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.rst, 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]
25 { vendor | video | native | none }
26 If set to vendor, prefer vendor-specific driver
27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
28 of the ACPI video.ko driver.
29 If set to video, use the ACPI video.ko driver.
30 If set to native, use the device's native backlight mode.
31 If set to none, disable the ACPI backlight interface.
33 acpi_force_32bit_fadt_addr
34 force FADT to use 32 bit addresses rather than the
35 64 bit X_* addresses. Some firmware have broken 64
36 bit addresses for force ACPI ignore these and use
37 the older legacy 32 bit addresses.
39 acpica_no_return_repair [HW, ACPI]
40 Disable AML predefined validation mechanism
41 This mechanism can repair the evaluation result to make
42 the return objects more ACPI specification compliant.
43 This option is useful for developers to identify the
44 root cause of an AML interpreter issue when the issue
45 has something to do with the repair mechanism.
47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
51 debug output. Bits in debug_layer correspond to a
52 _COMPONENT in an ACPI source file, e.g.,
53 #define _COMPONENT ACPI_PCI_COMPONENT
54 Bits in debug_level correspond to a level in
55 ACPI_DEBUG_PRINT statements, e.g.,
56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
57 The debug_level mask defaults to "info". See
58 Documentation/firmware-guide/acpi/debug.rst for more information about
59 debug layers and levels.
61 Enable processor driver info messages:
62 acpi.debug_layer=0x20000000
63 Enable PCI/PCI interrupt routing info messages:
64 acpi.debug_layer=0x400000
65 Enable AML "Debug" output, i.e., stores to the Debug
66 object while interpreting AML:
67 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
68 Enable all messages related to ACPI hardware:
69 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
71 Some values produce so much output that the system is
72 unusable. The "log_buf_len" parameter may be useful
73 if you need to capture more output.
75 acpi_enforce_resources= [ACPI]
77 Check for resource conflicts between native drivers
78 and ACPI OperationRegions (SystemIO and SystemMemory
79 only). IO ports and memory declared in ACPI might be
80 used by the ACPI subsystem in arbitrary AML code and
81 can interfere with legacy drivers.
82 strict (default): access to resources claimed by ACPI
83 is denied; legacy drivers trying to access reserved
84 resources will fail to bind to device using them.
85 lax: access to resources claimed by ACPI is allowed;
86 legacy drivers trying to access reserved resources
87 will bind successfully but a warning message is logged.
88 no: ACPI OperationRegions are not marked as reserved,
89 no further checks are performed.
91 acpi_force_table_verification [HW,ACPI]
92 Enable table checksum verification during early stage.
93 By default, this is disabled due to x86 early mapping
96 acpi_irq_balance [HW,ACPI]
97 ACPI will balance active IRQs
100 acpi_irq_nobalance [HW,ACPI]
101 ACPI will not move active IRQs (default)
104 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
105 Format: <irq>,<irq>...
107 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
109 Format: <irq>,<irq>...
111 acpi_mask_gpe= [HW,ACPI]
112 Due to the existence of _Lxx/_Exx, some GPEs triggered
113 by unsupported hardware/firmware features can result in
114 GPE floodings that cannot be automatically disabled by
116 This facility can be used to prevent such uncontrolled
120 acpi_no_auto_serialize [HW,ACPI]
121 Disable auto-serialization of AML methods
122 AML control methods that contain the opcodes to create
123 named objects will be marked as "Serialized" by the
124 auto-serialization feature.
125 This feature is enabled by default.
126 This option allows to turn off the feature.
128 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
131 acpi_no_static_ssdt [HW,ACPI]
132 Disable installation of static SSDTs at early boot time
133 By default, SSDTs contained in the RSDT/XSDT will be
134 installed automatically and they will appear under
135 /sys/firmware/acpi/tables.
136 This option turns off this feature.
137 Note that specifying this option does not affect
138 dynamic table installation which will install SSDT
139 tables to /sys/firmware/acpi/tables/dynamic.
141 acpi_no_watchdog [HW,ACPI,WDT]
142 Ignore the ACPI-based watchdog interface (WDAT) and let
143 a native driver control the watchdog device instead.
145 acpi_rsdp= [ACPI,EFI,KEXEC]
146 Pass the RSDP address to the kernel, mostly used
147 on machines running EFI runtime service to boot the
148 second kernel for kdump.
150 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
151 Format: To spoof as Windows 98: ="Microsoft Windows"
153 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
154 of 2 which is mandated by ACPI 6) as the supported ACPI
155 specification revision (when using this switch, it may
156 be necessary to carry out a cold reboot _twice_ in a
157 row to make it take effect on the platform firmware).
159 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
160 acpi_osi="string1" # add string1
161 acpi_osi="!string2" # remove string2
162 acpi_osi=!* # remove all strings
163 acpi_osi=! # disable all built-in OS vendor
165 acpi_osi=!! # enable all built-in OS vendor
167 acpi_osi= # disable all strings
169 'acpi_osi=!' can be used in combination with single or
170 multiple 'acpi_osi="string1"' to support specific OS
171 vendor string(s). Note that such command can only
172 affect the default state of the OS vendor strings, thus
173 it cannot affect the default state of the feature group
174 strings and the current state of the OS vendor strings,
175 specifying it multiple times through kernel command line
176 is meaningless. This command is useful when one do not
177 care about the state of the feature group strings which
178 should be controlled by the OSPM.
180 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
181 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
182 can make '_OSI("Windows 2000")' TRUE.
184 'acpi_osi=' cannot be used in combination with other
185 'acpi_osi=' command lines, the _OSI method will not
186 exist in the ACPI namespace. NOTE that such command can
187 only affect the _OSI support state, thus specifying it
188 multiple times through kernel command line is also
191 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
194 'acpi_osi=!*' can be used in combination with single or
195 multiple 'acpi_osi="string1"' to support specific
196 string(s). Note that such command can affect the
197 current state of both the OS vendor strings and the
198 feature group strings, thus specifying it multiple times
199 through kernel command line is meaningful. But it may
200 still not able to affect the final state of a string if
201 there are quirks related to this string. This command
202 is useful when one want to control the state of the
203 feature group strings to debug BIOS issues related to
206 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
207 '_OSI("Module Device")' FALSE.
208 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
209 '_OSI("Module Device")' TRUE.
210 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
212 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
214 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
215 they all will make '_OSI("Windows 2000")' TRUE.
218 Override the pmtimer bug detection: force the kernel
219 to assume that this machine's pmtimer latches its value
220 and always returns good values.
222 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
223 Format: { level | edge | high | low }
225 acpi_skip_timer_override [HW,ACPI]
226 Recognize and ignore IRQ0/pin2 Interrupt Override.
227 For broken nForce2 BIOS resulting in XT-PIC timer.
229 acpi_sleep= [HW,ACPI] Sleep options
230 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
231 old_ordering, nonvs, sci_force_enable, nobl }
232 See Documentation/power/video.rst for information on
234 s3_beep is for debugging; it makes the PC's speaker beep
235 as soon as the kernel's real-mode entry point is called.
236 s4_nohwsig prevents ACPI hardware signature from being
237 used during resume from hibernation.
238 old_ordering causes the ACPI 1.0 ordering of the _PTS
239 control method, with respect to putting devices into
240 low power states, to be enforced (the ACPI 2.0 ordering
241 of _PTS is used by default).
242 nonvs prevents the kernel from saving/restoring the
243 ACPI NVS memory during suspend/hibernation and resume.
244 sci_force_enable causes the kernel to set SCI_EN directly
245 on resume from S1/S3 (which is against the ACPI spec,
246 but some broken systems don't work without it).
247 nobl causes the internal blacklist of systems known to
248 behave incorrectly in some ways with respect to system
249 suspend and resume to be ignored (use wisely).
251 acpi_use_timer_override [HW,ACPI]
252 Use timer override. For some broken Nvidia NF5 boards
253 that require a timer override, but don't have HPET
255 add_efi_memmap [EFI; X86] Include EFI memory map in
256 kernel's map of available physical RAM.
259 { off | try_unsupported }
260 off: disable AGP support
261 try_unsupported: try to drive unsupported chipsets
262 (may crash computer or cause data corruption)
265 See Documentation/sound/alsa-configuration.rst
268 Allow the default userspace alignment fault handler
269 behaviour to be specified. Bit 0 enables warnings,
270 bit 1 enables fixups, and bit 2 sends a segfault.
272 align_va_addr= [X86-64]
273 Align virtual addresses by clearing slice [14:12] when
274 allocating a VMA at process creation time. This option
275 gives you up to 3% performance improvement on AMD F15h
276 machines (where it is enabled by default) for a
277 CPU-intensive style benchmark, and it can vary highly in
278 a microbenchmark depending on workload and compiler.
280 32: only for 32-bit processes
281 64: only for 64-bit processes
282 on: enable for both 32- and 64-bit processes
283 off: disable for both 32- and 64-bit processes
285 alloc_snapshot [FTRACE]
286 Allocate the ftrace snapshot buffer on boot up when the
287 main buffer is allocated. This is handy if debugging
288 and you need to use tracing_snapshot() on boot up, and
289 do not want to use tracing_snapshot_alloc() as it needs
290 to be done where GFP_KERNEL allocations are allowed.
292 amd_iommu= [HW,X86-64]
293 Pass parameters to the AMD IOMMU driver in the system.
295 fullflush - enable flushing of IO/TLB entries when
296 they are unmapped. Otherwise they are
297 flushed before they will be reused, which
299 off - do not initialize any AMD IOMMU found in
301 force_isolation - Force device isolation for all
302 devices. The IOMMU driver is not
303 allowed anymore to lift isolation
304 requirements as needed. This option
305 does not override iommu=pt
307 amd_iommu_dump= [HW,X86-64]
308 Enable AMD IOMMU driver option to dump the ACPI table
309 for AMD IOMMU. With this option enabled, AMD IOMMU
310 driver will print ACPI tables for AMD IOMMU during
311 IOMMU initialization.
313 amd_iommu_intr= [HW,X86-64]
314 Specifies one of the following AMD IOMMU interrupt
316 legacy - Use legacy interrupt remapping mode.
317 vapic - Use virtual APIC mode, which allows IOMMU
318 to inject interrupts directly into guest.
319 This mode requires kvm-amd.avic=1.
320 (Default when IOMMU HW support is present.)
322 amijoy.map= [HW,JOY] Amiga joystick support
323 Map of devices attached to JOY0DAT and JOY1DAT
325 See also Documentation/input/joydev/joystick.rst
327 analog.map= [HW,JOY] Analog joystick and gamepad support
328 Specifies type or capabilities of an analog joystick
329 connected to one of 16 gameports
330 Format: <type1>,<type2>,..<type16>
333 Power management functions (SPARCstation-4/5 + deriv.)
335 Disable APC CPU standby support. SPARCstation-Fox does
336 not play well with APC CPU idle - disable it if you have
337 APC and your system crashes randomly.
339 apic= [APIC,X86] Advanced Programmable Interrupt Controller
340 Change the output verbosity while booting
341 Format: { quiet (default) | verbose | debug }
342 Change the amount of debugging information output
343 when initialising the APIC and IO-APIC components.
344 For X86-32, this can also be used to specify an APIC
346 Format: apic=driver_name
347 Examples: apic=bigsmp
349 apic_extnmi= [APIC,X86] External NMI delivery setting
350 Format: { bsp (default) | all | none }
351 bsp: External NMI is delivered only to CPU 0
352 all: External NMIs are broadcast to all CPUs as a
354 none: External NMI is masked for all CPUs. This is
355 useful so that a dump capture kernel won't be
359 See Documentation/networking/ipv6.txt.
361 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
362 Limit apic dumping. The parameter defines the maximal
363 number of local apics being dumped. Also it is possible
364 to set it to "all" by meaning -- no limit here.
365 Format: { 1 (default) | 2 | ... | all }.
366 The parameter valid if only apic=debug or
367 apic=verbose is specified.
368 Example: apic=debug show_lapic=all
370 apm= [APM] Advanced Power Management
371 See header of arch/x86/kernel/apm_32.c.
373 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
374 Format: <io>,<irq>,<nodeID>
378 atarimouse= [HW,MOUSE] Atari Mouse
380 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
381 EzKey and similar keyboards
383 atkbd.reset= [HW] Reset keyboard during initialization
385 atkbd.set= [HW] Select keyboard code set
386 Format: <int> (2 = AT (default), 3 = PS/2)
388 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
391 atkbd.softraw= [HW] Choose between synthetic and real raw mode
392 Format: <bool> (0 = real, 1 = synthetic (default))
394 atkbd.softrepeat= [HW]
395 Use software keyboard repeat
397 audit= [KNL] Enable the audit sub-system
398 Format: { "0" | "1" | "off" | "on" }
399 0 | off - kernel audit is disabled and can not be
400 enabled until the next reboot
401 unset - kernel audit is initialized but disabled and
402 will be fully enabled by the userspace auditd.
403 1 | on - kernel audit is initialized and partially
404 enabled, storing at most audit_backlog_limit
405 messages in RAM until it is fully enabled by the
409 audit_backlog_limit= [KNL] Set the audit queue size limit.
410 Format: <int> (must be >=0)
413 bau= [X86_UV] Enable the BAU on SGI UV. The default
414 behavior is to disable the BAU (i.e. bau=0).
415 Format: { "0" | "1" }
418 unset - Disable the BAU.
420 baycom_epp= [HW,AX25]
423 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
425 See header of drivers/net/hamradio/baycom_par.c.
427 baycom_ser_fdx= [HW,AX25]
428 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
429 Format: <io>,<irq>,<mode>[,<baud>]
430 See header of drivers/net/hamradio/baycom_ser_fdx.c.
432 baycom_ser_hdx= [HW,AX25]
433 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
434 Format: <io>,<irq>,<mode>
435 See header of drivers/net/hamradio/baycom_ser_hdx.c.
437 blkdevparts= Manual partition parsing of block device(s) for
438 embedded devices based on command line input.
439 See Documentation/block/cmdline-partition.rst
441 boot_delay= Milliseconds to delay each printk during boot.
442 Values larger than 10 seconds (10000) are changed to
447 Extended command line options can be added to an initrd
448 and this will cause the kernel to look for it.
450 See Documentation/admin-guide/bootconfig.rst
453 Disable BERT OS support on buggy BIOSes.
455 bgrt_disable [ACPI][X86]
456 Disable BGRT to avoid flickering OEM logo.
458 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
459 bttv.radio= Most important insmod options are available as
461 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
464 bulk_remove=off [PPC] This parameter disables the use of the pSeries
465 firmware feature for flushing multiple hpte entries
468 c101= [NET] Moxa C101 synchronous serial card
470 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
471 Sometimes CPU hardware bugs make them report the cache
472 size incorrectly. The kernel will attempt work arounds
473 to fix known problems, but for some CPUs it is not
474 possible to determine what the correct size should be.
475 This option provides an override for these situations.
478 [NET] Specifies amount of time (in seconds) that
479 the kernel should wait for a network carrier. By default
480 it waits 120 seconds.
482 ca_keys= [KEYS] This parameter identifies a specific key(s) on
483 the system trusted keyring to be used for certificate
485 format: { id:<keyid> | builtin }
487 cca= [MIPS] Override the kernel pages' cache coherency
488 algorithm. Accepted values range from 0 to 7
489 inclusive. See arch/mips/include/asm/pgtable-bits.h
490 for platform specific values (SB1, Loongson3 and
493 ccw_timeout_log [S390]
494 See Documentation/s390/common_io.rst for details.
496 cgroup_disable= [KNL] Disable a particular controller
497 Format: {name of the controller(s) to disable}
498 The effects of cgroup_disable=foo are:
499 - foo isn't auto-mounted if you mount all cgroups in
501 - foo isn't visible as an individually mountable
503 {Currently only "memory" controller deal with this and
504 cut the overhead, others just disable the usage. So
505 only cgroup_disable=memory is actually worthy}
507 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
508 Format: { { controller | "all" | "named" }
509 [,{ controller | "all" | "named" }...] }
510 Like cgroup_disable, but only applies to cgroup v1;
511 the blacklisted controllers remain available in cgroup2.
512 "all" blacklists all controllers and "named" disables
513 named mounts. Specifying both "all" and "named" disables
516 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
518 nosocket -- Disable socket memory accounting.
519 nokmem -- Disable kernel memory accounting.
521 checkreqprot [SELINUX] Set initial checkreqprot flag value.
522 Format: { "0" | "1" }
523 See security/selinux/Kconfig help text.
524 0 -- check protection applied by kernel (includes
525 any implied execute protection).
526 1 -- check protection requested by application.
527 Default value is set via a kernel config option.
528 Value can be changed at runtime via
529 /sys/fs/selinux/checkreqprot.
530 Setting checkreqprot to 1 is deprecated.
533 See Documentation/s390/common_io.rst for details.
536 Prevents the clock framework from automatically gating
537 clocks that have not been explicitly enabled by a Linux
538 device driver but are enabled in hardware at reset or
539 by the bootloader/firmware. Note that this does not
540 force such clocks to be always-on nor does it reserve
541 those clocks in any way. This parameter is useful for
542 debug and development, but should not be needed on a
543 platform with proper driver support. For more
544 information, see Documentation/driver-api/clk.rst.
546 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
548 Forces specified clocksource (if available) to be used
549 when calculating gettimeofday(). If specified
550 clocksource is not available, it defaults to PIT.
551 Format: { pit | tsc | cyclone | pmtmr }
553 clocksource= Override the default clocksource
555 Override the default clocksource and use the clocksource
556 with the name specified.
557 Some clocksource names to choose from, depending on
559 [all] jiffies (this is the base, fallback clocksource)
561 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
562 pxa_timer,timer3,32k_counter,timer0_1
563 [X86-32] pit,hpet,tsc;
564 scx200_hrt on Geode; cyclone on IBM x440
572 clocksource.arm_arch_timer.evtstrm=
575 Enable/disable the eventstream feature of the ARM
576 architected timer so that code using WFE-based polling
577 loops can be debugged more effectively on production
580 clearcpuid=BITNUM [X86]
581 Disable CPUID feature X for the kernel. See
582 arch/x86/include/asm/cpufeatures.h for the valid bit
583 numbers. Note the Linux specific bits are not necessarily
584 stable over kernel options, but the vendor specific
586 Also note that user programs calling CPUID directly
587 or using the feature without checking anything
588 will still see it. This just prevents it from
589 being used by the kernel or shown in /proc/cpuinfo.
590 Also note the kernel might malfunction if you disable
593 cma=nn[MG]@[start[MG][-end[MG]]]
595 Sets the size of kernel global memory area for
596 contiguous memory allocations and optionally the
597 placement constraint by the physical address range of
598 memory allocations. A value of 0 disables CMA
599 altogether. For more information, see
600 include/linux/dma-contiguous.h
602 cmo_free_hint= [PPC] Format: { yes | no }
603 Specify whether pages are marked as being inactive
604 when they are freed. This is used in CMO environments
605 to determine OS memory pressure for page stealing by
609 coherent_pool=nn[KMG] [ARM,KNL]
610 Sets the size of memory pool for coherent, atomic dma
611 allocations, by default set to 256K.
613 com20020= [HW,NET] ARCnet - COM20020 chipset
615 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
617 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
621 ARCnet - COM90xx chipset (memory-mapped buffers)
622 Format: <io>[,<irq>[,<memstart>]]
624 condev= [HW,S390] console device
627 console= [KNL] Output console device and options.
629 tty<n> Use the virtual console device <n>.
633 Use the specified serial port. The options are of
634 the form "bbbbpnf", where "bbbb" is the baud rate,
635 "p" is parity ("n", "o", or "e"), "n" is number of
636 bits, and "f" is flow control ("r" for RTS or
637 omit it). Default is "9600n8".
639 See Documentation/admin-guide/serial-console.rst for more
641 Documentation/networking/netconsole.txt for an
644 uart[8250],io,<addr>[,options]
645 uart[8250],mmio,<addr>[,options]
646 uart[8250],mmio16,<addr>[,options]
647 uart[8250],mmio32,<addr>[,options]
648 uart[8250],0x<addr>[,options]
649 Start an early, polled-mode console on the 8250/16550
650 UART at the specified I/O port or MMIO address,
651 switching to the matching ttyS device later.
652 MMIO inter-register address stride is either 8-bit
653 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
654 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
655 to be equivalent to 'mmio'. 'options' are specified in
656 the same format described for ttyS above; if unspecified,
657 the h/w is not re-initialized.
659 hvc<n> Use the hypervisor console device <n>. This is for
660 both Xen and PowerPC hypervisors.
662 If the device connected to the port is not a TTY but a braille
663 device, prepend "brl," before the device type, for instance
665 For now, only VisioBraille is supported.
668 [KNL] Change console messages format
670 By default we print messages on consoles in
671 "[time stamp] text\n" format (time stamp may not be
672 printed, depending on CONFIG_PRINTK_TIME or
673 `printk_time' param).
675 Switch to syslog format: "<%u>[time stamp] text\n"
676 IOW, each message will have a facility and loglevel
677 prefix. The format is similar to one used by syslog()
678 syscall, or to executing "dmesg -S --raw" or to reading
681 consoleblank= [KNL] The console blank (screen saver) timeout in
682 seconds. A value of 0 disables the blank timer.
686 [KNL] Change the default value for
687 /proc/<pid>/coredump_filter.
688 See also Documentation/filesystems/proc.txt.
690 coresight_cpu_debug.enable
693 Enable/disable the CPU sampling based debugging.
694 0: default value, disable debugging
695 1: enable debugging at boot time
697 cpuidle.off=1 [CPU_IDLE]
698 disable the cpuidle sub-system
701 [CPU_IDLE] Name of the cpuidle governor to use.
703 cpufreq.off=1 [CPU_FREQ]
704 disable the cpufreq sub-system
707 [X86] Delay for N microsec between assert and de-assert
708 of APIC INIT to start processors. This delay occurs
709 on every CPU online, such as boot, and resume from suspend.
712 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
714 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
716 crashkernel=size[KMG][@offset[KMG]]
717 [KNL] Using kexec, Linux can switch to a 'crash kernel'
718 upon panic. This parameter reserves the physical
719 memory region [offset, offset + size] for that kernel
720 image. If '@offset' is omitted, then a suitable offset
721 is selected automatically.
722 [KNL, x86_64] select a region under 4G first, and
723 fall back to reserve region above 4G when '@offset'
724 hasn't been specified.
725 See Documentation/admin-guide/kdump/kdump.rst for further details.
727 crashkernel=range1:size1[,range2:size2,...][@offset]
728 [KNL] Same as above, but depends on the memory
729 in the running system. The syntax of range is
730 start-[end] where start and end are both
731 a memory unit (amount[KMG]). See also
732 Documentation/admin-guide/kdump/kdump.rst for an example.
734 crashkernel=size[KMG],high
735 [KNL, x86_64] range could be above 4G. Allow kernel
736 to allocate physical memory region from top, so could
737 be above 4G if system have more than 4G ram installed.
738 Otherwise memory region will be allocated below 4G, if
740 It will be ignored if crashkernel=X is specified.
741 crashkernel=size[KMG],low
742 [KNL, x86_64] range under 4G. When crashkernel=X,high
743 is passed, kernel could allocate physical memory region
744 above 4G, that cause second kernel crash on system
745 that require some amount of low memory, e.g. swiotlb
746 requires at least 64M+32K low memory, also enough extra
747 low memory is needed to make sure DMA buffers for 32-bit
748 devices won't run out. Kernel would try to allocate at
749 at least 256M below 4G automatically.
750 This one let user to specify own low range under 4G
751 for second kernel instead.
752 0: to disable low allocation.
753 It will be ignored when crashkernel=X,high is not used
754 or memory reserved is below 4G.
757 [KNL] Disable crypto self-tests
762 cs89x0_media= [HW,NET]
763 Format: { rj45 | aui | bnc }
766 See header of drivers/s390/block/dasd_devmap.c.
768 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
769 (one device per port)
770 Format: <port#>,<type>
771 See also Documentation/input/devices/joystick-parport.rst
773 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
775 Documentation/admin-guide/dynamic-debug-howto.rst for
776 details. Deprecated, see dyndbg.
778 debug [KNL] Enable kernel debugging (events log level).
781 [KNL] Enable printing [hashed] pointers early in the
782 boot sequence. If enabled, we use a weak hash instead
783 of siphash to hash pointers. Use this option if you are
784 seeing instances of '(___ptrval___)') and need to see a
785 value (hashed pointer) instead. Cryptographically
786 insecure, please do not use on production kernels.
789 [KNL] verbose self-tests
791 Print debugging info while doing the locking API
793 We default to 0 (no extra messages), setting it to
794 1 will print _a lot_ more information - normally
795 only useful to kernel developers.
797 debug_objects [KNL] Enable object debugging
800 [KNL] Disable object debugging
802 debug_guardpage_minorder=
803 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
804 parameter allows control of the order of pages that will
805 be intentionally kept free (and hence protected) by the
806 buddy allocator. Bigger value increase the probability
807 of catching random memory corruption, but reduce the
808 amount of memory for normal system use. The maximum
809 possible value is MAX_ORDER/2. Setting this parameter
810 to 1 or 2 should be enough to identify most random
811 memory corruption problems caused by bugs in kernel or
812 driver code when a CPU writes to (or reads from) a
813 random memory location. Note that there exists a class
814 of memory corruptions problems caused by buggy H/W or
815 F/W or by drivers badly programing DMA (basically when
816 memory is written at bus level and the CPU MMU is
817 bypassed) which are not detectable by
818 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
819 tracking down these problems.
822 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
823 enables the feature at boot time. By default, it is
824 disabled and the system will work mostly the same as a
825 kernel built without CONFIG_DEBUG_PAGEALLOC.
826 Note: to get most of debug_pagealloc error reports, it's
827 useful to also enable the page_owner functionality.
828 on: enable the feature
830 debugpat [X86] Enable PAT debugging
832 decnet.addr= [HW,NET]
833 Format: <area>[,<node>]
834 See also Documentation/networking/decnet.txt.
837 [same as hugepagesz=] The size of the default
838 HugeTLB page size. This is the size represented by
839 the legacy /proc/ hugepages APIs, used for SHM, and
840 default size when mounting hugetlbfs filesystems.
841 Defaults to the default architecture's huge page size
844 deferred_probe_timeout=
845 [KNL] Debugging option to set a timeout in seconds for
846 deferred probe to give up waiting on dependencies to
847 probe. Only specific dependencies (subsystems or
848 drivers) that have opted in will be ignored. A timeout of 0
849 will timeout at the end of initcalls. This option will also
850 dump out devices still on the deferred probe list after
854 Format: { on | off | def_only | inf_only | always }
855 on: s390 zlib hardware support for compression on
856 level 1 and decompression (default)
857 off: No s390 zlib hardware support
858 def_only: s390 zlib hardware support for deflate
859 only (compression on level 1)
860 inf_only: s390 zlib hardware support for inflate
862 always: Same as 'on' but ignores the selected compression
863 level always using hardware support (used for debugging)
866 Set number of hash buckets for dentry cache.
868 disable_1tb_segments [PPC]
869 Disables the use of 1TB hash page table segments. This
870 causes the kernel to fall back to 256MB segments which
871 can be useful when debugging issues that require an SLB
875 See Documentation/networking/ipv6.txt.
878 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
879 hardening is enabled for this boot. Hardened
880 usercopy checking is used to protect the kernel
881 from reading or writing beyond known memory
882 allocation boundaries as a proactive defense
883 against bounds-checking flaws in the kernel's
884 copy_to_user()/copy_from_user() interface.
885 on Perform hardened usercopy checks (default).
886 off Disable hardened usercopy checks.
889 Disable RADIX MMU mode on POWER9
892 Disable TLBIE instruction. Currently does not work
893 with KVM, with HASH MMU, or with coherent accelerators.
895 disable_cpu_apicid= [X86,APIC,SMP]
897 The number of initial APIC ID for the
898 corresponding CPU to be disabled at boot,
899 mostly used for the kdump 2nd kernel to
900 disable BSP to wake up multiple CPUs without
901 causing system reset or hang due to sending
904 perf_v4_pmi= [X86,INTEL]
906 Disable Intel PMU counter freezing feature.
907 The feature only exists starting from
908 Arch Perfmon v4 (Skylake and newer).
910 disable_ddw [PPC/PSERIES]
911 Disable Dynamic DMA Window support. Use this if
912 to workaround buggy firmware.
915 See Documentation/networking/ipv6.txt.
917 disable_mtrr_cleanup [X86]
918 The kernel tries to adjust MTRR layout from continuous
919 to discrete, to make X server driver able to add WB
920 entry later. This parameter disables that.
922 disable_mtrr_trim [X86, Intel and AMD only]
923 By default the kernel will trim any uncacheable
924 memory out of your available memory pool based on
925 MTRR settings. This parameter disables that behavior,
926 possibly causing your machine to run very slowly.
928 disable_timer_pin_1 [X86]
929 Disable PIN 1 of APIC timer
930 Can be useful to work around chipset bugs.
932 dis_ucode_ldr [X86] Disable the microcode loader.
934 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
935 this option disables the debugging code at boot.
937 dma_debug_entries=<number>
938 This option allows to tune the number of preallocated
939 entries for DMA-API debugging code. One entry is
940 required per DMA-API allocation. Use this if the
941 DMA-API debugging code disables itself because the
942 architectural default is too low.
944 dma_debug_driver=<driver_name>
945 With this option the DMA-API debugging driver
946 filter feature can be enabled at boot time. Just
947 pass the driver to filter for as the parameter.
948 The filter can be disabled or changed to another
949 driver later using sysfs.
951 driver_async_probe= [KNL]
952 List of driver names to be probed asynchronously.
953 Format: <driver_name1>,<driver_name2>...
955 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
956 Broken monitors, graphic adapters, KVMs and EDIDless
957 panels may send no or incorrect EDID data sets.
958 This parameter allows to specify an EDID data sets
959 in the /lib/firmware directory that are used instead.
960 Generic built-in EDID data sets are used, if one of
961 edid/1024x768.bin, edid/1280x1024.bin,
962 edid/1680x1050.bin, or edid/1920x1080.bin is given
963 and no file with the same name exists. Details and
964 instructions how to build your own EDID data are
965 available in Documentation/driver-api/edid.rst. An EDID
966 data set will only be used for a particular connector,
967 if its name and a colon are prepended to the EDID
968 name. Each connector may use a unique EDID data
969 set by separating the files with a comma. An EDID
970 data set with no connector name will be used for
971 any connectors not explicitly specified.
976 Format: {"off" | "known"}
977 Control how the dt_cpu_ftrs device-tree binding is
978 used for CPU feature discovery and setup (if it
980 off: Do not use it, fall back to legacy cpu table.
981 known: Do not pass through unknown features to guests
982 or userspace, only those that the kernel is aware of.
984 dump_apple_properties [X86]
985 Dump name and content of EFI device properties on
986 x86 Macs. Useful for driver authors to determine
987 what data is available or for reverse-engineering.
989 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
990 module.dyndbg[="val"]
991 Enable debug messages at boot time. See
992 Documentation/admin-guide/dynamic-debug-howto.rst
995 nompx [X86] Disables Intel Memory Protection Extensions.
996 See Documentation/x86/intel_mpx.rst for more
997 information about the feature.
999 nopku [X86] Disable Memory Protection Keys CPU feature found
1002 module.async_probe [KNL]
1003 Enable asynchronous probe on this module.
1005 early_ioremap_debug [KNL]
1006 Enable debug messages in early_ioremap support. This
1007 is useful for tracking down temporary early mappings
1008 which are not unmapped.
1010 earlycon= [KNL] Output early console device and options.
1012 When used with no options, the early console is
1013 determined by stdout-path property in device tree's
1014 chosen node or the ACPI SPCR table if supported by
1017 cdns,<addr>[,options]
1018 Start an early, polled-mode console on a Cadence
1019 (xuartps) serial port at the specified address. Only
1020 supported option is baud rate. If baud rate is not
1021 specified, the serial port must already be setup and
1024 uart[8250],io,<addr>[,options]
1025 uart[8250],mmio,<addr>[,options]
1026 uart[8250],mmio32,<addr>[,options]
1027 uart[8250],mmio32be,<addr>[,options]
1028 uart[8250],0x<addr>[,options]
1029 Start an early, polled-mode console on the 8250/16550
1030 UART at the specified I/O port or MMIO address.
1031 MMIO inter-register address stride is either 8-bit
1032 (mmio) or 32-bit (mmio32 or mmio32be).
1033 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1034 to be equivalent to 'mmio'. 'options' are specified
1035 in the same format described for "console=ttyS<n>"; if
1036 unspecified, the h/w is not initialized.
1040 Start an early, polled-mode console on a pl011 serial
1041 port at the specified address. The pl011 serial port
1042 must already be setup and configured. Options are not
1043 yet supported. If 'mmio32' is specified, then only
1044 the driver will use only 32-bit accessors to read/write
1045 the device registers.
1048 Start an early, polled-mode console on a meson serial
1049 port at the specified address. The serial port must
1050 already be setup and configured. Options are not yet
1054 Start an early, polled-mode console on an msm serial
1055 port at the specified address. The serial port
1056 must already be setup and configured. Options are not
1059 msm_serial_dm,<addr>
1060 Start an early, polled-mode console on an msm serial
1061 dm port at the specified address. The serial port
1062 must already be setup and configured. Options are not
1066 Start an early, polled-mode console on a serial port
1067 of an Actions Semi SoC, such as S500 or S900, at the
1068 specified address. The serial port must already be
1069 setup and configured. Options are not yet supported.
1072 Start an early, polled-mode console on a serial port
1073 of an RDA Micro SoC, such as RDA8810PL, at the
1074 specified address. The serial port must already be
1075 setup and configured. Options are not yet supported.
1078 Use RISC-V SBI (Supervisor Binary Interface) for early
1081 smh Use ARM semihosting calls for early console.
1089 Use early console provided by serial driver available
1090 on Samsung SoCs, requires selecting proper type and
1091 a correct base address of the selected UART port. The
1092 serial port must already be setup and configured.
1093 Options are not yet supported.
1096 Start an early, polled-mode console on a lantiq serial
1097 (lqasc) port at the specified address. The serial port
1098 must already be setup and configured. Options are not
1103 Use early console provided by Freescale LP UART driver
1104 found on Freescale Vybrid and QorIQ LS1021A processors.
1105 A valid base address must be provided, and the serial
1106 port must already be setup and configured.
1110 Start an early, polled-mode, output-only console on the
1111 Freescale i.MX UART at the specified address. The UART
1112 must already be setup and configured.
1115 Start an early, polled-mode console on the
1116 Armada 3700 serial port at the specified
1117 address. The serial port must already be setup
1118 and configured. Options are not yet supported.
1121 Start an early, polled-mode console on a Qualcomm
1122 Generic Interface (GENI) based serial port at the
1123 specified address. The serial port must already be
1124 setup and configured. Options are not yet supported.
1127 Start an early, unaccelerated console on the EFI
1128 memory mapped framebuffer (if available). On cache
1129 coherent non-x86 systems that use system memory for
1130 the framebuffer, pass the 'ram' option so that it is
1131 mapped with the correct attributes.
1134 Use early console provided by Freescale LINFlexD UART
1135 serial driver for NXP S32V234 SoCs. A valid base
1136 address must be provided, and the serial port must
1137 already be setup and configured.
1139 earlyprintk= [X86,SH,ARM,M68k,S390]
1143 earlyprintk=serial[,ttySn[,baudrate]]
1144 earlyprintk=serial[,0x...[,baudrate]]
1145 earlyprintk=ttySn[,baudrate]
1146 earlyprintk=dbgp[debugController#]
1147 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1148 earlyprintk=xdbc[xhciController#]
1150 earlyprintk is useful when the kernel crashes before
1151 the normal console is initialized. It is not enabled by
1152 default because it has some cosmetic problems.
1154 Append ",keep" to not disable it when the real console
1157 Only one of vga, efi, serial, or usb debug port can
1160 Currently only ttyS0 and ttyS1 may be specified by
1161 name. Other I/O ports may be explicitly specified
1162 on some architectures (x86 and arm at least) by
1163 replacing ttySn with an I/O port address, like this:
1164 earlyprintk=serial,0x1008,115200
1165 You can find the port for a given device in
1166 /proc/tty/driver/serial:
1167 2: uart:ST16650V2 port:00001008 irq:18 ...
1169 Interaction with the standard serial driver is not
1172 The VGA and EFI output is eventually overwritten by
1175 The xen output can only be used by Xen PV guests.
1177 The sclp output can only be used on s390.
1179 The optional "force" to "pciserial" enables use of a
1180 PCI device even when its classcode is not of the
1183 edac_report= [HW,EDAC] Control how to report EDAC event
1184 Format: {"on" | "off" | "force"}
1185 on: enable EDAC to report H/W event. May be overridden
1186 by other higher priority error reporting module.
1187 off: disable H/W event reporting through EDAC.
1188 force: enforce the use of EDAC to report H/W event.
1191 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1194 This is designed to be used in conjunction with
1195 the boot argument: earlyprintk=vga
1198 Format: {"off" | "on" | "skip[mbr]"}
1201 Format: { "old_map", "nochunk", "noruntime", "debug",
1202 "nosoftreserve", "disable_early_pci_dma",
1203 "no_disable_early_pci_dma" }
1204 old_map [X86-64]: switch to the old ioremap-based EFI
1205 runtime services mapping. [Needs CONFIG_X86_UV=y]
1206 nochunk: disable reading files in "chunks" in the EFI
1207 boot stub, as chunking can cause problems with some
1208 firmware implementations.
1209 noruntime : disable EFI runtime services support
1210 debug: enable misc debug output
1211 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1212 attribute may cause the kernel to reserve the
1213 memory range for a memory mapping driver to
1214 claim. Specify efi=nosoftreserve to disable this
1215 reservation and treat the memory by its base type
1216 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1217 disable_early_pci_dma: Disable the busmaster bit on all
1218 PCI bridges while in the EFI boot stub
1219 no_disable_early_pci_dma: Leave the busmaster bit set
1220 on all PCI bridges while in the EFI boot stub
1222 efi_no_storage_paranoia [EFI; X86]
1223 Using this parameter you can use more than 50% of
1224 your efi variable storage. Use this parameter only if
1225 you are really sure that your UEFI does sane gc and
1226 fulfills the spec otherwise your board may brick.
1228 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1229 Add arbitrary attribute to specific memory range by
1230 updating original EFI memory map.
1231 Region of memory which aa attribute is added to is
1234 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1235 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1236 attribute is added to range 0x100000000-0x180000000 and
1237 0x10a0000000-0x1120000000.
1239 If efi_fake_mem=8G@9G:0x40000 is specified, the
1240 EFI_MEMORY_SP(0x40000) attribute is added to
1241 range 0x240000000-0x43fffffff.
1243 Using this parameter you can do debugging of EFI memmap
1244 related features. For example, you can do debugging of
1245 Address Range Mirroring feature even if your box
1246 doesn't support it, or mark specific memory as
1249 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1250 that is to be dynamically loaded by Linux. If there are
1251 multiple variables with the same name but with different
1252 vendor GUIDs, all of them will be loaded. See
1253 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1256 eisa_irq_edge= [PARISC,HW]
1257 See header of drivers/parisc/eisa.c.
1260 See comment before function elanfreq_setup() in
1261 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1263 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1264 Specifies physical address of start of kernel core
1265 image elf header and optionally the size. Generally
1266 kexec loader will pass this option to capture kernel.
1267 See Documentation/admin-guide/kdump/kdump.rst for details.
1269 enable_mtrr_cleanup [X86]
1270 The kernel tries to adjust MTRR layout from continuous
1271 to discrete, to make X server driver able to add WB
1272 entry later. This parameter enables that.
1274 enable_timer_pin_1 [X86]
1275 Enable PIN 1 of APIC timer
1276 Can be useful to work around chipset bugs
1277 (in particular on some ATI chipsets).
1278 The kernel tries to set a reasonable default.
1280 enforcing [SELINUX] Set initial enforcing status.
1282 See security/selinux/Kconfig help text.
1283 0 -- permissive (log only, no denials).
1284 1 -- enforcing (deny and log).
1286 Value can be changed at runtime via
1287 /sys/fs/selinux/enforce.
1290 Disable Error Record Serialization Table (ERST)
1293 ether= [HW,NET] Ethernet cards parameters
1294 This option is obsoleted by the "netdev=" option, which
1295 has equivalent usage. See its documentation for details.
1299 Permit 'security.evm' to be updated regardless of
1300 current integrity status.
1304 fail_make_request=[KNL]
1305 General fault injection mechanism.
1306 Format: <interval>,<probability>,<space>,<times>
1307 See also Documentation/fault-injection/.
1310 See Documentation/admin-guide/blockdev/floppy.rst.
1312 force_pal_cache_flush
1313 [IA-64] Avoid check_sal_cache_flush which may hang on
1314 buggy SAL_CACHE_FLUSH implementations. Using this
1315 parameter will force ia64_sal_cache_flush to call
1316 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1319 Forcefully enable Physical Address Extension (PAE).
1320 Many Pentium M systems disable PAE but may have a
1321 functionally usable PAE implementation.
1322 Warning: use of this parameter will taint the kernel
1323 and may cause unknown problems.
1326 [FTRACE] will set and start the specified tracer
1327 as early as possible in order to facilitate early
1330 ftrace_dump_on_oops[=orig_cpu]
1331 [FTRACE] will dump the trace buffers on oops.
1332 If no parameter is passed, ftrace will dump
1333 buffers of all CPUs, but if you pass orig_cpu, it will
1334 dump only the buffer of the CPU that triggered the
1337 ftrace_filter=[function-list]
1338 [FTRACE] Limit the functions traced by the function
1339 tracer at boot up. function-list is a comma separated
1340 list of functions. This list can be changed at run
1341 time by the set_ftrace_filter file in the debugfs
1344 ftrace_notrace=[function-list]
1345 [FTRACE] Do not trace the functions specified in
1346 function-list. This list can be changed at run time
1347 by the set_ftrace_notrace file in the debugfs
1350 ftrace_graph_filter=[function-list]
1351 [FTRACE] Limit the top level callers functions traced
1352 by the function graph tracer at boot up.
1353 function-list is a comma separated list of functions
1354 that can be changed at run time by the
1355 set_graph_function file in the debugfs tracing directory.
1357 ftrace_graph_notrace=[function-list]
1358 [FTRACE] Do not trace from the functions specified in
1359 function-list. This list is a comma separated list of
1360 functions that can be changed at run time by the
1361 set_graph_notrace file in the debugfs tracing directory.
1363 ftrace_graph_max_depth=<uint>
1364 [FTRACE] Used with the function graph tracer. This is
1365 the max depth it will trace into a function. This value
1366 can be changed at run time by the max_graph_depth file
1367 in the tracefs tracing directory. default: 0 (no limit)
1369 fw_devlink= [KNL] Create device links between consumer and supplier
1370 devices by scanning the firmware to infer the
1371 consumer/supplier relationships. This feature is
1372 especially useful when drivers are loaded as modules as
1373 it ensures proper ordering of tasks like device probing
1374 (suppliers first, then consumers), supplier boot state
1375 clean up (only after all consumers have probed),
1376 suspend/resume & runtime PM (consumers first, then
1378 Format: { off | permissive | on | rpm }
1379 off -- Don't create device links from firmware info.
1380 permissive -- Create device links from firmware info
1381 but use it only for ordering boot state clean
1382 up (sync_state() calls).
1383 on -- Create device links from firmware info and use it
1384 to enforce probe and suspend/resume ordering.
1385 rpm -- Like "on", but also use to order runtime PM.
1388 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1389 support via parallel port (up to 5 devices per port)
1390 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1391 See also Documentation/input/devices/joystick-parport.rst
1395 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1399 gcov_persist= [GCOV] When non-zero (default), profiling data for
1400 kernel modules is saved and remains accessible via
1401 debugfs, even when the module is unloaded/reloaded.
1402 When zero, profiling data is discarded and associated
1403 debugfs files are removed at module unload time.
1405 goldfish [X86] Enable the goldfish android emulator platform.
1406 Don't use this when you are not running on the
1409 gpt [EFI] Forces disk with valid GPT signature but
1410 invalid Protective MBR to be treated as GPT. If the
1411 primary GPT is corrupted, it enables the backup/alternate
1412 GPT to be used instead.
1414 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1415 the "Enable 0" bit of the configuration register.
1418 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1419 the "Enable 0" bit of the configuration register.
1422 grcan.select= [HW] Select which physical interface to use.
1425 grcan.txsize= [HW] Sets the size of the tx buffer.
1426 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1428 grcan.rxsize= [HW] Sets the size of the rx buffer.
1429 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1432 gpio-mockup.gpio_mockup_ranges
1433 [HW] Sets the ranges of gpiochip of for this device.
1434 Format: <start1>,<end1>,<start2>,<end2>...
1436 hardlockup_all_cpu_backtrace=
1437 [KNL] Should the hard-lockup detector generate
1438 backtraces on all cpus.
1441 hashdist= [KNL,NUMA] Large hashes allocated during boot
1442 are distributed across NUMA nodes. Defaults on
1443 for 64-bit NUMA, off otherwise.
1444 Format: 0 | 1 (for off | on)
1446 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1448 hd= [EIDE] (E)IDE hard drive subsystem geometry
1449 Format: <cyl>,<head>,<sect>
1452 Disable Hardware Error Source Table (HEST) support;
1453 corresponding firmware-first mode error processing
1454 logic will be disabled.
1456 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1457 size of <nn>. This works even on boxes that have no
1458 highmem otherwise. This also works to reduce highmem
1459 size on bigger boxes.
1461 highres= [KNL] Enable/disable high resolution timer mode.
1462 Valid parameters: "on", "off"
1467 hpet= [X86-32,HPET] option to control HPET usage
1468 Format: { enable (default) | disable | force |
1470 disable: disable HPET and use PIT instead
1471 force: allow force enabled of undocumented chips (ICH4,
1473 verbose: show contents of HPET registers during setup
1475 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1476 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1478 hugetlb_cma= [HW] The size of a cma area used for allocation
1479 of gigantic hugepages.
1482 Reserve a cma area of given size and allocate gigantic
1483 hugepages using the cma allocator. If enabled, the
1484 boot-time allocation of gigantic hugepages is skipped.
1486 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1487 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1488 On x86-64 and powerpc, this option can be specified
1489 multiple times interleaved with hugepages= to reserve
1490 huge pages of different sizes. Valid pages sizes on
1491 x86-64 are 2M (when the CPU supports "pse") and 1G
1492 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1495 [KNL] Should the hung task detector generate panics.
1498 A nonzero value instructs the kernel to panic when a
1499 hung task is detected. The default value is controlled
1500 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1501 option. The value selected by this boot parameter can
1502 be changed later by the kernel.hung_task_panic sysctl.
1504 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1505 terminal devices. Valid values: 0..8
1506 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1507 If specified, z/VM IUCV HVC accepts connections
1508 from listed z/VM user IDs only.
1510 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1511 which allow the hypervisor to 'idle' the
1512 guest on lock contention.
1515 Do not unregister boot console at start. This is only
1516 useful for debugging when something happens in the window
1517 between unregistering the boot console and initializing
1520 i2c_bus= [HW] Override the default board specific I2C bus speed
1521 or register an additional I2C bus that is not
1522 registered from board initialization code.
1526 i8042.debug [HW] Toggle i8042 debug mode
1527 i8042.unmask_kbd_data
1528 [HW] Enable printing of interrupt data from the KBD port
1529 (disabled by default, and as a pre-condition
1530 requires that i8042.debug=1 be enabled)
1531 i8042.direct [HW] Put keyboard port into non-translated mode
1532 i8042.dumbkbd [HW] Pretend that controller can only read data from
1533 keyboard and cannot control its state
1534 (Don't attempt to blink the leds)
1535 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1536 i8042.nokbd [HW] Don't check/create keyboard port
1537 i8042.noloop [HW] Disable the AUX Loopback command while probing
1539 i8042.nomux [HW] Don't check presence of an active multiplexing
1541 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1543 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1544 i8042.reset [HW] Reset the controller during init, cleanup and
1545 suspend-to-ram transitions, only during s2r
1546 transitions, or never reset
1547 Format: { 1 | Y | y | 0 | N | n }
1548 1, Y, y: always reset controller
1549 0, N, n: don't ever reset controller
1550 Default: only on s2r transitions on x86; most other
1551 architectures force reset to be always executed
1552 i8042.unlock [HW] Unlock (ignore) the keylock
1553 i8042.kbdreset [HW] Reset device connected to KBD port
1557 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1558 indicates that the driver is running on unsupported
1560 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1561 does not match list of supported models.
1563 [HW] Report power status in /proc/i8k
1564 (disabled by default)
1565 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1568 i915.invert_brightness=
1569 [DRM] Invert the sense of the variable that is used to
1570 set the brightness of the panel backlight. Normally a
1571 brightness value of 0 indicates backlight switched off,
1572 and the maximum of the brightness value sets the backlight
1573 to maximum brightness. If this parameter is set to 0
1574 (default) and the machine requires it, or this parameter
1575 is set to 1, a brightness value of 0 sets the backlight
1576 to maximum brightness, and the maximum of the brightness
1577 value switches the backlight off.
1578 -1 -- never invert brightness
1579 0 -- machine default
1580 1 -- force brightness inversion
1583 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1585 ide-core.nodma= [HW] (E)IDE subsystem
1586 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1587 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1588 .cdrom .chs .ignore_cable are additional options
1589 See Documentation/ide/ide.rst.
1591 ide-generic.probe-mask= [HW] (E)IDE subsystem
1593 Probe mask for legacy ISA IDE ports. Depending on
1594 platform up to 6 ports are supported, enabled by
1595 setting corresponding bits in the mask to 1. The
1596 default value is 0x0, which has a special meaning.
1597 On systems that have PCI, it triggers scanning the
1598 PCI bus for the first and the second port, which
1599 are then probed. On systems without PCI the value
1600 of 0x0 enables probing the two first ports as if it
1603 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1604 Claim all unknown PCI IDE storage controllers.
1607 Format: idle=poll, idle=halt, idle=nomwait
1608 Poll forces a polling idle loop that can slightly
1609 improve the performance of waking up a idle CPU, but
1610 will use a lot of power and make the system run hot.
1612 idle=halt: Halt is forced to be used for CPU idle.
1613 In such case C2/C3 won't be used again.
1614 idle=nomwait: Disable mwait for CPU C-states
1616 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1617 Format: { strict | legacy | 2008 | relaxed }
1620 Choose which programs will be accepted for execution
1621 based on the IEEE 754 NaN encoding(s) supported by
1622 the FPU and the NaN encoding requested with the value
1623 of an ELF file header flag individually set by each
1624 binary. Hardware implementations are permitted to
1625 support either or both of the legacy and the 2008 NaN
1628 Available settings are as follows:
1629 strict accept binaries that request a NaN encoding
1630 supported by the FPU
1631 legacy only accept legacy-NaN binaries, if supported
1633 2008 only accept 2008-NaN binaries, if supported
1635 relaxed accept any binaries regardless of whether
1636 supported by the FPU
1638 The FPU emulator is always able to support both NaN
1639 encodings, so if no FPU hardware is present or it has
1640 been disabled with 'nofpu', then the settings of
1641 'legacy' and '2008' strap the emulator accordingly,
1642 'relaxed' straps the emulator for both legacy-NaN and
1643 2008-NaN, whereas 'strict' enables legacy-NaN only on
1644 legacy processors and both NaN encodings on MIPS32 or
1647 The setting for ABS.fmt/NEG.fmt instruction execution
1648 mode generally follows that for the NaN encoding,
1649 except where unsupported by hardware.
1651 ignore_loglevel [KNL]
1652 Ignore loglevel setting - this will print /all/
1653 kernel messages to the console. Useful for debugging.
1654 We also add it as printk module parameter, so users
1655 could change it dynamically, usually by
1656 /sys/module/printk/parameters/ignore_loglevel.
1659 Ignore RLIMIT_DATA setting for data mappings,
1660 print warning at first misuse. Can be changed via
1661 /sys/module/kernel/parameters/ignore_rlimit_data.
1663 ihash_entries= [KNL]
1664 Set number of hash buckets for inode cache.
1666 ima_appraise= [IMA] appraise integrity measurements
1667 Format: { "off" | "enforce" | "fix" | "log" }
1670 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1671 The builtin appraise policy appraises all files
1674 ima_canonical_fmt [IMA]
1675 Use the canonical format for the binary runtime
1676 measurements, instead of host native format.
1679 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1683 The list of supported hash algorithms is defined
1684 in crypto/hash_info.h.
1687 The builtin policies to load during IMA setup.
1688 Format: "tcb | appraise_tcb | secure_boot |
1691 The "tcb" policy measures all programs exec'd, files
1692 mmap'd for exec, and all files opened with the read
1693 mode bit set by either the effective uid (euid=0) or
1696 The "appraise_tcb" policy appraises the integrity of
1697 all files owned by root.
1699 The "secure_boot" policy appraises the integrity
1700 of files (eg. kexec kernel image, kernel modules,
1701 firmware, policy, etc) based on file signatures.
1703 The "fail_securely" policy forces file signature
1704 verification failure also on privileged mounted
1705 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1708 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1709 Load a policy which meets the needs of the Trusted
1710 Computing Base. This means IMA will measure all
1711 programs exec'd, files mmap'd for exec, and all files
1712 opened for read by uid=0.
1715 Select one of defined IMA measurements template formats.
1716 Formats: { "ima" | "ima-ng" | "ima-sig" }
1720 [IMA] Define a custom template format.
1721 Format: { "field1|...|fieldN" }
1723 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1724 Format: <min_file_size>
1725 Set the minimal file size for using asynchronous hash.
1726 If left unspecified, ahash usage is disabled.
1728 ahash performance varies for different data sizes on
1729 different crypto accelerators. This option can be used
1730 to achieve the best performance for a particular HW.
1732 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1734 Set hashing buffer size. Default: 4k.
1736 ahash performance varies for different chunk sizes on
1737 different crypto accelerators. This option can be used
1738 to achieve best performance for particular HW.
1742 Run specified binary instead of /sbin/init as init
1745 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1746 for working out where the kernel is dying during
1749 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1750 initcall functions. Useful for debugging built-in
1751 modules and initcalls.
1753 initrd= [BOOT] Specify the location of the initial ramdisk
1755 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1758 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1760 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1762 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1764 init_pkru= [x86] Specify the default memory protection keys rights
1765 register contents for all processes. 0x55555554 by
1766 default (disallow access to all but pkey 0). Can
1767 override in debugfs after boot.
1769 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1772 int_pln_enable [x86] Enable power limit notification interrupt
1774 integrity_audit=[IMA]
1775 Format: { "0" | "1" }
1776 0 -- basic integrity auditing messages. (Default)
1777 1 -- additional integrity auditing messages.
1779 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1781 Enable intel iommu driver.
1783 Disable intel iommu driver.
1784 igfx_off [Default Off]
1785 By default, gfx is mapped as normal device. If a gfx
1786 device has a dedicated DMAR unit, the DMAR unit is
1787 bypassed by not enabling DMAR with this option. In
1788 this case, gfx device will use physical address for
1791 With this option iommu will not optimize to look
1792 for io virtual address below 32-bit forcing dual
1793 address cycle on pci bus for cards supporting greater
1794 than 32-bit addressing. The default is to look
1795 for translation below 32-bit and if not available
1796 then look in the higher range.
1797 strict [Default Off]
1798 With this option on every unmap_single operation will
1799 result in a hardware IOTLB flush operation as opposed
1800 to batching them for performance.
1801 sp_off [Default Off]
1802 By default, super page will be supported if Intel IOMMU
1803 has the capability. With this option, super page will
1806 By default, scalable mode will be disabled even if the
1807 hardware advertises that it has support for the scalable
1808 mode translation. With this option set, scalable mode
1809 will be used on hardware which claims to support it.
1810 tboot_noforce [Default Off]
1811 Do not force the Intel IOMMU enabled under tboot.
1812 By default, tboot will force Intel IOMMU on, which
1813 could harm performance of some high-throughput
1814 devices like 40GBit network cards, even if identity
1816 Note that using this option lowers the security
1817 provided by tboot because it makes the system
1818 vulnerable to DMA attacks.
1819 nobounce [Default off]
1820 Disable bounce buffer for untrusted devices such as
1821 the Thunderbolt devices. This will treat the untrusted
1822 devices as the trusted ones, hence might expose security
1823 risks of DMA attacks.
1825 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1826 0 disables intel_idle and fall back on acpi_idle.
1827 1 to 9 specify maximum depth of C-state.
1831 Do not enable intel_pstate as the default
1832 scaling driver for the supported processors
1834 Use intel_pstate as a scaling driver, but configure it
1835 to work with generic cpufreq governors (instead of
1836 enabling its internal governor). This mode cannot be
1837 used along with the hardware-managed P-states (HWP)
1840 Enable intel_pstate on systems that prohibit it by default
1841 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1842 instead of acpi-cpufreq may disable platform features, such
1843 as thermal controls and power capping, that rely on ACPI
1844 P-States information being indicated to OSPM and therefore
1845 should be used with caution. This option does not work with
1846 processors that aren't supported by the intel_pstate driver
1847 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1849 Do not enable hardware P state control (HWP)
1852 Only load intel_pstate on systems which support
1853 hardware P state control (HWP) if available.
1855 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1856 Description Table, specifies preferred power management
1857 profile as "Enterprise Server" or "Performance Server",
1858 then this feature is turned on by default.
1860 Allow per-logical-CPU P-State performance control limits using
1861 cpufreq sysfs interface
1863 intremap= [X86-64, Intel-IOMMU]
1864 on enable Interrupt Remapping (default)
1865 off disable Interrupt Remapping
1866 nosid disable Source ID checking
1868 BIOS x2APIC opt-out request will be ignored
1869 nopost disable Interrupt Posting
1871 iomem= Disable strict checking of access to MMIO memory
1872 strict regions from userspace.
1887 nobypass [PPC/POWERNV]
1888 Disable IOMMU bypass, using IOMMU for PCI devices.
1890 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1891 Format: { "0" | "1" }
1893 Request that DMA unmap operations use deferred
1894 invalidation of hardware TLBs, for increased
1895 throughput at the cost of reduced device isolation.
1896 Will fall back to strict mode if not supported by
1897 the relevant IOMMU driver.
1898 1 - Strict mode (default).
1899 DMA unmap operations invalidate IOMMU hardware TLBs
1903 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
1904 Format: { "0" | "1" }
1905 0 - Use IOMMU translation for DMA.
1906 1 - Bypass the IOMMU for DMA.
1907 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1909 io7= [HW] IO7 for Marvel based alpha systems
1910 See comment before marvel_specify_io7 in
1911 arch/alpha/kernel/core_marvel.c.
1913 io_delay= [X86] I/O delay method
1915 Standard port 0x80 based delay
1917 Alternate port 0xed based delay (needed on some systems)
1919 Simple two microseconds delay
1924 See Documentation/admin-guide/nfs/nfsroot.rst.
1926 ipcmni_extend [KNL] Extend the maximum number of unique System V
1927 IPC identifiers from 32,768 to 16,777,216.
1929 irqaffinity= [SMP] Set the default irq affinity mask
1930 The argument is a cpu list, as described above.
1932 irqchip.gicv2_force_probe=
1935 Force the kernel to look for the second 4kB page
1936 of a GICv2 controller even if the memory range
1937 exposed by the device tree is too small.
1939 irqchip.gicv3_nolpi=
1941 Force the kernel to ignore the availability of
1942 LPIs (and by consequence ITSs). Intended for system
1943 that use the kernel as a bootloader, and thus want
1944 to let secondary kernels in charge of setting up
1947 irqchip.gicv3_pseudo_nmi= [ARM64]
1948 Enables support for pseudo-NMIs in the kernel. This
1949 requires the kernel to be built with
1950 CONFIG_ARM64_PSEUDO_NMI.
1953 When an interrupt is not handled search all handlers
1954 for it. Intended to get systems with badly broken
1958 When an interrupt is not handled search all handlers
1959 for it. Also check all handlers each timer
1960 interrupt. Intended to get systems with badly broken
1964 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1966 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1967 [Deprecated - use cpusets instead]
1968 Format: [flag-list,]<cpu-list>
1970 Specify one or more CPUs to isolate from disturbances
1971 specified in the flag list (default: domain):
1974 Disable the tick when a single task runs.
1976 A residual 1Hz tick is offloaded to workqueues, which you
1977 need to affine to housekeeping through the global
1978 workqueue's affinity configured via the
1979 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1980 by using the 'domain' flag described below.
1982 NOTE: by default the global workqueue runs on all CPUs,
1983 so to protect individual CPUs the 'cpumask' file has to
1984 be configured manually after bootup.
1987 Isolate from the general SMP balancing and scheduling
1988 algorithms. Note that performing domain isolation this way
1989 is irreversible: it's not possible to bring back a CPU to
1990 the domains once isolated through isolcpus. It's strongly
1991 advised to use cpusets instead to disable scheduler load
1992 balancing through the "cpuset.sched_load_balance" file.
1993 It offers a much more flexible interface where CPUs can
1994 move in and out of an isolated set anytime.
1996 You can move a process onto or off an "isolated" CPU via
1997 the CPU affinity syscalls or cpuset.
1998 <cpu number> begins at 0 and the maximum value is
1999 "number of CPUs in system - 1".
2003 Isolate from being targeted by managed interrupts
2004 which have an interrupt mask containing isolated
2005 CPUs. The affinity of managed interrupts is
2006 handled by the kernel and cannot be changed via
2007 the /proc/irq/* interfaces.
2009 This isolation is best effort and only effective
2010 if the automatically assigned interrupt mask of a
2011 device queue contains isolated and housekeeping
2012 CPUs. If housekeeping CPUs are online then such
2013 interrupts are directed to the housekeeping CPU
2014 so that IO submitted on the housekeeping CPU
2015 cannot disturb the isolated CPU.
2017 If a queue's affinity mask contains only isolated
2018 CPUs then this parameter has no effect on the
2019 interrupt routing decision, though interrupts are
2020 only delivered when tasks running on those
2021 isolated CPUs submit IO. IO submitted on
2022 housekeeping CPUs has no influence on those
2025 The format of <cpu-list> is described above.
2029 ivrs_ioapic [HW,X86_64]
2030 Provide an override to the IOAPIC-ID<->DEVICE-ID
2031 mapping provided in the IVRS ACPI table. For
2032 example, to map IOAPIC-ID decimal 10 to
2033 PCI device 00:14.0 write the parameter as:
2034 ivrs_ioapic[10]=00:14.0
2036 ivrs_hpet [HW,X86_64]
2037 Provide an override to the HPET-ID<->DEVICE-ID
2038 mapping provided in the IVRS ACPI table. For
2039 example, to map HPET-ID decimal 0 to
2040 PCI device 00:14.0 write the parameter as:
2041 ivrs_hpet[0]=00:14.0
2043 ivrs_acpihid [HW,X86_64]
2044 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2045 mapping provided in the IVRS ACPI table. For
2046 example, to map UART-HID:UID AMD0020:0 to
2047 PCI device 00:14.5 write the parameter as:
2048 ivrs_acpihid[00:14.5]=AMD0020:0
2050 js= [HW,JOY] Analog joystick
2051 See Documentation/input/joydev/joystick.rst.
2054 When CONFIG_RANDOMIZE_BASE is set, this disables
2055 kernel and module base offset ASLR (Address Space
2056 Layout Randomization).
2059 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2060 report on every invalid memory access. Without this
2061 parameter KASAN will print report only for the first
2066 kernelcore= [KNL,X86,IA-64,PPC]
2067 Format: nn[KMGTPE] | nn% | "mirror"
2068 This parameter specifies the amount of memory usable by
2069 the kernel for non-movable allocations. The requested
2070 amount is spread evenly throughout all nodes in the
2071 system as ZONE_NORMAL. The remaining memory is used for
2072 movable memory in its own zone, ZONE_MOVABLE. In the
2073 event, a node is too small to have both ZONE_NORMAL and
2074 ZONE_MOVABLE, kernelcore memory will take priority and
2075 other nodes will have a larger ZONE_MOVABLE.
2077 ZONE_MOVABLE is used for the allocation of pages that
2078 may be reclaimed or moved by the page migration
2079 subsystem. Note that allocations like PTEs-from-HighMem
2080 still use the HighMem zone if it exists, and the Normal
2081 zone if it does not.
2083 It is possible to specify the exact amount of memory in
2084 the form of "nn[KMGTPE]", a percentage of total system
2085 memory in the form of "nn%", or "mirror". If "mirror"
2086 option is specified, mirrored (reliable) memory is used
2087 for non-movable allocations and remaining memory is used
2088 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2089 are exclusive, so you cannot specify multiple forms.
2091 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2092 Format: <Controller#>[,poll interval]
2093 The controller # is the number of the ehci usb debug
2094 port as it is probed via PCI. The poll interval is
2095 optional and is the number seconds in between
2096 each poll cycle to the debug port in case you need
2097 the functionality for interrupting the kernel with
2098 gdb or control-c on the dbgp connection. When
2099 not using this parameter you use sysrq-g to break into
2100 the kernel debugger.
2102 kgdboc= [KGDB,HW] kgdb over consoles.
2103 Requires a tty driver that supports console polling,
2104 or a supported polling keyboard driver (non-usb).
2105 Serial only format: <serial_device>[,baud]
2106 keyboard only format: kbd
2107 keyboard and serial format: kbd,<serial_device>[,baud]
2108 Optional Kernel mode setting:
2109 kms, kbd format: kms,kbd
2110 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2112 kgdbwait [KGDB] Stop kernel execution and enter the
2113 kernel debugger at the earliest opportunity.
2115 kmac= [MIPS] korina ethernet MAC address.
2116 Configure the RouterBoard 532 series on-chip
2117 Ethernet adapter MAC address.
2119 kmemleak= [KNL] Boot-time kmemleak enable/disable
2120 Valid arguments: on, off
2122 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2125 kprobe_event=[probe-list]
2126 [FTRACE] Add kprobe events and enable at boot time.
2127 The probe-list is a semicolon delimited list of probe
2128 definitions. Each definition is same as kprobe_events
2129 interface, but the parameters are comma delimited.
2130 For example, to add a kprobe event on vfs_read with
2131 arg1 and arg2, add to the command line;
2133 kprobe_event=p,vfs_read,$arg1,$arg2
2135 See also Documentation/trace/kprobetrace.rst "Kernel
2136 Boot Parameter" section.
2138 kpti= [ARM64] Control page table isolation of user
2139 and kernel address spaces.
2140 Default: enabled on cores which need mitigation.
2144 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2145 Default is 0 (don't ignore, but inject #GP)
2147 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2148 Default is false (don't support).
2150 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2155 [KVM] Controls the software workaround for the
2156 X86_BUG_ITLB_MULTIHIT bug.
2157 force : Always deploy workaround.
2158 off : Never deploy workaround.
2159 auto : Deploy workaround based on the presence of
2160 X86_BUG_ITLB_MULTIHIT.
2164 If the software workaround is enabled for the host,
2165 guests do need not to enable it for nested guests.
2167 kvm.nx_huge_pages_recovery_ratio=
2168 [KVM] Controls how many 4KiB pages are periodically zapped
2169 back to huge pages. 0 disables the recovery, otherwise if
2170 the value is N KVM will zap 1/Nth of the 4KiB pages every
2171 minute. The default is 60.
2173 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2174 Default is 1 (enabled)
2176 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2178 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2180 kvm-arm.vgic_v3_group0_trap=
2181 [KVM,ARM] Trap guest accesses to GICv3 group-0
2184 kvm-arm.vgic_v3_group1_trap=
2185 [KVM,ARM] Trap guest accesses to GICv3 group-1
2188 kvm-arm.vgic_v3_common_trap=
2189 [KVM,ARM] Trap guest accesses to GICv3 common
2192 kvm-arm.vgic_v4_enable=
2193 [KVM,ARM] Allow use of GICv4 for direct injection of
2196 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2197 (virtualized MMU) support on capable Intel chips.
2198 Default is 1 (enabled)
2200 kvm-intel.emulate_invalid_guest_state=
2201 [KVM,Intel] Enable emulation of invalid guest states
2202 Default is 0 (disabled)
2204 kvm-intel.flexpriority=
2205 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2206 Default is 1 (enabled)
2209 [KVM,Intel] Enable VMX nesting (nVMX).
2210 Default is 0 (disabled)
2212 kvm-intel.unrestricted_guest=
2213 [KVM,Intel] Disable unrestricted guest feature
2214 (virtualized real and unpaged mode) on capable
2215 Intel chips. Default is 1 (enabled)
2217 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2220 Valid arguments: never, cond, always
2222 always: L1D cache flush on every VMENTER.
2223 cond: Flush L1D on VMENTER only when the code between
2224 VMEXIT and VMENTER can leak host memory.
2225 never: Disables the mitigation
2227 Default is cond (do L1 cache flush in specific instances)
2229 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2230 feature (tagged TLBs) on capable Intel chips.
2231 Default is 1 (enabled)
2233 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2236 The kernel PTE inversion protection is unconditionally
2237 enabled and cannot be disabled.
2240 Provides all available mitigations for the
2241 L1TF vulnerability. Disables SMT and
2242 enables all mitigations in the
2243 hypervisors, i.e. unconditional L1D flush.
2245 SMT control and L1D flush control via the
2246 sysfs interface is still possible after
2247 boot. Hypervisors will issue a warning
2248 when the first VM is started in a
2249 potentially insecure configuration,
2250 i.e. SMT enabled or L1D flush disabled.
2253 Same as 'full', but disables SMT and L1D
2254 flush runtime control. Implies the
2255 'nosmt=force' command line option.
2256 (i.e. sysfs control of SMT is disabled.)
2259 Leaves SMT enabled and enables the default
2260 hypervisor mitigation, i.e. conditional
2263 SMT control and L1D flush control via the
2264 sysfs interface is still possible after
2265 boot. Hypervisors will issue a warning
2266 when the first VM is started in a
2267 potentially insecure configuration,
2268 i.e. SMT enabled or L1D flush disabled.
2272 Disables SMT and enables the default
2273 hypervisor mitigation.
2275 SMT control and L1D flush control via the
2276 sysfs interface is still possible after
2277 boot. Hypervisors will issue a warning
2278 when the first VM is started in a
2279 potentially insecure configuration,
2280 i.e. SMT enabled or L1D flush disabled.
2283 Same as 'flush', but hypervisors will not
2284 warn when a VM is started in a potentially
2285 insecure configuration.
2288 Disables hypervisor mitigations and doesn't
2290 It also drops the swap size and available
2291 RAM limit restriction on both hypervisor and
2296 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2302 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2305 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2306 value for LAPIC timer one-shot implementation. Default
2307 back to the programmable timer unit in the LAPIC.
2309 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2312 libata.dma= [LIBATA] DMA control
2313 libata.dma=0 Disable all PATA and SATA DMA
2314 libata.dma=1 PATA and SATA Disk DMA only
2315 libata.dma=2 ATAPI (CDROM) DMA only
2316 libata.dma=4 Compact Flash DMA only
2317 Combinations also work, so libata.dma=3 enables DMA
2318 for disks and CDROMs, but not CFs.
2320 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2321 libata.ignore_hpa=0 keep BIOS limits (default)
2322 libata.ignore_hpa=1 ignore limits, using full disk
2324 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2328 libata.force= [LIBATA] Force configurations. The format is comma
2329 separated list of "[ID:]VAL" where ID is
2330 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2331 matching port, link or device. Basically, it matches
2332 the ATA ID string printed on console by libata. If
2333 the whole ID part is omitted, the last PORT and DEVICE
2334 values are used. If ID hasn't been specified yet, the
2335 configuration applies to all ports, links and devices.
2337 If only DEVICE is omitted, the parameter applies to
2338 the port and all links and devices behind it. DEVICE
2339 number of 0 either selects the first device or the
2340 first fan-out link behind PMP device. It does not
2341 select the host link. DEVICE number of 15 selects the
2342 host link and device attached to it.
2344 The VAL specifies the configuration to force. As long
2345 as there's no ambiguity shortcut notation is allowed.
2346 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2347 The following configurations can be forced.
2349 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2350 Any ID with matching PORT is used.
2352 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2354 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2355 udma[/][16,25,33,44,66,100,133] notation is also
2358 * [no]ncq: Turn on or off NCQ.
2360 * [no]ncqtrim: Turn off queued DSM TRIM.
2362 * nohrst, nosrst, norst: suppress hard, soft
2365 * rstonce: only attempt one reset during
2366 hot-unplug link recovery
2368 * dump_id: dump IDENTIFY data.
2370 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2372 * disable: Disable this device.
2374 If there are multiple matching configurations changing
2375 the same attribute, the last one is used.
2377 memblock=debug [KNL] Enable memblock debug messages.
2379 load_ramdisk= [RAM] List of ramdisks to load from floppy
2380 See Documentation/admin-guide/blockdev/ramdisk.rst.
2382 lockd.nlm_grace_period=P [NFS] Assign grace period.
2385 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2388 lockd.nlm_timeout=T [NFS] Assign timeout value.
2391 lockd.nlm_udpport=M [NFS] Assign UDP port.
2394 lockdown= [SECURITY]
2395 { integrity | confidentiality }
2396 Enable the kernel lockdown feature. If set to
2397 integrity, kernel features that allow userland to
2398 modify the running kernel are disabled. If set to
2399 confidentiality, kernel features that allow userland
2400 to extract confidential information from the kernel
2403 locktorture.nreaders_stress= [KNL]
2404 Set the number of locking read-acquisition kthreads.
2405 Defaults to being automatically set based on the
2406 number of online CPUs.
2408 locktorture.nwriters_stress= [KNL]
2409 Set the number of locking write-acquisition kthreads.
2411 locktorture.onoff_holdoff= [KNL]
2412 Set time (s) after boot for CPU-hotplug testing.
2414 locktorture.onoff_interval= [KNL]
2415 Set time (s) between CPU-hotplug operations, or
2416 zero to disable CPU-hotplug testing.
2418 locktorture.shuffle_interval= [KNL]
2419 Set task-shuffle interval (jiffies). Shuffling
2420 tasks allows some CPUs to go into dyntick-idle
2421 mode during the locktorture test.
2423 locktorture.shutdown_secs= [KNL]
2424 Set time (s) after boot system shutdown. This
2425 is useful for hands-off automated testing.
2427 locktorture.stat_interval= [KNL]
2428 Time (s) between statistics printk()s.
2430 locktorture.stutter= [KNL]
2431 Time (s) to stutter testing, for example,
2432 specifying five seconds causes the test to run for
2433 five seconds, wait for five seconds, and so on.
2434 This tests the locking primitive's ability to
2435 transition abruptly to and from idle.
2437 locktorture.torture_type= [KNL]
2438 Specify the locking implementation to test.
2440 locktorture.verbose= [KNL]
2441 Enable additional printk() statements.
2443 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2446 loglevel= All Kernel Messages with a loglevel smaller than the
2447 console loglevel will be printed to the console. It can
2448 also be changed with klogd or other programs. The
2449 loglevels are defined as follows:
2451 0 (KERN_EMERG) system is unusable
2452 1 (KERN_ALERT) action must be taken immediately
2453 2 (KERN_CRIT) critical conditions
2454 3 (KERN_ERR) error conditions
2455 4 (KERN_WARNING) warning conditions
2456 5 (KERN_NOTICE) normal but significant condition
2457 6 (KERN_INFO) informational
2458 7 (KERN_DEBUG) debug-level messages
2460 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2461 in bytes. n must be a power of two and greater
2462 than the minimal size. The minimal size is defined
2463 by LOG_BUF_SHIFT kernel config parameter. There is
2464 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2465 that allows to increase the default size depending on
2466 the number of CPUs. See init/Kconfig for more details.
2468 logo.nologo [FB] Disables display of the built-in Linux logo.
2469 This may be used to provide more screen space for
2470 kernel log messages and is useful when debugging
2471 kernel boot problems.
2473 lp=0 [LP] Specify parallel ports to use, e.g,
2474 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2475 lp=reset first parallel port). 'lp=0' disables the
2476 lp=auto printer driver. 'lp=reset' (which can be
2477 specified in addition to the ports) causes
2478 attached printers to be reset. Using
2479 lp=port1,port2,... specifies the parallel ports
2480 to associate lp devices with, starting with
2481 lp0. A port specification may be 'none' to skip
2482 that lp device, or a parport name such as
2483 'parport0'. Specifying 'lp=auto' instead of a
2484 port specification list means that device IDs
2485 from each port should be examined, to see if
2486 an IEEE 1284-compliant printer is attached; if
2487 so, the driver will manage that printer.
2488 See also header of drivers/char/lp.c.
2491 Sets loops_per_jiffy to given constant, thus avoiding
2492 time-consuming boot-time autodetection (up to 250 ms per
2493 CPU). 0 enables autodetection (default). To determine
2494 the correct value for your kernel, boot with normal
2495 autodetection and see what value is printed. Note that
2496 on SMP systems the preset will be applied to all CPUs,
2497 which is likely to cause problems if your CPUs need
2498 significantly divergent settings. An incorrect value
2499 will cause delays in the kernel to be wrong, leading to
2500 unpredictable I/O errors and other breakage. Although
2501 unlikely, in the extreme case this might damage your
2505 Format: <io>,<irq>,<dma>
2507 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2510 [SECURITY] Choose order of LSM initialization. This
2511 overrides CONFIG_LSM, and the "security=" parameter.
2513 machvec= [IA-64] Force the use of a particular machine-vector
2514 (machvec) in a generic kernel.
2515 Example: machvec=hpzx1
2517 machtype= [Loongson] Share the same kernel image file between different
2519 Example: machtype=lemote-yeeloong-2f-7inch
2521 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2522 than or equal to this physical address is ignored.
2524 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2525 will bring up during bootup. maxcpus=n : n >= 0 limits
2526 the kernel to bring up 'n' processors. Surely after
2527 bootup you can bring up the other plugged cpu by executing
2528 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2529 only takes effect during system bootup.
2530 While n=0 is a special case, it is equivalent to "nosmp",
2531 which also disables the IO APIC.
2533 max_loop= [LOOP] The number of loop block devices that get
2534 (loop.max_loop) unconditionally pre-created at init time. The default
2535 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2536 of statically allocating a predefined number, loop
2537 devices can be requested on-demand with the
2538 /dev/loop-control interface.
2540 mce [X86-32] Machine Check Exception
2542 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2544 md= [HW] RAID subsystems devices and level
2545 See Documentation/admin-guide/md.rst.
2548 Format: <first>,<last>
2549 Specifies range of consoles to be captured by the MDA.
2552 Control mitigation for the Micro-architectural Data
2553 Sampling (MDS) vulnerability.
2555 Certain CPUs are vulnerable to an exploit against CPU
2556 internal buffers which can forward information to a
2557 disclosure gadget under certain conditions.
2559 In vulnerable processors, the speculatively
2560 forwarded data can be used in a cache side channel
2561 attack, to access data to which the attacker does
2562 not have direct access.
2564 This parameter controls the MDS mitigation. The
2567 full - Enable MDS mitigation on vulnerable CPUs
2568 full,nosmt - Enable MDS mitigation and disable
2569 SMT on vulnerable CPUs
2570 off - Unconditionally disable MDS mitigation
2572 On TAA-affected machines, mds=off can be prevented by
2573 an active TAA mitigation as both vulnerabilities are
2574 mitigated with the same mechanism so in order to disable
2575 this mitigation, you need to specify tsx_async_abort=off
2578 Not specifying this option is equivalent to
2581 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2583 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2584 Amount of memory to be used in cases as follows:
2587 2 when the kernel is not able to see the whole system memory;
2588 3 memory that lies after 'mem=' boundary is excluded from
2589 the hypervisor, then assigned to KVM guests.
2591 [X86] Work as limiting max address. Use together
2592 with memmap= to avoid physical address space collisions.
2593 Without memmap= PCI devices could be placed at addresses
2594 belonging to unused RAM.
2596 Note that this only takes effects during boot time since
2597 in above case 3, memory may need be hot added after boot
2598 if system memory of hypervisor is not sufficient.
2600 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2604 [KNL,SH] Allow user to override the default size for
2605 per-device physically contiguous DMA buffers.
2607 memhp_default_state=online/offline
2608 [KNL] Set the initial state for the memory hotplug
2609 onlining policy. If not specified, the default value is
2610 set according to the
2611 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2613 See Documentation/admin-guide/mm/memory-hotplug.rst.
2615 memmap=exactmap [KNL,X86] Enable setting of an exact
2616 E820 memory map, as specified by the user.
2617 Such memmap=exactmap lines can be constructed based on
2618 BIOS output or other requirements. See the memmap=nn@ss
2621 memmap=nn[KMG]@ss[KMG]
2622 [KNL] Force usage of a specific region of memory.
2623 Region of memory to be used is from ss to ss+nn.
2624 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2625 which limits max address to nn[KMG].
2626 Multiple different regions can be specified,
2629 memmap=100M@2G,100M#3G,1G!1024G
2631 memmap=nn[KMG]#ss[KMG]
2632 [KNL,ACPI] Mark specific memory as ACPI data.
2633 Region of memory to be marked is from ss to ss+nn.
2635 memmap=nn[KMG]$ss[KMG]
2636 [KNL,ACPI] Mark specific memory as reserved.
2637 Region of memory to be reserved is from ss to ss+nn.
2638 Example: Exclude memory from 0x18690000-0x1869ffff
2639 memmap=64K$0x18690000
2641 memmap=0x10000$0x18690000
2642 Some bootloaders may need an escape character before '$',
2643 like Grub2, otherwise '$' and the following number
2646 memmap=nn[KMG]!ss[KMG]
2647 [KNL,X86] Mark specific memory as protected.
2648 Region of memory to be used, from ss to ss+nn.
2649 The memory region may be marked as e820 type 12 (0xc)
2650 and is NVDIMM or ADR memory.
2652 memmap=<size>%<offset>-<oldtype>+<newtype>
2653 [KNL,ACPI] Convert memory within the specified region
2654 from <oldtype> to <newtype>. If "-<oldtype>" is left
2655 out, the whole region will be marked as <newtype>,
2656 even if previously unavailable. If "+<newtype>" is left
2657 out, matching memory will be removed. Types are
2658 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2659 3 = ACPI, 12 = PRAM.
2661 memory_corruption_check=0/1 [X86]
2662 Some BIOSes seem to corrupt the first 64k of
2663 memory when doing things like suspend/resume.
2664 Setting this option will scan the memory
2665 looking for corruption. Enabling this will
2666 both detect corruption and prevent the kernel
2667 from using the memory being corrupted.
2668 However, its intended as a diagnostic tool; if
2669 repeatable BIOS-originated corruption always
2670 affects the same memory, you can use memmap=
2671 to prevent the kernel from using that memory.
2673 memory_corruption_check_size=size [X86]
2674 By default it checks for corruption in the low
2675 64k, making this memory unavailable for normal
2676 use. Use this parameter to scan for
2677 corruption in more or less memory.
2679 memory_corruption_check_period=seconds [X86]
2680 By default it checks for corruption every 60
2681 seconds. Use this parameter to check at some
2682 other rate. 0 disables periodic checking.
2684 memtest= [KNL,X86,ARM,PPC] Enable memtest
2686 default : 0 <disable>
2687 Specifies the number of memtest passes to be
2688 performed. Each pass selects another test
2689 pattern from a given set of patterns. Memtest
2690 fills the memory with this pattern, validates
2691 memory contents and reserves bad memory
2692 regions that are detected.
2694 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2695 Valid arguments: on, off
2696 Default (depends on kernel configuration option):
2697 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2698 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2699 mem_encrypt=on: Activate SME
2700 mem_encrypt=off: Do not activate SME
2702 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
2703 for details on when memory encryption can be activated.
2705 mem_sleep_default= [SUSPEND] Default system suspend mode:
2706 s2idle - Suspend-To-Idle
2707 shallow - Power-On Suspend or equivalent (if supported)
2708 deep - Suspend-To-RAM or equivalent (if supported)
2709 See Documentation/admin-guide/pm/sleep-states.rst.
2711 meye.*= [HW] Set MotionEye Camera parameters
2712 See Documentation/media/v4l-drivers/meye.rst.
2714 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2715 Multi-Function General Purpose Timers on AMD Geode
2718 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2719 the BIOS has incorrectly applied a workaround. TinyBIOS
2720 version 0.98 is known to be affected, 0.99 fixes the
2721 problem by letting the user disable the workaround.
2725 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2726 physical address is ignored.
2728 mini2440= [ARM,HW,KNL]
2729 Format:[0..2][b][c][t]
2731 MINI2440 configuration specification:
2732 0 - The attached screen is the 3.5" TFT
2733 1 - The attached screen is the 7" TFT
2734 2 - The VGA Shield is attached (1024x768)
2735 Leaving out the screen size parameter will not load
2736 the TFT driver, and the framebuffer will be left
2738 b - Enable backlight. The TFT backlight pin will be
2739 linked to the kernel VESA blanking code and a GPIO
2740 LED. This parameter is not necessary when using the
2742 c - Enable the s3c camera interface.
2743 t - Reserved for enabling touchscreen support. The
2744 touchscreen support is not enabled in the mainstream
2745 kernel as of 2.6.30, a preliminary port can be found
2746 in the "bleeding edge" mini2440 support kernel at
2747 http://repo.or.cz/w/linux-2.6/mini2440.git
2750 [X86,PPC,S390,ARM64] Control optional mitigations for
2751 CPU vulnerabilities. This is a set of curated,
2752 arch-independent options, each of which is an
2753 aggregation of existing arch-specific options.
2756 Disable all optional CPU mitigations. This
2757 improves system performance, but it may also
2758 expose users to several CPU vulnerabilities.
2759 Equivalent to: nopti [X86,PPC]
2761 nospectre_v1 [X86,PPC]
2763 nospectre_v2 [X86,PPC,S390,ARM64]
2764 spectre_v2_user=off [X86]
2765 spec_store_bypass_disable=off [X86,PPC]
2766 ssbd=force-off [ARM64]
2769 tsx_async_abort=off [X86]
2770 kvm.nx_huge_pages=off [X86]
2773 This does not have any effect on
2774 kvm.nx_huge_pages when
2775 kvm.nx_huge_pages=force.
2778 Mitigate all CPU vulnerabilities, but leave SMT
2779 enabled, even if it's vulnerable. This is for
2780 users who don't want to be surprised by SMT
2781 getting disabled across kernel upgrades, or who
2782 have other ways of avoiding SMT-based attacks.
2783 Equivalent to: (default behavior)
2786 Mitigate all CPU vulnerabilities, disabling SMT
2787 if needed. This is for users who always want to
2788 be fully mitigated, even if it means losing SMT.
2789 Equivalent to: l1tf=flush,nosmt [X86]
2790 mds=full,nosmt [X86]
2791 tsx_async_abort=full,nosmt [X86]
2794 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2795 parameter allows control of the logging verbosity for
2796 the additional memory initialisation checks. A value
2797 of 0 disables mminit logging and a level of 4 will
2798 log everything. Information is printed at KERN_DEBUG
2799 so loglevel=8 may also need to be specified.
2802 [KNL] When CONFIG_MODULE_SIG is set, this means that
2803 modules without (valid) signatures will fail to load.
2804 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2805 is always true, so this option does nothing.
2807 module_blacklist= [KNL] Do not load a comma-separated list of
2808 modules. Useful for debugging problem modules.
2811 [MOUSE] Maximum time between finger touching and
2812 leaving touchpad surface for touch to be considered
2813 a tap and be reported as a left button click (for
2814 touchpads working in absolute mode only).
2816 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2817 reporting absolute coordinates, such as tablets
2818 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2819 reporting absolute coordinates, such as tablets
2821 movablecore= [KNL,X86,IA-64,PPC]
2822 Format: nn[KMGTPE] | nn%
2823 This parameter is the complement to kernelcore=, it
2824 specifies the amount of memory used for migratable
2825 allocations. If both kernelcore and movablecore is
2826 specified, then kernelcore will be at *least* the
2827 specified value but may be more. If movablecore on its
2828 own is specified, the administrator must be careful
2829 that the amount of memory usable for all allocations
2832 movable_node [KNL] Boot-time switch to make hotplugable memory
2833 NUMA nodes to be movable. This means that the memory
2834 of such nodes will be usable only for movable
2835 allocations which rules out almost all kernel
2836 allocations. Use with caution!
2838 MTD_Partition= [MTD]
2839 Format: <name>,<region-number>,<size>,<offset>
2841 MTD_Region= [MTD] Format:
2842 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2845 See drivers/mtd/parsers/cmdlinepart.c
2847 multitce=off [PPC] This parameter disables the use of the pSeries
2848 firmware feature for updating multiple TCE entries
2851 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2853 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2855 boundary - index of last SLC block on Flex-OneNAND.
2856 The remaining blocks are configured as MLC blocks.
2857 lock - Configure if Flex-OneNAND boundary should be locked.
2858 Once locked, the boundary cannot be changed.
2859 1 indicates lock status, 0 indicates unlock status.
2862 ARM/S3C2412 JIVE boot control
2864 See arch/arm/mach-s3c2412/mach-jive.c
2866 mtouchusb.raw_coordinates=
2867 [HW] Make the MicroTouch USB driver use raw coordinates
2868 ('y', default) or cooked coordinates ('n')
2870 mtrr_chunk_size=nn[KMG] [X86]
2871 used for mtrr cleanup. It is largest continuous chunk
2872 that could hold holes aka. UC entries.
2874 mtrr_gran_size=nn[KMG] [X86]
2875 Used for mtrr cleanup. It is granularity of mtrr block.
2877 Large value could prevent small alignment from
2880 mtrr_spare_reg_nr=n [X86]
2882 Range: 0,7 : spare reg number
2884 Used for mtrr cleanup. It is spare mtrr entries number.
2885 Set to 2 or more if your graphical card needs more.
2887 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2889 netdev= [NET] Network devices parameters
2890 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2891 Note that mem_start is often overloaded to mean
2892 something different and driver-specific.
2893 This usage is only documented in each driver source
2897 [NETFILTER] Enable connection tracking flow accounting
2898 0 to disable accounting
2899 1 to enable accounting
2902 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2903 See Documentation/admin-guide/nfs/nfsroot.rst.
2905 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2906 See Documentation/admin-guide/nfs/nfsroot.rst.
2908 nfsrootdebug [NFS] enable nfsroot debugging messages.
2909 See Documentation/admin-guide/nfs/nfsroot.rst.
2911 nfs.callback_nr_threads=
2912 [NFSv4] set the total number of threads that the
2913 NFS client will assign to service NFSv4 callback
2916 nfs.callback_tcpport=
2917 [NFS] set the TCP port on which the NFSv4 callback
2918 channel should listen.
2921 [NFS] sets the pathname to the program which is used
2922 to update the NFS client cache entries.
2924 nfs.cache_getent_timeout=
2925 [NFS] sets the timeout after which an attempt to
2926 update a cache entry is deemed to have failed.
2928 nfs.idmap_cache_timeout=
2929 [NFS] set the maximum lifetime for idmapper cache
2933 [NFS] enable 64-bit inode numbers.
2934 If zero, the NFS client will fake up a 32-bit inode
2935 number for the readdir() and stat() syscalls instead
2936 of returning the full 64-bit number.
2937 The default is to return 64-bit inode numbers.
2939 nfs.max_session_cb_slots=
2940 [NFSv4.1] Sets the maximum number of session
2941 slots the client will assign to the callback
2942 channel. This determines the maximum number of
2943 callbacks the client will process in parallel for
2944 a particular server.
2946 nfs.max_session_slots=
2947 [NFSv4.1] Sets the maximum number of session slots
2948 the client will attempt to negotiate with the server.
2949 This limits the number of simultaneous RPC requests
2950 that the client can send to the NFSv4.1 server.
2951 Note that there is little point in setting this
2952 value higher than the max_tcp_slot_table_limit.
2954 nfs.nfs4_disable_idmapping=
2955 [NFSv4] When set to the default of '1', this option
2956 ensures that both the RPC level authentication
2957 scheme and the NFS level operations agree to use
2958 numeric uids/gids if the mount is using the
2959 'sec=sys' security flavour. In effect it is
2960 disabling idmapping, which can make migration from
2961 legacy NFSv2/v3 systems to NFSv4 easier.
2962 Servers that do not support this mode of operation
2963 will be autodetected by the client, and it will fall
2964 back to using the idmapper.
2965 To turn off this behaviour, set the value to '0'.
2967 [NFS4] Specify an additional fixed unique ident-
2968 ification string that NFSv4 clients can insert into
2969 their nfs_client_id4 string. This is typically a
2970 UUID that is generated at system install time.
2972 nfs.send_implementation_id =
2973 [NFSv4.1] Send client implementation identification
2974 information in exchange_id requests.
2975 If zero, no implementation identification information
2977 The default is to send the implementation identification
2980 nfs.recover_lost_locks =
2981 [NFSv4] Attempt to recover locks that were lost due
2982 to a lease timeout on the server. Please note that
2983 doing this risks data corruption, since there are
2984 no guarantees that the file will remain unchanged
2985 after the locks are lost.
2986 If you want to enable the kernel legacy behaviour of
2987 attempting to recover these locks, then set this
2989 The default parameter value of '0' causes the kernel
2990 not to attempt recovery of lost locks.
2992 nfs4.layoutstats_timer =
2993 [NFSv4.2] Change the rate at which the kernel sends
2994 layoutstats to the pNFS metadata server.
2996 Setting this to value to 0 causes the kernel to use
2997 whatever value is the default set by the layout
2998 driver. A non-zero value sets the minimum interval
2999 in seconds between layoutstats transmissions.
3001 nfsd.nfs4_disable_idmapping=
3002 [NFSv4] When set to the default of '1', the NFSv4
3003 server will return only numeric uids and gids to
3004 clients using auth_sys, and will accept numeric uids
3005 and gids from such clients. This is intended to ease
3006 migration from NFSv2/v3.
3008 nmi_debug= [KNL,SH] Specify one or more actions to take
3009 when a NMI is triggered.
3010 Format: [state][,regs][,debounce][,die]
3012 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3013 Format: [panic,][nopanic,][num]
3015 0 - turn hardlockup detector in nmi_watchdog off
3016 1 - turn hardlockup detector in nmi_watchdog on
3017 When panic is specified, panic when an NMI watchdog
3018 timeout occurs (or 'nopanic' to not panic on an NMI
3019 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3020 To disable both hard and soft lockup detectors,
3021 please see 'nowatchdog'.
3022 This is useful when you use a panic=... timeout and
3023 need the box quickly up again.
3025 These settings can be accessed at runtime via
3026 the nmi_watchdog and hardlockup_panic sysctls.
3028 netpoll.carrier_timeout=
3029 [NET] Specifies amount of time (in seconds) that
3030 netpoll should wait for a carrier. By default netpoll
3033 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3034 emulation library even if a 387 maths coprocessor
3037 no5lvl [X86-64] Disable 5-level paging mode. Forces
3038 kernel to use 4-level paging instead.
3041 [HW] Never suspend the console
3042 Disable suspending of consoles during suspend and
3043 hibernate operations. Once disabled, debugging
3044 messages can reach various consoles while the rest
3045 of the system is being put to sleep (ie, while
3046 debugging driver suspend/resume hooks). This may
3047 not work reliably with all consoles, but is known
3048 to work with serial and VGA consoles.
3049 To facilitate more flexible debugging, we also add
3050 console_suspend, a printk module parameter to control
3051 it. Users could use console_suspend (usually
3052 /sys/module/printk/parameters/console_suspend) to
3053 turn on/off it dynamically.
3055 novmcoredd [KNL,KDUMP]
3056 Disable device dump. Device dump allows drivers to
3057 append dump data to vmcore so you can collect driver
3058 specified debug info. Drivers can append the data
3059 without any limit and this data is stored in memory,
3060 so this may cause significant memory stress. Disabling
3061 device dump can help save memory but the driver debug
3062 data will be no longer available. This parameter
3063 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3066 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3067 caches in the slab allocator. Saves per-node memory,
3068 but will impact performance.
3072 noaltinstr [S390] Disables alternative instructions patching
3073 (CPU alternatives feature).
3075 noapic [SMP,APIC] Tells the kernel to not make use of any
3076 IOAPICs that may be present in the system.
3078 noautogroup Disable scheduler automatic task group creation.
3080 nobats [PPC] Do not use BATs for mapping kernel lowmem
3081 on "Classic" PPC cores.
3085 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
3087 nodelayacct [KNL] Disable per-task delay accounting
3089 nodsp [SH] Disable hardware DSP at boot time.
3091 noefi Disable EFI runtime services support.
3096 On X86-32 available only on PAE configured kernels.
3097 noexec=on: enable non-executable mappings (default)
3098 noexec=off: disable non-executable mappings
3101 Disable SMAP (Supervisor Mode Access Prevention)
3102 even if it is supported by processor.
3105 Disable SMEP (Supervisor Mode Execution Prevention)
3106 even if it is supported by processor.
3109 This affects only 32-bit executables.
3110 noexec32=on: enable non-executable mappings (default)
3111 read doesn't imply executable mappings
3112 noexec32=off: disable non-executable mappings
3113 read implies executable mappings
3115 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3117 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3118 register save and restore. The kernel will only save
3119 legacy floating-point registers on task switch.
3121 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings.
3123 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3124 Equivalent to smt=1.
3126 [KNL,x86] Disable symmetric multithreading (SMT).
3127 nosmt=force: Force disable SMT, cannot be undone
3128 via the sysfs control file.
3130 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3131 (bounds check bypass). With this option data leaks are
3132 possible in the system.
3134 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3135 the Spectre variant 2 (indirect branch prediction)
3136 vulnerability. System may allow data leaks with this
3139 nospec_store_bypass_disable
3140 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3142 noxsave [BUGS=X86] Disables x86 extended register state save
3143 and restore using xsave. The kernel will fallback to
3144 enabling legacy floating-point and sse state.
3146 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3147 register states. The kernel will fall back to use
3148 xsave to save the states. By using this parameter,
3149 performance of saving the states is degraded because
3150 xsave doesn't support modified optimization while
3151 xsaveopt supports it on xsaveopt enabled systems.
3153 noxsaves [X86] Disables xsaves and xrstors used in saving and
3154 restoring x86 extended register state in compacted
3155 form of xsave area. The kernel will fall back to use
3156 xsaveopt and xrstor to save and restore the states
3157 in standard form of xsave area. By using this
3158 parameter, xsave area per process might occupy more
3159 memory on xsaves enabled systems.
3161 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
3162 wfi(ARM) instruction doesn't work correctly and not to
3163 use it. This is also useful when using JTAG debugger.
3165 no_file_caps Tells the kernel not to honor file capabilities. The
3166 only way then for a file to be executed with privilege
3167 is to be setuid root or executed by root.
3169 nohalt [IA-64] Tells the kernel not to use the power saving
3170 function PAL_HALT_LIGHT when idle. This increases
3171 power-consumption. On the positive side, it reduces
3172 interrupt wake-up latency, which may improve performance
3173 in certain environments such as networked servers or
3176 nohibernate [HIBERNATION] Disable hibernation and resume.
3178 nohz= [KNL] Boottime enable/disable dynamic ticks
3179 Valid arguments: on, off
3182 nohz_full= [KNL,BOOT,SMP,ISOL]
3183 The argument is a cpu list, as described above.
3184 In kernels built with CONFIG_NO_HZ_FULL=y, set
3185 the specified list of CPUs whose tick will be stopped
3186 whenever possible. The boot CPU will be forced outside
3187 the range to maintain the timekeeping. Any CPUs
3188 in this list will have their RCU callbacks offloaded,
3189 just as if they had also been called out in the
3190 rcu_nocbs= boot parameter.
3192 noiotrap [SH] Disables trapped I/O port accesses.
3194 noirqdebug [X86-32] Disables the code which attempts to detect and
3195 disable unhandled interrupt sources.
3197 no_timer_check [X86,APIC] Disables the code which tests for
3198 broken timer IRQ sources.
3200 noisapnp [ISAPNP] Disables ISA PnP code.
3202 noinitrd [RAM] Tells the kernel not to load any configured
3205 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3207 [Deprecated - use intremap=off]
3211 noinvpcid [X86] Disable the INVPCID cpu feature.
3213 nojitter [IA-64] Disables jitter checking for ITC timers.
3215 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3217 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3221 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3222 clock and use the default one.
3224 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
3225 accounting. steal time is computed, but won't
3226 influence scheduler behaviour
3228 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3230 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3232 noltlbs [PPC] Do not use large page/tlb entries for kernel
3233 lowmem mapping on PPC40x and PPC8xx
3235 nomca [IA-64] Disable machine check abort handling
3237 nomce [X86-32] Disable Machine Check Exception
3239 nomfgpt [X86-32] Disable Multi-Function General Purpose
3240 Timer usage (for AMD Geode machines).
3242 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3243 shutdown the other cpus. Instead use the REBOOT_VECTOR
3246 nomodule Disable module load
3248 nopat [X86] Disable PAT (page attribute table extension of
3249 pagetables) support.
3251 nopcid [X86-64] Disable the PCID cpu feature.
3253 norandmaps Don't use address space randomization. Equivalent to
3254 echo 0 > /proc/sys/kernel/randomize_va_space
3256 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3257 with UP alternatives
3259 nordrand [X86] Disable kernel use of the RDRAND and
3260 RDSEED instructions even if they are supported
3261 by the processor. RDRAND and RDSEED are still
3262 available to user space applications.
3264 noresume [SWSUSP] Disables resume and restores original swap
3267 no-scroll [VGA] Disables scrollback.
3268 This is required for the Braillex ib80-piezo Braille
3269 reader made by F.H. Papenmeier (Germany).
3273 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3275 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3276 and disable the IO APIC. legacy for "maxcpus=0".
3278 nosoftlockup [KNL] Disable the soft-lockup detector.
3280 nosync [HW,M68K] Disables sync negotiation for all devices.
3282 nowatchdog [KNL] Disable both lockup detectors, i.e.
3283 soft-lockup and NMI watchdog (hard-lockup).
3287 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3289 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3290 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3291 Some features depend on CPU0. Known dependencies are:
3292 1. Resume from suspend/hibernate depends on CPU0.
3293 Suspend/hibernate will fail if CPU0 is offline and you
3294 need to online CPU0 before suspend/hibernate.
3295 2. PIC interrupts also depend on CPU0. CPU0 can't be
3296 removed if a PIC interrupt is detected.
3297 It's said poweroff/reboot may depend on CPU0 on some
3298 machines although I haven't seen such issues so far
3299 after CPU0 is offline on a few tested machines.
3300 If the dependencies are under your control, you can
3301 turn on cpu0_hotplug.
3303 nps_mtm_hs_ctr= [KNL,ARC]
3304 This parameter sets the maximum duration, in
3305 cycles, each HW thread of the CTOP can run
3306 without interruptions, before HW switches it.
3307 The actual maximum duration is 16 times this
3309 Format: integer between 1 and 255
3312 nptcg= [IA-64] Override max number of concurrent global TLB
3313 purges which is reported from either PAL_VM_SUMMARY or
3316 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3317 could support. nr_cpus=n : n >= 1 limits the kernel to
3318 support 'n' processors. It could be larger than the
3319 number of already plugged CPU during bootup, later in
3320 runtime you can physically add extra cpu until it reaches
3321 n. So during boot up some boot time memory for per-cpu
3322 variables need be pre-allocated for later physical cpu
3325 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3327 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3328 Allowed values are enable and disable
3330 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3331 'node', 'default' can be specified
3332 This can be set from sysctl after boot.
3333 See Documentation/admin-guide/sysctl/vm.rst for details.
3335 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3336 See Documentation/debugging-via-ohci1394.txt for more
3339 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3340 Rather than timing out after 20 ms if an EC
3341 command is not properly ACKed, override the length
3342 of the timeout. We have interrupts disabled while
3343 waiting for the ACK, so if this is set too high
3344 interrupts *may* be lost!
3346 omap_mux= [OMAP] Override bootloader pin multiplexing.
3347 Format: <mux_mode0.mode_name=value>...
3348 For example, to override I2C bus2:
3349 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3351 oprofile.timer= [HW]
3352 Use timer interrupt instead of performance counters
3354 oprofile.cpu_type= Force an oprofile cpu type
3355 This might be useful if you have an older oprofile
3356 userland or if you want common events.
3357 Format: { arch_perfmon }
3358 arch_perfmon: [X86] Force use of architectural
3359 perfmon on Intel CPUs instead of the
3360 CPU specific event set.
3361 timer: [X86] Force use of architectural NMI
3362 timer mode (see also oprofile.timer
3363 for generic hr timer mode)
3365 oops=panic Always panic on oopses. Default is to just kill the
3366 process, but there is a small probability of
3367 deadlocking the machine.
3368 This will also cause panics on machine check exceptions.
3369 Useful together with panic=30 to trigger a reboot.
3372 [KNL] Boolean flag to control whether the page allocator
3373 should randomize its free lists. The randomization may
3374 be automatically enabled if the kernel detects it is
3375 running on a platform with a direct-mapped memory-side
3376 cache, and this parameter can be used to
3377 override/disable that behavior. The state of the flag
3378 can be read from sysfs at:
3379 /sys/module/page_alloc/parameters/shuffle.
3381 page_owner= [KNL] Boot-time page_owner enabling option.
3382 Storage of the information about who allocated
3383 each page is disabled in default. With this switch,
3385 on: enable the feature
3387 page_poison= [KNL] Boot-time parameter changing the state of
3388 poisoning on the buddy allocator, available with
3389 CONFIG_PAGE_POISONING=y.
3390 off: turn off poisoning (default)
3391 on: turn on poisoning
3393 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3394 timeout > 0: seconds before rebooting
3395 timeout = 0: wait forever
3396 timeout < 0: reboot immediately
3399 panic_print= Bitmask for printing system info when panic happens.
3400 User can chose combination of the following bits:
3401 bit 0: print all tasks info
3402 bit 1: print system memory info
3403 bit 2: print timer info
3404 bit 3: print locks info if CONFIG_LOCKDEP is on
3405 bit 4: print ftrace buffer
3406 bit 5: print all printk messages in buffer
3408 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3411 crash_kexec_post_notifiers
3412 Run kdump after running panic-notifiers and dumping
3413 kmsg. This only for the users who doubt kdump always
3414 succeeds in any situation.
3415 Note that this also increases risks of kdump failure,
3416 because some panic notifiers can make the crashed
3417 kernel more unstable.
3419 parkbd.port= [HW] Parallel port number the keyboard adapter is
3420 connected to, default is 0.
3422 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3423 0 for XT, 1 for AT (default is AT).
3426 parport= [HW,PPT] Specify parallel ports. 0 disables.
3427 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3428 Use 'auto' to force the driver to use any
3429 IRQ/DMA settings detected (the default is to
3430 ignore detected IRQ/DMA settings because of
3431 possible conflicts). You can specify the base
3432 address, IRQ, and DMA settings; IRQ and DMA
3433 should be numbers, or 'auto' (for using detected
3434 settings on that particular port), or 'nofifo'
3435 (to avoid using a FIFO even if it is detected).
3436 Parallel ports are assigned in the order they
3437 are specified on the command line, starting
3440 parport_init_mode= [HW,PPT]
3441 Configure VIA parallel port to operate in
3442 a specific mode. This is necessary on Pegasos
3443 computer where firmware has no options for setting
3444 up parallel port mode and sets it to spp.
3445 Currently this function knows 686a and 8231 chips.
3446 Format: [spp|ps2|epp|ecp|ecpepp]
3449 Halt all CPUs after the first oops has been printed for
3450 the specified number of seconds. This is to be used if
3451 your oopses keep scrolling off the screen.
3456 See header of drivers/block/paride/pcd.c.
3457 See also Documentation/admin-guide/blockdev/paride.rst.
3459 pci=option[,option...] [PCI] various PCI subsystem options.
3461 Some options herein operate on a specific device
3462 or a set of devices (<pci_dev>). These are
3463 specified in one of the following formats:
3465 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3466 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3468 Note: the first format specifies a PCI
3469 bus/device/function address which may change
3470 if new hardware is inserted, if motherboard
3471 firmware changes, or due to changes caused
3472 by other kernel parameters. If the
3473 domain is left unspecified, it is
3474 taken to be zero. Optionally, a path
3475 to a device through multiple device/function
3476 addresses can be specified after the base
3477 address (this is more robust against
3478 renumbering issues). The second format
3479 selects devices using IDs from the
3480 configuration space which may match multiple
3481 devices in the system.
3483 earlydump dump PCI config space before the kernel
3485 off [X86] don't probe for the PCI bus
3486 bios [X86-32] force use of PCI BIOS, don't access
3487 the hardware directly. Use this if your machine
3488 has a non-standard PCI host bridge.
3489 nobios [X86-32] disallow use of PCI BIOS, only direct
3490 hardware access methods are allowed. Use this
3491 if you experience crashes upon bootup and you
3492 suspect they are caused by the BIOS.
3493 conf1 [X86] Force use of PCI Configuration Access
3494 Mechanism 1 (config address in IO port 0xCF8,
3495 data in IO port 0xCFC, both 32-bit).
3496 conf2 [X86] Force use of PCI Configuration Access
3497 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3498 the function, IO port 0xCFA, also 8-bit, sets
3499 bus number. The config space is then accessed
3500 through ports 0xC000-0xCFFF).
3501 See http://wiki.osdev.org/PCI for more info
3502 on the configuration access mechanisms.
3503 noaer [PCIE] If the PCIEAER kernel config parameter is
3504 enabled, this kernel boot option can be used to
3505 disable the use of PCIE advanced error reporting.
3506 nodomains [PCI] Disable support for multiple PCI
3507 root domains (aka PCI segments, in ACPI-speak).
3508 nommconf [X86] Disable use of MMCONFIG for PCI
3510 check_enable_amd_mmconf [X86] check for and enable
3511 properly configured MMIO access to PCI
3512 config space on AMD family 10h CPU
3513 nomsi [MSI] If the PCI_MSI kernel config parameter is
3514 enabled, this kernel boot option can be used to
3515 disable the use of MSI interrupts system-wide.
3516 noioapicquirk [APIC] Disable all boot interrupt quirks.
3517 Safety option to keep boot IRQs enabled. This
3518 should never be necessary.
3519 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3520 primary IO-APIC for bridges that cannot disable
3521 boot IRQs. This fixes a source of spurious IRQs
3522 when the system masks IRQs.
3523 noioapicreroute [APIC] Disable workaround that uses the
3524 boot IRQ equivalent of an IRQ that connects to
3525 a chipset where boot IRQs cannot be disabled.
3526 The opposite of ioapicreroute.
3527 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3528 routing table. These calls are known to be buggy
3529 on several machines and they hang the machine
3530 when used, but on other computers it's the only
3531 way to get the interrupt routing table. Try
3532 this option if the kernel is unable to allocate
3533 IRQs or discover secondary PCI buses on your
3535 rom [X86] Assign address space to expansion ROMs.
3536 Use with caution as certain devices share
3537 address decoders between ROMs and other
3539 norom [X86] Do not assign address space to
3540 expansion ROMs that do not already have
3541 BIOS assigned address ranges.
3542 nobar [X86] Do not assign address space to the
3543 BARs that weren't assigned by the BIOS.
3544 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3545 assigned automatically to PCI devices. You can
3546 make the kernel exclude IRQs of your ISA cards
3548 pirqaddr=0xAAAAA [X86] Specify the physical address
3549 of the PIRQ table (normally generated
3550 by the BIOS) if it is outside the
3551 F0000h-100000h range.
3552 lastbus=N [X86] Scan all buses thru bus #N. Can be
3553 useful if the kernel is unable to find your
3554 secondary buses and you want to tell it
3555 explicitly which ones they are.
3556 assign-busses [X86] Always assign all PCI bus
3557 numbers ourselves, overriding
3558 whatever the firmware may have done.
3559 usepirqmask [X86] Honor the possible IRQ mask stored
3560 in the BIOS $PIR table. This is needed on
3561 some systems with broken BIOSes, notably
3562 some HP Pavilion N5400 and Omnibook XE3
3563 notebooks. This will have no effect if ACPI
3564 IRQ routing is enabled.
3565 noacpi [X86] Do not use ACPI for IRQ routing
3566 or for PCI scanning.
3567 use_crs [X86] Use PCI host bridge window information
3568 from ACPI. On BIOSes from 2008 or later, this
3569 is enabled by default. If you need to use this,
3570 please report a bug.
3571 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3572 If you need to use this, please report a bug.
3573 routeirq Do IRQ routing for all PCI devices.
3574 This is normally done in pci_enable_device(),
3575 so this option is a temporary workaround
3576 for broken drivers that don't call it.
3577 skip_isa_align [X86] do not align io start addr, so can
3578 handle more pci cards
3579 noearly [X86] Don't do any early type 1 scanning.
3580 This might help on some broken boards which
3581 machine check when some devices' config space
3582 is read. But various workarounds are disabled
3583 and some IOMMU drivers will not work.
3584 bfsort Sort PCI devices into breadth-first order.
3585 This sorting is done to get a device
3586 order compatible with older (<= 2.4) kernels.
3587 nobfsort Don't sort PCI devices into breadth-first order.
3588 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3589 tuning and use the BIOS-configured MPS defaults.
3590 pcie_bus_safe Set every device's MPS to the largest value
3591 supported by all devices below the root complex.
3592 pcie_bus_perf Set device MPS to the largest allowable MPS
3593 based on its parent bus. Also set MRRS (Max
3594 Read Request Size) to the largest supported
3595 value (no larger than the MPS that the device
3596 or bus can support) for best performance.
3597 pcie_bus_peer2peer Set every device's MPS to 128B, which
3598 every device is guaranteed to support. This
3599 configuration allows peer-to-peer DMA between
3600 any pair of devices, possibly at the cost of
3601 reduced performance. This also guarantees
3602 that hot-added devices will work.
3603 cbiosize=nn[KMG] The fixed amount of bus space which is
3604 reserved for the CardBus bridge's IO window.
3605 The default value is 256 bytes.
3606 cbmemsize=nn[KMG] The fixed amount of bus space which is
3607 reserved for the CardBus bridge's memory
3608 window. The default value is 64 megabytes.
3611 [<order of align>@]<pci_dev>[; ...]
3612 Specifies alignment and device to reassign
3613 aligned memory resources. How to
3614 specify the device is described above.
3615 If <order of align> is not specified,
3616 PAGE_SIZE is used as alignment.
3617 A PCI-PCI bridge can be specified if resource
3618 windows need to be expanded.
3619 To specify the alignment for several
3620 instances of a device, the PCI vendor,
3621 device, subvendor, and subdevice may be
3622 specified, e.g., 12@pci:8086:9c22:103c:198f
3623 for 4096-byte alignment.
3624 ecrc= Enable/disable PCIe ECRC (transaction layer
3625 end-to-end CRC checking).
3626 bios: Use BIOS/firmware settings. This is the
3630 hpiosize=nn[KMG] The fixed amount of bus space which is
3631 reserved for hotplug bridge's IO window.
3632 Default size is 256 bytes.
3633 hpmmiosize=nn[KMG] The fixed amount of bus space which is
3634 reserved for hotplug bridge's MMIO window.
3635 Default size is 2 megabytes.
3636 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
3637 reserved for hotplug bridge's MMIO_PREF window.
3638 Default size is 2 megabytes.
3639 hpmemsize=nn[KMG] The fixed amount of bus space which is
3640 reserved for hotplug bridge's MMIO and
3642 Default size is 2 megabytes.
3643 hpbussize=nn The minimum amount of additional bus numbers
3644 reserved for buses below a hotplug bridge.
3646 realloc= Enable/disable reallocating PCI bridge resources
3647 if allocations done by BIOS are too small to
3648 accommodate resources required by all child
3650 off: Turn realloc off
3652 realloc same as realloc=on
3653 noari do not use PCIe ARI.
3654 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3655 do not use PCIe ATS (and IOMMU device IOTLB).
3656 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3657 only look for one device below a PCIe downstream
3659 big_root_window Try to add a big 64bit memory window to the PCIe
3660 root complex on AMD CPUs. Some GFX hardware
3661 can resize a BAR to allow access to all VRAM.
3662 Adding the window is slightly risky (it may
3663 conflict with unreported devices), so this
3665 disable_acs_redir=<pci_dev>[; ...]
3666 Specify one or more PCI devices (in the format
3667 specified above) separated by semicolons.
3668 Each device specified will have the PCI ACS
3669 redirect capabilities forced off which will
3670 allow P2P traffic between devices through
3671 bridges without forcing it upstream. Note:
3672 this removes isolation between devices and
3673 may put more devices in an IOMMU group.
3674 force_floating [S390] Force usage of floating interrupts.
3675 nomio [S390] Do not use MIO instructions.
3677 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3680 force Enable ASPM even on devices that claim not to support it.
3681 WARNING: Forcing ASPM on may cause system lockups.
3683 pcie_ports= [PCIE] PCIe port services handling:
3684 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3685 even if the platform doesn't give the OS permission to
3686 use them. This may cause conflicts if the platform
3687 also tries to use these services.
3688 dpc-native Use native PCIe service for DPC only. May
3689 cause conflicts if firmware uses AER or DPC.
3690 compat Disable native PCIe services (PME, AER, DPC, PCIe
3693 pcie_port_pm= [PCIE] PCIe port power management handling:
3694 off Disable power management of all PCIe ports
3695 force Forcibly enable power management of all PCIe ports
3697 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3698 nomsi Do not use MSI for native PCIe PME signaling (this makes
3699 all PCIe root ports use INTx for all services).
3701 pcmv= [HW,PCMCIA] BadgePAD 4
3705 Keep all power-domains already enabled by bootloader on,
3706 even if no driver has claimed them. This is useful
3707 for debug and development, but should not be
3708 needed on a platform with proper driver support.
3711 See Documentation/admin-guide/blockdev/paride.rst.
3713 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3716 See arch/parisc/kernel/pdc_chassis.c
3718 percpu_alloc= Select which percpu first chunk allocator to use.
3719 Currently supported values are "embed" and "page".
3720 Archs may support subset or none of the selections.
3721 See comments in mm/percpu.c for details on each
3722 allocator. This parameter is primarily for debugging
3723 and performance comparison.
3726 See Documentation/admin-guide/blockdev/paride.rst.
3729 See Documentation/admin-guide/blockdev/paride.rst.
3731 pirq= [SMP,APIC] Manual mp-table setup
3732 See Documentation/x86/i386/IO-APIC.rst.
3734 plip= [PPT,NET] Parallel port network link
3735 Format: { parport<nr> | timid | 0 }
3736 See also Documentation/admin-guide/parport.rst.
3738 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3739 Override pmtimer IOPort with a hex value.
3742 pm_debug_messages [SUSPEND,KNL]
3743 Enable suspend/resume debug messages during boot up.
3746 Enable PNP debug messages (depends on the
3747 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3748 via /sys/module/pnp/parameters/debug. We always show
3749 current resource usage; turning this on also shows
3750 possible settings and some assignment information.
3756 { on | off | curr | res | no-curr | no-res }
3759 [ISAPNP] Exclude IRQs for the autoconfiguration
3762 [ISAPNP] Exclude DMAs for the autoconfiguration
3764 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3765 Ranges are in pairs (I/O port base and size).
3768 [ISAPNP] Exclude memory regions for the
3770 Ranges are in pairs (memory base and size).
3772 ports= [IP_VS_FTP] IPVS ftp helper module
3774 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3776 Format: <port>,<port>....
3778 powersave=off [PPC] This option disables power saving features.
3779 It specifically disables cpuidle and sets the
3780 platform machine description specific power_save
3781 function to NULL. On Idle the CPU just reduces
3784 ppc_strict_facility_enable
3785 [PPC] This option catches any kernel floating point,
3786 Altivec, VSX and SPE outside of regions specifically
3787 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3788 There is some performance impact when enabling this.
3792 Disable Hardware Transactional Memory
3794 print-fatal-signals=
3795 [KNL] debug: print fatal signals
3797 If enabled, warn about various signal handling
3798 related application anomalies: too many signals,
3799 too many POSIX.1 timers, fatal signals causing a
3802 If you hit the warning due to signal overflow,
3803 you might want to try "ulimit -i unlimited".
3807 printk.always_kmsg_dump=
3808 Trigger kmsg_dump for cases other than kernel oops or
3810 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3813 printk.devkmsg={on,off,ratelimit}
3814 Control writing to /dev/kmsg.
3815 on - unlimited logging to /dev/kmsg from userspace
3816 off - logging to /dev/kmsg disabled
3817 ratelimit - ratelimit the logging
3820 printk.time= Show timing data prefixed to each printk message line
3821 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3823 processor.max_cstate= [HW,ACPI]
3824 Limit processor to maximum C-state
3825 max_cstate=9 overrides any DMI blacklist limit.
3827 processor.nocst [HW,ACPI]
3828 Ignore the _CST method to determine C-states,
3829 instead using the legacy FADT method
3831 profile= [KNL] Enable kernel profiling via /proc/profile
3832 Format: [<profiletype>,]<number>
3833 Param: <profiletype>: "schedule", "sleep", or "kvm"
3834 [defaults to kernel profiling]
3835 Param: "schedule" - profile schedule points.
3836 Param: "sleep" - profile D-state sleeping (millisecs).
3837 Requires CONFIG_SCHEDSTATS
3838 Param: "kvm" - profile VM exits.
3839 Param: <number> - step/bucket size as a power of 2 for
3840 statistical time based profiling.
3842 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3844 See Documentation/admin-guide/blockdev/ramdisk.rst.
3846 prot_virt= [S390] enable hosting protected virtual machines
3847 isolated from the hypervisor (if hardware supports
3851 psi= [KNL] Enable or disable pressure stall information
3855 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3856 probe for; one of (bare|imps|exps|lifebook|any).
3857 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3859 psmouse.resetafter= [HW,MOUSE]
3860 Try to reset the device after so many bad packets
3863 [HW,MOUSE] Set desired mouse resolution, in dpi.
3864 psmouse.smartscroll=
3865 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3866 0 = disabled, 1 = enabled (default).
3868 pstore.backend= Specify the name of the pstore backend to use
3871 See Documentation/admin-guide/blockdev/paride.rst.
3873 pti= [X86_64] Control Page Table Isolation of user and
3874 kernel address spaces. Disabling this feature
3875 removes hardening, but improves performance of
3876 system calls and interrupts.
3878 on - unconditionally enable
3879 off - unconditionally disable
3880 auto - kernel detects whether your CPU model is
3881 vulnerable to issues that PTI mitigates
3883 Not specifying this option is equivalent to pti=auto.
3886 Equivalent to pti=off
3889 [KNL] Number of legacy pty's. Overwrites compiled-in
3892 quiet [KNL] Disable most log messages
3897 See Documentation/admin-guide/md.rst.
3899 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3900 See Documentation/admin-guide/blockdev/ramdisk.rst.
3902 random.trust_cpu={on,off}
3903 [KNL] Enable or disable trusting the use of the
3904 CPU's random number generator (if available) to
3905 fully seed the kernel's CRNG. Default is controlled
3906 by CONFIG_RANDOM_TRUST_CPU.
3908 ras=option[,option,...] [KNL] RAS-specific options
3911 Disable the Correctable Errors Collector,
3912 see CONFIG_RAS_CEC help text.
3915 The argument is a cpu list, as described above,
3916 except that the string "all" can be used to
3917 specify every CPU on the system.
3919 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3920 the specified list of CPUs to be no-callback CPUs.
3921 Invocation of these CPUs' RCU callbacks will be
3922 offloaded to "rcuox/N" kthreads created for that
3923 purpose, where "x" is "p" for RCU-preempt, and
3924 "s" for RCU-sched, and "N" is the CPU number.
3925 This reduces OS jitter on the offloaded CPUs,
3926 which can be useful for HPC and real-time
3927 workloads. It can also improve energy efficiency
3928 for asymmetric multiprocessors.
3931 Rather than requiring that offloaded CPUs
3932 (specified by rcu_nocbs= above) explicitly
3933 awaken the corresponding "rcuoN" kthreads,
3934 make these kthreads poll for callbacks.
3935 This improves the real-time response for the
3936 offloaded CPUs by relieving them of the need to
3937 wake up the corresponding kthread, but degrades
3938 energy efficiency by requiring that the kthreads
3939 periodically wake up to do the polling.
3941 rcutree.blimit= [KNL]
3942 Set maximum number of finished RCU callbacks to
3943 process in one batch.
3945 rcutree.dump_tree= [KNL]
3946 Dump the structure of the rcu_node combining tree
3947 out at early boot. This is used for diagnostic
3948 purposes, to verify correct tree setup.
3950 rcutree.gp_cleanup_delay= [KNL]
3951 Set the number of jiffies to delay each step of
3952 RCU grace-period cleanup.
3954 rcutree.gp_init_delay= [KNL]
3955 Set the number of jiffies to delay each step of
3956 RCU grace-period initialization.
3958 rcutree.gp_preinit_delay= [KNL]
3959 Set the number of jiffies to delay each step of
3960 RCU grace-period pre-initialization, that is,
3961 the propagation of recent CPU-hotplug changes up
3962 the rcu_node combining tree.
3964 rcutree.use_softirq= [KNL]
3965 If set to zero, move all RCU_SOFTIRQ processing to
3966 per-CPU rcuc kthreads. Defaults to a non-zero
3967 value, meaning that RCU_SOFTIRQ is used by default.
3968 Specify rcutree.use_softirq=0 to use rcuc kthreads.
3970 rcutree.rcu_fanout_exact= [KNL]
3971 Disable autobalancing of the rcu_node combining
3972 tree. This is used by rcutorture, and might
3973 possibly be useful for architectures having high
3974 cache-to-cache transfer latencies.
3976 rcutree.rcu_fanout_leaf= [KNL]
3977 Change the number of CPUs assigned to each
3978 leaf rcu_node structure. Useful for very
3979 large systems, which will choose the value 64,
3980 and for NUMA systems with large remote-access
3981 latencies, which will choose a value aligned
3982 with the appropriate hardware boundaries.
3984 rcutree.jiffies_till_first_fqs= [KNL]
3985 Set delay from grace-period initialization to
3986 first attempt to force quiescent states.
3987 Units are jiffies, minimum value is zero,
3988 and maximum value is HZ.
3990 rcutree.jiffies_till_next_fqs= [KNL]
3991 Set delay between subsequent attempts to force
3992 quiescent states. Units are jiffies, minimum
3993 value is one, and maximum value is HZ.
3995 rcutree.jiffies_till_sched_qs= [KNL]
3996 Set required age in jiffies for a
3997 given grace period before RCU starts
3998 soliciting quiescent-state help from
3999 rcu_note_context_switch() and cond_resched().
4000 If not specified, the kernel will calculate
4001 a value based on the most recent settings
4002 of rcutree.jiffies_till_first_fqs
4003 and rcutree.jiffies_till_next_fqs.
4004 This calculated value may be viewed in
4005 rcutree.jiffies_to_sched_qs. Any attempt to set
4006 rcutree.jiffies_to_sched_qs will be cheerfully
4009 rcutree.kthread_prio= [KNL,BOOT]
4010 Set the SCHED_FIFO priority of the RCU per-CPU
4011 kthreads (rcuc/N). This value is also used for
4012 the priority of the RCU boost threads (rcub/N)
4013 and for the RCU grace-period kthreads (rcu_bh,
4014 rcu_preempt, and rcu_sched). If RCU_BOOST is
4015 set, valid values are 1-99 and the default is 1
4016 (the least-favored priority). Otherwise, when
4017 RCU_BOOST is not set, valid values are 0-99 and
4018 the default is zero (non-realtime operation).
4020 rcutree.rcu_nocb_gp_stride= [KNL]
4021 Set the number of NOCB callback kthreads in
4022 each group, which defaults to the square root
4023 of the number of CPUs. Larger numbers reduce
4024 the wakeup overhead on the global grace-period
4025 kthread, but increases that same overhead on
4026 each group's NOCB grace-period kthread.
4028 rcutree.qhimark= [KNL]
4029 Set threshold of queued RCU callbacks beyond which
4030 batch limiting is disabled.
4032 rcutree.qlowmark= [KNL]
4033 Set threshold of queued RCU callbacks below which
4034 batch limiting is re-enabled.
4036 rcutree.qovld= [KNL]
4037 Set threshold of queued RCU callbacks beyond which
4038 RCU's force-quiescent-state scan will aggressively
4039 enlist help from cond_resched() and sched IPIs to
4040 help CPUs more quickly reach quiescent states.
4041 Set to less than zero to make this be set based
4042 on rcutree.qhimark at boot time and to zero to
4043 disable more aggressive help enlistment.
4045 rcutree.rcu_idle_gp_delay= [KNL]
4046 Set wakeup interval for idle CPUs that have
4047 RCU callbacks (RCU_FAST_NO_HZ=y).
4049 rcutree.rcu_idle_lazy_gp_delay= [KNL]
4050 Set wakeup interval for idle CPUs that have
4051 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
4052 Lazy RCU callbacks are those which RCU can
4053 prove do nothing more than free memory.
4055 rcutree.rcu_kick_kthreads= [KNL]
4056 Cause the grace-period kthread to get an extra
4057 wake_up() if it sleeps three times longer than
4058 it should at force-quiescent-state time.
4059 This wake_up() will be accompanied by a
4060 WARN_ONCE() splat and an ftrace_dump().
4062 rcutree.sysrq_rcu= [KNL]
4063 Commandeer a sysrq key to dump out Tree RCU's
4064 rcu_node tree with an eye towards determining
4065 why a new grace period has not yet started.
4067 rcuperf.gp_async= [KNL]
4068 Measure performance of asynchronous
4069 grace-period primitives such as call_rcu().
4071 rcuperf.gp_async_max= [KNL]
4072 Specify the maximum number of outstanding
4073 callbacks per writer thread. When a writer
4074 thread exceeds this limit, it invokes the
4075 corresponding flavor of rcu_barrier() to allow
4076 previously posted callbacks to drain.
4078 rcuperf.gp_exp= [KNL]
4079 Measure performance of expedited synchronous
4080 grace-period primitives.
4082 rcuperf.holdoff= [KNL]
4083 Set test-start holdoff period. The purpose of
4084 this parameter is to delay the start of the
4085 test until boot completes in order to avoid
4088 rcuperf.kfree_rcu_test= [KNL]
4089 Set to measure performance of kfree_rcu() flooding.
4091 rcuperf.kfree_nthreads= [KNL]
4092 The number of threads running loops of kfree_rcu().
4094 rcuperf.kfree_alloc_num= [KNL]
4095 Number of allocations and frees done in an iteration.
4097 rcuperf.kfree_loops= [KNL]
4098 Number of loops doing rcuperf.kfree_alloc_num number
4099 of allocations and frees.
4101 rcuperf.nreaders= [KNL]
4102 Set number of RCU readers. The value -1 selects
4103 N, where N is the number of CPUs. A value
4104 "n" less than -1 selects N-n+1, where N is again
4105 the number of CPUs. For example, -2 selects N
4106 (the number of CPUs), -3 selects N+1, and so on.
4107 A value of "n" less than or equal to -N selects
4110 rcuperf.nwriters= [KNL]
4111 Set number of RCU writers. The values operate
4112 the same as for rcuperf.nreaders.
4113 N, where N is the number of CPUs
4115 rcuperf.perf_type= [KNL]
4116 Specify the RCU implementation to test.
4118 rcuperf.shutdown= [KNL]
4119 Shut the system down after performance tests
4120 complete. This is useful for hands-off automated
4123 rcuperf.verbose= [KNL]
4124 Enable additional printk() statements.
4126 rcuperf.writer_holdoff= [KNL]
4127 Write-side holdoff between grace periods,
4128 in microseconds. The default of zero says
4131 rcutorture.fqs_duration= [KNL]
4132 Set duration of force_quiescent_state bursts
4135 rcutorture.fqs_holdoff= [KNL]
4136 Set holdoff time within force_quiescent_state bursts
4139 rcutorture.fqs_stutter= [KNL]
4140 Set wait time between force_quiescent_state bursts
4143 rcutorture.fwd_progress= [KNL]
4144 Enable RCU grace-period forward-progress testing
4145 for the types of RCU supporting this notion.
4147 rcutorture.fwd_progress_div= [KNL]
4148 Specify the fraction of a CPU-stall-warning
4149 period to do tight-loop forward-progress testing.
4151 rcutorture.fwd_progress_holdoff= [KNL]
4152 Number of seconds to wait between successive
4153 forward-progress tests.
4155 rcutorture.fwd_progress_need_resched= [KNL]
4156 Enclose cond_resched() calls within checks for
4157 need_resched() during tight-loop forward-progress
4160 rcutorture.gp_cond= [KNL]
4161 Use conditional/asynchronous update-side
4162 primitives, if available.
4164 rcutorture.gp_exp= [KNL]
4165 Use expedited update-side primitives, if available.
4167 rcutorture.gp_normal= [KNL]
4168 Use normal (non-expedited) asynchronous
4169 update-side primitives, if available.
4171 rcutorture.gp_sync= [KNL]
4172 Use normal (non-expedited) synchronous
4173 update-side primitives, if available. If all
4174 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4175 rcutorture.gp_normal=, and rcutorture.gp_sync=
4176 are zero, rcutorture acts as if is interpreted
4177 they are all non-zero.
4179 rcutorture.n_barrier_cbs= [KNL]
4180 Set callbacks/threads for rcu_barrier() testing.
4182 rcutorture.nfakewriters= [KNL]
4183 Set number of concurrent RCU writers. These just
4184 stress RCU, they don't participate in the actual
4185 test, hence the "fake".
4187 rcutorture.nreaders= [KNL]
4188 Set number of RCU readers. The value -1 selects
4189 N-1, where N is the number of CPUs. A value
4190 "n" less than -1 selects N-n-2, where N is again
4191 the number of CPUs. For example, -2 selects N
4192 (the number of CPUs), -3 selects N+1, and so on.
4194 rcutorture.object_debug= [KNL]
4195 Enable debug-object double-call_rcu() testing.
4197 rcutorture.onoff_holdoff= [KNL]
4198 Set time (s) after boot for CPU-hotplug testing.
4200 rcutorture.onoff_interval= [KNL]
4201 Set time (jiffies) between CPU-hotplug operations,
4202 or zero to disable CPU-hotplug testing.
4204 rcutorture.shuffle_interval= [KNL]
4205 Set task-shuffle interval (s). Shuffling tasks
4206 allows some CPUs to go into dyntick-idle mode
4207 during the rcutorture test.
4209 rcutorture.shutdown_secs= [KNL]
4210 Set time (s) after boot system shutdown. This
4211 is useful for hands-off automated testing.
4213 rcutorture.stall_cpu= [KNL]
4214 Duration of CPU stall (s) to test RCU CPU stall
4215 warnings, zero to disable.
4217 rcutorture.stall_cpu_holdoff= [KNL]
4218 Time to wait (s) after boot before inducing stall.
4220 rcutorture.stall_cpu_irqsoff= [KNL]
4221 Disable interrupts while stalling if set.
4223 rcutorture.stat_interval= [KNL]
4224 Time (s) between statistics printk()s.
4226 rcutorture.stutter= [KNL]
4227 Time (s) to stutter testing, for example, specifying
4228 five seconds causes the test to run for five seconds,
4229 wait for five seconds, and so on. This tests RCU's
4230 ability to transition abruptly to and from idle.
4232 rcutorture.test_boost= [KNL]
4233 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4234 "Maybe" means test if the RCU implementation
4235 under test support RCU priority boosting.
4237 rcutorture.test_boost_duration= [KNL]
4238 Duration (s) of each individual boost test.
4240 rcutorture.test_boost_interval= [KNL]
4241 Interval (s) between each boost test.
4243 rcutorture.test_no_idle_hz= [KNL]
4244 Test RCU's dyntick-idle handling. See also the
4245 rcutorture.shuffle_interval parameter.
4247 rcutorture.torture_type= [KNL]
4248 Specify the RCU implementation to test.
4250 rcutorture.verbose= [KNL]
4251 Enable additional printk() statements.
4253 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4254 Dump ftrace buffer after reporting RCU CPU
4257 rcupdate.rcu_cpu_stall_suppress= [KNL]
4258 Suppress RCU CPU stall warning messages.
4260 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
4261 Suppress RCU CPU stall warning messages and
4262 rcutorture writer stall warnings that occur
4263 during early boot, that is, during the time
4264 before the init task is spawned.
4266 rcupdate.rcu_cpu_stall_timeout= [KNL]
4267 Set timeout for RCU CPU stall warning messages.
4269 rcupdate.rcu_expedited= [KNL]
4270 Use expedited grace-period primitives, for
4271 example, synchronize_rcu_expedited() instead
4272 of synchronize_rcu(). This reduces latency,
4273 but can increase CPU utilization, degrade
4274 real-time latency, and degrade energy efficiency.
4275 No effect on CONFIG_TINY_RCU kernels.
4277 rcupdate.rcu_normal= [KNL]
4278 Use only normal grace-period primitives,
4279 for example, synchronize_rcu() instead of
4280 synchronize_rcu_expedited(). This improves
4281 real-time latency, CPU utilization, and
4282 energy efficiency, but can expose users to
4283 increased grace-period latency. This parameter
4284 overrides rcupdate.rcu_expedited. No effect on
4285 CONFIG_TINY_RCU kernels.
4287 rcupdate.rcu_normal_after_boot= [KNL]
4288 Once boot has completed (that is, after
4289 rcu_end_inkernel_boot() has been invoked), use
4290 only normal grace-period primitives. No effect
4291 on CONFIG_TINY_RCU kernels.
4293 rcupdate.rcu_task_stall_timeout= [KNL]
4294 Set timeout in jiffies for RCU task stall warning
4295 messages. Disable with a value less than or equal
4298 rcupdate.rcu_self_test= [KNL]
4299 Run the RCU early boot self tests
4303 Run specified binary instead of /init from the ramdisk,
4304 used for early userspace startup. See initrd.
4307 force - Override the decision by the kernel to hide the
4308 advertisement of RDRAND support (this affects
4309 certain AMD processors because of buggy BIOS
4310 support, specifically around the suspend/resume
4314 Turn on/off individual RDT features. List is:
4315 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4317 E.g. to turn on cmt and turn off mba use:
4321 Format (x86 or x86_64):
4322 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4324 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4326 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4327 (prefix with 'panic_' to set mode for panic
4329 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4330 reboot_force is either force or not specified,
4331 reboot_cpu is s[mp]#### with #### being the processor
4332 to be used for rebooting.
4335 [KNL, SMP] Set scheduler's default relax_domain_level.
4336 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4338 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4339 Format: <base1>,<size1>[,<base2>,<size2>,...]
4340 Reserve I/O ports or memory so the kernel won't use
4341 them. If <base> is less than 0x10000, the region
4342 is assumed to be I/O ports; otherwise it is memory.
4344 reservetop= [X86-32]
4346 Reserves a hole at the top of the kernel virtual
4351 Set the amount of memory to reserve for BIOS at
4352 the bottom of the address space.
4354 reset_devices [KNL] Force drivers to reset the underlying device
4355 during initialization.
4358 Specify the partition device for software suspend
4360 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4362 resume_offset= [SWSUSP]
4363 Specify the offset from the beginning of the partition
4364 given by "resume=" at which the swap header is located,
4365 in <PAGE_SIZE> units (needed only for swap files).
4366 See Documentation/power/swsusp-and-swap-files.rst
4368 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4369 read the resume files
4371 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4372 Useful for devices that are detected asynchronously
4373 (e.g. USB and MMC devices).
4375 hibernate= [HIBERNATION]
4376 noresume Don't check if there's a hibernation image
4377 present during boot.
4378 nocompress Don't compress/decompress hibernation images.
4379 no Disable hibernation and resume.
4380 protect_image Turn on image protection during restoration
4381 (that will set all pages holding image data
4382 during restoration read-only).
4384 retain_initrd [RAM] Keep initrd memory after extraction
4386 rfkill.default_state=
4387 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4388 etc. communication is blocked by default.
4391 rfkill.master_switch_mode=
4392 0 The "airplane mode" button does nothing.
4393 1 The "airplane mode" button toggles between everything
4394 blocked and the previous configuration.
4395 2 The "airplane mode" button toggles between everything
4396 blocked and everything unblocked.
4398 rhash_entries= [KNL,NET]
4399 Set number of hash buckets for route cache
4402 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4405 ro [KNL] Mount root device read-only on boot
4408 on Mark read-only kernel memory as read-only (default).
4409 off Leave read-only kernel memory writable for debugging.
4412 Enable the uart passthrough on the designated usb port
4413 on Rockchip SoCs. When active, the signals of the
4414 debug-uart get routed to the D+ and D- pins of the usb
4415 port and the regular usb controller gets disabled.
4417 root= [KNL] Root filesystem
4418 See name_to_dev_t comment in init/do_mounts.c.
4420 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4421 mount the root filesystem
4423 rootflags= [KNL] Set root filesystem mount option string
4425 rootfstype= [KNL] Set root filesystem type
4427 rootwait [KNL] Wait (indefinitely) for root device to show up.
4428 Useful for devices that are detected asynchronously
4429 (e.g. USB and MMC devices).
4431 rproc_mem=nn[KMG][@address]
4432 [KNL,ARM,CMA] Remoteproc physical memory block.
4433 Memory area to be used by remote processor image,
4436 rw [KNL] Mount root device read-write on boot
4438 S [KNL] Run init in single mode
4440 s390_iommu= [HW,S390]
4441 Set s390 IOTLB flushing mode
4443 With strict flushing every unmap operation will result in
4444 an IOTLB flush. Default is lazy flushing before reuse,
4448 See drivers/net/irda/sa1100_ir.c.
4450 sbni= [NET] Granch SBNI12 leased line adapter
4452 sched_debug [KNL] Enables verbose scheduler debug messages.
4454 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4455 Allowed values are enable and disable. This feature
4456 incurs a small amount of overhead in the scheduler
4457 but is useful for debugging and performance tuning.
4459 sched_thermal_decay_shift=
4460 [KNL, SMP] Set a decay shift for scheduler thermal
4461 pressure signal. Thermal pressure signal follows the
4462 default decay period of other scheduler pelt
4463 signals(usually 32 ms but configurable). Setting
4464 sched_thermal_decay_shift will left shift the decay
4465 period for the thermal pressure signal by the shift
4467 i.e. with the default pelt decay period of 32 ms
4468 sched_thermal_decay_shift thermal pressure decay pr
4472 Format: integer between 0 and 10
4475 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4476 xtime_lock contention on larger systems, and/or RCU lock
4477 contention on all systems with CONFIG_MAXSMP set.
4478 Format: { "0" | "1" }
4479 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4481 Note: increases power consumption, thus should only be
4482 enabled if running jitter sensitive (HPC/RT) workloads.
4484 security= [SECURITY] Choose a legacy "major" security module to
4485 enable at boot. This has been deprecated by the
4488 selinux= [SELINUX] Disable or enable SELinux at boot time.
4489 Format: { "0" | "1" }
4490 See security/selinux/Kconfig help text.
4495 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4496 Format: { "0" | "1" }
4497 See security/apparmor/Kconfig help text
4500 Default value is set via kernel config option.
4502 serialnumber [BUGS=X86-32]
4505 Maximal number of shapers.
4513 Disable merging of slabs with similar size. May be
4514 necessary if there is some reason to distinguish
4515 allocs to different slabs, especially in hardened
4516 environments where the risk of heap overflows and
4517 layout control by attackers can usually be
4518 frustrated by disabling merging. This will reduce
4519 most of the exposure of a heap attack to a single
4520 cache (risks via metadata attacks are mostly
4521 unchanged). Debug options disable merging on their
4523 For more information see Documentation/vm/slub.rst.
4525 slab_max_order= [MM, SLAB]
4526 Determines the maximum allowed order for slabs.
4527 A high setting may cause OOMs due to memory
4528 fragmentation. Defaults to 1 for systems with
4529 more than 32MB of RAM, 0 otherwise.
4531 slub_debug[=options[,slabs]] [MM, SLUB]
4532 Enabling slub_debug allows one to determine the
4533 culprit if slab objects become corrupted. Enabling
4534 slub_debug can create guard zones around objects and
4535 may poison objects when not in use. Also tracks the
4536 last alloc / free. For more information see
4537 Documentation/vm/slub.rst.
4539 slub_memcg_sysfs= [MM, SLUB]
4540 Determines whether to enable sysfs directories for
4541 memory cgroup sub-caches. 1 to enable, 0 to disable.
4542 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4543 Enabling this can lead to a very high number of debug
4544 directories and files being created under
4547 slub_max_order= [MM, SLUB]
4548 Determines the maximum allowed order for slabs.
4549 A high setting may cause OOMs due to memory
4550 fragmentation. For more information see
4551 Documentation/vm/slub.rst.
4553 slub_min_objects= [MM, SLUB]
4554 The minimum number of objects per slab. SLUB will
4555 increase the slab order up to slub_max_order to
4556 generate a sufficiently large slab able to contain
4557 the number of objects indicated. The higher the number
4558 of objects the smaller the overhead of tracking slabs
4559 and the less frequently locks need to be acquired.
4560 For more information see Documentation/vm/slub.rst.
4562 slub_min_order= [MM, SLUB]
4563 Determines the minimum page order for slabs. Must be
4564 lower than slub_max_order.
4565 For more information see Documentation/vm/slub.rst.
4567 slub_nomerge [MM, SLUB]
4568 Same with slab_nomerge. This is supported for legacy.
4569 See slab_nomerge for more information.
4572 Format: <io1>[,<io2>[,...,<io8>]]
4574 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4575 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4576 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4577 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4578 smsc-ircc2.ircc_irq= [HW] IRQ line
4579 smsc-ircc2.ircc_dma= [HW] DMA channel
4580 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4581 0: Toshiba Satellite 1800 (GP data pin select)
4582 1: Fast pin select (default)
4585 smt [KNL,S390] Set the maximum number of threads (logical
4586 CPUs) to use per physical CPU on systems capable of
4587 symmetric multithreading (SMT). Will be capped to the
4588 actual hardware limit.
4590 Default: -1 (no limit)
4593 [KNL] Should the soft-lockup detector generate panics.
4596 A nonzero value instructs the soft-lockup detector
4597 to panic the machine when a soft-lockup occurs. It is
4598 also controlled by the kernel.softlockup_panic sysctl
4599 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
4600 respective build-time switch to that functionality.
4602 softlockup_all_cpu_backtrace=
4603 [KNL] Should the soft-lockup detector generate
4604 backtraces on all cpus.
4607 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4608 See Documentation/admin-guide/laptops/sonypi.rst
4610 spectre_v2= [X86] Control mitigation of Spectre variant 2
4611 (indirect branch speculation) vulnerability.
4612 The default operation protects the kernel from
4615 on - unconditionally enable, implies
4617 off - unconditionally disable, implies
4619 auto - kernel detects whether your CPU model is
4622 Selecting 'on' will, and 'auto' may, choose a
4623 mitigation method at run time according to the
4624 CPU, the available microcode, the setting of the
4625 CONFIG_RETPOLINE configuration option, and the
4626 compiler with which the kernel was built.
4628 Selecting 'on' will also enable the mitigation
4629 against user space to user space task attacks.
4631 Selecting 'off' will disable both the kernel and
4632 the user space protections.
4634 Specific mitigations can also be selected manually:
4636 retpoline - replace indirect branches
4637 retpoline,generic - google's original retpoline
4638 retpoline,amd - AMD-specific minimal thunk
4640 Not specifying this option is equivalent to
4644 [X86] Control mitigation of Spectre variant 2
4645 (indirect branch speculation) vulnerability between
4648 on - Unconditionally enable mitigations. Is
4649 enforced by spectre_v2=on
4651 off - Unconditionally disable mitigations. Is
4652 enforced by spectre_v2=off
4654 prctl - Indirect branch speculation is enabled,
4655 but mitigation can be enabled via prctl
4656 per thread. The mitigation control state
4657 is inherited on fork.
4660 - Like "prctl" above, but only STIBP is
4661 controlled per thread. IBPB is issued
4662 always when switching between different user
4666 - Same as "prctl" above, but all seccomp
4667 threads will enable the mitigation unless
4668 they explicitly opt out.
4671 - Like "seccomp" above, but only STIBP is
4672 controlled per thread. IBPB is issued
4673 always when switching between different
4674 user space processes.
4676 auto - Kernel selects the mitigation depending on
4677 the available CPU features and vulnerability.
4680 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4682 Not specifying this option is equivalent to
4683 spectre_v2_user=auto.
4685 spec_store_bypass_disable=
4686 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4687 (Speculative Store Bypass vulnerability)
4689 Certain CPUs are vulnerable to an exploit against a
4690 a common industry wide performance optimization known
4691 as "Speculative Store Bypass" in which recent stores
4692 to the same memory location may not be observed by
4693 later loads during speculative execution. The idea
4694 is that such stores are unlikely and that they can
4695 be detected prior to instruction retirement at the
4696 end of a particular speculation execution window.
4698 In vulnerable processors, the speculatively forwarded
4699 store can be used in a cache side channel attack, for
4700 example to read memory to which the attacker does not
4701 directly have access (e.g. inside sandboxed code).
4703 This parameter controls whether the Speculative Store
4704 Bypass optimization is used.
4706 On x86 the options are:
4708 on - Unconditionally disable Speculative Store Bypass
4709 off - Unconditionally enable Speculative Store Bypass
4710 auto - Kernel detects whether the CPU model contains an
4711 implementation of Speculative Store Bypass and
4712 picks the most appropriate mitigation. If the
4713 CPU is not vulnerable, "off" is selected. If the
4714 CPU is vulnerable the default mitigation is
4715 architecture and Kconfig dependent. See below.
4716 prctl - Control Speculative Store Bypass per thread
4717 via prctl. Speculative Store Bypass is enabled
4718 for a process by default. The state of the control
4719 is inherited on fork.
4720 seccomp - Same as "prctl" above, but all seccomp threads
4721 will disable SSB unless they explicitly opt out.
4723 Default mitigations:
4724 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4726 On powerpc the options are:
4728 on,auto - On Power8 and Power9 insert a store-forwarding
4729 barrier on kernel entry and exit. On Power7
4730 perform a software flush on kernel entry and
4734 Not specifying this option is equivalent to
4735 spec_store_bypass_disable=auto.
4737 spia_io_base= [HW,MTD]
4743 [X86] Enable split lock detection
4745 When enabled (and if hardware support is present), atomic
4746 instructions that access data across cache line
4747 boundaries will result in an alignment check exception.
4751 warn - the kernel will emit rate limited warnings
4752 about applications triggering the #AC
4753 exception. This mode is the default on CPUs
4754 that supports split lock detection.
4756 fatal - the kernel will send SIGBUS to applications
4757 that trigger the #AC exception.
4759 If an #AC exception is hit in the kernel or in
4760 firmware (i.e. not while executing in user mode)
4761 the kernel will oops in either "warn" or "fatal"
4764 srcutree.counter_wrap_check [KNL]
4765 Specifies how frequently to check for
4766 grace-period sequence counter wrap for the
4767 srcu_data structure's ->srcu_gp_seq_needed field.
4768 The greater the number of bits set in this kernel
4769 parameter, the less frequently counter wrap will
4770 be checked for. Note that the bottom two bits
4773 srcutree.exp_holdoff [KNL]
4774 Specifies how many nanoseconds must elapse
4775 since the end of the last SRCU grace period for
4776 a given srcu_struct until the next normal SRCU
4777 grace period will be considered for automatic
4778 expediting. Set to zero to disable automatic
4782 Speculative Store Bypass Disable control
4784 On CPUs that are vulnerable to the Speculative
4785 Store Bypass vulnerability and offer a
4786 firmware based mitigation, this parameter
4787 indicates how the mitigation should be used:
4789 force-on: Unconditionally enable mitigation for
4790 for both kernel and userspace
4791 force-off: Unconditionally disable mitigation for
4792 for both kernel and userspace
4793 kernel: Always enable mitigation in the
4794 kernel, and offer a prctl interface
4795 to allow userspace to register its
4796 interest in being mitigated too.
4798 stack_guard_gap= [MM]
4799 override the default stack gap protection. The value
4800 is in page units and it defines how many pages prior
4801 to (for stacks growing down) resp. after (for stacks
4802 growing up) the main stack are reserved for no other
4803 mapping. Default value is 256 pages.
4806 Enabled the stack tracer on boot up.
4808 stacktrace_filter=[function-list]
4809 [FTRACE] Limit the functions that the stack tracer
4810 will trace at boot up. function-list is a comma separated
4811 list of functions. This list can be changed at run
4812 time by the stack_trace_filter file in the debugfs
4813 tracing directory. Note, this enables stack tracing
4814 and the stacktrace above is not needed.
4818 Set the STI (builtin display/keyboard on the HP-PARISC
4819 machines) console (graphic card) which should be used
4820 as the initial boot-console.
4821 See also comment in drivers/video/console/sticore.c.
4824 See comment in drivers/video/console/sticore.c.
4827 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4829 sunrpc.min_resvport=
4830 sunrpc.max_resvport=
4832 SunRPC servers often require that client requests
4833 originate from a privileged port (i.e. a port in the
4834 range 0 < portnr < 1024).
4835 An administrator who wishes to reserve some of these
4836 ports for other uses may adjust the range that the
4837 kernel's sunrpc client considers to be privileged
4838 using these two parameters to set the minimum and
4839 maximum port values.
4841 sunrpc.svc_rpc_per_connection_limit=
4843 Limit the number of requests that the server will
4844 process in parallel from a single connection.
4845 The default value is 0 (no limit).
4849 Control how the NFS server code allocates CPUs to
4850 service thread pools. Depending on how many NICs
4851 you have and where their interrupts are bound, this
4852 option will affect which CPUs will do NFS serving.
4853 Note: this parameter cannot be changed while the
4854 NFS server is running.
4856 auto the server chooses an appropriate mode
4857 automatically using heuristics
4858 global a single global pool contains all CPUs
4859 percpu one pool for each CPU
4860 pernode one pool for each NUMA node (equivalent
4861 to global on non-NUMA machines)
4863 sunrpc.tcp_slot_table_entries=
4864 sunrpc.udp_slot_table_entries=
4866 Sets the upper limit on the number of simultaneous
4867 RPC calls that can be sent from the client to a
4868 server. Increasing these values may allow you to
4869 improve throughput, but will also increase the
4870 amount of memory reserved for use by the client.
4872 suspend.pm_test_delay=
4874 Sets the number of seconds to remain in a suspend test
4875 mode before resuming the system (see
4876 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4877 is set. Default value is 5.
4880 Format: { on | off | y | n | 1 | 0 }
4881 This parameter controls use of the Protected
4882 Execution Facility on pSeries.
4885 [KNL] Enable accounting of swap in memory resource
4886 controller if no parameter or 1 is given or disable
4887 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
4889 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4890 Format: { <int> | force | noforce }
4891 <int> -- Number of I/O TLB slabs
4892 force -- force using of bounce buffers even if they
4893 wouldn't be automatically used by the kernel
4894 noforce -- Never use bounce buffers (for debugging)
4898 sysfs.deprecated=0|1 [KNL]
4899 Enable/disable old style sysfs layout for old udev
4900 on older distributions. When this option is enabled
4901 very new udev will not work anymore. When this option
4902 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4903 in older udev will not work anymore.
4904 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4905 the kernel configuration.
4907 sysrq_always_enabled
4909 Ignore sysrq setting - this boot parameter will
4910 neutralize any effect of /proc/sys/kernel/sysrq.
4911 Useful for debugging.
4913 tcpmhash_entries= [KNL,NET]
4914 Set the number of tcp_metrics_hash slots.
4915 Default value is 8192 or 16384 depending on total
4916 ram pages. This is used to specify the TCP metrics
4917 cache size. See Documentation/networking/ip-sysctl.txt
4918 "tcp_no_metrics_save" section for more details.
4922 test_suspend= [SUSPEND][,N]
4923 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4924 standby suspend) or "freeze" (for suspend type freeze)
4925 as the system sleep state during system startup with
4926 the optional capability to repeat N number of times.
4927 The system is woken from this state using a
4928 wakeup-capable RTC alarm.
4930 thash_entries= [KNL,NET]
4931 Set number of hash buckets for TCP connection
4933 thermal.act= [HW,ACPI]
4934 -1: disable all active trip points in all thermal zones
4935 <degrees C>: override all lowest active trip points
4937 thermal.crt= [HW,ACPI]
4938 -1: disable all critical trip points in all thermal zones
4939 <degrees C>: override all critical trip points
4941 thermal.nocrt= [HW,ACPI]
4942 Set to disable actions on ACPI thermal zone
4943 critical and hot trip points.
4945 thermal.off= [HW,ACPI]
4946 1: disable ACPI thermal control
4948 thermal.psv= [HW,ACPI]
4949 -1: disable all passive trip points
4950 <degrees C>: override all passive trip points to this
4953 thermal.tzp= [HW,ACPI]
4954 Specify global default ACPI thermal zone polling rate
4955 <deci-seconds>: poll all this frequency
4956 0: no polling (default)
4959 Force threading of all interrupt handlers except those
4960 marked explicitly IRQF_NO_THREAD.
4964 Specify if the kernel should make use of the cpu
4965 topology information if the hardware supports this.
4966 The scheduler will make use of this information and
4967 e.g. base its process migration decisions on it.
4970 topology_updates= [KNL, PPC, NUMA]
4972 Specify if the kernel should ignore (off)
4973 topology updates sent by the hypervisor to this
4976 torture.disable_onoff_at_boot= [KNL]
4977 Prevent the CPU-hotplug component of torturing
4978 until after init has spawned.
4982 tpm_suspend_pcr=[HW,TPM]
4983 Format: integer pcr id
4984 Specify that at suspend time, the tpm driver
4985 should extend the specified pcr with zeros,
4986 as a workaround for some chips which fail to
4987 flush the last written pcr on TPM_SaveState.
4988 This will guarantee that all the other pcrs
4991 trace_buf_size=nn[KMG]
4992 [FTRACE] will set tracing buffer size on each cpu.
4994 trace_event=[event-list]
4995 [FTRACE] Set and start specified trace events in order
4996 to facilitate early boot debugging. The event-list is a
4997 comma separated list of trace events to enable. See
4998 also Documentation/trace/events.rst
5000 trace_options=[option-list]
5001 [FTRACE] Enable or disable tracer options at boot.
5002 The option-list is a comma delimited list of options
5003 that can be enabled or disabled just as if you were
5004 to echo the option name into
5006 /sys/kernel/debug/tracing/trace_options
5008 For example, to enable stacktrace option (to dump the
5009 stack trace of each event), add to the command line:
5011 trace_options=stacktrace
5013 See also Documentation/trace/ftrace.rst "trace options"
5017 Have the tracepoints sent to printk as well as the
5018 tracing ring buffer. This is useful for early boot up
5019 where the system hangs or reboots and does not give the
5020 option for reading the tracing buffer or performing a
5021 ftrace_dump_on_oops.
5023 To turn off having tracepoints sent to printk,
5024 echo 0 > /proc/sys/kernel/tracepoint_printk
5025 Note, echoing 1 into this file without the
5026 tracepoint_printk kernel cmdline option has no effect.
5030 Having tracepoints sent to printk() and activating high
5031 frequency tracepoints such as irq or sched, can cause
5032 the system to live lock.
5035 [FTRACE] enable this option to disable tracing when a
5036 warning is hit. This turns off "tracing_on". Tracing can
5037 be enabled again by echoing '1' into the "tracing_on"
5038 file located in /sys/kernel/debug/tracing/
5040 This option is useful, as it disables the trace before
5041 the WARNING dump is called, which prevents the trace to
5042 be filled with content caused by the warning output.
5044 This option can also be set at run time via the sysctl
5045 option: kernel/traceoff_on_warning
5047 transparent_hugepage=
5049 Format: [always|madvise|never]
5050 Can be used to control the default behavior of the system
5051 with respect to transparent hugepages.
5052 See Documentation/admin-guide/mm/transhuge.rst
5055 tsc= Disable clocksource stability checks for TSC.
5057 [x86] reliable: mark tsc clocksource as reliable, this
5058 disables clocksource verification at runtime, as well
5059 as the stability checks done at bootup. Used to enable
5060 high-resolution timer mode on older hardware, and in
5061 virtualized environment.
5062 [x86] noirqtime: Do not use TSC to do irq accounting.
5063 Used to run time disable IRQ_TIME_ACCOUNTING on any
5064 platforms where RDTSC is slow and this accounting
5066 [x86] unstable: mark the TSC clocksource as unstable, this
5067 marks the TSC unconditionally unstable at bootup and
5068 avoids any further wobbles once the TSC watchdog notices.
5069 [x86] nowatchdog: disable clocksource watchdog. Used
5070 in situations with strict latency requirements (where
5071 interruptions from clocksource watchdog are not
5074 tsx= [X86] Control Transactional Synchronization
5075 Extensions (TSX) feature in Intel processors that
5076 support TSX control.
5078 This parameter controls the TSX feature. The options are:
5080 on - Enable TSX on the system. Although there are
5081 mitigations for all known security vulnerabilities,
5082 TSX has been known to be an accelerator for
5083 several previous speculation-related CVEs, and
5084 so there may be unknown security risks associated
5085 with leaving it enabled.
5087 off - Disable TSX on the system. (Note that this
5088 option takes effect only on newer CPUs which are
5089 not vulnerable to MDS, i.e., have
5090 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
5091 the new IA32_TSX_CTRL MSR through a microcode
5092 update. This new MSR allows for the reliable
5093 deactivation of the TSX functionality.)
5095 auto - Disable TSX if X86_BUG_TAA is present,
5096 otherwise enable TSX on the system.
5098 Not specifying this option is equivalent to tsx=off.
5100 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5103 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
5104 Abort (TAA) vulnerability.
5106 Similar to Micro-architectural Data Sampling (MDS)
5107 certain CPUs that support Transactional
5108 Synchronization Extensions (TSX) are vulnerable to an
5109 exploit against CPU internal buffers which can forward
5110 information to a disclosure gadget under certain
5113 In vulnerable processors, the speculatively forwarded
5114 data can be used in a cache side channel attack, to
5115 access data to which the attacker does not have direct
5118 This parameter controls the TAA mitigation. The
5121 full - Enable TAA mitigation on vulnerable CPUs
5124 full,nosmt - Enable TAA mitigation and disable SMT on
5125 vulnerable CPUs. If TSX is disabled, SMT
5126 is not disabled because CPU is not
5127 vulnerable to cross-thread TAA attacks.
5128 off - Unconditionally disable TAA mitigation
5130 On MDS-affected machines, tsx_async_abort=off can be
5131 prevented by an active MDS mitigation as both vulnerabilities
5132 are mitigated with the same mechanism so in order to disable
5133 this mitigation, you need to specify mds=off too.
5135 Not specifying this option is equivalent to
5136 tsx_async_abort=full. On CPUs which are MDS affected
5137 and deploy MDS mitigation, TAA mitigation is not
5138 required and doesn't provide any additional
5142 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5144 turbografx.map[2|3]= [HW,JOY]
5145 TurboGraFX parallel port interface
5147 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
5148 See also Documentation/input/devices/joystick-parport.rst
5150 udbg-immortal [PPC] When debugging early kernel crashes that
5151 happen after console_init() and before a proper
5152 console driver takes over, this boot options might
5153 help "seeing" what's going on.
5155 uhash_entries= [KNL,NET]
5156 Set number of hash buckets for UDP/UDP-Lite connections
5159 [USB] Ignore overcurrent events (default N).
5160 Some badly-designed motherboards generate lots of
5161 bogus events, for ports that aren't wired to
5162 anything. Set this parameter to avoid log spamming.
5163 Note that genuine overcurrent events won't be
5167 [X86] Cause panic on unknown NMI.
5169 usbcore.authorized_default=
5170 [USB] Default USB device authorization:
5171 (default -1 = authorized except for wireless USB,
5172 0 = not authorized, 1 = authorized, 2 = authorized
5173 if device connected to internal port)
5175 usbcore.autosuspend=
5176 [USB] The autosuspend time delay (in seconds) used
5177 for newly-detected USB devices (default 2). This
5178 is the time required before an idle device will be
5179 autosuspended. Devices for which the delay is set
5180 to a negative value won't be autosuspended at all.
5182 usbcore.usbfs_snoop=
5183 [USB] Set to log all usbfs traffic (default 0 = off).
5185 usbcore.usbfs_snoop_max=
5186 [USB] Maximum number of bytes to snoop in each URB
5189 usbcore.blinkenlights=
5190 [USB] Set to cycle leds on hubs (default 0 = off).
5192 usbcore.old_scheme_first=
5193 [USB] Start with the old device initialization
5194 scheme, applies only to low and full-speed devices
5197 usbcore.usbfs_memory_mb=
5198 [USB] Memory limit (in MB) for buffers allocated by
5199 usbfs (default = 16, 0 = max = 2047).
5201 usbcore.use_both_schemes=
5202 [USB] Try the other device initialization scheme
5203 if the first one fails (default 1 = enabled).
5205 usbcore.initial_descriptor_timeout=
5206 [USB] Specifies timeout for the initial 64-byte
5207 USB_REQ_GET_DESCRIPTOR request in milliseconds
5208 (default 5000 = 5.0 seconds).
5210 usbcore.nousb [USB] Disable the USB subsystem
5213 [USB] A list of quirk entries to augment the built-in
5214 usb core quirk list. List entries are separated by
5215 commas. Each entry has the form
5216 VendorID:ProductID:Flags. The IDs are 4-digit hex
5217 numbers and Flags is a set of letters. Each letter
5218 will change the built-in quirk; setting it if it is
5219 clear and clearing it if it is set. The letters have
5220 the following meanings:
5221 a = USB_QUIRK_STRING_FETCH_255 (string
5222 descriptors must not be fetched using
5224 b = USB_QUIRK_RESET_RESUME (device can't resume
5225 correctly so reset it instead);
5226 c = USB_QUIRK_NO_SET_INTF (device can't handle
5227 Set-Interface requests);
5228 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
5229 handle its Configuration or Interface
5231 e = USB_QUIRK_RESET (device can't be reset
5232 (e.g morph devices), don't use reset);
5233 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
5234 more interface descriptions than the
5235 bNumInterfaces count, and can't handle
5236 talking to these interfaces);
5237 g = USB_QUIRK_DELAY_INIT (device needs a pause
5238 during initialization, after we read
5239 the device descriptor);
5240 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
5241 high speed and super speed interrupt
5242 endpoints, the USB 2.0 and USB 3.0 spec
5243 require the interval in microframes (1
5244 microframe = 125 microseconds) to be
5245 calculated as interval = 2 ^
5247 Devices with this quirk report their
5248 bInterval as the result of this
5249 calculation instead of the exponent
5250 variable used in the calculation);
5251 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
5252 handle device_qualifier descriptor
5254 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
5255 generates spurious wakeup, ignore
5256 remote wakeup capability);
5257 k = USB_QUIRK_NO_LPM (device can't handle Link
5259 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
5260 (Device reports its bInterval as linear
5261 frames instead of the USB 2.0
5263 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
5264 to be disconnected before suspend to
5265 prevent spurious wakeup);
5266 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
5267 pause after every control message);
5268 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
5269 delay after resetting its port);
5270 Example: quirks=0781:5580:bk,0a5c:5834:gij
5273 [USBHID] The interval which mice are to be polled at.
5276 [USBHID] The interval which joysticks are to be polled at.
5279 [USBHID] The interval which keyboards are to be polled at.
5281 usb-storage.delay_use=
5282 [UMS] The delay in seconds before a new device is
5283 scanned for Logical Units (default 1).
5286 [UMS] A list of quirks entries to supplement or
5287 override the built-in unusual_devs list. List
5288 entries are separated by commas. Each entry has
5289 the form VID:PID:Flags where VID and PID are Vendor
5290 and Product ID values (4-digit hex numbers) and
5291 Flags is a set of characters, each corresponding
5292 to a common usb-storage quirk flag as follows:
5293 a = SANE_SENSE (collect more than 18 bytes
5294 of sense data, not on uas);
5295 b = BAD_SENSE (don't collect more than 18
5296 bytes of sense data, not on uas);
5297 c = FIX_CAPACITY (decrease the reported
5298 device capacity by one sector);
5299 d = NO_READ_DISC_INFO (don't use
5300 READ_DISC_INFO command, not on uas);
5301 e = NO_READ_CAPACITY_16 (don't use
5302 READ_CAPACITY_16 command);
5303 f = NO_REPORT_OPCODES (don't use report opcodes
5305 g = MAX_SECTORS_240 (don't transfer more than
5306 240 sectors at a time, uas only);
5307 h = CAPACITY_HEURISTICS (decrease the
5308 reported device capacity by one
5309 sector if the number is odd);
5310 i = IGNORE_DEVICE (don't bind to this
5312 j = NO_REPORT_LUNS (don't use report luns
5314 l = NOT_LOCKABLE (don't try to lock and
5315 unlock ejectable media, not on uas);
5316 m = MAX_SECTORS_64 (don't transfer more
5317 than 64 sectors = 32 KB at a time,
5319 n = INITIAL_READ10 (force a retry of the
5320 initial READ(10) command, not on uas);
5321 o = CAPACITY_OK (accept the capacity
5322 reported by the device, not on uas);
5323 p = WRITE_CACHE (the device cache is ON
5324 by default, not on uas);
5325 r = IGNORE_RESIDUE (the device reports
5326 bogus residue values, not on uas);
5327 s = SINGLE_LUN (the device has only one
5329 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
5330 commands, uas only);
5331 u = IGNORE_UAS (don't bind to the uas driver);
5332 w = NO_WP_DETECT (don't test whether the
5333 medium is write-protected).
5334 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
5335 even if the device claims no cache,
5337 Example: quirks=0419:aaf5:rl,0421:0433:rc
5339 user_debug= [KNL,ARM]
5341 See arch/arm/Kconfig.debug help text.
5342 1 - undefined instruction events
5344 4 - invalid data aborts
5347 Example: user_debug=31
5350 [X86] Flags controlling user PTE allocations.
5352 nohigh = do not allocate PTE pages in
5353 HIGHMEM regardless of setting
5357 On X86_32, this is an alias for vdso32=. Otherwise:
5359 vdso=1: enable VDSO (the default)
5360 vdso=0: disable VDSO mapping
5362 vdso32= [X86] Control the 32-bit vDSO
5363 vdso32=1: enable 32-bit VDSO
5364 vdso32=0 or vdso32=2: disable 32-bit VDSO
5366 See the help text for CONFIG_COMPAT_VDSO for more
5367 details. If CONFIG_COMPAT_VDSO is set, the default is
5368 vdso32=0; otherwise, the default is vdso32=1.
5370 For compatibility with older kernels, vdso32=2 is an
5373 Try vdso32=0 if you encounter an error that says:
5374 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
5377 vector=percpu: enable percpu vector domain
5379 video= [FB] Frame buffer configuration
5380 See Documentation/fb/modedb.rst.
5382 video.brightness_switch_enabled= [0,1]
5383 If set to 1, on receiving an ACPI notify event
5384 generated by hotkey, video driver will adjust brightness
5385 level and then send out the event to user space through
5386 the allocated input device; If set to 0, video driver
5387 will only send out the event without touching backlight
5392 [VMMIO] Memory mapped virtio (platform) device.
5394 <size>@<baseaddr>:<irq>[:<id>]
5396 <size> := size (can use standard suffixes
5398 <baseaddr> := physical base address
5399 <irq> := interrupt number (as passed to
5401 <id> := (optional) platform device id
5403 virtio_mmio.device=1K@0x100b0000:48:7
5405 Can be used multiple times for multiple devices.
5407 vga= [BOOT,X86-32] Select a particular video mode
5408 See Documentation/x86/boot.rst and
5409 Documentation/admin-guide/svga.rst.
5410 Use vga=ask for menu.
5411 This is actually a boot loader parameter; the value is
5412 passed to the kernel using a special protocol.
5414 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
5415 May slow down system boot speed, especially when
5416 enabled on systems with a large amount of memory.
5417 All options are enabled by default, and this
5418 interface is meant to allow for selectively
5419 enabling or disabling specific virtual memory
5422 Available options are:
5423 P Enable page structure init time poisoning
5424 - Disable all of the above options
5426 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
5427 size of <nn>. This can be used to increase the
5428 minimum size (128MB on x86). It can also be used to
5429 decrease the size and leave more room for directly
5432 vmcp_cma=nn[MG] [KNL,S390]
5433 Sets the memory size reserved for contiguous memory
5434 allocations for the vmcp device driver.
5436 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5439 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5442 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
5446 Controls the behavior of vsyscalls (i.e. calls to
5447 fixed addresses of 0xffffffffff600x00 from legacy
5448 code). Most statically-linked binaries and older
5449 versions of glibc use these calls. Because these
5450 functions are at fixed addresses, they make nice
5451 targets for exploits that can control RIP.
5453 emulate [default] Vsyscalls turn into traps and are
5454 emulated reasonably safely. The vsyscall
5457 xonly Vsyscalls turn into traps and are
5458 emulated reasonably safely. The vsyscall
5459 page is not readable.
5461 none Vsyscalls don't work at all. This makes
5462 them quite hard to use for exploits but
5463 might break your system.
5465 vt.color= [VT] Default text color.
5466 Format: 0xYX, X = foreground, Y = background.
5467 Default: 0x07 = light gray on black.
5469 vt.cur_default= [VT] Default cursor shape.
5470 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5471 the parameters of the <Esc>[?A;B;Cc escape sequence;
5472 see VGA-softcursor.txt. Default: 2 = underline.
5474 vt.default_blu= [VT]
5475 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5476 Change the default blue palette of the console.
5477 This is a 16-member array composed of values
5480 vt.default_grn= [VT]
5481 Format: <green0>,<green1>,<green2>,...,<green15>
5482 Change the default green palette of the console.
5483 This is a 16-member array composed of values
5486 vt.default_red= [VT]
5487 Format: <red0>,<red1>,<red2>,...,<red15>
5488 Change the default red palette of the console.
5489 This is a 16-member array composed of values
5495 Set system-wide default UTF-8 mode for all tty's.
5496 Default is 1, i.e. UTF-8 mode is enabled for all
5497 newly opened terminals.
5499 vt.global_cursor_default=
5502 Set system-wide default for whether a cursor
5503 is shown on new VTs. Default is -1,
5504 i.e. cursors will be created by default unless
5505 overridden by individual drivers. 0 will hide
5506 cursors, 1 will display them.
5508 vt.italic= [VT] Default color for italic text; 0-15.
5511 vt.underline= [VT] Default color for underlined text; 0-15.
5514 watchdog timers [HW,WDT] For information on watchdog timers,
5515 see Documentation/watchdog/watchdog-parameters.rst
5516 or other driver-specific files in the
5517 Documentation/watchdog/ directory.
5521 Set the hard lockup detector stall duration
5522 threshold in seconds. The soft lockup detector
5523 threshold is set to twice the value. A value of 0
5524 disables both lockup detectors. Default is 10
5527 workqueue.watchdog_thresh=
5528 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5529 warn stall conditions and dump internal state to
5530 help debugging. 0 disables workqueue stall
5531 detection; otherwise, it's the stall threshold
5532 duration in seconds. The default value is 30 and
5533 it can be updated at runtime by writing to the
5534 corresponding sysfs file.
5536 workqueue.disable_numa
5537 By default, all work items queued to unbound
5538 workqueues are affine to the NUMA nodes they're
5539 issued on, which results in better behavior in
5540 general. If NUMA affinity needs to be disabled for
5541 whatever reason, this option can be used. Note
5542 that this also can be controlled per-workqueue for
5543 workqueues visible under /sys/bus/workqueue/.
5545 workqueue.power_efficient
5546 Per-cpu workqueues are generally preferred because
5547 they show better performance thanks to cache
5548 locality; unfortunately, per-cpu workqueues tend to
5549 be more power hungry than unbound workqueues.
5551 Enabling this makes the per-cpu workqueues which
5552 were observed to contribute significantly to power
5553 consumption unbound, leading to measurably lower
5554 power usage at the cost of small performance
5557 The default value of this parameter is determined by
5558 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5560 workqueue.debug_force_rr_cpu
5561 Workqueue used to implicitly guarantee that work
5562 items queued without explicit CPU specified are put
5563 on the local CPU. This guarantee is no longer true
5564 and while local CPU is still preferred work items
5565 may be put on foreign CPUs. This debug option
5566 forces round-robin CPU selection to flush out
5567 usages which depend on the now broken guarantee.
5568 When enabled, memory and cache locality will be
5571 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5572 default x2apic cluster mode on platforms
5575 x86_intel_mid_timer= [X86-32,APBT]
5576 Choose timer option for x86 Intel MID platform.
5577 Two valid options are apbt timer only and lapic timer
5578 plus one apbt timer for broadcast timer.
5579 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5581 xen_512gb_limit [KNL,X86-64,XEN]
5582 Restricts the kernel running paravirtualized under Xen
5583 to use only up to 512 GB of RAM. The reason to do so is
5584 crash analysis tools and Xen tools for doing domain
5585 save/restore/migration must be enabled to handle larger
5588 xen_emul_unplug= [HW,X86,XEN]
5589 Unplug Xen emulated devices
5590 Format: [unplug0,][unplug1]
5591 ide-disks -- unplug primary master IDE devices
5592 aux-ide-disks -- unplug non-primary-master IDE devices
5593 nics -- unplug network devices
5594 all -- unplug all emulated devices (NICs and IDE disks)
5595 unnecessary -- unplugging emulated devices is
5596 unnecessary even if the host did not respond to
5598 never -- do not unplug even if version check succeeds
5600 xen_legacy_crash [X86,XEN]
5601 Crash from Xen panic notifier, without executing late
5602 panic() code such as dumping handler.
5604 xen_nopvspin [X86,XEN]
5605 Disables the ticketlock slowpath using Xen PV
5609 Disables the PV optimizations forcing the HVM guest to
5610 run as generic HVM guest with no PV drivers.
5611 This option is obsoleted by the "nopv" option, which
5612 has equivalent effect for XEN platform.
5614 xen_scrub_pages= [XEN]
5615 Boolean option to control scrubbing pages before giving them back
5616 to Xen, for use by other domains. Can be also changed at runtime
5617 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5618 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5620 xen_timer_slop= [X86-64,XEN]
5621 Set the timer slop (in nanoseconds) for the virtual Xen
5622 timers (default is 100000). This adjusts the minimum
5623 delta of virtualized Xen timers, where lower values
5624 improve timer resolution at the expense of processing
5625 more timer interrupts.
5627 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
5628 Disables the PV optimizations forcing the guest to run
5629 as generic guest with no PV drivers. Currently support
5630 XEN HVM, KVM, HYPER_V and VMWARE guest.
5632 xirc2ps_cs= [NET,PCMCIA]
5634 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5637 By default on POWER9 and above, the kernel will
5638 natively use the XIVE interrupt controller. This option
5639 allows the fallback firmware mode to be used:
5641 off Fallback to firmware control of XIVE interrupt
5642 controller on both pseries and powernv
5643 platforms. Only useful on POWER9 and above.
5645 xhci-hcd.quirks [USB,KNL]
5646 A hex value specifying bitmask with supplemental xhci
5647 host controller quirks. Meaning of each bit can be
5648 consulted in header drivers/usb/host/xhci.h.
5651 Format: { early | on | rw | ro | off }
5652 Controls if xmon debugger is enabled. Default is off.
5653 Passing only "xmon" is equivalent to "xmon=early".
5654 early Call xmon as early as possible on boot; xmon
5655 debugger is called from setup_arch().
5656 on xmon debugger hooks will be installed so xmon
5657 is only called on a kernel crash. Default mode,
5658 i.e. either "ro" or "rw" mode, is controlled
5659 with CONFIG_XMON_DEFAULT_RO_MODE.
5660 rw xmon debugger hooks will be installed so xmon
5661 is called only on a kernel crash, mode is write,
5662 meaning SPR registers, memory and, other data
5663 can be written using xmon commands.
5664 ro same as "rw" option above but SPR registers,
5665 memory, and other data can't be written using
5667 off xmon is disabled.
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