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
1444 ima_canonical_fmt [IMA]
1445 Use the canonical format for the binary runtime
1446 measurements, instead of host native format.
1449 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1453 The list of supported hash algorithms is defined
1454 in crypto/hash_info.h.
1457 The builtin measurement policy to load during IMA
1458 setup. Specyfing "tcb" as the value, measures all
1459 programs exec'd, files mmap'd for exec, and all files
1460 opened with the read mode bit set by either the
1461 effective uid (euid=0) or uid=0.
1464 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1465 Load a policy which meets the needs of the Trusted
1466 Computing Base. This means IMA will measure all
1467 programs exec'd, files mmap'd for exec, and all files
1468 opened for read by uid=0.
1471 Select one of defined IMA measurements template formats.
1472 Formats: { "ima" | "ima-ng" | "ima-sig" }
1476 [IMA] Define a custom template format.
1477 Format: { "field1|...|fieldN" }
1479 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1480 Format: <min_file_size>
1481 Set the minimal file size for using asynchronous hash.
1482 If left unspecified, ahash usage is disabled.
1484 ahash performance varies for different data sizes on
1485 different crypto accelerators. This option can be used
1486 to achieve the best performance for a particular HW.
1488 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1490 Set hashing buffer size. Default: 4k.
1492 ahash performance varies for different chunk sizes on
1493 different crypto accelerators. This option can be used
1494 to achieve best performance for particular HW.
1498 Run specified binary instead of /sbin/init as init
1501 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1502 for working out where the kernel is dying during
1505 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1506 initcall functions. Useful for debugging built-in
1507 modules and initcalls.
1509 initrd= [BOOT] Specify the location of the initial ramdisk
1511 init_pkru= [x86] Specify the default memory protection keys rights
1512 register contents for all processes. 0x55555554 by
1513 default (disallow access to all but pkey 0). Can
1514 override in debugfs after boot.
1516 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1519 int_pln_enable [x86] Enable power limit notification interrupt
1521 integrity_audit=[IMA]
1522 Format: { "0" | "1" }
1523 0 -- basic integrity auditing messages. (Default)
1524 1 -- additional integrity auditing messages.
1526 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1528 Enable intel iommu driver.
1530 Disable intel iommu driver.
1531 igfx_off [Default Off]
1532 By default, gfx is mapped as normal device. If a gfx
1533 device has a dedicated DMAR unit, the DMAR unit is
1534 bypassed by not enabling DMAR with this option. In
1535 this case, gfx device will use physical address for
1538 With this option iommu will not optimize to look
1539 for io virtual address below 32-bit forcing dual
1540 address cycle on pci bus for cards supporting greater
1541 than 32-bit addressing. The default is to look
1542 for translation below 32-bit and if not available
1543 then look in the higher range.
1544 strict [Default Off]
1545 With this option on every unmap_single operation will
1546 result in a hardware IOTLB flush operation as opposed
1547 to batching them for performance.
1548 sp_off [Default Off]
1549 By default, super page will be supported if Intel IOMMU
1550 has the capability. With this option, super page will
1552 ecs_off [Default Off]
1553 By default, extended context tables will be supported if
1554 the hardware advertises that it has support both for the
1555 extended tables themselves, and also PASID support. With
1556 this option set, extended tables will not be used even
1557 on hardware which claims to support them.
1559 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1560 0 disables intel_idle and fall back on acpi_idle.
1561 1 to 9 specify maximum depth of C-state.
1565 Do not enable intel_pstate as the default
1566 scaling driver for the supported processors
1568 Use intel_pstate as a scaling driver, but configure it
1569 to work with generic cpufreq governors (instead of
1570 enabling its internal governor). This mode cannot be
1571 used along with the hardware-managed P-states (HWP)
1574 Enable intel_pstate on systems that prohibit it by default
1575 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1576 instead of acpi-cpufreq may disable platform features, such
1577 as thermal controls and power capping, that rely on ACPI
1578 P-States information being indicated to OSPM and therefore
1579 should be used with caution. This option does not work with
1580 processors that aren't supported by the intel_pstate driver
1581 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1583 Do not enable hardware P state control (HWP)
1586 Only load intel_pstate on systems which support
1587 hardware P state control (HWP) if available.
1589 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1590 Description Table, specifies preferred power management
1591 profile as "Enterprise Server" or "Performance Server",
1592 then this feature is turned on by default.
1594 Allow per-logical-CPU P-State performance control limits using
1595 cpufreq sysfs interface
1597 intremap= [X86-64, Intel-IOMMU]
1598 on enable Interrupt Remapping (default)
1599 off disable Interrupt Remapping
1600 nosid disable Source ID checking
1602 BIOS x2APIC opt-out request will be ignored
1603 nopost disable Interrupt Posting
1605 iomem= Disable strict checking of access to MMIO memory
1606 strict regions from userspace.
1621 nobypass [PPC/POWERNV]
1622 Disable IOMMU bypass, using IOMMU for PCI devices.
1625 io7= [HW] IO7 for Marvel based alpha systems
1626 See comment before marvel_specify_io7 in
1627 arch/alpha/kernel/core_marvel.c.
1629 io_delay= [X86] I/O delay method
1631 Standard port 0x80 based delay
1633 Alternate port 0xed based delay (needed on some systems)
1635 Simple two microseconds delay
1640 See Documentation/filesystems/nfs/nfsroot.txt.
1642 irqaffinity= [SMP] Set the default irq affinity mask
1643 The argument is a cpu list, as described above.
1646 When an interrupt is not handled search all handlers
1647 for it. Intended to get systems with badly broken
1651 When an interrupt is not handled search all handlers
1652 for it. Also check all handlers each timer
1653 interrupt. Intended to get systems with badly broken
1657 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1659 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1660 The argument is a cpu list, as described above.
1662 This option can be used to specify one or more CPUs
1663 to isolate from the general SMP balancing and scheduling
1664 algorithms. You can move a process onto or off an
1665 "isolated" CPU via the CPU affinity syscalls or cpuset.
1666 <cpu number> begins at 0 and the maximum value is
1667 "number of CPUs in system - 1".
1669 This option is the preferred way to isolate CPUs. The
1670 alternative -- manually setting the CPU mask of all
1671 tasks in the system -- can cause problems and
1672 suboptimal load balancer performance.
1676 ivrs_ioapic [HW,X86_64]
1677 Provide an override to the IOAPIC-ID<->DEVICE-ID
1678 mapping provided in the IVRS ACPI table. For
1679 example, to map IOAPIC-ID decimal 10 to
1680 PCI device 00:14.0 write the parameter as:
1681 ivrs_ioapic[10]=00:14.0
1683 ivrs_hpet [HW,X86_64]
1684 Provide an override to the HPET-ID<->DEVICE-ID
1685 mapping provided in the IVRS ACPI table. For
1686 example, to map HPET-ID decimal 0 to
1687 PCI device 00:14.0 write the parameter as:
1688 ivrs_hpet[0]=00:14.0
1690 ivrs_acpihid [HW,X86_64]
1691 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1692 mapping provided in the IVRS ACPI table. For
1693 example, to map UART-HID:UID AMD0020:0 to
1694 PCI device 00:14.5 write the parameter as:
1695 ivrs_acpihid[00:14.5]=AMD0020:0
1697 js= [HW,JOY] Analog joystick
1698 See Documentation/input/joystick.txt.
1701 When CONFIG_RANDOMIZE_BASE is set, this disables
1702 kernel and module base offset ASLR (Address Space
1703 Layout Randomization).
1707 kernelcore= [KNL,X86,IA-64,PPC]
1708 Format: nn[KMGTPE] | "mirror"
1710 specifies the amount of memory usable by the kernel
1711 for non-movable allocations. The requested amount is
1712 spread evenly throughout all nodes in the system. The
1713 remaining memory in each node is used for Movable
1714 pages. In the event, a node is too small to have both
1715 kernelcore and Movable pages, kernelcore pages will
1716 take priority and other nodes will have a larger number
1717 of Movable pages. The Movable zone is used for the
1718 allocation of pages that may be reclaimed or moved
1719 by the page migration subsystem. This means that
1720 HugeTLB pages may not be allocated from this zone.
1721 Note that allocations like PTEs-from-HighMem still
1722 use the HighMem zone if it exists, and the Normal
1723 zone if it does not.
1725 Instead of specifying the amount of memory (nn[KMGTPE]),
1726 you can specify "mirror" option. In case "mirror"
1727 option is specified, mirrored (reliable) memory is used
1728 for non-movable allocations and remaining memory is used
1729 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1730 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1733 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1734 Format: <Controller#>[,poll interval]
1735 The controller # is the number of the ehci usb debug
1736 port as it is probed via PCI. The poll interval is
1737 optional and is the number seconds in between
1738 each poll cycle to the debug port in case you need
1739 the functionality for interrupting the kernel with
1740 gdb or control-c on the dbgp connection. When
1741 not using this parameter you use sysrq-g to break into
1742 the kernel debugger.
1744 kgdboc= [KGDB,HW] kgdb over consoles.
1745 Requires a tty driver that supports console polling,
1746 or a supported polling keyboard driver (non-usb).
1747 Serial only format: <serial_device>[,baud]
1748 keyboard only format: kbd
1749 keyboard and serial format: kbd,<serial_device>[,baud]
1750 Optional Kernel mode setting:
1751 kms, kbd format: kms,kbd
1752 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1754 kgdbwait [KGDB] Stop kernel execution and enter the
1755 kernel debugger at the earliest opportunity.
1757 kmac= [MIPS] korina ethernet MAC address.
1758 Configure the RouterBoard 532 series on-chip
1759 Ethernet adapter MAC address.
1761 kmemleak= [KNL] Boot-time kmemleak enable/disable
1762 Valid arguments: on, off
1764 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1767 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1768 Valid arguments: 0, 1, 2
1769 kmemcheck=0 (disabled)
1770 kmemcheck=1 (enabled)
1771 kmemcheck=2 (one-shot mode)
1772 Default: 2 (one-shot mode)
1774 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1775 Default is 0 (don't ignore, but inject #GP)
1777 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1781 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1782 Default is 1 (enabled)
1784 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1786 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1788 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1789 (virtualized MMU) support on capable Intel chips.
1790 Default is 1 (enabled)
1792 kvm-intel.emulate_invalid_guest_state=
1793 [KVM,Intel] Enable emulation of invalid guest states
1794 Default is 0 (disabled)
1796 kvm-intel.flexpriority=
1797 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1798 Default is 1 (enabled)
1801 [KVM,Intel] Enable VMX nesting (nVMX).
1802 Default is 0 (disabled)
1804 kvm-intel.unrestricted_guest=
1805 [KVM,Intel] Disable unrestricted guest feature
1806 (virtualized real and unpaged mode) on capable
1807 Intel chips. Default is 1 (enabled)
1809 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1810 feature (tagged TLBs) on capable Intel chips.
1811 Default is 1 (enabled)
1817 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1820 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1821 value for LAPIC timer one-shot implementation. Default
1822 back to the programmable timer unit in the LAPIC.
1824 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1827 libata.dma= [LIBATA] DMA control
1828 libata.dma=0 Disable all PATA and SATA DMA
1829 libata.dma=1 PATA and SATA Disk DMA only
1830 libata.dma=2 ATAPI (CDROM) DMA only
1831 libata.dma=4 Compact Flash DMA only
1832 Combinations also work, so libata.dma=3 enables DMA
1833 for disks and CDROMs, but not CFs.
1835 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1836 libata.ignore_hpa=0 keep BIOS limits (default)
1837 libata.ignore_hpa=1 ignore limits, using full disk
1839 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1843 libata.force= [LIBATA] Force configurations. The format is comma
1844 separated list of "[ID:]VAL" where ID is
1845 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1846 matching port, link or device. Basically, it matches
1847 the ATA ID string printed on console by libata. If
1848 the whole ID part is omitted, the last PORT and DEVICE
1849 values are used. If ID hasn't been specified yet, the
1850 configuration applies to all ports, links and devices.
1852 If only DEVICE is omitted, the parameter applies to
1853 the port and all links and devices behind it. DEVICE
1854 number of 0 either selects the first device or the
1855 first fan-out link behind PMP device. It does not
1856 select the host link. DEVICE number of 15 selects the
1857 host link and device attached to it.
1859 The VAL specifies the configuration to force. As long
1860 as there's no ambiguity shortcut notation is allowed.
1861 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1862 The following configurations can be forced.
1864 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1865 Any ID with matching PORT is used.
1867 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1869 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1870 udma[/][16,25,33,44,66,100,133] notation is also
1873 * [no]ncq: Turn on or off NCQ.
1875 * [no]ncqtrim: Turn off queued DSM TRIM.
1877 * nohrst, nosrst, norst: suppress hard, soft
1880 * rstonce: only attempt one reset during
1881 hot-unplug link recovery
1883 * dump_id: dump IDENTIFY data.
1885 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1887 * disable: Disable this device.
1889 If there are multiple matching configurations changing
1890 the same attribute, the last one is used.
1892 memblock=debug [KNL] Enable memblock debug messages.
1894 load_ramdisk= [RAM] List of ramdisks to load from floppy
1895 See Documentation/blockdev/ramdisk.txt.
1897 lockd.nlm_grace_period=P [NFS] Assign grace period.
1900 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1903 lockd.nlm_timeout=T [NFS] Assign timeout value.
1906 lockd.nlm_udpport=M [NFS] Assign UDP port.
1909 locktorture.nreaders_stress= [KNL]
1910 Set the number of locking read-acquisition kthreads.
1911 Defaults to being automatically set based on the
1912 number of online CPUs.
1914 locktorture.nwriters_stress= [KNL]
1915 Set the number of locking write-acquisition kthreads.
1917 locktorture.onoff_holdoff= [KNL]
1918 Set time (s) after boot for CPU-hotplug testing.
1920 locktorture.onoff_interval= [KNL]
1921 Set time (s) between CPU-hotplug operations, or
1922 zero to disable CPU-hotplug testing.
1924 locktorture.shuffle_interval= [KNL]
1925 Set task-shuffle interval (jiffies). Shuffling
1926 tasks allows some CPUs to go into dyntick-idle
1927 mode during the locktorture test.
1929 locktorture.shutdown_secs= [KNL]
1930 Set time (s) after boot system shutdown. This
1931 is useful for hands-off automated testing.
1933 locktorture.stat_interval= [KNL]
1934 Time (s) between statistics printk()s.
1936 locktorture.stutter= [KNL]
1937 Time (s) to stutter testing, for example,
1938 specifying five seconds causes the test to run for
1939 five seconds, wait for five seconds, and so on.
1940 This tests the locking primitive's ability to
1941 transition abruptly to and from idle.
1943 locktorture.torture_runnable= [BOOT]
1944 Start locktorture running at boot time.
1946 locktorture.torture_type= [KNL]
1947 Specify the locking implementation to test.
1949 locktorture.verbose= [KNL]
1950 Enable additional printk() statements.
1952 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1955 loglevel= All Kernel Messages with a loglevel smaller than the
1956 console loglevel will be printed to the console. It can
1957 also be changed with klogd or other programs. The
1958 loglevels are defined as follows:
1960 0 (KERN_EMERG) system is unusable
1961 1 (KERN_ALERT) action must be taken immediately
1962 2 (KERN_CRIT) critical conditions
1963 3 (KERN_ERR) error conditions
1964 4 (KERN_WARNING) warning conditions
1965 5 (KERN_NOTICE) normal but significant condition
1966 6 (KERN_INFO) informational
1967 7 (KERN_DEBUG) debug-level messages
1969 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1970 in bytes. n must be a power of two and greater
1971 than the minimal size. The minimal size is defined
1972 by LOG_BUF_SHIFT kernel config parameter. There is
1973 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1974 that allows to increase the default size depending on
1975 the number of CPUs. See init/Kconfig for more details.
1977 logo.nologo [FB] Disables display of the built-in Linux logo.
1978 This may be used to provide more screen space for
1979 kernel log messages and is useful when debugging
1980 kernel boot problems.
1982 lp=0 [LP] Specify parallel ports to use, e.g,
1983 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1984 lp=reset first parallel port). 'lp=0' disables the
1985 lp=auto printer driver. 'lp=reset' (which can be
1986 specified in addition to the ports) causes
1987 attached printers to be reset. Using
1988 lp=port1,port2,... specifies the parallel ports
1989 to associate lp devices with, starting with
1990 lp0. A port specification may be 'none' to skip
1991 that lp device, or a parport name such as
1992 'parport0'. Specifying 'lp=auto' instead of a
1993 port specification list means that device IDs
1994 from each port should be examined, to see if
1995 an IEEE 1284-compliant printer is attached; if
1996 so, the driver will manage that printer.
1997 See also header of drivers/char/lp.c.
2000 Sets loops_per_jiffy to given constant, thus avoiding
2001 time-consuming boot-time autodetection (up to 250 ms per
2002 CPU). 0 enables autodetection (default). To determine
2003 the correct value for your kernel, boot with normal
2004 autodetection and see what value is printed. Note that
2005 on SMP systems the preset will be applied to all CPUs,
2006 which is likely to cause problems if your CPUs need
2007 significantly divergent settings. An incorrect value
2008 will cause delays in the kernel to be wrong, leading to
2009 unpredictable I/O errors and other breakage. Although
2010 unlikely, in the extreme case this might damage your
2014 Format: <io>,<irq>,<dma>
2016 machvec= [IA-64] Force the use of a particular machine-vector
2017 (machvec) in a generic kernel.
2018 Example: machvec=hpzx1_swiotlb
2020 machtype= [Loongson] Share the same kernel image file between different
2022 Example: machtype=lemote-yeeloong-2f-7inch
2024 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2025 than or equal to this physical address is ignored.
2027 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2028 will bring up during bootup. maxcpus=n : n >= 0 limits
2029 the kernel to bring up 'n' processors. Surely after
2030 bootup you can bring up the other plugged cpu by executing
2031 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2032 only takes effect during system bootup.
2033 While n=0 is a special case, it is equivalent to "nosmp",
2034 which also disables the IO APIC.
2036 max_loop= [LOOP] The number of loop block devices that get
2037 (loop.max_loop) unconditionally pre-created at init time. The default
2038 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2039 of statically allocating a predefined number, loop
2040 devices can be requested on-demand with the
2041 /dev/loop-control interface.
2043 mce [X86-32] Machine Check Exception
2045 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2047 md= [HW] RAID subsystems devices and level
2048 See Documentation/admin-guide/md.rst.
2051 Format: <first>,<last>
2052 Specifies range of consoles to be captured by the MDA.
2054 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2055 Amount of memory to be used when the kernel is not able
2056 to see the whole system memory or for test.
2057 [X86] Work as limiting max address. Use together
2058 with memmap= to avoid physical address space collisions.
2059 Without memmap= PCI devices could be placed at addresses
2060 belonging to unused RAM.
2062 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2066 [KNL,SH] Allow user to override the default size for
2067 per-device physically contiguous DMA buffers.
2069 memhp_default_state=online/offline
2070 [KNL] Set the initial state for the memory hotplug
2071 onlining policy. If not specified, the default value is
2072 set according to the
2073 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2075 See Documentation/memory-hotplug.txt.
2077 memmap=exactmap [KNL,X86] Enable setting of an exact
2078 E820 memory map, as specified by the user.
2079 Such memmap=exactmap lines can be constructed based on
2080 BIOS output or other requirements. See the memmap=nn@ss
2083 memmap=nn[KMG]@ss[KMG]
2084 [KNL] Force usage of a specific region of memory.
2085 Region of memory to be used is from ss to ss+nn.
2087 memmap=nn[KMG]#ss[KMG]
2088 [KNL,ACPI] Mark specific memory as ACPI data.
2089 Region of memory to be marked is from ss to ss+nn.
2091 memmap=nn[KMG]$ss[KMG]
2092 [KNL,ACPI] Mark specific memory as reserved.
2093 Region of memory to be reserved is from ss to ss+nn.
2094 Example: Exclude memory from 0x18690000-0x1869ffff
2095 memmap=64K$0x18690000
2097 memmap=0x10000$0x18690000
2099 memmap=nn[KMG]!ss[KMG]
2100 [KNL,X86] Mark specific memory as protected.
2101 Region of memory to be used, from ss to ss+nn.
2102 The memory region may be marked as e820 type 12 (0xc)
2103 and is NVDIMM or ADR memory.
2105 memory_corruption_check=0/1 [X86]
2106 Some BIOSes seem to corrupt the first 64k of
2107 memory when doing things like suspend/resume.
2108 Setting this option will scan the memory
2109 looking for corruption. Enabling this will
2110 both detect corruption and prevent the kernel
2111 from using the memory being corrupted.
2112 However, its intended as a diagnostic tool; if
2113 repeatable BIOS-originated corruption always
2114 affects the same memory, you can use memmap=
2115 to prevent the kernel from using that memory.
2117 memory_corruption_check_size=size [X86]
2118 By default it checks for corruption in the low
2119 64k, making this memory unavailable for normal
2120 use. Use this parameter to scan for
2121 corruption in more or less memory.
2123 memory_corruption_check_period=seconds [X86]
2124 By default it checks for corruption every 60
2125 seconds. Use this parameter to check at some
2126 other rate. 0 disables periodic checking.
2128 memtest= [KNL,X86,ARM] Enable memtest
2130 default : 0 <disable>
2131 Specifies the number of memtest passes to be
2132 performed. Each pass selects another test
2133 pattern from a given set of patterns. Memtest
2134 fills the memory with this pattern, validates
2135 memory contents and reserves bad memory
2136 regions that are detected.
2138 mem_sleep_default= [SUSPEND] Default system suspend mode:
2139 s2idle - Suspend-To-Idle
2140 shallow - Power-On Suspend or equivalent (if supported)
2141 deep - Suspend-To-RAM or equivalent (if supported)
2142 See Documentation/power/states.txt.
2144 meye.*= [HW] Set MotionEye Camera parameters
2145 See Documentation/video4linux/meye.txt.
2147 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2148 Multi-Function General Purpose Timers on AMD Geode
2151 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2152 the BIOS has incorrectly applied a workaround. TinyBIOS
2153 version 0.98 is known to be affected, 0.99 fixes the
2154 problem by letting the user disable the workaround.
2158 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2159 physical address is ignored.
2161 mini2440= [ARM,HW,KNL]
2162 Format:[0..2][b][c][t]
2164 MINI2440 configuration specification:
2165 0 - The attached screen is the 3.5" TFT
2166 1 - The attached screen is the 7" TFT
2167 2 - The VGA Shield is attached (1024x768)
2168 Leaving out the screen size parameter will not load
2169 the TFT driver, and the framebuffer will be left
2171 b - Enable backlight. The TFT backlight pin will be
2172 linked to the kernel VESA blanking code and a GPIO
2173 LED. This parameter is not necessary when using the
2175 c - Enable the s3c camera interface.
2176 t - Reserved for enabling touchscreen support. The
2177 touchscreen support is not enabled in the mainstream
2178 kernel as of 2.6.30, a preliminary port can be found
2179 in the "bleeding edge" mini2440 support kernel at
2180 http://repo.or.cz/w/linux-2.6/mini2440.git
2183 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2184 parameter allows control of the logging verbosity for
2185 the additional memory initialisation checks. A value
2186 of 0 disables mminit logging and a level of 4 will
2187 log everything. Information is printed at KERN_DEBUG
2188 so loglevel=8 may also need to be specified.
2191 [KNL] When CONFIG_MODULE_SIG is set, this means that
2192 modules without (valid) signatures will fail to load.
2193 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2194 is always true, so this option does nothing.
2196 module_blacklist= [KNL] Do not load a comma-separated list of
2197 modules. Useful for debugging problem modules.
2200 [MOUSE] Maximum time between finger touching and
2201 leaving touchpad surface for touch to be considered
2202 a tap and be reported as a left button click (for
2203 touchpads working in absolute mode only).
2205 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2206 reporting absolute coordinates, such as tablets
2207 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2208 reporting absolute coordinates, such as tablets
2210 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2211 is similar to kernelcore except it specifies the
2212 amount of memory used for migratable allocations.
2213 If both kernelcore and movablecore is specified,
2214 then kernelcore will be at *least* the specified
2215 value but may be more. If movablecore on its own
2216 is specified, the administrator must be careful
2217 that the amount of memory usable for all allocations
2220 movable_node [KNL] Boot-time switch to enable the effects
2221 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2223 MTD_Partition= [MTD]
2224 Format: <name>,<region-number>,<size>,<offset>
2226 MTD_Region= [MTD] Format:
2227 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2230 See drivers/mtd/cmdlinepart.c.
2232 multitce=off [PPC] This parameter disables the use of the pSeries
2233 firmware feature for updating multiple TCE entries
2236 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2238 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2240 boundary - index of last SLC block on Flex-OneNAND.
2241 The remaining blocks are configured as MLC blocks.
2242 lock - Configure if Flex-OneNAND boundary should be locked.
2243 Once locked, the boundary cannot be changed.
2244 1 indicates lock status, 0 indicates unlock status.
2247 ARM/S3C2412 JIVE boot control
2249 See arch/arm/mach-s3c2412/mach-jive.c
2251 mtouchusb.raw_coordinates=
2252 [HW] Make the MicroTouch USB driver use raw coordinates
2253 ('y', default) or cooked coordinates ('n')
2255 mtrr_chunk_size=nn[KMG] [X86]
2256 used for mtrr cleanup. It is largest continuous chunk
2257 that could hold holes aka. UC entries.
2259 mtrr_gran_size=nn[KMG] [X86]
2260 Used for mtrr cleanup. It is granularity of mtrr block.
2262 Large value could prevent small alignment from
2265 mtrr_spare_reg_nr=n [X86]
2267 Range: 0,7 : spare reg number
2269 Used for mtrr cleanup. It is spare mtrr entries number.
2270 Set to 2 or more if your graphical card needs more.
2272 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2274 netdev= [NET] Network devices parameters
2275 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2276 Note that mem_start is often overloaded to mean
2277 something different and driver-specific.
2278 This usage is only documented in each driver source
2282 [NETFILTER] Enable connection tracking flow accounting
2283 0 to disable accounting
2284 1 to enable accounting
2287 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2288 See Documentation/filesystems/nfs/nfsroot.txt.
2290 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2291 See Documentation/filesystems/nfs/nfsroot.txt.
2293 nfsrootdebug [NFS] enable nfsroot debugging messages.
2294 See Documentation/filesystems/nfs/nfsroot.txt.
2296 nfs.callback_nr_threads=
2297 [NFSv4] set the total number of threads that the
2298 NFS client will assign to service NFSv4 callback
2301 nfs.callback_tcpport=
2302 [NFS] set the TCP port on which the NFSv4 callback
2303 channel should listen.
2306 [NFS] sets the pathname to the program which is used
2307 to update the NFS client cache entries.
2309 nfs.cache_getent_timeout=
2310 [NFS] sets the timeout after which an attempt to
2311 update a cache entry is deemed to have failed.
2313 nfs.idmap_cache_timeout=
2314 [NFS] set the maximum lifetime for idmapper cache
2318 [NFS] enable 64-bit inode numbers.
2319 If zero, the NFS client will fake up a 32-bit inode
2320 number for the readdir() and stat() syscalls instead
2321 of returning the full 64-bit number.
2322 The default is to return 64-bit inode numbers.
2324 nfs.max_session_cb_slots=
2325 [NFSv4.1] Sets the maximum number of session
2326 slots the client will assign to the callback
2327 channel. This determines the maximum number of
2328 callbacks the client will process in parallel for
2329 a particular server.
2331 nfs.max_session_slots=
2332 [NFSv4.1] Sets the maximum number of session slots
2333 the client will attempt to negotiate with the server.
2334 This limits the number of simultaneous RPC requests
2335 that the client can send to the NFSv4.1 server.
2336 Note that there is little point in setting this
2337 value higher than the max_tcp_slot_table_limit.
2339 nfs.nfs4_disable_idmapping=
2340 [NFSv4] When set to the default of '1', this option
2341 ensures that both the RPC level authentication
2342 scheme and the NFS level operations agree to use
2343 numeric uids/gids if the mount is using the
2344 'sec=sys' security flavour. In effect it is
2345 disabling idmapping, which can make migration from
2346 legacy NFSv2/v3 systems to NFSv4 easier.
2347 Servers that do not support this mode of operation
2348 will be autodetected by the client, and it will fall
2349 back to using the idmapper.
2350 To turn off this behaviour, set the value to '0'.
2352 [NFS4] Specify an additional fixed unique ident-
2353 ification string that NFSv4 clients can insert into
2354 their nfs_client_id4 string. This is typically a
2355 UUID that is generated at system install time.
2357 nfs.send_implementation_id =
2358 [NFSv4.1] Send client implementation identification
2359 information in exchange_id requests.
2360 If zero, no implementation identification information
2362 The default is to send the implementation identification
2365 nfs.recover_lost_locks =
2366 [NFSv4] Attempt to recover locks that were lost due
2367 to a lease timeout on the server. Please note that
2368 doing this risks data corruption, since there are
2369 no guarantees that the file will remain unchanged
2370 after the locks are lost.
2371 If you want to enable the kernel legacy behaviour of
2372 attempting to recover these locks, then set this
2374 The default parameter value of '0' causes the kernel
2375 not to attempt recovery of lost locks.
2377 nfs4.layoutstats_timer =
2378 [NFSv4.2] Change the rate at which the kernel sends
2379 layoutstats to the pNFS metadata server.
2381 Setting this to value to 0 causes the kernel to use
2382 whatever value is the default set by the layout
2383 driver. A non-zero value sets the minimum interval
2384 in seconds between layoutstats transmissions.
2386 nfsd.nfs4_disable_idmapping=
2387 [NFSv4] When set to the default of '1', the NFSv4
2388 server will return only numeric uids and gids to
2389 clients using auth_sys, and will accept numeric uids
2390 and gids from such clients. This is intended to ease
2391 migration from NFSv2/v3.
2393 objlayoutdriver.osd_login_prog=
2394 [NFS] [OBJLAYOUT] sets the pathname to the program which
2395 is used to automatically discover and login into new
2396 osd-targets. Please see:
2397 Documentation/filesystems/pnfs.txt for more explanations
2399 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2400 when a NMI is triggered.
2401 Format: [state][,regs][,debounce][,die]
2403 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2404 Format: [panic,][nopanic,][num]
2406 0 - turn hardlockup detector in nmi_watchdog off
2407 1 - turn hardlockup detector in nmi_watchdog on
2408 When panic is specified, panic when an NMI watchdog
2409 timeout occurs (or 'nopanic' to override the opposite
2410 default). To disable both hard and soft lockup detectors,
2411 please see 'nowatchdog'.
2412 This is useful when you use a panic=... timeout and
2413 need the box quickly up again.
2415 netpoll.carrier_timeout=
2416 [NET] Specifies amount of time (in seconds) that
2417 netpoll should wait for a carrier. By default netpoll
2420 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2421 emulation library even if a 387 maths coprocessor
2425 [HW] Never suspend the console
2426 Disable suspending of consoles during suspend and
2427 hibernate operations. Once disabled, debugging
2428 messages can reach various consoles while the rest
2429 of the system is being put to sleep (ie, while
2430 debugging driver suspend/resume hooks). This may
2431 not work reliably with all consoles, but is known
2432 to work with serial and VGA consoles.
2433 To facilitate more flexible debugging, we also add
2434 console_suspend, a printk module parameter to control
2435 it. Users could use console_suspend (usually
2436 /sys/module/printk/parameters/console_suspend) to
2437 turn on/off it dynamically.
2439 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2440 caches in the slab allocator. Saves per-node memory,
2441 but will impact performance.
2445 noapic [SMP,APIC] Tells the kernel to not make use of any
2446 IOAPICs that may be present in the system.
2448 noautogroup Disable scheduler automatic task group creation.
2450 nobats [PPC] Do not use BATs for mapping kernel lowmem
2451 on "Classic" PPC cores.
2455 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2457 nodelayacct [KNL] Disable per-task delay accounting
2459 nodsp [SH] Disable hardware DSP at boot time.
2461 noefi Disable EFI runtime services support.
2466 On X86-32 available only on PAE configured kernels.
2467 noexec=on: enable non-executable mappings (default)
2468 noexec=off: disable non-executable mappings
2471 Disable SMAP (Supervisor Mode Access Prevention)
2472 even if it is supported by processor.
2475 Disable SMEP (Supervisor Mode Execution Prevention)
2476 even if it is supported by processor.
2479 This affects only 32-bit executables.
2480 noexec32=on: enable non-executable mappings (default)
2481 read doesn't imply executable mappings
2482 noexec32=off: disable non-executable mappings
2483 read implies executable mappings
2485 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2487 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2488 register save and restore. The kernel will only save
2489 legacy floating-point registers on task switch.
2491 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2493 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2494 Equivalent to smt=1.
2496 noxsave [BUGS=X86] Disables x86 extended register state save
2497 and restore using xsave. The kernel will fallback to
2498 enabling legacy floating-point and sse state.
2500 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2501 register states. The kernel will fall back to use
2502 xsave to save the states. By using this parameter,
2503 performance of saving the states is degraded because
2504 xsave doesn't support modified optimization while
2505 xsaveopt supports it on xsaveopt enabled systems.
2507 noxsaves [X86] Disables xsaves and xrstors used in saving and
2508 restoring x86 extended register state in compacted
2509 form of xsave area. The kernel will fall back to use
2510 xsaveopt and xrstor to save and restore the states
2511 in standard form of xsave area. By using this
2512 parameter, xsave area per process might occupy more
2513 memory on xsaves enabled systems.
2515 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2516 wfi(ARM) instruction doesn't work correctly and not to
2517 use it. This is also useful when using JTAG debugger.
2519 no_file_caps Tells the kernel not to honor file capabilities. The
2520 only way then for a file to be executed with privilege
2521 is to be setuid root or executed by root.
2523 nohalt [IA-64] Tells the kernel not to use the power saving
2524 function PAL_HALT_LIGHT when idle. This increases
2525 power-consumption. On the positive side, it reduces
2526 interrupt wake-up latency, which may improve performance
2527 in certain environments such as networked servers or
2530 nohibernate [HIBERNATION] Disable hibernation and resume.
2532 nohz= [KNL] Boottime enable/disable dynamic ticks
2533 Valid arguments: on, off
2536 nohz_full= [KNL,BOOT]
2537 The argument is a cpu list, as described above.
2538 In kernels built with CONFIG_NO_HZ_FULL=y, set
2539 the specified list of CPUs whose tick will be stopped
2540 whenever possible. The boot CPU will be forced outside
2541 the range to maintain the timekeeping.
2542 The CPUs in this range must also be included in the
2545 noiotrap [SH] Disables trapped I/O port accesses.
2547 noirqdebug [X86-32] Disables the code which attempts to detect and
2548 disable unhandled interrupt sources.
2550 no_timer_check [X86,APIC] Disables the code which tests for
2551 broken timer IRQ sources.
2553 noisapnp [ISAPNP] Disables ISA PnP code.
2555 noinitrd [RAM] Tells the kernel not to load any configured
2558 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2560 [Deprecated - use intremap=off]
2564 noinvpcid [X86] Disable the INVPCID cpu feature.
2566 nojitter [IA-64] Disables jitter checking for ITC timers.
2568 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2570 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2574 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2575 clock and use the default one.
2577 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2578 steal time is computed, but won't influence scheduler
2581 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2583 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2585 noltlbs [PPC] Do not use large page/tlb entries for kernel
2586 lowmem mapping on PPC40x and PPC8xx
2588 nomca [IA-64] Disable machine check abort handling
2590 nomce [X86-32] Disable Machine Check Exception
2592 nomfgpt [X86-32] Disable Multi-Function General Purpose
2593 Timer usage (for AMD Geode machines).
2595 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2596 shutdown the other cpus. Instead use the REBOOT_VECTOR
2599 nomodule Disable module load
2601 nopat [X86] Disable PAT (page attribute table extension of
2602 pagetables) support.
2604 norandmaps Don't use address space randomization. Equivalent to
2605 echo 0 > /proc/sys/kernel/randomize_va_space
2607 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2609 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2610 with UP alternatives
2612 nordrand [X86] Disable kernel use of the RDRAND and
2613 RDSEED instructions even if they are supported
2614 by the processor. RDRAND and RDSEED are still
2615 available to user space applications.
2617 noresume [SWSUSP] Disables resume and restores original swap
2620 no-scroll [VGA] Disables scrollback.
2621 This is required for the Braillex ib80-piezo Braille
2622 reader made by F.H. Papenmeier (Germany).
2626 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2628 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2629 and disable the IO APIC. legacy for "maxcpus=0".
2631 nosoftlockup [KNL] Disable the soft-lockup detector.
2633 nosync [HW,M68K] Disables sync negotiation for all devices.
2635 notsc [BUGS=X86-32] Disable Time Stamp Counter
2637 nowatchdog [KNL] Disable both lockup detectors, i.e.
2638 soft-lockup and NMI watchdog (hard-lockup).
2642 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2644 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2645 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2646 Some features depend on CPU0. Known dependencies are:
2647 1. Resume from suspend/hibernate depends on CPU0.
2648 Suspend/hibernate will fail if CPU0 is offline and you
2649 need to online CPU0 before suspend/hibernate.
2650 2. PIC interrupts also depend on CPU0. CPU0 can't be
2651 removed if a PIC interrupt is detected.
2652 It's said poweroff/reboot may depend on CPU0 on some
2653 machines although I haven't seen such issues so far
2654 after CPU0 is offline on a few tested machines.
2655 If the dependencies are under your control, you can
2656 turn on cpu0_hotplug.
2658 nptcg= [IA-64] Override max number of concurrent global TLB
2659 purges which is reported from either PAL_VM_SUMMARY or
2662 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2663 could support. nr_cpus=n : n >= 1 limits the kernel to
2664 support 'n' processors. It could be larger than the
2665 number of already plugged CPU during bootup, later in
2666 runtime you can physically add extra cpu until it reaches
2667 n. So during boot up some boot time memory for per-cpu
2668 variables need be pre-allocated for later physical cpu
2671 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2673 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2674 Allowed values are enable and disable
2676 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2677 one of ['zone', 'node', 'default'] can be specified
2678 This can be set from sysctl after boot.
2679 See Documentation/sysctl/vm.txt for details.
2681 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2682 See Documentation/debugging-via-ohci1394.txt for more
2685 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2686 Rather than timing out after 20 ms if an EC
2687 command is not properly ACKed, override the length
2688 of the timeout. We have interrupts disabled while
2689 waiting for the ACK, so if this is set too high
2690 interrupts *may* be lost!
2692 omap_mux= [OMAP] Override bootloader pin multiplexing.
2693 Format: <mux_mode0.mode_name=value>...
2694 For example, to override I2C bus2:
2695 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2697 oprofile.timer= [HW]
2698 Use timer interrupt instead of performance counters
2700 oprofile.cpu_type= Force an oprofile cpu type
2701 This might be useful if you have an older oprofile
2702 userland or if you want common events.
2703 Format: { arch_perfmon }
2704 arch_perfmon: [X86] Force use of architectural
2705 perfmon on Intel CPUs instead of the
2706 CPU specific event set.
2707 timer: [X86] Force use of architectural NMI
2708 timer mode (see also oprofile.timer
2709 for generic hr timer mode)
2711 oops=panic Always panic on oopses. Default is to just kill the
2712 process, but there is a small probability of
2713 deadlocking the machine.
2714 This will also cause panics on machine check exceptions.
2715 Useful together with panic=30 to trigger a reboot.
2718 See Documentation/sound/oss/oss-parameters.txt
2720 page_owner= [KNL] Boot-time page_owner enabling option.
2721 Storage of the information about who allocated
2722 each page is disabled in default. With this switch,
2724 on: enable the feature
2726 page_poison= [KNL] Boot-time parameter changing the state of
2727 poisoning on the buddy allocator.
2728 off: turn off poisoning
2729 on: turn on poisoning
2731 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2732 timeout > 0: seconds before rebooting
2733 timeout = 0: wait forever
2734 timeout < 0: reboot immediately
2737 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2740 crash_kexec_post_notifiers
2741 Run kdump after running panic-notifiers and dumping
2742 kmsg. This only for the users who doubt kdump always
2743 succeeds in any situation.
2744 Note that this also increases risks of kdump failure,
2745 because some panic notifiers can make the crashed
2746 kernel more unstable.
2748 parkbd.port= [HW] Parallel port number the keyboard adapter is
2749 connected to, default is 0.
2751 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2752 0 for XT, 1 for AT (default is AT).
2755 parport= [HW,PPT] Specify parallel ports. 0 disables.
2756 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2757 Use 'auto' to force the driver to use any
2758 IRQ/DMA settings detected (the default is to
2759 ignore detected IRQ/DMA settings because of
2760 possible conflicts). You can specify the base
2761 address, IRQ, and DMA settings; IRQ and DMA
2762 should be numbers, or 'auto' (for using detected
2763 settings on that particular port), or 'nofifo'
2764 (to avoid using a FIFO even if it is detected).
2765 Parallel ports are assigned in the order they
2766 are specified on the command line, starting
2769 parport_init_mode= [HW,PPT]
2770 Configure VIA parallel port to operate in
2771 a specific mode. This is necessary on Pegasos
2772 computer where firmware has no options for setting
2773 up parallel port mode and sets it to spp.
2774 Currently this function knows 686a and 8231 chips.
2775 Format: [spp|ps2|epp|ecp|ecpepp]
2778 Halt all CPUs after the first oops has been printed for
2779 the specified number of seconds. This is to be used if
2780 your oopses keep scrolling off the screen.
2785 See header of drivers/block/paride/pcd.c.
2786 See also Documentation/blockdev/paride.txt.
2788 pci=option[,option...] [PCI] various PCI subsystem options:
2789 earlydump [X86] dump PCI config space before the kernel
2791 off [X86] don't probe for the PCI bus
2792 bios [X86-32] force use of PCI BIOS, don't access
2793 the hardware directly. Use this if your machine
2794 has a non-standard PCI host bridge.
2795 nobios [X86-32] disallow use of PCI BIOS, only direct
2796 hardware access methods are allowed. Use this
2797 if you experience crashes upon bootup and you
2798 suspect they are caused by the BIOS.
2799 conf1 [X86] Force use of PCI Configuration Access
2800 Mechanism 1 (config address in IO port 0xCF8,
2801 data in IO port 0xCFC, both 32-bit).
2802 conf2 [X86] Force use of PCI Configuration Access
2803 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2804 the function, IO port 0xCFA, also 8-bit, sets
2805 bus number. The config space is then accessed
2806 through ports 0xC000-0xCFFF).
2807 See http://wiki.osdev.org/PCI for more info
2808 on the configuration access mechanisms.
2809 noaer [PCIE] If the PCIEAER kernel config parameter is
2810 enabled, this kernel boot option can be used to
2811 disable the use of PCIE advanced error reporting.
2812 nodomains [PCI] Disable support for multiple PCI
2813 root domains (aka PCI segments, in ACPI-speak).
2814 nommconf [X86] Disable use of MMCONFIG for PCI
2816 check_enable_amd_mmconf [X86] check for and enable
2817 properly configured MMIO access to PCI
2818 config space on AMD family 10h CPU
2819 nomsi [MSI] If the PCI_MSI kernel config parameter is
2820 enabled, this kernel boot option can be used to
2821 disable the use of MSI interrupts system-wide.
2822 noioapicquirk [APIC] Disable all boot interrupt quirks.
2823 Safety option to keep boot IRQs enabled. This
2824 should never be necessary.
2825 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2826 primary IO-APIC for bridges that cannot disable
2827 boot IRQs. This fixes a source of spurious IRQs
2828 when the system masks IRQs.
2829 noioapicreroute [APIC] Disable workaround that uses the
2830 boot IRQ equivalent of an IRQ that connects to
2831 a chipset where boot IRQs cannot be disabled.
2832 The opposite of ioapicreroute.
2833 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2834 routing table. These calls are known to be buggy
2835 on several machines and they hang the machine
2836 when used, but on other computers it's the only
2837 way to get the interrupt routing table. Try
2838 this option if the kernel is unable to allocate
2839 IRQs or discover secondary PCI buses on your
2841 rom [X86] Assign address space to expansion ROMs.
2842 Use with caution as certain devices share
2843 address decoders between ROMs and other
2845 norom [X86] Do not assign address space to
2846 expansion ROMs that do not already have
2847 BIOS assigned address ranges.
2848 nobar [X86] Do not assign address space to the
2849 BARs that weren't assigned by the BIOS.
2850 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2851 assigned automatically to PCI devices. You can
2852 make the kernel exclude IRQs of your ISA cards
2854 pirqaddr=0xAAAAA [X86] Specify the physical address
2855 of the PIRQ table (normally generated
2856 by the BIOS) if it is outside the
2857 F0000h-100000h range.
2858 lastbus=N [X86] Scan all buses thru bus #N. Can be
2859 useful if the kernel is unable to find your
2860 secondary buses and you want to tell it
2861 explicitly which ones they are.
2862 assign-busses [X86] Always assign all PCI bus
2863 numbers ourselves, overriding
2864 whatever the firmware may have done.
2865 usepirqmask [X86] Honor the possible IRQ mask stored
2866 in the BIOS $PIR table. This is needed on
2867 some systems with broken BIOSes, notably
2868 some HP Pavilion N5400 and Omnibook XE3
2869 notebooks. This will have no effect if ACPI
2870 IRQ routing is enabled.
2871 noacpi [X86] Do not use ACPI for IRQ routing
2872 or for PCI scanning.
2873 use_crs [X86] Use PCI host bridge window information
2874 from ACPI. On BIOSes from 2008 or later, this
2875 is enabled by default. If you need to use this,
2876 please report a bug.
2877 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2878 If you need to use this, please report a bug.
2879 routeirq Do IRQ routing for all PCI devices.
2880 This is normally done in pci_enable_device(),
2881 so this option is a temporary workaround
2882 for broken drivers that don't call it.
2883 skip_isa_align [X86] do not align io start addr, so can
2884 handle more pci cards
2885 noearly [X86] Don't do any early type 1 scanning.
2886 This might help on some broken boards which
2887 machine check when some devices' config space
2888 is read. But various workarounds are disabled
2889 and some IOMMU drivers will not work.
2890 bfsort Sort PCI devices into breadth-first order.
2891 This sorting is done to get a device
2892 order compatible with older (<= 2.4) kernels.
2893 nobfsort Don't sort PCI devices into breadth-first order.
2894 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2895 tuning and use the BIOS-configured MPS defaults.
2896 pcie_bus_safe Set every device's MPS to the largest value
2897 supported by all devices below the root complex.
2898 pcie_bus_perf Set device MPS to the largest allowable MPS
2899 based on its parent bus. Also set MRRS (Max
2900 Read Request Size) to the largest supported
2901 value (no larger than the MPS that the device
2902 or bus can support) for best performance.
2903 pcie_bus_peer2peer Set every device's MPS to 128B, which
2904 every device is guaranteed to support. This
2905 configuration allows peer-to-peer DMA between
2906 any pair of devices, possibly at the cost of
2907 reduced performance. This also guarantees
2908 that hot-added devices will work.
2909 cbiosize=nn[KMG] The fixed amount of bus space which is
2910 reserved for the CardBus bridge's IO window.
2911 The default value is 256 bytes.
2912 cbmemsize=nn[KMG] The fixed amount of bus space which is
2913 reserved for the CardBus bridge's memory
2914 window. The default value is 64 megabytes.
2917 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2918 [<order of align>@]pci:<vendor>:<device>\
2919 [:<subvendor>:<subdevice>][; ...]
2920 Specifies alignment and device to reassign
2921 aligned memory resources.
2922 If <order of align> is not specified,
2923 PAGE_SIZE is used as alignment.
2924 PCI-PCI bridge can be specified, if resource
2925 windows need to be expanded.
2926 To specify the alignment for several
2927 instances of a device, the PCI vendor,
2928 device, subvendor, and subdevice may be
2929 specified, e.g., 4096@pci:8086:9c22:103c:198f
2930 ecrc= Enable/disable PCIe ECRC (transaction layer
2931 end-to-end CRC checking).
2932 bios: Use BIOS/firmware settings. This is the
2936 hpiosize=nn[KMG] The fixed amount of bus space which is
2937 reserved for hotplug bridge's IO window.
2938 Default size is 256 bytes.
2939 hpmemsize=nn[KMG] The fixed amount of bus space which is
2940 reserved for hotplug bridge's memory window.
2941 Default size is 2 megabytes.
2942 hpbussize=nn The minimum amount of additional bus numbers
2943 reserved for buses below a hotplug bridge.
2945 realloc= Enable/disable reallocating PCI bridge resources
2946 if allocations done by BIOS are too small to
2947 accommodate resources required by all child
2949 off: Turn realloc off
2951 realloc same as realloc=on
2952 noari do not use PCIe ARI.
2953 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2954 only look for one device below a PCIe downstream
2957 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2960 force Enable ASPM even on devices that claim not to support it.
2961 WARNING: Forcing ASPM on may cause system lockups.
2963 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2964 nomsi Do not use MSI for PCI Express Native Hotplug (this
2965 makes all PCIe ports use INTx for hotplug services).
2967 pcie_ports= [PCIE] PCIe ports handling:
2968 auto Ask the BIOS whether or not to use native PCIe services
2969 associated with PCIe ports (PME, hot-plug, AER). Use
2970 them only if that is allowed by the BIOS.
2971 native Use native PCIe services associated with PCIe ports
2973 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2976 pcie_port_pm= [PCIE] PCIe port power management handling:
2977 off Disable power management of all PCIe ports
2978 force Forcibly enable power management of all PCIe ports
2980 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2981 nomsi Do not use MSI for native PCIe PME signaling (this makes
2982 all PCIe root ports use INTx for all services).
2984 pcmv= [HW,PCMCIA] BadgePAD 4
2988 Keep all power-domains already enabled by bootloader on,
2989 even if no driver has claimed them. This is useful
2990 for debug and development, but should not be
2991 needed on a platform with proper driver support.
2994 See Documentation/blockdev/paride.txt.
2996 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2999 See arch/parisc/kernel/pdc_chassis.c
3001 percpu_alloc= Select which percpu first chunk allocator to use.
3002 Currently supported values are "embed" and "page".
3003 Archs may support subset or none of the selections.
3004 See comments in mm/percpu.c for details on each
3005 allocator. This parameter is primarily for debugging
3006 and performance comparison.
3009 See Documentation/blockdev/paride.txt.
3012 See Documentation/blockdev/paride.txt.
3014 pirq= [SMP,APIC] Manual mp-table setup
3015 See Documentation/x86/i386/IO-APIC.txt.
3017 plip= [PPT,NET] Parallel port network link
3018 Format: { parport<nr> | timid | 0 }
3019 See also Documentation/parport.txt.
3021 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3022 Override pmtimer IOPort with a hex value.
3026 Enable PNP debug messages (depends on the
3027 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3028 via /sys/module/pnp/parameters/debug. We always show
3029 current resource usage; turning this on also shows
3030 possible settings and some assignment information.
3036 { on | off | curr | res | no-curr | no-res }
3039 [ISAPNP] Exclude IRQs for the autoconfiguration
3042 [ISAPNP] Exclude DMAs for the autoconfiguration
3044 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3045 Ranges are in pairs (I/O port base and size).
3048 [ISAPNP] Exclude memory regions for the
3050 Ranges are in pairs (memory base and size).
3052 ports= [IP_VS_FTP] IPVS ftp helper module
3054 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3056 Format: <port>,<port>....
3058 powersave=off [PPC] This option disables power saving features.
3059 It specifically disables cpuidle and sets the
3060 platform machine description specific power_save
3061 function to NULL. On Idle the CPU just reduces
3064 ppc_strict_facility_enable
3065 [PPC] This option catches any kernel floating point,
3066 Altivec, VSX and SPE outside of regions specifically
3067 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3068 There is some performance impact when enabling this.
3070 print-fatal-signals=
3071 [KNL] debug: print fatal signals
3073 If enabled, warn about various signal handling
3074 related application anomalies: too many signals,
3075 too many POSIX.1 timers, fatal signals causing a
3078 If you hit the warning due to signal overflow,
3079 you might want to try "ulimit -i unlimited".
3083 printk.always_kmsg_dump=
3084 Trigger kmsg_dump for cases other than kernel oops or
3086 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3089 printk.devkmsg={on,off,ratelimit}
3090 Control writing to /dev/kmsg.
3091 on - unlimited logging to /dev/kmsg from userspace
3092 off - logging to /dev/kmsg disabled
3093 ratelimit - ratelimit the logging
3096 printk.time= Show timing data prefixed to each printk message line
3097 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3099 processor.max_cstate= [HW,ACPI]
3100 Limit processor to maximum C-state
3101 max_cstate=9 overrides any DMI blacklist limit.
3103 processor.nocst [HW,ACPI]
3104 Ignore the _CST method to determine C-states,
3105 instead using the legacy FADT method
3107 profile= [KNL] Enable kernel profiling via /proc/profile
3108 Format: [schedule,]<number>
3109 Param: "schedule" - profile schedule points.
3110 Param: <number> - step/bucket size as a power of 2 for
3111 statistical time based profiling.
3112 Param: "sleep" - profile D-state sleeping (millisecs).
3113 Requires CONFIG_SCHEDSTATS
3114 Param: "kvm" - profile VM exits.
3116 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3118 See Documentation/blockdev/ramdisk.txt.
3120 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3121 probe for; one of (bare|imps|exps|lifebook|any).
3122 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3124 psmouse.resetafter= [HW,MOUSE]
3125 Try to reset the device after so many bad packets
3128 [HW,MOUSE] Set desired mouse resolution, in dpi.
3129 psmouse.smartscroll=
3130 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3131 0 = disabled, 1 = enabled (default).
3133 pstore.backend= Specify the name of the pstore backend to use
3136 See Documentation/blockdev/paride.txt.
3139 [KNL] Number of legacy pty's. Overwrites compiled-in
3142 quiet [KNL] Disable most log messages
3147 See Documentation/admin-guide/md.rst.
3149 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3150 See Documentation/blockdev/ramdisk.txt.
3153 The argument is a cpu list, as described above.
3155 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3156 the specified list of CPUs to be no-callback CPUs.
3157 Invocation of these CPUs' RCU callbacks will
3158 be offloaded to "rcuox/N" kthreads created for
3159 that purpose, where "x" is "b" for RCU-bh, "p"
3160 for RCU-preempt, and "s" for RCU-sched, and "N"
3161 is the CPU number. This reduces OS jitter on the
3162 offloaded CPUs, which can be useful for HPC and
3163 real-time workloads. It can also improve energy
3164 efficiency for asymmetric multiprocessors.
3167 Rather than requiring that offloaded CPUs
3168 (specified by rcu_nocbs= above) explicitly
3169 awaken the corresponding "rcuoN" kthreads,
3170 make these kthreads poll for callbacks.
3171 This improves the real-time response for the
3172 offloaded CPUs by relieving them of the need to
3173 wake up the corresponding kthread, but degrades
3174 energy efficiency by requiring that the kthreads
3175 periodically wake up to do the polling.
3177 rcutree.blimit= [KNL]
3178 Set maximum number of finished RCU callbacks to
3179 process in one batch.
3181 rcutree.dump_tree= [KNL]
3182 Dump the structure of the rcu_node combining tree
3183 out at early boot. This is used for diagnostic
3184 purposes, to verify correct tree setup.
3186 rcutree.gp_cleanup_delay= [KNL]
3187 Set the number of jiffies to delay each step of
3188 RCU grace-period cleanup. This only has effect
3189 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3191 rcutree.gp_init_delay= [KNL]
3192 Set the number of jiffies to delay each step of
3193 RCU grace-period initialization. This only has
3194 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3197 rcutree.gp_preinit_delay= [KNL]
3198 Set the number of jiffies to delay each step of
3199 RCU grace-period pre-initialization, that is,
3200 the propagation of recent CPU-hotplug changes up
3201 the rcu_node combining tree. This only has effect
3202 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3204 rcutree.rcu_fanout_exact= [KNL]
3205 Disable autobalancing of the rcu_node combining
3206 tree. This is used by rcutorture, and might
3207 possibly be useful for architectures having high
3208 cache-to-cache transfer latencies.
3210 rcutree.rcu_fanout_leaf= [KNL]
3211 Change the number of CPUs assigned to each
3212 leaf rcu_node structure. Useful for very
3213 large systems, which will choose the value 64,
3214 and for NUMA systems with large remote-access
3215 latencies, which will choose a value aligned
3216 with the appropriate hardware boundaries.
3218 rcutree.jiffies_till_sched_qs= [KNL]
3219 Set required age in jiffies for a
3220 given grace period before RCU starts
3221 soliciting quiescent-state help from
3222 rcu_note_context_switch().
3224 rcutree.jiffies_till_first_fqs= [KNL]
3225 Set delay from grace-period initialization to
3226 first attempt to force quiescent states.
3227 Units are jiffies, minimum value is zero,
3228 and maximum value is HZ.
3230 rcutree.jiffies_till_next_fqs= [KNL]
3231 Set delay between subsequent attempts to force
3232 quiescent states. Units are jiffies, minimum
3233 value is one, and maximum value is HZ.
3235 rcutree.kthread_prio= [KNL,BOOT]
3236 Set the SCHED_FIFO priority of the RCU per-CPU
3237 kthreads (rcuc/N). This value is also used for
3238 the priority of the RCU boost threads (rcub/N)
3239 and for the RCU grace-period kthreads (rcu_bh,
3240 rcu_preempt, and rcu_sched). If RCU_BOOST is
3241 set, valid values are 1-99 and the default is 1
3242 (the least-favored priority). Otherwise, when
3243 RCU_BOOST is not set, valid values are 0-99 and
3244 the default is zero (non-realtime operation).
3246 rcutree.rcu_nocb_leader_stride= [KNL]
3247 Set the number of NOCB kthread groups, which
3248 defaults to the square root of the number of
3249 CPUs. Larger numbers reduces the wakeup overhead
3250 on the per-CPU grace-period kthreads, but increases
3251 that same overhead on each group's leader.
3253 rcutree.qhimark= [KNL]
3254 Set threshold of queued RCU callbacks beyond which
3255 batch limiting is disabled.
3257 rcutree.qlowmark= [KNL]
3258 Set threshold of queued RCU callbacks below which
3259 batch limiting is re-enabled.
3261 rcutree.rcu_idle_gp_delay= [KNL]
3262 Set wakeup interval for idle CPUs that have
3263 RCU callbacks (RCU_FAST_NO_HZ=y).
3265 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3266 Set wakeup interval for idle CPUs that have
3267 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3268 Lazy RCU callbacks are those which RCU can
3269 prove do nothing more than free memory.
3271 rcuperf.gp_exp= [KNL]
3272 Measure performance of expedited synchronous
3273 grace-period primitives.
3275 rcuperf.holdoff= [KNL]
3276 Set test-start holdoff period. The purpose of
3277 this parameter is to delay the start of the
3278 test until boot completes in order to avoid
3281 rcuperf.nreaders= [KNL]
3282 Set number of RCU readers. The value -1 selects
3283 N, where N is the number of CPUs. A value
3284 "n" less than -1 selects N-n+1, where N is again
3285 the number of CPUs. For example, -2 selects N
3286 (the number of CPUs), -3 selects N+1, and so on.
3287 A value of "n" less than or equal to -N selects
3290 rcuperf.nwriters= [KNL]
3291 Set number of RCU writers. The values operate
3292 the same as for rcuperf.nreaders.
3293 N, where N is the number of CPUs
3295 rcuperf.perf_runnable= [BOOT]
3296 Start rcuperf running at boot time.
3298 rcuperf.shutdown= [KNL]
3299 Shut the system down after performance tests
3300 complete. This is useful for hands-off automated
3303 rcuperf.perf_type= [KNL]
3304 Specify the RCU implementation to test.
3306 rcuperf.verbose= [KNL]
3307 Enable additional printk() statements.
3309 rcutorture.cbflood_inter_holdoff= [KNL]
3310 Set holdoff time (jiffies) between successive
3311 callback-flood tests.
3313 rcutorture.cbflood_intra_holdoff= [KNL]
3314 Set holdoff time (jiffies) between successive
3315 bursts of callbacks within a given callback-flood
3318 rcutorture.cbflood_n_burst= [KNL]
3319 Set the number of bursts making up a given
3320 callback-flood test. Set this to zero to
3321 disable callback-flood testing.
3323 rcutorture.cbflood_n_per_burst= [KNL]
3324 Set the number of callbacks to be registered
3325 in a given burst of a callback-flood test.
3327 rcutorture.fqs_duration= [KNL]
3328 Set duration of force_quiescent_state bursts
3331 rcutorture.fqs_holdoff= [KNL]
3332 Set holdoff time within force_quiescent_state bursts
3335 rcutorture.fqs_stutter= [KNL]
3336 Set wait time between force_quiescent_state bursts
3339 rcutorture.gp_cond= [KNL]
3340 Use conditional/asynchronous update-side
3341 primitives, if available.
3343 rcutorture.gp_exp= [KNL]
3344 Use expedited update-side primitives, if available.
3346 rcutorture.gp_normal= [KNL]
3347 Use normal (non-expedited) asynchronous
3348 update-side primitives, if available.
3350 rcutorture.gp_sync= [KNL]
3351 Use normal (non-expedited) synchronous
3352 update-side primitives, if available. If all
3353 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3354 rcutorture.gp_normal=, and rcutorture.gp_sync=
3355 are zero, rcutorture acts as if is interpreted
3356 they are all non-zero.
3358 rcutorture.n_barrier_cbs= [KNL]
3359 Set callbacks/threads for rcu_barrier() testing.
3361 rcutorture.nfakewriters= [KNL]
3362 Set number of concurrent RCU writers. These just
3363 stress RCU, they don't participate in the actual
3364 test, hence the "fake".
3366 rcutorture.nreaders= [KNL]
3367 Set number of RCU readers. The value -1 selects
3368 N-1, where N is the number of CPUs. A value
3369 "n" less than -1 selects N-n-2, where N is again
3370 the number of CPUs. For example, -2 selects N
3371 (the number of CPUs), -3 selects N+1, and so on.
3373 rcutorture.object_debug= [KNL]
3374 Enable debug-object double-call_rcu() testing.
3376 rcutorture.onoff_holdoff= [KNL]
3377 Set time (s) after boot for CPU-hotplug testing.
3379 rcutorture.onoff_interval= [KNL]
3380 Set time (s) between CPU-hotplug operations, or
3381 zero to disable CPU-hotplug testing.
3383 rcutorture.shuffle_interval= [KNL]
3384 Set task-shuffle interval (s). Shuffling tasks
3385 allows some CPUs to go into dyntick-idle mode
3386 during the rcutorture test.
3388 rcutorture.shutdown_secs= [KNL]
3389 Set time (s) after boot system shutdown. This
3390 is useful for hands-off automated testing.
3392 rcutorture.stall_cpu= [KNL]
3393 Duration of CPU stall (s) to test RCU CPU stall
3394 warnings, zero to disable.
3396 rcutorture.stall_cpu_holdoff= [KNL]
3397 Time to wait (s) after boot before inducing stall.
3399 rcutorture.stat_interval= [KNL]
3400 Time (s) between statistics printk()s.
3402 rcutorture.stutter= [KNL]
3403 Time (s) to stutter testing, for example, specifying
3404 five seconds causes the test to run for five seconds,
3405 wait for five seconds, and so on. This tests RCU's
3406 ability to transition abruptly to and from idle.
3408 rcutorture.test_boost= [KNL]
3409 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3410 "Maybe" means test if the RCU implementation
3411 under test support RCU priority boosting.
3413 rcutorture.test_boost_duration= [KNL]
3414 Duration (s) of each individual boost test.
3416 rcutorture.test_boost_interval= [KNL]
3417 Interval (s) between each boost test.
3419 rcutorture.test_no_idle_hz= [KNL]
3420 Test RCU's dyntick-idle handling. See also the
3421 rcutorture.shuffle_interval parameter.
3423 rcutorture.torture_runnable= [BOOT]
3424 Start rcutorture running at boot time.
3426 rcutorture.torture_type= [KNL]
3427 Specify the RCU implementation to test.
3429 rcutorture.verbose= [KNL]
3430 Enable additional printk() statements.
3432 rcupdate.rcu_cpu_stall_suppress= [KNL]
3433 Suppress RCU CPU stall warning messages.
3435 rcupdate.rcu_cpu_stall_timeout= [KNL]
3436 Set timeout for RCU CPU stall warning messages.
3438 rcupdate.rcu_expedited= [KNL]
3439 Use expedited grace-period primitives, for
3440 example, synchronize_rcu_expedited() instead
3441 of synchronize_rcu(). This reduces latency,
3442 but can increase CPU utilization, degrade
3443 real-time latency, and degrade energy efficiency.
3444 No effect on CONFIG_TINY_RCU kernels.
3446 rcupdate.rcu_normal= [KNL]
3447 Use only normal grace-period primitives,
3448 for example, synchronize_rcu() instead of
3449 synchronize_rcu_expedited(). This improves
3450 real-time latency, CPU utilization, and
3451 energy efficiency, but can expose users to
3452 increased grace-period latency. This parameter
3453 overrides rcupdate.rcu_expedited. No effect on
3454 CONFIG_TINY_RCU kernels.
3456 rcupdate.rcu_normal_after_boot= [KNL]
3457 Once boot has completed (that is, after
3458 rcu_end_inkernel_boot() has been invoked), use
3459 only normal grace-period primitives. No effect
3460 on CONFIG_TINY_RCU kernels.
3462 rcupdate.rcu_task_stall_timeout= [KNL]
3463 Set timeout in jiffies for RCU task stall warning
3464 messages. Disable with a value less than or equal
3467 rcupdate.rcu_self_test= [KNL]
3468 Run the RCU early boot self tests
3470 rcupdate.rcu_self_test_bh= [KNL]
3471 Run the RCU bh early boot self tests
3473 rcupdate.rcu_self_test_sched= [KNL]
3474 Run the RCU sched early boot self tests
3478 Run specified binary instead of /init from the ramdisk,
3479 used for early userspace startup. See initrd.
3482 Format (x86 or x86_64):
3483 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3485 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3487 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3488 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3489 reboot_force is either force or not specified,
3490 reboot_cpu is s[mp]#### with #### being the processor
3491 to be used for rebooting.
3494 [KNL, SMP] Set scheduler's default relax_domain_level.
3495 See Documentation/cgroup-v1/cpusets.txt.
3497 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3499 reservetop= [X86-32]
3501 Reserves a hole at the top of the kernel virtual
3506 Set the amount of memory to reserve for BIOS at
3507 the bottom of the address space.
3509 reset_devices [KNL] Force drivers to reset the underlying device
3510 during initialization.
3513 Specify the partition device for software suspend
3515 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3517 resume_offset= [SWSUSP]
3518 Specify the offset from the beginning of the partition
3519 given by "resume=" at which the swap header is located,
3520 in <PAGE_SIZE> units (needed only for swap files).
3521 See Documentation/power/swsusp-and-swap-files.txt
3523 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3524 read the resume files
3526 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3527 Useful for devices that are detected asynchronously
3528 (e.g. USB and MMC devices).
3530 hibernate= [HIBERNATION]
3531 noresume Don't check if there's a hibernation image
3532 present during boot.
3533 nocompress Don't compress/decompress hibernation images.
3534 no Disable hibernation and resume.
3535 protect_image Turn on image protection during restoration
3536 (that will set all pages holding image data
3537 during restoration read-only).
3539 retain_initrd [RAM] Keep initrd memory after extraction
3541 rfkill.default_state=
3542 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3543 etc. communication is blocked by default.
3546 rfkill.master_switch_mode=
3547 0 The "airplane mode" button does nothing.
3548 1 The "airplane mode" button toggles between everything
3549 blocked and the previous configuration.
3550 2 The "airplane mode" button toggles between everything
3551 blocked and everything unblocked.
3553 rhash_entries= [KNL,NET]
3554 Set number of hash buckets for route cache
3556 ro [KNL] Mount root device read-only on boot
3559 on Mark read-only kernel memory as read-only (default).
3560 off Leave read-only kernel memory writable for debugging.
3563 Enable the uart passthrough on the designated usb port
3564 on Rockchip SoCs. When active, the signals of the
3565 debug-uart get routed to the D+ and D- pins of the usb
3566 port and the regular usb controller gets disabled.
3568 root= [KNL] Root filesystem
3569 See name_to_dev_t comment in init/do_mounts.c.
3571 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3572 mount the root filesystem
3574 rootflags= [KNL] Set root filesystem mount option string
3576 rootfstype= [KNL] Set root filesystem type
3578 rootwait [KNL] Wait (indefinitely) for root device to show up.
3579 Useful for devices that are detected asynchronously
3580 (e.g. USB and MMC devices).
3582 rproc_mem=nn[KMG][@address]
3583 [KNL,ARM,CMA] Remoteproc physical memory block.
3584 Memory area to be used by remote processor image,
3587 rw [KNL] Mount root device read-write on boot
3589 S [KNL] Run init in single mode
3591 s390_iommu= [HW,S390]
3592 Set s390 IOTLB flushing mode
3594 With strict flushing every unmap operation will result in
3595 an IOTLB flush. Default is lazy flushing before reuse,
3599 See drivers/net/irda/sa1100_ir.c.
3601 sbni= [NET] Granch SBNI12 leased line adapter
3603 sched_debug [KNL] Enables verbose scheduler debug messages.
3605 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3606 Allowed values are enable and disable. This feature
3607 incurs a small amount of overhead in the scheduler
3608 but is useful for debugging and performance tuning.
3610 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3611 xtime_lock contention on larger systems, and/or RCU lock
3612 contention on all systems with CONFIG_MAXSMP set.
3613 Format: { "0" | "1" }
3614 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3616 Note: increases power consumption, thus should only be
3617 enabled if running jitter sensitive (HPC/RT) workloads.
3619 security= [SECURITY] Choose a security module to enable at boot.
3620 If this boot parameter is not specified, only the first
3621 security module asking for security registration will be
3622 loaded. An invalid security module name will be treated
3623 as if no module has been chosen.
3625 selinux= [SELINUX] Disable or enable SELinux at boot time.
3626 Format: { "0" | "1" }
3627 See security/selinux/Kconfig help text.
3630 Default value is set via kernel config option.
3631 If enabled at boot time, /selinux/disable can be used
3632 later to disable prior to initial policy load.
3634 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3635 Format: { "0" | "1" }
3636 See security/apparmor/Kconfig help text
3639 Default value is set via kernel config option.
3641 serialnumber [BUGS=X86-32]
3644 Maximal number of shapers.
3652 Disable merging of slabs with similar size. May be
3653 necessary if there is some reason to distinguish
3654 allocs to different slabs. Debug options disable
3655 merging on their own.
3656 For more information see Documentation/vm/slub.txt.
3658 slab_max_order= [MM, SLAB]
3659 Determines the maximum allowed order for slabs.
3660 A high setting may cause OOMs due to memory
3661 fragmentation. Defaults to 1 for systems with
3662 more than 32MB of RAM, 0 otherwise.
3664 slub_debug[=options[,slabs]] [MM, SLUB]
3665 Enabling slub_debug allows one to determine the
3666 culprit if slab objects become corrupted. Enabling
3667 slub_debug can create guard zones around objects and
3668 may poison objects when not in use. Also tracks the
3669 last alloc / free. For more information see
3670 Documentation/vm/slub.txt.
3672 slub_max_order= [MM, SLUB]
3673 Determines the maximum allowed order for slabs.
3674 A high setting may cause OOMs due to memory
3675 fragmentation. For more information see
3676 Documentation/vm/slub.txt.
3678 slub_min_objects= [MM, SLUB]
3679 The minimum number of objects per slab. SLUB will
3680 increase the slab order up to slub_max_order to
3681 generate a sufficiently large slab able to contain
3682 the number of objects indicated. The higher the number
3683 of objects the smaller the overhead of tracking slabs
3684 and the less frequently locks need to be acquired.
3685 For more information see Documentation/vm/slub.txt.
3687 slub_min_order= [MM, SLUB]
3688 Determines the minimum page order for slabs. Must be
3689 lower than slub_max_order.
3690 For more information see Documentation/vm/slub.txt.
3692 slub_nomerge [MM, SLUB]
3693 Same with slab_nomerge. This is supported for legacy.
3694 See slab_nomerge for more information.
3697 Format: <io1>[,<io2>[,...,<io8>]]
3699 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3700 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3701 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3702 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3703 smsc-ircc2.ircc_irq= [HW] IRQ line
3704 smsc-ircc2.ircc_dma= [HW] DMA channel
3705 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3706 0: Toshiba Satellite 1800 (GP data pin select)
3707 1: Fast pin select (default)
3710 smt [KNL,S390] Set the maximum number of threads (logical
3711 CPUs) to use per physical CPU on systems capable of
3712 symmetric multithreading (SMT). Will be capped to the
3713 actual hardware limit.
3715 Default: -1 (no limit)
3718 [KNL] Should the soft-lockup detector generate panics.
3721 softlockup_all_cpu_backtrace=
3722 [KNL] Should the soft-lockup detector generate
3723 backtraces on all cpus.
3726 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3727 See Documentation/laptops/sonypi.txt
3729 spia_io_base= [HW,MTD]
3735 Enabled the stack tracer on boot up.
3737 stacktrace_filter=[function-list]
3738 [FTRACE] Limit the functions that the stack tracer
3739 will trace at boot up. function-list is a comma separated
3740 list of functions. This list can be changed at run
3741 time by the stack_trace_filter file in the debugfs
3742 tracing directory. Note, this enables stack tracing
3743 and the stacktrace above is not needed.
3747 Set the STI (builtin display/keyboard on the HP-PARISC
3748 machines) console (graphic card) which should be used
3749 as the initial boot-console.
3750 See also comment in drivers/video/console/sticore.c.
3753 See comment in drivers/video/console/sticore.c.
3756 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3758 sunrpc.min_resvport=
3759 sunrpc.max_resvport=
3761 SunRPC servers often require that client requests
3762 originate from a privileged port (i.e. a port in the
3763 range 0 < portnr < 1024).
3764 An administrator who wishes to reserve some of these
3765 ports for other uses may adjust the range that the
3766 kernel's sunrpc client considers to be privileged
3767 using these two parameters to set the minimum and
3768 maximum port values.
3770 sunrpc.svc_rpc_per_connection_limit=
3772 Limit the number of requests that the server will
3773 process in parallel from a single connection.
3774 The default value is 0 (no limit).
3778 Control how the NFS server code allocates CPUs to
3779 service thread pools. Depending on how many NICs
3780 you have and where their interrupts are bound, this
3781 option will affect which CPUs will do NFS serving.
3782 Note: this parameter cannot be changed while the
3783 NFS server is running.
3785 auto the server chooses an appropriate mode
3786 automatically using heuristics
3787 global a single global pool contains all CPUs
3788 percpu one pool for each CPU
3789 pernode one pool for each NUMA node (equivalent
3790 to global on non-NUMA machines)
3792 sunrpc.tcp_slot_table_entries=
3793 sunrpc.udp_slot_table_entries=
3795 Sets the upper limit on the number of simultaneous
3796 RPC calls that can be sent from the client to a
3797 server. Increasing these values may allow you to
3798 improve throughput, but will also increase the
3799 amount of memory reserved for use by the client.
3801 suspend.pm_test_delay=
3803 Sets the number of seconds to remain in a suspend test
3804 mode before resuming the system (see
3805 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3806 is set. Default value is 5.
3809 [KNL] Enable accounting of swap in memory resource
3810 controller if no parameter or 1 is given or disable
3811 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3813 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3814 Format: { <int> | force }
3815 <int> -- Number of I/O TLB slabs
3816 force -- force using of bounce buffers even if they
3817 wouldn't be automatically used by the kernel
3821 sysfs.deprecated=0|1 [KNL]
3822 Enable/disable old style sysfs layout for old udev
3823 on older distributions. When this option is enabled
3824 very new udev will not work anymore. When this option
3825 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3826 in older udev will not work anymore.
3827 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3828 the kernel configuration.
3830 sysrq_always_enabled
3832 Ignore sysrq setting - this boot parameter will
3833 neutralize any effect of /proc/sys/kernel/sysrq.
3834 Useful for debugging.
3836 tcpmhash_entries= [KNL,NET]
3837 Set the number of tcp_metrics_hash slots.
3838 Default value is 8192 or 16384 depending on total
3839 ram pages. This is used to specify the TCP metrics
3840 cache size. See Documentation/networking/ip-sysctl.txt
3841 "tcp_no_metrics_save" section for more details.
3845 test_suspend= [SUSPEND][,N]
3846 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3847 standby suspend) or "freeze" (for suspend type freeze)
3848 as the system sleep state during system startup with
3849 the optional capability to repeat N number of times.
3850 The system is woken from this state using a
3851 wakeup-capable RTC alarm.
3853 thash_entries= [KNL,NET]
3854 Set number of hash buckets for TCP connection
3856 thermal.act= [HW,ACPI]
3857 -1: disable all active trip points in all thermal zones
3858 <degrees C>: override all lowest active trip points
3860 thermal.crt= [HW,ACPI]
3861 -1: disable all critical trip points in all thermal zones
3862 <degrees C>: override all critical trip points
3864 thermal.nocrt= [HW,ACPI]
3865 Set to disable actions on ACPI thermal zone
3866 critical and hot trip points.
3868 thermal.off= [HW,ACPI]
3869 1: disable ACPI thermal control
3871 thermal.psv= [HW,ACPI]
3872 -1: disable all passive trip points
3873 <degrees C>: override all passive trip points to this
3876 thermal.tzp= [HW,ACPI]
3877 Specify global default ACPI thermal zone polling rate
3878 <deci-seconds>: poll all this frequency
3879 0: no polling (default)
3882 Force threading of all interrupt handlers except those
3883 marked explicitly IRQF_NO_THREAD.
3886 Enable the Transcendent memory driver if built-in.
3888 tmem.cleancache=0|1 [KNL, XEN]
3889 Default is on (1). Disable the usage of the cleancache
3890 API to send anonymous pages to the hypervisor.
3892 tmem.frontswap=0|1 [KNL, XEN]
3893 Default is on (1). Disable the usage of the frontswap
3894 API to send swap pages to the hypervisor. If disabled
3895 the selfballooning and selfshrinking are force disabled.
3897 tmem.selfballooning=0|1 [KNL, XEN]
3898 Default is on (1). Disable the driving of swap pages
3901 tmem.selfshrinking=0|1 [KNL, XEN]
3902 Default is on (1). Partial swapoff that immediately
3903 transfers pages from Xen hypervisor back to the
3904 kernel based on different criteria.
3908 Specify if the kernel should make use of the cpu
3909 topology information if the hardware supports this.
3910 The scheduler will make use of this information and
3911 e.g. base its process migration decisions on it.
3914 topology_updates= [KNL, PPC, NUMA]
3916 Specify if the kernel should ignore (off)
3917 topology updates sent by the hypervisor to this
3922 tpm_suspend_pcr=[HW,TPM]
3923 Format: integer pcr id
3924 Specify that at suspend time, the tpm driver
3925 should extend the specified pcr with zeros,
3926 as a workaround for some chips which fail to
3927 flush the last written pcr on TPM_SaveState.
3928 This will guarantee that all the other pcrs
3931 trace_buf_size=nn[KMG]
3932 [FTRACE] will set tracing buffer size on each cpu.
3934 trace_event=[event-list]
3935 [FTRACE] Set and start specified trace events in order
3936 to facilitate early boot debugging. The event-list is a
3937 comma separated list of trace events to enable. See
3938 also Documentation/trace/events.txt
3940 trace_options=[option-list]
3941 [FTRACE] Enable or disable tracer options at boot.
3942 The option-list is a comma delimited list of options
3943 that can be enabled or disabled just as if you were
3944 to echo the option name into
3946 /sys/kernel/debug/tracing/trace_options
3948 For example, to enable stacktrace option (to dump the
3949 stack trace of each event), add to the command line:
3951 trace_options=stacktrace
3953 See also Documentation/trace/ftrace.txt "trace options"
3957 Have the tracepoints sent to printk as well as the
3958 tracing ring buffer. This is useful for early boot up
3959 where the system hangs or reboots and does not give the
3960 option for reading the tracing buffer or performing a
3961 ftrace_dump_on_oops.
3963 To turn off having tracepoints sent to printk,
3964 echo 0 > /proc/sys/kernel/tracepoint_printk
3965 Note, echoing 1 into this file without the
3966 tracepoint_printk kernel cmdline option has no effect.
3970 Having tracepoints sent to printk() and activating high
3971 frequency tracepoints such as irq or sched, can cause
3972 the system to live lock.
3975 [FTRACE] enable this option to disable tracing when a
3976 warning is hit. This turns off "tracing_on". Tracing can
3977 be enabled again by echoing '1' into the "tracing_on"
3978 file located in /sys/kernel/debug/tracing/
3980 This option is useful, as it disables the trace before
3981 the WARNING dump is called, which prevents the trace to
3982 be filled with content caused by the warning output.
3984 This option can also be set at run time via the sysctl
3985 option: kernel/traceoff_on_warning
3987 transparent_hugepage=
3989 Format: [always|madvise|never]
3990 Can be used to control the default behavior of the system
3991 with respect to transparent hugepages.
3992 See Documentation/vm/transhuge.txt for more details.
3994 tsc= Disable clocksource stability checks for TSC.
3996 [x86] reliable: mark tsc clocksource as reliable, this
3997 disables clocksource verification at runtime, as well
3998 as the stability checks done at bootup. Used to enable
3999 high-resolution timer mode on older hardware, and in
4000 virtualized environment.
4001 [x86] noirqtime: Do not use TSC to do irq accounting.
4002 Used to run time disable IRQ_TIME_ACCOUNTING on any
4003 platforms where RDTSC is slow and this accounting
4006 turbografx.map[2|3]= [HW,JOY]
4007 TurboGraFX parallel port interface
4009 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4010 See also Documentation/input/joystick-parport.txt
4012 udbg-immortal [PPC] When debugging early kernel crashes that
4013 happen after console_init() and before a proper
4014 console driver takes over, this boot options might
4015 help "seeing" what's going on.
4017 uhash_entries= [KNL,NET]
4018 Set number of hash buckets for UDP/UDP-Lite connections
4021 [USB] Ignore overcurrent events (default N).
4022 Some badly-designed motherboards generate lots of
4023 bogus events, for ports that aren't wired to
4024 anything. Set this parameter to avoid log spamming.
4025 Note that genuine overcurrent events won't be
4029 [X86] Cause panic on unknown NMI.
4031 usbcore.authorized_default=
4032 [USB] Default USB device authorization:
4033 (default -1 = authorized except for wireless USB,
4034 0 = not authorized, 1 = authorized)
4036 usbcore.autosuspend=
4037 [USB] The autosuspend time delay (in seconds) used
4038 for newly-detected USB devices (default 2). This
4039 is the time required before an idle device will be
4040 autosuspended. Devices for which the delay is set
4041 to a negative value won't be autosuspended at all.
4043 usbcore.usbfs_snoop=
4044 [USB] Set to log all usbfs traffic (default 0 = off).
4046 usbcore.usbfs_snoop_max=
4047 [USB] Maximum number of bytes to snoop in each URB
4050 usbcore.blinkenlights=
4051 [USB] Set to cycle leds on hubs (default 0 = off).
4053 usbcore.old_scheme_first=
4054 [USB] Start with the old device initialization
4055 scheme (default 0 = off).
4057 usbcore.usbfs_memory_mb=
4058 [USB] Memory limit (in MB) for buffers allocated by
4059 usbfs (default = 16, 0 = max = 2047).
4061 usbcore.use_both_schemes=
4062 [USB] Try the other device initialization scheme
4063 if the first one fails (default 1 = enabled).
4065 usbcore.initial_descriptor_timeout=
4066 [USB] Specifies timeout for the initial 64-byte
4067 USB_REQ_GET_DESCRIPTOR request in milliseconds
4068 (default 5000 = 5.0 seconds).
4070 usbcore.nousb [USB] Disable the USB subsystem
4073 [USBHID] The interval which mice are to be polled at.
4075 usb-storage.delay_use=
4076 [UMS] The delay in seconds before a new device is
4077 scanned for Logical Units (default 1).
4080 [UMS] A list of quirks entries to supplement or
4081 override the built-in unusual_devs list. List
4082 entries are separated by commas. Each entry has
4083 the form VID:PID:Flags where VID and PID are Vendor
4084 and Product ID values (4-digit hex numbers) and
4085 Flags is a set of characters, each corresponding
4086 to a common usb-storage quirk flag as follows:
4087 a = SANE_SENSE (collect more than 18 bytes
4089 b = BAD_SENSE (don't collect more than 18
4090 bytes of sense data);
4091 c = FIX_CAPACITY (decrease the reported
4092 device capacity by one sector);
4093 d = NO_READ_DISC_INFO (don't use
4094 READ_DISC_INFO command);
4095 e = NO_READ_CAPACITY_16 (don't use
4096 READ_CAPACITY_16 command);
4097 f = NO_REPORT_OPCODES (don't use report opcodes
4099 g = MAX_SECTORS_240 (don't transfer more than
4100 240 sectors at a time, uas only);
4101 h = CAPACITY_HEURISTICS (decrease the
4102 reported device capacity by one
4103 sector if the number is odd);
4104 i = IGNORE_DEVICE (don't bind to this
4106 j = NO_REPORT_LUNS (don't use report luns
4108 l = NOT_LOCKABLE (don't try to lock and
4109 unlock ejectable media);
4110 m = MAX_SECTORS_64 (don't transfer more
4111 than 64 sectors = 32 KB at a time);
4112 n = INITIAL_READ10 (force a retry of the
4113 initial READ(10) command);
4114 o = CAPACITY_OK (accept the capacity
4115 reported by the device);
4116 p = WRITE_CACHE (the device cache is ON
4118 r = IGNORE_RESIDUE (the device reports
4119 bogus residue values);
4120 s = SINGLE_LUN (the device has only one
4122 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4123 commands, uas only);
4124 u = IGNORE_UAS (don't bind to the uas driver);
4125 w = NO_WP_DETECT (don't test whether the
4126 medium is write-protected).
4127 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4128 even if the device claims no cache)
4129 Example: quirks=0419:aaf5:rl,0421:0433:rc
4131 user_debug= [KNL,ARM]
4133 See arch/arm/Kconfig.debug help text.
4134 1 - undefined instruction events
4136 4 - invalid data aborts
4139 Example: user_debug=31
4142 [X86] Flags controlling user PTE allocations.
4144 nohigh = do not allocate PTE pages in
4145 HIGHMEM regardless of setting
4149 On X86_32, this is an alias for vdso32=. Otherwise:
4151 vdso=1: enable VDSO (the default)
4152 vdso=0: disable VDSO mapping
4154 vdso32= [X86] Control the 32-bit vDSO
4155 vdso32=1: enable 32-bit VDSO
4156 vdso32=0 or vdso32=2: disable 32-bit VDSO
4158 See the help text for CONFIG_COMPAT_VDSO for more
4159 details. If CONFIG_COMPAT_VDSO is set, the default is
4160 vdso32=0; otherwise, the default is vdso32=1.
4162 For compatibility with older kernels, vdso32=2 is an
4165 Try vdso32=0 if you encounter an error that says:
4166 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4169 vector=percpu: enable percpu vector domain
4171 video= [FB] Frame buffer configuration
4172 See Documentation/fb/modedb.txt.
4174 video.brightness_switch_enabled= [0,1]
4175 If set to 1, on receiving an ACPI notify event
4176 generated by hotkey, video driver will adjust brightness
4177 level and then send out the event to user space through
4178 the allocated input device; If set to 0, video driver
4179 will only send out the event without touching backlight
4184 [VMMIO] Memory mapped virtio (platform) device.
4186 <size>@<baseaddr>:<irq>[:<id>]
4188 <size> := size (can use standard suffixes
4190 <baseaddr> := physical base address
4191 <irq> := interrupt number (as passed to
4193 <id> := (optional) platform device id
4195 virtio_mmio.device=1K@0x100b0000:48:7
4197 Can be used multiple times for multiple devices.
4199 vga= [BOOT,X86-32] Select a particular video mode
4200 See Documentation/x86/boot.txt and
4201 Documentation/svga.txt.
4202 Use vga=ask for menu.
4203 This is actually a boot loader parameter; the value is
4204 passed to the kernel using a special protocol.
4206 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4207 size of <nn>. This can be used to increase the
4208 minimum size (128MB on x86). It can also be used to
4209 decrease the size and leave more room for directly
4212 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4215 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4218 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4222 Controls the behavior of vsyscalls (i.e. calls to
4223 fixed addresses of 0xffffffffff600x00 from legacy
4224 code). Most statically-linked binaries and older
4225 versions of glibc use these calls. Because these
4226 functions are at fixed addresses, they make nice
4227 targets for exploits that can control RIP.
4229 emulate [default] Vsyscalls turn into traps and are
4230 emulated reasonably safely.
4232 native Vsyscalls are native syscall instructions.
4233 This is a little bit faster than trapping
4234 and makes a few dynamic recompilers work
4235 better than they would in emulation mode.
4236 It also makes exploits much easier to write.
4238 none Vsyscalls don't work at all. This makes
4239 them quite hard to use for exploits but
4240 might break your system.
4242 vt.color= [VT] Default text color.
4243 Format: 0xYX, X = foreground, Y = background.
4244 Default: 0x07 = light gray on black.
4246 vt.cur_default= [VT] Default cursor shape.
4247 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4248 the parameters of the <Esc>[?A;B;Cc escape sequence;
4249 see VGA-softcursor.txt. Default: 2 = underline.
4251 vt.default_blu= [VT]
4252 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4253 Change the default blue palette of the console.
4254 This is a 16-member array composed of values
4257 vt.default_grn= [VT]
4258 Format: <green0>,<green1>,<green2>,...,<green15>
4259 Change the default green palette of the console.
4260 This is a 16-member array composed of values
4263 vt.default_red= [VT]
4264 Format: <red0>,<red1>,<red2>,...,<red15>
4265 Change the default red palette of the console.
4266 This is a 16-member array composed of values
4272 Set system-wide default UTF-8 mode for all tty's.
4273 Default is 1, i.e. UTF-8 mode is enabled for all
4274 newly opened terminals.
4276 vt.global_cursor_default=
4279 Set system-wide default for whether a cursor
4280 is shown on new VTs. Default is -1,
4281 i.e. cursors will be created by default unless
4282 overridden by individual drivers. 0 will hide
4283 cursors, 1 will display them.
4285 vt.italic= [VT] Default color for italic text; 0-15.
4288 vt.underline= [VT] Default color for underlined text; 0-15.
4291 watchdog timers [HW,WDT] For information on watchdog timers,
4292 see Documentation/watchdog/watchdog-parameters.txt
4293 or other driver-specific files in the
4294 Documentation/watchdog/ directory.
4296 workqueue.watchdog_thresh=
4297 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4298 warn stall conditions and dump internal state to
4299 help debugging. 0 disables workqueue stall
4300 detection; otherwise, it's the stall threshold
4301 duration in seconds. The default value is 30 and
4302 it can be updated at runtime by writing to the
4303 corresponding sysfs file.
4305 workqueue.disable_numa
4306 By default, all work items queued to unbound
4307 workqueues are affine to the NUMA nodes they're
4308 issued on, which results in better behavior in
4309 general. If NUMA affinity needs to be disabled for
4310 whatever reason, this option can be used. Note
4311 that this also can be controlled per-workqueue for
4312 workqueues visible under /sys/bus/workqueue/.
4314 workqueue.power_efficient
4315 Per-cpu workqueues are generally preferred because
4316 they show better performance thanks to cache
4317 locality; unfortunately, per-cpu workqueues tend to
4318 be more power hungry than unbound workqueues.
4320 Enabling this makes the per-cpu workqueues which
4321 were observed to contribute significantly to power
4322 consumption unbound, leading to measurably lower
4323 power usage at the cost of small performance
4326 The default value of this parameter is determined by
4327 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4329 workqueue.debug_force_rr_cpu
4330 Workqueue used to implicitly guarantee that work
4331 items queued without explicit CPU specified are put
4332 on the local CPU. This guarantee is no longer true
4333 and while local CPU is still preferred work items
4334 may be put on foreign CPUs. This debug option
4335 forces round-robin CPU selection to flush out
4336 usages which depend on the now broken guarantee.
4337 When enabled, memory and cache locality will be
4340 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4341 default x2apic cluster mode on platforms
4344 x86_intel_mid_timer= [X86-32,APBT]
4345 Choose timer option for x86 Intel MID platform.
4346 Two valid options are apbt timer only and lapic timer
4347 plus one apbt timer for broadcast timer.
4348 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4350 xen_512gb_limit [KNL,X86-64,XEN]
4351 Restricts the kernel running paravirtualized under Xen
4352 to use only up to 512 GB of RAM. The reason to do so is
4353 crash analysis tools and Xen tools for doing domain
4354 save/restore/migration must be enabled to handle larger
4357 xen_emul_unplug= [HW,X86,XEN]
4358 Unplug Xen emulated devices
4359 Format: [unplug0,][unplug1]
4360 ide-disks -- unplug primary master IDE devices
4361 aux-ide-disks -- unplug non-primary-master IDE devices
4362 nics -- unplug network devices
4363 all -- unplug all emulated devices (NICs and IDE disks)
4364 unnecessary -- unplugging emulated devices is
4365 unnecessary even if the host did not respond to
4367 never -- do not unplug even if version check succeeds
4369 xen_nopvspin [X86,XEN]
4370 Disables the ticketlock slowpath using Xen PV
4374 Disables the PV optimizations forcing the HVM guest to
4375 run as generic HVM guest with no PV drivers.
4377 xirc2ps_cs= [NET,PCMCIA]
4379 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
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