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 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1479 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1480 On x86-64 and powerpc, this option can be specified
1481 multiple times interleaved with hugepages= to reserve
1482 huge pages of different sizes. Valid pages sizes on
1483 x86-64 are 2M (when the CPU supports "pse") and 1G
1484 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1487 [KNL] Should the hung task detector generate panics.
1490 A nonzero value instructs the kernel to panic when a
1491 hung task is detected. The default value is controlled
1492 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1493 option. The value selected by this boot parameter can
1494 be changed later by the kernel.hung_task_panic sysctl.
1496 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1497 terminal devices. Valid values: 0..8
1498 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1499 If specified, z/VM IUCV HVC accepts connections
1500 from listed z/VM user IDs only.
1502 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1503 which allow the hypervisor to 'idle' the
1504 guest on lock contention.
1507 Do not unregister boot console at start. This is only
1508 useful for debugging when something happens in the window
1509 between unregistering the boot console and initializing
1512 i2c_bus= [HW] Override the default board specific I2C bus speed
1513 or register an additional I2C bus that is not
1514 registered from board initialization code.
1518 i8042.debug [HW] Toggle i8042 debug mode
1519 i8042.unmask_kbd_data
1520 [HW] Enable printing of interrupt data from the KBD port
1521 (disabled by default, and as a pre-condition
1522 requires that i8042.debug=1 be enabled)
1523 i8042.direct [HW] Put keyboard port into non-translated mode
1524 i8042.dumbkbd [HW] Pretend that controller can only read data from
1525 keyboard and cannot control its state
1526 (Don't attempt to blink the leds)
1527 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1528 i8042.nokbd [HW] Don't check/create keyboard port
1529 i8042.noloop [HW] Disable the AUX Loopback command while probing
1531 i8042.nomux [HW] Don't check presence of an active multiplexing
1533 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1535 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1536 i8042.reset [HW] Reset the controller during init, cleanup and
1537 suspend-to-ram transitions, only during s2r
1538 transitions, or never reset
1539 Format: { 1 | Y | y | 0 | N | n }
1540 1, Y, y: always reset controller
1541 0, N, n: don't ever reset controller
1542 Default: only on s2r transitions on x86; most other
1543 architectures force reset to be always executed
1544 i8042.unlock [HW] Unlock (ignore) the keylock
1545 i8042.kbdreset [HW] Reset device connected to KBD port
1549 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1550 indicates that the driver is running on unsupported
1552 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1553 does not match list of supported models.
1555 [HW] Report power status in /proc/i8k
1556 (disabled by default)
1557 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1560 i915.invert_brightness=
1561 [DRM] Invert the sense of the variable that is used to
1562 set the brightness of the panel backlight. Normally a
1563 brightness value of 0 indicates backlight switched off,
1564 and the maximum of the brightness value sets the backlight
1565 to maximum brightness. If this parameter is set to 0
1566 (default) and the machine requires it, or this parameter
1567 is set to 1, a brightness value of 0 sets the backlight
1568 to maximum brightness, and the maximum of the brightness
1569 value switches the backlight off.
1570 -1 -- never invert brightness
1571 0 -- machine default
1572 1 -- force brightness inversion
1575 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1577 ide-core.nodma= [HW] (E)IDE subsystem
1578 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1579 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1580 .cdrom .chs .ignore_cable are additional options
1581 See Documentation/ide/ide.rst.
1583 ide-generic.probe-mask= [HW] (E)IDE subsystem
1585 Probe mask for legacy ISA IDE ports. Depending on
1586 platform up to 6 ports are supported, enabled by
1587 setting corresponding bits in the mask to 1. The
1588 default value is 0x0, which has a special meaning.
1589 On systems that have PCI, it triggers scanning the
1590 PCI bus for the first and the second port, which
1591 are then probed. On systems without PCI the value
1592 of 0x0 enables probing the two first ports as if it
1595 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1596 Claim all unknown PCI IDE storage controllers.
1599 Format: idle=poll, idle=halt, idle=nomwait
1600 Poll forces a polling idle loop that can slightly
1601 improve the performance of waking up a idle CPU, but
1602 will use a lot of power and make the system run hot.
1604 idle=halt: Halt is forced to be used for CPU idle.
1605 In such case C2/C3 won't be used again.
1606 idle=nomwait: Disable mwait for CPU C-states
1608 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1609 Format: { strict | legacy | 2008 | relaxed }
1612 Choose which programs will be accepted for execution
1613 based on the IEEE 754 NaN encoding(s) supported by
1614 the FPU and the NaN encoding requested with the value
1615 of an ELF file header flag individually set by each
1616 binary. Hardware implementations are permitted to
1617 support either or both of the legacy and the 2008 NaN
1620 Available settings are as follows:
1621 strict accept binaries that request a NaN encoding
1622 supported by the FPU
1623 legacy only accept legacy-NaN binaries, if supported
1625 2008 only accept 2008-NaN binaries, if supported
1627 relaxed accept any binaries regardless of whether
1628 supported by the FPU
1630 The FPU emulator is always able to support both NaN
1631 encodings, so if no FPU hardware is present or it has
1632 been disabled with 'nofpu', then the settings of
1633 'legacy' and '2008' strap the emulator accordingly,
1634 'relaxed' straps the emulator for both legacy-NaN and
1635 2008-NaN, whereas 'strict' enables legacy-NaN only on
1636 legacy processors and both NaN encodings on MIPS32 or
1639 The setting for ABS.fmt/NEG.fmt instruction execution
1640 mode generally follows that for the NaN encoding,
1641 except where unsupported by hardware.
1643 ignore_loglevel [KNL]
1644 Ignore loglevel setting - this will print /all/
1645 kernel messages to the console. Useful for debugging.
1646 We also add it as printk module parameter, so users
1647 could change it dynamically, usually by
1648 /sys/module/printk/parameters/ignore_loglevel.
1651 Ignore RLIMIT_DATA setting for data mappings,
1652 print warning at first misuse. Can be changed via
1653 /sys/module/kernel/parameters/ignore_rlimit_data.
1655 ihash_entries= [KNL]
1656 Set number of hash buckets for inode cache.
1658 ima_appraise= [IMA] appraise integrity measurements
1659 Format: { "off" | "enforce" | "fix" | "log" }
1662 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1663 The builtin appraise policy appraises all files
1666 ima_canonical_fmt [IMA]
1667 Use the canonical format for the binary runtime
1668 measurements, instead of host native format.
1671 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1675 The list of supported hash algorithms is defined
1676 in crypto/hash_info.h.
1679 The builtin policies to load during IMA setup.
1680 Format: "tcb | appraise_tcb | secure_boot |
1683 The "tcb" policy measures all programs exec'd, files
1684 mmap'd for exec, and all files opened with the read
1685 mode bit set by either the effective uid (euid=0) or
1688 The "appraise_tcb" policy appraises the integrity of
1689 all files owned by root.
1691 The "secure_boot" policy appraises the integrity
1692 of files (eg. kexec kernel image, kernel modules,
1693 firmware, policy, etc) based on file signatures.
1695 The "fail_securely" policy forces file signature
1696 verification failure also on privileged mounted
1697 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1700 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1701 Load a policy which meets the needs of the Trusted
1702 Computing Base. This means IMA will measure all
1703 programs exec'd, files mmap'd for exec, and all files
1704 opened for read by uid=0.
1707 Select one of defined IMA measurements template formats.
1708 Formats: { "ima" | "ima-ng" | "ima-sig" }
1712 [IMA] Define a custom template format.
1713 Format: { "field1|...|fieldN" }
1715 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1716 Format: <min_file_size>
1717 Set the minimal file size for using asynchronous hash.
1718 If left unspecified, ahash usage is disabled.
1720 ahash performance varies for different data sizes on
1721 different crypto accelerators. This option can be used
1722 to achieve the best performance for a particular HW.
1724 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1726 Set hashing buffer size. Default: 4k.
1728 ahash performance varies for different chunk sizes on
1729 different crypto accelerators. This option can be used
1730 to achieve best performance for particular HW.
1734 Run specified binary instead of /sbin/init as init
1737 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1738 for working out where the kernel is dying during
1741 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1742 initcall functions. Useful for debugging built-in
1743 modules and initcalls.
1745 initrd= [BOOT] Specify the location of the initial ramdisk
1747 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1750 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1752 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1754 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1756 init_pkru= [x86] Specify the default memory protection keys rights
1757 register contents for all processes. 0x55555554 by
1758 default (disallow access to all but pkey 0). Can
1759 override in debugfs after boot.
1761 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1764 int_pln_enable [x86] Enable power limit notification interrupt
1766 integrity_audit=[IMA]
1767 Format: { "0" | "1" }
1768 0 -- basic integrity auditing messages. (Default)
1769 1 -- additional integrity auditing messages.
1771 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1773 Enable intel iommu driver.
1775 Disable intel iommu driver.
1776 igfx_off [Default Off]
1777 By default, gfx is mapped as normal device. If a gfx
1778 device has a dedicated DMAR unit, the DMAR unit is
1779 bypassed by not enabling DMAR with this option. In
1780 this case, gfx device will use physical address for
1783 With this option iommu will not optimize to look
1784 for io virtual address below 32-bit forcing dual
1785 address cycle on pci bus for cards supporting greater
1786 than 32-bit addressing. The default is to look
1787 for translation below 32-bit and if not available
1788 then look in the higher range.
1789 strict [Default Off]
1790 With this option on every unmap_single operation will
1791 result in a hardware IOTLB flush operation as opposed
1792 to batching them for performance.
1793 sp_off [Default Off]
1794 By default, super page will be supported if Intel IOMMU
1795 has the capability. With this option, super page will
1798 By default, scalable mode will be disabled even if the
1799 hardware advertises that it has support for the scalable
1800 mode translation. With this option set, scalable mode
1801 will be used on hardware which claims to support it.
1802 tboot_noforce [Default Off]
1803 Do not force the Intel IOMMU enabled under tboot.
1804 By default, tboot will force Intel IOMMU on, which
1805 could harm performance of some high-throughput
1806 devices like 40GBit network cards, even if identity
1808 Note that using this option lowers the security
1809 provided by tboot because it makes the system
1810 vulnerable to DMA attacks.
1811 nobounce [Default off]
1812 Disable bounce buffer for untrusted devices such as
1813 the Thunderbolt devices. This will treat the untrusted
1814 devices as the trusted ones, hence might expose security
1815 risks of DMA attacks.
1817 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1818 0 disables intel_idle and fall back on acpi_idle.
1819 1 to 9 specify maximum depth of C-state.
1823 Do not enable intel_pstate as the default
1824 scaling driver for the supported processors
1826 Use intel_pstate as a scaling driver, but configure it
1827 to work with generic cpufreq governors (instead of
1828 enabling its internal governor). This mode cannot be
1829 used along with the hardware-managed P-states (HWP)
1832 Enable intel_pstate on systems that prohibit it by default
1833 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1834 instead of acpi-cpufreq may disable platform features, such
1835 as thermal controls and power capping, that rely on ACPI
1836 P-States information being indicated to OSPM and therefore
1837 should be used with caution. This option does not work with
1838 processors that aren't supported by the intel_pstate driver
1839 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1841 Do not enable hardware P state control (HWP)
1844 Only load intel_pstate on systems which support
1845 hardware P state control (HWP) if available.
1847 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1848 Description Table, specifies preferred power management
1849 profile as "Enterprise Server" or "Performance Server",
1850 then this feature is turned on by default.
1852 Allow per-logical-CPU P-State performance control limits using
1853 cpufreq sysfs interface
1855 intremap= [X86-64, Intel-IOMMU]
1856 on enable Interrupt Remapping (default)
1857 off disable Interrupt Remapping
1858 nosid disable Source ID checking
1860 BIOS x2APIC opt-out request will be ignored
1861 nopost disable Interrupt Posting
1863 iomem= Disable strict checking of access to MMIO memory
1864 strict regions from userspace.
1879 nobypass [PPC/POWERNV]
1880 Disable IOMMU bypass, using IOMMU for PCI devices.
1882 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1883 Format: { "0" | "1" }
1885 Request that DMA unmap operations use deferred
1886 invalidation of hardware TLBs, for increased
1887 throughput at the cost of reduced device isolation.
1888 Will fall back to strict mode if not supported by
1889 the relevant IOMMU driver.
1890 1 - Strict mode (default).
1891 DMA unmap operations invalidate IOMMU hardware TLBs
1895 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
1896 Format: { "0" | "1" }
1897 0 - Use IOMMU translation for DMA.
1898 1 - Bypass the IOMMU for DMA.
1899 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1901 io7= [HW] IO7 for Marvel based alpha systems
1902 See comment before marvel_specify_io7 in
1903 arch/alpha/kernel/core_marvel.c.
1905 io_delay= [X86] I/O delay method
1907 Standard port 0x80 based delay
1909 Alternate port 0xed based delay (needed on some systems)
1911 Simple two microseconds delay
1916 See Documentation/admin-guide/nfs/nfsroot.rst.
1918 ipcmni_extend [KNL] Extend the maximum number of unique System V
1919 IPC identifiers from 32,768 to 16,777,216.
1921 irqaffinity= [SMP] Set the default irq affinity mask
1922 The argument is a cpu list, as described above.
1924 irqchip.gicv2_force_probe=
1927 Force the kernel to look for the second 4kB page
1928 of a GICv2 controller even if the memory range
1929 exposed by the device tree is too small.
1931 irqchip.gicv3_nolpi=
1933 Force the kernel to ignore the availability of
1934 LPIs (and by consequence ITSs). Intended for system
1935 that use the kernel as a bootloader, and thus want
1936 to let secondary kernels in charge of setting up
1939 irqchip.gicv3_pseudo_nmi= [ARM64]
1940 Enables support for pseudo-NMIs in the kernel. This
1941 requires the kernel to be built with
1942 CONFIG_ARM64_PSEUDO_NMI.
1945 When an interrupt is not handled search all handlers
1946 for it. Intended to get systems with badly broken
1950 When an interrupt is not handled search all handlers
1951 for it. Also check all handlers each timer
1952 interrupt. Intended to get systems with badly broken
1956 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1958 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1959 [Deprecated - use cpusets instead]
1960 Format: [flag-list,]<cpu-list>
1962 Specify one or more CPUs to isolate from disturbances
1963 specified in the flag list (default: domain):
1966 Disable the tick when a single task runs.
1968 A residual 1Hz tick is offloaded to workqueues, which you
1969 need to affine to housekeeping through the global
1970 workqueue's affinity configured via the
1971 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1972 by using the 'domain' flag described below.
1974 NOTE: by default the global workqueue runs on all CPUs,
1975 so to protect individual CPUs the 'cpumask' file has to
1976 be configured manually after bootup.
1979 Isolate from the general SMP balancing and scheduling
1980 algorithms. Note that performing domain isolation this way
1981 is irreversible: it's not possible to bring back a CPU to
1982 the domains once isolated through isolcpus. It's strongly
1983 advised to use cpusets instead to disable scheduler load
1984 balancing through the "cpuset.sched_load_balance" file.
1985 It offers a much more flexible interface where CPUs can
1986 move in and out of an isolated set anytime.
1988 You can move a process onto or off an "isolated" CPU via
1989 the CPU affinity syscalls or cpuset.
1990 <cpu number> begins at 0 and the maximum value is
1991 "number of CPUs in system - 1".
1995 Isolate from being targeted by managed interrupts
1996 which have an interrupt mask containing isolated
1997 CPUs. The affinity of managed interrupts is
1998 handled by the kernel and cannot be changed via
1999 the /proc/irq/* interfaces.
2001 This isolation is best effort and only effective
2002 if the automatically assigned interrupt mask of a
2003 device queue contains isolated and housekeeping
2004 CPUs. If housekeeping CPUs are online then such
2005 interrupts are directed to the housekeeping CPU
2006 so that IO submitted on the housekeeping CPU
2007 cannot disturb the isolated CPU.
2009 If a queue's affinity mask contains only isolated
2010 CPUs then this parameter has no effect on the
2011 interrupt routing decision, though interrupts are
2012 only delivered when tasks running on those
2013 isolated CPUs submit IO. IO submitted on
2014 housekeeping CPUs has no influence on those
2017 The format of <cpu-list> is described above.
2021 ivrs_ioapic [HW,X86_64]
2022 Provide an override to the IOAPIC-ID<->DEVICE-ID
2023 mapping provided in the IVRS ACPI table. For
2024 example, to map IOAPIC-ID decimal 10 to
2025 PCI device 00:14.0 write the parameter as:
2026 ivrs_ioapic[10]=00:14.0
2028 ivrs_hpet [HW,X86_64]
2029 Provide an override to the HPET-ID<->DEVICE-ID
2030 mapping provided in the IVRS ACPI table. For
2031 example, to map HPET-ID decimal 0 to
2032 PCI device 00:14.0 write the parameter as:
2033 ivrs_hpet[0]=00:14.0
2035 ivrs_acpihid [HW,X86_64]
2036 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2037 mapping provided in the IVRS ACPI table. For
2038 example, to map UART-HID:UID AMD0020:0 to
2039 PCI device 00:14.5 write the parameter as:
2040 ivrs_acpihid[00:14.5]=AMD0020:0
2042 js= [HW,JOY] Analog joystick
2043 See Documentation/input/joydev/joystick.rst.
2046 When CONFIG_RANDOMIZE_BASE is set, this disables
2047 kernel and module base offset ASLR (Address Space
2048 Layout Randomization).
2051 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2052 report on every invalid memory access. Without this
2053 parameter KASAN will print report only for the first
2058 kernelcore= [KNL,X86,IA-64,PPC]
2059 Format: nn[KMGTPE] | nn% | "mirror"
2060 This parameter specifies the amount of memory usable by
2061 the kernel for non-movable allocations. The requested
2062 amount is spread evenly throughout all nodes in the
2063 system as ZONE_NORMAL. The remaining memory is used for
2064 movable memory in its own zone, ZONE_MOVABLE. In the
2065 event, a node is too small to have both ZONE_NORMAL and
2066 ZONE_MOVABLE, kernelcore memory will take priority and
2067 other nodes will have a larger ZONE_MOVABLE.
2069 ZONE_MOVABLE is used for the allocation of pages that
2070 may be reclaimed or moved by the page migration
2071 subsystem. Note that allocations like PTEs-from-HighMem
2072 still use the HighMem zone if it exists, and the Normal
2073 zone if it does not.
2075 It is possible to specify the exact amount of memory in
2076 the form of "nn[KMGTPE]", a percentage of total system
2077 memory in the form of "nn%", or "mirror". If "mirror"
2078 option is specified, mirrored (reliable) memory is used
2079 for non-movable allocations and remaining memory is used
2080 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2081 are exclusive, so you cannot specify multiple forms.
2083 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2084 Format: <Controller#>[,poll interval]
2085 The controller # is the number of the ehci usb debug
2086 port as it is probed via PCI. The poll interval is
2087 optional and is the number seconds in between
2088 each poll cycle to the debug port in case you need
2089 the functionality for interrupting the kernel with
2090 gdb or control-c on the dbgp connection. When
2091 not using this parameter you use sysrq-g to break into
2092 the kernel debugger.
2094 kgdboc= [KGDB,HW] kgdb over consoles.
2095 Requires a tty driver that supports console polling,
2096 or a supported polling keyboard driver (non-usb).
2097 Serial only format: <serial_device>[,baud]
2098 keyboard only format: kbd
2099 keyboard and serial format: kbd,<serial_device>[,baud]
2100 Optional Kernel mode setting:
2101 kms, kbd format: kms,kbd
2102 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2104 kgdbwait [KGDB] Stop kernel execution and enter the
2105 kernel debugger at the earliest opportunity.
2107 kmac= [MIPS] korina ethernet MAC address.
2108 Configure the RouterBoard 532 series on-chip
2109 Ethernet adapter MAC address.
2111 kmemleak= [KNL] Boot-time kmemleak enable/disable
2112 Valid arguments: on, off
2114 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2117 kprobe_event=[probe-list]
2118 [FTRACE] Add kprobe events and enable at boot time.
2119 The probe-list is a semicolon delimited list of probe
2120 definitions. Each definition is same as kprobe_events
2121 interface, but the parameters are comma delimited.
2122 For example, to add a kprobe event on vfs_read with
2123 arg1 and arg2, add to the command line;
2125 kprobe_event=p,vfs_read,$arg1,$arg2
2127 See also Documentation/trace/kprobetrace.rst "Kernel
2128 Boot Parameter" section.
2130 kpti= [ARM64] Control page table isolation of user
2131 and kernel address spaces.
2132 Default: enabled on cores which need mitigation.
2136 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2137 Default is 0 (don't ignore, but inject #GP)
2139 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2140 Default is false (don't support).
2142 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2147 [KVM] Controls the software workaround for the
2148 X86_BUG_ITLB_MULTIHIT bug.
2149 force : Always deploy workaround.
2150 off : Never deploy workaround.
2151 auto : Deploy workaround based on the presence of
2152 X86_BUG_ITLB_MULTIHIT.
2156 If the software workaround is enabled for the host,
2157 guests do need not to enable it for nested guests.
2159 kvm.nx_huge_pages_recovery_ratio=
2160 [KVM] Controls how many 4KiB pages are periodically zapped
2161 back to huge pages. 0 disables the recovery, otherwise if
2162 the value is N KVM will zap 1/Nth of the 4KiB pages every
2163 minute. The default is 60.
2165 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2166 Default is 1 (enabled)
2168 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2170 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2172 kvm-arm.vgic_v3_group0_trap=
2173 [KVM,ARM] Trap guest accesses to GICv3 group-0
2176 kvm-arm.vgic_v3_group1_trap=
2177 [KVM,ARM] Trap guest accesses to GICv3 group-1
2180 kvm-arm.vgic_v3_common_trap=
2181 [KVM,ARM] Trap guest accesses to GICv3 common
2184 kvm-arm.vgic_v4_enable=
2185 [KVM,ARM] Allow use of GICv4 for direct injection of
2188 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2189 (virtualized MMU) support on capable Intel chips.
2190 Default is 1 (enabled)
2192 kvm-intel.emulate_invalid_guest_state=
2193 [KVM,Intel] Enable emulation of invalid guest states
2194 Default is 0 (disabled)
2196 kvm-intel.flexpriority=
2197 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2198 Default is 1 (enabled)
2201 [KVM,Intel] Enable VMX nesting (nVMX).
2202 Default is 0 (disabled)
2204 kvm-intel.unrestricted_guest=
2205 [KVM,Intel] Disable unrestricted guest feature
2206 (virtualized real and unpaged mode) on capable
2207 Intel chips. Default is 1 (enabled)
2209 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2212 Valid arguments: never, cond, always
2214 always: L1D cache flush on every VMENTER.
2215 cond: Flush L1D on VMENTER only when the code between
2216 VMEXIT and VMENTER can leak host memory.
2217 never: Disables the mitigation
2219 Default is cond (do L1 cache flush in specific instances)
2221 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2222 feature (tagged TLBs) on capable Intel chips.
2223 Default is 1 (enabled)
2225 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2228 The kernel PTE inversion protection is unconditionally
2229 enabled and cannot be disabled.
2232 Provides all available mitigations for the
2233 L1TF vulnerability. Disables SMT and
2234 enables all mitigations in the
2235 hypervisors, i.e. unconditional L1D flush.
2237 SMT control and L1D flush control via the
2238 sysfs interface is still possible after
2239 boot. Hypervisors will issue a warning
2240 when the first VM is started in a
2241 potentially insecure configuration,
2242 i.e. SMT enabled or L1D flush disabled.
2245 Same as 'full', but disables SMT and L1D
2246 flush runtime control. Implies the
2247 'nosmt=force' command line option.
2248 (i.e. sysfs control of SMT is disabled.)
2251 Leaves SMT enabled and enables the default
2252 hypervisor mitigation, i.e. conditional
2255 SMT control and L1D flush control via the
2256 sysfs interface is still possible after
2257 boot. Hypervisors will issue a warning
2258 when the first VM is started in a
2259 potentially insecure configuration,
2260 i.e. SMT enabled or L1D flush disabled.
2264 Disables SMT and enables the default
2265 hypervisor mitigation.
2267 SMT control and L1D flush control via the
2268 sysfs interface is still possible after
2269 boot. Hypervisors will issue a warning
2270 when the first VM is started in a
2271 potentially insecure configuration,
2272 i.e. SMT enabled or L1D flush disabled.
2275 Same as 'flush', but hypervisors will not
2276 warn when a VM is started in a potentially
2277 insecure configuration.
2280 Disables hypervisor mitigations and doesn't
2282 It also drops the swap size and available
2283 RAM limit restriction on both hypervisor and
2288 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2294 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2297 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2298 value for LAPIC timer one-shot implementation. Default
2299 back to the programmable timer unit in the LAPIC.
2301 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2304 libata.dma= [LIBATA] DMA control
2305 libata.dma=0 Disable all PATA and SATA DMA
2306 libata.dma=1 PATA and SATA Disk DMA only
2307 libata.dma=2 ATAPI (CDROM) DMA only
2308 libata.dma=4 Compact Flash DMA only
2309 Combinations also work, so libata.dma=3 enables DMA
2310 for disks and CDROMs, but not CFs.
2312 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2313 libata.ignore_hpa=0 keep BIOS limits (default)
2314 libata.ignore_hpa=1 ignore limits, using full disk
2316 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2320 libata.force= [LIBATA] Force configurations. The format is comma
2321 separated list of "[ID:]VAL" where ID is
2322 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2323 matching port, link or device. Basically, it matches
2324 the ATA ID string printed on console by libata. If
2325 the whole ID part is omitted, the last PORT and DEVICE
2326 values are used. If ID hasn't been specified yet, the
2327 configuration applies to all ports, links and devices.
2329 If only DEVICE is omitted, the parameter applies to
2330 the port and all links and devices behind it. DEVICE
2331 number of 0 either selects the first device or the
2332 first fan-out link behind PMP device. It does not
2333 select the host link. DEVICE number of 15 selects the
2334 host link and device attached to it.
2336 The VAL specifies the configuration to force. As long
2337 as there's no ambiguity shortcut notation is allowed.
2338 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2339 The following configurations can be forced.
2341 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2342 Any ID with matching PORT is used.
2344 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2346 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2347 udma[/][16,25,33,44,66,100,133] notation is also
2350 * [no]ncq: Turn on or off NCQ.
2352 * [no]ncqtrim: Turn off queued DSM TRIM.
2354 * nohrst, nosrst, norst: suppress hard, soft
2357 * rstonce: only attempt one reset during
2358 hot-unplug link recovery
2360 * dump_id: dump IDENTIFY data.
2362 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2364 * disable: Disable this device.
2366 If there are multiple matching configurations changing
2367 the same attribute, the last one is used.
2369 memblock=debug [KNL] Enable memblock debug messages.
2371 load_ramdisk= [RAM] List of ramdisks to load from floppy
2372 See Documentation/admin-guide/blockdev/ramdisk.rst.
2374 lockd.nlm_grace_period=P [NFS] Assign grace period.
2377 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2380 lockd.nlm_timeout=T [NFS] Assign timeout value.
2383 lockd.nlm_udpport=M [NFS] Assign UDP port.
2386 lockdown= [SECURITY]
2387 { integrity | confidentiality }
2388 Enable the kernel lockdown feature. If set to
2389 integrity, kernel features that allow userland to
2390 modify the running kernel are disabled. If set to
2391 confidentiality, kernel features that allow userland
2392 to extract confidential information from the kernel
2395 locktorture.nreaders_stress= [KNL]
2396 Set the number of locking read-acquisition kthreads.
2397 Defaults to being automatically set based on the
2398 number of online CPUs.
2400 locktorture.nwriters_stress= [KNL]
2401 Set the number of locking write-acquisition kthreads.
2403 locktorture.onoff_holdoff= [KNL]
2404 Set time (s) after boot for CPU-hotplug testing.
2406 locktorture.onoff_interval= [KNL]
2407 Set time (s) between CPU-hotplug operations, or
2408 zero to disable CPU-hotplug testing.
2410 locktorture.shuffle_interval= [KNL]
2411 Set task-shuffle interval (jiffies). Shuffling
2412 tasks allows some CPUs to go into dyntick-idle
2413 mode during the locktorture test.
2415 locktorture.shutdown_secs= [KNL]
2416 Set time (s) after boot system shutdown. This
2417 is useful for hands-off automated testing.
2419 locktorture.stat_interval= [KNL]
2420 Time (s) between statistics printk()s.
2422 locktorture.stutter= [KNL]
2423 Time (s) to stutter testing, for example,
2424 specifying five seconds causes the test to run for
2425 five seconds, wait for five seconds, and so on.
2426 This tests the locking primitive's ability to
2427 transition abruptly to and from idle.
2429 locktorture.torture_type= [KNL]
2430 Specify the locking implementation to test.
2432 locktorture.verbose= [KNL]
2433 Enable additional printk() statements.
2435 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2438 loglevel= All Kernel Messages with a loglevel smaller than the
2439 console loglevel will be printed to the console. It can
2440 also be changed with klogd or other programs. The
2441 loglevels are defined as follows:
2443 0 (KERN_EMERG) system is unusable
2444 1 (KERN_ALERT) action must be taken immediately
2445 2 (KERN_CRIT) critical conditions
2446 3 (KERN_ERR) error conditions
2447 4 (KERN_WARNING) warning conditions
2448 5 (KERN_NOTICE) normal but significant condition
2449 6 (KERN_INFO) informational
2450 7 (KERN_DEBUG) debug-level messages
2452 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2453 in bytes. n must be a power of two and greater
2454 than the minimal size. The minimal size is defined
2455 by LOG_BUF_SHIFT kernel config parameter. There is
2456 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2457 that allows to increase the default size depending on
2458 the number of CPUs. See init/Kconfig for more details.
2460 logo.nologo [FB] Disables display of the built-in Linux logo.
2461 This may be used to provide more screen space for
2462 kernel log messages and is useful when debugging
2463 kernel boot problems.
2465 lp=0 [LP] Specify parallel ports to use, e.g,
2466 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2467 lp=reset first parallel port). 'lp=0' disables the
2468 lp=auto printer driver. 'lp=reset' (which can be
2469 specified in addition to the ports) causes
2470 attached printers to be reset. Using
2471 lp=port1,port2,... specifies the parallel ports
2472 to associate lp devices with, starting with
2473 lp0. A port specification may be 'none' to skip
2474 that lp device, or a parport name such as
2475 'parport0'. Specifying 'lp=auto' instead of a
2476 port specification list means that device IDs
2477 from each port should be examined, to see if
2478 an IEEE 1284-compliant printer is attached; if
2479 so, the driver will manage that printer.
2480 See also header of drivers/char/lp.c.
2483 Sets loops_per_jiffy to given constant, thus avoiding
2484 time-consuming boot-time autodetection (up to 250 ms per
2485 CPU). 0 enables autodetection (default). To determine
2486 the correct value for your kernel, boot with normal
2487 autodetection and see what value is printed. Note that
2488 on SMP systems the preset will be applied to all CPUs,
2489 which is likely to cause problems if your CPUs need
2490 significantly divergent settings. An incorrect value
2491 will cause delays in the kernel to be wrong, leading to
2492 unpredictable I/O errors and other breakage. Although
2493 unlikely, in the extreme case this might damage your
2497 Format: <io>,<irq>,<dma>
2499 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2502 [SECURITY] Choose order of LSM initialization. This
2503 overrides CONFIG_LSM, and the "security=" parameter.
2505 machvec= [IA-64] Force the use of a particular machine-vector
2506 (machvec) in a generic kernel.
2507 Example: machvec=hpzx1
2509 machtype= [Loongson] Share the same kernel image file between different
2511 Example: machtype=lemote-yeeloong-2f-7inch
2513 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2514 than or equal to this physical address is ignored.
2516 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2517 will bring up during bootup. maxcpus=n : n >= 0 limits
2518 the kernel to bring up 'n' processors. Surely after
2519 bootup you can bring up the other plugged cpu by executing
2520 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2521 only takes effect during system bootup.
2522 While n=0 is a special case, it is equivalent to "nosmp",
2523 which also disables the IO APIC.
2525 max_loop= [LOOP] The number of loop block devices that get
2526 (loop.max_loop) unconditionally pre-created at init time. The default
2527 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2528 of statically allocating a predefined number, loop
2529 devices can be requested on-demand with the
2530 /dev/loop-control interface.
2532 mce [X86-32] Machine Check Exception
2534 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2536 md= [HW] RAID subsystems devices and level
2537 See Documentation/admin-guide/md.rst.
2540 Format: <first>,<last>
2541 Specifies range of consoles to be captured by the MDA.
2544 Control mitigation for the Micro-architectural Data
2545 Sampling (MDS) vulnerability.
2547 Certain CPUs are vulnerable to an exploit against CPU
2548 internal buffers which can forward information to a
2549 disclosure gadget under certain conditions.
2551 In vulnerable processors, the speculatively
2552 forwarded data can be used in a cache side channel
2553 attack, to access data to which the attacker does
2554 not have direct access.
2556 This parameter controls the MDS mitigation. The
2559 full - Enable MDS mitigation on vulnerable CPUs
2560 full,nosmt - Enable MDS mitigation and disable
2561 SMT on vulnerable CPUs
2562 off - Unconditionally disable MDS mitigation
2564 On TAA-affected machines, mds=off can be prevented by
2565 an active TAA mitigation as both vulnerabilities are
2566 mitigated with the same mechanism so in order to disable
2567 this mitigation, you need to specify tsx_async_abort=off
2570 Not specifying this option is equivalent to
2573 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2575 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2576 Amount of memory to be used in cases as follows:
2579 2 when the kernel is not able to see the whole system memory;
2580 3 memory that lies after 'mem=' boundary is excluded from
2581 the hypervisor, then assigned to KVM guests.
2583 [X86] Work as limiting max address. Use together
2584 with memmap= to avoid physical address space collisions.
2585 Without memmap= PCI devices could be placed at addresses
2586 belonging to unused RAM.
2588 Note that this only takes effects during boot time since
2589 in above case 3, memory may need be hot added after boot
2590 if system memory of hypervisor is not sufficient.
2592 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2596 [KNL,SH] Allow user to override the default size for
2597 per-device physically contiguous DMA buffers.
2599 memhp_default_state=online/offline
2600 [KNL] Set the initial state for the memory hotplug
2601 onlining policy. If not specified, the default value is
2602 set according to the
2603 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2605 See Documentation/admin-guide/mm/memory-hotplug.rst.
2607 memmap=exactmap [KNL,X86] Enable setting of an exact
2608 E820 memory map, as specified by the user.
2609 Such memmap=exactmap lines can be constructed based on
2610 BIOS output or other requirements. See the memmap=nn@ss
2613 memmap=nn[KMG]@ss[KMG]
2614 [KNL] Force usage of a specific region of memory.
2615 Region of memory to be used is from ss to ss+nn.
2616 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2617 which limits max address to nn[KMG].
2618 Multiple different regions can be specified,
2621 memmap=100M@2G,100M#3G,1G!1024G
2623 memmap=nn[KMG]#ss[KMG]
2624 [KNL,ACPI] Mark specific memory as ACPI data.
2625 Region of memory to be marked is from ss to ss+nn.
2627 memmap=nn[KMG]$ss[KMG]
2628 [KNL,ACPI] Mark specific memory as reserved.
2629 Region of memory to be reserved is from ss to ss+nn.
2630 Example: Exclude memory from 0x18690000-0x1869ffff
2631 memmap=64K$0x18690000
2633 memmap=0x10000$0x18690000
2634 Some bootloaders may need an escape character before '$',
2635 like Grub2, otherwise '$' and the following number
2638 memmap=nn[KMG]!ss[KMG]
2639 [KNL,X86] Mark specific memory as protected.
2640 Region of memory to be used, from ss to ss+nn.
2641 The memory region may be marked as e820 type 12 (0xc)
2642 and is NVDIMM or ADR memory.
2644 memmap=<size>%<offset>-<oldtype>+<newtype>
2645 [KNL,ACPI] Convert memory within the specified region
2646 from <oldtype> to <newtype>. If "-<oldtype>" is left
2647 out, the whole region will be marked as <newtype>,
2648 even if previously unavailable. If "+<newtype>" is left
2649 out, matching memory will be removed. Types are
2650 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2651 3 = ACPI, 12 = PRAM.
2653 memory_corruption_check=0/1 [X86]
2654 Some BIOSes seem to corrupt the first 64k of
2655 memory when doing things like suspend/resume.
2656 Setting this option will scan the memory
2657 looking for corruption. Enabling this will
2658 both detect corruption and prevent the kernel
2659 from using the memory being corrupted.
2660 However, its intended as a diagnostic tool; if
2661 repeatable BIOS-originated corruption always
2662 affects the same memory, you can use memmap=
2663 to prevent the kernel from using that memory.
2665 memory_corruption_check_size=size [X86]
2666 By default it checks for corruption in the low
2667 64k, making this memory unavailable for normal
2668 use. Use this parameter to scan for
2669 corruption in more or less memory.
2671 memory_corruption_check_period=seconds [X86]
2672 By default it checks for corruption every 60
2673 seconds. Use this parameter to check at some
2674 other rate. 0 disables periodic checking.
2676 memtest= [KNL,X86,ARM,PPC] Enable memtest
2678 default : 0 <disable>
2679 Specifies the number of memtest passes to be
2680 performed. Each pass selects another test
2681 pattern from a given set of patterns. Memtest
2682 fills the memory with this pattern, validates
2683 memory contents and reserves bad memory
2684 regions that are detected.
2686 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2687 Valid arguments: on, off
2688 Default (depends on kernel configuration option):
2689 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2690 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2691 mem_encrypt=on: Activate SME
2692 mem_encrypt=off: Do not activate SME
2694 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
2695 for details on when memory encryption can be activated.
2697 mem_sleep_default= [SUSPEND] Default system suspend mode:
2698 s2idle - Suspend-To-Idle
2699 shallow - Power-On Suspend or equivalent (if supported)
2700 deep - Suspend-To-RAM or equivalent (if supported)
2701 See Documentation/admin-guide/pm/sleep-states.rst.
2703 meye.*= [HW] Set MotionEye Camera parameters
2704 See Documentation/media/v4l-drivers/meye.rst.
2706 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2707 Multi-Function General Purpose Timers on AMD Geode
2710 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2711 the BIOS has incorrectly applied a workaround. TinyBIOS
2712 version 0.98 is known to be affected, 0.99 fixes the
2713 problem by letting the user disable the workaround.
2717 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2718 physical address is ignored.
2720 mini2440= [ARM,HW,KNL]
2721 Format:[0..2][b][c][t]
2723 MINI2440 configuration specification:
2724 0 - The attached screen is the 3.5" TFT
2725 1 - The attached screen is the 7" TFT
2726 2 - The VGA Shield is attached (1024x768)
2727 Leaving out the screen size parameter will not load
2728 the TFT driver, and the framebuffer will be left
2730 b - Enable backlight. The TFT backlight pin will be
2731 linked to the kernel VESA blanking code and a GPIO
2732 LED. This parameter is not necessary when using the
2734 c - Enable the s3c camera interface.
2735 t - Reserved for enabling touchscreen support. The
2736 touchscreen support is not enabled in the mainstream
2737 kernel as of 2.6.30, a preliminary port can be found
2738 in the "bleeding edge" mini2440 support kernel at
2739 http://repo.or.cz/w/linux-2.6/mini2440.git
2742 [X86,PPC,S390,ARM64] Control optional mitigations for
2743 CPU vulnerabilities. This is a set of curated,
2744 arch-independent options, each of which is an
2745 aggregation of existing arch-specific options.
2748 Disable all optional CPU mitigations. This
2749 improves system performance, but it may also
2750 expose users to several CPU vulnerabilities.
2751 Equivalent to: nopti [X86,PPC]
2753 nospectre_v1 [X86,PPC]
2755 nospectre_v2 [X86,PPC,S390,ARM64]
2756 spectre_v2_user=off [X86]
2757 spec_store_bypass_disable=off [X86,PPC]
2758 ssbd=force-off [ARM64]
2761 tsx_async_abort=off [X86]
2762 kvm.nx_huge_pages=off [X86]
2765 This does not have any effect on
2766 kvm.nx_huge_pages when
2767 kvm.nx_huge_pages=force.
2770 Mitigate all CPU vulnerabilities, but leave SMT
2771 enabled, even if it's vulnerable. This is for
2772 users who don't want to be surprised by SMT
2773 getting disabled across kernel upgrades, or who
2774 have other ways of avoiding SMT-based attacks.
2775 Equivalent to: (default behavior)
2778 Mitigate all CPU vulnerabilities, disabling SMT
2779 if needed. This is for users who always want to
2780 be fully mitigated, even if it means losing SMT.
2781 Equivalent to: l1tf=flush,nosmt [X86]
2782 mds=full,nosmt [X86]
2783 tsx_async_abort=full,nosmt [X86]
2786 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2787 parameter allows control of the logging verbosity for
2788 the additional memory initialisation checks. A value
2789 of 0 disables mminit logging and a level of 4 will
2790 log everything. Information is printed at KERN_DEBUG
2791 so loglevel=8 may also need to be specified.
2794 [KNL] When CONFIG_MODULE_SIG is set, this means that
2795 modules without (valid) signatures will fail to load.
2796 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2797 is always true, so this option does nothing.
2799 module_blacklist= [KNL] Do not load a comma-separated list of
2800 modules. Useful for debugging problem modules.
2803 [MOUSE] Maximum time between finger touching and
2804 leaving touchpad surface for touch to be considered
2805 a tap and be reported as a left button click (for
2806 touchpads working in absolute mode only).
2808 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2809 reporting absolute coordinates, such as tablets
2810 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2811 reporting absolute coordinates, such as tablets
2813 movablecore= [KNL,X86,IA-64,PPC]
2814 Format: nn[KMGTPE] | nn%
2815 This parameter is the complement to kernelcore=, it
2816 specifies the amount of memory used for migratable
2817 allocations. If both kernelcore and movablecore is
2818 specified, then kernelcore will be at *least* the
2819 specified value but may be more. If movablecore on its
2820 own is specified, the administrator must be careful
2821 that the amount of memory usable for all allocations
2824 movable_node [KNL] Boot-time switch to make hotplugable memory
2825 NUMA nodes to be movable. This means that the memory
2826 of such nodes will be usable only for movable
2827 allocations which rules out almost all kernel
2828 allocations. Use with caution!
2830 MTD_Partition= [MTD]
2831 Format: <name>,<region-number>,<size>,<offset>
2833 MTD_Region= [MTD] Format:
2834 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2837 See drivers/mtd/parsers/cmdlinepart.c
2839 multitce=off [PPC] This parameter disables the use of the pSeries
2840 firmware feature for updating multiple TCE entries
2843 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2845 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2847 boundary - index of last SLC block on Flex-OneNAND.
2848 The remaining blocks are configured as MLC blocks.
2849 lock - Configure if Flex-OneNAND boundary should be locked.
2850 Once locked, the boundary cannot be changed.
2851 1 indicates lock status, 0 indicates unlock status.
2854 ARM/S3C2412 JIVE boot control
2856 See arch/arm/mach-s3c2412/mach-jive.c
2858 mtouchusb.raw_coordinates=
2859 [HW] Make the MicroTouch USB driver use raw coordinates
2860 ('y', default) or cooked coordinates ('n')
2862 mtrr_chunk_size=nn[KMG] [X86]
2863 used for mtrr cleanup. It is largest continuous chunk
2864 that could hold holes aka. UC entries.
2866 mtrr_gran_size=nn[KMG] [X86]
2867 Used for mtrr cleanup. It is granularity of mtrr block.
2869 Large value could prevent small alignment from
2872 mtrr_spare_reg_nr=n [X86]
2874 Range: 0,7 : spare reg number
2876 Used for mtrr cleanup. It is spare mtrr entries number.
2877 Set to 2 or more if your graphical card needs more.
2879 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2881 netdev= [NET] Network devices parameters
2882 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2883 Note that mem_start is often overloaded to mean
2884 something different and driver-specific.
2885 This usage is only documented in each driver source
2889 [NETFILTER] Enable connection tracking flow accounting
2890 0 to disable accounting
2891 1 to enable accounting
2894 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2895 See Documentation/admin-guide/nfs/nfsroot.rst.
2897 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2898 See Documentation/admin-guide/nfs/nfsroot.rst.
2900 nfsrootdebug [NFS] enable nfsroot debugging messages.
2901 See Documentation/admin-guide/nfs/nfsroot.rst.
2903 nfs.callback_nr_threads=
2904 [NFSv4] set the total number of threads that the
2905 NFS client will assign to service NFSv4 callback
2908 nfs.callback_tcpport=
2909 [NFS] set the TCP port on which the NFSv4 callback
2910 channel should listen.
2913 [NFS] sets the pathname to the program which is used
2914 to update the NFS client cache entries.
2916 nfs.cache_getent_timeout=
2917 [NFS] sets the timeout after which an attempt to
2918 update a cache entry is deemed to have failed.
2920 nfs.idmap_cache_timeout=
2921 [NFS] set the maximum lifetime for idmapper cache
2925 [NFS] enable 64-bit inode numbers.
2926 If zero, the NFS client will fake up a 32-bit inode
2927 number for the readdir() and stat() syscalls instead
2928 of returning the full 64-bit number.
2929 The default is to return 64-bit inode numbers.
2931 nfs.max_session_cb_slots=
2932 [NFSv4.1] Sets the maximum number of session
2933 slots the client will assign to the callback
2934 channel. This determines the maximum number of
2935 callbacks the client will process in parallel for
2936 a particular server.
2938 nfs.max_session_slots=
2939 [NFSv4.1] Sets the maximum number of session slots
2940 the client will attempt to negotiate with the server.
2941 This limits the number of simultaneous RPC requests
2942 that the client can send to the NFSv4.1 server.
2943 Note that there is little point in setting this
2944 value higher than the max_tcp_slot_table_limit.
2946 nfs.nfs4_disable_idmapping=
2947 [NFSv4] When set to the default of '1', this option
2948 ensures that both the RPC level authentication
2949 scheme and the NFS level operations agree to use
2950 numeric uids/gids if the mount is using the
2951 'sec=sys' security flavour. In effect it is
2952 disabling idmapping, which can make migration from
2953 legacy NFSv2/v3 systems to NFSv4 easier.
2954 Servers that do not support this mode of operation
2955 will be autodetected by the client, and it will fall
2956 back to using the idmapper.
2957 To turn off this behaviour, set the value to '0'.
2959 [NFS4] Specify an additional fixed unique ident-
2960 ification string that NFSv4 clients can insert into
2961 their nfs_client_id4 string. This is typically a
2962 UUID that is generated at system install time.
2964 nfs.send_implementation_id =
2965 [NFSv4.1] Send client implementation identification
2966 information in exchange_id requests.
2967 If zero, no implementation identification information
2969 The default is to send the implementation identification
2972 nfs.recover_lost_locks =
2973 [NFSv4] Attempt to recover locks that were lost due
2974 to a lease timeout on the server. Please note that
2975 doing this risks data corruption, since there are
2976 no guarantees that the file will remain unchanged
2977 after the locks are lost.
2978 If you want to enable the kernel legacy behaviour of
2979 attempting to recover these locks, then set this
2981 The default parameter value of '0' causes the kernel
2982 not to attempt recovery of lost locks.
2984 nfs4.layoutstats_timer =
2985 [NFSv4.2] Change the rate at which the kernel sends
2986 layoutstats to the pNFS metadata server.
2988 Setting this to value to 0 causes the kernel to use
2989 whatever value is the default set by the layout
2990 driver. A non-zero value sets the minimum interval
2991 in seconds between layoutstats transmissions.
2993 nfsd.nfs4_disable_idmapping=
2994 [NFSv4] When set to the default of '1', the NFSv4
2995 server will return only numeric uids and gids to
2996 clients using auth_sys, and will accept numeric uids
2997 and gids from such clients. This is intended to ease
2998 migration from NFSv2/v3.
3000 nmi_debug= [KNL,SH] Specify one or more actions to take
3001 when a NMI is triggered.
3002 Format: [state][,regs][,debounce][,die]
3004 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3005 Format: [panic,][nopanic,][num]
3007 0 - turn hardlockup detector in nmi_watchdog off
3008 1 - turn hardlockup detector in nmi_watchdog on
3009 When panic is specified, panic when an NMI watchdog
3010 timeout occurs (or 'nopanic' to not panic on an NMI
3011 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3012 To disable both hard and soft lockup detectors,
3013 please see 'nowatchdog'.
3014 This is useful when you use a panic=... timeout and
3015 need the box quickly up again.
3017 These settings can be accessed at runtime via
3018 the nmi_watchdog and hardlockup_panic sysctls.
3020 netpoll.carrier_timeout=
3021 [NET] Specifies amount of time (in seconds) that
3022 netpoll should wait for a carrier. By default netpoll
3025 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3026 emulation library even if a 387 maths coprocessor
3029 no5lvl [X86-64] Disable 5-level paging mode. Forces
3030 kernel to use 4-level paging instead.
3033 [HW] Never suspend the console
3034 Disable suspending of consoles during suspend and
3035 hibernate operations. Once disabled, debugging
3036 messages can reach various consoles while the rest
3037 of the system is being put to sleep (ie, while
3038 debugging driver suspend/resume hooks). This may
3039 not work reliably with all consoles, but is known
3040 to work with serial and VGA consoles.
3041 To facilitate more flexible debugging, we also add
3042 console_suspend, a printk module parameter to control
3043 it. Users could use console_suspend (usually
3044 /sys/module/printk/parameters/console_suspend) to
3045 turn on/off it dynamically.
3047 novmcoredd [KNL,KDUMP]
3048 Disable device dump. Device dump allows drivers to
3049 append dump data to vmcore so you can collect driver
3050 specified debug info. Drivers can append the data
3051 without any limit and this data is stored in memory,
3052 so this may cause significant memory stress. Disabling
3053 device dump can help save memory but the driver debug
3054 data will be no longer available. This parameter
3055 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3058 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3059 caches in the slab allocator. Saves per-node memory,
3060 but will impact performance.
3064 noaltinstr [S390] Disables alternative instructions patching
3065 (CPU alternatives feature).
3067 noapic [SMP,APIC] Tells the kernel to not make use of any
3068 IOAPICs that may be present in the system.
3070 noautogroup Disable scheduler automatic task group creation.
3072 nobats [PPC] Do not use BATs for mapping kernel lowmem
3073 on "Classic" PPC cores.
3077 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
3079 nodelayacct [KNL] Disable per-task delay accounting
3081 nodsp [SH] Disable hardware DSP at boot time.
3083 noefi Disable EFI runtime services support.
3088 On X86-32 available only on PAE configured kernels.
3089 noexec=on: enable non-executable mappings (default)
3090 noexec=off: disable non-executable mappings
3093 Disable SMAP (Supervisor Mode Access Prevention)
3094 even if it is supported by processor.
3097 Disable SMEP (Supervisor Mode Execution Prevention)
3098 even if it is supported by processor.
3101 This affects only 32-bit executables.
3102 noexec32=on: enable non-executable mappings (default)
3103 read doesn't imply executable mappings
3104 noexec32=off: disable non-executable mappings
3105 read implies executable mappings
3107 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3109 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3110 register save and restore. The kernel will only save
3111 legacy floating-point registers on task switch.
3113 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings.
3115 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3116 Equivalent to smt=1.
3118 [KNL,x86] Disable symmetric multithreading (SMT).
3119 nosmt=force: Force disable SMT, cannot be undone
3120 via the sysfs control file.
3122 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3123 (bounds check bypass). With this option data leaks are
3124 possible in the system.
3126 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3127 the Spectre variant 2 (indirect branch prediction)
3128 vulnerability. System may allow data leaks with this
3131 nospec_store_bypass_disable
3132 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3134 noxsave [BUGS=X86] Disables x86 extended register state save
3135 and restore using xsave. The kernel will fallback to
3136 enabling legacy floating-point and sse state.
3138 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3139 register states. The kernel will fall back to use
3140 xsave to save the states. By using this parameter,
3141 performance of saving the states is degraded because
3142 xsave doesn't support modified optimization while
3143 xsaveopt supports it on xsaveopt enabled systems.
3145 noxsaves [X86] Disables xsaves and xrstors used in saving and
3146 restoring x86 extended register state in compacted
3147 form of xsave area. The kernel will fall back to use
3148 xsaveopt and xrstor to save and restore the states
3149 in standard form of xsave area. By using this
3150 parameter, xsave area per process might occupy more
3151 memory on xsaves enabled systems.
3153 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
3154 wfi(ARM) instruction doesn't work correctly and not to
3155 use it. This is also useful when using JTAG debugger.
3157 no_file_caps Tells the kernel not to honor file capabilities. The
3158 only way then for a file to be executed with privilege
3159 is to be setuid root or executed by root.
3161 nohalt [IA-64] Tells the kernel not to use the power saving
3162 function PAL_HALT_LIGHT when idle. This increases
3163 power-consumption. On the positive side, it reduces
3164 interrupt wake-up latency, which may improve performance
3165 in certain environments such as networked servers or
3168 nohibernate [HIBERNATION] Disable hibernation and resume.
3170 nohz= [KNL] Boottime enable/disable dynamic ticks
3171 Valid arguments: on, off
3174 nohz_full= [KNL,BOOT,SMP,ISOL]
3175 The argument is a cpu list, as described above.
3176 In kernels built with CONFIG_NO_HZ_FULL=y, set
3177 the specified list of CPUs whose tick will be stopped
3178 whenever possible. The boot CPU will be forced outside
3179 the range to maintain the timekeeping. Any CPUs
3180 in this list will have their RCU callbacks offloaded,
3181 just as if they had also been called out in the
3182 rcu_nocbs= boot parameter.
3184 noiotrap [SH] Disables trapped I/O port accesses.
3186 noirqdebug [X86-32] Disables the code which attempts to detect and
3187 disable unhandled interrupt sources.
3189 no_timer_check [X86,APIC] Disables the code which tests for
3190 broken timer IRQ sources.
3192 noisapnp [ISAPNP] Disables ISA PnP code.
3194 noinitrd [RAM] Tells the kernel not to load any configured
3197 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3199 [Deprecated - use intremap=off]
3203 noinvpcid [X86] Disable the INVPCID cpu feature.
3205 nojitter [IA-64] Disables jitter checking for ITC timers.
3207 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3209 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3213 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3214 clock and use the default one.
3216 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
3217 accounting. steal time is computed, but won't
3218 influence scheduler behaviour
3220 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3222 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3224 noltlbs [PPC] Do not use large page/tlb entries for kernel
3225 lowmem mapping on PPC40x and PPC8xx
3227 nomca [IA-64] Disable machine check abort handling
3229 nomce [X86-32] Disable Machine Check Exception
3231 nomfgpt [X86-32] Disable Multi-Function General Purpose
3232 Timer usage (for AMD Geode machines).
3234 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3235 shutdown the other cpus. Instead use the REBOOT_VECTOR
3238 nomodule Disable module load
3240 nopat [X86] Disable PAT (page attribute table extension of
3241 pagetables) support.
3243 nopcid [X86-64] Disable the PCID cpu feature.
3245 norandmaps Don't use address space randomization. Equivalent to
3246 echo 0 > /proc/sys/kernel/randomize_va_space
3248 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3249 with UP alternatives
3251 nordrand [X86] Disable kernel use of the RDRAND and
3252 RDSEED instructions even if they are supported
3253 by the processor. RDRAND and RDSEED are still
3254 available to user space applications.
3256 noresume [SWSUSP] Disables resume and restores original swap
3259 no-scroll [VGA] Disables scrollback.
3260 This is required for the Braillex ib80-piezo Braille
3261 reader made by F.H. Papenmeier (Germany).
3265 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3267 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3268 and disable the IO APIC. legacy for "maxcpus=0".
3270 nosoftlockup [KNL] Disable the soft-lockup detector.
3272 nosync [HW,M68K] Disables sync negotiation for all devices.
3274 nowatchdog [KNL] Disable both lockup detectors, i.e.
3275 soft-lockup and NMI watchdog (hard-lockup).
3279 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3281 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3282 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3283 Some features depend on CPU0. Known dependencies are:
3284 1. Resume from suspend/hibernate depends on CPU0.
3285 Suspend/hibernate will fail if CPU0 is offline and you
3286 need to online CPU0 before suspend/hibernate.
3287 2. PIC interrupts also depend on CPU0. CPU0 can't be
3288 removed if a PIC interrupt is detected.
3289 It's said poweroff/reboot may depend on CPU0 on some
3290 machines although I haven't seen such issues so far
3291 after CPU0 is offline on a few tested machines.
3292 If the dependencies are under your control, you can
3293 turn on cpu0_hotplug.
3295 nps_mtm_hs_ctr= [KNL,ARC]
3296 This parameter sets the maximum duration, in
3297 cycles, each HW thread of the CTOP can run
3298 without interruptions, before HW switches it.
3299 The actual maximum duration is 16 times this
3301 Format: integer between 1 and 255
3304 nptcg= [IA-64] Override max number of concurrent global TLB
3305 purges which is reported from either PAL_VM_SUMMARY or
3308 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3309 could support. nr_cpus=n : n >= 1 limits the kernel to
3310 support 'n' processors. It could be larger than the
3311 number of already plugged CPU during bootup, later in
3312 runtime you can physically add extra cpu until it reaches
3313 n. So during boot up some boot time memory for per-cpu
3314 variables need be pre-allocated for later physical cpu
3317 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3319 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3320 Allowed values are enable and disable
3322 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3323 'node', 'default' can be specified
3324 This can be set from sysctl after boot.
3325 See Documentation/admin-guide/sysctl/vm.rst for details.
3327 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3328 See Documentation/debugging-via-ohci1394.txt for more
3331 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3332 Rather than timing out after 20 ms if an EC
3333 command is not properly ACKed, override the length
3334 of the timeout. We have interrupts disabled while
3335 waiting for the ACK, so if this is set too high
3336 interrupts *may* be lost!
3338 omap_mux= [OMAP] Override bootloader pin multiplexing.
3339 Format: <mux_mode0.mode_name=value>...
3340 For example, to override I2C bus2:
3341 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3343 oprofile.timer= [HW]
3344 Use timer interrupt instead of performance counters
3346 oprofile.cpu_type= Force an oprofile cpu type
3347 This might be useful if you have an older oprofile
3348 userland or if you want common events.
3349 Format: { arch_perfmon }
3350 arch_perfmon: [X86] Force use of architectural
3351 perfmon on Intel CPUs instead of the
3352 CPU specific event set.
3353 timer: [X86] Force use of architectural NMI
3354 timer mode (see also oprofile.timer
3355 for generic hr timer mode)
3357 oops=panic Always panic on oopses. Default is to just kill the
3358 process, but there is a small probability of
3359 deadlocking the machine.
3360 This will also cause panics on machine check exceptions.
3361 Useful together with panic=30 to trigger a reboot.
3364 [KNL] Boolean flag to control whether the page allocator
3365 should randomize its free lists. The randomization may
3366 be automatically enabled if the kernel detects it is
3367 running on a platform with a direct-mapped memory-side
3368 cache, and this parameter can be used to
3369 override/disable that behavior. The state of the flag
3370 can be read from sysfs at:
3371 /sys/module/page_alloc/parameters/shuffle.
3373 page_owner= [KNL] Boot-time page_owner enabling option.
3374 Storage of the information about who allocated
3375 each page is disabled in default. With this switch,
3377 on: enable the feature
3379 page_poison= [KNL] Boot-time parameter changing the state of
3380 poisoning on the buddy allocator, available with
3381 CONFIG_PAGE_POISONING=y.
3382 off: turn off poisoning (default)
3383 on: turn on poisoning
3385 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3386 timeout > 0: seconds before rebooting
3387 timeout = 0: wait forever
3388 timeout < 0: reboot immediately
3391 panic_print= Bitmask for printing system info when panic happens.
3392 User can chose combination of the following bits:
3393 bit 0: print all tasks info
3394 bit 1: print system memory info
3395 bit 2: print timer info
3396 bit 3: print locks info if CONFIG_LOCKDEP is on
3397 bit 4: print ftrace buffer
3398 bit 5: print all printk messages in buffer
3400 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3403 crash_kexec_post_notifiers
3404 Run kdump after running panic-notifiers and dumping
3405 kmsg. This only for the users who doubt kdump always
3406 succeeds in any situation.
3407 Note that this also increases risks of kdump failure,
3408 because some panic notifiers can make the crashed
3409 kernel more unstable.
3411 parkbd.port= [HW] Parallel port number the keyboard adapter is
3412 connected to, default is 0.
3414 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3415 0 for XT, 1 for AT (default is AT).
3418 parport= [HW,PPT] Specify parallel ports. 0 disables.
3419 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3420 Use 'auto' to force the driver to use any
3421 IRQ/DMA settings detected (the default is to
3422 ignore detected IRQ/DMA settings because of
3423 possible conflicts). You can specify the base
3424 address, IRQ, and DMA settings; IRQ and DMA
3425 should be numbers, or 'auto' (for using detected
3426 settings on that particular port), or 'nofifo'
3427 (to avoid using a FIFO even if it is detected).
3428 Parallel ports are assigned in the order they
3429 are specified on the command line, starting
3432 parport_init_mode= [HW,PPT]
3433 Configure VIA parallel port to operate in
3434 a specific mode. This is necessary on Pegasos
3435 computer where firmware has no options for setting
3436 up parallel port mode and sets it to spp.
3437 Currently this function knows 686a and 8231 chips.
3438 Format: [spp|ps2|epp|ecp|ecpepp]
3441 Halt all CPUs after the first oops has been printed for
3442 the specified number of seconds. This is to be used if
3443 your oopses keep scrolling off the screen.
3448 See header of drivers/block/paride/pcd.c.
3449 See also Documentation/admin-guide/blockdev/paride.rst.
3451 pci=option[,option...] [PCI] various PCI subsystem options.
3453 Some options herein operate on a specific device
3454 or a set of devices (<pci_dev>). These are
3455 specified in one of the following formats:
3457 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3458 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3460 Note: the first format specifies a PCI
3461 bus/device/function address which may change
3462 if new hardware is inserted, if motherboard
3463 firmware changes, or due to changes caused
3464 by other kernel parameters. If the
3465 domain is left unspecified, it is
3466 taken to be zero. Optionally, a path
3467 to a device through multiple device/function
3468 addresses can be specified after the base
3469 address (this is more robust against
3470 renumbering issues). The second format
3471 selects devices using IDs from the
3472 configuration space which may match multiple
3473 devices in the system.
3475 earlydump dump PCI config space before the kernel
3477 off [X86] don't probe for the PCI bus
3478 bios [X86-32] force use of PCI BIOS, don't access
3479 the hardware directly. Use this if your machine
3480 has a non-standard PCI host bridge.
3481 nobios [X86-32] disallow use of PCI BIOS, only direct
3482 hardware access methods are allowed. Use this
3483 if you experience crashes upon bootup and you
3484 suspect they are caused by the BIOS.
3485 conf1 [X86] Force use of PCI Configuration Access
3486 Mechanism 1 (config address in IO port 0xCF8,
3487 data in IO port 0xCFC, both 32-bit).
3488 conf2 [X86] Force use of PCI Configuration Access
3489 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3490 the function, IO port 0xCFA, also 8-bit, sets
3491 bus number. The config space is then accessed
3492 through ports 0xC000-0xCFFF).
3493 See http://wiki.osdev.org/PCI for more info
3494 on the configuration access mechanisms.
3495 noaer [PCIE] If the PCIEAER kernel config parameter is
3496 enabled, this kernel boot option can be used to
3497 disable the use of PCIE advanced error reporting.
3498 nodomains [PCI] Disable support for multiple PCI
3499 root domains (aka PCI segments, in ACPI-speak).
3500 nommconf [X86] Disable use of MMCONFIG for PCI
3502 check_enable_amd_mmconf [X86] check for and enable
3503 properly configured MMIO access to PCI
3504 config space on AMD family 10h CPU
3505 nomsi [MSI] If the PCI_MSI kernel config parameter is
3506 enabled, this kernel boot option can be used to
3507 disable the use of MSI interrupts system-wide.
3508 noioapicquirk [APIC] Disable all boot interrupt quirks.
3509 Safety option to keep boot IRQs enabled. This
3510 should never be necessary.
3511 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3512 primary IO-APIC for bridges that cannot disable
3513 boot IRQs. This fixes a source of spurious IRQs
3514 when the system masks IRQs.
3515 noioapicreroute [APIC] Disable workaround that uses the
3516 boot IRQ equivalent of an IRQ that connects to
3517 a chipset where boot IRQs cannot be disabled.
3518 The opposite of ioapicreroute.
3519 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3520 routing table. These calls are known to be buggy
3521 on several machines and they hang the machine
3522 when used, but on other computers it's the only
3523 way to get the interrupt routing table. Try
3524 this option if the kernel is unable to allocate
3525 IRQs or discover secondary PCI buses on your
3527 rom [X86] Assign address space to expansion ROMs.
3528 Use with caution as certain devices share
3529 address decoders between ROMs and other
3531 norom [X86] Do not assign address space to
3532 expansion ROMs that do not already have
3533 BIOS assigned address ranges.
3534 nobar [X86] Do not assign address space to the
3535 BARs that weren't assigned by the BIOS.
3536 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3537 assigned automatically to PCI devices. You can
3538 make the kernel exclude IRQs of your ISA cards
3540 pirqaddr=0xAAAAA [X86] Specify the physical address
3541 of the PIRQ table (normally generated
3542 by the BIOS) if it is outside the
3543 F0000h-100000h range.
3544 lastbus=N [X86] Scan all buses thru bus #N. Can be
3545 useful if the kernel is unable to find your
3546 secondary buses and you want to tell it
3547 explicitly which ones they are.
3548 assign-busses [X86] Always assign all PCI bus
3549 numbers ourselves, overriding
3550 whatever the firmware may have done.
3551 usepirqmask [X86] Honor the possible IRQ mask stored
3552 in the BIOS $PIR table. This is needed on
3553 some systems with broken BIOSes, notably
3554 some HP Pavilion N5400 and Omnibook XE3
3555 notebooks. This will have no effect if ACPI
3556 IRQ routing is enabled.
3557 noacpi [X86] Do not use ACPI for IRQ routing
3558 or for PCI scanning.
3559 use_crs [X86] Use PCI host bridge window information
3560 from ACPI. On BIOSes from 2008 or later, this
3561 is enabled by default. If you need to use this,
3562 please report a bug.
3563 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3564 If you need to use this, please report a bug.
3565 routeirq Do IRQ routing for all PCI devices.
3566 This is normally done in pci_enable_device(),
3567 so this option is a temporary workaround
3568 for broken drivers that don't call it.
3569 skip_isa_align [X86] do not align io start addr, so can
3570 handle more pci cards
3571 noearly [X86] Don't do any early type 1 scanning.
3572 This might help on some broken boards which
3573 machine check when some devices' config space
3574 is read. But various workarounds are disabled
3575 and some IOMMU drivers will not work.
3576 bfsort Sort PCI devices into breadth-first order.
3577 This sorting is done to get a device
3578 order compatible with older (<= 2.4) kernels.
3579 nobfsort Don't sort PCI devices into breadth-first order.
3580 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3581 tuning and use the BIOS-configured MPS defaults.
3582 pcie_bus_safe Set every device's MPS to the largest value
3583 supported by all devices below the root complex.
3584 pcie_bus_perf Set device MPS to the largest allowable MPS
3585 based on its parent bus. Also set MRRS (Max
3586 Read Request Size) to the largest supported
3587 value (no larger than the MPS that the device
3588 or bus can support) for best performance.
3589 pcie_bus_peer2peer Set every device's MPS to 128B, which
3590 every device is guaranteed to support. This
3591 configuration allows peer-to-peer DMA between
3592 any pair of devices, possibly at the cost of
3593 reduced performance. This also guarantees
3594 that hot-added devices will work.
3595 cbiosize=nn[KMG] The fixed amount of bus space which is
3596 reserved for the CardBus bridge's IO window.
3597 The default value is 256 bytes.
3598 cbmemsize=nn[KMG] The fixed amount of bus space which is
3599 reserved for the CardBus bridge's memory
3600 window. The default value is 64 megabytes.
3603 [<order of align>@]<pci_dev>[; ...]
3604 Specifies alignment and device to reassign
3605 aligned memory resources. How to
3606 specify the device is described above.
3607 If <order of align> is not specified,
3608 PAGE_SIZE is used as alignment.
3609 A PCI-PCI bridge can be specified if resource
3610 windows need to be expanded.
3611 To specify the alignment for several
3612 instances of a device, the PCI vendor,
3613 device, subvendor, and subdevice may be
3614 specified, e.g., 12@pci:8086:9c22:103c:198f
3615 for 4096-byte alignment.
3616 ecrc= Enable/disable PCIe ECRC (transaction layer
3617 end-to-end CRC checking).
3618 bios: Use BIOS/firmware settings. This is the
3622 hpiosize=nn[KMG] The fixed amount of bus space which is
3623 reserved for hotplug bridge's IO window.
3624 Default size is 256 bytes.
3625 hpmmiosize=nn[KMG] The fixed amount of bus space which is
3626 reserved for hotplug bridge's MMIO window.
3627 Default size is 2 megabytes.
3628 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
3629 reserved for hotplug bridge's MMIO_PREF window.
3630 Default size is 2 megabytes.
3631 hpmemsize=nn[KMG] The fixed amount of bus space which is
3632 reserved for hotplug bridge's MMIO and
3634 Default size is 2 megabytes.
3635 hpbussize=nn The minimum amount of additional bus numbers
3636 reserved for buses below a hotplug bridge.
3638 realloc= Enable/disable reallocating PCI bridge resources
3639 if allocations done by BIOS are too small to
3640 accommodate resources required by all child
3642 off: Turn realloc off
3644 realloc same as realloc=on
3645 noari do not use PCIe ARI.
3646 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3647 do not use PCIe ATS (and IOMMU device IOTLB).
3648 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3649 only look for one device below a PCIe downstream
3651 big_root_window Try to add a big 64bit memory window to the PCIe
3652 root complex on AMD CPUs. Some GFX hardware
3653 can resize a BAR to allow access to all VRAM.
3654 Adding the window is slightly risky (it may
3655 conflict with unreported devices), so this
3657 disable_acs_redir=<pci_dev>[; ...]
3658 Specify one or more PCI devices (in the format
3659 specified above) separated by semicolons.
3660 Each device specified will have the PCI ACS
3661 redirect capabilities forced off which will
3662 allow P2P traffic between devices through
3663 bridges without forcing it upstream. Note:
3664 this removes isolation between devices and
3665 may put more devices in an IOMMU group.
3666 force_floating [S390] Force usage of floating interrupts.
3667 nomio [S390] Do not use MIO instructions.
3669 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3672 force Enable ASPM even on devices that claim not to support it.
3673 WARNING: Forcing ASPM on may cause system lockups.
3675 pcie_ports= [PCIE] PCIe port services handling:
3676 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3677 even if the platform doesn't give the OS permission to
3678 use them. This may cause conflicts if the platform
3679 also tries to use these services.
3680 dpc-native Use native PCIe service for DPC only. May
3681 cause conflicts if firmware uses AER or DPC.
3682 compat Disable native PCIe services (PME, AER, DPC, PCIe
3685 pcie_port_pm= [PCIE] PCIe port power management handling:
3686 off Disable power management of all PCIe ports
3687 force Forcibly enable power management of all PCIe ports
3689 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3690 nomsi Do not use MSI for native PCIe PME signaling (this makes
3691 all PCIe root ports use INTx for all services).
3693 pcmv= [HW,PCMCIA] BadgePAD 4
3697 Keep all power-domains already enabled by bootloader on,
3698 even if no driver has claimed them. This is useful
3699 for debug and development, but should not be
3700 needed on a platform with proper driver support.
3703 See Documentation/admin-guide/blockdev/paride.rst.
3705 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3708 See arch/parisc/kernel/pdc_chassis.c
3710 percpu_alloc= Select which percpu first chunk allocator to use.
3711 Currently supported values are "embed" and "page".
3712 Archs may support subset or none of the selections.
3713 See comments in mm/percpu.c for details on each
3714 allocator. This parameter is primarily for debugging
3715 and performance comparison.
3718 See Documentation/admin-guide/blockdev/paride.rst.
3721 See Documentation/admin-guide/blockdev/paride.rst.
3723 pirq= [SMP,APIC] Manual mp-table setup
3724 See Documentation/x86/i386/IO-APIC.rst.
3726 plip= [PPT,NET] Parallel port network link
3727 Format: { parport<nr> | timid | 0 }
3728 See also Documentation/admin-guide/parport.rst.
3730 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3731 Override pmtimer IOPort with a hex value.
3734 pm_debug_messages [SUSPEND,KNL]
3735 Enable suspend/resume debug messages during boot up.
3738 Enable PNP debug messages (depends on the
3739 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3740 via /sys/module/pnp/parameters/debug. We always show
3741 current resource usage; turning this on also shows
3742 possible settings and some assignment information.
3748 { on | off | curr | res | no-curr | no-res }
3751 [ISAPNP] Exclude IRQs for the autoconfiguration
3754 [ISAPNP] Exclude DMAs for the autoconfiguration
3756 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3757 Ranges are in pairs (I/O port base and size).
3760 [ISAPNP] Exclude memory regions for the
3762 Ranges are in pairs (memory base and size).
3764 ports= [IP_VS_FTP] IPVS ftp helper module
3766 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3768 Format: <port>,<port>....
3770 powersave=off [PPC] This option disables power saving features.
3771 It specifically disables cpuidle and sets the
3772 platform machine description specific power_save
3773 function to NULL. On Idle the CPU just reduces
3776 ppc_strict_facility_enable
3777 [PPC] This option catches any kernel floating point,
3778 Altivec, VSX and SPE outside of regions specifically
3779 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3780 There is some performance impact when enabling this.
3784 Disable Hardware Transactional Memory
3786 print-fatal-signals=
3787 [KNL] debug: print fatal signals
3789 If enabled, warn about various signal handling
3790 related application anomalies: too many signals,
3791 too many POSIX.1 timers, fatal signals causing a
3794 If you hit the warning due to signal overflow,
3795 you might want to try "ulimit -i unlimited".
3799 printk.always_kmsg_dump=
3800 Trigger kmsg_dump for cases other than kernel oops or
3802 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3805 printk.devkmsg={on,off,ratelimit}
3806 Control writing to /dev/kmsg.
3807 on - unlimited logging to /dev/kmsg from userspace
3808 off - logging to /dev/kmsg disabled
3809 ratelimit - ratelimit the logging
3812 printk.time= Show timing data prefixed to each printk message line
3813 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3815 processor.max_cstate= [HW,ACPI]
3816 Limit processor to maximum C-state
3817 max_cstate=9 overrides any DMI blacklist limit.
3819 processor.nocst [HW,ACPI]
3820 Ignore the _CST method to determine C-states,
3821 instead using the legacy FADT method
3823 profile= [KNL] Enable kernel profiling via /proc/profile
3824 Format: [<profiletype>,]<number>
3825 Param: <profiletype>: "schedule", "sleep", or "kvm"
3826 [defaults to kernel profiling]
3827 Param: "schedule" - profile schedule points.
3828 Param: "sleep" - profile D-state sleeping (millisecs).
3829 Requires CONFIG_SCHEDSTATS
3830 Param: "kvm" - profile VM exits.
3831 Param: <number> - step/bucket size as a power of 2 for
3832 statistical time based profiling.
3834 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3836 See Documentation/admin-guide/blockdev/ramdisk.rst.
3838 prot_virt= [S390] enable hosting protected virtual machines
3839 isolated from the hypervisor (if hardware supports
3843 psi= [KNL] Enable or disable pressure stall information
3847 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3848 probe for; one of (bare|imps|exps|lifebook|any).
3849 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3851 psmouse.resetafter= [HW,MOUSE]
3852 Try to reset the device after so many bad packets
3855 [HW,MOUSE] Set desired mouse resolution, in dpi.
3856 psmouse.smartscroll=
3857 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3858 0 = disabled, 1 = enabled (default).
3860 pstore.backend= Specify the name of the pstore backend to use
3863 See Documentation/admin-guide/blockdev/paride.rst.
3865 pti= [X86_64] Control Page Table Isolation of user and
3866 kernel address spaces. Disabling this feature
3867 removes hardening, but improves performance of
3868 system calls and interrupts.
3870 on - unconditionally enable
3871 off - unconditionally disable
3872 auto - kernel detects whether your CPU model is
3873 vulnerable to issues that PTI mitigates
3875 Not specifying this option is equivalent to pti=auto.
3878 Equivalent to pti=off
3881 [KNL] Number of legacy pty's. Overwrites compiled-in
3884 quiet [KNL] Disable most log messages
3889 See Documentation/admin-guide/md.rst.
3891 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3892 See Documentation/admin-guide/blockdev/ramdisk.rst.
3894 random.trust_cpu={on,off}
3895 [KNL] Enable or disable trusting the use of the
3896 CPU's random number generator (if available) to
3897 fully seed the kernel's CRNG. Default is controlled
3898 by CONFIG_RANDOM_TRUST_CPU.
3900 ras=option[,option,...] [KNL] RAS-specific options
3903 Disable the Correctable Errors Collector,
3904 see CONFIG_RAS_CEC help text.
3907 The argument is a cpu list, as described above,
3908 except that the string "all" can be used to
3909 specify every CPU on the system.
3911 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3912 the specified list of CPUs to be no-callback CPUs.
3913 Invocation of these CPUs' RCU callbacks will be
3914 offloaded to "rcuox/N" kthreads created for that
3915 purpose, where "x" is "p" for RCU-preempt, and
3916 "s" for RCU-sched, and "N" is the CPU number.
3917 This reduces OS jitter on the offloaded CPUs,
3918 which can be useful for HPC and real-time
3919 workloads. It can also improve energy efficiency
3920 for asymmetric multiprocessors.
3923 Rather than requiring that offloaded CPUs
3924 (specified by rcu_nocbs= above) explicitly
3925 awaken the corresponding "rcuoN" kthreads,
3926 make these kthreads poll for callbacks.
3927 This improves the real-time response for the
3928 offloaded CPUs by relieving them of the need to
3929 wake up the corresponding kthread, but degrades
3930 energy efficiency by requiring that the kthreads
3931 periodically wake up to do the polling.
3933 rcutree.blimit= [KNL]
3934 Set maximum number of finished RCU callbacks to
3935 process in one batch.
3937 rcutree.dump_tree= [KNL]
3938 Dump the structure of the rcu_node combining tree
3939 out at early boot. This is used for diagnostic
3940 purposes, to verify correct tree setup.
3942 rcutree.gp_cleanup_delay= [KNL]
3943 Set the number of jiffies to delay each step of
3944 RCU grace-period cleanup.
3946 rcutree.gp_init_delay= [KNL]
3947 Set the number of jiffies to delay each step of
3948 RCU grace-period initialization.
3950 rcutree.gp_preinit_delay= [KNL]
3951 Set the number of jiffies to delay each step of
3952 RCU grace-period pre-initialization, that is,
3953 the propagation of recent CPU-hotplug changes up
3954 the rcu_node combining tree.
3956 rcutree.use_softirq= [KNL]
3957 If set to zero, move all RCU_SOFTIRQ processing to
3958 per-CPU rcuc kthreads. Defaults to a non-zero
3959 value, meaning that RCU_SOFTIRQ is used by default.
3960 Specify rcutree.use_softirq=0 to use rcuc kthreads.
3962 rcutree.rcu_fanout_exact= [KNL]
3963 Disable autobalancing of the rcu_node combining
3964 tree. This is used by rcutorture, and might
3965 possibly be useful for architectures having high
3966 cache-to-cache transfer latencies.
3968 rcutree.rcu_fanout_leaf= [KNL]
3969 Change the number of CPUs assigned to each
3970 leaf rcu_node structure. Useful for very
3971 large systems, which will choose the value 64,
3972 and for NUMA systems with large remote-access
3973 latencies, which will choose a value aligned
3974 with the appropriate hardware boundaries.
3976 rcutree.jiffies_till_first_fqs= [KNL]
3977 Set delay from grace-period initialization to
3978 first attempt to force quiescent states.
3979 Units are jiffies, minimum value is zero,
3980 and maximum value is HZ.
3982 rcutree.jiffies_till_next_fqs= [KNL]
3983 Set delay between subsequent attempts to force
3984 quiescent states. Units are jiffies, minimum
3985 value is one, and maximum value is HZ.
3987 rcutree.jiffies_till_sched_qs= [KNL]
3988 Set required age in jiffies for a
3989 given grace period before RCU starts
3990 soliciting quiescent-state help from
3991 rcu_note_context_switch() and cond_resched().
3992 If not specified, the kernel will calculate
3993 a value based on the most recent settings
3994 of rcutree.jiffies_till_first_fqs
3995 and rcutree.jiffies_till_next_fqs.
3996 This calculated value may be viewed in
3997 rcutree.jiffies_to_sched_qs. Any attempt to set
3998 rcutree.jiffies_to_sched_qs will be cheerfully
4001 rcutree.kthread_prio= [KNL,BOOT]
4002 Set the SCHED_FIFO priority of the RCU per-CPU
4003 kthreads (rcuc/N). This value is also used for
4004 the priority of the RCU boost threads (rcub/N)
4005 and for the RCU grace-period kthreads (rcu_bh,
4006 rcu_preempt, and rcu_sched). If RCU_BOOST is
4007 set, valid values are 1-99 and the default is 1
4008 (the least-favored priority). Otherwise, when
4009 RCU_BOOST is not set, valid values are 0-99 and
4010 the default is zero (non-realtime operation).
4012 rcutree.rcu_nocb_gp_stride= [KNL]
4013 Set the number of NOCB callback kthreads in
4014 each group, which defaults to the square root
4015 of the number of CPUs. Larger numbers reduce
4016 the wakeup overhead on the global grace-period
4017 kthread, but increases that same overhead on
4018 each group's NOCB grace-period kthread.
4020 rcutree.qhimark= [KNL]
4021 Set threshold of queued RCU callbacks beyond which
4022 batch limiting is disabled.
4024 rcutree.qlowmark= [KNL]
4025 Set threshold of queued RCU callbacks below which
4026 batch limiting is re-enabled.
4028 rcutree.qovld= [KNL]
4029 Set threshold of queued RCU callbacks beyond which
4030 RCU's force-quiescent-state scan will aggressively
4031 enlist help from cond_resched() and sched IPIs to
4032 help CPUs more quickly reach quiescent states.
4033 Set to less than zero to make this be set based
4034 on rcutree.qhimark at boot time and to zero to
4035 disable more aggressive help enlistment.
4037 rcutree.rcu_idle_gp_delay= [KNL]
4038 Set wakeup interval for idle CPUs that have
4039 RCU callbacks (RCU_FAST_NO_HZ=y).
4041 rcutree.rcu_idle_lazy_gp_delay= [KNL]
4042 Set wakeup interval for idle CPUs that have
4043 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
4044 Lazy RCU callbacks are those which RCU can
4045 prove do nothing more than free memory.
4047 rcutree.rcu_kick_kthreads= [KNL]
4048 Cause the grace-period kthread to get an extra
4049 wake_up() if it sleeps three times longer than
4050 it should at force-quiescent-state time.
4051 This wake_up() will be accompanied by a
4052 WARN_ONCE() splat and an ftrace_dump().
4054 rcutree.sysrq_rcu= [KNL]
4055 Commandeer a sysrq key to dump out Tree RCU's
4056 rcu_node tree with an eye towards determining
4057 why a new grace period has not yet started.
4059 rcuperf.gp_async= [KNL]
4060 Measure performance of asynchronous
4061 grace-period primitives such as call_rcu().
4063 rcuperf.gp_async_max= [KNL]
4064 Specify the maximum number of outstanding
4065 callbacks per writer thread. When a writer
4066 thread exceeds this limit, it invokes the
4067 corresponding flavor of rcu_barrier() to allow
4068 previously posted callbacks to drain.
4070 rcuperf.gp_exp= [KNL]
4071 Measure performance of expedited synchronous
4072 grace-period primitives.
4074 rcuperf.holdoff= [KNL]
4075 Set test-start holdoff period. The purpose of
4076 this parameter is to delay the start of the
4077 test until boot completes in order to avoid
4080 rcuperf.kfree_rcu_test= [KNL]
4081 Set to measure performance of kfree_rcu() flooding.
4083 rcuperf.kfree_nthreads= [KNL]
4084 The number of threads running loops of kfree_rcu().
4086 rcuperf.kfree_alloc_num= [KNL]
4087 Number of allocations and frees done in an iteration.
4089 rcuperf.kfree_loops= [KNL]
4090 Number of loops doing rcuperf.kfree_alloc_num number
4091 of allocations and frees.
4093 rcuperf.nreaders= [KNL]
4094 Set number of RCU readers. The value -1 selects
4095 N, where N is the number of CPUs. A value
4096 "n" less than -1 selects N-n+1, where N is again
4097 the number of CPUs. For example, -2 selects N
4098 (the number of CPUs), -3 selects N+1, and so on.
4099 A value of "n" less than or equal to -N selects
4102 rcuperf.nwriters= [KNL]
4103 Set number of RCU writers. The values operate
4104 the same as for rcuperf.nreaders.
4105 N, where N is the number of CPUs
4107 rcuperf.perf_type= [KNL]
4108 Specify the RCU implementation to test.
4110 rcuperf.shutdown= [KNL]
4111 Shut the system down after performance tests
4112 complete. This is useful for hands-off automated
4115 rcuperf.verbose= [KNL]
4116 Enable additional printk() statements.
4118 rcuperf.writer_holdoff= [KNL]
4119 Write-side holdoff between grace periods,
4120 in microseconds. The default of zero says
4123 rcutorture.fqs_duration= [KNL]
4124 Set duration of force_quiescent_state bursts
4127 rcutorture.fqs_holdoff= [KNL]
4128 Set holdoff time within force_quiescent_state bursts
4131 rcutorture.fqs_stutter= [KNL]
4132 Set wait time between force_quiescent_state bursts
4135 rcutorture.fwd_progress= [KNL]
4136 Enable RCU grace-period forward-progress testing
4137 for the types of RCU supporting this notion.
4139 rcutorture.fwd_progress_div= [KNL]
4140 Specify the fraction of a CPU-stall-warning
4141 period to do tight-loop forward-progress testing.
4143 rcutorture.fwd_progress_holdoff= [KNL]
4144 Number of seconds to wait between successive
4145 forward-progress tests.
4147 rcutorture.fwd_progress_need_resched= [KNL]
4148 Enclose cond_resched() calls within checks for
4149 need_resched() during tight-loop forward-progress
4152 rcutorture.gp_cond= [KNL]
4153 Use conditional/asynchronous update-side
4154 primitives, if available.
4156 rcutorture.gp_exp= [KNL]
4157 Use expedited update-side primitives, if available.
4159 rcutorture.gp_normal= [KNL]
4160 Use normal (non-expedited) asynchronous
4161 update-side primitives, if available.
4163 rcutorture.gp_sync= [KNL]
4164 Use normal (non-expedited) synchronous
4165 update-side primitives, if available. If all
4166 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4167 rcutorture.gp_normal=, and rcutorture.gp_sync=
4168 are zero, rcutorture acts as if is interpreted
4169 they are all non-zero.
4171 rcutorture.n_barrier_cbs= [KNL]
4172 Set callbacks/threads for rcu_barrier() testing.
4174 rcutorture.nfakewriters= [KNL]
4175 Set number of concurrent RCU writers. These just
4176 stress RCU, they don't participate in the actual
4177 test, hence the "fake".
4179 rcutorture.nreaders= [KNL]
4180 Set number of RCU readers. The value -1 selects
4181 N-1, where N is the number of CPUs. A value
4182 "n" less than -1 selects N-n-2, where N is again
4183 the number of CPUs. For example, -2 selects N
4184 (the number of CPUs), -3 selects N+1, and so on.
4186 rcutorture.object_debug= [KNL]
4187 Enable debug-object double-call_rcu() testing.
4189 rcutorture.onoff_holdoff= [KNL]
4190 Set time (s) after boot for CPU-hotplug testing.
4192 rcutorture.onoff_interval= [KNL]
4193 Set time (jiffies) between CPU-hotplug operations,
4194 or zero to disable CPU-hotplug testing.
4196 rcutorture.shuffle_interval= [KNL]
4197 Set task-shuffle interval (s). Shuffling tasks
4198 allows some CPUs to go into dyntick-idle mode
4199 during the rcutorture test.
4201 rcutorture.shutdown_secs= [KNL]
4202 Set time (s) after boot system shutdown. This
4203 is useful for hands-off automated testing.
4205 rcutorture.stall_cpu= [KNL]
4206 Duration of CPU stall (s) to test RCU CPU stall
4207 warnings, zero to disable.
4209 rcutorture.stall_cpu_holdoff= [KNL]
4210 Time to wait (s) after boot before inducing stall.
4212 rcutorture.stall_cpu_irqsoff= [KNL]
4213 Disable interrupts while stalling if set.
4215 rcutorture.stat_interval= [KNL]
4216 Time (s) between statistics printk()s.
4218 rcutorture.stutter= [KNL]
4219 Time (s) to stutter testing, for example, specifying
4220 five seconds causes the test to run for five seconds,
4221 wait for five seconds, and so on. This tests RCU's
4222 ability to transition abruptly to and from idle.
4224 rcutorture.test_boost= [KNL]
4225 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4226 "Maybe" means test if the RCU implementation
4227 under test support RCU priority boosting.
4229 rcutorture.test_boost_duration= [KNL]
4230 Duration (s) of each individual boost test.
4232 rcutorture.test_boost_interval= [KNL]
4233 Interval (s) between each boost test.
4235 rcutorture.test_no_idle_hz= [KNL]
4236 Test RCU's dyntick-idle handling. See also the
4237 rcutorture.shuffle_interval parameter.
4239 rcutorture.torture_type= [KNL]
4240 Specify the RCU implementation to test.
4242 rcutorture.verbose= [KNL]
4243 Enable additional printk() statements.
4245 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4246 Dump ftrace buffer after reporting RCU CPU
4249 rcupdate.rcu_cpu_stall_suppress= [KNL]
4250 Suppress RCU CPU stall warning messages.
4252 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
4253 Suppress RCU CPU stall warning messages and
4254 rcutorture writer stall warnings that occur
4255 during early boot, that is, during the time
4256 before the init task is spawned.
4258 rcupdate.rcu_cpu_stall_timeout= [KNL]
4259 Set timeout for RCU CPU stall warning messages.
4261 rcupdate.rcu_expedited= [KNL]
4262 Use expedited grace-period primitives, for
4263 example, synchronize_rcu_expedited() instead
4264 of synchronize_rcu(). This reduces latency,
4265 but can increase CPU utilization, degrade
4266 real-time latency, and degrade energy efficiency.
4267 No effect on CONFIG_TINY_RCU kernels.
4269 rcupdate.rcu_normal= [KNL]
4270 Use only normal grace-period primitives,
4271 for example, synchronize_rcu() instead of
4272 synchronize_rcu_expedited(). This improves
4273 real-time latency, CPU utilization, and
4274 energy efficiency, but can expose users to
4275 increased grace-period latency. This parameter
4276 overrides rcupdate.rcu_expedited. No effect on
4277 CONFIG_TINY_RCU kernels.
4279 rcupdate.rcu_normal_after_boot= [KNL]
4280 Once boot has completed (that is, after
4281 rcu_end_inkernel_boot() has been invoked), use
4282 only normal grace-period primitives. No effect
4283 on CONFIG_TINY_RCU kernels.
4285 rcupdate.rcu_task_stall_timeout= [KNL]
4286 Set timeout in jiffies for RCU task stall warning
4287 messages. Disable with a value less than or equal
4290 rcupdate.rcu_self_test= [KNL]
4291 Run the RCU early boot self tests
4295 Run specified binary instead of /init from the ramdisk,
4296 used for early userspace startup. See initrd.
4299 force - Override the decision by the kernel to hide the
4300 advertisement of RDRAND support (this affects
4301 certain AMD processors because of buggy BIOS
4302 support, specifically around the suspend/resume
4306 Turn on/off individual RDT features. List is:
4307 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4309 E.g. to turn on cmt and turn off mba use:
4313 Format (x86 or x86_64):
4314 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4316 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4318 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4319 (prefix with 'panic_' to set mode for panic
4321 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4322 reboot_force is either force or not specified,
4323 reboot_cpu is s[mp]#### with #### being the processor
4324 to be used for rebooting.
4327 [KNL, SMP] Set scheduler's default relax_domain_level.
4328 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4330 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4331 Format: <base1>,<size1>[,<base2>,<size2>,...]
4332 Reserve I/O ports or memory so the kernel won't use
4333 them. If <base> is less than 0x10000, the region
4334 is assumed to be I/O ports; otherwise it is memory.
4336 reservetop= [X86-32]
4338 Reserves a hole at the top of the kernel virtual
4343 Set the amount of memory to reserve for BIOS at
4344 the bottom of the address space.
4346 reset_devices [KNL] Force drivers to reset the underlying device
4347 during initialization.
4350 Specify the partition device for software suspend
4352 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4354 resume_offset= [SWSUSP]
4355 Specify the offset from the beginning of the partition
4356 given by "resume=" at which the swap header is located,
4357 in <PAGE_SIZE> units (needed only for swap files).
4358 See Documentation/power/swsusp-and-swap-files.rst
4360 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4361 read the resume files
4363 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4364 Useful for devices that are detected asynchronously
4365 (e.g. USB and MMC devices).
4367 hibernate= [HIBERNATION]
4368 noresume Don't check if there's a hibernation image
4369 present during boot.
4370 nocompress Don't compress/decompress hibernation images.
4371 no Disable hibernation and resume.
4372 protect_image Turn on image protection during restoration
4373 (that will set all pages holding image data
4374 during restoration read-only).
4376 retain_initrd [RAM] Keep initrd memory after extraction
4378 rfkill.default_state=
4379 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4380 etc. communication is blocked by default.
4383 rfkill.master_switch_mode=
4384 0 The "airplane mode" button does nothing.
4385 1 The "airplane mode" button toggles between everything
4386 blocked and the previous configuration.
4387 2 The "airplane mode" button toggles between everything
4388 blocked and everything unblocked.
4390 rhash_entries= [KNL,NET]
4391 Set number of hash buckets for route cache
4394 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4397 ro [KNL] Mount root device read-only on boot
4400 on Mark read-only kernel memory as read-only (default).
4401 off Leave read-only kernel memory writable for debugging.
4404 Enable the uart passthrough on the designated usb port
4405 on Rockchip SoCs. When active, the signals of the
4406 debug-uart get routed to the D+ and D- pins of the usb
4407 port and the regular usb controller gets disabled.
4409 root= [KNL] Root filesystem
4410 See name_to_dev_t comment in init/do_mounts.c.
4412 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4413 mount the root filesystem
4415 rootflags= [KNL] Set root filesystem mount option string
4417 rootfstype= [KNL] Set root filesystem type
4419 rootwait [KNL] Wait (indefinitely) for root device to show up.
4420 Useful for devices that are detected asynchronously
4421 (e.g. USB and MMC devices).
4423 rproc_mem=nn[KMG][@address]
4424 [KNL,ARM,CMA] Remoteproc physical memory block.
4425 Memory area to be used by remote processor image,
4428 rw [KNL] Mount root device read-write on boot
4430 S [KNL] Run init in single mode
4432 s390_iommu= [HW,S390]
4433 Set s390 IOTLB flushing mode
4435 With strict flushing every unmap operation will result in
4436 an IOTLB flush. Default is lazy flushing before reuse,
4440 See drivers/net/irda/sa1100_ir.c.
4442 sbni= [NET] Granch SBNI12 leased line adapter
4444 sched_debug [KNL] Enables verbose scheduler debug messages.
4446 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4447 Allowed values are enable and disable. This feature
4448 incurs a small amount of overhead in the scheduler
4449 but is useful for debugging and performance tuning.
4451 sched_thermal_decay_shift=
4452 [KNL, SMP] Set a decay shift for scheduler thermal
4453 pressure signal. Thermal pressure signal follows the
4454 default decay period of other scheduler pelt
4455 signals(usually 32 ms but configurable). Setting
4456 sched_thermal_decay_shift will left shift the decay
4457 period for the thermal pressure signal by the shift
4459 i.e. with the default pelt decay period of 32 ms
4460 sched_thermal_decay_shift thermal pressure decay pr
4464 Format: integer between 0 and 10
4467 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4468 xtime_lock contention on larger systems, and/or RCU lock
4469 contention on all systems with CONFIG_MAXSMP set.
4470 Format: { "0" | "1" }
4471 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4473 Note: increases power consumption, thus should only be
4474 enabled if running jitter sensitive (HPC/RT) workloads.
4476 security= [SECURITY] Choose a legacy "major" security module to
4477 enable at boot. This has been deprecated by the
4480 selinux= [SELINUX] Disable or enable SELinux at boot time.
4481 Format: { "0" | "1" }
4482 See security/selinux/Kconfig help text.
4487 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4488 Format: { "0" | "1" }
4489 See security/apparmor/Kconfig help text
4492 Default value is set via kernel config option.
4494 serialnumber [BUGS=X86-32]
4497 Maximal number of shapers.
4505 Disable merging of slabs with similar size. May be
4506 necessary if there is some reason to distinguish
4507 allocs to different slabs, especially in hardened
4508 environments where the risk of heap overflows and
4509 layout control by attackers can usually be
4510 frustrated by disabling merging. This will reduce
4511 most of the exposure of a heap attack to a single
4512 cache (risks via metadata attacks are mostly
4513 unchanged). Debug options disable merging on their
4515 For more information see Documentation/vm/slub.rst.
4517 slab_max_order= [MM, SLAB]
4518 Determines the maximum allowed order for slabs.
4519 A high setting may cause OOMs due to memory
4520 fragmentation. Defaults to 1 for systems with
4521 more than 32MB of RAM, 0 otherwise.
4523 slub_debug[=options[,slabs]] [MM, SLUB]
4524 Enabling slub_debug allows one to determine the
4525 culprit if slab objects become corrupted. Enabling
4526 slub_debug can create guard zones around objects and
4527 may poison objects when not in use. Also tracks the
4528 last alloc / free. For more information see
4529 Documentation/vm/slub.rst.
4531 slub_memcg_sysfs= [MM, SLUB]
4532 Determines whether to enable sysfs directories for
4533 memory cgroup sub-caches. 1 to enable, 0 to disable.
4534 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4535 Enabling this can lead to a very high number of debug
4536 directories and files being created under
4539 slub_max_order= [MM, SLUB]
4540 Determines the maximum allowed order for slabs.
4541 A high setting may cause OOMs due to memory
4542 fragmentation. For more information see
4543 Documentation/vm/slub.rst.
4545 slub_min_objects= [MM, SLUB]
4546 The minimum number of objects per slab. SLUB will
4547 increase the slab order up to slub_max_order to
4548 generate a sufficiently large slab able to contain
4549 the number of objects indicated. The higher the number
4550 of objects the smaller the overhead of tracking slabs
4551 and the less frequently locks need to be acquired.
4552 For more information see Documentation/vm/slub.rst.
4554 slub_min_order= [MM, SLUB]
4555 Determines the minimum page order for slabs. Must be
4556 lower than slub_max_order.
4557 For more information see Documentation/vm/slub.rst.
4559 slub_nomerge [MM, SLUB]
4560 Same with slab_nomerge. This is supported for legacy.
4561 See slab_nomerge for more information.
4564 Format: <io1>[,<io2>[,...,<io8>]]
4566 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4567 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4568 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4569 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4570 smsc-ircc2.ircc_irq= [HW] IRQ line
4571 smsc-ircc2.ircc_dma= [HW] DMA channel
4572 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4573 0: Toshiba Satellite 1800 (GP data pin select)
4574 1: Fast pin select (default)
4577 smt [KNL,S390] Set the maximum number of threads (logical
4578 CPUs) to use per physical CPU on systems capable of
4579 symmetric multithreading (SMT). Will be capped to the
4580 actual hardware limit.
4582 Default: -1 (no limit)
4585 [KNL] Should the soft-lockup detector generate panics.
4588 A nonzero value instructs the soft-lockup detector
4589 to panic the machine when a soft-lockup occurs. It is
4590 also controlled by the kernel.softlockup_panic sysctl
4591 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
4592 respective build-time switch to that functionality.
4594 softlockup_all_cpu_backtrace=
4595 [KNL] Should the soft-lockup detector generate
4596 backtraces on all cpus.
4599 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4600 See Documentation/admin-guide/laptops/sonypi.rst
4602 spectre_v2= [X86] Control mitigation of Spectre variant 2
4603 (indirect branch speculation) vulnerability.
4604 The default operation protects the kernel from
4607 on - unconditionally enable, implies
4609 off - unconditionally disable, implies
4611 auto - kernel detects whether your CPU model is
4614 Selecting 'on' will, and 'auto' may, choose a
4615 mitigation method at run time according to the
4616 CPU, the available microcode, the setting of the
4617 CONFIG_RETPOLINE configuration option, and the
4618 compiler with which the kernel was built.
4620 Selecting 'on' will also enable the mitigation
4621 against user space to user space task attacks.
4623 Selecting 'off' will disable both the kernel and
4624 the user space protections.
4626 Specific mitigations can also be selected manually:
4628 retpoline - replace indirect branches
4629 retpoline,generic - google's original retpoline
4630 retpoline,amd - AMD-specific minimal thunk
4632 Not specifying this option is equivalent to
4636 [X86] Control mitigation of Spectre variant 2
4637 (indirect branch speculation) vulnerability between
4640 on - Unconditionally enable mitigations. Is
4641 enforced by spectre_v2=on
4643 off - Unconditionally disable mitigations. Is
4644 enforced by spectre_v2=off
4646 prctl - Indirect branch speculation is enabled,
4647 but mitigation can be enabled via prctl
4648 per thread. The mitigation control state
4649 is inherited on fork.
4652 - Like "prctl" above, but only STIBP is
4653 controlled per thread. IBPB is issued
4654 always when switching between different user
4658 - Same as "prctl" above, but all seccomp
4659 threads will enable the mitigation unless
4660 they explicitly opt out.
4663 - Like "seccomp" above, but only STIBP is
4664 controlled per thread. IBPB is issued
4665 always when switching between different
4666 user space processes.
4668 auto - Kernel selects the mitigation depending on
4669 the available CPU features and vulnerability.
4672 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4674 Not specifying this option is equivalent to
4675 spectre_v2_user=auto.
4677 spec_store_bypass_disable=
4678 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4679 (Speculative Store Bypass vulnerability)
4681 Certain CPUs are vulnerable to an exploit against a
4682 a common industry wide performance optimization known
4683 as "Speculative Store Bypass" in which recent stores
4684 to the same memory location may not be observed by
4685 later loads during speculative execution. The idea
4686 is that such stores are unlikely and that they can
4687 be detected prior to instruction retirement at the
4688 end of a particular speculation execution window.
4690 In vulnerable processors, the speculatively forwarded
4691 store can be used in a cache side channel attack, for
4692 example to read memory to which the attacker does not
4693 directly have access (e.g. inside sandboxed code).
4695 This parameter controls whether the Speculative Store
4696 Bypass optimization is used.
4698 On x86 the options are:
4700 on - Unconditionally disable Speculative Store Bypass
4701 off - Unconditionally enable Speculative Store Bypass
4702 auto - Kernel detects whether the CPU model contains an
4703 implementation of Speculative Store Bypass and
4704 picks the most appropriate mitigation. If the
4705 CPU is not vulnerable, "off" is selected. If the
4706 CPU is vulnerable the default mitigation is
4707 architecture and Kconfig dependent. See below.
4708 prctl - Control Speculative Store Bypass per thread
4709 via prctl. Speculative Store Bypass is enabled
4710 for a process by default. The state of the control
4711 is inherited on fork.
4712 seccomp - Same as "prctl" above, but all seccomp threads
4713 will disable SSB unless they explicitly opt out.
4715 Default mitigations:
4716 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4718 On powerpc the options are:
4720 on,auto - On Power8 and Power9 insert a store-forwarding
4721 barrier on kernel entry and exit. On Power7
4722 perform a software flush on kernel entry and
4726 Not specifying this option is equivalent to
4727 spec_store_bypass_disable=auto.
4729 spia_io_base= [HW,MTD]
4735 [X86] Enable split lock detection
4737 When enabled (and if hardware support is present), atomic
4738 instructions that access data across cache line
4739 boundaries will result in an alignment check exception.
4743 warn - the kernel will emit rate limited warnings
4744 about applications triggering the #AC
4745 exception. This mode is the default on CPUs
4746 that supports split lock detection.
4748 fatal - the kernel will send SIGBUS to applications
4749 that trigger the #AC exception.
4751 If an #AC exception is hit in the kernel or in
4752 firmware (i.e. not while executing in user mode)
4753 the kernel will oops in either "warn" or "fatal"
4756 srcutree.counter_wrap_check [KNL]
4757 Specifies how frequently to check for
4758 grace-period sequence counter wrap for the
4759 srcu_data structure's ->srcu_gp_seq_needed field.
4760 The greater the number of bits set in this kernel
4761 parameter, the less frequently counter wrap will
4762 be checked for. Note that the bottom two bits
4765 srcutree.exp_holdoff [KNL]
4766 Specifies how many nanoseconds must elapse
4767 since the end of the last SRCU grace period for
4768 a given srcu_struct until the next normal SRCU
4769 grace period will be considered for automatic
4770 expediting. Set to zero to disable automatic
4774 Speculative Store Bypass Disable control
4776 On CPUs that are vulnerable to the Speculative
4777 Store Bypass vulnerability and offer a
4778 firmware based mitigation, this parameter
4779 indicates how the mitigation should be used:
4781 force-on: Unconditionally enable mitigation for
4782 for both kernel and userspace
4783 force-off: Unconditionally disable mitigation for
4784 for both kernel and userspace
4785 kernel: Always enable mitigation in the
4786 kernel, and offer a prctl interface
4787 to allow userspace to register its
4788 interest in being mitigated too.
4790 stack_guard_gap= [MM]
4791 override the default stack gap protection. The value
4792 is in page units and it defines how many pages prior
4793 to (for stacks growing down) resp. after (for stacks
4794 growing up) the main stack are reserved for no other
4795 mapping. Default value is 256 pages.
4798 Enabled the stack tracer on boot up.
4800 stacktrace_filter=[function-list]
4801 [FTRACE] Limit the functions that the stack tracer
4802 will trace at boot up. function-list is a comma separated
4803 list of functions. This list can be changed at run
4804 time by the stack_trace_filter file in the debugfs
4805 tracing directory. Note, this enables stack tracing
4806 and the stacktrace above is not needed.
4810 Set the STI (builtin display/keyboard on the HP-PARISC
4811 machines) console (graphic card) which should be used
4812 as the initial boot-console.
4813 See also comment in drivers/video/console/sticore.c.
4816 See comment in drivers/video/console/sticore.c.
4819 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4821 sunrpc.min_resvport=
4822 sunrpc.max_resvport=
4824 SunRPC servers often require that client requests
4825 originate from a privileged port (i.e. a port in the
4826 range 0 < portnr < 1024).
4827 An administrator who wishes to reserve some of these
4828 ports for other uses may adjust the range that the
4829 kernel's sunrpc client considers to be privileged
4830 using these two parameters to set the minimum and
4831 maximum port values.
4833 sunrpc.svc_rpc_per_connection_limit=
4835 Limit the number of requests that the server will
4836 process in parallel from a single connection.
4837 The default value is 0 (no limit).
4841 Control how the NFS server code allocates CPUs to
4842 service thread pools. Depending on how many NICs
4843 you have and where their interrupts are bound, this
4844 option will affect which CPUs will do NFS serving.
4845 Note: this parameter cannot be changed while the
4846 NFS server is running.
4848 auto the server chooses an appropriate mode
4849 automatically using heuristics
4850 global a single global pool contains all CPUs
4851 percpu one pool for each CPU
4852 pernode one pool for each NUMA node (equivalent
4853 to global on non-NUMA machines)
4855 sunrpc.tcp_slot_table_entries=
4856 sunrpc.udp_slot_table_entries=
4858 Sets the upper limit on the number of simultaneous
4859 RPC calls that can be sent from the client to a
4860 server. Increasing these values may allow you to
4861 improve throughput, but will also increase the
4862 amount of memory reserved for use by the client.
4864 suspend.pm_test_delay=
4866 Sets the number of seconds to remain in a suspend test
4867 mode before resuming the system (see
4868 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4869 is set. Default value is 5.
4872 Format: { on | off | y | n | 1 | 0 }
4873 This parameter controls use of the Protected
4874 Execution Facility on pSeries.
4877 [KNL] Enable accounting of swap in memory resource
4878 controller if no parameter or 1 is given or disable
4879 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
4881 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4882 Format: { <int> | force | noforce }
4883 <int> -- Number of I/O TLB slabs
4884 force -- force using of bounce buffers even if they
4885 wouldn't be automatically used by the kernel
4886 noforce -- Never use bounce buffers (for debugging)
4890 sysfs.deprecated=0|1 [KNL]
4891 Enable/disable old style sysfs layout for old udev
4892 on older distributions. When this option is enabled
4893 very new udev will not work anymore. When this option
4894 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4895 in older udev will not work anymore.
4896 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4897 the kernel configuration.
4899 sysrq_always_enabled
4901 Ignore sysrq setting - this boot parameter will
4902 neutralize any effect of /proc/sys/kernel/sysrq.
4903 Useful for debugging.
4905 tcpmhash_entries= [KNL,NET]
4906 Set the number of tcp_metrics_hash slots.
4907 Default value is 8192 or 16384 depending on total
4908 ram pages. This is used to specify the TCP metrics
4909 cache size. See Documentation/networking/ip-sysctl.txt
4910 "tcp_no_metrics_save" section for more details.
4914 test_suspend= [SUSPEND][,N]
4915 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4916 standby suspend) or "freeze" (for suspend type freeze)
4917 as the system sleep state during system startup with
4918 the optional capability to repeat N number of times.
4919 The system is woken from this state using a
4920 wakeup-capable RTC alarm.
4922 thash_entries= [KNL,NET]
4923 Set number of hash buckets for TCP connection
4925 thermal.act= [HW,ACPI]
4926 -1: disable all active trip points in all thermal zones
4927 <degrees C>: override all lowest active trip points
4929 thermal.crt= [HW,ACPI]
4930 -1: disable all critical trip points in all thermal zones
4931 <degrees C>: override all critical trip points
4933 thermal.nocrt= [HW,ACPI]
4934 Set to disable actions on ACPI thermal zone
4935 critical and hot trip points.
4937 thermal.off= [HW,ACPI]
4938 1: disable ACPI thermal control
4940 thermal.psv= [HW,ACPI]
4941 -1: disable all passive trip points
4942 <degrees C>: override all passive trip points to this
4945 thermal.tzp= [HW,ACPI]
4946 Specify global default ACPI thermal zone polling rate
4947 <deci-seconds>: poll all this frequency
4948 0: no polling (default)
4951 Force threading of all interrupt handlers except those
4952 marked explicitly IRQF_NO_THREAD.
4956 Specify if the kernel should make use of the cpu
4957 topology information if the hardware supports this.
4958 The scheduler will make use of this information and
4959 e.g. base its process migration decisions on it.
4962 topology_updates= [KNL, PPC, NUMA]
4964 Specify if the kernel should ignore (off)
4965 topology updates sent by the hypervisor to this
4968 torture.disable_onoff_at_boot= [KNL]
4969 Prevent the CPU-hotplug component of torturing
4970 until after init has spawned.
4974 tpm_suspend_pcr=[HW,TPM]
4975 Format: integer pcr id
4976 Specify that at suspend time, the tpm driver
4977 should extend the specified pcr with zeros,
4978 as a workaround for some chips which fail to
4979 flush the last written pcr on TPM_SaveState.
4980 This will guarantee that all the other pcrs
4983 trace_buf_size=nn[KMG]
4984 [FTRACE] will set tracing buffer size on each cpu.
4986 trace_event=[event-list]
4987 [FTRACE] Set and start specified trace events in order
4988 to facilitate early boot debugging. The event-list is a
4989 comma separated list of trace events to enable. See
4990 also Documentation/trace/events.rst
4992 trace_options=[option-list]
4993 [FTRACE] Enable or disable tracer options at boot.
4994 The option-list is a comma delimited list of options
4995 that can be enabled or disabled just as if you were
4996 to echo the option name into
4998 /sys/kernel/debug/tracing/trace_options
5000 For example, to enable stacktrace option (to dump the
5001 stack trace of each event), add to the command line:
5003 trace_options=stacktrace
5005 See also Documentation/trace/ftrace.rst "trace options"
5009 Have the tracepoints sent to printk as well as the
5010 tracing ring buffer. This is useful for early boot up
5011 where the system hangs or reboots and does not give the
5012 option for reading the tracing buffer or performing a
5013 ftrace_dump_on_oops.
5015 To turn off having tracepoints sent to printk,
5016 echo 0 > /proc/sys/kernel/tracepoint_printk
5017 Note, echoing 1 into this file without the
5018 tracepoint_printk kernel cmdline option has no effect.
5022 Having tracepoints sent to printk() and activating high
5023 frequency tracepoints such as irq or sched, can cause
5024 the system to live lock.
5027 [FTRACE] enable this option to disable tracing when a
5028 warning is hit. This turns off "tracing_on". Tracing can
5029 be enabled again by echoing '1' into the "tracing_on"
5030 file located in /sys/kernel/debug/tracing/
5032 This option is useful, as it disables the trace before
5033 the WARNING dump is called, which prevents the trace to
5034 be filled with content caused by the warning output.
5036 This option can also be set at run time via the sysctl
5037 option: kernel/traceoff_on_warning
5039 transparent_hugepage=
5041 Format: [always|madvise|never]
5042 Can be used to control the default behavior of the system
5043 with respect to transparent hugepages.
5044 See Documentation/admin-guide/mm/transhuge.rst
5047 tsc= Disable clocksource stability checks for TSC.
5049 [x86] reliable: mark tsc clocksource as reliable, this
5050 disables clocksource verification at runtime, as well
5051 as the stability checks done at bootup. Used to enable
5052 high-resolution timer mode on older hardware, and in
5053 virtualized environment.
5054 [x86] noirqtime: Do not use TSC to do irq accounting.
5055 Used to run time disable IRQ_TIME_ACCOUNTING on any
5056 platforms where RDTSC is slow and this accounting
5058 [x86] unstable: mark the TSC clocksource as unstable, this
5059 marks the TSC unconditionally unstable at bootup and
5060 avoids any further wobbles once the TSC watchdog notices.
5061 [x86] nowatchdog: disable clocksource watchdog. Used
5062 in situations with strict latency requirements (where
5063 interruptions from clocksource watchdog are not
5066 tsx= [X86] Control Transactional Synchronization
5067 Extensions (TSX) feature in Intel processors that
5068 support TSX control.
5070 This parameter controls the TSX feature. The options are:
5072 on - Enable TSX on the system. Although there are
5073 mitigations for all known security vulnerabilities,
5074 TSX has been known to be an accelerator for
5075 several previous speculation-related CVEs, and
5076 so there may be unknown security risks associated
5077 with leaving it enabled.
5079 off - Disable TSX on the system. (Note that this
5080 option takes effect only on newer CPUs which are
5081 not vulnerable to MDS, i.e., have
5082 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
5083 the new IA32_TSX_CTRL MSR through a microcode
5084 update. This new MSR allows for the reliable
5085 deactivation of the TSX functionality.)
5087 auto - Disable TSX if X86_BUG_TAA is present,
5088 otherwise enable TSX on the system.
5090 Not specifying this option is equivalent to tsx=off.
5092 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5095 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
5096 Abort (TAA) vulnerability.
5098 Similar to Micro-architectural Data Sampling (MDS)
5099 certain CPUs that support Transactional
5100 Synchronization Extensions (TSX) are vulnerable to an
5101 exploit against CPU internal buffers which can forward
5102 information to a disclosure gadget under certain
5105 In vulnerable processors, the speculatively forwarded
5106 data can be used in a cache side channel attack, to
5107 access data to which the attacker does not have direct
5110 This parameter controls the TAA mitigation. The
5113 full - Enable TAA mitigation on vulnerable CPUs
5116 full,nosmt - Enable TAA mitigation and disable SMT on
5117 vulnerable CPUs. If TSX is disabled, SMT
5118 is not disabled because CPU is not
5119 vulnerable to cross-thread TAA attacks.
5120 off - Unconditionally disable TAA mitigation
5122 On MDS-affected machines, tsx_async_abort=off can be
5123 prevented by an active MDS mitigation as both vulnerabilities
5124 are mitigated with the same mechanism so in order to disable
5125 this mitigation, you need to specify mds=off too.
5127 Not specifying this option is equivalent to
5128 tsx_async_abort=full. On CPUs which are MDS affected
5129 and deploy MDS mitigation, TAA mitigation is not
5130 required and doesn't provide any additional
5134 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5136 turbografx.map[2|3]= [HW,JOY]
5137 TurboGraFX parallel port interface
5139 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
5140 See also Documentation/input/devices/joystick-parport.rst
5142 udbg-immortal [PPC] When debugging early kernel crashes that
5143 happen after console_init() and before a proper
5144 console driver takes over, this boot options might
5145 help "seeing" what's going on.
5147 uhash_entries= [KNL,NET]
5148 Set number of hash buckets for UDP/UDP-Lite connections
5151 [USB] Ignore overcurrent events (default N).
5152 Some badly-designed motherboards generate lots of
5153 bogus events, for ports that aren't wired to
5154 anything. Set this parameter to avoid log spamming.
5155 Note that genuine overcurrent events won't be
5159 [X86] Cause panic on unknown NMI.
5161 usbcore.authorized_default=
5162 [USB] Default USB device authorization:
5163 (default -1 = authorized except for wireless USB,
5164 0 = not authorized, 1 = authorized, 2 = authorized
5165 if device connected to internal port)
5167 usbcore.autosuspend=
5168 [USB] The autosuspend time delay (in seconds) used
5169 for newly-detected USB devices (default 2). This
5170 is the time required before an idle device will be
5171 autosuspended. Devices for which the delay is set
5172 to a negative value won't be autosuspended at all.
5174 usbcore.usbfs_snoop=
5175 [USB] Set to log all usbfs traffic (default 0 = off).
5177 usbcore.usbfs_snoop_max=
5178 [USB] Maximum number of bytes to snoop in each URB
5181 usbcore.blinkenlights=
5182 [USB] Set to cycle leds on hubs (default 0 = off).
5184 usbcore.old_scheme_first=
5185 [USB] Start with the old device initialization
5186 scheme, applies only to low and full-speed devices
5189 usbcore.usbfs_memory_mb=
5190 [USB] Memory limit (in MB) for buffers allocated by
5191 usbfs (default = 16, 0 = max = 2047).
5193 usbcore.use_both_schemes=
5194 [USB] Try the other device initialization scheme
5195 if the first one fails (default 1 = enabled).
5197 usbcore.initial_descriptor_timeout=
5198 [USB] Specifies timeout for the initial 64-byte
5199 USB_REQ_GET_DESCRIPTOR request in milliseconds
5200 (default 5000 = 5.0 seconds).
5202 usbcore.nousb [USB] Disable the USB subsystem
5205 [USB] A list of quirk entries to augment the built-in
5206 usb core quirk list. List entries are separated by
5207 commas. Each entry has the form
5208 VendorID:ProductID:Flags. The IDs are 4-digit hex
5209 numbers and Flags is a set of letters. Each letter
5210 will change the built-in quirk; setting it if it is
5211 clear and clearing it if it is set. The letters have
5212 the following meanings:
5213 a = USB_QUIRK_STRING_FETCH_255 (string
5214 descriptors must not be fetched using
5216 b = USB_QUIRK_RESET_RESUME (device can't resume
5217 correctly so reset it instead);
5218 c = USB_QUIRK_NO_SET_INTF (device can't handle
5219 Set-Interface requests);
5220 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
5221 handle its Configuration or Interface
5223 e = USB_QUIRK_RESET (device can't be reset
5224 (e.g morph devices), don't use reset);
5225 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
5226 more interface descriptions than the
5227 bNumInterfaces count, and can't handle
5228 talking to these interfaces);
5229 g = USB_QUIRK_DELAY_INIT (device needs a pause
5230 during initialization, after we read
5231 the device descriptor);
5232 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
5233 high speed and super speed interrupt
5234 endpoints, the USB 2.0 and USB 3.0 spec
5235 require the interval in microframes (1
5236 microframe = 125 microseconds) to be
5237 calculated as interval = 2 ^
5239 Devices with this quirk report their
5240 bInterval as the result of this
5241 calculation instead of the exponent
5242 variable used in the calculation);
5243 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
5244 handle device_qualifier descriptor
5246 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
5247 generates spurious wakeup, ignore
5248 remote wakeup capability);
5249 k = USB_QUIRK_NO_LPM (device can't handle Link
5251 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
5252 (Device reports its bInterval as linear
5253 frames instead of the USB 2.0
5255 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
5256 to be disconnected before suspend to
5257 prevent spurious wakeup);
5258 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
5259 pause after every control message);
5260 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
5261 delay after resetting its port);
5262 Example: quirks=0781:5580:bk,0a5c:5834:gij
5265 [USBHID] The interval which mice are to be polled at.
5268 [USBHID] The interval which joysticks are to be polled at.
5271 [USBHID] The interval which keyboards are to be polled at.
5273 usb-storage.delay_use=
5274 [UMS] The delay in seconds before a new device is
5275 scanned for Logical Units (default 1).
5278 [UMS] A list of quirks entries to supplement or
5279 override the built-in unusual_devs list. List
5280 entries are separated by commas. Each entry has
5281 the form VID:PID:Flags where VID and PID are Vendor
5282 and Product ID values (4-digit hex numbers) and
5283 Flags is a set of characters, each corresponding
5284 to a common usb-storage quirk flag as follows:
5285 a = SANE_SENSE (collect more than 18 bytes
5286 of sense data, not on uas);
5287 b = BAD_SENSE (don't collect more than 18
5288 bytes of sense data, not on uas);
5289 c = FIX_CAPACITY (decrease the reported
5290 device capacity by one sector);
5291 d = NO_READ_DISC_INFO (don't use
5292 READ_DISC_INFO command, not on uas);
5293 e = NO_READ_CAPACITY_16 (don't use
5294 READ_CAPACITY_16 command);
5295 f = NO_REPORT_OPCODES (don't use report opcodes
5297 g = MAX_SECTORS_240 (don't transfer more than
5298 240 sectors at a time, uas only);
5299 h = CAPACITY_HEURISTICS (decrease the
5300 reported device capacity by one
5301 sector if the number is odd);
5302 i = IGNORE_DEVICE (don't bind to this
5304 j = NO_REPORT_LUNS (don't use report luns
5306 l = NOT_LOCKABLE (don't try to lock and
5307 unlock ejectable media, not on uas);
5308 m = MAX_SECTORS_64 (don't transfer more
5309 than 64 sectors = 32 KB at a time,
5311 n = INITIAL_READ10 (force a retry of the
5312 initial READ(10) command, not on uas);
5313 o = CAPACITY_OK (accept the capacity
5314 reported by the device, not on uas);
5315 p = WRITE_CACHE (the device cache is ON
5316 by default, not on uas);
5317 r = IGNORE_RESIDUE (the device reports
5318 bogus residue values, not on uas);
5319 s = SINGLE_LUN (the device has only one
5321 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
5322 commands, uas only);
5323 u = IGNORE_UAS (don't bind to the uas driver);
5324 w = NO_WP_DETECT (don't test whether the
5325 medium is write-protected).
5326 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
5327 even if the device claims no cache,
5329 Example: quirks=0419:aaf5:rl,0421:0433:rc
5331 user_debug= [KNL,ARM]
5333 See arch/arm/Kconfig.debug help text.
5334 1 - undefined instruction events
5336 4 - invalid data aborts
5339 Example: user_debug=31
5342 [X86] Flags controlling user PTE allocations.
5344 nohigh = do not allocate PTE pages in
5345 HIGHMEM regardless of setting
5349 On X86_32, this is an alias for vdso32=. Otherwise:
5351 vdso=1: enable VDSO (the default)
5352 vdso=0: disable VDSO mapping
5354 vdso32= [X86] Control the 32-bit vDSO
5355 vdso32=1: enable 32-bit VDSO
5356 vdso32=0 or vdso32=2: disable 32-bit VDSO
5358 See the help text for CONFIG_COMPAT_VDSO for more
5359 details. If CONFIG_COMPAT_VDSO is set, the default is
5360 vdso32=0; otherwise, the default is vdso32=1.
5362 For compatibility with older kernels, vdso32=2 is an
5365 Try vdso32=0 if you encounter an error that says:
5366 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
5369 vector=percpu: enable percpu vector domain
5371 video= [FB] Frame buffer configuration
5372 See Documentation/fb/modedb.rst.
5374 video.brightness_switch_enabled= [0,1]
5375 If set to 1, on receiving an ACPI notify event
5376 generated by hotkey, video driver will adjust brightness
5377 level and then send out the event to user space through
5378 the allocated input device; If set to 0, video driver
5379 will only send out the event without touching backlight
5384 [VMMIO] Memory mapped virtio (platform) device.
5386 <size>@<baseaddr>:<irq>[:<id>]
5388 <size> := size (can use standard suffixes
5390 <baseaddr> := physical base address
5391 <irq> := interrupt number (as passed to
5393 <id> := (optional) platform device id
5395 virtio_mmio.device=1K@0x100b0000:48:7
5397 Can be used multiple times for multiple devices.
5399 vga= [BOOT,X86-32] Select a particular video mode
5400 See Documentation/x86/boot.rst and
5401 Documentation/admin-guide/svga.rst.
5402 Use vga=ask for menu.
5403 This is actually a boot loader parameter; the value is
5404 passed to the kernel using a special protocol.
5406 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
5407 May slow down system boot speed, especially when
5408 enabled on systems with a large amount of memory.
5409 All options are enabled by default, and this
5410 interface is meant to allow for selectively
5411 enabling or disabling specific virtual memory
5414 Available options are:
5415 P Enable page structure init time poisoning
5416 - Disable all of the above options
5418 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
5419 size of <nn>. This can be used to increase the
5420 minimum size (128MB on x86). It can also be used to
5421 decrease the size and leave more room for directly
5424 vmcp_cma=nn[MG] [KNL,S390]
5425 Sets the memory size reserved for contiguous memory
5426 allocations for the vmcp device driver.
5428 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5431 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5434 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
5438 Controls the behavior of vsyscalls (i.e. calls to
5439 fixed addresses of 0xffffffffff600x00 from legacy
5440 code). Most statically-linked binaries and older
5441 versions of glibc use these calls. Because these
5442 functions are at fixed addresses, they make nice
5443 targets for exploits that can control RIP.
5445 emulate [default] Vsyscalls turn into traps and are
5446 emulated reasonably safely. The vsyscall
5449 xonly Vsyscalls turn into traps and are
5450 emulated reasonably safely. The vsyscall
5451 page is not readable.
5453 none Vsyscalls don't work at all. This makes
5454 them quite hard to use for exploits but
5455 might break your system.
5457 vt.color= [VT] Default text color.
5458 Format: 0xYX, X = foreground, Y = background.
5459 Default: 0x07 = light gray on black.
5461 vt.cur_default= [VT] Default cursor shape.
5462 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5463 the parameters of the <Esc>[?A;B;Cc escape sequence;
5464 see VGA-softcursor.txt. Default: 2 = underline.
5466 vt.default_blu= [VT]
5467 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5468 Change the default blue palette of the console.
5469 This is a 16-member array composed of values
5472 vt.default_grn= [VT]
5473 Format: <green0>,<green1>,<green2>,...,<green15>
5474 Change the default green palette of the console.
5475 This is a 16-member array composed of values
5478 vt.default_red= [VT]
5479 Format: <red0>,<red1>,<red2>,...,<red15>
5480 Change the default red palette of the console.
5481 This is a 16-member array composed of values
5487 Set system-wide default UTF-8 mode for all tty's.
5488 Default is 1, i.e. UTF-8 mode is enabled for all
5489 newly opened terminals.
5491 vt.global_cursor_default=
5494 Set system-wide default for whether a cursor
5495 is shown on new VTs. Default is -1,
5496 i.e. cursors will be created by default unless
5497 overridden by individual drivers. 0 will hide
5498 cursors, 1 will display them.
5500 vt.italic= [VT] Default color for italic text; 0-15.
5503 vt.underline= [VT] Default color for underlined text; 0-15.
5506 watchdog timers [HW,WDT] For information on watchdog timers,
5507 see Documentation/watchdog/watchdog-parameters.rst
5508 or other driver-specific files in the
5509 Documentation/watchdog/ directory.
5513 Set the hard lockup detector stall duration
5514 threshold in seconds. The soft lockup detector
5515 threshold is set to twice the value. A value of 0
5516 disables both lockup detectors. Default is 10
5519 workqueue.watchdog_thresh=
5520 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5521 warn stall conditions and dump internal state to
5522 help debugging. 0 disables workqueue stall
5523 detection; otherwise, it's the stall threshold
5524 duration in seconds. The default value is 30 and
5525 it can be updated at runtime by writing to the
5526 corresponding sysfs file.
5528 workqueue.disable_numa
5529 By default, all work items queued to unbound
5530 workqueues are affine to the NUMA nodes they're
5531 issued on, which results in better behavior in
5532 general. If NUMA affinity needs to be disabled for
5533 whatever reason, this option can be used. Note
5534 that this also can be controlled per-workqueue for
5535 workqueues visible under /sys/bus/workqueue/.
5537 workqueue.power_efficient
5538 Per-cpu workqueues are generally preferred because
5539 they show better performance thanks to cache
5540 locality; unfortunately, per-cpu workqueues tend to
5541 be more power hungry than unbound workqueues.
5543 Enabling this makes the per-cpu workqueues which
5544 were observed to contribute significantly to power
5545 consumption unbound, leading to measurably lower
5546 power usage at the cost of small performance
5549 The default value of this parameter is determined by
5550 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5552 workqueue.debug_force_rr_cpu
5553 Workqueue used to implicitly guarantee that work
5554 items queued without explicit CPU specified are put
5555 on the local CPU. This guarantee is no longer true
5556 and while local CPU is still preferred work items
5557 may be put on foreign CPUs. This debug option
5558 forces round-robin CPU selection to flush out
5559 usages which depend on the now broken guarantee.
5560 When enabled, memory and cache locality will be
5563 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5564 default x2apic cluster mode on platforms
5567 x86_intel_mid_timer= [X86-32,APBT]
5568 Choose timer option for x86 Intel MID platform.
5569 Two valid options are apbt timer only and lapic timer
5570 plus one apbt timer for broadcast timer.
5571 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5573 xen_512gb_limit [KNL,X86-64,XEN]
5574 Restricts the kernel running paravirtualized under Xen
5575 to use only up to 512 GB of RAM. The reason to do so is
5576 crash analysis tools and Xen tools for doing domain
5577 save/restore/migration must be enabled to handle larger
5580 xen_emul_unplug= [HW,X86,XEN]
5581 Unplug Xen emulated devices
5582 Format: [unplug0,][unplug1]
5583 ide-disks -- unplug primary master IDE devices
5584 aux-ide-disks -- unplug non-primary-master IDE devices
5585 nics -- unplug network devices
5586 all -- unplug all emulated devices (NICs and IDE disks)
5587 unnecessary -- unplugging emulated devices is
5588 unnecessary even if the host did not respond to
5590 never -- do not unplug even if version check succeeds
5592 xen_legacy_crash [X86,XEN]
5593 Crash from Xen panic notifier, without executing late
5594 panic() code such as dumping handler.
5596 xen_nopvspin [X86,XEN]
5597 Disables the ticketlock slowpath using Xen PV
5601 Disables the PV optimizations forcing the HVM guest to
5602 run as generic HVM guest with no PV drivers.
5603 This option is obsoleted by the "nopv" option, which
5604 has equivalent effect for XEN platform.
5606 xen_scrub_pages= [XEN]
5607 Boolean option to control scrubbing pages before giving them back
5608 to Xen, for use by other domains. Can be also changed at runtime
5609 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5610 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5612 xen_timer_slop= [X86-64,XEN]
5613 Set the timer slop (in nanoseconds) for the virtual Xen
5614 timers (default is 100000). This adjusts the minimum
5615 delta of virtualized Xen timers, where lower values
5616 improve timer resolution at the expense of processing
5617 more timer interrupts.
5619 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
5620 Disables the PV optimizations forcing the guest to run
5621 as generic guest with no PV drivers. Currently support
5622 XEN HVM, KVM, HYPER_V and VMWARE guest.
5624 xirc2ps_cs= [NET,PCMCIA]
5626 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5629 By default on POWER9 and above, the kernel will
5630 natively use the XIVE interrupt controller. This option
5631 allows the fallback firmware mode to be used:
5633 off Fallback to firmware control of XIVE interrupt
5634 controller on both pseries and powernv
5635 platforms. Only useful on POWER9 and above.
5637 xhci-hcd.quirks [USB,KNL]
5638 A hex value specifying bitmask with supplemental xhci
5639 host controller quirks. Meaning of each bit can be
5640 consulted in header drivers/usb/host/xhci.h.
5643 Format: { early | on | rw | ro | off }
5644 Controls if xmon debugger is enabled. Default is off.
5645 Passing only "xmon" is equivalent to "xmon=early".
5646 early Call xmon as early as possible on boot; xmon
5647 debugger is called from setup_arch().
5648 on xmon debugger hooks will be installed so xmon
5649 is only called on a kernel crash. Default mode,
5650 i.e. either "ro" or "rw" mode, is controlled
5651 with CONFIG_XMON_DEFAULT_RO_MODE.
5652 rw xmon debugger hooks will be installed so xmon
5653 is called only on a kernel crash, mode is write,
5654 meaning SPR registers, memory and, other data
5655 can be written using xmon commands.
5656 ro same as "rw" option above but SPR registers,
5657 memory, and other data can't be written using
5659 off xmon is disabled.
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