1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
117 Support masking of GPEs numbered from 0x00 to 0x7f.
119 acpi_no_auto_serialize [HW,ACPI]
120 Disable auto-serialization of AML methods
121 AML control methods that contain the opcodes to create
122 named objects will be marked as "Serialized" by the
123 auto-serialization feature.
124 This feature is enabled by default.
125 This option allows to turn off the feature.
127 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
130 acpi_no_static_ssdt [HW,ACPI]
131 Disable installation of static SSDTs at early boot time
132 By default, SSDTs contained in the RSDT/XSDT will be
133 installed automatically and they will appear under
134 /sys/firmware/acpi/tables.
135 This option turns off this feature.
136 Note that specifying this option does not affect
137 dynamic table installation which will install SSDT
138 tables to /sys/firmware/acpi/tables/dynamic.
140 acpi_rsdp= [ACPI,EFI,KEXEC]
141 Pass the RSDP address to the kernel, mostly used
142 on machines running EFI runtime service to boot the
143 second kernel for kdump.
145 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
146 Format: To spoof as Windows 98: ="Microsoft Windows"
148 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
149 of 2 which is mandated by ACPI 6) as the supported ACPI
150 specification revision (when using this switch, it may
151 be necessary to carry out a cold reboot _twice_ in a
152 row to make it take effect on the platform firmware).
154 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
155 acpi_osi="string1" # add string1
156 acpi_osi="!string2" # remove string2
157 acpi_osi=!* # remove all strings
158 acpi_osi=! # disable all built-in OS vendor
160 acpi_osi=!! # enable all built-in OS vendor
162 acpi_osi= # disable all strings
164 'acpi_osi=!' can be used in combination with single or
165 multiple 'acpi_osi="string1"' to support specific OS
166 vendor string(s). Note that such command can only
167 affect the default state of the OS vendor strings, thus
168 it cannot affect the default state of the feature group
169 strings and the current state of the OS vendor strings,
170 specifying it multiple times through kernel command line
171 is meaningless. This command is useful when one do not
172 care about the state of the feature group strings which
173 should be controlled by the OSPM.
175 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
176 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
177 can make '_OSI("Windows 2000")' TRUE.
179 'acpi_osi=' cannot be used in combination with other
180 'acpi_osi=' command lines, the _OSI method will not
181 exist in the ACPI namespace. NOTE that such command can
182 only affect the _OSI support state, thus specifying it
183 multiple times through kernel command line is also
186 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
189 'acpi_osi=!*' can be used in combination with single or
190 multiple 'acpi_osi="string1"' to support specific
191 string(s). Note that such command can affect the
192 current state of both the OS vendor strings and the
193 feature group strings, thus specifying it multiple times
194 through kernel command line is meaningful. But it may
195 still not able to affect the final state of a string if
196 there are quirks related to this string. This command
197 is useful when one want to control the state of the
198 feature group strings to debug BIOS issues related to
201 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
202 '_OSI("Module Device")' FALSE.
203 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
204 '_OSI("Module Device")' TRUE.
205 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
207 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
209 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
210 they all will make '_OSI("Windows 2000")' TRUE.
213 Override the pmtimer bug detection: force the kernel
214 to assume that this machine's pmtimer latches its value
215 and always returns good values.
217 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
218 Format: { level | edge | high | low }
220 acpi_skip_timer_override [HW,ACPI]
221 Recognize and ignore IRQ0/pin2 Interrupt Override.
222 For broken nForce2 BIOS resulting in XT-PIC timer.
224 acpi_sleep= [HW,ACPI] Sleep options
225 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
226 old_ordering, nonvs, sci_force_enable }
227 See Documentation/power/video.txt for information on
229 s3_beep is for debugging; it makes the PC's speaker beep
230 as soon as the kernel's real-mode entry point is called.
231 s4_nohwsig prevents ACPI hardware signature from being
232 used during resume from hibernation.
233 old_ordering causes the ACPI 1.0 ordering of the _PTS
234 control method, with respect to putting devices into
235 low power states, to be enforced (the ACPI 2.0 ordering
236 of _PTS is used by default).
237 nonvs prevents the kernel from saving/restoring the
238 ACPI NVS memory during suspend/hibernation and resume.
239 sci_force_enable causes the kernel to set SCI_EN directly
240 on resume from S1/S3 (which is against the ACPI spec,
241 but some broken systems don't work without it).
243 acpi_use_timer_override [HW,ACPI]
244 Use timer override. For some broken Nvidia NF5 boards
245 that require a timer override, but don't have HPET
247 add_efi_memmap [EFI; X86] Include EFI memory map in
248 kernel's map of available physical RAM.
251 { off | try_unsupported }
252 off: disable AGP support
253 try_unsupported: try to drive unsupported chipsets
254 (may crash computer or cause data corruption)
257 See Documentation/sound/alsa/alsa-parameters.txt
260 Allow the default userspace alignment fault handler
261 behaviour to be specified. Bit 0 enables warnings,
262 bit 1 enables fixups, and bit 2 sends a segfault.
264 align_va_addr= [X86-64]
265 Align virtual addresses by clearing slice [14:12] when
266 allocating a VMA at process creation time. This option
267 gives you up to 3% performance improvement on AMD F15h
268 machines (where it is enabled by default) for a
269 CPU-intensive style benchmark, and it can vary highly in
270 a microbenchmark depending on workload and compiler.
272 32: only for 32-bit processes
273 64: only for 64-bit processes
274 on: enable for both 32- and 64-bit processes
275 off: disable for both 32- and 64-bit processes
277 alloc_snapshot [FTRACE]
278 Allocate the ftrace snapshot buffer on boot up when the
279 main buffer is allocated. This is handy if debugging
280 and you need to use tracing_snapshot() on boot up, and
281 do not want to use tracing_snapshot_alloc() as it needs
282 to be done where GFP_KERNEL allocations are allowed.
284 amd_iommu= [HW,X86-64]
285 Pass parameters to the AMD IOMMU driver in the system.
287 fullflush - enable flushing of IO/TLB entries when
288 they are unmapped. Otherwise they are
289 flushed before they will be reused, which
291 off - do not initialize any AMD IOMMU found in
293 force_isolation - Force device isolation for all
294 devices. The IOMMU driver is not
295 allowed anymore to lift isolation
296 requirements as needed. This option
297 does not override iommu=pt
299 amd_iommu_dump= [HW,X86-64]
300 Enable AMD IOMMU driver option to dump the ACPI table
301 for AMD IOMMU. With this option enabled, AMD IOMMU
302 driver will print ACPI tables for AMD IOMMU during
303 IOMMU initialization.
305 amd_iommu_intr= [HW,X86-64]
306 Specifies one of the following AMD IOMMU interrupt
308 legacy - Use legacy interrupt remapping mode.
309 vapic - Use virtual APIC mode, which allows IOMMU
310 to inject interrupts directly into guest.
311 This mode requires kvm-amd.avic=1.
312 (Default when IOMMU HW support is present.)
314 amijoy.map= [HW,JOY] Amiga joystick support
315 Map of devices attached to JOY0DAT and JOY1DAT
317 See also Documentation/input/joystick.txt
319 analog.map= [HW,JOY] Analog joystick and gamepad support
320 Specifies type or capabilities of an analog joystick
321 connected to one of 16 gameports
322 Format: <type1>,<type2>,..<type16>
325 Power management functions (SPARCstation-4/5 + deriv.)
327 Disable APC CPU standby support. SPARCstation-Fox does
328 not play well with APC CPU idle - disable it if you have
329 APC and your system crashes randomly.
331 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
332 Change the output verbosity whilst booting
333 Format: { quiet (default) | verbose | debug }
334 Change the amount of debugging information output
335 when initialising the APIC and IO-APIC components.
337 apic_extnmi= [APIC,X86] External NMI delivery setting
338 Format: { bsp (default) | all | none }
339 bsp: External NMI is delivered only to CPU 0
340 all: External NMIs are broadcast to all CPUs as a
342 none: External NMI is masked for all CPUs. This is
343 useful so that a dump capture kernel won't be
347 See Documentation/networking/ipv6.txt.
349 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
350 Limit apic dumping. The parameter defines the maximal
351 number of local apics being dumped. Also it is possible
352 to set it to "all" by meaning -- no limit here.
353 Format: { 1 (default) | 2 | ... | all }.
354 The parameter valid if only apic=debug or
355 apic=verbose is specified.
356 Example: apic=debug show_lapic=all
358 apm= [APM] Advanced Power Management
359 See header of arch/x86/kernel/apm_32.c.
361 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
362 Format: <io>,<irq>,<nodeID>
366 atarimouse= [HW,MOUSE] Atari Mouse
368 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
369 EzKey and similar keyboards
371 atkbd.reset= [HW] Reset keyboard during initialization
373 atkbd.set= [HW] Select keyboard code set
374 Format: <int> (2 = AT (default), 3 = PS/2)
376 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
379 atkbd.softraw= [HW] Choose between synthetic and real raw mode
380 Format: <bool> (0 = real, 1 = synthetic (default))
382 atkbd.softrepeat= [HW]
383 Use software keyboard repeat
385 audit= [KNL] Enable the audit sub-system
386 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
387 0 - kernel audit is disabled and can not be enabled
388 until the next reboot
389 unset - kernel audit is initialized but disabled and
390 will be fully enabled by the userspace auditd.
391 1 - kernel audit is initialized and partially enabled,
392 storing at most audit_backlog_limit messages in
393 RAM until it is fully enabled by the userspace
397 audit_backlog_limit= [KNL] Set the audit queue size limit.
398 Format: <int> (must be >=0)
401 bau= [X86_UV] Enable the BAU on SGI UV. The default
402 behavior is to disable the BAU (i.e. bau=0).
403 Format: { "0" | "1" }
406 unset - Disable the BAU.
408 baycom_epp= [HW,AX25]
411 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
413 See header of drivers/net/hamradio/baycom_par.c.
415 baycom_ser_fdx= [HW,AX25]
416 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
417 Format: <io>,<irq>,<mode>[,<baud>]
418 See header of drivers/net/hamradio/baycom_ser_fdx.c.
420 baycom_ser_hdx= [HW,AX25]
421 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
422 Format: <io>,<irq>,<mode>
423 See header of drivers/net/hamradio/baycom_ser_hdx.c.
425 blkdevparts= Manual partition parsing of block device(s) for
426 embedded devices based on command line input.
427 See Documentation/block/cmdline-partition.txt
429 boot_delay= Milliseconds to delay each printk during boot.
430 Values larger than 10 seconds (10000) are changed to
434 bootmem_debug [KNL] Enable bootmem allocator debug messages.
437 Disable BERT OS support on buggy BIOSes.
439 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
440 bttv.radio= Most important insmod options are available as
442 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
445 bulk_remove=off [PPC] This parameter disables the use of the pSeries
446 firmware feature for flushing multiple hpte entries
449 c101= [NET] Moxa C101 synchronous serial card
451 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
452 Sometimes CPU hardware bugs make them report the cache
453 size incorrectly. The kernel will attempt work arounds
454 to fix known problems, but for some CPUs it is not
455 possible to determine what the correct size should be.
456 This option provides an override for these situations.
458 ca_keys= [KEYS] This parameter identifies a specific key(s) on
459 the system trusted keyring to be used for certificate
461 format: { id:<keyid> | builtin }
463 cca= [MIPS] Override the kernel pages' cache coherency
464 algorithm. Accepted values range from 0 to 7
465 inclusive. See arch/mips/include/asm/pgtable-bits.h
466 for platform specific values (SB1, Loongson3 and
469 ccw_timeout_log [S390]
470 See Documentation/s390/CommonIO for details.
472 cgroup_disable= [KNL] Disable a particular controller
473 Format: {name of the controller(s) to disable}
474 The effects of cgroup_disable=foo are:
475 - foo isn't auto-mounted if you mount all cgroups in
477 - foo isn't visible as an individually mountable
479 {Currently only "memory" controller deal with this and
480 cut the overhead, others just disable the usage. So
481 only cgroup_disable=memory is actually worthy}
483 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
484 Format: { controller[,controller...] | "all" }
485 Like cgroup_disable, but only applies to cgroup v1;
486 the blacklisted controllers remain available in cgroup2.
488 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
490 nosocket -- Disable socket memory accounting.
491 nokmem -- Disable kernel memory accounting.
493 checkreqprot [SELINUX] Set initial checkreqprot flag value.
494 Format: { "0" | "1" }
495 See security/selinux/Kconfig help text.
496 0 -- check protection applied by kernel (includes
497 any implied execute protection).
498 1 -- check protection requested by application.
499 Default value is set via a kernel config option.
500 Value can be changed at runtime via
501 /selinux/checkreqprot.
504 See Documentation/s390/CommonIO for details.
507 Prevents the clock framework from automatically gating
508 clocks that have not been explicitly enabled by a Linux
509 device driver but are enabled in hardware at reset or
510 by the bootloader/firmware. Note that this does not
511 force such clocks to be always-on nor does it reserve
512 those clocks in any way. This parameter is useful for
513 debug and development, but should not be needed on a
514 platform with proper driver support. For more
515 information, see Documentation/clk.txt.
517 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
519 Forces specified clocksource (if available) to be used
520 when calculating gettimeofday(). If specified
521 clocksource is not available, it defaults to PIT.
522 Format: { pit | tsc | cyclone | pmtmr }
524 clocksource= Override the default clocksource
526 Override the default clocksource and use the clocksource
527 with the name specified.
528 Some clocksource names to choose from, depending on
530 [all] jiffies (this is the base, fallback clocksource)
532 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
533 pxa_timer,timer3,32k_counter,timer0_1
535 [X86-32] pit,hpet,tsc;
536 scx200_hrt on Geode; cyclone on IBM x440
544 clocksource.arm_arch_timer.evtstrm=
547 Enable/disable the eventstream feature of the ARM
548 architected timer so that code using WFE-based polling
549 loops can be debugged more effectively on production
552 clearcpuid=BITNUM [X86]
553 Disable CPUID feature X for the kernel. See
554 arch/x86/include/asm/cpufeatures.h for the valid bit
555 numbers. Note the Linux specific bits are not necessarily
556 stable over kernel options, but the vendor specific
558 Also note that user programs calling CPUID directly
559 or using the feature without checking anything
560 will still see it. This just prevents it from
561 being used by the kernel or shown in /proc/cpuinfo.
562 Also note the kernel might malfunction if you disable
565 cma=nn[MG]@[start[MG][-end[MG]]]
567 Sets the size of kernel global memory area for
568 contiguous memory allocations and optionally the
569 placement constraint by the physical address range of
570 memory allocations. A value of 0 disables CMA
571 altogether. For more information, see
572 include/linux/dma-contiguous.h
574 cmo_free_hint= [PPC] Format: { yes | no }
575 Specify whether pages are marked as being inactive
576 when they are freed. This is used in CMO environments
577 to determine OS memory pressure for page stealing by
581 coherent_pool=nn[KMG] [ARM,KNL]
582 Sets the size of memory pool for coherent, atomic dma
583 allocations, by default set to 256K.
585 code_bytes [X86] How many bytes of object code to print
590 com20020= [HW,NET] ARCnet - COM20020 chipset
592 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
594 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
598 ARCnet - COM90xx chipset (memory-mapped buffers)
599 Format: <io>[,<irq>[,<memstart>]]
601 condev= [HW,S390] console device
604 console= [KNL] Output console device and options.
606 tty<n> Use the virtual console device <n>.
610 Use the specified serial port. The options are of
611 the form "bbbbpnf", where "bbbb" is the baud rate,
612 "p" is parity ("n", "o", or "e"), "n" is number of
613 bits, and "f" is flow control ("r" for RTS or
614 omit it). Default is "9600n8".
616 See Documentation/admin-guide/serial-console.rst for more
618 Documentation/networking/netconsole.txt for an
621 uart[8250],io,<addr>[,options]
622 uart[8250],mmio,<addr>[,options]
623 uart[8250],mmio16,<addr>[,options]
624 uart[8250],mmio32,<addr>[,options]
625 uart[8250],0x<addr>[,options]
626 Start an early, polled-mode console on the 8250/16550
627 UART at the specified I/O port or MMIO address,
628 switching to the matching ttyS device later.
629 MMIO inter-register address stride is either 8-bit
630 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
631 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
632 to be equivalent to 'mmio'. 'options' are specified in
633 the same format described for ttyS above; if unspecified,
634 the h/w is not re-initialized.
636 hvc<n> Use the hypervisor console device <n>. This is for
637 both Xen and PowerPC hypervisors.
639 If the device connected to the port is not a TTY but a braille
640 device, prepend "brl," before the device type, for instance
642 For now, only VisioBraille is supported.
644 consoleblank= [KNL] The console blank (screen saver) timeout in
645 seconds. Defaults to 10*60 = 10mins. A value of 0
646 disables the blank timer.
649 [KNL] Change the default value for
650 /proc/<pid>/coredump_filter.
651 See also Documentation/filesystems/proc.txt.
653 cpuidle.off=1 [CPU_IDLE]
654 disable the cpuidle sub-system
657 [X86] Delay for N microsec between assert and de-assert
658 of APIC INIT to start processors. This delay occurs
659 on every CPU online, such as boot, and resume from suspend.
662 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
664 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
666 crashkernel=size[KMG][@offset[KMG]]
667 [KNL] Using kexec, Linux can switch to a 'crash kernel'
668 upon panic. This parameter reserves the physical
669 memory region [offset, offset + size] for that kernel
670 image. If '@offset' is omitted, then a suitable offset
671 is selected automatically. Check
672 Documentation/kdump/kdump.txt for further details.
674 crashkernel=range1:size1[,range2:size2,...][@offset]
675 [KNL] Same as above, but depends on the memory
676 in the running system. The syntax of range is
677 start-[end] where start and end are both
678 a memory unit (amount[KMG]). See also
679 Documentation/kdump/kdump.txt for an example.
681 crashkernel=size[KMG],high
682 [KNL, x86_64] range could be above 4G. Allow kernel
683 to allocate physical memory region from top, so could
684 be above 4G if system have more than 4G ram installed.
685 Otherwise memory region will be allocated below 4G, if
687 It will be ignored if crashkernel=X is specified.
688 crashkernel=size[KMG],low
689 [KNL, x86_64] range under 4G. When crashkernel=X,high
690 is passed, kernel could allocate physical memory region
691 above 4G, that cause second kernel crash on system
692 that require some amount of low memory, e.g. swiotlb
693 requires at least 64M+32K low memory, also enough extra
694 low memory is needed to make sure DMA buffers for 32-bit
695 devices won't run out. Kernel would try to allocate at
696 at least 256M below 4G automatically.
697 This one let user to specify own low range under 4G
698 for second kernel instead.
699 0: to disable low allocation.
700 It will be ignored when crashkernel=X,high is not used
701 or memory reserved is below 4G.
704 [KNL] Disable crypto self-tests
709 cs89x0_media= [HW,NET]
710 Format: { rj45 | aui | bnc }
713 See header of drivers/s390/block/dasd_devmap.c.
715 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
716 (one device per port)
717 Format: <port#>,<type>
718 See also Documentation/input/joystick-parport.txt
720 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
721 time. See Documentation/dynamic-debug-howto.txt for
722 details. Deprecated, see dyndbg.
724 debug [KNL] Enable kernel debugging (events log level).
727 [KNL] verbose self-tests
729 Print debugging info while doing the locking API
731 We default to 0 (no extra messages), setting it to
732 1 will print _a lot_ more information - normally
733 only useful to kernel developers.
735 debug_objects [KNL] Enable object debugging
738 [KNL] Disable object debugging
740 debug_guardpage_minorder=
741 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
742 parameter allows control of the order of pages that will
743 be intentionally kept free (and hence protected) by the
744 buddy allocator. Bigger value increase the probability
745 of catching random memory corruption, but reduce the
746 amount of memory for normal system use. The maximum
747 possible value is MAX_ORDER/2. Setting this parameter
748 to 1 or 2 should be enough to identify most random
749 memory corruption problems caused by bugs in kernel or
750 driver code when a CPU writes to (or reads from) a
751 random memory location. Note that there exists a class
752 of memory corruptions problems caused by buggy H/W or
753 F/W or by drivers badly programing DMA (basically when
754 memory is written at bus level and the CPU MMU is
755 bypassed) which are not detectable by
756 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
757 tracking down these problems.
760 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
761 parameter enables the feature at boot time. In
762 default, it is disabled. We can avoid allocating huge
763 chunk of memory for debug pagealloc if we don't enable
764 it at boot time and the system will work mostly same
765 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
766 on: enable the feature
768 debugpat [X86] Enable PAT debugging
770 decnet.addr= [HW,NET]
771 Format: <area>[,<node>]
772 See also Documentation/networking/decnet.txt.
775 [same as hugepagesz=] The size of the default
776 HugeTLB page size. This is the size represented by
777 the legacy /proc/ hugepages APIs, used for SHM, and
778 default size when mounting hugetlbfs filesystems.
779 Defaults to the default architecture's huge page size
783 Set number of hash buckets for dentry cache.
785 disable_1tb_segments [PPC]
786 Disables the use of 1TB hash page table segments. This
787 causes the kernel to fall back to 256MB segments which
788 can be useful when debugging issues that require an SLB
792 See Documentation/networking/ipv6.txt.
795 Disable RADIX MMU mode on POWER9
797 disable_cpu_apicid= [X86,APIC,SMP]
799 The number of initial APIC ID for the
800 corresponding CPU to be disabled at boot,
801 mostly used for the kdump 2nd kernel to
802 disable BSP to wake up multiple CPUs without
803 causing system reset or hang due to sending
806 disable_ddw [PPC/PSERIES]
807 Disable Dynamic DMA Window support. Use this if
808 to workaround buggy firmware.
811 See Documentation/networking/ipv6.txt.
813 disable_mtrr_cleanup [X86]
814 The kernel tries to adjust MTRR layout from continuous
815 to discrete, to make X server driver able to add WB
816 entry later. This parameter disables that.
818 disable_mtrr_trim [X86, Intel and AMD only]
819 By default the kernel will trim any uncacheable
820 memory out of your available memory pool based on
821 MTRR settings. This parameter disables that behavior,
822 possibly causing your machine to run very slowly.
824 disable_timer_pin_1 [X86]
825 Disable PIN 1 of APIC timer
826 Can be useful to work around chipset bugs.
828 dis_ucode_ldr [X86] Disable the microcode loader.
830 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
831 this option disables the debugging code at boot.
833 dma_debug_entries=<number>
834 This option allows to tune the number of preallocated
835 entries for DMA-API debugging code. One entry is
836 required per DMA-API allocation. Use this if the
837 DMA-API debugging code disables itself because the
838 architectural default is too low.
840 dma_debug_driver=<driver_name>
841 With this option the DMA-API debugging driver
842 filter feature can be enabled at boot time. Just
843 pass the driver to filter for as the parameter.
844 The filter can be disabled or changed to another
845 driver later using sysfs.
847 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
848 Broken monitors, graphic adapters, KVMs and EDIDless
849 panels may send no or incorrect EDID data sets.
850 This parameter allows to specify an EDID data sets
851 in the /lib/firmware directory that are used instead.
852 Generic built-in EDID data sets are used, if one of
853 edid/1024x768.bin, edid/1280x1024.bin,
854 edid/1680x1050.bin, or edid/1920x1080.bin is given
855 and no file with the same name exists. Details and
856 instructions how to build your own EDID data are
857 available in Documentation/EDID/HOWTO.txt. An EDID
858 data set will only be used for a particular connector,
859 if its name and a colon are prepended to the EDID
860 name. Each connector may use a unique EDID data
861 set by separating the files with a comma. An EDID
862 data set with no connector name will be used for
863 any connectors not explicitly specified.
867 dump_apple_properties [X86]
868 Dump name and content of EFI device properties on
869 x86 Macs. Useful for driver authors to determine
870 what data is available or for reverse-engineering.
872 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
873 module.dyndbg[="val"]
874 Enable debug messages at boot time. See
875 Documentation/dynamic-debug-howto.txt for details.
877 nompx [X86] Disables Intel Memory Protection Extensions.
878 See Documentation/x86/intel_mpx.txt for more
879 information about the feature.
881 nopku [X86] Disable Memory Protection Keys CPU feature found
884 module.async_probe [KNL]
885 Enable asynchronous probe on this module.
887 early_ioremap_debug [KNL]
888 Enable debug messages in early_ioremap support. This
889 is useful for tracking down temporary early mappings
890 which are not unmapped.
892 earlycon= [KNL] Output early console device and options.
894 When used with no options, the early console is
895 determined by the stdout-path property in device
898 cdns,<addr>[,options]
899 Start an early, polled-mode console on a Cadence
900 (xuartps) serial port at the specified address. Only
901 supported option is baud rate. If baud rate is not
902 specified, the serial port must already be setup and
905 uart[8250],io,<addr>[,options]
906 uart[8250],mmio,<addr>[,options]
907 uart[8250],mmio32,<addr>[,options]
908 uart[8250],mmio32be,<addr>[,options]
909 uart[8250],0x<addr>[,options]
910 Start an early, polled-mode console on the 8250/16550
911 UART at the specified I/O port or MMIO address.
912 MMIO inter-register address stride is either 8-bit
913 (mmio) or 32-bit (mmio32 or mmio32be).
914 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
915 to be equivalent to 'mmio'. 'options' are specified
916 in the same format described for "console=ttyS<n>"; if
917 unspecified, the h/w is not initialized.
921 Start an early, polled-mode console on a pl011 serial
922 port at the specified address. The pl011 serial port
923 must already be setup and configured. Options are not
924 yet supported. If 'mmio32' is specified, then only
925 the driver will use only 32-bit accessors to read/write
926 the device registers.
929 Start an early, polled-mode console on a meson serial
930 port at the specified address. The serial port must
931 already be setup and configured. Options are not yet
935 Start an early, polled-mode console on an msm serial
936 port at the specified address. The serial port
937 must already be setup and configured. Options are not
941 Start an early, polled-mode console on an msm serial
942 dm port at the specified address. The serial port
943 must already be setup and configured. Options are not
946 smh Use ARM semihosting calls for early console.
954 Use early console provided by serial driver available
955 on Samsung SoCs, requires selecting proper type and
956 a correct base address of the selected UART port. The
957 serial port must already be setup and configured.
958 Options are not yet supported.
962 Use early console provided by Freescale LP UART driver
963 found on Freescale Vybrid and QorIQ LS1021A processors.
964 A valid base address must be provided, and the serial
965 port must already be setup and configured.
967 armada3700_uart,<addr>
968 Start an early, polled-mode console on the
969 Armada 3700 serial port at the specified
970 address. The serial port must already be setup
971 and configured. Options are not yet supported.
973 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
978 earlyprintk=serial[,ttySn[,baudrate]]
979 earlyprintk=serial[,0x...[,baudrate]]
980 earlyprintk=ttySn[,baudrate]
981 earlyprintk=dbgp[debugController#]
982 earlyprintk=pciserial,bus:device.function[,baudrate]
984 earlyprintk is useful when the kernel crashes before
985 the normal console is initialized. It is not enabled by
986 default because it has some cosmetic problems.
988 Append ",keep" to not disable it when the real console
991 Only one of vga, efi, serial, or usb debug port can
994 Currently only ttyS0 and ttyS1 may be specified by
995 name. Other I/O ports may be explicitly specified
996 on some architectures (x86 and arm at least) by
997 replacing ttySn with an I/O port address, like this:
998 earlyprintk=serial,0x1008,115200
999 You can find the port for a given device in
1000 /proc/tty/driver/serial:
1001 2: uart:ST16650V2 port:00001008 irq:18 ...
1003 Interaction with the standard serial driver is not
1006 The VGA and EFI output is eventually overwritten by
1009 The xen output can only be used by Xen PV guests.
1011 The sclp output can only be used on s390.
1013 edac_report= [HW,EDAC] Control how to report EDAC event
1014 Format: {"on" | "off" | "force"}
1015 on: enable EDAC to report H/W event. May be overridden
1016 by other higher priority error reporting module.
1017 off: disable H/W event reporting through EDAC.
1018 force: enforce the use of EDAC to report H/W event.
1021 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1024 This is designed to be used in conjunction with
1025 the boot argument: earlyprintk=vga
1028 Format: {"off" | "on" | "skip[mbr]"}
1031 Format: { "old_map", "nochunk", "noruntime", "debug" }
1032 old_map [X86-64]: switch to the old ioremap-based EFI
1033 runtime services mapping. 32-bit still uses this one by
1035 nochunk: disable reading files in "chunks" in the EFI
1036 boot stub, as chunking can cause problems with some
1037 firmware implementations.
1038 noruntime : disable EFI runtime services support
1039 debug: enable misc debug output
1041 efi_no_storage_paranoia [EFI; X86]
1042 Using this parameter you can use more than 50% of
1043 your efi variable storage. Use this parameter only if
1044 you are really sure that your UEFI does sane gc and
1045 fulfills the spec otherwise your board may brick.
1047 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1048 Add arbitrary attribute to specific memory range by
1049 updating original EFI memory map.
1050 Region of memory which aa attribute is added to is
1052 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1053 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1054 attribute is added to range 0x100000000-0x180000000 and
1055 0x10a0000000-0x1120000000.
1057 Using this parameter you can do debugging of EFI memmap
1058 related feature. For example, you can do debugging of
1059 Address Range Mirroring feature even if your box
1062 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1063 that is to be dynamically loaded by Linux. If there are
1064 multiple variables with the same name but with different
1065 vendor GUIDs, all of them will be loaded. See
1066 Documentation/acpi/ssdt-overlays.txt for details.
1069 eisa_irq_edge= [PARISC,HW]
1070 See header of drivers/parisc/eisa.c.
1073 See comment before function elanfreq_setup() in
1074 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1077 Format: {"cfq" | "deadline" | "noop"}
1078 See Documentation/block/cfq-iosched.txt and
1079 Documentation/block/deadline-iosched.txt for details.
1081 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1082 Specifies physical address of start of kernel core
1083 image elf header and optionally the size. Generally
1084 kexec loader will pass this option to capture kernel.
1085 See Documentation/kdump/kdump.txt for details.
1087 enable_mtrr_cleanup [X86]
1088 The kernel tries to adjust MTRR layout from continuous
1089 to discrete, to make X server driver able to add WB
1090 entry later. This parameter enables that.
1092 enable_timer_pin_1 [X86]
1093 Enable PIN 1 of APIC timer
1094 Can be useful to work around chipset bugs
1095 (in particular on some ATI chipsets).
1096 The kernel tries to set a reasonable default.
1098 enforcing [SELINUX] Set initial enforcing status.
1100 See security/selinux/Kconfig help text.
1101 0 -- permissive (log only, no denials).
1102 1 -- enforcing (deny and log).
1104 Value can be changed at runtime via /selinux/enforce.
1107 Disable Error Record Serialization Table (ERST)
1110 ether= [HW,NET] Ethernet cards parameters
1111 This option is obsoleted by the "netdev=" option, which
1112 has equivalent usage. See its documentation for details.
1116 Permit 'security.evm' to be updated regardless of
1117 current integrity status.
1121 fail_make_request=[KNL]
1122 General fault injection mechanism.
1123 Format: <interval>,<probability>,<space>,<times>
1124 See also Documentation/fault-injection/.
1127 See Documentation/blockdev/floppy.txt.
1129 force_pal_cache_flush
1130 [IA-64] Avoid check_sal_cache_flush which may hang on
1131 buggy SAL_CACHE_FLUSH implementations. Using this
1132 parameter will force ia64_sal_cache_flush to call
1133 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1136 Forcefully enable Physical Address Extension (PAE).
1137 Many Pentium M systems disable PAE but may have a
1138 functionally usable PAE implementation.
1139 Warning: use of this parameter will taint the kernel
1140 and may cause unknown problems.
1143 [FTRACE] will set and start the specified tracer
1144 as early as possible in order to facilitate early
1147 ftrace_dump_on_oops[=orig_cpu]
1148 [FTRACE] will dump the trace buffers on oops.
1149 If no parameter is passed, ftrace will dump
1150 buffers of all CPUs, but if you pass orig_cpu, it will
1151 dump only the buffer of the CPU that triggered the
1154 ftrace_filter=[function-list]
1155 [FTRACE] Limit the functions traced by the function
1156 tracer at boot up. function-list is a comma separated
1157 list of functions. This list can be changed at run
1158 time by the set_ftrace_filter file in the debugfs
1161 ftrace_notrace=[function-list]
1162 [FTRACE] Do not trace the functions specified in
1163 function-list. This list can be changed at run time
1164 by the set_ftrace_notrace file in the debugfs
1167 ftrace_graph_filter=[function-list]
1168 [FTRACE] Limit the top level callers functions traced
1169 by the function graph tracer at boot up.
1170 function-list is a comma separated list of functions
1171 that can be changed at run time by the
1172 set_graph_function file in the debugfs tracing directory.
1174 ftrace_graph_notrace=[function-list]
1175 [FTRACE] Do not trace from the functions specified in
1176 function-list. This list is a comma separated list of
1177 functions that can be changed at run time by the
1178 set_graph_notrace file in the debugfs tracing directory.
1181 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1182 support via parallel port (up to 5 devices per port)
1183 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1184 See also Documentation/input/joystick-parport.txt
1188 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1192 gcov_persist= [GCOV] When non-zero (default), profiling data for
1193 kernel modules is saved and remains accessible via
1194 debugfs, even when the module is unloaded/reloaded.
1195 When zero, profiling data is discarded and associated
1196 debugfs files are removed at module unload time.
1198 gpt [EFI] Forces disk with valid GPT signature but
1199 invalid Protective MBR to be treated as GPT. If the
1200 primary GPT is corrupted, it enables the backup/alternate
1201 GPT to be used instead.
1203 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1204 the "Enable 0" bit of the configuration register.
1207 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1208 the "Enable 0" bit of the configuration register.
1211 grcan.select= [HW] Select which physical interface to use.
1214 grcan.txsize= [HW] Sets the size of the tx buffer.
1215 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1217 grcan.rxsize= [HW] Sets the size of the rx buffer.
1218 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1221 gpio-mockup.gpio_mockup_ranges
1222 [HW] Sets the ranges of gpiochip of for this device.
1223 Format: <start1>,<end1>,<start2>,<end2>...
1225 hardlockup_all_cpu_backtrace=
1226 [KNL] Should the hard-lockup detector generate
1227 backtraces on all cpus.
1230 hashdist= [KNL,NUMA] Large hashes allocated during boot
1231 are distributed across NUMA nodes. Defaults on
1232 for 64-bit NUMA, off otherwise.
1233 Format: 0 | 1 (for off | on)
1235 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1237 hd= [EIDE] (E)IDE hard drive subsystem geometry
1238 Format: <cyl>,<head>,<sect>
1241 Disable Hardware Error Source Table (HEST) support;
1242 corresponding firmware-first mode error processing
1243 logic will be disabled.
1245 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1246 size of <nn>. This works even on boxes that have no
1247 highmem otherwise. This also works to reduce highmem
1248 size on bigger boxes.
1250 highres= [KNL] Enable/disable high resolution timer mode.
1251 Valid parameters: "on", "off"
1255 See Documentation/isdn/README.HiSax.
1259 hpet= [X86-32,HPET] option to control HPET usage
1260 Format: { enable (default) | disable | force |
1262 disable: disable HPET and use PIT instead
1263 force: allow force enabled of undocumented chips (ICH4,
1265 verbose: show contents of HPET registers during setup
1267 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1268 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1270 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1271 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1272 On x86-64 and powerpc, this option can be specified
1273 multiple times interleaved with hugepages= to reserve
1274 huge pages of different sizes. Valid pages sizes on
1275 x86-64 are 2M (when the CPU supports "pse") and 1G
1276 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1278 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1279 terminal devices. Valid values: 0..8
1280 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1281 If specified, z/VM IUCV HVC accepts connections
1282 from listed z/VM user IDs only.
1284 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1285 hardware thread id mappings.
1286 Format: <cpu>:<hwthread>
1289 Do not unregister boot console at start. This is only
1290 useful for debugging when something happens in the window
1291 between unregistering the boot console and initializing
1294 i2c_bus= [HW] Override the default board specific I2C bus speed
1295 or register an additional I2C bus that is not
1296 registered from board initialization code.
1300 i8042.debug [HW] Toggle i8042 debug mode
1301 i8042.unmask_kbd_data
1302 [HW] Enable printing of interrupt data from the KBD port
1303 (disabled by default, and as a pre-condition
1304 requires that i8042.debug=1 be enabled)
1305 i8042.direct [HW] Put keyboard port into non-translated mode
1306 i8042.dumbkbd [HW] Pretend that controller can only read data from
1307 keyboard and cannot control its state
1308 (Don't attempt to blink the leds)
1309 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1310 i8042.nokbd [HW] Don't check/create keyboard port
1311 i8042.noloop [HW] Disable the AUX Loopback command while probing
1313 i8042.nomux [HW] Don't check presence of an active multiplexing
1315 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1317 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1318 i8042.reset [HW] Reset the controller during init, cleanup and
1319 suspend-to-ram transitions, only during s2r
1320 transitions, or never reset
1321 Format: { 1 | Y | y | 0 | N | n }
1322 1, Y, y: always reset controller
1323 0, N, n: don't ever reset controller
1324 Default: only on s2r transitions on x86; most other
1325 architectures force reset to be always executed
1326 i8042.unlock [HW] Unlock (ignore) the keylock
1327 i8042.kbdreset [HW] Reset device connected to KBD port
1331 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1332 indicates that the driver is running on unsupported
1334 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1335 does not match list of supported models.
1337 [HW] Report power status in /proc/i8k
1338 (disabled by default)
1339 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1342 i915.invert_brightness=
1343 [DRM] Invert the sense of the variable that is used to
1344 set the brightness of the panel backlight. Normally a
1345 brightness value of 0 indicates backlight switched off,
1346 and the maximum of the brightness value sets the backlight
1347 to maximum brightness. If this parameter is set to 0
1348 (default) and the machine requires it, or this parameter
1349 is set to 1, a brightness value of 0 sets the backlight
1350 to maximum brightness, and the maximum of the brightness
1351 value switches the backlight off.
1352 -1 -- never invert brightness
1353 0 -- machine default
1354 1 -- force brightness inversion
1357 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1359 ide-core.nodma= [HW] (E)IDE subsystem
1360 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1361 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1362 .cdrom .chs .ignore_cable are additional options
1363 See Documentation/ide/ide.txt.
1365 ide-generic.probe-mask= [HW] (E)IDE subsystem
1367 Probe mask for legacy ISA IDE ports. Depending on
1368 platform up to 6 ports are supported, enabled by
1369 setting corresponding bits in the mask to 1. The
1370 default value is 0x0, which has a special meaning.
1371 On systems that have PCI, it triggers scanning the
1372 PCI bus for the first and the second port, which
1373 are then probed. On systems without PCI the value
1374 of 0x0 enables probing the two first ports as if it
1377 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1378 Claim all unknown PCI IDE storage controllers.
1381 Format: idle=poll, idle=halt, idle=nomwait
1382 Poll forces a polling idle loop that can slightly
1383 improve the performance of waking up a idle CPU, but
1384 will use a lot of power and make the system run hot.
1386 idle=halt: Halt is forced to be used for CPU idle.
1387 In such case C2/C3 won't be used again.
1388 idle=nomwait: Disable mwait for CPU C-states
1390 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1391 Format: { strict | legacy | 2008 | relaxed }
1394 Choose which programs will be accepted for execution
1395 based on the IEEE 754 NaN encoding(s) supported by
1396 the FPU and the NaN encoding requested with the value
1397 of an ELF file header flag individually set by each
1398 binary. Hardware implementations are permitted to
1399 support either or both of the legacy and the 2008 NaN
1402 Available settings are as follows:
1403 strict accept binaries that request a NaN encoding
1404 supported by the FPU
1405 legacy only accept legacy-NaN binaries, if supported
1407 2008 only accept 2008-NaN binaries, if supported
1409 relaxed accept any binaries regardless of whether
1410 supported by the FPU
1412 The FPU emulator is always able to support both NaN
1413 encodings, so if no FPU hardware is present or it has
1414 been disabled with 'nofpu', then the settings of
1415 'legacy' and '2008' strap the emulator accordingly,
1416 'relaxed' straps the emulator for both legacy-NaN and
1417 2008-NaN, whereas 'strict' enables legacy-NaN only on
1418 legacy processors and both NaN encodings on MIPS32 or
1421 The setting for ABS.fmt/NEG.fmt instruction execution
1422 mode generally follows that for the NaN encoding,
1423 except where unsupported by hardware.
1425 ignore_loglevel [KNL]
1426 Ignore loglevel setting - this will print /all/
1427 kernel messages to the console. Useful for debugging.
1428 We also add it as printk module parameter, so users
1429 could change it dynamically, usually by
1430 /sys/module/printk/parameters/ignore_loglevel.
1433 Ignore RLIMIT_DATA setting for data mappings,
1434 print warning at first misuse. Can be changed via
1435 /sys/module/kernel/parameters/ignore_rlimit_data.
1437 ihash_entries= [KNL]
1438 Set number of hash buckets for inode cache.
1440 ima_appraise= [IMA] appraise integrity measurements
1441 Format: { "off" | "enforce" | "fix" | "log" }
1444 ima_appraise_tcb [IMA]
1445 The builtin appraise policy appraises all files
1448 ima_canonical_fmt [IMA]
1449 Use the canonical format for the binary runtime
1450 measurements, instead of host native format.
1453 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1457 The list of supported hash algorithms is defined
1458 in crypto/hash_info.h.
1461 The builtin measurement policy to load during IMA
1462 setup. Specyfing "tcb" as the value, measures all
1463 programs exec'd, files mmap'd for exec, and all files
1464 opened with the read mode bit set by either the
1465 effective uid (euid=0) or uid=0.
1468 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1469 Load a policy which meets the needs of the Trusted
1470 Computing Base. This means IMA will measure all
1471 programs exec'd, files mmap'd for exec, and all files
1472 opened for read by uid=0.
1475 Select one of defined IMA measurements template formats.
1476 Formats: { "ima" | "ima-ng" | "ima-sig" }
1480 [IMA] Define a custom template format.
1481 Format: { "field1|...|fieldN" }
1483 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1484 Format: <min_file_size>
1485 Set the minimal file size for using asynchronous hash.
1486 If left unspecified, ahash usage is disabled.
1488 ahash performance varies for different data sizes on
1489 different crypto accelerators. This option can be used
1490 to achieve the best performance for a particular HW.
1492 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1494 Set hashing buffer size. Default: 4k.
1496 ahash performance varies for different chunk sizes on
1497 different crypto accelerators. This option can be used
1498 to achieve best performance for particular HW.
1502 Run specified binary instead of /sbin/init as init
1505 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1506 for working out where the kernel is dying during
1509 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1510 initcall functions. Useful for debugging built-in
1511 modules and initcalls.
1513 initrd= [BOOT] Specify the location of the initial ramdisk
1515 init_pkru= [x86] Specify the default memory protection keys rights
1516 register contents for all processes. 0x55555554 by
1517 default (disallow access to all but pkey 0). Can
1518 override in debugfs after boot.
1520 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1523 int_pln_enable [x86] Enable power limit notification interrupt
1525 integrity_audit=[IMA]
1526 Format: { "0" | "1" }
1527 0 -- basic integrity auditing messages. (Default)
1528 1 -- additional integrity auditing messages.
1530 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1532 Enable intel iommu driver.
1534 Disable intel iommu driver.
1535 igfx_off [Default Off]
1536 By default, gfx is mapped as normal device. If a gfx
1537 device has a dedicated DMAR unit, the DMAR unit is
1538 bypassed by not enabling DMAR with this option. In
1539 this case, gfx device will use physical address for
1542 With this option iommu will not optimize to look
1543 for io virtual address below 32-bit forcing dual
1544 address cycle on pci bus for cards supporting greater
1545 than 32-bit addressing. The default is to look
1546 for translation below 32-bit and if not available
1547 then look in the higher range.
1548 strict [Default Off]
1549 With this option on every unmap_single operation will
1550 result in a hardware IOTLB flush operation as opposed
1551 to batching them for performance.
1552 sp_off [Default Off]
1553 By default, super page will be supported if Intel IOMMU
1554 has the capability. With this option, super page will
1556 ecs_off [Default Off]
1557 By default, extended context tables will be supported if
1558 the hardware advertises that it has support both for the
1559 extended tables themselves, and also PASID support. With
1560 this option set, extended tables will not be used even
1561 on hardware which claims to support them.
1563 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1564 0 disables intel_idle and fall back on acpi_idle.
1565 1 to 9 specify maximum depth of C-state.
1569 Do not enable intel_pstate as the default
1570 scaling driver for the supported processors
1572 Use intel_pstate as a scaling driver, but configure it
1573 to work with generic cpufreq governors (instead of
1574 enabling its internal governor). This mode cannot be
1575 used along with the hardware-managed P-states (HWP)
1578 Enable intel_pstate on systems that prohibit it by default
1579 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1580 instead of acpi-cpufreq may disable platform features, such
1581 as thermal controls and power capping, that rely on ACPI
1582 P-States information being indicated to OSPM and therefore
1583 should be used with caution. This option does not work with
1584 processors that aren't supported by the intel_pstate driver
1585 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1587 Do not enable hardware P state control (HWP)
1590 Only load intel_pstate on systems which support
1591 hardware P state control (HWP) if available.
1593 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1594 Description Table, specifies preferred power management
1595 profile as "Enterprise Server" or "Performance Server",
1596 then this feature is turned on by default.
1598 Allow per-logical-CPU P-State performance control limits using
1599 cpufreq sysfs interface
1601 intremap= [X86-64, Intel-IOMMU]
1602 on enable Interrupt Remapping (default)
1603 off disable Interrupt Remapping
1604 nosid disable Source ID checking
1606 BIOS x2APIC opt-out request will be ignored
1607 nopost disable Interrupt Posting
1609 iomem= Disable strict checking of access to MMIO memory
1610 strict regions from userspace.
1625 nobypass [PPC/POWERNV]
1626 Disable IOMMU bypass, using IOMMU for PCI devices.
1629 io7= [HW] IO7 for Marvel based alpha systems
1630 See comment before marvel_specify_io7 in
1631 arch/alpha/kernel/core_marvel.c.
1633 io_delay= [X86] I/O delay method
1635 Standard port 0x80 based delay
1637 Alternate port 0xed based delay (needed on some systems)
1639 Simple two microseconds delay
1644 See Documentation/filesystems/nfs/nfsroot.txt.
1646 irqaffinity= [SMP] Set the default irq affinity mask
1647 The argument is a cpu list, as described above.
1650 When an interrupt is not handled search all handlers
1651 for it. Intended to get systems with badly broken
1655 When an interrupt is not handled search all handlers
1656 for it. Also check all handlers each timer
1657 interrupt. Intended to get systems with badly broken
1661 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1663 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1664 The argument is a cpu list, as described above.
1666 This option can be used to specify one or more CPUs
1667 to isolate from the general SMP balancing and scheduling
1668 algorithms. You can move a process onto or off an
1669 "isolated" CPU via the CPU affinity syscalls or cpuset.
1670 <cpu number> begins at 0 and the maximum value is
1671 "number of CPUs in system - 1".
1673 This option is the preferred way to isolate CPUs. The
1674 alternative -- manually setting the CPU mask of all
1675 tasks in the system -- can cause problems and
1676 suboptimal load balancer performance.
1680 ivrs_ioapic [HW,X86_64]
1681 Provide an override to the IOAPIC-ID<->DEVICE-ID
1682 mapping provided in the IVRS ACPI table. For
1683 example, to map IOAPIC-ID decimal 10 to
1684 PCI device 00:14.0 write the parameter as:
1685 ivrs_ioapic[10]=00:14.0
1687 ivrs_hpet [HW,X86_64]
1688 Provide an override to the HPET-ID<->DEVICE-ID
1689 mapping provided in the IVRS ACPI table. For
1690 example, to map HPET-ID decimal 0 to
1691 PCI device 00:14.0 write the parameter as:
1692 ivrs_hpet[0]=00:14.0
1694 ivrs_acpihid [HW,X86_64]
1695 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1696 mapping provided in the IVRS ACPI table. For
1697 example, to map UART-HID:UID AMD0020:0 to
1698 PCI device 00:14.5 write the parameter as:
1699 ivrs_acpihid[00:14.5]=AMD0020:0
1701 js= [HW,JOY] Analog joystick
1702 See Documentation/input/joystick.txt.
1705 When CONFIG_RANDOMIZE_BASE is set, this disables
1706 kernel and module base offset ASLR (Address Space
1707 Layout Randomization).
1711 kernelcore= [KNL,X86,IA-64,PPC]
1712 Format: nn[KMGTPE] | "mirror"
1714 specifies the amount of memory usable by the kernel
1715 for non-movable allocations. The requested amount is
1716 spread evenly throughout all nodes in the system. The
1717 remaining memory in each node is used for Movable
1718 pages. In the event, a node is too small to have both
1719 kernelcore and Movable pages, kernelcore pages will
1720 take priority and other nodes will have a larger number
1721 of Movable pages. The Movable zone is used for the
1722 allocation of pages that may be reclaimed or moved
1723 by the page migration subsystem. This means that
1724 HugeTLB pages may not be allocated from this zone.
1725 Note that allocations like PTEs-from-HighMem still
1726 use the HighMem zone if it exists, and the Normal
1727 zone if it does not.
1729 Instead of specifying the amount of memory (nn[KMGTPE]),
1730 you can specify "mirror" option. In case "mirror"
1731 option is specified, mirrored (reliable) memory is used
1732 for non-movable allocations and remaining memory is used
1733 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1734 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1737 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1738 Format: <Controller#>[,poll interval]
1739 The controller # is the number of the ehci usb debug
1740 port as it is probed via PCI. The poll interval is
1741 optional and is the number seconds in between
1742 each poll cycle to the debug port in case you need
1743 the functionality for interrupting the kernel with
1744 gdb or control-c on the dbgp connection. When
1745 not using this parameter you use sysrq-g to break into
1746 the kernel debugger.
1748 kgdboc= [KGDB,HW] kgdb over consoles.
1749 Requires a tty driver that supports console polling,
1750 or a supported polling keyboard driver (non-usb).
1751 Serial only format: <serial_device>[,baud]
1752 keyboard only format: kbd
1753 keyboard and serial format: kbd,<serial_device>[,baud]
1754 Optional Kernel mode setting:
1755 kms, kbd format: kms,kbd
1756 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1758 kgdbwait [KGDB] Stop kernel execution and enter the
1759 kernel debugger at the earliest opportunity.
1761 kmac= [MIPS] korina ethernet MAC address.
1762 Configure the RouterBoard 532 series on-chip
1763 Ethernet adapter MAC address.
1765 kmemleak= [KNL] Boot-time kmemleak enable/disable
1766 Valid arguments: on, off
1768 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1771 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1772 Valid arguments: 0, 1, 2
1773 kmemcheck=0 (disabled)
1774 kmemcheck=1 (enabled)
1775 kmemcheck=2 (one-shot mode)
1776 Default: 2 (one-shot mode)
1778 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1779 Default is 0 (don't ignore, but inject #GP)
1781 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1785 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1786 Default is 1 (enabled)
1788 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1790 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1792 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1793 (virtualized MMU) support on capable Intel chips.
1794 Default is 1 (enabled)
1796 kvm-intel.emulate_invalid_guest_state=
1797 [KVM,Intel] Enable emulation of invalid guest states
1798 Default is 0 (disabled)
1800 kvm-intel.flexpriority=
1801 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1802 Default is 1 (enabled)
1805 [KVM,Intel] Enable VMX nesting (nVMX).
1806 Default is 0 (disabled)
1808 kvm-intel.unrestricted_guest=
1809 [KVM,Intel] Disable unrestricted guest feature
1810 (virtualized real and unpaged mode) on capable
1811 Intel chips. Default is 1 (enabled)
1813 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1814 feature (tagged TLBs) on capable Intel chips.
1815 Default is 1 (enabled)
1821 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1824 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1825 value for LAPIC timer one-shot implementation. Default
1826 back to the programmable timer unit in the LAPIC.
1828 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1831 libata.dma= [LIBATA] DMA control
1832 libata.dma=0 Disable all PATA and SATA DMA
1833 libata.dma=1 PATA and SATA Disk DMA only
1834 libata.dma=2 ATAPI (CDROM) DMA only
1835 libata.dma=4 Compact Flash DMA only
1836 Combinations also work, so libata.dma=3 enables DMA
1837 for disks and CDROMs, but not CFs.
1839 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1840 libata.ignore_hpa=0 keep BIOS limits (default)
1841 libata.ignore_hpa=1 ignore limits, using full disk
1843 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1847 libata.force= [LIBATA] Force configurations. The format is comma
1848 separated list of "[ID:]VAL" where ID is
1849 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1850 matching port, link or device. Basically, it matches
1851 the ATA ID string printed on console by libata. If
1852 the whole ID part is omitted, the last PORT and DEVICE
1853 values are used. If ID hasn't been specified yet, the
1854 configuration applies to all ports, links and devices.
1856 If only DEVICE is omitted, the parameter applies to
1857 the port and all links and devices behind it. DEVICE
1858 number of 0 either selects the first device or the
1859 first fan-out link behind PMP device. It does not
1860 select the host link. DEVICE number of 15 selects the
1861 host link and device attached to it.
1863 The VAL specifies the configuration to force. As long
1864 as there's no ambiguity shortcut notation is allowed.
1865 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1866 The following configurations can be forced.
1868 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1869 Any ID with matching PORT is used.
1871 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1873 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1874 udma[/][16,25,33,44,66,100,133] notation is also
1877 * [no]ncq: Turn on or off NCQ.
1879 * [no]ncqtrim: Turn off queued DSM TRIM.
1881 * nohrst, nosrst, norst: suppress hard, soft
1884 * rstonce: only attempt one reset during
1885 hot-unplug link recovery
1887 * dump_id: dump IDENTIFY data.
1889 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1891 * disable: Disable this device.
1893 If there are multiple matching configurations changing
1894 the same attribute, the last one is used.
1896 memblock=debug [KNL] Enable memblock debug messages.
1898 load_ramdisk= [RAM] List of ramdisks to load from floppy
1899 See Documentation/blockdev/ramdisk.txt.
1901 lockd.nlm_grace_period=P [NFS] Assign grace period.
1904 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1907 lockd.nlm_timeout=T [NFS] Assign timeout value.
1910 lockd.nlm_udpport=M [NFS] Assign UDP port.
1913 locktorture.nreaders_stress= [KNL]
1914 Set the number of locking read-acquisition kthreads.
1915 Defaults to being automatically set based on the
1916 number of online CPUs.
1918 locktorture.nwriters_stress= [KNL]
1919 Set the number of locking write-acquisition kthreads.
1921 locktorture.onoff_holdoff= [KNL]
1922 Set time (s) after boot for CPU-hotplug testing.
1924 locktorture.onoff_interval= [KNL]
1925 Set time (s) between CPU-hotplug operations, or
1926 zero to disable CPU-hotplug testing.
1928 locktorture.shuffle_interval= [KNL]
1929 Set task-shuffle interval (jiffies). Shuffling
1930 tasks allows some CPUs to go into dyntick-idle
1931 mode during the locktorture test.
1933 locktorture.shutdown_secs= [KNL]
1934 Set time (s) after boot system shutdown. This
1935 is useful for hands-off automated testing.
1937 locktorture.stat_interval= [KNL]
1938 Time (s) between statistics printk()s.
1940 locktorture.stutter= [KNL]
1941 Time (s) to stutter testing, for example,
1942 specifying five seconds causes the test to run for
1943 five seconds, wait for five seconds, and so on.
1944 This tests the locking primitive's ability to
1945 transition abruptly to and from idle.
1947 locktorture.torture_runnable= [BOOT]
1948 Start locktorture running at boot time.
1950 locktorture.torture_type= [KNL]
1951 Specify the locking implementation to test.
1953 locktorture.verbose= [KNL]
1954 Enable additional printk() statements.
1956 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1959 loglevel= All Kernel Messages with a loglevel smaller than the
1960 console loglevel will be printed to the console. It can
1961 also be changed with klogd or other programs. The
1962 loglevels are defined as follows:
1964 0 (KERN_EMERG) system is unusable
1965 1 (KERN_ALERT) action must be taken immediately
1966 2 (KERN_CRIT) critical conditions
1967 3 (KERN_ERR) error conditions
1968 4 (KERN_WARNING) warning conditions
1969 5 (KERN_NOTICE) normal but significant condition
1970 6 (KERN_INFO) informational
1971 7 (KERN_DEBUG) debug-level messages
1973 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1974 in bytes. n must be a power of two and greater
1975 than the minimal size. The minimal size is defined
1976 by LOG_BUF_SHIFT kernel config parameter. There is
1977 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1978 that allows to increase the default size depending on
1979 the number of CPUs. See init/Kconfig for more details.
1981 logo.nologo [FB] Disables display of the built-in Linux logo.
1982 This may be used to provide more screen space for
1983 kernel log messages and is useful when debugging
1984 kernel boot problems.
1986 lp=0 [LP] Specify parallel ports to use, e.g,
1987 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1988 lp=reset first parallel port). 'lp=0' disables the
1989 lp=auto printer driver. 'lp=reset' (which can be
1990 specified in addition to the ports) causes
1991 attached printers to be reset. Using
1992 lp=port1,port2,... specifies the parallel ports
1993 to associate lp devices with, starting with
1994 lp0. A port specification may be 'none' to skip
1995 that lp device, or a parport name such as
1996 'parport0'. Specifying 'lp=auto' instead of a
1997 port specification list means that device IDs
1998 from each port should be examined, to see if
1999 an IEEE 1284-compliant printer is attached; if
2000 so, the driver will manage that printer.
2001 See also header of drivers/char/lp.c.
2004 Sets loops_per_jiffy to given constant, thus avoiding
2005 time-consuming boot-time autodetection (up to 250 ms per
2006 CPU). 0 enables autodetection (default). To determine
2007 the correct value for your kernel, boot with normal
2008 autodetection and see what value is printed. Note that
2009 on SMP systems the preset will be applied to all CPUs,
2010 which is likely to cause problems if your CPUs need
2011 significantly divergent settings. An incorrect value
2012 will cause delays in the kernel to be wrong, leading to
2013 unpredictable I/O errors and other breakage. Although
2014 unlikely, in the extreme case this might damage your
2018 Format: <io>,<irq>,<dma>
2020 machvec= [IA-64] Force the use of a particular machine-vector
2021 (machvec) in a generic kernel.
2022 Example: machvec=hpzx1_swiotlb
2024 machtype= [Loongson] Share the same kernel image file between different
2026 Example: machtype=lemote-yeeloong-2f-7inch
2028 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2029 than or equal to this physical address is ignored.
2031 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2032 will bring up during bootup. maxcpus=n : n >= 0 limits
2033 the kernel to bring up 'n' processors. Surely after
2034 bootup you can bring up the other plugged cpu by executing
2035 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2036 only takes effect during system bootup.
2037 While n=0 is a special case, it is equivalent to "nosmp",
2038 which also disables the IO APIC.
2040 max_loop= [LOOP] The number of loop block devices that get
2041 (loop.max_loop) unconditionally pre-created at init time. The default
2042 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2043 of statically allocating a predefined number, loop
2044 devices can be requested on-demand with the
2045 /dev/loop-control interface.
2047 mce [X86-32] Machine Check Exception
2049 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2051 md= [HW] RAID subsystems devices and level
2052 See Documentation/admin-guide/md.rst.
2055 Format: <first>,<last>
2056 Specifies range of consoles to be captured by the MDA.
2058 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2059 Amount of memory to be used when the kernel is not able
2060 to see the whole system memory or for test.
2061 [X86] Work as limiting max address. Use together
2062 with memmap= to avoid physical address space collisions.
2063 Without memmap= PCI devices could be placed at addresses
2064 belonging to unused RAM.
2066 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2070 [KNL,SH] Allow user to override the default size for
2071 per-device physically contiguous DMA buffers.
2073 memhp_default_state=online/offline
2074 [KNL] Set the initial state for the memory hotplug
2075 onlining policy. If not specified, the default value is
2076 set according to the
2077 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2079 See Documentation/memory-hotplug.txt.
2081 memmap=exactmap [KNL,X86] Enable setting of an exact
2082 E820 memory map, as specified by the user.
2083 Such memmap=exactmap lines can be constructed based on
2084 BIOS output or other requirements. See the memmap=nn@ss
2087 memmap=nn[KMG]@ss[KMG]
2088 [KNL] Force usage of a specific region of memory.
2089 Region of memory to be used is from ss to ss+nn.
2091 memmap=nn[KMG]#ss[KMG]
2092 [KNL,ACPI] Mark specific memory as ACPI data.
2093 Region of memory to be marked is from ss to ss+nn.
2095 memmap=nn[KMG]$ss[KMG]
2096 [KNL,ACPI] Mark specific memory as reserved.
2097 Region of memory to be reserved is from ss to ss+nn.
2098 Example: Exclude memory from 0x18690000-0x1869ffff
2099 memmap=64K$0x18690000
2101 memmap=0x10000$0x18690000
2103 memmap=nn[KMG]!ss[KMG]
2104 [KNL,X86] Mark specific memory as protected.
2105 Region of memory to be used, from ss to ss+nn.
2106 The memory region may be marked as e820 type 12 (0xc)
2107 and is NVDIMM or ADR memory.
2109 memory_corruption_check=0/1 [X86]
2110 Some BIOSes seem to corrupt the first 64k of
2111 memory when doing things like suspend/resume.
2112 Setting this option will scan the memory
2113 looking for corruption. Enabling this will
2114 both detect corruption and prevent the kernel
2115 from using the memory being corrupted.
2116 However, its intended as a diagnostic tool; if
2117 repeatable BIOS-originated corruption always
2118 affects the same memory, you can use memmap=
2119 to prevent the kernel from using that memory.
2121 memory_corruption_check_size=size [X86]
2122 By default it checks for corruption in the low
2123 64k, making this memory unavailable for normal
2124 use. Use this parameter to scan for
2125 corruption in more or less memory.
2127 memory_corruption_check_period=seconds [X86]
2128 By default it checks for corruption every 60
2129 seconds. Use this parameter to check at some
2130 other rate. 0 disables periodic checking.
2132 memtest= [KNL,X86,ARM] Enable memtest
2134 default : 0 <disable>
2135 Specifies the number of memtest passes to be
2136 performed. Each pass selects another test
2137 pattern from a given set of patterns. Memtest
2138 fills the memory with this pattern, validates
2139 memory contents and reserves bad memory
2140 regions that are detected.
2142 mem_sleep_default= [SUSPEND] Default system suspend mode:
2143 s2idle - Suspend-To-Idle
2144 shallow - Power-On Suspend or equivalent (if supported)
2145 deep - Suspend-To-RAM or equivalent (if supported)
2146 See Documentation/power/states.txt.
2148 meye.*= [HW] Set MotionEye Camera parameters
2149 See Documentation/video4linux/meye.txt.
2151 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2152 Multi-Function General Purpose Timers on AMD Geode
2155 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2156 the BIOS has incorrectly applied a workaround. TinyBIOS
2157 version 0.98 is known to be affected, 0.99 fixes the
2158 problem by letting the user disable the workaround.
2162 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2163 physical address is ignored.
2165 mini2440= [ARM,HW,KNL]
2166 Format:[0..2][b][c][t]
2168 MINI2440 configuration specification:
2169 0 - The attached screen is the 3.5" TFT
2170 1 - The attached screen is the 7" TFT
2171 2 - The VGA Shield is attached (1024x768)
2172 Leaving out the screen size parameter will not load
2173 the TFT driver, and the framebuffer will be left
2175 b - Enable backlight. The TFT backlight pin will be
2176 linked to the kernel VESA blanking code and a GPIO
2177 LED. This parameter is not necessary when using the
2179 c - Enable the s3c camera interface.
2180 t - Reserved for enabling touchscreen support. The
2181 touchscreen support is not enabled in the mainstream
2182 kernel as of 2.6.30, a preliminary port can be found
2183 in the "bleeding edge" mini2440 support kernel at
2184 http://repo.or.cz/w/linux-2.6/mini2440.git
2187 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2188 parameter allows control of the logging verbosity for
2189 the additional memory initialisation checks. A value
2190 of 0 disables mminit logging and a level of 4 will
2191 log everything. Information is printed at KERN_DEBUG
2192 so loglevel=8 may also need to be specified.
2195 [KNL] When CONFIG_MODULE_SIG is set, this means that
2196 modules without (valid) signatures will fail to load.
2197 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2198 is always true, so this option does nothing.
2200 module_blacklist= [KNL] Do not load a comma-separated list of
2201 modules. Useful for debugging problem modules.
2204 [MOUSE] Maximum time between finger touching and
2205 leaving touchpad surface for touch to be considered
2206 a tap and be reported as a left button click (for
2207 touchpads working in absolute mode only).
2209 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2210 reporting absolute coordinates, such as tablets
2211 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2212 reporting absolute coordinates, such as tablets
2214 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2215 is similar to kernelcore except it specifies the
2216 amount of memory used for migratable allocations.
2217 If both kernelcore and movablecore is specified,
2218 then kernelcore will be at *least* the specified
2219 value but may be more. If movablecore on its own
2220 is specified, the administrator must be careful
2221 that the amount of memory usable for all allocations
2224 movable_node [KNL] Boot-time switch to enable the effects
2225 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2227 MTD_Partition= [MTD]
2228 Format: <name>,<region-number>,<size>,<offset>
2230 MTD_Region= [MTD] Format:
2231 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2234 See drivers/mtd/cmdlinepart.c.
2236 multitce=off [PPC] This parameter disables the use of the pSeries
2237 firmware feature for updating multiple TCE entries
2240 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2242 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2244 boundary - index of last SLC block on Flex-OneNAND.
2245 The remaining blocks are configured as MLC blocks.
2246 lock - Configure if Flex-OneNAND boundary should be locked.
2247 Once locked, the boundary cannot be changed.
2248 1 indicates lock status, 0 indicates unlock status.
2251 ARM/S3C2412 JIVE boot control
2253 See arch/arm/mach-s3c2412/mach-jive.c
2255 mtouchusb.raw_coordinates=
2256 [HW] Make the MicroTouch USB driver use raw coordinates
2257 ('y', default) or cooked coordinates ('n')
2259 mtrr_chunk_size=nn[KMG] [X86]
2260 used for mtrr cleanup. It is largest continuous chunk
2261 that could hold holes aka. UC entries.
2263 mtrr_gran_size=nn[KMG] [X86]
2264 Used for mtrr cleanup. It is granularity of mtrr block.
2266 Large value could prevent small alignment from
2269 mtrr_spare_reg_nr=n [X86]
2271 Range: 0,7 : spare reg number
2273 Used for mtrr cleanup. It is spare mtrr entries number.
2274 Set to 2 or more if your graphical card needs more.
2276 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2278 netdev= [NET] Network devices parameters
2279 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2280 Note that mem_start is often overloaded to mean
2281 something different and driver-specific.
2282 This usage is only documented in each driver source
2286 [NETFILTER] Enable connection tracking flow accounting
2287 0 to disable accounting
2288 1 to enable accounting
2291 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2292 See Documentation/filesystems/nfs/nfsroot.txt.
2294 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2295 See Documentation/filesystems/nfs/nfsroot.txt.
2297 nfsrootdebug [NFS] enable nfsroot debugging messages.
2298 See Documentation/filesystems/nfs/nfsroot.txt.
2300 nfs.callback_nr_threads=
2301 [NFSv4] set the total number of threads that the
2302 NFS client will assign to service NFSv4 callback
2305 nfs.callback_tcpport=
2306 [NFS] set the TCP port on which the NFSv4 callback
2307 channel should listen.
2310 [NFS] sets the pathname to the program which is used
2311 to update the NFS client cache entries.
2313 nfs.cache_getent_timeout=
2314 [NFS] sets the timeout after which an attempt to
2315 update a cache entry is deemed to have failed.
2317 nfs.idmap_cache_timeout=
2318 [NFS] set the maximum lifetime for idmapper cache
2322 [NFS] enable 64-bit inode numbers.
2323 If zero, the NFS client will fake up a 32-bit inode
2324 number for the readdir() and stat() syscalls instead
2325 of returning the full 64-bit number.
2326 The default is to return 64-bit inode numbers.
2328 nfs.max_session_cb_slots=
2329 [NFSv4.1] Sets the maximum number of session
2330 slots the client will assign to the callback
2331 channel. This determines the maximum number of
2332 callbacks the client will process in parallel for
2333 a particular server.
2335 nfs.max_session_slots=
2336 [NFSv4.1] Sets the maximum number of session slots
2337 the client will attempt to negotiate with the server.
2338 This limits the number of simultaneous RPC requests
2339 that the client can send to the NFSv4.1 server.
2340 Note that there is little point in setting this
2341 value higher than the max_tcp_slot_table_limit.
2343 nfs.nfs4_disable_idmapping=
2344 [NFSv4] When set to the default of '1', this option
2345 ensures that both the RPC level authentication
2346 scheme and the NFS level operations agree to use
2347 numeric uids/gids if the mount is using the
2348 'sec=sys' security flavour. In effect it is
2349 disabling idmapping, which can make migration from
2350 legacy NFSv2/v3 systems to NFSv4 easier.
2351 Servers that do not support this mode of operation
2352 will be autodetected by the client, and it will fall
2353 back to using the idmapper.
2354 To turn off this behaviour, set the value to '0'.
2356 [NFS4] Specify an additional fixed unique ident-
2357 ification string that NFSv4 clients can insert into
2358 their nfs_client_id4 string. This is typically a
2359 UUID that is generated at system install time.
2361 nfs.send_implementation_id =
2362 [NFSv4.1] Send client implementation identification
2363 information in exchange_id requests.
2364 If zero, no implementation identification information
2366 The default is to send the implementation identification
2369 nfs.recover_lost_locks =
2370 [NFSv4] Attempt to recover locks that were lost due
2371 to a lease timeout on the server. Please note that
2372 doing this risks data corruption, since there are
2373 no guarantees that the file will remain unchanged
2374 after the locks are lost.
2375 If you want to enable the kernel legacy behaviour of
2376 attempting to recover these locks, then set this
2378 The default parameter value of '0' causes the kernel
2379 not to attempt recovery of lost locks.
2381 nfs4.layoutstats_timer =
2382 [NFSv4.2] Change the rate at which the kernel sends
2383 layoutstats to the pNFS metadata server.
2385 Setting this to value to 0 causes the kernel to use
2386 whatever value is the default set by the layout
2387 driver. A non-zero value sets the minimum interval
2388 in seconds between layoutstats transmissions.
2390 nfsd.nfs4_disable_idmapping=
2391 [NFSv4] When set to the default of '1', the NFSv4
2392 server will return only numeric uids and gids to
2393 clients using auth_sys, and will accept numeric uids
2394 and gids from such clients. This is intended to ease
2395 migration from NFSv2/v3.
2397 objlayoutdriver.osd_login_prog=
2398 [NFS] [OBJLAYOUT] sets the pathname to the program which
2399 is used to automatically discover and login into new
2400 osd-targets. Please see:
2401 Documentation/filesystems/pnfs.txt for more explanations
2403 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2404 when a NMI is triggered.
2405 Format: [state][,regs][,debounce][,die]
2407 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2408 Format: [panic,][nopanic,][num]
2410 0 - turn hardlockup detector in nmi_watchdog off
2411 1 - turn hardlockup detector in nmi_watchdog on
2412 When panic is specified, panic when an NMI watchdog
2413 timeout occurs (or 'nopanic' to override the opposite
2414 default). To disable both hard and soft lockup detectors,
2415 please see 'nowatchdog'.
2416 This is useful when you use a panic=... timeout and
2417 need the box quickly up again.
2419 netpoll.carrier_timeout=
2420 [NET] Specifies amount of time (in seconds) that
2421 netpoll should wait for a carrier. By default netpoll
2424 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2425 emulation library even if a 387 maths coprocessor
2429 [HW] Never suspend the console
2430 Disable suspending of consoles during suspend and
2431 hibernate operations. Once disabled, debugging
2432 messages can reach various consoles while the rest
2433 of the system is being put to sleep (ie, while
2434 debugging driver suspend/resume hooks). This may
2435 not work reliably with all consoles, but is known
2436 to work with serial and VGA consoles.
2437 To facilitate more flexible debugging, we also add
2438 console_suspend, a printk module parameter to control
2439 it. Users could use console_suspend (usually
2440 /sys/module/printk/parameters/console_suspend) to
2441 turn on/off it dynamically.
2443 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2444 caches in the slab allocator. Saves per-node memory,
2445 but will impact performance.
2449 noapic [SMP,APIC] Tells the kernel to not make use of any
2450 IOAPICs that may be present in the system.
2452 noautogroup Disable scheduler automatic task group creation.
2454 nobats [PPC] Do not use BATs for mapping kernel lowmem
2455 on "Classic" PPC cores.
2459 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2461 nodelayacct [KNL] Disable per-task delay accounting
2463 nodsp [SH] Disable hardware DSP at boot time.
2465 noefi Disable EFI runtime services support.
2470 On X86-32 available only on PAE configured kernels.
2471 noexec=on: enable non-executable mappings (default)
2472 noexec=off: disable non-executable mappings
2475 Disable SMAP (Supervisor Mode Access Prevention)
2476 even if it is supported by processor.
2479 Disable SMEP (Supervisor Mode Execution Prevention)
2480 even if it is supported by processor.
2483 This affects only 32-bit executables.
2484 noexec32=on: enable non-executable mappings (default)
2485 read doesn't imply executable mappings
2486 noexec32=off: disable non-executable mappings
2487 read implies executable mappings
2489 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2491 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2492 register save and restore. The kernel will only save
2493 legacy floating-point registers on task switch.
2495 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2497 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2498 Equivalent to smt=1.
2500 noxsave [BUGS=X86] Disables x86 extended register state save
2501 and restore using xsave. The kernel will fallback to
2502 enabling legacy floating-point and sse state.
2504 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2505 register states. The kernel will fall back to use
2506 xsave to save the states. By using this parameter,
2507 performance of saving the states is degraded because
2508 xsave doesn't support modified optimization while
2509 xsaveopt supports it on xsaveopt enabled systems.
2511 noxsaves [X86] Disables xsaves and xrstors used in saving and
2512 restoring x86 extended register state in compacted
2513 form of xsave area. The kernel will fall back to use
2514 xsaveopt and xrstor to save and restore the states
2515 in standard form of xsave area. By using this
2516 parameter, xsave area per process might occupy more
2517 memory on xsaves enabled systems.
2519 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2520 wfi(ARM) instruction doesn't work correctly and not to
2521 use it. This is also useful when using JTAG debugger.
2523 no_file_caps Tells the kernel not to honor file capabilities. The
2524 only way then for a file to be executed with privilege
2525 is to be setuid root or executed by root.
2527 nohalt [IA-64] Tells the kernel not to use the power saving
2528 function PAL_HALT_LIGHT when idle. This increases
2529 power-consumption. On the positive side, it reduces
2530 interrupt wake-up latency, which may improve performance
2531 in certain environments such as networked servers or
2534 nohibernate [HIBERNATION] Disable hibernation and resume.
2536 nohz= [KNL] Boottime enable/disable dynamic ticks
2537 Valid arguments: on, off
2540 nohz_full= [KNL,BOOT]
2541 The argument is a cpu list, as described above.
2542 In kernels built with CONFIG_NO_HZ_FULL=y, set
2543 the specified list of CPUs whose tick will be stopped
2544 whenever possible. The boot CPU will be forced outside
2545 the range to maintain the timekeeping.
2546 The CPUs in this range must also be included in the
2549 noiotrap [SH] Disables trapped I/O port accesses.
2551 noirqdebug [X86-32] Disables the code which attempts to detect and
2552 disable unhandled interrupt sources.
2554 no_timer_check [X86,APIC] Disables the code which tests for
2555 broken timer IRQ sources.
2557 noisapnp [ISAPNP] Disables ISA PnP code.
2559 noinitrd [RAM] Tells the kernel not to load any configured
2562 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2564 [Deprecated - use intremap=off]
2568 noinvpcid [X86] Disable the INVPCID cpu feature.
2570 nojitter [IA-64] Disables jitter checking for ITC timers.
2572 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2574 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2578 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2579 clock and use the default one.
2581 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2582 steal time is computed, but won't influence scheduler
2585 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2587 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2589 noltlbs [PPC] Do not use large page/tlb entries for kernel
2590 lowmem mapping on PPC40x and PPC8xx
2592 nomca [IA-64] Disable machine check abort handling
2594 nomce [X86-32] Disable Machine Check Exception
2596 nomfgpt [X86-32] Disable Multi-Function General Purpose
2597 Timer usage (for AMD Geode machines).
2599 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2600 shutdown the other cpus. Instead use the REBOOT_VECTOR
2603 nomodule Disable module load
2605 nopat [X86] Disable PAT (page attribute table extension of
2606 pagetables) support.
2608 norandmaps Don't use address space randomization. Equivalent to
2609 echo 0 > /proc/sys/kernel/randomize_va_space
2611 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2613 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2614 with UP alternatives
2616 nordrand [X86] Disable kernel use of the RDRAND and
2617 RDSEED instructions even if they are supported
2618 by the processor. RDRAND and RDSEED are still
2619 available to user space applications.
2621 noresume [SWSUSP] Disables resume and restores original swap
2624 no-scroll [VGA] Disables scrollback.
2625 This is required for the Braillex ib80-piezo Braille
2626 reader made by F.H. Papenmeier (Germany).
2630 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2632 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2633 and disable the IO APIC. legacy for "maxcpus=0".
2635 nosoftlockup [KNL] Disable the soft-lockup detector.
2637 nosync [HW,M68K] Disables sync negotiation for all devices.
2639 notsc [BUGS=X86-32] Disable Time Stamp Counter
2641 nowatchdog [KNL] Disable both lockup detectors, i.e.
2642 soft-lockup and NMI watchdog (hard-lockup).
2646 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2648 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2649 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2650 Some features depend on CPU0. Known dependencies are:
2651 1. Resume from suspend/hibernate depends on CPU0.
2652 Suspend/hibernate will fail if CPU0 is offline and you
2653 need to online CPU0 before suspend/hibernate.
2654 2. PIC interrupts also depend on CPU0. CPU0 can't be
2655 removed if a PIC interrupt is detected.
2656 It's said poweroff/reboot may depend on CPU0 on some
2657 machines although I haven't seen such issues so far
2658 after CPU0 is offline on a few tested machines.
2659 If the dependencies are under your control, you can
2660 turn on cpu0_hotplug.
2662 nptcg= [IA-64] Override max number of concurrent global TLB
2663 purges which is reported from either PAL_VM_SUMMARY or
2666 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2667 could support. nr_cpus=n : n >= 1 limits the kernel to
2668 support 'n' processors. It could be larger than the
2669 number of already plugged CPU during bootup, later in
2670 runtime you can physically add extra cpu until it reaches
2671 n. So during boot up some boot time memory for per-cpu
2672 variables need be pre-allocated for later physical cpu
2675 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2677 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2678 Allowed values are enable and disable
2680 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2681 one of ['zone', 'node', 'default'] can be specified
2682 This can be set from sysctl after boot.
2683 See Documentation/sysctl/vm.txt for details.
2685 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2686 See Documentation/debugging-via-ohci1394.txt for more
2689 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2690 Rather than timing out after 20 ms if an EC
2691 command is not properly ACKed, override the length
2692 of the timeout. We have interrupts disabled while
2693 waiting for the ACK, so if this is set too high
2694 interrupts *may* be lost!
2696 omap_mux= [OMAP] Override bootloader pin multiplexing.
2697 Format: <mux_mode0.mode_name=value>...
2698 For example, to override I2C bus2:
2699 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2701 oprofile.timer= [HW]
2702 Use timer interrupt instead of performance counters
2704 oprofile.cpu_type= Force an oprofile cpu type
2705 This might be useful if you have an older oprofile
2706 userland or if you want common events.
2707 Format: { arch_perfmon }
2708 arch_perfmon: [X86] Force use of architectural
2709 perfmon on Intel CPUs instead of the
2710 CPU specific event set.
2711 timer: [X86] Force use of architectural NMI
2712 timer mode (see also oprofile.timer
2713 for generic hr timer mode)
2715 oops=panic Always panic on oopses. Default is to just kill the
2716 process, but there is a small probability of
2717 deadlocking the machine.
2718 This will also cause panics on machine check exceptions.
2719 Useful together with panic=30 to trigger a reboot.
2722 See Documentation/sound/oss/oss-parameters.txt
2724 page_owner= [KNL] Boot-time page_owner enabling option.
2725 Storage of the information about who allocated
2726 each page is disabled in default. With this switch,
2728 on: enable the feature
2730 page_poison= [KNL] Boot-time parameter changing the state of
2731 poisoning on the buddy allocator.
2732 off: turn off poisoning
2733 on: turn on poisoning
2735 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2736 timeout > 0: seconds before rebooting
2737 timeout = 0: wait forever
2738 timeout < 0: reboot immediately
2741 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2744 crash_kexec_post_notifiers
2745 Run kdump after running panic-notifiers and dumping
2746 kmsg. This only for the users who doubt kdump always
2747 succeeds in any situation.
2748 Note that this also increases risks of kdump failure,
2749 because some panic notifiers can make the crashed
2750 kernel more unstable.
2752 parkbd.port= [HW] Parallel port number the keyboard adapter is
2753 connected to, default is 0.
2755 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2756 0 for XT, 1 for AT (default is AT).
2759 parport= [HW,PPT] Specify parallel ports. 0 disables.
2760 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2761 Use 'auto' to force the driver to use any
2762 IRQ/DMA settings detected (the default is to
2763 ignore detected IRQ/DMA settings because of
2764 possible conflicts). You can specify the base
2765 address, IRQ, and DMA settings; IRQ and DMA
2766 should be numbers, or 'auto' (for using detected
2767 settings on that particular port), or 'nofifo'
2768 (to avoid using a FIFO even if it is detected).
2769 Parallel ports are assigned in the order they
2770 are specified on the command line, starting
2773 parport_init_mode= [HW,PPT]
2774 Configure VIA parallel port to operate in
2775 a specific mode. This is necessary on Pegasos
2776 computer where firmware has no options for setting
2777 up parallel port mode and sets it to spp.
2778 Currently this function knows 686a and 8231 chips.
2779 Format: [spp|ps2|epp|ecp|ecpepp]
2782 Halt all CPUs after the first oops has been printed for
2783 the specified number of seconds. This is to be used if
2784 your oopses keep scrolling off the screen.
2789 See header of drivers/block/paride/pcd.c.
2790 See also Documentation/blockdev/paride.txt.
2792 pci=option[,option...] [PCI] various PCI subsystem options:
2793 earlydump [X86] dump PCI config space before the kernel
2795 off [X86] don't probe for the PCI bus
2796 bios [X86-32] force use of PCI BIOS, don't access
2797 the hardware directly. Use this if your machine
2798 has a non-standard PCI host bridge.
2799 nobios [X86-32] disallow use of PCI BIOS, only direct
2800 hardware access methods are allowed. Use this
2801 if you experience crashes upon bootup and you
2802 suspect they are caused by the BIOS.
2803 conf1 [X86] Force use of PCI Configuration Access
2804 Mechanism 1 (config address in IO port 0xCF8,
2805 data in IO port 0xCFC, both 32-bit).
2806 conf2 [X86] Force use of PCI Configuration Access
2807 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2808 the function, IO port 0xCFA, also 8-bit, sets
2809 bus number. The config space is then accessed
2810 through ports 0xC000-0xCFFF).
2811 See http://wiki.osdev.org/PCI for more info
2812 on the configuration access mechanisms.
2813 noaer [PCIE] If the PCIEAER kernel config parameter is
2814 enabled, this kernel boot option can be used to
2815 disable the use of PCIE advanced error reporting.
2816 nodomains [PCI] Disable support for multiple PCI
2817 root domains (aka PCI segments, in ACPI-speak).
2818 nommconf [X86] Disable use of MMCONFIG for PCI
2820 check_enable_amd_mmconf [X86] check for and enable
2821 properly configured MMIO access to PCI
2822 config space on AMD family 10h CPU
2823 nomsi [MSI] If the PCI_MSI kernel config parameter is
2824 enabled, this kernel boot option can be used to
2825 disable the use of MSI interrupts system-wide.
2826 noioapicquirk [APIC] Disable all boot interrupt quirks.
2827 Safety option to keep boot IRQs enabled. This
2828 should never be necessary.
2829 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2830 primary IO-APIC for bridges that cannot disable
2831 boot IRQs. This fixes a source of spurious IRQs
2832 when the system masks IRQs.
2833 noioapicreroute [APIC] Disable workaround that uses the
2834 boot IRQ equivalent of an IRQ that connects to
2835 a chipset where boot IRQs cannot be disabled.
2836 The opposite of ioapicreroute.
2837 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2838 routing table. These calls are known to be buggy
2839 on several machines and they hang the machine
2840 when used, but on other computers it's the only
2841 way to get the interrupt routing table. Try
2842 this option if the kernel is unable to allocate
2843 IRQs or discover secondary PCI buses on your
2845 rom [X86] Assign address space to expansion ROMs.
2846 Use with caution as certain devices share
2847 address decoders between ROMs and other
2849 norom [X86] Do not assign address space to
2850 expansion ROMs that do not already have
2851 BIOS assigned address ranges.
2852 nobar [X86] Do not assign address space to the
2853 BARs that weren't assigned by the BIOS.
2854 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2855 assigned automatically to PCI devices. You can
2856 make the kernel exclude IRQs of your ISA cards
2858 pirqaddr=0xAAAAA [X86] Specify the physical address
2859 of the PIRQ table (normally generated
2860 by the BIOS) if it is outside the
2861 F0000h-100000h range.
2862 lastbus=N [X86] Scan all buses thru bus #N. Can be
2863 useful if the kernel is unable to find your
2864 secondary buses and you want to tell it
2865 explicitly which ones they are.
2866 assign-busses [X86] Always assign all PCI bus
2867 numbers ourselves, overriding
2868 whatever the firmware may have done.
2869 usepirqmask [X86] Honor the possible IRQ mask stored
2870 in the BIOS $PIR table. This is needed on
2871 some systems with broken BIOSes, notably
2872 some HP Pavilion N5400 and Omnibook XE3
2873 notebooks. This will have no effect if ACPI
2874 IRQ routing is enabled.
2875 noacpi [X86] Do not use ACPI for IRQ routing
2876 or for PCI scanning.
2877 use_crs [X86] Use PCI host bridge window information
2878 from ACPI. On BIOSes from 2008 or later, this
2879 is enabled by default. If you need to use this,
2880 please report a bug.
2881 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2882 If you need to use this, please report a bug.
2883 routeirq Do IRQ routing for all PCI devices.
2884 This is normally done in pci_enable_device(),
2885 so this option is a temporary workaround
2886 for broken drivers that don't call it.
2887 skip_isa_align [X86] do not align io start addr, so can
2888 handle more pci cards
2889 noearly [X86] Don't do any early type 1 scanning.
2890 This might help on some broken boards which
2891 machine check when some devices' config space
2892 is read. But various workarounds are disabled
2893 and some IOMMU drivers will not work.
2894 bfsort Sort PCI devices into breadth-first order.
2895 This sorting is done to get a device
2896 order compatible with older (<= 2.4) kernels.
2897 nobfsort Don't sort PCI devices into breadth-first order.
2898 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2899 tuning and use the BIOS-configured MPS defaults.
2900 pcie_bus_safe Set every device's MPS to the largest value
2901 supported by all devices below the root complex.
2902 pcie_bus_perf Set device MPS to the largest allowable MPS
2903 based on its parent bus. Also set MRRS (Max
2904 Read Request Size) to the largest supported
2905 value (no larger than the MPS that the device
2906 or bus can support) for best performance.
2907 pcie_bus_peer2peer Set every device's MPS to 128B, which
2908 every device is guaranteed to support. This
2909 configuration allows peer-to-peer DMA between
2910 any pair of devices, possibly at the cost of
2911 reduced performance. This also guarantees
2912 that hot-added devices will work.
2913 cbiosize=nn[KMG] The fixed amount of bus space which is
2914 reserved for the CardBus bridge's IO window.
2915 The default value is 256 bytes.
2916 cbmemsize=nn[KMG] The fixed amount of bus space which is
2917 reserved for the CardBus bridge's memory
2918 window. The default value is 64 megabytes.
2921 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2922 [<order of align>@]pci:<vendor>:<device>\
2923 [:<subvendor>:<subdevice>][; ...]
2924 Specifies alignment and device to reassign
2925 aligned memory resources.
2926 If <order of align> is not specified,
2927 PAGE_SIZE is used as alignment.
2928 PCI-PCI bridge can be specified, if resource
2929 windows need to be expanded.
2930 To specify the alignment for several
2931 instances of a device, the PCI vendor,
2932 device, subvendor, and subdevice may be
2933 specified, e.g., 4096@pci:8086:9c22:103c:198f
2934 ecrc= Enable/disable PCIe ECRC (transaction layer
2935 end-to-end CRC checking).
2936 bios: Use BIOS/firmware settings. This is the
2940 hpiosize=nn[KMG] The fixed amount of bus space which is
2941 reserved for hotplug bridge's IO window.
2942 Default size is 256 bytes.
2943 hpmemsize=nn[KMG] The fixed amount of bus space which is
2944 reserved for hotplug bridge's memory window.
2945 Default size is 2 megabytes.
2946 hpbussize=nn The minimum amount of additional bus numbers
2947 reserved for buses below a hotplug bridge.
2949 realloc= Enable/disable reallocating PCI bridge resources
2950 if allocations done by BIOS are too small to
2951 accommodate resources required by all child
2953 off: Turn realloc off
2955 realloc same as realloc=on
2956 noari do not use PCIe ARI.
2957 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2958 only look for one device below a PCIe downstream
2961 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2964 force Enable ASPM even on devices that claim not to support it.
2965 WARNING: Forcing ASPM on may cause system lockups.
2967 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2968 nomsi Do not use MSI for PCI Express Native Hotplug (this
2969 makes all PCIe ports use INTx for hotplug services).
2971 pcie_ports= [PCIE] PCIe ports handling:
2972 auto Ask the BIOS whether or not to use native PCIe services
2973 associated with PCIe ports (PME, hot-plug, AER). Use
2974 them only if that is allowed by the BIOS.
2975 native Use native PCIe services associated with PCIe ports
2977 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2980 pcie_port_pm= [PCIE] PCIe port power management handling:
2981 off Disable power management of all PCIe ports
2982 force Forcibly enable power management of all PCIe ports
2984 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2985 nomsi Do not use MSI for native PCIe PME signaling (this makes
2986 all PCIe root ports use INTx for all services).
2988 pcmv= [HW,PCMCIA] BadgePAD 4
2992 Keep all power-domains already enabled by bootloader on,
2993 even if no driver has claimed them. This is useful
2994 for debug and development, but should not be
2995 needed on a platform with proper driver support.
2998 See Documentation/blockdev/paride.txt.
3000 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3003 See arch/parisc/kernel/pdc_chassis.c
3005 percpu_alloc= Select which percpu first chunk allocator to use.
3006 Currently supported values are "embed" and "page".
3007 Archs may support subset or none of the selections.
3008 See comments in mm/percpu.c for details on each
3009 allocator. This parameter is primarily for debugging
3010 and performance comparison.
3013 See Documentation/blockdev/paride.txt.
3016 See Documentation/blockdev/paride.txt.
3018 pirq= [SMP,APIC] Manual mp-table setup
3019 See Documentation/x86/i386/IO-APIC.txt.
3021 plip= [PPT,NET] Parallel port network link
3022 Format: { parport<nr> | timid | 0 }
3023 See also Documentation/parport.txt.
3025 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3026 Override pmtimer IOPort with a hex value.
3030 Enable PNP debug messages (depends on the
3031 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3032 via /sys/module/pnp/parameters/debug. We always show
3033 current resource usage; turning this on also shows
3034 possible settings and some assignment information.
3040 { on | off | curr | res | no-curr | no-res }
3043 [ISAPNP] Exclude IRQs for the autoconfiguration
3046 [ISAPNP] Exclude DMAs for the autoconfiguration
3048 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3049 Ranges are in pairs (I/O port base and size).
3052 [ISAPNP] Exclude memory regions for the
3054 Ranges are in pairs (memory base and size).
3056 ports= [IP_VS_FTP] IPVS ftp helper module
3058 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3060 Format: <port>,<port>....
3062 powersave=off [PPC] This option disables power saving features.
3063 It specifically disables cpuidle and sets the
3064 platform machine description specific power_save
3065 function to NULL. On Idle the CPU just reduces
3068 ppc_strict_facility_enable
3069 [PPC] This option catches any kernel floating point,
3070 Altivec, VSX and SPE outside of regions specifically
3071 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3072 There is some performance impact when enabling this.
3074 print-fatal-signals=
3075 [KNL] debug: print fatal signals
3077 If enabled, warn about various signal handling
3078 related application anomalies: too many signals,
3079 too many POSIX.1 timers, fatal signals causing a
3082 If you hit the warning due to signal overflow,
3083 you might want to try "ulimit -i unlimited".
3087 printk.always_kmsg_dump=
3088 Trigger kmsg_dump for cases other than kernel oops or
3090 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3093 printk.devkmsg={on,off,ratelimit}
3094 Control writing to /dev/kmsg.
3095 on - unlimited logging to /dev/kmsg from userspace
3096 off - logging to /dev/kmsg disabled
3097 ratelimit - ratelimit the logging
3100 printk.time= Show timing data prefixed to each printk message line
3101 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3103 processor.max_cstate= [HW,ACPI]
3104 Limit processor to maximum C-state
3105 max_cstate=9 overrides any DMI blacklist limit.
3107 processor.nocst [HW,ACPI]
3108 Ignore the _CST method to determine C-states,
3109 instead using the legacy FADT method
3111 profile= [KNL] Enable kernel profiling via /proc/profile
3112 Format: [schedule,]<number>
3113 Param: "schedule" - profile schedule points.
3114 Param: <number> - step/bucket size as a power of 2 for
3115 statistical time based profiling.
3116 Param: "sleep" - profile D-state sleeping (millisecs).
3117 Requires CONFIG_SCHEDSTATS
3118 Param: "kvm" - profile VM exits.
3120 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3122 See Documentation/blockdev/ramdisk.txt.
3124 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3125 probe for; one of (bare|imps|exps|lifebook|any).
3126 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3128 psmouse.resetafter= [HW,MOUSE]
3129 Try to reset the device after so many bad packets
3132 [HW,MOUSE] Set desired mouse resolution, in dpi.
3133 psmouse.smartscroll=
3134 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3135 0 = disabled, 1 = enabled (default).
3137 pstore.backend= Specify the name of the pstore backend to use
3140 See Documentation/blockdev/paride.txt.
3143 [KNL] Number of legacy pty's. Overwrites compiled-in
3146 quiet [KNL] Disable most log messages
3151 See Documentation/admin-guide/md.rst.
3153 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3154 See Documentation/blockdev/ramdisk.txt.
3157 The argument is a cpu list, as described above.
3159 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3160 the specified list of CPUs to be no-callback CPUs.
3161 Invocation of these CPUs' RCU callbacks will
3162 be offloaded to "rcuox/N" kthreads created for
3163 that purpose, where "x" is "b" for RCU-bh, "p"
3164 for RCU-preempt, and "s" for RCU-sched, and "N"
3165 is the CPU number. This reduces OS jitter on the
3166 offloaded CPUs, which can be useful for HPC and
3167 real-time workloads. It can also improve energy
3168 efficiency for asymmetric multiprocessors.
3171 Rather than requiring that offloaded CPUs
3172 (specified by rcu_nocbs= above) explicitly
3173 awaken the corresponding "rcuoN" kthreads,
3174 make these kthreads poll for callbacks.
3175 This improves the real-time response for the
3176 offloaded CPUs by relieving them of the need to
3177 wake up the corresponding kthread, but degrades
3178 energy efficiency by requiring that the kthreads
3179 periodically wake up to do the polling.
3181 rcutree.blimit= [KNL]
3182 Set maximum number of finished RCU callbacks to
3183 process in one batch.
3185 rcutree.dump_tree= [KNL]
3186 Dump the structure of the rcu_node combining tree
3187 out at early boot. This is used for diagnostic
3188 purposes, to verify correct tree setup.
3190 rcutree.gp_cleanup_delay= [KNL]
3191 Set the number of jiffies to delay each step of
3192 RCU grace-period cleanup. This only has effect
3193 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3195 rcutree.gp_init_delay= [KNL]
3196 Set the number of jiffies to delay each step of
3197 RCU grace-period initialization. This only has
3198 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3201 rcutree.gp_preinit_delay= [KNL]
3202 Set the number of jiffies to delay each step of
3203 RCU grace-period pre-initialization, that is,
3204 the propagation of recent CPU-hotplug changes up
3205 the rcu_node combining tree. This only has effect
3206 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3208 rcutree.rcu_fanout_exact= [KNL]
3209 Disable autobalancing of the rcu_node combining
3210 tree. This is used by rcutorture, and might
3211 possibly be useful for architectures having high
3212 cache-to-cache transfer latencies.
3214 rcutree.rcu_fanout_leaf= [KNL]
3215 Change the number of CPUs assigned to each
3216 leaf rcu_node structure. Useful for very
3217 large systems, which will choose the value 64,
3218 and for NUMA systems with large remote-access
3219 latencies, which will choose a value aligned
3220 with the appropriate hardware boundaries.
3222 rcutree.jiffies_till_sched_qs= [KNL]
3223 Set required age in jiffies for a
3224 given grace period before RCU starts
3225 soliciting quiescent-state help from
3226 rcu_note_context_switch().
3228 rcutree.jiffies_till_first_fqs= [KNL]
3229 Set delay from grace-period initialization to
3230 first attempt to force quiescent states.
3231 Units are jiffies, minimum value is zero,
3232 and maximum value is HZ.
3234 rcutree.jiffies_till_next_fqs= [KNL]
3235 Set delay between subsequent attempts to force
3236 quiescent states. Units are jiffies, minimum
3237 value is one, and maximum value is HZ.
3239 rcutree.kthread_prio= [KNL,BOOT]
3240 Set the SCHED_FIFO priority of the RCU per-CPU
3241 kthreads (rcuc/N). This value is also used for
3242 the priority of the RCU boost threads (rcub/N)
3243 and for the RCU grace-period kthreads (rcu_bh,
3244 rcu_preempt, and rcu_sched). If RCU_BOOST is
3245 set, valid values are 1-99 and the default is 1
3246 (the least-favored priority). Otherwise, when
3247 RCU_BOOST is not set, valid values are 0-99 and
3248 the default is zero (non-realtime operation).
3250 rcutree.rcu_nocb_leader_stride= [KNL]
3251 Set the number of NOCB kthread groups, which
3252 defaults to the square root of the number of
3253 CPUs. Larger numbers reduces the wakeup overhead
3254 on the per-CPU grace-period kthreads, but increases
3255 that same overhead on each group's leader.
3257 rcutree.qhimark= [KNL]
3258 Set threshold of queued RCU callbacks beyond which
3259 batch limiting is disabled.
3261 rcutree.qlowmark= [KNL]
3262 Set threshold of queued RCU callbacks below which
3263 batch limiting is re-enabled.
3265 rcutree.rcu_idle_gp_delay= [KNL]
3266 Set wakeup interval for idle CPUs that have
3267 RCU callbacks (RCU_FAST_NO_HZ=y).
3269 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3270 Set wakeup interval for idle CPUs that have
3271 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3272 Lazy RCU callbacks are those which RCU can
3273 prove do nothing more than free memory.
3275 rcutree.rcu_kick_kthreads= [KNL]
3276 Cause the grace-period kthread to get an extra
3277 wake_up() if it sleeps three times longer than
3278 it should at force-quiescent-state time.
3279 This wake_up() will be accompanied by a
3280 WARN_ONCE() splat and an ftrace_dump().
3282 rcuperf.gp_exp= [KNL]
3283 Measure performance of expedited synchronous
3284 grace-period primitives.
3286 rcuperf.holdoff= [KNL]
3287 Set test-start holdoff period. The purpose of
3288 this parameter is to delay the start of the
3289 test until boot completes in order to avoid
3292 rcuperf.nreaders= [KNL]
3293 Set number of RCU readers. The value -1 selects
3294 N, where N is the number of CPUs. A value
3295 "n" less than -1 selects N-n+1, where N is again
3296 the number of CPUs. For example, -2 selects N
3297 (the number of CPUs), -3 selects N+1, and so on.
3298 A value of "n" less than or equal to -N selects
3301 rcuperf.nwriters= [KNL]
3302 Set number of RCU writers. The values operate
3303 the same as for rcuperf.nreaders.
3304 N, where N is the number of CPUs
3306 rcuperf.perf_runnable= [BOOT]
3307 Start rcuperf running at boot time.
3309 rcuperf.shutdown= [KNL]
3310 Shut the system down after performance tests
3311 complete. This is useful for hands-off automated
3314 rcuperf.perf_type= [KNL]
3315 Specify the RCU implementation to test.
3317 rcuperf.verbose= [KNL]
3318 Enable additional printk() statements.
3320 rcutorture.cbflood_inter_holdoff= [KNL]
3321 Set holdoff time (jiffies) between successive
3322 callback-flood tests.
3324 rcutorture.cbflood_intra_holdoff= [KNL]
3325 Set holdoff time (jiffies) between successive
3326 bursts of callbacks within a given callback-flood
3329 rcutorture.cbflood_n_burst= [KNL]
3330 Set the number of bursts making up a given
3331 callback-flood test. Set this to zero to
3332 disable callback-flood testing.
3334 rcutorture.cbflood_n_per_burst= [KNL]
3335 Set the number of callbacks to be registered
3336 in a given burst of a callback-flood test.
3338 rcutorture.fqs_duration= [KNL]
3339 Set duration of force_quiescent_state bursts
3342 rcutorture.fqs_holdoff= [KNL]
3343 Set holdoff time within force_quiescent_state bursts
3346 rcutorture.fqs_stutter= [KNL]
3347 Set wait time between force_quiescent_state bursts
3350 rcutorture.gp_cond= [KNL]
3351 Use conditional/asynchronous update-side
3352 primitives, if available.
3354 rcutorture.gp_exp= [KNL]
3355 Use expedited update-side primitives, if available.
3357 rcutorture.gp_normal= [KNL]
3358 Use normal (non-expedited) asynchronous
3359 update-side primitives, if available.
3361 rcutorture.gp_sync= [KNL]
3362 Use normal (non-expedited) synchronous
3363 update-side primitives, if available. If all
3364 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3365 rcutorture.gp_normal=, and rcutorture.gp_sync=
3366 are zero, rcutorture acts as if is interpreted
3367 they are all non-zero.
3369 rcutorture.n_barrier_cbs= [KNL]
3370 Set callbacks/threads for rcu_barrier() testing.
3372 rcutorture.nfakewriters= [KNL]
3373 Set number of concurrent RCU writers. These just
3374 stress RCU, they don't participate in the actual
3375 test, hence the "fake".
3377 rcutorture.nreaders= [KNL]
3378 Set number of RCU readers. The value -1 selects
3379 N-1, where N is the number of CPUs. A value
3380 "n" less than -1 selects N-n-2, where N is again
3381 the number of CPUs. For example, -2 selects N
3382 (the number of CPUs), -3 selects N+1, and so on.
3384 rcutorture.object_debug= [KNL]
3385 Enable debug-object double-call_rcu() testing.
3387 rcutorture.onoff_holdoff= [KNL]
3388 Set time (s) after boot for CPU-hotplug testing.
3390 rcutorture.onoff_interval= [KNL]
3391 Set time (s) between CPU-hotplug operations, or
3392 zero to disable CPU-hotplug testing.
3394 rcutorture.shuffle_interval= [KNL]
3395 Set task-shuffle interval (s). Shuffling tasks
3396 allows some CPUs to go into dyntick-idle mode
3397 during the rcutorture test.
3399 rcutorture.shutdown_secs= [KNL]
3400 Set time (s) after boot system shutdown. This
3401 is useful for hands-off automated testing.
3403 rcutorture.stall_cpu= [KNL]
3404 Duration of CPU stall (s) to test RCU CPU stall
3405 warnings, zero to disable.
3407 rcutorture.stall_cpu_holdoff= [KNL]
3408 Time to wait (s) after boot before inducing stall.
3410 rcutorture.stat_interval= [KNL]
3411 Time (s) between statistics printk()s.
3413 rcutorture.stutter= [KNL]
3414 Time (s) to stutter testing, for example, specifying
3415 five seconds causes the test to run for five seconds,
3416 wait for five seconds, and so on. This tests RCU's
3417 ability to transition abruptly to and from idle.
3419 rcutorture.test_boost= [KNL]
3420 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3421 "Maybe" means test if the RCU implementation
3422 under test support RCU priority boosting.
3424 rcutorture.test_boost_duration= [KNL]
3425 Duration (s) of each individual boost test.
3427 rcutorture.test_boost_interval= [KNL]
3428 Interval (s) between each boost test.
3430 rcutorture.test_no_idle_hz= [KNL]
3431 Test RCU's dyntick-idle handling. See also the
3432 rcutorture.shuffle_interval parameter.
3434 rcutorture.torture_runnable= [BOOT]
3435 Start rcutorture running at boot time.
3437 rcutorture.torture_type= [KNL]
3438 Specify the RCU implementation to test.
3440 rcutorture.verbose= [KNL]
3441 Enable additional printk() statements.
3443 rcupdate.rcu_cpu_stall_suppress= [KNL]
3444 Suppress RCU CPU stall warning messages.
3446 rcupdate.rcu_cpu_stall_timeout= [KNL]
3447 Set timeout for RCU CPU stall warning messages.
3449 rcupdate.rcu_expedited= [KNL]
3450 Use expedited grace-period primitives, for
3451 example, synchronize_rcu_expedited() instead
3452 of synchronize_rcu(). This reduces latency,
3453 but can increase CPU utilization, degrade
3454 real-time latency, and degrade energy efficiency.
3455 No effect on CONFIG_TINY_RCU kernels.
3457 rcupdate.rcu_normal= [KNL]
3458 Use only normal grace-period primitives,
3459 for example, synchronize_rcu() instead of
3460 synchronize_rcu_expedited(). This improves
3461 real-time latency, CPU utilization, and
3462 energy efficiency, but can expose users to
3463 increased grace-period latency. This parameter
3464 overrides rcupdate.rcu_expedited. No effect on
3465 CONFIG_TINY_RCU kernels.
3467 rcupdate.rcu_normal_after_boot= [KNL]
3468 Once boot has completed (that is, after
3469 rcu_end_inkernel_boot() has been invoked), use
3470 only normal grace-period primitives. No effect
3471 on CONFIG_TINY_RCU kernels.
3473 rcupdate.rcu_task_stall_timeout= [KNL]
3474 Set timeout in jiffies for RCU task stall warning
3475 messages. Disable with a value less than or equal
3478 rcupdate.rcu_self_test= [KNL]
3479 Run the RCU early boot self tests
3481 rcupdate.rcu_self_test_bh= [KNL]
3482 Run the RCU bh early boot self tests
3484 rcupdate.rcu_self_test_sched= [KNL]
3485 Run the RCU sched early boot self tests
3489 Run specified binary instead of /init from the ramdisk,
3490 used for early userspace startup. See initrd.
3493 Format (x86 or x86_64):
3494 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3496 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3498 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3499 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3500 reboot_force is either force or not specified,
3501 reboot_cpu is s[mp]#### with #### being the processor
3502 to be used for rebooting.
3505 [KNL, SMP] Set scheduler's default relax_domain_level.
3506 See Documentation/cgroup-v1/cpusets.txt.
3508 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3510 reservetop= [X86-32]
3512 Reserves a hole at the top of the kernel virtual
3517 Set the amount of memory to reserve for BIOS at
3518 the bottom of the address space.
3520 reset_devices [KNL] Force drivers to reset the underlying device
3521 during initialization.
3524 Specify the partition device for software suspend
3526 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3528 resume_offset= [SWSUSP]
3529 Specify the offset from the beginning of the partition
3530 given by "resume=" at which the swap header is located,
3531 in <PAGE_SIZE> units (needed only for swap files).
3532 See Documentation/power/swsusp-and-swap-files.txt
3534 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3535 read the resume files
3537 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3538 Useful for devices that are detected asynchronously
3539 (e.g. USB and MMC devices).
3541 hibernate= [HIBERNATION]
3542 noresume Don't check if there's a hibernation image
3543 present during boot.
3544 nocompress Don't compress/decompress hibernation images.
3545 no Disable hibernation and resume.
3546 protect_image Turn on image protection during restoration
3547 (that will set all pages holding image data
3548 during restoration read-only).
3550 retain_initrd [RAM] Keep initrd memory after extraction
3552 rfkill.default_state=
3553 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3554 etc. communication is blocked by default.
3557 rfkill.master_switch_mode=
3558 0 The "airplane mode" button does nothing.
3559 1 The "airplane mode" button toggles between everything
3560 blocked and the previous configuration.
3561 2 The "airplane mode" button toggles between everything
3562 blocked and everything unblocked.
3564 rhash_entries= [KNL,NET]
3565 Set number of hash buckets for route cache
3568 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3571 ro [KNL] Mount root device read-only on boot
3574 on Mark read-only kernel memory as read-only (default).
3575 off Leave read-only kernel memory writable for debugging.
3578 Enable the uart passthrough on the designated usb port
3579 on Rockchip SoCs. When active, the signals of the
3580 debug-uart get routed to the D+ and D- pins of the usb
3581 port and the regular usb controller gets disabled.
3583 root= [KNL] Root filesystem
3584 See name_to_dev_t comment in init/do_mounts.c.
3586 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3587 mount the root filesystem
3589 rootflags= [KNL] Set root filesystem mount option string
3591 rootfstype= [KNL] Set root filesystem type
3593 rootwait [KNL] Wait (indefinitely) for root device to show up.
3594 Useful for devices that are detected asynchronously
3595 (e.g. USB and MMC devices).
3597 rproc_mem=nn[KMG][@address]
3598 [KNL,ARM,CMA] Remoteproc physical memory block.
3599 Memory area to be used by remote processor image,
3602 rw [KNL] Mount root device read-write on boot
3604 S [KNL] Run init in single mode
3606 s390_iommu= [HW,S390]
3607 Set s390 IOTLB flushing mode
3609 With strict flushing every unmap operation will result in
3610 an IOTLB flush. Default is lazy flushing before reuse,
3614 See drivers/net/irda/sa1100_ir.c.
3616 sbni= [NET] Granch SBNI12 leased line adapter
3618 sched_debug [KNL] Enables verbose scheduler debug messages.
3620 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3621 Allowed values are enable and disable. This feature
3622 incurs a small amount of overhead in the scheduler
3623 but is useful for debugging and performance tuning.
3625 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3626 xtime_lock contention on larger systems, and/or RCU lock
3627 contention on all systems with CONFIG_MAXSMP set.
3628 Format: { "0" | "1" }
3629 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3631 Note: increases power consumption, thus should only be
3632 enabled if running jitter sensitive (HPC/RT) workloads.
3634 security= [SECURITY] Choose a security module to enable at boot.
3635 If this boot parameter is not specified, only the first
3636 security module asking for security registration will be
3637 loaded. An invalid security module name will be treated
3638 as if no module has been chosen.
3640 selinux= [SELINUX] Disable or enable SELinux at boot time.
3641 Format: { "0" | "1" }
3642 See security/selinux/Kconfig help text.
3645 Default value is set via kernel config option.
3646 If enabled at boot time, /selinux/disable can be used
3647 later to disable prior to initial policy load.
3649 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3650 Format: { "0" | "1" }
3651 See security/apparmor/Kconfig help text
3654 Default value is set via kernel config option.
3656 serialnumber [BUGS=X86-32]
3659 Maximal number of shapers.
3667 Disable merging of slabs with similar size. May be
3668 necessary if there is some reason to distinguish
3669 allocs to different slabs. Debug options disable
3670 merging on their own.
3671 For more information see Documentation/vm/slub.txt.
3673 slab_max_order= [MM, SLAB]
3674 Determines the maximum allowed order for slabs.
3675 A high setting may cause OOMs due to memory
3676 fragmentation. Defaults to 1 for systems with
3677 more than 32MB of RAM, 0 otherwise.
3679 slub_debug[=options[,slabs]] [MM, SLUB]
3680 Enabling slub_debug allows one to determine the
3681 culprit if slab objects become corrupted. Enabling
3682 slub_debug can create guard zones around objects and
3683 may poison objects when not in use. Also tracks the
3684 last alloc / free. For more information see
3685 Documentation/vm/slub.txt.
3687 slub_max_order= [MM, SLUB]
3688 Determines the maximum allowed order for slabs.
3689 A high setting may cause OOMs due to memory
3690 fragmentation. For more information see
3691 Documentation/vm/slub.txt.
3693 slub_min_objects= [MM, SLUB]
3694 The minimum number of objects per slab. SLUB will
3695 increase the slab order up to slub_max_order to
3696 generate a sufficiently large slab able to contain
3697 the number of objects indicated. The higher the number
3698 of objects the smaller the overhead of tracking slabs
3699 and the less frequently locks need to be acquired.
3700 For more information see Documentation/vm/slub.txt.
3702 slub_min_order= [MM, SLUB]
3703 Determines the minimum page order for slabs. Must be
3704 lower than slub_max_order.
3705 For more information see Documentation/vm/slub.txt.
3707 slub_nomerge [MM, SLUB]
3708 Same with slab_nomerge. This is supported for legacy.
3709 See slab_nomerge for more information.
3712 Format: <io1>[,<io2>[,...,<io8>]]
3714 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3715 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3716 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3717 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3718 smsc-ircc2.ircc_irq= [HW] IRQ line
3719 smsc-ircc2.ircc_dma= [HW] DMA channel
3720 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3721 0: Toshiba Satellite 1800 (GP data pin select)
3722 1: Fast pin select (default)
3725 smt [KNL,S390] Set the maximum number of threads (logical
3726 CPUs) to use per physical CPU on systems capable of
3727 symmetric multithreading (SMT). Will be capped to the
3728 actual hardware limit.
3730 Default: -1 (no limit)
3733 [KNL] Should the soft-lockup detector generate panics.
3736 softlockup_all_cpu_backtrace=
3737 [KNL] Should the soft-lockup detector generate
3738 backtraces on all cpus.
3741 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3742 See Documentation/laptops/sonypi.txt
3744 spia_io_base= [HW,MTD]
3750 Enabled the stack tracer on boot up.
3752 stacktrace_filter=[function-list]
3753 [FTRACE] Limit the functions that the stack tracer
3754 will trace at boot up. function-list is a comma separated
3755 list of functions. This list can be changed at run
3756 time by the stack_trace_filter file in the debugfs
3757 tracing directory. Note, this enables stack tracing
3758 and the stacktrace above is not needed.
3762 Set the STI (builtin display/keyboard on the HP-PARISC
3763 machines) console (graphic card) which should be used
3764 as the initial boot-console.
3765 See also comment in drivers/video/console/sticore.c.
3768 See comment in drivers/video/console/sticore.c.
3771 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3773 sunrpc.min_resvport=
3774 sunrpc.max_resvport=
3776 SunRPC servers often require that client requests
3777 originate from a privileged port (i.e. a port in the
3778 range 0 < portnr < 1024).
3779 An administrator who wishes to reserve some of these
3780 ports for other uses may adjust the range that the
3781 kernel's sunrpc client considers to be privileged
3782 using these two parameters to set the minimum and
3783 maximum port values.
3785 sunrpc.svc_rpc_per_connection_limit=
3787 Limit the number of requests that the server will
3788 process in parallel from a single connection.
3789 The default value is 0 (no limit).
3793 Control how the NFS server code allocates CPUs to
3794 service thread pools. Depending on how many NICs
3795 you have and where their interrupts are bound, this
3796 option will affect which CPUs will do NFS serving.
3797 Note: this parameter cannot be changed while the
3798 NFS server is running.
3800 auto the server chooses an appropriate mode
3801 automatically using heuristics
3802 global a single global pool contains all CPUs
3803 percpu one pool for each CPU
3804 pernode one pool for each NUMA node (equivalent
3805 to global on non-NUMA machines)
3807 sunrpc.tcp_slot_table_entries=
3808 sunrpc.udp_slot_table_entries=
3810 Sets the upper limit on the number of simultaneous
3811 RPC calls that can be sent from the client to a
3812 server. Increasing these values may allow you to
3813 improve throughput, but will also increase the
3814 amount of memory reserved for use by the client.
3816 suspend.pm_test_delay=
3818 Sets the number of seconds to remain in a suspend test
3819 mode before resuming the system (see
3820 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3821 is set. Default value is 5.
3824 [KNL] Enable accounting of swap in memory resource
3825 controller if no parameter or 1 is given or disable
3826 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3828 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3829 Format: { <int> | force | noforce }
3830 <int> -- Number of I/O TLB slabs
3831 force -- force using of bounce buffers even if they
3832 wouldn't be automatically used by the kernel
3833 noforce -- Never use bounce buffers (for debugging)
3837 sysfs.deprecated=0|1 [KNL]
3838 Enable/disable old style sysfs layout for old udev
3839 on older distributions. When this option is enabled
3840 very new udev will not work anymore. When this option
3841 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3842 in older udev will not work anymore.
3843 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3844 the kernel configuration.
3846 sysrq_always_enabled
3848 Ignore sysrq setting - this boot parameter will
3849 neutralize any effect of /proc/sys/kernel/sysrq.
3850 Useful for debugging.
3852 tcpmhash_entries= [KNL,NET]
3853 Set the number of tcp_metrics_hash slots.
3854 Default value is 8192 or 16384 depending on total
3855 ram pages. This is used to specify the TCP metrics
3856 cache size. See Documentation/networking/ip-sysctl.txt
3857 "tcp_no_metrics_save" section for more details.
3861 test_suspend= [SUSPEND][,N]
3862 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3863 standby suspend) or "freeze" (for suspend type freeze)
3864 as the system sleep state during system startup with
3865 the optional capability to repeat N number of times.
3866 The system is woken from this state using a
3867 wakeup-capable RTC alarm.
3869 thash_entries= [KNL,NET]
3870 Set number of hash buckets for TCP connection
3872 thermal.act= [HW,ACPI]
3873 -1: disable all active trip points in all thermal zones
3874 <degrees C>: override all lowest active trip points
3876 thermal.crt= [HW,ACPI]
3877 -1: disable all critical trip points in all thermal zones
3878 <degrees C>: override all critical trip points
3880 thermal.nocrt= [HW,ACPI]
3881 Set to disable actions on ACPI thermal zone
3882 critical and hot trip points.
3884 thermal.off= [HW,ACPI]
3885 1: disable ACPI thermal control
3887 thermal.psv= [HW,ACPI]
3888 -1: disable all passive trip points
3889 <degrees C>: override all passive trip points to this
3892 thermal.tzp= [HW,ACPI]
3893 Specify global default ACPI thermal zone polling rate
3894 <deci-seconds>: poll all this frequency
3895 0: no polling (default)
3898 Force threading of all interrupt handlers except those
3899 marked explicitly IRQF_NO_THREAD.
3902 Enable the Transcendent memory driver if built-in.
3904 tmem.cleancache=0|1 [KNL, XEN]
3905 Default is on (1). Disable the usage of the cleancache
3906 API to send anonymous pages to the hypervisor.
3908 tmem.frontswap=0|1 [KNL, XEN]
3909 Default is on (1). Disable the usage of the frontswap
3910 API to send swap pages to the hypervisor. If disabled
3911 the selfballooning and selfshrinking are force disabled.
3913 tmem.selfballooning=0|1 [KNL, XEN]
3914 Default is on (1). Disable the driving of swap pages
3917 tmem.selfshrinking=0|1 [KNL, XEN]
3918 Default is on (1). Partial swapoff that immediately
3919 transfers pages from Xen hypervisor back to the
3920 kernel based on different criteria.
3924 Specify if the kernel should make use of the cpu
3925 topology information if the hardware supports this.
3926 The scheduler will make use of this information and
3927 e.g. base its process migration decisions on it.
3930 topology_updates= [KNL, PPC, NUMA]
3932 Specify if the kernel should ignore (off)
3933 topology updates sent by the hypervisor to this
3938 tpm_suspend_pcr=[HW,TPM]
3939 Format: integer pcr id
3940 Specify that at suspend time, the tpm driver
3941 should extend the specified pcr with zeros,
3942 as a workaround for some chips which fail to
3943 flush the last written pcr on TPM_SaveState.
3944 This will guarantee that all the other pcrs
3947 trace_buf_size=nn[KMG]
3948 [FTRACE] will set tracing buffer size on each cpu.
3950 trace_event=[event-list]
3951 [FTRACE] Set and start specified trace events in order
3952 to facilitate early boot debugging. The event-list is a
3953 comma separated list of trace events to enable. See
3954 also Documentation/trace/events.txt
3956 trace_options=[option-list]
3957 [FTRACE] Enable or disable tracer options at boot.
3958 The option-list is a comma delimited list of options
3959 that can be enabled or disabled just as if you were
3960 to echo the option name into
3962 /sys/kernel/debug/tracing/trace_options
3964 For example, to enable stacktrace option (to dump the
3965 stack trace of each event), add to the command line:
3967 trace_options=stacktrace
3969 See also Documentation/trace/ftrace.txt "trace options"
3973 Have the tracepoints sent to printk as well as the
3974 tracing ring buffer. This is useful for early boot up
3975 where the system hangs or reboots and does not give the
3976 option for reading the tracing buffer or performing a
3977 ftrace_dump_on_oops.
3979 To turn off having tracepoints sent to printk,
3980 echo 0 > /proc/sys/kernel/tracepoint_printk
3981 Note, echoing 1 into this file without the
3982 tracepoint_printk kernel cmdline option has no effect.
3986 Having tracepoints sent to printk() and activating high
3987 frequency tracepoints such as irq or sched, can cause
3988 the system to live lock.
3991 [FTRACE] enable this option to disable tracing when a
3992 warning is hit. This turns off "tracing_on". Tracing can
3993 be enabled again by echoing '1' into the "tracing_on"
3994 file located in /sys/kernel/debug/tracing/
3996 This option is useful, as it disables the trace before
3997 the WARNING dump is called, which prevents the trace to
3998 be filled with content caused by the warning output.
4000 This option can also be set at run time via the sysctl
4001 option: kernel/traceoff_on_warning
4003 transparent_hugepage=
4005 Format: [always|madvise|never]
4006 Can be used to control the default behavior of the system
4007 with respect to transparent hugepages.
4008 See Documentation/vm/transhuge.txt for more details.
4010 tsc= Disable clocksource stability checks for TSC.
4012 [x86] reliable: mark tsc clocksource as reliable, this
4013 disables clocksource verification at runtime, as well
4014 as the stability checks done at bootup. Used to enable
4015 high-resolution timer mode on older hardware, and in
4016 virtualized environment.
4017 [x86] noirqtime: Do not use TSC to do irq accounting.
4018 Used to run time disable IRQ_TIME_ACCOUNTING on any
4019 platforms where RDTSC is slow and this accounting
4022 turbografx.map[2|3]= [HW,JOY]
4023 TurboGraFX parallel port interface
4025 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4026 See also Documentation/input/joystick-parport.txt
4028 udbg-immortal [PPC] When debugging early kernel crashes that
4029 happen after console_init() and before a proper
4030 console driver takes over, this boot options might
4031 help "seeing" what's going on.
4033 uhash_entries= [KNL,NET]
4034 Set number of hash buckets for UDP/UDP-Lite connections
4037 [USB] Ignore overcurrent events (default N).
4038 Some badly-designed motherboards generate lots of
4039 bogus events, for ports that aren't wired to
4040 anything. Set this parameter to avoid log spamming.
4041 Note that genuine overcurrent events won't be
4045 [X86] Cause panic on unknown NMI.
4047 usbcore.authorized_default=
4048 [USB] Default USB device authorization:
4049 (default -1 = authorized except for wireless USB,
4050 0 = not authorized, 1 = authorized)
4052 usbcore.autosuspend=
4053 [USB] The autosuspend time delay (in seconds) used
4054 for newly-detected USB devices (default 2). This
4055 is the time required before an idle device will be
4056 autosuspended. Devices for which the delay is set
4057 to a negative value won't be autosuspended at all.
4059 usbcore.usbfs_snoop=
4060 [USB] Set to log all usbfs traffic (default 0 = off).
4062 usbcore.usbfs_snoop_max=
4063 [USB] Maximum number of bytes to snoop in each URB
4066 usbcore.blinkenlights=
4067 [USB] Set to cycle leds on hubs (default 0 = off).
4069 usbcore.old_scheme_first=
4070 [USB] Start with the old device initialization
4071 scheme (default 0 = off).
4073 usbcore.usbfs_memory_mb=
4074 [USB] Memory limit (in MB) for buffers allocated by
4075 usbfs (default = 16, 0 = max = 2047).
4077 usbcore.use_both_schemes=
4078 [USB] Try the other device initialization scheme
4079 if the first one fails (default 1 = enabled).
4081 usbcore.initial_descriptor_timeout=
4082 [USB] Specifies timeout for the initial 64-byte
4083 USB_REQ_GET_DESCRIPTOR request in milliseconds
4084 (default 5000 = 5.0 seconds).
4086 usbcore.nousb [USB] Disable the USB subsystem
4089 [USBHID] The interval which mice are to be polled at.
4091 usb-storage.delay_use=
4092 [UMS] The delay in seconds before a new device is
4093 scanned for Logical Units (default 1).
4096 [UMS] A list of quirks entries to supplement or
4097 override the built-in unusual_devs list. List
4098 entries are separated by commas. Each entry has
4099 the form VID:PID:Flags where VID and PID are Vendor
4100 and Product ID values (4-digit hex numbers) and
4101 Flags is a set of characters, each corresponding
4102 to a common usb-storage quirk flag as follows:
4103 a = SANE_SENSE (collect more than 18 bytes
4105 b = BAD_SENSE (don't collect more than 18
4106 bytes of sense data);
4107 c = FIX_CAPACITY (decrease the reported
4108 device capacity by one sector);
4109 d = NO_READ_DISC_INFO (don't use
4110 READ_DISC_INFO command);
4111 e = NO_READ_CAPACITY_16 (don't use
4112 READ_CAPACITY_16 command);
4113 f = NO_REPORT_OPCODES (don't use report opcodes
4115 g = MAX_SECTORS_240 (don't transfer more than
4116 240 sectors at a time, uas only);
4117 h = CAPACITY_HEURISTICS (decrease the
4118 reported device capacity by one
4119 sector if the number is odd);
4120 i = IGNORE_DEVICE (don't bind to this
4122 j = NO_REPORT_LUNS (don't use report luns
4124 l = NOT_LOCKABLE (don't try to lock and
4125 unlock ejectable media);
4126 m = MAX_SECTORS_64 (don't transfer more
4127 than 64 sectors = 32 KB at a time);
4128 n = INITIAL_READ10 (force a retry of the
4129 initial READ(10) command);
4130 o = CAPACITY_OK (accept the capacity
4131 reported by the device);
4132 p = WRITE_CACHE (the device cache is ON
4134 r = IGNORE_RESIDUE (the device reports
4135 bogus residue values);
4136 s = SINGLE_LUN (the device has only one
4138 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4139 commands, uas only);
4140 u = IGNORE_UAS (don't bind to the uas driver);
4141 w = NO_WP_DETECT (don't test whether the
4142 medium is write-protected).
4143 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4144 even if the device claims no cache)
4145 Example: quirks=0419:aaf5:rl,0421:0433:rc
4147 user_debug= [KNL,ARM]
4149 See arch/arm/Kconfig.debug help text.
4150 1 - undefined instruction events
4152 4 - invalid data aborts
4155 Example: user_debug=31
4158 [X86] Flags controlling user PTE allocations.
4160 nohigh = do not allocate PTE pages in
4161 HIGHMEM regardless of setting
4165 On X86_32, this is an alias for vdso32=. Otherwise:
4167 vdso=1: enable VDSO (the default)
4168 vdso=0: disable VDSO mapping
4170 vdso32= [X86] Control the 32-bit vDSO
4171 vdso32=1: enable 32-bit VDSO
4172 vdso32=0 or vdso32=2: disable 32-bit VDSO
4174 See the help text for CONFIG_COMPAT_VDSO for more
4175 details. If CONFIG_COMPAT_VDSO is set, the default is
4176 vdso32=0; otherwise, the default is vdso32=1.
4178 For compatibility with older kernels, vdso32=2 is an
4181 Try vdso32=0 if you encounter an error that says:
4182 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4185 vector=percpu: enable percpu vector domain
4187 video= [FB] Frame buffer configuration
4188 See Documentation/fb/modedb.txt.
4190 video.brightness_switch_enabled= [0,1]
4191 If set to 1, on receiving an ACPI notify event
4192 generated by hotkey, video driver will adjust brightness
4193 level and then send out the event to user space through
4194 the allocated input device; If set to 0, video driver
4195 will only send out the event without touching backlight
4200 [VMMIO] Memory mapped virtio (platform) device.
4202 <size>@<baseaddr>:<irq>[:<id>]
4204 <size> := size (can use standard suffixes
4206 <baseaddr> := physical base address
4207 <irq> := interrupt number (as passed to
4209 <id> := (optional) platform device id
4211 virtio_mmio.device=1K@0x100b0000:48:7
4213 Can be used multiple times for multiple devices.
4215 vga= [BOOT,X86-32] Select a particular video mode
4216 See Documentation/x86/boot.txt and
4217 Documentation/svga.txt.
4218 Use vga=ask for menu.
4219 This is actually a boot loader parameter; the value is
4220 passed to the kernel using a special protocol.
4222 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4223 size of <nn>. This can be used to increase the
4224 minimum size (128MB on x86). It can also be used to
4225 decrease the size and leave more room for directly
4228 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4231 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4234 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4238 Controls the behavior of vsyscalls (i.e. calls to
4239 fixed addresses of 0xffffffffff600x00 from legacy
4240 code). Most statically-linked binaries and older
4241 versions of glibc use these calls. Because these
4242 functions are at fixed addresses, they make nice
4243 targets for exploits that can control RIP.
4245 emulate [default] Vsyscalls turn into traps and are
4246 emulated reasonably safely.
4248 native Vsyscalls are native syscall instructions.
4249 This is a little bit faster than trapping
4250 and makes a few dynamic recompilers work
4251 better than they would in emulation mode.
4252 It also makes exploits much easier to write.
4254 none Vsyscalls don't work at all. This makes
4255 them quite hard to use for exploits but
4256 might break your system.
4258 vt.color= [VT] Default text color.
4259 Format: 0xYX, X = foreground, Y = background.
4260 Default: 0x07 = light gray on black.
4262 vt.cur_default= [VT] Default cursor shape.
4263 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4264 the parameters of the <Esc>[?A;B;Cc escape sequence;
4265 see VGA-softcursor.txt. Default: 2 = underline.
4267 vt.default_blu= [VT]
4268 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4269 Change the default blue palette of the console.
4270 This is a 16-member array composed of values
4273 vt.default_grn= [VT]
4274 Format: <green0>,<green1>,<green2>,...,<green15>
4275 Change the default green palette of the console.
4276 This is a 16-member array composed of values
4279 vt.default_red= [VT]
4280 Format: <red0>,<red1>,<red2>,...,<red15>
4281 Change the default red palette of the console.
4282 This is a 16-member array composed of values
4288 Set system-wide default UTF-8 mode for all tty's.
4289 Default is 1, i.e. UTF-8 mode is enabled for all
4290 newly opened terminals.
4292 vt.global_cursor_default=
4295 Set system-wide default for whether a cursor
4296 is shown on new VTs. Default is -1,
4297 i.e. cursors will be created by default unless
4298 overridden by individual drivers. 0 will hide
4299 cursors, 1 will display them.
4301 vt.italic= [VT] Default color for italic text; 0-15.
4304 vt.underline= [VT] Default color for underlined text; 0-15.
4307 watchdog timers [HW,WDT] For information on watchdog timers,
4308 see Documentation/watchdog/watchdog-parameters.txt
4309 or other driver-specific files in the
4310 Documentation/watchdog/ directory.
4312 workqueue.watchdog_thresh=
4313 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4314 warn stall conditions and dump internal state to
4315 help debugging. 0 disables workqueue stall
4316 detection; otherwise, it's the stall threshold
4317 duration in seconds. The default value is 30 and
4318 it can be updated at runtime by writing to the
4319 corresponding sysfs file.
4321 workqueue.disable_numa
4322 By default, all work items queued to unbound
4323 workqueues are affine to the NUMA nodes they're
4324 issued on, which results in better behavior in
4325 general. If NUMA affinity needs to be disabled for
4326 whatever reason, this option can be used. Note
4327 that this also can be controlled per-workqueue for
4328 workqueues visible under /sys/bus/workqueue/.
4330 workqueue.power_efficient
4331 Per-cpu workqueues are generally preferred because
4332 they show better performance thanks to cache
4333 locality; unfortunately, per-cpu workqueues tend to
4334 be more power hungry than unbound workqueues.
4336 Enabling this makes the per-cpu workqueues which
4337 were observed to contribute significantly to power
4338 consumption unbound, leading to measurably lower
4339 power usage at the cost of small performance
4342 The default value of this parameter is determined by
4343 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4345 workqueue.debug_force_rr_cpu
4346 Workqueue used to implicitly guarantee that work
4347 items queued without explicit CPU specified are put
4348 on the local CPU. This guarantee is no longer true
4349 and while local CPU is still preferred work items
4350 may be put on foreign CPUs. This debug option
4351 forces round-robin CPU selection to flush out
4352 usages which depend on the now broken guarantee.
4353 When enabled, memory and cache locality will be
4356 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4357 default x2apic cluster mode on platforms
4360 x86_intel_mid_timer= [X86-32,APBT]
4361 Choose timer option for x86 Intel MID platform.
4362 Two valid options are apbt timer only and lapic timer
4363 plus one apbt timer for broadcast timer.
4364 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4366 xen_512gb_limit [KNL,X86-64,XEN]
4367 Restricts the kernel running paravirtualized under Xen
4368 to use only up to 512 GB of RAM. The reason to do so is
4369 crash analysis tools and Xen tools for doing domain
4370 save/restore/migration must be enabled to handle larger
4373 xen_emul_unplug= [HW,X86,XEN]
4374 Unplug Xen emulated devices
4375 Format: [unplug0,][unplug1]
4376 ide-disks -- unplug primary master IDE devices
4377 aux-ide-disks -- unplug non-primary-master IDE devices
4378 nics -- unplug network devices
4379 all -- unplug all emulated devices (NICs and IDE disks)
4380 unnecessary -- unplugging emulated devices is
4381 unnecessary even if the host did not respond to
4383 never -- do not unplug even if version check succeeds
4385 xen_nopvspin [X86,XEN]
4386 Disables the ticketlock slowpath using Xen PV
4390 Disables the PV optimizations forcing the HVM guest to
4391 run as generic HVM guest with no PV drivers.
4393 xirc2ps_cs= [NET,PCMCIA]
4395 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
projects / linux-2.6-block.git / blob