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_no_auto_serialize [HW,ACPI]
110 Disable auto-serialization of AML methods
111 AML control methods that contain the opcodes to create
112 named objects will be marked as "Serialized" by the
113 auto-serialization feature.
114 This feature is enabled by default.
115 This option allows to turn off the feature.
117 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
120 acpi_no_static_ssdt [HW,ACPI]
121 Disable installation of static SSDTs at early boot time
122 By default, SSDTs contained in the RSDT/XSDT will be
123 installed automatically and they will appear under
124 /sys/firmware/acpi/tables.
125 This option turns off this feature.
126 Note that specifying this option does not affect
127 dynamic table installation which will install SSDT
128 tables to /sys/firmware/acpi/tables/dynamic.
130 acpi_rsdp= [ACPI,EFI,KEXEC]
131 Pass the RSDP address to the kernel, mostly used
132 on machines running EFI runtime service to boot the
133 second kernel for kdump.
135 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
136 Format: To spoof as Windows 98: ="Microsoft Windows"
138 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
139 of 2 which is mandated by ACPI 6) as the supported ACPI
140 specification revision (when using this switch, it may
141 be necessary to carry out a cold reboot _twice_ in a
142 row to make it take effect on the platform firmware).
144 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
145 acpi_osi="string1" # add string1
146 acpi_osi="!string2" # remove string2
147 acpi_osi=!* # remove all strings
148 acpi_osi=! # disable all built-in OS vendor
150 acpi_osi=!! # enable all built-in OS vendor
152 acpi_osi= # disable all strings
154 'acpi_osi=!' can be used in combination with single or
155 multiple 'acpi_osi="string1"' to support specific OS
156 vendor string(s). Note that such command can only
157 affect the default state of the OS vendor strings, thus
158 it cannot affect the default state of the feature group
159 strings and the current state of the OS vendor strings,
160 specifying it multiple times through kernel command line
161 is meaningless. This command is useful when one do not
162 care about the state of the feature group strings which
163 should be controlled by the OSPM.
165 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
166 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
167 can make '_OSI("Windows 2000")' TRUE.
169 'acpi_osi=' cannot be used in combination with other
170 'acpi_osi=' command lines, the _OSI method will not
171 exist in the ACPI namespace. NOTE that such command can
172 only affect the _OSI support state, thus specifying it
173 multiple times through kernel command line is also
176 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
179 'acpi_osi=!*' can be used in combination with single or
180 multiple 'acpi_osi="string1"' to support specific
181 string(s). Note that such command can affect the
182 current state of both the OS vendor strings and the
183 feature group strings, thus specifying it multiple times
184 through kernel command line is meaningful. But it may
185 still not able to affect the final state of a string if
186 there are quirks related to this string. This command
187 is useful when one want to control the state of the
188 feature group strings to debug BIOS issues related to
191 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
192 '_OSI("Module Device")' FALSE.
193 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
194 '_OSI("Module Device")' TRUE.
195 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
197 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
199 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
200 they all will make '_OSI("Windows 2000")' TRUE.
203 Override the pmtimer bug detection: force the kernel
204 to assume that this machine's pmtimer latches its value
205 and always returns good values.
207 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
208 Format: { level | edge | high | low }
210 acpi_skip_timer_override [HW,ACPI]
211 Recognize and ignore IRQ0/pin2 Interrupt Override.
212 For broken nForce2 BIOS resulting in XT-PIC timer.
214 acpi_sleep= [HW,ACPI] Sleep options
215 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
216 old_ordering, nonvs, sci_force_enable }
217 See Documentation/power/video.txt for information on
219 s3_beep is for debugging; it makes the PC's speaker beep
220 as soon as the kernel's real-mode entry point is called.
221 s4_nohwsig prevents ACPI hardware signature from being
222 used during resume from hibernation.
223 old_ordering causes the ACPI 1.0 ordering of the _PTS
224 control method, with respect to putting devices into
225 low power states, to be enforced (the ACPI 2.0 ordering
226 of _PTS is used by default).
227 nonvs prevents the kernel from saving/restoring the
228 ACPI NVS memory during suspend/hibernation and resume.
229 sci_force_enable causes the kernel to set SCI_EN directly
230 on resume from S1/S3 (which is against the ACPI spec,
231 but some broken systems don't work without it).
233 acpi_use_timer_override [HW,ACPI]
234 Use timer override. For some broken Nvidia NF5 boards
235 that require a timer override, but don't have HPET
237 add_efi_memmap [EFI; X86] Include EFI memory map in
238 kernel's map of available physical RAM.
241 { off | try_unsupported }
242 off: disable AGP support
243 try_unsupported: try to drive unsupported chipsets
244 (may crash computer or cause data corruption)
247 See Documentation/sound/alsa/alsa-parameters.txt
250 Allow the default userspace alignment fault handler
251 behaviour to be specified. Bit 0 enables warnings,
252 bit 1 enables fixups, and bit 2 sends a segfault.
254 align_va_addr= [X86-64]
255 Align virtual addresses by clearing slice [14:12] when
256 allocating a VMA at process creation time. This option
257 gives you up to 3% performance improvement on AMD F15h
258 machines (where it is enabled by default) for a
259 CPU-intensive style benchmark, and it can vary highly in
260 a microbenchmark depending on workload and compiler.
262 32: only for 32-bit processes
263 64: only for 64-bit processes
264 on: enable for both 32- and 64-bit processes
265 off: disable for both 32- and 64-bit processes
267 alloc_snapshot [FTRACE]
268 Allocate the ftrace snapshot buffer on boot up when the
269 main buffer is allocated. This is handy if debugging
270 and you need to use tracing_snapshot() on boot up, and
271 do not want to use tracing_snapshot_alloc() as it needs
272 to be done where GFP_KERNEL allocations are allowed.
274 amd_iommu= [HW,X86-64]
275 Pass parameters to the AMD IOMMU driver in the system.
277 fullflush - enable flushing of IO/TLB entries when
278 they are unmapped. Otherwise they are
279 flushed before they will be reused, which
281 off - do not initialize any AMD IOMMU found in
283 force_isolation - Force device isolation for all
284 devices. The IOMMU driver is not
285 allowed anymore to lift isolation
286 requirements as needed. This option
287 does not override iommu=pt
289 amd_iommu_dump= [HW,X86-64]
290 Enable AMD IOMMU driver option to dump the ACPI table
291 for AMD IOMMU. With this option enabled, AMD IOMMU
292 driver will print ACPI tables for AMD IOMMU during
293 IOMMU initialization.
295 amd_iommu_intr= [HW,X86-64]
296 Specifies one of the following AMD IOMMU interrupt
298 legacy - Use legacy interrupt remapping mode.
299 vapic - Use virtual APIC mode, which allows IOMMU
300 to inject interrupts directly into guest.
301 This mode requires kvm-amd.avic=1.
302 (Default when IOMMU HW support is present.)
304 amijoy.map= [HW,JOY] Amiga joystick support
305 Map of devices attached to JOY0DAT and JOY1DAT
307 See also Documentation/input/joystick.txt
309 analog.map= [HW,JOY] Analog joystick and gamepad support
310 Specifies type or capabilities of an analog joystick
311 connected to one of 16 gameports
312 Format: <type1>,<type2>,..<type16>
315 Power management functions (SPARCstation-4/5 + deriv.)
317 Disable APC CPU standby support. SPARCstation-Fox does
318 not play well with APC CPU idle - disable it if you have
319 APC and your system crashes randomly.
321 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
322 Change the output verbosity whilst booting
323 Format: { quiet (default) | verbose | debug }
324 Change the amount of debugging information output
325 when initialising the APIC and IO-APIC components.
327 apic_extnmi= [APIC,X86] External NMI delivery setting
328 Format: { bsp (default) | all | none }
329 bsp: External NMI is delivered only to CPU 0
330 all: External NMIs are broadcast to all CPUs as a
332 none: External NMI is masked for all CPUs. This is
333 useful so that a dump capture kernel won't be
337 See Documentation/networking/ipv6.txt.
339 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
340 Limit apic dumping. The parameter defines the maximal
341 number of local apics being dumped. Also it is possible
342 to set it to "all" by meaning -- no limit here.
343 Format: { 1 (default) | 2 | ... | all }.
344 The parameter valid if only apic=debug or
345 apic=verbose is specified.
346 Example: apic=debug show_lapic=all
348 apm= [APM] Advanced Power Management
349 See header of arch/x86/kernel/apm_32.c.
351 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
352 Format: <io>,<irq>,<nodeID>
356 atarimouse= [HW,MOUSE] Atari Mouse
358 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
359 EzKey and similar keyboards
361 atkbd.reset= [HW] Reset keyboard during initialization
363 atkbd.set= [HW] Select keyboard code set
364 Format: <int> (2 = AT (default), 3 = PS/2)
366 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
369 atkbd.softraw= [HW] Choose between synthetic and real raw mode
370 Format: <bool> (0 = real, 1 = synthetic (default))
372 atkbd.softrepeat= [HW]
373 Use software keyboard repeat
375 audit= [KNL] Enable the audit sub-system
376 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
377 0 - kernel audit is disabled and can not be enabled
378 until the next reboot
379 unset - kernel audit is initialized but disabled and
380 will be fully enabled by the userspace auditd.
381 1 - kernel audit is initialized and partially enabled,
382 storing at most audit_backlog_limit messages in
383 RAM until it is fully enabled by the userspace
387 audit_backlog_limit= [KNL] Set the audit queue size limit.
388 Format: <int> (must be >=0)
391 bau= [X86_UV] Enable the BAU on SGI UV. The default
392 behavior is to disable the BAU (i.e. bau=0).
393 Format: { "0" | "1" }
396 unset - Disable the BAU.
398 baycom_epp= [HW,AX25]
401 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
403 See header of drivers/net/hamradio/baycom_par.c.
405 baycom_ser_fdx= [HW,AX25]
406 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
407 Format: <io>,<irq>,<mode>[,<baud>]
408 See header of drivers/net/hamradio/baycom_ser_fdx.c.
410 baycom_ser_hdx= [HW,AX25]
411 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
412 Format: <io>,<irq>,<mode>
413 See header of drivers/net/hamradio/baycom_ser_hdx.c.
415 blkdevparts= Manual partition parsing of block device(s) for
416 embedded devices based on command line input.
417 See Documentation/block/cmdline-partition.txt
419 boot_delay= Milliseconds to delay each printk during boot.
420 Values larger than 10 seconds (10000) are changed to
424 bootmem_debug [KNL] Enable bootmem allocator debug messages.
427 Disable BERT OS support on buggy BIOSes.
429 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
430 bttv.radio= Most important insmod options are available as
432 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
435 bulk_remove=off [PPC] This parameter disables the use of the pSeries
436 firmware feature for flushing multiple hpte entries
439 c101= [NET] Moxa C101 synchronous serial card
441 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
442 Sometimes CPU hardware bugs make them report the cache
443 size incorrectly. The kernel will attempt work arounds
444 to fix known problems, but for some CPUs it is not
445 possible to determine what the correct size should be.
446 This option provides an override for these situations.
448 ca_keys= [KEYS] This parameter identifies a specific key(s) on
449 the system trusted keyring to be used for certificate
451 format: { id:<keyid> | builtin }
453 cca= [MIPS] Override the kernel pages' cache coherency
454 algorithm. Accepted values range from 0 to 7
455 inclusive. See arch/mips/include/asm/pgtable-bits.h
456 for platform specific values (SB1, Loongson3 and
459 ccw_timeout_log [S390]
460 See Documentation/s390/CommonIO for details.
462 cgroup_disable= [KNL] Disable a particular controller
463 Format: {name of the controller(s) to disable}
464 The effects of cgroup_disable=foo are:
465 - foo isn't auto-mounted if you mount all cgroups in
467 - foo isn't visible as an individually mountable
469 {Currently only "memory" controller deal with this and
470 cut the overhead, others just disable the usage. So
471 only cgroup_disable=memory is actually worthy}
473 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
474 Format: { controller[,controller...] | "all" }
475 Like cgroup_disable, but only applies to cgroup v1;
476 the blacklisted controllers remain available in cgroup2.
478 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
480 nosocket -- Disable socket memory accounting.
481 nokmem -- Disable kernel memory accounting.
483 checkreqprot [SELINUX] Set initial checkreqprot flag value.
484 Format: { "0" | "1" }
485 See security/selinux/Kconfig help text.
486 0 -- check protection applied by kernel (includes
487 any implied execute protection).
488 1 -- check protection requested by application.
489 Default value is set via a kernel config option.
490 Value can be changed at runtime via
491 /selinux/checkreqprot.
494 See Documentation/s390/CommonIO for details.
497 Prevents the clock framework from automatically gating
498 clocks that have not been explicitly enabled by a Linux
499 device driver but are enabled in hardware at reset or
500 by the bootloader/firmware. Note that this does not
501 force such clocks to be always-on nor does it reserve
502 those clocks in any way. This parameter is useful for
503 debug and development, but should not be needed on a
504 platform with proper driver support. For more
505 information, see Documentation/clk.txt.
507 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
509 Forces specified clocksource (if available) to be used
510 when calculating gettimeofday(). If specified
511 clocksource is not available, it defaults to PIT.
512 Format: { pit | tsc | cyclone | pmtmr }
514 clocksource= Override the default clocksource
516 Override the default clocksource and use the clocksource
517 with the name specified.
518 Some clocksource names to choose from, depending on
520 [all] jiffies (this is the base, fallback clocksource)
522 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
523 pxa_timer,timer3,32k_counter,timer0_1
525 [X86-32] pit,hpet,tsc;
526 scx200_hrt on Geode; cyclone on IBM x440
534 clocksource.arm_arch_timer.evtstrm=
537 Enable/disable the eventstream feature of the ARM
538 architected timer so that code using WFE-based polling
539 loops can be debugged more effectively on production
542 clocksource.arm_arch_timer.fsl-a008585=
545 Enable/disable the workaround of Freescale/NXP
546 erratum A-008585. This can be useful for KVM
547 guests, if the guest device tree doesn't show the
548 erratum. If unspecified, the workaround is
549 enabled based on the device tree.
551 clearcpuid=BITNUM [X86]
552 Disable CPUID feature X for the kernel. See
553 arch/x86/include/asm/cpufeatures.h for the valid bit
554 numbers. Note the Linux specific bits are not necessarily
555 stable over kernel options, but the vendor specific
557 Also note that user programs calling CPUID directly
558 or using the feature without checking anything
559 will still see it. This just prevents it from
560 being used by the kernel or shown in /proc/cpuinfo.
561 Also note the kernel might malfunction if you disable
564 cma=nn[MG]@[start[MG][-end[MG]]]
566 Sets the size of kernel global memory area for
567 contiguous memory allocations and optionally the
568 placement constraint by the physical address range of
569 memory allocations. A value of 0 disables CMA
570 altogether. For more information, see
571 include/linux/dma-contiguous.h
573 cmo_free_hint= [PPC] Format: { yes | no }
574 Specify whether pages are marked as being inactive
575 when they are freed. This is used in CMO environments
576 to determine OS memory pressure for page stealing by
580 coherent_pool=nn[KMG] [ARM,KNL]
581 Sets the size of memory pool for coherent, atomic dma
582 allocations, by default set to 256K.
584 code_bytes [X86] How many bytes of object code to print
589 com20020= [HW,NET] ARCnet - COM20020 chipset
591 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
593 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
597 ARCnet - COM90xx chipset (memory-mapped buffers)
598 Format: <io>[,<irq>[,<memstart>]]
600 condev= [HW,S390] console device
603 console= [KNL] Output console device and options.
605 tty<n> Use the virtual console device <n>.
609 Use the specified serial port. The options are of
610 the form "bbbbpnf", where "bbbb" is the baud rate,
611 "p" is parity ("n", "o", or "e"), "n" is number of
612 bits, and "f" is flow control ("r" for RTS or
613 omit it). Default is "9600n8".
615 See Documentation/admin-guide/serial-console.rst for more
617 Documentation/networking/netconsole.txt for an
620 uart[8250],io,<addr>[,options]
621 uart[8250],mmio,<addr>[,options]
622 uart[8250],mmio16,<addr>[,options]
623 uart[8250],mmio32,<addr>[,options]
624 uart[8250],0x<addr>[,options]
625 Start an early, polled-mode console on the 8250/16550
626 UART at the specified I/O port or MMIO address,
627 switching to the matching ttyS device later.
628 MMIO inter-register address stride is either 8-bit
629 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
630 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
631 to be equivalent to 'mmio'. 'options' are specified in
632 the same format described for ttyS above; if unspecified,
633 the h/w is not re-initialized.
635 hvc<n> Use the hypervisor console device <n>. This is for
636 both Xen and PowerPC hypervisors.
638 If the device connected to the port is not a TTY but a braille
639 device, prepend "brl," before the device type, for instance
641 For now, only VisioBraille is supported.
643 consoleblank= [KNL] The console blank (screen saver) timeout in
644 seconds. Defaults to 10*60 = 10mins. A value of 0
645 disables the blank timer.
648 [KNL] Change the default value for
649 /proc/<pid>/coredump_filter.
650 See also Documentation/filesystems/proc.txt.
652 cpuidle.off=1 [CPU_IDLE]
653 disable the cpuidle sub-system
656 [X86] Delay for N microsec between assert and de-assert
657 of APIC INIT to start processors. This delay occurs
658 on every CPU online, such as boot, and resume from suspend.
661 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
663 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
665 crashkernel=size[KMG][@offset[KMG]]
666 [KNL] Using kexec, Linux can switch to a 'crash kernel'
667 upon panic. This parameter reserves the physical
668 memory region [offset, offset + size] for that kernel
669 image. If '@offset' is omitted, then a suitable offset
670 is selected automatically. Check
671 Documentation/kdump/kdump.txt for further details.
673 crashkernel=range1:size1[,range2:size2,...][@offset]
674 [KNL] Same as above, but depends on the memory
675 in the running system. The syntax of range is
676 start-[end] where start and end are both
677 a memory unit (amount[KMG]). See also
678 Documentation/kdump/kdump.txt for an example.
680 crashkernel=size[KMG],high
681 [KNL, x86_64] range could be above 4G. Allow kernel
682 to allocate physical memory region from top, so could
683 be above 4G if system have more than 4G ram installed.
684 Otherwise memory region will be allocated below 4G, if
686 It will be ignored if crashkernel=X is specified.
687 crashkernel=size[KMG],low
688 [KNL, x86_64] range under 4G. When crashkernel=X,high
689 is passed, kernel could allocate physical memory region
690 above 4G, that cause second kernel crash on system
691 that require some amount of low memory, e.g. swiotlb
692 requires at least 64M+32K low memory, also enough extra
693 low memory is needed to make sure DMA buffers for 32-bit
694 devices won't run out. Kernel would try to allocate at
695 at least 256M below 4G automatically.
696 This one let user to specify own low range under 4G
697 for second kernel instead.
698 0: to disable low allocation.
699 It will be ignored when crashkernel=X,high is not used
700 or memory reserved is below 4G.
703 [KNL] Disable crypto self-tests
708 cs89x0_media= [HW,NET]
709 Format: { rj45 | aui | bnc }
712 See header of drivers/s390/block/dasd_devmap.c.
714 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
715 (one device per port)
716 Format: <port#>,<type>
717 See also Documentation/input/joystick-parport.txt
719 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
720 time. See Documentation/dynamic-debug-howto.txt for
721 details. Deprecated, see dyndbg.
723 debug [KNL] Enable kernel debugging (events log level).
726 [KNL] verbose self-tests
728 Print debugging info while doing the locking API
730 We default to 0 (no extra messages), setting it to
731 1 will print _a lot_ more information - normally
732 only useful to kernel developers.
734 debug_objects [KNL] Enable object debugging
737 [KNL] Disable object debugging
739 debug_guardpage_minorder=
740 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
741 parameter allows control of the order of pages that will
742 be intentionally kept free (and hence protected) by the
743 buddy allocator. Bigger value increase the probability
744 of catching random memory corruption, but reduce the
745 amount of memory for normal system use. The maximum
746 possible value is MAX_ORDER/2. Setting this parameter
747 to 1 or 2 should be enough to identify most random
748 memory corruption problems caused by bugs in kernel or
749 driver code when a CPU writes to (or reads from) a
750 random memory location. Note that there exists a class
751 of memory corruptions problems caused by buggy H/W or
752 F/W or by drivers badly programing DMA (basically when
753 memory is written at bus level and the CPU MMU is
754 bypassed) which are not detectable by
755 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
756 tracking down these problems.
759 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
760 parameter enables the feature at boot time. In
761 default, it is disabled. We can avoid allocating huge
762 chunk of memory for debug pagealloc if we don't enable
763 it at boot time and the system will work mostly same
764 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
765 on: enable the feature
767 debugpat [X86] Enable PAT debugging
769 decnet.addr= [HW,NET]
770 Format: <area>[,<node>]
771 See also Documentation/networking/decnet.txt.
774 [same as hugepagesz=] The size of the default
775 HugeTLB page size. This is the size represented by
776 the legacy /proc/ hugepages APIs, used for SHM, and
777 default size when mounting hugetlbfs filesystems.
778 Defaults to the default architecture's huge page size
782 Set number of hash buckets for dentry cache.
784 disable_1tb_segments [PPC]
785 Disables the use of 1TB hash page table segments. This
786 causes the kernel to fall back to 256MB segments which
787 can be useful when debugging issues that require an SLB
791 See Documentation/networking/ipv6.txt.
794 Disable RADIX MMU mode on POWER9
796 disable_cpu_apicid= [X86,APIC,SMP]
798 The number of initial APIC ID for the
799 corresponding CPU to be disabled at boot,
800 mostly used for the kdump 2nd kernel to
801 disable BSP to wake up multiple CPUs without
802 causing system reset or hang due to sending
805 disable_ddw [PPC/PSERIES]
806 Disable Dynamic DMA Window support. Use this if
807 to workaround buggy firmware.
810 See Documentation/networking/ipv6.txt.
812 disable_mtrr_cleanup [X86]
813 The kernel tries to adjust MTRR layout from continuous
814 to discrete, to make X server driver able to add WB
815 entry later. This parameter disables that.
817 disable_mtrr_trim [X86, Intel and AMD only]
818 By default the kernel will trim any uncacheable
819 memory out of your available memory pool based on
820 MTRR settings. This parameter disables that behavior,
821 possibly causing your machine to run very slowly.
823 disable_timer_pin_1 [X86]
824 Disable PIN 1 of APIC timer
825 Can be useful to work around chipset bugs.
827 dis_ucode_ldr [X86] Disable the microcode loader.
829 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
830 this option disables the debugging code at boot.
832 dma_debug_entries=<number>
833 This option allows to tune the number of preallocated
834 entries for DMA-API debugging code. One entry is
835 required per DMA-API allocation. Use this if the
836 DMA-API debugging code disables itself because the
837 architectural default is too low.
839 dma_debug_driver=<driver_name>
840 With this option the DMA-API debugging driver
841 filter feature can be enabled at boot time. Just
842 pass the driver to filter for as the parameter.
843 The filter can be disabled or changed to another
844 driver later using sysfs.
846 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
847 Broken monitors, graphic adapters, KVMs and EDIDless
848 panels may send no or incorrect EDID data sets.
849 This parameter allows to specify an EDID data sets
850 in the /lib/firmware directory that are used instead.
851 Generic built-in EDID data sets are used, if one of
852 edid/1024x768.bin, edid/1280x1024.bin,
853 edid/1680x1050.bin, or edid/1920x1080.bin is given
854 and no file with the same name exists. Details and
855 instructions how to build your own EDID data are
856 available in Documentation/EDID/HOWTO.txt. An EDID
857 data set will only be used for a particular connector,
858 if its name and a colon are prepended to the EDID
859 name. Each connector may use a unique EDID data
860 set by separating the files with a comma. An EDID
861 data set with no connector name will be used for
862 any connectors not explicitly specified.
866 dump_apple_properties [X86]
867 Dump name and content of EFI device properties on
868 x86 Macs. Useful for driver authors to determine
869 what data is available or for reverse-engineering.
871 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
872 module.dyndbg[="val"]
873 Enable debug messages at boot time. See
874 Documentation/dynamic-debug-howto.txt for details.
876 nompx [X86] Disables Intel Memory Protection Extensions.
877 See Documentation/x86/intel_mpx.txt for more
878 information about the feature.
880 nopku [X86] Disable Memory Protection Keys CPU feature found
883 module.async_probe [KNL]
884 Enable asynchronous probe on this module.
886 early_ioremap_debug [KNL]
887 Enable debug messages in early_ioremap support. This
888 is useful for tracking down temporary early mappings
889 which are not unmapped.
891 earlycon= [KNL] Output early console device and options.
893 When used with no options, the early console is
894 determined by the stdout-path property in device
897 cdns,<addr>[,options]
898 Start an early, polled-mode console on a Cadence
899 (xuartps) serial port at the specified address. Only
900 supported option is baud rate. If baud rate is not
901 specified, the serial port must already be setup and
904 uart[8250],io,<addr>[,options]
905 uart[8250],mmio,<addr>[,options]
906 uart[8250],mmio32,<addr>[,options]
907 uart[8250],mmio32be,<addr>[,options]
908 uart[8250],0x<addr>[,options]
909 Start an early, polled-mode console on the 8250/16550
910 UART at the specified I/O port or MMIO address.
911 MMIO inter-register address stride is either 8-bit
912 (mmio) or 32-bit (mmio32 or mmio32be).
913 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
914 to be equivalent to 'mmio'. 'options' are specified
915 in the same format described for "console=ttyS<n>"; if
916 unspecified, the h/w is not initialized.
920 Start an early, polled-mode console on a pl011 serial
921 port at the specified address. The pl011 serial port
922 must already be setup and configured. Options are not
923 yet supported. If 'mmio32' is specified, then only
924 the driver will use only 32-bit accessors to read/write
925 the device registers.
928 Start an early, polled-mode console on a meson serial
929 port at the specified address. The serial port must
930 already be setup and configured. Options are not yet
934 Start an early, polled-mode console on an msm serial
935 port at the specified address. The serial port
936 must already be setup and configured. Options are not
940 Start an early, polled-mode console on an msm serial
941 dm port at the specified address. The serial port
942 must already be setup and configured. Options are not
945 smh Use ARM semihosting calls for early console.
953 Use early console provided by serial driver available
954 on Samsung SoCs, requires selecting proper type and
955 a correct base address of the selected UART port. The
956 serial port must already be setup and configured.
957 Options are not yet supported.
961 Use early console provided by Freescale LP UART driver
962 found on Freescale Vybrid and QorIQ LS1021A processors.
963 A valid base address must be provided, and the serial
964 port must already be setup and configured.
966 armada3700_uart,<addr>
967 Start an early, polled-mode console on the
968 Armada 3700 serial port at the specified
969 address. The serial port must already be setup
970 and configured. Options are not yet supported.
972 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
976 earlyprintk=serial[,ttySn[,baudrate]]
977 earlyprintk=serial[,0x...[,baudrate]]
978 earlyprintk=ttySn[,baudrate]
979 earlyprintk=dbgp[debugController#]
980 earlyprintk=pciserial,bus:device.function[,baudrate]
982 earlyprintk is useful when the kernel crashes before
983 the normal console is initialized. It is not enabled by
984 default because it has some cosmetic problems.
986 Append ",keep" to not disable it when the real console
989 Only one of vga, efi, serial, or usb debug port can
992 Currently only ttyS0 and ttyS1 may be specified by
993 name. Other I/O ports may be explicitly specified
994 on some architectures (x86 and arm at least) by
995 replacing ttySn with an I/O port address, like this:
996 earlyprintk=serial,0x1008,115200
997 You can find the port for a given device in
998 /proc/tty/driver/serial:
999 2: uart:ST16650V2 port:00001008 irq:18 ...
1001 Interaction with the standard serial driver is not
1004 The VGA and EFI output is eventually overwritten by
1007 The xen output can only be used by Xen PV guests.
1009 edac_report= [HW,EDAC] Control how to report EDAC event
1010 Format: {"on" | "off" | "force"}
1011 on: enable EDAC to report H/W event. May be overridden
1012 by other higher priority error reporting module.
1013 off: disable H/W event reporting through EDAC.
1014 force: enforce the use of EDAC to report H/W event.
1017 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1020 This is designed to be used in conjunction with
1021 the boot argument: earlyprintk=vga
1024 Format: {"off" | "on" | "skip[mbr]"}
1027 Format: { "old_map", "nochunk", "noruntime", "debug" }
1028 old_map [X86-64]: switch to the old ioremap-based EFI
1029 runtime services mapping. 32-bit still uses this one by
1031 nochunk: disable reading files in "chunks" in the EFI
1032 boot stub, as chunking can cause problems with some
1033 firmware implementations.
1034 noruntime : disable EFI runtime services support
1035 debug: enable misc debug output
1037 efi_no_storage_paranoia [EFI; X86]
1038 Using this parameter you can use more than 50% of
1039 your efi variable storage. Use this parameter only if
1040 you are really sure that your UEFI does sane gc and
1041 fulfills the spec otherwise your board may brick.
1043 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1044 Add arbitrary attribute to specific memory range by
1045 updating original EFI memory map.
1046 Region of memory which aa attribute is added to is
1048 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1049 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1050 attribute is added to range 0x100000000-0x180000000 and
1051 0x10a0000000-0x1120000000.
1053 Using this parameter you can do debugging of EFI memmap
1054 related feature. For example, you can do debugging of
1055 Address Range Mirroring feature even if your box
1058 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1059 that is to be dynamically loaded by Linux. If there are
1060 multiple variables with the same name but with different
1061 vendor GUIDs, all of them will be loaded. See
1062 Documentation/acpi/ssdt-overlays.txt for details.
1065 eisa_irq_edge= [PARISC,HW]
1066 See header of drivers/parisc/eisa.c.
1069 See comment before function elanfreq_setup() in
1070 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1073 Format: {"cfq" | "deadline" | "noop"}
1074 See Documentation/block/cfq-iosched.txt and
1075 Documentation/block/deadline-iosched.txt for details.
1077 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1078 Specifies physical address of start of kernel core
1079 image elf header and optionally the size. Generally
1080 kexec loader will pass this option to capture kernel.
1081 See Documentation/kdump/kdump.txt for details.
1083 enable_mtrr_cleanup [X86]
1084 The kernel tries to adjust MTRR layout from continuous
1085 to discrete, to make X server driver able to add WB
1086 entry later. This parameter enables that.
1088 enable_timer_pin_1 [X86]
1089 Enable PIN 1 of APIC timer
1090 Can be useful to work around chipset bugs
1091 (in particular on some ATI chipsets).
1092 The kernel tries to set a reasonable default.
1094 enforcing [SELINUX] Set initial enforcing status.
1096 See security/selinux/Kconfig help text.
1097 0 -- permissive (log only, no denials).
1098 1 -- enforcing (deny and log).
1100 Value can be changed at runtime via /selinux/enforce.
1103 Disable Error Record Serialization Table (ERST)
1106 ether= [HW,NET] Ethernet cards parameters
1107 This option is obsoleted by the "netdev=" option, which
1108 has equivalent usage. See its documentation for details.
1112 Permit 'security.evm' to be updated regardless of
1113 current integrity status.
1117 fail_make_request=[KNL]
1118 General fault injection mechanism.
1119 Format: <interval>,<probability>,<space>,<times>
1120 See also Documentation/fault-injection/.
1123 See Documentation/blockdev/floppy.txt.
1125 force_pal_cache_flush
1126 [IA-64] Avoid check_sal_cache_flush which may hang on
1127 buggy SAL_CACHE_FLUSH implementations. Using this
1128 parameter will force ia64_sal_cache_flush to call
1129 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1132 Forcefully enable Physical Address Extension (PAE).
1133 Many Pentium M systems disable PAE but may have a
1134 functionally usable PAE implementation.
1135 Warning: use of this parameter will taint the kernel
1136 and may cause unknown problems.
1139 [FTRACE] will set and start the specified tracer
1140 as early as possible in order to facilitate early
1143 ftrace_dump_on_oops[=orig_cpu]
1144 [FTRACE] will dump the trace buffers on oops.
1145 If no parameter is passed, ftrace will dump
1146 buffers of all CPUs, but if you pass orig_cpu, it will
1147 dump only the buffer of the CPU that triggered the
1150 ftrace_filter=[function-list]
1151 [FTRACE] Limit the functions traced by the function
1152 tracer at boot up. function-list is a comma separated
1153 list of functions. This list can be changed at run
1154 time by the set_ftrace_filter file in the debugfs
1157 ftrace_notrace=[function-list]
1158 [FTRACE] Do not trace the functions specified in
1159 function-list. This list can be changed at run time
1160 by the set_ftrace_notrace file in the debugfs
1163 ftrace_graph_filter=[function-list]
1164 [FTRACE] Limit the top level callers functions traced
1165 by the function graph tracer at boot up.
1166 function-list is a comma separated list of functions
1167 that can be changed at run time by the
1168 set_graph_function file in the debugfs tracing directory.
1170 ftrace_graph_notrace=[function-list]
1171 [FTRACE] Do not trace from the functions specified in
1172 function-list. This list is a comma separated list of
1173 functions that can be changed at run time by the
1174 set_graph_notrace file in the debugfs tracing directory.
1177 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1178 support via parallel port (up to 5 devices per port)
1179 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1180 See also Documentation/input/joystick-parport.txt
1184 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1188 gcov_persist= [GCOV] When non-zero (default), profiling data for
1189 kernel modules is saved and remains accessible via
1190 debugfs, even when the module is unloaded/reloaded.
1191 When zero, profiling data is discarded and associated
1192 debugfs files are removed at module unload time.
1194 gpt [EFI] Forces disk with valid GPT signature but
1195 invalid Protective MBR to be treated as GPT. If the
1196 primary GPT is corrupted, it enables the backup/alternate
1197 GPT to be used instead.
1199 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1200 the "Enable 0" bit of the configuration register.
1203 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1204 the "Enable 0" bit of the configuration register.
1207 grcan.select= [HW] Select which physical interface to use.
1210 grcan.txsize= [HW] Sets the size of the tx buffer.
1211 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1213 grcan.rxsize= [HW] Sets the size of the rx buffer.
1214 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1217 gpio-mockup.gpio_mockup_ranges
1218 [HW] Sets the ranges of gpiochip of for this device.
1219 Format: <start1>,<end1>,<start2>,<end2>...
1221 hardlockup_all_cpu_backtrace=
1222 [KNL] Should the hard-lockup detector generate
1223 backtraces on all cpus.
1226 hashdist= [KNL,NUMA] Large hashes allocated during boot
1227 are distributed across NUMA nodes. Defaults on
1228 for 64-bit NUMA, off otherwise.
1229 Format: 0 | 1 (for off | on)
1231 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1233 hd= [EIDE] (E)IDE hard drive subsystem geometry
1234 Format: <cyl>,<head>,<sect>
1237 Disable Hardware Error Source Table (HEST) support;
1238 corresponding firmware-first mode error processing
1239 logic will be disabled.
1241 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1242 size of <nn>. This works even on boxes that have no
1243 highmem otherwise. This also works to reduce highmem
1244 size on bigger boxes.
1246 highres= [KNL] Enable/disable high resolution timer mode.
1247 Valid parameters: "on", "off"
1251 See Documentation/isdn/README.HiSax.
1255 hpet= [X86-32,HPET] option to control HPET usage
1256 Format: { enable (default) | disable | force |
1258 disable: disable HPET and use PIT instead
1259 force: allow force enabled of undocumented chips (ICH4,
1261 verbose: show contents of HPET registers during setup
1263 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1264 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1266 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1267 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1268 On x86-64 and powerpc, this option can be specified
1269 multiple times interleaved with hugepages= to reserve
1270 huge pages of different sizes. Valid pages sizes on
1271 x86-64 are 2M (when the CPU supports "pse") and 1G
1272 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1274 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1275 terminal devices. Valid values: 0..8
1276 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1277 If specified, z/VM IUCV HVC accepts connections
1278 from listed z/VM user IDs only.
1280 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1281 hardware thread id mappings.
1282 Format: <cpu>:<hwthread>
1285 Do not unregister boot console at start. This is only
1286 useful for debugging when something happens in the window
1287 between unregistering the boot console and initializing
1290 i2c_bus= [HW] Override the default board specific I2C bus speed
1291 or register an additional I2C bus that is not
1292 registered from board initialization code.
1296 i8042.debug [HW] Toggle i8042 debug mode
1297 i8042.unmask_kbd_data
1298 [HW] Enable printing of interrupt data from the KBD port
1299 (disabled by default, and as a pre-condition
1300 requires that i8042.debug=1 be enabled)
1301 i8042.direct [HW] Put keyboard port into non-translated mode
1302 i8042.dumbkbd [HW] Pretend that controller can only read data from
1303 keyboard and cannot control its state
1304 (Don't attempt to blink the leds)
1305 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1306 i8042.nokbd [HW] Don't check/create keyboard port
1307 i8042.noloop [HW] Disable the AUX Loopback command while probing
1309 i8042.nomux [HW] Don't check presence of an active multiplexing
1311 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1313 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1314 i8042.reset [HW] Reset the controller during init, cleanup and
1315 suspend-to-ram transitions, only during s2r
1316 transitions, or never reset
1317 Format: { 1 | Y | y | 0 | N | n }
1318 1, Y, y: always reset controller
1319 0, N, n: don't ever reset controller
1320 Default: only on s2r transitions on x86; most other
1321 architectures force reset to be always executed
1322 i8042.unlock [HW] Unlock (ignore) the keylock
1323 i8042.kbdreset [HW] Reset device connected to KBD port
1327 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1328 indicates that the driver is running on unsupported
1330 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1331 does not match list of supported models.
1333 [HW] Report power status in /proc/i8k
1334 (disabled by default)
1335 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1338 i915.invert_brightness=
1339 [DRM] Invert the sense of the variable that is used to
1340 set the brightness of the panel backlight. Normally a
1341 brightness value of 0 indicates backlight switched off,
1342 and the maximum of the brightness value sets the backlight
1343 to maximum brightness. If this parameter is set to 0
1344 (default) and the machine requires it, or this parameter
1345 is set to 1, a brightness value of 0 sets the backlight
1346 to maximum brightness, and the maximum of the brightness
1347 value switches the backlight off.
1348 -1 -- never invert brightness
1349 0 -- machine default
1350 1 -- force brightness inversion
1353 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1355 ide-core.nodma= [HW] (E)IDE subsystem
1356 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1357 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1358 .cdrom .chs .ignore_cable are additional options
1359 See Documentation/ide/ide.txt.
1361 ide-generic.probe-mask= [HW] (E)IDE subsystem
1363 Probe mask for legacy ISA IDE ports. Depending on
1364 platform up to 6 ports are supported, enabled by
1365 setting corresponding bits in the mask to 1. The
1366 default value is 0x0, which has a special meaning.
1367 On systems that have PCI, it triggers scanning the
1368 PCI bus for the first and the second port, which
1369 are then probed. On systems without PCI the value
1370 of 0x0 enables probing the two first ports as if it
1373 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1374 Claim all unknown PCI IDE storage controllers.
1377 Format: idle=poll, idle=halt, idle=nomwait
1378 Poll forces a polling idle loop that can slightly
1379 improve the performance of waking up a idle CPU, but
1380 will use a lot of power and make the system run hot.
1382 idle=halt: Halt is forced to be used for CPU idle.
1383 In such case C2/C3 won't be used again.
1384 idle=nomwait: Disable mwait for CPU C-states
1386 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1387 Format: { strict | legacy | 2008 | relaxed }
1390 Choose which programs will be accepted for execution
1391 based on the IEEE 754 NaN encoding(s) supported by
1392 the FPU and the NaN encoding requested with the value
1393 of an ELF file header flag individually set by each
1394 binary. Hardware implementations are permitted to
1395 support either or both of the legacy and the 2008 NaN
1398 Available settings are as follows:
1399 strict accept binaries that request a NaN encoding
1400 supported by the FPU
1401 legacy only accept legacy-NaN binaries, if supported
1403 2008 only accept 2008-NaN binaries, if supported
1405 relaxed accept any binaries regardless of whether
1406 supported by the FPU
1408 The FPU emulator is always able to support both NaN
1409 encodings, so if no FPU hardware is present or it has
1410 been disabled with 'nofpu', then the settings of
1411 'legacy' and '2008' strap the emulator accordingly,
1412 'relaxed' straps the emulator for both legacy-NaN and
1413 2008-NaN, whereas 'strict' enables legacy-NaN only on
1414 legacy processors and both NaN encodings on MIPS32 or
1417 The setting for ABS.fmt/NEG.fmt instruction execution
1418 mode generally follows that for the NaN encoding,
1419 except where unsupported by hardware.
1421 ignore_loglevel [KNL]
1422 Ignore loglevel setting - this will print /all/
1423 kernel messages to the console. Useful for debugging.
1424 We also add it as printk module parameter, so users
1425 could change it dynamically, usually by
1426 /sys/module/printk/parameters/ignore_loglevel.
1429 Ignore RLIMIT_DATA setting for data mappings,
1430 print warning at first misuse. Can be changed via
1431 /sys/module/kernel/parameters/ignore_rlimit_data.
1433 ihash_entries= [KNL]
1434 Set number of hash buckets for inode cache.
1436 ima_appraise= [IMA] appraise integrity measurements
1437 Format: { "off" | "enforce" | "fix" | "log" }
1440 ima_appraise_tcb [IMA]
1441 The builtin appraise policy appraises all files
1445 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1449 The list of supported hash algorithms is defined
1450 in crypto/hash_info.h.
1453 The builtin measurement policy to load during IMA
1454 setup. Specyfing "tcb" as the value, measures all
1455 programs exec'd, files mmap'd for exec, and all files
1456 opened with the read mode bit set by either the
1457 effective uid (euid=0) or uid=0.
1460 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1461 Load a policy which meets the needs of the Trusted
1462 Computing Base. This means IMA will measure all
1463 programs exec'd, files mmap'd for exec, and all files
1464 opened for read by uid=0.
1467 Select one of defined IMA measurements template formats.
1468 Formats: { "ima" | "ima-ng" | "ima-sig" }
1472 [IMA] Define a custom template format.
1473 Format: { "field1|...|fieldN" }
1475 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1476 Format: <min_file_size>
1477 Set the minimal file size for using asynchronous hash.
1478 If left unspecified, ahash usage is disabled.
1480 ahash performance varies for different data sizes on
1481 different crypto accelerators. This option can be used
1482 to achieve the best performance for a particular HW.
1484 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1486 Set hashing buffer size. Default: 4k.
1488 ahash performance varies for different chunk sizes on
1489 different crypto accelerators. This option can be used
1490 to achieve best performance for particular HW.
1494 Run specified binary instead of /sbin/init as init
1497 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1498 for working out where the kernel is dying during
1501 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1502 initcall functions. Useful for debugging built-in
1503 modules and initcalls.
1505 initrd= [BOOT] Specify the location of the initial ramdisk
1507 init_pkru= [x86] Specify the default memory protection keys rights
1508 register contents for all processes. 0x55555554 by
1509 default (disallow access to all but pkey 0). Can
1510 override in debugfs after boot.
1512 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1515 int_pln_enable [x86] Enable power limit notification interrupt
1517 integrity_audit=[IMA]
1518 Format: { "0" | "1" }
1519 0 -- basic integrity auditing messages. (Default)
1520 1 -- additional integrity auditing messages.
1522 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1524 Enable intel iommu driver.
1526 Disable intel iommu driver.
1527 igfx_off [Default Off]
1528 By default, gfx is mapped as normal device. If a gfx
1529 device has a dedicated DMAR unit, the DMAR unit is
1530 bypassed by not enabling DMAR with this option. In
1531 this case, gfx device will use physical address for
1534 With this option iommu will not optimize to look
1535 for io virtual address below 32-bit forcing dual
1536 address cycle on pci bus for cards supporting greater
1537 than 32-bit addressing. The default is to look
1538 for translation below 32-bit and if not available
1539 then look in the higher range.
1540 strict [Default Off]
1541 With this option on every unmap_single operation will
1542 result in a hardware IOTLB flush operation as opposed
1543 to batching them for performance.
1544 sp_off [Default Off]
1545 By default, super page will be supported if Intel IOMMU
1546 has the capability. With this option, super page will
1548 ecs_off [Default Off]
1549 By default, extended context tables will be supported if
1550 the hardware advertises that it has support both for the
1551 extended tables themselves, and also PASID support. With
1552 this option set, extended tables will not be used even
1553 on hardware which claims to support them.
1555 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1556 0 disables intel_idle and fall back on acpi_idle.
1557 1 to 9 specify maximum depth of C-state.
1561 Do not enable intel_pstate as the default
1562 scaling driver for the supported processors
1564 Use intel_pstate as a scaling driver, but configure it
1565 to work with generic cpufreq governors (instead of
1566 enabling its internal governor). This mode cannot be
1567 used along with the hardware-managed P-states (HWP)
1570 Enable intel_pstate on systems that prohibit it by default
1571 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1572 instead of acpi-cpufreq may disable platform features, such
1573 as thermal controls and power capping, that rely on ACPI
1574 P-States information being indicated to OSPM and therefore
1575 should be used with caution. This option does not work with
1576 processors that aren't supported by the intel_pstate driver
1577 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1579 Do not enable hardware P state control (HWP)
1582 Only load intel_pstate on systems which support
1583 hardware P state control (HWP) if available.
1585 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1586 Description Table, specifies preferred power management
1587 profile as "Enterprise Server" or "Performance Server",
1588 then this feature is turned on by default.
1590 Allow per-logical-CPU P-State performance control limits using
1591 cpufreq sysfs interface
1593 intremap= [X86-64, Intel-IOMMU]
1594 on enable Interrupt Remapping (default)
1595 off disable Interrupt Remapping
1596 nosid disable Source ID checking
1598 BIOS x2APIC opt-out request will be ignored
1599 nopost disable Interrupt Posting
1601 iomem= Disable strict checking of access to MMIO memory
1602 strict regions from userspace.
1617 nobypass [PPC/POWERNV]
1618 Disable IOMMU bypass, using IOMMU for PCI devices.
1621 io7= [HW] IO7 for Marvel based alpha systems
1622 See comment before marvel_specify_io7 in
1623 arch/alpha/kernel/core_marvel.c.
1625 io_delay= [X86] I/O delay method
1627 Standard port 0x80 based delay
1629 Alternate port 0xed based delay (needed on some systems)
1631 Simple two microseconds delay
1636 See Documentation/filesystems/nfs/nfsroot.txt.
1638 irqaffinity= [SMP] Set the default irq affinity mask
1639 The argument is a cpu list, as described above.
1642 When an interrupt is not handled search all handlers
1643 for it. Intended to get systems with badly broken
1647 When an interrupt is not handled search all handlers
1648 for it. Also check all handlers each timer
1649 interrupt. Intended to get systems with badly broken
1653 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1655 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1656 The argument is a cpu list, as described above.
1658 This option can be used to specify one or more CPUs
1659 to isolate from the general SMP balancing and scheduling
1660 algorithms. You can move a process onto or off an
1661 "isolated" CPU via the CPU affinity syscalls or cpuset.
1662 <cpu number> begins at 0 and the maximum value is
1663 "number of CPUs in system - 1".
1665 This option is the preferred way to isolate CPUs. The
1666 alternative -- manually setting the CPU mask of all
1667 tasks in the system -- can cause problems and
1668 suboptimal load balancer performance.
1672 ivrs_ioapic [HW,X86_64]
1673 Provide an override to the IOAPIC-ID<->DEVICE-ID
1674 mapping provided in the IVRS ACPI table. For
1675 example, to map IOAPIC-ID decimal 10 to
1676 PCI device 00:14.0 write the parameter as:
1677 ivrs_ioapic[10]=00:14.0
1679 ivrs_hpet [HW,X86_64]
1680 Provide an override to the HPET-ID<->DEVICE-ID
1681 mapping provided in the IVRS ACPI table. For
1682 example, to map HPET-ID decimal 0 to
1683 PCI device 00:14.0 write the parameter as:
1684 ivrs_hpet[0]=00:14.0
1686 ivrs_acpihid [HW,X86_64]
1687 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1688 mapping provided in the IVRS ACPI table. For
1689 example, to map UART-HID:UID AMD0020:0 to
1690 PCI device 00:14.5 write the parameter as:
1691 ivrs_acpihid[00:14.5]=AMD0020:0
1693 js= [HW,JOY] Analog joystick
1694 See Documentation/input/joystick.txt.
1697 When CONFIG_RANDOMIZE_BASE is set, this disables
1698 kernel and module base offset ASLR (Address Space
1699 Layout Randomization).
1703 kernelcore= [KNL,X86,IA-64,PPC]
1704 Format: nn[KMGTPE] | "mirror"
1706 specifies the amount of memory usable by the kernel
1707 for non-movable allocations. The requested amount is
1708 spread evenly throughout all nodes in the system. The
1709 remaining memory in each node is used for Movable
1710 pages. In the event, a node is too small to have both
1711 kernelcore and Movable pages, kernelcore pages will
1712 take priority and other nodes will have a larger number
1713 of Movable pages. The Movable zone is used for the
1714 allocation of pages that may be reclaimed or moved
1715 by the page migration subsystem. This means that
1716 HugeTLB pages may not be allocated from this zone.
1717 Note that allocations like PTEs-from-HighMem still
1718 use the HighMem zone if it exists, and the Normal
1719 zone if it does not.
1721 Instead of specifying the amount of memory (nn[KMGTPE]),
1722 you can specify "mirror" option. In case "mirror"
1723 option is specified, mirrored (reliable) memory is used
1724 for non-movable allocations and remaining memory is used
1725 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1726 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1729 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1730 Format: <Controller#>[,poll interval]
1731 The controller # is the number of the ehci usb debug
1732 port as it is probed via PCI. The poll interval is
1733 optional and is the number seconds in between
1734 each poll cycle to the debug port in case you need
1735 the functionality for interrupting the kernel with
1736 gdb or control-c on the dbgp connection. When
1737 not using this parameter you use sysrq-g to break into
1738 the kernel debugger.
1740 kgdboc= [KGDB,HW] kgdb over consoles.
1741 Requires a tty driver that supports console polling,
1742 or a supported polling keyboard driver (non-usb).
1743 Serial only format: <serial_device>[,baud]
1744 keyboard only format: kbd
1745 keyboard and serial format: kbd,<serial_device>[,baud]
1746 Optional Kernel mode setting:
1747 kms, kbd format: kms,kbd
1748 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1750 kgdbwait [KGDB] Stop kernel execution and enter the
1751 kernel debugger at the earliest opportunity.
1753 kmac= [MIPS] korina ethernet MAC address.
1754 Configure the RouterBoard 532 series on-chip
1755 Ethernet adapter MAC address.
1757 kmemleak= [KNL] Boot-time kmemleak enable/disable
1758 Valid arguments: on, off
1760 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1763 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1764 Valid arguments: 0, 1, 2
1765 kmemcheck=0 (disabled)
1766 kmemcheck=1 (enabled)
1767 kmemcheck=2 (one-shot mode)
1768 Default: 2 (one-shot mode)
1770 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1771 Default is 0 (don't ignore, but inject #GP)
1773 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1777 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1778 Default is 1 (enabled)
1780 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1782 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1784 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1785 (virtualized MMU) support on capable Intel chips.
1786 Default is 1 (enabled)
1788 kvm-intel.emulate_invalid_guest_state=
1789 [KVM,Intel] Enable emulation of invalid guest states
1790 Default is 0 (disabled)
1792 kvm-intel.flexpriority=
1793 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1794 Default is 1 (enabled)
1797 [KVM,Intel] Enable VMX nesting (nVMX).
1798 Default is 0 (disabled)
1800 kvm-intel.unrestricted_guest=
1801 [KVM,Intel] Disable unrestricted guest feature
1802 (virtualized real and unpaged mode) on capable
1803 Intel chips. Default is 1 (enabled)
1805 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1806 feature (tagged TLBs) on capable Intel chips.
1807 Default is 1 (enabled)
1813 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1816 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1817 value for LAPIC timer one-shot implementation. Default
1818 back to the programmable timer unit in the LAPIC.
1820 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1823 libata.dma= [LIBATA] DMA control
1824 libata.dma=0 Disable all PATA and SATA DMA
1825 libata.dma=1 PATA and SATA Disk DMA only
1826 libata.dma=2 ATAPI (CDROM) DMA only
1827 libata.dma=4 Compact Flash DMA only
1828 Combinations also work, so libata.dma=3 enables DMA
1829 for disks and CDROMs, but not CFs.
1831 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1832 libata.ignore_hpa=0 keep BIOS limits (default)
1833 libata.ignore_hpa=1 ignore limits, using full disk
1835 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1839 libata.force= [LIBATA] Force configurations. The format is comma
1840 separated list of "[ID:]VAL" where ID is
1841 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1842 matching port, link or device. Basically, it matches
1843 the ATA ID string printed on console by libata. If
1844 the whole ID part is omitted, the last PORT and DEVICE
1845 values are used. If ID hasn't been specified yet, the
1846 configuration applies to all ports, links and devices.
1848 If only DEVICE is omitted, the parameter applies to
1849 the port and all links and devices behind it. DEVICE
1850 number of 0 either selects the first device or the
1851 first fan-out link behind PMP device. It does not
1852 select the host link. DEVICE number of 15 selects the
1853 host link and device attached to it.
1855 The VAL specifies the configuration to force. As long
1856 as there's no ambiguity shortcut notation is allowed.
1857 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1858 The following configurations can be forced.
1860 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1861 Any ID with matching PORT is used.
1863 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1865 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1866 udma[/][16,25,33,44,66,100,133] notation is also
1869 * [no]ncq: Turn on or off NCQ.
1871 * [no]ncqtrim: Turn off queued DSM TRIM.
1873 * nohrst, nosrst, norst: suppress hard, soft
1876 * rstonce: only attempt one reset during
1877 hot-unplug link recovery
1879 * dump_id: dump IDENTIFY data.
1881 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1883 * disable: Disable this device.
1885 If there are multiple matching configurations changing
1886 the same attribute, the last one is used.
1888 memblock=debug [KNL] Enable memblock debug messages.
1890 load_ramdisk= [RAM] List of ramdisks to load from floppy
1891 See Documentation/blockdev/ramdisk.txt.
1893 lockd.nlm_grace_period=P [NFS] Assign grace period.
1896 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1899 lockd.nlm_timeout=T [NFS] Assign timeout value.
1902 lockd.nlm_udpport=M [NFS] Assign UDP port.
1905 locktorture.nreaders_stress= [KNL]
1906 Set the number of locking read-acquisition kthreads.
1907 Defaults to being automatically set based on the
1908 number of online CPUs.
1910 locktorture.nwriters_stress= [KNL]
1911 Set the number of locking write-acquisition kthreads.
1913 locktorture.onoff_holdoff= [KNL]
1914 Set time (s) after boot for CPU-hotplug testing.
1916 locktorture.onoff_interval= [KNL]
1917 Set time (s) between CPU-hotplug operations, or
1918 zero to disable CPU-hotplug testing.
1920 locktorture.shuffle_interval= [KNL]
1921 Set task-shuffle interval (jiffies). Shuffling
1922 tasks allows some CPUs to go into dyntick-idle
1923 mode during the locktorture test.
1925 locktorture.shutdown_secs= [KNL]
1926 Set time (s) after boot system shutdown. This
1927 is useful for hands-off automated testing.
1929 locktorture.stat_interval= [KNL]
1930 Time (s) between statistics printk()s.
1932 locktorture.stutter= [KNL]
1933 Time (s) to stutter testing, for example,
1934 specifying five seconds causes the test to run for
1935 five seconds, wait for five seconds, and so on.
1936 This tests the locking primitive's ability to
1937 transition abruptly to and from idle.
1939 locktorture.torture_runnable= [BOOT]
1940 Start locktorture running at boot time.
1942 locktorture.torture_type= [KNL]
1943 Specify the locking implementation to test.
1945 locktorture.verbose= [KNL]
1946 Enable additional printk() statements.
1948 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1951 loglevel= All Kernel Messages with a loglevel smaller than the
1952 console loglevel will be printed to the console. It can
1953 also be changed with klogd or other programs. The
1954 loglevels are defined as follows:
1956 0 (KERN_EMERG) system is unusable
1957 1 (KERN_ALERT) action must be taken immediately
1958 2 (KERN_CRIT) critical conditions
1959 3 (KERN_ERR) error conditions
1960 4 (KERN_WARNING) warning conditions
1961 5 (KERN_NOTICE) normal but significant condition
1962 6 (KERN_INFO) informational
1963 7 (KERN_DEBUG) debug-level messages
1965 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1966 in bytes. n must be a power of two and greater
1967 than the minimal size. The minimal size is defined
1968 by LOG_BUF_SHIFT kernel config parameter. There is
1969 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1970 that allows to increase the default size depending on
1971 the number of CPUs. See init/Kconfig for more details.
1973 logo.nologo [FB] Disables display of the built-in Linux logo.
1974 This may be used to provide more screen space for
1975 kernel log messages and is useful when debugging
1976 kernel boot problems.
1978 lp=0 [LP] Specify parallel ports to use, e.g,
1979 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1980 lp=reset first parallel port). 'lp=0' disables the
1981 lp=auto printer driver. 'lp=reset' (which can be
1982 specified in addition to the ports) causes
1983 attached printers to be reset. Using
1984 lp=port1,port2,... specifies the parallel ports
1985 to associate lp devices with, starting with
1986 lp0. A port specification may be 'none' to skip
1987 that lp device, or a parport name such as
1988 'parport0'. Specifying 'lp=auto' instead of a
1989 port specification list means that device IDs
1990 from each port should be examined, to see if
1991 an IEEE 1284-compliant printer is attached; if
1992 so, the driver will manage that printer.
1993 See also header of drivers/char/lp.c.
1996 Sets loops_per_jiffy to given constant, thus avoiding
1997 time-consuming boot-time autodetection (up to 250 ms per
1998 CPU). 0 enables autodetection (default). To determine
1999 the correct value for your kernel, boot with normal
2000 autodetection and see what value is printed. Note that
2001 on SMP systems the preset will be applied to all CPUs,
2002 which is likely to cause problems if your CPUs need
2003 significantly divergent settings. An incorrect value
2004 will cause delays in the kernel to be wrong, leading to
2005 unpredictable I/O errors and other breakage. Although
2006 unlikely, in the extreme case this might damage your
2010 Format: <io>,<irq>,<dma>
2012 machvec= [IA-64] Force the use of a particular machine-vector
2013 (machvec) in a generic kernel.
2014 Example: machvec=hpzx1_swiotlb
2016 machtype= [Loongson] Share the same kernel image file between different
2018 Example: machtype=lemote-yeeloong-2f-7inch
2020 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2021 than or equal to this physical address is ignored.
2023 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2024 will bring up during bootup. maxcpus=n : n >= 0 limits
2025 the kernel to bring up 'n' processors. Surely after
2026 bootup you can bring up the other plugged cpu by executing
2027 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2028 only takes effect during system bootup.
2029 While n=0 is a special case, it is equivalent to "nosmp",
2030 which also disables the IO APIC.
2032 max_loop= [LOOP] The number of loop block devices that get
2033 (loop.max_loop) unconditionally pre-created at init time. The default
2034 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2035 of statically allocating a predefined number, loop
2036 devices can be requested on-demand with the
2037 /dev/loop-control interface.
2039 mce [X86-32] Machine Check Exception
2041 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2043 md= [HW] RAID subsystems devices and level
2044 See Documentation/admin-guide/md.rst.
2047 Format: <first>,<last>
2048 Specifies range of consoles to be captured by the MDA.
2050 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2051 Amount of memory to be used when the kernel is not able
2052 to see the whole system memory or for test.
2053 [X86] Work as limiting max address. Use together
2054 with memmap= to avoid physical address space collisions.
2055 Without memmap= PCI devices could be placed at addresses
2056 belonging to unused RAM.
2058 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2062 [KNL,SH] Allow user to override the default size for
2063 per-device physically contiguous DMA buffers.
2065 memhp_default_state=online/offline
2066 [KNL] Set the initial state for the memory hotplug
2067 onlining policy. If not specified, the default value is
2068 set according to the
2069 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2071 See Documentation/memory-hotplug.txt.
2073 memmap=exactmap [KNL,X86] Enable setting of an exact
2074 E820 memory map, as specified by the user.
2075 Such memmap=exactmap lines can be constructed based on
2076 BIOS output or other requirements. See the memmap=nn@ss
2079 memmap=nn[KMG]@ss[KMG]
2080 [KNL] Force usage of a specific region of memory.
2081 Region of memory to be used is from ss to ss+nn.
2083 memmap=nn[KMG]#ss[KMG]
2084 [KNL,ACPI] Mark specific memory as ACPI data.
2085 Region of memory to be marked is from ss to ss+nn.
2087 memmap=nn[KMG]$ss[KMG]
2088 [KNL,ACPI] Mark specific memory as reserved.
2089 Region of memory to be reserved is from ss to ss+nn.
2090 Example: Exclude memory from 0x18690000-0x1869ffff
2091 memmap=64K$0x18690000
2093 memmap=0x10000$0x18690000
2095 memmap=nn[KMG]!ss[KMG]
2096 [KNL,X86] Mark specific memory as protected.
2097 Region of memory to be used, from ss to ss+nn.
2098 The memory region may be marked as e820 type 12 (0xc)
2099 and is NVDIMM or ADR memory.
2101 memory_corruption_check=0/1 [X86]
2102 Some BIOSes seem to corrupt the first 64k of
2103 memory when doing things like suspend/resume.
2104 Setting this option will scan the memory
2105 looking for corruption. Enabling this will
2106 both detect corruption and prevent the kernel
2107 from using the memory being corrupted.
2108 However, its intended as a diagnostic tool; if
2109 repeatable BIOS-originated corruption always
2110 affects the same memory, you can use memmap=
2111 to prevent the kernel from using that memory.
2113 memory_corruption_check_size=size [X86]
2114 By default it checks for corruption in the low
2115 64k, making this memory unavailable for normal
2116 use. Use this parameter to scan for
2117 corruption in more or less memory.
2119 memory_corruption_check_period=seconds [X86]
2120 By default it checks for corruption every 60
2121 seconds. Use this parameter to check at some
2122 other rate. 0 disables periodic checking.
2124 memtest= [KNL,X86,ARM] Enable memtest
2126 default : 0 <disable>
2127 Specifies the number of memtest passes to be
2128 performed. Each pass selects another test
2129 pattern from a given set of patterns. Memtest
2130 fills the memory with this pattern, validates
2131 memory contents and reserves bad memory
2132 regions that are detected.
2134 mem_sleep_default= [SUSPEND] Default system suspend mode:
2135 s2idle - Suspend-To-Idle
2136 shallow - Power-On Suspend or equivalent (if supported)
2137 deep - Suspend-To-RAM or equivalent (if supported)
2138 See Documentation/power/states.txt.
2140 meye.*= [HW] Set MotionEye Camera parameters
2141 See Documentation/video4linux/meye.txt.
2143 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2144 Multi-Function General Purpose Timers on AMD Geode
2147 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2148 the BIOS has incorrectly applied a workaround. TinyBIOS
2149 version 0.98 is known to be affected, 0.99 fixes the
2150 problem by letting the user disable the workaround.
2154 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2155 physical address is ignored.
2157 mini2440= [ARM,HW,KNL]
2158 Format:[0..2][b][c][t]
2160 MINI2440 configuration specification:
2161 0 - The attached screen is the 3.5" TFT
2162 1 - The attached screen is the 7" TFT
2163 2 - The VGA Shield is attached (1024x768)
2164 Leaving out the screen size parameter will not load
2165 the TFT driver, and the framebuffer will be left
2167 b - Enable backlight. The TFT backlight pin will be
2168 linked to the kernel VESA blanking code and a GPIO
2169 LED. This parameter is not necessary when using the
2171 c - Enable the s3c camera interface.
2172 t - Reserved for enabling touchscreen support. The
2173 touchscreen support is not enabled in the mainstream
2174 kernel as of 2.6.30, a preliminary port can be found
2175 in the "bleeding edge" mini2440 support kernel at
2176 http://repo.or.cz/w/linux-2.6/mini2440.git
2179 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2180 parameter allows control of the logging verbosity for
2181 the additional memory initialisation checks. A value
2182 of 0 disables mminit logging and a level of 4 will
2183 log everything. Information is printed at KERN_DEBUG
2184 so loglevel=8 may also need to be specified.
2187 [KNL] When CONFIG_MODULE_SIG is set, this means that
2188 modules without (valid) signatures will fail to load.
2189 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2190 is always true, so this option does nothing.
2192 module_blacklist= [KNL] Do not load a comma-separated list of
2193 modules. Useful for debugging problem modules.
2196 [MOUSE] Maximum time between finger touching and
2197 leaving touchpad surface for touch to be considered
2198 a tap and be reported as a left button click (for
2199 touchpads working in absolute mode only).
2201 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2202 reporting absolute coordinates, such as tablets
2203 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2204 reporting absolute coordinates, such as tablets
2206 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2207 is similar to kernelcore except it specifies the
2208 amount of memory used for migratable allocations.
2209 If both kernelcore and movablecore is specified,
2210 then kernelcore will be at *least* the specified
2211 value but may be more. If movablecore on its own
2212 is specified, the administrator must be careful
2213 that the amount of memory usable for all allocations
2216 movable_node [KNL] Boot-time switch to enable the effects
2217 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2219 MTD_Partition= [MTD]
2220 Format: <name>,<region-number>,<size>,<offset>
2222 MTD_Region= [MTD] Format:
2223 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2226 See drivers/mtd/cmdlinepart.c.
2228 multitce=off [PPC] This parameter disables the use of the pSeries
2229 firmware feature for updating multiple TCE entries
2232 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2234 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2236 boundary - index of last SLC block on Flex-OneNAND.
2237 The remaining blocks are configured as MLC blocks.
2238 lock - Configure if Flex-OneNAND boundary should be locked.
2239 Once locked, the boundary cannot be changed.
2240 1 indicates lock status, 0 indicates unlock status.
2243 ARM/S3C2412 JIVE boot control
2245 See arch/arm/mach-s3c2412/mach-jive.c
2247 mtouchusb.raw_coordinates=
2248 [HW] Make the MicroTouch USB driver use raw coordinates
2249 ('y', default) or cooked coordinates ('n')
2251 mtrr_chunk_size=nn[KMG] [X86]
2252 used for mtrr cleanup. It is largest continuous chunk
2253 that could hold holes aka. UC entries.
2255 mtrr_gran_size=nn[KMG] [X86]
2256 Used for mtrr cleanup. It is granularity of mtrr block.
2258 Large value could prevent small alignment from
2261 mtrr_spare_reg_nr=n [X86]
2263 Range: 0,7 : spare reg number
2265 Used for mtrr cleanup. It is spare mtrr entries number.
2266 Set to 2 or more if your graphical card needs more.
2268 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2270 netdev= [NET] Network devices parameters
2271 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2272 Note that mem_start is often overloaded to mean
2273 something different and driver-specific.
2274 This usage is only documented in each driver source
2278 [NETFILTER] Enable connection tracking flow accounting
2279 0 to disable accounting
2280 1 to enable accounting
2283 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2284 See Documentation/filesystems/nfs/nfsroot.txt.
2286 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2287 See Documentation/filesystems/nfs/nfsroot.txt.
2289 nfsrootdebug [NFS] enable nfsroot debugging messages.
2290 See Documentation/filesystems/nfs/nfsroot.txt.
2292 nfs.callback_nr_threads=
2293 [NFSv4] set the total number of threads that the
2294 NFS client will assign to service NFSv4 callback
2297 nfs.callback_tcpport=
2298 [NFS] set the TCP port on which the NFSv4 callback
2299 channel should listen.
2302 [NFS] sets the pathname to the program which is used
2303 to update the NFS client cache entries.
2305 nfs.cache_getent_timeout=
2306 [NFS] sets the timeout after which an attempt to
2307 update a cache entry is deemed to have failed.
2309 nfs.idmap_cache_timeout=
2310 [NFS] set the maximum lifetime for idmapper cache
2314 [NFS] enable 64-bit inode numbers.
2315 If zero, the NFS client will fake up a 32-bit inode
2316 number for the readdir() and stat() syscalls instead
2317 of returning the full 64-bit number.
2318 The default is to return 64-bit inode numbers.
2320 nfs.max_session_cb_slots=
2321 [NFSv4.1] Sets the maximum number of session
2322 slots the client will assign to the callback
2323 channel. This determines the maximum number of
2324 callbacks the client will process in parallel for
2325 a particular server.
2327 nfs.max_session_slots=
2328 [NFSv4.1] Sets the maximum number of session slots
2329 the client will attempt to negotiate with the server.
2330 This limits the number of simultaneous RPC requests
2331 that the client can send to the NFSv4.1 server.
2332 Note that there is little point in setting this
2333 value higher than the max_tcp_slot_table_limit.
2335 nfs.nfs4_disable_idmapping=
2336 [NFSv4] When set to the default of '1', this option
2337 ensures that both the RPC level authentication
2338 scheme and the NFS level operations agree to use
2339 numeric uids/gids if the mount is using the
2340 'sec=sys' security flavour. In effect it is
2341 disabling idmapping, which can make migration from
2342 legacy NFSv2/v3 systems to NFSv4 easier.
2343 Servers that do not support this mode of operation
2344 will be autodetected by the client, and it will fall
2345 back to using the idmapper.
2346 To turn off this behaviour, set the value to '0'.
2348 [NFS4] Specify an additional fixed unique ident-
2349 ification string that NFSv4 clients can insert into
2350 their nfs_client_id4 string. This is typically a
2351 UUID that is generated at system install time.
2353 nfs.send_implementation_id =
2354 [NFSv4.1] Send client implementation identification
2355 information in exchange_id requests.
2356 If zero, no implementation identification information
2358 The default is to send the implementation identification
2361 nfs.recover_lost_locks =
2362 [NFSv4] Attempt to recover locks that were lost due
2363 to a lease timeout on the server. Please note that
2364 doing this risks data corruption, since there are
2365 no guarantees that the file will remain unchanged
2366 after the locks are lost.
2367 If you want to enable the kernel legacy behaviour of
2368 attempting to recover these locks, then set this
2370 The default parameter value of '0' causes the kernel
2371 not to attempt recovery of lost locks.
2373 nfs4.layoutstats_timer =
2374 [NFSv4.2] Change the rate at which the kernel sends
2375 layoutstats to the pNFS metadata server.
2377 Setting this to value to 0 causes the kernel to use
2378 whatever value is the default set by the layout
2379 driver. A non-zero value sets the minimum interval
2380 in seconds between layoutstats transmissions.
2382 nfsd.nfs4_disable_idmapping=
2383 [NFSv4] When set to the default of '1', the NFSv4
2384 server will return only numeric uids and gids to
2385 clients using auth_sys, and will accept numeric uids
2386 and gids from such clients. This is intended to ease
2387 migration from NFSv2/v3.
2389 objlayoutdriver.osd_login_prog=
2390 [NFS] [OBJLAYOUT] sets the pathname to the program which
2391 is used to automatically discover and login into new
2392 osd-targets. Please see:
2393 Documentation/filesystems/pnfs.txt for more explanations
2395 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2396 when a NMI is triggered.
2397 Format: [state][,regs][,debounce][,die]
2399 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2400 Format: [panic,][nopanic,][num]
2402 0 - turn hardlockup detector in nmi_watchdog off
2403 1 - turn hardlockup detector in nmi_watchdog on
2404 When panic is specified, panic when an NMI watchdog
2405 timeout occurs (or 'nopanic' to override the opposite
2406 default). To disable both hard and soft lockup detectors,
2407 please see 'nowatchdog'.
2408 This is useful when you use a panic=... timeout and
2409 need the box quickly up again.
2411 netpoll.carrier_timeout=
2412 [NET] Specifies amount of time (in seconds) that
2413 netpoll should wait for a carrier. By default netpoll
2416 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2417 emulation library even if a 387 maths coprocessor
2421 [HW] Never suspend the console
2422 Disable suspending of consoles during suspend and
2423 hibernate operations. Once disabled, debugging
2424 messages can reach various consoles while the rest
2425 of the system is being put to sleep (ie, while
2426 debugging driver suspend/resume hooks). This may
2427 not work reliably with all consoles, but is known
2428 to work with serial and VGA consoles.
2429 To facilitate more flexible debugging, we also add
2430 console_suspend, a printk module parameter to control
2431 it. Users could use console_suspend (usually
2432 /sys/module/printk/parameters/console_suspend) to
2433 turn on/off it dynamically.
2435 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2436 caches in the slab allocator. Saves per-node memory,
2437 but will impact performance.
2441 noapic [SMP,APIC] Tells the kernel to not make use of any
2442 IOAPICs that may be present in the system.
2444 noautogroup Disable scheduler automatic task group creation.
2446 nobats [PPC] Do not use BATs for mapping kernel lowmem
2447 on "Classic" PPC cores.
2451 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2453 nodelayacct [KNL] Disable per-task delay accounting
2455 nodsp [SH] Disable hardware DSP at boot time.
2457 noefi Disable EFI runtime services support.
2462 On X86-32 available only on PAE configured kernels.
2463 noexec=on: enable non-executable mappings (default)
2464 noexec=off: disable non-executable mappings
2467 Disable SMAP (Supervisor Mode Access Prevention)
2468 even if it is supported by processor.
2471 Disable SMEP (Supervisor Mode Execution Prevention)
2472 even if it is supported by processor.
2475 This affects only 32-bit executables.
2476 noexec32=on: enable non-executable mappings (default)
2477 read doesn't imply executable mappings
2478 noexec32=off: disable non-executable mappings
2479 read implies executable mappings
2481 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2483 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2484 register save and restore. The kernel will only save
2485 legacy floating-point registers on task switch.
2487 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2489 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2490 Equivalent to smt=1.
2492 noxsave [BUGS=X86] Disables x86 extended register state save
2493 and restore using xsave. The kernel will fallback to
2494 enabling legacy floating-point and sse state.
2496 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2497 register states. The kernel will fall back to use
2498 xsave to save the states. By using this parameter,
2499 performance of saving the states is degraded because
2500 xsave doesn't support modified optimization while
2501 xsaveopt supports it on xsaveopt enabled systems.
2503 noxsaves [X86] Disables xsaves and xrstors used in saving and
2504 restoring x86 extended register state in compacted
2505 form of xsave area. The kernel will fall back to use
2506 xsaveopt and xrstor to save and restore the states
2507 in standard form of xsave area. By using this
2508 parameter, xsave area per process might occupy more
2509 memory on xsaves enabled systems.
2511 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2512 wfi(ARM) instruction doesn't work correctly and not to
2513 use it. This is also useful when using JTAG debugger.
2515 no_file_caps Tells the kernel not to honor file capabilities. The
2516 only way then for a file to be executed with privilege
2517 is to be setuid root or executed by root.
2519 nohalt [IA-64] Tells the kernel not to use the power saving
2520 function PAL_HALT_LIGHT when idle. This increases
2521 power-consumption. On the positive side, it reduces
2522 interrupt wake-up latency, which may improve performance
2523 in certain environments such as networked servers or
2526 nohibernate [HIBERNATION] Disable hibernation and resume.
2528 nohz= [KNL] Boottime enable/disable dynamic ticks
2529 Valid arguments: on, off
2532 nohz_full= [KNL,BOOT]
2533 The argument is a cpu list, as described above.
2534 In kernels built with CONFIG_NO_HZ_FULL=y, set
2535 the specified list of CPUs whose tick will be stopped
2536 whenever possible. The boot CPU will be forced outside
2537 the range to maintain the timekeeping.
2538 The CPUs in this range must also be included in the
2541 noiotrap [SH] Disables trapped I/O port accesses.
2543 noirqdebug [X86-32] Disables the code which attempts to detect and
2544 disable unhandled interrupt sources.
2546 no_timer_check [X86,APIC] Disables the code which tests for
2547 broken timer IRQ sources.
2549 noisapnp [ISAPNP] Disables ISA PnP code.
2551 noinitrd [RAM] Tells the kernel not to load any configured
2554 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2556 [Deprecated - use intremap=off]
2560 noinvpcid [X86] Disable the INVPCID cpu feature.
2562 nojitter [IA-64] Disables jitter checking for ITC timers.
2564 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2566 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2570 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2571 clock and use the default one.
2573 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2574 steal time is computed, but won't influence scheduler
2577 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2579 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2581 noltlbs [PPC] Do not use large page/tlb entries for kernel
2582 lowmem mapping on PPC40x and PPC8xx
2584 nomca [IA-64] Disable machine check abort handling
2586 nomce [X86-32] Disable Machine Check Exception
2588 nomfgpt [X86-32] Disable Multi-Function General Purpose
2589 Timer usage (for AMD Geode machines).
2591 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2592 shutdown the other cpus. Instead use the REBOOT_VECTOR
2595 nomodule Disable module load
2597 nopat [X86] Disable PAT (page attribute table extension of
2598 pagetables) support.
2600 norandmaps Don't use address space randomization. Equivalent to
2601 echo 0 > /proc/sys/kernel/randomize_va_space
2603 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2605 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2606 with UP alternatives
2608 nordrand [X86] Disable kernel use of the RDRAND and
2609 RDSEED instructions even if they are supported
2610 by the processor. RDRAND and RDSEED are still
2611 available to user space applications.
2613 noresume [SWSUSP] Disables resume and restores original swap
2616 no-scroll [VGA] Disables scrollback.
2617 This is required for the Braillex ib80-piezo Braille
2618 reader made by F.H. Papenmeier (Germany).
2622 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2624 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2625 and disable the IO APIC. legacy for "maxcpus=0".
2627 nosoftlockup [KNL] Disable the soft-lockup detector.
2629 nosync [HW,M68K] Disables sync negotiation for all devices.
2631 notsc [BUGS=X86-32] Disable Time Stamp Counter
2633 nowatchdog [KNL] Disable both lockup detectors, i.e.
2634 soft-lockup and NMI watchdog (hard-lockup).
2638 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2640 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2641 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2642 Some features depend on CPU0. Known dependencies are:
2643 1. Resume from suspend/hibernate depends on CPU0.
2644 Suspend/hibernate will fail if CPU0 is offline and you
2645 need to online CPU0 before suspend/hibernate.
2646 2. PIC interrupts also depend on CPU0. CPU0 can't be
2647 removed if a PIC interrupt is detected.
2648 It's said poweroff/reboot may depend on CPU0 on some
2649 machines although I haven't seen such issues so far
2650 after CPU0 is offline on a few tested machines.
2651 If the dependencies are under your control, you can
2652 turn on cpu0_hotplug.
2654 nptcg= [IA-64] Override max number of concurrent global TLB
2655 purges which is reported from either PAL_VM_SUMMARY or
2658 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2659 could support. nr_cpus=n : n >= 1 limits the kernel to
2660 support 'n' processors. It could be larger than the
2661 number of already plugged CPU during bootup, later in
2662 runtime you can physically add extra cpu until it reaches
2663 n. So during boot up some boot time memory for per-cpu
2664 variables need be pre-allocated for later physical cpu
2667 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2669 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2670 Allowed values are enable and disable
2672 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2673 one of ['zone', 'node', 'default'] can be specified
2674 This can be set from sysctl after boot.
2675 See Documentation/sysctl/vm.txt for details.
2677 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2678 See Documentation/debugging-via-ohci1394.txt for more
2681 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2682 Rather than timing out after 20 ms if an EC
2683 command is not properly ACKed, override the length
2684 of the timeout. We have interrupts disabled while
2685 waiting for the ACK, so if this is set too high
2686 interrupts *may* be lost!
2688 omap_mux= [OMAP] Override bootloader pin multiplexing.
2689 Format: <mux_mode0.mode_name=value>...
2690 For example, to override I2C bus2:
2691 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2693 oprofile.timer= [HW]
2694 Use timer interrupt instead of performance counters
2696 oprofile.cpu_type= Force an oprofile cpu type
2697 This might be useful if you have an older oprofile
2698 userland or if you want common events.
2699 Format: { arch_perfmon }
2700 arch_perfmon: [X86] Force use of architectural
2701 perfmon on Intel CPUs instead of the
2702 CPU specific event set.
2703 timer: [X86] Force use of architectural NMI
2704 timer mode (see also oprofile.timer
2705 for generic hr timer mode)
2707 oops=panic Always panic on oopses. Default is to just kill the
2708 process, but there is a small probability of
2709 deadlocking the machine.
2710 This will also cause panics on machine check exceptions.
2711 Useful together with panic=30 to trigger a reboot.
2714 See Documentation/sound/oss/oss-parameters.txt
2716 page_owner= [KNL] Boot-time page_owner enabling option.
2717 Storage of the information about who allocated
2718 each page is disabled in default. With this switch,
2720 on: enable the feature
2722 page_poison= [KNL] Boot-time parameter changing the state of
2723 poisoning on the buddy allocator.
2724 off: turn off poisoning
2725 on: turn on poisoning
2727 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2728 timeout > 0: seconds before rebooting
2729 timeout = 0: wait forever
2730 timeout < 0: reboot immediately
2733 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2736 crash_kexec_post_notifiers
2737 Run kdump after running panic-notifiers and dumping
2738 kmsg. This only for the users who doubt kdump always
2739 succeeds in any situation.
2740 Note that this also increases risks of kdump failure,
2741 because some panic notifiers can make the crashed
2742 kernel more unstable.
2744 parkbd.port= [HW] Parallel port number the keyboard adapter is
2745 connected to, default is 0.
2747 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2748 0 for XT, 1 for AT (default is AT).
2751 parport= [HW,PPT] Specify parallel ports. 0 disables.
2752 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2753 Use 'auto' to force the driver to use any
2754 IRQ/DMA settings detected (the default is to
2755 ignore detected IRQ/DMA settings because of
2756 possible conflicts). You can specify the base
2757 address, IRQ, and DMA settings; IRQ and DMA
2758 should be numbers, or 'auto' (for using detected
2759 settings on that particular port), or 'nofifo'
2760 (to avoid using a FIFO even if it is detected).
2761 Parallel ports are assigned in the order they
2762 are specified on the command line, starting
2765 parport_init_mode= [HW,PPT]
2766 Configure VIA parallel port to operate in
2767 a specific mode. This is necessary on Pegasos
2768 computer where firmware has no options for setting
2769 up parallel port mode and sets it to spp.
2770 Currently this function knows 686a and 8231 chips.
2771 Format: [spp|ps2|epp|ecp|ecpepp]
2774 Halt all CPUs after the first oops has been printed for
2775 the specified number of seconds. This is to be used if
2776 your oopses keep scrolling off the screen.
2781 See header of drivers/block/paride/pcd.c.
2782 See also Documentation/blockdev/paride.txt.
2784 pci=option[,option...] [PCI] various PCI subsystem options:
2785 earlydump [X86] dump PCI config space before the kernel
2787 off [X86] don't probe for the PCI bus
2788 bios [X86-32] force use of PCI BIOS, don't access
2789 the hardware directly. Use this if your machine
2790 has a non-standard PCI host bridge.
2791 nobios [X86-32] disallow use of PCI BIOS, only direct
2792 hardware access methods are allowed. Use this
2793 if you experience crashes upon bootup and you
2794 suspect they are caused by the BIOS.
2795 conf1 [X86] Force use of PCI Configuration Access
2796 Mechanism 1 (config address in IO port 0xCF8,
2797 data in IO port 0xCFC, both 32-bit).
2798 conf2 [X86] Force use of PCI Configuration Access
2799 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2800 the function, IO port 0xCFA, also 8-bit, sets
2801 bus number. The config space is then accessed
2802 through ports 0xC000-0xCFFF).
2803 See http://wiki.osdev.org/PCI for more info
2804 on the configuration access mechanisms.
2805 noaer [PCIE] If the PCIEAER kernel config parameter is
2806 enabled, this kernel boot option can be used to
2807 disable the use of PCIE advanced error reporting.
2808 nodomains [PCI] Disable support for multiple PCI
2809 root domains (aka PCI segments, in ACPI-speak).
2810 nommconf [X86] Disable use of MMCONFIG for PCI
2812 check_enable_amd_mmconf [X86] check for and enable
2813 properly configured MMIO access to PCI
2814 config space on AMD family 10h CPU
2815 nomsi [MSI] If the PCI_MSI kernel config parameter is
2816 enabled, this kernel boot option can be used to
2817 disable the use of MSI interrupts system-wide.
2818 noioapicquirk [APIC] Disable all boot interrupt quirks.
2819 Safety option to keep boot IRQs enabled. This
2820 should never be necessary.
2821 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2822 primary IO-APIC for bridges that cannot disable
2823 boot IRQs. This fixes a source of spurious IRQs
2824 when the system masks IRQs.
2825 noioapicreroute [APIC] Disable workaround that uses the
2826 boot IRQ equivalent of an IRQ that connects to
2827 a chipset where boot IRQs cannot be disabled.
2828 The opposite of ioapicreroute.
2829 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2830 routing table. These calls are known to be buggy
2831 on several machines and they hang the machine
2832 when used, but on other computers it's the only
2833 way to get the interrupt routing table. Try
2834 this option if the kernel is unable to allocate
2835 IRQs or discover secondary PCI buses on your
2837 rom [X86] Assign address space to expansion ROMs.
2838 Use with caution as certain devices share
2839 address decoders between ROMs and other
2841 norom [X86] Do not assign address space to
2842 expansion ROMs that do not already have
2843 BIOS assigned address ranges.
2844 nobar [X86] Do not assign address space to the
2845 BARs that weren't assigned by the BIOS.
2846 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2847 assigned automatically to PCI devices. You can
2848 make the kernel exclude IRQs of your ISA cards
2850 pirqaddr=0xAAAAA [X86] Specify the physical address
2851 of the PIRQ table (normally generated
2852 by the BIOS) if it is outside the
2853 F0000h-100000h range.
2854 lastbus=N [X86] Scan all buses thru bus #N. Can be
2855 useful if the kernel is unable to find your
2856 secondary buses and you want to tell it
2857 explicitly which ones they are.
2858 assign-busses [X86] Always assign all PCI bus
2859 numbers ourselves, overriding
2860 whatever the firmware may have done.
2861 usepirqmask [X86] Honor the possible IRQ mask stored
2862 in the BIOS $PIR table. This is needed on
2863 some systems with broken BIOSes, notably
2864 some HP Pavilion N5400 and Omnibook XE3
2865 notebooks. This will have no effect if ACPI
2866 IRQ routing is enabled.
2867 noacpi [X86] Do not use ACPI for IRQ routing
2868 or for PCI scanning.
2869 use_crs [X86] Use PCI host bridge window information
2870 from ACPI. On BIOSes from 2008 or later, this
2871 is enabled by default. If you need to use this,
2872 please report a bug.
2873 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2874 If you need to use this, please report a bug.
2875 routeirq Do IRQ routing for all PCI devices.
2876 This is normally done in pci_enable_device(),
2877 so this option is a temporary workaround
2878 for broken drivers that don't call it.
2879 skip_isa_align [X86] do not align io start addr, so can
2880 handle more pci cards
2881 noearly [X86] Don't do any early type 1 scanning.
2882 This might help on some broken boards which
2883 machine check when some devices' config space
2884 is read. But various workarounds are disabled
2885 and some IOMMU drivers will not work.
2886 bfsort Sort PCI devices into breadth-first order.
2887 This sorting is done to get a device
2888 order compatible with older (<= 2.4) kernels.
2889 nobfsort Don't sort PCI devices into breadth-first order.
2890 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2891 tuning and use the BIOS-configured MPS defaults.
2892 pcie_bus_safe Set every device's MPS to the largest value
2893 supported by all devices below the root complex.
2894 pcie_bus_perf Set device MPS to the largest allowable MPS
2895 based on its parent bus. Also set MRRS (Max
2896 Read Request Size) to the largest supported
2897 value (no larger than the MPS that the device
2898 or bus can support) for best performance.
2899 pcie_bus_peer2peer Set every device's MPS to 128B, which
2900 every device is guaranteed to support. This
2901 configuration allows peer-to-peer DMA between
2902 any pair of devices, possibly at the cost of
2903 reduced performance. This also guarantees
2904 that hot-added devices will work.
2905 cbiosize=nn[KMG] The fixed amount of bus space which is
2906 reserved for the CardBus bridge's IO window.
2907 The default value is 256 bytes.
2908 cbmemsize=nn[KMG] The fixed amount of bus space which is
2909 reserved for the CardBus bridge's memory
2910 window. The default value is 64 megabytes.
2913 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2914 [<order of align>@]pci:<vendor>:<device>\
2915 [:<subvendor>:<subdevice>][; ...]
2916 Specifies alignment and device to reassign
2917 aligned memory resources.
2918 If <order of align> is not specified,
2919 PAGE_SIZE is used as alignment.
2920 PCI-PCI bridge can be specified, if resource
2921 windows need to be expanded.
2922 To specify the alignment for several
2923 instances of a device, the PCI vendor,
2924 device, subvendor, and subdevice may be
2925 specified, e.g., 4096@pci:8086:9c22:103c:198f
2926 ecrc= Enable/disable PCIe ECRC (transaction layer
2927 end-to-end CRC checking).
2928 bios: Use BIOS/firmware settings. This is the
2932 hpiosize=nn[KMG] The fixed amount of bus space which is
2933 reserved for hotplug bridge's IO window.
2934 Default size is 256 bytes.
2935 hpmemsize=nn[KMG] The fixed amount of bus space which is
2936 reserved for hotplug bridge's memory window.
2937 Default size is 2 megabytes.
2938 hpbussize=nn The minimum amount of additional bus numbers
2939 reserved for buses below a hotplug bridge.
2941 realloc= Enable/disable reallocating PCI bridge resources
2942 if allocations done by BIOS are too small to
2943 accommodate resources required by all child
2945 off: Turn realloc off
2947 realloc same as realloc=on
2948 noari do not use PCIe ARI.
2949 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2950 only look for one device below a PCIe downstream
2953 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2956 force Enable ASPM even on devices that claim not to support it.
2957 WARNING: Forcing ASPM on may cause system lockups.
2959 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2960 nomsi Do not use MSI for PCI Express Native Hotplug (this
2961 makes all PCIe ports use INTx for hotplug services).
2963 pcie_ports= [PCIE] PCIe ports handling:
2964 auto Ask the BIOS whether or not to use native PCIe services
2965 associated with PCIe ports (PME, hot-plug, AER). Use
2966 them only if that is allowed by the BIOS.
2967 native Use native PCIe services associated with PCIe ports
2969 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2972 pcie_port_pm= [PCIE] PCIe port power management handling:
2973 off Disable power management of all PCIe ports
2974 force Forcibly enable power management of all PCIe ports
2976 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2977 nomsi Do not use MSI for native PCIe PME signaling (this makes
2978 all PCIe root ports use INTx for all services).
2980 pcmv= [HW,PCMCIA] BadgePAD 4
2984 Keep all power-domains already enabled by bootloader on,
2985 even if no driver has claimed them. This is useful
2986 for debug and development, but should not be
2987 needed on a platform with proper driver support.
2990 See Documentation/blockdev/paride.txt.
2992 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2995 See arch/parisc/kernel/pdc_chassis.c
2997 percpu_alloc= Select which percpu first chunk allocator to use.
2998 Currently supported values are "embed" and "page".
2999 Archs may support subset or none of the selections.
3000 See comments in mm/percpu.c for details on each
3001 allocator. This parameter is primarily for debugging
3002 and performance comparison.
3005 See Documentation/blockdev/paride.txt.
3008 See Documentation/blockdev/paride.txt.
3010 pirq= [SMP,APIC] Manual mp-table setup
3011 See Documentation/x86/i386/IO-APIC.txt.
3013 plip= [PPT,NET] Parallel port network link
3014 Format: { parport<nr> | timid | 0 }
3015 See also Documentation/parport.txt.
3017 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3018 Override pmtimer IOPort with a hex value.
3022 Enable PNP debug messages (depends on the
3023 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3024 via /sys/module/pnp/parameters/debug. We always show
3025 current resource usage; turning this on also shows
3026 possible settings and some assignment information.
3032 { on | off | curr | res | no-curr | no-res }
3035 [ISAPNP] Exclude IRQs for the autoconfiguration
3038 [ISAPNP] Exclude DMAs for the autoconfiguration
3040 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3041 Ranges are in pairs (I/O port base and size).
3044 [ISAPNP] Exclude memory regions for the
3046 Ranges are in pairs (memory base and size).
3048 ports= [IP_VS_FTP] IPVS ftp helper module
3050 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3052 Format: <port>,<port>....
3054 powersave=off [PPC] This option disables power saving features.
3055 It specifically disables cpuidle and sets the
3056 platform machine description specific power_save
3057 function to NULL. On Idle the CPU just reduces
3060 ppc_strict_facility_enable
3061 [PPC] This option catches any kernel floating point,
3062 Altivec, VSX and SPE outside of regions specifically
3063 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3064 There is some performance impact when enabling this.
3066 print-fatal-signals=
3067 [KNL] debug: print fatal signals
3069 If enabled, warn about various signal handling
3070 related application anomalies: too many signals,
3071 too many POSIX.1 timers, fatal signals causing a
3074 If you hit the warning due to signal overflow,
3075 you might want to try "ulimit -i unlimited".
3079 printk.always_kmsg_dump=
3080 Trigger kmsg_dump for cases other than kernel oops or
3082 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3085 printk.devkmsg={on,off,ratelimit}
3086 Control writing to /dev/kmsg.
3087 on - unlimited logging to /dev/kmsg from userspace
3088 off - logging to /dev/kmsg disabled
3089 ratelimit - ratelimit the logging
3092 printk.time= Show timing data prefixed to each printk message line
3093 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3095 processor.max_cstate= [HW,ACPI]
3096 Limit processor to maximum C-state
3097 max_cstate=9 overrides any DMI blacklist limit.
3099 processor.nocst [HW,ACPI]
3100 Ignore the _CST method to determine C-states,
3101 instead using the legacy FADT method
3103 profile= [KNL] Enable kernel profiling via /proc/profile
3104 Format: [schedule,]<number>
3105 Param: "schedule" - profile schedule points.
3106 Param: <number> - step/bucket size as a power of 2 for
3107 statistical time based profiling.
3108 Param: "sleep" - profile D-state sleeping (millisecs).
3109 Requires CONFIG_SCHEDSTATS
3110 Param: "kvm" - profile VM exits.
3112 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3114 See Documentation/blockdev/ramdisk.txt.
3116 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3117 probe for; one of (bare|imps|exps|lifebook|any).
3118 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3120 psmouse.resetafter= [HW,MOUSE]
3121 Try to reset the device after so many bad packets
3124 [HW,MOUSE] Set desired mouse resolution, in dpi.
3125 psmouse.smartscroll=
3126 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3127 0 = disabled, 1 = enabled (default).
3129 pstore.backend= Specify the name of the pstore backend to use
3132 See Documentation/blockdev/paride.txt.
3135 [KNL] Number of legacy pty's. Overwrites compiled-in
3138 quiet [KNL] Disable most log messages
3143 See Documentation/admin-guide/md.rst.
3145 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3146 See Documentation/blockdev/ramdisk.txt.
3149 The argument is a cpu list, as described above.
3151 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3152 the specified list of CPUs to be no-callback CPUs.
3153 Invocation of these CPUs' RCU callbacks will
3154 be offloaded to "rcuox/N" kthreads created for
3155 that purpose, where "x" is "b" for RCU-bh, "p"
3156 for RCU-preempt, and "s" for RCU-sched, and "N"
3157 is the CPU number. This reduces OS jitter on the
3158 offloaded CPUs, which can be useful for HPC and
3159 real-time workloads. It can also improve energy
3160 efficiency for asymmetric multiprocessors.
3163 Rather than requiring that offloaded CPUs
3164 (specified by rcu_nocbs= above) explicitly
3165 awaken the corresponding "rcuoN" kthreads,
3166 make these kthreads poll for callbacks.
3167 This improves the real-time response for the
3168 offloaded CPUs by relieving them of the need to
3169 wake up the corresponding kthread, but degrades
3170 energy efficiency by requiring that the kthreads
3171 periodically wake up to do the polling.
3173 rcutree.blimit= [KNL]
3174 Set maximum number of finished RCU callbacks to
3175 process in one batch.
3177 rcutree.dump_tree= [KNL]
3178 Dump the structure of the rcu_node combining tree
3179 out at early boot. This is used for diagnostic
3180 purposes, to verify correct tree setup.
3182 rcutree.gp_cleanup_delay= [KNL]
3183 Set the number of jiffies to delay each step of
3184 RCU grace-period cleanup. This only has effect
3185 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3187 rcutree.gp_init_delay= [KNL]
3188 Set the number of jiffies to delay each step of
3189 RCU grace-period initialization. This only has
3190 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3193 rcutree.gp_preinit_delay= [KNL]
3194 Set the number of jiffies to delay each step of
3195 RCU grace-period pre-initialization, that is,
3196 the propagation of recent CPU-hotplug changes up
3197 the rcu_node combining tree. This only has effect
3198 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3200 rcutree.rcu_fanout_exact= [KNL]
3201 Disable autobalancing of the rcu_node combining
3202 tree. This is used by rcutorture, and might
3203 possibly be useful for architectures having high
3204 cache-to-cache transfer latencies.
3206 rcutree.rcu_fanout_leaf= [KNL]
3207 Change the number of CPUs assigned to each
3208 leaf rcu_node structure. Useful for very
3209 large systems, which will choose the value 64,
3210 and for NUMA systems with large remote-access
3211 latencies, which will choose a value aligned
3212 with the appropriate hardware boundaries.
3214 rcutree.jiffies_till_sched_qs= [KNL]
3215 Set required age in jiffies for a
3216 given grace period before RCU starts
3217 soliciting quiescent-state help from
3218 rcu_note_context_switch().
3220 rcutree.jiffies_till_first_fqs= [KNL]
3221 Set delay from grace-period initialization to
3222 first attempt to force quiescent states.
3223 Units are jiffies, minimum value is zero,
3224 and maximum value is HZ.
3226 rcutree.jiffies_till_next_fqs= [KNL]
3227 Set delay between subsequent attempts to force
3228 quiescent states. Units are jiffies, minimum
3229 value is one, and maximum value is HZ.
3231 rcutree.kthread_prio= [KNL,BOOT]
3232 Set the SCHED_FIFO priority of the RCU per-CPU
3233 kthreads (rcuc/N). This value is also used for
3234 the priority of the RCU boost threads (rcub/N)
3235 and for the RCU grace-period kthreads (rcu_bh,
3236 rcu_preempt, and rcu_sched). If RCU_BOOST is
3237 set, valid values are 1-99 and the default is 1
3238 (the least-favored priority). Otherwise, when
3239 RCU_BOOST is not set, valid values are 0-99 and
3240 the default is zero (non-realtime operation).
3242 rcutree.rcu_nocb_leader_stride= [KNL]
3243 Set the number of NOCB kthread groups, which
3244 defaults to the square root of the number of
3245 CPUs. Larger numbers reduces the wakeup overhead
3246 on the per-CPU grace-period kthreads, but increases
3247 that same overhead on each group's leader.
3249 rcutree.qhimark= [KNL]
3250 Set threshold of queued RCU callbacks beyond which
3251 batch limiting is disabled.
3253 rcutree.qlowmark= [KNL]
3254 Set threshold of queued RCU callbacks below which
3255 batch limiting is re-enabled.
3257 rcutree.rcu_idle_gp_delay= [KNL]
3258 Set wakeup interval for idle CPUs that have
3259 RCU callbacks (RCU_FAST_NO_HZ=y).
3261 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3262 Set wakeup interval for idle CPUs that have
3263 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3264 Lazy RCU callbacks are those which RCU can
3265 prove do nothing more than free memory.
3267 rcuperf.gp_exp= [KNL]
3268 Measure performance of expedited synchronous
3269 grace-period primitives.
3271 rcuperf.holdoff= [KNL]
3272 Set test-start holdoff period. The purpose of
3273 this parameter is to delay the start of the
3274 test until boot completes in order to avoid
3277 rcuperf.nreaders= [KNL]
3278 Set number of RCU readers. The value -1 selects
3279 N, where N is the number of CPUs. A value
3280 "n" less than -1 selects N-n+1, where N is again
3281 the number of CPUs. For example, -2 selects N
3282 (the number of CPUs), -3 selects N+1, and so on.
3283 A value of "n" less than or equal to -N selects
3286 rcuperf.nwriters= [KNL]
3287 Set number of RCU writers. The values operate
3288 the same as for rcuperf.nreaders.
3289 N, where N is the number of CPUs
3291 rcuperf.perf_runnable= [BOOT]
3292 Start rcuperf running at boot time.
3294 rcuperf.shutdown= [KNL]
3295 Shut the system down after performance tests
3296 complete. This is useful for hands-off automated
3299 rcuperf.perf_type= [KNL]
3300 Specify the RCU implementation to test.
3302 rcuperf.verbose= [KNL]
3303 Enable additional printk() statements.
3305 rcutorture.cbflood_inter_holdoff= [KNL]
3306 Set holdoff time (jiffies) between successive
3307 callback-flood tests.
3309 rcutorture.cbflood_intra_holdoff= [KNL]
3310 Set holdoff time (jiffies) between successive
3311 bursts of callbacks within a given callback-flood
3314 rcutorture.cbflood_n_burst= [KNL]
3315 Set the number of bursts making up a given
3316 callback-flood test. Set this to zero to
3317 disable callback-flood testing.
3319 rcutorture.cbflood_n_per_burst= [KNL]
3320 Set the number of callbacks to be registered
3321 in a given burst of a callback-flood test.
3323 rcutorture.fqs_duration= [KNL]
3324 Set duration of force_quiescent_state bursts
3327 rcutorture.fqs_holdoff= [KNL]
3328 Set holdoff time within force_quiescent_state bursts
3331 rcutorture.fqs_stutter= [KNL]
3332 Set wait time between force_quiescent_state bursts
3335 rcutorture.gp_cond= [KNL]
3336 Use conditional/asynchronous update-side
3337 primitives, if available.
3339 rcutorture.gp_exp= [KNL]
3340 Use expedited update-side primitives, if available.
3342 rcutorture.gp_normal= [KNL]
3343 Use normal (non-expedited) asynchronous
3344 update-side primitives, if available.
3346 rcutorture.gp_sync= [KNL]
3347 Use normal (non-expedited) synchronous
3348 update-side primitives, if available. If all
3349 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3350 rcutorture.gp_normal=, and rcutorture.gp_sync=
3351 are zero, rcutorture acts as if is interpreted
3352 they are all non-zero.
3354 rcutorture.n_barrier_cbs= [KNL]
3355 Set callbacks/threads for rcu_barrier() testing.
3357 rcutorture.nfakewriters= [KNL]
3358 Set number of concurrent RCU writers. These just
3359 stress RCU, they don't participate in the actual
3360 test, hence the "fake".
3362 rcutorture.nreaders= [KNL]
3363 Set number of RCU readers. The value -1 selects
3364 N-1, where N is the number of CPUs. A value
3365 "n" less than -1 selects N-n-2, where N is again
3366 the number of CPUs. For example, -2 selects N
3367 (the number of CPUs), -3 selects N+1, and so on.
3369 rcutorture.object_debug= [KNL]
3370 Enable debug-object double-call_rcu() testing.
3372 rcutorture.onoff_holdoff= [KNL]
3373 Set time (s) after boot for CPU-hotplug testing.
3375 rcutorture.onoff_interval= [KNL]
3376 Set time (s) between CPU-hotplug operations, or
3377 zero to disable CPU-hotplug testing.
3379 rcutorture.shuffle_interval= [KNL]
3380 Set task-shuffle interval (s). Shuffling tasks
3381 allows some CPUs to go into dyntick-idle mode
3382 during the rcutorture test.
3384 rcutorture.shutdown_secs= [KNL]
3385 Set time (s) after boot system shutdown. This
3386 is useful for hands-off automated testing.
3388 rcutorture.stall_cpu= [KNL]
3389 Duration of CPU stall (s) to test RCU CPU stall
3390 warnings, zero to disable.
3392 rcutorture.stall_cpu_holdoff= [KNL]
3393 Time to wait (s) after boot before inducing stall.
3395 rcutorture.stat_interval= [KNL]
3396 Time (s) between statistics printk()s.
3398 rcutorture.stutter= [KNL]
3399 Time (s) to stutter testing, for example, specifying
3400 five seconds causes the test to run for five seconds,
3401 wait for five seconds, and so on. This tests RCU's
3402 ability to transition abruptly to and from idle.
3404 rcutorture.test_boost= [KNL]
3405 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3406 "Maybe" means test if the RCU implementation
3407 under test support RCU priority boosting.
3409 rcutorture.test_boost_duration= [KNL]
3410 Duration (s) of each individual boost test.
3412 rcutorture.test_boost_interval= [KNL]
3413 Interval (s) between each boost test.
3415 rcutorture.test_no_idle_hz= [KNL]
3416 Test RCU's dyntick-idle handling. See also the
3417 rcutorture.shuffle_interval parameter.
3419 rcutorture.torture_runnable= [BOOT]
3420 Start rcutorture running at boot time.
3422 rcutorture.torture_type= [KNL]
3423 Specify the RCU implementation to test.
3425 rcutorture.verbose= [KNL]
3426 Enable additional printk() statements.
3428 rcupdate.rcu_cpu_stall_suppress= [KNL]
3429 Suppress RCU CPU stall warning messages.
3431 rcupdate.rcu_cpu_stall_timeout= [KNL]
3432 Set timeout for RCU CPU stall warning messages.
3434 rcupdate.rcu_expedited= [KNL]
3435 Use expedited grace-period primitives, for
3436 example, synchronize_rcu_expedited() instead
3437 of synchronize_rcu(). This reduces latency,
3438 but can increase CPU utilization, degrade
3439 real-time latency, and degrade energy efficiency.
3440 No effect on CONFIG_TINY_RCU kernels.
3442 rcupdate.rcu_normal= [KNL]
3443 Use only normal grace-period primitives,
3444 for example, synchronize_rcu() instead of
3445 synchronize_rcu_expedited(). This improves
3446 real-time latency, CPU utilization, and
3447 energy efficiency, but can expose users to
3448 increased grace-period latency. This parameter
3449 overrides rcupdate.rcu_expedited. No effect on
3450 CONFIG_TINY_RCU kernels.
3452 rcupdate.rcu_normal_after_boot= [KNL]
3453 Once boot has completed (that is, after
3454 rcu_end_inkernel_boot() has been invoked), use
3455 only normal grace-period primitives. No effect
3456 on CONFIG_TINY_RCU kernels.
3458 rcupdate.rcu_task_stall_timeout= [KNL]
3459 Set timeout in jiffies for RCU task stall warning
3460 messages. Disable with a value less than or equal
3463 rcupdate.rcu_self_test= [KNL]
3464 Run the RCU early boot self tests
3466 rcupdate.rcu_self_test_bh= [KNL]
3467 Run the RCU bh early boot self tests
3469 rcupdate.rcu_self_test_sched= [KNL]
3470 Run the RCU sched early boot self tests
3474 Run specified binary instead of /init from the ramdisk,
3475 used for early userspace startup. See initrd.
3478 Format (x86 or x86_64):
3479 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3481 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3483 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3484 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3485 reboot_force is either force or not specified,
3486 reboot_cpu is s[mp]#### with #### being the processor
3487 to be used for rebooting.
3490 [KNL, SMP] Set scheduler's default relax_domain_level.
3491 See Documentation/cgroup-v1/cpusets.txt.
3493 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3495 reservetop= [X86-32]
3497 Reserves a hole at the top of the kernel virtual
3502 Set the amount of memory to reserve for BIOS at
3503 the bottom of the address space.
3505 reset_devices [KNL] Force drivers to reset the underlying device
3506 during initialization.
3509 Specify the partition device for software suspend
3511 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3513 resume_offset= [SWSUSP]
3514 Specify the offset from the beginning of the partition
3515 given by "resume=" at which the swap header is located,
3516 in <PAGE_SIZE> units (needed only for swap files).
3517 See Documentation/power/swsusp-and-swap-files.txt
3519 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3520 read the resume files
3522 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3523 Useful for devices that are detected asynchronously
3524 (e.g. USB and MMC devices).
3526 hibernate= [HIBERNATION]
3527 noresume Don't check if there's a hibernation image
3528 present during boot.
3529 nocompress Don't compress/decompress hibernation images.
3530 no Disable hibernation and resume.
3531 protect_image Turn on image protection during restoration
3532 (that will set all pages holding image data
3533 during restoration read-only).
3535 retain_initrd [RAM] Keep initrd memory after extraction
3537 rfkill.default_state=
3538 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3539 etc. communication is blocked by default.
3542 rfkill.master_switch_mode=
3543 0 The "airplane mode" button does nothing.
3544 1 The "airplane mode" button toggles between everything
3545 blocked and the previous configuration.
3546 2 The "airplane mode" button toggles between everything
3547 blocked and everything unblocked.
3549 rhash_entries= [KNL,NET]
3550 Set number of hash buckets for route cache
3552 ro [KNL] Mount root device read-only on boot
3555 on Mark read-only kernel memory as read-only (default).
3556 off Leave read-only kernel memory writable for debugging.
3559 Enable the uart passthrough on the designated usb port
3560 on Rockchip SoCs. When active, the signals of the
3561 debug-uart get routed to the D+ and D- pins of the usb
3562 port and the regular usb controller gets disabled.
3564 root= [KNL] Root filesystem
3565 See name_to_dev_t comment in init/do_mounts.c.
3567 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3568 mount the root filesystem
3570 rootflags= [KNL] Set root filesystem mount option string
3572 rootfstype= [KNL] Set root filesystem type
3574 rootwait [KNL] Wait (indefinitely) for root device to show up.
3575 Useful for devices that are detected asynchronously
3576 (e.g. USB and MMC devices).
3578 rproc_mem=nn[KMG][@address]
3579 [KNL,ARM,CMA] Remoteproc physical memory block.
3580 Memory area to be used by remote processor image,
3583 rw [KNL] Mount root device read-write on boot
3585 S [KNL] Run init in single mode
3587 s390_iommu= [HW,S390]
3588 Set s390 IOTLB flushing mode
3590 With strict flushing every unmap operation will result in
3591 an IOTLB flush. Default is lazy flushing before reuse,
3595 See drivers/net/irda/sa1100_ir.c.
3597 sbni= [NET] Granch SBNI12 leased line adapter
3599 sched_debug [KNL] Enables verbose scheduler debug messages.
3601 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3602 Allowed values are enable and disable. This feature
3603 incurs a small amount of overhead in the scheduler
3604 but is useful for debugging and performance tuning.
3606 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3607 xtime_lock contention on larger systems, and/or RCU lock
3608 contention on all systems with CONFIG_MAXSMP set.
3609 Format: { "0" | "1" }
3610 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3612 Note: increases power consumption, thus should only be
3613 enabled if running jitter sensitive (HPC/RT) workloads.
3615 security= [SECURITY] Choose a security module to enable at boot.
3616 If this boot parameter is not specified, only the first
3617 security module asking for security registration will be
3618 loaded. An invalid security module name will be treated
3619 as if no module has been chosen.
3621 selinux= [SELINUX] Disable or enable SELinux at boot time.
3622 Format: { "0" | "1" }
3623 See security/selinux/Kconfig help text.
3626 Default value is set via kernel config option.
3627 If enabled at boot time, /selinux/disable can be used
3628 later to disable prior to initial policy load.
3630 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3631 Format: { "0" | "1" }
3632 See security/apparmor/Kconfig help text
3635 Default value is set via kernel config option.
3637 serialnumber [BUGS=X86-32]
3640 Maximal number of shapers.
3648 Disable merging of slabs with similar size. May be
3649 necessary if there is some reason to distinguish
3650 allocs to different slabs. Debug options disable
3651 merging on their own.
3652 For more information see Documentation/vm/slub.txt.
3654 slab_max_order= [MM, SLAB]
3655 Determines the maximum allowed order for slabs.
3656 A high setting may cause OOMs due to memory
3657 fragmentation. Defaults to 1 for systems with
3658 more than 32MB of RAM, 0 otherwise.
3660 slub_debug[=options[,slabs]] [MM, SLUB]
3661 Enabling slub_debug allows one to determine the
3662 culprit if slab objects become corrupted. Enabling
3663 slub_debug can create guard zones around objects and
3664 may poison objects when not in use. Also tracks the
3665 last alloc / free. For more information see
3666 Documentation/vm/slub.txt.
3668 slub_max_order= [MM, SLUB]
3669 Determines the maximum allowed order for slabs.
3670 A high setting may cause OOMs due to memory
3671 fragmentation. For more information see
3672 Documentation/vm/slub.txt.
3674 slub_min_objects= [MM, SLUB]
3675 The minimum number of objects per slab. SLUB will
3676 increase the slab order up to slub_max_order to
3677 generate a sufficiently large slab able to contain
3678 the number of objects indicated. The higher the number
3679 of objects the smaller the overhead of tracking slabs
3680 and the less frequently locks need to be acquired.
3681 For more information see Documentation/vm/slub.txt.
3683 slub_min_order= [MM, SLUB]
3684 Determines the minimum page order for slabs. Must be
3685 lower than slub_max_order.
3686 For more information see Documentation/vm/slub.txt.
3688 slub_nomerge [MM, SLUB]
3689 Same with slab_nomerge. This is supported for legacy.
3690 See slab_nomerge for more information.
3693 Format: <io1>[,<io2>[,...,<io8>]]
3695 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3696 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3697 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3698 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3699 smsc-ircc2.ircc_irq= [HW] IRQ line
3700 smsc-ircc2.ircc_dma= [HW] DMA channel
3701 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3702 0: Toshiba Satellite 1800 (GP data pin select)
3703 1: Fast pin select (default)
3706 smt [KNL,S390] Set the maximum number of threads (logical
3707 CPUs) to use per physical CPU on systems capable of
3708 symmetric multithreading (SMT). Will be capped to the
3709 actual hardware limit.
3711 Default: -1 (no limit)
3714 [KNL] Should the soft-lockup detector generate panics.
3717 softlockup_all_cpu_backtrace=
3718 [KNL] Should the soft-lockup detector generate
3719 backtraces on all cpus.
3722 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3723 See Documentation/laptops/sonypi.txt
3725 spia_io_base= [HW,MTD]
3731 Enabled the stack tracer on boot up.
3733 stacktrace_filter=[function-list]
3734 [FTRACE] Limit the functions that the stack tracer
3735 will trace at boot up. function-list is a comma separated
3736 list of functions. This list can be changed at run
3737 time by the stack_trace_filter file in the debugfs
3738 tracing directory. Note, this enables stack tracing
3739 and the stacktrace above is not needed.
3743 Set the STI (builtin display/keyboard on the HP-PARISC
3744 machines) console (graphic card) which should be used
3745 as the initial boot-console.
3746 See also comment in drivers/video/console/sticore.c.
3749 See comment in drivers/video/console/sticore.c.
3752 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3754 sunrpc.min_resvport=
3755 sunrpc.max_resvport=
3757 SunRPC servers often require that client requests
3758 originate from a privileged port (i.e. a port in the
3759 range 0 < portnr < 1024).
3760 An administrator who wishes to reserve some of these
3761 ports for other uses may adjust the range that the
3762 kernel's sunrpc client considers to be privileged
3763 using these two parameters to set the minimum and
3764 maximum port values.
3766 sunrpc.svc_rpc_per_connection_limit=
3768 Limit the number of requests that the server will
3769 process in parallel from a single connection.
3770 The default value is 0 (no limit).
3774 Control how the NFS server code allocates CPUs to
3775 service thread pools. Depending on how many NICs
3776 you have and where their interrupts are bound, this
3777 option will affect which CPUs will do NFS serving.
3778 Note: this parameter cannot be changed while the
3779 NFS server is running.
3781 auto the server chooses an appropriate mode
3782 automatically using heuristics
3783 global a single global pool contains all CPUs
3784 percpu one pool for each CPU
3785 pernode one pool for each NUMA node (equivalent
3786 to global on non-NUMA machines)
3788 sunrpc.tcp_slot_table_entries=
3789 sunrpc.udp_slot_table_entries=
3791 Sets the upper limit on the number of simultaneous
3792 RPC calls that can be sent from the client to a
3793 server. Increasing these values may allow you to
3794 improve throughput, but will also increase the
3795 amount of memory reserved for use by the client.
3797 suspend.pm_test_delay=
3799 Sets the number of seconds to remain in a suspend test
3800 mode before resuming the system (see
3801 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3802 is set. Default value is 5.
3805 [KNL] Enable accounting of swap in memory resource
3806 controller if no parameter or 1 is given or disable
3807 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3809 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3810 Format: { <int> | force }
3811 <int> -- Number of I/O TLB slabs
3812 force -- force using of bounce buffers even if they
3813 wouldn't be automatically used by the kernel
3817 sysfs.deprecated=0|1 [KNL]
3818 Enable/disable old style sysfs layout for old udev
3819 on older distributions. When this option is enabled
3820 very new udev will not work anymore. When this option
3821 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3822 in older udev will not work anymore.
3823 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3824 the kernel configuration.
3826 sysrq_always_enabled
3828 Ignore sysrq setting - this boot parameter will
3829 neutralize any effect of /proc/sys/kernel/sysrq.
3830 Useful for debugging.
3832 tcpmhash_entries= [KNL,NET]
3833 Set the number of tcp_metrics_hash slots.
3834 Default value is 8192 or 16384 depending on total
3835 ram pages. This is used to specify the TCP metrics
3836 cache size. See Documentation/networking/ip-sysctl.txt
3837 "tcp_no_metrics_save" section for more details.
3841 test_suspend= [SUSPEND][,N]
3842 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3843 standby suspend) or "freeze" (for suspend type freeze)
3844 as the system sleep state during system startup with
3845 the optional capability to repeat N number of times.
3846 The system is woken from this state using a
3847 wakeup-capable RTC alarm.
3849 thash_entries= [KNL,NET]
3850 Set number of hash buckets for TCP connection
3852 thermal.act= [HW,ACPI]
3853 -1: disable all active trip points in all thermal zones
3854 <degrees C>: override all lowest active trip points
3856 thermal.crt= [HW,ACPI]
3857 -1: disable all critical trip points in all thermal zones
3858 <degrees C>: override all critical trip points
3860 thermal.nocrt= [HW,ACPI]
3861 Set to disable actions on ACPI thermal zone
3862 critical and hot trip points.
3864 thermal.off= [HW,ACPI]
3865 1: disable ACPI thermal control
3867 thermal.psv= [HW,ACPI]
3868 -1: disable all passive trip points
3869 <degrees C>: override all passive trip points to this
3872 thermal.tzp= [HW,ACPI]
3873 Specify global default ACPI thermal zone polling rate
3874 <deci-seconds>: poll all this frequency
3875 0: no polling (default)
3878 Force threading of all interrupt handlers except those
3879 marked explicitly IRQF_NO_THREAD.
3882 Enable the Transcendent memory driver if built-in.
3884 tmem.cleancache=0|1 [KNL, XEN]
3885 Default is on (1). Disable the usage of the cleancache
3886 API to send anonymous pages to the hypervisor.
3888 tmem.frontswap=0|1 [KNL, XEN]
3889 Default is on (1). Disable the usage of the frontswap
3890 API to send swap pages to the hypervisor. If disabled
3891 the selfballooning and selfshrinking are force disabled.
3893 tmem.selfballooning=0|1 [KNL, XEN]
3894 Default is on (1). Disable the driving of swap pages
3897 tmem.selfshrinking=0|1 [KNL, XEN]
3898 Default is on (1). Partial swapoff that immediately
3899 transfers pages from Xen hypervisor back to the
3900 kernel based on different criteria.
3904 Specify if the kernel should make use of the cpu
3905 topology information if the hardware supports this.
3906 The scheduler will make use of this information and
3907 e.g. base its process migration decisions on it.
3910 topology_updates= [KNL, PPC, NUMA]
3912 Specify if the kernel should ignore (off)
3913 topology updates sent by the hypervisor to this
3918 tpm_suspend_pcr=[HW,TPM]
3919 Format: integer pcr id
3920 Specify that at suspend time, the tpm driver
3921 should extend the specified pcr with zeros,
3922 as a workaround for some chips which fail to
3923 flush the last written pcr on TPM_SaveState.
3924 This will guarantee that all the other pcrs
3927 trace_buf_size=nn[KMG]
3928 [FTRACE] will set tracing buffer size on each cpu.
3930 trace_event=[event-list]
3931 [FTRACE] Set and start specified trace events in order
3932 to facilitate early boot debugging. The event-list is a
3933 comma separated list of trace events to enable. See
3934 also Documentation/trace/events.txt
3936 trace_options=[option-list]
3937 [FTRACE] Enable or disable tracer options at boot.
3938 The option-list is a comma delimited list of options
3939 that can be enabled or disabled just as if you were
3940 to echo the option name into
3942 /sys/kernel/debug/tracing/trace_options
3944 For example, to enable stacktrace option (to dump the
3945 stack trace of each event), add to the command line:
3947 trace_options=stacktrace
3949 See also Documentation/trace/ftrace.txt "trace options"
3953 Have the tracepoints sent to printk as well as the
3954 tracing ring buffer. This is useful for early boot up
3955 where the system hangs or reboots and does not give the
3956 option for reading the tracing buffer or performing a
3957 ftrace_dump_on_oops.
3959 To turn off having tracepoints sent to printk,
3960 echo 0 > /proc/sys/kernel/tracepoint_printk
3961 Note, echoing 1 into this file without the
3962 tracepoint_printk kernel cmdline option has no effect.
3966 Having tracepoints sent to printk() and activating high
3967 frequency tracepoints such as irq or sched, can cause
3968 the system to live lock.
3971 [FTRACE] enable this option to disable tracing when a
3972 warning is hit. This turns off "tracing_on". Tracing can
3973 be enabled again by echoing '1' into the "tracing_on"
3974 file located in /sys/kernel/debug/tracing/
3976 This option is useful, as it disables the trace before
3977 the WARNING dump is called, which prevents the trace to
3978 be filled with content caused by the warning output.
3980 This option can also be set at run time via the sysctl
3981 option: kernel/traceoff_on_warning
3983 transparent_hugepage=
3985 Format: [always|madvise|never]
3986 Can be used to control the default behavior of the system
3987 with respect to transparent hugepages.
3988 See Documentation/vm/transhuge.txt for more details.
3990 tsc= Disable clocksource stability checks for TSC.
3992 [x86] reliable: mark tsc clocksource as reliable, this
3993 disables clocksource verification at runtime, as well
3994 as the stability checks done at bootup. Used to enable
3995 high-resolution timer mode on older hardware, and in
3996 virtualized environment.
3997 [x86] noirqtime: Do not use TSC to do irq accounting.
3998 Used to run time disable IRQ_TIME_ACCOUNTING on any
3999 platforms where RDTSC is slow and this accounting
4002 turbografx.map[2|3]= [HW,JOY]
4003 TurboGraFX parallel port interface
4005 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4006 See also Documentation/input/joystick-parport.txt
4008 udbg-immortal [PPC] When debugging early kernel crashes that
4009 happen after console_init() and before a proper
4010 console driver takes over, this boot options might
4011 help "seeing" what's going on.
4013 uhash_entries= [KNL,NET]
4014 Set number of hash buckets for UDP/UDP-Lite connections
4017 [USB] Ignore overcurrent events (default N).
4018 Some badly-designed motherboards generate lots of
4019 bogus events, for ports that aren't wired to
4020 anything. Set this parameter to avoid log spamming.
4021 Note that genuine overcurrent events won't be
4025 [X86] Cause panic on unknown NMI.
4027 usbcore.authorized_default=
4028 [USB] Default USB device authorization:
4029 (default -1 = authorized except for wireless USB,
4030 0 = not authorized, 1 = authorized)
4032 usbcore.autosuspend=
4033 [USB] The autosuspend time delay (in seconds) used
4034 for newly-detected USB devices (default 2). This
4035 is the time required before an idle device will be
4036 autosuspended. Devices for which the delay is set
4037 to a negative value won't be autosuspended at all.
4039 usbcore.usbfs_snoop=
4040 [USB] Set to log all usbfs traffic (default 0 = off).
4042 usbcore.usbfs_snoop_max=
4043 [USB] Maximum number of bytes to snoop in each URB
4046 usbcore.blinkenlights=
4047 [USB] Set to cycle leds on hubs (default 0 = off).
4049 usbcore.old_scheme_first=
4050 [USB] Start with the old device initialization
4051 scheme (default 0 = off).
4053 usbcore.usbfs_memory_mb=
4054 [USB] Memory limit (in MB) for buffers allocated by
4055 usbfs (default = 16, 0 = max = 2047).
4057 usbcore.use_both_schemes=
4058 [USB] Try the other device initialization scheme
4059 if the first one fails (default 1 = enabled).
4061 usbcore.initial_descriptor_timeout=
4062 [USB] Specifies timeout for the initial 64-byte
4063 USB_REQ_GET_DESCRIPTOR request in milliseconds
4064 (default 5000 = 5.0 seconds).
4066 usbcore.nousb [USB] Disable the USB subsystem
4069 [USBHID] The interval which mice are to be polled at.
4071 usb-storage.delay_use=
4072 [UMS] The delay in seconds before a new device is
4073 scanned for Logical Units (default 1).
4076 [UMS] A list of quirks entries to supplement or
4077 override the built-in unusual_devs list. List
4078 entries are separated by commas. Each entry has
4079 the form VID:PID:Flags where VID and PID are Vendor
4080 and Product ID values (4-digit hex numbers) and
4081 Flags is a set of characters, each corresponding
4082 to a common usb-storage quirk flag as follows:
4083 a = SANE_SENSE (collect more than 18 bytes
4085 b = BAD_SENSE (don't collect more than 18
4086 bytes of sense data);
4087 c = FIX_CAPACITY (decrease the reported
4088 device capacity by one sector);
4089 d = NO_READ_DISC_INFO (don't use
4090 READ_DISC_INFO command);
4091 e = NO_READ_CAPACITY_16 (don't use
4092 READ_CAPACITY_16 command);
4093 f = NO_REPORT_OPCODES (don't use report opcodes
4095 g = MAX_SECTORS_240 (don't transfer more than
4096 240 sectors at a time, uas only);
4097 h = CAPACITY_HEURISTICS (decrease the
4098 reported device capacity by one
4099 sector if the number is odd);
4100 i = IGNORE_DEVICE (don't bind to this
4102 j = NO_REPORT_LUNS (don't use report luns
4104 l = NOT_LOCKABLE (don't try to lock and
4105 unlock ejectable media);
4106 m = MAX_SECTORS_64 (don't transfer more
4107 than 64 sectors = 32 KB at a time);
4108 n = INITIAL_READ10 (force a retry of the
4109 initial READ(10) command);
4110 o = CAPACITY_OK (accept the capacity
4111 reported by the device);
4112 p = WRITE_CACHE (the device cache is ON
4114 r = IGNORE_RESIDUE (the device reports
4115 bogus residue values);
4116 s = SINGLE_LUN (the device has only one
4118 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4119 commands, uas only);
4120 u = IGNORE_UAS (don't bind to the uas driver);
4121 w = NO_WP_DETECT (don't test whether the
4122 medium is write-protected).
4123 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4124 even if the device claims no cache)
4125 Example: quirks=0419:aaf5:rl,0421:0433:rc
4127 user_debug= [KNL,ARM]
4129 See arch/arm/Kconfig.debug help text.
4130 1 - undefined instruction events
4132 4 - invalid data aborts
4135 Example: user_debug=31
4138 [X86] Flags controlling user PTE allocations.
4140 nohigh = do not allocate PTE pages in
4141 HIGHMEM regardless of setting
4145 On X86_32, this is an alias for vdso32=. Otherwise:
4147 vdso=1: enable VDSO (the default)
4148 vdso=0: disable VDSO mapping
4150 vdso32= [X86] Control the 32-bit vDSO
4151 vdso32=1: enable 32-bit VDSO
4152 vdso32=0 or vdso32=2: disable 32-bit VDSO
4154 See the help text for CONFIG_COMPAT_VDSO for more
4155 details. If CONFIG_COMPAT_VDSO is set, the default is
4156 vdso32=0; otherwise, the default is vdso32=1.
4158 For compatibility with older kernels, vdso32=2 is an
4161 Try vdso32=0 if you encounter an error that says:
4162 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4165 vector=percpu: enable percpu vector domain
4167 video= [FB] Frame buffer configuration
4168 See Documentation/fb/modedb.txt.
4170 video.brightness_switch_enabled= [0,1]
4171 If set to 1, on receiving an ACPI notify event
4172 generated by hotkey, video driver will adjust brightness
4173 level and then send out the event to user space through
4174 the allocated input device; If set to 0, video driver
4175 will only send out the event without touching backlight
4180 [VMMIO] Memory mapped virtio (platform) device.
4182 <size>@<baseaddr>:<irq>[:<id>]
4184 <size> := size (can use standard suffixes
4186 <baseaddr> := physical base address
4187 <irq> := interrupt number (as passed to
4189 <id> := (optional) platform device id
4191 virtio_mmio.device=1K@0x100b0000:48:7
4193 Can be used multiple times for multiple devices.
4195 vga= [BOOT,X86-32] Select a particular video mode
4196 See Documentation/x86/boot.txt and
4197 Documentation/svga.txt.
4198 Use vga=ask for menu.
4199 This is actually a boot loader parameter; the value is
4200 passed to the kernel using a special protocol.
4202 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4203 size of <nn>. This can be used to increase the
4204 minimum size (128MB on x86). It can also be used to
4205 decrease the size and leave more room for directly
4208 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4211 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4214 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4218 Controls the behavior of vsyscalls (i.e. calls to
4219 fixed addresses of 0xffffffffff600x00 from legacy
4220 code). Most statically-linked binaries and older
4221 versions of glibc use these calls. Because these
4222 functions are at fixed addresses, they make nice
4223 targets for exploits that can control RIP.
4225 emulate [default] Vsyscalls turn into traps and are
4226 emulated reasonably safely.
4228 native Vsyscalls are native syscall instructions.
4229 This is a little bit faster than trapping
4230 and makes a few dynamic recompilers work
4231 better than they would in emulation mode.
4232 It also makes exploits much easier to write.
4234 none Vsyscalls don't work at all. This makes
4235 them quite hard to use for exploits but
4236 might break your system.
4238 vt.color= [VT] Default text color.
4239 Format: 0xYX, X = foreground, Y = background.
4240 Default: 0x07 = light gray on black.
4242 vt.cur_default= [VT] Default cursor shape.
4243 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4244 the parameters of the <Esc>[?A;B;Cc escape sequence;
4245 see VGA-softcursor.txt. Default: 2 = underline.
4247 vt.default_blu= [VT]
4248 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4249 Change the default blue palette of the console.
4250 This is a 16-member array composed of values
4253 vt.default_grn= [VT]
4254 Format: <green0>,<green1>,<green2>,...,<green15>
4255 Change the default green palette of the console.
4256 This is a 16-member array composed of values
4259 vt.default_red= [VT]
4260 Format: <red0>,<red1>,<red2>,...,<red15>
4261 Change the default red palette of the console.
4262 This is a 16-member array composed of values
4268 Set system-wide default UTF-8 mode for all tty's.
4269 Default is 1, i.e. UTF-8 mode is enabled for all
4270 newly opened terminals.
4272 vt.global_cursor_default=
4275 Set system-wide default for whether a cursor
4276 is shown on new VTs. Default is -1,
4277 i.e. cursors will be created by default unless
4278 overridden by individual drivers. 0 will hide
4279 cursors, 1 will display them.
4281 vt.italic= [VT] Default color for italic text; 0-15.
4284 vt.underline= [VT] Default color for underlined text; 0-15.
4287 watchdog timers [HW,WDT] For information on watchdog timers,
4288 see Documentation/watchdog/watchdog-parameters.txt
4289 or other driver-specific files in the
4290 Documentation/watchdog/ directory.
4292 workqueue.watchdog_thresh=
4293 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4294 warn stall conditions and dump internal state to
4295 help debugging. 0 disables workqueue stall
4296 detection; otherwise, it's the stall threshold
4297 duration in seconds. The default value is 30 and
4298 it can be updated at runtime by writing to the
4299 corresponding sysfs file.
4301 workqueue.disable_numa
4302 By default, all work items queued to unbound
4303 workqueues are affine to the NUMA nodes they're
4304 issued on, which results in better behavior in
4305 general. If NUMA affinity needs to be disabled for
4306 whatever reason, this option can be used. Note
4307 that this also can be controlled per-workqueue for
4308 workqueues visible under /sys/bus/workqueue/.
4310 workqueue.power_efficient
4311 Per-cpu workqueues are generally preferred because
4312 they show better performance thanks to cache
4313 locality; unfortunately, per-cpu workqueues tend to
4314 be more power hungry than unbound workqueues.
4316 Enabling this makes the per-cpu workqueues which
4317 were observed to contribute significantly to power
4318 consumption unbound, leading to measurably lower
4319 power usage at the cost of small performance
4322 The default value of this parameter is determined by
4323 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4325 workqueue.debug_force_rr_cpu
4326 Workqueue used to implicitly guarantee that work
4327 items queued without explicit CPU specified are put
4328 on the local CPU. This guarantee is no longer true
4329 and while local CPU is still preferred work items
4330 may be put on foreign CPUs. This debug option
4331 forces round-robin CPU selection to flush out
4332 usages which depend on the now broken guarantee.
4333 When enabled, memory and cache locality will be
4336 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4337 default x2apic cluster mode on platforms
4340 x86_intel_mid_timer= [X86-32,APBT]
4341 Choose timer option for x86 Intel MID platform.
4342 Two valid options are apbt timer only and lapic timer
4343 plus one apbt timer for broadcast timer.
4344 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4346 xen_512gb_limit [KNL,X86-64,XEN]
4347 Restricts the kernel running paravirtualized under Xen
4348 to use only up to 512 GB of RAM. The reason to do so is
4349 crash analysis tools and Xen tools for doing domain
4350 save/restore/migration must be enabled to handle larger
4353 xen_emul_unplug= [HW,X86,XEN]
4354 Unplug Xen emulated devices
4355 Format: [unplug0,][unplug1]
4356 ide-disks -- unplug primary master IDE devices
4357 aux-ide-disks -- unplug non-primary-master IDE devices
4358 nics -- unplug network devices
4359 all -- unplug all emulated devices (NICs and IDE disks)
4360 unnecessary -- unplugging emulated devices is
4361 unnecessary even if the host did not respond to
4363 never -- do not unplug even if version check succeeds
4365 xen_nopvspin [X86,XEN]
4366 Disables the ticketlock slowpath using Xen PV
4370 Disables the PV optimizations forcing the HVM guest to
4371 run as generic HVM guest with no PV drivers.
4373 xirc2ps_cs= [NET,PCMCIA]
4375 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]