1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
159 acpi_osi=!! # enable all built-in OS vendor
161 acpi_osi= # disable all strings
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
259 See Documentation/sound/alsa/alsa-parameters.txt
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
293 off - do not initialize any AMD IOMMU found in
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
319 See also Documentation/input/joydev/joystick.rst
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
327 Power management functions (SPARCstation-4/5 + deriv.)
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity whilst booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
393 0 - kernel audit is disabled and can not be enabled
394 until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 - kernel audit is initialized and partially enabled,
398 storing at most audit_backlog_limit messages in
399 RAM until it is fully enabled by the userspace
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
464 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
467 format: { id:<keyid> | builtin }
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
483 - foo isn't visible as an individually mountable
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
510 See Documentation/s390/CommonIO for details.
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/clk.txt.
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
530 clocksource= Override the default clocksource
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
536 [all] jiffies (this is the base, fallback clocksource)
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
549 clocksource.arm_arch_timer.evtstrm=
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
570 cma=nn[MG]@[start[MG][-end[MG]]]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
590 code_bytes [X86] How many bytes of object code to print
595 com20020= [HW,NET] ARCnet - COM20020 chipset
597 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
599 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
603 ARCnet - COM90xx chipset (memory-mapped buffers)
604 Format: <io>[,<irq>[,<memstart>]]
606 condev= [HW,S390] console device
609 console= [KNL] Output console device and options.
611 tty<n> Use the virtual console device <n>.
615 Use the specified serial port. The options are of
616 the form "bbbbpnf", where "bbbb" is the baud rate,
617 "p" is parity ("n", "o", or "e"), "n" is number of
618 bits, and "f" is flow control ("r" for RTS or
619 omit it). Default is "9600n8".
621 See Documentation/admin-guide/serial-console.rst for more
623 Documentation/networking/netconsole.txt for an
626 uart[8250],io,<addr>[,options]
627 uart[8250],mmio,<addr>[,options]
628 uart[8250],mmio16,<addr>[,options]
629 uart[8250],mmio32,<addr>[,options]
630 uart[8250],0x<addr>[,options]
631 Start an early, polled-mode console on the 8250/16550
632 UART at the specified I/O port or MMIO address,
633 switching to the matching ttyS device later.
634 MMIO inter-register address stride is either 8-bit
635 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
636 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
637 to be equivalent to 'mmio'. 'options' are specified in
638 the same format described for ttyS above; if unspecified,
639 the h/w is not re-initialized.
641 hvc<n> Use the hypervisor console device <n>. This is for
642 both Xen and PowerPC hypervisors.
644 If the device connected to the port is not a TTY but a braille
645 device, prepend "brl," before the device type, for instance
647 For now, only VisioBraille is supported.
649 consoleblank= [KNL] The console blank (screen saver) timeout in
650 seconds. A value of 0 disables the blank timer.
654 [KNL] Change the default value for
655 /proc/<pid>/coredump_filter.
656 See also Documentation/filesystems/proc.txt.
658 coresight_cpu_debug.enable
661 Enable/disable the CPU sampling based debugging.
662 0: default value, disable debugging
663 1: enable debugging at boot time
665 cpuidle.off=1 [CPU_IDLE]
666 disable the cpuidle sub-system
668 cpufreq.off=1 [CPU_FREQ]
669 disable the cpufreq sub-system
672 [X86] Delay for N microsec between assert and de-assert
673 of APIC INIT to start processors. This delay occurs
674 on every CPU online, such as boot, and resume from suspend.
677 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
679 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
681 crashkernel=size[KMG][@offset[KMG]]
682 [KNL] Using kexec, Linux can switch to a 'crash kernel'
683 upon panic. This parameter reserves the physical
684 memory region [offset, offset + size] for that kernel
685 image. If '@offset' is omitted, then a suitable offset
686 is selected automatically. Check
687 Documentation/kdump/kdump.txt for further details.
689 crashkernel=range1:size1[,range2:size2,...][@offset]
690 [KNL] Same as above, but depends on the memory
691 in the running system. The syntax of range is
692 start-[end] where start and end are both
693 a memory unit (amount[KMG]). See also
694 Documentation/kdump/kdump.txt for an example.
696 crashkernel=size[KMG],high
697 [KNL, x86_64] range could be above 4G. Allow kernel
698 to allocate physical memory region from top, so could
699 be above 4G if system have more than 4G ram installed.
700 Otherwise memory region will be allocated below 4G, if
702 It will be ignored if crashkernel=X is specified.
703 crashkernel=size[KMG],low
704 [KNL, x86_64] range under 4G. When crashkernel=X,high
705 is passed, kernel could allocate physical memory region
706 above 4G, that cause second kernel crash on system
707 that require some amount of low memory, e.g. swiotlb
708 requires at least 64M+32K low memory, also enough extra
709 low memory is needed to make sure DMA buffers for 32-bit
710 devices won't run out. Kernel would try to allocate at
711 at least 256M below 4G automatically.
712 This one let user to specify own low range under 4G
713 for second kernel instead.
714 0: to disable low allocation.
715 It will be ignored when crashkernel=X,high is not used
716 or memory reserved is below 4G.
719 [KNL] Disable crypto self-tests
724 cs89x0_media= [HW,NET]
725 Format: { rj45 | aui | bnc }
728 See header of drivers/s390/block/dasd_devmap.c.
730 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
731 (one device per port)
732 Format: <port#>,<type>
733 See also Documentation/input/devices/joystick-parport.rst
735 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
737 Documentation/admin-guide/dynamic-debug-howto.rst for
738 details. Deprecated, see dyndbg.
740 debug [KNL] Enable kernel debugging (events log level).
743 [KNL] verbose self-tests
745 Print debugging info while doing the locking API
747 We default to 0 (no extra messages), setting it to
748 1 will print _a lot_ more information - normally
749 only useful to kernel developers.
751 debug_objects [KNL] Enable object debugging
754 [KNL] Disable object debugging
756 debug_guardpage_minorder=
757 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
758 parameter allows control of the order of pages that will
759 be intentionally kept free (and hence protected) by the
760 buddy allocator. Bigger value increase the probability
761 of catching random memory corruption, but reduce the
762 amount of memory for normal system use. The maximum
763 possible value is MAX_ORDER/2. Setting this parameter
764 to 1 or 2 should be enough to identify most random
765 memory corruption problems caused by bugs in kernel or
766 driver code when a CPU writes to (or reads from) a
767 random memory location. Note that there exists a class
768 of memory corruptions problems caused by buggy H/W or
769 F/W or by drivers badly programing DMA (basically when
770 memory is written at bus level and the CPU MMU is
771 bypassed) which are not detectable by
772 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
773 tracking down these problems.
776 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
777 parameter enables the feature at boot time. In
778 default, it is disabled. We can avoid allocating huge
779 chunk of memory for debug pagealloc if we don't enable
780 it at boot time and the system will work mostly same
781 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
782 on: enable the feature
784 debugpat [X86] Enable PAT debugging
786 decnet.addr= [HW,NET]
787 Format: <area>[,<node>]
788 See also Documentation/networking/decnet.txt.
791 [same as hugepagesz=] The size of the default
792 HugeTLB page size. This is the size represented by
793 the legacy /proc/ hugepages APIs, used for SHM, and
794 default size when mounting hugetlbfs filesystems.
795 Defaults to the default architecture's huge page size
799 Set number of hash buckets for dentry cache.
801 disable_1tb_segments [PPC]
802 Disables the use of 1TB hash page table segments. This
803 causes the kernel to fall back to 256MB segments which
804 can be useful when debugging issues that require an SLB
808 See Documentation/networking/ipv6.txt.
811 Disable RADIX MMU mode on POWER9
813 disable_cpu_apicid= [X86,APIC,SMP]
815 The number of initial APIC ID for the
816 corresponding CPU to be disabled at boot,
817 mostly used for the kdump 2nd kernel to
818 disable BSP to wake up multiple CPUs without
819 causing system reset or hang due to sending
822 disable_ddw [PPC/PSERIES]
823 Disable Dynamic DMA Window support. Use this if
824 to workaround buggy firmware.
827 See Documentation/networking/ipv6.txt.
829 disable_mtrr_cleanup [X86]
830 The kernel tries to adjust MTRR layout from continuous
831 to discrete, to make X server driver able to add WB
832 entry later. This parameter disables that.
834 disable_mtrr_trim [X86, Intel and AMD only]
835 By default the kernel will trim any uncacheable
836 memory out of your available memory pool based on
837 MTRR settings. This parameter disables that behavior,
838 possibly causing your machine to run very slowly.
840 disable_timer_pin_1 [X86]
841 Disable PIN 1 of APIC timer
842 Can be useful to work around chipset bugs.
844 dis_ucode_ldr [X86] Disable the microcode loader.
846 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
847 this option disables the debugging code at boot.
849 dma_debug_entries=<number>
850 This option allows to tune the number of preallocated
851 entries for DMA-API debugging code. One entry is
852 required per DMA-API allocation. Use this if the
853 DMA-API debugging code disables itself because the
854 architectural default is too low.
856 dma_debug_driver=<driver_name>
857 With this option the DMA-API debugging driver
858 filter feature can be enabled at boot time. Just
859 pass the driver to filter for as the parameter.
860 The filter can be disabled or changed to another
861 driver later using sysfs.
863 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
864 Broken monitors, graphic adapters, KVMs and EDIDless
865 panels may send no or incorrect EDID data sets.
866 This parameter allows to specify an EDID data sets
867 in the /lib/firmware directory that are used instead.
868 Generic built-in EDID data sets are used, if one of
869 edid/1024x768.bin, edid/1280x1024.bin,
870 edid/1680x1050.bin, or edid/1920x1080.bin is given
871 and no file with the same name exists. Details and
872 instructions how to build your own EDID data are
873 available in Documentation/EDID/HOWTO.txt. An EDID
874 data set will only be used for a particular connector,
875 if its name and a colon are prepended to the EDID
876 name. Each connector may use a unique EDID data
877 set by separating the files with a comma. An EDID
878 data set with no connector name will be used for
879 any connectors not explicitly specified.
884 Format: {"off" | "known"}
885 Control how the dt_cpu_ftrs device-tree binding is
886 used for CPU feature discovery and setup (if it
888 off: Do not use it, fall back to legacy cpu table.
889 known: Do not pass through unknown features to guests
890 or userspace, only those that the kernel is aware of.
892 dump_apple_properties [X86]
893 Dump name and content of EFI device properties on
894 x86 Macs. Useful for driver authors to determine
895 what data is available or for reverse-engineering.
897 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
898 module.dyndbg[="val"]
899 Enable debug messages at boot time. See
900 Documentation/admin-guide/dynamic-debug-howto.rst
903 nompx [X86] Disables Intel Memory Protection Extensions.
904 See Documentation/x86/intel_mpx.txt for more
905 information about the feature.
907 nopku [X86] Disable Memory Protection Keys CPU feature found
910 module.async_probe [KNL]
911 Enable asynchronous probe on this module.
913 early_ioremap_debug [KNL]
914 Enable debug messages in early_ioremap support. This
915 is useful for tracking down temporary early mappings
916 which are not unmapped.
918 earlycon= [KNL] Output early console device and options.
920 When used with no options, the early console is
921 determined by the stdout-path property in device
924 cdns,<addr>[,options]
925 Start an early, polled-mode console on a Cadence
926 (xuartps) serial port at the specified address. Only
927 supported option is baud rate. If baud rate is not
928 specified, the serial port must already be setup and
931 uart[8250],io,<addr>[,options]
932 uart[8250],mmio,<addr>[,options]
933 uart[8250],mmio32,<addr>[,options]
934 uart[8250],mmio32be,<addr>[,options]
935 uart[8250],0x<addr>[,options]
936 Start an early, polled-mode console on the 8250/16550
937 UART at the specified I/O port or MMIO address.
938 MMIO inter-register address stride is either 8-bit
939 (mmio) or 32-bit (mmio32 or mmio32be).
940 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
941 to be equivalent to 'mmio'. 'options' are specified
942 in the same format described for "console=ttyS<n>"; if
943 unspecified, the h/w is not initialized.
947 Start an early, polled-mode console on a pl011 serial
948 port at the specified address. The pl011 serial port
949 must already be setup and configured. Options are not
950 yet supported. If 'mmio32' is specified, then only
951 the driver will use only 32-bit accessors to read/write
952 the device registers.
955 Start an early, polled-mode console on a meson serial
956 port at the specified address. The serial port must
957 already be setup and configured. Options are not yet
961 Start an early, polled-mode console on an msm serial
962 port at the specified address. The serial port
963 must already be setup and configured. Options are not
967 Start an early, polled-mode console on an msm serial
968 dm port at the specified address. The serial port
969 must already be setup and configured. Options are not
973 Start an early, polled-mode console on a serial port
974 of an Actions Semi SoC, such as S500 or S900, at the
975 specified address. The serial port must already be
976 setup and configured. Options are not yet supported.
978 smh Use ARM semihosting calls for early console.
986 Use early console provided by serial driver available
987 on Samsung SoCs, requires selecting proper type and
988 a correct base address of the selected UART port. The
989 serial port must already be setup and configured.
990 Options are not yet supported.
993 Start an early, polled-mode console on a lantiq serial
994 (lqasc) port at the specified address. The serial port
995 must already be setup and configured. Options are not
1000 Use early console provided by Freescale LP UART driver
1001 found on Freescale Vybrid and QorIQ LS1021A processors.
1002 A valid base address must be provided, and the serial
1003 port must already be setup and configured.
1006 Start an early, polled-mode console on the
1007 Armada 3700 serial port at the specified
1008 address. The serial port must already be setup
1009 and configured. Options are not yet supported.
1011 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1016 earlyprintk=serial[,ttySn[,baudrate]]
1017 earlyprintk=serial[,0x...[,baudrate]]
1018 earlyprintk=ttySn[,baudrate]
1019 earlyprintk=dbgp[debugController#]
1020 earlyprintk=pciserial,bus:device.function[,baudrate]
1021 earlyprintk=xdbc[xhciController#]
1023 earlyprintk is useful when the kernel crashes before
1024 the normal console is initialized. It is not enabled by
1025 default because it has some cosmetic problems.
1027 Append ",keep" to not disable it when the real console
1030 Only one of vga, efi, serial, or usb debug port can
1033 Currently only ttyS0 and ttyS1 may be specified by
1034 name. Other I/O ports may be explicitly specified
1035 on some architectures (x86 and arm at least) by
1036 replacing ttySn with an I/O port address, like this:
1037 earlyprintk=serial,0x1008,115200
1038 You can find the port for a given device in
1039 /proc/tty/driver/serial:
1040 2: uart:ST16650V2 port:00001008 irq:18 ...
1042 Interaction with the standard serial driver is not
1045 The VGA and EFI output is eventually overwritten by
1048 The xen output can only be used by Xen PV guests.
1050 The sclp output can only be used on s390.
1052 edac_report= [HW,EDAC] Control how to report EDAC event
1053 Format: {"on" | "off" | "force"}
1054 on: enable EDAC to report H/W event. May be overridden
1055 by other higher priority error reporting module.
1056 off: disable H/W event reporting through EDAC.
1057 force: enforce the use of EDAC to report H/W event.
1060 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1063 This is designed to be used in conjunction with
1064 the boot argument: earlyprintk=vga
1067 Format: {"off" | "on" | "skip[mbr]"}
1070 Format: { "old_map", "nochunk", "noruntime", "debug" }
1071 old_map [X86-64]: switch to the old ioremap-based EFI
1072 runtime services mapping. 32-bit still uses this one by
1074 nochunk: disable reading files in "chunks" in the EFI
1075 boot stub, as chunking can cause problems with some
1076 firmware implementations.
1077 noruntime : disable EFI runtime services support
1078 debug: enable misc debug output
1080 efi_no_storage_paranoia [EFI; X86]
1081 Using this parameter you can use more than 50% of
1082 your efi variable storage. Use this parameter only if
1083 you are really sure that your UEFI does sane gc and
1084 fulfills the spec otherwise your board may brick.
1086 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1087 Add arbitrary attribute to specific memory range by
1088 updating original EFI memory map.
1089 Region of memory which aa attribute is added to is
1091 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1092 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1093 attribute is added to range 0x100000000-0x180000000 and
1094 0x10a0000000-0x1120000000.
1096 Using this parameter you can do debugging of EFI memmap
1097 related feature. For example, you can do debugging of
1098 Address Range Mirroring feature even if your box
1101 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1102 that is to be dynamically loaded by Linux. If there are
1103 multiple variables with the same name but with different
1104 vendor GUIDs, all of them will be loaded. See
1105 Documentation/acpi/ssdt-overlays.txt for details.
1108 eisa_irq_edge= [PARISC,HW]
1109 See header of drivers/parisc/eisa.c.
1112 See comment before function elanfreq_setup() in
1113 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1116 Format: {"cfq" | "deadline" | "noop"}
1117 See Documentation/block/cfq-iosched.txt and
1118 Documentation/block/deadline-iosched.txt for details.
1120 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1121 Specifies physical address of start of kernel core
1122 image elf header and optionally the size. Generally
1123 kexec loader will pass this option to capture kernel.
1124 See Documentation/kdump/kdump.txt for details.
1126 enable_mtrr_cleanup [X86]
1127 The kernel tries to adjust MTRR layout from continuous
1128 to discrete, to make X server driver able to add WB
1129 entry later. This parameter enables that.
1131 enable_timer_pin_1 [X86]
1132 Enable PIN 1 of APIC timer
1133 Can be useful to work around chipset bugs
1134 (in particular on some ATI chipsets).
1135 The kernel tries to set a reasonable default.
1137 enforcing [SELINUX] Set initial enforcing status.
1139 See security/selinux/Kconfig help text.
1140 0 -- permissive (log only, no denials).
1141 1 -- enforcing (deny and log).
1143 Value can be changed at runtime via /selinux/enforce.
1146 Disable Error Record Serialization Table (ERST)
1149 ether= [HW,NET] Ethernet cards parameters
1150 This option is obsoleted by the "netdev=" option, which
1151 has equivalent usage. See its documentation for details.
1155 Permit 'security.evm' to be updated regardless of
1156 current integrity status.
1160 fail_make_request=[KNL]
1161 General fault injection mechanism.
1162 Format: <interval>,<probability>,<space>,<times>
1163 See also Documentation/fault-injection/.
1166 See Documentation/blockdev/floppy.txt.
1168 force_pal_cache_flush
1169 [IA-64] Avoid check_sal_cache_flush which may hang on
1170 buggy SAL_CACHE_FLUSH implementations. Using this
1171 parameter will force ia64_sal_cache_flush to call
1172 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1175 Forcefully enable Physical Address Extension (PAE).
1176 Many Pentium M systems disable PAE but may have a
1177 functionally usable PAE implementation.
1178 Warning: use of this parameter will taint the kernel
1179 and may cause unknown problems.
1182 [FTRACE] will set and start the specified tracer
1183 as early as possible in order to facilitate early
1186 ftrace_dump_on_oops[=orig_cpu]
1187 [FTRACE] will dump the trace buffers on oops.
1188 If no parameter is passed, ftrace will dump
1189 buffers of all CPUs, but if you pass orig_cpu, it will
1190 dump only the buffer of the CPU that triggered the
1193 ftrace_filter=[function-list]
1194 [FTRACE] Limit the functions traced by the function
1195 tracer at boot up. function-list is a comma separated
1196 list of functions. This list can be changed at run
1197 time by the set_ftrace_filter file in the debugfs
1200 ftrace_notrace=[function-list]
1201 [FTRACE] Do not trace the functions specified in
1202 function-list. This list can be changed at run time
1203 by the set_ftrace_notrace file in the debugfs
1206 ftrace_graph_filter=[function-list]
1207 [FTRACE] Limit the top level callers functions traced
1208 by the function graph tracer at boot up.
1209 function-list is a comma separated list of functions
1210 that can be changed at run time by the
1211 set_graph_function file in the debugfs tracing directory.
1213 ftrace_graph_notrace=[function-list]
1214 [FTRACE] Do not trace from the functions specified in
1215 function-list. This list is a comma separated list of
1216 functions that can be changed at run time by the
1217 set_graph_notrace file in the debugfs tracing directory.
1219 ftrace_graph_max_depth=<uint>
1220 [FTRACE] Used with the function graph tracer. This is
1221 the max depth it will trace into a function. This value
1222 can be changed at run time by the max_graph_depth file
1223 in the tracefs tracing directory. default: 0 (no limit)
1226 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1227 support via parallel port (up to 5 devices per port)
1228 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1229 See also Documentation/input/devices/joystick-parport.rst
1233 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1237 gcov_persist= [GCOV] When non-zero (default), profiling data for
1238 kernel modules is saved and remains accessible via
1239 debugfs, even when the module is unloaded/reloaded.
1240 When zero, profiling data is discarded and associated
1241 debugfs files are removed at module unload time.
1243 goldfish [X86] Enable the goldfish android emulator platform.
1244 Don't use this when you are not running on the
1247 gpt [EFI] Forces disk with valid GPT signature but
1248 invalid Protective MBR to be treated as GPT. If the
1249 primary GPT is corrupted, it enables the backup/alternate
1250 GPT to be used instead.
1252 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1253 the "Enable 0" bit of the configuration register.
1256 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1257 the "Enable 0" bit of the configuration register.
1260 grcan.select= [HW] Select which physical interface to use.
1263 grcan.txsize= [HW] Sets the size of the tx buffer.
1264 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1266 grcan.rxsize= [HW] Sets the size of the rx buffer.
1267 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1270 gpio-mockup.gpio_mockup_ranges
1271 [HW] Sets the ranges of gpiochip of for this device.
1272 Format: <start1>,<end1>,<start2>,<end2>...
1274 hardlockup_all_cpu_backtrace=
1275 [KNL] Should the hard-lockup detector generate
1276 backtraces on all cpus.
1279 hashdist= [KNL,NUMA] Large hashes allocated during boot
1280 are distributed across NUMA nodes. Defaults on
1281 for 64-bit NUMA, off otherwise.
1282 Format: 0 | 1 (for off | on)
1284 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1286 hd= [EIDE] (E)IDE hard drive subsystem geometry
1287 Format: <cyl>,<head>,<sect>
1290 Disable Hardware Error Source Table (HEST) support;
1291 corresponding firmware-first mode error processing
1292 logic will be disabled.
1294 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1295 size of <nn>. This works even on boxes that have no
1296 highmem otherwise. This also works to reduce highmem
1297 size on bigger boxes.
1299 highres= [KNL] Enable/disable high resolution timer mode.
1300 Valid parameters: "on", "off"
1304 See Documentation/isdn/README.HiSax.
1308 hpet= [X86-32,HPET] option to control HPET usage
1309 Format: { enable (default) | disable | force |
1311 disable: disable HPET and use PIT instead
1312 force: allow force enabled of undocumented chips (ICH4,
1314 verbose: show contents of HPET registers during setup
1316 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1317 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1319 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1320 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1321 On x86-64 and powerpc, this option can be specified
1322 multiple times interleaved with hugepages= to reserve
1323 huge pages of different sizes. Valid pages sizes on
1324 x86-64 are 2M (when the CPU supports "pse") and 1G
1325 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1327 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1328 terminal devices. Valid values: 0..8
1329 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1330 If specified, z/VM IUCV HVC accepts connections
1331 from listed z/VM user IDs only.
1333 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1334 hardware thread id mappings.
1335 Format: <cpu>:<hwthread>
1338 Do not unregister boot console at start. This is only
1339 useful for debugging when something happens in the window
1340 between unregistering the boot console and initializing
1343 i2c_bus= [HW] Override the default board specific I2C bus speed
1344 or register an additional I2C bus that is not
1345 registered from board initialization code.
1349 i8042.debug [HW] Toggle i8042 debug mode
1350 i8042.unmask_kbd_data
1351 [HW] Enable printing of interrupt data from the KBD port
1352 (disabled by default, and as a pre-condition
1353 requires that i8042.debug=1 be enabled)
1354 i8042.direct [HW] Put keyboard port into non-translated mode
1355 i8042.dumbkbd [HW] Pretend that controller can only read data from
1356 keyboard and cannot control its state
1357 (Don't attempt to blink the leds)
1358 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1359 i8042.nokbd [HW] Don't check/create keyboard port
1360 i8042.noloop [HW] Disable the AUX Loopback command while probing
1362 i8042.nomux [HW] Don't check presence of an active multiplexing
1364 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1366 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1367 i8042.reset [HW] Reset the controller during init, cleanup and
1368 suspend-to-ram transitions, only during s2r
1369 transitions, or never reset
1370 Format: { 1 | Y | y | 0 | N | n }
1371 1, Y, y: always reset controller
1372 0, N, n: don't ever reset controller
1373 Default: only on s2r transitions on x86; most other
1374 architectures force reset to be always executed
1375 i8042.unlock [HW] Unlock (ignore) the keylock
1376 i8042.kbdreset [HW] Reset device connected to KBD port
1380 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1381 indicates that the driver is running on unsupported
1383 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1384 does not match list of supported models.
1386 [HW] Report power status in /proc/i8k
1387 (disabled by default)
1388 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1391 i915.invert_brightness=
1392 [DRM] Invert the sense of the variable that is used to
1393 set the brightness of the panel backlight. Normally a
1394 brightness value of 0 indicates backlight switched off,
1395 and the maximum of the brightness value sets the backlight
1396 to maximum brightness. If this parameter is set to 0
1397 (default) and the machine requires it, or this parameter
1398 is set to 1, a brightness value of 0 sets the backlight
1399 to maximum brightness, and the maximum of the brightness
1400 value switches the backlight off.
1401 -1 -- never invert brightness
1402 0 -- machine default
1403 1 -- force brightness inversion
1406 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1408 ide-core.nodma= [HW] (E)IDE subsystem
1409 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1410 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1411 .cdrom .chs .ignore_cable are additional options
1412 See Documentation/ide/ide.txt.
1414 ide-generic.probe-mask= [HW] (E)IDE subsystem
1416 Probe mask for legacy ISA IDE ports. Depending on
1417 platform up to 6 ports are supported, enabled by
1418 setting corresponding bits in the mask to 1. The
1419 default value is 0x0, which has a special meaning.
1420 On systems that have PCI, it triggers scanning the
1421 PCI bus for the first and the second port, which
1422 are then probed. On systems without PCI the value
1423 of 0x0 enables probing the two first ports as if it
1426 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1427 Claim all unknown PCI IDE storage controllers.
1430 Format: idle=poll, idle=halt, idle=nomwait
1431 Poll forces a polling idle loop that can slightly
1432 improve the performance of waking up a idle CPU, but
1433 will use a lot of power and make the system run hot.
1435 idle=halt: Halt is forced to be used for CPU idle.
1436 In such case C2/C3 won't be used again.
1437 idle=nomwait: Disable mwait for CPU C-states
1439 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1440 Format: { strict | legacy | 2008 | relaxed }
1443 Choose which programs will be accepted for execution
1444 based on the IEEE 754 NaN encoding(s) supported by
1445 the FPU and the NaN encoding requested with the value
1446 of an ELF file header flag individually set by each
1447 binary. Hardware implementations are permitted to
1448 support either or both of the legacy and the 2008 NaN
1451 Available settings are as follows:
1452 strict accept binaries that request a NaN encoding
1453 supported by the FPU
1454 legacy only accept legacy-NaN binaries, if supported
1456 2008 only accept 2008-NaN binaries, if supported
1458 relaxed accept any binaries regardless of whether
1459 supported by the FPU
1461 The FPU emulator is always able to support both NaN
1462 encodings, so if no FPU hardware is present or it has
1463 been disabled with 'nofpu', then the settings of
1464 'legacy' and '2008' strap the emulator accordingly,
1465 'relaxed' straps the emulator for both legacy-NaN and
1466 2008-NaN, whereas 'strict' enables legacy-NaN only on
1467 legacy processors and both NaN encodings on MIPS32 or
1470 The setting for ABS.fmt/NEG.fmt instruction execution
1471 mode generally follows that for the NaN encoding,
1472 except where unsupported by hardware.
1474 ignore_loglevel [KNL]
1475 Ignore loglevel setting - this will print /all/
1476 kernel messages to the console. Useful for debugging.
1477 We also add it as printk module parameter, so users
1478 could change it dynamically, usually by
1479 /sys/module/printk/parameters/ignore_loglevel.
1482 Ignore RLIMIT_DATA setting for data mappings,
1483 print warning at first misuse. Can be changed via
1484 /sys/module/kernel/parameters/ignore_rlimit_data.
1486 ihash_entries= [KNL]
1487 Set number of hash buckets for inode cache.
1489 ima_appraise= [IMA] appraise integrity measurements
1490 Format: { "off" | "enforce" | "fix" | "log" }
1493 ima_appraise_tcb [IMA]
1494 The builtin appraise policy appraises all files
1497 ima_canonical_fmt [IMA]
1498 Use the canonical format for the binary runtime
1499 measurements, instead of host native format.
1502 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1506 The list of supported hash algorithms is defined
1507 in crypto/hash_info.h.
1510 The builtin policies to load during IMA setup.
1511 Format: "tcb | appraise_tcb | secure_boot"
1513 The "tcb" policy measures all programs exec'd, files
1514 mmap'd for exec, and all files opened with the read
1515 mode bit set by either the effective uid (euid=0) or
1518 The "appraise_tcb" policy appraises the integrity of
1519 all files owned by root. (This is the equivalent
1520 of ima_appraise_tcb.)
1522 The "secure_boot" policy appraises the integrity
1523 of files (eg. kexec kernel image, kernel modules,
1524 firmware, policy, etc) based on file signatures.
1526 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1527 Load a policy which meets the needs of the Trusted
1528 Computing Base. This means IMA will measure all
1529 programs exec'd, files mmap'd for exec, and all files
1530 opened for read by uid=0.
1533 Select one of defined IMA measurements template formats.
1534 Formats: { "ima" | "ima-ng" | "ima-sig" }
1538 [IMA] Define a custom template format.
1539 Format: { "field1|...|fieldN" }
1541 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1542 Format: <min_file_size>
1543 Set the minimal file size for using asynchronous hash.
1544 If left unspecified, ahash usage is disabled.
1546 ahash performance varies for different data sizes on
1547 different crypto accelerators. This option can be used
1548 to achieve the best performance for a particular HW.
1550 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1552 Set hashing buffer size. Default: 4k.
1554 ahash performance varies for different chunk sizes on
1555 different crypto accelerators. This option can be used
1556 to achieve best performance for particular HW.
1560 Run specified binary instead of /sbin/init as init
1563 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1564 for working out where the kernel is dying during
1567 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1568 initcall functions. Useful for debugging built-in
1569 modules and initcalls.
1571 initrd= [BOOT] Specify the location of the initial ramdisk
1573 init_pkru= [x86] Specify the default memory protection keys rights
1574 register contents for all processes. 0x55555554 by
1575 default (disallow access to all but pkey 0). Can
1576 override in debugfs after boot.
1578 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1581 int_pln_enable [x86] Enable power limit notification interrupt
1583 integrity_audit=[IMA]
1584 Format: { "0" | "1" }
1585 0 -- basic integrity auditing messages. (Default)
1586 1 -- additional integrity auditing messages.
1588 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1590 Enable intel iommu driver.
1592 Disable intel iommu driver.
1593 igfx_off [Default Off]
1594 By default, gfx is mapped as normal device. If a gfx
1595 device has a dedicated DMAR unit, the DMAR unit is
1596 bypassed by not enabling DMAR with this option. In
1597 this case, gfx device will use physical address for
1600 With this option iommu will not optimize to look
1601 for io virtual address below 32-bit forcing dual
1602 address cycle on pci bus for cards supporting greater
1603 than 32-bit addressing. The default is to look
1604 for translation below 32-bit and if not available
1605 then look in the higher range.
1606 strict [Default Off]
1607 With this option on every unmap_single operation will
1608 result in a hardware IOTLB flush operation as opposed
1609 to batching them for performance.
1610 sp_off [Default Off]
1611 By default, super page will be supported if Intel IOMMU
1612 has the capability. With this option, super page will
1614 ecs_off [Default Off]
1615 By default, extended context tables will be supported if
1616 the hardware advertises that it has support both for the
1617 extended tables themselves, and also PASID support. With
1618 this option set, extended tables will not be used even
1619 on hardware which claims to support them.
1620 tboot_noforce [Default Off]
1621 Do not force the Intel IOMMU enabled under tboot.
1622 By default, tboot will force Intel IOMMU on, which
1623 could harm performance of some high-throughput
1624 devices like 40GBit network cards, even if identity
1626 Note that using this option lowers the security
1627 provided by tboot because it makes the system
1628 vulnerable to DMA attacks.
1630 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1631 0 disables intel_idle and fall back on acpi_idle.
1632 1 to 9 specify maximum depth of C-state.
1636 Do not enable intel_pstate as the default
1637 scaling driver for the supported processors
1639 Use intel_pstate as a scaling driver, but configure it
1640 to work with generic cpufreq governors (instead of
1641 enabling its internal governor). This mode cannot be
1642 used along with the hardware-managed P-states (HWP)
1645 Enable intel_pstate on systems that prohibit it by default
1646 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1647 instead of acpi-cpufreq may disable platform features, such
1648 as thermal controls and power capping, that rely on ACPI
1649 P-States information being indicated to OSPM and therefore
1650 should be used with caution. This option does not work with
1651 processors that aren't supported by the intel_pstate driver
1652 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1654 Do not enable hardware P state control (HWP)
1657 Only load intel_pstate on systems which support
1658 hardware P state control (HWP) if available.
1660 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1661 Description Table, specifies preferred power management
1662 profile as "Enterprise Server" or "Performance Server",
1663 then this feature is turned on by default.
1665 Allow per-logical-CPU P-State performance control limits using
1666 cpufreq sysfs interface
1668 intremap= [X86-64, Intel-IOMMU]
1669 on enable Interrupt Remapping (default)
1670 off disable Interrupt Remapping
1671 nosid disable Source ID checking
1673 BIOS x2APIC opt-out request will be ignored
1674 nopost disable Interrupt Posting
1676 iomem= Disable strict checking of access to MMIO memory
1677 strict regions from userspace.
1692 nobypass [PPC/POWERNV]
1693 Disable IOMMU bypass, using IOMMU for PCI devices.
1696 [ARM64] Configure DMA to bypass the IOMMU by default.
1697 Format: { "0" | "1" }
1698 0 - Use IOMMU translation for DMA.
1699 1 - Bypass the IOMMU for DMA.
1700 unset - Use IOMMU translation for DMA.
1702 io7= [HW] IO7 for Marvel based alpha systems
1703 See comment before marvel_specify_io7 in
1704 arch/alpha/kernel/core_marvel.c.
1706 io_delay= [X86] I/O delay method
1708 Standard port 0x80 based delay
1710 Alternate port 0xed based delay (needed on some systems)
1712 Simple two microseconds delay
1717 See Documentation/filesystems/nfs/nfsroot.txt.
1719 irqaffinity= [SMP] Set the default irq affinity mask
1720 The argument is a cpu list, as described above.
1722 irqchip.gicv2_force_probe=
1725 Force the kernel to look for the second 4kB page
1726 of a GICv2 controller even if the memory range
1727 exposed by the device tree is too small.
1730 When an interrupt is not handled search all handlers
1731 for it. Intended to get systems with badly broken
1735 When an interrupt is not handled search all handlers
1736 for it. Also check all handlers each timer
1737 interrupt. Intended to get systems with badly broken
1741 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1743 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1744 [Deprecated - use cpusets instead]
1745 Format: [flag-list,]<cpu-list>
1747 Specify one or more CPUs to isolate from disturbances
1748 specified in the flag list (default: domain):
1751 Disable the tick when a single task runs.
1753 Isolate from the general SMP balancing and scheduling
1754 algorithms. Note that performing domain isolation this way
1755 is irreversible: it's not possible to bring back a CPU to
1756 the domains once isolated through isolcpus. It's strongly
1757 advised to use cpusets instead to disable scheduler load
1758 balancing through the "cpuset.sched_load_balance" file.
1759 It offers a much more flexible interface where CPUs can
1760 move in and out of an isolated set anytime.
1762 You can move a process onto or off an "isolated" CPU via
1763 the CPU affinity syscalls or cpuset.
1764 <cpu number> begins at 0 and the maximum value is
1765 "number of CPUs in system - 1".
1767 The format of <cpu-list> is described above.
1773 ivrs_ioapic [HW,X86_64]
1774 Provide an override to the IOAPIC-ID<->DEVICE-ID
1775 mapping provided in the IVRS ACPI table. For
1776 example, to map IOAPIC-ID decimal 10 to
1777 PCI device 00:14.0 write the parameter as:
1778 ivrs_ioapic[10]=00:14.0
1780 ivrs_hpet [HW,X86_64]
1781 Provide an override to the HPET-ID<->DEVICE-ID
1782 mapping provided in the IVRS ACPI table. For
1783 example, to map HPET-ID decimal 0 to
1784 PCI device 00:14.0 write the parameter as:
1785 ivrs_hpet[0]=00:14.0
1787 ivrs_acpihid [HW,X86_64]
1788 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1789 mapping provided in the IVRS ACPI table. For
1790 example, to map UART-HID:UID AMD0020:0 to
1791 PCI device 00:14.5 write the parameter as:
1792 ivrs_acpihid[00:14.5]=AMD0020:0
1794 js= [HW,JOY] Analog joystick
1795 See Documentation/input/joydev/joystick.rst.
1798 When CONFIG_RANDOMIZE_BASE is set, this disables
1799 kernel and module base offset ASLR (Address Space
1800 Layout Randomization).
1803 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1804 report on every invalid memory access. Without this
1805 parameter KASAN will print report only for the first
1810 kernelcore= [KNL,X86,IA-64,PPC]
1811 Format: nn[KMGTPE] | "mirror"
1813 specifies the amount of memory usable by the kernel
1814 for non-movable allocations. The requested amount is
1815 spread evenly throughout all nodes in the system. The
1816 remaining memory in each node is used for Movable
1817 pages. In the event, a node is too small to have both
1818 kernelcore and Movable pages, kernelcore pages will
1819 take priority and other nodes will have a larger number
1820 of Movable pages. The Movable zone is used for the
1821 allocation of pages that may be reclaimed or moved
1822 by the page migration subsystem. This means that
1823 HugeTLB pages may not be allocated from this zone.
1824 Note that allocations like PTEs-from-HighMem still
1825 use the HighMem zone if it exists, and the Normal
1826 zone if it does not.
1828 Instead of specifying the amount of memory (nn[KMGTPE]),
1829 you can specify "mirror" option. In case "mirror"
1830 option is specified, mirrored (reliable) memory is used
1831 for non-movable allocations and remaining memory is used
1832 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1833 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1836 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1837 Format: <Controller#>[,poll interval]
1838 The controller # is the number of the ehci usb debug
1839 port as it is probed via PCI. The poll interval is
1840 optional and is the number seconds in between
1841 each poll cycle to the debug port in case you need
1842 the functionality for interrupting the kernel with
1843 gdb or control-c on the dbgp connection. When
1844 not using this parameter you use sysrq-g to break into
1845 the kernel debugger.
1847 kgdboc= [KGDB,HW] kgdb over consoles.
1848 Requires a tty driver that supports console polling,
1849 or a supported polling keyboard driver (non-usb).
1850 Serial only format: <serial_device>[,baud]
1851 keyboard only format: kbd
1852 keyboard and serial format: kbd,<serial_device>[,baud]
1853 Optional Kernel mode setting:
1854 kms, kbd format: kms,kbd
1855 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1857 kgdbwait [KGDB] Stop kernel execution and enter the
1858 kernel debugger at the earliest opportunity.
1860 kmac= [MIPS] korina ethernet MAC address.
1861 Configure the RouterBoard 532 series on-chip
1862 Ethernet adapter MAC address.
1864 kmemleak= [KNL] Boot-time kmemleak enable/disable
1865 Valid arguments: on, off
1867 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1870 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1871 Default is 0 (don't ignore, but inject #GP)
1873 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1877 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1878 Default is 1 (enabled)
1880 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1882 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1884 kvm-arm.vgic_v3_group0_trap=
1885 [KVM,ARM] Trap guest accesses to GICv3 group-0
1888 kvm-arm.vgic_v3_group1_trap=
1889 [KVM,ARM] Trap guest accesses to GICv3 group-1
1892 kvm-arm.vgic_v3_common_trap=
1893 [KVM,ARM] Trap guest accesses to GICv3 common
1896 kvm-arm.vgic_v4_enable=
1897 [KVM,ARM] Allow use of GICv4 for direct injection of
1900 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1901 (virtualized MMU) support on capable Intel chips.
1902 Default is 1 (enabled)
1904 kvm-intel.emulate_invalid_guest_state=
1905 [KVM,Intel] Enable emulation of invalid guest states
1906 Default is 0 (disabled)
1908 kvm-intel.flexpriority=
1909 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1910 Default is 1 (enabled)
1913 [KVM,Intel] Enable VMX nesting (nVMX).
1914 Default is 0 (disabled)
1916 kvm-intel.unrestricted_guest=
1917 [KVM,Intel] Disable unrestricted guest feature
1918 (virtualized real and unpaged mode) on capable
1919 Intel chips. Default is 1 (enabled)
1921 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1922 feature (tagged TLBs) on capable Intel chips.
1923 Default is 1 (enabled)
1929 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1932 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1933 value for LAPIC timer one-shot implementation. Default
1934 back to the programmable timer unit in the LAPIC.
1936 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1939 libata.dma= [LIBATA] DMA control
1940 libata.dma=0 Disable all PATA and SATA DMA
1941 libata.dma=1 PATA and SATA Disk DMA only
1942 libata.dma=2 ATAPI (CDROM) DMA only
1943 libata.dma=4 Compact Flash DMA only
1944 Combinations also work, so libata.dma=3 enables DMA
1945 for disks and CDROMs, but not CFs.
1947 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1948 libata.ignore_hpa=0 keep BIOS limits (default)
1949 libata.ignore_hpa=1 ignore limits, using full disk
1951 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1955 libata.force= [LIBATA] Force configurations. The format is comma
1956 separated list of "[ID:]VAL" where ID is
1957 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1958 matching port, link or device. Basically, it matches
1959 the ATA ID string printed on console by libata. If
1960 the whole ID part is omitted, the last PORT and DEVICE
1961 values are used. If ID hasn't been specified yet, the
1962 configuration applies to all ports, links and devices.
1964 If only DEVICE is omitted, the parameter applies to
1965 the port and all links and devices behind it. DEVICE
1966 number of 0 either selects the first device or the
1967 first fan-out link behind PMP device. It does not
1968 select the host link. DEVICE number of 15 selects the
1969 host link and device attached to it.
1971 The VAL specifies the configuration to force. As long
1972 as there's no ambiguity shortcut notation is allowed.
1973 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1974 The following configurations can be forced.
1976 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1977 Any ID with matching PORT is used.
1979 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1981 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1982 udma[/][16,25,33,44,66,100,133] notation is also
1985 * [no]ncq: Turn on or off NCQ.
1987 * [no]ncqtrim: Turn off queued DSM TRIM.
1989 * nohrst, nosrst, norst: suppress hard, soft
1992 * rstonce: only attempt one reset during
1993 hot-unplug link recovery
1995 * dump_id: dump IDENTIFY data.
1997 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1999 * disable: Disable this device.
2001 If there are multiple matching configurations changing
2002 the same attribute, the last one is used.
2004 memblock=debug [KNL] Enable memblock debug messages.
2006 load_ramdisk= [RAM] List of ramdisks to load from floppy
2007 See Documentation/blockdev/ramdisk.txt.
2009 lockd.nlm_grace_period=P [NFS] Assign grace period.
2012 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2015 lockd.nlm_timeout=T [NFS] Assign timeout value.
2018 lockd.nlm_udpport=M [NFS] Assign UDP port.
2021 locktorture.nreaders_stress= [KNL]
2022 Set the number of locking read-acquisition kthreads.
2023 Defaults to being automatically set based on the
2024 number of online CPUs.
2026 locktorture.nwriters_stress= [KNL]
2027 Set the number of locking write-acquisition kthreads.
2029 locktorture.onoff_holdoff= [KNL]
2030 Set time (s) after boot for CPU-hotplug testing.
2032 locktorture.onoff_interval= [KNL]
2033 Set time (s) between CPU-hotplug operations, or
2034 zero to disable CPU-hotplug testing.
2036 locktorture.shuffle_interval= [KNL]
2037 Set task-shuffle interval (jiffies). Shuffling
2038 tasks allows some CPUs to go into dyntick-idle
2039 mode during the locktorture test.
2041 locktorture.shutdown_secs= [KNL]
2042 Set time (s) after boot system shutdown. This
2043 is useful for hands-off automated testing.
2045 locktorture.stat_interval= [KNL]
2046 Time (s) between statistics printk()s.
2048 locktorture.stutter= [KNL]
2049 Time (s) to stutter testing, for example,
2050 specifying five seconds causes the test to run for
2051 five seconds, wait for five seconds, and so on.
2052 This tests the locking primitive's ability to
2053 transition abruptly to and from idle.
2055 locktorture.torture_type= [KNL]
2056 Specify the locking implementation to test.
2058 locktorture.verbose= [KNL]
2059 Enable additional printk() statements.
2061 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2064 loglevel= All Kernel Messages with a loglevel smaller than the
2065 console loglevel will be printed to the console. It can
2066 also be changed with klogd or other programs. The
2067 loglevels are defined as follows:
2069 0 (KERN_EMERG) system is unusable
2070 1 (KERN_ALERT) action must be taken immediately
2071 2 (KERN_CRIT) critical conditions
2072 3 (KERN_ERR) error conditions
2073 4 (KERN_WARNING) warning conditions
2074 5 (KERN_NOTICE) normal but significant condition
2075 6 (KERN_INFO) informational
2076 7 (KERN_DEBUG) debug-level messages
2078 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2079 in bytes. n must be a power of two and greater
2080 than the minimal size. The minimal size is defined
2081 by LOG_BUF_SHIFT kernel config parameter. There is
2082 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2083 that allows to increase the default size depending on
2084 the number of CPUs. See init/Kconfig for more details.
2086 logo.nologo [FB] Disables display of the built-in Linux logo.
2087 This may be used to provide more screen space for
2088 kernel log messages and is useful when debugging
2089 kernel boot problems.
2091 lp=0 [LP] Specify parallel ports to use, e.g,
2092 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2093 lp=reset first parallel port). 'lp=0' disables the
2094 lp=auto printer driver. 'lp=reset' (which can be
2095 specified in addition to the ports) causes
2096 attached printers to be reset. Using
2097 lp=port1,port2,... specifies the parallel ports
2098 to associate lp devices with, starting with
2099 lp0. A port specification may be 'none' to skip
2100 that lp device, or a parport name such as
2101 'parport0'. Specifying 'lp=auto' instead of a
2102 port specification list means that device IDs
2103 from each port should be examined, to see if
2104 an IEEE 1284-compliant printer is attached; if
2105 so, the driver will manage that printer.
2106 See also header of drivers/char/lp.c.
2109 Sets loops_per_jiffy to given constant, thus avoiding
2110 time-consuming boot-time autodetection (up to 250 ms per
2111 CPU). 0 enables autodetection (default). To determine
2112 the correct value for your kernel, boot with normal
2113 autodetection and see what value is printed. Note that
2114 on SMP systems the preset will be applied to all CPUs,
2115 which is likely to cause problems if your CPUs need
2116 significantly divergent settings. An incorrect value
2117 will cause delays in the kernel to be wrong, leading to
2118 unpredictable I/O errors and other breakage. Although
2119 unlikely, in the extreme case this might damage your
2123 Format: <io>,<irq>,<dma>
2125 machvec= [IA-64] Force the use of a particular machine-vector
2126 (machvec) in a generic kernel.
2127 Example: machvec=hpzx1_swiotlb
2129 machtype= [Loongson] Share the same kernel image file between different
2131 Example: machtype=lemote-yeeloong-2f-7inch
2133 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2134 than or equal to this physical address is ignored.
2136 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2137 will bring up during bootup. maxcpus=n : n >= 0 limits
2138 the kernel to bring up 'n' processors. Surely after
2139 bootup you can bring up the other plugged cpu by executing
2140 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2141 only takes effect during system bootup.
2142 While n=0 is a special case, it is equivalent to "nosmp",
2143 which also disables the IO APIC.
2145 max_loop= [LOOP] The number of loop block devices that get
2146 (loop.max_loop) unconditionally pre-created at init time. The default
2147 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2148 of statically allocating a predefined number, loop
2149 devices can be requested on-demand with the
2150 /dev/loop-control interface.
2152 mce [X86-32] Machine Check Exception
2154 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2156 md= [HW] RAID subsystems devices and level
2157 See Documentation/admin-guide/md.rst.
2160 Format: <first>,<last>
2161 Specifies range of consoles to be captured by the MDA.
2163 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2164 Amount of memory to be used when the kernel is not able
2165 to see the whole system memory or for test.
2166 [X86] Work as limiting max address. Use together
2167 with memmap= to avoid physical address space collisions.
2168 Without memmap= PCI devices could be placed at addresses
2169 belonging to unused RAM.
2171 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2175 [KNL,SH] Allow user to override the default size for
2176 per-device physically contiguous DMA buffers.
2178 memhp_default_state=online/offline
2179 [KNL] Set the initial state for the memory hotplug
2180 onlining policy. If not specified, the default value is
2181 set according to the
2182 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2184 See Documentation/memory-hotplug.txt.
2186 memmap=exactmap [KNL,X86] Enable setting of an exact
2187 E820 memory map, as specified by the user.
2188 Such memmap=exactmap lines can be constructed based on
2189 BIOS output or other requirements. See the memmap=nn@ss
2192 memmap=nn[KMG]@ss[KMG]
2193 [KNL] Force usage of a specific region of memory.
2194 Region of memory to be used is from ss to ss+nn.
2195 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2196 which limits max address to nn[KMG].
2197 Multiple different regions can be specified,
2200 memmap=100M@2G,100M#3G,1G!1024G
2202 memmap=nn[KMG]#ss[KMG]
2203 [KNL,ACPI] Mark specific memory as ACPI data.
2204 Region of memory to be marked is from ss to ss+nn.
2206 memmap=nn[KMG]$ss[KMG]
2207 [KNL,ACPI] Mark specific memory as reserved.
2208 Region of memory to be reserved is from ss to ss+nn.
2209 Example: Exclude memory from 0x18690000-0x1869ffff
2210 memmap=64K$0x18690000
2212 memmap=0x10000$0x18690000
2213 Some bootloaders may need an escape character before '$',
2214 like Grub2, otherwise '$' and the following number
2217 memmap=nn[KMG]!ss[KMG]
2218 [KNL,X86] Mark specific memory as protected.
2219 Region of memory to be used, from ss to ss+nn.
2220 The memory region may be marked as e820 type 12 (0xc)
2221 and is NVDIMM or ADR memory.
2223 memory_corruption_check=0/1 [X86]
2224 Some BIOSes seem to corrupt the first 64k of
2225 memory when doing things like suspend/resume.
2226 Setting this option will scan the memory
2227 looking for corruption. Enabling this will
2228 both detect corruption and prevent the kernel
2229 from using the memory being corrupted.
2230 However, its intended as a diagnostic tool; if
2231 repeatable BIOS-originated corruption always
2232 affects the same memory, you can use memmap=
2233 to prevent the kernel from using that memory.
2235 memory_corruption_check_size=size [X86]
2236 By default it checks for corruption in the low
2237 64k, making this memory unavailable for normal
2238 use. Use this parameter to scan for
2239 corruption in more or less memory.
2241 memory_corruption_check_period=seconds [X86]
2242 By default it checks for corruption every 60
2243 seconds. Use this parameter to check at some
2244 other rate. 0 disables periodic checking.
2246 memtest= [KNL,X86,ARM] Enable memtest
2248 default : 0 <disable>
2249 Specifies the number of memtest passes to be
2250 performed. Each pass selects another test
2251 pattern from a given set of patterns. Memtest
2252 fills the memory with this pattern, validates
2253 memory contents and reserves bad memory
2254 regions that are detected.
2256 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2257 Valid arguments: on, off
2258 Default (depends on kernel configuration option):
2259 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2260 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2261 mem_encrypt=on: Activate SME
2262 mem_encrypt=off: Do not activate SME
2264 Refer to Documentation/x86/amd-memory-encryption.txt
2265 for details on when memory encryption can be activated.
2267 mem_sleep_default= [SUSPEND] Default system suspend mode:
2268 s2idle - Suspend-To-Idle
2269 shallow - Power-On Suspend or equivalent (if supported)
2270 deep - Suspend-To-RAM or equivalent (if supported)
2271 See Documentation/admin-guide/pm/sleep-states.rst.
2273 meye.*= [HW] Set MotionEye Camera parameters
2274 See Documentation/media/v4l-drivers/meye.rst.
2276 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2277 Multi-Function General Purpose Timers on AMD Geode
2280 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2281 the BIOS has incorrectly applied a workaround. TinyBIOS
2282 version 0.98 is known to be affected, 0.99 fixes the
2283 problem by letting the user disable the workaround.
2287 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2288 physical address is ignored.
2290 mini2440= [ARM,HW,KNL]
2291 Format:[0..2][b][c][t]
2293 MINI2440 configuration specification:
2294 0 - The attached screen is the 3.5" TFT
2295 1 - The attached screen is the 7" TFT
2296 2 - The VGA Shield is attached (1024x768)
2297 Leaving out the screen size parameter will not load
2298 the TFT driver, and the framebuffer will be left
2300 b - Enable backlight. The TFT backlight pin will be
2301 linked to the kernel VESA blanking code and a GPIO
2302 LED. This parameter is not necessary when using the
2304 c - Enable the s3c camera interface.
2305 t - Reserved for enabling touchscreen support. The
2306 touchscreen support is not enabled in the mainstream
2307 kernel as of 2.6.30, a preliminary port can be found
2308 in the "bleeding edge" mini2440 support kernel at
2309 http://repo.or.cz/w/linux-2.6/mini2440.git
2312 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2313 parameter allows control of the logging verbosity for
2314 the additional memory initialisation checks. A value
2315 of 0 disables mminit logging and a level of 4 will
2316 log everything. Information is printed at KERN_DEBUG
2317 so loglevel=8 may also need to be specified.
2320 [KNL] When CONFIG_MODULE_SIG is set, this means that
2321 modules without (valid) signatures will fail to load.
2322 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2323 is always true, so this option does nothing.
2325 module_blacklist= [KNL] Do not load a comma-separated list of
2326 modules. Useful for debugging problem modules.
2329 [MOUSE] Maximum time between finger touching and
2330 leaving touchpad surface for touch to be considered
2331 a tap and be reported as a left button click (for
2332 touchpads working in absolute mode only).
2334 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2335 reporting absolute coordinates, such as tablets
2336 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2337 reporting absolute coordinates, such as tablets
2339 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2340 is similar to kernelcore except it specifies the
2341 amount of memory used for migratable allocations.
2342 If both kernelcore and movablecore is specified,
2343 then kernelcore will be at *least* the specified
2344 value but may be more. If movablecore on its own
2345 is specified, the administrator must be careful
2346 that the amount of memory usable for all allocations
2349 movable_node [KNL] Boot-time switch to make hotplugable memory
2350 NUMA nodes to be movable. This means that the memory
2351 of such nodes will be usable only for movable
2352 allocations which rules out almost all kernel
2353 allocations. Use with caution!
2355 MTD_Partition= [MTD]
2356 Format: <name>,<region-number>,<size>,<offset>
2358 MTD_Region= [MTD] Format:
2359 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2362 See drivers/mtd/cmdlinepart.c.
2364 multitce=off [PPC] This parameter disables the use of the pSeries
2365 firmware feature for updating multiple TCE entries
2368 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2370 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2372 boundary - index of last SLC block on Flex-OneNAND.
2373 The remaining blocks are configured as MLC blocks.
2374 lock - Configure if Flex-OneNAND boundary should be locked.
2375 Once locked, the boundary cannot be changed.
2376 1 indicates lock status, 0 indicates unlock status.
2379 ARM/S3C2412 JIVE boot control
2381 See arch/arm/mach-s3c2412/mach-jive.c
2383 mtouchusb.raw_coordinates=
2384 [HW] Make the MicroTouch USB driver use raw coordinates
2385 ('y', default) or cooked coordinates ('n')
2387 mtrr_chunk_size=nn[KMG] [X86]
2388 used for mtrr cleanup. It is largest continuous chunk
2389 that could hold holes aka. UC entries.
2391 mtrr_gran_size=nn[KMG] [X86]
2392 Used for mtrr cleanup. It is granularity of mtrr block.
2394 Large value could prevent small alignment from
2397 mtrr_spare_reg_nr=n [X86]
2399 Range: 0,7 : spare reg number
2401 Used for mtrr cleanup. It is spare mtrr entries number.
2402 Set to 2 or more if your graphical card needs more.
2404 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2406 netdev= [NET] Network devices parameters
2407 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2408 Note that mem_start is often overloaded to mean
2409 something different and driver-specific.
2410 This usage is only documented in each driver source
2414 [NETFILTER] Enable connection tracking flow accounting
2415 0 to disable accounting
2416 1 to enable accounting
2419 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2420 See Documentation/filesystems/nfs/nfsroot.txt.
2422 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2423 See Documentation/filesystems/nfs/nfsroot.txt.
2425 nfsrootdebug [NFS] enable nfsroot debugging messages.
2426 See Documentation/filesystems/nfs/nfsroot.txt.
2428 nfs.callback_nr_threads=
2429 [NFSv4] set the total number of threads that the
2430 NFS client will assign to service NFSv4 callback
2433 nfs.callback_tcpport=
2434 [NFS] set the TCP port on which the NFSv4 callback
2435 channel should listen.
2438 [NFS] sets the pathname to the program which is used
2439 to update the NFS client cache entries.
2441 nfs.cache_getent_timeout=
2442 [NFS] sets the timeout after which an attempt to
2443 update a cache entry is deemed to have failed.
2445 nfs.idmap_cache_timeout=
2446 [NFS] set the maximum lifetime for idmapper cache
2450 [NFS] enable 64-bit inode numbers.
2451 If zero, the NFS client will fake up a 32-bit inode
2452 number for the readdir() and stat() syscalls instead
2453 of returning the full 64-bit number.
2454 The default is to return 64-bit inode numbers.
2456 nfs.max_session_cb_slots=
2457 [NFSv4.1] Sets the maximum number of session
2458 slots the client will assign to the callback
2459 channel. This determines the maximum number of
2460 callbacks the client will process in parallel for
2461 a particular server.
2463 nfs.max_session_slots=
2464 [NFSv4.1] Sets the maximum number of session slots
2465 the client will attempt to negotiate with the server.
2466 This limits the number of simultaneous RPC requests
2467 that the client can send to the NFSv4.1 server.
2468 Note that there is little point in setting this
2469 value higher than the max_tcp_slot_table_limit.
2471 nfs.nfs4_disable_idmapping=
2472 [NFSv4] When set to the default of '1', this option
2473 ensures that both the RPC level authentication
2474 scheme and the NFS level operations agree to use
2475 numeric uids/gids if the mount is using the
2476 'sec=sys' security flavour. In effect it is
2477 disabling idmapping, which can make migration from
2478 legacy NFSv2/v3 systems to NFSv4 easier.
2479 Servers that do not support this mode of operation
2480 will be autodetected by the client, and it will fall
2481 back to using the idmapper.
2482 To turn off this behaviour, set the value to '0'.
2484 [NFS4] Specify an additional fixed unique ident-
2485 ification string that NFSv4 clients can insert into
2486 their nfs_client_id4 string. This is typically a
2487 UUID that is generated at system install time.
2489 nfs.send_implementation_id =
2490 [NFSv4.1] Send client implementation identification
2491 information in exchange_id requests.
2492 If zero, no implementation identification information
2494 The default is to send the implementation identification
2497 nfs.recover_lost_locks =
2498 [NFSv4] Attempt to recover locks that were lost due
2499 to a lease timeout on the server. Please note that
2500 doing this risks data corruption, since there are
2501 no guarantees that the file will remain unchanged
2502 after the locks are lost.
2503 If you want to enable the kernel legacy behaviour of
2504 attempting to recover these locks, then set this
2506 The default parameter value of '0' causes the kernel
2507 not to attempt recovery of lost locks.
2509 nfs4.layoutstats_timer =
2510 [NFSv4.2] Change the rate at which the kernel sends
2511 layoutstats to the pNFS metadata server.
2513 Setting this to value to 0 causes the kernel to use
2514 whatever value is the default set by the layout
2515 driver. A non-zero value sets the minimum interval
2516 in seconds between layoutstats transmissions.
2518 nfsd.nfs4_disable_idmapping=
2519 [NFSv4] When set to the default of '1', the NFSv4
2520 server will return only numeric uids and gids to
2521 clients using auth_sys, and will accept numeric uids
2522 and gids from such clients. This is intended to ease
2523 migration from NFSv2/v3.
2525 nmi_debug= [KNL,SH] Specify one or more actions to take
2526 when a NMI is triggered.
2527 Format: [state][,regs][,debounce][,die]
2529 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2530 Format: [panic,][nopanic,][num]
2532 0 - turn hardlockup detector in nmi_watchdog off
2533 1 - turn hardlockup detector in nmi_watchdog on
2534 When panic is specified, panic when an NMI watchdog
2535 timeout occurs (or 'nopanic' to override the opposite
2536 default). To disable both hard and soft lockup detectors,
2537 please see 'nowatchdog'.
2538 This is useful when you use a panic=... timeout and
2539 need the box quickly up again.
2541 netpoll.carrier_timeout=
2542 [NET] Specifies amount of time (in seconds) that
2543 netpoll should wait for a carrier. By default netpoll
2546 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2547 emulation library even if a 387 maths coprocessor
2551 [HW] Never suspend the console
2552 Disable suspending of consoles during suspend and
2553 hibernate operations. Once disabled, debugging
2554 messages can reach various consoles while the rest
2555 of the system is being put to sleep (ie, while
2556 debugging driver suspend/resume hooks). This may
2557 not work reliably with all consoles, but is known
2558 to work with serial and VGA consoles.
2559 To facilitate more flexible debugging, we also add
2560 console_suspend, a printk module parameter to control
2561 it. Users could use console_suspend (usually
2562 /sys/module/printk/parameters/console_suspend) to
2563 turn on/off it dynamically.
2565 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2566 caches in the slab allocator. Saves per-node memory,
2567 but will impact performance.
2571 noaltinstr [S390] Disables alternative instructions patching
2572 (CPU alternatives feature).
2574 noapic [SMP,APIC] Tells the kernel to not make use of any
2575 IOAPICs that may be present in the system.
2577 noautogroup Disable scheduler automatic task group creation.
2579 nobats [PPC] Do not use BATs for mapping kernel lowmem
2580 on "Classic" PPC cores.
2584 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2586 nodelayacct [KNL] Disable per-task delay accounting
2588 nodsp [SH] Disable hardware DSP at boot time.
2590 noefi Disable EFI runtime services support.
2595 On X86-32 available only on PAE configured kernels.
2596 noexec=on: enable non-executable mappings (default)
2597 noexec=off: disable non-executable mappings
2600 Disable SMAP (Supervisor Mode Access Prevention)
2601 even if it is supported by processor.
2604 Disable SMEP (Supervisor Mode Execution Prevention)
2605 even if it is supported by processor.
2608 This affects only 32-bit executables.
2609 noexec32=on: enable non-executable mappings (default)
2610 read doesn't imply executable mappings
2611 noexec32=off: disable non-executable mappings
2612 read implies executable mappings
2614 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2616 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2617 register save and restore. The kernel will only save
2618 legacy floating-point registers on task switch.
2620 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2622 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2623 Equivalent to smt=1.
2625 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2626 (indirect branch prediction) vulnerability. System may
2627 allow data leaks with this option, which is equivalent
2630 noxsave [BUGS=X86] Disables x86 extended register state save
2631 and restore using xsave. The kernel will fallback to
2632 enabling legacy floating-point and sse state.
2634 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2635 register states. The kernel will fall back to use
2636 xsave to save the states. By using this parameter,
2637 performance of saving the states is degraded because
2638 xsave doesn't support modified optimization while
2639 xsaveopt supports it on xsaveopt enabled systems.
2641 noxsaves [X86] Disables xsaves and xrstors used in saving and
2642 restoring x86 extended register state in compacted
2643 form of xsave area. The kernel will fall back to use
2644 xsaveopt and xrstor to save and restore the states
2645 in standard form of xsave area. By using this
2646 parameter, xsave area per process might occupy more
2647 memory on xsaves enabled systems.
2649 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2650 wfi(ARM) instruction doesn't work correctly and not to
2651 use it. This is also useful when using JTAG debugger.
2653 no_file_caps Tells the kernel not to honor file capabilities. The
2654 only way then for a file to be executed with privilege
2655 is to be setuid root or executed by root.
2657 nohalt [IA-64] Tells the kernel not to use the power saving
2658 function PAL_HALT_LIGHT when idle. This increases
2659 power-consumption. On the positive side, it reduces
2660 interrupt wake-up latency, which may improve performance
2661 in certain environments such as networked servers or
2664 nohibernate [HIBERNATION] Disable hibernation and resume.
2666 nohz= [KNL] Boottime enable/disable dynamic ticks
2667 Valid arguments: on, off
2670 nohz_full= [KNL,BOOT,SMP,ISOL]
2671 The argument is a cpu list, as described above.
2672 In kernels built with CONFIG_NO_HZ_FULL=y, set
2673 the specified list of CPUs whose tick will be stopped
2674 whenever possible. The boot CPU will be forced outside
2675 the range to maintain the timekeeping. Any CPUs
2676 in this list will have their RCU callbacks offloaded,
2677 just as if they had also been called out in the
2678 rcu_nocbs= boot parameter.
2680 noiotrap [SH] Disables trapped I/O port accesses.
2682 noirqdebug [X86-32] Disables the code which attempts to detect and
2683 disable unhandled interrupt sources.
2685 no_timer_check [X86,APIC] Disables the code which tests for
2686 broken timer IRQ sources.
2688 noisapnp [ISAPNP] Disables ISA PnP code.
2690 noinitrd [RAM] Tells the kernel not to load any configured
2693 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2695 [Deprecated - use intremap=off]
2699 noinvpcid [X86] Disable the INVPCID cpu feature.
2701 nojitter [IA-64] Disables jitter checking for ITC timers.
2703 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2705 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2709 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2710 clock and use the default one.
2712 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2713 steal time is computed, but won't influence scheduler
2716 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2718 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2720 noltlbs [PPC] Do not use large page/tlb entries for kernel
2721 lowmem mapping on PPC40x and PPC8xx
2723 nomca [IA-64] Disable machine check abort handling
2725 nomce [X86-32] Disable Machine Check Exception
2727 nomfgpt [X86-32] Disable Multi-Function General Purpose
2728 Timer usage (for AMD Geode machines).
2730 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2731 shutdown the other cpus. Instead use the REBOOT_VECTOR
2734 nomodule Disable module load
2736 nopat [X86] Disable PAT (page attribute table extension of
2737 pagetables) support.
2739 nopcid [X86-64] Disable the PCID cpu feature.
2741 norandmaps Don't use address space randomization. Equivalent to
2742 echo 0 > /proc/sys/kernel/randomize_va_space
2744 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2746 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2747 with UP alternatives
2749 nordrand [X86] Disable kernel use of the RDRAND and
2750 RDSEED instructions even if they are supported
2751 by the processor. RDRAND and RDSEED are still
2752 available to user space applications.
2754 noresume [SWSUSP] Disables resume and restores original swap
2757 no-scroll [VGA] Disables scrollback.
2758 This is required for the Braillex ib80-piezo Braille
2759 reader made by F.H. Papenmeier (Germany).
2763 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2765 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2766 and disable the IO APIC. legacy for "maxcpus=0".
2768 nosoftlockup [KNL] Disable the soft-lockup detector.
2770 nosync [HW,M68K] Disables sync negotiation for all devices.
2772 notsc [BUGS=X86-32] Disable Time Stamp Counter
2774 nowatchdog [KNL] Disable both lockup detectors, i.e.
2775 soft-lockup and NMI watchdog (hard-lockup).
2779 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2781 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2782 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2783 Some features depend on CPU0. Known dependencies are:
2784 1. Resume from suspend/hibernate depends on CPU0.
2785 Suspend/hibernate will fail if CPU0 is offline and you
2786 need to online CPU0 before suspend/hibernate.
2787 2. PIC interrupts also depend on CPU0. CPU0 can't be
2788 removed if a PIC interrupt is detected.
2789 It's said poweroff/reboot may depend on CPU0 on some
2790 machines although I haven't seen such issues so far
2791 after CPU0 is offline on a few tested machines.
2792 If the dependencies are under your control, you can
2793 turn on cpu0_hotplug.
2795 nps_mtm_hs_ctr= [KNL,ARC]
2796 This parameter sets the maximum duration, in
2797 cycles, each HW thread of the CTOP can run
2798 without interruptions, before HW switches it.
2799 The actual maximum duration is 16 times this
2801 Format: integer between 1 and 255
2804 nptcg= [IA-64] Override max number of concurrent global TLB
2805 purges which is reported from either PAL_VM_SUMMARY or
2808 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2809 could support. nr_cpus=n : n >= 1 limits the kernel to
2810 support 'n' processors. It could be larger than the
2811 number of already plugged CPU during bootup, later in
2812 runtime you can physically add extra cpu until it reaches
2813 n. So during boot up some boot time memory for per-cpu
2814 variables need be pre-allocated for later physical cpu
2817 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2819 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2820 Allowed values are enable and disable
2822 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2823 'node', 'default' can be specified
2824 This can be set from sysctl after boot.
2825 See Documentation/sysctl/vm.txt for details.
2827 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2828 See Documentation/debugging-via-ohci1394.txt for more
2831 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2832 Rather than timing out after 20 ms if an EC
2833 command is not properly ACKed, override the length
2834 of the timeout. We have interrupts disabled while
2835 waiting for the ACK, so if this is set too high
2836 interrupts *may* be lost!
2838 omap_mux= [OMAP] Override bootloader pin multiplexing.
2839 Format: <mux_mode0.mode_name=value>...
2840 For example, to override I2C bus2:
2841 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2843 oprofile.timer= [HW]
2844 Use timer interrupt instead of performance counters
2846 oprofile.cpu_type= Force an oprofile cpu type
2847 This might be useful if you have an older oprofile
2848 userland or if you want common events.
2849 Format: { arch_perfmon }
2850 arch_perfmon: [X86] Force use of architectural
2851 perfmon on Intel CPUs instead of the
2852 CPU specific event set.
2853 timer: [X86] Force use of architectural NMI
2854 timer mode (see also oprofile.timer
2855 for generic hr timer mode)
2857 oops=panic Always panic on oopses. Default is to just kill the
2858 process, but there is a small probability of
2859 deadlocking the machine.
2860 This will also cause panics on machine check exceptions.
2861 Useful together with panic=30 to trigger a reboot.
2864 See Documentation/sound/oss/oss-parameters.txt
2866 page_owner= [KNL] Boot-time page_owner enabling option.
2867 Storage of the information about who allocated
2868 each page is disabled in default. With this switch,
2870 on: enable the feature
2872 page_poison= [KNL] Boot-time parameter changing the state of
2873 poisoning on the buddy allocator.
2874 off: turn off poisoning
2875 on: turn on poisoning
2877 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2878 timeout > 0: seconds before rebooting
2879 timeout = 0: wait forever
2880 timeout < 0: reboot immediately
2883 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2886 crash_kexec_post_notifiers
2887 Run kdump after running panic-notifiers and dumping
2888 kmsg. This only for the users who doubt kdump always
2889 succeeds in any situation.
2890 Note that this also increases risks of kdump failure,
2891 because some panic notifiers can make the crashed
2892 kernel more unstable.
2894 parkbd.port= [HW] Parallel port number the keyboard adapter is
2895 connected to, default is 0.
2897 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2898 0 for XT, 1 for AT (default is AT).
2901 parport= [HW,PPT] Specify parallel ports. 0 disables.
2902 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2903 Use 'auto' to force the driver to use any
2904 IRQ/DMA settings detected (the default is to
2905 ignore detected IRQ/DMA settings because of
2906 possible conflicts). You can specify the base
2907 address, IRQ, and DMA settings; IRQ and DMA
2908 should be numbers, or 'auto' (for using detected
2909 settings on that particular port), or 'nofifo'
2910 (to avoid using a FIFO even if it is detected).
2911 Parallel ports are assigned in the order they
2912 are specified on the command line, starting
2915 parport_init_mode= [HW,PPT]
2916 Configure VIA parallel port to operate in
2917 a specific mode. This is necessary on Pegasos
2918 computer where firmware has no options for setting
2919 up parallel port mode and sets it to spp.
2920 Currently this function knows 686a and 8231 chips.
2921 Format: [spp|ps2|epp|ecp|ecpepp]
2924 Halt all CPUs after the first oops has been printed for
2925 the specified number of seconds. This is to be used if
2926 your oopses keep scrolling off the screen.
2931 See header of drivers/block/paride/pcd.c.
2932 See also Documentation/blockdev/paride.txt.
2934 pci=option[,option...] [PCI] various PCI subsystem options:
2935 earlydump [X86] dump PCI config space before the kernel
2937 off [X86] don't probe for the PCI bus
2938 bios [X86-32] force use of PCI BIOS, don't access
2939 the hardware directly. Use this if your machine
2940 has a non-standard PCI host bridge.
2941 nobios [X86-32] disallow use of PCI BIOS, only direct
2942 hardware access methods are allowed. Use this
2943 if you experience crashes upon bootup and you
2944 suspect they are caused by the BIOS.
2945 conf1 [X86] Force use of PCI Configuration Access
2946 Mechanism 1 (config address in IO port 0xCF8,
2947 data in IO port 0xCFC, both 32-bit).
2948 conf2 [X86] Force use of PCI Configuration Access
2949 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2950 the function, IO port 0xCFA, also 8-bit, sets
2951 bus number. The config space is then accessed
2952 through ports 0xC000-0xCFFF).
2953 See http://wiki.osdev.org/PCI for more info
2954 on the configuration access mechanisms.
2955 noaer [PCIE] If the PCIEAER kernel config parameter is
2956 enabled, this kernel boot option can be used to
2957 disable the use of PCIE advanced error reporting.
2958 nodomains [PCI] Disable support for multiple PCI
2959 root domains (aka PCI segments, in ACPI-speak).
2960 nommconf [X86] Disable use of MMCONFIG for PCI
2962 check_enable_amd_mmconf [X86] check for and enable
2963 properly configured MMIO access to PCI
2964 config space on AMD family 10h CPU
2965 nomsi [MSI] If the PCI_MSI kernel config parameter is
2966 enabled, this kernel boot option can be used to
2967 disable the use of MSI interrupts system-wide.
2968 noioapicquirk [APIC] Disable all boot interrupt quirks.
2969 Safety option to keep boot IRQs enabled. This
2970 should never be necessary.
2971 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2972 primary IO-APIC for bridges that cannot disable
2973 boot IRQs. This fixes a source of spurious IRQs
2974 when the system masks IRQs.
2975 noioapicreroute [APIC] Disable workaround that uses the
2976 boot IRQ equivalent of an IRQ that connects to
2977 a chipset where boot IRQs cannot be disabled.
2978 The opposite of ioapicreroute.
2979 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2980 routing table. These calls are known to be buggy
2981 on several machines and they hang the machine
2982 when used, but on other computers it's the only
2983 way to get the interrupt routing table. Try
2984 this option if the kernel is unable to allocate
2985 IRQs or discover secondary PCI buses on your
2987 rom [X86] Assign address space to expansion ROMs.
2988 Use with caution as certain devices share
2989 address decoders between ROMs and other
2991 norom [X86] Do not assign address space to
2992 expansion ROMs that do not already have
2993 BIOS assigned address ranges.
2994 nobar [X86] Do not assign address space to the
2995 BARs that weren't assigned by the BIOS.
2996 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2997 assigned automatically to PCI devices. You can
2998 make the kernel exclude IRQs of your ISA cards
3000 pirqaddr=0xAAAAA [X86] Specify the physical address
3001 of the PIRQ table (normally generated
3002 by the BIOS) if it is outside the
3003 F0000h-100000h range.
3004 lastbus=N [X86] Scan all buses thru bus #N. Can be
3005 useful if the kernel is unable to find your
3006 secondary buses and you want to tell it
3007 explicitly which ones they are.
3008 assign-busses [X86] Always assign all PCI bus
3009 numbers ourselves, overriding
3010 whatever the firmware may have done.
3011 usepirqmask [X86] Honor the possible IRQ mask stored
3012 in the BIOS $PIR table. This is needed on
3013 some systems with broken BIOSes, notably
3014 some HP Pavilion N5400 and Omnibook XE3
3015 notebooks. This will have no effect if ACPI
3016 IRQ routing is enabled.
3017 noacpi [X86] Do not use ACPI for IRQ routing
3018 or for PCI scanning.
3019 use_crs [X86] Use PCI host bridge window information
3020 from ACPI. On BIOSes from 2008 or later, this
3021 is enabled by default. If you need to use this,
3022 please report a bug.
3023 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3024 If you need to use this, please report a bug.
3025 routeirq Do IRQ routing for all PCI devices.
3026 This is normally done in pci_enable_device(),
3027 so this option is a temporary workaround
3028 for broken drivers that don't call it.
3029 skip_isa_align [X86] do not align io start addr, so can
3030 handle more pci cards
3031 noearly [X86] Don't do any early type 1 scanning.
3032 This might help on some broken boards which
3033 machine check when some devices' config space
3034 is read. But various workarounds are disabled
3035 and some IOMMU drivers will not work.
3036 bfsort Sort PCI devices into breadth-first order.
3037 This sorting is done to get a device
3038 order compatible with older (<= 2.4) kernels.
3039 nobfsort Don't sort PCI devices into breadth-first order.
3040 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3041 tuning and use the BIOS-configured MPS defaults.
3042 pcie_bus_safe Set every device's MPS to the largest value
3043 supported by all devices below the root complex.
3044 pcie_bus_perf Set device MPS to the largest allowable MPS
3045 based on its parent bus. Also set MRRS (Max
3046 Read Request Size) to the largest supported
3047 value (no larger than the MPS that the device
3048 or bus can support) for best performance.
3049 pcie_bus_peer2peer Set every device's MPS to 128B, which
3050 every device is guaranteed to support. This
3051 configuration allows peer-to-peer DMA between
3052 any pair of devices, possibly at the cost of
3053 reduced performance. This also guarantees
3054 that hot-added devices will work.
3055 cbiosize=nn[KMG] The fixed amount of bus space which is
3056 reserved for the CardBus bridge's IO window.
3057 The default value is 256 bytes.
3058 cbmemsize=nn[KMG] The fixed amount of bus space which is
3059 reserved for the CardBus bridge's memory
3060 window. The default value is 64 megabytes.
3063 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3064 [<order of align>@]pci:<vendor>:<device>\
3065 [:<subvendor>:<subdevice>][; ...]
3066 Specifies alignment and device to reassign
3067 aligned memory resources.
3068 If <order of align> is not specified,
3069 PAGE_SIZE is used as alignment.
3070 PCI-PCI bridge can be specified, if resource
3071 windows need to be expanded.
3072 To specify the alignment for several
3073 instances of a device, the PCI vendor,
3074 device, subvendor, and subdevice may be
3075 specified, e.g., 4096@pci:8086:9c22:103c:198f
3076 ecrc= Enable/disable PCIe ECRC (transaction layer
3077 end-to-end CRC checking).
3078 bios: Use BIOS/firmware settings. This is the
3082 hpiosize=nn[KMG] The fixed amount of bus space which is
3083 reserved for hotplug bridge's IO window.
3084 Default size is 256 bytes.
3085 hpmemsize=nn[KMG] The fixed amount of bus space which is
3086 reserved for hotplug bridge's memory window.
3087 Default size is 2 megabytes.
3088 hpbussize=nn The minimum amount of additional bus numbers
3089 reserved for buses below a hotplug bridge.
3091 realloc= Enable/disable reallocating PCI bridge resources
3092 if allocations done by BIOS are too small to
3093 accommodate resources required by all child
3095 off: Turn realloc off
3097 realloc same as realloc=on
3098 noari do not use PCIe ARI.
3099 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3100 only look for one device below a PCIe downstream
3102 big_root_window Try to add a big 64bit memory window to the PCIe
3103 root complex on AMD CPUs. Some GFX hardware
3104 can resize a BAR to allow access to all VRAM.
3105 Adding the window is slightly risky (it may
3106 conflict with unreported devices), so this
3109 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3112 force Enable ASPM even on devices that claim not to support it.
3113 WARNING: Forcing ASPM on may cause system lockups.
3115 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3116 nomsi Do not use MSI for PCI Express Native Hotplug (this
3117 makes all PCIe ports use INTx for hotplug services).
3119 pcie_ports= [PCIE] PCIe ports handling:
3120 auto Ask the BIOS whether or not to use native PCIe services
3121 associated with PCIe ports (PME, hot-plug, AER). Use
3122 them only if that is allowed by the BIOS.
3123 native Use native PCIe services associated with PCIe ports
3125 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3128 pcie_port_pm= [PCIE] PCIe port power management handling:
3129 off Disable power management of all PCIe ports
3130 force Forcibly enable power management of all PCIe ports
3132 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3133 nomsi Do not use MSI for native PCIe PME signaling (this makes
3134 all PCIe root ports use INTx for all services).
3136 pcmv= [HW,PCMCIA] BadgePAD 4
3140 Keep all power-domains already enabled by bootloader on,
3141 even if no driver has claimed them. This is useful
3142 for debug and development, but should not be
3143 needed on a platform with proper driver support.
3146 See Documentation/blockdev/paride.txt.
3148 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3151 See arch/parisc/kernel/pdc_chassis.c
3153 percpu_alloc= Select which percpu first chunk allocator to use.
3154 Currently supported values are "embed" and "page".
3155 Archs may support subset or none of the selections.
3156 See comments in mm/percpu.c for details on each
3157 allocator. This parameter is primarily for debugging
3158 and performance comparison.
3161 See Documentation/blockdev/paride.txt.
3164 See Documentation/blockdev/paride.txt.
3166 pirq= [SMP,APIC] Manual mp-table setup
3167 See Documentation/x86/i386/IO-APIC.txt.
3169 plip= [PPT,NET] Parallel port network link
3170 Format: { parport<nr> | timid | 0 }
3171 See also Documentation/admin-guide/parport.rst.
3173 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3174 Override pmtimer IOPort with a hex value.
3178 Enable PNP debug messages (depends on the
3179 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3180 via /sys/module/pnp/parameters/debug. We always show
3181 current resource usage; turning this on also shows
3182 possible settings and some assignment information.
3188 { on | off | curr | res | no-curr | no-res }
3191 [ISAPNP] Exclude IRQs for the autoconfiguration
3194 [ISAPNP] Exclude DMAs for the autoconfiguration
3196 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3197 Ranges are in pairs (I/O port base and size).
3200 [ISAPNP] Exclude memory regions for the
3202 Ranges are in pairs (memory base and size).
3204 ports= [IP_VS_FTP] IPVS ftp helper module
3206 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3208 Format: <port>,<port>....
3210 powersave=off [PPC] This option disables power saving features.
3211 It specifically disables cpuidle and sets the
3212 platform machine description specific power_save
3213 function to NULL. On Idle the CPU just reduces
3216 ppc_strict_facility_enable
3217 [PPC] This option catches any kernel floating point,
3218 Altivec, VSX and SPE outside of regions specifically
3219 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3220 There is some performance impact when enabling this.
3224 Disable Hardware Transactional Memory
3226 print-fatal-signals=
3227 [KNL] debug: print fatal signals
3229 If enabled, warn about various signal handling
3230 related application anomalies: too many signals,
3231 too many POSIX.1 timers, fatal signals causing a
3234 If you hit the warning due to signal overflow,
3235 you might want to try "ulimit -i unlimited".
3239 printk.always_kmsg_dump=
3240 Trigger kmsg_dump for cases other than kernel oops or
3242 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3245 printk.devkmsg={on,off,ratelimit}
3246 Control writing to /dev/kmsg.
3247 on - unlimited logging to /dev/kmsg from userspace
3248 off - logging to /dev/kmsg disabled
3249 ratelimit - ratelimit the logging
3252 printk.time= Show timing data prefixed to each printk message line
3253 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3255 processor.max_cstate= [HW,ACPI]
3256 Limit processor to maximum C-state
3257 max_cstate=9 overrides any DMI blacklist limit.
3259 processor.nocst [HW,ACPI]
3260 Ignore the _CST method to determine C-states,
3261 instead using the legacy FADT method
3263 profile= [KNL] Enable kernel profiling via /proc/profile
3264 Format: [<profiletype>,]<number>
3265 Param: <profiletype>: "schedule", "sleep", or "kvm"
3266 [defaults to kernel profiling]
3267 Param: "schedule" - profile schedule points.
3268 Param: "sleep" - profile D-state sleeping (millisecs).
3269 Requires CONFIG_SCHEDSTATS
3270 Param: "kvm" - profile VM exits.
3271 Param: <number> - step/bucket size as a power of 2 for
3272 statistical time based profiling.
3274 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3276 See Documentation/blockdev/ramdisk.txt.
3278 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3279 probe for; one of (bare|imps|exps|lifebook|any).
3280 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3282 psmouse.resetafter= [HW,MOUSE]
3283 Try to reset the device after so many bad packets
3286 [HW,MOUSE] Set desired mouse resolution, in dpi.
3287 psmouse.smartscroll=
3288 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3289 0 = disabled, 1 = enabled (default).
3291 pstore.backend= Specify the name of the pstore backend to use
3294 See Documentation/blockdev/paride.txt.
3296 pti= [X86_64] Control Page Table Isolation of user and
3297 kernel address spaces. Disabling this feature
3298 removes hardening, but improves performance of
3299 system calls and interrupts.
3301 on - unconditionally enable
3302 off - unconditionally disable
3303 auto - kernel detects whether your CPU model is
3304 vulnerable to issues that PTI mitigates
3306 Not specifying this option is equivalent to pti=auto.
3309 Equivalent to pti=off
3312 [KNL] Number of legacy pty's. Overwrites compiled-in
3315 quiet [KNL] Disable most log messages
3320 See Documentation/admin-guide/md.rst.
3322 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3323 See Documentation/blockdev/ramdisk.txt.
3325 ras=option[,option,...] [KNL] RAS-specific options
3328 Disable the Correctable Errors Collector,
3329 see CONFIG_RAS_CEC help text.
3332 The argument is a cpu list, as described above.
3334 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3335 the specified list of CPUs to be no-callback CPUs.
3336 Invocation of these CPUs' RCU callbacks will
3337 be offloaded to "rcuox/N" kthreads created for
3338 that purpose, where "x" is "b" for RCU-bh, "p"
3339 for RCU-preempt, and "s" for RCU-sched, and "N"
3340 is the CPU number. This reduces OS jitter on the
3341 offloaded CPUs, which can be useful for HPC and
3342 real-time workloads. It can also improve energy
3343 efficiency for asymmetric multiprocessors.
3346 Rather than requiring that offloaded CPUs
3347 (specified by rcu_nocbs= above) explicitly
3348 awaken the corresponding "rcuoN" kthreads,
3349 make these kthreads poll for callbacks.
3350 This improves the real-time response for the
3351 offloaded CPUs by relieving them of the need to
3352 wake up the corresponding kthread, but degrades
3353 energy efficiency by requiring that the kthreads
3354 periodically wake up to do the polling.
3356 rcutree.blimit= [KNL]
3357 Set maximum number of finished RCU callbacks to
3358 process in one batch.
3360 rcutree.dump_tree= [KNL]
3361 Dump the structure of the rcu_node combining tree
3362 out at early boot. This is used for diagnostic
3363 purposes, to verify correct tree setup.
3365 rcutree.gp_cleanup_delay= [KNL]
3366 Set the number of jiffies to delay each step of
3367 RCU grace-period cleanup.
3369 rcutree.gp_init_delay= [KNL]
3370 Set the number of jiffies to delay each step of
3371 RCU grace-period initialization.
3373 rcutree.gp_preinit_delay= [KNL]
3374 Set the number of jiffies to delay each step of
3375 RCU grace-period pre-initialization, that is,
3376 the propagation of recent CPU-hotplug changes up
3377 the rcu_node combining tree.
3379 rcutree.rcu_fanout_exact= [KNL]
3380 Disable autobalancing of the rcu_node combining
3381 tree. This is used by rcutorture, and might
3382 possibly be useful for architectures having high
3383 cache-to-cache transfer latencies.
3385 rcutree.rcu_fanout_leaf= [KNL]
3386 Change the number of CPUs assigned to each
3387 leaf rcu_node structure. Useful for very
3388 large systems, which will choose the value 64,
3389 and for NUMA systems with large remote-access
3390 latencies, which will choose a value aligned
3391 with the appropriate hardware boundaries.
3393 rcutree.jiffies_till_sched_qs= [KNL]
3394 Set required age in jiffies for a
3395 given grace period before RCU starts
3396 soliciting quiescent-state help from
3397 rcu_note_context_switch().
3399 rcutree.jiffies_till_first_fqs= [KNL]
3400 Set delay from grace-period initialization to
3401 first attempt to force quiescent states.
3402 Units are jiffies, minimum value is zero,
3403 and maximum value is HZ.
3405 rcutree.jiffies_till_next_fqs= [KNL]
3406 Set delay between subsequent attempts to force
3407 quiescent states. Units are jiffies, minimum
3408 value is one, and maximum value is HZ.
3410 rcutree.kthread_prio= [KNL,BOOT]
3411 Set the SCHED_FIFO priority of the RCU per-CPU
3412 kthreads (rcuc/N). This value is also used for
3413 the priority of the RCU boost threads (rcub/N)
3414 and for the RCU grace-period kthreads (rcu_bh,
3415 rcu_preempt, and rcu_sched). If RCU_BOOST is
3416 set, valid values are 1-99 and the default is 1
3417 (the least-favored priority). Otherwise, when
3418 RCU_BOOST is not set, valid values are 0-99 and
3419 the default is zero (non-realtime operation).
3421 rcutree.rcu_nocb_leader_stride= [KNL]
3422 Set the number of NOCB kthread groups, which
3423 defaults to the square root of the number of
3424 CPUs. Larger numbers reduces the wakeup overhead
3425 on the per-CPU grace-period kthreads, but increases
3426 that same overhead on each group's leader.
3428 rcutree.qhimark= [KNL]
3429 Set threshold of queued RCU callbacks beyond which
3430 batch limiting is disabled.
3432 rcutree.qlowmark= [KNL]
3433 Set threshold of queued RCU callbacks below which
3434 batch limiting is re-enabled.
3436 rcutree.rcu_idle_gp_delay= [KNL]
3437 Set wakeup interval for idle CPUs that have
3438 RCU callbacks (RCU_FAST_NO_HZ=y).
3440 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3441 Set wakeup interval for idle CPUs that have
3442 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3443 Lazy RCU callbacks are those which RCU can
3444 prove do nothing more than free memory.
3446 rcutree.rcu_kick_kthreads= [KNL]
3447 Cause the grace-period kthread to get an extra
3448 wake_up() if it sleeps three times longer than
3449 it should at force-quiescent-state time.
3450 This wake_up() will be accompanied by a
3451 WARN_ONCE() splat and an ftrace_dump().
3453 rcuperf.gp_async= [KNL]
3454 Measure performance of asynchronous
3455 grace-period primitives such as call_rcu().
3457 rcuperf.gp_async_max= [KNL]
3458 Specify the maximum number of outstanding
3459 callbacks per writer thread. When a writer
3460 thread exceeds this limit, it invokes the
3461 corresponding flavor of rcu_barrier() to allow
3462 previously posted callbacks to drain.
3464 rcuperf.gp_exp= [KNL]
3465 Measure performance of expedited synchronous
3466 grace-period primitives.
3468 rcuperf.holdoff= [KNL]
3469 Set test-start holdoff period. The purpose of
3470 this parameter is to delay the start of the
3471 test until boot completes in order to avoid
3474 rcuperf.nreaders= [KNL]
3475 Set number of RCU readers. The value -1 selects
3476 N, where N is the number of CPUs. A value
3477 "n" less than -1 selects N-n+1, where N is again
3478 the number of CPUs. For example, -2 selects N
3479 (the number of CPUs), -3 selects N+1, and so on.
3480 A value of "n" less than or equal to -N selects
3483 rcuperf.nwriters= [KNL]
3484 Set number of RCU writers. The values operate
3485 the same as for rcuperf.nreaders.
3486 N, where N is the number of CPUs
3488 rcuperf.perf_type= [KNL]
3489 Specify the RCU implementation to test.
3491 rcuperf.shutdown= [KNL]
3492 Shut the system down after performance tests
3493 complete. This is useful for hands-off automated
3496 rcuperf.verbose= [KNL]
3497 Enable additional printk() statements.
3499 rcuperf.writer_holdoff= [KNL]
3500 Write-side holdoff between grace periods,
3501 in microseconds. The default of zero says
3504 rcutorture.cbflood_inter_holdoff= [KNL]
3505 Set holdoff time (jiffies) between successive
3506 callback-flood tests.
3508 rcutorture.cbflood_intra_holdoff= [KNL]
3509 Set holdoff time (jiffies) between successive
3510 bursts of callbacks within a given callback-flood
3513 rcutorture.cbflood_n_burst= [KNL]
3514 Set the number of bursts making up a given
3515 callback-flood test. Set this to zero to
3516 disable callback-flood testing.
3518 rcutorture.cbflood_n_per_burst= [KNL]
3519 Set the number of callbacks to be registered
3520 in a given burst of a callback-flood test.
3522 rcutorture.fqs_duration= [KNL]
3523 Set duration of force_quiescent_state bursts
3526 rcutorture.fqs_holdoff= [KNL]
3527 Set holdoff time within force_quiescent_state bursts
3530 rcutorture.fqs_stutter= [KNL]
3531 Set wait time between force_quiescent_state bursts
3534 rcutorture.gp_cond= [KNL]
3535 Use conditional/asynchronous update-side
3536 primitives, if available.
3538 rcutorture.gp_exp= [KNL]
3539 Use expedited update-side primitives, if available.
3541 rcutorture.gp_normal= [KNL]
3542 Use normal (non-expedited) asynchronous
3543 update-side primitives, if available.
3545 rcutorture.gp_sync= [KNL]
3546 Use normal (non-expedited) synchronous
3547 update-side primitives, if available. If all
3548 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3549 rcutorture.gp_normal=, and rcutorture.gp_sync=
3550 are zero, rcutorture acts as if is interpreted
3551 they are all non-zero.
3553 rcutorture.n_barrier_cbs= [KNL]
3554 Set callbacks/threads for rcu_barrier() testing.
3556 rcutorture.nfakewriters= [KNL]
3557 Set number of concurrent RCU writers. These just
3558 stress RCU, they don't participate in the actual
3559 test, hence the "fake".
3561 rcutorture.nreaders= [KNL]
3562 Set number of RCU readers. The value -1 selects
3563 N-1, where N is the number of CPUs. A value
3564 "n" less than -1 selects N-n-2, where N is again
3565 the number of CPUs. For example, -2 selects N
3566 (the number of CPUs), -3 selects N+1, and so on.
3568 rcutorture.object_debug= [KNL]
3569 Enable debug-object double-call_rcu() testing.
3571 rcutorture.onoff_holdoff= [KNL]
3572 Set time (s) after boot for CPU-hotplug testing.
3574 rcutorture.onoff_interval= [KNL]
3575 Set time (s) between CPU-hotplug operations, or
3576 zero to disable CPU-hotplug testing.
3578 rcutorture.shuffle_interval= [KNL]
3579 Set task-shuffle interval (s). Shuffling tasks
3580 allows some CPUs to go into dyntick-idle mode
3581 during the rcutorture test.
3583 rcutorture.shutdown_secs= [KNL]
3584 Set time (s) after boot system shutdown. This
3585 is useful for hands-off automated testing.
3587 rcutorture.stall_cpu= [KNL]
3588 Duration of CPU stall (s) to test RCU CPU stall
3589 warnings, zero to disable.
3591 rcutorture.stall_cpu_holdoff= [KNL]
3592 Time to wait (s) after boot before inducing stall.
3594 rcutorture.stall_cpu_irqsoff= [KNL]
3595 Disable interrupts while stalling if set.
3597 rcutorture.stat_interval= [KNL]
3598 Time (s) between statistics printk()s.
3600 rcutorture.stutter= [KNL]
3601 Time (s) to stutter testing, for example, specifying
3602 five seconds causes the test to run for five seconds,
3603 wait for five seconds, and so on. This tests RCU's
3604 ability to transition abruptly to and from idle.
3606 rcutorture.test_boost= [KNL]
3607 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3608 "Maybe" means test if the RCU implementation
3609 under test support RCU priority boosting.
3611 rcutorture.test_boost_duration= [KNL]
3612 Duration (s) of each individual boost test.
3614 rcutorture.test_boost_interval= [KNL]
3615 Interval (s) between each boost test.
3617 rcutorture.test_no_idle_hz= [KNL]
3618 Test RCU's dyntick-idle handling. See also the
3619 rcutorture.shuffle_interval parameter.
3621 rcutorture.torture_type= [KNL]
3622 Specify the RCU implementation to test.
3624 rcutorture.verbose= [KNL]
3625 Enable additional printk() statements.
3627 rcupdate.rcu_cpu_stall_suppress= [KNL]
3628 Suppress RCU CPU stall warning messages.
3630 rcupdate.rcu_cpu_stall_timeout= [KNL]
3631 Set timeout for RCU CPU stall warning messages.
3633 rcupdate.rcu_expedited= [KNL]
3634 Use expedited grace-period primitives, for
3635 example, synchronize_rcu_expedited() instead
3636 of synchronize_rcu(). This reduces latency,
3637 but can increase CPU utilization, degrade
3638 real-time latency, and degrade energy efficiency.
3639 No effect on CONFIG_TINY_RCU kernels.
3641 rcupdate.rcu_normal= [KNL]
3642 Use only normal grace-period primitives,
3643 for example, synchronize_rcu() instead of
3644 synchronize_rcu_expedited(). This improves
3645 real-time latency, CPU utilization, and
3646 energy efficiency, but can expose users to
3647 increased grace-period latency. This parameter
3648 overrides rcupdate.rcu_expedited. No effect on
3649 CONFIG_TINY_RCU kernels.
3651 rcupdate.rcu_normal_after_boot= [KNL]
3652 Once boot has completed (that is, after
3653 rcu_end_inkernel_boot() has been invoked), use
3654 only normal grace-period primitives. No effect
3655 on CONFIG_TINY_RCU kernels.
3657 rcupdate.rcu_task_stall_timeout= [KNL]
3658 Set timeout in jiffies for RCU task stall warning
3659 messages. Disable with a value less than or equal
3662 rcupdate.rcu_self_test= [KNL]
3663 Run the RCU early boot self tests
3665 rcupdate.rcu_self_test_bh= [KNL]
3666 Run the RCU bh early boot self tests
3668 rcupdate.rcu_self_test_sched= [KNL]
3669 Run the RCU sched early boot self tests
3673 Run specified binary instead of /init from the ramdisk,
3674 used for early userspace startup. See initrd.
3677 Turn on/off individual RDT features. List is:
3678 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3680 E.g. to turn on cmt and turn off mba use:
3684 Format (x86 or x86_64):
3685 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3687 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3689 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3690 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3691 reboot_force is either force or not specified,
3692 reboot_cpu is s[mp]#### with #### being the processor
3693 to be used for rebooting.
3696 [KNL, SMP] Set scheduler's default relax_domain_level.
3697 See Documentation/cgroup-v1/cpusets.txt.
3699 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3701 reservetop= [X86-32]
3703 Reserves a hole at the top of the kernel virtual
3708 Set the amount of memory to reserve for BIOS at
3709 the bottom of the address space.
3711 reset_devices [KNL] Force drivers to reset the underlying device
3712 during initialization.
3715 Specify the partition device for software suspend
3717 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3719 resume_offset= [SWSUSP]
3720 Specify the offset from the beginning of the partition
3721 given by "resume=" at which the swap header is located,
3722 in <PAGE_SIZE> units (needed only for swap files).
3723 See Documentation/power/swsusp-and-swap-files.txt
3725 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3726 read the resume files
3728 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3729 Useful for devices that are detected asynchronously
3730 (e.g. USB and MMC devices).
3732 hibernate= [HIBERNATION]
3733 noresume Don't check if there's a hibernation image
3734 present during boot.
3735 nocompress Don't compress/decompress hibernation images.
3736 no Disable hibernation and resume.
3737 protect_image Turn on image protection during restoration
3738 (that will set all pages holding image data
3739 during restoration read-only).
3741 retain_initrd [RAM] Keep initrd memory after extraction
3743 rfkill.default_state=
3744 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3745 etc. communication is blocked by default.
3748 rfkill.master_switch_mode=
3749 0 The "airplane mode" button does nothing.
3750 1 The "airplane mode" button toggles between everything
3751 blocked and the previous configuration.
3752 2 The "airplane mode" button toggles between everything
3753 blocked and everything unblocked.
3755 rhash_entries= [KNL,NET]
3756 Set number of hash buckets for route cache
3759 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3762 ro [KNL] Mount root device read-only on boot
3765 on Mark read-only kernel memory as read-only (default).
3766 off Leave read-only kernel memory writable for debugging.
3769 Enable the uart passthrough on the designated usb port
3770 on Rockchip SoCs. When active, the signals of the
3771 debug-uart get routed to the D+ and D- pins of the usb
3772 port and the regular usb controller gets disabled.
3774 root= [KNL] Root filesystem
3775 See name_to_dev_t comment in init/do_mounts.c.
3777 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3778 mount the root filesystem
3780 rootflags= [KNL] Set root filesystem mount option string
3782 rootfstype= [KNL] Set root filesystem type
3784 rootwait [KNL] Wait (indefinitely) for root device to show up.
3785 Useful for devices that are detected asynchronously
3786 (e.g. USB and MMC devices).
3788 rproc_mem=nn[KMG][@address]
3789 [KNL,ARM,CMA] Remoteproc physical memory block.
3790 Memory area to be used by remote processor image,
3793 rw [KNL] Mount root device read-write on boot
3795 S [KNL] Run init in single mode
3797 s390_iommu= [HW,S390]
3798 Set s390 IOTLB flushing mode
3800 With strict flushing every unmap operation will result in
3801 an IOTLB flush. Default is lazy flushing before reuse,
3805 See drivers/net/irda/sa1100_ir.c.
3807 sbni= [NET] Granch SBNI12 leased line adapter
3809 sched_debug [KNL] Enables verbose scheduler debug messages.
3811 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3812 Allowed values are enable and disable. This feature
3813 incurs a small amount of overhead in the scheduler
3814 but is useful for debugging and performance tuning.
3816 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3817 xtime_lock contention on larger systems, and/or RCU lock
3818 contention on all systems with CONFIG_MAXSMP set.
3819 Format: { "0" | "1" }
3820 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3822 Note: increases power consumption, thus should only be
3823 enabled if running jitter sensitive (HPC/RT) workloads.
3825 security= [SECURITY] Choose a security module to enable at boot.
3826 If this boot parameter is not specified, only the first
3827 security module asking for security registration will be
3828 loaded. An invalid security module name will be treated
3829 as if no module has been chosen.
3831 selinux= [SELINUX] Disable or enable SELinux at boot time.
3832 Format: { "0" | "1" }
3833 See security/selinux/Kconfig help text.
3836 Default value is set via kernel config option.
3837 If enabled at boot time, /selinux/disable can be used
3838 later to disable prior to initial policy load.
3840 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3841 Format: { "0" | "1" }
3842 See security/apparmor/Kconfig help text
3845 Default value is set via kernel config option.
3847 serialnumber [BUGS=X86-32]
3850 Maximal number of shapers.
3858 Disable merging of slabs with similar size. May be
3859 necessary if there is some reason to distinguish
3860 allocs to different slabs, especially in hardened
3861 environments where the risk of heap overflows and
3862 layout control by attackers can usually be
3863 frustrated by disabling merging. This will reduce
3864 most of the exposure of a heap attack to a single
3865 cache (risks via metadata attacks are mostly
3866 unchanged). Debug options disable merging on their
3868 For more information see Documentation/vm/slub.txt.
3870 slab_max_order= [MM, SLAB]
3871 Determines the maximum allowed order for slabs.
3872 A high setting may cause OOMs due to memory
3873 fragmentation. Defaults to 1 for systems with
3874 more than 32MB of RAM, 0 otherwise.
3876 slub_debug[=options[,slabs]] [MM, SLUB]
3877 Enabling slub_debug allows one to determine the
3878 culprit if slab objects become corrupted. Enabling
3879 slub_debug can create guard zones around objects and
3880 may poison objects when not in use. Also tracks the
3881 last alloc / free. For more information see
3882 Documentation/vm/slub.txt.
3884 slub_memcg_sysfs= [MM, SLUB]
3885 Determines whether to enable sysfs directories for
3886 memory cgroup sub-caches. 1 to enable, 0 to disable.
3887 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
3888 Enabling this can lead to a very high number of debug
3889 directories and files being created under
3892 slub_max_order= [MM, SLUB]
3893 Determines the maximum allowed order for slabs.
3894 A high setting may cause OOMs due to memory
3895 fragmentation. For more information see
3896 Documentation/vm/slub.txt.
3898 slub_min_objects= [MM, SLUB]
3899 The minimum number of objects per slab. SLUB will
3900 increase the slab order up to slub_max_order to
3901 generate a sufficiently large slab able to contain
3902 the number of objects indicated. The higher the number
3903 of objects the smaller the overhead of tracking slabs
3904 and the less frequently locks need to be acquired.
3905 For more information see Documentation/vm/slub.txt.
3907 slub_min_order= [MM, SLUB]
3908 Determines the minimum page order for slabs. Must be
3909 lower than slub_max_order.
3910 For more information see Documentation/vm/slub.txt.
3912 slub_nomerge [MM, SLUB]
3913 Same with slab_nomerge. This is supported for legacy.
3914 See slab_nomerge for more information.
3917 Format: <io1>[,<io2>[,...,<io8>]]
3919 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3920 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3921 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3922 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3923 smsc-ircc2.ircc_irq= [HW] IRQ line
3924 smsc-ircc2.ircc_dma= [HW] DMA channel
3925 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3926 0: Toshiba Satellite 1800 (GP data pin select)
3927 1: Fast pin select (default)
3930 smt [KNL,S390] Set the maximum number of threads (logical
3931 CPUs) to use per physical CPU on systems capable of
3932 symmetric multithreading (SMT). Will be capped to the
3933 actual hardware limit.
3935 Default: -1 (no limit)
3938 [KNL] Should the soft-lockup detector generate panics.
3941 A nonzero value instructs the soft-lockup detector
3942 to panic the machine when a soft-lockup occurs. This
3943 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
3944 which is the respective build-time switch to that
3947 softlockup_all_cpu_backtrace=
3948 [KNL] Should the soft-lockup detector generate
3949 backtraces on all cpus.
3952 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3953 See Documentation/laptops/sonypi.txt
3955 spectre_v2= [X86] Control mitigation of Spectre variant 2
3956 (indirect branch speculation) vulnerability.
3958 on - unconditionally enable
3959 off - unconditionally disable
3960 auto - kernel detects whether your CPU model is
3963 Selecting 'on' will, and 'auto' may, choose a
3964 mitigation method at run time according to the
3965 CPU, the available microcode, the setting of the
3966 CONFIG_RETPOLINE configuration option, and the
3967 compiler with which the kernel was built.
3969 Specific mitigations can also be selected manually:
3971 retpoline - replace indirect branches
3972 retpoline,generic - google's original retpoline
3973 retpoline,amd - AMD-specific minimal thunk
3975 Not specifying this option is equivalent to
3978 spia_io_base= [HW,MTD]
3983 srcutree.counter_wrap_check [KNL]
3984 Specifies how frequently to check for
3985 grace-period sequence counter wrap for the
3986 srcu_data structure's ->srcu_gp_seq_needed field.
3987 The greater the number of bits set in this kernel
3988 parameter, the less frequently counter wrap will
3989 be checked for. Note that the bottom two bits
3992 srcutree.exp_holdoff [KNL]
3993 Specifies how many nanoseconds must elapse
3994 since the end of the last SRCU grace period for
3995 a given srcu_struct until the next normal SRCU
3996 grace period will be considered for automatic
3997 expediting. Set to zero to disable automatic
4000 stack_guard_gap= [MM]
4001 override the default stack gap protection. The value
4002 is in page units and it defines how many pages prior
4003 to (for stacks growing down) resp. after (for stacks
4004 growing up) the main stack are reserved for no other
4005 mapping. Default value is 256 pages.
4008 Enabled the stack tracer on boot up.
4010 stacktrace_filter=[function-list]
4011 [FTRACE] Limit the functions that the stack tracer
4012 will trace at boot up. function-list is a comma separated
4013 list of functions. This list can be changed at run
4014 time by the stack_trace_filter file in the debugfs
4015 tracing directory. Note, this enables stack tracing
4016 and the stacktrace above is not needed.
4020 Set the STI (builtin display/keyboard on the HP-PARISC
4021 machines) console (graphic card) which should be used
4022 as the initial boot-console.
4023 See also comment in drivers/video/console/sticore.c.
4026 See comment in drivers/video/console/sticore.c.
4029 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4031 sunrpc.min_resvport=
4032 sunrpc.max_resvport=
4034 SunRPC servers often require that client requests
4035 originate from a privileged port (i.e. a port in the
4036 range 0 < portnr < 1024).
4037 An administrator who wishes to reserve some of these
4038 ports for other uses may adjust the range that the
4039 kernel's sunrpc client considers to be privileged
4040 using these two parameters to set the minimum and
4041 maximum port values.
4043 sunrpc.svc_rpc_per_connection_limit=
4045 Limit the number of requests that the server will
4046 process in parallel from a single connection.
4047 The default value is 0 (no limit).
4051 Control how the NFS server code allocates CPUs to
4052 service thread pools. Depending on how many NICs
4053 you have and where their interrupts are bound, this
4054 option will affect which CPUs will do NFS serving.
4055 Note: this parameter cannot be changed while the
4056 NFS server is running.
4058 auto the server chooses an appropriate mode
4059 automatically using heuristics
4060 global a single global pool contains all CPUs
4061 percpu one pool for each CPU
4062 pernode one pool for each NUMA node (equivalent
4063 to global on non-NUMA machines)
4065 sunrpc.tcp_slot_table_entries=
4066 sunrpc.udp_slot_table_entries=
4068 Sets the upper limit on the number of simultaneous
4069 RPC calls that can be sent from the client to a
4070 server. Increasing these values may allow you to
4071 improve throughput, but will also increase the
4072 amount of memory reserved for use by the client.
4074 suspend.pm_test_delay=
4076 Sets the number of seconds to remain in a suspend test
4077 mode before resuming the system (see
4078 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4079 is set. Default value is 5.
4082 [KNL] Enable accounting of swap in memory resource
4083 controller if no parameter or 1 is given or disable
4084 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4086 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4087 Format: { <int> | force | noforce }
4088 <int> -- Number of I/O TLB slabs
4089 force -- force using of bounce buffers even if they
4090 wouldn't be automatically used by the kernel
4091 noforce -- Never use bounce buffers (for debugging)
4095 sysfs.deprecated=0|1 [KNL]
4096 Enable/disable old style sysfs layout for old udev
4097 on older distributions. When this option is enabled
4098 very new udev will not work anymore. When this option
4099 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4100 in older udev will not work anymore.
4101 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4102 the kernel configuration.
4104 sysrq_always_enabled
4106 Ignore sysrq setting - this boot parameter will
4107 neutralize any effect of /proc/sys/kernel/sysrq.
4108 Useful for debugging.
4110 tcpmhash_entries= [KNL,NET]
4111 Set the number of tcp_metrics_hash slots.
4112 Default value is 8192 or 16384 depending on total
4113 ram pages. This is used to specify the TCP metrics
4114 cache size. See Documentation/networking/ip-sysctl.txt
4115 "tcp_no_metrics_save" section for more details.
4119 test_suspend= [SUSPEND][,N]
4120 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4121 standby suspend) or "freeze" (for suspend type freeze)
4122 as the system sleep state during system startup with
4123 the optional capability to repeat N number of times.
4124 The system is woken from this state using a
4125 wakeup-capable RTC alarm.
4127 thash_entries= [KNL,NET]
4128 Set number of hash buckets for TCP connection
4130 thermal.act= [HW,ACPI]
4131 -1: disable all active trip points in all thermal zones
4132 <degrees C>: override all lowest active trip points
4134 thermal.crt= [HW,ACPI]
4135 -1: disable all critical trip points in all thermal zones
4136 <degrees C>: override all critical trip points
4138 thermal.nocrt= [HW,ACPI]
4139 Set to disable actions on ACPI thermal zone
4140 critical and hot trip points.
4142 thermal.off= [HW,ACPI]
4143 1: disable ACPI thermal control
4145 thermal.psv= [HW,ACPI]
4146 -1: disable all passive trip points
4147 <degrees C>: override all passive trip points to this
4150 thermal.tzp= [HW,ACPI]
4151 Specify global default ACPI thermal zone polling rate
4152 <deci-seconds>: poll all this frequency
4153 0: no polling (default)
4156 Force threading of all interrupt handlers except those
4157 marked explicitly IRQF_NO_THREAD.
4160 Enable the Transcendent memory driver if built-in.
4162 tmem.cleancache=0|1 [KNL, XEN]
4163 Default is on (1). Disable the usage of the cleancache
4164 API to send anonymous pages to the hypervisor.
4166 tmem.frontswap=0|1 [KNL, XEN]
4167 Default is on (1). Disable the usage of the frontswap
4168 API to send swap pages to the hypervisor. If disabled
4169 the selfballooning and selfshrinking are force disabled.
4171 tmem.selfballooning=0|1 [KNL, XEN]
4172 Default is on (1). Disable the driving of swap pages
4175 tmem.selfshrinking=0|1 [KNL, XEN]
4176 Default is on (1). Partial swapoff that immediately
4177 transfers pages from Xen hypervisor back to the
4178 kernel based on different criteria.
4182 Specify if the kernel should make use of the cpu
4183 topology information if the hardware supports this.
4184 The scheduler will make use of this information and
4185 e.g. base its process migration decisions on it.
4188 topology_updates= [KNL, PPC, NUMA]
4190 Specify if the kernel should ignore (off)
4191 topology updates sent by the hypervisor to this
4196 tpm_suspend_pcr=[HW,TPM]
4197 Format: integer pcr id
4198 Specify that at suspend time, the tpm driver
4199 should extend the specified pcr with zeros,
4200 as a workaround for some chips which fail to
4201 flush the last written pcr on TPM_SaveState.
4202 This will guarantee that all the other pcrs
4205 trace_buf_size=nn[KMG]
4206 [FTRACE] will set tracing buffer size on each cpu.
4208 trace_event=[event-list]
4209 [FTRACE] Set and start specified trace events in order
4210 to facilitate early boot debugging. The event-list is a
4211 comma separated list of trace events to enable. See
4212 also Documentation/trace/events.txt
4214 trace_options=[option-list]
4215 [FTRACE] Enable or disable tracer options at boot.
4216 The option-list is a comma delimited list of options
4217 that can be enabled or disabled just as if you were
4218 to echo the option name into
4220 /sys/kernel/debug/tracing/trace_options
4222 For example, to enable stacktrace option (to dump the
4223 stack trace of each event), add to the command line:
4225 trace_options=stacktrace
4227 See also Documentation/trace/ftrace.txt "trace options"
4231 Have the tracepoints sent to printk as well as the
4232 tracing ring buffer. This is useful for early boot up
4233 where the system hangs or reboots and does not give the
4234 option for reading the tracing buffer or performing a
4235 ftrace_dump_on_oops.
4237 To turn off having tracepoints sent to printk,
4238 echo 0 > /proc/sys/kernel/tracepoint_printk
4239 Note, echoing 1 into this file without the
4240 tracepoint_printk kernel cmdline option has no effect.
4244 Having tracepoints sent to printk() and activating high
4245 frequency tracepoints such as irq or sched, can cause
4246 the system to live lock.
4249 [FTRACE] enable this option to disable tracing when a
4250 warning is hit. This turns off "tracing_on". Tracing can
4251 be enabled again by echoing '1' into the "tracing_on"
4252 file located in /sys/kernel/debug/tracing/
4254 This option is useful, as it disables the trace before
4255 the WARNING dump is called, which prevents the trace to
4256 be filled with content caused by the warning output.
4258 This option can also be set at run time via the sysctl
4259 option: kernel/traceoff_on_warning
4261 transparent_hugepage=
4263 Format: [always|madvise|never]
4264 Can be used to control the default behavior of the system
4265 with respect to transparent hugepages.
4266 See Documentation/vm/transhuge.txt for more details.
4268 tsc= Disable clocksource stability checks for TSC.
4270 [x86] reliable: mark tsc clocksource as reliable, this
4271 disables clocksource verification at runtime, as well
4272 as the stability checks done at bootup. Used to enable
4273 high-resolution timer mode on older hardware, and in
4274 virtualized environment.
4275 [x86] noirqtime: Do not use TSC to do irq accounting.
4276 Used to run time disable IRQ_TIME_ACCOUNTING on any
4277 platforms where RDTSC is slow and this accounting
4279 [x86] unstable: mark the TSC clocksource as unstable, this
4280 marks the TSC unconditionally unstable at bootup and
4281 avoids any further wobbles once the TSC watchdog notices.
4283 turbografx.map[2|3]= [HW,JOY]
4284 TurboGraFX parallel port interface
4286 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4287 See also Documentation/input/devices/joystick-parport.rst
4289 udbg-immortal [PPC] When debugging early kernel crashes that
4290 happen after console_init() and before a proper
4291 console driver takes over, this boot options might
4292 help "seeing" what's going on.
4294 uhash_entries= [KNL,NET]
4295 Set number of hash buckets for UDP/UDP-Lite connections
4298 [USB] Ignore overcurrent events (default N).
4299 Some badly-designed motherboards generate lots of
4300 bogus events, for ports that aren't wired to
4301 anything. Set this parameter to avoid log spamming.
4302 Note that genuine overcurrent events won't be
4306 [X86] Cause panic on unknown NMI.
4308 usbcore.authorized_default=
4309 [USB] Default USB device authorization:
4310 (default -1 = authorized except for wireless USB,
4311 0 = not authorized, 1 = authorized)
4313 usbcore.autosuspend=
4314 [USB] The autosuspend time delay (in seconds) used
4315 for newly-detected USB devices (default 2). This
4316 is the time required before an idle device will be
4317 autosuspended. Devices for which the delay is set
4318 to a negative value won't be autosuspended at all.
4320 usbcore.usbfs_snoop=
4321 [USB] Set to log all usbfs traffic (default 0 = off).
4323 usbcore.usbfs_snoop_max=
4324 [USB] Maximum number of bytes to snoop in each URB
4327 usbcore.blinkenlights=
4328 [USB] Set to cycle leds on hubs (default 0 = off).
4330 usbcore.old_scheme_first=
4331 [USB] Start with the old device initialization
4332 scheme (default 0 = off).
4334 usbcore.usbfs_memory_mb=
4335 [USB] Memory limit (in MB) for buffers allocated by
4336 usbfs (default = 16, 0 = max = 2047).
4338 usbcore.use_both_schemes=
4339 [USB] Try the other device initialization scheme
4340 if the first one fails (default 1 = enabled).
4342 usbcore.initial_descriptor_timeout=
4343 [USB] Specifies timeout for the initial 64-byte
4344 USB_REQ_GET_DESCRIPTOR request in milliseconds
4345 (default 5000 = 5.0 seconds).
4347 usbcore.nousb [USB] Disable the USB subsystem
4350 [USBHID] The interval which mice are to be polled at.
4353 [USBHID] The interval which joysticks are to be polled at.
4355 usb-storage.delay_use=
4356 [UMS] The delay in seconds before a new device is
4357 scanned for Logical Units (default 1).
4360 [UMS] A list of quirks entries to supplement or
4361 override the built-in unusual_devs list. List
4362 entries are separated by commas. Each entry has
4363 the form VID:PID:Flags where VID and PID are Vendor
4364 and Product ID values (4-digit hex numbers) and
4365 Flags is a set of characters, each corresponding
4366 to a common usb-storage quirk flag as follows:
4367 a = SANE_SENSE (collect more than 18 bytes
4369 b = BAD_SENSE (don't collect more than 18
4370 bytes of sense data);
4371 c = FIX_CAPACITY (decrease the reported
4372 device capacity by one sector);
4373 d = NO_READ_DISC_INFO (don't use
4374 READ_DISC_INFO command);
4375 e = NO_READ_CAPACITY_16 (don't use
4376 READ_CAPACITY_16 command);
4377 f = NO_REPORT_OPCODES (don't use report opcodes
4379 g = MAX_SECTORS_240 (don't transfer more than
4380 240 sectors at a time, uas only);
4381 h = CAPACITY_HEURISTICS (decrease the
4382 reported device capacity by one
4383 sector if the number is odd);
4384 i = IGNORE_DEVICE (don't bind to this
4386 j = NO_REPORT_LUNS (don't use report luns
4388 l = NOT_LOCKABLE (don't try to lock and
4389 unlock ejectable media);
4390 m = MAX_SECTORS_64 (don't transfer more
4391 than 64 sectors = 32 KB at a time);
4392 n = INITIAL_READ10 (force a retry of the
4393 initial READ(10) command);
4394 o = CAPACITY_OK (accept the capacity
4395 reported by the device);
4396 p = WRITE_CACHE (the device cache is ON
4398 r = IGNORE_RESIDUE (the device reports
4399 bogus residue values);
4400 s = SINGLE_LUN (the device has only one
4402 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4403 commands, uas only);
4404 u = IGNORE_UAS (don't bind to the uas driver);
4405 w = NO_WP_DETECT (don't test whether the
4406 medium is write-protected).
4407 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4408 even if the device claims no cache)
4409 Example: quirks=0419:aaf5:rl,0421:0433:rc
4411 user_debug= [KNL,ARM]
4413 See arch/arm/Kconfig.debug help text.
4414 1 - undefined instruction events
4416 4 - invalid data aborts
4419 Example: user_debug=31
4422 [X86] Flags controlling user PTE allocations.
4424 nohigh = do not allocate PTE pages in
4425 HIGHMEM regardless of setting
4429 On X86_32, this is an alias for vdso32=. Otherwise:
4431 vdso=1: enable VDSO (the default)
4432 vdso=0: disable VDSO mapping
4434 vdso32= [X86] Control the 32-bit vDSO
4435 vdso32=1: enable 32-bit VDSO
4436 vdso32=0 or vdso32=2: disable 32-bit VDSO
4438 See the help text for CONFIG_COMPAT_VDSO for more
4439 details. If CONFIG_COMPAT_VDSO is set, the default is
4440 vdso32=0; otherwise, the default is vdso32=1.
4442 For compatibility with older kernels, vdso32=2 is an
4445 Try vdso32=0 if you encounter an error that says:
4446 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4449 vector=percpu: enable percpu vector domain
4451 video= [FB] Frame buffer configuration
4452 See Documentation/fb/modedb.txt.
4454 video.brightness_switch_enabled= [0,1]
4455 If set to 1, on receiving an ACPI notify event
4456 generated by hotkey, video driver will adjust brightness
4457 level and then send out the event to user space through
4458 the allocated input device; If set to 0, video driver
4459 will only send out the event without touching backlight
4464 [VMMIO] Memory mapped virtio (platform) device.
4466 <size>@<baseaddr>:<irq>[:<id>]
4468 <size> := size (can use standard suffixes
4470 <baseaddr> := physical base address
4471 <irq> := interrupt number (as passed to
4473 <id> := (optional) platform device id
4475 virtio_mmio.device=1K@0x100b0000:48:7
4477 Can be used multiple times for multiple devices.
4479 vga= [BOOT,X86-32] Select a particular video mode
4480 See Documentation/x86/boot.txt and
4481 Documentation/svga.txt.
4482 Use vga=ask for menu.
4483 This is actually a boot loader parameter; the value is
4484 passed to the kernel using a special protocol.
4486 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4487 size of <nn>. This can be used to increase the
4488 minimum size (128MB on x86). It can also be used to
4489 decrease the size and leave more room for directly
4492 vmcp_cma=nn[MG] [KNL,S390]
4493 Sets the memory size reserved for contiguous memory
4494 allocations for the vmcp device driver.
4496 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4499 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4502 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4506 Controls the behavior of vsyscalls (i.e. calls to
4507 fixed addresses of 0xffffffffff600x00 from legacy
4508 code). Most statically-linked binaries and older
4509 versions of glibc use these calls. Because these
4510 functions are at fixed addresses, they make nice
4511 targets for exploits that can control RIP.
4513 emulate [default] Vsyscalls turn into traps and are
4514 emulated reasonably safely.
4516 native Vsyscalls are native syscall instructions.
4517 This is a little bit faster than trapping
4518 and makes a few dynamic recompilers work
4519 better than they would in emulation mode.
4520 It also makes exploits much easier to write.
4522 none Vsyscalls don't work at all. This makes
4523 them quite hard to use for exploits but
4524 might break your system.
4526 vt.color= [VT] Default text color.
4527 Format: 0xYX, X = foreground, Y = background.
4528 Default: 0x07 = light gray on black.
4530 vt.cur_default= [VT] Default cursor shape.
4531 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4532 the parameters of the <Esc>[?A;B;Cc escape sequence;
4533 see VGA-softcursor.txt. Default: 2 = underline.
4535 vt.default_blu= [VT]
4536 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4537 Change the default blue palette of the console.
4538 This is a 16-member array composed of values
4541 vt.default_grn= [VT]
4542 Format: <green0>,<green1>,<green2>,...,<green15>
4543 Change the default green palette of the console.
4544 This is a 16-member array composed of values
4547 vt.default_red= [VT]
4548 Format: <red0>,<red1>,<red2>,...,<red15>
4549 Change the default red palette of the console.
4550 This is a 16-member array composed of values
4556 Set system-wide default UTF-8 mode for all tty's.
4557 Default is 1, i.e. UTF-8 mode is enabled for all
4558 newly opened terminals.
4560 vt.global_cursor_default=
4563 Set system-wide default for whether a cursor
4564 is shown on new VTs. Default is -1,
4565 i.e. cursors will be created by default unless
4566 overridden by individual drivers. 0 will hide
4567 cursors, 1 will display them.
4569 vt.italic= [VT] Default color for italic text; 0-15.
4572 vt.underline= [VT] Default color for underlined text; 0-15.
4575 watchdog timers [HW,WDT] For information on watchdog timers,
4576 see Documentation/watchdog/watchdog-parameters.txt
4577 or other driver-specific files in the
4578 Documentation/watchdog/ directory.
4580 workqueue.watchdog_thresh=
4581 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4582 warn stall conditions and dump internal state to
4583 help debugging. 0 disables workqueue stall
4584 detection; otherwise, it's the stall threshold
4585 duration in seconds. The default value is 30 and
4586 it can be updated at runtime by writing to the
4587 corresponding sysfs file.
4589 workqueue.disable_numa
4590 By default, all work items queued to unbound
4591 workqueues are affine to the NUMA nodes they're
4592 issued on, which results in better behavior in
4593 general. If NUMA affinity needs to be disabled for
4594 whatever reason, this option can be used. Note
4595 that this also can be controlled per-workqueue for
4596 workqueues visible under /sys/bus/workqueue/.
4598 workqueue.power_efficient
4599 Per-cpu workqueues are generally preferred because
4600 they show better performance thanks to cache
4601 locality; unfortunately, per-cpu workqueues tend to
4602 be more power hungry than unbound workqueues.
4604 Enabling this makes the per-cpu workqueues which
4605 were observed to contribute significantly to power
4606 consumption unbound, leading to measurably lower
4607 power usage at the cost of small performance
4610 The default value of this parameter is determined by
4611 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4613 workqueue.debug_force_rr_cpu
4614 Workqueue used to implicitly guarantee that work
4615 items queued without explicit CPU specified are put
4616 on the local CPU. This guarantee is no longer true
4617 and while local CPU is still preferred work items
4618 may be put on foreign CPUs. This debug option
4619 forces round-robin CPU selection to flush out
4620 usages which depend on the now broken guarantee.
4621 When enabled, memory and cache locality will be
4624 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4625 default x2apic cluster mode on platforms
4628 x86_intel_mid_timer= [X86-32,APBT]
4629 Choose timer option for x86 Intel MID platform.
4630 Two valid options are apbt timer only and lapic timer
4631 plus one apbt timer for broadcast timer.
4632 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4634 xen_512gb_limit [KNL,X86-64,XEN]
4635 Restricts the kernel running paravirtualized under Xen
4636 to use only up to 512 GB of RAM. The reason to do so is
4637 crash analysis tools and Xen tools for doing domain
4638 save/restore/migration must be enabled to handle larger
4641 xen_emul_unplug= [HW,X86,XEN]
4642 Unplug Xen emulated devices
4643 Format: [unplug0,][unplug1]
4644 ide-disks -- unplug primary master IDE devices
4645 aux-ide-disks -- unplug non-primary-master IDE devices
4646 nics -- unplug network devices
4647 all -- unplug all emulated devices (NICs and IDE disks)
4648 unnecessary -- unplugging emulated devices is
4649 unnecessary even if the host did not respond to
4651 never -- do not unplug even if version check succeeds
4653 xen_nopvspin [X86,XEN]
4654 Disables the ticketlock slowpath using Xen PV
4658 Disables the PV optimizations forcing the HVM guest to
4659 run as generic HVM guest with no PV drivers.
4661 xirc2ps_cs= [NET,PCMCIA]
4663 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
git.samba.org / sfrench / cifs-2.6.git / blob