1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
117 Support masking of GPEs numbered from 0x00 to 0x7f.
119 acpi_no_auto_serialize [HW,ACPI]
120 Disable auto-serialization of AML methods
121 AML control methods that contain the opcodes to create
122 named objects will be marked as "Serialized" by the
123 auto-serialization feature.
124 This feature is enabled by default.
125 This option allows to turn off the feature.
127 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
130 acpi_no_static_ssdt [HW,ACPI]
131 Disable installation of static SSDTs at early boot time
132 By default, SSDTs contained in the RSDT/XSDT will be
133 installed automatically and they will appear under
134 /sys/firmware/acpi/tables.
135 This option turns off this feature.
136 Note that specifying this option does not affect
137 dynamic table installation which will install SSDT
138 tables to /sys/firmware/acpi/tables/dynamic.
140 acpi_rsdp= [ACPI,EFI,KEXEC]
141 Pass the RSDP address to the kernel, mostly used
142 on machines running EFI runtime service to boot the
143 second kernel for kdump.
145 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
146 Format: To spoof as Windows 98: ="Microsoft Windows"
148 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
149 of 2 which is mandated by ACPI 6) as the supported ACPI
150 specification revision (when using this switch, it may
151 be necessary to carry out a cold reboot _twice_ in a
152 row to make it take effect on the platform firmware).
154 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
155 acpi_osi="string1" # add string1
156 acpi_osi="!string2" # remove string2
157 acpi_osi=!* # remove all strings
158 acpi_osi=! # disable all built-in OS vendor
160 acpi_osi=!! # enable all built-in OS vendor
162 acpi_osi= # disable all strings
164 'acpi_osi=!' can be used in combination with single or
165 multiple 'acpi_osi="string1"' to support specific OS
166 vendor string(s). Note that such command can only
167 affect the default state of the OS vendor strings, thus
168 it cannot affect the default state of the feature group
169 strings and the current state of the OS vendor strings,
170 specifying it multiple times through kernel command line
171 is meaningless. This command is useful when one do not
172 care about the state of the feature group strings which
173 should be controlled by the OSPM.
175 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
176 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
177 can make '_OSI("Windows 2000")' TRUE.
179 'acpi_osi=' cannot be used in combination with other
180 'acpi_osi=' command lines, the _OSI method will not
181 exist in the ACPI namespace. NOTE that such command can
182 only affect the _OSI support state, thus specifying it
183 multiple times through kernel command line is also
186 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
189 'acpi_osi=!*' can be used in combination with single or
190 multiple 'acpi_osi="string1"' to support specific
191 string(s). Note that such command can affect the
192 current state of both the OS vendor strings and the
193 feature group strings, thus specifying it multiple times
194 through kernel command line is meaningful. But it may
195 still not able to affect the final state of a string if
196 there are quirks related to this string. This command
197 is useful when one want to control the state of the
198 feature group strings to debug BIOS issues related to
201 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
202 '_OSI("Module Device")' FALSE.
203 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
204 '_OSI("Module Device")' TRUE.
205 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
207 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
209 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
210 they all will make '_OSI("Windows 2000")' TRUE.
213 Override the pmtimer bug detection: force the kernel
214 to assume that this machine's pmtimer latches its value
215 and always returns good values.
217 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
218 Format: { level | edge | high | low }
220 acpi_skip_timer_override [HW,ACPI]
221 Recognize and ignore IRQ0/pin2 Interrupt Override.
222 For broken nForce2 BIOS resulting in XT-PIC timer.
224 acpi_sleep= [HW,ACPI] Sleep options
225 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
226 old_ordering, nonvs, sci_force_enable }
227 See Documentation/power/video.txt for information on
229 s3_beep is for debugging; it makes the PC's speaker beep
230 as soon as the kernel's real-mode entry point is called.
231 s4_nohwsig prevents ACPI hardware signature from being
232 used during resume from hibernation.
233 old_ordering causes the ACPI 1.0 ordering of the _PTS
234 control method, with respect to putting devices into
235 low power states, to be enforced (the ACPI 2.0 ordering
236 of _PTS is used by default).
237 nonvs prevents the kernel from saving/restoring the
238 ACPI NVS memory during suspend/hibernation and resume.
239 sci_force_enable causes the kernel to set SCI_EN directly
240 on resume from S1/S3 (which is against the ACPI spec,
241 but some broken systems don't work without it).
243 acpi_use_timer_override [HW,ACPI]
244 Use timer override. For some broken Nvidia NF5 boards
245 that require a timer override, but don't have HPET
247 add_efi_memmap [EFI; X86] Include EFI memory map in
248 kernel's map of available physical RAM.
251 { off | try_unsupported }
252 off: disable AGP support
253 try_unsupported: try to drive unsupported chipsets
254 (may crash computer or cause data corruption)
257 See Documentation/sound/alsa/alsa-parameters.txt
260 Allow the default userspace alignment fault handler
261 behaviour to be specified. Bit 0 enables warnings,
262 bit 1 enables fixups, and bit 2 sends a segfault.
264 align_va_addr= [X86-64]
265 Align virtual addresses by clearing slice [14:12] when
266 allocating a VMA at process creation time. This option
267 gives you up to 3% performance improvement on AMD F15h
268 machines (where it is enabled by default) for a
269 CPU-intensive style benchmark, and it can vary highly in
270 a microbenchmark depending on workload and compiler.
272 32: only for 32-bit processes
273 64: only for 64-bit processes
274 on: enable for both 32- and 64-bit processes
275 off: disable for both 32- and 64-bit processes
277 alloc_snapshot [FTRACE]
278 Allocate the ftrace snapshot buffer on boot up when the
279 main buffer is allocated. This is handy if debugging
280 and you need to use tracing_snapshot() on boot up, and
281 do not want to use tracing_snapshot_alloc() as it needs
282 to be done where GFP_KERNEL allocations are allowed.
284 amd_iommu= [HW,X86-64]
285 Pass parameters to the AMD IOMMU driver in the system.
287 fullflush - enable flushing of IO/TLB entries when
288 they are unmapped. Otherwise they are
289 flushed before they will be reused, which
291 off - do not initialize any AMD IOMMU found in
293 force_isolation - Force device isolation for all
294 devices. The IOMMU driver is not
295 allowed anymore to lift isolation
296 requirements as needed. This option
297 does not override iommu=pt
299 amd_iommu_dump= [HW,X86-64]
300 Enable AMD IOMMU driver option to dump the ACPI table
301 for AMD IOMMU. With this option enabled, AMD IOMMU
302 driver will print ACPI tables for AMD IOMMU during
303 IOMMU initialization.
305 amd_iommu_intr= [HW,X86-64]
306 Specifies one of the following AMD IOMMU interrupt
308 legacy - Use legacy interrupt remapping mode.
309 vapic - Use virtual APIC mode, which allows IOMMU
310 to inject interrupts directly into guest.
311 This mode requires kvm-amd.avic=1.
312 (Default when IOMMU HW support is present.)
314 amijoy.map= [HW,JOY] Amiga joystick support
315 Map of devices attached to JOY0DAT and JOY1DAT
317 See also Documentation/input/joystick.txt
319 analog.map= [HW,JOY] Analog joystick and gamepad support
320 Specifies type or capabilities of an analog joystick
321 connected to one of 16 gameports
322 Format: <type1>,<type2>,..<type16>
325 Power management functions (SPARCstation-4/5 + deriv.)
327 Disable APC CPU standby support. SPARCstation-Fox does
328 not play well with APC CPU idle - disable it if you have
329 APC and your system crashes randomly.
331 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
332 Change the output verbosity whilst booting
333 Format: { quiet (default) | verbose | debug }
334 Change the amount of debugging information output
335 when initialising the APIC and IO-APIC components.
337 apic_extnmi= [APIC,X86] External NMI delivery setting
338 Format: { bsp (default) | all | none }
339 bsp: External NMI is delivered only to CPU 0
340 all: External NMIs are broadcast to all CPUs as a
342 none: External NMI is masked for all CPUs. This is
343 useful so that a dump capture kernel won't be
347 See Documentation/networking/ipv6.txt.
349 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
350 Limit apic dumping. The parameter defines the maximal
351 number of local apics being dumped. Also it is possible
352 to set it to "all" by meaning -- no limit here.
353 Format: { 1 (default) | 2 | ... | all }.
354 The parameter valid if only apic=debug or
355 apic=verbose is specified.
356 Example: apic=debug show_lapic=all
358 apm= [APM] Advanced Power Management
359 See header of arch/x86/kernel/apm_32.c.
361 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
362 Format: <io>,<irq>,<nodeID>
366 atarimouse= [HW,MOUSE] Atari Mouse
368 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
369 EzKey and similar keyboards
371 atkbd.reset= [HW] Reset keyboard during initialization
373 atkbd.set= [HW] Select keyboard code set
374 Format: <int> (2 = AT (default), 3 = PS/2)
376 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
379 atkbd.softraw= [HW] Choose between synthetic and real raw mode
380 Format: <bool> (0 = real, 1 = synthetic (default))
382 atkbd.softrepeat= [HW]
383 Use software keyboard repeat
385 audit= [KNL] Enable the audit sub-system
386 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
387 0 - kernel audit is disabled and can not be enabled
388 until the next reboot
389 unset - kernel audit is initialized but disabled and
390 will be fully enabled by the userspace auditd.
391 1 - kernel audit is initialized and partially enabled,
392 storing at most audit_backlog_limit messages in
393 RAM until it is fully enabled by the userspace
397 audit_backlog_limit= [KNL] Set the audit queue size limit.
398 Format: <int> (must be >=0)
401 bau= [X86_UV] Enable the BAU on SGI UV. The default
402 behavior is to disable the BAU (i.e. bau=0).
403 Format: { "0" | "1" }
406 unset - Disable the BAU.
408 baycom_epp= [HW,AX25]
411 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
413 See header of drivers/net/hamradio/baycom_par.c.
415 baycom_ser_fdx= [HW,AX25]
416 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
417 Format: <io>,<irq>,<mode>[,<baud>]
418 See header of drivers/net/hamradio/baycom_ser_fdx.c.
420 baycom_ser_hdx= [HW,AX25]
421 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
422 Format: <io>,<irq>,<mode>
423 See header of drivers/net/hamradio/baycom_ser_hdx.c.
425 blkdevparts= Manual partition parsing of block device(s) for
426 embedded devices based on command line input.
427 See Documentation/block/cmdline-partition.txt
429 boot_delay= Milliseconds to delay each printk during boot.
430 Values larger than 10 seconds (10000) are changed to
434 bootmem_debug [KNL] Enable bootmem allocator debug messages.
437 Disable BERT OS support on buggy BIOSes.
439 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
440 bttv.radio= Most important insmod options are available as
442 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
445 bulk_remove=off [PPC] This parameter disables the use of the pSeries
446 firmware feature for flushing multiple hpte entries
449 c101= [NET] Moxa C101 synchronous serial card
451 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
452 Sometimes CPU hardware bugs make them report the cache
453 size incorrectly. The kernel will attempt work arounds
454 to fix known problems, but for some CPUs it is not
455 possible to determine what the correct size should be.
456 This option provides an override for these situations.
458 ca_keys= [KEYS] This parameter identifies a specific key(s) on
459 the system trusted keyring to be used for certificate
461 format: { id:<keyid> | builtin }
463 cca= [MIPS] Override the kernel pages' cache coherency
464 algorithm. Accepted values range from 0 to 7
465 inclusive. See arch/mips/include/asm/pgtable-bits.h
466 for platform specific values (SB1, Loongson3 and
469 ccw_timeout_log [S390]
470 See Documentation/s390/CommonIO for details.
472 cgroup_disable= [KNL] Disable a particular controller
473 Format: {name of the controller(s) to disable}
474 The effects of cgroup_disable=foo are:
475 - foo isn't auto-mounted if you mount all cgroups in
477 - foo isn't visible as an individually mountable
479 {Currently only "memory" controller deal with this and
480 cut the overhead, others just disable the usage. So
481 only cgroup_disable=memory is actually worthy}
483 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
484 Format: { controller[,controller...] | "all" }
485 Like cgroup_disable, but only applies to cgroup v1;
486 the blacklisted controllers remain available in cgroup2.
488 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
490 nosocket -- Disable socket memory accounting.
491 nokmem -- Disable kernel memory accounting.
493 checkreqprot [SELINUX] Set initial checkreqprot flag value.
494 Format: { "0" | "1" }
495 See security/selinux/Kconfig help text.
496 0 -- check protection applied by kernel (includes
497 any implied execute protection).
498 1 -- check protection requested by application.
499 Default value is set via a kernel config option.
500 Value can be changed at runtime via
501 /selinux/checkreqprot.
504 See Documentation/s390/CommonIO for details.
507 Prevents the clock framework from automatically gating
508 clocks that have not been explicitly enabled by a Linux
509 device driver but are enabled in hardware at reset or
510 by the bootloader/firmware. Note that this does not
511 force such clocks to be always-on nor does it reserve
512 those clocks in any way. This parameter is useful for
513 debug and development, but should not be needed on a
514 platform with proper driver support. For more
515 information, see Documentation/clk.txt.
517 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
519 Forces specified clocksource (if available) to be used
520 when calculating gettimeofday(). If specified
521 clocksource is not available, it defaults to PIT.
522 Format: { pit | tsc | cyclone | pmtmr }
524 clocksource= Override the default clocksource
526 Override the default clocksource and use the clocksource
527 with the name specified.
528 Some clocksource names to choose from, depending on
530 [all] jiffies (this is the base, fallback clocksource)
532 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
533 pxa_timer,timer3,32k_counter,timer0_1
534 [X86-32] pit,hpet,tsc;
535 scx200_hrt on Geode; cyclone on IBM x440
543 clocksource.arm_arch_timer.evtstrm=
546 Enable/disable the eventstream feature of the ARM
547 architected timer so that code using WFE-based polling
548 loops can be debugged more effectively on production
551 clearcpuid=BITNUM [X86]
552 Disable CPUID feature X for the kernel. See
553 arch/x86/include/asm/cpufeatures.h for the valid bit
554 numbers. Note the Linux specific bits are not necessarily
555 stable over kernel options, but the vendor specific
557 Also note that user programs calling CPUID directly
558 or using the feature without checking anything
559 will still see it. This just prevents it from
560 being used by the kernel or shown in /proc/cpuinfo.
561 Also note the kernel might malfunction if you disable
564 cma=nn[MG]@[start[MG][-end[MG]]]
566 Sets the size of kernel global memory area for
567 contiguous memory allocations and optionally the
568 placement constraint by the physical address range of
569 memory allocations. A value of 0 disables CMA
570 altogether. For more information, see
571 include/linux/dma-contiguous.h
573 cmo_free_hint= [PPC] Format: { yes | no }
574 Specify whether pages are marked as being inactive
575 when they are freed. This is used in CMO environments
576 to determine OS memory pressure for page stealing by
580 coherent_pool=nn[KMG] [ARM,KNL]
581 Sets the size of memory pool for coherent, atomic dma
582 allocations, by default set to 256K.
584 code_bytes [X86] How many bytes of object code to print
589 com20020= [HW,NET] ARCnet - COM20020 chipset
591 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
593 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
597 ARCnet - COM90xx chipset (memory-mapped buffers)
598 Format: <io>[,<irq>[,<memstart>]]
600 condev= [HW,S390] console device
603 console= [KNL] Output console device and options.
605 tty<n> Use the virtual console device <n>.
609 Use the specified serial port. The options are of
610 the form "bbbbpnf", where "bbbb" is the baud rate,
611 "p" is parity ("n", "o", or "e"), "n" is number of
612 bits, and "f" is flow control ("r" for RTS or
613 omit it). Default is "9600n8".
615 See Documentation/admin-guide/serial-console.rst for more
617 Documentation/networking/netconsole.txt for an
620 uart[8250],io,<addr>[,options]
621 uart[8250],mmio,<addr>[,options]
622 uart[8250],mmio16,<addr>[,options]
623 uart[8250],mmio32,<addr>[,options]
624 uart[8250],0x<addr>[,options]
625 Start an early, polled-mode console on the 8250/16550
626 UART at the specified I/O port or MMIO address,
627 switching to the matching ttyS device later.
628 MMIO inter-register address stride is either 8-bit
629 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
630 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
631 to be equivalent to 'mmio'. 'options' are specified in
632 the same format described for ttyS above; if unspecified,
633 the h/w is not re-initialized.
635 hvc<n> Use the hypervisor console device <n>. This is for
636 both Xen and PowerPC hypervisors.
638 If the device connected to the port is not a TTY but a braille
639 device, prepend "brl," before the device type, for instance
641 For now, only VisioBraille is supported.
643 consoleblank= [KNL] The console blank (screen saver) timeout in
644 seconds. Defaults to 10*60 = 10mins. A value of 0
645 disables the blank timer.
648 [KNL] Change the default value for
649 /proc/<pid>/coredump_filter.
650 See also Documentation/filesystems/proc.txt.
652 cpuidle.off=1 [CPU_IDLE]
653 disable the cpuidle sub-system
655 cpufreq.off=1 [CPU_FREQ]
656 disable the cpufreq sub-system
659 [X86] Delay for N microsec between assert and de-assert
660 of APIC INIT to start processors. This delay occurs
661 on every CPU online, such as boot, and resume from suspend.
664 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
666 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
668 crashkernel=size[KMG][@offset[KMG]]
669 [KNL] Using kexec, Linux can switch to a 'crash kernel'
670 upon panic. This parameter reserves the physical
671 memory region [offset, offset + size] for that kernel
672 image. If '@offset' is omitted, then a suitable offset
673 is selected automatically. Check
674 Documentation/kdump/kdump.txt for further details.
676 crashkernel=range1:size1[,range2:size2,...][@offset]
677 [KNL] Same as above, but depends on the memory
678 in the running system. The syntax of range is
679 start-[end] where start and end are both
680 a memory unit (amount[KMG]). See also
681 Documentation/kdump/kdump.txt for an example.
683 crashkernel=size[KMG],high
684 [KNL, x86_64] range could be above 4G. Allow kernel
685 to allocate physical memory region from top, so could
686 be above 4G if system have more than 4G ram installed.
687 Otherwise memory region will be allocated below 4G, if
689 It will be ignored if crashkernel=X is specified.
690 crashkernel=size[KMG],low
691 [KNL, x86_64] range under 4G. When crashkernel=X,high
692 is passed, kernel could allocate physical memory region
693 above 4G, that cause second kernel crash on system
694 that require some amount of low memory, e.g. swiotlb
695 requires at least 64M+32K low memory, also enough extra
696 low memory is needed to make sure DMA buffers for 32-bit
697 devices won't run out. Kernel would try to allocate at
698 at least 256M below 4G automatically.
699 This one let user to specify own low range under 4G
700 for second kernel instead.
701 0: to disable low allocation.
702 It will be ignored when crashkernel=X,high is not used
703 or memory reserved is below 4G.
706 [KNL] Disable crypto self-tests
711 cs89x0_media= [HW,NET]
712 Format: { rj45 | aui | bnc }
715 See header of drivers/s390/block/dasd_devmap.c.
717 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
718 (one device per port)
719 Format: <port#>,<type>
720 See also Documentation/input/joystick-parport.txt
722 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
723 time. See Documentation/dynamic-debug-howto.txt for
724 details. Deprecated, see dyndbg.
726 debug [KNL] Enable kernel debugging (events log level).
729 [KNL] verbose self-tests
731 Print debugging info while doing the locking API
733 We default to 0 (no extra messages), setting it to
734 1 will print _a lot_ more information - normally
735 only useful to kernel developers.
737 debug_objects [KNL] Enable object debugging
740 [KNL] Disable object debugging
742 debug_guardpage_minorder=
743 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
744 parameter allows control of the order of pages that will
745 be intentionally kept free (and hence protected) by the
746 buddy allocator. Bigger value increase the probability
747 of catching random memory corruption, but reduce the
748 amount of memory for normal system use. The maximum
749 possible value is MAX_ORDER/2. Setting this parameter
750 to 1 or 2 should be enough to identify most random
751 memory corruption problems caused by bugs in kernel or
752 driver code when a CPU writes to (or reads from) a
753 random memory location. Note that there exists a class
754 of memory corruptions problems caused by buggy H/W or
755 F/W or by drivers badly programing DMA (basically when
756 memory is written at bus level and the CPU MMU is
757 bypassed) which are not detectable by
758 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
759 tracking down these problems.
762 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
763 parameter enables the feature at boot time. In
764 default, it is disabled. We can avoid allocating huge
765 chunk of memory for debug pagealloc if we don't enable
766 it at boot time and the system will work mostly same
767 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
768 on: enable the feature
770 debugpat [X86] Enable PAT debugging
772 decnet.addr= [HW,NET]
773 Format: <area>[,<node>]
774 See also Documentation/networking/decnet.txt.
777 [same as hugepagesz=] The size of the default
778 HugeTLB page size. This is the size represented by
779 the legacy /proc/ hugepages APIs, used for SHM, and
780 default size when mounting hugetlbfs filesystems.
781 Defaults to the default architecture's huge page size
785 Set number of hash buckets for dentry cache.
787 disable_1tb_segments [PPC]
788 Disables the use of 1TB hash page table segments. This
789 causes the kernel to fall back to 256MB segments which
790 can be useful when debugging issues that require an SLB
794 See Documentation/networking/ipv6.txt.
797 Disable RADIX MMU mode on POWER9
799 disable_cpu_apicid= [X86,APIC,SMP]
801 The number of initial APIC ID for the
802 corresponding CPU to be disabled at boot,
803 mostly used for the kdump 2nd kernel to
804 disable BSP to wake up multiple CPUs without
805 causing system reset or hang due to sending
808 disable_ddw [PPC/PSERIES]
809 Disable Dynamic DMA Window support. Use this if
810 to workaround buggy firmware.
813 See Documentation/networking/ipv6.txt.
815 disable_mtrr_cleanup [X86]
816 The kernel tries to adjust MTRR layout from continuous
817 to discrete, to make X server driver able to add WB
818 entry later. This parameter disables that.
820 disable_mtrr_trim [X86, Intel and AMD only]
821 By default the kernel will trim any uncacheable
822 memory out of your available memory pool based on
823 MTRR settings. This parameter disables that behavior,
824 possibly causing your machine to run very slowly.
826 disable_timer_pin_1 [X86]
827 Disable PIN 1 of APIC timer
828 Can be useful to work around chipset bugs.
830 dis_ucode_ldr [X86] Disable the microcode loader.
832 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
833 this option disables the debugging code at boot.
835 dma_debug_entries=<number>
836 This option allows to tune the number of preallocated
837 entries for DMA-API debugging code. One entry is
838 required per DMA-API allocation. Use this if the
839 DMA-API debugging code disables itself because the
840 architectural default is too low.
842 dma_debug_driver=<driver_name>
843 With this option the DMA-API debugging driver
844 filter feature can be enabled at boot time. Just
845 pass the driver to filter for as the parameter.
846 The filter can be disabled or changed to another
847 driver later using sysfs.
849 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
850 Broken monitors, graphic adapters, KVMs and EDIDless
851 panels may send no or incorrect EDID data sets.
852 This parameter allows to specify an EDID data sets
853 in the /lib/firmware directory that are used instead.
854 Generic built-in EDID data sets are used, if one of
855 edid/1024x768.bin, edid/1280x1024.bin,
856 edid/1680x1050.bin, or edid/1920x1080.bin is given
857 and no file with the same name exists. Details and
858 instructions how to build your own EDID data are
859 available in Documentation/EDID/HOWTO.txt. An EDID
860 data set will only be used for a particular connector,
861 if its name and a colon are prepended to the EDID
862 name. Each connector may use a unique EDID data
863 set by separating the files with a comma. An EDID
864 data set with no connector name will be used for
865 any connectors not explicitly specified.
869 dump_apple_properties [X86]
870 Dump name and content of EFI device properties on
871 x86 Macs. Useful for driver authors to determine
872 what data is available or for reverse-engineering.
874 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
875 module.dyndbg[="val"]
876 Enable debug messages at boot time. See
877 Documentation/dynamic-debug-howto.txt for details.
879 nompx [X86] Disables Intel Memory Protection Extensions.
880 See Documentation/x86/intel_mpx.txt for more
881 information about the feature.
883 nopku [X86] Disable Memory Protection Keys CPU feature found
886 module.async_probe [KNL]
887 Enable asynchronous probe on this module.
889 early_ioremap_debug [KNL]
890 Enable debug messages in early_ioremap support. This
891 is useful for tracking down temporary early mappings
892 which are not unmapped.
894 earlycon= [KNL] Output early console device and options.
896 When used with no options, the early console is
897 determined by the stdout-path property in device
900 cdns,<addr>[,options]
901 Start an early, polled-mode console on a Cadence
902 (xuartps) serial port at the specified address. Only
903 supported option is baud rate. If baud rate is not
904 specified, the serial port must already be setup and
907 uart[8250],io,<addr>[,options]
908 uart[8250],mmio,<addr>[,options]
909 uart[8250],mmio32,<addr>[,options]
910 uart[8250],mmio32be,<addr>[,options]
911 uart[8250],0x<addr>[,options]
912 Start an early, polled-mode console on the 8250/16550
913 UART at the specified I/O port or MMIO address.
914 MMIO inter-register address stride is either 8-bit
915 (mmio) or 32-bit (mmio32 or mmio32be).
916 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
917 to be equivalent to 'mmio'. 'options' are specified
918 in the same format described for "console=ttyS<n>"; if
919 unspecified, the h/w is not initialized.
923 Start an early, polled-mode console on a pl011 serial
924 port at the specified address. The pl011 serial port
925 must already be setup and configured. Options are not
926 yet supported. If 'mmio32' is specified, then only
927 the driver will use only 32-bit accessors to read/write
928 the device registers.
931 Start an early, polled-mode console on a meson serial
932 port at the specified address. The serial port must
933 already be setup and configured. Options are not yet
937 Start an early, polled-mode console on an msm serial
938 port at the specified address. The serial port
939 must already be setup and configured. Options are not
943 Start an early, polled-mode console on an msm serial
944 dm port at the specified address. The serial port
945 must already be setup and configured. Options are not
948 smh Use ARM semihosting calls for early console.
956 Use early console provided by serial driver available
957 on Samsung SoCs, requires selecting proper type and
958 a correct base address of the selected UART port. The
959 serial port must already be setup and configured.
960 Options are not yet supported.
963 Start an early, polled-mode console on a lantiq serial
964 (lqasc) port at the specified address. The serial port
965 must already be setup and configured. Options are not
970 Use early console provided by Freescale LP UART driver
971 found on Freescale Vybrid and QorIQ LS1021A processors.
972 A valid base address must be provided, and the serial
973 port must already be setup and configured.
975 armada3700_uart,<addr>
976 Start an early, polled-mode console on the
977 Armada 3700 serial port at the specified
978 address. The serial port must already be setup
979 and configured. Options are not yet supported.
981 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
986 earlyprintk=serial[,ttySn[,baudrate]]
987 earlyprintk=serial[,0x...[,baudrate]]
988 earlyprintk=ttySn[,baudrate]
989 earlyprintk=dbgp[debugController#]
990 earlyprintk=pciserial,bus:device.function[,baudrate]
991 earlyprintk=xdbc[xhciController#]
993 earlyprintk is useful when the kernel crashes before
994 the normal console is initialized. It is not enabled by
995 default because it has some cosmetic problems.
997 Append ",keep" to not disable it when the real console
1000 Only one of vga, efi, serial, or usb debug port can
1003 Currently only ttyS0 and ttyS1 may be specified by
1004 name. Other I/O ports may be explicitly specified
1005 on some architectures (x86 and arm at least) by
1006 replacing ttySn with an I/O port address, like this:
1007 earlyprintk=serial,0x1008,115200
1008 You can find the port for a given device in
1009 /proc/tty/driver/serial:
1010 2: uart:ST16650V2 port:00001008 irq:18 ...
1012 Interaction with the standard serial driver is not
1015 The VGA and EFI output is eventually overwritten by
1018 The xen output can only be used by Xen PV guests.
1020 The sclp output can only be used on s390.
1022 edac_report= [HW,EDAC] Control how to report EDAC event
1023 Format: {"on" | "off" | "force"}
1024 on: enable EDAC to report H/W event. May be overridden
1025 by other higher priority error reporting module.
1026 off: disable H/W event reporting through EDAC.
1027 force: enforce the use of EDAC to report H/W event.
1030 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1033 This is designed to be used in conjunction with
1034 the boot argument: earlyprintk=vga
1037 Format: {"off" | "on" | "skip[mbr]"}
1040 Format: { "old_map", "nochunk", "noruntime", "debug" }
1041 old_map [X86-64]: switch to the old ioremap-based EFI
1042 runtime services mapping. 32-bit still uses this one by
1044 nochunk: disable reading files in "chunks" in the EFI
1045 boot stub, as chunking can cause problems with some
1046 firmware implementations.
1047 noruntime : disable EFI runtime services support
1048 debug: enable misc debug output
1050 efi_no_storage_paranoia [EFI; X86]
1051 Using this parameter you can use more than 50% of
1052 your efi variable storage. Use this parameter only if
1053 you are really sure that your UEFI does sane gc and
1054 fulfills the spec otherwise your board may brick.
1056 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1057 Add arbitrary attribute to specific memory range by
1058 updating original EFI memory map.
1059 Region of memory which aa attribute is added to is
1061 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1062 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1063 attribute is added to range 0x100000000-0x180000000 and
1064 0x10a0000000-0x1120000000.
1066 Using this parameter you can do debugging of EFI memmap
1067 related feature. For example, you can do debugging of
1068 Address Range Mirroring feature even if your box
1071 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1072 that is to be dynamically loaded by Linux. If there are
1073 multiple variables with the same name but with different
1074 vendor GUIDs, all of them will be loaded. See
1075 Documentation/acpi/ssdt-overlays.txt for details.
1078 eisa_irq_edge= [PARISC,HW]
1079 See header of drivers/parisc/eisa.c.
1082 See comment before function elanfreq_setup() in
1083 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1086 Format: {"cfq" | "deadline" | "noop"}
1087 See Documentation/block/cfq-iosched.txt and
1088 Documentation/block/deadline-iosched.txt for details.
1090 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1091 Specifies physical address of start of kernel core
1092 image elf header and optionally the size. Generally
1093 kexec loader will pass this option to capture kernel.
1094 See Documentation/kdump/kdump.txt for details.
1096 enable_mtrr_cleanup [X86]
1097 The kernel tries to adjust MTRR layout from continuous
1098 to discrete, to make X server driver able to add WB
1099 entry later. This parameter enables that.
1101 enable_timer_pin_1 [X86]
1102 Enable PIN 1 of APIC timer
1103 Can be useful to work around chipset bugs
1104 (in particular on some ATI chipsets).
1105 The kernel tries to set a reasonable default.
1107 enforcing [SELINUX] Set initial enforcing status.
1109 See security/selinux/Kconfig help text.
1110 0 -- permissive (log only, no denials).
1111 1 -- enforcing (deny and log).
1113 Value can be changed at runtime via /selinux/enforce.
1116 Disable Error Record Serialization Table (ERST)
1119 ether= [HW,NET] Ethernet cards parameters
1120 This option is obsoleted by the "netdev=" option, which
1121 has equivalent usage. See its documentation for details.
1125 Permit 'security.evm' to be updated regardless of
1126 current integrity status.
1130 fail_make_request=[KNL]
1131 General fault injection mechanism.
1132 Format: <interval>,<probability>,<space>,<times>
1133 See also Documentation/fault-injection/.
1136 See Documentation/blockdev/floppy.txt.
1138 force_pal_cache_flush
1139 [IA-64] Avoid check_sal_cache_flush which may hang on
1140 buggy SAL_CACHE_FLUSH implementations. Using this
1141 parameter will force ia64_sal_cache_flush to call
1142 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1145 Forcefully enable Physical Address Extension (PAE).
1146 Many Pentium M systems disable PAE but may have a
1147 functionally usable PAE implementation.
1148 Warning: use of this parameter will taint the kernel
1149 and may cause unknown problems.
1152 [FTRACE] will set and start the specified tracer
1153 as early as possible in order to facilitate early
1156 ftrace_dump_on_oops[=orig_cpu]
1157 [FTRACE] will dump the trace buffers on oops.
1158 If no parameter is passed, ftrace will dump
1159 buffers of all CPUs, but if you pass orig_cpu, it will
1160 dump only the buffer of the CPU that triggered the
1163 ftrace_filter=[function-list]
1164 [FTRACE] Limit the functions traced by the function
1165 tracer at boot up. function-list is a comma separated
1166 list of functions. This list can be changed at run
1167 time by the set_ftrace_filter file in the debugfs
1170 ftrace_notrace=[function-list]
1171 [FTRACE] Do not trace the functions specified in
1172 function-list. This list can be changed at run time
1173 by the set_ftrace_notrace file in the debugfs
1176 ftrace_graph_filter=[function-list]
1177 [FTRACE] Limit the top level callers functions traced
1178 by the function graph tracer at boot up.
1179 function-list is a comma separated list of functions
1180 that can be changed at run time by the
1181 set_graph_function file in the debugfs tracing directory.
1183 ftrace_graph_notrace=[function-list]
1184 [FTRACE] Do not trace from the functions specified in
1185 function-list. This list is a comma separated list of
1186 functions that can be changed at run time by the
1187 set_graph_notrace file in the debugfs tracing directory.
1189 ftrace_graph_max_depth=<uint>
1190 [FTRACE] Used with the function graph tracer. This is
1191 the max depth it will trace into a function. This value
1192 can be changed at run time by the max_graph_depth file
1193 in the tracefs tracing directory. default: 0 (no limit)
1196 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1197 support via parallel port (up to 5 devices per port)
1198 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1199 See also Documentation/input/joystick-parport.txt
1203 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1207 gcov_persist= [GCOV] When non-zero (default), profiling data for
1208 kernel modules is saved and remains accessible via
1209 debugfs, even when the module is unloaded/reloaded.
1210 When zero, profiling data is discarded and associated
1211 debugfs files are removed at module unload time.
1213 goldfish [X86] Enable the goldfish android emulator platform.
1214 Don't use this when you are not running on the
1217 gpt [EFI] Forces disk with valid GPT signature but
1218 invalid Protective MBR to be treated as GPT. If the
1219 primary GPT is corrupted, it enables the backup/alternate
1220 GPT to be used instead.
1222 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1223 the "Enable 0" bit of the configuration register.
1226 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1227 the "Enable 0" bit of the configuration register.
1230 grcan.select= [HW] Select which physical interface to use.
1233 grcan.txsize= [HW] Sets the size of the tx buffer.
1234 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1236 grcan.rxsize= [HW] Sets the size of the rx buffer.
1237 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1240 gpio-mockup.gpio_mockup_ranges
1241 [HW] Sets the ranges of gpiochip of for this device.
1242 Format: <start1>,<end1>,<start2>,<end2>...
1244 hardlockup_all_cpu_backtrace=
1245 [KNL] Should the hard-lockup detector generate
1246 backtraces on all cpus.
1249 hashdist= [KNL,NUMA] Large hashes allocated during boot
1250 are distributed across NUMA nodes. Defaults on
1251 for 64-bit NUMA, off otherwise.
1252 Format: 0 | 1 (for off | on)
1254 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1256 hd= [EIDE] (E)IDE hard drive subsystem geometry
1257 Format: <cyl>,<head>,<sect>
1260 Disable Hardware Error Source Table (HEST) support;
1261 corresponding firmware-first mode error processing
1262 logic will be disabled.
1264 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1265 size of <nn>. This works even on boxes that have no
1266 highmem otherwise. This also works to reduce highmem
1267 size on bigger boxes.
1269 highres= [KNL] Enable/disable high resolution timer mode.
1270 Valid parameters: "on", "off"
1274 See Documentation/isdn/README.HiSax.
1278 hpet= [X86-32,HPET] option to control HPET usage
1279 Format: { enable (default) | disable | force |
1281 disable: disable HPET and use PIT instead
1282 force: allow force enabled of undocumented chips (ICH4,
1284 verbose: show contents of HPET registers during setup
1286 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1287 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1289 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1290 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1291 On x86-64 and powerpc, this option can be specified
1292 multiple times interleaved with hugepages= to reserve
1293 huge pages of different sizes. Valid pages sizes on
1294 x86-64 are 2M (when the CPU supports "pse") and 1G
1295 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1297 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1298 terminal devices. Valid values: 0..8
1299 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1300 If specified, z/VM IUCV HVC accepts connections
1301 from listed z/VM user IDs only.
1303 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1304 hardware thread id mappings.
1305 Format: <cpu>:<hwthread>
1308 Do not unregister boot console at start. This is only
1309 useful for debugging when something happens in the window
1310 between unregistering the boot console and initializing
1313 i2c_bus= [HW] Override the default board specific I2C bus speed
1314 or register an additional I2C bus that is not
1315 registered from board initialization code.
1319 i8042.debug [HW] Toggle i8042 debug mode
1320 i8042.unmask_kbd_data
1321 [HW] Enable printing of interrupt data from the KBD port
1322 (disabled by default, and as a pre-condition
1323 requires that i8042.debug=1 be enabled)
1324 i8042.direct [HW] Put keyboard port into non-translated mode
1325 i8042.dumbkbd [HW] Pretend that controller can only read data from
1326 keyboard and cannot control its state
1327 (Don't attempt to blink the leds)
1328 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1329 i8042.nokbd [HW] Don't check/create keyboard port
1330 i8042.noloop [HW] Disable the AUX Loopback command while probing
1332 i8042.nomux [HW] Don't check presence of an active multiplexing
1334 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1336 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1337 i8042.reset [HW] Reset the controller during init, cleanup and
1338 suspend-to-ram transitions, only during s2r
1339 transitions, or never reset
1340 Format: { 1 | Y | y | 0 | N | n }
1341 1, Y, y: always reset controller
1342 0, N, n: don't ever reset controller
1343 Default: only on s2r transitions on x86; most other
1344 architectures force reset to be always executed
1345 i8042.unlock [HW] Unlock (ignore) the keylock
1346 i8042.kbdreset [HW] Reset device connected to KBD port
1350 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1351 indicates that the driver is running on unsupported
1353 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1354 does not match list of supported models.
1356 [HW] Report power status in /proc/i8k
1357 (disabled by default)
1358 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1361 i915.invert_brightness=
1362 [DRM] Invert the sense of the variable that is used to
1363 set the brightness of the panel backlight. Normally a
1364 brightness value of 0 indicates backlight switched off,
1365 and the maximum of the brightness value sets the backlight
1366 to maximum brightness. If this parameter is set to 0
1367 (default) and the machine requires it, or this parameter
1368 is set to 1, a brightness value of 0 sets the backlight
1369 to maximum brightness, and the maximum of the brightness
1370 value switches the backlight off.
1371 -1 -- never invert brightness
1372 0 -- machine default
1373 1 -- force brightness inversion
1376 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1378 ide-core.nodma= [HW] (E)IDE subsystem
1379 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1380 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1381 .cdrom .chs .ignore_cable are additional options
1382 See Documentation/ide/ide.txt.
1384 ide-generic.probe-mask= [HW] (E)IDE subsystem
1386 Probe mask for legacy ISA IDE ports. Depending on
1387 platform up to 6 ports are supported, enabled by
1388 setting corresponding bits in the mask to 1. The
1389 default value is 0x0, which has a special meaning.
1390 On systems that have PCI, it triggers scanning the
1391 PCI bus for the first and the second port, which
1392 are then probed. On systems without PCI the value
1393 of 0x0 enables probing the two first ports as if it
1396 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1397 Claim all unknown PCI IDE storage controllers.
1400 Format: idle=poll, idle=halt, idle=nomwait
1401 Poll forces a polling idle loop that can slightly
1402 improve the performance of waking up a idle CPU, but
1403 will use a lot of power and make the system run hot.
1405 idle=halt: Halt is forced to be used for CPU idle.
1406 In such case C2/C3 won't be used again.
1407 idle=nomwait: Disable mwait for CPU C-states
1409 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1410 Format: { strict | legacy | 2008 | relaxed }
1413 Choose which programs will be accepted for execution
1414 based on the IEEE 754 NaN encoding(s) supported by
1415 the FPU and the NaN encoding requested with the value
1416 of an ELF file header flag individually set by each
1417 binary. Hardware implementations are permitted to
1418 support either or both of the legacy and the 2008 NaN
1421 Available settings are as follows:
1422 strict accept binaries that request a NaN encoding
1423 supported by the FPU
1424 legacy only accept legacy-NaN binaries, if supported
1426 2008 only accept 2008-NaN binaries, if supported
1428 relaxed accept any binaries regardless of whether
1429 supported by the FPU
1431 The FPU emulator is always able to support both NaN
1432 encodings, so if no FPU hardware is present or it has
1433 been disabled with 'nofpu', then the settings of
1434 'legacy' and '2008' strap the emulator accordingly,
1435 'relaxed' straps the emulator for both legacy-NaN and
1436 2008-NaN, whereas 'strict' enables legacy-NaN only on
1437 legacy processors and both NaN encodings on MIPS32 or
1440 The setting for ABS.fmt/NEG.fmt instruction execution
1441 mode generally follows that for the NaN encoding,
1442 except where unsupported by hardware.
1444 ignore_loglevel [KNL]
1445 Ignore loglevel setting - this will print /all/
1446 kernel messages to the console. Useful for debugging.
1447 We also add it as printk module parameter, so users
1448 could change it dynamically, usually by
1449 /sys/module/printk/parameters/ignore_loglevel.
1452 Ignore RLIMIT_DATA setting for data mappings,
1453 print warning at first misuse. Can be changed via
1454 /sys/module/kernel/parameters/ignore_rlimit_data.
1456 ihash_entries= [KNL]
1457 Set number of hash buckets for inode cache.
1459 ima_appraise= [IMA] appraise integrity measurements
1460 Format: { "off" | "enforce" | "fix" | "log" }
1463 ima_appraise_tcb [IMA]
1464 The builtin appraise policy appraises all files
1467 ima_canonical_fmt [IMA]
1468 Use the canonical format for the binary runtime
1469 measurements, instead of host native format.
1472 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1476 The list of supported hash algorithms is defined
1477 in crypto/hash_info.h.
1480 The builtin measurement policy to load during IMA
1481 setup. Specyfing "tcb" as the value, measures all
1482 programs exec'd, files mmap'd for exec, and all files
1483 opened with the read mode bit set by either the
1484 effective uid (euid=0) or uid=0.
1487 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1488 Load a policy which meets the needs of the Trusted
1489 Computing Base. This means IMA will measure all
1490 programs exec'd, files mmap'd for exec, and all files
1491 opened for read by uid=0.
1494 Select one of defined IMA measurements template formats.
1495 Formats: { "ima" | "ima-ng" | "ima-sig" }
1499 [IMA] Define a custom template format.
1500 Format: { "field1|...|fieldN" }
1502 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1503 Format: <min_file_size>
1504 Set the minimal file size for using asynchronous hash.
1505 If left unspecified, ahash usage is disabled.
1507 ahash performance varies for different data sizes on
1508 different crypto accelerators. This option can be used
1509 to achieve the best performance for a particular HW.
1511 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1513 Set hashing buffer size. Default: 4k.
1515 ahash performance varies for different chunk sizes on
1516 different crypto accelerators. This option can be used
1517 to achieve best performance for particular HW.
1521 Run specified binary instead of /sbin/init as init
1524 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1525 for working out where the kernel is dying during
1528 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1529 initcall functions. Useful for debugging built-in
1530 modules and initcalls.
1532 initrd= [BOOT] Specify the location of the initial ramdisk
1534 init_pkru= [x86] Specify the default memory protection keys rights
1535 register contents for all processes. 0x55555554 by
1536 default (disallow access to all but pkey 0). Can
1537 override in debugfs after boot.
1539 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1542 int_pln_enable [x86] Enable power limit notification interrupt
1544 integrity_audit=[IMA]
1545 Format: { "0" | "1" }
1546 0 -- basic integrity auditing messages. (Default)
1547 1 -- additional integrity auditing messages.
1549 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1551 Enable intel iommu driver.
1553 Disable intel iommu driver.
1554 igfx_off [Default Off]
1555 By default, gfx is mapped as normal device. If a gfx
1556 device has a dedicated DMAR unit, the DMAR unit is
1557 bypassed by not enabling DMAR with this option. In
1558 this case, gfx device will use physical address for
1561 With this option iommu will not optimize to look
1562 for io virtual address below 32-bit forcing dual
1563 address cycle on pci bus for cards supporting greater
1564 than 32-bit addressing. The default is to look
1565 for translation below 32-bit and if not available
1566 then look in the higher range.
1567 strict [Default Off]
1568 With this option on every unmap_single operation will
1569 result in a hardware IOTLB flush operation as opposed
1570 to batching them for performance.
1571 sp_off [Default Off]
1572 By default, super page will be supported if Intel IOMMU
1573 has the capability. With this option, super page will
1575 ecs_off [Default Off]
1576 By default, extended context tables will be supported if
1577 the hardware advertises that it has support both for the
1578 extended tables themselves, and also PASID support. With
1579 this option set, extended tables will not be used even
1580 on hardware which claims to support them.
1581 tboot_noforce [Default Off]
1582 Do not force the Intel IOMMU enabled under tboot.
1583 By default, tboot will force Intel IOMMU on, which
1584 could harm performance of some high-throughput
1585 devices like 40GBit network cards, even if identity
1587 Note that using this option lowers the security
1588 provided by tboot because it makes the system
1589 vulnerable to DMA attacks.
1591 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1592 0 disables intel_idle and fall back on acpi_idle.
1593 1 to 9 specify maximum depth of C-state.
1597 Do not enable intel_pstate as the default
1598 scaling driver for the supported processors
1600 Use intel_pstate as a scaling driver, but configure it
1601 to work with generic cpufreq governors (instead of
1602 enabling its internal governor). This mode cannot be
1603 used along with the hardware-managed P-states (HWP)
1606 Enable intel_pstate on systems that prohibit it by default
1607 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1608 instead of acpi-cpufreq may disable platform features, such
1609 as thermal controls and power capping, that rely on ACPI
1610 P-States information being indicated to OSPM and therefore
1611 should be used with caution. This option does not work with
1612 processors that aren't supported by the intel_pstate driver
1613 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1615 Do not enable hardware P state control (HWP)
1618 Only load intel_pstate on systems which support
1619 hardware P state control (HWP) if available.
1621 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1622 Description Table, specifies preferred power management
1623 profile as "Enterprise Server" or "Performance Server",
1624 then this feature is turned on by default.
1626 Allow per-logical-CPU P-State performance control limits using
1627 cpufreq sysfs interface
1629 intremap= [X86-64, Intel-IOMMU]
1630 on enable Interrupt Remapping (default)
1631 off disable Interrupt Remapping
1632 nosid disable Source ID checking
1634 BIOS x2APIC opt-out request will be ignored
1635 nopost disable Interrupt Posting
1637 iomem= Disable strict checking of access to MMIO memory
1638 strict regions from userspace.
1653 nobypass [PPC/POWERNV]
1654 Disable IOMMU bypass, using IOMMU for PCI devices.
1657 [ARM64] Configure DMA to bypass the IOMMU by default.
1658 Format: { "0" | "1" }
1659 0 - Use IOMMU translation for DMA.
1660 1 - Bypass the IOMMU for DMA.
1661 unset - Use IOMMU translation for DMA.
1663 io7= [HW] IO7 for Marvel based alpha systems
1664 See comment before marvel_specify_io7 in
1665 arch/alpha/kernel/core_marvel.c.
1667 io_delay= [X86] I/O delay method
1669 Standard port 0x80 based delay
1671 Alternate port 0xed based delay (needed on some systems)
1673 Simple two microseconds delay
1678 See Documentation/filesystems/nfs/nfsroot.txt.
1680 irqaffinity= [SMP] Set the default irq affinity mask
1681 The argument is a cpu list, as described above.
1684 When an interrupt is not handled search all handlers
1685 for it. Intended to get systems with badly broken
1689 When an interrupt is not handled search all handlers
1690 for it. Also check all handlers each timer
1691 interrupt. Intended to get systems with badly broken
1695 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1697 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1698 The argument is a cpu list, as described above.
1700 This option can be used to specify one or more CPUs
1701 to isolate from the general SMP balancing and scheduling
1702 algorithms. You can move a process onto or off an
1703 "isolated" CPU via the CPU affinity syscalls or cpuset.
1704 <cpu number> begins at 0 and the maximum value is
1705 "number of CPUs in system - 1".
1707 This option is the preferred way to isolate CPUs. The
1708 alternative -- manually setting the CPU mask of all
1709 tasks in the system -- can cause problems and
1710 suboptimal load balancer performance.
1714 ivrs_ioapic [HW,X86_64]
1715 Provide an override to the IOAPIC-ID<->DEVICE-ID
1716 mapping provided in the IVRS ACPI table. For
1717 example, to map IOAPIC-ID decimal 10 to
1718 PCI device 00:14.0 write the parameter as:
1719 ivrs_ioapic[10]=00:14.0
1721 ivrs_hpet [HW,X86_64]
1722 Provide an override to the HPET-ID<->DEVICE-ID
1723 mapping provided in the IVRS ACPI table. For
1724 example, to map HPET-ID decimal 0 to
1725 PCI device 00:14.0 write the parameter as:
1726 ivrs_hpet[0]=00:14.0
1728 ivrs_acpihid [HW,X86_64]
1729 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1730 mapping provided in the IVRS ACPI table. For
1731 example, to map UART-HID:UID AMD0020:0 to
1732 PCI device 00:14.5 write the parameter as:
1733 ivrs_acpihid[00:14.5]=AMD0020:0
1735 js= [HW,JOY] Analog joystick
1736 See Documentation/input/joystick.txt.
1739 When CONFIG_RANDOMIZE_BASE is set, this disables
1740 kernel and module base offset ASLR (Address Space
1741 Layout Randomization).
1744 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1745 report on every invalid memory access. Without this
1746 parameter KASAN will print report only for the first
1751 kernelcore= [KNL,X86,IA-64,PPC]
1752 Format: nn[KMGTPE] | "mirror"
1754 specifies the amount of memory usable by the kernel
1755 for non-movable allocations. The requested amount is
1756 spread evenly throughout all nodes in the system. The
1757 remaining memory in each node is used for Movable
1758 pages. In the event, a node is too small to have both
1759 kernelcore and Movable pages, kernelcore pages will
1760 take priority and other nodes will have a larger number
1761 of Movable pages. The Movable zone is used for the
1762 allocation of pages that may be reclaimed or moved
1763 by the page migration subsystem. This means that
1764 HugeTLB pages may not be allocated from this zone.
1765 Note that allocations like PTEs-from-HighMem still
1766 use the HighMem zone if it exists, and the Normal
1767 zone if it does not.
1769 Instead of specifying the amount of memory (nn[KMGTPE]),
1770 you can specify "mirror" option. In case "mirror"
1771 option is specified, mirrored (reliable) memory is used
1772 for non-movable allocations and remaining memory is used
1773 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1774 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1777 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1778 Format: <Controller#>[,poll interval]
1779 The controller # is the number of the ehci usb debug
1780 port as it is probed via PCI. The poll interval is
1781 optional and is the number seconds in between
1782 each poll cycle to the debug port in case you need
1783 the functionality for interrupting the kernel with
1784 gdb or control-c on the dbgp connection. When
1785 not using this parameter you use sysrq-g to break into
1786 the kernel debugger.
1788 kgdboc= [KGDB,HW] kgdb over consoles.
1789 Requires a tty driver that supports console polling,
1790 or a supported polling keyboard driver (non-usb).
1791 Serial only format: <serial_device>[,baud]
1792 keyboard only format: kbd
1793 keyboard and serial format: kbd,<serial_device>[,baud]
1794 Optional Kernel mode setting:
1795 kms, kbd format: kms,kbd
1796 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1798 kgdbwait [KGDB] Stop kernel execution and enter the
1799 kernel debugger at the earliest opportunity.
1801 kmac= [MIPS] korina ethernet MAC address.
1802 Configure the RouterBoard 532 series on-chip
1803 Ethernet adapter MAC address.
1805 kmemleak= [KNL] Boot-time kmemleak enable/disable
1806 Valid arguments: on, off
1808 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1811 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1812 Valid arguments: 0, 1, 2
1813 kmemcheck=0 (disabled)
1814 kmemcheck=1 (enabled)
1815 kmemcheck=2 (one-shot mode)
1816 Default: 2 (one-shot mode)
1818 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1819 Default is 0 (don't ignore, but inject #GP)
1821 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1825 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1826 Default is 1 (enabled)
1828 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1830 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1832 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1833 (virtualized MMU) support on capable Intel chips.
1834 Default is 1 (enabled)
1836 kvm-intel.emulate_invalid_guest_state=
1837 [KVM,Intel] Enable emulation of invalid guest states
1838 Default is 0 (disabled)
1840 kvm-intel.flexpriority=
1841 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1842 Default is 1 (enabled)
1845 [KVM,Intel] Enable VMX nesting (nVMX).
1846 Default is 0 (disabled)
1848 kvm-intel.unrestricted_guest=
1849 [KVM,Intel] Disable unrestricted guest feature
1850 (virtualized real and unpaged mode) on capable
1851 Intel chips. Default is 1 (enabled)
1853 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1854 feature (tagged TLBs) on capable Intel chips.
1855 Default is 1 (enabled)
1861 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1864 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1865 value for LAPIC timer one-shot implementation. Default
1866 back to the programmable timer unit in the LAPIC.
1868 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1871 libata.dma= [LIBATA] DMA control
1872 libata.dma=0 Disable all PATA and SATA DMA
1873 libata.dma=1 PATA and SATA Disk DMA only
1874 libata.dma=2 ATAPI (CDROM) DMA only
1875 libata.dma=4 Compact Flash DMA only
1876 Combinations also work, so libata.dma=3 enables DMA
1877 for disks and CDROMs, but not CFs.
1879 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1880 libata.ignore_hpa=0 keep BIOS limits (default)
1881 libata.ignore_hpa=1 ignore limits, using full disk
1883 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1887 libata.force= [LIBATA] Force configurations. The format is comma
1888 separated list of "[ID:]VAL" where ID is
1889 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1890 matching port, link or device. Basically, it matches
1891 the ATA ID string printed on console by libata. If
1892 the whole ID part is omitted, the last PORT and DEVICE
1893 values are used. If ID hasn't been specified yet, the
1894 configuration applies to all ports, links and devices.
1896 If only DEVICE is omitted, the parameter applies to
1897 the port and all links and devices behind it. DEVICE
1898 number of 0 either selects the first device or the
1899 first fan-out link behind PMP device. It does not
1900 select the host link. DEVICE number of 15 selects the
1901 host link and device attached to it.
1903 The VAL specifies the configuration to force. As long
1904 as there's no ambiguity shortcut notation is allowed.
1905 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1906 The following configurations can be forced.
1908 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1909 Any ID with matching PORT is used.
1911 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1913 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1914 udma[/][16,25,33,44,66,100,133] notation is also
1917 * [no]ncq: Turn on or off NCQ.
1919 * [no]ncqtrim: Turn off queued DSM TRIM.
1921 * nohrst, nosrst, norst: suppress hard, soft
1924 * rstonce: only attempt one reset during
1925 hot-unplug link recovery
1927 * dump_id: dump IDENTIFY data.
1929 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1931 * disable: Disable this device.
1933 If there are multiple matching configurations changing
1934 the same attribute, the last one is used.
1936 memblock=debug [KNL] Enable memblock debug messages.
1938 load_ramdisk= [RAM] List of ramdisks to load from floppy
1939 See Documentation/blockdev/ramdisk.txt.
1941 lockd.nlm_grace_period=P [NFS] Assign grace period.
1944 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1947 lockd.nlm_timeout=T [NFS] Assign timeout value.
1950 lockd.nlm_udpport=M [NFS] Assign UDP port.
1953 locktorture.nreaders_stress= [KNL]
1954 Set the number of locking read-acquisition kthreads.
1955 Defaults to being automatically set based on the
1956 number of online CPUs.
1958 locktorture.nwriters_stress= [KNL]
1959 Set the number of locking write-acquisition kthreads.
1961 locktorture.onoff_holdoff= [KNL]
1962 Set time (s) after boot for CPU-hotplug testing.
1964 locktorture.onoff_interval= [KNL]
1965 Set time (s) between CPU-hotplug operations, or
1966 zero to disable CPU-hotplug testing.
1968 locktorture.shuffle_interval= [KNL]
1969 Set task-shuffle interval (jiffies). Shuffling
1970 tasks allows some CPUs to go into dyntick-idle
1971 mode during the locktorture test.
1973 locktorture.shutdown_secs= [KNL]
1974 Set time (s) after boot system shutdown. This
1975 is useful for hands-off automated testing.
1977 locktorture.stat_interval= [KNL]
1978 Time (s) between statistics printk()s.
1980 locktorture.stutter= [KNL]
1981 Time (s) to stutter testing, for example,
1982 specifying five seconds causes the test to run for
1983 five seconds, wait for five seconds, and so on.
1984 This tests the locking primitive's ability to
1985 transition abruptly to and from idle.
1987 locktorture.torture_runnable= [BOOT]
1988 Start locktorture running at boot time.
1990 locktorture.torture_type= [KNL]
1991 Specify the locking implementation to test.
1993 locktorture.verbose= [KNL]
1994 Enable additional printk() statements.
1996 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1999 loglevel= All Kernel Messages with a loglevel smaller than the
2000 console loglevel will be printed to the console. It can
2001 also be changed with klogd or other programs. The
2002 loglevels are defined as follows:
2004 0 (KERN_EMERG) system is unusable
2005 1 (KERN_ALERT) action must be taken immediately
2006 2 (KERN_CRIT) critical conditions
2007 3 (KERN_ERR) error conditions
2008 4 (KERN_WARNING) warning conditions
2009 5 (KERN_NOTICE) normal but significant condition
2010 6 (KERN_INFO) informational
2011 7 (KERN_DEBUG) debug-level messages
2013 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2014 in bytes. n must be a power of two and greater
2015 than the minimal size. The minimal size is defined
2016 by LOG_BUF_SHIFT kernel config parameter. There is
2017 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2018 that allows to increase the default size depending on
2019 the number of CPUs. See init/Kconfig for more details.
2021 logo.nologo [FB] Disables display of the built-in Linux logo.
2022 This may be used to provide more screen space for
2023 kernel log messages and is useful when debugging
2024 kernel boot problems.
2026 lp=0 [LP] Specify parallel ports to use, e.g,
2027 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2028 lp=reset first parallel port). 'lp=0' disables the
2029 lp=auto printer driver. 'lp=reset' (which can be
2030 specified in addition to the ports) causes
2031 attached printers to be reset. Using
2032 lp=port1,port2,... specifies the parallel ports
2033 to associate lp devices with, starting with
2034 lp0. A port specification may be 'none' to skip
2035 that lp device, or a parport name such as
2036 'parport0'. Specifying 'lp=auto' instead of a
2037 port specification list means that device IDs
2038 from each port should be examined, to see if
2039 an IEEE 1284-compliant printer is attached; if
2040 so, the driver will manage that printer.
2041 See also header of drivers/char/lp.c.
2044 Sets loops_per_jiffy to given constant, thus avoiding
2045 time-consuming boot-time autodetection (up to 250 ms per
2046 CPU). 0 enables autodetection (default). To determine
2047 the correct value for your kernel, boot with normal
2048 autodetection and see what value is printed. Note that
2049 on SMP systems the preset will be applied to all CPUs,
2050 which is likely to cause problems if your CPUs need
2051 significantly divergent settings. An incorrect value
2052 will cause delays in the kernel to be wrong, leading to
2053 unpredictable I/O errors and other breakage. Although
2054 unlikely, in the extreme case this might damage your
2058 Format: <io>,<irq>,<dma>
2060 machvec= [IA-64] Force the use of a particular machine-vector
2061 (machvec) in a generic kernel.
2062 Example: machvec=hpzx1_swiotlb
2064 machtype= [Loongson] Share the same kernel image file between different
2066 Example: machtype=lemote-yeeloong-2f-7inch
2068 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2069 than or equal to this physical address is ignored.
2071 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2072 will bring up during bootup. maxcpus=n : n >= 0 limits
2073 the kernel to bring up 'n' processors. Surely after
2074 bootup you can bring up the other plugged cpu by executing
2075 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2076 only takes effect during system bootup.
2077 While n=0 is a special case, it is equivalent to "nosmp",
2078 which also disables the IO APIC.
2080 max_loop= [LOOP] The number of loop block devices that get
2081 (loop.max_loop) unconditionally pre-created at init time. The default
2082 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2083 of statically allocating a predefined number, loop
2084 devices can be requested on-demand with the
2085 /dev/loop-control interface.
2087 mce [X86-32] Machine Check Exception
2089 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2091 md= [HW] RAID subsystems devices and level
2092 See Documentation/admin-guide/md.rst.
2095 Format: <first>,<last>
2096 Specifies range of consoles to be captured by the MDA.
2098 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2099 Amount of memory to be used when the kernel is not able
2100 to see the whole system memory or for test.
2101 [X86] Work as limiting max address. Use together
2102 with memmap= to avoid physical address space collisions.
2103 Without memmap= PCI devices could be placed at addresses
2104 belonging to unused RAM.
2106 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2110 [KNL,SH] Allow user to override the default size for
2111 per-device physically contiguous DMA buffers.
2113 memhp_default_state=online/offline
2114 [KNL] Set the initial state for the memory hotplug
2115 onlining policy. If not specified, the default value is
2116 set according to the
2117 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2119 See Documentation/memory-hotplug.txt.
2121 memmap=exactmap [KNL,X86] Enable setting of an exact
2122 E820 memory map, as specified by the user.
2123 Such memmap=exactmap lines can be constructed based on
2124 BIOS output or other requirements. See the memmap=nn@ss
2127 memmap=nn[KMG]@ss[KMG]
2128 [KNL] Force usage of a specific region of memory.
2129 Region of memory to be used is from ss to ss+nn.
2131 memmap=nn[KMG]#ss[KMG]
2132 [KNL,ACPI] Mark specific memory as ACPI data.
2133 Region of memory to be marked is from ss to ss+nn.
2135 memmap=nn[KMG]$ss[KMG]
2136 [KNL,ACPI] Mark specific memory as reserved.
2137 Region of memory to be reserved is from ss to ss+nn.
2138 Example: Exclude memory from 0x18690000-0x1869ffff
2139 memmap=64K$0x18690000
2141 memmap=0x10000$0x18690000
2143 memmap=nn[KMG]!ss[KMG]
2144 [KNL,X86] Mark specific memory as protected.
2145 Region of memory to be used, from ss to ss+nn.
2146 The memory region may be marked as e820 type 12 (0xc)
2147 and is NVDIMM or ADR memory.
2149 memory_corruption_check=0/1 [X86]
2150 Some BIOSes seem to corrupt the first 64k of
2151 memory when doing things like suspend/resume.
2152 Setting this option will scan the memory
2153 looking for corruption. Enabling this will
2154 both detect corruption and prevent the kernel
2155 from using the memory being corrupted.
2156 However, its intended as a diagnostic tool; if
2157 repeatable BIOS-originated corruption always
2158 affects the same memory, you can use memmap=
2159 to prevent the kernel from using that memory.
2161 memory_corruption_check_size=size [X86]
2162 By default it checks for corruption in the low
2163 64k, making this memory unavailable for normal
2164 use. Use this parameter to scan for
2165 corruption in more or less memory.
2167 memory_corruption_check_period=seconds [X86]
2168 By default it checks for corruption every 60
2169 seconds. Use this parameter to check at some
2170 other rate. 0 disables periodic checking.
2172 memtest= [KNL,X86,ARM] Enable memtest
2174 default : 0 <disable>
2175 Specifies the number of memtest passes to be
2176 performed. Each pass selects another test
2177 pattern from a given set of patterns. Memtest
2178 fills the memory with this pattern, validates
2179 memory contents and reserves bad memory
2180 regions that are detected.
2182 mem_sleep_default= [SUSPEND] Default system suspend mode:
2183 s2idle - Suspend-To-Idle
2184 shallow - Power-On Suspend or equivalent (if supported)
2185 deep - Suspend-To-RAM or equivalent (if supported)
2186 See Documentation/power/states.txt.
2188 meye.*= [HW] Set MotionEye Camera parameters
2189 See Documentation/video4linux/meye.txt.
2191 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2192 Multi-Function General Purpose Timers on AMD Geode
2195 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2196 the BIOS has incorrectly applied a workaround. TinyBIOS
2197 version 0.98 is known to be affected, 0.99 fixes the
2198 problem by letting the user disable the workaround.
2202 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2203 physical address is ignored.
2205 mini2440= [ARM,HW,KNL]
2206 Format:[0..2][b][c][t]
2208 MINI2440 configuration specification:
2209 0 - The attached screen is the 3.5" TFT
2210 1 - The attached screen is the 7" TFT
2211 2 - The VGA Shield is attached (1024x768)
2212 Leaving out the screen size parameter will not load
2213 the TFT driver, and the framebuffer will be left
2215 b - Enable backlight. The TFT backlight pin will be
2216 linked to the kernel VESA blanking code and a GPIO
2217 LED. This parameter is not necessary when using the
2219 c - Enable the s3c camera interface.
2220 t - Reserved for enabling touchscreen support. The
2221 touchscreen support is not enabled in the mainstream
2222 kernel as of 2.6.30, a preliminary port can be found
2223 in the "bleeding edge" mini2440 support kernel at
2224 http://repo.or.cz/w/linux-2.6/mini2440.git
2227 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2228 parameter allows control of the logging verbosity for
2229 the additional memory initialisation checks. A value
2230 of 0 disables mminit logging and a level of 4 will
2231 log everything. Information is printed at KERN_DEBUG
2232 so loglevel=8 may also need to be specified.
2235 [KNL] When CONFIG_MODULE_SIG is set, this means that
2236 modules without (valid) signatures will fail to load.
2237 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2238 is always true, so this option does nothing.
2240 module_blacklist= [KNL] Do not load a comma-separated list of
2241 modules. Useful for debugging problem modules.
2244 [MOUSE] Maximum time between finger touching and
2245 leaving touchpad surface for touch to be considered
2246 a tap and be reported as a left button click (for
2247 touchpads working in absolute mode only).
2249 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2250 reporting absolute coordinates, such as tablets
2251 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2252 reporting absolute coordinates, such as tablets
2254 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2255 is similar to kernelcore except it specifies the
2256 amount of memory used for migratable allocations.
2257 If both kernelcore and movablecore is specified,
2258 then kernelcore will be at *least* the specified
2259 value but may be more. If movablecore on its own
2260 is specified, the administrator must be careful
2261 that the amount of memory usable for all allocations
2264 movable_node [KNL] Boot-time switch to enable the effects
2265 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2267 MTD_Partition= [MTD]
2268 Format: <name>,<region-number>,<size>,<offset>
2270 MTD_Region= [MTD] Format:
2271 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2274 See drivers/mtd/cmdlinepart.c.
2276 multitce=off [PPC] This parameter disables the use of the pSeries
2277 firmware feature for updating multiple TCE entries
2280 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2282 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2284 boundary - index of last SLC block on Flex-OneNAND.
2285 The remaining blocks are configured as MLC blocks.
2286 lock - Configure if Flex-OneNAND boundary should be locked.
2287 Once locked, the boundary cannot be changed.
2288 1 indicates lock status, 0 indicates unlock status.
2291 ARM/S3C2412 JIVE boot control
2293 See arch/arm/mach-s3c2412/mach-jive.c
2295 mtouchusb.raw_coordinates=
2296 [HW] Make the MicroTouch USB driver use raw coordinates
2297 ('y', default) or cooked coordinates ('n')
2299 mtrr_chunk_size=nn[KMG] [X86]
2300 used for mtrr cleanup. It is largest continuous chunk
2301 that could hold holes aka. UC entries.
2303 mtrr_gran_size=nn[KMG] [X86]
2304 Used for mtrr cleanup. It is granularity of mtrr block.
2306 Large value could prevent small alignment from
2309 mtrr_spare_reg_nr=n [X86]
2311 Range: 0,7 : spare reg number
2313 Used for mtrr cleanup. It is spare mtrr entries number.
2314 Set to 2 or more if your graphical card needs more.
2316 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2318 netdev= [NET] Network devices parameters
2319 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2320 Note that mem_start is often overloaded to mean
2321 something different and driver-specific.
2322 This usage is only documented in each driver source
2326 [NETFILTER] Enable connection tracking flow accounting
2327 0 to disable accounting
2328 1 to enable accounting
2331 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2332 See Documentation/filesystems/nfs/nfsroot.txt.
2334 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2335 See Documentation/filesystems/nfs/nfsroot.txt.
2337 nfsrootdebug [NFS] enable nfsroot debugging messages.
2338 See Documentation/filesystems/nfs/nfsroot.txt.
2340 nfs.callback_nr_threads=
2341 [NFSv4] set the total number of threads that the
2342 NFS client will assign to service NFSv4 callback
2345 nfs.callback_tcpport=
2346 [NFS] set the TCP port on which the NFSv4 callback
2347 channel should listen.
2350 [NFS] sets the pathname to the program which is used
2351 to update the NFS client cache entries.
2353 nfs.cache_getent_timeout=
2354 [NFS] sets the timeout after which an attempt to
2355 update a cache entry is deemed to have failed.
2357 nfs.idmap_cache_timeout=
2358 [NFS] set the maximum lifetime for idmapper cache
2362 [NFS] enable 64-bit inode numbers.
2363 If zero, the NFS client will fake up a 32-bit inode
2364 number for the readdir() and stat() syscalls instead
2365 of returning the full 64-bit number.
2366 The default is to return 64-bit inode numbers.
2368 nfs.max_session_cb_slots=
2369 [NFSv4.1] Sets the maximum number of session
2370 slots the client will assign to the callback
2371 channel. This determines the maximum number of
2372 callbacks the client will process in parallel for
2373 a particular server.
2375 nfs.max_session_slots=
2376 [NFSv4.1] Sets the maximum number of session slots
2377 the client will attempt to negotiate with the server.
2378 This limits the number of simultaneous RPC requests
2379 that the client can send to the NFSv4.1 server.
2380 Note that there is little point in setting this
2381 value higher than the max_tcp_slot_table_limit.
2383 nfs.nfs4_disable_idmapping=
2384 [NFSv4] When set to the default of '1', this option
2385 ensures that both the RPC level authentication
2386 scheme and the NFS level operations agree to use
2387 numeric uids/gids if the mount is using the
2388 'sec=sys' security flavour. In effect it is
2389 disabling idmapping, which can make migration from
2390 legacy NFSv2/v3 systems to NFSv4 easier.
2391 Servers that do not support this mode of operation
2392 will be autodetected by the client, and it will fall
2393 back to using the idmapper.
2394 To turn off this behaviour, set the value to '0'.
2396 [NFS4] Specify an additional fixed unique ident-
2397 ification string that NFSv4 clients can insert into
2398 their nfs_client_id4 string. This is typically a
2399 UUID that is generated at system install time.
2401 nfs.send_implementation_id =
2402 [NFSv4.1] Send client implementation identification
2403 information in exchange_id requests.
2404 If zero, no implementation identification information
2406 The default is to send the implementation identification
2409 nfs.recover_lost_locks =
2410 [NFSv4] Attempt to recover locks that were lost due
2411 to a lease timeout on the server. Please note that
2412 doing this risks data corruption, since there are
2413 no guarantees that the file will remain unchanged
2414 after the locks are lost.
2415 If you want to enable the kernel legacy behaviour of
2416 attempting to recover these locks, then set this
2418 The default parameter value of '0' causes the kernel
2419 not to attempt recovery of lost locks.
2421 nfs4.layoutstats_timer =
2422 [NFSv4.2] Change the rate at which the kernel sends
2423 layoutstats to the pNFS metadata server.
2425 Setting this to value to 0 causes the kernel to use
2426 whatever value is the default set by the layout
2427 driver. A non-zero value sets the minimum interval
2428 in seconds between layoutstats transmissions.
2430 nfsd.nfs4_disable_idmapping=
2431 [NFSv4] When set to the default of '1', the NFSv4
2432 server will return only numeric uids and gids to
2433 clients using auth_sys, and will accept numeric uids
2434 and gids from such clients. This is intended to ease
2435 migration from NFSv2/v3.
2437 objlayoutdriver.osd_login_prog=
2438 [NFS] [OBJLAYOUT] sets the pathname to the program which
2439 is used to automatically discover and login into new
2440 osd-targets. Please see:
2441 Documentation/filesystems/pnfs.txt for more explanations
2443 nmi_debug= [KNL,SH] Specify one or more actions to take
2444 when a NMI is triggered.
2445 Format: [state][,regs][,debounce][,die]
2447 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2448 Format: [panic,][nopanic,][num]
2450 0 - turn hardlockup detector in nmi_watchdog off
2451 1 - turn hardlockup detector in nmi_watchdog on
2452 When panic is specified, panic when an NMI watchdog
2453 timeout occurs (or 'nopanic' to override the opposite
2454 default). To disable both hard and soft lockup detectors,
2455 please see 'nowatchdog'.
2456 This is useful when you use a panic=... timeout and
2457 need the box quickly up again.
2459 netpoll.carrier_timeout=
2460 [NET] Specifies amount of time (in seconds) that
2461 netpoll should wait for a carrier. By default netpoll
2464 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2465 emulation library even if a 387 maths coprocessor
2469 [HW] Never suspend the console
2470 Disable suspending of consoles during suspend and
2471 hibernate operations. Once disabled, debugging
2472 messages can reach various consoles while the rest
2473 of the system is being put to sleep (ie, while
2474 debugging driver suspend/resume hooks). This may
2475 not work reliably with all consoles, but is known
2476 to work with serial and VGA consoles.
2477 To facilitate more flexible debugging, we also add
2478 console_suspend, a printk module parameter to control
2479 it. Users could use console_suspend (usually
2480 /sys/module/printk/parameters/console_suspend) to
2481 turn on/off it dynamically.
2483 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2484 caches in the slab allocator. Saves per-node memory,
2485 but will impact performance.
2489 noapic [SMP,APIC] Tells the kernel to not make use of any
2490 IOAPICs that may be present in the system.
2492 noautogroup Disable scheduler automatic task group creation.
2494 nobats [PPC] Do not use BATs for mapping kernel lowmem
2495 on "Classic" PPC cores.
2499 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2501 nodelayacct [KNL] Disable per-task delay accounting
2503 nodsp [SH] Disable hardware DSP at boot time.
2505 noefi Disable EFI runtime services support.
2510 On X86-32 available only on PAE configured kernels.
2511 noexec=on: enable non-executable mappings (default)
2512 noexec=off: disable non-executable mappings
2515 Disable SMAP (Supervisor Mode Access Prevention)
2516 even if it is supported by processor.
2519 Disable SMEP (Supervisor Mode Execution Prevention)
2520 even if it is supported by processor.
2523 This affects only 32-bit executables.
2524 noexec32=on: enable non-executable mappings (default)
2525 read doesn't imply executable mappings
2526 noexec32=off: disable non-executable mappings
2527 read implies executable mappings
2529 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2531 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2532 register save and restore. The kernel will only save
2533 legacy floating-point registers on task switch.
2535 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2537 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2538 Equivalent to smt=1.
2540 noxsave [BUGS=X86] Disables x86 extended register state save
2541 and restore using xsave. The kernel will fallback to
2542 enabling legacy floating-point and sse state.
2544 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2545 register states. The kernel will fall back to use
2546 xsave to save the states. By using this parameter,
2547 performance of saving the states is degraded because
2548 xsave doesn't support modified optimization while
2549 xsaveopt supports it on xsaveopt enabled systems.
2551 noxsaves [X86] Disables xsaves and xrstors used in saving and
2552 restoring x86 extended register state in compacted
2553 form of xsave area. The kernel will fall back to use
2554 xsaveopt and xrstor to save and restore the states
2555 in standard form of xsave area. By using this
2556 parameter, xsave area per process might occupy more
2557 memory on xsaves enabled systems.
2559 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2560 wfi(ARM) instruction doesn't work correctly and not to
2561 use it. This is also useful when using JTAG debugger.
2563 no_file_caps Tells the kernel not to honor file capabilities. The
2564 only way then for a file to be executed with privilege
2565 is to be setuid root or executed by root.
2567 nohalt [IA-64] Tells the kernel not to use the power saving
2568 function PAL_HALT_LIGHT when idle. This increases
2569 power-consumption. On the positive side, it reduces
2570 interrupt wake-up latency, which may improve performance
2571 in certain environments such as networked servers or
2574 nohibernate [HIBERNATION] Disable hibernation and resume.
2576 nohz= [KNL] Boottime enable/disable dynamic ticks
2577 Valid arguments: on, off
2580 nohz_full= [KNL,BOOT]
2581 The argument is a cpu list, as described above.
2582 In kernels built with CONFIG_NO_HZ_FULL=y, set
2583 the specified list of CPUs whose tick will be stopped
2584 whenever possible. The boot CPU will be forced outside
2585 the range to maintain the timekeeping.
2586 The CPUs in this range must also be included in the
2589 noiotrap [SH] Disables trapped I/O port accesses.
2591 noirqdebug [X86-32] Disables the code which attempts to detect and
2592 disable unhandled interrupt sources.
2594 no_timer_check [X86,APIC] Disables the code which tests for
2595 broken timer IRQ sources.
2597 noisapnp [ISAPNP] Disables ISA PnP code.
2599 noinitrd [RAM] Tells the kernel not to load any configured
2602 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2604 [Deprecated - use intremap=off]
2608 noinvpcid [X86] Disable the INVPCID cpu feature.
2610 nojitter [IA-64] Disables jitter checking for ITC timers.
2612 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2614 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2618 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2619 clock and use the default one.
2621 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2622 steal time is computed, but won't influence scheduler
2625 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2627 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2629 noltlbs [PPC] Do not use large page/tlb entries for kernel
2630 lowmem mapping on PPC40x and PPC8xx
2632 nomca [IA-64] Disable machine check abort handling
2634 nomce [X86-32] Disable Machine Check Exception
2636 nomfgpt [X86-32] Disable Multi-Function General Purpose
2637 Timer usage (for AMD Geode machines).
2639 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2640 shutdown the other cpus. Instead use the REBOOT_VECTOR
2643 nomodule Disable module load
2645 nopat [X86] Disable PAT (page attribute table extension of
2646 pagetables) support.
2648 norandmaps Don't use address space randomization. Equivalent to
2649 echo 0 > /proc/sys/kernel/randomize_va_space
2651 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2653 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2654 with UP alternatives
2656 nordrand [X86] Disable kernel use of the RDRAND and
2657 RDSEED instructions even if they are supported
2658 by the processor. RDRAND and RDSEED are still
2659 available to user space applications.
2661 noresume [SWSUSP] Disables resume and restores original swap
2664 no-scroll [VGA] Disables scrollback.
2665 This is required for the Braillex ib80-piezo Braille
2666 reader made by F.H. Papenmeier (Germany).
2670 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2672 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2673 and disable the IO APIC. legacy for "maxcpus=0".
2675 nosoftlockup [KNL] Disable the soft-lockup detector.
2677 nosync [HW,M68K] Disables sync negotiation for all devices.
2679 notsc [BUGS=X86-32] Disable Time Stamp Counter
2681 nowatchdog [KNL] Disable both lockup detectors, i.e.
2682 soft-lockup and NMI watchdog (hard-lockup).
2686 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2688 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2689 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2690 Some features depend on CPU0. Known dependencies are:
2691 1. Resume from suspend/hibernate depends on CPU0.
2692 Suspend/hibernate will fail if CPU0 is offline and you
2693 need to online CPU0 before suspend/hibernate.
2694 2. PIC interrupts also depend on CPU0. CPU0 can't be
2695 removed if a PIC interrupt is detected.
2696 It's said poweroff/reboot may depend on CPU0 on some
2697 machines although I haven't seen such issues so far
2698 after CPU0 is offline on a few tested machines.
2699 If the dependencies are under your control, you can
2700 turn on cpu0_hotplug.
2702 nptcg= [IA-64] Override max number of concurrent global TLB
2703 purges which is reported from either PAL_VM_SUMMARY or
2706 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2707 could support. nr_cpus=n : n >= 1 limits the kernel to
2708 support 'n' processors. It could be larger than the
2709 number of already plugged CPU during bootup, later in
2710 runtime you can physically add extra cpu until it reaches
2711 n. So during boot up some boot time memory for per-cpu
2712 variables need be pre-allocated for later physical cpu
2715 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2717 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2718 Allowed values are enable and disable
2720 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2721 one of ['zone', 'node', 'default'] can be specified
2722 This can be set from sysctl after boot.
2723 See Documentation/sysctl/vm.txt for details.
2725 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2726 See Documentation/debugging-via-ohci1394.txt for more
2729 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2730 Rather than timing out after 20 ms if an EC
2731 command is not properly ACKed, override the length
2732 of the timeout. We have interrupts disabled while
2733 waiting for the ACK, so if this is set too high
2734 interrupts *may* be lost!
2736 omap_mux= [OMAP] Override bootloader pin multiplexing.
2737 Format: <mux_mode0.mode_name=value>...
2738 For example, to override I2C bus2:
2739 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2741 oprofile.timer= [HW]
2742 Use timer interrupt instead of performance counters
2744 oprofile.cpu_type= Force an oprofile cpu type
2745 This might be useful if you have an older oprofile
2746 userland or if you want common events.
2747 Format: { arch_perfmon }
2748 arch_perfmon: [X86] Force use of architectural
2749 perfmon on Intel CPUs instead of the
2750 CPU specific event set.
2751 timer: [X86] Force use of architectural NMI
2752 timer mode (see also oprofile.timer
2753 for generic hr timer mode)
2755 oops=panic Always panic on oopses. Default is to just kill the
2756 process, but there is a small probability of
2757 deadlocking the machine.
2758 This will also cause panics on machine check exceptions.
2759 Useful together with panic=30 to trigger a reboot.
2762 See Documentation/sound/oss/oss-parameters.txt
2764 page_owner= [KNL] Boot-time page_owner enabling option.
2765 Storage of the information about who allocated
2766 each page is disabled in default. With this switch,
2768 on: enable the feature
2770 page_poison= [KNL] Boot-time parameter changing the state of
2771 poisoning on the buddy allocator.
2772 off: turn off poisoning
2773 on: turn on poisoning
2775 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2776 timeout > 0: seconds before rebooting
2777 timeout = 0: wait forever
2778 timeout < 0: reboot immediately
2781 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2784 crash_kexec_post_notifiers
2785 Run kdump after running panic-notifiers and dumping
2786 kmsg. This only for the users who doubt kdump always
2787 succeeds in any situation.
2788 Note that this also increases risks of kdump failure,
2789 because some panic notifiers can make the crashed
2790 kernel more unstable.
2792 parkbd.port= [HW] Parallel port number the keyboard adapter is
2793 connected to, default is 0.
2795 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2796 0 for XT, 1 for AT (default is AT).
2799 parport= [HW,PPT] Specify parallel ports. 0 disables.
2800 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2801 Use 'auto' to force the driver to use any
2802 IRQ/DMA settings detected (the default is to
2803 ignore detected IRQ/DMA settings because of
2804 possible conflicts). You can specify the base
2805 address, IRQ, and DMA settings; IRQ and DMA
2806 should be numbers, or 'auto' (for using detected
2807 settings on that particular port), or 'nofifo'
2808 (to avoid using a FIFO even if it is detected).
2809 Parallel ports are assigned in the order they
2810 are specified on the command line, starting
2813 parport_init_mode= [HW,PPT]
2814 Configure VIA parallel port to operate in
2815 a specific mode. This is necessary on Pegasos
2816 computer where firmware has no options for setting
2817 up parallel port mode and sets it to spp.
2818 Currently this function knows 686a and 8231 chips.
2819 Format: [spp|ps2|epp|ecp|ecpepp]
2822 Halt all CPUs after the first oops has been printed for
2823 the specified number of seconds. This is to be used if
2824 your oopses keep scrolling off the screen.
2829 See header of drivers/block/paride/pcd.c.
2830 See also Documentation/blockdev/paride.txt.
2832 pci=option[,option...] [PCI] various PCI subsystem options:
2833 earlydump [X86] dump PCI config space before the kernel
2835 off [X86] don't probe for the PCI bus
2836 bios [X86-32] force use of PCI BIOS, don't access
2837 the hardware directly. Use this if your machine
2838 has a non-standard PCI host bridge.
2839 nobios [X86-32] disallow use of PCI BIOS, only direct
2840 hardware access methods are allowed. Use this
2841 if you experience crashes upon bootup and you
2842 suspect they are caused by the BIOS.
2843 conf1 [X86] Force use of PCI Configuration Access
2844 Mechanism 1 (config address in IO port 0xCF8,
2845 data in IO port 0xCFC, both 32-bit).
2846 conf2 [X86] Force use of PCI Configuration Access
2847 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2848 the function, IO port 0xCFA, also 8-bit, sets
2849 bus number. The config space is then accessed
2850 through ports 0xC000-0xCFFF).
2851 See http://wiki.osdev.org/PCI for more info
2852 on the configuration access mechanisms.
2853 noaer [PCIE] If the PCIEAER kernel config parameter is
2854 enabled, this kernel boot option can be used to
2855 disable the use of PCIE advanced error reporting.
2856 nodomains [PCI] Disable support for multiple PCI
2857 root domains (aka PCI segments, in ACPI-speak).
2858 nommconf [X86] Disable use of MMCONFIG for PCI
2860 check_enable_amd_mmconf [X86] check for and enable
2861 properly configured MMIO access to PCI
2862 config space on AMD family 10h CPU
2863 nomsi [MSI] If the PCI_MSI kernel config parameter is
2864 enabled, this kernel boot option can be used to
2865 disable the use of MSI interrupts system-wide.
2866 noioapicquirk [APIC] Disable all boot interrupt quirks.
2867 Safety option to keep boot IRQs enabled. This
2868 should never be necessary.
2869 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2870 primary IO-APIC for bridges that cannot disable
2871 boot IRQs. This fixes a source of spurious IRQs
2872 when the system masks IRQs.
2873 noioapicreroute [APIC] Disable workaround that uses the
2874 boot IRQ equivalent of an IRQ that connects to
2875 a chipset where boot IRQs cannot be disabled.
2876 The opposite of ioapicreroute.
2877 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2878 routing table. These calls are known to be buggy
2879 on several machines and they hang the machine
2880 when used, but on other computers it's the only
2881 way to get the interrupt routing table. Try
2882 this option if the kernel is unable to allocate
2883 IRQs or discover secondary PCI buses on your
2885 rom [X86] Assign address space to expansion ROMs.
2886 Use with caution as certain devices share
2887 address decoders between ROMs and other
2889 norom [X86] Do not assign address space to
2890 expansion ROMs that do not already have
2891 BIOS assigned address ranges.
2892 nobar [X86] Do not assign address space to the
2893 BARs that weren't assigned by the BIOS.
2894 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2895 assigned automatically to PCI devices. You can
2896 make the kernel exclude IRQs of your ISA cards
2898 pirqaddr=0xAAAAA [X86] Specify the physical address
2899 of the PIRQ table (normally generated
2900 by the BIOS) if it is outside the
2901 F0000h-100000h range.
2902 lastbus=N [X86] Scan all buses thru bus #N. Can be
2903 useful if the kernel is unable to find your
2904 secondary buses and you want to tell it
2905 explicitly which ones they are.
2906 assign-busses [X86] Always assign all PCI bus
2907 numbers ourselves, overriding
2908 whatever the firmware may have done.
2909 usepirqmask [X86] Honor the possible IRQ mask stored
2910 in the BIOS $PIR table. This is needed on
2911 some systems with broken BIOSes, notably
2912 some HP Pavilion N5400 and Omnibook XE3
2913 notebooks. This will have no effect if ACPI
2914 IRQ routing is enabled.
2915 noacpi [X86] Do not use ACPI for IRQ routing
2916 or for PCI scanning.
2917 use_crs [X86] Use PCI host bridge window information
2918 from ACPI. On BIOSes from 2008 or later, this
2919 is enabled by default. If you need to use this,
2920 please report a bug.
2921 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2922 If you need to use this, please report a bug.
2923 routeirq Do IRQ routing for all PCI devices.
2924 This is normally done in pci_enable_device(),
2925 so this option is a temporary workaround
2926 for broken drivers that don't call it.
2927 skip_isa_align [X86] do not align io start addr, so can
2928 handle more pci cards
2929 noearly [X86] Don't do any early type 1 scanning.
2930 This might help on some broken boards which
2931 machine check when some devices' config space
2932 is read. But various workarounds are disabled
2933 and some IOMMU drivers will not work.
2934 bfsort Sort PCI devices into breadth-first order.
2935 This sorting is done to get a device
2936 order compatible with older (<= 2.4) kernels.
2937 nobfsort Don't sort PCI devices into breadth-first order.
2938 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2939 tuning and use the BIOS-configured MPS defaults.
2940 pcie_bus_safe Set every device's MPS to the largest value
2941 supported by all devices below the root complex.
2942 pcie_bus_perf Set device MPS to the largest allowable MPS
2943 based on its parent bus. Also set MRRS (Max
2944 Read Request Size) to the largest supported
2945 value (no larger than the MPS that the device
2946 or bus can support) for best performance.
2947 pcie_bus_peer2peer Set every device's MPS to 128B, which
2948 every device is guaranteed to support. This
2949 configuration allows peer-to-peer DMA between
2950 any pair of devices, possibly at the cost of
2951 reduced performance. This also guarantees
2952 that hot-added devices will work.
2953 cbiosize=nn[KMG] The fixed amount of bus space which is
2954 reserved for the CardBus bridge's IO window.
2955 The default value is 256 bytes.
2956 cbmemsize=nn[KMG] The fixed amount of bus space which is
2957 reserved for the CardBus bridge's memory
2958 window. The default value is 64 megabytes.
2961 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2962 [<order of align>@]pci:<vendor>:<device>\
2963 [:<subvendor>:<subdevice>][; ...]
2964 Specifies alignment and device to reassign
2965 aligned memory resources.
2966 If <order of align> is not specified,
2967 PAGE_SIZE is used as alignment.
2968 PCI-PCI bridge can be specified, if resource
2969 windows need to be expanded.
2970 To specify the alignment for several
2971 instances of a device, the PCI vendor,
2972 device, subvendor, and subdevice may be
2973 specified, e.g., 4096@pci:8086:9c22:103c:198f
2974 ecrc= Enable/disable PCIe ECRC (transaction layer
2975 end-to-end CRC checking).
2976 bios: Use BIOS/firmware settings. This is the
2980 hpiosize=nn[KMG] The fixed amount of bus space which is
2981 reserved for hotplug bridge's IO window.
2982 Default size is 256 bytes.
2983 hpmemsize=nn[KMG] The fixed amount of bus space which is
2984 reserved for hotplug bridge's memory window.
2985 Default size is 2 megabytes.
2986 hpbussize=nn The minimum amount of additional bus numbers
2987 reserved for buses below a hotplug bridge.
2989 realloc= Enable/disable reallocating PCI bridge resources
2990 if allocations done by BIOS are too small to
2991 accommodate resources required by all child
2993 off: Turn realloc off
2995 realloc same as realloc=on
2996 noari do not use PCIe ARI.
2997 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2998 only look for one device below a PCIe downstream
3001 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3004 force Enable ASPM even on devices that claim not to support it.
3005 WARNING: Forcing ASPM on may cause system lockups.
3007 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3008 nomsi Do not use MSI for PCI Express Native Hotplug (this
3009 makes all PCIe ports use INTx for hotplug services).
3011 pcie_ports= [PCIE] PCIe ports handling:
3012 auto Ask the BIOS whether or not to use native PCIe services
3013 associated with PCIe ports (PME, hot-plug, AER). Use
3014 them only if that is allowed by the BIOS.
3015 native Use native PCIe services associated with PCIe ports
3017 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3020 pcie_port_pm= [PCIE] PCIe port power management handling:
3021 off Disable power management of all PCIe ports
3022 force Forcibly enable power management of all PCIe ports
3024 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3025 nomsi Do not use MSI for native PCIe PME signaling (this makes
3026 all PCIe root ports use INTx for all services).
3028 pcmv= [HW,PCMCIA] BadgePAD 4
3032 Keep all power-domains already enabled by bootloader on,
3033 even if no driver has claimed them. This is useful
3034 for debug and development, but should not be
3035 needed on a platform with proper driver support.
3038 See Documentation/blockdev/paride.txt.
3040 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3043 See arch/parisc/kernel/pdc_chassis.c
3045 percpu_alloc= Select which percpu first chunk allocator to use.
3046 Currently supported values are "embed" and "page".
3047 Archs may support subset or none of the selections.
3048 See comments in mm/percpu.c for details on each
3049 allocator. This parameter is primarily for debugging
3050 and performance comparison.
3053 See Documentation/blockdev/paride.txt.
3056 See Documentation/blockdev/paride.txt.
3058 pirq= [SMP,APIC] Manual mp-table setup
3059 See Documentation/x86/i386/IO-APIC.txt.
3061 plip= [PPT,NET] Parallel port network link
3062 Format: { parport<nr> | timid | 0 }
3063 See also Documentation/parport.txt.
3065 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3066 Override pmtimer IOPort with a hex value.
3070 Enable PNP debug messages (depends on the
3071 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3072 via /sys/module/pnp/parameters/debug. We always show
3073 current resource usage; turning this on also shows
3074 possible settings and some assignment information.
3080 { on | off | curr | res | no-curr | no-res }
3083 [ISAPNP] Exclude IRQs for the autoconfiguration
3086 [ISAPNP] Exclude DMAs for the autoconfiguration
3088 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3089 Ranges are in pairs (I/O port base and size).
3092 [ISAPNP] Exclude memory regions for the
3094 Ranges are in pairs (memory base and size).
3096 ports= [IP_VS_FTP] IPVS ftp helper module
3098 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3100 Format: <port>,<port>....
3102 powersave=off [PPC] This option disables power saving features.
3103 It specifically disables cpuidle and sets the
3104 platform machine description specific power_save
3105 function to NULL. On Idle the CPU just reduces
3108 ppc_strict_facility_enable
3109 [PPC] This option catches any kernel floating point,
3110 Altivec, VSX and SPE outside of regions specifically
3111 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3112 There is some performance impact when enabling this.
3114 print-fatal-signals=
3115 [KNL] debug: print fatal signals
3117 If enabled, warn about various signal handling
3118 related application anomalies: too many signals,
3119 too many POSIX.1 timers, fatal signals causing a
3122 If you hit the warning due to signal overflow,
3123 you might want to try "ulimit -i unlimited".
3127 printk.always_kmsg_dump=
3128 Trigger kmsg_dump for cases other than kernel oops or
3130 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3133 printk.devkmsg={on,off,ratelimit}
3134 Control writing to /dev/kmsg.
3135 on - unlimited logging to /dev/kmsg from userspace
3136 off - logging to /dev/kmsg disabled
3137 ratelimit - ratelimit the logging
3140 printk.time= Show timing data prefixed to each printk message line
3141 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3143 processor.max_cstate= [HW,ACPI]
3144 Limit processor to maximum C-state
3145 max_cstate=9 overrides any DMI blacklist limit.
3147 processor.nocst [HW,ACPI]
3148 Ignore the _CST method to determine C-states,
3149 instead using the legacy FADT method
3151 profile= [KNL] Enable kernel profiling via /proc/profile
3152 Format: [schedule,]<number>
3153 Param: "schedule" - profile schedule points.
3154 Param: <number> - step/bucket size as a power of 2 for
3155 statistical time based profiling.
3156 Param: "sleep" - profile D-state sleeping (millisecs).
3157 Requires CONFIG_SCHEDSTATS
3158 Param: "kvm" - profile VM exits.
3160 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3162 See Documentation/blockdev/ramdisk.txt.
3164 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3165 probe for; one of (bare|imps|exps|lifebook|any).
3166 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3168 psmouse.resetafter= [HW,MOUSE]
3169 Try to reset the device after so many bad packets
3172 [HW,MOUSE] Set desired mouse resolution, in dpi.
3173 psmouse.smartscroll=
3174 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3175 0 = disabled, 1 = enabled (default).
3177 pstore.backend= Specify the name of the pstore backend to use
3180 See Documentation/blockdev/paride.txt.
3183 [KNL] Number of legacy pty's. Overwrites compiled-in
3186 quiet [KNL] Disable most log messages
3191 See Documentation/admin-guide/md.rst.
3193 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3194 See Documentation/blockdev/ramdisk.txt.
3196 ras=option[,option,...] [KNL] RAS-specific options
3199 Disable the Correctable Errors Collector,
3200 see CONFIG_RAS_CEC help text.
3203 The argument is a cpu list, as described above.
3205 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3206 the specified list of CPUs to be no-callback CPUs.
3207 Invocation of these CPUs' RCU callbacks will
3208 be offloaded to "rcuox/N" kthreads created for
3209 that purpose, where "x" is "b" for RCU-bh, "p"
3210 for RCU-preempt, and "s" for RCU-sched, and "N"
3211 is the CPU number. This reduces OS jitter on the
3212 offloaded CPUs, which can be useful for HPC and
3213 real-time workloads. It can also improve energy
3214 efficiency for asymmetric multiprocessors.
3217 Rather than requiring that offloaded CPUs
3218 (specified by rcu_nocbs= above) explicitly
3219 awaken the corresponding "rcuoN" kthreads,
3220 make these kthreads poll for callbacks.
3221 This improves the real-time response for the
3222 offloaded CPUs by relieving them of the need to
3223 wake up the corresponding kthread, but degrades
3224 energy efficiency by requiring that the kthreads
3225 periodically wake up to do the polling.
3227 rcutree.blimit= [KNL]
3228 Set maximum number of finished RCU callbacks to
3229 process in one batch.
3231 rcutree.dump_tree= [KNL]
3232 Dump the structure of the rcu_node combining tree
3233 out at early boot. This is used for diagnostic
3234 purposes, to verify correct tree setup.
3236 rcutree.gp_cleanup_delay= [KNL]
3237 Set the number of jiffies to delay each step of
3238 RCU grace-period cleanup. This only has effect
3239 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3241 rcutree.gp_init_delay= [KNL]
3242 Set the number of jiffies to delay each step of
3243 RCU grace-period initialization. This only has
3244 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3247 rcutree.gp_preinit_delay= [KNL]
3248 Set the number of jiffies to delay each step of
3249 RCU grace-period pre-initialization, that is,
3250 the propagation of recent CPU-hotplug changes up
3251 the rcu_node combining tree. This only has effect
3252 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3254 rcutree.rcu_fanout_exact= [KNL]
3255 Disable autobalancing of the rcu_node combining
3256 tree. This is used by rcutorture, and might
3257 possibly be useful for architectures having high
3258 cache-to-cache transfer latencies.
3260 rcutree.rcu_fanout_leaf= [KNL]
3261 Change the number of CPUs assigned to each
3262 leaf rcu_node structure. Useful for very
3263 large systems, which will choose the value 64,
3264 and for NUMA systems with large remote-access
3265 latencies, which will choose a value aligned
3266 with the appropriate hardware boundaries.
3268 rcutree.jiffies_till_sched_qs= [KNL]
3269 Set required age in jiffies for a
3270 given grace period before RCU starts
3271 soliciting quiescent-state help from
3272 rcu_note_context_switch().
3274 rcutree.jiffies_till_first_fqs= [KNL]
3275 Set delay from grace-period initialization to
3276 first attempt to force quiescent states.
3277 Units are jiffies, minimum value is zero,
3278 and maximum value is HZ.
3280 rcutree.jiffies_till_next_fqs= [KNL]
3281 Set delay between subsequent attempts to force
3282 quiescent states. Units are jiffies, minimum
3283 value is one, and maximum value is HZ.
3285 rcutree.kthread_prio= [KNL,BOOT]
3286 Set the SCHED_FIFO priority of the RCU per-CPU
3287 kthreads (rcuc/N). This value is also used for
3288 the priority of the RCU boost threads (rcub/N)
3289 and for the RCU grace-period kthreads (rcu_bh,
3290 rcu_preempt, and rcu_sched). If RCU_BOOST is
3291 set, valid values are 1-99 and the default is 1
3292 (the least-favored priority). Otherwise, when
3293 RCU_BOOST is not set, valid values are 0-99 and
3294 the default is zero (non-realtime operation).
3296 rcutree.rcu_nocb_leader_stride= [KNL]
3297 Set the number of NOCB kthread groups, which
3298 defaults to the square root of the number of
3299 CPUs. Larger numbers reduces the wakeup overhead
3300 on the per-CPU grace-period kthreads, but increases
3301 that same overhead on each group's leader.
3303 rcutree.qhimark= [KNL]
3304 Set threshold of queued RCU callbacks beyond which
3305 batch limiting is disabled.
3307 rcutree.qlowmark= [KNL]
3308 Set threshold of queued RCU callbacks below which
3309 batch limiting is re-enabled.
3311 rcutree.rcu_idle_gp_delay= [KNL]
3312 Set wakeup interval for idle CPUs that have
3313 RCU callbacks (RCU_FAST_NO_HZ=y).
3315 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3316 Set wakeup interval for idle CPUs that have
3317 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3318 Lazy RCU callbacks are those which RCU can
3319 prove do nothing more than free memory.
3321 rcutree.rcu_kick_kthreads= [KNL]
3322 Cause the grace-period kthread to get an extra
3323 wake_up() if it sleeps three times longer than
3324 it should at force-quiescent-state time.
3325 This wake_up() will be accompanied by a
3326 WARN_ONCE() splat and an ftrace_dump().
3328 rcuperf.gp_exp= [KNL]
3329 Measure performance of expedited synchronous
3330 grace-period primitives.
3332 rcuperf.holdoff= [KNL]
3333 Set test-start holdoff period. The purpose of
3334 this parameter is to delay the start of the
3335 test until boot completes in order to avoid
3338 rcuperf.nreaders= [KNL]
3339 Set number of RCU readers. The value -1 selects
3340 N, where N is the number of CPUs. A value
3341 "n" less than -1 selects N-n+1, where N is again
3342 the number of CPUs. For example, -2 selects N
3343 (the number of CPUs), -3 selects N+1, and so on.
3344 A value of "n" less than or equal to -N selects
3347 rcuperf.nwriters= [KNL]
3348 Set number of RCU writers. The values operate
3349 the same as for rcuperf.nreaders.
3350 N, where N is the number of CPUs
3352 rcuperf.perf_runnable= [BOOT]
3353 Start rcuperf running at boot time.
3355 rcuperf.shutdown= [KNL]
3356 Shut the system down after performance tests
3357 complete. This is useful for hands-off automated
3360 rcuperf.perf_type= [KNL]
3361 Specify the RCU implementation to test.
3363 rcuperf.verbose= [KNL]
3364 Enable additional printk() statements.
3366 rcutorture.cbflood_inter_holdoff= [KNL]
3367 Set holdoff time (jiffies) between successive
3368 callback-flood tests.
3370 rcutorture.cbflood_intra_holdoff= [KNL]
3371 Set holdoff time (jiffies) between successive
3372 bursts of callbacks within a given callback-flood
3375 rcutorture.cbflood_n_burst= [KNL]
3376 Set the number of bursts making up a given
3377 callback-flood test. Set this to zero to
3378 disable callback-flood testing.
3380 rcutorture.cbflood_n_per_burst= [KNL]
3381 Set the number of callbacks to be registered
3382 in a given burst of a callback-flood test.
3384 rcutorture.fqs_duration= [KNL]
3385 Set duration of force_quiescent_state bursts
3388 rcutorture.fqs_holdoff= [KNL]
3389 Set holdoff time within force_quiescent_state bursts
3392 rcutorture.fqs_stutter= [KNL]
3393 Set wait time between force_quiescent_state bursts
3396 rcutorture.gp_cond= [KNL]
3397 Use conditional/asynchronous update-side
3398 primitives, if available.
3400 rcutorture.gp_exp= [KNL]
3401 Use expedited update-side primitives, if available.
3403 rcutorture.gp_normal= [KNL]
3404 Use normal (non-expedited) asynchronous
3405 update-side primitives, if available.
3407 rcutorture.gp_sync= [KNL]
3408 Use normal (non-expedited) synchronous
3409 update-side primitives, if available. If all
3410 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3411 rcutorture.gp_normal=, and rcutorture.gp_sync=
3412 are zero, rcutorture acts as if is interpreted
3413 they are all non-zero.
3415 rcutorture.n_barrier_cbs= [KNL]
3416 Set callbacks/threads for rcu_barrier() testing.
3418 rcutorture.nfakewriters= [KNL]
3419 Set number of concurrent RCU writers. These just
3420 stress RCU, they don't participate in the actual
3421 test, hence the "fake".
3423 rcutorture.nreaders= [KNL]
3424 Set number of RCU readers. The value -1 selects
3425 N-1, where N is the number of CPUs. A value
3426 "n" less than -1 selects N-n-2, where N is again
3427 the number of CPUs. For example, -2 selects N
3428 (the number of CPUs), -3 selects N+1, and so on.
3430 rcutorture.object_debug= [KNL]
3431 Enable debug-object double-call_rcu() testing.
3433 rcutorture.onoff_holdoff= [KNL]
3434 Set time (s) after boot for CPU-hotplug testing.
3436 rcutorture.onoff_interval= [KNL]
3437 Set time (s) between CPU-hotplug operations, or
3438 zero to disable CPU-hotplug testing.
3440 rcutorture.shuffle_interval= [KNL]
3441 Set task-shuffle interval (s). Shuffling tasks
3442 allows some CPUs to go into dyntick-idle mode
3443 during the rcutorture test.
3445 rcutorture.shutdown_secs= [KNL]
3446 Set time (s) after boot system shutdown. This
3447 is useful for hands-off automated testing.
3449 rcutorture.stall_cpu= [KNL]
3450 Duration of CPU stall (s) to test RCU CPU stall
3451 warnings, zero to disable.
3453 rcutorture.stall_cpu_holdoff= [KNL]
3454 Time to wait (s) after boot before inducing stall.
3456 rcutorture.stat_interval= [KNL]
3457 Time (s) between statistics printk()s.
3459 rcutorture.stutter= [KNL]
3460 Time (s) to stutter testing, for example, specifying
3461 five seconds causes the test to run for five seconds,
3462 wait for five seconds, and so on. This tests RCU's
3463 ability to transition abruptly to and from idle.
3465 rcutorture.test_boost= [KNL]
3466 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3467 "Maybe" means test if the RCU implementation
3468 under test support RCU priority boosting.
3470 rcutorture.test_boost_duration= [KNL]
3471 Duration (s) of each individual boost test.
3473 rcutorture.test_boost_interval= [KNL]
3474 Interval (s) between each boost test.
3476 rcutorture.test_no_idle_hz= [KNL]
3477 Test RCU's dyntick-idle handling. See also the
3478 rcutorture.shuffle_interval parameter.
3480 rcutorture.torture_runnable= [BOOT]
3481 Start rcutorture running at boot time.
3483 rcutorture.torture_type= [KNL]
3484 Specify the RCU implementation to test.
3486 rcutorture.verbose= [KNL]
3487 Enable additional printk() statements.
3489 rcupdate.rcu_cpu_stall_suppress= [KNL]
3490 Suppress RCU CPU stall warning messages.
3492 rcupdate.rcu_cpu_stall_timeout= [KNL]
3493 Set timeout for RCU CPU stall warning messages.
3495 rcupdate.rcu_expedited= [KNL]
3496 Use expedited grace-period primitives, for
3497 example, synchronize_rcu_expedited() instead
3498 of synchronize_rcu(). This reduces latency,
3499 but can increase CPU utilization, degrade
3500 real-time latency, and degrade energy efficiency.
3501 No effect on CONFIG_TINY_RCU kernels.
3503 rcupdate.rcu_normal= [KNL]
3504 Use only normal grace-period primitives,
3505 for example, synchronize_rcu() instead of
3506 synchronize_rcu_expedited(). This improves
3507 real-time latency, CPU utilization, and
3508 energy efficiency, but can expose users to
3509 increased grace-period latency. This parameter
3510 overrides rcupdate.rcu_expedited. No effect on
3511 CONFIG_TINY_RCU kernels.
3513 rcupdate.rcu_normal_after_boot= [KNL]
3514 Once boot has completed (that is, after
3515 rcu_end_inkernel_boot() has been invoked), use
3516 only normal grace-period primitives. No effect
3517 on CONFIG_TINY_RCU kernels.
3519 rcupdate.rcu_task_stall_timeout= [KNL]
3520 Set timeout in jiffies for RCU task stall warning
3521 messages. Disable with a value less than or equal
3524 rcupdate.rcu_self_test= [KNL]
3525 Run the RCU early boot self tests
3527 rcupdate.rcu_self_test_bh= [KNL]
3528 Run the RCU bh early boot self tests
3530 rcupdate.rcu_self_test_sched= [KNL]
3531 Run the RCU sched early boot self tests
3535 Run specified binary instead of /init from the ramdisk,
3536 used for early userspace startup. See initrd.
3539 Format (x86 or x86_64):
3540 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3542 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3544 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3545 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3546 reboot_force is either force or not specified,
3547 reboot_cpu is s[mp]#### with #### being the processor
3548 to be used for rebooting.
3551 [KNL, SMP] Set scheduler's default relax_domain_level.
3552 See Documentation/cgroup-v1/cpusets.txt.
3554 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3556 reservetop= [X86-32]
3558 Reserves a hole at the top of the kernel virtual
3563 Set the amount of memory to reserve for BIOS at
3564 the bottom of the address space.
3566 reset_devices [KNL] Force drivers to reset the underlying device
3567 during initialization.
3570 Specify the partition device for software suspend
3572 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3574 resume_offset= [SWSUSP]
3575 Specify the offset from the beginning of the partition
3576 given by "resume=" at which the swap header is located,
3577 in <PAGE_SIZE> units (needed only for swap files).
3578 See Documentation/power/swsusp-and-swap-files.txt
3580 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3581 read the resume files
3583 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3584 Useful for devices that are detected asynchronously
3585 (e.g. USB and MMC devices).
3587 hibernate= [HIBERNATION]
3588 noresume Don't check if there's a hibernation image
3589 present during boot.
3590 nocompress Don't compress/decompress hibernation images.
3591 no Disable hibernation and resume.
3592 protect_image Turn on image protection during restoration
3593 (that will set all pages holding image data
3594 during restoration read-only).
3596 retain_initrd [RAM] Keep initrd memory after extraction
3598 rfkill.default_state=
3599 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3600 etc. communication is blocked by default.
3603 rfkill.master_switch_mode=
3604 0 The "airplane mode" button does nothing.
3605 1 The "airplane mode" button toggles between everything
3606 blocked and the previous configuration.
3607 2 The "airplane mode" button toggles between everything
3608 blocked and everything unblocked.
3610 rhash_entries= [KNL,NET]
3611 Set number of hash buckets for route cache
3614 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3617 ro [KNL] Mount root device read-only on boot
3620 on Mark read-only kernel memory as read-only (default).
3621 off Leave read-only kernel memory writable for debugging.
3624 Enable the uart passthrough on the designated usb port
3625 on Rockchip SoCs. When active, the signals of the
3626 debug-uart get routed to the D+ and D- pins of the usb
3627 port and the regular usb controller gets disabled.
3629 root= [KNL] Root filesystem
3630 See name_to_dev_t comment in init/do_mounts.c.
3632 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3633 mount the root filesystem
3635 rootflags= [KNL] Set root filesystem mount option string
3637 rootfstype= [KNL] Set root filesystem type
3639 rootwait [KNL] Wait (indefinitely) for root device to show up.
3640 Useful for devices that are detected asynchronously
3641 (e.g. USB and MMC devices).
3643 rproc_mem=nn[KMG][@address]
3644 [KNL,ARM,CMA] Remoteproc physical memory block.
3645 Memory area to be used by remote processor image,
3648 rw [KNL] Mount root device read-write on boot
3650 S [KNL] Run init in single mode
3652 s390_iommu= [HW,S390]
3653 Set s390 IOTLB flushing mode
3655 With strict flushing every unmap operation will result in
3656 an IOTLB flush. Default is lazy flushing before reuse,
3660 See drivers/net/irda/sa1100_ir.c.
3662 sbni= [NET] Granch SBNI12 leased line adapter
3664 sched_debug [KNL] Enables verbose scheduler debug messages.
3666 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3667 Allowed values are enable and disable. This feature
3668 incurs a small amount of overhead in the scheduler
3669 but is useful for debugging and performance tuning.
3671 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3672 xtime_lock contention on larger systems, and/or RCU lock
3673 contention on all systems with CONFIG_MAXSMP set.
3674 Format: { "0" | "1" }
3675 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3677 Note: increases power consumption, thus should only be
3678 enabled if running jitter sensitive (HPC/RT) workloads.
3680 security= [SECURITY] Choose a security module to enable at boot.
3681 If this boot parameter is not specified, only the first
3682 security module asking for security registration will be
3683 loaded. An invalid security module name will be treated
3684 as if no module has been chosen.
3686 selinux= [SELINUX] Disable or enable SELinux at boot time.
3687 Format: { "0" | "1" }
3688 See security/selinux/Kconfig help text.
3691 Default value is set via kernel config option.
3692 If enabled at boot time, /selinux/disable can be used
3693 later to disable prior to initial policy load.
3695 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3696 Format: { "0" | "1" }
3697 See security/apparmor/Kconfig help text
3700 Default value is set via kernel config option.
3702 serialnumber [BUGS=X86-32]
3705 Maximal number of shapers.
3713 Disable merging of slabs with similar size. May be
3714 necessary if there is some reason to distinguish
3715 allocs to different slabs. Debug options disable
3716 merging on their own.
3717 For more information see Documentation/vm/slub.txt.
3719 slab_max_order= [MM, SLAB]
3720 Determines the maximum allowed order for slabs.
3721 A high setting may cause OOMs due to memory
3722 fragmentation. Defaults to 1 for systems with
3723 more than 32MB of RAM, 0 otherwise.
3725 slub_debug[=options[,slabs]] [MM, SLUB]
3726 Enabling slub_debug allows one to determine the
3727 culprit if slab objects become corrupted. Enabling
3728 slub_debug can create guard zones around objects and
3729 may poison objects when not in use. Also tracks the
3730 last alloc / free. For more information see
3731 Documentation/vm/slub.txt.
3733 slub_memcg_sysfs= [MM, SLUB]
3734 Determines whether to enable sysfs directories for
3735 memory cgroup sub-caches. 1 to enable, 0 to disable.
3736 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
3737 Enabling this can lead to a very high number of debug
3738 directories and files being created under
3741 slub_max_order= [MM, SLUB]
3742 Determines the maximum allowed order for slabs.
3743 A high setting may cause OOMs due to memory
3744 fragmentation. For more information see
3745 Documentation/vm/slub.txt.
3747 slub_min_objects= [MM, SLUB]
3748 The minimum number of objects per slab. SLUB will
3749 increase the slab order up to slub_max_order to
3750 generate a sufficiently large slab able to contain
3751 the number of objects indicated. The higher the number
3752 of objects the smaller the overhead of tracking slabs
3753 and the less frequently locks need to be acquired.
3754 For more information see Documentation/vm/slub.txt.
3756 slub_min_order= [MM, SLUB]
3757 Determines the minimum page order for slabs. Must be
3758 lower than slub_max_order.
3759 For more information see Documentation/vm/slub.txt.
3761 slub_nomerge [MM, SLUB]
3762 Same with slab_nomerge. This is supported for legacy.
3763 See slab_nomerge for more information.
3766 Format: <io1>[,<io2>[,...,<io8>]]
3768 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3769 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3770 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3771 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3772 smsc-ircc2.ircc_irq= [HW] IRQ line
3773 smsc-ircc2.ircc_dma= [HW] DMA channel
3774 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3775 0: Toshiba Satellite 1800 (GP data pin select)
3776 1: Fast pin select (default)
3779 smt [KNL,S390] Set the maximum number of threads (logical
3780 CPUs) to use per physical CPU on systems capable of
3781 symmetric multithreading (SMT). Will be capped to the
3782 actual hardware limit.
3784 Default: -1 (no limit)
3787 [KNL] Should the soft-lockup detector generate panics.
3790 softlockup_all_cpu_backtrace=
3791 [KNL] Should the soft-lockup detector generate
3792 backtraces on all cpus.
3795 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3796 See Documentation/laptops/sonypi.txt
3798 spia_io_base= [HW,MTD]
3803 srcutree.exp_holdoff [KNL]
3804 Specifies how many nanoseconds must elapse
3805 since the end of the last SRCU grace period for
3806 a given srcu_struct until the next normal SRCU
3807 grace period will be considered for automatic
3808 expediting. Set to zero to disable automatic
3812 Enabled the stack tracer on boot up.
3814 stacktrace_filter=[function-list]
3815 [FTRACE] Limit the functions that the stack tracer
3816 will trace at boot up. function-list is a comma separated
3817 list of functions. This list can be changed at run
3818 time by the stack_trace_filter file in the debugfs
3819 tracing directory. Note, this enables stack tracing
3820 and the stacktrace above is not needed.
3824 Set the STI (builtin display/keyboard on the HP-PARISC
3825 machines) console (graphic card) which should be used
3826 as the initial boot-console.
3827 See also comment in drivers/video/console/sticore.c.
3830 See comment in drivers/video/console/sticore.c.
3833 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3835 sunrpc.min_resvport=
3836 sunrpc.max_resvport=
3838 SunRPC servers often require that client requests
3839 originate from a privileged port (i.e. a port in the
3840 range 0 < portnr < 1024).
3841 An administrator who wishes to reserve some of these
3842 ports for other uses may adjust the range that the
3843 kernel's sunrpc client considers to be privileged
3844 using these two parameters to set the minimum and
3845 maximum port values.
3847 sunrpc.svc_rpc_per_connection_limit=
3849 Limit the number of requests that the server will
3850 process in parallel from a single connection.
3851 The default value is 0 (no limit).
3855 Control how the NFS server code allocates CPUs to
3856 service thread pools. Depending on how many NICs
3857 you have and where their interrupts are bound, this
3858 option will affect which CPUs will do NFS serving.
3859 Note: this parameter cannot be changed while the
3860 NFS server is running.
3862 auto the server chooses an appropriate mode
3863 automatically using heuristics
3864 global a single global pool contains all CPUs
3865 percpu one pool for each CPU
3866 pernode one pool for each NUMA node (equivalent
3867 to global on non-NUMA machines)
3869 sunrpc.tcp_slot_table_entries=
3870 sunrpc.udp_slot_table_entries=
3872 Sets the upper limit on the number of simultaneous
3873 RPC calls that can be sent from the client to a
3874 server. Increasing these values may allow you to
3875 improve throughput, but will also increase the
3876 amount of memory reserved for use by the client.
3878 suspend.pm_test_delay=
3880 Sets the number of seconds to remain in a suspend test
3881 mode before resuming the system (see
3882 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3883 is set. Default value is 5.
3886 [KNL] Enable accounting of swap in memory resource
3887 controller if no parameter or 1 is given or disable
3888 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3890 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3891 Format: { <int> | force | noforce }
3892 <int> -- Number of I/O TLB slabs
3893 force -- force using of bounce buffers even if they
3894 wouldn't be automatically used by the kernel
3895 noforce -- Never use bounce buffers (for debugging)
3899 sysfs.deprecated=0|1 [KNL]
3900 Enable/disable old style sysfs layout for old udev
3901 on older distributions. When this option is enabled
3902 very new udev will not work anymore. When this option
3903 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3904 in older udev will not work anymore.
3905 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3906 the kernel configuration.
3908 sysrq_always_enabled
3910 Ignore sysrq setting - this boot parameter will
3911 neutralize any effect of /proc/sys/kernel/sysrq.
3912 Useful for debugging.
3914 tcpmhash_entries= [KNL,NET]
3915 Set the number of tcp_metrics_hash slots.
3916 Default value is 8192 or 16384 depending on total
3917 ram pages. This is used to specify the TCP metrics
3918 cache size. See Documentation/networking/ip-sysctl.txt
3919 "tcp_no_metrics_save" section for more details.
3923 test_suspend= [SUSPEND][,N]
3924 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3925 standby suspend) or "freeze" (for suspend type freeze)
3926 as the system sleep state during system startup with
3927 the optional capability to repeat N number of times.
3928 The system is woken from this state using a
3929 wakeup-capable RTC alarm.
3931 thash_entries= [KNL,NET]
3932 Set number of hash buckets for TCP connection
3934 thermal.act= [HW,ACPI]
3935 -1: disable all active trip points in all thermal zones
3936 <degrees C>: override all lowest active trip points
3938 thermal.crt= [HW,ACPI]
3939 -1: disable all critical trip points in all thermal zones
3940 <degrees C>: override all critical trip points
3942 thermal.nocrt= [HW,ACPI]
3943 Set to disable actions on ACPI thermal zone
3944 critical and hot trip points.
3946 thermal.off= [HW,ACPI]
3947 1: disable ACPI thermal control
3949 thermal.psv= [HW,ACPI]
3950 -1: disable all passive trip points
3951 <degrees C>: override all passive trip points to this
3954 thermal.tzp= [HW,ACPI]
3955 Specify global default ACPI thermal zone polling rate
3956 <deci-seconds>: poll all this frequency
3957 0: no polling (default)
3960 Force threading of all interrupt handlers except those
3961 marked explicitly IRQF_NO_THREAD.
3964 Enable the Transcendent memory driver if built-in.
3966 tmem.cleancache=0|1 [KNL, XEN]
3967 Default is on (1). Disable the usage of the cleancache
3968 API to send anonymous pages to the hypervisor.
3970 tmem.frontswap=0|1 [KNL, XEN]
3971 Default is on (1). Disable the usage of the frontswap
3972 API to send swap pages to the hypervisor. If disabled
3973 the selfballooning and selfshrinking are force disabled.
3975 tmem.selfballooning=0|1 [KNL, XEN]
3976 Default is on (1). Disable the driving of swap pages
3979 tmem.selfshrinking=0|1 [KNL, XEN]
3980 Default is on (1). Partial swapoff that immediately
3981 transfers pages from Xen hypervisor back to the
3982 kernel based on different criteria.
3986 Specify if the kernel should make use of the cpu
3987 topology information if the hardware supports this.
3988 The scheduler will make use of this information and
3989 e.g. base its process migration decisions on it.
3992 topology_updates= [KNL, PPC, NUMA]
3994 Specify if the kernel should ignore (off)
3995 topology updates sent by the hypervisor to this
4000 tpm_suspend_pcr=[HW,TPM]
4001 Format: integer pcr id
4002 Specify that at suspend time, the tpm driver
4003 should extend the specified pcr with zeros,
4004 as a workaround for some chips which fail to
4005 flush the last written pcr on TPM_SaveState.
4006 This will guarantee that all the other pcrs
4009 trace_buf_size=nn[KMG]
4010 [FTRACE] will set tracing buffer size on each cpu.
4012 trace_event=[event-list]
4013 [FTRACE] Set and start specified trace events in order
4014 to facilitate early boot debugging. The event-list is a
4015 comma separated list of trace events to enable. See
4016 also Documentation/trace/events.txt
4018 trace_options=[option-list]
4019 [FTRACE] Enable or disable tracer options at boot.
4020 The option-list is a comma delimited list of options
4021 that can be enabled or disabled just as if you were
4022 to echo the option name into
4024 /sys/kernel/debug/tracing/trace_options
4026 For example, to enable stacktrace option (to dump the
4027 stack trace of each event), add to the command line:
4029 trace_options=stacktrace
4031 See also Documentation/trace/ftrace.txt "trace options"
4035 Have the tracepoints sent to printk as well as the
4036 tracing ring buffer. This is useful for early boot up
4037 where the system hangs or reboots and does not give the
4038 option for reading the tracing buffer or performing a
4039 ftrace_dump_on_oops.
4041 To turn off having tracepoints sent to printk,
4042 echo 0 > /proc/sys/kernel/tracepoint_printk
4043 Note, echoing 1 into this file without the
4044 tracepoint_printk kernel cmdline option has no effect.
4048 Having tracepoints sent to printk() and activating high
4049 frequency tracepoints such as irq or sched, can cause
4050 the system to live lock.
4053 [FTRACE] enable this option to disable tracing when a
4054 warning is hit. This turns off "tracing_on". Tracing can
4055 be enabled again by echoing '1' into the "tracing_on"
4056 file located in /sys/kernel/debug/tracing/
4058 This option is useful, as it disables the trace before
4059 the WARNING dump is called, which prevents the trace to
4060 be filled with content caused by the warning output.
4062 This option can also be set at run time via the sysctl
4063 option: kernel/traceoff_on_warning
4065 transparent_hugepage=
4067 Format: [always|madvise|never]
4068 Can be used to control the default behavior of the system
4069 with respect to transparent hugepages.
4070 See Documentation/vm/transhuge.txt for more details.
4072 tsc= Disable clocksource stability checks for TSC.
4074 [x86] reliable: mark tsc clocksource as reliable, this
4075 disables clocksource verification at runtime, as well
4076 as the stability checks done at bootup. Used to enable
4077 high-resolution timer mode on older hardware, and in
4078 virtualized environment.
4079 [x86] noirqtime: Do not use TSC to do irq accounting.
4080 Used to run time disable IRQ_TIME_ACCOUNTING on any
4081 platforms where RDTSC is slow and this accounting
4084 turbografx.map[2|3]= [HW,JOY]
4085 TurboGraFX parallel port interface
4087 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4088 See also Documentation/input/joystick-parport.txt
4090 udbg-immortal [PPC] When debugging early kernel crashes that
4091 happen after console_init() and before a proper
4092 console driver takes over, this boot options might
4093 help "seeing" what's going on.
4095 uhash_entries= [KNL,NET]
4096 Set number of hash buckets for UDP/UDP-Lite connections
4099 [USB] Ignore overcurrent events (default N).
4100 Some badly-designed motherboards generate lots of
4101 bogus events, for ports that aren't wired to
4102 anything. Set this parameter to avoid log spamming.
4103 Note that genuine overcurrent events won't be
4107 [X86] Cause panic on unknown NMI.
4109 usbcore.authorized_default=
4110 [USB] Default USB device authorization:
4111 (default -1 = authorized except for wireless USB,
4112 0 = not authorized, 1 = authorized)
4114 usbcore.autosuspend=
4115 [USB] The autosuspend time delay (in seconds) used
4116 for newly-detected USB devices (default 2). This
4117 is the time required before an idle device will be
4118 autosuspended. Devices for which the delay is set
4119 to a negative value won't be autosuspended at all.
4121 usbcore.usbfs_snoop=
4122 [USB] Set to log all usbfs traffic (default 0 = off).
4124 usbcore.usbfs_snoop_max=
4125 [USB] Maximum number of bytes to snoop in each URB
4128 usbcore.blinkenlights=
4129 [USB] Set to cycle leds on hubs (default 0 = off).
4131 usbcore.old_scheme_first=
4132 [USB] Start with the old device initialization
4133 scheme (default 0 = off).
4135 usbcore.usbfs_memory_mb=
4136 [USB] Memory limit (in MB) for buffers allocated by
4137 usbfs (default = 16, 0 = max = 2047).
4139 usbcore.use_both_schemes=
4140 [USB] Try the other device initialization scheme
4141 if the first one fails (default 1 = enabled).
4143 usbcore.initial_descriptor_timeout=
4144 [USB] Specifies timeout for the initial 64-byte
4145 USB_REQ_GET_DESCRIPTOR request in milliseconds
4146 (default 5000 = 5.0 seconds).
4148 usbcore.nousb [USB] Disable the USB subsystem
4151 [USBHID] The interval which mice are to be polled at.
4154 [USBHID] The interval which joysticks are to be polled at.
4156 usb-storage.delay_use=
4157 [UMS] The delay in seconds before a new device is
4158 scanned for Logical Units (default 1).
4161 [UMS] A list of quirks entries to supplement or
4162 override the built-in unusual_devs list. List
4163 entries are separated by commas. Each entry has
4164 the form VID:PID:Flags where VID and PID are Vendor
4165 and Product ID values (4-digit hex numbers) and
4166 Flags is a set of characters, each corresponding
4167 to a common usb-storage quirk flag as follows:
4168 a = SANE_SENSE (collect more than 18 bytes
4170 b = BAD_SENSE (don't collect more than 18
4171 bytes of sense data);
4172 c = FIX_CAPACITY (decrease the reported
4173 device capacity by one sector);
4174 d = NO_READ_DISC_INFO (don't use
4175 READ_DISC_INFO command);
4176 e = NO_READ_CAPACITY_16 (don't use
4177 READ_CAPACITY_16 command);
4178 f = NO_REPORT_OPCODES (don't use report opcodes
4180 g = MAX_SECTORS_240 (don't transfer more than
4181 240 sectors at a time, uas only);
4182 h = CAPACITY_HEURISTICS (decrease the
4183 reported device capacity by one
4184 sector if the number is odd);
4185 i = IGNORE_DEVICE (don't bind to this
4187 j = NO_REPORT_LUNS (don't use report luns
4189 l = NOT_LOCKABLE (don't try to lock and
4190 unlock ejectable media);
4191 m = MAX_SECTORS_64 (don't transfer more
4192 than 64 sectors = 32 KB at a time);
4193 n = INITIAL_READ10 (force a retry of the
4194 initial READ(10) command);
4195 o = CAPACITY_OK (accept the capacity
4196 reported by the device);
4197 p = WRITE_CACHE (the device cache is ON
4199 r = IGNORE_RESIDUE (the device reports
4200 bogus residue values);
4201 s = SINGLE_LUN (the device has only one
4203 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4204 commands, uas only);
4205 u = IGNORE_UAS (don't bind to the uas driver);
4206 w = NO_WP_DETECT (don't test whether the
4207 medium is write-protected).
4208 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4209 even if the device claims no cache)
4210 Example: quirks=0419:aaf5:rl,0421:0433:rc
4212 user_debug= [KNL,ARM]
4214 See arch/arm/Kconfig.debug help text.
4215 1 - undefined instruction events
4217 4 - invalid data aborts
4220 Example: user_debug=31
4223 [X86] Flags controlling user PTE allocations.
4225 nohigh = do not allocate PTE pages in
4226 HIGHMEM regardless of setting
4230 On X86_32, this is an alias for vdso32=. Otherwise:
4232 vdso=1: enable VDSO (the default)
4233 vdso=0: disable VDSO mapping
4235 vdso32= [X86] Control the 32-bit vDSO
4236 vdso32=1: enable 32-bit VDSO
4237 vdso32=0 or vdso32=2: disable 32-bit VDSO
4239 See the help text for CONFIG_COMPAT_VDSO for more
4240 details. If CONFIG_COMPAT_VDSO is set, the default is
4241 vdso32=0; otherwise, the default is vdso32=1.
4243 For compatibility with older kernels, vdso32=2 is an
4246 Try vdso32=0 if you encounter an error that says:
4247 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4250 vector=percpu: enable percpu vector domain
4252 video= [FB] Frame buffer configuration
4253 See Documentation/fb/modedb.txt.
4255 video.brightness_switch_enabled= [0,1]
4256 If set to 1, on receiving an ACPI notify event
4257 generated by hotkey, video driver will adjust brightness
4258 level and then send out the event to user space through
4259 the allocated input device; If set to 0, video driver
4260 will only send out the event without touching backlight
4265 [VMMIO] Memory mapped virtio (platform) device.
4267 <size>@<baseaddr>:<irq>[:<id>]
4269 <size> := size (can use standard suffixes
4271 <baseaddr> := physical base address
4272 <irq> := interrupt number (as passed to
4274 <id> := (optional) platform device id
4276 virtio_mmio.device=1K@0x100b0000:48:7
4278 Can be used multiple times for multiple devices.
4280 vga= [BOOT,X86-32] Select a particular video mode
4281 See Documentation/x86/boot.txt and
4282 Documentation/svga.txt.
4283 Use vga=ask for menu.
4284 This is actually a boot loader parameter; the value is
4285 passed to the kernel using a special protocol.
4287 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4288 size of <nn>. This can be used to increase the
4289 minimum size (128MB on x86). It can also be used to
4290 decrease the size and leave more room for directly
4293 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4296 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4299 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4303 Controls the behavior of vsyscalls (i.e. calls to
4304 fixed addresses of 0xffffffffff600x00 from legacy
4305 code). Most statically-linked binaries and older
4306 versions of glibc use these calls. Because these
4307 functions are at fixed addresses, they make nice
4308 targets for exploits that can control RIP.
4310 emulate [default] Vsyscalls turn into traps and are
4311 emulated reasonably safely.
4313 native Vsyscalls are native syscall instructions.
4314 This is a little bit faster than trapping
4315 and makes a few dynamic recompilers work
4316 better than they would in emulation mode.
4317 It also makes exploits much easier to write.
4319 none Vsyscalls don't work at all. This makes
4320 them quite hard to use for exploits but
4321 might break your system.
4323 vt.color= [VT] Default text color.
4324 Format: 0xYX, X = foreground, Y = background.
4325 Default: 0x07 = light gray on black.
4327 vt.cur_default= [VT] Default cursor shape.
4328 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4329 the parameters of the <Esc>[?A;B;Cc escape sequence;
4330 see VGA-softcursor.txt. Default: 2 = underline.
4332 vt.default_blu= [VT]
4333 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4334 Change the default blue palette of the console.
4335 This is a 16-member array composed of values
4338 vt.default_grn= [VT]
4339 Format: <green0>,<green1>,<green2>,...,<green15>
4340 Change the default green palette of the console.
4341 This is a 16-member array composed of values
4344 vt.default_red= [VT]
4345 Format: <red0>,<red1>,<red2>,...,<red15>
4346 Change the default red palette of the console.
4347 This is a 16-member array composed of values
4353 Set system-wide default UTF-8 mode for all tty's.
4354 Default is 1, i.e. UTF-8 mode is enabled for all
4355 newly opened terminals.
4357 vt.global_cursor_default=
4360 Set system-wide default for whether a cursor
4361 is shown on new VTs. Default is -1,
4362 i.e. cursors will be created by default unless
4363 overridden by individual drivers. 0 will hide
4364 cursors, 1 will display them.
4366 vt.italic= [VT] Default color for italic text; 0-15.
4369 vt.underline= [VT] Default color for underlined text; 0-15.
4372 watchdog timers [HW,WDT] For information on watchdog timers,
4373 see Documentation/watchdog/watchdog-parameters.txt
4374 or other driver-specific files in the
4375 Documentation/watchdog/ directory.
4377 workqueue.watchdog_thresh=
4378 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4379 warn stall conditions and dump internal state to
4380 help debugging. 0 disables workqueue stall
4381 detection; otherwise, it's the stall threshold
4382 duration in seconds. The default value is 30 and
4383 it can be updated at runtime by writing to the
4384 corresponding sysfs file.
4386 workqueue.disable_numa
4387 By default, all work items queued to unbound
4388 workqueues are affine to the NUMA nodes they're
4389 issued on, which results in better behavior in
4390 general. If NUMA affinity needs to be disabled for
4391 whatever reason, this option can be used. Note
4392 that this also can be controlled per-workqueue for
4393 workqueues visible under /sys/bus/workqueue/.
4395 workqueue.power_efficient
4396 Per-cpu workqueues are generally preferred because
4397 they show better performance thanks to cache
4398 locality; unfortunately, per-cpu workqueues tend to
4399 be more power hungry than unbound workqueues.
4401 Enabling this makes the per-cpu workqueues which
4402 were observed to contribute significantly to power
4403 consumption unbound, leading to measurably lower
4404 power usage at the cost of small performance
4407 The default value of this parameter is determined by
4408 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4410 workqueue.debug_force_rr_cpu
4411 Workqueue used to implicitly guarantee that work
4412 items queued without explicit CPU specified are put
4413 on the local CPU. This guarantee is no longer true
4414 and while local CPU is still preferred work items
4415 may be put on foreign CPUs. This debug option
4416 forces round-robin CPU selection to flush out
4417 usages which depend on the now broken guarantee.
4418 When enabled, memory and cache locality will be
4421 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4422 default x2apic cluster mode on platforms
4425 x86_intel_mid_timer= [X86-32,APBT]
4426 Choose timer option for x86 Intel MID platform.
4427 Two valid options are apbt timer only and lapic timer
4428 plus one apbt timer for broadcast timer.
4429 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4431 xen_512gb_limit [KNL,X86-64,XEN]
4432 Restricts the kernel running paravirtualized under Xen
4433 to use only up to 512 GB of RAM. The reason to do so is
4434 crash analysis tools and Xen tools for doing domain
4435 save/restore/migration must be enabled to handle larger
4438 xen_emul_unplug= [HW,X86,XEN]
4439 Unplug Xen emulated devices
4440 Format: [unplug0,][unplug1]
4441 ide-disks -- unplug primary master IDE devices
4442 aux-ide-disks -- unplug non-primary-master IDE devices
4443 nics -- unplug network devices
4444 all -- unplug all emulated devices (NICs and IDE disks)
4445 unnecessary -- unplugging emulated devices is
4446 unnecessary even if the host did not respond to
4448 never -- do not unplug even if version check succeeds
4450 xen_nopvspin [X86,XEN]
4451 Disables the ticketlock slowpath using Xen PV
4455 Disables the PV optimizations forcing the HVM guest to
4456 run as generic HVM guest with no PV drivers.
4458 xirc2ps_cs= [NET,PCMCIA]
4460 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
git.samba.org / sfrench / cifs-2.6.git / blob