manual mp-table setup
3162 See Documentation/x86/i386/IO-APIC.txt.
3164 plip= [PPT,NET] Parallel port network link
3165 Format: { parport<nr> | timid | 0 }
3166 See also Documentation/admin-guide/parport.rst.
3168 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3169 Override pmtimer IOPort with a hex value.
3173 Enable PNP debug messages (depends on the
3174 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3175 via /sys/module/pnp/parameters/debug. We always show
3176 current resource usage; turning this on also shows
3177 possible settings and some assignment information.
3183 { on | off | curr | res | no-curr | no-res }
3186 [ISAPNP] Exclude IRQs for the autoconfiguration
3189 [ISAPNP] Exclude DMAs for the autoconfiguration
3191 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3192 Ranges are in pairs (I/O port base and size).
3195 [ISAPNP] Exclude memory regions for the
3197 Ranges are in pairs (memory base and size).
3199 ports= [IP_VS_FTP] IPVS ftp helper module
3201 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3203 Format: <port>,<port>....
3205 powersave=off [PPC] This option disables power saving features.
3206 It specifically disables cpuidle and sets the
3207 platform machine description specific power_save
3208 function to NULL. On Idle the CPU just reduces
3211 ppc_strict_facility_enable
3212 [PPC] This option catches any kernel floating point,
3213 Altivec, VSX and SPE outside of regions specifically
3214 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3215 There is some performance impact when enabling this.
3219 Disable Hardware Transactional Memory
3221 print-fatal-signals=
3222 [KNL] debug: print fatal signals
3224 If enabled, warn about various signal handling
3225 related application anomalies: too many signals,
3226 too many POSIX.1 timers, fatal signals causing a
3229 If you hit the warning due to signal overflow,
3230 you might want to try "ulimit -i unlimited".
3234 printk.always_kmsg_dump=
3235 Trigger kmsg_dump for cases other than kernel oops or
3237 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3240 printk.devkmsg={on,off,ratelimit}
3241 Control writing to /dev/kmsg.
3242 on - unlimited logging to /dev/kmsg from userspace
3243 off - logging to /dev/kmsg disabled
3244 ratelimit - ratelimit the logging
3247 printk.time= Show timing data prefixed to each printk message line
3248 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3250 processor.max_cstate= [HW,ACPI]
3251 Limit processor to maximum C-state
3252 max_cstate=9 overrides any DMI blacklist limit.
3254 processor.nocst [HW,ACPI]
3255 Ignore the _CST method to determine C-states,
3256 instead using the legacy FADT method
3258 profile= [KNL] Enable kernel profiling via /proc/profile
3259 Format: [<profiletype>,]<number>
3260 Param: <profiletype>: "schedule", "sleep", or "kvm"
3261 [defaults to kernel profiling]
3262 Param: "schedule" - profile schedule points.
3263 Param: "sleep" - profile D-state sleeping (millisecs).
3264 Requires CONFIG_SCHEDSTATS
3265 Param: "kvm" - profile VM exits.
3266 Param: <number> - step/bucket size as a power of 2 for
3267 statistical time based profiling.
3269 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3271 See Documentation/blockdev/ramdisk.txt.
3273 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3274 probe for; one of (bare|imps|exps|lifebook|any).
3275 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3277 psmouse.resetafter= [HW,MOUSE]
3278 Try to reset the device after so many bad packets
3281 [HW,MOUSE] Set desired mouse resolution, in dpi.
3282 psmouse.smartscroll=
3283 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3284 0 = disabled, 1 = enabled (default).
3286 pstore.backend= Specify the name of the pstore backend to use
3289 See Documentation/blockdev/paride.txt.
3292 Control user/kernel address space isolation:
3295 auto - default setting
3298 [KNL] Number of legacy pty's. Overwrites compiled-in
3301 quiet [KNL] Disable most log messages
3306 See Documentation/admin-guide/md.rst.
3308 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3309 See Documentation/blockdev/ramdisk.txt.
3311 ras=option[,option,...] [KNL] RAS-specific options
3314 Disable the Correctable Errors Collector,
3315 see CONFIG_RAS_CEC help text.
3318 The argument is a cpu list, as described above.
3320 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3321 the specified list of CPUs to be no-callback CPUs.
3322 Invocation of these CPUs' RCU callbacks will
3323 be offloaded to "rcuox/N" kthreads created for
3324 that purpose, where "x" is "b" for RCU-bh, "p"
3325 for RCU-preempt, and "s" for RCU-sched, and "N"
3326 is the CPU number. This reduces OS jitter on the
3327 offloaded CPUs, which can be useful for HPC and
3328 real-time workloads. It can also improve energy
3329 efficiency for asymmetric multiprocessors.
3332 Rather than requiring that offloaded CPUs
3333 (specified by rcu_nocbs= above) explicitly
3334 awaken the corresponding "rcuoN" kthreads,
3335 make these kthreads poll for callbacks.
3336 This improves the real-time response for the
3337 offloaded CPUs by relieving them of the need to
3338 wake up the corresponding kthread, but degrades
3339 energy efficiency by requiring that the kthreads
3340 periodically wake up to do the polling.
3342 rcutree.blimit= [KNL]
3343 Set maximum number of finished RCU callbacks to
3344 process in one batch.
3346 rcutree.dump_tree= [KNL]
3347 Dump the structure of the rcu_node combining tree
3348 out at early boot. This is used for diagnostic
3349 purposes, to verify correct tree setup.
3351 rcutree.gp_cleanup_delay= [KNL]
3352 Set the number of jiffies to delay each step of
3353 RCU grace-period cleanup.
3355 rcutree.gp_init_delay= [KNL]
3356 Set the number of jiffies to delay each step of
3357 RCU grace-period initialization.
3359 rcutree.gp_preinit_delay= [KNL]
3360 Set the number of jiffies to delay each step of
3361 RCU grace-period pre-initialization, that is,
3362 the propagation of recent CPU-hotplug changes up
3363 the rcu_node combining tree.
3365 rcutree.rcu_fanout_exact= [KNL]
3366 Disable autobalancing of the rcu_node combining
3367 tree. This is used by rcutorture, and might
3368 possibly be useful for architectures having high
3369 cache-to-cache transfer latencies.
3371 rcutree.rcu_fanout_leaf= [KNL]
3372 Change the number of CPUs assigned to each
3373 leaf rcu_node structure. Useful for very
3374 large systems, which will choose the value 64,
3375 and for NUMA systems with large remote-access
3376 latencies, which will choose a value aligned
3377 with the appropriate hardware boundaries.
3379 rcutree.jiffies_till_sched_qs= [KNL]
3380 Set required age in jiffies for a
3381 given grace period before RCU starts
3382 soliciting quiescent-state help from
3383 rcu_note_context_switch().
3385 rcutree.jiffies_till_first_fqs= [KNL]
3386 Set delay from grace-period initialization to
3387 first attempt to force quiescent states.
3388 Units are jiffies, minimum value is zero,
3389 and maximum value is HZ.
3391 rcutree.jiffies_till_next_fqs= [KNL]
3392 Set delay between subsequent attempts to force
3393 quiescent states. Units are jiffies, minimum
3394 value is one, and maximum value is HZ.
3396 rcutree.kthread_prio= [KNL,BOOT]
3397 Set the SCHED_FIFO priority of the RCU per-CPU
3398 kthreads (rcuc/N). This value is also used for
3399 the priority of the RCU boost threads (rcub/N)
3400 and for the RCU grace-period kthreads (rcu_bh,
3401 rcu_preempt, and rcu_sched). If RCU_BOOST is
3402 set, valid values are 1-99 and the default is 1
3403 (the least-favored priority). Otherwise, when
3404 RCU_BOOST is not set, valid values are 0-99 and
3405 the default is zero (non-realtime operation).
3407 rcutree.rcu_nocb_leader_stride= [KNL]
3408 Set the number of NOCB kthread groups, which
3409 defaults to the square root of the number of
3410 CPUs. Larger numbers reduces the wakeup overhead
3411 on the per-CPU grace-period kthreads, but increases
3412 that same overhead on each group's leader.
3414 rcutree.qhimark= [KNL]
3415 Set threshold of queued RCU callbacks beyond which
3416 batch limiting is disabled.
3418 rcutree.qlowmark= [KNL]
3419 Set threshold of queued RCU callbacks below which
3420 batch limiting is re-enabled.
3422 rcutree.rcu_idle_gp_delay= [KNL]
3423 Set wakeup interval for idle CPUs that have
3424 RCU callbacks (RCU_FAST_NO_HZ=y).
3426 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3427 Set wakeup interval for idle CPUs that have
3428 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3429 Lazy RCU callbacks are those which RCU can
3430 prove do nothing more than free memory.
3432 rcutree.rcu_kick_kthreads= [KNL]
3433 Cause the grace-period kthread to get an extra
3434 wake_up() if it sleeps three times longer than
3435 it should at force-quiescent-state time.
3436 This wake_up() will be accompanied by a
3437 WARN_ONCE() splat and an ftrace_dump().
3439 rcuperf.gp_async= [KNL]
3440 Measure performance of asynchronous
3441 grace-period primitives such as call_rcu().
3443 rcuperf.gp_async_max= [KNL]
3444 Specify the maximum number of outstanding
3445 callbacks per writer thread. When a writer
3446 thread exceeds this limit, it invokes the
3447 corresponding flavor of rcu_barrier() to allow
3448 previously posted callbacks to drain.
3450 rcuperf.gp_exp= [KNL]
3451 Measure performance of expedited synchronous
3452 grace-period primitives.
3454 rcuperf.holdoff= [KNL]
3455 Set test-start holdoff period. The purpose of
3456 this parameter is to delay the start of the
3457 test until boot completes in order to avoid
3460 rcuperf.nreaders= [KNL]
3461 Set number of RCU readers. The value -1 selects
3462 N, where N is the number of CPUs. A value
3463 "n" less than -1 selects N-n+1, where N is again
3464 the number of CPUs. For example, -2 selects N
3465 (the number of CPUs), -3 selects N+1, and so on.
3466 A value of "n" less than or equal to -N selects
3469 rcuperf.nwriters= [KNL]
3470 Set number of RCU writers. The values operate
3471 the same as for rcuperf.nreaders.
3472 N, where N is the number of CPUs
3474 rcuperf.perf_runnable= [BOOT]
3475 Start rcuperf running at boot time.
3477 rcuperf.perf_type= [KNL]
3478 Specify the RCU implementation to test.
3480 rcuperf.shutdown= [KNL]
3481 Shut the system down after performance tests
3482 complete. This is useful for hands-off automated
3485 rcuperf.verbose= [KNL]
3486 Enable additional printk() statements.
3488 rcuperf.writer_holdoff= [KNL]
3489 Write-side holdoff between grace periods,
3490 in microseconds. The default of zero says
3493 rcutorture.cbflood_inter_holdoff= [KNL]
3494 Set holdoff time (jiffies) between successive
3495 callback-flood tests.
3497 rcutorture.cbflood_intra_holdoff= [KNL]
3498 Set holdoff time (jiffies) between successive
3499 bursts of callbacks within a given callback-flood
3502 rcutorture.cbflood_n_burst= [KNL]
3503 Set the number of bursts making up a given
3504 callback-flood test. Set this to zero to
3505 disable callback-flood testing.
3507 rcutorture.cbflood_n_per_burst= [KNL]
3508 Set the number of callbacks to be registered
3509 in a given burst of a callback-flood test.
3511 rcutorture.fqs_duration= [KNL]
3512 Set duration of force_quiescent_state bursts
3515 rcutorture.fqs_holdoff= [KNL]
3516 Set holdoff time within force_quiescent_state bursts
3519 rcutorture.fqs_stutter= [KNL]
3520 Set wait time between force_quiescent_state bursts
3523 rcutorture.gp_cond= [KNL]
3524 Use conditional/asynchronous update-side
3525 primitives, if available.
3527 rcutorture.gp_exp= [KNL]
3528 Use expedited update-side primitives, if available.
3530 rcutorture.gp_normal= [KNL]
3531 Use normal (non-expedited) asynchronous
3532 update-side primitives, if available.
3534 rcutorture.gp_sync= [KNL]
3535 Use normal (non-expedited) synchronous
3536 update-side primitives, if available. If all
3537 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3538 rcutorture.gp_normal=, and rcutorture.gp_sync=
3539 are zero, rcutorture acts as if is interpreted
3540 they are all non-zero.
3542 rcutorture.n_barrier_cbs= [KNL]
3543 Set callbacks/threads for rcu_barrier() testing.
3545 rcutorture.nfakewriters= [KNL]
3546 Set number of concurrent RCU writers. These just
3547 stress RCU, they don't participate in the actual
3548 test, hence the "fake".
3550 rcutorture.nreaders= [KNL]
3551 Set number of RCU readers. The value -1 selects
3552 N-1, where N is the number of CPUs. A value
3553 "n" less than -1 selects N-n-2, where N is again
3554 the number of CPUs. For example, -2 selects N
3555 (the number of CPUs), -3 selects N+1, and so on.
3557 rcutorture.object_debug= [KNL]
3558 Enable debug-object double-call_rcu() testing.
3560 rcutorture.onoff_holdoff= [KNL]
3561 Set time (s) after boot for CPU-hotplug testing.
3563 rcutorture.onoff_interval= [KNL]
3564 Set time (s) between CPU-hotplug operations, or
3565 zero to disable CPU-hotplug testing.
3567 rcutorture.shuffle_interval= [KNL]
3568 Set task-shuffle interval (s). Shuffling tasks
3569 allows some CPUs to go into dyntick-idle mode
3570 during the rcutorture test.
3572 rcutorture.shutdown_secs= [KNL]
3573 Set time (s) after boot system shutdown. This
3574 is useful for hands-off automated testing.
3576 rcutorture.stall_cpu= [KNL]
3577 Duration of CPU stall (s) to test RCU CPU stall
3578 warnings, zero to disable.
3580 rcutorture.stall_cpu_holdoff= [KNL]
3581 Time to wait (s) after boot before inducing stall.
3583 rcutorture.stall_cpu_irqsoff= [KNL]
3584 Disable interrupts while stalling if set.
3586 rcutorture.stat_interval= [KNL]
3587 Time (s) between statistics printk()s.
3589 rcutorture.stutter= [KNL]
3590 Time (s) to stutter testing, for example, specifying
3591 five seconds causes the test to run for five seconds,
3592 wait for five seconds, and so on. This tests RCU's
3593 ability to transition abruptly to and from idle.
3595 rcutorture.test_boost= [KNL]
3596 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3597 "Maybe" means test if the RCU implementation
3598 under test support RCU priority boosting.
3600 rcutorture.test_boost_duration= [KNL]
3601 Duration (s) of each individual boost test.
3603 rcutorture.test_boost_interval= [KNL]
3604 Interval (s) between each boost test.
3606 rcutorture.test_no_idle_hz= [KNL]
3607 Test RCU's dyntick-idle handling. See also the
3608 rcutorture.shuffle_interval parameter.
3610 rcutorture.torture_runnable= [BOOT]
3611 Start rcutorture running at boot time.
3613 rcutorture.torture_type= [KNL]
3614 Specify the RCU implementation to test.
3616 rcutorture.verbose= [KNL]
3617 Enable additional printk() statements.
3619 rcupdate.rcu_cpu_stall_suppress= [KNL]
3620 Suppress RCU CPU stall warning messages.
3622 rcupdate.rcu_cpu_stall_timeout= [KNL]
3623 Set timeout for RCU CPU stall warning messages.
3625 rcupdate.rcu_expedited= [KNL]
3626 Use expedited grace-period primitives, for
3627 example, synchronize_rcu_expedited() instead
3628 of synchronize_rcu(). This reduces latency,
3629 but can increase CPU utilization, degrade
3630 real-time latency, and degrade energy efficiency.
3631 No effect on CONFIG_TINY_RCU kernels.
3633 rcupdate.rcu_normal= [KNL]
3634 Use only normal grace-period primitives,
3635 for example, synchronize_rcu() instead of
3636 synchronize_rcu_expedited(). This improves
3637 real-time latency, CPU utilization, and
3638 energy efficiency, but can expose users to
3639 increased grace-period latency. This parameter
3640 overrides rcupdate.rcu_expedited. No effect on
3641 CONFIG_TINY_RCU kernels.
3643 rcupdate.rcu_normal_after_boot= [KNL]
3644 Once boot has completed (that is, after
3645 rcu_end_inkernel_boot() has been invoked), use
3646 only normal grace-period primitives. No effect
3647 on CONFIG_TINY_RCU kernels.
3649 rcupdate.rcu_task_stall_timeout= [KNL]
3650 Set timeout in jiffies for RCU task stall warning
3651 messages. Disable with a value less than or equal
3654 rcupdate.rcu_self_test= [KNL]
3655 Run the RCU early boot self tests
3657 rcupdate.rcu_self_test_bh= [KNL]
3658 Run the RCU bh early boot self tests
3660 rcupdate.rcu_self_test_sched= [KNL]
3661 Run the RCU sched early boot self tests
3665 Run specified binary instead of /init from the ramdisk,
3666 used for early userspace startup. See initrd.
3669 Turn on/off individual RDT features. List is:
3670 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, mba.
3671 E.g. to turn on cmt and turn off mba use:
3675 Format (x86 or x86_64):
3676 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3678 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3680 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3681 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3682 reboot_force is either force or not specified,
3683 reboot_cpu is s[mp]#### with #### being the processor
3684 to be used for rebooting.
3687 [KNL, SMP] Set scheduler's default relax_domain_level.
3688 See Documentation/cgroup-v1/cpusets.txt.
3690 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3692 reservetop= [X86-32]
3694 Reserves a hole at the top of the kernel virtual
3699 Set the amount of memory to reserve for BIOS at
3700 the bottom of the address space.
3702 reset_devices [KNL] Force drivers to reset the underlying device
3703 during initialization.
3706 Specify the partition device for software suspend
3708 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3710 resume_offset= [SWSUSP]
3711 Specify the offset from the beginning of the partition
3712 given by "resume=" at which the swap header is located,
3713 in <PAGE_SIZE> units (needed only for swap files).
3714 See Documentation/power/swsusp-and-swap-files.txt
3716 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3717 read the resume files
3719 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3720 Useful for devices that are detected asynchronously
3721 (e.g. USB and MMC devices).
3723 hibernate= [HIBERNATION]
3724 noresume Don't check if there's a hibernation image
3725 present during boot.
3726 nocompress Don't compress/decompress hibernation images.
3727 no Disable hibernation and resume.
3728 protect_image Turn on image protection during restoration
3729 (that will set all pages holding image data
3730 during restoration read-only).
3732 retain_initrd [RAM] Keep initrd memory after extraction
3734 rfkill.default_state=
3735 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3736 etc. communication is blocked by default.
3739 rfkill.master_switch_mode=
3740 0 The "airplane mode" button does nothing.
3741 1 The "airplane mode" button toggles between everything
3742 blocked and the previous configuration.
3743 2 The "airplane mode" button toggles between everything
3744 blocked and everything unblocked.
3746 rhash_entries= [KNL,NET]
3747 Set number of hash buckets for route cache
3750 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3753 ro [KNL] Mount root device read-only on boot
3756 on Mark read-only kernel memory as read-only (default).
3757 off Leave read-only kernel memory writable for debugging.
3760 Enable the uart passthrough on the designated usb port
3761 on Rockchip SoCs. When active, the signals of the
3762 debug-uart get routed to the D+ and D- pins of the usb
3763 port and the regular usb controller gets disabled.
3765 root= [KNL] Root filesystem
3766 See name_to_dev_t comment in init/do_mounts.c.
3768 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3769 mount the root filesystem
3771 rootflags= [KNL] Set root filesystem mount option string
3773 rootfstype= [KNL] Set root filesystem type
3775 rootwait [KNL] Wait (indefinitely) for root device to show up.
3776 Useful for devices that are detected asynchronously
3777 (e.g. USB and MMC devices).
3779 rproc_mem=nn[KMG][@address]
3780 [KNL,ARM,CMA] Remoteproc physical memory block.
3781 Memory area to be used by remote processor image,
3784 rw [KNL] Mount root device read-write on boot
3786 S [KNL] Run init in single mode
3788 s390_iommu= [HW,S390]
3789 Set s390 IOTLB flushing mode
3791 With strict flushing every unmap operation will result in
3792 an IOTLB flush. Default is lazy flushing before reuse,
3796 See drivers/net/irda/sa1100_ir.c.
3798 sbni= [NET] Granch SBNI12 leased line adapter
3800 sched_debug [KNL] Enables verbose scheduler debug messages.
3802 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3803 Allowed values are enable and disable. This feature
3804 incurs a small amount of overhead in the scheduler
3805 but is useful for debugging and performance tuning.
3807 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3808 xtime_lock contention on larger systems, and/or RCU lock
3809 contention on all systems with CONFIG_MAXSMP set.
3810 Format: { "0" | "1" }
3811 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3813 Note: increases power consumption, thus should only be
3814 enabled if running jitter sensitive (HPC/RT) workloads.
3816 security= [SECURITY] Choose a security module to enable at boot.
3817 If this boot parameter is not specified, only the first
3818 security module asking for security registration will be
3819 loaded. An invalid security module name will be treated
3820 as if no module has been chosen.
3822 selinux= [SELINUX] Disable or enable SELinux at boot time.
3823 Format: { "0" | "1" }
3824 See security/selinux/Kconfig help text.
3827 Default value is set via kernel config option.
3828 If enabled at boot time, /selinux/disable can be used
3829 later to disable prior to initial policy load.
3831 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3832 Format: { "0" | "1" }
3833 See security/apparmor/Kconfig help text
3836 Default value is set via kernel config option.
3838 serialnumber [BUGS=X86-32]
3841 Maximal number of shapers.
3849 Disable merging of slabs with similar size. May be
3850 necessary if there is some reason to distinguish
3851 allocs to different slabs, especially in hardened
3852 environments where the risk of heap overflows and
3853 layout control by attackers can usually be
3854 frustrated by disabling merging. This will reduce
3855 most of the exposure of a heap attack to a single
3856 cache (risks via metadata attacks are mostly
3857 unchanged). Debug options disable merging on their
3859 For more information see Documentation/vm/slub.txt.
3861 slab_max_order= [MM, SLAB]
3862 Determines the maximum allowed order for slabs.
3863 A high setting may cause OOMs due to memory
3864 fragmentation. Defaults to 1 for systems with
3865 more than 32MB of RAM, 0 otherwise.
3867 slub_debug[=options[,slabs]] [MM, SLUB]
3868 Enabling slub_debug allows one to determine the
3869 culprit if slab objects become corrupted. Enabling
3870 slub_debug can create guard zones around objects and
3871 may poison objects when not in use. Also tracks the
3872 last alloc / free. For more information see
3873 Documentation/vm/slub.txt.
3875 slub_memcg_sysfs= [MM, SLUB]
3876 Determines whether to enable sysfs directories for
3877 memory cgroup sub-caches. 1 to enable, 0 to disable.
3878 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
3879 Enabling this can lead to a very high number of debug
3880 directories and files being created under
3883 slub_max_order= [MM, SLUB]
3884 Determines the maximum allowed order for slabs.
3885 A high setting may cause OOMs due to memory
3886 fragmentation. For more information see
3887 Documentation/vm/slub.txt.
3889 slub_min_objects= [MM, SLUB]
3890 The minimum number of objects per slab. SLUB will
3891 increase the slab order up to slub_max_order to
3892 generate a sufficiently large slab able to contain
3893 the number of objects indicated. The higher the number
3894 of objects the smaller the overhead of tracking slabs
3895 and the less frequently locks need to be acquired.
3896 For more information see Documentation/vm/slub.txt.
3898 slub_min_order= [MM, SLUB]
3899 Determines the minimum page order for slabs. Must be
3900 lower than slub_max_order.
3901 For more information see Documentation/vm/slub.txt.
3903 slub_nomerge [MM, SLUB]
3904 Same with slab_nomerge. This is supported for legacy.
3905 See slab_nomerge for more information.
3908 Format: <io1>[,<io2>[,...,<io8>]]
3910 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3911 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3912 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3913 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3914 smsc-ircc2.ircc_irq= [HW] IRQ line
3915 smsc-ircc2.ircc_dma= [HW] DMA channel
3916 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3917 0: Toshiba Satellite 1800 (GP data pin select)
3918 1: Fast pin select (default)
3921 smt [KNL,S390] Set the maximum number of threads (logical
3922 CPUs) to use per physical CPU on systems capable of
3923 symmetric multithreading (SMT). Will be capped to the
3924 actual hardware limit.
3926 Default: -1 (no limit)
3929 [KNL] Should the soft-lockup detector generate panics.
3932 A nonzero value instructs the soft-lockup detector
3933 to panic the machine when a soft-lockup occurs. This
3934 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
3935 which is the respective build-time switch to that
3938 softlockup_all_cpu_backtrace=
3939 [KNL] Should the soft-lockup detector generate
3940 backtraces on all cpus.
3943 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3944 See Documentation/laptops/sonypi.txt
3946 spia_io_base= [HW,MTD]
3951 srcutree.counter_wrap_check [KNL]
3952 Specifies how frequently to check for
3953 grace-period sequence counter wrap for the
3954 srcu_data structure's ->srcu_gp_seq_needed field.
3955 The greater the number of bits set in this kernel
3956 parameter, the less frequently counter wrap will
3957 be checked for. Note that the bottom two bits
3960 srcutree.exp_holdoff [KNL]
3961 Specifies how many nanoseconds must elapse
3962 since the end of the last SRCU grace period for
3963 a given srcu_struct until the next normal SRCU
3964 grace period will be considered for automatic
3965 expediting. Set to zero to disable automatic
3968 stack_guard_gap= [MM]
3969 override the default stack gap protection. The value
3970 is in page units and it defines how many pages prior
3971 to (for stacks growing down) resp. after (for stacks
3972 growing up) the main stack are reserved for no other
3973 mapping. Default value is 256 pages.
3976 Enabled the stack tracer on boot up.
3978 stacktrace_filter=[function-list]
3979 [FTRACE] Limit the functions that the stack tracer
3980 will trace at boot up. function-list is a comma separated
3981 list of functions. This list can be changed at run
3982 time by the stack_trace_filter file in the debugfs
3983 tracing directory. Note, this enables stack tracing
3984 and the stacktrace above is not needed.
3988 Set the STI (builtin display/keyboard on the HP-PARISC
3989 machines) console (graphic card) which should be used
3990 as the initial boot-console.
3991 See also comment in drivers/video/console/sticore.c.
3994 See comment in drivers/video/console/sticore.c.
3997 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3999 sunrpc.min_resvport=
4000 sunrpc.max_resvport=
4002 SunRPC servers often require that client requests
4003 originate from a privileged port (i.e. a port in the
4004 range 0 < portnr < 1024).
4005 An administrator who wishes to reserve some of these
4006 ports for other uses may adjust the range that the
4007 kernel's sunrpc client considers to be privileged
4008 using these two parameters to set the minimum and
4009 maximum port values.
4011 sunrpc.svc_rpc_per_connection_limit=
4013 Limit the number of requests that the server will
4014 process in parallel from a single connection.
4015 The default value is 0 (no limit).
4019 Control how the NFS server code allocates CPUs to
4020 service thread pools. Depending on how many NICs
4021 you have and where their interrupts are bound, this
4022 option will affect which CPUs will do NFS serving.
4023 Note: this parameter cannot be changed while the
4024 NFS server is running.
4026 auto the server chooses an appropriate mode
4027 automatically using heuristics
4028 global a single global pool contains all CPUs
4029 percpu one pool for each CPU
4030 pernode one pool for each NUMA node (equivalent
4031 to global on non-NUMA machines)
4033 sunrpc.tcp_slot_table_entries=
4034 sunrpc.udp_slot_table_entries=
4036 Sets the upper limit on the number of simultaneous
4037 RPC calls that can be sent from the client to a
4038 server. Increasing these values may allow you to
4039 improve throughput, but will also increase the
4040 amount of memory reserved for use by the client.
4042 suspend.pm_test_delay=
4044 Sets the number of seconds to remain in a suspend test
4045 mode before resuming the system (see
4046 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4047 is set. Default value is 5.
4050 [KNL] Enable accounting of swap in memory resource
4051 controller if no parameter or 1 is given or disable
4052 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4054 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4055 Format: { <int> | force | noforce }
4056 <int> -- Number of I/O TLB slabs
4057 force -- force using of bounce buffers even if they
4058 wouldn't be automatically used by the kernel
4059 noforce -- Never use bounce buffers (for debugging)
4063 sysfs.deprecated=0|1 [KNL]
4064 Enable/disable old style sysfs layout for old udev
4065 on older distributions. When this option is enabled
4066 very new udev will not work anymore. When this option
4067 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4068 in older udev will not work anymore.
4069 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4070 the kernel configuration.
4072 sysrq_always_enabled
4074 Ignore sysrq setting - this boot parameter will
4075 neutralize any effect of /proc/sys/kernel/sysrq.
4076 Useful for debugging.
4078 tcpmhash_entries= [KNL,NET]
4079 Set the number of tcp_metrics_hash slots.
4080 Default value is 8192 or 16384 depending on total
4081 ram pages. This is used to specify the TCP metrics
4082 cache size. See Documentation/networking/ip-sysctl.txt
4083 "tcp_no_metrics_save" section for more details.
4087 test_suspend= [SUSPEND][,N]
4088 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4089 standby suspend) or "freeze" (for suspend type freeze)
4090 as the system sleep state during system startup with
4091 the optional capability to repeat N number of times.
4092 The system is woken from this state using a
4093 wakeup-capable RTC alarm.
4095 thash_entries= [KNL,NET]
4096 Set number of hash buckets for TCP connection
4098 thermal.act= [HW,ACPI]
4099 -1: disable all active trip points in all thermal zones
4100 <degrees C>: override all lowest active trip points
4102 thermal.crt= [HW,ACPI]
4103 -1: disable all critical trip points in all thermal zones
4104 <degrees C>: override all critical trip points
4106 thermal.nocrt= [HW,ACPI]
4107 Set to disable actions on ACPI thermal zone
4108 critical and hot trip points.
4110 thermal.off= [HW,ACPI]
4111 1: disable ACPI thermal control
4113 thermal.psv= [HW,ACPI]
4114 -1: disable all passive trip points
4115 <degrees C>: override all passive trip points to this
4118 thermal.tzp= [HW,ACPI]
4119 Specify global default ACPI thermal zone polling rate
4120 <deci-seconds>: poll all this frequency
4121 0: no polling (default)
4124 Force threading of all interrupt handlers except those
4125 marked explicitly IRQF_NO_THREAD.
4128 Enable the Transcendent memory driver if built-in.
4130 tmem.cleancache=0|1 [KNL, XEN]
4131 Default is on (1). Disable the usage of the cleancache
4132 API to send anonymous pages to the hypervisor.
4134 tmem.frontswap=0|1 [KNL, XEN]
4135 Default is on (1). Disable the usage of the frontswap
4136 API to send swap pages to the hypervisor. If disabled
4137 the selfballooning and selfshrinking are force disabled.
4139 tmem.selfballooning=0|1 [KNL, XEN]
4140 Default is on (1). Disable the driving of swap pages
4143 tmem.selfshrinking=0|1 [KNL, XEN]
4144 Default is on (1). Partial swapoff that immediately
4145 transfers pages from Xen hypervisor back to the
4146 kernel based on different criteria.
4150 Specify if the kernel should make use of the cpu
4151 topology information if the hardware supports this.
4152 The scheduler will make use of this information and
4153 e.g. base its process migration decisions on it.
4156 topology_updates= [KNL, PPC, NUMA]
4158 Specify if the kernel should ignore (off)
4159 topology updates sent by the hypervisor to this
4164 tpm_suspend_pcr=[HW,TPM]
4165 Format: integer pcr id
4166 Specify that at suspend time, the tpm driver
4167 should extend the specified pcr with zeros,
4168 as a workaround for some chips which fail to
4169 flush the last written pcr on TPM_SaveState.
4170 This will guarantee that all the other pcrs
4173 trace_buf_size=nn[KMG]
4174 [FTRACE] will set tracing buffer size on each cpu.
4176 trace_event=[event-list]
4177 [FTRACE] Set and start specified trace events in order
4178 to facilitate early boot debugging. The event-list is a
4179 comma separated list of trace events to enable. See
4180 also Documentation/trace/events.txt
4182 trace_options=[option-list]
4183 [FTRACE] Enable or disable tracer options at boot.
4184 The option-list is a comma delimited list of options
4185 that can be enabled or disabled just as if you were
4186 to echo the option name into
4188 /sys/kernel/debug/tracing/trace_options
4190 For example, to enable stacktrace option (to dump the
4191 stack trace of each event), add to the command line:
4193 trace_options=stacktrace
4195 See also Documentation/trace/ftrace.txt "trace options"
4199 Have the tracepoints sent to printk as well as the
4200 tracing ring buffer. This is useful for early boot up
4201 where the system hangs or reboots and does not give the
4202 option for reading the tracing buffer or performing a
4203 ftrace_dump_on_oops.
4205 To turn off having tracepoints sent to printk,
4206 echo 0 > /proc/sys/kernel/tracepoint_printk
4207 Note, echoing 1 into this file without the
4208 tracepoint_printk kernel cmdline option has no effect.
4212 Having tracepoints sent to printk() and activating high
4213 frequency tracepoints such as irq or sched, can cause
4214 the system to live lock.
4217 [FTRACE] enable this option to disable tracing when a
4218 warning is hit. This turns off "tracing_on". Tracing can
4219 be enabled again by echoing '1' into the "tracing_on"
4220 file located in /sys/kernel/debug/tracing/
4222 This option is useful, as it disables the trace before
4223 the WARNING dump is called, which prevents the trace to
4224 be filled with content caused by the warning output.
4226 This option can also be set at run time via the sysctl
4227 option: kernel/traceoff_on_warning
4229 transparent_hugepage=
4231 Format: [always|madvise|never]
4232 Can be used to control the default behavior of the system
4233 with respect to transparent hugepages.
4234 See Documentation/vm/transhuge.txt for more details.
4236 tsc= Disable clocksource stability checks for TSC.
4238 [x86] reliable: mark tsc clocksource as reliable, this
4239 disables clocksource verification at runtime, as well
4240 as the stability checks done at bootup. Used to enable
4241 high-resolution timer mode on older hardware, and in
4242 virtualized environment.
4243 [x86] noirqtime: Do not use TSC to do irq accounting.
4244 Used to run time disable IRQ_TIME_ACCOUNTING on any
4245 platforms where RDTSC is slow and this accounting
4247 [x86] unstable: mark the TSC clocksource as unstable, this
4248 marks the TSC unconditionally unstable at bootup and
4249 avoids any further wobbles once the TSC watchdog notices.
4251 turbografx.map[2|3]= [HW,JOY]
4252 TurboGraFX parallel port interface
4254 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4255 See also Documentation/input/devices/joystick-parport.rst
4257 udbg-immortal [PPC] When debugging early kernel crashes that
4258 happen after console_init() and before a proper
4259 console driver takes over, this boot options might
4260 help "seeing" what's going on.
4262 uhash_entries= [KNL,NET]
4263 Set number of hash buckets for UDP/UDP-Lite connections
4266 [USB] Ignore overcurrent events (default N).
4267 Some badly-designed motherboards generate lots of
4268 bogus events, for ports that aren't wired to
4269 anything. Set this parameter to avoid log spamming.
4270 Note that genuine overcurrent events won't be
4274 [X86] Cause panic on unknown NMI.
4276 usbcore.authorized_default=
4277 [USB] Default USB device authorization:
4278 (default -1 = authorized except for wireless USB,
4279 0 = not authorized, 1 = authorized)
4281 usbcore.autosuspend=
4282 [USB] The autosuspend time delay (in seconds) used
4283 for newly-detected USB devices (default 2). This
4284 is the time required before an idle device will be
4285 autosuspended. Devices for which the delay is set
4286 to a negative value won't be autosuspended at all.
4288 usbcore.usbfs_snoop=
4289 [USB] Set to log all usbfs traffic (default 0 = off).
4291 usbcore.usbfs_snoop_max=
4292 [USB] Maximum number of bytes to snoop in each URB
4295 usbcore.blinkenlights=
4296 [USB] Set to cycle leds on hubs (default 0 = off).
4298 usbcore.old_scheme_first=
4299 [USB] Start with the old device initialization
4300 scheme (default 0 = off).
4302 usbcore.usbfs_memory_mb=
4303 [USB] Memory limit (in MB) for buffers allocated by
4304 usbfs (default = 16, 0 = max = 2047).
4306 usbcore.use_both_schemes=
4307 [USB] Try the other device initialization scheme
4308 if the first one fails (default 1 = enabled).
4310 usbcore.initial_descriptor_timeout=
4311 [USB] Specifies timeout for the initial 64-byte
4312 USB_REQ_GET_DESCRIPTOR request in milliseconds
4313 (default 5000 = 5.0 seconds).
4315 usbcore.nousb [USB] Disable the USB subsystem
4318 [USBHID] The interval which mice are to be polled at.
4321 [USBHID] The interval which joysticks are to be polled at.
4323 usb-storage.delay_use=
4324 [UMS] The delay in seconds before a new device is
4325 scanned for Logical Units (default 1).
4328 [UMS] A list of quirks entries to supplement or
4329 override the built-in unusual_devs list. List
4330 entries are separated by commas. Each entry has
4331 the form VID:PID:Flags where VID and PID are Vendor
4332 and Product ID values (4-digit hex numbers) and
4333 Flags is a set of characters, each corresponding
4334 to a common usb-storage quirk flag as follows:
4335 a = SANE_SENSE (collect more than 18 bytes
4337 b = BAD_SENSE (don't collect more than 18
4338 bytes of sense data);
4339 c = FIX_CAPACITY (decrease the reported
4340 device capacity by one sector);
4341 d = NO_READ_DISC_INFO (don't use
4342 READ_DISC_INFO command);
4343 e = NO_READ_CAPACITY_16 (don't use
4344 READ_CAPACITY_16 command);
4345 f = NO_REPORT_OPCODES (don't use report opcodes
4347 g = MAX_SECTORS_240 (don't transfer more than
4348 240 sectors at a time, uas only);
4349 h = CAPACITY_HEURISTICS (decrease the
4350 reported device capacity by one
4351 sector if the number is odd);
4352 i = IGNORE_DEVICE (don't bind to this
4354 j = NO_REPORT_LUNS (don't use report luns
4356 l = NOT_LOCKABLE (don't try to lock and
4357 unlock ejectable media);
4358 m = MAX_SECTORS_64 (don't transfer more
4359 than 64 sectors = 32 KB at a time);
4360 n = INITIAL_READ10 (force a retry of the
4361 initial READ(10) command);
4362 o = CAPACITY_OK (accept the capacity
4363 reported by the device);
4364 p = WRITE_CACHE (the device cache is ON
4366 r = IGNORE_RESIDUE (the device reports
4367 bogus residue values);
4368 s = SINGLE_LUN (the device has only one
4370 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4371 commands, uas only);
4372 u = IGNORE_UAS (don't bind to the uas driver);
4373 w = NO_WP_DETECT (don't test whether the
4374 medium is write-protected).
4375 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4376 even if the device claims no cache)
4377 Example: quirks=0419:aaf5:rl,0421:0433:rc
4379 user_debug= [KNL,ARM]
4381 See arch/arm/Kconfig.debug help text.
4382 1 - undefined instruction events
4384 4 - invalid data aborts
4387 Example: user_debug=31
4390 [X86] Flags controlling user PTE allocations.
4392 nohigh = do not allocate PTE pages in
4393 HIGHMEM regardless of setting
4397 On X86_32, this is an alias for vdso32=. Otherwise:
4399 vdso=1: enable VDSO (the default)
4400 vdso=0: disable VDSO mapping
4402 vdso32= [X86] Control the 32-bit vDSO
4403 vdso32=1: enable 32-bit VDSO
4404 vdso32=0 or vdso32=2: disable 32-bit VDSO
4406 See the help text for CONFIG_COMPAT_VDSO for more
4407 details. If CONFIG_COMPAT_VDSO is set, the default is
4408 vdso32=0; otherwise, the default is vdso32=1.
4410 For compatibility with older kernels, vdso32=2 is an
4413 Try vdso32=0 if you encounter an error that says:
4414 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4417 vector=percpu: enable percpu vector domain
4419 video= [FB] Frame buffer configuration
4420 See Documentation/fb/modedb.txt.
4422 video.brightness_switch_enabled= [0,1]
4423 If set to 1, on receiving an ACPI notify event
4424 generated by hotkey, video driver will adjust brightness
4425 level and then send out the event to user space through
4426 the allocated input device; If set to 0, video driver
4427 will only send out the event without touching backlight
4432 [VMMIO] Memory mapped virtio (platform) device.
4434 <size>@<baseaddr>:<irq>[:<id>]
4436 <size> := size (can use standard suffixes
4438 <baseaddr> := physical base address
4439 <irq> := interrupt number (as passed to
4441 <id> := (optional) platform device id
4443 virtio_mmio.device=1K@0x100b0000:48:7
4445 Can be used multiple times for multiple devices.
4447 vga= [BOOT,X86-32] Select a particular video mode
4448 See Documentation/x86/boot.txt and
4449 Documentation/svga.txt.
4450 Use vga=ask for menu.
4451 This is actually a boot loader parameter; the value is
4452 passed to the kernel using a special protocol.
4454 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4455 size of <nn>. This can be used to increase the
4456 minimum size (128MB on x86). It can also be used to
4457 decrease the size and leave more room for directly
4460 vmcp_cma=nn[MG] [KNL,S390]
4461 Sets the memory size reserved for contiguous memory
4462 allocations for the vmcp device driver.
4464 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4467 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4470 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4474 Controls the behavior of vsyscalls (i.e. calls to
4475 fixed addresses of 0xffffffffff600x00 from legacy
4476 code). Most statically-linked binaries and older
4477 versions of glibc use these calls. Because these
4478 functions are at fixed addresses, they make nice
4479 targets for exploits that can control RIP.
4481 emulate [default] Vsyscalls turn into traps and are
4482 emulated reasonably safely.
4484 native Vsyscalls are native syscall instructions.
4485 This is a little bit faster than trapping
4486 and makes a few dynamic recompilers work
4487 better than they would in emulation mode.
4488 It also makes exploits much easier to write.
4490 none Vsyscalls don't work at all. This makes
4491 them quite hard to use for exploits but
4492 might break your system.
4494 vt.color= [VT] Default text color.
4495 Format: 0xYX, X = foreground, Y = background.
4496 Default: 0x07 = light gray on black.
4498 vt.cur_default= [VT] Default cursor shape.
4499 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4500 the parameters of the <Esc>[?A;B;Cc escape sequence;
4501 see VGA-softcursor.txt. Default: 2 = underline.
4503 vt.default_blu= [VT]
4504 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4505 Change the default blue palette of the console.
4506 This is a 16-member array composed of values
4509 vt.default_grn= [VT]
4510 Format: <green0>,<green1>,<green2>,...,<green15>
4511 Change the default green palette of the console.
4512 This is a 16-member array composed of values
4515 vt.default_red= [VT]
4516 Format: <red0>,<red1>,<red2>,...,<red15>
4517 Change the default red palette of the console.
4518 This is a 16-member array composed of values
4524 Set system-wide default UTF-8 mode for all tty's.
4525 Default is 1, i.e. UTF-8 mode is enabled for all
4526 newly opened terminals.
4528 vt.global_cursor_default=
4531 Set system-wide default for whether a cursor
4532 is shown on new VTs. Default is -1,
4533 i.e. cursors will be created by default unless
4534 overridden by individual drivers. 0 will hide
4535 cursors, 1 will display them.
4537 vt.italic= [VT] Default color for italic text; 0-15.
4540 vt.underline= [VT] Default color for underlined text; 0-15.
4543 watchdog timers [HW,WDT] For information on watchdog timers,
4544 see Documentation/watchdog/watchdog-parameters.txt
4545 or other driver-specific files in the
4546 Documentation/watchdog/ directory.
4548 workqueue.watchdog_thresh=
4549 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4550 warn stall conditions and dump internal state to
4551 help debugging. 0 disables workqueue stall
4552 detection; otherwise, it's the stall threshold
4553 duration in seconds. The default value is 30 and
4554 it can be updated at runtime by writing to the
4555 corresponding sysfs file.
4557 workqueue.disable_numa
4558 By default, all work items queued to unbound
4559 workqueues are affine to the NUMA nodes they're
4560 issued on, which results in better behavior in
4561 general. If NUMA affinity needs to be disabled for
4562 whatever reason, this option can be used. Note
4563 that this also can be controlled per-workqueue for
4564 workqueues visible under /sys/bus/workqueue/.
4566 workqueue.power_efficient
4567 Per-cpu workqueues are generally preferred because
4568 they show better performance thanks to cache
4569 locality; unfortunately, per-cpu workqueues tend to
4570 be more power hungry than unbound workqueues.
4572 Enabling this makes the per-cpu workqueues which
4573 were observed to contribute significantly to power
4574 consumption unbound, leading to measurably lower
4575 power usage at the cost of small performance
4578 The default value of this parameter is determined by
4579 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4581 workqueue.debug_force_rr_cpu
4582 Workqueue used to implicitly guarantee that work
4583 items queued without explicit CPU specified are put
4584 on the local CPU. This guarantee is no longer true
4585 and while local CPU is still preferred work items
4586 may be put on foreign CPUs. This debug option
4587 forces round-robin CPU selection to flush out
4588 usages which depend on the now broken guarantee.
4589 When enabled, memory and cache locality will be
4592 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4593 default x2apic cluster mode on platforms
4596 x86_intel_mid_timer= [X86-32,APBT]
4597 Choose timer option for x86 Intel MID platform.
4598 Two valid options are apbt timer only and lapic timer
4599 plus one apbt timer for broadcast timer.
4600 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4602 xen_512gb_limit [KNL,X86-64,XEN]
4603 Restricts the kernel running paravirtualized under Xen
4604 to use only up to 512 GB of RAM. The reason to do so is
4605 crash analysis tools and Xen tools for doing domain
4606 save/restore/migration must be enabled to handle larger
4609 xen_emul_unplug= [HW,X86,XEN]
4610 Unplug Xen emulated devices
4611 Format: [unplug0,][unplug1]
4612 ide-disks -- unplug primary master IDE devices
4613 aux-ide-disks -- unplug non-primary-master IDE devices
4614 nics -- unplug network devices
4615 all -- unplug all emulated devices (NICs and IDE disks)
4616 unnecessary -- unplugging emulated devices is
4617 unnecessary even if the host did not respond to
4619 never -- do not unplug even if version check succeeds
4621 xen_nopvspin [X86,XEN]
4622 Disables the ticketlock slowpath using Xen PV
4626 Disables the PV optimizations forcing the HVM guest to
4627 run as generic HVM guest with no PV drivers.
4629 xirc2ps_cs= [NET,PCMCIA]
4631 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
git.samba.org / sfrench / cifs-2.6.git / blob