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 clocksource.arm_arch_timer.fsl-a008585=
555 Enable/disable the workaround of Freescale/NXP
556 erratum A-008585. This can be useful for KVM
557 guests, if the guest device tree doesn't show the
558 erratum. If unspecified, the workaround is
559 enabled based on the device tree.
561 clearcpuid=BITNUM [X86]
562 Disable CPUID feature X for the kernel. See
563 arch/x86/include/asm/cpufeatures.h for the valid bit
564 numbers. Note the Linux specific bits are not necessarily
565 stable over kernel options, but the vendor specific
567 Also note that user programs calling CPUID directly
568 or using the feature without checking anything
569 will still see it. This just prevents it from
570 being used by the kernel or shown in /proc/cpuinfo.
571 Also note the kernel might malfunction if you disable
574 cma=nn[MG]@[start[MG][-end[MG]]]
576 Sets the size of kernel global memory area for
577 contiguous memory allocations and optionally the
578 placement constraint by the physical address range of
579 memory allocations. A value of 0 disables CMA
580 altogether. For more information, see
581 include/linux/dma-contiguous.h
583 cmo_free_hint= [PPC] Format: { yes | no }
584 Specify whether pages are marked as being inactive
585 when they are freed. This is used in CMO environments
586 to determine OS memory pressure for page stealing by
590 coherent_pool=nn[KMG] [ARM,KNL]
591 Sets the size of memory pool for coherent, atomic dma
592 allocations, by default set to 256K.
594 code_bytes [X86] How many bytes of object code to print
599 com20020= [HW,NET] ARCnet - COM20020 chipset
601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
607 ARCnet - COM90xx chipset (memory-mapped buffers)
608 Format: <io>[,<irq>[,<memstart>]]
610 condev= [HW,S390] console device
613 console= [KNL] Output console device and options.
615 tty<n> Use the virtual console device <n>.
619 Use the specified serial port. The options are of
620 the form "bbbbpnf", where "bbbb" is the baud rate,
621 "p" is parity ("n", "o", or "e"), "n" is number of
622 bits, and "f" is flow control ("r" for RTS or
623 omit it). Default is "9600n8".
625 See Documentation/admin-guide/serial-console.rst for more
627 Documentation/networking/netconsole.txt for an
630 uart[8250],io,<addr>[,options]
631 uart[8250],mmio,<addr>[,options]
632 uart[8250],mmio16,<addr>[,options]
633 uart[8250],mmio32,<addr>[,options]
634 uart[8250],0x<addr>[,options]
635 Start an early, polled-mode console on the 8250/16550
636 UART at the specified I/O port or MMIO address,
637 switching to the matching ttyS device later.
638 MMIO inter-register address stride is either 8-bit
639 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
640 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
641 to be equivalent to 'mmio'. 'options' are specified in
642 the same format described for ttyS above; if unspecified,
643 the h/w is not re-initialized.
645 hvc<n> Use the hypervisor console device <n>. This is for
646 both Xen and PowerPC hypervisors.
648 If the device connected to the port is not a TTY but a braille
649 device, prepend "brl," before the device type, for instance
651 For now, only VisioBraille is supported.
653 consoleblank= [KNL] The console blank (screen saver) timeout in
654 seconds. Defaults to 10*60 = 10mins. A value of 0
655 disables the blank timer.
658 [KNL] Change the default value for
659 /proc/<pid>/coredump_filter.
660 See also Documentation/filesystems/proc.txt.
662 cpuidle.off=1 [CPU_IDLE]
663 disable the cpuidle sub-system
666 [X86] Delay for N microsec between assert and de-assert
667 of APIC INIT to start processors. This delay occurs
668 on every CPU online, such as boot, and resume from suspend.
671 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
673 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
675 crashkernel=size[KMG][@offset[KMG]]
676 [KNL] Using kexec, Linux can switch to a 'crash kernel'
677 upon panic. This parameter reserves the physical
678 memory region [offset, offset + size] for that kernel
679 image. If '@offset' is omitted, then a suitable offset
680 is selected automatically. Check
681 Documentation/kdump/kdump.txt for further details.
683 crashkernel=range1:size1[,range2:size2,...][@offset]
684 [KNL] Same as above, but depends on the memory
685 in the running system. The syntax of range is
686 start-[end] where start and end are both
687 a memory unit (amount[KMG]). See also
688 Documentation/kdump/kdump.txt for an example.
690 crashkernel=size[KMG],high
691 [KNL, x86_64] range could be above 4G. Allow kernel
692 to allocate physical memory region from top, so could
693 be above 4G if system have more than 4G ram installed.
694 Otherwise memory region will be allocated below 4G, if
696 It will be ignored if crashkernel=X is specified.
697 crashkernel=size[KMG],low
698 [KNL, x86_64] range under 4G. When crashkernel=X,high
699 is passed, kernel could allocate physical memory region
700 above 4G, that cause second kernel crash on system
701 that require some amount of low memory, e.g. swiotlb
702 requires at least 64M+32K low memory, also enough extra
703 low memory is needed to make sure DMA buffers for 32-bit
704 devices won't run out. Kernel would try to allocate at
705 at least 256M below 4G automatically.
706 This one let user to specify own low range under 4G
707 for second kernel instead.
708 0: to disable low allocation.
709 It will be ignored when crashkernel=X,high is not used
710 or memory reserved is below 4G.
713 [KNL] Disable crypto self-tests
718 cs89x0_media= [HW,NET]
719 Format: { rj45 | aui | bnc }
722 See header of drivers/s390/block/dasd_devmap.c.
724 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
725 (one device per port)
726 Format: <port#>,<type>
727 See also Documentation/input/joystick-parport.txt
729 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
730 time. See Documentation/dynamic-debug-howto.txt for
731 details. Deprecated, see dyndbg.
733 debug [KNL] Enable kernel debugging (events log level).
736 [KNL] verbose self-tests
738 Print debugging info while doing the locking API
740 We default to 0 (no extra messages), setting it to
741 1 will print _a lot_ more information - normally
742 only useful to kernel developers.
744 debug_objects [KNL] Enable object debugging
747 [KNL] Disable object debugging
749 debug_guardpage_minorder=
750 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
751 parameter allows control of the order of pages that will
752 be intentionally kept free (and hence protected) by the
753 buddy allocator. Bigger value increase the probability
754 of catching random memory corruption, but reduce the
755 amount of memory for normal system use. The maximum
756 possible value is MAX_ORDER/2. Setting this parameter
757 to 1 or 2 should be enough to identify most random
758 memory corruption problems caused by bugs in kernel or
759 driver code when a CPU writes to (or reads from) a
760 random memory location. Note that there exists a class
761 of memory corruptions problems caused by buggy H/W or
762 F/W or by drivers badly programing DMA (basically when
763 memory is written at bus level and the CPU MMU is
764 bypassed) which are not detectable by
765 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
766 tracking down these problems.
769 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
770 parameter enables the feature at boot time. In
771 default, it is disabled. We can avoid allocating huge
772 chunk of memory for debug pagealloc if we don't enable
773 it at boot time and the system will work mostly same
774 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
775 on: enable the feature
777 debugpat [X86] Enable PAT debugging
779 decnet.addr= [HW,NET]
780 Format: <area>[,<node>]
781 See also Documentation/networking/decnet.txt.
784 [same as hugepagesz=] The size of the default
785 HugeTLB page size. This is the size represented by
786 the legacy /proc/ hugepages APIs, used for SHM, and
787 default size when mounting hugetlbfs filesystems.
788 Defaults to the default architecture's huge page size
792 Set number of hash buckets for dentry cache.
794 disable_1tb_segments [PPC]
795 Disables the use of 1TB hash page table segments. This
796 causes the kernel to fall back to 256MB segments which
797 can be useful when debugging issues that require an SLB
801 See Documentation/networking/ipv6.txt.
804 Disable RADIX MMU mode on POWER9
806 disable_cpu_apicid= [X86,APIC,SMP]
808 The number of initial APIC ID for the
809 corresponding CPU to be disabled at boot,
810 mostly used for the kdump 2nd kernel to
811 disable BSP to wake up multiple CPUs without
812 causing system reset or hang due to sending
815 disable_ddw [PPC/PSERIES]
816 Disable Dynamic DMA Window support. Use this if
817 to workaround buggy firmware.
820 See Documentation/networking/ipv6.txt.
822 disable_mtrr_cleanup [X86]
823 The kernel tries to adjust MTRR layout from continuous
824 to discrete, to make X server driver able to add WB
825 entry later. This parameter disables that.
827 disable_mtrr_trim [X86, Intel and AMD only]
828 By default the kernel will trim any uncacheable
829 memory out of your available memory pool based on
830 MTRR settings. This parameter disables that behavior,
831 possibly causing your machine to run very slowly.
833 disable_timer_pin_1 [X86]
834 Disable PIN 1 of APIC timer
835 Can be useful to work around chipset bugs.
837 dis_ucode_ldr [X86] Disable the microcode loader.
839 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
840 this option disables the debugging code at boot.
842 dma_debug_entries=<number>
843 This option allows to tune the number of preallocated
844 entries for DMA-API debugging code. One entry is
845 required per DMA-API allocation. Use this if the
846 DMA-API debugging code disables itself because the
847 architectural default is too low.
849 dma_debug_driver=<driver_name>
850 With this option the DMA-API debugging driver
851 filter feature can be enabled at boot time. Just
852 pass the driver to filter for as the parameter.
853 The filter can be disabled or changed to another
854 driver later using sysfs.
856 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
857 Broken monitors, graphic adapters, KVMs and EDIDless
858 panels may send no or incorrect EDID data sets.
859 This parameter allows to specify an EDID data sets
860 in the /lib/firmware directory that are used instead.
861 Generic built-in EDID data sets are used, if one of
862 edid/1024x768.bin, edid/1280x1024.bin,
863 edid/1680x1050.bin, or edid/1920x1080.bin is given
864 and no file with the same name exists. Details and
865 instructions how to build your own EDID data are
866 available in Documentation/EDID/HOWTO.txt. An EDID
867 data set will only be used for a particular connector,
868 if its name and a colon are prepended to the EDID
869 name. Each connector may use a unique EDID data
870 set by separating the files with a comma. An EDID
871 data set with no connector name will be used for
872 any connectors not explicitly specified.
876 dump_apple_properties [X86]
877 Dump name and content of EFI device properties on
878 x86 Macs. Useful for driver authors to determine
879 what data is available or for reverse-engineering.
881 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
882 module.dyndbg[="val"]
883 Enable debug messages at boot time. See
884 Documentation/dynamic-debug-howto.txt for details.
886 nompx [X86] Disables Intel Memory Protection Extensions.
887 See Documentation/x86/intel_mpx.txt for more
888 information about the feature.
890 nopku [X86] Disable Memory Protection Keys CPU feature found
893 module.async_probe [KNL]
894 Enable asynchronous probe on this module.
896 early_ioremap_debug [KNL]
897 Enable debug messages in early_ioremap support. This
898 is useful for tracking down temporary early mappings
899 which are not unmapped.
901 earlycon= [KNL] Output early console device and options.
903 When used with no options, the early console is
904 determined by the stdout-path property in device
907 cdns,<addr>[,options]
908 Start an early, polled-mode console on a Cadence
909 (xuartps) serial port at the specified address. Only
910 supported option is baud rate. If baud rate is not
911 specified, the serial port must already be setup and
914 uart[8250],io,<addr>[,options]
915 uart[8250],mmio,<addr>[,options]
916 uart[8250],mmio32,<addr>[,options]
917 uart[8250],mmio32be,<addr>[,options]
918 uart[8250],0x<addr>[,options]
919 Start an early, polled-mode console on the 8250/16550
920 UART at the specified I/O port or MMIO address.
921 MMIO inter-register address stride is either 8-bit
922 (mmio) or 32-bit (mmio32 or mmio32be).
923 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
924 to be equivalent to 'mmio'. 'options' are specified
925 in the same format described for "console=ttyS<n>"; if
926 unspecified, the h/w is not initialized.
930 Start an early, polled-mode console on a pl011 serial
931 port at the specified address. The pl011 serial port
932 must already be setup and configured. Options are not
933 yet supported. If 'mmio32' is specified, then only
934 the driver will use only 32-bit accessors to read/write
935 the device registers.
938 Start an early, polled-mode console on a meson serial
939 port at the specified address. The serial port must
940 already be setup and configured. Options are not yet
944 Start an early, polled-mode console on an msm serial
945 port at the specified address. The serial port
946 must already be setup and configured. Options are not
950 Start an early, polled-mode console on an msm serial
951 dm port at the specified address. The serial port
952 must already be setup and configured. Options are not
955 smh Use ARM semihosting calls for early console.
963 Use early console provided by serial driver available
964 on Samsung SoCs, requires selecting proper type and
965 a correct base address of the selected UART port. The
966 serial port must already be setup and configured.
967 Options are not yet supported.
971 Use early console provided by Freescale LP UART driver
972 found on Freescale Vybrid and QorIQ LS1021A processors.
973 A valid base address must be provided, and the serial
974 port must already be setup and configured.
976 armada3700_uart,<addr>
977 Start an early, polled-mode console on the
978 Armada 3700 serial port at the specified
979 address. The serial port must already be setup
980 and configured. Options are not yet supported.
982 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
986 earlyprintk=serial[,ttySn[,baudrate]]
987 earlyprintk=serial[,0x...[,baudrate]]
988 earlyprintk=ttySn[,baudrate]
989 earlyprintk=dbgp[debugController#]
990 earlyprintk=pciserial,bus:device.function[,baudrate]
992 earlyprintk is useful when the kernel crashes before
993 the normal console is initialized. It is not enabled by
994 default because it has some cosmetic problems.
996 Append ",keep" to not disable it when the real console
999 Only one of vga, efi, serial, or usb debug port can
1002 Currently only ttyS0 and ttyS1 may be specified by
1003 name. Other I/O ports may be explicitly specified
1004 on some architectures (x86 and arm at least) by
1005 replacing ttySn with an I/O port address, like this:
1006 earlyprintk=serial,0x1008,115200
1007 You can find the port for a given device in
1008 /proc/tty/driver/serial:
1009 2: uart:ST16650V2 port:00001008 irq:18 ...
1011 Interaction with the standard serial driver is not
1014 The VGA and EFI output is eventually overwritten by
1017 The xen output can only be used by Xen PV guests.
1019 edac_report= [HW,EDAC] Control how to report EDAC event
1020 Format: {"on" | "off" | "force"}
1021 on: enable EDAC to report H/W event. May be overridden
1022 by other higher priority error reporting module.
1023 off: disable H/W event reporting through EDAC.
1024 force: enforce the use of EDAC to report H/W event.
1027 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1030 This is designed to be used in conjunction with
1031 the boot argument: earlyprintk=vga
1034 Format: {"off" | "on" | "skip[mbr]"}
1037 Format: { "old_map", "nochunk", "noruntime", "debug" }
1038 old_map [X86-64]: switch to the old ioremap-based EFI
1039 runtime services mapping. 32-bit still uses this one by
1041 nochunk: disable reading files in "chunks" in the EFI
1042 boot stub, as chunking can cause problems with some
1043 firmware implementations.
1044 noruntime : disable EFI runtime services support
1045 debug: enable misc debug output
1047 efi_no_storage_paranoia [EFI; X86]
1048 Using this parameter you can use more than 50% of
1049 your efi variable storage. Use this parameter only if
1050 you are really sure that your UEFI does sane gc and
1051 fulfills the spec otherwise your board may brick.
1053 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1054 Add arbitrary attribute to specific memory range by
1055 updating original EFI memory map.
1056 Region of memory which aa attribute is added to is
1058 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1059 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1060 attribute is added to range 0x100000000-0x180000000 and
1061 0x10a0000000-0x1120000000.
1063 Using this parameter you can do debugging of EFI memmap
1064 related feature. For example, you can do debugging of
1065 Address Range Mirroring feature even if your box
1068 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1069 that is to be dynamically loaded by Linux. If there are
1070 multiple variables with the same name but with different
1071 vendor GUIDs, all of them will be loaded. See
1072 Documentation/acpi/ssdt-overlays.txt for details.
1075 eisa_irq_edge= [PARISC,HW]
1076 See header of drivers/parisc/eisa.c.
1079 See comment before function elanfreq_setup() in
1080 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1083 Format: {"cfq" | "deadline" | "noop"}
1084 See Documentation/block/cfq-iosched.txt and
1085 Documentation/block/deadline-iosched.txt for details.
1087 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1088 Specifies physical address of start of kernel core
1089 image elf header and optionally the size. Generally
1090 kexec loader will pass this option to capture kernel.
1091 See Documentation/kdump/kdump.txt for details.
1093 enable_mtrr_cleanup [X86]
1094 The kernel tries to adjust MTRR layout from continuous
1095 to discrete, to make X server driver able to add WB
1096 entry later. This parameter enables that.
1098 enable_timer_pin_1 [X86]
1099 Enable PIN 1 of APIC timer
1100 Can be useful to work around chipset bugs
1101 (in particular on some ATI chipsets).
1102 The kernel tries to set a reasonable default.
1104 enforcing [SELINUX] Set initial enforcing status.
1106 See security/selinux/Kconfig help text.
1107 0 -- permissive (log only, no denials).
1108 1 -- enforcing (deny and log).
1110 Value can be changed at runtime via /selinux/enforce.
1113 Disable Error Record Serialization Table (ERST)
1116 ether= [HW,NET] Ethernet cards parameters
1117 This option is obsoleted by the "netdev=" option, which
1118 has equivalent usage. See its documentation for details.
1122 Permit 'security.evm' to be updated regardless of
1123 current integrity status.
1127 fail_make_request=[KNL]
1128 General fault injection mechanism.
1129 Format: <interval>,<probability>,<space>,<times>
1130 See also Documentation/fault-injection/.
1133 See Documentation/blockdev/floppy.txt.
1135 force_pal_cache_flush
1136 [IA-64] Avoid check_sal_cache_flush which may hang on
1137 buggy SAL_CACHE_FLUSH implementations. Using this
1138 parameter will force ia64_sal_cache_flush to call
1139 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1142 Forcefully enable Physical Address Extension (PAE).
1143 Many Pentium M systems disable PAE but may have a
1144 functionally usable PAE implementation.
1145 Warning: use of this parameter will taint the kernel
1146 and may cause unknown problems.
1149 [FTRACE] will set and start the specified tracer
1150 as early as possible in order to facilitate early
1153 ftrace_dump_on_oops[=orig_cpu]
1154 [FTRACE] will dump the trace buffers on oops.
1155 If no parameter is passed, ftrace will dump
1156 buffers of all CPUs, but if you pass orig_cpu, it will
1157 dump only the buffer of the CPU that triggered the
1160 ftrace_filter=[function-list]
1161 [FTRACE] Limit the functions traced by the function
1162 tracer at boot up. function-list is a comma separated
1163 list of functions. This list can be changed at run
1164 time by the set_ftrace_filter file in the debugfs
1167 ftrace_notrace=[function-list]
1168 [FTRACE] Do not trace the functions specified in
1169 function-list. This list can be changed at run time
1170 by the set_ftrace_notrace file in the debugfs
1173 ftrace_graph_filter=[function-list]
1174 [FTRACE] Limit the top level callers functions traced
1175 by the function graph tracer at boot up.
1176 function-list is a comma separated list of functions
1177 that can be changed at run time by the
1178 set_graph_function file in the debugfs tracing directory.
1180 ftrace_graph_notrace=[function-list]
1181 [FTRACE] Do not trace from the functions specified in
1182 function-list. This list is a comma separated list of
1183 functions that can be changed at run time by the
1184 set_graph_notrace file in the debugfs tracing directory.
1187 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1188 support via parallel port (up to 5 devices per port)
1189 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1190 See also Documentation/input/joystick-parport.txt
1194 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1198 gcov_persist= [GCOV] When non-zero (default), profiling data for
1199 kernel modules is saved and remains accessible via
1200 debugfs, even when the module is unloaded/reloaded.
1201 When zero, profiling data is discarded and associated
1202 debugfs files are removed at module unload time.
1204 gpt [EFI] Forces disk with valid GPT signature but
1205 invalid Protective MBR to be treated as GPT. If the
1206 primary GPT is corrupted, it enables the backup/alternate
1207 GPT to be used instead.
1209 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1210 the "Enable 0" bit of the configuration register.
1213 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1214 the "Enable 0" bit of the configuration register.
1217 grcan.select= [HW] Select which physical interface to use.
1220 grcan.txsize= [HW] Sets the size of the tx buffer.
1221 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1223 grcan.rxsize= [HW] Sets the size of the rx buffer.
1224 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1227 gpio-mockup.gpio_mockup_ranges
1228 [HW] Sets the ranges of gpiochip of for this device.
1229 Format: <start1>,<end1>,<start2>,<end2>...
1231 hardlockup_all_cpu_backtrace=
1232 [KNL] Should the hard-lockup detector generate
1233 backtraces on all cpus.
1236 hashdist= [KNL,NUMA] Large hashes allocated during boot
1237 are distributed across NUMA nodes. Defaults on
1238 for 64-bit NUMA, off otherwise.
1239 Format: 0 | 1 (for off | on)
1241 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1243 hd= [EIDE] (E)IDE hard drive subsystem geometry
1244 Format: <cyl>,<head>,<sect>
1247 Disable Hardware Error Source Table (HEST) support;
1248 corresponding firmware-first mode error processing
1249 logic will be disabled.
1251 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1252 size of <nn>. This works even on boxes that have no
1253 highmem otherwise. This also works to reduce highmem
1254 size on bigger boxes.
1256 highres= [KNL] Enable/disable high resolution timer mode.
1257 Valid parameters: "on", "off"
1261 See Documentation/isdn/README.HiSax.
1265 hpet= [X86-32,HPET] option to control HPET usage
1266 Format: { enable (default) | disable | force |
1268 disable: disable HPET and use PIT instead
1269 force: allow force enabled of undocumented chips (ICH4,
1271 verbose: show contents of HPET registers during setup
1273 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1274 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1276 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1277 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1278 On x86-64 and powerpc, this option can be specified
1279 multiple times interleaved with hugepages= to reserve
1280 huge pages of different sizes. Valid pages sizes on
1281 x86-64 are 2M (when the CPU supports "pse") and 1G
1282 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1284 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1285 terminal devices. Valid values: 0..8
1286 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1287 If specified, z/VM IUCV HVC accepts connections
1288 from listed z/VM user IDs only.
1290 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1291 hardware thread id mappings.
1292 Format: <cpu>:<hwthread>
1295 Do not unregister boot console at start. This is only
1296 useful for debugging when something happens in the window
1297 between unregistering the boot console and initializing
1300 i2c_bus= [HW] Override the default board specific I2C bus speed
1301 or register an additional I2C bus that is not
1302 registered from board initialization code.
1306 i8042.debug [HW] Toggle i8042 debug mode
1307 i8042.unmask_kbd_data
1308 [HW] Enable printing of interrupt data from the KBD port
1309 (disabled by default, and as a pre-condition
1310 requires that i8042.debug=1 be enabled)
1311 i8042.direct [HW] Put keyboard port into non-translated mode
1312 i8042.dumbkbd [HW] Pretend that controller can only read data from
1313 keyboard and cannot control its state
1314 (Don't attempt to blink the leds)
1315 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1316 i8042.nokbd [HW] Don't check/create keyboard port
1317 i8042.noloop [HW] Disable the AUX Loopback command while probing
1319 i8042.nomux [HW] Don't check presence of an active multiplexing
1321 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1323 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1324 i8042.reset [HW] Reset the controller during init, cleanup and
1325 suspend-to-ram transitions, only during s2r
1326 transitions, or never reset
1327 Format: { 1 | Y | y | 0 | N | n }
1328 1, Y, y: always reset controller
1329 0, N, n: don't ever reset controller
1330 Default: only on s2r transitions on x86; most other
1331 architectures force reset to be always executed
1332 i8042.unlock [HW] Unlock (ignore) the keylock
1333 i8042.kbdreset [HW] Reset device connected to KBD port
1337 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1338 indicates that the driver is running on unsupported
1340 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1341 does not match list of supported models.
1343 [HW] Report power status in /proc/i8k
1344 (disabled by default)
1345 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1348 i915.invert_brightness=
1349 [DRM] Invert the sense of the variable that is used to
1350 set the brightness of the panel backlight. Normally a
1351 brightness value of 0 indicates backlight switched off,
1352 and the maximum of the brightness value sets the backlight
1353 to maximum brightness. If this parameter is set to 0
1354 (default) and the machine requires it, or this parameter
1355 is set to 1, a brightness value of 0 sets the backlight
1356 to maximum brightness, and the maximum of the brightness
1357 value switches the backlight off.
1358 -1 -- never invert brightness
1359 0 -- machine default
1360 1 -- force brightness inversion
1363 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1365 ide-core.nodma= [HW] (E)IDE subsystem
1366 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1367 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1368 .cdrom .chs .ignore_cable are additional options
1369 See Documentation/ide/ide.txt.
1371 ide-generic.probe-mask= [HW] (E)IDE subsystem
1373 Probe mask for legacy ISA IDE ports. Depending on
1374 platform up to 6 ports are supported, enabled by
1375 setting corresponding bits in the mask to 1. The
1376 default value is 0x0, which has a special meaning.
1377 On systems that have PCI, it triggers scanning the
1378 PCI bus for the first and the second port, which
1379 are then probed. On systems without PCI the value
1380 of 0x0 enables probing the two first ports as if it
1383 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1384 Claim all unknown PCI IDE storage controllers.
1387 Format: idle=poll, idle=halt, idle=nomwait
1388 Poll forces a polling idle loop that can slightly
1389 improve the performance of waking up a idle CPU, but
1390 will use a lot of power and make the system run hot.
1392 idle=halt: Halt is forced to be used for CPU idle.
1393 In such case C2/C3 won't be used again.
1394 idle=nomwait: Disable mwait for CPU C-states
1396 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1397 Format: { strict | legacy | 2008 | relaxed }
1400 Choose which programs will be accepted for execution
1401 based on the IEEE 754 NaN encoding(s) supported by
1402 the FPU and the NaN encoding requested with the value
1403 of an ELF file header flag individually set by each
1404 binary. Hardware implementations are permitted to
1405 support either or both of the legacy and the 2008 NaN
1408 Available settings are as follows:
1409 strict accept binaries that request a NaN encoding
1410 supported by the FPU
1411 legacy only accept legacy-NaN binaries, if supported
1413 2008 only accept 2008-NaN binaries, if supported
1415 relaxed accept any binaries regardless of whether
1416 supported by the FPU
1418 The FPU emulator is always able to support both NaN
1419 encodings, so if no FPU hardware is present or it has
1420 been disabled with 'nofpu', then the settings of
1421 'legacy' and '2008' strap the emulator accordingly,
1422 'relaxed' straps the emulator for both legacy-NaN and
1423 2008-NaN, whereas 'strict' enables legacy-NaN only on
1424 legacy processors and both NaN encodings on MIPS32 or
1427 The setting for ABS.fmt/NEG.fmt instruction execution
1428 mode generally follows that for the NaN encoding,
1429 except where unsupported by hardware.
1431 ignore_loglevel [KNL]
1432 Ignore loglevel setting - this will print /all/
1433 kernel messages to the console. Useful for debugging.
1434 We also add it as printk module parameter, so users
1435 could change it dynamically, usually by
1436 /sys/module/printk/parameters/ignore_loglevel.
1439 Ignore RLIMIT_DATA setting for data mappings,
1440 print warning at first misuse. Can be changed via
1441 /sys/module/kernel/parameters/ignore_rlimit_data.
1443 ihash_entries= [KNL]
1444 Set number of hash buckets for inode cache.
1446 ima_appraise= [IMA] appraise integrity measurements
1447 Format: { "off" | "enforce" | "fix" | "log" }
1450 ima_appraise_tcb [IMA]
1451 The builtin appraise policy appraises all files
1454 ima_canonical_fmt [IMA]
1455 Use the canonical format for the binary runtime
1456 measurements, instead of host native format.
1459 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1463 The list of supported hash algorithms is defined
1464 in crypto/hash_info.h.
1467 The builtin measurement policy to load during IMA
1468 setup. Specyfing "tcb" as the value, measures all
1469 programs exec'd, files mmap'd for exec, and all files
1470 opened with the read mode bit set by either the
1471 effective uid (euid=0) or uid=0.
1474 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1475 Load a policy which meets the needs of the Trusted
1476 Computing Base. This means IMA will measure all
1477 programs exec'd, files mmap'd for exec, and all files
1478 opened for read by uid=0.
1481 Select one of defined IMA measurements template formats.
1482 Formats: { "ima" | "ima-ng" | "ima-sig" }
1486 [IMA] Define a custom template format.
1487 Format: { "field1|...|fieldN" }
1489 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1490 Format: <min_file_size>
1491 Set the minimal file size for using asynchronous hash.
1492 If left unspecified, ahash usage is disabled.
1494 ahash performance varies for different data sizes on
1495 different crypto accelerators. This option can be used
1496 to achieve the best performance for a particular HW.
1498 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1500 Set hashing buffer size. Default: 4k.
1502 ahash performance varies for different chunk sizes on
1503 different crypto accelerators. This option can be used
1504 to achieve best performance for particular HW.
1508 Run specified binary instead of /sbin/init as init
1511 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1512 for working out where the kernel is dying during
1515 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1516 initcall functions. Useful for debugging built-in
1517 modules and initcalls.
1519 initrd= [BOOT] Specify the location of the initial ramdisk
1521 init_pkru= [x86] Specify the default memory protection keys rights
1522 register contents for all processes. 0x55555554 by
1523 default (disallow access to all but pkey 0). Can
1524 override in debugfs after boot.
1526 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1529 int_pln_enable [x86] Enable power limit notification interrupt
1531 integrity_audit=[IMA]
1532 Format: { "0" | "1" }
1533 0 -- basic integrity auditing messages. (Default)
1534 1 -- additional integrity auditing messages.
1536 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1538 Enable intel iommu driver.
1540 Disable intel iommu driver.
1541 igfx_off [Default Off]
1542 By default, gfx is mapped as normal device. If a gfx
1543 device has a dedicated DMAR unit, the DMAR unit is
1544 bypassed by not enabling DMAR with this option. In
1545 this case, gfx device will use physical address for
1548 With this option iommu will not optimize to look
1549 for io virtual address below 32-bit forcing dual
1550 address cycle on pci bus for cards supporting greater
1551 than 32-bit addressing. The default is to look
1552 for translation below 32-bit and if not available
1553 then look in the higher range.
1554 strict [Default Off]
1555 With this option on every unmap_single operation will
1556 result in a hardware IOTLB flush operation as opposed
1557 to batching them for performance.
1558 sp_off [Default Off]
1559 By default, super page will be supported if Intel IOMMU
1560 has the capability. With this option, super page will
1562 ecs_off [Default Off]
1563 By default, extended context tables will be supported if
1564 the hardware advertises that it has support both for the
1565 extended tables themselves, and also PASID support. With
1566 this option set, extended tables will not be used even
1567 on hardware which claims to support them.
1569 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1570 0 disables intel_idle and fall back on acpi_idle.
1571 1 to 9 specify maximum depth of C-state.
1575 Do not enable intel_pstate as the default
1576 scaling driver for the supported processors
1578 Use intel_pstate as a scaling driver, but configure it
1579 to work with generic cpufreq governors (instead of
1580 enabling its internal governor). This mode cannot be
1581 used along with the hardware-managed P-states (HWP)
1584 Enable intel_pstate on systems that prohibit it by default
1585 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1586 instead of acpi-cpufreq may disable platform features, such
1587 as thermal controls and power capping, that rely on ACPI
1588 P-States information being indicated to OSPM and therefore
1589 should be used with caution. This option does not work with
1590 processors that aren't supported by the intel_pstate driver
1591 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1593 Do not enable hardware P state control (HWP)
1596 Only load intel_pstate on systems which support
1597 hardware P state control (HWP) if available.
1599 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1600 Description Table, specifies preferred power management
1601 profile as "Enterprise Server" or "Performance Server",
1602 then this feature is turned on by default.
1604 Allow per-logical-CPU P-State performance control limits using
1605 cpufreq sysfs interface
1607 intremap= [X86-64, Intel-IOMMU]
1608 on enable Interrupt Remapping (default)
1609 off disable Interrupt Remapping
1610 nosid disable Source ID checking
1612 BIOS x2APIC opt-out request will be ignored
1613 nopost disable Interrupt Posting
1615 iomem= Disable strict checking of access to MMIO memory
1616 strict regions from userspace.
1631 nobypass [PPC/POWERNV]
1632 Disable IOMMU bypass, using IOMMU for PCI devices.
1635 io7= [HW] IO7 for Marvel based alpha systems
1636 See comment before marvel_specify_io7 in
1637 arch/alpha/kernel/core_marvel.c.
1639 io_delay= [X86] I/O delay method
1641 Standard port 0x80 based delay
1643 Alternate port 0xed based delay (needed on some systems)
1645 Simple two microseconds delay
1650 See Documentation/filesystems/nfs/nfsroot.txt.
1652 irqaffinity= [SMP] Set the default irq affinity mask
1653 The argument is a cpu list, as described above.
1656 When an interrupt is not handled search all handlers
1657 for it. Intended to get systems with badly broken
1661 When an interrupt is not handled search all handlers
1662 for it. Also check all handlers each timer
1663 interrupt. Intended to get systems with badly broken
1667 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1669 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1670 The argument is a cpu list, as described above.
1672 This option can be used to specify one or more CPUs
1673 to isolate from the general SMP balancing and scheduling
1674 algorithms. You can move a process onto or off an
1675 "isolated" CPU via the CPU affinity syscalls or cpuset.
1676 <cpu number> begins at 0 and the maximum value is
1677 "number of CPUs in system - 1".
1679 This option is the preferred way to isolate CPUs. The
1680 alternative -- manually setting the CPU mask of all
1681 tasks in the system -- can cause problems and
1682 suboptimal load balancer performance.
1686 ivrs_ioapic [HW,X86_64]
1687 Provide an override to the IOAPIC-ID<->DEVICE-ID
1688 mapping provided in the IVRS ACPI table. For
1689 example, to map IOAPIC-ID decimal 10 to
1690 PCI device 00:14.0 write the parameter as:
1691 ivrs_ioapic[10]=00:14.0
1693 ivrs_hpet [HW,X86_64]
1694 Provide an override to the HPET-ID<->DEVICE-ID
1695 mapping provided in the IVRS ACPI table. For
1696 example, to map HPET-ID decimal 0 to
1697 PCI device 00:14.0 write the parameter as:
1698 ivrs_hpet[0]=00:14.0
1700 ivrs_acpihid [HW,X86_64]
1701 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1702 mapping provided in the IVRS ACPI table. For
1703 example, to map UART-HID:UID AMD0020:0 to
1704 PCI device 00:14.5 write the parameter as:
1705 ivrs_acpihid[00:14.5]=AMD0020:0
1707 js= [HW,JOY] Analog joystick
1708 See Documentation/input/joystick.txt.
1711 When CONFIG_RANDOMIZE_BASE is set, this disables
1712 kernel and module base offset ASLR (Address Space
1713 Layout Randomization).
1717 kernelcore= [KNL,X86,IA-64,PPC]
1718 Format: nn[KMGTPE] | "mirror"
1720 specifies the amount of memory usable by the kernel
1721 for non-movable allocations. The requested amount is
1722 spread evenly throughout all nodes in the system. The
1723 remaining memory in each node is used for Movable
1724 pages. In the event, a node is too small to have both
1725 kernelcore and Movable pages, kernelcore pages will
1726 take priority and other nodes will have a larger number
1727 of Movable pages. The Movable zone is used for the
1728 allocation of pages that may be reclaimed or moved
1729 by the page migration subsystem. This means that
1730 HugeTLB pages may not be allocated from this zone.
1731 Note that allocations like PTEs-from-HighMem still
1732 use the HighMem zone if it exists, and the Normal
1733 zone if it does not.
1735 Instead of specifying the amount of memory (nn[KMGTPE]),
1736 you can specify "mirror" option. In case "mirror"
1737 option is specified, mirrored (reliable) memory is used
1738 for non-movable allocations and remaining memory is used
1739 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1740 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1743 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1744 Format: <Controller#>[,poll interval]
1745 The controller # is the number of the ehci usb debug
1746 port as it is probed via PCI. The poll interval is
1747 optional and is the number seconds in between
1748 each poll cycle to the debug port in case you need
1749 the functionality for interrupting the kernel with
1750 gdb or control-c on the dbgp connection. When
1751 not using this parameter you use sysrq-g to break into
1752 the kernel debugger.
1754 kgdboc= [KGDB,HW] kgdb over consoles.
1755 Requires a tty driver that supports console polling,
1756 or a supported polling keyboard driver (non-usb).
1757 Serial only format: <serial_device>[,baud]
1758 keyboard only format: kbd
1759 keyboard and serial format: kbd,<serial_device>[,baud]
1760 Optional Kernel mode setting:
1761 kms, kbd format: kms,kbd
1762 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1764 kgdbwait [KGDB] Stop kernel execution and enter the
1765 kernel debugger at the earliest opportunity.
1767 kmac= [MIPS] korina ethernet MAC address.
1768 Configure the RouterBoard 532 series on-chip
1769 Ethernet adapter MAC address.
1771 kmemleak= [KNL] Boot-time kmemleak enable/disable
1772 Valid arguments: on, off
1774 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1777 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1778 Valid arguments: 0, 1, 2
1779 kmemcheck=0 (disabled)
1780 kmemcheck=1 (enabled)
1781 kmemcheck=2 (one-shot mode)
1782 Default: 2 (one-shot mode)
1784 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1785 Default is 0 (don't ignore, but inject #GP)
1787 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1791 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1792 Default is 1 (enabled)
1794 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1796 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1798 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1799 (virtualized MMU) support on capable Intel chips.
1800 Default is 1 (enabled)
1802 kvm-intel.emulate_invalid_guest_state=
1803 [KVM,Intel] Enable emulation of invalid guest states
1804 Default is 0 (disabled)
1806 kvm-intel.flexpriority=
1807 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1808 Default is 1 (enabled)
1811 [KVM,Intel] Enable VMX nesting (nVMX).
1812 Default is 0 (disabled)
1814 kvm-intel.unrestricted_guest=
1815 [KVM,Intel] Disable unrestricted guest feature
1816 (virtualized real and unpaged mode) on capable
1817 Intel chips. Default is 1 (enabled)
1819 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1820 feature (tagged TLBs) on capable Intel chips.
1821 Default is 1 (enabled)
1827 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1830 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1831 value for LAPIC timer one-shot implementation. Default
1832 back to the programmable timer unit in the LAPIC.
1834 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1837 libata.dma= [LIBATA] DMA control
1838 libata.dma=0 Disable all PATA and SATA DMA
1839 libata.dma=1 PATA and SATA Disk DMA only
1840 libata.dma=2 ATAPI (CDROM) DMA only
1841 libata.dma=4 Compact Flash DMA only
1842 Combinations also work, so libata.dma=3 enables DMA
1843 for disks and CDROMs, but not CFs.
1845 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1846 libata.ignore_hpa=0 keep BIOS limits (default)
1847 libata.ignore_hpa=1 ignore limits, using full disk
1849 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1853 libata.force= [LIBATA] Force configurations. The format is comma
1854 separated list of "[ID:]VAL" where ID is
1855 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1856 matching port, link or device. Basically, it matches
1857 the ATA ID string printed on console by libata. If
1858 the whole ID part is omitted, the last PORT and DEVICE
1859 values are used. If ID hasn't been specified yet, the
1860 configuration applies to all ports, links and devices.
1862 If only DEVICE is omitted, the parameter applies to
1863 the port and all links and devices behind it. DEVICE
1864 number of 0 either selects the first device or the
1865 first fan-out link behind PMP device. It does not
1866 select the host link. DEVICE number of 15 selects the
1867 host link and device attached to it.
1869 The VAL specifies the configuration to force. As long
1870 as there's no ambiguity shortcut notation is allowed.
1871 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1872 The following configurations can be forced.
1874 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1875 Any ID with matching PORT is used.
1877 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1879 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1880 udma[/][16,25,33,44,66,100,133] notation is also
1883 * [no]ncq: Turn on or off NCQ.
1885 * [no]ncqtrim: Turn off queued DSM TRIM.
1887 * nohrst, nosrst, norst: suppress hard, soft
1890 * rstonce: only attempt one reset during
1891 hot-unplug link recovery
1893 * dump_id: dump IDENTIFY data.
1895 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1897 * disable: Disable this device.
1899 If there are multiple matching configurations changing
1900 the same attribute, the last one is used.
1902 memblock=debug [KNL] Enable memblock debug messages.
1904 load_ramdisk= [RAM] List of ramdisks to load from floppy
1905 See Documentation/blockdev/ramdisk.txt.
1907 lockd.nlm_grace_period=P [NFS] Assign grace period.
1910 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1913 lockd.nlm_timeout=T [NFS] Assign timeout value.
1916 lockd.nlm_udpport=M [NFS] Assign UDP port.
1919 locktorture.nreaders_stress= [KNL]
1920 Set the number of locking read-acquisition kthreads.
1921 Defaults to being automatically set based on the
1922 number of online CPUs.
1924 locktorture.nwriters_stress= [KNL]
1925 Set the number of locking write-acquisition kthreads.
1927 locktorture.onoff_holdoff= [KNL]
1928 Set time (s) after boot for CPU-hotplug testing.
1930 locktorture.onoff_interval= [KNL]
1931 Set time (s) between CPU-hotplug operations, or
1932 zero to disable CPU-hotplug testing.
1934 locktorture.shuffle_interval= [KNL]
1935 Set task-shuffle interval (jiffies). Shuffling
1936 tasks allows some CPUs to go into dyntick-idle
1937 mode during the locktorture test.
1939 locktorture.shutdown_secs= [KNL]
1940 Set time (s) after boot system shutdown. This
1941 is useful for hands-off automated testing.
1943 locktorture.stat_interval= [KNL]
1944 Time (s) between statistics printk()s.
1946 locktorture.stutter= [KNL]
1947 Time (s) to stutter testing, for example,
1948 specifying five seconds causes the test to run for
1949 five seconds, wait for five seconds, and so on.
1950 This tests the locking primitive's ability to
1951 transition abruptly to and from idle.
1953 locktorture.torture_runnable= [BOOT]
1954 Start locktorture running at boot time.
1956 locktorture.torture_type= [KNL]
1957 Specify the locking implementation to test.
1959 locktorture.verbose= [KNL]
1960 Enable additional printk() statements.
1962 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1965 loglevel= All Kernel Messages with a loglevel smaller than the
1966 console loglevel will be printed to the console. It can
1967 also be changed with klogd or other programs. The
1968 loglevels are defined as follows:
1970 0 (KERN_EMERG) system is unusable
1971 1 (KERN_ALERT) action must be taken immediately
1972 2 (KERN_CRIT) critical conditions
1973 3 (KERN_ERR) error conditions
1974 4 (KERN_WARNING) warning conditions
1975 5 (KERN_NOTICE) normal but significant condition
1976 6 (KERN_INFO) informational
1977 7 (KERN_DEBUG) debug-level messages
1979 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1980 in bytes. n must be a power of two and greater
1981 than the minimal size. The minimal size is defined
1982 by LOG_BUF_SHIFT kernel config parameter. There is
1983 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1984 that allows to increase the default size depending on
1985 the number of CPUs. See init/Kconfig for more details.
1987 logo.nologo [FB] Disables display of the built-in Linux logo.
1988 This may be used to provide more screen space for
1989 kernel log messages and is useful when debugging
1990 kernel boot problems.
1992 lp=0 [LP] Specify parallel ports to use, e.g,
1993 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1994 lp=reset first parallel port). 'lp=0' disables the
1995 lp=auto printer driver. 'lp=reset' (which can be
1996 specified in addition to the ports) causes
1997 attached printers to be reset. Using
1998 lp=port1,port2,... specifies the parallel ports
1999 to associate lp devices with, starting with
2000 lp0. A port specification may be 'none' to skip
2001 that lp device, or a parport name such as
2002 'parport0'. Specifying 'lp=auto' instead of a
2003 port specification list means that device IDs
2004 from each port should be examined, to see if
2005 an IEEE 1284-compliant printer is attached; if
2006 so, the driver will manage that printer.
2007 See also header of drivers/char/lp.c.
2010 Sets loops_per_jiffy to given constant, thus avoiding
2011 time-consuming boot-time autodetection (up to 250 ms per
2012 CPU). 0 enables autodetection (default). To determine
2013 the correct value for your kernel, boot with normal
2014 autodetection and see what value is printed. Note that
2015 on SMP systems the preset will be applied to all CPUs,
2016 which is likely to cause problems if your CPUs need
2017 significantly divergent settings. An incorrect value
2018 will cause delays in the kernel to be wrong, leading to
2019 unpredictable I/O errors and other breakage. Although
2020 unlikely, in the extreme case this might damage your
2024 Format: <io>,<irq>,<dma>
2026 machvec= [IA-64] Force the use of a particular machine-vector
2027 (machvec) in a generic kernel.
2028 Example: machvec=hpzx1_swiotlb
2030 machtype= [Loongson] Share the same kernel image file between different
2032 Example: machtype=lemote-yeeloong-2f-7inch
2034 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2035 than or equal to this physical address is ignored.
2037 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2038 will bring up during bootup. maxcpus=n : n >= 0 limits
2039 the kernel to bring up 'n' processors. Surely after
2040 bootup you can bring up the other plugged cpu by executing
2041 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2042 only takes effect during system bootup.
2043 While n=0 is a special case, it is equivalent to "nosmp",
2044 which also disables the IO APIC.
2046 max_loop= [LOOP] The number of loop block devices that get
2047 (loop.max_loop) unconditionally pre-created at init time. The default
2048 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2049 of statically allocating a predefined number, loop
2050 devices can be requested on-demand with the
2051 /dev/loop-control interface.
2053 mce [X86-32] Machine Check Exception
2055 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2057 md= [HW] RAID subsystems devices and level
2058 See Documentation/admin-guide/md.rst.
2061 Format: <first>,<last>
2062 Specifies range of consoles to be captured by the MDA.
2064 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2065 Amount of memory to be used when the kernel is not able
2066 to see the whole system memory or for test.
2067 [X86] Work as limiting max address. Use together
2068 with memmap= to avoid physical address space collisions.
2069 Without memmap= PCI devices could be placed at addresses
2070 belonging to unused RAM.
2072 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2076 [KNL,SH] Allow user to override the default size for
2077 per-device physically contiguous DMA buffers.
2079 memhp_default_state=online/offline
2080 [KNL] Set the initial state for the memory hotplug
2081 onlining policy. If not specified, the default value is
2082 set according to the
2083 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2085 See Documentation/memory-hotplug.txt.
2087 memmap=exactmap [KNL,X86] Enable setting of an exact
2088 E820 memory map, as specified by the user.
2089 Such memmap=exactmap lines can be constructed based on
2090 BIOS output or other requirements. See the memmap=nn@ss
2093 memmap=nn[KMG]@ss[KMG]
2094 [KNL] Force usage of a specific region of memory.
2095 Region of memory to be used is from ss to ss+nn.
2097 memmap=nn[KMG]#ss[KMG]
2098 [KNL,ACPI] Mark specific memory as ACPI data.
2099 Region of memory to be marked is from ss to ss+nn.
2101 memmap=nn[KMG]$ss[KMG]
2102 [KNL,ACPI] Mark specific memory as reserved.
2103 Region of memory to be reserved is from ss to ss+nn.
2104 Example: Exclude memory from 0x18690000-0x1869ffff
2105 memmap=64K$0x18690000
2107 memmap=0x10000$0x18690000
2109 memmap=nn[KMG]!ss[KMG]
2110 [KNL,X86] Mark specific memory as protected.
2111 Region of memory to be used, from ss to ss+nn.
2112 The memory region may be marked as e820 type 12 (0xc)
2113 and is NVDIMM or ADR memory.
2115 memory_corruption_check=0/1 [X86]
2116 Some BIOSes seem to corrupt the first 64k of
2117 memory when doing things like suspend/resume.
2118 Setting this option will scan the memory
2119 looking for corruption. Enabling this will
2120 both detect corruption and prevent the kernel
2121 from using the memory being corrupted.
2122 However, its intended as a diagnostic tool; if
2123 repeatable BIOS-originated corruption always
2124 affects the same memory, you can use memmap=
2125 to prevent the kernel from using that memory.
2127 memory_corruption_check_size=size [X86]
2128 By default it checks for corruption in the low
2129 64k, making this memory unavailable for normal
2130 use. Use this parameter to scan for
2131 corruption in more or less memory.
2133 memory_corruption_check_period=seconds [X86]
2134 By default it checks for corruption every 60
2135 seconds. Use this parameter to check at some
2136 other rate. 0 disables periodic checking.
2138 memtest= [KNL,X86,ARM] Enable memtest
2140 default : 0 <disable>
2141 Specifies the number of memtest passes to be
2142 performed. Each pass selects another test
2143 pattern from a given set of patterns. Memtest
2144 fills the memory with this pattern, validates
2145 memory contents and reserves bad memory
2146 regions that are detected.
2148 mem_sleep_default= [SUSPEND] Default system suspend mode:
2149 s2idle - Suspend-To-Idle
2150 shallow - Power-On Suspend or equivalent (if supported)
2151 deep - Suspend-To-RAM or equivalent (if supported)
2152 See Documentation/power/states.txt.
2154 meye.*= [HW] Set MotionEye Camera parameters
2155 See Documentation/video4linux/meye.txt.
2157 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2158 Multi-Function General Purpose Timers on AMD Geode
2161 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2162 the BIOS has incorrectly applied a workaround. TinyBIOS
2163 version 0.98 is known to be affected, 0.99 fixes the
2164 problem by letting the user disable the workaround.
2168 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2169 physical address is ignored.
2171 mini2440= [ARM,HW,KNL]
2172 Format:[0..2][b][c][t]
2174 MINI2440 configuration specification:
2175 0 - The attached screen is the 3.5" TFT
2176 1 - The attached screen is the 7" TFT
2177 2 - The VGA Shield is attached (1024x768)
2178 Leaving out the screen size parameter will not load
2179 the TFT driver, and the framebuffer will be left
2181 b - Enable backlight. The TFT backlight pin will be
2182 linked to the kernel VESA blanking code and a GPIO
2183 LED. This parameter is not necessary when using the
2185 c - Enable the s3c camera interface.
2186 t - Reserved for enabling touchscreen support. The
2187 touchscreen support is not enabled in the mainstream
2188 kernel as of 2.6.30, a preliminary port can be found
2189 in the "bleeding edge" mini2440 support kernel at
2190 http://repo.or.cz/w/linux-2.6/mini2440.git
2193 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2194 parameter allows control of the logging verbosity for
2195 the additional memory initialisation checks. A value
2196 of 0 disables mminit logging and a level of 4 will
2197 log everything. Information is printed at KERN_DEBUG
2198 so loglevel=8 may also need to be specified.
2201 [KNL] When CONFIG_MODULE_SIG is set, this means that
2202 modules without (valid) signatures will fail to load.
2203 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2204 is always true, so this option does nothing.
2206 module_blacklist= [KNL] Do not load a comma-separated list of
2207 modules. Useful for debugging problem modules.
2210 [MOUSE] Maximum time between finger touching and
2211 leaving touchpad surface for touch to be considered
2212 a tap and be reported as a left button click (for
2213 touchpads working in absolute mode only).
2215 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2216 reporting absolute coordinates, such as tablets
2217 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2218 reporting absolute coordinates, such as tablets
2220 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2221 is similar to kernelcore except it specifies the
2222 amount of memory used for migratable allocations.
2223 If both kernelcore and movablecore is specified,
2224 then kernelcore will be at *least* the specified
2225 value but may be more. If movablecore on its own
2226 is specified, the administrator must be careful
2227 that the amount of memory usable for all allocations
2230 movable_node [KNL] Boot-time switch to enable the effects
2231 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2233 MTD_Partition= [MTD]
2234 Format: <name>,<region-number>,<size>,<offset>
2236 MTD_Region= [MTD] Format:
2237 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2240 See drivers/mtd/cmdlinepart.c.
2242 multitce=off [PPC] This parameter disables the use of the pSeries
2243 firmware feature for updating multiple TCE entries
2246 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2248 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2250 boundary - index of last SLC block on Flex-OneNAND.
2251 The remaining blocks are configured as MLC blocks.
2252 lock - Configure if Flex-OneNAND boundary should be locked.
2253 Once locked, the boundary cannot be changed.
2254 1 indicates lock status, 0 indicates unlock status.
2257 ARM/S3C2412 JIVE boot control
2259 See arch/arm/mach-s3c2412/mach-jive.c
2261 mtouchusb.raw_coordinates=
2262 [HW] Make the MicroTouch USB driver use raw coordinates
2263 ('y', default) or cooked coordinates ('n')
2265 mtrr_chunk_size=nn[KMG] [X86]
2266 used for mtrr cleanup. It is largest continuous chunk
2267 that could hold holes aka. UC entries.
2269 mtrr_gran_size=nn[KMG] [X86]
2270 Used for mtrr cleanup. It is granularity of mtrr block.
2272 Large value could prevent small alignment from
2275 mtrr_spare_reg_nr=n [X86]
2277 Range: 0,7 : spare reg number
2279 Used for mtrr cleanup. It is spare mtrr entries number.
2280 Set to 2 or more if your graphical card needs more.
2282 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2284 netdev= [NET] Network devices parameters
2285 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2286 Note that mem_start is often overloaded to mean
2287 something different and driver-specific.
2288 This usage is only documented in each driver source
2292 [NETFILTER] Enable connection tracking flow accounting
2293 0 to disable accounting
2294 1 to enable accounting
2297 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2298 See Documentation/filesystems/nfs/nfsroot.txt.
2300 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2301 See Documentation/filesystems/nfs/nfsroot.txt.
2303 nfsrootdebug [NFS] enable nfsroot debugging messages.
2304 See Documentation/filesystems/nfs/nfsroot.txt.
2306 nfs.callback_nr_threads=
2307 [NFSv4] set the total number of threads that the
2308 NFS client will assign to service NFSv4 callback
2311 nfs.callback_tcpport=
2312 [NFS] set the TCP port on which the NFSv4 callback
2313 channel should listen.
2316 [NFS] sets the pathname to the program which is used
2317 to update the NFS client cache entries.
2319 nfs.cache_getent_timeout=
2320 [NFS] sets the timeout after which an attempt to
2321 update a cache entry is deemed to have failed.
2323 nfs.idmap_cache_timeout=
2324 [NFS] set the maximum lifetime for idmapper cache
2328 [NFS] enable 64-bit inode numbers.
2329 If zero, the NFS client will fake up a 32-bit inode
2330 number for the readdir() and stat() syscalls instead
2331 of returning the full 64-bit number.
2332 The default is to return 64-bit inode numbers.
2334 nfs.max_session_cb_slots=
2335 [NFSv4.1] Sets the maximum number of session
2336 slots the client will assign to the callback
2337 channel. This determines the maximum number of
2338 callbacks the client will process in parallel for
2339 a particular server.
2341 nfs.max_session_slots=
2342 [NFSv4.1] Sets the maximum number of session slots
2343 the client will attempt to negotiate with the server.
2344 This limits the number of simultaneous RPC requests
2345 that the client can send to the NFSv4.1 server.
2346 Note that there is little point in setting this
2347 value higher than the max_tcp_slot_table_limit.
2349 nfs.nfs4_disable_idmapping=
2350 [NFSv4] When set to the default of '1', this option
2351 ensures that both the RPC level authentication
2352 scheme and the NFS level operations agree to use
2353 numeric uids/gids if the mount is using the
2354 'sec=sys' security flavour. In effect it is
2355 disabling idmapping, which can make migration from
2356 legacy NFSv2/v3 systems to NFSv4 easier.
2357 Servers that do not support this mode of operation
2358 will be autodetected by the client, and it will fall
2359 back to using the idmapper.
2360 To turn off this behaviour, set the value to '0'.
2362 [NFS4] Specify an additional fixed unique ident-
2363 ification string that NFSv4 clients can insert into
2364 their nfs_client_id4 string. This is typically a
2365 UUID that is generated at system install time.
2367 nfs.send_implementation_id =
2368 [NFSv4.1] Send client implementation identification
2369 information in exchange_id requests.
2370 If zero, no implementation identification information
2372 The default is to send the implementation identification
2375 nfs.recover_lost_locks =
2376 [NFSv4] Attempt to recover locks that were lost due
2377 to a lease timeout on the server. Please note that
2378 doing this risks data corruption, since there are
2379 no guarantees that the file will remain unchanged
2380 after the locks are lost.
2381 If you want to enable the kernel legacy behaviour of
2382 attempting to recover these locks, then set this
2384 The default parameter value of '0' causes the kernel
2385 not to attempt recovery of lost locks.
2387 nfs4.layoutstats_timer =
2388 [NFSv4.2] Change the rate at which the kernel sends
2389 layoutstats to the pNFS metadata server.
2391 Setting this to value to 0 causes the kernel to use
2392 whatever value is the default set by the layout
2393 driver. A non-zero value sets the minimum interval
2394 in seconds between layoutstats transmissions.
2396 nfsd.nfs4_disable_idmapping=
2397 [NFSv4] When set to the default of '1', the NFSv4
2398 server will return only numeric uids and gids to
2399 clients using auth_sys, and will accept numeric uids
2400 and gids from such clients. This is intended to ease
2401 migration from NFSv2/v3.
2403 objlayoutdriver.osd_login_prog=
2404 [NFS] [OBJLAYOUT] sets the pathname to the program which
2405 is used to automatically discover and login into new
2406 osd-targets. Please see:
2407 Documentation/filesystems/pnfs.txt for more explanations
2409 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2410 when a NMI is triggered.
2411 Format: [state][,regs][,debounce][,die]
2413 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2414 Format: [panic,][nopanic,][num]
2416 0 - turn hardlockup detector in nmi_watchdog off
2417 1 - turn hardlockup detector in nmi_watchdog on
2418 When panic is specified, panic when an NMI watchdog
2419 timeout occurs (or 'nopanic' to override the opposite
2420 default). To disable both hard and soft lockup detectors,
2421 please see 'nowatchdog'.
2422 This is useful when you use a panic=... timeout and
2423 need the box quickly up again.
2425 netpoll.carrier_timeout=
2426 [NET] Specifies amount of time (in seconds) that
2427 netpoll should wait for a carrier. By default netpoll
2430 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2431 emulation library even if a 387 maths coprocessor
2435 [HW] Never suspend the console
2436 Disable suspending of consoles during suspend and
2437 hibernate operations. Once disabled, debugging
2438 messages can reach various consoles while the rest
2439 of the system is being put to sleep (ie, while
2440 debugging driver suspend/resume hooks). This may
2441 not work reliably with all consoles, but is known
2442 to work with serial and VGA consoles.
2443 To facilitate more flexible debugging, we also add
2444 console_suspend, a printk module parameter to control
2445 it. Users could use console_suspend (usually
2446 /sys/module/printk/parameters/console_suspend) to
2447 turn on/off it dynamically.
2449 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2450 caches in the slab allocator. Saves per-node memory,
2451 but will impact performance.
2455 noapic [SMP,APIC] Tells the kernel to not make use of any
2456 IOAPICs that may be present in the system.
2458 noautogroup Disable scheduler automatic task group creation.
2460 nobats [PPC] Do not use BATs for mapping kernel lowmem
2461 on "Classic" PPC cores.
2465 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2467 nodelayacct [KNL] Disable per-task delay accounting
2469 nodsp [SH] Disable hardware DSP at boot time.
2471 noefi Disable EFI runtime services support.
2476 On X86-32 available only on PAE configured kernels.
2477 noexec=on: enable non-executable mappings (default)
2478 noexec=off: disable non-executable mappings
2481 Disable SMAP (Supervisor Mode Access Prevention)
2482 even if it is supported by processor.
2485 Disable SMEP (Supervisor Mode Execution Prevention)
2486 even if it is supported by processor.
2489 This affects only 32-bit executables.
2490 noexec32=on: enable non-executable mappings (default)
2491 read doesn't imply executable mappings
2492 noexec32=off: disable non-executable mappings
2493 read implies executable mappings
2495 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2497 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2498 register save and restore. The kernel will only save
2499 legacy floating-point registers on task switch.
2501 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2503 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2504 Equivalent to smt=1.
2506 noxsave [BUGS=X86] Disables x86 extended register state save
2507 and restore using xsave. The kernel will fallback to
2508 enabling legacy floating-point and sse state.
2510 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2511 register states. The kernel will fall back to use
2512 xsave to save the states. By using this parameter,
2513 performance of saving the states is degraded because
2514 xsave doesn't support modified optimization while
2515 xsaveopt supports it on xsaveopt enabled systems.
2517 noxsaves [X86] Disables xsaves and xrstors used in saving and
2518 restoring x86 extended register state in compacted
2519 form of xsave area. The kernel will fall back to use
2520 xsaveopt and xrstor to save and restore the states
2521 in standard form of xsave area. By using this
2522 parameter, xsave area per process might occupy more
2523 memory on xsaves enabled systems.
2525 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2526 wfi(ARM) instruction doesn't work correctly and not to
2527 use it. This is also useful when using JTAG debugger.
2529 no_file_caps Tells the kernel not to honor file capabilities. The
2530 only way then for a file to be executed with privilege
2531 is to be setuid root or executed by root.
2533 nohalt [IA-64] Tells the kernel not to use the power saving
2534 function PAL_HALT_LIGHT when idle. This increases
2535 power-consumption. On the positive side, it reduces
2536 interrupt wake-up latency, which may improve performance
2537 in certain environments such as networked servers or
2540 nohibernate [HIBERNATION] Disable hibernation and resume.
2542 nohz= [KNL] Boottime enable/disable dynamic ticks
2543 Valid arguments: on, off
2546 nohz_full= [KNL,BOOT]
2547 The argument is a cpu list, as described above.
2548 In kernels built with CONFIG_NO_HZ_FULL=y, set
2549 the specified list of CPUs whose tick will be stopped
2550 whenever possible. The boot CPU will be forced outside
2551 the range to maintain the timekeeping.
2552 The CPUs in this range must also be included in the
2555 noiotrap [SH] Disables trapped I/O port accesses.
2557 noirqdebug [X86-32] Disables the code which attempts to detect and
2558 disable unhandled interrupt sources.
2560 no_timer_check [X86,APIC] Disables the code which tests for
2561 broken timer IRQ sources.
2563 noisapnp [ISAPNP] Disables ISA PnP code.
2565 noinitrd [RAM] Tells the kernel not to load any configured
2568 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2570 [Deprecated - use intremap=off]
2574 noinvpcid [X86] Disable the INVPCID cpu feature.
2576 nojitter [IA-64] Disables jitter checking for ITC timers.
2578 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2580 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2584 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2585 clock and use the default one.
2587 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2588 steal time is computed, but won't influence scheduler
2591 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2593 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2595 noltlbs [PPC] Do not use large page/tlb entries for kernel
2596 lowmem mapping on PPC40x and PPC8xx
2598 nomca [IA-64] Disable machine check abort handling
2600 nomce [X86-32] Disable Machine Check Exception
2602 nomfgpt [X86-32] Disable Multi-Function General Purpose
2603 Timer usage (for AMD Geode machines).
2605 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2606 shutdown the other cpus. Instead use the REBOOT_VECTOR
2609 nomodule Disable module load
2611 nopat [X86] Disable PAT (page attribute table extension of
2612 pagetables) support.
2614 norandmaps Don't use address space randomization. Equivalent to
2615 echo 0 > /proc/sys/kernel/randomize_va_space
2617 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2619 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2620 with UP alternatives
2622 nordrand [X86] Disable kernel use of the RDRAND and
2623 RDSEED instructions even if they are supported
2624 by the processor. RDRAND and RDSEED are still
2625 available to user space applications.
2627 noresume [SWSUSP] Disables resume and restores original swap
2630 no-scroll [VGA] Disables scrollback.
2631 This is required for the Braillex ib80-piezo Braille
2632 reader made by F.H. Papenmeier (Germany).
2636 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2638 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2639 and disable the IO APIC. legacy for "maxcpus=0".
2641 nosoftlockup [KNL] Disable the soft-lockup detector.
2643 nosync [HW,M68K] Disables sync negotiation for all devices.
2645 notsc [BUGS=X86-32] Disable Time Stamp Counter
2647 nowatchdog [KNL] Disable both lockup detectors, i.e.
2648 soft-lockup and NMI watchdog (hard-lockup).
2652 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2654 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2655 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2656 Some features depend on CPU0. Known dependencies are:
2657 1. Resume from suspend/hibernate depends on CPU0.
2658 Suspend/hibernate will fail if CPU0 is offline and you
2659 need to online CPU0 before suspend/hibernate.
2660 2. PIC interrupts also depend on CPU0. CPU0 can't be
2661 removed if a PIC interrupt is detected.
2662 It's said poweroff/reboot may depend on CPU0 on some
2663 machines although I haven't seen such issues so far
2664 after CPU0 is offline on a few tested machines.
2665 If the dependencies are under your control, you can
2666 turn on cpu0_hotplug.
2668 nptcg= [IA-64] Override max number of concurrent global TLB
2669 purges which is reported from either PAL_VM_SUMMARY or
2672 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2673 could support. nr_cpus=n : n >= 1 limits the kernel to
2674 support 'n' processors. It could be larger than the
2675 number of already plugged CPU during bootup, later in
2676 runtime you can physically add extra cpu until it reaches
2677 n. So during boot up some boot time memory for per-cpu
2678 variables need be pre-allocated for later physical cpu
2681 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2683 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2684 Allowed values are enable and disable
2686 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2687 one of ['zone', 'node', 'default'] can be specified
2688 This can be set from sysctl after boot.
2689 See Documentation/sysctl/vm.txt for details.
2691 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2692 See Documentation/debugging-via-ohci1394.txt for more
2695 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2696 Rather than timing out after 20 ms if an EC
2697 command is not properly ACKed, override the length
2698 of the timeout. We have interrupts disabled while
2699 waiting for the ACK, so if this is set too high
2700 interrupts *may* be lost!
2702 omap_mux= [OMAP] Override bootloader pin multiplexing.
2703 Format: <mux_mode0.mode_name=value>...
2704 For example, to override I2C bus2:
2705 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2707 oprofile.timer= [HW]
2708 Use timer interrupt instead of performance counters
2710 oprofile.cpu_type= Force an oprofile cpu type
2711 This might be useful if you have an older oprofile
2712 userland or if you want common events.
2713 Format: { arch_perfmon }
2714 arch_perfmon: [X86] Force use of architectural
2715 perfmon on Intel CPUs instead of the
2716 CPU specific event set.
2717 timer: [X86] Force use of architectural NMI
2718 timer mode (see also oprofile.timer
2719 for generic hr timer mode)
2721 oops=panic Always panic on oopses. Default is to just kill the
2722 process, but there is a small probability of
2723 deadlocking the machine.
2724 This will also cause panics on machine check exceptions.
2725 Useful together with panic=30 to trigger a reboot.
2728 See Documentation/sound/oss/oss-parameters.txt
2730 page_owner= [KNL] Boot-time page_owner enabling option.
2731 Storage of the information about who allocated
2732 each page is disabled in default. With this switch,
2734 on: enable the feature
2736 page_poison= [KNL] Boot-time parameter changing the state of
2737 poisoning on the buddy allocator.
2738 off: turn off poisoning
2739 on: turn on poisoning
2741 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2742 timeout > 0: seconds before rebooting
2743 timeout = 0: wait forever
2744 timeout < 0: reboot immediately
2747 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2750 crash_kexec_post_notifiers
2751 Run kdump after running panic-notifiers and dumping
2752 kmsg. This only for the users who doubt kdump always
2753 succeeds in any situation.
2754 Note that this also increases risks of kdump failure,
2755 because some panic notifiers can make the crashed
2756 kernel more unstable.
2758 parkbd.port= [HW] Parallel port number the keyboard adapter is
2759 connected to, default is 0.
2761 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2762 0 for XT, 1 for AT (default is AT).
2765 parport= [HW,PPT] Specify parallel ports. 0 disables.
2766 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2767 Use 'auto' to force the driver to use any
2768 IRQ/DMA settings detected (the default is to
2769 ignore detected IRQ/DMA settings because of
2770 possible conflicts). You can specify the base
2771 address, IRQ, and DMA settings; IRQ and DMA
2772 should be numbers, or 'auto' (for using detected
2773 settings on that particular port), or 'nofifo'
2774 (to avoid using a FIFO even if it is detected).
2775 Parallel ports are assigned in the order they
2776 are specified on the command line, starting
2779 parport_init_mode= [HW,PPT]
2780 Configure VIA parallel port to operate in
2781 a specific mode. This is necessary on Pegasos
2782 computer where firmware has no options for setting
2783 up parallel port mode and sets it to spp.
2784 Currently this function knows 686a and 8231 chips.
2785 Format: [spp|ps2|epp|ecp|ecpepp]
2788 Halt all CPUs after the first oops has been printed for
2789 the specified number of seconds. This is to be used if
2790 your oopses keep scrolling off the screen.
2795 See header of drivers/block/paride/pcd.c.
2796 See also Documentation/blockdev/paride.txt.
2798 pci=option[,option...] [PCI] various PCI subsystem options:
2799 earlydump [X86] dump PCI config space before the kernel
2801 off [X86] don't probe for the PCI bus
2802 bios [X86-32] force use of PCI BIOS, don't access
2803 the hardware directly. Use this if your machine
2804 has a non-standard PCI host bridge.
2805 nobios [X86-32] disallow use of PCI BIOS, only direct
2806 hardware access methods are allowed. Use this
2807 if you experience crashes upon bootup and you
2808 suspect they are caused by the BIOS.
2809 conf1 [X86] Force use of PCI Configuration Access
2810 Mechanism 1 (config address in IO port 0xCF8,
2811 data in IO port 0xCFC, both 32-bit).
2812 conf2 [X86] Force use of PCI Configuration Access
2813 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2814 the function, IO port 0xCFA, also 8-bit, sets
2815 bus number. The config space is then accessed
2816 through ports 0xC000-0xCFFF).
2817 See http://wiki.osdev.org/PCI for more info
2818 on the configuration access mechanisms.
2819 noaer [PCIE] If the PCIEAER kernel config parameter is
2820 enabled, this kernel boot option can be used to
2821 disable the use of PCIE advanced error reporting.
2822 nodomains [PCI] Disable support for multiple PCI
2823 root domains (aka PCI segments, in ACPI-speak).
2824 nommconf [X86] Disable use of MMCONFIG for PCI
2826 check_enable_amd_mmconf [X86] check for and enable
2827 properly configured MMIO access to PCI
2828 config space on AMD family 10h CPU
2829 nomsi [MSI] If the PCI_MSI kernel config parameter is
2830 enabled, this kernel boot option can be used to
2831 disable the use of MSI interrupts system-wide.
2832 noioapicquirk [APIC] Disable all boot interrupt quirks.
2833 Safety option to keep boot IRQs enabled. This
2834 should never be necessary.
2835 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2836 primary IO-APIC for bridges that cannot disable
2837 boot IRQs. This fixes a source of spurious IRQs
2838 when the system masks IRQs.
2839 noioapicreroute [APIC] Disable workaround that uses the
2840 boot IRQ equivalent of an IRQ that connects to
2841 a chipset where boot IRQs cannot be disabled.
2842 The opposite of ioapicreroute.
2843 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2844 routing table. These calls are known to be buggy
2845 on several machines and they hang the machine
2846 when used, but on other computers it's the only
2847 way to get the interrupt routing table. Try
2848 this option if the kernel is unable to allocate
2849 IRQs or discover secondary PCI buses on your
2851 rom [X86] Assign address space to expansion ROMs.
2852 Use with caution as certain devices share
2853 address decoders between ROMs and other
2855 norom [X86] Do not assign address space to
2856 expansion ROMs that do not already have
2857 BIOS assigned address ranges.
2858 nobar [X86] Do not assign address space to the
2859 BARs that weren't assigned by the BIOS.
2860 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2861 assigned automatically to PCI devices. You can
2862 make the kernel exclude IRQs of your ISA cards
2864 pirqaddr=0xAAAAA [X86] Specify the physical address
2865 of the PIRQ table (normally generated
2866 by the BIOS) if it is outside the
2867 F0000h-100000h range.
2868 lastbus=N [X86] Scan all buses thru bus #N. Can be
2869 useful if the kernel is unable to find your
2870 secondary buses and you want to tell it
2871 explicitly which ones they are.
2872 assign-busses [X86] Always assign all PCI bus
2873 numbers ourselves, overriding
2874 whatever the firmware may have done.
2875 usepirqmask [X86] Honor the possible IRQ mask stored
2876 in the BIOS $PIR table. This is needed on
2877 some systems with broken BIOSes, notably
2878 some HP Pavilion N5400 and Omnibook XE3
2879 notebooks. This will have no effect if ACPI
2880 IRQ routing is enabled.
2881 noacpi [X86] Do not use ACPI for IRQ routing
2882 or for PCI scanning.
2883 use_crs [X86] Use PCI host bridge window information
2884 from ACPI. On BIOSes from 2008 or later, this
2885 is enabled by default. If you need to use this,
2886 please report a bug.
2887 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2888 If you need to use this, please report a bug.
2889 routeirq Do IRQ routing for all PCI devices.
2890 This is normally done in pci_enable_device(),
2891 so this option is a temporary workaround
2892 for broken drivers that don't call it.
2893 skip_isa_align [X86] do not align io start addr, so can
2894 handle more pci cards
2895 noearly [X86] Don't do any early type 1 scanning.
2896 This might help on some broken boards which
2897 machine check when some devices' config space
2898 is read. But various workarounds are disabled
2899 and some IOMMU drivers will not work.
2900 bfsort Sort PCI devices into breadth-first order.
2901 This sorting is done to get a device
2902 order compatible with older (<= 2.4) kernels.
2903 nobfsort Don't sort PCI devices into breadth-first order.
2904 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2905 tuning and use the BIOS-configured MPS defaults.
2906 pcie_bus_safe Set every device's MPS to the largest value
2907 supported by all devices below the root complex.
2908 pcie_bus_perf Set device MPS to the largest allowable MPS
2909 based on its parent bus. Also set MRRS (Max
2910 Read Request Size) to the largest supported
2911 value (no larger than the MPS that the device
2912 or bus can support) for best performance.
2913 pcie_bus_peer2peer Set every device's MPS to 128B, which
2914 every device is guaranteed to support. This
2915 configuration allows peer-to-peer DMA between
2916 any pair of devices, possibly at the cost of
2917 reduced performance. This also guarantees
2918 that hot-added devices will work.
2919 cbiosize=nn[KMG] The fixed amount of bus space which is
2920 reserved for the CardBus bridge's IO window.
2921 The default value is 256 bytes.
2922 cbmemsize=nn[KMG] The fixed amount of bus space which is
2923 reserved for the CardBus bridge's memory
2924 window. The default value is 64 megabytes.
2927 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2928 [<order of align>@]pci:<vendor>:<device>\
2929 [:<subvendor>:<subdevice>][; ...]
2930 Specifies alignment and device to reassign
2931 aligned memory resources.
2932 If <order of align> is not specified,
2933 PAGE_SIZE is used as alignment.
2934 PCI-PCI bridge can be specified, if resource
2935 windows need to be expanded.
2936 To specify the alignment for several
2937 instances of a device, the PCI vendor,
2938 device, subvendor, and subdevice may be
2939 specified, e.g., 4096@pci:8086:9c22:103c:198f
2940 ecrc= Enable/disable PCIe ECRC (transaction layer
2941 end-to-end CRC checking).
2942 bios: Use BIOS/firmware settings. This is the
2946 hpiosize=nn[KMG] The fixed amount of bus space which is
2947 reserved for hotplug bridge's IO window.
2948 Default size is 256 bytes.
2949 hpmemsize=nn[KMG] The fixed amount of bus space which is
2950 reserved for hotplug bridge's memory window.
2951 Default size is 2 megabytes.
2952 hpbussize=nn The minimum amount of additional bus numbers
2953 reserved for buses below a hotplug bridge.
2955 realloc= Enable/disable reallocating PCI bridge resources
2956 if allocations done by BIOS are too small to
2957 accommodate resources required by all child
2959 off: Turn realloc off
2961 realloc same as realloc=on
2962 noari do not use PCIe ARI.
2963 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2964 only look for one device below a PCIe downstream
2967 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2970 force Enable ASPM even on devices that claim not to support it.
2971 WARNING: Forcing ASPM on may cause system lockups.
2973 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2974 nomsi Do not use MSI for PCI Express Native Hotplug (this
2975 makes all PCIe ports use INTx for hotplug services).
2977 pcie_ports= [PCIE] PCIe ports handling:
2978 auto Ask the BIOS whether or not to use native PCIe services
2979 associated with PCIe ports (PME, hot-plug, AER). Use
2980 them only if that is allowed by the BIOS.
2981 native Use native PCIe services associated with PCIe ports
2983 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2986 pcie_port_pm= [PCIE] PCIe port power management handling:
2987 off Disable power management of all PCIe ports
2988 force Forcibly enable power management of all PCIe ports
2990 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2991 nomsi Do not use MSI for native PCIe PME signaling (this makes
2992 all PCIe root ports use INTx for all services).
2994 pcmv= [HW,PCMCIA] BadgePAD 4
2998 Keep all power-domains already enabled by bootloader on,
2999 even if no driver has claimed them. This is useful
3000 for debug and development, but should not be
3001 needed on a platform with proper driver support.
3004 See Documentation/blockdev/paride.txt.
3006 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3009 See arch/parisc/kernel/pdc_chassis.c
3011 percpu_alloc= Select which percpu first chunk allocator to use.
3012 Currently supported values are "embed" and "page".
3013 Archs may support subset or none of the selections.
3014 See comments in mm/percpu.c for details on each
3015 allocator. This parameter is primarily for debugging
3016 and performance comparison.
3019 See Documentation/blockdev/paride.txt.
3022 See Documentation/blockdev/paride.txt.
3024 pirq= [SMP,APIC] Manual mp-table setup
3025 See Documentation/x86/i386/IO-APIC.txt.
3027 plip= [PPT,NET] Parallel port network link
3028 Format: { parport<nr> | timid | 0 }
3029 See also Documentation/parport.txt.
3031 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3032 Override pmtimer IOPort with a hex value.
3036 Enable PNP debug messages (depends on the
3037 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3038 via /sys/module/pnp/parameters/debug. We always show
3039 current resource usage; turning this on also shows
3040 possible settings and some assignment information.
3046 { on | off | curr | res | no-curr | no-res }
3049 [ISAPNP] Exclude IRQs for the autoconfiguration
3052 [ISAPNP] Exclude DMAs for the autoconfiguration
3054 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3055 Ranges are in pairs (I/O port base and size).
3058 [ISAPNP] Exclude memory regions for the
3060 Ranges are in pairs (memory base and size).
3062 ports= [IP_VS_FTP] IPVS ftp helper module
3064 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3066 Format: <port>,<port>....
3068 powersave=off [PPC] This option disables power saving features.
3069 It specifically disables cpuidle and sets the
3070 platform machine description specific power_save
3071 function to NULL. On Idle the CPU just reduces
3074 ppc_strict_facility_enable
3075 [PPC] This option catches any kernel floating point,
3076 Altivec, VSX and SPE outside of regions specifically
3077 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3078 There is some performance impact when enabling this.
3080 print-fatal-signals=
3081 [KNL] debug: print fatal signals
3083 If enabled, warn about various signal handling
3084 related application anomalies: too many signals,
3085 too many POSIX.1 timers, fatal signals causing a
3088 If you hit the warning due to signal overflow,
3089 you might want to try "ulimit -i unlimited".
3093 printk.always_kmsg_dump=
3094 Trigger kmsg_dump for cases other than kernel oops or
3096 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3099 printk.devkmsg={on,off,ratelimit}
3100 Control writing to /dev/kmsg.
3101 on - unlimited logging to /dev/kmsg from userspace
3102 off - logging to /dev/kmsg disabled
3103 ratelimit - ratelimit the logging
3106 printk.time= Show timing data prefixed to each printk message line
3107 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3109 processor.max_cstate= [HW,ACPI]
3110 Limit processor to maximum C-state
3111 max_cstate=9 overrides any DMI blacklist limit.
3113 processor.nocst [HW,ACPI]
3114 Ignore the _CST method to determine C-states,
3115 instead using the legacy FADT method
3117 profile= [KNL] Enable kernel profiling via /proc/profile
3118 Format: [schedule,]<number>
3119 Param: "schedule" - profile schedule points.
3120 Param: <number> - step/bucket size as a power of 2 for
3121 statistical time based profiling.
3122 Param: "sleep" - profile D-state sleeping (millisecs).
3123 Requires CONFIG_SCHEDSTATS
3124 Param: "kvm" - profile VM exits.
3126 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3128 See Documentation/blockdev/ramdisk.txt.
3130 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3131 probe for; one of (bare|imps|exps|lifebook|any).
3132 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3134 psmouse.resetafter= [HW,MOUSE]
3135 Try to reset the device after so many bad packets
3138 [HW,MOUSE] Set desired mouse resolution, in dpi.
3139 psmouse.smartscroll=
3140 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3141 0 = disabled, 1 = enabled (default).
3143 pstore.backend= Specify the name of the pstore backend to use
3146 See Documentation/blockdev/paride.txt.
3149 [KNL] Number of legacy pty's. Overwrites compiled-in
3152 quiet [KNL] Disable most log messages
3157 See Documentation/admin-guide/md.rst.
3159 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3160 See Documentation/blockdev/ramdisk.txt.
3163 The argument is a cpu list, as described above.
3165 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3166 the specified list of CPUs to be no-callback CPUs.
3167 Invocation of these CPUs' RCU callbacks will
3168 be offloaded to "rcuox/N" kthreads created for
3169 that purpose, where "x" is "b" for RCU-bh, "p"
3170 for RCU-preempt, and "s" for RCU-sched, and "N"
3171 is the CPU number. This reduces OS jitter on the
3172 offloaded CPUs, which can be useful for HPC and
3173 real-time workloads. It can also improve energy
3174 efficiency for asymmetric multiprocessors.
3177 Rather than requiring that offloaded CPUs
3178 (specified by rcu_nocbs= above) explicitly
3179 awaken the corresponding "rcuoN" kthreads,
3180 make these kthreads poll for callbacks.
3181 This improves the real-time response for the
3182 offloaded CPUs by relieving them of the need to
3183 wake up the corresponding kthread, but degrades
3184 energy efficiency by requiring that the kthreads
3185 periodically wake up to do the polling.
3187 rcutree.blimit= [KNL]
3188 Set maximum number of finished RCU callbacks to
3189 process in one batch.
3191 rcutree.dump_tree= [KNL]
3192 Dump the structure of the rcu_node combining tree
3193 out at early boot. This is used for diagnostic
3194 purposes, to verify correct tree setup.
3196 rcutree.gp_cleanup_delay= [KNL]
3197 Set the number of jiffies to delay each step of
3198 RCU grace-period cleanup. This only has effect
3199 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3201 rcutree.gp_init_delay= [KNL]
3202 Set the number of jiffies to delay each step of
3203 RCU grace-period initialization. This only has
3204 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3207 rcutree.gp_preinit_delay= [KNL]
3208 Set the number of jiffies to delay each step of
3209 RCU grace-period pre-initialization, that is,
3210 the propagation of recent CPU-hotplug changes up
3211 the rcu_node combining tree. This only has effect
3212 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3214 rcutree.rcu_fanout_exact= [KNL]
3215 Disable autobalancing of the rcu_node combining
3216 tree. This is used by rcutorture, and might
3217 possibly be useful for architectures having high
3218 cache-to-cache transfer latencies.
3220 rcutree.rcu_fanout_leaf= [KNL]
3221 Change the number of CPUs assigned to each
3222 leaf rcu_node structure. Useful for very
3223 large systems, which will choose the value 64,
3224 and for NUMA systems with large remote-access
3225 latencies, which will choose a value aligned
3226 with the appropriate hardware boundaries.
3228 rcutree.jiffies_till_sched_qs= [KNL]
3229 Set required age in jiffies for a
3230 given grace period before RCU starts
3231 soliciting quiescent-state help from
3232 rcu_note_context_switch().
3234 rcutree.jiffies_till_first_fqs= [KNL]
3235 Set delay from grace-period initialization to
3236 first attempt to force quiescent states.
3237 Units are jiffies, minimum value is zero,
3238 and maximum value is HZ.
3240 rcutree.jiffies_till_next_fqs= [KNL]
3241 Set delay between subsequent attempts to force
3242 quiescent states. Units are jiffies, minimum
3243 value is one, and maximum value is HZ.
3245 rcutree.kthread_prio= [KNL,BOOT]
3246 Set the SCHED_FIFO priority of the RCU per-CPU
3247 kthreads (rcuc/N). This value is also used for
3248 the priority of the RCU boost threads (rcub/N)
3249 and for the RCU grace-period kthreads (rcu_bh,
3250 rcu_preempt, and rcu_sched). If RCU_BOOST is
3251 set, valid values are 1-99 and the default is 1
3252 (the least-favored priority). Otherwise, when
3253 RCU_BOOST is not set, valid values are 0-99 and
3254 the default is zero (non-realtime operation).
3256 rcutree.rcu_nocb_leader_stride= [KNL]
3257 Set the number of NOCB kthread groups, which
3258 defaults to the square root of the number of
3259 CPUs. Larger numbers reduces the wakeup overhead
3260 on the per-CPU grace-period kthreads, but increases
3261 that same overhead on each group's leader.
3263 rcutree.qhimark= [KNL]
3264 Set threshold of queued RCU callbacks beyond which
3265 batch limiting is disabled.
3267 rcutree.qlowmark= [KNL]
3268 Set threshold of queued RCU callbacks below which
3269 batch limiting is re-enabled.
3271 rcutree.rcu_idle_gp_delay= [KNL]
3272 Set wakeup interval for idle CPUs that have
3273 RCU callbacks (RCU_FAST_NO_HZ=y).
3275 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3276 Set wakeup interval for idle CPUs that have
3277 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3278 Lazy RCU callbacks are those which RCU can
3279 prove do nothing more than free memory.
3281 rcuperf.gp_exp= [KNL]
3282 Measure performance of expedited synchronous
3283 grace-period primitives.
3285 rcuperf.holdoff= [KNL]
3286 Set test-start holdoff period. The purpose of
3287 this parameter is to delay the start of the
3288 test until boot completes in order to avoid
3291 rcuperf.nreaders= [KNL]
3292 Set number of RCU readers. The value -1 selects
3293 N, where N is the number of CPUs. A value
3294 "n" less than -1 selects N-n+1, where N is again
3295 the number of CPUs. For example, -2 selects N
3296 (the number of CPUs), -3 selects N+1, and so on.
3297 A value of "n" less than or equal to -N selects
3300 rcuperf.nwriters= [KNL]
3301 Set number of RCU writers. The values operate
3302 the same as for rcuperf.nreaders.
3303 N, where N is the number of CPUs
3305 rcuperf.perf_runnable= [BOOT]
3306 Start rcuperf running at boot time.
3308 rcuperf.shutdown= [KNL]
3309 Shut the system down after performance tests
3310 complete. This is useful for hands-off automated
3313 rcuperf.perf_type= [KNL]
3314 Specify the RCU implementation to test.
3316 rcuperf.verbose= [KNL]
3317 Enable additional printk() statements.
3319 rcutorture.cbflood_inter_holdoff= [KNL]
3320 Set holdoff time (jiffies) between successive
3321 callback-flood tests.
3323 rcutorture.cbflood_intra_holdoff= [KNL]
3324 Set holdoff time (jiffies) between successive
3325 bursts of callbacks within a given callback-flood
3328 rcutorture.cbflood_n_burst= [KNL]
3329 Set the number of bursts making up a given
3330 callback-flood test. Set this to zero to
3331 disable callback-flood testing.
3333 rcutorture.cbflood_n_per_burst= [KNL]
3334 Set the number of callbacks to be registered
3335 in a given burst of a callback-flood test.
3337 rcutorture.fqs_duration= [KNL]
3338 Set duration of force_quiescent_state bursts
3341 rcutorture.fqs_holdoff= [KNL]
3342 Set holdoff time within force_quiescent_state bursts
3345 rcutorture.fqs_stutter= [KNL]
3346 Set wait time between force_quiescent_state bursts
3349 rcutorture.gp_cond= [KNL]
3350 Use conditional/asynchronous update-side
3351 primitives, if available.
3353 rcutorture.gp_exp= [KNL]
3354 Use expedited update-side primitives, if available.
3356 rcutorture.gp_normal= [KNL]
3357 Use normal (non-expedited) asynchronous
3358 update-side primitives, if available.
3360 rcutorture.gp_sync= [KNL]
3361 Use normal (non-expedited) synchronous
3362 update-side primitives, if available. If all
3363 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3364 rcutorture.gp_normal=, and rcutorture.gp_sync=
3365 are zero, rcutorture acts as if is interpreted
3366 they are all non-zero.
3368 rcutorture.n_barrier_cbs= [KNL]
3369 Set callbacks/threads for rcu_barrier() testing.
3371 rcutorture.nfakewriters= [KNL]
3372 Set number of concurrent RCU writers. These just
3373 stress RCU, they don't participate in the actual
3374 test, hence the "fake".
3376 rcutorture.nreaders= [KNL]
3377 Set number of RCU readers. The value -1 selects
3378 N-1, where N is the number of CPUs. A value
3379 "n" less than -1 selects N-n-2, where N is again
3380 the number of CPUs. For example, -2 selects N
3381 (the number of CPUs), -3 selects N+1, and so on.
3383 rcutorture.object_debug= [KNL]
3384 Enable debug-object double-call_rcu() testing.
3386 rcutorture.onoff_holdoff= [KNL]
3387 Set time (s) after boot for CPU-hotplug testing.
3389 rcutorture.onoff_interval= [KNL]
3390 Set time (s) between CPU-hotplug operations, or
3391 zero to disable CPU-hotplug testing.
3393 rcutorture.shuffle_interval= [KNL]
3394 Set task-shuffle interval (s). Shuffling tasks
3395 allows some CPUs to go into dyntick-idle mode
3396 during the rcutorture test.
3398 rcutorture.shutdown_secs= [KNL]
3399 Set time (s) after boot system shutdown. This
3400 is useful for hands-off automated testing.
3402 rcutorture.stall_cpu= [KNL]
3403 Duration of CPU stall (s) to test RCU CPU stall
3404 warnings, zero to disable.
3406 rcutorture.stall_cpu_holdoff= [KNL]
3407 Time to wait (s) after boot before inducing stall.
3409 rcutorture.stat_interval= [KNL]
3410 Time (s) between statistics printk()s.
3412 rcutorture.stutter= [KNL]
3413 Time (s) to stutter testing, for example, specifying
3414 five seconds causes the test to run for five seconds,
3415 wait for five seconds, and so on. This tests RCU's
3416 ability to transition abruptly to and from idle.
3418 rcutorture.test_boost= [KNL]
3419 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3420 "Maybe" means test if the RCU implementation
3421 under test support RCU priority boosting.
3423 rcutorture.test_boost_duration= [KNL]
3424 Duration (s) of each individual boost test.
3426 rcutorture.test_boost_interval= [KNL]
3427 Interval (s) between each boost test.
3429 rcutorture.test_no_idle_hz= [KNL]
3430 Test RCU's dyntick-idle handling. See also the
3431 rcutorture.shuffle_interval parameter.
3433 rcutorture.torture_runnable= [BOOT]
3434 Start rcutorture running at boot time.
3436 rcutorture.torture_type= [KNL]
3437 Specify the RCU implementation to test.
3439 rcutorture.verbose= [KNL]
3440 Enable additional printk() statements.
3442 rcupdate.rcu_cpu_stall_suppress= [KNL]
3443 Suppress RCU CPU stall warning messages.
3445 rcupdate.rcu_cpu_stall_timeout= [KNL]
3446 Set timeout for RCU CPU stall warning messages.
3448 rcupdate.rcu_expedited= [KNL]
3449 Use expedited grace-period primitives, for
3450 example, synchronize_rcu_expedited() instead
3451 of synchronize_rcu(). This reduces latency,
3452 but can increase CPU utilization, degrade
3453 real-time latency, and degrade energy efficiency.
3454 No effect on CONFIG_TINY_RCU kernels.
3456 rcupdate.rcu_normal= [KNL]
3457 Use only normal grace-period primitives,
3458 for example, synchronize_rcu() instead of
3459 synchronize_rcu_expedited(). This improves
3460 real-time latency, CPU utilization, and
3461 energy efficiency, but can expose users to
3462 increased grace-period latency. This parameter
3463 overrides rcupdate.rcu_expedited. No effect on
3464 CONFIG_TINY_RCU kernels.
3466 rcupdate.rcu_normal_after_boot= [KNL]
3467 Once boot has completed (that is, after
3468 rcu_end_inkernel_boot() has been invoked), use
3469 only normal grace-period primitives. No effect
3470 on CONFIG_TINY_RCU kernels.
3472 rcupdate.rcu_task_stall_timeout= [KNL]
3473 Set timeout in jiffies for RCU task stall warning
3474 messages. Disable with a value less than or equal
3477 rcupdate.rcu_self_test= [KNL]
3478 Run the RCU early boot self tests
3480 rcupdate.rcu_self_test_bh= [KNL]
3481 Run the RCU bh early boot self tests
3483 rcupdate.rcu_self_test_sched= [KNL]
3484 Run the RCU sched early boot self tests
3488 Run specified binary instead of /init from the ramdisk,
3489 used for early userspace startup. See initrd.
3492 Format (x86 or x86_64):
3493 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3495 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3497 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3498 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3499 reboot_force is either force or not specified,
3500 reboot_cpu is s[mp]#### with #### being the processor
3501 to be used for rebooting.
3504 [KNL, SMP] Set scheduler's default relax_domain_level.
3505 See Documentation/cgroup-v1/cpusets.txt.
3507 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3509 reservetop= [X86-32]
3511 Reserves a hole at the top of the kernel virtual
3516 Set the amount of memory to reserve for BIOS at
3517 the bottom of the address space.
3519 reset_devices [KNL] Force drivers to reset the underlying device
3520 during initialization.
3523 Specify the partition device for software suspend
3525 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3527 resume_offset= [SWSUSP]
3528 Specify the offset from the beginning of the partition
3529 given by "resume=" at which the swap header is located,
3530 in <PAGE_SIZE> units (needed only for swap files).
3531 See Documentation/power/swsusp-and-swap-files.txt
3533 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3534 read the resume files
3536 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3537 Useful for devices that are detected asynchronously
3538 (e.g. USB and MMC devices).
3540 hibernate= [HIBERNATION]
3541 noresume Don't check if there's a hibernation image
3542 present during boot.
3543 nocompress Don't compress/decompress hibernation images.
3544 no Disable hibernation and resume.
3545 protect_image Turn on image protection during restoration
3546 (that will set all pages holding image data
3547 during restoration read-only).
3549 retain_initrd [RAM] Keep initrd memory after extraction
3551 rfkill.default_state=
3552 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3553 etc. communication is blocked by default.
3556 rfkill.master_switch_mode=
3557 0 The "airplane mode" button does nothing.
3558 1 The "airplane mode" button toggles between everything
3559 blocked and the previous configuration.
3560 2 The "airplane mode" button toggles between everything
3561 blocked and everything unblocked.
3563 rhash_entries= [KNL,NET]
3564 Set number of hash buckets for route cache
3566 ro [KNL] Mount root device read-only on boot
3569 on Mark read-only kernel memory as read-only (default).
3570 off Leave read-only kernel memory writable for debugging.
3573 Enable the uart passthrough on the designated usb port
3574 on Rockchip SoCs. When active, the signals of the
3575 debug-uart get routed to the D+ and D- pins of the usb
3576 port and the regular usb controller gets disabled.
3578 root= [KNL] Root filesystem
3579 See name_to_dev_t comment in init/do_mounts.c.
3581 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3582 mount the root filesystem
3584 rootflags= [KNL] Set root filesystem mount option string
3586 rootfstype= [KNL] Set root filesystem type
3588 rootwait [KNL] Wait (indefinitely) for root device to show up.
3589 Useful for devices that are detected asynchronously
3590 (e.g. USB and MMC devices).
3592 rproc_mem=nn[KMG][@address]
3593 [KNL,ARM,CMA] Remoteproc physical memory block.
3594 Memory area to be used by remote processor image,
3597 rw [KNL] Mount root device read-write on boot
3599 S [KNL] Run init in single mode
3601 s390_iommu= [HW,S390]
3602 Set s390 IOTLB flushing mode
3604 With strict flushing every unmap operation will result in
3605 an IOTLB flush. Default is lazy flushing before reuse,
3609 See drivers/net/irda/sa1100_ir.c.
3611 sbni= [NET] Granch SBNI12 leased line adapter
3613 sched_debug [KNL] Enables verbose scheduler debug messages.
3615 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3616 Allowed values are enable and disable. This feature
3617 incurs a small amount of overhead in the scheduler
3618 but is useful for debugging and performance tuning.
3620 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3621 xtime_lock contention on larger systems, and/or RCU lock
3622 contention on all systems with CONFIG_MAXSMP set.
3623 Format: { "0" | "1" }
3624 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3626 Note: increases power consumption, thus should only be
3627 enabled if running jitter sensitive (HPC/RT) workloads.
3629 security= [SECURITY] Choose a security module to enable at boot.
3630 If this boot parameter is not specified, only the first
3631 security module asking for security registration will be
3632 loaded. An invalid security module name will be treated
3633 as if no module has been chosen.
3635 selinux= [SELINUX] Disable or enable SELinux at boot time.
3636 Format: { "0" | "1" }
3637 See security/selinux/Kconfig help text.
3640 Default value is set via kernel config option.
3641 If enabled at boot time, /selinux/disable can be used
3642 later to disable prior to initial policy load.
3644 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3645 Format: { "0" | "1" }
3646 See security/apparmor/Kconfig help text
3649 Default value is set via kernel config option.
3651 serialnumber [BUGS=X86-32]
3654 Maximal number of shapers.
3662 Disable merging of slabs with similar size. May be
3663 necessary if there is some reason to distinguish
3664 allocs to different slabs. Debug options disable
3665 merging on their own.
3666 For more information see Documentation/vm/slub.txt.
3668 slab_max_order= [MM, SLAB]
3669 Determines the maximum allowed order for slabs.
3670 A high setting may cause OOMs due to memory
3671 fragmentation. Defaults to 1 for systems with
3672 more than 32MB of RAM, 0 otherwise.
3674 slub_debug[=options[,slabs]] [MM, SLUB]
3675 Enabling slub_debug allows one to determine the
3676 culprit if slab objects become corrupted. Enabling
3677 slub_debug can create guard zones around objects and
3678 may poison objects when not in use. Also tracks the
3679 last alloc / free. For more information see
3680 Documentation/vm/slub.txt.
3682 slub_max_order= [MM, SLUB]
3683 Determines the maximum allowed order for slabs.
3684 A high setting may cause OOMs due to memory
3685 fragmentation. For more information see
3686 Documentation/vm/slub.txt.
3688 slub_min_objects= [MM, SLUB]
3689 The minimum number of objects per slab. SLUB will
3690 increase the slab order up to slub_max_order to
3691 generate a sufficiently large slab able to contain
3692 the number of objects indicated. The higher the number
3693 of objects the smaller the overhead of tracking slabs
3694 and the less frequently locks need to be acquired.
3695 For more information see Documentation/vm/slub.txt.
3697 slub_min_order= [MM, SLUB]
3698 Determines the minimum page order for slabs. Must be
3699 lower than slub_max_order.
3700 For more information see Documentation/vm/slub.txt.
3702 slub_nomerge [MM, SLUB]
3703 Same with slab_nomerge. This is supported for legacy.
3704 See slab_nomerge for more information.
3707 Format: <io1>[,<io2>[,...,<io8>]]
3709 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3710 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3711 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3712 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3713 smsc-ircc2.ircc_irq= [HW] IRQ line
3714 smsc-ircc2.ircc_dma= [HW] DMA channel
3715 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3716 0: Toshiba Satellite 1800 (GP data pin select)
3717 1: Fast pin select (default)
3720 smt [KNL,S390] Set the maximum number of threads (logical
3721 CPUs) to use per physical CPU on systems capable of
3722 symmetric multithreading (SMT). Will be capped to the
3723 actual hardware limit.
3725 Default: -1 (no limit)
3728 [KNL] Should the soft-lockup detector generate panics.
3731 softlockup_all_cpu_backtrace=
3732 [KNL] Should the soft-lockup detector generate
3733 backtraces on all cpus.
3736 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3737 See Documentation/laptops/sonypi.txt
3739 spia_io_base= [HW,MTD]
3745 Enabled the stack tracer on boot up.
3747 stacktrace_filter=[function-list]
3748 [FTRACE] Limit the functions that the stack tracer
3749 will trace at boot up. function-list is a comma separated
3750 list of functions. This list can be changed at run
3751 time by the stack_trace_filter file in the debugfs
3752 tracing directory. Note, this enables stack tracing
3753 and the stacktrace above is not needed.
3757 Set the STI (builtin display/keyboard on the HP-PARISC
3758 machines) console (graphic card) which should be used
3759 as the initial boot-console.
3760 See also comment in drivers/video/console/sticore.c.
3763 See comment in drivers/video/console/sticore.c.
3766 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3768 sunrpc.min_resvport=
3769 sunrpc.max_resvport=
3771 SunRPC servers often require that client requests
3772 originate from a privileged port (i.e. a port in the
3773 range 0 < portnr < 1024).
3774 An administrator who wishes to reserve some of these
3775 ports for other uses may adjust the range that the
3776 kernel's sunrpc client considers to be privileged
3777 using these two parameters to set the minimum and
3778 maximum port values.
3780 sunrpc.svc_rpc_per_connection_limit=
3782 Limit the number of requests that the server will
3783 process in parallel from a single connection.
3784 The default value is 0 (no limit).
3788 Control how the NFS server code allocates CPUs to
3789 service thread pools. Depending on how many NICs
3790 you have and where their interrupts are bound, this
3791 option will affect which CPUs will do NFS serving.
3792 Note: this parameter cannot be changed while the
3793 NFS server is running.
3795 auto the server chooses an appropriate mode
3796 automatically using heuristics
3797 global a single global pool contains all CPUs
3798 percpu one pool for each CPU
3799 pernode one pool for each NUMA node (equivalent
3800 to global on non-NUMA machines)
3802 sunrpc.tcp_slot_table_entries=
3803 sunrpc.udp_slot_table_entries=
3805 Sets the upper limit on the number of simultaneous
3806 RPC calls that can be sent from the client to a
3807 server. Increasing these values may allow you to
3808 improve throughput, but will also increase the
3809 amount of memory reserved for use by the client.
3811 suspend.pm_test_delay=
3813 Sets the number of seconds to remain in a suspend test
3814 mode before resuming the system (see
3815 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3816 is set. Default value is 5.
3819 [KNL] Enable accounting of swap in memory resource
3820 controller if no parameter or 1 is given or disable
3821 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3823 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3824 Format: { <int> | force | noforce }
3825 <int> -- Number of I/O TLB slabs
3826 force -- force using of bounce buffers even if they
3827 wouldn't be automatically used by the kernel
3828 noforce -- Never use bounce buffers (for debugging)
3832 sysfs.deprecated=0|1 [KNL]
3833 Enable/disable old style sysfs layout for old udev
3834 on older distributions. When this option is enabled
3835 very new udev will not work anymore. When this option
3836 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3837 in older udev will not work anymore.
3838 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3839 the kernel configuration.
3841 sysrq_always_enabled
3843 Ignore sysrq setting - this boot parameter will
3844 neutralize any effect of /proc/sys/kernel/sysrq.
3845 Useful for debugging.
3847 tcpmhash_entries= [KNL,NET]
3848 Set the number of tcp_metrics_hash slots.
3849 Default value is 8192 or 16384 depending on total
3850 ram pages. This is used to specify the TCP metrics
3851 cache size. See Documentation/networking/ip-sysctl.txt
3852 "tcp_no_metrics_save" section for more details.
3856 test_suspend= [SUSPEND][,N]
3857 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3858 standby suspend) or "freeze" (for suspend type freeze)
3859 as the system sleep state during system startup with
3860 the optional capability to repeat N number of times.
3861 The system is woken from this state using a
3862 wakeup-capable RTC alarm.
3864 thash_entries= [KNL,NET]
3865 Set number of hash buckets for TCP connection
3867 thermal.act= [HW,ACPI]
3868 -1: disable all active trip points in all thermal zones
3869 <degrees C>: override all lowest active trip points
3871 thermal.crt= [HW,ACPI]
3872 -1: disable all critical trip points in all thermal zones
3873 <degrees C>: override all critical trip points
3875 thermal.nocrt= [HW,ACPI]
3876 Set to disable actions on ACPI thermal zone
3877 critical and hot trip points.
3879 thermal.off= [HW,ACPI]
3880 1: disable ACPI thermal control
3882 thermal.psv= [HW,ACPI]
3883 -1: disable all passive trip points
3884 <degrees C>: override all passive trip points to this
3887 thermal.tzp= [HW,ACPI]
3888 Specify global default ACPI thermal zone polling rate
3889 <deci-seconds>: poll all this frequency
3890 0: no polling (default)
3893 Force threading of all interrupt handlers except those
3894 marked explicitly IRQF_NO_THREAD.
3897 Enable the Transcendent memory driver if built-in.
3899 tmem.cleancache=0|1 [KNL, XEN]
3900 Default is on (1). Disable the usage of the cleancache
3901 API to send anonymous pages to the hypervisor.
3903 tmem.frontswap=0|1 [KNL, XEN]
3904 Default is on (1). Disable the usage of the frontswap
3905 API to send swap pages to the hypervisor. If disabled
3906 the selfballooning and selfshrinking are force disabled.
3908 tmem.selfballooning=0|1 [KNL, XEN]
3909 Default is on (1). Disable the driving of swap pages
3912 tmem.selfshrinking=0|1 [KNL, XEN]
3913 Default is on (1). Partial swapoff that immediately
3914 transfers pages from Xen hypervisor back to the
3915 kernel based on different criteria.
3919 Specify if the kernel should make use of the cpu
3920 topology information if the hardware supports this.
3921 The scheduler will make use of this information and
3922 e.g. base its process migration decisions on it.
3925 topology_updates= [KNL, PPC, NUMA]
3927 Specify if the kernel should ignore (off)
3928 topology updates sent by the hypervisor to this
3933 tpm_suspend_pcr=[HW,TPM]
3934 Format: integer pcr id
3935 Specify that at suspend time, the tpm driver
3936 should extend the specified pcr with zeros,
3937 as a workaround for some chips which fail to
3938 flush the last written pcr on TPM_SaveState.
3939 This will guarantee that all the other pcrs
3942 trace_buf_size=nn[KMG]
3943 [FTRACE] will set tracing buffer size on each cpu.
3945 trace_event=[event-list]
3946 [FTRACE] Set and start specified trace events in order
3947 to facilitate early boot debugging. The event-list is a
3948 comma separated list of trace events to enable. See
3949 also Documentation/trace/events.txt
3951 trace_options=[option-list]
3952 [FTRACE] Enable or disable tracer options at boot.
3953 The option-list is a comma delimited list of options
3954 that can be enabled or disabled just as if you were
3955 to echo the option name into
3957 /sys/kernel/debug/tracing/trace_options
3959 For example, to enable stacktrace option (to dump the
3960 stack trace of each event), add to the command line:
3962 trace_options=stacktrace
3964 See also Documentation/trace/ftrace.txt "trace options"
3968 Have the tracepoints sent to printk as well as the
3969 tracing ring buffer. This is useful for early boot up
3970 where the system hangs or reboots and does not give the
3971 option for reading the tracing buffer or performing a
3972 ftrace_dump_on_oops.
3974 To turn off having tracepoints sent to printk,
3975 echo 0 > /proc/sys/kernel/tracepoint_printk
3976 Note, echoing 1 into this file without the
3977 tracepoint_printk kernel cmdline option has no effect.
3981 Having tracepoints sent to printk() and activating high
3982 frequency tracepoints such as irq or sched, can cause
3983 the system to live lock.
3986 [FTRACE] enable this option to disable tracing when a
3987 warning is hit. This turns off "tracing_on". Tracing can
3988 be enabled again by echoing '1' into the "tracing_on"
3989 file located in /sys/kernel/debug/tracing/
3991 This option is useful, as it disables the trace before
3992 the WARNING dump is called, which prevents the trace to
3993 be filled with content caused by the warning output.
3995 This option can also be set at run time via the sysctl
3996 option: kernel/traceoff_on_warning
3998 transparent_hugepage=
4000 Format: [always|madvise|never]
4001 Can be used to control the default behavior of the system
4002 with respect to transparent hugepages.
4003 See Documentation/vm/transhuge.txt for more details.
4005 tsc= Disable clocksource stability checks for TSC.
4007 [x86] reliable: mark tsc clocksource as reliable, this
4008 disables clocksource verification at runtime, as well
4009 as the stability checks done at bootup. Used to enable
4010 high-resolution timer mode on older hardware, and in
4011 virtualized environment.
4012 [x86] noirqtime: Do not use TSC to do irq accounting.
4013 Used to run time disable IRQ_TIME_ACCOUNTING on any
4014 platforms where RDTSC is slow and this accounting
4017 turbografx.map[2|3]= [HW,JOY]
4018 TurboGraFX parallel port interface
4020 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4021 See also Documentation/input/joystick-parport.txt
4023 udbg-immortal [PPC] When debugging early kernel crashes that
4024 happen after console_init() and before a proper
4025 console driver takes over, this boot options might
4026 help "seeing" what's going on.
4028 uhash_entries= [KNL,NET]
4029 Set number of hash buckets for UDP/UDP-Lite connections
4032 [USB] Ignore overcurrent events (default N).
4033 Some badly-designed motherboards generate lots of
4034 bogus events, for ports that aren't wired to
4035 anything. Set this parameter to avoid log spamming.
4036 Note that genuine overcurrent events won't be
4040 [X86] Cause panic on unknown NMI.
4042 usbcore.authorized_default=
4043 [USB] Default USB device authorization:
4044 (default -1 = authorized except for wireless USB,
4045 0 = not authorized, 1 = authorized)
4047 usbcore.autosuspend=
4048 [USB] The autosuspend time delay (in seconds) used
4049 for newly-detected USB devices (default 2). This
4050 is the time required before an idle device will be
4051 autosuspended. Devices for which the delay is set
4052 to a negative value won't be autosuspended at all.
4054 usbcore.usbfs_snoop=
4055 [USB] Set to log all usbfs traffic (default 0 = off).
4057 usbcore.usbfs_snoop_max=
4058 [USB] Maximum number of bytes to snoop in each URB
4061 usbcore.blinkenlights=
4062 [USB] Set to cycle leds on hubs (default 0 = off).
4064 usbcore.old_scheme_first=
4065 [USB] Start with the old device initialization
4066 scheme (default 0 = off).
4068 usbcore.usbfs_memory_mb=
4069 [USB] Memory limit (in MB) for buffers allocated by
4070 usbfs (default = 16, 0 = max = 2047).
4072 usbcore.use_both_schemes=
4073 [USB] Try the other device initialization scheme
4074 if the first one fails (default 1 = enabled).
4076 usbcore.initial_descriptor_timeout=
4077 [USB] Specifies timeout for the initial 64-byte
4078 USB_REQ_GET_DESCRIPTOR request in milliseconds
4079 (default 5000 = 5.0 seconds).
4081 usbcore.nousb [USB] Disable the USB subsystem
4084 [USBHID] The interval which mice are to be polled at.
4086 usb-storage.delay_use=
4087 [UMS] The delay in seconds before a new device is
4088 scanned for Logical Units (default 1).
4091 [UMS] A list of quirks entries to supplement or
4092 override the built-in unusual_devs list. List
4093 entries are separated by commas. Each entry has
4094 the form VID:PID:Flags where VID and PID are Vendor
4095 and Product ID values (4-digit hex numbers) and
4096 Flags is a set of characters, each corresponding
4097 to a common usb-storage quirk flag as follows:
4098 a = SANE_SENSE (collect more than 18 bytes
4100 b = BAD_SENSE (don't collect more than 18
4101 bytes of sense data);
4102 c = FIX_CAPACITY (decrease the reported
4103 device capacity by one sector);
4104 d = NO_READ_DISC_INFO (don't use
4105 READ_DISC_INFO command);
4106 e = NO_READ_CAPACITY_16 (don't use
4107 READ_CAPACITY_16 command);
4108 f = NO_REPORT_OPCODES (don't use report opcodes
4110 g = MAX_SECTORS_240 (don't transfer more than
4111 240 sectors at a time, uas only);
4112 h = CAPACITY_HEURISTICS (decrease the
4113 reported device capacity by one
4114 sector if the number is odd);
4115 i = IGNORE_DEVICE (don't bind to this
4117 j = NO_REPORT_LUNS (don't use report luns
4119 l = NOT_LOCKABLE (don't try to lock and
4120 unlock ejectable media);
4121 m = MAX_SECTORS_64 (don't transfer more
4122 than 64 sectors = 32 KB at a time);
4123 n = INITIAL_READ10 (force a retry of the
4124 initial READ(10) command);
4125 o = CAPACITY_OK (accept the capacity
4126 reported by the device);
4127 p = WRITE_CACHE (the device cache is ON
4129 r = IGNORE_RESIDUE (the device reports
4130 bogus residue values);
4131 s = SINGLE_LUN (the device has only one
4133 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4134 commands, uas only);
4135 u = IGNORE_UAS (don't bind to the uas driver);
4136 w = NO_WP_DETECT (don't test whether the
4137 medium is write-protected).
4138 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4139 even if the device claims no cache)
4140 Example: quirks=0419:aaf5:rl,0421:0433:rc
4142 user_debug= [KNL,ARM]
4144 See arch/arm/Kconfig.debug help text.
4145 1 - undefined instruction events
4147 4 - invalid data aborts
4150 Example: user_debug=31
4153 [X86] Flags controlling user PTE allocations.
4155 nohigh = do not allocate PTE pages in
4156 HIGHMEM regardless of setting
4160 On X86_32, this is an alias for vdso32=. Otherwise:
4162 vdso=1: enable VDSO (the default)
4163 vdso=0: disable VDSO mapping
4165 vdso32= [X86] Control the 32-bit vDSO
4166 vdso32=1: enable 32-bit VDSO
4167 vdso32=0 or vdso32=2: disable 32-bit VDSO
4169 See the help text for CONFIG_COMPAT_VDSO for more
4170 details. If CONFIG_COMPAT_VDSO is set, the default is
4171 vdso32=0; otherwise, the default is vdso32=1.
4173 For compatibility with older kernels, vdso32=2 is an
4176 Try vdso32=0 if you encounter an error that says:
4177 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4180 vector=percpu: enable percpu vector domain
4182 video= [FB] Frame buffer configuration
4183 See Documentation/fb/modedb.txt.
4185 video.brightness_switch_enabled= [0,1]
4186 If set to 1, on receiving an ACPI notify event
4187 generated by hotkey, video driver will adjust brightness
4188 level and then send out the event to user space through
4189 the allocated input device; If set to 0, video driver
4190 will only send out the event without touching backlight
4195 [VMMIO] Memory mapped virtio (platform) device.
4197 <size>@<baseaddr>:<irq>[:<id>]
4199 <size> := size (can use standard suffixes
4201 <baseaddr> := physical base address
4202 <irq> := interrupt number (as passed to
4204 <id> := (optional) platform device id
4206 virtio_mmio.device=1K@0x100b0000:48:7
4208 Can be used multiple times for multiple devices.
4210 vga= [BOOT,X86-32] Select a particular video mode
4211 See Documentation/x86/boot.txt and
4212 Documentation/svga.txt.
4213 Use vga=ask for menu.
4214 This is actually a boot loader parameter; the value is
4215 passed to the kernel using a special protocol.
4217 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4218 size of <nn>. This can be used to increase the
4219 minimum size (128MB on x86). It can also be used to
4220 decrease the size and leave more room for directly
4223 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4226 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4229 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4233 Controls the behavior of vsyscalls (i.e. calls to
4234 fixed addresses of 0xffffffffff600x00 from legacy
4235 code). Most statically-linked binaries and older
4236 versions of glibc use these calls. Because these
4237 functions are at fixed addresses, they make nice
4238 targets for exploits that can control RIP.
4240 emulate [default] Vsyscalls turn into traps and are
4241 emulated reasonably safely.
4243 native Vsyscalls are native syscall instructions.
4244 This is a little bit faster than trapping
4245 and makes a few dynamic recompilers work
4246 better than they would in emulation mode.
4247 It also makes exploits much easier to write.
4249 none Vsyscalls don't work at all. This makes
4250 them quite hard to use for exploits but
4251 might break your system.
4253 vt.color= [VT] Default text color.
4254 Format: 0xYX, X = foreground, Y = background.
4255 Default: 0x07 = light gray on black.
4257 vt.cur_default= [VT] Default cursor shape.
4258 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4259 the parameters of the <Esc>[?A;B;Cc escape sequence;
4260 see VGA-softcursor.txt. Default: 2 = underline.
4262 vt.default_blu= [VT]
4263 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4264 Change the default blue palette of the console.
4265 This is a 16-member array composed of values
4268 vt.default_grn= [VT]
4269 Format: <green0>,<green1>,<green2>,...,<green15>
4270 Change the default green palette of the console.
4271 This is a 16-member array composed of values
4274 vt.default_red= [VT]
4275 Format: <red0>,<red1>,<red2>,...,<red15>
4276 Change the default red palette of the console.
4277 This is a 16-member array composed of values
4283 Set system-wide default UTF-8 mode for all tty's.
4284 Default is 1, i.e. UTF-8 mode is enabled for all
4285 newly opened terminals.
4287 vt.global_cursor_default=
4290 Set system-wide default for whether a cursor
4291 is shown on new VTs. Default is -1,
4292 i.e. cursors will be created by default unless
4293 overridden by individual drivers. 0 will hide
4294 cursors, 1 will display them.
4296 vt.italic= [VT] Default color for italic text; 0-15.
4299 vt.underline= [VT] Default color for underlined text; 0-15.
4302 watchdog timers [HW,WDT] For information on watchdog timers,
4303 see Documentation/watchdog/watchdog-parameters.txt
4304 or other driver-specific files in the
4305 Documentation/watchdog/ directory.
4307 workqueue.watchdog_thresh=
4308 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4309 warn stall conditions and dump internal state to
4310 help debugging. 0 disables workqueue stall
4311 detection; otherwise, it's the stall threshold
4312 duration in seconds. The default value is 30 and
4313 it can be updated at runtime by writing to the
4314 corresponding sysfs file.
4316 workqueue.disable_numa
4317 By default, all work items queued to unbound
4318 workqueues are affine to the NUMA nodes they're
4319 issued on, which results in better behavior in
4320 general. If NUMA affinity needs to be disabled for
4321 whatever reason, this option can be used. Note
4322 that this also can be controlled per-workqueue for
4323 workqueues visible under /sys/bus/workqueue/.
4325 workqueue.power_efficient
4326 Per-cpu workqueues are generally preferred because
4327 they show better performance thanks to cache
4328 locality; unfortunately, per-cpu workqueues tend to
4329 be more power hungry than unbound workqueues.
4331 Enabling this makes the per-cpu workqueues which
4332 were observed to contribute significantly to power
4333 consumption unbound, leading to measurably lower
4334 power usage at the cost of small performance
4337 The default value of this parameter is determined by
4338 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4340 workqueue.debug_force_rr_cpu
4341 Workqueue used to implicitly guarantee that work
4342 items queued without explicit CPU specified are put
4343 on the local CPU. This guarantee is no longer true
4344 and while local CPU is still preferred work items
4345 may be put on foreign CPUs. This debug option
4346 forces round-robin CPU selection to flush out
4347 usages which depend on the now broken guarantee.
4348 When enabled, memory and cache locality will be
4351 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4352 default x2apic cluster mode on platforms
4355 x86_intel_mid_timer= [X86-32,APBT]
4356 Choose timer option for x86 Intel MID platform.
4357 Two valid options are apbt timer only and lapic timer
4358 plus one apbt timer for broadcast timer.
4359 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4361 xen_512gb_limit [KNL,X86-64,XEN]
4362 Restricts the kernel running paravirtualized under Xen
4363 to use only up to 512 GB of RAM. The reason to do so is
4364 crash analysis tools and Xen tools for doing domain
4365 save/restore/migration must be enabled to handle larger
4368 xen_emul_unplug= [HW,X86,XEN]
4369 Unplug Xen emulated devices
4370 Format: [unplug0,][unplug1]
4371 ide-disks -- unplug primary master IDE devices
4372 aux-ide-disks -- unplug non-primary-master IDE devices
4373 nics -- unplug network devices
4374 all -- unplug all emulated devices (NICs and IDE disks)
4375 unnecessary -- unplugging emulated devices is
4376 unnecessary even if the host did not respond to
4378 never -- do not unplug even if version check succeeds
4380 xen_nopvspin [X86,XEN]
4381 Disables the ticketlock slowpath using Xen PV
4385 Disables the PV optimizations forcing the HVM guest to
4386 run as generic HVM guest with no PV drivers.
4388 xirc2ps_cs= [NET,PCMCIA]
4390 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
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