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
535 [X86-32] pit,hpet,tsc;
536 scx200_hrt on Geode; cyclone on IBM x440
544 clocksource.arm_arch_timer.evtstrm=
547 Enable/disable the eventstream feature of the ARM
548 architected timer so that code using WFE-based polling
549 loops can be debugged more effectively on production
552 clearcpuid=BITNUM [X86]
553 Disable CPUID feature X for the kernel. See
554 arch/x86/include/asm/cpufeatures.h for the valid bit
555 numbers. Note the Linux specific bits are not necessarily
556 stable over kernel options, but the vendor specific
558 Also note that user programs calling CPUID directly
559 or using the feature without checking anything
560 will still see it. This just prevents it from
561 being used by the kernel or shown in /proc/cpuinfo.
562 Also note the kernel might malfunction if you disable
565 cma=nn[MG]@[start[MG][-end[MG]]]
567 Sets the size of kernel global memory area for
568 contiguous memory allocations and optionally the
569 placement constraint by the physical address range of
570 memory allocations. A value of 0 disables CMA
571 altogether. For more information, see
572 include/linux/dma-contiguous.h
574 cmo_free_hint= [PPC] Format: { yes | no }
575 Specify whether pages are marked as being inactive
576 when they are freed. This is used in CMO environments
577 to determine OS memory pressure for page stealing by
581 coherent_pool=nn[KMG] [ARM,KNL]
582 Sets the size of memory pool for coherent, atomic dma
583 allocations, by default set to 256K.
585 code_bytes [X86] How many bytes of object code to print
590 com20020= [HW,NET] ARCnet - COM20020 chipset
592 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
594 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
598 ARCnet - COM90xx chipset (memory-mapped buffers)
599 Format: <io>[,<irq>[,<memstart>]]
601 condev= [HW,S390] console device
604 console= [KNL] Output console device and options.
606 tty<n> Use the virtual console device <n>.
610 Use the specified serial port. The options are of
611 the form "bbbbpnf", where "bbbb" is the baud rate,
612 "p" is parity ("n", "o", or "e"), "n" is number of
613 bits, and "f" is flow control ("r" for RTS or
614 omit it). Default is "9600n8".
616 See Documentation/admin-guide/serial-console.rst for more
618 Documentation/networking/netconsole.txt for an
621 uart[8250],io,<addr>[,options]
622 uart[8250],mmio,<addr>[,options]
623 uart[8250],mmio16,<addr>[,options]
624 uart[8250],mmio32,<addr>[,options]
625 uart[8250],0x<addr>[,options]
626 Start an early, polled-mode console on the 8250/16550
627 UART at the specified I/O port or MMIO address,
628 switching to the matching ttyS device later.
629 MMIO inter-register address stride is either 8-bit
630 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
631 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
632 to be equivalent to 'mmio'. 'options' are specified in
633 the same format described for ttyS above; if unspecified,
634 the h/w is not re-initialized.
636 hvc<n> Use the hypervisor console device <n>. This is for
637 both Xen and PowerPC hypervisors.
639 If the device connected to the port is not a TTY but a braille
640 device, prepend "brl," before the device type, for instance
642 For now, only VisioBraille is supported.
644 consoleblank= [KNL] The console blank (screen saver) timeout in
645 seconds. Defaults to 10*60 = 10mins. A value of 0
646 disables the blank timer.
649 [KNL] Change the default value for
650 /proc/<pid>/coredump_filter.
651 See also Documentation/filesystems/proc.txt.
653 cpufreq_driver= [X86] Allow only the named cpu frequency scaling driver
654 to register. Example: cpufreq_driver=powernow-k8
655 Format: { none | STRING }
657 cpuidle.off=1 [CPU_IDLE]
658 disable the cpuidle sub-system
661 [X86] Delay for N microsec between assert and de-assert
662 of APIC INIT to start processors. This delay occurs
663 on every CPU online, such as boot, and resume from suspend.
666 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
668 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
670 crashkernel=size[KMG][@offset[KMG]]
671 [KNL] Using kexec, Linux can switch to a 'crash kernel'
672 upon panic. This parameter reserves the physical
673 memory region [offset, offset + size] for that kernel
674 image. If '@offset' is omitted, then a suitable offset
675 is selected automatically. Check
676 Documentation/kdump/kdump.txt for further details.
678 crashkernel=range1:size1[,range2:size2,...][@offset]
679 [KNL] Same as above, but depends on the memory
680 in the running system. The syntax of range is
681 start-[end] where start and end are both
682 a memory unit (amount[KMG]). See also
683 Documentation/kdump/kdump.txt for an example.
685 crashkernel=size[KMG],high
686 [KNL, x86_64] range could be above 4G. Allow kernel
687 to allocate physical memory region from top, so could
688 be above 4G if system have more than 4G ram installed.
689 Otherwise memory region will be allocated below 4G, if
691 It will be ignored if crashkernel=X is specified.
692 crashkernel=size[KMG],low
693 [KNL, x86_64] range under 4G. When crashkernel=X,high
694 is passed, kernel could allocate physical memory region
695 above 4G, that cause second kernel crash on system
696 that require some amount of low memory, e.g. swiotlb
697 requires at least 64M+32K low memory, also enough extra
698 low memory is needed to make sure DMA buffers for 32-bit
699 devices won't run out. Kernel would try to allocate at
700 at least 256M below 4G automatically.
701 This one let user to specify own low range under 4G
702 for second kernel instead.
703 0: to disable low allocation.
704 It will be ignored when crashkernel=X,high is not used
705 or memory reserved is below 4G.
708 [KNL] Disable crypto self-tests
713 cs89x0_media= [HW,NET]
714 Format: { rj45 | aui | bnc }
717 See header of drivers/s390/block/dasd_devmap.c.
719 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
720 (one device per port)
721 Format: <port#>,<type>
722 See also Documentation/input/joystick-parport.txt
724 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
725 time. See Documentation/dynamic-debug-howto.txt for
726 details. Deprecated, see dyndbg.
728 debug [KNL] Enable kernel debugging (events log level).
731 [KNL] verbose self-tests
733 Print debugging info while doing the locking API
735 We default to 0 (no extra messages), setting it to
736 1 will print _a lot_ more information - normally
737 only useful to kernel developers.
739 debug_objects [KNL] Enable object debugging
742 [KNL] Disable object debugging
744 debug_guardpage_minorder=
745 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
746 parameter allows control of the order of pages that will
747 be intentionally kept free (and hence protected) by the
748 buddy allocator. Bigger value increase the probability
749 of catching random memory corruption, but reduce the
750 amount of memory for normal system use. The maximum
751 possible value is MAX_ORDER/2. Setting this parameter
752 to 1 or 2 should be enough to identify most random
753 memory corruption problems caused by bugs in kernel or
754 driver code when a CPU writes to (or reads from) a
755 random memory location. Note that there exists a class
756 of memory corruptions problems caused by buggy H/W or
757 F/W or by drivers badly programing DMA (basically when
758 memory is written at bus level and the CPU MMU is
759 bypassed) which are not detectable by
760 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
761 tracking down these problems.
764 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
765 parameter enables the feature at boot time. In
766 default, it is disabled. We can avoid allocating huge
767 chunk of memory for debug pagealloc if we don't enable
768 it at boot time and the system will work mostly same
769 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
770 on: enable the feature
772 debugpat [X86] Enable PAT debugging
774 decnet.addr= [HW,NET]
775 Format: <area>[,<node>]
776 See also Documentation/networking/decnet.txt.
779 [same as hugepagesz=] The size of the default
780 HugeTLB page size. This is the size represented by
781 the legacy /proc/ hugepages APIs, used for SHM, and
782 default size when mounting hugetlbfs filesystems.
783 Defaults to the default architecture's huge page size
787 Set number of hash buckets for dentry cache.
789 disable_1tb_segments [PPC]
790 Disables the use of 1TB hash page table segments. This
791 causes the kernel to fall back to 256MB segments which
792 can be useful when debugging issues that require an SLB
796 See Documentation/networking/ipv6.txt.
799 Disable RADIX MMU mode on POWER9
801 disable_cpu_apicid= [X86,APIC,SMP]
803 The number of initial APIC ID for the
804 corresponding CPU to be disabled at boot,
805 mostly used for the kdump 2nd kernel to
806 disable BSP to wake up multiple CPUs without
807 causing system reset or hang due to sending
810 disable_ddw [PPC/PSERIES]
811 Disable Dynamic DMA Window support. Use this if
812 to workaround buggy firmware.
815 See Documentation/networking/ipv6.txt.
817 disable_mtrr_cleanup [X86]
818 The kernel tries to adjust MTRR layout from continuous
819 to discrete, to make X server driver able to add WB
820 entry later. This parameter disables that.
822 disable_mtrr_trim [X86, Intel and AMD only]
823 By default the kernel will trim any uncacheable
824 memory out of your available memory pool based on
825 MTRR settings. This parameter disables that behavior,
826 possibly causing your machine to run very slowly.
828 disable_timer_pin_1 [X86]
829 Disable PIN 1 of APIC timer
830 Can be useful to work around chipset bugs.
832 dis_ucode_ldr [X86] Disable the microcode loader.
834 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
835 this option disables the debugging code at boot.
837 dma_debug_entries=<number>
838 This option allows to tune the number of preallocated
839 entries for DMA-API debugging code. One entry is
840 required per DMA-API allocation. Use this if the
841 DMA-API debugging code disables itself because the
842 architectural default is too low.
844 dma_debug_driver=<driver_name>
845 With this option the DMA-API debugging driver
846 filter feature can be enabled at boot time. Just
847 pass the driver to filter for as the parameter.
848 The filter can be disabled or changed to another
849 driver later using sysfs.
851 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
852 Broken monitors, graphic adapters, KVMs and EDIDless
853 panels may send no or incorrect EDID data sets.
854 This parameter allows to specify an EDID data sets
855 in the /lib/firmware directory that are used instead.
856 Generic built-in EDID data sets are used, if one of
857 edid/1024x768.bin, edid/1280x1024.bin,
858 edid/1680x1050.bin, or edid/1920x1080.bin is given
859 and no file with the same name exists. Details and
860 instructions how to build your own EDID data are
861 available in Documentation/EDID/HOWTO.txt. An EDID
862 data set will only be used for a particular connector,
863 if its name and a colon are prepended to the EDID
864 name. Each connector may use a unique EDID data
865 set by separating the files with a comma. An EDID
866 data set with no connector name will be used for
867 any connectors not explicitly specified.
871 dump_apple_properties [X86]
872 Dump name and content of EFI device properties on
873 x86 Macs. Useful for driver authors to determine
874 what data is available or for reverse-engineering.
876 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
877 module.dyndbg[="val"]
878 Enable debug messages at boot time. See
879 Documentation/dynamic-debug-howto.txt for details.
881 nompx [X86] Disables Intel Memory Protection Extensions.
882 See Documentation/x86/intel_mpx.txt for more
883 information about the feature.
885 nopku [X86] Disable Memory Protection Keys CPU feature found
888 module.async_probe [KNL]
889 Enable asynchronous probe on this module.
891 early_ioremap_debug [KNL]
892 Enable debug messages in early_ioremap support. This
893 is useful for tracking down temporary early mappings
894 which are not unmapped.
896 earlycon= [KNL] Output early console device and options.
898 When used with no options, the early console is
899 determined by the stdout-path property in device
902 cdns,<addr>[,options]
903 Start an early, polled-mode console on a Cadence
904 (xuartps) serial port at the specified address. Only
905 supported option is baud rate. If baud rate is not
906 specified, the serial port must already be setup and
909 uart[8250],io,<addr>[,options]
910 uart[8250],mmio,<addr>[,options]
911 uart[8250],mmio32,<addr>[,options]
912 uart[8250],mmio32be,<addr>[,options]
913 uart[8250],0x<addr>[,options]
914 Start an early, polled-mode console on the 8250/16550
915 UART at the specified I/O port or MMIO address.
916 MMIO inter-register address stride is either 8-bit
917 (mmio) or 32-bit (mmio32 or mmio32be).
918 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
919 to be equivalent to 'mmio'. 'options' are specified
920 in the same format described for "console=ttyS<n>"; if
921 unspecified, the h/w is not initialized.
925 Start an early, polled-mode console on a pl011 serial
926 port at the specified address. The pl011 serial port
927 must already be setup and configured. Options are not
928 yet supported. If 'mmio32' is specified, then only
929 the driver will use only 32-bit accessors to read/write
930 the device registers.
933 Start an early, polled-mode console on a meson serial
934 port at the specified address. The serial port must
935 already be setup and configured. Options are not yet
939 Start an early, polled-mode console on an msm serial
940 port at the specified address. The serial port
941 must already be setup and configured. Options are not
945 Start an early, polled-mode console on an msm serial
946 dm port at the specified address. The serial port
947 must already be setup and configured. Options are not
950 smh Use ARM semihosting calls for early console.
958 Use early console provided by serial driver available
959 on Samsung SoCs, requires selecting proper type and
960 a correct base address of the selected UART port. The
961 serial port must already be setup and configured.
962 Options are not yet supported.
966 Use early console provided by Freescale LP UART driver
967 found on Freescale Vybrid and QorIQ LS1021A processors.
968 A valid base address must be provided, and the serial
969 port must already be setup and configured.
971 armada3700_uart,<addr>
972 Start an early, polled-mode console on the
973 Armada 3700 serial port at the specified
974 address. The serial port must already be setup
975 and configured. Options are not yet supported.
977 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
981 earlyprintk=serial[,ttySn[,baudrate]]
982 earlyprintk=serial[,0x...[,baudrate]]
983 earlyprintk=ttySn[,baudrate]
984 earlyprintk=dbgp[debugController#]
985 earlyprintk=pciserial,bus:device.function[,baudrate]
987 earlyprintk is useful when the kernel crashes before
988 the normal console is initialized. It is not enabled by
989 default because it has some cosmetic problems.
991 Append ",keep" to not disable it when the real console
994 Only one of vga, efi, serial, or usb debug port can
997 Currently only ttyS0 and ttyS1 may be specified by
998 name. Other I/O ports may be explicitly specified
999 on some architectures (x86 and arm at least) by
1000 replacing ttySn with an I/O port address, like this:
1001 earlyprintk=serial,0x1008,115200
1002 You can find the port for a given device in
1003 /proc/tty/driver/serial:
1004 2: uart:ST16650V2 port:00001008 irq:18 ...
1006 Interaction with the standard serial driver is not
1009 The VGA and EFI output is eventually overwritten by
1012 The xen output can only be used by Xen PV guests.
1014 edac_report= [HW,EDAC] Control how to report EDAC event
1015 Format: {"on" | "off" | "force"}
1016 on: enable EDAC to report H/W event. May be overridden
1017 by other higher priority error reporting module.
1018 off: disable H/W event reporting through EDAC.
1019 force: enforce the use of EDAC to report H/W event.
1022 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1025 This is designed to be used in conjunction with
1026 the boot argument: earlyprintk=vga
1029 Format: {"off" | "on" | "skip[mbr]"}
1032 Format: { "old_map", "nochunk", "noruntime", "debug" }
1033 old_map [X86-64]: switch to the old ioremap-based EFI
1034 runtime services mapping. 32-bit still uses this one by
1036 nochunk: disable reading files in "chunks" in the EFI
1037 boot stub, as chunking can cause problems with some
1038 firmware implementations.
1039 noruntime : disable EFI runtime services support
1040 debug: enable misc debug output
1042 efi_no_storage_paranoia [EFI; X86]
1043 Using this parameter you can use more than 50% of
1044 your efi variable storage. Use this parameter only if
1045 you are really sure that your UEFI does sane gc and
1046 fulfills the spec otherwise your board may brick.
1048 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1049 Add arbitrary attribute to specific memory range by
1050 updating original EFI memory map.
1051 Region of memory which aa attribute is added to is
1053 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1054 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1055 attribute is added to range 0x100000000-0x180000000 and
1056 0x10a0000000-0x1120000000.
1058 Using this parameter you can do debugging of EFI memmap
1059 related feature. For example, you can do debugging of
1060 Address Range Mirroring feature even if your box
1063 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1064 that is to be dynamically loaded by Linux. If there are
1065 multiple variables with the same name but with different
1066 vendor GUIDs, all of them will be loaded. See
1067 Documentation/acpi/ssdt-overlays.txt for details.
1070 eisa_irq_edge= [PARISC,HW]
1071 See header of drivers/parisc/eisa.c.
1074 See comment before function elanfreq_setup() in
1075 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1078 Format: {"cfq" | "deadline" | "noop"}
1079 See Documentation/block/cfq-iosched.txt and
1080 Documentation/block/deadline-iosched.txt for details.
1082 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1083 Specifies physical address of start of kernel core
1084 image elf header and optionally the size. Generally
1085 kexec loader will pass this option to capture kernel.
1086 See Documentation/kdump/kdump.txt for details.
1088 enable_mtrr_cleanup [X86]
1089 The kernel tries to adjust MTRR layout from continuous
1090 to discrete, to make X server driver able to add WB
1091 entry later. This parameter enables that.
1093 enable_timer_pin_1 [X86]
1094 Enable PIN 1 of APIC timer
1095 Can be useful to work around chipset bugs
1096 (in particular on some ATI chipsets).
1097 The kernel tries to set a reasonable default.
1099 enforcing [SELINUX] Set initial enforcing status.
1101 See security/selinux/Kconfig help text.
1102 0 -- permissive (log only, no denials).
1103 1 -- enforcing (deny and log).
1105 Value can be changed at runtime via /selinux/enforce.
1108 Disable Error Record Serialization Table (ERST)
1111 ether= [HW,NET] Ethernet cards parameters
1112 This option is obsoleted by the "netdev=" option, which
1113 has equivalent usage. See its documentation for details.
1117 Permit 'security.evm' to be updated regardless of
1118 current integrity status.
1122 fail_make_request=[KNL]
1123 General fault injection mechanism.
1124 Format: <interval>,<probability>,<space>,<times>
1125 See also Documentation/fault-injection/.
1128 See Documentation/blockdev/floppy.txt.
1130 force_pal_cache_flush
1131 [IA-64] Avoid check_sal_cache_flush which may hang on
1132 buggy SAL_CACHE_FLUSH implementations. Using this
1133 parameter will force ia64_sal_cache_flush to call
1134 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1137 Forcefully enable Physical Address Extension (PAE).
1138 Many Pentium M systems disable PAE but may have a
1139 functionally usable PAE implementation.
1140 Warning: use of this parameter will taint the kernel
1141 and may cause unknown problems.
1144 [FTRACE] will set and start the specified tracer
1145 as early as possible in order to facilitate early
1148 ftrace_dump_on_oops[=orig_cpu]
1149 [FTRACE] will dump the trace buffers on oops.
1150 If no parameter is passed, ftrace will dump
1151 buffers of all CPUs, but if you pass orig_cpu, it will
1152 dump only the buffer of the CPU that triggered the
1155 ftrace_filter=[function-list]
1156 [FTRACE] Limit the functions traced by the function
1157 tracer at boot up. function-list is a comma separated
1158 list of functions. This list can be changed at run
1159 time by the set_ftrace_filter file in the debugfs
1162 ftrace_notrace=[function-list]
1163 [FTRACE] Do not trace the functions specified in
1164 function-list. This list can be changed at run time
1165 by the set_ftrace_notrace file in the debugfs
1168 ftrace_graph_filter=[function-list]
1169 [FTRACE] Limit the top level callers functions traced
1170 by the function graph tracer at boot up.
1171 function-list is a comma separated list of functions
1172 that can be changed at run time by the
1173 set_graph_function file in the debugfs tracing directory.
1175 ftrace_graph_notrace=[function-list]
1176 [FTRACE] Do not trace from the functions specified in
1177 function-list. This list is a comma separated list of
1178 functions that can be changed at run time by the
1179 set_graph_notrace file in the debugfs tracing directory.
1182 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1183 support via parallel port (up to 5 devices per port)
1184 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1185 See also Documentation/input/joystick-parport.txt
1189 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1193 gcov_persist= [GCOV] When non-zero (default), profiling data for
1194 kernel modules is saved and remains accessible via
1195 debugfs, even when the module is unloaded/reloaded.
1196 When zero, profiling data is discarded and associated
1197 debugfs files are removed at module unload time.
1199 goldfish [X86] Enable the goldfish android emulator platform.
1200 Don't use this when you are not running on the
1203 gpt [EFI] Forces disk with valid GPT signature but
1204 invalid Protective MBR to be treated as GPT. If the
1205 primary GPT is corrupted, it enables the backup/alternate
1206 GPT to be used instead.
1208 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1209 the "Enable 0" bit of the configuration register.
1212 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1213 the "Enable 0" bit of the configuration register.
1216 grcan.select= [HW] Select which physical interface to use.
1219 grcan.txsize= [HW] Sets the size of the tx buffer.
1220 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1222 grcan.rxsize= [HW] Sets the size of the rx buffer.
1223 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1226 gpio-mockup.gpio_mockup_ranges
1227 [HW] Sets the ranges of gpiochip of for this device.
1228 Format: <start1>,<end1>,<start2>,<end2>...
1230 hardlockup_all_cpu_backtrace=
1231 [KNL] Should the hard-lockup detector generate
1232 backtraces on all cpus.
1235 hashdist= [KNL,NUMA] Large hashes allocated during boot
1236 are distributed across NUMA nodes. Defaults on
1237 for 64-bit NUMA, off otherwise.
1238 Format: 0 | 1 (for off | on)
1240 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1242 hd= [EIDE] (E)IDE hard drive subsystem geometry
1243 Format: <cyl>,<head>,<sect>
1246 Disable Hardware Error Source Table (HEST) support;
1247 corresponding firmware-first mode error processing
1248 logic will be disabled.
1250 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1251 size of <nn>. This works even on boxes that have no
1252 highmem otherwise. This also works to reduce highmem
1253 size on bigger boxes.
1255 highres= [KNL] Enable/disable high resolution timer mode.
1256 Valid parameters: "on", "off"
1260 See Documentation/isdn/README.HiSax.
1264 hpet= [X86-32,HPET] option to control HPET usage
1265 Format: { enable (default) | disable | force |
1267 disable: disable HPET and use PIT instead
1268 force: allow force enabled of undocumented chips (ICH4,
1270 verbose: show contents of HPET registers during setup
1272 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1273 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1275 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1276 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1277 On x86-64 and powerpc, this option can be specified
1278 multiple times interleaved with hugepages= to reserve
1279 huge pages of different sizes. Valid pages sizes on
1280 x86-64 are 2M (when the CPU supports "pse") and 1G
1281 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1283 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1284 terminal devices. Valid values: 0..8
1285 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1286 If specified, z/VM IUCV HVC accepts connections
1287 from listed z/VM user IDs only.
1289 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1290 hardware thread id mappings.
1291 Format: <cpu>:<hwthread>
1294 Do not unregister boot console at start. This is only
1295 useful for debugging when something happens in the window
1296 between unregistering the boot console and initializing
1299 i2c_bus= [HW] Override the default board specific I2C bus speed
1300 or register an additional I2C bus that is not
1301 registered from board initialization code.
1305 i8042.debug [HW] Toggle i8042 debug mode
1306 i8042.unmask_kbd_data
1307 [HW] Enable printing of interrupt data from the KBD port
1308 (disabled by default, and as a pre-condition
1309 requires that i8042.debug=1 be enabled)
1310 i8042.direct [HW] Put keyboard port into non-translated mode
1311 i8042.dumbkbd [HW] Pretend that controller can only read data from
1312 keyboard and cannot control its state
1313 (Don't attempt to blink the leds)
1314 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1315 i8042.nokbd [HW] Don't check/create keyboard port
1316 i8042.noloop [HW] Disable the AUX Loopback command while probing
1318 i8042.nomux [HW] Don't check presence of an active multiplexing
1320 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1322 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1323 i8042.reset [HW] Reset the controller during init, cleanup and
1324 suspend-to-ram transitions, only during s2r
1325 transitions, or never reset
1326 Format: { 1 | Y | y | 0 | N | n }
1327 1, Y, y: always reset controller
1328 0, N, n: don't ever reset controller
1329 Default: only on s2r transitions on x86; most other
1330 architectures force reset to be always executed
1331 i8042.unlock [HW] Unlock (ignore) the keylock
1332 i8042.kbdreset [HW] Reset device connected to KBD port
1336 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1337 indicates that the driver is running on unsupported
1339 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1340 does not match list of supported models.
1342 [HW] Report power status in /proc/i8k
1343 (disabled by default)
1344 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1347 i915.invert_brightness=
1348 [DRM] Invert the sense of the variable that is used to
1349 set the brightness of the panel backlight. Normally a
1350 brightness value of 0 indicates backlight switched off,
1351 and the maximum of the brightness value sets the backlight
1352 to maximum brightness. If this parameter is set to 0
1353 (default) and the machine requires it, or this parameter
1354 is set to 1, a brightness value of 0 sets the backlight
1355 to maximum brightness, and the maximum of the brightness
1356 value switches the backlight off.
1357 -1 -- never invert brightness
1358 0 -- machine default
1359 1 -- force brightness inversion
1362 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1364 ide-core.nodma= [HW] (E)IDE subsystem
1365 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1366 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1367 .cdrom .chs .ignore_cable are additional options
1368 See Documentation/ide/ide.txt.
1370 ide-generic.probe-mask= [HW] (E)IDE subsystem
1372 Probe mask for legacy ISA IDE ports. Depending on
1373 platform up to 6 ports are supported, enabled by
1374 setting corresponding bits in the mask to 1. The
1375 default value is 0x0, which has a special meaning.
1376 On systems that have PCI, it triggers scanning the
1377 PCI bus for the first and the second port, which
1378 are then probed. On systems without PCI the value
1379 of 0x0 enables probing the two first ports as if it
1382 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1383 Claim all unknown PCI IDE storage controllers.
1386 Format: idle=poll, idle=halt, idle=nomwait
1387 Poll forces a polling idle loop that can slightly
1388 improve the performance of waking up a idle CPU, but
1389 will use a lot of power and make the system run hot.
1391 idle=halt: Halt is forced to be used for CPU idle.
1392 In such case C2/C3 won't be used again.
1393 idle=nomwait: Disable mwait for CPU C-states
1395 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1396 Format: { strict | legacy | 2008 | relaxed }
1399 Choose which programs will be accepted for execution
1400 based on the IEEE 754 NaN encoding(s) supported by
1401 the FPU and the NaN encoding requested with the value
1402 of an ELF file header flag individually set by each
1403 binary. Hardware implementations are permitted to
1404 support either or both of the legacy and the 2008 NaN
1407 Available settings are as follows:
1408 strict accept binaries that request a NaN encoding
1409 supported by the FPU
1410 legacy only accept legacy-NaN binaries, if supported
1412 2008 only accept 2008-NaN binaries, if supported
1414 relaxed accept any binaries regardless of whether
1415 supported by the FPU
1417 The FPU emulator is always able to support both NaN
1418 encodings, so if no FPU hardware is present or it has
1419 been disabled with 'nofpu', then the settings of
1420 'legacy' and '2008' strap the emulator accordingly,
1421 'relaxed' straps the emulator for both legacy-NaN and
1422 2008-NaN, whereas 'strict' enables legacy-NaN only on
1423 legacy processors and both NaN encodings on MIPS32 or
1426 The setting for ABS.fmt/NEG.fmt instruction execution
1427 mode generally follows that for the NaN encoding,
1428 except where unsupported by hardware.
1430 ignore_loglevel [KNL]
1431 Ignore loglevel setting - this will print /all/
1432 kernel messages to the console. Useful for debugging.
1433 We also add it as printk module parameter, so users
1434 could change it dynamically, usually by
1435 /sys/module/printk/parameters/ignore_loglevel.
1438 Ignore RLIMIT_DATA setting for data mappings,
1439 print warning at first misuse. Can be changed via
1440 /sys/module/kernel/parameters/ignore_rlimit_data.
1442 ihash_entries= [KNL]
1443 Set number of hash buckets for inode cache.
1445 ima_appraise= [IMA] appraise integrity measurements
1446 Format: { "off" | "enforce" | "fix" | "log" }
1449 ima_appraise_tcb [IMA]
1450 The builtin appraise policy appraises all files
1453 ima_canonical_fmt [IMA]
1454 Use the canonical format for the binary runtime
1455 measurements, instead of host native format.
1458 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1462 The list of supported hash algorithms is defined
1463 in crypto/hash_info.h.
1466 The builtin measurement policy to load during IMA
1467 setup. Specyfing "tcb" as the value, measures all
1468 programs exec'd, files mmap'd for exec, and all files
1469 opened with the read mode bit set by either the
1470 effective uid (euid=0) or uid=0.
1473 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1474 Load a policy which meets the needs of the Trusted
1475 Computing Base. This means IMA will measure all
1476 programs exec'd, files mmap'd for exec, and all files
1477 opened for read by uid=0.
1480 Select one of defined IMA measurements template formats.
1481 Formats: { "ima" | "ima-ng" | "ima-sig" }
1485 [IMA] Define a custom template format.
1486 Format: { "field1|...|fieldN" }
1488 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1489 Format: <min_file_size>
1490 Set the minimal file size for using asynchronous hash.
1491 If left unspecified, ahash usage is disabled.
1493 ahash performance varies for different data sizes on
1494 different crypto accelerators. This option can be used
1495 to achieve the best performance for a particular HW.
1497 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1499 Set hashing buffer size. Default: 4k.
1501 ahash performance varies for different chunk sizes on
1502 different crypto accelerators. This option can be used
1503 to achieve best performance for particular HW.
1507 Run specified binary instead of /sbin/init as init
1510 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1511 for working out where the kernel is dying during
1514 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1515 initcall functions. Useful for debugging built-in
1516 modules and initcalls.
1518 initrd= [BOOT] Specify the location of the initial ramdisk
1520 init_pkru= [x86] Specify the default memory protection keys rights
1521 register contents for all processes. 0x55555554 by
1522 default (disallow access to all but pkey 0). Can
1523 override in debugfs after boot.
1525 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1528 int_pln_enable [x86] Enable power limit notification interrupt
1530 integrity_audit=[IMA]
1531 Format: { "0" | "1" }
1532 0 -- basic integrity auditing messages. (Default)
1533 1 -- additional integrity auditing messages.
1535 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1537 Enable intel iommu driver.
1539 Disable intel iommu driver.
1540 igfx_off [Default Off]
1541 By default, gfx is mapped as normal device. If a gfx
1542 device has a dedicated DMAR unit, the DMAR unit is
1543 bypassed by not enabling DMAR with this option. In
1544 this case, gfx device will use physical address for
1547 With this option iommu will not optimize to look
1548 for io virtual address below 32-bit forcing dual
1549 address cycle on pci bus for cards supporting greater
1550 than 32-bit addressing. The default is to look
1551 for translation below 32-bit and if not available
1552 then look in the higher range.
1553 strict [Default Off]
1554 With this option on every unmap_single operation will
1555 result in a hardware IOTLB flush operation as opposed
1556 to batching them for performance.
1557 sp_off [Default Off]
1558 By default, super page will be supported if Intel IOMMU
1559 has the capability. With this option, super page will
1561 ecs_off [Default Off]
1562 By default, extended context tables will be supported if
1563 the hardware advertises that it has support both for the
1564 extended tables themselves, and also PASID support. With
1565 this option set, extended tables will not be used even
1566 on hardware which claims to support them.
1568 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1569 0 disables intel_idle and fall back on acpi_idle.
1570 1 to 9 specify maximum depth of C-state.
1574 Do not enable intel_pstate as the default
1575 scaling driver for the supported processors
1577 Use intel_pstate as a scaling driver, but configure it
1578 to work with generic cpufreq governors (instead of
1579 enabling its internal governor). This mode cannot be
1580 used along with the hardware-managed P-states (HWP)
1583 Enable intel_pstate on systems that prohibit it by default
1584 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1585 instead of acpi-cpufreq may disable platform features, such
1586 as thermal controls and power capping, that rely on ACPI
1587 P-States information being indicated to OSPM and therefore
1588 should be used with caution. This option does not work with
1589 processors that aren't supported by the intel_pstate driver
1590 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1592 Do not enable hardware P state control (HWP)
1595 Only load intel_pstate on systems which support
1596 hardware P state control (HWP) if available.
1598 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1599 Description Table, specifies preferred power management
1600 profile as "Enterprise Server" or "Performance Server",
1601 then this feature is turned on by default.
1603 Allow per-logical-CPU P-State performance control limits using
1604 cpufreq sysfs interface
1606 intremap= [X86-64, Intel-IOMMU]
1607 on enable Interrupt Remapping (default)
1608 off disable Interrupt Remapping
1609 nosid disable Source ID checking
1611 BIOS x2APIC opt-out request will be ignored
1612 nopost disable Interrupt Posting
1614 iomem= Disable strict checking of access to MMIO memory
1615 strict regions from userspace.
1630 nobypass [PPC/POWERNV]
1631 Disable IOMMU bypass, using IOMMU for PCI devices.
1634 io7= [HW] IO7 for Marvel based alpha systems
1635 See comment before marvel_specify_io7 in
1636 arch/alpha/kernel/core_marvel.c.
1638 io_delay= [X86] I/O delay method
1640 Standard port 0x80 based delay
1642 Alternate port 0xed based delay (needed on some systems)
1644 Simple two microseconds delay
1649 See Documentation/filesystems/nfs/nfsroot.txt.
1651 irqaffinity= [SMP] Set the default irq affinity mask
1652 The argument is a cpu list, as described above.
1655 When an interrupt is not handled search all handlers
1656 for it. Intended to get systems with badly broken
1660 When an interrupt is not handled search all handlers
1661 for it. Also check all handlers each timer
1662 interrupt. Intended to get systems with badly broken
1666 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1668 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1669 The argument is a cpu list, as described above.
1671 This option can be used to specify one or more CPUs
1672 to isolate from the general SMP balancing and scheduling
1673 algorithms. You can move a process onto or off an
1674 "isolated" CPU via the CPU affinity syscalls or cpuset.
1675 <cpu number> begins at 0 and the maximum value is
1676 "number of CPUs in system - 1".
1678 This option is the preferred way to isolate CPUs. The
1679 alternative -- manually setting the CPU mask of all
1680 tasks in the system -- can cause problems and
1681 suboptimal load balancer performance.
1685 ivrs_ioapic [HW,X86_64]
1686 Provide an override to the IOAPIC-ID<->DEVICE-ID
1687 mapping provided in the IVRS ACPI table. For
1688 example, to map IOAPIC-ID decimal 10 to
1689 PCI device 00:14.0 write the parameter as:
1690 ivrs_ioapic[10]=00:14.0
1692 ivrs_hpet [HW,X86_64]
1693 Provide an override to the HPET-ID<->DEVICE-ID
1694 mapping provided in the IVRS ACPI table. For
1695 example, to map HPET-ID decimal 0 to
1696 PCI device 00:14.0 write the parameter as:
1697 ivrs_hpet[0]=00:14.0
1699 ivrs_acpihid [HW,X86_64]
1700 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1701 mapping provided in the IVRS ACPI table. For
1702 example, to map UART-HID:UID AMD0020:0 to
1703 PCI device 00:14.5 write the parameter as:
1704 ivrs_acpihid[00:14.5]=AMD0020:0
1706 js= [HW,JOY] Analog joystick
1707 See Documentation/input/joystick.txt.
1710 When CONFIG_RANDOMIZE_BASE is set, this disables
1711 kernel and module base offset ASLR (Address Space
1712 Layout Randomization).
1716 kernelcore= [KNL,X86,IA-64,PPC]
1717 Format: nn[KMGTPE] | "mirror"
1719 specifies the amount of memory usable by the kernel
1720 for non-movable allocations. The requested amount is
1721 spread evenly throughout all nodes in the system. The
1722 remaining memory in each node is used for Movable
1723 pages. In the event, a node is too small to have both
1724 kernelcore and Movable pages, kernelcore pages will
1725 take priority and other nodes will have a larger number
1726 of Movable pages. The Movable zone is used for the
1727 allocation of pages that may be reclaimed or moved
1728 by the page migration subsystem. This means that
1729 HugeTLB pages may not be allocated from this zone.
1730 Note that allocations like PTEs-from-HighMem still
1731 use the HighMem zone if it exists, and the Normal
1732 zone if it does not.
1734 Instead of specifying the amount of memory (nn[KMGTPE]),
1735 you can specify "mirror" option. In case "mirror"
1736 option is specified, mirrored (reliable) memory is used
1737 for non-movable allocations and remaining memory is used
1738 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1739 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1742 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1743 Format: <Controller#>[,poll interval]
1744 The controller # is the number of the ehci usb debug
1745 port as it is probed via PCI. The poll interval is
1746 optional and is the number seconds in between
1747 each poll cycle to the debug port in case you need
1748 the functionality for interrupting the kernel with
1749 gdb or control-c on the dbgp connection. When
1750 not using this parameter you use sysrq-g to break into
1751 the kernel debugger.
1753 kgdboc= [KGDB,HW] kgdb over consoles.
1754 Requires a tty driver that supports console polling,
1755 or a supported polling keyboard driver (non-usb).
1756 Serial only format: <serial_device>[,baud]
1757 keyboard only format: kbd
1758 keyboard and serial format: kbd,<serial_device>[,baud]
1759 Optional Kernel mode setting:
1760 kms, kbd format: kms,kbd
1761 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1763 kgdbwait [KGDB] Stop kernel execution and enter the
1764 kernel debugger at the earliest opportunity.
1766 kmac= [MIPS] korina ethernet MAC address.
1767 Configure the RouterBoard 532 series on-chip
1768 Ethernet adapter MAC address.
1770 kmemleak= [KNL] Boot-time kmemleak enable/disable
1771 Valid arguments: on, off
1773 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1776 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1777 Valid arguments: 0, 1, 2
1778 kmemcheck=0 (disabled)
1779 kmemcheck=1 (enabled)
1780 kmemcheck=2 (one-shot mode)
1781 Default: 2 (one-shot mode)
1783 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1784 Default is 0 (don't ignore, but inject #GP)
1786 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1790 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1791 Default is 1 (enabled)
1793 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1795 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1797 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1798 (virtualized MMU) support on capable Intel chips.
1799 Default is 1 (enabled)
1801 kvm-intel.emulate_invalid_guest_state=
1802 [KVM,Intel] Enable emulation of invalid guest states
1803 Default is 0 (disabled)
1805 kvm-intel.flexpriority=
1806 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1807 Default is 1 (enabled)
1810 [KVM,Intel] Enable VMX nesting (nVMX).
1811 Default is 0 (disabled)
1813 kvm-intel.unrestricted_guest=
1814 [KVM,Intel] Disable unrestricted guest feature
1815 (virtualized real and unpaged mode) on capable
1816 Intel chips. Default is 1 (enabled)
1818 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1819 feature (tagged TLBs) on capable Intel chips.
1820 Default is 1 (enabled)
1826 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1829 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1830 value for LAPIC timer one-shot implementation. Default
1831 back to the programmable timer unit in the LAPIC.
1833 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1836 libata.dma= [LIBATA] DMA control
1837 libata.dma=0 Disable all PATA and SATA DMA
1838 libata.dma=1 PATA and SATA Disk DMA only
1839 libata.dma=2 ATAPI (CDROM) DMA only
1840 libata.dma=4 Compact Flash DMA only
1841 Combinations also work, so libata.dma=3 enables DMA
1842 for disks and CDROMs, but not CFs.
1844 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1845 libata.ignore_hpa=0 keep BIOS limits (default)
1846 libata.ignore_hpa=1 ignore limits, using full disk
1848 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1852 libata.force= [LIBATA] Force configurations. The format is comma
1853 separated list of "[ID:]VAL" where ID is
1854 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1855 matching port, link or device. Basically, it matches
1856 the ATA ID string printed on console by libata. If
1857 the whole ID part is omitted, the last PORT and DEVICE
1858 values are used. If ID hasn't been specified yet, the
1859 configuration applies to all ports, links and devices.
1861 If only DEVICE is omitted, the parameter applies to
1862 the port and all links and devices behind it. DEVICE
1863 number of 0 either selects the first device or the
1864 first fan-out link behind PMP device. It does not
1865 select the host link. DEVICE number of 15 selects the
1866 host link and device attached to it.
1868 The VAL specifies the configuration to force. As long
1869 as there's no ambiguity shortcut notation is allowed.
1870 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1871 The following configurations can be forced.
1873 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1874 Any ID with matching PORT is used.
1876 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1878 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1879 udma[/][16,25,33,44,66,100,133] notation is also
1882 * [no]ncq: Turn on or off NCQ.
1884 * [no]ncqtrim: Turn off queued DSM TRIM.
1886 * nohrst, nosrst, norst: suppress hard, soft
1889 * rstonce: only attempt one reset during
1890 hot-unplug link recovery
1892 * dump_id: dump IDENTIFY data.
1894 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1896 * disable: Disable this device.
1898 If there are multiple matching configurations changing
1899 the same attribute, the last one is used.
1901 memblock=debug [KNL] Enable memblock debug messages.
1903 load_ramdisk= [RAM] List of ramdisks to load from floppy
1904 See Documentation/blockdev/ramdisk.txt.
1906 lockd.nlm_grace_period=P [NFS] Assign grace period.
1909 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1912 lockd.nlm_timeout=T [NFS] Assign timeout value.
1915 lockd.nlm_udpport=M [NFS] Assign UDP port.
1918 locktorture.nreaders_stress= [KNL]
1919 Set the number of locking read-acquisition kthreads.
1920 Defaults to being automatically set based on the
1921 number of online CPUs.
1923 locktorture.nwriters_stress= [KNL]
1924 Set the number of locking write-acquisition kthreads.
1926 locktorture.onoff_holdoff= [KNL]
1927 Set time (s) after boot for CPU-hotplug testing.
1929 locktorture.onoff_interval= [KNL]
1930 Set time (s) between CPU-hotplug operations, or
1931 zero to disable CPU-hotplug testing.
1933 locktorture.shuffle_interval= [KNL]
1934 Set task-shuffle interval (jiffies). Shuffling
1935 tasks allows some CPUs to go into dyntick-idle
1936 mode during the locktorture test.
1938 locktorture.shutdown_secs= [KNL]
1939 Set time (s) after boot system shutdown. This
1940 is useful for hands-off automated testing.
1942 locktorture.stat_interval= [KNL]
1943 Time (s) between statistics printk()s.
1945 locktorture.stutter= [KNL]
1946 Time (s) to stutter testing, for example,
1947 specifying five seconds causes the test to run for
1948 five seconds, wait for five seconds, and so on.
1949 This tests the locking primitive's ability to
1950 transition abruptly to and from idle.
1952 locktorture.torture_runnable= [BOOT]
1953 Start locktorture running at boot time.
1955 locktorture.torture_type= [KNL]
1956 Specify the locking implementation to test.
1958 locktorture.verbose= [KNL]
1959 Enable additional printk() statements.
1961 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1964 loglevel= All Kernel Messages with a loglevel smaller than the
1965 console loglevel will be printed to the console. It can
1966 also be changed with klogd or other programs. The
1967 loglevels are defined as follows:
1969 0 (KERN_EMERG) system is unusable
1970 1 (KERN_ALERT) action must be taken immediately
1971 2 (KERN_CRIT) critical conditions
1972 3 (KERN_ERR) error conditions
1973 4 (KERN_WARNING) warning conditions
1974 5 (KERN_NOTICE) normal but significant condition
1975 6 (KERN_INFO) informational
1976 7 (KERN_DEBUG) debug-level messages
1978 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1979 in bytes. n must be a power of two and greater
1980 than the minimal size. The minimal size is defined
1981 by LOG_BUF_SHIFT kernel config parameter. There is
1982 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1983 that allows to increase the default size depending on
1984 the number of CPUs. See init/Kconfig for more details.
1986 logo.nologo [FB] Disables display of the built-in Linux logo.
1987 This may be used to provide more screen space for
1988 kernel log messages and is useful when debugging
1989 kernel boot problems.
1991 lp=0 [LP] Specify parallel ports to use, e.g,
1992 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1993 lp=reset first parallel port). 'lp=0' disables the
1994 lp=auto printer driver. 'lp=reset' (which can be
1995 specified in addition to the ports) causes
1996 attached printers to be reset. Using
1997 lp=port1,port2,... specifies the parallel ports
1998 to associate lp devices with, starting with
1999 lp0. A port specification may be 'none' to skip
2000 that lp device, or a parport name such as
2001 'parport0'. Specifying 'lp=auto' instead of a
2002 port specification list means that device IDs
2003 from each port should be examined, to see if
2004 an IEEE 1284-compliant printer is attached; if
2005 so, the driver will manage that printer.
2006 See also header of drivers/char/lp.c.
2009 Sets loops_per_jiffy to given constant, thus avoiding
2010 time-consuming boot-time autodetection (up to 250 ms per
2011 CPU). 0 enables autodetection (default). To determine
2012 the correct value for your kernel, boot with normal
2013 autodetection and see what value is printed. Note that
2014 on SMP systems the preset will be applied to all CPUs,
2015 which is likely to cause problems if your CPUs need
2016 significantly divergent settings. An incorrect value
2017 will cause delays in the kernel to be wrong, leading to
2018 unpredictable I/O errors and other breakage. Although
2019 unlikely, in the extreme case this might damage your
2023 Format: <io>,<irq>,<dma>
2025 machvec= [IA-64] Force the use of a particular machine-vector
2026 (machvec) in a generic kernel.
2027 Example: machvec=hpzx1_swiotlb
2029 machtype= [Loongson] Share the same kernel image file between different
2031 Example: machtype=lemote-yeeloong-2f-7inch
2033 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2034 than or equal to this physical address is ignored.
2036 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2037 will bring up during bootup. maxcpus=n : n >= 0 limits
2038 the kernel to bring up 'n' processors. Surely after
2039 bootup you can bring up the other plugged cpu by executing
2040 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2041 only takes effect during system bootup.
2042 While n=0 is a special case, it is equivalent to "nosmp",
2043 which also disables the IO APIC.
2045 max_loop= [LOOP] The number of loop block devices that get
2046 (loop.max_loop) unconditionally pre-created at init time. The default
2047 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2048 of statically allocating a predefined number, loop
2049 devices can be requested on-demand with the
2050 /dev/loop-control interface.
2052 mce [X86-32] Machine Check Exception
2054 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2056 md= [HW] RAID subsystems devices and level
2057 See Documentation/admin-guide/md.rst.
2060 Format: <first>,<last>
2061 Specifies range of consoles to be captured by the MDA.
2063 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2064 Amount of memory to be used when the kernel is not able
2065 to see the whole system memory or for test.
2066 [X86] Work as limiting max address. Use together
2067 with memmap= to avoid physical address space collisions.
2068 Without memmap= PCI devices could be placed at addresses
2069 belonging to unused RAM.
2071 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2075 [KNL,SH] Allow user to override the default size for
2076 per-device physically contiguous DMA buffers.
2078 memhp_default_state=online/offline
2079 [KNL] Set the initial state for the memory hotplug
2080 onlining policy. If not specified, the default value is
2081 set according to the
2082 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2084 See Documentation/memory-hotplug.txt.
2086 memmap=exactmap [KNL,X86] Enable setting of an exact
2087 E820 memory map, as specified by the user.
2088 Such memmap=exactmap lines can be constructed based on
2089 BIOS output or other requirements. See the memmap=nn@ss
2092 memmap=nn[KMG]@ss[KMG]
2093 [KNL] Force usage of a specific region of memory.
2094 Region of memory to be used is from ss to ss+nn.
2096 memmap=nn[KMG]#ss[KMG]
2097 [KNL,ACPI] Mark specific memory as ACPI data.
2098 Region of memory to be marked is from ss to ss+nn.
2100 memmap=nn[KMG]$ss[KMG]
2101 [KNL,ACPI] Mark specific memory as reserved.
2102 Region of memory to be reserved is from ss to ss+nn.
2103 Example: Exclude memory from 0x18690000-0x1869ffff
2104 memmap=64K$0x18690000
2106 memmap=0x10000$0x18690000
2108 memmap=nn[KMG]!ss[KMG]
2109 [KNL,X86] Mark specific memory as protected.
2110 Region of memory to be used, from ss to ss+nn.
2111 The memory region may be marked as e820 type 12 (0xc)
2112 and is NVDIMM or ADR memory.
2114 memory_corruption_check=0/1 [X86]
2115 Some BIOSes seem to corrupt the first 64k of
2116 memory when doing things like suspend/resume.
2117 Setting this option will scan the memory
2118 looking for corruption. Enabling this will
2119 both detect corruption and prevent the kernel
2120 from using the memory being corrupted.
2121 However, its intended as a diagnostic tool; if
2122 repeatable BIOS-originated corruption always
2123 affects the same memory, you can use memmap=
2124 to prevent the kernel from using that memory.
2126 memory_corruption_check_size=size [X86]
2127 By default it checks for corruption in the low
2128 64k, making this memory unavailable for normal
2129 use. Use this parameter to scan for
2130 corruption in more or less memory.
2132 memory_corruption_check_period=seconds [X86]
2133 By default it checks for corruption every 60
2134 seconds. Use this parameter to check at some
2135 other rate. 0 disables periodic checking.
2137 memtest= [KNL,X86,ARM] Enable memtest
2139 default : 0 <disable>
2140 Specifies the number of memtest passes to be
2141 performed. Each pass selects another test
2142 pattern from a given set of patterns. Memtest
2143 fills the memory with this pattern, validates
2144 memory contents and reserves bad memory
2145 regions that are detected.
2147 mem_sleep_default= [SUSPEND] Default system suspend mode:
2148 s2idle - Suspend-To-Idle
2149 shallow - Power-On Suspend or equivalent (if supported)
2150 deep - Suspend-To-RAM or equivalent (if supported)
2151 See Documentation/power/states.txt.
2153 meye.*= [HW] Set MotionEye Camera parameters
2154 See Documentation/video4linux/meye.txt.
2156 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2157 Multi-Function General Purpose Timers on AMD Geode
2160 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2161 the BIOS has incorrectly applied a workaround. TinyBIOS
2162 version 0.98 is known to be affected, 0.99 fixes the
2163 problem by letting the user disable the workaround.
2167 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2168 physical address is ignored.
2170 mini2440= [ARM,HW,KNL]
2171 Format:[0..2][b][c][t]
2173 MINI2440 configuration specification:
2174 0 - The attached screen is the 3.5" TFT
2175 1 - The attached screen is the 7" TFT
2176 2 - The VGA Shield is attached (1024x768)
2177 Leaving out the screen size parameter will not load
2178 the TFT driver, and the framebuffer will be left
2180 b - Enable backlight. The TFT backlight pin will be
2181 linked to the kernel VESA blanking code and a GPIO
2182 LED. This parameter is not necessary when using the
2184 c - Enable the s3c camera interface.
2185 t - Reserved for enabling touchscreen support. The
2186 touchscreen support is not enabled in the mainstream
2187 kernel as of 2.6.30, a preliminary port can be found
2188 in the "bleeding edge" mini2440 support kernel at
2189 http://repo.or.cz/w/linux-2.6/mini2440.git
2192 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2193 parameter allows control of the logging verbosity for
2194 the additional memory initialisation checks. A value
2195 of 0 disables mminit logging and a level of 4 will
2196 log everything. Information is printed at KERN_DEBUG
2197 so loglevel=8 may also need to be specified.
2200 [KNL] When CONFIG_MODULE_SIG is set, this means that
2201 modules without (valid) signatures will fail to load.
2202 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2203 is always true, so this option does nothing.
2205 module_blacklist= [KNL] Do not load a comma-separated list of
2206 modules. Useful for debugging problem modules.
2209 [MOUSE] Maximum time between finger touching and
2210 leaving touchpad surface for touch to be considered
2211 a tap and be reported as a left button click (for
2212 touchpads working in absolute mode only).
2214 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2215 reporting absolute coordinates, such as tablets
2216 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2217 reporting absolute coordinates, such as tablets
2219 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2220 is similar to kernelcore except it specifies the
2221 amount of memory used for migratable allocations.
2222 If both kernelcore and movablecore is specified,
2223 then kernelcore will be at *least* the specified
2224 value but may be more. If movablecore on its own
2225 is specified, the administrator must be careful
2226 that the amount of memory usable for all allocations
2229 movable_node [KNL] Boot-time switch to enable the effects
2230 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2232 MTD_Partition= [MTD]
2233 Format: <name>,<region-number>,<size>,<offset>
2235 MTD_Region= [MTD] Format:
2236 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2239 See drivers/mtd/cmdlinepart.c.
2241 multitce=off [PPC] This parameter disables the use of the pSeries
2242 firmware feature for updating multiple TCE entries
2245 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2247 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2249 boundary - index of last SLC block on Flex-OneNAND.
2250 The remaining blocks are configured as MLC blocks.
2251 lock - Configure if Flex-OneNAND boundary should be locked.
2252 Once locked, the boundary cannot be changed.
2253 1 indicates lock status, 0 indicates unlock status.
2256 ARM/S3C2412 JIVE boot control
2258 See arch/arm/mach-s3c2412/mach-jive.c
2260 mtouchusb.raw_coordinates=
2261 [HW] Make the MicroTouch USB driver use raw coordinates
2262 ('y', default) or cooked coordinates ('n')
2264 mtrr_chunk_size=nn[KMG] [X86]
2265 used for mtrr cleanup. It is largest continuous chunk
2266 that could hold holes aka. UC entries.
2268 mtrr_gran_size=nn[KMG] [X86]
2269 Used for mtrr cleanup. It is granularity of mtrr block.
2271 Large value could prevent small alignment from
2274 mtrr_spare_reg_nr=n [X86]
2276 Range: 0,7 : spare reg number
2278 Used for mtrr cleanup. It is spare mtrr entries number.
2279 Set to 2 or more if your graphical card needs more.
2281 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2283 netdev= [NET] Network devices parameters
2284 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2285 Note that mem_start is often overloaded to mean
2286 something different and driver-specific.
2287 This usage is only documented in each driver source
2291 [NETFILTER] Enable connection tracking flow accounting
2292 0 to disable accounting
2293 1 to enable accounting
2296 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2297 See Documentation/filesystems/nfs/nfsroot.txt.
2299 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2300 See Documentation/filesystems/nfs/nfsroot.txt.
2302 nfsrootdebug [NFS] enable nfsroot debugging messages.
2303 See Documentation/filesystems/nfs/nfsroot.txt.
2305 nfs.callback_nr_threads=
2306 [NFSv4] set the total number of threads that the
2307 NFS client will assign to service NFSv4 callback
2310 nfs.callback_tcpport=
2311 [NFS] set the TCP port on which the NFSv4 callback
2312 channel should listen.
2315 [NFS] sets the pathname to the program which is used
2316 to update the NFS client cache entries.
2318 nfs.cache_getent_timeout=
2319 [NFS] sets the timeout after which an attempt to
2320 update a cache entry is deemed to have failed.
2322 nfs.idmap_cache_timeout=
2323 [NFS] set the maximum lifetime for idmapper cache
2327 [NFS] enable 64-bit inode numbers.
2328 If zero, the NFS client will fake up a 32-bit inode
2329 number for the readdir() and stat() syscalls instead
2330 of returning the full 64-bit number.
2331 The default is to return 64-bit inode numbers.
2333 nfs.max_session_cb_slots=
2334 [NFSv4.1] Sets the maximum number of session
2335 slots the client will assign to the callback
2336 channel. This determines the maximum number of
2337 callbacks the client will process in parallel for
2338 a particular server.
2340 nfs.max_session_slots=
2341 [NFSv4.1] Sets the maximum number of session slots
2342 the client will attempt to negotiate with the server.
2343 This limits the number of simultaneous RPC requests
2344 that the client can send to the NFSv4.1 server.
2345 Note that there is little point in setting this
2346 value higher than the max_tcp_slot_table_limit.
2348 nfs.nfs4_disable_idmapping=
2349 [NFSv4] When set to the default of '1', this option
2350 ensures that both the RPC level authentication
2351 scheme and the NFS level operations agree to use
2352 numeric uids/gids if the mount is using the
2353 'sec=sys' security flavour. In effect it is
2354 disabling idmapping, which can make migration from
2355 legacy NFSv2/v3 systems to NFSv4 easier.
2356 Servers that do not support this mode of operation
2357 will be autodetected by the client, and it will fall
2358 back to using the idmapper.
2359 To turn off this behaviour, set the value to '0'.
2361 [NFS4] Specify an additional fixed unique ident-
2362 ification string that NFSv4 clients can insert into
2363 their nfs_client_id4 string. This is typically a
2364 UUID that is generated at system install time.
2366 nfs.send_implementation_id =
2367 [NFSv4.1] Send client implementation identification
2368 information in exchange_id requests.
2369 If zero, no implementation identification information
2371 The default is to send the implementation identification
2374 nfs.recover_lost_locks =
2375 [NFSv4] Attempt to recover locks that were lost due
2376 to a lease timeout on the server. Please note that
2377 doing this risks data corruption, since there are
2378 no guarantees that the file will remain unchanged
2379 after the locks are lost.
2380 If you want to enable the kernel legacy behaviour of
2381 attempting to recover these locks, then set this
2383 The default parameter value of '0' causes the kernel
2384 not to attempt recovery of lost locks.
2386 nfs4.layoutstats_timer =
2387 [NFSv4.2] Change the rate at which the kernel sends
2388 layoutstats to the pNFS metadata server.
2390 Setting this to value to 0 causes the kernel to use
2391 whatever value is the default set by the layout
2392 driver. A non-zero value sets the minimum interval
2393 in seconds between layoutstats transmissions.
2395 nfsd.nfs4_disable_idmapping=
2396 [NFSv4] When set to the default of '1', the NFSv4
2397 server will return only numeric uids and gids to
2398 clients using auth_sys, and will accept numeric uids
2399 and gids from such clients. This is intended to ease
2400 migration from NFSv2/v3.
2402 objlayoutdriver.osd_login_prog=
2403 [NFS] [OBJLAYOUT] sets the pathname to the program which
2404 is used to automatically discover and login into new
2405 osd-targets. Please see:
2406 Documentation/filesystems/pnfs.txt for more explanations
2408 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2409 when a NMI is triggered.
2410 Format: [state][,regs][,debounce][,die]
2412 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2413 Format: [panic,][nopanic,][num]
2415 0 - turn hardlockup detector in nmi_watchdog off
2416 1 - turn hardlockup detector in nmi_watchdog on
2417 When panic is specified, panic when an NMI watchdog
2418 timeout occurs (or 'nopanic' to override the opposite
2419 default). To disable both hard and soft lockup detectors,
2420 please see 'nowatchdog'.
2421 This is useful when you use a panic=... timeout and
2422 need the box quickly up again.
2424 netpoll.carrier_timeout=
2425 [NET] Specifies amount of time (in seconds) that
2426 netpoll should wait for a carrier. By default netpoll
2429 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2430 emulation library even if a 387 maths coprocessor
2434 [HW] Never suspend the console
2435 Disable suspending of consoles during suspend and
2436 hibernate operations. Once disabled, debugging
2437 messages can reach various consoles while the rest
2438 of the system is being put to sleep (ie, while
2439 debugging driver suspend/resume hooks). This may
2440 not work reliably with all consoles, but is known
2441 to work with serial and VGA consoles.
2442 To facilitate more flexible debugging, we also add
2443 console_suspend, a printk module parameter to control
2444 it. Users could use console_suspend (usually
2445 /sys/module/printk/parameters/console_suspend) to
2446 turn on/off it dynamically.
2448 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2449 caches in the slab allocator. Saves per-node memory,
2450 but will impact performance.
2454 noapic [SMP,APIC] Tells the kernel to not make use of any
2455 IOAPICs that may be present in the system.
2457 noautogroup Disable scheduler automatic task group creation.
2459 nobats [PPC] Do not use BATs for mapping kernel lowmem
2460 on "Classic" PPC cores.
2464 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2466 nodelayacct [KNL] Disable per-task delay accounting
2468 nodsp [SH] Disable hardware DSP at boot time.
2470 noefi Disable EFI runtime services support.
2475 On X86-32 available only on PAE configured kernels.
2476 noexec=on: enable non-executable mappings (default)
2477 noexec=off: disable non-executable mappings
2480 Disable SMAP (Supervisor Mode Access Prevention)
2481 even if it is supported by processor.
2484 Disable SMEP (Supervisor Mode Execution Prevention)
2485 even if it is supported by processor.
2488 This affects only 32-bit executables.
2489 noexec32=on: enable non-executable mappings (default)
2490 read doesn't imply executable mappings
2491 noexec32=off: disable non-executable mappings
2492 read implies executable mappings
2494 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2496 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2497 register save and restore. The kernel will only save
2498 legacy floating-point registers on task switch.
2500 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2502 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2503 Equivalent to smt=1.
2505 noxsave [BUGS=X86] Disables x86 extended register state save
2506 and restore using xsave. The kernel will fallback to
2507 enabling legacy floating-point and sse state.
2509 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2510 register states. The kernel will fall back to use
2511 xsave to save the states. By using this parameter,
2512 performance of saving the states is degraded because
2513 xsave doesn't support modified optimization while
2514 xsaveopt supports it on xsaveopt enabled systems.
2516 noxsaves [X86] Disables xsaves and xrstors used in saving and
2517 restoring x86 extended register state in compacted
2518 form of xsave area. The kernel will fall back to use
2519 xsaveopt and xrstor to save and restore the states
2520 in standard form of xsave area. By using this
2521 parameter, xsave area per process might occupy more
2522 memory on xsaves enabled systems.
2524 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2525 wfi(ARM) instruction doesn't work correctly and not to
2526 use it. This is also useful when using JTAG debugger.
2528 no_file_caps Tells the kernel not to honor file capabilities. The
2529 only way then for a file to be executed with privilege
2530 is to be setuid root or executed by root.
2532 nohalt [IA-64] Tells the kernel not to use the power saving
2533 function PAL_HALT_LIGHT when idle. This increases
2534 power-consumption. On the positive side, it reduces
2535 interrupt wake-up latency, which may improve performance
2536 in certain environments such as networked servers or
2539 nohibernate [HIBERNATION] Disable hibernation and resume.
2541 nohz= [KNL] Boottime enable/disable dynamic ticks
2542 Valid arguments: on, off
2545 nohz_full= [KNL,BOOT]
2546 The argument is a cpu list, as described above.
2547 In kernels built with CONFIG_NO_HZ_FULL=y, set
2548 the specified list of CPUs whose tick will be stopped
2549 whenever possible. The boot CPU will be forced outside
2550 the range to maintain the timekeeping.
2551 The CPUs in this range must also be included in the
2554 noiotrap [SH] Disables trapped I/O port accesses.
2556 noirqdebug [X86-32] Disables the code which attempts to detect and
2557 disable unhandled interrupt sources.
2559 no_timer_check [X86,APIC] Disables the code which tests for
2560 broken timer IRQ sources.
2562 noisapnp [ISAPNP] Disables ISA PnP code.
2564 noinitrd [RAM] Tells the kernel not to load any configured
2567 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2569 [Deprecated - use intremap=off]
2573 noinvpcid [X86] Disable the INVPCID cpu feature.
2575 nojitter [IA-64] Disables jitter checking for ITC timers.
2577 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2579 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2583 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2584 clock and use the default one.
2586 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2587 steal time is computed, but won't influence scheduler
2590 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2592 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2594 noltlbs [PPC] Do not use large page/tlb entries for kernel
2595 lowmem mapping on PPC40x and PPC8xx
2597 nomca [IA-64] Disable machine check abort handling
2599 nomce [X86-32] Disable Machine Check Exception
2601 nomfgpt [X86-32] Disable Multi-Function General Purpose
2602 Timer usage (for AMD Geode machines).
2604 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2605 shutdown the other cpus. Instead use the REBOOT_VECTOR
2608 nomodule Disable module load
2610 nopat [X86] Disable PAT (page attribute table extension of
2611 pagetables) support.
2613 norandmaps Don't use address space randomization. Equivalent to
2614 echo 0 > /proc/sys/kernel/randomize_va_space
2616 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2618 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2619 with UP alternatives
2621 nordrand [X86] Disable kernel use of the RDRAND and
2622 RDSEED instructions even if they are supported
2623 by the processor. RDRAND and RDSEED are still
2624 available to user space applications.
2626 noresume [SWSUSP] Disables resume and restores original swap
2629 no-scroll [VGA] Disables scrollback.
2630 This is required for the Braillex ib80-piezo Braille
2631 reader made by F.H. Papenmeier (Germany).
2635 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2637 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2638 and disable the IO APIC. legacy for "maxcpus=0".
2640 nosoftlockup [KNL] Disable the soft-lockup detector.
2642 nosync [HW,M68K] Disables sync negotiation for all devices.
2644 notsc [BUGS=X86-32] Disable Time Stamp Counter
2646 nowatchdog [KNL] Disable both lockup detectors, i.e.
2647 soft-lockup and NMI watchdog (hard-lockup).
2651 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2653 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2654 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2655 Some features depend on CPU0. Known dependencies are:
2656 1. Resume from suspend/hibernate depends on CPU0.
2657 Suspend/hibernate will fail if CPU0 is offline and you
2658 need to online CPU0 before suspend/hibernate.
2659 2. PIC interrupts also depend on CPU0. CPU0 can't be
2660 removed if a PIC interrupt is detected.
2661 It's said poweroff/reboot may depend on CPU0 on some
2662 machines although I haven't seen such issues so far
2663 after CPU0 is offline on a few tested machines.
2664 If the dependencies are under your control, you can
2665 turn on cpu0_hotplug.
2667 nptcg= [IA-64] Override max number of concurrent global TLB
2668 purges which is reported from either PAL_VM_SUMMARY or
2671 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2672 could support. nr_cpus=n : n >= 1 limits the kernel to
2673 support 'n' processors. It could be larger than the
2674 number of already plugged CPU during bootup, later in
2675 runtime you can physically add extra cpu until it reaches
2676 n. So during boot up some boot time memory for per-cpu
2677 variables need be pre-allocated for later physical cpu
2680 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2682 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2683 Allowed values are enable and disable
2685 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2686 one of ['zone', 'node', 'default'] can be specified
2687 This can be set from sysctl after boot.
2688 See Documentation/sysctl/vm.txt for details.
2690 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2691 See Documentation/debugging-via-ohci1394.txt for more
2694 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2695 Rather than timing out after 20 ms if an EC
2696 command is not properly ACKed, override the length
2697 of the timeout. We have interrupts disabled while
2698 waiting for the ACK, so if this is set too high
2699 interrupts *may* be lost!
2701 omap_mux= [OMAP] Override bootloader pin multiplexing.
2702 Format: <mux_mode0.mode_name=value>...
2703 For example, to override I2C bus2:
2704 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2706 oprofile.timer= [HW]
2707 Use timer interrupt instead of performance counters
2709 oprofile.cpu_type= Force an oprofile cpu type
2710 This might be useful if you have an older oprofile
2711 userland or if you want common events.
2712 Format: { arch_perfmon }
2713 arch_perfmon: [X86] Force use of architectural
2714 perfmon on Intel CPUs instead of the
2715 CPU specific event set.
2716 timer: [X86] Force use of architectural NMI
2717 timer mode (see also oprofile.timer
2718 for generic hr timer mode)
2720 oops=panic Always panic on oopses. Default is to just kill the
2721 process, but there is a small probability of
2722 deadlocking the machine.
2723 This will also cause panics on machine check exceptions.
2724 Useful together with panic=30 to trigger a reboot.
2727 See Documentation/sound/oss/oss-parameters.txt
2729 page_owner= [KNL] Boot-time page_owner enabling option.
2730 Storage of the information about who allocated
2731 each page is disabled in default. With this switch,
2733 on: enable the feature
2735 page_poison= [KNL] Boot-time parameter changing the state of
2736 poisoning on the buddy allocator.
2737 off: turn off poisoning
2738 on: turn on poisoning
2740 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2741 timeout > 0: seconds before rebooting
2742 timeout = 0: wait forever
2743 timeout < 0: reboot immediately
2746 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2749 crash_kexec_post_notifiers
2750 Run kdump after running panic-notifiers and dumping
2751 kmsg. This only for the users who doubt kdump always
2752 succeeds in any situation.
2753 Note that this also increases risks of kdump failure,
2754 because some panic notifiers can make the crashed
2755 kernel more unstable.
2757 parkbd.port= [HW] Parallel port number the keyboard adapter is
2758 connected to, default is 0.
2760 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2761 0 for XT, 1 for AT (default is AT).
2764 parport= [HW,PPT] Specify parallel ports. 0 disables.
2765 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2766 Use 'auto' to force the driver to use any
2767 IRQ/DMA settings detected (the default is to
2768 ignore detected IRQ/DMA settings because of
2769 possible conflicts). You can specify the base
2770 address, IRQ, and DMA settings; IRQ and DMA
2771 should be numbers, or 'auto' (for using detected
2772 settings on that particular port), or 'nofifo'
2773 (to avoid using a FIFO even if it is detected).
2774 Parallel ports are assigned in the order they
2775 are specified on the command line, starting
2778 parport_init_mode= [HW,PPT]
2779 Configure VIA parallel port to operate in
2780 a specific mode. This is necessary on Pegasos
2781 computer where firmware has no options for setting
2782 up parallel port mode and sets it to spp.
2783 Currently this function knows 686a and 8231 chips.
2784 Format: [spp|ps2|epp|ecp|ecpepp]
2787 Halt all CPUs after the first oops has been printed for
2788 the specified number of seconds. This is to be used if
2789 your oopses keep scrolling off the screen.
2794 See header of drivers/block/paride/pcd.c.
2795 See also Documentation/blockdev/paride.txt.
2797 pci=option[,option...] [PCI] various PCI subsystem options:
2798 earlydump [X86] dump PCI config space before the kernel
2800 off [X86] don't probe for the PCI bus
2801 bios [X86-32] force use of PCI BIOS, don't access
2802 the hardware directly. Use this if your machine
2803 has a non-standard PCI host bridge.
2804 nobios [X86-32] disallow use of PCI BIOS, only direct
2805 hardware access methods are allowed. Use this
2806 if you experience crashes upon bootup and you
2807 suspect they are caused by the BIOS.
2808 conf1 [X86] Force use of PCI Configuration Access
2809 Mechanism 1 (config address in IO port 0xCF8,
2810 data in IO port 0xCFC, both 32-bit).
2811 conf2 [X86] Force use of PCI Configuration Access
2812 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2813 the function, IO port 0xCFA, also 8-bit, sets
2814 bus number. The config space is then accessed
2815 through ports 0xC000-0xCFFF).
2816 See http://wiki.osdev.org/PCI for more info
2817 on the configuration access mechanisms.
2818 noaer [PCIE] If the PCIEAER kernel config parameter is
2819 enabled, this kernel boot option can be used to
2820 disable the use of PCIE advanced error reporting.
2821 nodomains [PCI] Disable support for multiple PCI
2822 root domains (aka PCI segments, in ACPI-speak).
2823 nommconf [X86] Disable use of MMCONFIG for PCI
2825 check_enable_amd_mmconf [X86] check for and enable
2826 properly configured MMIO access to PCI
2827 config space on AMD family 10h CPU
2828 nomsi [MSI] If the PCI_MSI kernel config parameter is
2829 enabled, this kernel boot option can be used to
2830 disable the use of MSI interrupts system-wide.
2831 noioapicquirk [APIC] Disable all boot interrupt quirks.
2832 Safety option to keep boot IRQs enabled. This
2833 should never be necessary.
2834 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2835 primary IO-APIC for bridges that cannot disable
2836 boot IRQs. This fixes a source of spurious IRQs
2837 when the system masks IRQs.
2838 noioapicreroute [APIC] Disable workaround that uses the
2839 boot IRQ equivalent of an IRQ that connects to
2840 a chipset where boot IRQs cannot be disabled.
2841 The opposite of ioapicreroute.
2842 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2843 routing table. These calls are known to be buggy
2844 on several machines and they hang the machine
2845 when used, but on other computers it's the only
2846 way to get the interrupt routing table. Try
2847 this option if the kernel is unable to allocate
2848 IRQs or discover secondary PCI buses on your
2850 rom [X86] Assign address space to expansion ROMs.
2851 Use with caution as certain devices share
2852 address decoders between ROMs and other
2854 norom [X86] Do not assign address space to
2855 expansion ROMs that do not already have
2856 BIOS assigned address ranges.
2857 nobar [X86] Do not assign address space to the
2858 BARs that weren't assigned by the BIOS.
2859 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2860 assigned automatically to PCI devices. You can
2861 make the kernel exclude IRQs of your ISA cards
2863 pirqaddr=0xAAAAA [X86] Specify the physical address
2864 of the PIRQ table (normally generated
2865 by the BIOS) if it is outside the
2866 F0000h-100000h range.
2867 lastbus=N [X86] Scan all buses thru bus #N. Can be
2868 useful if the kernel is unable to find your
2869 secondary buses and you want to tell it
2870 explicitly which ones they are.
2871 assign-busses [X86] Always assign all PCI bus
2872 numbers ourselves, overriding
2873 whatever the firmware may have done.
2874 usepirqmask [X86] Honor the possible IRQ mask stored
2875 in the BIOS $PIR table. This is needed on
2876 some systems with broken BIOSes, notably
2877 some HP Pavilion N5400 and Omnibook XE3
2878 notebooks. This will have no effect if ACPI
2879 IRQ routing is enabled.
2880 noacpi [X86] Do not use ACPI for IRQ routing
2881 or for PCI scanning.
2882 use_crs [X86] Use PCI host bridge window information
2883 from ACPI. On BIOSes from 2008 or later, this
2884 is enabled by default. If you need to use this,
2885 please report a bug.
2886 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2887 If you need to use this, please report a bug.
2888 routeirq Do IRQ routing for all PCI devices.
2889 This is normally done in pci_enable_device(),
2890 so this option is a temporary workaround
2891 for broken drivers that don't call it.
2892 skip_isa_align [X86] do not align io start addr, so can
2893 handle more pci cards
2894 noearly [X86] Don't do any early type 1 scanning.
2895 This might help on some broken boards which
2896 machine check when some devices' config space
2897 is read. But various workarounds are disabled
2898 and some IOMMU drivers will not work.
2899 bfsort Sort PCI devices into breadth-first order.
2900 This sorting is done to get a device
2901 order compatible with older (<= 2.4) kernels.
2902 nobfsort Don't sort PCI devices into breadth-first order.
2903 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2904 tuning and use the BIOS-configured MPS defaults.
2905 pcie_bus_safe Set every device's MPS to the largest value
2906 supported by all devices below the root complex.
2907 pcie_bus_perf Set device MPS to the largest allowable MPS
2908 based on its parent bus. Also set MRRS (Max
2909 Read Request Size) to the largest supported
2910 value (no larger than the MPS that the device
2911 or bus can support) for best performance.
2912 pcie_bus_peer2peer Set every device's MPS to 128B, which
2913 every device is guaranteed to support. This
2914 configuration allows peer-to-peer DMA between
2915 any pair of devices, possibly at the cost of
2916 reduced performance. This also guarantees
2917 that hot-added devices will work.
2918 cbiosize=nn[KMG] The fixed amount of bus space which is
2919 reserved for the CardBus bridge's IO window.
2920 The default value is 256 bytes.
2921 cbmemsize=nn[KMG] The fixed amount of bus space which is
2922 reserved for the CardBus bridge's memory
2923 window. The default value is 64 megabytes.
2926 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2927 [<order of align>@]pci:<vendor>:<device>\
2928 [:<subvendor>:<subdevice>][; ...]
2929 Specifies alignment and device to reassign
2930 aligned memory resources.
2931 If <order of align> is not specified,
2932 PAGE_SIZE is used as alignment.
2933 PCI-PCI bridge can be specified, if resource
2934 windows need to be expanded.
2935 To specify the alignment for several
2936 instances of a device, the PCI vendor,
2937 device, subvendor, and subdevice may be
2938 specified, e.g., 4096@pci:8086:9c22:103c:198f
2939 ecrc= Enable/disable PCIe ECRC (transaction layer
2940 end-to-end CRC checking).
2941 bios: Use BIOS/firmware settings. This is the
2945 hpiosize=nn[KMG] The fixed amount of bus space which is
2946 reserved for hotplug bridge's IO window.
2947 Default size is 256 bytes.
2948 hpmemsize=nn[KMG] The fixed amount of bus space which is
2949 reserved for hotplug bridge's memory window.
2950 Default size is 2 megabytes.
2951 hpbussize=nn The minimum amount of additional bus numbers
2952 reserved for buses below a hotplug bridge.
2954 realloc= Enable/disable reallocating PCI bridge resources
2955 if allocations done by BIOS are too small to
2956 accommodate resources required by all child
2958 off: Turn realloc off
2960 realloc same as realloc=on
2961 noari do not use PCIe ARI.
2962 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2963 only look for one device below a PCIe downstream
2966 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2969 force Enable ASPM even on devices that claim not to support it.
2970 WARNING: Forcing ASPM on may cause system lockups.
2972 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2973 nomsi Do not use MSI for PCI Express Native Hotplug (this
2974 makes all PCIe ports use INTx for hotplug services).
2976 pcie_ports= [PCIE] PCIe ports handling:
2977 auto Ask the BIOS whether or not to use native PCIe services
2978 associated with PCIe ports (PME, hot-plug, AER). Use
2979 them only if that is allowed by the BIOS.
2980 native Use native PCIe services associated with PCIe ports
2982 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2985 pcie_port_pm= [PCIE] PCIe port power management handling:
2986 off Disable power management of all PCIe ports
2987 force Forcibly enable power management of all PCIe ports
2989 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2990 nomsi Do not use MSI for native PCIe PME signaling (this makes
2991 all PCIe root ports use INTx for all services).
2993 pcmv= [HW,PCMCIA] BadgePAD 4
2997 Keep all power-domains already enabled by bootloader on,
2998 even if no driver has claimed them. This is useful
2999 for debug and development, but should not be
3000 needed on a platform with proper driver support.
3003 See Documentation/blockdev/paride.txt.
3005 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3008 See arch/parisc/kernel/pdc_chassis.c
3010 percpu_alloc= Select which percpu first chunk allocator to use.
3011 Currently supported values are "embed" and "page".
3012 Archs may support subset or none of the selections.
3013 See comments in mm/percpu.c for details on each
3014 allocator. This parameter is primarily for debugging
3015 and performance comparison.
3018 See Documentation/blockdev/paride.txt.
3021 See Documentation/blockdev/paride.txt.
3023 pirq= [SMP,APIC] Manual mp-table setup
3024 See Documentation/x86/i386/IO-APIC.txt.
3026 plip= [PPT,NET] Parallel port network link
3027 Format: { parport<nr> | timid | 0 }
3028 See also Documentation/parport.txt.
3030 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3031 Override pmtimer IOPort with a hex value.
3035 Enable PNP debug messages (depends on the
3036 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3037 via /sys/module/pnp/parameters/debug. We always show
3038 current resource usage; turning this on also shows
3039 possible settings and some assignment information.
3045 { on | off | curr | res | no-curr | no-res }
3048 [ISAPNP] Exclude IRQs for the autoconfiguration
3051 [ISAPNP] Exclude DMAs for the autoconfiguration
3053 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3054 Ranges are in pairs (I/O port base and size).
3057 [ISAPNP] Exclude memory regions for the
3059 Ranges are in pairs (memory base and size).
3061 ports= [IP_VS_FTP] IPVS ftp helper module
3063 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3065 Format: <port>,<port>....
3067 powersave=off [PPC] This option disables power saving features.
3068 It specifically disables cpuidle and sets the
3069 platform machine description specific power_save
3070 function to NULL. On Idle the CPU just reduces
3073 ppc_strict_facility_enable
3074 [PPC] This option catches any kernel floating point,
3075 Altivec, VSX and SPE outside of regions specifically
3076 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3077 There is some performance impact when enabling this.
3079 print-fatal-signals=
3080 [KNL] debug: print fatal signals
3082 If enabled, warn about various signal handling
3083 related application anomalies: too many signals,
3084 too many POSIX.1 timers, fatal signals causing a
3087 If you hit the warning due to signal overflow,
3088 you might want to try "ulimit -i unlimited".
3092 printk.always_kmsg_dump=
3093 Trigger kmsg_dump for cases other than kernel oops or
3095 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3098 printk.devkmsg={on,off,ratelimit}
3099 Control writing to /dev/kmsg.
3100 on - unlimited logging to /dev/kmsg from userspace
3101 off - logging to /dev/kmsg disabled
3102 ratelimit - ratelimit the logging
3105 printk.time= Show timing data prefixed to each printk message line
3106 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3108 processor.max_cstate= [HW,ACPI]
3109 Limit processor to maximum C-state
3110 max_cstate=9 overrides any DMI blacklist limit.
3112 processor.nocst [HW,ACPI]
3113 Ignore the _CST method to determine C-states,
3114 instead using the legacy FADT method
3116 profile= [KNL] Enable kernel profiling via /proc/profile
3117 Format: [schedule,]<number>
3118 Param: "schedule" - profile schedule points.
3119 Param: <number> - step/bucket size as a power of 2 for
3120 statistical time based profiling.
3121 Param: "sleep" - profile D-state sleeping (millisecs).
3122 Requires CONFIG_SCHEDSTATS
3123 Param: "kvm" - profile VM exits.
3125 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3127 See Documentation/blockdev/ramdisk.txt.
3129 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3130 probe for; one of (bare|imps|exps|lifebook|any).
3131 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3133 psmouse.resetafter= [HW,MOUSE]
3134 Try to reset the device after so many bad packets
3137 [HW,MOUSE] Set desired mouse resolution, in dpi.
3138 psmouse.smartscroll=
3139 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3140 0 = disabled, 1 = enabled (default).
3142 pstore.backend= Specify the name of the pstore backend to use
3145 See Documentation/blockdev/paride.txt.
3148 [KNL] Number of legacy pty's. Overwrites compiled-in
3151 quiet [KNL] Disable most log messages
3156 See Documentation/admin-guide/md.rst.
3158 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3159 See Documentation/blockdev/ramdisk.txt.
3162 The argument is a cpu list, as described above.
3164 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3165 the specified list of CPUs to be no-callback CPUs.
3166 Invocation of these CPUs' RCU callbacks will
3167 be offloaded to "rcuox/N" kthreads created for
3168 that purpose, where "x" is "b" for RCU-bh, "p"
3169 for RCU-preempt, and "s" for RCU-sched, and "N"
3170 is the CPU number. This reduces OS jitter on the
3171 offloaded CPUs, which can be useful for HPC and
3172 real-time workloads. It can also improve energy
3173 efficiency for asymmetric multiprocessors.
3176 Rather than requiring that offloaded CPUs
3177 (specified by rcu_nocbs= above) explicitly
3178 awaken the corresponding "rcuoN" kthreads,
3179 make these kthreads poll for callbacks.
3180 This improves the real-time response for the
3181 offloaded CPUs by relieving them of the need to
3182 wake up the corresponding kthread, but degrades
3183 energy efficiency by requiring that the kthreads
3184 periodically wake up to do the polling.
3186 rcutree.blimit= [KNL]
3187 Set maximum number of finished RCU callbacks to
3188 process in one batch.
3190 rcutree.dump_tree= [KNL]
3191 Dump the structure of the rcu_node combining tree
3192 out at early boot. This is used for diagnostic
3193 purposes, to verify correct tree setup.
3195 rcutree.gp_cleanup_delay= [KNL]
3196 Set the number of jiffies to delay each step of
3197 RCU grace-period cleanup. This only has effect
3198 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3200 rcutree.gp_init_delay= [KNL]
3201 Set the number of jiffies to delay each step of
3202 RCU grace-period initialization. This only has
3203 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3206 rcutree.gp_preinit_delay= [KNL]
3207 Set the number of jiffies to delay each step of
3208 RCU grace-period pre-initialization, that is,
3209 the propagation of recent CPU-hotplug changes up
3210 the rcu_node combining tree. This only has effect
3211 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3213 rcutree.rcu_fanout_exact= [KNL]
3214 Disable autobalancing of the rcu_node combining
3215 tree. This is used by rcutorture, and might
3216 possibly be useful for architectures having high
3217 cache-to-cache transfer latencies.
3219 rcutree.rcu_fanout_leaf= [KNL]
3220 Change the number of CPUs assigned to each
3221 leaf rcu_node structure. Useful for very
3222 large systems, which will choose the value 64,
3223 and for NUMA systems with large remote-access
3224 latencies, which will choose a value aligned
3225 with the appropriate hardware boundaries.
3227 rcutree.jiffies_till_sched_qs= [KNL]
3228 Set required age in jiffies for a
3229 given grace period before RCU starts
3230 soliciting quiescent-state help from
3231 rcu_note_context_switch().
3233 rcutree.jiffies_till_first_fqs= [KNL]
3234 Set delay from grace-period initialization to
3235 first attempt to force quiescent states.
3236 Units are jiffies, minimum value is zero,
3237 and maximum value is HZ.
3239 rcutree.jiffies_till_next_fqs= [KNL]
3240 Set delay between subsequent attempts to force
3241 quiescent states. Units are jiffies, minimum
3242 value is one, and maximum value is HZ.
3244 rcutree.kthread_prio= [KNL,BOOT]
3245 Set the SCHED_FIFO priority of the RCU per-CPU
3246 kthreads (rcuc/N). This value is also used for
3247 the priority of the RCU boost threads (rcub/N)
3248 and for the RCU grace-period kthreads (rcu_bh,
3249 rcu_preempt, and rcu_sched). If RCU_BOOST is
3250 set, valid values are 1-99 and the default is 1
3251 (the least-favored priority). Otherwise, when
3252 RCU_BOOST is not set, valid values are 0-99 and
3253 the default is zero (non-realtime operation).
3255 rcutree.rcu_nocb_leader_stride= [KNL]
3256 Set the number of NOCB kthread groups, which
3257 defaults to the square root of the number of
3258 CPUs. Larger numbers reduces the wakeup overhead
3259 on the per-CPU grace-period kthreads, but increases
3260 that same overhead on each group's leader.
3262 rcutree.qhimark= [KNL]
3263 Set threshold of queued RCU callbacks beyond which
3264 batch limiting is disabled.
3266 rcutree.qlowmark= [KNL]
3267 Set threshold of queued RCU callbacks below which
3268 batch limiting is re-enabled.
3270 rcutree.rcu_idle_gp_delay= [KNL]
3271 Set wakeup interval for idle CPUs that have
3272 RCU callbacks (RCU_FAST_NO_HZ=y).
3274 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3275 Set wakeup interval for idle CPUs that have
3276 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3277 Lazy RCU callbacks are those which RCU can
3278 prove do nothing more than free memory.
3280 rcuperf.gp_exp= [KNL]
3281 Measure performance of expedited synchronous
3282 grace-period primitives.
3284 rcuperf.holdoff= [KNL]
3285 Set test-start holdoff period. The purpose of
3286 this parameter is to delay the start of the
3287 test until boot completes in order to avoid
3290 rcuperf.nreaders= [KNL]
3291 Set number of RCU readers. The value -1 selects
3292 N, where N is the number of CPUs. A value
3293 "n" less than -1 selects N-n+1, where N is again
3294 the number of CPUs. For example, -2 selects N
3295 (the number of CPUs), -3 selects N+1, and so on.
3296 A value of "n" less than or equal to -N selects
3299 rcuperf.nwriters= [KNL]
3300 Set number of RCU writers. The values operate
3301 the same as for rcuperf.nreaders.
3302 N, where N is the number of CPUs
3304 rcuperf.perf_runnable= [BOOT]
3305 Start rcuperf running at boot time.
3307 rcuperf.shutdown= [KNL]
3308 Shut the system down after performance tests
3309 complete. This is useful for hands-off automated
3312 rcuperf.perf_type= [KNL]
3313 Specify the RCU implementation to test.
3315 rcuperf.verbose= [KNL]
3316 Enable additional printk() statements.
3318 rcutorture.cbflood_inter_holdoff= [KNL]
3319 Set holdoff time (jiffies) between successive
3320 callback-flood tests.
3322 rcutorture.cbflood_intra_holdoff= [KNL]
3323 Set holdoff time (jiffies) between successive
3324 bursts of callbacks within a given callback-flood
3327 rcutorture.cbflood_n_burst= [KNL]
3328 Set the number of bursts making up a given
3329 callback-flood test. Set this to zero to
3330 disable callback-flood testing.
3332 rcutorture.cbflood_n_per_burst= [KNL]
3333 Set the number of callbacks to be registered
3334 in a given burst of a callback-flood test.
3336 rcutorture.fqs_duration= [KNL]
3337 Set duration of force_quiescent_state bursts
3340 rcutorture.fqs_holdoff= [KNL]
3341 Set holdoff time within force_quiescent_state bursts
3344 rcutorture.fqs_stutter= [KNL]
3345 Set wait time between force_quiescent_state bursts
3348 rcutorture.gp_cond= [KNL]
3349 Use conditional/asynchronous update-side
3350 primitives, if available.
3352 rcutorture.gp_exp= [KNL]
3353 Use expedited update-side primitives, if available.
3355 rcutorture.gp_normal= [KNL]
3356 Use normal (non-expedited) asynchronous
3357 update-side primitives, if available.
3359 rcutorture.gp_sync= [KNL]
3360 Use normal (non-expedited) synchronous
3361 update-side primitives, if available. If all
3362 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3363 rcutorture.gp_normal=, and rcutorture.gp_sync=
3364 are zero, rcutorture acts as if is interpreted
3365 they are all non-zero.
3367 rcutorture.n_barrier_cbs= [KNL]
3368 Set callbacks/threads for rcu_barrier() testing.
3370 rcutorture.nfakewriters= [KNL]
3371 Set number of concurrent RCU writers. These just
3372 stress RCU, they don't participate in the actual
3373 test, hence the "fake".
3375 rcutorture.nreaders= [KNL]
3376 Set number of RCU readers. The value -1 selects
3377 N-1, where N is the number of CPUs. A value
3378 "n" less than -1 selects N-n-2, where N is again
3379 the number of CPUs. For example, -2 selects N
3380 (the number of CPUs), -3 selects N+1, and so on.
3382 rcutorture.object_debug= [KNL]
3383 Enable debug-object double-call_rcu() testing.
3385 rcutorture.onoff_holdoff= [KNL]
3386 Set time (s) after boot for CPU-hotplug testing.
3388 rcutorture.onoff_interval= [KNL]
3389 Set time (s) between CPU-hotplug operations, or
3390 zero to disable CPU-hotplug testing.
3392 rcutorture.shuffle_interval= [KNL]
3393 Set task-shuffle interval (s). Shuffling tasks
3394 allows some CPUs to go into dyntick-idle mode
3395 during the rcutorture test.
3397 rcutorture.shutdown_secs= [KNL]
3398 Set time (s) after boot system shutdown. This
3399 is useful for hands-off automated testing.
3401 rcutorture.stall_cpu= [KNL]
3402 Duration of CPU stall (s) to test RCU CPU stall
3403 warnings, zero to disable.
3405 rcutorture.stall_cpu_holdoff= [KNL]
3406 Time to wait (s) after boot before inducing stall.
3408 rcutorture.stat_interval= [KNL]
3409 Time (s) between statistics printk()s.
3411 rcutorture.stutter= [KNL]
3412 Time (s) to stutter testing, for example, specifying
3413 five seconds causes the test to run for five seconds,
3414 wait for five seconds, and so on. This tests RCU's
3415 ability to transition abruptly to and from idle.
3417 rcutorture.test_boost= [KNL]
3418 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3419 "Maybe" means test if the RCU implementation
3420 under test support RCU priority boosting.
3422 rcutorture.test_boost_duration= [KNL]
3423 Duration (s) of each individual boost test.
3425 rcutorture.test_boost_interval= [KNL]
3426 Interval (s) between each boost test.
3428 rcutorture.test_no_idle_hz= [KNL]
3429 Test RCU's dyntick-idle handling. See also the
3430 rcutorture.shuffle_interval parameter.
3432 rcutorture.torture_runnable= [BOOT]
3433 Start rcutorture running at boot time.
3435 rcutorture.torture_type= [KNL]
3436 Specify the RCU implementation to test.
3438 rcutorture.verbose= [KNL]
3439 Enable additional printk() statements.
3441 rcupdate.rcu_cpu_stall_suppress= [KNL]
3442 Suppress RCU CPU stall warning messages.
3444 rcupdate.rcu_cpu_stall_timeout= [KNL]
3445 Set timeout for RCU CPU stall warning messages.
3447 rcupdate.rcu_expedited= [KNL]
3448 Use expedited grace-period primitives, for
3449 example, synchronize_rcu_expedited() instead
3450 of synchronize_rcu(). This reduces latency,
3451 but can increase CPU utilization, degrade
3452 real-time latency, and degrade energy efficiency.
3453 No effect on CONFIG_TINY_RCU kernels.
3455 rcupdate.rcu_normal= [KNL]
3456 Use only normal grace-period primitives,
3457 for example, synchronize_rcu() instead of
3458 synchronize_rcu_expedited(). This improves
3459 real-time latency, CPU utilization, and
3460 energy efficiency, but can expose users to
3461 increased grace-period latency. This parameter
3462 overrides rcupdate.rcu_expedited. No effect on
3463 CONFIG_TINY_RCU kernels.
3465 rcupdate.rcu_normal_after_boot= [KNL]
3466 Once boot has completed (that is, after
3467 rcu_end_inkernel_boot() has been invoked), use
3468 only normal grace-period primitives. No effect
3469 on CONFIG_TINY_RCU kernels.
3471 rcupdate.rcu_task_stall_timeout= [KNL]
3472 Set timeout in jiffies for RCU task stall warning
3473 messages. Disable with a value less than or equal
3476 rcupdate.rcu_self_test= [KNL]
3477 Run the RCU early boot self tests
3479 rcupdate.rcu_self_test_bh= [KNL]
3480 Run the RCU bh early boot self tests
3482 rcupdate.rcu_self_test_sched= [KNL]
3483 Run the RCU sched early boot self tests
3487 Run specified binary instead of /init from the ramdisk,
3488 used for early userspace startup. See initrd.
3491 Format (x86 or x86_64):
3492 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3494 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3496 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3497 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3498 reboot_force is either force or not specified,
3499 reboot_cpu is s[mp]#### with #### being the processor
3500 to be used for rebooting.
3503 [KNL, SMP] Set scheduler's default relax_domain_level.
3504 See Documentation/cgroup-v1/cpusets.txt.
3506 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3508 reservetop= [X86-32]
3510 Reserves a hole at the top of the kernel virtual
3515 Set the amount of memory to reserve for BIOS at
3516 the bottom of the address space.
3518 reset_devices [KNL] Force drivers to reset the underlying device
3519 during initialization.
3522 Specify the partition device for software suspend
3524 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3526 resume_offset= [SWSUSP]
3527 Specify the offset from the beginning of the partition
3528 given by "resume=" at which the swap header is located,
3529 in <PAGE_SIZE> units (needed only for swap files).
3530 See Documentation/power/swsusp-and-swap-files.txt
3532 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3533 read the resume files
3535 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3536 Useful for devices that are detected asynchronously
3537 (e.g. USB and MMC devices).
3539 hibernate= [HIBERNATION]
3540 noresume Don't check if there's a hibernation image
3541 present during boot.
3542 nocompress Don't compress/decompress hibernation images.
3543 no Disable hibernation and resume.
3544 protect_image Turn on image protection during restoration
3545 (that will set all pages holding image data
3546 during restoration read-only).
3548 retain_initrd [RAM] Keep initrd memory after extraction
3550 rfkill.default_state=
3551 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3552 etc. communication is blocked by default.
3555 rfkill.master_switch_mode=
3556 0 The "airplane mode" button does nothing.
3557 1 The "airplane mode" button toggles between everything
3558 blocked and the previous configuration.
3559 2 The "airplane mode" button toggles between everything
3560 blocked and everything unblocked.
3562 rhash_entries= [KNL,NET]
3563 Set number of hash buckets for route cache
3566 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3569 ro [KNL] Mount root device read-only on boot
3572 on Mark read-only kernel memory as read-only (default).
3573 off Leave read-only kernel memory writable for debugging.
3576 Enable the uart passthrough on the designated usb port
3577 on Rockchip SoCs. When active, the signals of the
3578 debug-uart get routed to the D+ and D- pins of the usb
3579 port and the regular usb controller gets disabled.
3581 root= [KNL] Root filesystem
3582 See name_to_dev_t comment in init/do_mounts.c.
3584 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3585 mount the root filesystem
3587 rootflags= [KNL] Set root filesystem mount option string
3589 rootfstype= [KNL] Set root filesystem type
3591 rootwait [KNL] Wait (indefinitely) for root device to show up.
3592 Useful for devices that are detected asynchronously
3593 (e.g. USB and MMC devices).
3595 rproc_mem=nn[KMG][@address]
3596 [KNL,ARM,CMA] Remoteproc physical memory block.
3597 Memory area to be used by remote processor image,
3600 rw [KNL] Mount root device read-write on boot
3602 S [KNL] Run init in single mode
3604 s390_iommu= [HW,S390]
3605 Set s390 IOTLB flushing mode
3607 With strict flushing every unmap operation will result in
3608 an IOTLB flush. Default is lazy flushing before reuse,
3612 See drivers/net/irda/sa1100_ir.c.
3614 sbni= [NET] Granch SBNI12 leased line adapter
3616 sched_debug [KNL] Enables verbose scheduler debug messages.
3618 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3619 Allowed values are enable and disable. This feature
3620 incurs a small amount of overhead in the scheduler
3621 but is useful for debugging and performance tuning.
3623 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3624 xtime_lock contention on larger systems, and/or RCU lock
3625 contention on all systems with CONFIG_MAXSMP set.
3626 Format: { "0" | "1" }
3627 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3629 Note: increases power consumption, thus should only be
3630 enabled if running jitter sensitive (HPC/RT) workloads.
3632 security= [SECURITY] Choose a security module to enable at boot.
3633 If this boot parameter is not specified, only the first
3634 security module asking for security registration will be
3635 loaded. An invalid security module name will be treated
3636 as if no module has been chosen.
3638 selinux= [SELINUX] Disable or enable SELinux at boot time.
3639 Format: { "0" | "1" }
3640 See security/selinux/Kconfig help text.
3643 Default value is set via kernel config option.
3644 If enabled at boot time, /selinux/disable can be used
3645 later to disable prior to initial policy load.
3647 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3648 Format: { "0" | "1" }
3649 See security/apparmor/Kconfig help text
3652 Default value is set via kernel config option.
3654 serialnumber [BUGS=X86-32]
3657 Maximal number of shapers.
3665 Disable merging of slabs with similar size. May be
3666 necessary if there is some reason to distinguish
3667 allocs to different slabs. Debug options disable
3668 merging on their own.
3669 For more information see Documentation/vm/slub.txt.
3671 slab_max_order= [MM, SLAB]
3672 Determines the maximum allowed order for slabs.
3673 A high setting may cause OOMs due to memory
3674 fragmentation. Defaults to 1 for systems with
3675 more than 32MB of RAM, 0 otherwise.
3677 slub_debug[=options[,slabs]] [MM, SLUB]
3678 Enabling slub_debug allows one to determine the
3679 culprit if slab objects become corrupted. Enabling
3680 slub_debug can create guard zones around objects and
3681 may poison objects when not in use. Also tracks the
3682 last alloc / free. For more information see
3683 Documentation/vm/slub.txt.
3685 slub_max_order= [MM, SLUB]
3686 Determines the maximum allowed order for slabs.
3687 A high setting may cause OOMs due to memory
3688 fragmentation. For more information see
3689 Documentation/vm/slub.txt.
3691 slub_min_objects= [MM, SLUB]
3692 The minimum number of objects per slab. SLUB will
3693 increase the slab order up to slub_max_order to
3694 generate a sufficiently large slab able to contain
3695 the number of objects indicated. The higher the number
3696 of objects the smaller the overhead of tracking slabs
3697 and the less frequently locks need to be acquired.
3698 For more information see Documentation/vm/slub.txt.
3700 slub_min_order= [MM, SLUB]
3701 Determines the minimum page order for slabs. Must be
3702 lower than slub_max_order.
3703 For more information see Documentation/vm/slub.txt.
3705 slub_nomerge [MM, SLUB]
3706 Same with slab_nomerge. This is supported for legacy.
3707 See slab_nomerge for more information.
3710 Format: <io1>[,<io2>[,...,<io8>]]
3712 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3713 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3714 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3715 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3716 smsc-ircc2.ircc_irq= [HW] IRQ line
3717 smsc-ircc2.ircc_dma= [HW] DMA channel
3718 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3719 0: Toshiba Satellite 1800 (GP data pin select)
3720 1: Fast pin select (default)
3723 smt [KNL,S390] Set the maximum number of threads (logical
3724 CPUs) to use per physical CPU on systems capable of
3725 symmetric multithreading (SMT). Will be capped to the
3726 actual hardware limit.
3728 Default: -1 (no limit)
3731 [KNL] Should the soft-lockup detector generate panics.
3734 softlockup_all_cpu_backtrace=
3735 [KNL] Should the soft-lockup detector generate
3736 backtraces on all cpus.
3739 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3740 See Documentation/laptops/sonypi.txt
3742 spia_io_base= [HW,MTD]
3748 Enabled the stack tracer on boot up.
3750 stacktrace_filter=[function-list]
3751 [FTRACE] Limit the functions that the stack tracer
3752 will trace at boot up. function-list is a comma separated
3753 list of functions. This list can be changed at run
3754 time by the stack_trace_filter file in the debugfs
3755 tracing directory. Note, this enables stack tracing
3756 and the stacktrace above is not needed.
3760 Set the STI (builtin display/keyboard on the HP-PARISC
3761 machines) console (graphic card) which should be used
3762 as the initial boot-console.
3763 See also comment in drivers/video/console/sticore.c.
3766 See comment in drivers/video/console/sticore.c.
3769 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3771 sunrpc.min_resvport=
3772 sunrpc.max_resvport=
3774 SunRPC servers often require that client requests
3775 originate from a privileged port (i.e. a port in the
3776 range 0 < portnr < 1024).
3777 An administrator who wishes to reserve some of these
3778 ports for other uses may adjust the range that the
3779 kernel's sunrpc client considers to be privileged
3780 using these two parameters to set the minimum and
3781 maximum port values.
3783 sunrpc.svc_rpc_per_connection_limit=
3785 Limit the number of requests that the server will
3786 process in parallel from a single connection.
3787 The default value is 0 (no limit).
3791 Control how the NFS server code allocates CPUs to
3792 service thread pools. Depending on how many NICs
3793 you have and where their interrupts are bound, this
3794 option will affect which CPUs will do NFS serving.
3795 Note: this parameter cannot be changed while the
3796 NFS server is running.
3798 auto the server chooses an appropriate mode
3799 automatically using heuristics
3800 global a single global pool contains all CPUs
3801 percpu one pool for each CPU
3802 pernode one pool for each NUMA node (equivalent
3803 to global on non-NUMA machines)
3805 sunrpc.tcp_slot_table_entries=
3806 sunrpc.udp_slot_table_entries=
3808 Sets the upper limit on the number of simultaneous
3809 RPC calls that can be sent from the client to a
3810 server. Increasing these values may allow you to
3811 improve throughput, but will also increase the
3812 amount of memory reserved for use by the client.
3814 suspend.pm_test_delay=
3816 Sets the number of seconds to remain in a suspend test
3817 mode before resuming the system (see
3818 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3819 is set. Default value is 5.
3822 [KNL] Enable accounting of swap in memory resource
3823 controller if no parameter or 1 is given or disable
3824 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3826 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3827 Format: { <int> | force | noforce }
3828 <int> -- Number of I/O TLB slabs
3829 force -- force using of bounce buffers even if they
3830 wouldn't be automatically used by the kernel
3831 noforce -- Never use bounce buffers (for debugging)
3835 sysfs.deprecated=0|1 [KNL]
3836 Enable/disable old style sysfs layout for old udev
3837 on older distributions. When this option is enabled
3838 very new udev will not work anymore. When this option
3839 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3840 in older udev will not work anymore.
3841 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3842 the kernel configuration.
3844 sysrq_always_enabled
3846 Ignore sysrq setting - this boot parameter will
3847 neutralize any effect of /proc/sys/kernel/sysrq.
3848 Useful for debugging.
3850 tcpmhash_entries= [KNL,NET]
3851 Set the number of tcp_metrics_hash slots.
3852 Default value is 8192 or 16384 depending on total
3853 ram pages. This is used to specify the TCP metrics
3854 cache size. See Documentation/networking/ip-sysctl.txt
3855 "tcp_no_metrics_save" section for more details.
3859 test_suspend= [SUSPEND][,N]
3860 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3861 standby suspend) or "freeze" (for suspend type freeze)
3862 as the system sleep state during system startup with
3863 the optional capability to repeat N number of times.
3864 The system is woken from this state using a
3865 wakeup-capable RTC alarm.
3867 thash_entries= [KNL,NET]
3868 Set number of hash buckets for TCP connection
3870 thermal.act= [HW,ACPI]
3871 -1: disable all active trip points in all thermal zones
3872 <degrees C>: override all lowest active trip points
3874 thermal.crt= [HW,ACPI]
3875 -1: disable all critical trip points in all thermal zones
3876 <degrees C>: override all critical trip points
3878 thermal.nocrt= [HW,ACPI]
3879 Set to disable actions on ACPI thermal zone
3880 critical and hot trip points.
3882 thermal.off= [HW,ACPI]
3883 1: disable ACPI thermal control
3885 thermal.psv= [HW,ACPI]
3886 -1: disable all passive trip points
3887 <degrees C>: override all passive trip points to this
3890 thermal.tzp= [HW,ACPI]
3891 Specify global default ACPI thermal zone polling rate
3892 <deci-seconds>: poll all this frequency
3893 0: no polling (default)
3896 Force threading of all interrupt handlers except those
3897 marked explicitly IRQF_NO_THREAD.
3900 Enable the Transcendent memory driver if built-in.
3902 tmem.cleancache=0|1 [KNL, XEN]
3903 Default is on (1). Disable the usage of the cleancache
3904 API to send anonymous pages to the hypervisor.
3906 tmem.frontswap=0|1 [KNL, XEN]
3907 Default is on (1). Disable the usage of the frontswap
3908 API to send swap pages to the hypervisor. If disabled
3909 the selfballooning and selfshrinking are force disabled.
3911 tmem.selfballooning=0|1 [KNL, XEN]
3912 Default is on (1). Disable the driving of swap pages
3915 tmem.selfshrinking=0|1 [KNL, XEN]
3916 Default is on (1). Partial swapoff that immediately
3917 transfers pages from Xen hypervisor back to the
3918 kernel based on different criteria.
3922 Specify if the kernel should make use of the cpu
3923 topology information if the hardware supports this.
3924 The scheduler will make use of this information and
3925 e.g. base its process migration decisions on it.
3928 topology_updates= [KNL, PPC, NUMA]
3930 Specify if the kernel should ignore (off)
3931 topology updates sent by the hypervisor to this
3936 tpm_suspend_pcr=[HW,TPM]
3937 Format: integer pcr id
3938 Specify that at suspend time, the tpm driver
3939 should extend the specified pcr with zeros,
3940 as a workaround for some chips which fail to
3941 flush the last written pcr on TPM_SaveState.
3942 This will guarantee that all the other pcrs
3945 trace_buf_size=nn[KMG]
3946 [FTRACE] will set tracing buffer size on each cpu.
3948 trace_event=[event-list]
3949 [FTRACE] Set and start specified trace events in order
3950 to facilitate early boot debugging. The event-list is a
3951 comma separated list of trace events to enable. See
3952 also Documentation/trace/events.txt
3954 trace_options=[option-list]
3955 [FTRACE] Enable or disable tracer options at boot.
3956 The option-list is a comma delimited list of options
3957 that can be enabled or disabled just as if you were
3958 to echo the option name into
3960 /sys/kernel/debug/tracing/trace_options
3962 For example, to enable stacktrace option (to dump the
3963 stack trace of each event), add to the command line:
3965 trace_options=stacktrace
3967 See also Documentation/trace/ftrace.txt "trace options"
3971 Have the tracepoints sent to printk as well as the
3972 tracing ring buffer. This is useful for early boot up
3973 where the system hangs or reboots and does not give the
3974 option for reading the tracing buffer or performing a
3975 ftrace_dump_on_oops.
3977 To turn off having tracepoints sent to printk,
3978 echo 0 > /proc/sys/kernel/tracepoint_printk
3979 Note, echoing 1 into this file without the
3980 tracepoint_printk kernel cmdline option has no effect.
3984 Having tracepoints sent to printk() and activating high
3985 frequency tracepoints such as irq or sched, can cause
3986 the system to live lock.
3989 [FTRACE] enable this option to disable tracing when a
3990 warning is hit. This turns off "tracing_on". Tracing can
3991 be enabled again by echoing '1' into the "tracing_on"
3992 file located in /sys/kernel/debug/tracing/
3994 This option is useful, as it disables the trace before
3995 the WARNING dump is called, which prevents the trace to
3996 be filled with content caused by the warning output.
3998 This option can also be set at run time via the sysctl
3999 option: kernel/traceoff_on_warning
4001 transparent_hugepage=
4003 Format: [always|madvise|never]
4004 Can be used to control the default behavior of the system
4005 with respect to transparent hugepages.
4006 See Documentation/vm/transhuge.txt for more details.
4008 tsc= Disable clocksource stability checks for TSC.
4010 [x86] reliable: mark tsc clocksource as reliable, this
4011 disables clocksource verification at runtime, as well
4012 as the stability checks done at bootup. Used to enable
4013 high-resolution timer mode on older hardware, and in
4014 virtualized environment.
4015 [x86] noirqtime: Do not use TSC to do irq accounting.
4016 Used to run time disable IRQ_TIME_ACCOUNTING on any
4017 platforms where RDTSC is slow and this accounting
4020 turbografx.map[2|3]= [HW,JOY]
4021 TurboGraFX parallel port interface
4023 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4024 See also Documentation/input/joystick-parport.txt
4026 udbg-immortal [PPC] When debugging early kernel crashes that
4027 happen after console_init() and before a proper
4028 console driver takes over, this boot options might
4029 help "seeing" what's going on.
4031 uhash_entries= [KNL,NET]
4032 Set number of hash buckets for UDP/UDP-Lite connections
4035 [USB] Ignore overcurrent events (default N).
4036 Some badly-designed motherboards generate lots of
4037 bogus events, for ports that aren't wired to
4038 anything. Set this parameter to avoid log spamming.
4039 Note that genuine overcurrent events won't be
4043 [X86] Cause panic on unknown NMI.
4045 usbcore.authorized_default=
4046 [USB] Default USB device authorization:
4047 (default -1 = authorized except for wireless USB,
4048 0 = not authorized, 1 = authorized)
4050 usbcore.autosuspend=
4051 [USB] The autosuspend time delay (in seconds) used
4052 for newly-detected USB devices (default 2). This
4053 is the time required before an idle device will be
4054 autosuspended. Devices for which the delay is set
4055 to a negative value won't be autosuspended at all.
4057 usbcore.usbfs_snoop=
4058 [USB] Set to log all usbfs traffic (default 0 = off).
4060 usbcore.usbfs_snoop_max=
4061 [USB] Maximum number of bytes to snoop in each URB
4064 usbcore.blinkenlights=
4065 [USB] Set to cycle leds on hubs (default 0 = off).
4067 usbcore.old_scheme_first=
4068 [USB] Start with the old device initialization
4069 scheme (default 0 = off).
4071 usbcore.usbfs_memory_mb=
4072 [USB] Memory limit (in MB) for buffers allocated by
4073 usbfs (default = 16, 0 = max = 2047).
4075 usbcore.use_both_schemes=
4076 [USB] Try the other device initialization scheme
4077 if the first one fails (default 1 = enabled).
4079 usbcore.initial_descriptor_timeout=
4080 [USB] Specifies timeout for the initial 64-byte
4081 USB_REQ_GET_DESCRIPTOR request in milliseconds
4082 (default 5000 = 5.0 seconds).
4084 usbcore.nousb [USB] Disable the USB subsystem
4087 [USBHID] The interval which mice are to be polled at.
4089 usb-storage.delay_use=
4090 [UMS] The delay in seconds before a new device is
4091 scanned for Logical Units (default 1).
4094 [UMS] A list of quirks entries to supplement or
4095 override the built-in unusual_devs list. List
4096 entries are separated by commas. Each entry has
4097 the form VID:PID:Flags where VID and PID are Vendor
4098 and Product ID values (4-digit hex numbers) and
4099 Flags is a set of characters, each corresponding
4100 to a common usb-storage quirk flag as follows:
4101 a = SANE_SENSE (collect more than 18 bytes
4103 b = BAD_SENSE (don't collect more than 18
4104 bytes of sense data);
4105 c = FIX_CAPACITY (decrease the reported
4106 device capacity by one sector);
4107 d = NO_READ_DISC_INFO (don't use
4108 READ_DISC_INFO command);
4109 e = NO_READ_CAPACITY_16 (don't use
4110 READ_CAPACITY_16 command);
4111 f = NO_REPORT_OPCODES (don't use report opcodes
4113 g = MAX_SECTORS_240 (don't transfer more than
4114 240 sectors at a time, uas only);
4115 h = CAPACITY_HEURISTICS (decrease the
4116 reported device capacity by one
4117 sector if the number is odd);
4118 i = IGNORE_DEVICE (don't bind to this
4120 j = NO_REPORT_LUNS (don't use report luns
4122 l = NOT_LOCKABLE (don't try to lock and
4123 unlock ejectable media);
4124 m = MAX_SECTORS_64 (don't transfer more
4125 than 64 sectors = 32 KB at a time);
4126 n = INITIAL_READ10 (force a retry of the
4127 initial READ(10) command);
4128 o = CAPACITY_OK (accept the capacity
4129 reported by the device);
4130 p = WRITE_CACHE (the device cache is ON
4132 r = IGNORE_RESIDUE (the device reports
4133 bogus residue values);
4134 s = SINGLE_LUN (the device has only one
4136 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4137 commands, uas only);
4138 u = IGNORE_UAS (don't bind to the uas driver);
4139 w = NO_WP_DETECT (don't test whether the
4140 medium is write-protected).
4141 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4142 even if the device claims no cache)
4143 Example: quirks=0419:aaf5:rl,0421:0433:rc
4145 user_debug= [KNL,ARM]
4147 See arch/arm/Kconfig.debug help text.
4148 1 - undefined instruction events
4150 4 - invalid data aborts
4153 Example: user_debug=31
4156 [X86] Flags controlling user PTE allocations.
4158 nohigh = do not allocate PTE pages in
4159 HIGHMEM regardless of setting
4163 On X86_32, this is an alias for vdso32=. Otherwise:
4165 vdso=1: enable VDSO (the default)
4166 vdso=0: disable VDSO mapping
4168 vdso32= [X86] Control the 32-bit vDSO
4169 vdso32=1: enable 32-bit VDSO
4170 vdso32=0 or vdso32=2: disable 32-bit VDSO
4172 See the help text for CONFIG_COMPAT_VDSO for more
4173 details. If CONFIG_COMPAT_VDSO is set, the default is
4174 vdso32=0; otherwise, the default is vdso32=1.
4176 For compatibility with older kernels, vdso32=2 is an
4179 Try vdso32=0 if you encounter an error that says:
4180 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4183 vector=percpu: enable percpu vector domain
4185 video= [FB] Frame buffer configuration
4186 See Documentation/fb/modedb.txt.
4188 video.brightness_switch_enabled= [0,1]
4189 If set to 1, on receiving an ACPI notify event
4190 generated by hotkey, video driver will adjust brightness
4191 level and then send out the event to user space through
4192 the allocated input device; If set to 0, video driver
4193 will only send out the event without touching backlight
4198 [VMMIO] Memory mapped virtio (platform) device.
4200 <size>@<baseaddr>:<irq>[:<id>]
4202 <size> := size (can use standard suffixes
4204 <baseaddr> := physical base address
4205 <irq> := interrupt number (as passed to
4207 <id> := (optional) platform device id
4209 virtio_mmio.device=1K@0x100b0000:48:7
4211 Can be used multiple times for multiple devices.
4213 vga= [BOOT,X86-32] Select a particular video mode
4214 See Documentation/x86/boot.txt and
4215 Documentation/svga.txt.
4216 Use vga=ask for menu.
4217 This is actually a boot loader parameter; the value is
4218 passed to the kernel using a special protocol.
4220 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4221 size of <nn>. This can be used to increase the
4222 minimum size (128MB on x86). It can also be used to
4223 decrease the size and leave more room for directly
4226 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4229 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4232 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4236 Controls the behavior of vsyscalls (i.e. calls to
4237 fixed addresses of 0xffffffffff600x00 from legacy
4238 code). Most statically-linked binaries and older
4239 versions of glibc use these calls. Because these
4240 functions are at fixed addresses, they make nice
4241 targets for exploits that can control RIP.
4243 emulate [default] Vsyscalls turn into traps and are
4244 emulated reasonably safely.
4246 native Vsyscalls are native syscall instructions.
4247 This is a little bit faster than trapping
4248 and makes a few dynamic recompilers work
4249 better than they would in emulation mode.
4250 It also makes exploits much easier to write.
4252 none Vsyscalls don't work at all. This makes
4253 them quite hard to use for exploits but
4254 might break your system.
4256 vt.color= [VT] Default text color.
4257 Format: 0xYX, X = foreground, Y = background.
4258 Default: 0x07 = light gray on black.
4260 vt.cur_default= [VT] Default cursor shape.
4261 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4262 the parameters of the <Esc>[?A;B;Cc escape sequence;
4263 see VGA-softcursor.txt. Default: 2 = underline.
4265 vt.default_blu= [VT]
4266 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4267 Change the default blue palette of the console.
4268 This is a 16-member array composed of values
4271 vt.default_grn= [VT]
4272 Format: <green0>,<green1>,<green2>,...,<green15>
4273 Change the default green palette of the console.
4274 This is a 16-member array composed of values
4277 vt.default_red= [VT]
4278 Format: <red0>,<red1>,<red2>,...,<red15>
4279 Change the default red palette of the console.
4280 This is a 16-member array composed of values
4286 Set system-wide default UTF-8 mode for all tty's.
4287 Default is 1, i.e. UTF-8 mode is enabled for all
4288 newly opened terminals.
4290 vt.global_cursor_default=
4293 Set system-wide default for whether a cursor
4294 is shown on new VTs. Default is -1,
4295 i.e. cursors will be created by default unless
4296 overridden by individual drivers. 0 will hide
4297 cursors, 1 will display them.
4299 vt.italic= [VT] Default color for italic text; 0-15.
4302 vt.underline= [VT] Default color for underlined text; 0-15.
4305 watchdog timers [HW,WDT] For information on watchdog timers,
4306 see Documentation/watchdog/watchdog-parameters.txt
4307 or other driver-specific files in the
4308 Documentation/watchdog/ directory.
4310 workqueue.watchdog_thresh=
4311 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4312 warn stall conditions and dump internal state to
4313 help debugging. 0 disables workqueue stall
4314 detection; otherwise, it's the stall threshold
4315 duration in seconds. The default value is 30 and
4316 it can be updated at runtime by writing to the
4317 corresponding sysfs file.
4319 workqueue.disable_numa
4320 By default, all work items queued to unbound
4321 workqueues are affine to the NUMA nodes they're
4322 issued on, which results in better behavior in
4323 general. If NUMA affinity needs to be disabled for
4324 whatever reason, this option can be used. Note
4325 that this also can be controlled per-workqueue for
4326 workqueues visible under /sys/bus/workqueue/.
4328 workqueue.power_efficient
4329 Per-cpu workqueues are generally preferred because
4330 they show better performance thanks to cache
4331 locality; unfortunately, per-cpu workqueues tend to
4332 be more power hungry than unbound workqueues.
4334 Enabling this makes the per-cpu workqueues which
4335 were observed to contribute significantly to power
4336 consumption unbound, leading to measurably lower
4337 power usage at the cost of small performance
4340 The default value of this parameter is determined by
4341 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4343 workqueue.debug_force_rr_cpu
4344 Workqueue used to implicitly guarantee that work
4345 items queued without explicit CPU specified are put
4346 on the local CPU. This guarantee is no longer true
4347 and while local CPU is still preferred work items
4348 may be put on foreign CPUs. This debug option
4349 forces round-robin CPU selection to flush out
4350 usages which depend on the now broken guarantee.
4351 When enabled, memory and cache locality will be
4354 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4355 default x2apic cluster mode on platforms
4358 x86_intel_mid_timer= [X86-32,APBT]
4359 Choose timer option for x86 Intel MID platform.
4360 Two valid options are apbt timer only and lapic timer
4361 plus one apbt timer for broadcast timer.
4362 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4364 xen_512gb_limit [KNL,X86-64,XEN]
4365 Restricts the kernel running paravirtualized under Xen
4366 to use only up to 512 GB of RAM. The reason to do so is
4367 crash analysis tools and Xen tools for doing domain
4368 save/restore/migration must be enabled to handle larger
4371 xen_emul_unplug= [HW,X86,XEN]
4372 Unplug Xen emulated devices
4373 Format: [unplug0,][unplug1]
4374 ide-disks -- unplug primary master IDE devices
4375 aux-ide-disks -- unplug non-primary-master IDE devices
4376 nics -- unplug network devices
4377 all -- unplug all emulated devices (NICs and IDE disks)
4378 unnecessary -- unplugging emulated devices is
4379 unnecessary even if the host did not respond to
4381 never -- do not unplug even if version check succeeds
4383 xen_nopvspin [X86,XEN]
4384 Disables the ticketlock slowpath using Xen PV
4388 Disables the PV optimizations forcing the HVM guest to
4389 run as generic HVM guest with no PV drivers.
4391 xirc2ps_cs= [NET,PCMCIA]
4393 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]