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.rst.
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/admin-guide/media/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[,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 kernel/dma/contiguous.c
604 Sets the size of kernel per-numa memory area for
605 contiguous memory allocations. A value of 0 disables
606 per-numa CMA altogether. And If this option is not
607 specificed, the default value is 0.
608 With per-numa CMA enabled, DMA users on node nid will
609 first try to allocate buffer from the pernuma area
610 which is located in node nid, if the allocation fails,
611 they will fallback to the global default memory area.
613 cmo_free_hint= [PPC] Format: { yes | no }
614 Specify whether pages are marked as being inactive
615 when they are freed. This is used in CMO environments
616 to determine OS memory pressure for page stealing by
620 coherent_pool=nn[KMG] [ARM,KNL]
621 Sets the size of memory pool for coherent, atomic dma
622 allocations, by default set to 256K.
624 com20020= [HW,NET] ARCnet - COM20020 chipset
626 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
628 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
632 ARCnet - COM90xx chipset (memory-mapped buffers)
633 Format: <io>[,<irq>[,<memstart>]]
635 condev= [HW,S390] console device
638 console= [KNL] Output console device and options.
640 tty<n> Use the virtual console device <n>.
644 Use the specified serial port. The options are of
645 the form "bbbbpnf", where "bbbb" is the baud rate,
646 "p" is parity ("n", "o", or "e"), "n" is number of
647 bits, and "f" is flow control ("r" for RTS or
648 omit it). Default is "9600n8".
650 See Documentation/admin-guide/serial-console.rst for more
652 Documentation/networking/netconsole.rst for an
655 uart[8250],io,<addr>[,options]
656 uart[8250],mmio,<addr>[,options]
657 uart[8250],mmio16,<addr>[,options]
658 uart[8250],mmio32,<addr>[,options]
659 uart[8250],0x<addr>[,options]
660 Start an early, polled-mode console on the 8250/16550
661 UART at the specified I/O port or MMIO address,
662 switching to the matching ttyS device later.
663 MMIO inter-register address stride is either 8-bit
664 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
665 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
666 to be equivalent to 'mmio'. 'options' are specified in
667 the same format described for ttyS above; if unspecified,
668 the h/w is not re-initialized.
670 hvc<n> Use the hypervisor console device <n>. This is for
671 both Xen and PowerPC hypervisors.
673 If the device connected to the port is not a TTY but a braille
674 device, prepend "brl," before the device type, for instance
676 For now, only VisioBraille is supported.
679 [KNL] Change console messages format
681 By default we print messages on consoles in
682 "[time stamp] text\n" format (time stamp may not be
683 printed, depending on CONFIG_PRINTK_TIME or
684 `printk_time' param).
686 Switch to syslog format: "<%u>[time stamp] text\n"
687 IOW, each message will have a facility and loglevel
688 prefix. The format is similar to one used by syslog()
689 syscall, or to executing "dmesg -S --raw" or to reading
692 consoleblank= [KNL] The console blank (screen saver) timeout in
693 seconds. A value of 0 disables the blank timer.
697 [KNL] Change the default value for
698 /proc/<pid>/coredump_filter.
699 See also Documentation/filesystems/proc.rst.
701 coresight_cpu_debug.enable
704 Enable/disable the CPU sampling based debugging.
705 0: default value, disable debugging
706 1: enable debugging at boot time
708 cpuidle.off=1 [CPU_IDLE]
709 disable the cpuidle sub-system
712 [CPU_IDLE] Name of the cpuidle governor to use.
714 cpufreq.off=1 [CPU_FREQ]
715 disable the cpufreq sub-system
717 cpufreq.default_governor=
718 [CPU_FREQ] Name of the default cpufreq governor or
719 policy to use. This governor must be registered in the
720 kernel before the cpufreq driver probes.
723 [X86] Delay for N microsec between assert and de-assert
724 of APIC INIT to start processors. This delay occurs
725 on every CPU online, such as boot, and resume from suspend.
728 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
730 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
732 crashkernel=size[KMG][@offset[KMG]]
733 [KNL] Using kexec, Linux can switch to a 'crash kernel'
734 upon panic. This parameter reserves the physical
735 memory region [offset, offset + size] for that kernel
736 image. If '@offset' is omitted, then a suitable offset
737 is selected automatically.
738 [KNL, X86-64] Select a region under 4G first, and
739 fall back to reserve region above 4G when '@offset'
740 hasn't been specified.
741 See Documentation/admin-guide/kdump/kdump.rst for further details.
743 crashkernel=range1:size1[,range2:size2,...][@offset]
744 [KNL] Same as above, but depends on the memory
745 in the running system. The syntax of range is
746 start-[end] where start and end are both
747 a memory unit (amount[KMG]). See also
748 Documentation/admin-guide/kdump/kdump.rst for an example.
750 crashkernel=size[KMG],high
751 [KNL, X86-64] range could be above 4G. Allow kernel
752 to allocate physical memory region from top, so could
753 be above 4G if system have more than 4G ram installed.
754 Otherwise memory region will be allocated below 4G, if
756 It will be ignored if crashkernel=X is specified.
757 crashkernel=size[KMG],low
758 [KNL, X86-64] range under 4G. When crashkernel=X,high
759 is passed, kernel could allocate physical memory region
760 above 4G, that cause second kernel crash on system
761 that require some amount of low memory, e.g. swiotlb
762 requires at least 64M+32K low memory, also enough extra
763 low memory is needed to make sure DMA buffers for 32-bit
764 devices won't run out. Kernel would try to allocate at
765 at least 256M below 4G automatically.
766 This one let user to specify own low range under 4G
767 for second kernel instead.
768 0: to disable low allocation.
769 It will be ignored when crashkernel=X,high is not used
770 or memory reserved is below 4G.
773 [KNL] Disable crypto self-tests
778 cs89x0_media= [HW,NET]
779 Format: { rj45 | aui | bnc }
782 See header of drivers/s390/block/dasd_devmap.c.
784 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
785 (one device per port)
786 Format: <port#>,<type>
787 See also Documentation/input/devices/joystick-parport.rst
789 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
791 Documentation/admin-guide/dynamic-debug-howto.rst for
792 details. Deprecated, see dyndbg.
794 debug [KNL] Enable kernel debugging (events log level).
797 [KNL] Enable printing [hashed] pointers early in the
798 boot sequence. If enabled, we use a weak hash instead
799 of siphash to hash pointers. Use this option if you are
800 seeing instances of '(___ptrval___)') and need to see a
801 value (hashed pointer) instead. Cryptographically
802 insecure, please do not use on production kernels.
805 [KNL] verbose self-tests
807 Print debugging info while doing the locking API
809 We default to 0 (no extra messages), setting it to
810 1 will print _a lot_ more information - normally
811 only useful to kernel developers.
813 debug_objects [KNL] Enable object debugging
816 [KNL] Disable object debugging
818 debug_guardpage_minorder=
819 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
820 parameter allows control of the order of pages that will
821 be intentionally kept free (and hence protected) by the
822 buddy allocator. Bigger value increase the probability
823 of catching random memory corruption, but reduce the
824 amount of memory for normal system use. The maximum
825 possible value is MAX_ORDER/2. Setting this parameter
826 to 1 or 2 should be enough to identify most random
827 memory corruption problems caused by bugs in kernel or
828 driver code when a CPU writes to (or reads from) a
829 random memory location. Note that there exists a class
830 of memory corruptions problems caused by buggy H/W or
831 F/W or by drivers badly programing DMA (basically when
832 memory is written at bus level and the CPU MMU is
833 bypassed) which are not detectable by
834 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
835 tracking down these problems.
838 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
839 enables the feature at boot time. By default, it is
840 disabled and the system will work mostly the same as a
841 kernel built without CONFIG_DEBUG_PAGEALLOC.
842 Note: to get most of debug_pagealloc error reports, it's
843 useful to also enable the page_owner functionality.
844 on: enable the feature
846 debugfs= [KNL] This parameter enables what is exposed to userspace
847 and debugfs internal clients.
848 Format: { on, no-mount, off }
849 on: All functions are enabled.
851 Filesystem is not registered but kernel clients can
852 access APIs and a crashkernel can be used to read
853 its content. There is nothing to mount.
854 off: Filesystem is not registered and clients
855 get a -EPERM as result when trying to register files
856 or directories within debugfs.
857 This is equivalent of the runtime functionality if
858 debugfs was not enabled in the kernel at all.
859 Default value is set in build-time with a kernel configuration.
861 debugpat [X86] Enable PAT debugging
863 decnet.addr= [HW,NET]
864 Format: <area>[,<node>]
865 See also Documentation/networking/decnet.rst.
868 [HW] The size of the default HugeTLB page. This is
869 the size represented by the legacy /proc/ hugepages
870 APIs. In addition, this is the default hugetlb size
871 used for shmget(), mmap() and mounting hugetlbfs
872 filesystems. If not specified, defaults to the
873 architecture's default huge page size. Huge page
874 sizes are architecture dependent. See also
875 Documentation/admin-guide/mm/hugetlbpage.rst.
878 deferred_probe_timeout=
879 [KNL] Debugging option to set a timeout in seconds for
880 deferred probe to give up waiting on dependencies to
881 probe. Only specific dependencies (subsystems or
882 drivers) that have opted in will be ignored. A timeout of 0
883 will timeout at the end of initcalls. This option will also
884 dump out devices still on the deferred probe list after
888 Format: { on | off | def_only | inf_only | always }
889 on: s390 zlib hardware support for compression on
890 level 1 and decompression (default)
891 off: No s390 zlib hardware support
892 def_only: s390 zlib hardware support for deflate
893 only (compression on level 1)
894 inf_only: s390 zlib hardware support for inflate
896 always: Same as 'on' but ignores the selected compression
897 level always using hardware support (used for debugging)
900 Set number of hash buckets for dentry cache.
902 disable_1tb_segments [PPC]
903 Disables the use of 1TB hash page table segments. This
904 causes the kernel to fall back to 256MB segments which
905 can be useful when debugging issues that require an SLB
909 Limits the number of kernel SLB entries, and flushes
910 them frequently to increase the rate of SLB faults
914 See Documentation/networking/ipv6.rst.
917 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
918 hardening is enabled for this boot. Hardened
919 usercopy checking is used to protect the kernel
920 from reading or writing beyond known memory
921 allocation boundaries as a proactive defense
922 against bounds-checking flaws in the kernel's
923 copy_to_user()/copy_from_user() interface.
924 on Perform hardened usercopy checks (default).
925 off Disable hardened usercopy checks.
928 Disable RADIX MMU mode on POWER9
930 radix_hcall_invalidate=on [PPC/PSERIES]
931 Disable RADIX GTSE feature and use hcall for TLB
935 Disable TLBIE instruction. Currently does not work
936 with KVM, with HASH MMU, or with coherent accelerators.
938 disable_cpu_apicid= [X86,APIC,SMP]
940 The number of initial APIC ID for the
941 corresponding CPU to be disabled at boot,
942 mostly used for the kdump 2nd kernel to
943 disable BSP to wake up multiple CPUs without
944 causing system reset or hang due to sending
947 perf_v4_pmi= [X86,INTEL]
949 Disable Intel PMU counter freezing feature.
950 The feature only exists starting from
951 Arch Perfmon v4 (Skylake and newer).
953 disable_ddw [PPC/PSERIES]
954 Disable Dynamic DMA Window support. Use this
955 to workaround buggy firmware.
958 See Documentation/networking/ipv6.rst.
960 disable_mtrr_cleanup [X86]
961 The kernel tries to adjust MTRR layout from continuous
962 to discrete, to make X server driver able to add WB
963 entry later. This parameter disables that.
965 disable_mtrr_trim [X86, Intel and AMD only]
966 By default the kernel will trim any uncacheable
967 memory out of your available memory pool based on
968 MTRR settings. This parameter disables that behavior,
969 possibly causing your machine to run very slowly.
971 disable_timer_pin_1 [X86]
972 Disable PIN 1 of APIC timer
973 Can be useful to work around chipset bugs.
975 dis_ucode_ldr [X86] Disable the microcode loader.
977 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
978 this option disables the debugging code at boot.
980 dma_debug_entries=<number>
981 This option allows to tune the number of preallocated
982 entries for DMA-API debugging code. One entry is
983 required per DMA-API allocation. Use this if the
984 DMA-API debugging code disables itself because the
985 architectural default is too low.
987 dma_debug_driver=<driver_name>
988 With this option the DMA-API debugging driver
989 filter feature can be enabled at boot time. Just
990 pass the driver to filter for as the parameter.
991 The filter can be disabled or changed to another
992 driver later using sysfs.
994 driver_async_probe= [KNL]
995 List of driver names to be probed asynchronously.
996 Format: <driver_name1>,<driver_name2>...
998 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
999 Broken monitors, graphic adapters, KVMs and EDIDless
1000 panels may send no or incorrect EDID data sets.
1001 This parameter allows to specify an EDID data sets
1002 in the /lib/firmware directory that are used instead.
1003 Generic built-in EDID data sets are used, if one of
1004 edid/1024x768.bin, edid/1280x1024.bin,
1005 edid/1680x1050.bin, or edid/1920x1080.bin is given
1006 and no file with the same name exists. Details and
1007 instructions how to build your own EDID data are
1008 available in Documentation/admin-guide/edid.rst. An EDID
1009 data set will only be used for a particular connector,
1010 if its name and a colon are prepended to the EDID
1011 name. Each connector may use a unique EDID data
1012 set by separating the files with a comma. An EDID
1013 data set with no connector name will be used for
1014 any connectors not explicitly specified.
1019 Format: {"off" | "known"}
1020 Control how the dt_cpu_ftrs device-tree binding is
1021 used for CPU feature discovery and setup (if it
1023 off: Do not use it, fall back to legacy cpu table.
1024 known: Do not pass through unknown features to guests
1025 or userspace, only those that the kernel is aware of.
1027 dump_apple_properties [X86]
1028 Dump name and content of EFI device properties on
1029 x86 Macs. Useful for driver authors to determine
1030 what data is available or for reverse-engineering.
1032 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1033 <module>.dyndbg[="val"]
1034 Enable debug messages at boot time. See
1035 Documentation/admin-guide/dynamic-debug-howto.rst
1038 nopku [X86] Disable Memory Protection Keys CPU feature found
1041 <module>.async_probe [KNL]
1042 Enable asynchronous probe on this module.
1044 early_ioremap_debug [KNL]
1045 Enable debug messages in early_ioremap support. This
1046 is useful for tracking down temporary early mappings
1047 which are not unmapped.
1049 earlycon= [KNL] Output early console device and options.
1051 When used with no options, the early console is
1052 determined by stdout-path property in device tree's
1053 chosen node or the ACPI SPCR table if supported by
1056 cdns,<addr>[,options]
1057 Start an early, polled-mode console on a Cadence
1058 (xuartps) serial port at the specified address. Only
1059 supported option is baud rate. If baud rate is not
1060 specified, the serial port must already be setup and
1063 uart[8250],io,<addr>[,options]
1064 uart[8250],mmio,<addr>[,options]
1065 uart[8250],mmio32,<addr>[,options]
1066 uart[8250],mmio32be,<addr>[,options]
1067 uart[8250],0x<addr>[,options]
1068 Start an early, polled-mode console on the 8250/16550
1069 UART at the specified I/O port or MMIO address.
1070 MMIO inter-register address stride is either 8-bit
1071 (mmio) or 32-bit (mmio32 or mmio32be).
1072 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1073 to be equivalent to 'mmio'. 'options' are specified
1074 in the same format described for "console=ttyS<n>"; if
1075 unspecified, the h/w is not initialized.
1079 Start an early, polled-mode console on a pl011 serial
1080 port at the specified address. The pl011 serial port
1081 must already be setup and configured. Options are not
1082 yet supported. If 'mmio32' is specified, then only
1083 the driver will use only 32-bit accessors to read/write
1084 the device registers.
1087 Start an early, polled-mode console on a meson serial
1088 port at the specified address. The serial port must
1089 already be setup and configured. Options are not yet
1093 Start an early, polled-mode console on an msm serial
1094 port at the specified address. The serial port
1095 must already be setup and configured. Options are not
1098 msm_serial_dm,<addr>
1099 Start an early, polled-mode console on an msm serial
1100 dm port at the specified address. The serial port
1101 must already be setup and configured. Options are not
1105 Start an early, polled-mode console on a serial port
1106 of an Actions Semi SoC, such as S500 or S900, at the
1107 specified address. The serial port must already be
1108 setup and configured. Options are not yet supported.
1111 Start an early, polled-mode console on a serial port
1112 of an RDA Micro SoC, such as RDA8810PL, at the
1113 specified address. The serial port must already be
1114 setup and configured. Options are not yet supported.
1117 Use RISC-V SBI (Supervisor Binary Interface) for early
1120 smh Use ARM semihosting calls for early console.
1128 Use early console provided by serial driver available
1129 on Samsung SoCs, requires selecting proper type and
1130 a correct base address of the selected UART port. The
1131 serial port must already be setup and configured.
1132 Options are not yet supported.
1135 Start an early, polled-mode console on a lantiq serial
1136 (lqasc) port at the specified address. The serial port
1137 must already be setup and configured. Options are not
1142 Use early console provided by Freescale LP UART driver
1143 found on Freescale Vybrid and QorIQ LS1021A processors.
1144 A valid base address must be provided, and the serial
1145 port must already be setup and configured.
1149 Start an early, polled-mode, output-only console on the
1150 Freescale i.MX UART at the specified address. The UART
1151 must already be setup and configured.
1154 Start an early, polled-mode console on the
1155 Armada 3700 serial port at the specified
1156 address. The serial port must already be setup
1157 and configured. Options are not yet supported.
1160 Start an early, polled-mode console on a Qualcomm
1161 Generic Interface (GENI) based serial port at the
1162 specified address. The serial port must already be
1163 setup and configured. Options are not yet supported.
1166 Start an early, unaccelerated console on the EFI
1167 memory mapped framebuffer (if available). On cache
1168 coherent non-x86 systems that use system memory for
1169 the framebuffer, pass the 'ram' option so that it is
1170 mapped with the correct attributes.
1173 Use early console provided by Freescale LINFlexD UART
1174 serial driver for NXP S32V234 SoCs. A valid base
1175 address must be provided, and the serial port must
1176 already be setup and configured.
1178 earlyprintk= [X86,SH,ARM,M68k,S390]
1182 earlyprintk=serial[,ttySn[,baudrate]]
1183 earlyprintk=serial[,0x...[,baudrate]]
1184 earlyprintk=ttySn[,baudrate]
1185 earlyprintk=dbgp[debugController#]
1186 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1187 earlyprintk=xdbc[xhciController#]
1189 earlyprintk is useful when the kernel crashes before
1190 the normal console is initialized. It is not enabled by
1191 default because it has some cosmetic problems.
1193 Append ",keep" to not disable it when the real console
1196 Only one of vga, efi, serial, or usb debug port can
1199 Currently only ttyS0 and ttyS1 may be specified by
1200 name. Other I/O ports may be explicitly specified
1201 on some architectures (x86 and arm at least) by
1202 replacing ttySn with an I/O port address, like this:
1203 earlyprintk=serial,0x1008,115200
1204 You can find the port for a given device in
1205 /proc/tty/driver/serial:
1206 2: uart:ST16650V2 port:00001008 irq:18 ...
1208 Interaction with the standard serial driver is not
1211 The VGA and EFI output is eventually overwritten by
1214 The xen output can only be used by Xen PV guests.
1216 The sclp output can only be used on s390.
1218 The optional "force" to "pciserial" enables use of a
1219 PCI device even when its classcode is not of the
1222 edac_report= [HW,EDAC] Control how to report EDAC event
1223 Format: {"on" | "off" | "force"}
1224 on: enable EDAC to report H/W event. May be overridden
1225 by other higher priority error reporting module.
1226 off: disable H/W event reporting through EDAC.
1227 force: enforce the use of EDAC to report H/W event.
1230 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1233 This is designed to be used in conjunction with
1234 the boot argument: earlyprintk=vga
1236 This parameter works in place of the kgdboc parameter
1237 but can only be used if the backing tty is available
1238 very early in the boot process. For early debugging
1239 via a serial port see kgdboc_earlycon instead.
1242 Format: {"off" | "on" | "skip[mbr]"}
1245 Format: { "debug", "disable_early_pci_dma",
1246 "nochunk", "noruntime", "nosoftreserve",
1247 "novamap", "no_disable_early_pci_dma" }
1248 debug: enable misc debug output.
1249 disable_early_pci_dma: disable the busmaster bit on all
1250 PCI bridges while in the EFI boot stub.
1251 nochunk: disable reading files in "chunks" in the EFI
1252 boot stub, as chunking can cause problems with some
1253 firmware implementations.
1254 noruntime : disable EFI runtime services support
1255 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1256 attribute may cause the kernel to reserve the
1257 memory range for a memory mapping driver to
1258 claim. Specify efi=nosoftreserve to disable this
1259 reservation and treat the memory by its base type
1260 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1261 novamap: do not call SetVirtualAddressMap().
1262 no_disable_early_pci_dma: Leave the busmaster bit set
1263 on all PCI bridges while in the EFI boot stub
1265 efi_no_storage_paranoia [EFI; X86]
1266 Using this parameter you can use more than 50% of
1267 your efi variable storage. Use this parameter only if
1268 you are really sure that your UEFI does sane gc and
1269 fulfills the spec otherwise your board may brick.
1271 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1272 Add arbitrary attribute to specific memory range by
1273 updating original EFI memory map.
1274 Region of memory which aa attribute is added to is
1277 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1278 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1279 attribute is added to range 0x100000000-0x180000000 and
1280 0x10a0000000-0x1120000000.
1282 If efi_fake_mem=8G@9G:0x40000 is specified, the
1283 EFI_MEMORY_SP(0x40000) attribute is added to
1284 range 0x240000000-0x43fffffff.
1286 Using this parameter you can do debugging of EFI memmap
1287 related features. For example, you can do debugging of
1288 Address Range Mirroring feature even if your box
1289 doesn't support it, or mark specific memory as
1292 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1293 that is to be dynamically loaded by Linux. If there are
1294 multiple variables with the same name but with different
1295 vendor GUIDs, all of them will be loaded. See
1296 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1299 eisa_irq_edge= [PARISC,HW]
1300 See header of drivers/parisc/eisa.c.
1303 See comment before function elanfreq_setup() in
1304 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1306 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1307 Specifies physical address of start of kernel core
1308 image elf header and optionally the size. Generally
1309 kexec loader will pass this option to capture kernel.
1310 See Documentation/admin-guide/kdump/kdump.rst for details.
1312 enable_mtrr_cleanup [X86]
1313 The kernel tries to adjust MTRR layout from continuous
1314 to discrete, to make X server driver able to add WB
1315 entry later. This parameter enables that.
1317 enable_timer_pin_1 [X86]
1318 Enable PIN 1 of APIC timer
1319 Can be useful to work around chipset bugs
1320 (in particular on some ATI chipsets).
1321 The kernel tries to set a reasonable default.
1323 enforcing [SELINUX] Set initial enforcing status.
1325 See security/selinux/Kconfig help text.
1326 0 -- permissive (log only, no denials).
1327 1 -- enforcing (deny and log).
1329 Value can be changed at runtime via
1330 /sys/fs/selinux/enforce.
1333 Disable Error Record Serialization Table (ERST)
1336 ether= [HW,NET] Ethernet cards parameters
1337 This option is obsoleted by the "netdev=" option, which
1338 has equivalent usage. See its documentation for details.
1342 Permit 'security.evm' to be updated regardless of
1343 current integrity status.
1347 fail_make_request=[KNL]
1348 General fault injection mechanism.
1349 Format: <interval>,<probability>,<space>,<times>
1350 See also Documentation/fault-injection/.
1353 See Documentation/admin-guide/blockdev/floppy.rst.
1355 force_pal_cache_flush
1356 [IA-64] Avoid check_sal_cache_flush which may hang on
1357 buggy SAL_CACHE_FLUSH implementations. Using this
1358 parameter will force ia64_sal_cache_flush to call
1359 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1362 Forcefully enable Physical Address Extension (PAE).
1363 Many Pentium M systems disable PAE but may have a
1364 functionally usable PAE implementation.
1365 Warning: use of this parameter will taint the kernel
1366 and may cause unknown problems.
1369 [FTRACE] will set and start the specified tracer
1370 as early as possible in order to facilitate early
1373 ftrace_dump_on_oops[=orig_cpu]
1374 [FTRACE] will dump the trace buffers on oops.
1375 If no parameter is passed, ftrace will dump
1376 buffers of all CPUs, but if you pass orig_cpu, it will
1377 dump only the buffer of the CPU that triggered the
1380 ftrace_filter=[function-list]
1381 [FTRACE] Limit the functions traced by the function
1382 tracer at boot up. function-list is a comma separated
1383 list of functions. This list can be changed at run
1384 time by the set_ftrace_filter file in the debugfs
1387 ftrace_notrace=[function-list]
1388 [FTRACE] Do not trace the functions specified in
1389 function-list. This list can be changed at run time
1390 by the set_ftrace_notrace file in the debugfs
1393 ftrace_graph_filter=[function-list]
1394 [FTRACE] Limit the top level callers functions traced
1395 by the function graph tracer at boot up.
1396 function-list is a comma separated list of functions
1397 that can be changed at run time by the
1398 set_graph_function file in the debugfs tracing directory.
1400 ftrace_graph_notrace=[function-list]
1401 [FTRACE] Do not trace from the functions specified in
1402 function-list. This list is a comma separated list of
1403 functions that can be changed at run time by the
1404 set_graph_notrace file in the debugfs tracing directory.
1406 ftrace_graph_max_depth=<uint>
1407 [FTRACE] Used with the function graph tracer. This is
1408 the max depth it will trace into a function. This value
1409 can be changed at run time by the max_graph_depth file
1410 in the tracefs tracing directory. default: 0 (no limit)
1412 fw_devlink= [KNL] Create device links between consumer and supplier
1413 devices by scanning the firmware to infer the
1414 consumer/supplier relationships. This feature is
1415 especially useful when drivers are loaded as modules as
1416 it ensures proper ordering of tasks like device probing
1417 (suppliers first, then consumers), supplier boot state
1418 clean up (only after all consumers have probed),
1419 suspend/resume & runtime PM (consumers first, then
1421 Format: { off | permissive | on | rpm }
1422 off -- Don't create device links from firmware info.
1423 permissive -- Create device links from firmware info
1424 but use it only for ordering boot state clean
1425 up (sync_state() calls).
1426 on -- Create device links from firmware info and use it
1427 to enforce probe and suspend/resume ordering.
1428 rpm -- Like "on", but also use to order runtime PM.
1431 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1432 support via parallel port (up to 5 devices per port)
1433 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1434 See also Documentation/input/devices/joystick-parport.rst
1438 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART
1442 gcov_persist= [GCOV] When non-zero (default), profiling data for
1443 kernel modules is saved and remains accessible via
1444 debugfs, even when the module is unloaded/reloaded.
1445 When zero, profiling data is discarded and associated
1446 debugfs files are removed at module unload time.
1448 goldfish [X86] Enable the goldfish android emulator platform.
1449 Don't use this when you are not running on the
1452 gpt [EFI] Forces disk with valid GPT signature but
1453 invalid Protective MBR to be treated as GPT. If the
1454 primary GPT is corrupted, it enables the backup/alternate
1455 GPT to be used instead.
1457 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1458 the "Enable 0" bit of the configuration register.
1461 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1462 the "Enable 0" bit of the configuration register.
1465 grcan.select= [HW] Select which physical interface to use.
1468 grcan.txsize= [HW] Sets the size of the tx buffer.
1469 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1471 grcan.rxsize= [HW] Sets the size of the rx buffer.
1472 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1475 gpio-mockup.gpio_mockup_ranges
1476 [HW] Sets the ranges of gpiochip of for this device.
1477 Format: <start1>,<end1>,<start2>,<end2>...
1479 hardlockup_all_cpu_backtrace=
1480 [KNL] Should the hard-lockup detector generate
1481 backtraces on all cpus.
1484 hashdist= [KNL,NUMA] Large hashes allocated during boot
1485 are distributed across NUMA nodes. Defaults on
1486 for 64-bit NUMA, off otherwise.
1487 Format: 0 | 1 (for off | on)
1489 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1491 hd= [EIDE] (E)IDE hard drive subsystem geometry
1492 Format: <cyl>,<head>,<sect>
1495 Disable Hardware Error Source Table (HEST) support;
1496 corresponding firmware-first mode error processing
1497 logic will be disabled.
1499 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1500 size of <nn>. This works even on boxes that have no
1501 highmem otherwise. This also works to reduce highmem
1502 size on bigger boxes.
1504 highres= [KNL] Enable/disable high resolution timer mode.
1505 Valid parameters: "on", "off"
1510 hpet= [X86-32,HPET] option to control HPET usage
1511 Format: { enable (default) | disable | force |
1513 disable: disable HPET and use PIT instead
1514 force: allow force enabled of undocumented chips (ICH4,
1516 verbose: show contents of HPET registers during setup
1518 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1519 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1521 hugetlb_cma= [HW] The size of a cma area used for allocation
1522 of gigantic hugepages.
1525 Reserve a cma area of given size and allocate gigantic
1526 hugepages using the cma allocator. If enabled, the
1527 boot-time allocation of gigantic hugepages is skipped.
1529 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1530 If this follows hugepagesz (below), it specifies
1531 the number of pages of hugepagesz to be allocated.
1532 If this is the first HugeTLB parameter on the command
1533 line, it specifies the number of pages to allocate for
1534 the default huge page size. See also
1535 Documentation/admin-guide/mm/hugetlbpage.rst.
1539 [HW] The size of the HugeTLB pages. This is used in
1540 conjunction with hugepages (above) to allocate huge
1541 pages of a specific size at boot. The pair
1542 hugepagesz=X hugepages=Y can be specified once for
1543 each supported huge page size. Huge page sizes are
1544 architecture dependent. See also
1545 Documentation/admin-guide/mm/hugetlbpage.rst.
1549 [KNL] Should the hung task detector generate panics.
1552 A value of 1 instructs the kernel to panic when a
1553 hung task is detected. The default value is controlled
1554 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1555 option. The value selected by this boot parameter can
1556 be changed later by the kernel.hung_task_panic sysctl.
1558 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1559 terminal devices. Valid values: 0..8
1560 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1561 If specified, z/VM IUCV HVC accepts connections
1562 from listed z/VM user IDs only.
1564 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1565 which allow the hypervisor to 'idle' the
1566 guest on lock contention.
1569 Do not unregister boot console at start. This is only
1570 useful for debugging when something happens in the window
1571 between unregistering the boot console and initializing
1574 i2c_bus= [HW] Override the default board specific I2C bus speed
1575 or register an additional I2C bus that is not
1576 registered from board initialization code.
1580 i8042.debug [HW] Toggle i8042 debug mode
1581 i8042.unmask_kbd_data
1582 [HW] Enable printing of interrupt data from the KBD port
1583 (disabled by default, and as a pre-condition
1584 requires that i8042.debug=1 be enabled)
1585 i8042.direct [HW] Put keyboard port into non-translated mode
1586 i8042.dumbkbd [HW] Pretend that controller can only read data from
1587 keyboard and cannot control its state
1588 (Don't attempt to blink the leds)
1589 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1590 i8042.nokbd [HW] Don't check/create keyboard port
1591 i8042.noloop [HW] Disable the AUX Loopback command while probing
1593 i8042.nomux [HW] Don't check presence of an active multiplexing
1595 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1597 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1598 i8042.reset [HW] Reset the controller during init, cleanup and
1599 suspend-to-ram transitions, only during s2r
1600 transitions, or never reset
1601 Format: { 1 | Y | y | 0 | N | n }
1602 1, Y, y: always reset controller
1603 0, N, n: don't ever reset controller
1604 Default: only on s2r transitions on x86; most other
1605 architectures force reset to be always executed
1606 i8042.unlock [HW] Unlock (ignore) the keylock
1607 i8042.kbdreset [HW] Reset device connected to KBD port
1611 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1612 indicates that the driver is running on unsupported
1614 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1615 does not match list of supported models.
1617 [HW] Report power status in /proc/i8k
1618 (disabled by default)
1619 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1622 i915.invert_brightness=
1623 [DRM] Invert the sense of the variable that is used to
1624 set the brightness of the panel backlight. Normally a
1625 brightness value of 0 indicates backlight switched off,
1626 and the maximum of the brightness value sets the backlight
1627 to maximum brightness. If this parameter is set to 0
1628 (default) and the machine requires it, or this parameter
1629 is set to 1, a brightness value of 0 sets the backlight
1630 to maximum brightness, and the maximum of the brightness
1631 value switches the backlight off.
1632 -1 -- never invert brightness
1633 0 -- machine default
1634 1 -- force brightness inversion
1637 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1639 ide-core.nodma= [HW] (E)IDE subsystem
1640 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1641 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1642 .cdrom .chs .ignore_cable are additional options
1643 See Documentation/ide/ide.rst.
1645 ide-generic.probe-mask= [HW] (E)IDE subsystem
1647 Probe mask for legacy ISA IDE ports. Depending on
1648 platform up to 6 ports are supported, enabled by
1649 setting corresponding bits in the mask to 1. The
1650 default value is 0x0, which has a special meaning.
1651 On systems that have PCI, it triggers scanning the
1652 PCI bus for the first and the second port, which
1653 are then probed. On systems without PCI the value
1654 of 0x0 enables probing the two first ports as if it
1657 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1658 Claim all unknown PCI IDE storage controllers.
1661 Format: idle=poll, idle=halt, idle=nomwait
1662 Poll forces a polling idle loop that can slightly
1663 improve the performance of waking up a idle CPU, but
1664 will use a lot of power and make the system run hot.
1666 idle=halt: Halt is forced to be used for CPU idle.
1667 In such case C2/C3 won't be used again.
1668 idle=nomwait: Disable mwait for CPU C-states
1670 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1671 Format: { strict | legacy | 2008 | relaxed }
1674 Choose which programs will be accepted for execution
1675 based on the IEEE 754 NaN encoding(s) supported by
1676 the FPU and the NaN encoding requested with the value
1677 of an ELF file header flag individually set by each
1678 binary. Hardware implementations are permitted to
1679 support either or both of the legacy and the 2008 NaN
1682 Available settings are as follows:
1683 strict accept binaries that request a NaN encoding
1684 supported by the FPU
1685 legacy only accept legacy-NaN binaries, if supported
1687 2008 only accept 2008-NaN binaries, if supported
1689 relaxed accept any binaries regardless of whether
1690 supported by the FPU
1692 The FPU emulator is always able to support both NaN
1693 encodings, so if no FPU hardware is present or it has
1694 been disabled with 'nofpu', then the settings of
1695 'legacy' and '2008' strap the emulator accordingly,
1696 'relaxed' straps the emulator for both legacy-NaN and
1697 2008-NaN, whereas 'strict' enables legacy-NaN only on
1698 legacy processors and both NaN encodings on MIPS32 or
1701 The setting for ABS.fmt/NEG.fmt instruction execution
1702 mode generally follows that for the NaN encoding,
1703 except where unsupported by hardware.
1705 ignore_loglevel [KNL]
1706 Ignore loglevel setting - this will print /all/
1707 kernel messages to the console. Useful for debugging.
1708 We also add it as printk module parameter, so users
1709 could change it dynamically, usually by
1710 /sys/module/printk/parameters/ignore_loglevel.
1713 Ignore RLIMIT_DATA setting for data mappings,
1714 print warning at first misuse. Can be changed via
1715 /sys/module/kernel/parameters/ignore_rlimit_data.
1717 ihash_entries= [KNL]
1718 Set number of hash buckets for inode cache.
1720 ima_appraise= [IMA] appraise integrity measurements
1721 Format: { "off" | "enforce" | "fix" | "log" }
1724 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1725 The builtin appraise policy appraises all files
1728 ima_canonical_fmt [IMA]
1729 Use the canonical format for the binary runtime
1730 measurements, instead of host native format.
1733 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1737 The list of supported hash algorithms is defined
1738 in crypto/hash_info.h.
1741 The builtin policies to load during IMA setup.
1742 Format: "tcb | appraise_tcb | secure_boot |
1745 The "tcb" policy measures all programs exec'd, files
1746 mmap'd for exec, and all files opened with the read
1747 mode bit set by either the effective uid (euid=0) or
1750 The "appraise_tcb" policy appraises the integrity of
1751 all files owned by root.
1753 The "secure_boot" policy appraises the integrity
1754 of files (eg. kexec kernel image, kernel modules,
1755 firmware, policy, etc) based on file signatures.
1757 The "fail_securely" policy forces file signature
1758 verification failure also on privileged mounted
1759 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1762 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1763 Load a policy which meets the needs of the Trusted
1764 Computing Base. This means IMA will measure all
1765 programs exec'd, files mmap'd for exec, and all files
1766 opened for read by uid=0.
1769 Select one of defined IMA measurements template formats.
1770 Formats: { "ima" | "ima-ng" | "ima-sig" }
1774 [IMA] Define a custom template format.
1775 Format: { "field1|...|fieldN" }
1777 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1778 Format: <min_file_size>
1779 Set the minimal file size for using asynchronous hash.
1780 If left unspecified, ahash usage is disabled.
1782 ahash performance varies for different data sizes on
1783 different crypto accelerators. This option can be used
1784 to achieve the best performance for a particular HW.
1786 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1788 Set hashing buffer size. Default: 4k.
1790 ahash performance varies for different chunk sizes on
1791 different crypto accelerators. This option can be used
1792 to achieve best performance for particular HW.
1796 Run specified binary instead of /sbin/init as init
1799 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1800 for working out where the kernel is dying during
1803 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1804 initcall functions. Useful for debugging built-in
1805 modules and initcalls.
1807 initrd= [BOOT] Specify the location of the initial ramdisk
1809 initrdmem= [KNL] Specify a physical address and size from which to
1810 load the initrd. If an initrd is compiled in or
1811 specified in the bootparams, it takes priority over this
1813 Format: ss[KMG],nn[KMG]
1816 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1819 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1821 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1823 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1825 init_pkru= [X86] Specify the default memory protection keys rights
1826 register contents for all processes. 0x55555554 by
1827 default (disallow access to all but pkey 0). Can
1828 override in debugfs after boot.
1830 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1833 int_pln_enable [X86] Enable power limit notification interrupt
1835 integrity_audit=[IMA]
1836 Format: { "0" | "1" }
1837 0 -- basic integrity auditing messages. (Default)
1838 1 -- additional integrity auditing messages.
1840 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1842 Enable intel iommu driver.
1844 Disable intel iommu driver.
1845 igfx_off [Default Off]
1846 By default, gfx is mapped as normal device. If a gfx
1847 device has a dedicated DMAR unit, the DMAR unit is
1848 bypassed by not enabling DMAR with this option. In
1849 this case, gfx device will use physical address for
1852 With this option iommu will not optimize to look
1853 for io virtual address below 32-bit forcing dual
1854 address cycle on pci bus for cards supporting greater
1855 than 32-bit addressing. The default is to look
1856 for translation below 32-bit and if not available
1857 then look in the higher range.
1858 strict [Default Off]
1859 With this option on every unmap_single operation will
1860 result in a hardware IOTLB flush operation as opposed
1861 to batching them for performance.
1862 sp_off [Default Off]
1863 By default, super page will be supported if Intel IOMMU
1864 has the capability. With this option, super page will
1867 By default, scalable mode will be disabled even if the
1868 hardware advertises that it has support for the scalable
1869 mode translation. With this option set, scalable mode
1870 will be used on hardware which claims to support it.
1871 tboot_noforce [Default Off]
1872 Do not force the Intel IOMMU enabled under tboot.
1873 By default, tboot will force Intel IOMMU on, which
1874 could harm performance of some high-throughput
1875 devices like 40GBit network cards, even if identity
1877 Note that using this option lowers the security
1878 provided by tboot because it makes the system
1879 vulnerable to DMA attacks.
1880 nobounce [Default off]
1881 Disable bounce buffer for untrusted devices such as
1882 the Thunderbolt devices. This will treat the untrusted
1883 devices as the trusted ones, hence might expose security
1884 risks of DMA attacks.
1886 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1887 0 disables intel_idle and fall back on acpi_idle.
1888 1 to 9 specify maximum depth of C-state.
1892 Do not enable intel_pstate as the default
1893 scaling driver for the supported processors
1895 Use intel_pstate as a scaling driver, but configure it
1896 to work with generic cpufreq governors (instead of
1897 enabling its internal governor). This mode cannot be
1898 used along with the hardware-managed P-states (HWP)
1901 Enable intel_pstate on systems that prohibit it by default
1902 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1903 instead of acpi-cpufreq may disable platform features, such
1904 as thermal controls and power capping, that rely on ACPI
1905 P-States information being indicated to OSPM and therefore
1906 should be used with caution. This option does not work with
1907 processors that aren't supported by the intel_pstate driver
1908 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1910 Do not enable hardware P state control (HWP)
1913 Only load intel_pstate on systems which support
1914 hardware P state control (HWP) if available.
1916 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1917 Description Table, specifies preferred power management
1918 profile as "Enterprise Server" or "Performance Server",
1919 then this feature is turned on by default.
1921 Allow per-logical-CPU P-State performance control limits using
1922 cpufreq sysfs interface
1924 intremap= [X86-64, Intel-IOMMU]
1925 on enable Interrupt Remapping (default)
1926 off disable Interrupt Remapping
1927 nosid disable Source ID checking
1929 BIOS x2APIC opt-out request will be ignored
1930 nopost disable Interrupt Posting
1932 iomem= Disable strict checking of access to MMIO memory
1933 strict regions from userspace.
1948 nobypass [PPC/POWERNV]
1949 Disable IOMMU bypass, using IOMMU for PCI devices.
1951 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1952 Format: { "0" | "1" }
1954 Request that DMA unmap operations use deferred
1955 invalidation of hardware TLBs, for increased
1956 throughput at the cost of reduced device isolation.
1957 Will fall back to strict mode if not supported by
1958 the relevant IOMMU driver.
1959 1 - Strict mode (default).
1960 DMA unmap operations invalidate IOMMU hardware TLBs
1964 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
1965 Format: { "0" | "1" }
1966 0 - Use IOMMU translation for DMA.
1967 1 - Bypass the IOMMU for DMA.
1968 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1970 io7= [HW] IO7 for Marvel-based Alpha systems
1971 See comment before marvel_specify_io7 in
1972 arch/alpha/kernel/core_marvel.c.
1974 io_delay= [X86] I/O delay method
1976 Standard port 0x80 based delay
1978 Alternate port 0xed based delay (needed on some systems)
1980 Simple two microseconds delay
1985 See Documentation/admin-guide/nfs/nfsroot.rst.
1987 ipcmni_extend [KNL] Extend the maximum number of unique System V
1988 IPC identifiers from 32,768 to 16,777,216.
1990 irqaffinity= [SMP] Set the default irq affinity mask
1991 The argument is a cpu list, as described above.
1993 irqchip.gicv2_force_probe=
1996 Force the kernel to look for the second 4kB page
1997 of a GICv2 controller even if the memory range
1998 exposed by the device tree is too small.
2000 irqchip.gicv3_nolpi=
2002 Force the kernel to ignore the availability of
2003 LPIs (and by consequence ITSs). Intended for system
2004 that use the kernel as a bootloader, and thus want
2005 to let secondary kernels in charge of setting up
2008 irqchip.gicv3_pseudo_nmi= [ARM64]
2009 Enables support for pseudo-NMIs in the kernel. This
2010 requires the kernel to be built with
2011 CONFIG_ARM64_PSEUDO_NMI.
2014 When an interrupt is not handled search all handlers
2015 for it. Intended to get systems with badly broken
2019 When an interrupt is not handled search all handlers
2020 for it. Also check all handlers each timer
2021 interrupt. Intended to get systems with badly broken
2025 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2027 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2028 [Deprecated - use cpusets instead]
2029 Format: [flag-list,]<cpu-list>
2031 Specify one or more CPUs to isolate from disturbances
2032 specified in the flag list (default: domain):
2035 Disable the tick when a single task runs.
2037 A residual 1Hz tick is offloaded to workqueues, which you
2038 need to affine to housekeeping through the global
2039 workqueue's affinity configured via the
2040 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2041 by using the 'domain' flag described below.
2043 NOTE: by default the global workqueue runs on all CPUs,
2044 so to protect individual CPUs the 'cpumask' file has to
2045 be configured manually after bootup.
2048 Isolate from the general SMP balancing and scheduling
2049 algorithms. Note that performing domain isolation this way
2050 is irreversible: it's not possible to bring back a CPU to
2051 the domains once isolated through isolcpus. It's strongly
2052 advised to use cpusets instead to disable scheduler load
2053 balancing through the "cpuset.sched_load_balance" file.
2054 It offers a much more flexible interface where CPUs can
2055 move in and out of an isolated set anytime.
2057 You can move a process onto or off an "isolated" CPU via
2058 the CPU affinity syscalls or cpuset.
2059 <cpu number> begins at 0 and the maximum value is
2060 "number of CPUs in system - 1".
2064 Isolate from being targeted by managed interrupts
2065 which have an interrupt mask containing isolated
2066 CPUs. The affinity of managed interrupts is
2067 handled by the kernel and cannot be changed via
2068 the /proc/irq/* interfaces.
2070 This isolation is best effort and only effective
2071 if the automatically assigned interrupt mask of a
2072 device queue contains isolated and housekeeping
2073 CPUs. If housekeeping CPUs are online then such
2074 interrupts are directed to the housekeeping CPU
2075 so that IO submitted on the housekeeping CPU
2076 cannot disturb the isolated CPU.
2078 If a queue's affinity mask contains only isolated
2079 CPUs then this parameter has no effect on the
2080 interrupt routing decision, though interrupts are
2081 only delivered when tasks running on those
2082 isolated CPUs submit IO. IO submitted on
2083 housekeeping CPUs has no influence on those
2086 The format of <cpu-list> is described above.
2090 ivrs_ioapic [HW,X86-64]
2091 Provide an override to the IOAPIC-ID<->DEVICE-ID
2092 mapping provided in the IVRS ACPI table. For
2093 example, to map IOAPIC-ID decimal 10 to
2094 PCI device 00:14.0 write the parameter as:
2095 ivrs_ioapic[10]=00:14.0
2097 ivrs_hpet [HW,X86-64]
2098 Provide an override to the HPET-ID<->DEVICE-ID
2099 mapping provided in the IVRS ACPI table. For
2100 example, to map HPET-ID decimal 0 to
2101 PCI device 00:14.0 write the parameter as:
2102 ivrs_hpet[0]=00:14.0
2104 ivrs_acpihid [HW,X86-64]
2105 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2106 mapping provided in the IVRS ACPI table. For
2107 example, to map UART-HID:UID AMD0020:0 to
2108 PCI device 00:14.5 write the parameter as:
2109 ivrs_acpihid[00:14.5]=AMD0020:0
2111 js= [HW,JOY] Analog joystick
2112 See Documentation/input/joydev/joystick.rst.
2115 When CONFIG_RANDOMIZE_BASE is set, this disables
2116 kernel and module base offset ASLR (Address Space
2117 Layout Randomization).
2120 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2121 report on every invalid memory access. Without this
2122 parameter KASAN will print report only for the first
2127 kernelcore= [KNL,X86,IA-64,PPC]
2128 Format: nn[KMGTPE] | nn% | "mirror"
2129 This parameter specifies the amount of memory usable by
2130 the kernel for non-movable allocations. The requested
2131 amount is spread evenly throughout all nodes in the
2132 system as ZONE_NORMAL. The remaining memory is used for
2133 movable memory in its own zone, ZONE_MOVABLE. In the
2134 event, a node is too small to have both ZONE_NORMAL and
2135 ZONE_MOVABLE, kernelcore memory will take priority and
2136 other nodes will have a larger ZONE_MOVABLE.
2138 ZONE_MOVABLE is used for the allocation of pages that
2139 may be reclaimed or moved by the page migration
2140 subsystem. Note that allocations like PTEs-from-HighMem
2141 still use the HighMem zone if it exists, and the Normal
2142 zone if it does not.
2144 It is possible to specify the exact amount of memory in
2145 the form of "nn[KMGTPE]", a percentage of total system
2146 memory in the form of "nn%", or "mirror". If "mirror"
2147 option is specified, mirrored (reliable) memory is used
2148 for non-movable allocations and remaining memory is used
2149 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2150 are exclusive, so you cannot specify multiple forms.
2152 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2153 Format: <Controller#>[,poll interval]
2154 The controller # is the number of the ehci usb debug
2155 port as it is probed via PCI. The poll interval is
2156 optional and is the number seconds in between
2157 each poll cycle to the debug port in case you need
2158 the functionality for interrupting the kernel with
2159 gdb or control-c on the dbgp connection. When
2160 not using this parameter you use sysrq-g to break into
2161 the kernel debugger.
2163 kgdboc= [KGDB,HW] kgdb over consoles.
2164 Requires a tty driver that supports console polling,
2165 or a supported polling keyboard driver (non-usb).
2166 Serial only format: <serial_device>[,baud]
2167 keyboard only format: kbd
2168 keyboard and serial format: kbd,<serial_device>[,baud]
2169 Optional Kernel mode setting:
2170 kms, kbd format: kms,kbd
2171 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2173 kgdboc_earlycon= [KGDB,HW]
2174 If the boot console provides the ability to read
2175 characters and can work in polling mode, you can use
2176 this parameter to tell kgdb to use it as a backend
2177 until the normal console is registered. Intended to
2178 be used together with the kgdboc parameter which
2179 specifies the normal console to transition to.
2181 The name of the early console should be specified
2182 as the value of this parameter. Note that the name of
2183 the early console might be different than the tty
2184 name passed to kgdboc. It's OK to leave the value
2185 blank and the first boot console that implements
2186 read() will be picked.
2188 kgdbwait [KGDB] Stop kernel execution and enter the
2189 kernel debugger at the earliest opportunity.
2191 kmac= [MIPS] Korina ethernet MAC address.
2192 Configure the RouterBoard 532 series on-chip
2193 Ethernet adapter MAC address.
2195 kmemleak= [KNL] Boot-time kmemleak enable/disable
2196 Valid arguments: on, off
2198 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2201 kprobe_event=[probe-list]
2202 [FTRACE] Add kprobe events and enable at boot time.
2203 The probe-list is a semicolon delimited list of probe
2204 definitions. Each definition is same as kprobe_events
2205 interface, but the parameters are comma delimited.
2206 For example, to add a kprobe event on vfs_read with
2207 arg1 and arg2, add to the command line;
2209 kprobe_event=p,vfs_read,$arg1,$arg2
2211 See also Documentation/trace/kprobetrace.rst "Kernel
2212 Boot Parameter" section.
2214 kpti= [ARM64] Control page table isolation of user
2215 and kernel address spaces.
2216 Default: enabled on cores which need mitigation.
2220 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2221 Default is 0 (don't ignore, but inject #GP)
2223 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2224 Default is false (don't support).
2226 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2231 [KVM] Controls the software workaround for the
2232 X86_BUG_ITLB_MULTIHIT bug.
2233 force : Always deploy workaround.
2234 off : Never deploy workaround.
2235 auto : Deploy workaround based on the presence of
2236 X86_BUG_ITLB_MULTIHIT.
2240 If the software workaround is enabled for the host,
2241 guests do need not to enable it for nested guests.
2243 kvm.nx_huge_pages_recovery_ratio=
2244 [KVM] Controls how many 4KiB pages are periodically zapped
2245 back to huge pages. 0 disables the recovery, otherwise if
2246 the value is N KVM will zap 1/Nth of the 4KiB pages every
2247 minute. The default is 60.
2249 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2250 Default is 1 (enabled)
2252 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2254 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2256 kvm-arm.vgic_v3_group0_trap=
2257 [KVM,ARM] Trap guest accesses to GICv3 group-0
2260 kvm-arm.vgic_v3_group1_trap=
2261 [KVM,ARM] Trap guest accesses to GICv3 group-1
2264 kvm-arm.vgic_v3_common_trap=
2265 [KVM,ARM] Trap guest accesses to GICv3 common
2268 kvm-arm.vgic_v4_enable=
2269 [KVM,ARM] Allow use of GICv4 for direct injection of
2272 kvm_cma_resv_ratio=n [PPC]
2273 Reserves given percentage from system memory area for
2274 contiguous memory allocation for KVM hash pagetable
2276 By default it reserves 5% of total system memory.
2280 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2281 (virtualized MMU) support on capable Intel chips.
2282 Default is 1 (enabled)
2284 kvm-intel.emulate_invalid_guest_state=
2285 [KVM,Intel] Enable emulation of invalid guest states
2286 Default is 0 (disabled)
2288 kvm-intel.flexpriority=
2289 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2290 Default is 1 (enabled)
2293 [KVM,Intel] Enable VMX nesting (nVMX).
2294 Default is 0 (disabled)
2296 kvm-intel.unrestricted_guest=
2297 [KVM,Intel] Disable unrestricted guest feature
2298 (virtualized real and unpaged mode) on capable
2299 Intel chips. Default is 1 (enabled)
2301 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2304 Valid arguments: never, cond, always
2306 always: L1D cache flush on every VMENTER.
2307 cond: Flush L1D on VMENTER only when the code between
2308 VMEXIT and VMENTER can leak host memory.
2309 never: Disables the mitigation
2311 Default is cond (do L1 cache flush in specific instances)
2313 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2314 feature (tagged TLBs) on capable Intel chips.
2315 Default is 1 (enabled)
2317 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2320 The kernel PTE inversion protection is unconditionally
2321 enabled and cannot be disabled.
2324 Provides all available mitigations for the
2325 L1TF vulnerability. Disables SMT and
2326 enables all mitigations in the
2327 hypervisors, i.e. unconditional L1D flush.
2329 SMT control and L1D flush control via the
2330 sysfs interface is still possible after
2331 boot. Hypervisors will issue a warning
2332 when the first VM is started in a
2333 potentially insecure configuration,
2334 i.e. SMT enabled or L1D flush disabled.
2337 Same as 'full', but disables SMT and L1D
2338 flush runtime control. Implies the
2339 'nosmt=force' command line option.
2340 (i.e. sysfs control of SMT is disabled.)
2343 Leaves SMT enabled and enables the default
2344 hypervisor mitigation, i.e. conditional
2347 SMT control and L1D flush control via the
2348 sysfs interface is still possible after
2349 boot. Hypervisors will issue a warning
2350 when the first VM is started in a
2351 potentially insecure configuration,
2352 i.e. SMT enabled or L1D flush disabled.
2356 Disables SMT and enables the default
2357 hypervisor mitigation.
2359 SMT control and L1D flush control via the
2360 sysfs interface is still possible after
2361 boot. Hypervisors will issue a warning
2362 when the first VM is started in a
2363 potentially insecure configuration,
2364 i.e. SMT enabled or L1D flush disabled.
2367 Same as 'flush', but hypervisors will not
2368 warn when a VM is started in a potentially
2369 insecure configuration.
2372 Disables hypervisor mitigations and doesn't
2374 It also drops the swap size and available
2375 RAM limit restriction on both hypervisor and
2380 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2386 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2389 lapic= [X86,APIC] Do not use TSC deadline
2390 value for LAPIC timer one-shot implementation. Default
2391 back to the programmable timer unit in the LAPIC.
2392 Format: notscdeadline
2394 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2397 libata.dma= [LIBATA] DMA control
2398 libata.dma=0 Disable all PATA and SATA DMA
2399 libata.dma=1 PATA and SATA Disk DMA only
2400 libata.dma=2 ATAPI (CDROM) DMA only
2401 libata.dma=4 Compact Flash DMA only
2402 Combinations also work, so libata.dma=3 enables DMA
2403 for disks and CDROMs, but not CFs.
2405 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2406 libata.ignore_hpa=0 keep BIOS limits (default)
2407 libata.ignore_hpa=1 ignore limits, using full disk
2409 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2413 libata.force= [LIBATA] Force configurations. The format is comma
2414 separated list of "[ID:]VAL" where ID is
2415 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2416 matching port, link or device. Basically, it matches
2417 the ATA ID string printed on console by libata. If
2418 the whole ID part is omitted, the last PORT and DEVICE
2419 values are used. If ID hasn't been specified yet, the
2420 configuration applies to all ports, links and devices.
2422 If only DEVICE is omitted, the parameter applies to
2423 the port and all links and devices behind it. DEVICE
2424 number of 0 either selects the first device or the
2425 first fan-out link behind PMP device. It does not
2426 select the host link. DEVICE number of 15 selects the
2427 host link and device attached to it.
2429 The VAL specifies the configuration to force. As long
2430 as there's no ambiguity shortcut notation is allowed.
2431 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2432 The following configurations can be forced.
2434 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2435 Any ID with matching PORT is used.
2437 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2439 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2440 udma[/][16,25,33,44,66,100,133] notation is also
2443 * [no]ncq: Turn on or off NCQ.
2445 * [no]ncqtrim: Turn off queued DSM TRIM.
2447 * nohrst, nosrst, norst: suppress hard, soft
2450 * rstonce: only attempt one reset during
2451 hot-unplug link recovery
2453 * dump_id: dump IDENTIFY data.
2455 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2457 * disable: Disable this device.
2459 If there are multiple matching configurations changing
2460 the same attribute, the last one is used.
2462 memblock=debug [KNL] Enable memblock debug messages.
2464 load_ramdisk= [RAM] [Deprecated]
2466 lockd.nlm_grace_period=P [NFS] Assign grace period.
2469 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2472 lockd.nlm_timeout=T [NFS] Assign timeout value.
2475 lockd.nlm_udpport=M [NFS] Assign UDP port.
2478 lockdown= [SECURITY]
2479 { integrity | confidentiality }
2480 Enable the kernel lockdown feature. If set to
2481 integrity, kernel features that allow userland to
2482 modify the running kernel are disabled. If set to
2483 confidentiality, kernel features that allow userland
2484 to extract confidential information from the kernel
2487 locktorture.nreaders_stress= [KNL]
2488 Set the number of locking read-acquisition kthreads.
2489 Defaults to being automatically set based on the
2490 number of online CPUs.
2492 locktorture.nwriters_stress= [KNL]
2493 Set the number of locking write-acquisition kthreads.
2495 locktorture.onoff_holdoff= [KNL]
2496 Set time (s) after boot for CPU-hotplug testing.
2498 locktorture.onoff_interval= [KNL]
2499 Set time (s) between CPU-hotplug operations, or
2500 zero to disable CPU-hotplug testing.
2502 locktorture.shuffle_interval= [KNL]
2503 Set task-shuffle interval (jiffies). Shuffling
2504 tasks allows some CPUs to go into dyntick-idle
2505 mode during the locktorture test.
2507 locktorture.shutdown_secs= [KNL]
2508 Set time (s) after boot system shutdown. This
2509 is useful for hands-off automated testing.
2511 locktorture.stat_interval= [KNL]
2512 Time (s) between statistics printk()s.
2514 locktorture.stutter= [KNL]
2515 Time (s) to stutter testing, for example,
2516 specifying five seconds causes the test to run for
2517 five seconds, wait for five seconds, and so on.
2518 This tests the locking primitive's ability to
2519 transition abruptly to and from idle.
2521 locktorture.torture_type= [KNL]
2522 Specify the locking implementation to test.
2524 locktorture.verbose= [KNL]
2525 Enable additional printk() statements.
2527 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2530 loglevel= All Kernel Messages with a loglevel smaller than the
2531 console loglevel will be printed to the console. It can
2532 also be changed with klogd or other programs. The
2533 loglevels are defined as follows:
2535 0 (KERN_EMERG) system is unusable
2536 1 (KERN_ALERT) action must be taken immediately
2537 2 (KERN_CRIT) critical conditions
2538 3 (KERN_ERR) error conditions
2539 4 (KERN_WARNING) warning conditions
2540 5 (KERN_NOTICE) normal but significant condition
2541 6 (KERN_INFO) informational
2542 7 (KERN_DEBUG) debug-level messages
2544 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2545 in bytes. n must be a power of two and greater
2546 than the minimal size. The minimal size is defined
2547 by LOG_BUF_SHIFT kernel config parameter. There is
2548 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2549 that allows to increase the default size depending on
2550 the number of CPUs. See init/Kconfig for more details.
2552 logo.nologo [FB] Disables display of the built-in Linux logo.
2553 This may be used to provide more screen space for
2554 kernel log messages and is useful when debugging
2555 kernel boot problems.
2557 lp=0 [LP] Specify parallel ports to use, e.g,
2558 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2559 lp=reset first parallel port). 'lp=0' disables the
2560 lp=auto printer driver. 'lp=reset' (which can be
2561 specified in addition to the ports) causes
2562 attached printers to be reset. Using
2563 lp=port1,port2,... specifies the parallel ports
2564 to associate lp devices with, starting with
2565 lp0. A port specification may be 'none' to skip
2566 that lp device, or a parport name such as
2567 'parport0'. Specifying 'lp=auto' instead of a
2568 port specification list means that device IDs
2569 from each port should be examined, to see if
2570 an IEEE 1284-compliant printer is attached; if
2571 so, the driver will manage that printer.
2572 See also header of drivers/char/lp.c.
2575 Sets loops_per_jiffy to given constant, thus avoiding
2576 time-consuming boot-time autodetection (up to 250 ms per
2577 CPU). 0 enables autodetection (default). To determine
2578 the correct value for your kernel, boot with normal
2579 autodetection and see what value is printed. Note that
2580 on SMP systems the preset will be applied to all CPUs,
2581 which is likely to cause problems if your CPUs need
2582 significantly divergent settings. An incorrect value
2583 will cause delays in the kernel to be wrong, leading to
2584 unpredictable I/O errors and other breakage. Although
2585 unlikely, in the extreme case this might damage your
2589 Format: <io>,<irq>,<dma>
2591 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2594 [SECURITY] Choose order of LSM initialization. This
2595 overrides CONFIG_LSM, and the "security=" parameter.
2597 machvec= [IA-64] Force the use of a particular machine-vector
2598 (machvec) in a generic kernel.
2599 Example: machvec=hpzx1
2601 machtype= [Loongson] Share the same kernel image file between
2602 different yeeloong laptops.
2603 Example: machtype=lemote-yeeloong-2f-7inch
2605 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2606 than or equal to this physical address is ignored.
2608 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2609 will bring up during bootup. maxcpus=n : n >= 0 limits
2610 the kernel to bring up 'n' processors. Surely after
2611 bootup you can bring up the other plugged cpu by executing
2612 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2613 only takes effect during system bootup.
2614 While n=0 is a special case, it is equivalent to "nosmp",
2615 which also disables the IO APIC.
2617 max_loop= [LOOP] The number of loop block devices that get
2618 (loop.max_loop) unconditionally pre-created at init time. The default
2619 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2620 of statically allocating a predefined number, loop
2621 devices can be requested on-demand with the
2622 /dev/loop-control interface.
2624 mce [X86-32] Machine Check Exception
2626 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2628 md= [HW] RAID subsystems devices and level
2629 See Documentation/admin-guide/md.rst.
2632 Format: <first>,<last>
2633 Specifies range of consoles to be captured by the MDA.
2636 Control mitigation for the Micro-architectural Data
2637 Sampling (MDS) vulnerability.
2639 Certain CPUs are vulnerable to an exploit against CPU
2640 internal buffers which can forward information to a
2641 disclosure gadget under certain conditions.
2643 In vulnerable processors, the speculatively
2644 forwarded data can be used in a cache side channel
2645 attack, to access data to which the attacker does
2646 not have direct access.
2648 This parameter controls the MDS mitigation. The
2651 full - Enable MDS mitigation on vulnerable CPUs
2652 full,nosmt - Enable MDS mitigation and disable
2653 SMT on vulnerable CPUs
2654 off - Unconditionally disable MDS mitigation
2656 On TAA-affected machines, mds=off can be prevented by
2657 an active TAA mitigation as both vulnerabilities are
2658 mitigated with the same mechanism so in order to disable
2659 this mitigation, you need to specify tsx_async_abort=off
2662 Not specifying this option is equivalent to
2665 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2667 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2668 Amount of memory to be used in cases as follows:
2671 2 when the kernel is not able to see the whole system memory;
2672 3 memory that lies after 'mem=' boundary is excluded from
2673 the hypervisor, then assigned to KVM guests.
2675 [X86] Work as limiting max address. Use together
2676 with memmap= to avoid physical address space collisions.
2677 Without memmap= PCI devices could be placed at addresses
2678 belonging to unused RAM.
2680 Note that this only takes effects during boot time since
2681 in above case 3, memory may need be hot added after boot
2682 if system memory of hypervisor is not sufficient.
2684 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2688 [KNL,SH] Allow user to override the default size for
2689 per-device physically contiguous DMA buffers.
2691 memhp_default_state=online/offline
2692 [KNL] Set the initial state for the memory hotplug
2693 onlining policy. If not specified, the default value is
2694 set according to the
2695 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2697 See Documentation/admin-guide/mm/memory-hotplug.rst.
2699 memmap=exactmap [KNL,X86] Enable setting of an exact
2700 E820 memory map, as specified by the user.
2701 Such memmap=exactmap lines can be constructed based on
2702 BIOS output or other requirements. See the memmap=nn@ss
2705 memmap=nn[KMG]@ss[KMG]
2706 [KNL] Force usage of a specific region of memory.
2707 Region of memory to be used is from ss to ss+nn.
2708 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2709 which limits max address to nn[KMG].
2710 Multiple different regions can be specified,
2713 memmap=100M@2G,100M#3G,1G!1024G
2715 memmap=nn[KMG]#ss[KMG]
2716 [KNL,ACPI] Mark specific memory as ACPI data.
2717 Region of memory to be marked is from ss to ss+nn.
2719 memmap=nn[KMG]$ss[KMG]
2720 [KNL,ACPI] Mark specific memory as reserved.
2721 Region of memory to be reserved is from ss to ss+nn.
2722 Example: Exclude memory from 0x18690000-0x1869ffff
2723 memmap=64K$0x18690000
2725 memmap=0x10000$0x18690000
2726 Some bootloaders may need an escape character before '$',
2727 like Grub2, otherwise '$' and the following number
2730 memmap=nn[KMG]!ss[KMG]
2731 [KNL,X86] Mark specific memory as protected.
2732 Region of memory to be used, from ss to ss+nn.
2733 The memory region may be marked as e820 type 12 (0xc)
2734 and is NVDIMM or ADR memory.
2736 memmap=<size>%<offset>-<oldtype>+<newtype>
2737 [KNL,ACPI] Convert memory within the specified region
2738 from <oldtype> to <newtype>. If "-<oldtype>" is left
2739 out, the whole region will be marked as <newtype>,
2740 even if previously unavailable. If "+<newtype>" is left
2741 out, matching memory will be removed. Types are
2742 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2743 3 = ACPI, 12 = PRAM.
2745 memory_corruption_check=0/1 [X86]
2746 Some BIOSes seem to corrupt the first 64k of
2747 memory when doing things like suspend/resume.
2748 Setting this option will scan the memory
2749 looking for corruption. Enabling this will
2750 both detect corruption and prevent the kernel
2751 from using the memory being corrupted.
2752 However, its intended as a diagnostic tool; if
2753 repeatable BIOS-originated corruption always
2754 affects the same memory, you can use memmap=
2755 to prevent the kernel from using that memory.
2757 memory_corruption_check_size=size [X86]
2758 By default it checks for corruption in the low
2759 64k, making this memory unavailable for normal
2760 use. Use this parameter to scan for
2761 corruption in more or less memory.
2763 memory_corruption_check_period=seconds [X86]
2764 By default it checks for corruption every 60
2765 seconds. Use this parameter to check at some
2766 other rate. 0 disables periodic checking.
2768 memtest= [KNL,X86,ARM,PPC] Enable memtest
2770 default : 0 <disable>
2771 Specifies the number of memtest passes to be
2772 performed. Each pass selects another test
2773 pattern from a given set of patterns. Memtest
2774 fills the memory with this pattern, validates
2775 memory contents and reserves bad memory
2776 regions that are detected.
2778 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2779 Valid arguments: on, off
2780 Default (depends on kernel configuration option):
2781 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2782 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2783 mem_encrypt=on: Activate SME
2784 mem_encrypt=off: Do not activate SME
2786 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
2787 for details on when memory encryption can be activated.
2789 mem_sleep_default= [SUSPEND] Default system suspend mode:
2790 s2idle - Suspend-To-Idle
2791 shallow - Power-On Suspend or equivalent (if supported)
2792 deep - Suspend-To-RAM or equivalent (if supported)
2793 See Documentation/admin-guide/pm/sleep-states.rst.
2795 meye.*= [HW] Set MotionEye Camera parameters
2796 See Documentation/admin-guide/media/meye.rst.
2798 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2799 Multi-Function General Purpose Timers on AMD Geode
2802 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2803 the BIOS has incorrectly applied a workaround. TinyBIOS
2804 version 0.98 is known to be affected, 0.99 fixes the
2805 problem by letting the user disable the workaround.
2809 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2810 physical address is ignored.
2812 mini2440= [ARM,HW,KNL]
2813 Format:[0..2][b][c][t]
2815 MINI2440 configuration specification:
2816 0 - The attached screen is the 3.5" TFT
2817 1 - The attached screen is the 7" TFT
2818 2 - The VGA Shield is attached (1024x768)
2819 Leaving out the screen size parameter will not load
2820 the TFT driver, and the framebuffer will be left
2822 b - Enable backlight. The TFT backlight pin will be
2823 linked to the kernel VESA blanking code and a GPIO
2824 LED. This parameter is not necessary when using the
2826 c - Enable the s3c camera interface.
2827 t - Reserved for enabling touchscreen support. The
2828 touchscreen support is not enabled in the mainstream
2829 kernel as of 2.6.30, a preliminary port can be found
2830 in the "bleeding edge" mini2440 support kernel at
2831 https://repo.or.cz/w/linux-2.6/mini2440.git
2834 [X86,PPC,S390,ARM64] Control optional mitigations for
2835 CPU vulnerabilities. This is a set of curated,
2836 arch-independent options, each of which is an
2837 aggregation of existing arch-specific options.
2840 Disable all optional CPU mitigations. This
2841 improves system performance, but it may also
2842 expose users to several CPU vulnerabilities.
2843 Equivalent to: nopti [X86,PPC]
2845 nospectre_v1 [X86,PPC]
2847 nospectre_v2 [X86,PPC,S390,ARM64]
2848 spectre_v2_user=off [X86]
2849 spec_store_bypass_disable=off [X86,PPC]
2850 ssbd=force-off [ARM64]
2853 tsx_async_abort=off [X86]
2854 kvm.nx_huge_pages=off [X86]
2857 This does not have any effect on
2858 kvm.nx_huge_pages when
2859 kvm.nx_huge_pages=force.
2862 Mitigate all CPU vulnerabilities, but leave SMT
2863 enabled, even if it's vulnerable. This is for
2864 users who don't want to be surprised by SMT
2865 getting disabled across kernel upgrades, or who
2866 have other ways of avoiding SMT-based attacks.
2867 Equivalent to: (default behavior)
2870 Mitigate all CPU vulnerabilities, disabling SMT
2871 if needed. This is for users who always want to
2872 be fully mitigated, even if it means losing SMT.
2873 Equivalent to: l1tf=flush,nosmt [X86]
2874 mds=full,nosmt [X86]
2875 tsx_async_abort=full,nosmt [X86]
2878 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2879 parameter allows control of the logging verbosity for
2880 the additional memory initialisation checks. A value
2881 of 0 disables mminit logging and a level of 4 will
2882 log everything. Information is printed at KERN_DEBUG
2883 so loglevel=8 may also need to be specified.
2886 [KNL] When CONFIG_MODULE_SIG is set, this means that
2887 modules without (valid) signatures will fail to load.
2888 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2889 is always true, so this option does nothing.
2891 module_blacklist= [KNL] Do not load a comma-separated list of
2892 modules. Useful for debugging problem modules.
2895 [MOUSE] Maximum time between finger touching and
2896 leaving touchpad surface for touch to be considered
2897 a tap and be reported as a left button click (for
2898 touchpads working in absolute mode only).
2900 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2901 reporting absolute coordinates, such as tablets
2902 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2903 reporting absolute coordinates, such as tablets
2905 movablecore= [KNL,X86,IA-64,PPC]
2906 Format: nn[KMGTPE] | nn%
2907 This parameter is the complement to kernelcore=, it
2908 specifies the amount of memory used for migratable
2909 allocations. If both kernelcore and movablecore is
2910 specified, then kernelcore will be at *least* the
2911 specified value but may be more. If movablecore on its
2912 own is specified, the administrator must be careful
2913 that the amount of memory usable for all allocations
2916 movable_node [KNL] Boot-time switch to make hotplugable memory
2917 NUMA nodes to be movable. This means that the memory
2918 of such nodes will be usable only for movable
2919 allocations which rules out almost all kernel
2920 allocations. Use with caution!
2922 MTD_Partition= [MTD]
2923 Format: <name>,<region-number>,<size>,<offset>
2925 MTD_Region= [MTD] Format:
2926 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2929 See drivers/mtd/parsers/cmdlinepart.c
2931 multitce=off [PPC] This parameter disables the use of the pSeries
2932 firmware feature for updating multiple TCE entries
2935 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2937 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2939 boundary - index of last SLC block on Flex-OneNAND.
2940 The remaining blocks are configured as MLC blocks.
2941 lock - Configure if Flex-OneNAND boundary should be locked.
2942 Once locked, the boundary cannot be changed.
2943 1 indicates lock status, 0 indicates unlock status.
2946 ARM/S3C2412 JIVE boot control
2948 See arch/arm/mach-s3c2412/mach-jive.c
2950 mtouchusb.raw_coordinates=
2951 [HW] Make the MicroTouch USB driver use raw coordinates
2952 ('y', default) or cooked coordinates ('n')
2954 mtrr_chunk_size=nn[KMG] [X86]
2955 used for mtrr cleanup. It is largest continuous chunk
2956 that could hold holes aka. UC entries.
2958 mtrr_gran_size=nn[KMG] [X86]
2959 Used for mtrr cleanup. It is granularity of mtrr block.
2961 Large value could prevent small alignment from
2964 mtrr_spare_reg_nr=n [X86]
2966 Range: 0,7 : spare reg number
2968 Used for mtrr cleanup. It is spare mtrr entries number.
2969 Set to 2 or more if your graphical card needs more.
2971 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2973 netdev= [NET] Network devices parameters
2974 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2975 Note that mem_start is often overloaded to mean
2976 something different and driver-specific.
2977 This usage is only documented in each driver source
2981 [NETFILTER] Enable connection tracking flow accounting
2982 0 to disable accounting
2983 1 to enable accounting
2986 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2987 See Documentation/admin-guide/nfs/nfsroot.rst.
2989 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2990 See Documentation/admin-guide/nfs/nfsroot.rst.
2992 nfsrootdebug [NFS] enable nfsroot debugging messages.
2993 See Documentation/admin-guide/nfs/nfsroot.rst.
2995 nfs.callback_nr_threads=
2996 [NFSv4] set the total number of threads that the
2997 NFS client will assign to service NFSv4 callback
3000 nfs.callback_tcpport=
3001 [NFS] set the TCP port on which the NFSv4 callback
3002 channel should listen.
3005 [NFS] sets the pathname to the program which is used
3006 to update the NFS client cache entries.
3008 nfs.cache_getent_timeout=
3009 [NFS] sets the timeout after which an attempt to
3010 update a cache entry is deemed to have failed.
3012 nfs.idmap_cache_timeout=
3013 [NFS] set the maximum lifetime for idmapper cache
3017 [NFS] enable 64-bit inode numbers.
3018 If zero, the NFS client will fake up a 32-bit inode
3019 number for the readdir() and stat() syscalls instead
3020 of returning the full 64-bit number.
3021 The default is to return 64-bit inode numbers.
3023 nfs.max_session_cb_slots=
3024 [NFSv4.1] Sets the maximum number of session
3025 slots the client will assign to the callback
3026 channel. This determines the maximum number of
3027 callbacks the client will process in parallel for
3028 a particular server.
3030 nfs.max_session_slots=
3031 [NFSv4.1] Sets the maximum number of session slots
3032 the client will attempt to negotiate with the server.
3033 This limits the number of simultaneous RPC requests
3034 that the client can send to the NFSv4.1 server.
3035 Note that there is little point in setting this
3036 value higher than the max_tcp_slot_table_limit.
3038 nfs.nfs4_disable_idmapping=
3039 [NFSv4] When set to the default of '1', this option
3040 ensures that both the RPC level authentication
3041 scheme and the NFS level operations agree to use
3042 numeric uids/gids if the mount is using the
3043 'sec=sys' security flavour. In effect it is
3044 disabling idmapping, which can make migration from
3045 legacy NFSv2/v3 systems to NFSv4 easier.
3046 Servers that do not support this mode of operation
3047 will be autodetected by the client, and it will fall
3048 back to using the idmapper.
3049 To turn off this behaviour, set the value to '0'.
3051 [NFS4] Specify an additional fixed unique ident-
3052 ification string that NFSv4 clients can insert into
3053 their nfs_client_id4 string. This is typically a
3054 UUID that is generated at system install time.
3056 nfs.send_implementation_id =
3057 [NFSv4.1] Send client implementation identification
3058 information in exchange_id requests.
3059 If zero, no implementation identification information
3061 The default is to send the implementation identification
3064 nfs.recover_lost_locks =
3065 [NFSv4] Attempt to recover locks that were lost due
3066 to a lease timeout on the server. Please note that
3067 doing this risks data corruption, since there are
3068 no guarantees that the file will remain unchanged
3069 after the locks are lost.
3070 If you want to enable the kernel legacy behaviour of
3071 attempting to recover these locks, then set this
3073 The default parameter value of '0' causes the kernel
3074 not to attempt recovery of lost locks.
3076 nfs4.layoutstats_timer =
3077 [NFSv4.2] Change the rate at which the kernel sends
3078 layoutstats to the pNFS metadata server.
3080 Setting this to value to 0 causes the kernel to use
3081 whatever value is the default set by the layout
3082 driver. A non-zero value sets the minimum interval
3083 in seconds between layoutstats transmissions.
3085 nfsd.nfs4_disable_idmapping=
3086 [NFSv4] When set to the default of '1', the NFSv4
3087 server will return only numeric uids and gids to
3088 clients using auth_sys, and will accept numeric uids
3089 and gids from such clients. This is intended to ease
3090 migration from NFSv2/v3.
3092 nmi_debug= [KNL,SH] Specify one or more actions to take
3093 when a NMI is triggered.
3094 Format: [state][,regs][,debounce][,die]
3096 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3097 Format: [panic,][nopanic,][num]
3099 0 - turn hardlockup detector in nmi_watchdog off
3100 1 - turn hardlockup detector in nmi_watchdog on
3101 When panic is specified, panic when an NMI watchdog
3102 timeout occurs (or 'nopanic' to not panic on an NMI
3103 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3104 To disable both hard and soft lockup detectors,
3105 please see 'nowatchdog'.
3106 This is useful when you use a panic=... timeout and
3107 need the box quickly up again.
3109 These settings can be accessed at runtime via
3110 the nmi_watchdog and hardlockup_panic sysctls.
3112 netpoll.carrier_timeout=
3113 [NET] Specifies amount of time (in seconds) that
3114 netpoll should wait for a carrier. By default netpoll
3117 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3118 emulation library even if a 387 maths coprocessor
3121 no5lvl [X86-64] Disable 5-level paging mode. Forces
3122 kernel to use 4-level paging instead.
3124 nofsgsbase [X86] Disables FSGSBASE instructions.
3127 [HW] Never suspend the console
3128 Disable suspending of consoles during suspend and
3129 hibernate operations. Once disabled, debugging
3130 messages can reach various consoles while the rest
3131 of the system is being put to sleep (ie, while
3132 debugging driver suspend/resume hooks). This may
3133 not work reliably with all consoles, but is known
3134 to work with serial and VGA consoles.
3135 To facilitate more flexible debugging, we also add
3136 console_suspend, a printk module parameter to control
3137 it. Users could use console_suspend (usually
3138 /sys/module/printk/parameters/console_suspend) to
3139 turn on/off it dynamically.
3141 novmcoredd [KNL,KDUMP]
3142 Disable device dump. Device dump allows drivers to
3143 append dump data to vmcore so you can collect driver
3144 specified debug info. Drivers can append the data
3145 without any limit and this data is stored in memory,
3146 so this may cause significant memory stress. Disabling
3147 device dump can help save memory but the driver debug
3148 data will be no longer available. This parameter
3149 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3152 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3153 caches in the slab allocator. Saves per-node memory,
3154 but will impact performance.
3158 noaltinstr [S390] Disables alternative instructions patching
3159 (CPU alternatives feature).
3161 noapic [SMP,APIC] Tells the kernel to not make use of any
3162 IOAPICs that may be present in the system.
3164 noautogroup Disable scheduler automatic task group creation.
3166 nobats [PPC] Do not use BATs for mapping kernel lowmem
3167 on "Classic" PPC cores.
3171 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
3173 nodelayacct [KNL] Disable per-task delay accounting
3175 nodsp [SH] Disable hardware DSP at boot time.
3177 noefi Disable EFI runtime services support.
3182 On X86-32 available only on PAE configured kernels.
3183 noexec=on: enable non-executable mappings (default)
3184 noexec=off: disable non-executable mappings
3187 Disable SMAP (Supervisor Mode Access Prevention)
3188 even if it is supported by processor.
3191 Disable SMEP (Supervisor Mode Execution Prevention)
3192 even if it is supported by processor.
3195 This affects only 32-bit executables.
3196 noexec32=on: enable non-executable mappings (default)
3197 read doesn't imply executable mappings
3198 noexec32=off: disable non-executable mappings
3199 read implies executable mappings
3201 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3203 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3204 register save and restore. The kernel will only save
3205 legacy floating-point registers on task switch.
3207 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
3209 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3210 Equivalent to smt=1.
3212 [KNL,X86] Disable symmetric multithreading (SMT).
3213 nosmt=force: Force disable SMT, cannot be undone
3214 via the sysfs control file.
3216 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3217 (bounds check bypass). With this option data leaks are
3218 possible in the system.
3220 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3221 the Spectre variant 2 (indirect branch prediction)
3222 vulnerability. System may allow data leaks with this
3225 nospec_store_bypass_disable
3226 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3228 noxsave [BUGS=X86] Disables x86 extended register state save
3229 and restore using xsave. The kernel will fallback to
3230 enabling legacy floating-point and sse state.
3232 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3233 register states. The kernel will fall back to use
3234 xsave to save the states. By using this parameter,
3235 performance of saving the states is degraded because
3236 xsave doesn't support modified optimization while
3237 xsaveopt supports it on xsaveopt enabled systems.
3239 noxsaves [X86] Disables xsaves and xrstors used in saving and
3240 restoring x86 extended register state in compacted
3241 form of xsave area. The kernel will fall back to use
3242 xsaveopt and xrstor to save and restore the states
3243 in standard form of xsave area. By using this
3244 parameter, xsave area per process might occupy more
3245 memory on xsaves enabled systems.
3247 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
3248 wfi(ARM) instruction doesn't work correctly and not to
3249 use it. This is also useful when using JTAG debugger.
3251 no_file_caps Tells the kernel not to honor file capabilities. The
3252 only way then for a file to be executed with privilege
3253 is to be setuid root or executed by root.
3255 nohalt [IA-64] Tells the kernel not to use the power saving
3256 function PAL_HALT_LIGHT when idle. This increases
3257 power-consumption. On the positive side, it reduces
3258 interrupt wake-up latency, which may improve performance
3259 in certain environments such as networked servers or
3262 nohibernate [HIBERNATION] Disable hibernation and resume.
3264 nohz= [KNL] Boottime enable/disable dynamic ticks
3265 Valid arguments: on, off
3268 nohz_full= [KNL,BOOT,SMP,ISOL]
3269 The argument is a cpu list, as described above.
3270 In kernels built with CONFIG_NO_HZ_FULL=y, set
3271 the specified list of CPUs whose tick will be stopped
3272 whenever possible. The boot CPU will be forced outside
3273 the range to maintain the timekeeping. Any CPUs
3274 in this list will have their RCU callbacks offloaded,
3275 just as if they had also been called out in the
3276 rcu_nocbs= boot parameter.
3278 noiotrap [SH] Disables trapped I/O port accesses.
3280 noirqdebug [X86-32] Disables the code which attempts to detect and
3281 disable unhandled interrupt sources.
3283 no_timer_check [X86,APIC] Disables the code which tests for
3284 broken timer IRQ sources.
3286 noisapnp [ISAPNP] Disables ISA PnP code.
3288 noinitrd [RAM] Tells the kernel not to load any configured
3291 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3293 [Deprecated - use intremap=off]
3297 noinvpcid [X86] Disable the INVPCID cpu feature.
3299 nojitter [IA-64] Disables jitter checking for ITC timers.
3301 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3303 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3307 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3308 clock and use the default one.
3310 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
3311 accounting. steal time is computed, but won't
3312 influence scheduler behaviour
3314 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3316 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3318 noltlbs [PPC] Do not use large page/tlb entries for kernel
3319 lowmem mapping on PPC40x and PPC8xx
3321 nomca [IA-64] Disable machine check abort handling
3323 nomce [X86-32] Disable Machine Check Exception
3325 nomfgpt [X86-32] Disable Multi-Function General Purpose
3326 Timer usage (for AMD Geode machines).
3328 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3329 shutdown the other cpus. Instead use the REBOOT_VECTOR
3332 nomodule Disable module load
3334 nopat [X86] Disable PAT (page attribute table extension of
3335 pagetables) support.
3337 nopcid [X86-64] Disable the PCID cpu feature.
3339 norandmaps Don't use address space randomization. Equivalent to
3340 echo 0 > /proc/sys/kernel/randomize_va_space
3342 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3343 with UP alternatives
3345 nordrand [X86] Disable kernel use of the RDRAND and
3346 RDSEED instructions even if they are supported
3347 by the processor. RDRAND and RDSEED are still
3348 available to user space applications.
3350 noresume [SWSUSP] Disables resume and restores original swap
3353 no-scroll [VGA] Disables scrollback.
3354 This is required for the Braillex ib80-piezo Braille
3355 reader made by F.H. Papenmeier (Germany).
3359 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3361 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3362 and disable the IO APIC. legacy for "maxcpus=0".
3364 nosoftlockup [KNL] Disable the soft-lockup detector.
3366 nosync [HW,M68K] Disables sync negotiation for all devices.
3368 nowatchdog [KNL] Disable both lockup detectors, i.e.
3369 soft-lockup and NMI watchdog (hard-lockup).
3373 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3375 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3376 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3377 Some features depend on CPU0. Known dependencies are:
3378 1. Resume from suspend/hibernate depends on CPU0.
3379 Suspend/hibernate will fail if CPU0 is offline and you
3380 need to online CPU0 before suspend/hibernate.
3381 2. PIC interrupts also depend on CPU0. CPU0 can't be
3382 removed if a PIC interrupt is detected.
3383 It's said poweroff/reboot may depend on CPU0 on some
3384 machines although I haven't seen such issues so far
3385 after CPU0 is offline on a few tested machines.
3386 If the dependencies are under your control, you can
3387 turn on cpu0_hotplug.
3389 nps_mtm_hs_ctr= [KNL,ARC]
3390 This parameter sets the maximum duration, in
3391 cycles, each HW thread of the CTOP can run
3392 without interruptions, before HW switches it.
3393 The actual maximum duration is 16 times this
3395 Format: integer between 1 and 255
3398 nptcg= [IA-64] Override max number of concurrent global TLB
3399 purges which is reported from either PAL_VM_SUMMARY or
3402 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3403 could support. nr_cpus=n : n >= 1 limits the kernel to
3404 support 'n' processors. It could be larger than the
3405 number of already plugged CPU during bootup, later in
3406 runtime you can physically add extra cpu until it reaches
3407 n. So during boot up some boot time memory for per-cpu
3408 variables need be pre-allocated for later physical cpu
3411 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3413 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3414 Allowed values are enable and disable
3416 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3417 'node', 'default' can be specified
3418 This can be set from sysctl after boot.
3419 See Documentation/admin-guide/sysctl/vm.rst for details.
3421 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3422 See Documentation/core-api/debugging-via-ohci1394.rst for more
3425 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3426 Rather than timing out after 20 ms if an EC
3427 command is not properly ACKed, override the length
3428 of the timeout. We have interrupts disabled while
3429 waiting for the ACK, so if this is set too high
3430 interrupts *may* be lost!
3432 omap_mux= [OMAP] Override bootloader pin multiplexing.
3433 Format: <mux_mode0.mode_name=value>...
3434 For example, to override I2C bus2:
3435 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3437 oprofile.timer= [HW]
3438 Use timer interrupt instead of performance counters
3440 oprofile.cpu_type= Force an oprofile cpu type
3441 This might be useful if you have an older oprofile
3442 userland or if you want common events.
3443 Format: { arch_perfmon }
3444 arch_perfmon: [X86] Force use of architectural
3445 perfmon on Intel CPUs instead of the
3446 CPU specific event set.
3447 timer: [X86] Force use of architectural NMI
3448 timer mode (see also oprofile.timer
3449 for generic hr timer mode)
3451 oops=panic Always panic on oopses. Default is to just kill the
3452 process, but there is a small probability of
3453 deadlocking the machine.
3454 This will also cause panics on machine check exceptions.
3455 Useful together with panic=30 to trigger a reboot.
3458 [KNL] Boolean flag to control whether the page allocator
3459 should randomize its free lists. The randomization may
3460 be automatically enabled if the kernel detects it is
3461 running on a platform with a direct-mapped memory-side
3462 cache, and this parameter can be used to
3463 override/disable that behavior. The state of the flag
3464 can be read from sysfs at:
3465 /sys/module/page_alloc/parameters/shuffle.
3467 page_owner= [KNL] Boot-time page_owner enabling option.
3468 Storage of the information about who allocated
3469 each page is disabled in default. With this switch,
3471 on: enable the feature
3473 page_poison= [KNL] Boot-time parameter changing the state of
3474 poisoning on the buddy allocator, available with
3475 CONFIG_PAGE_POISONING=y.
3476 off: turn off poisoning (default)
3477 on: turn on poisoning
3479 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3480 timeout > 0: seconds before rebooting
3481 timeout = 0: wait forever
3482 timeout < 0: reboot immediately
3485 panic_print= Bitmask for printing system info when panic happens.
3486 User can chose combination of the following bits:
3487 bit 0: print all tasks info
3488 bit 1: print system memory info
3489 bit 2: print timer info
3490 bit 3: print locks info if CONFIG_LOCKDEP is on
3491 bit 4: print ftrace buffer
3492 bit 5: print all printk messages in buffer
3494 panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
3495 Format: <hex>[,nousertaint]
3496 Hexadecimal bitmask representing the set of TAINT flags
3497 that will cause the kernel to panic when add_taint() is
3498 called with any of the flags in this set.
3499 The optional switch "nousertaint" can be utilized to
3500 prevent userspace forced crashes by writing to sysctl
3501 /proc/sys/kernel/tainted any flagset matching with the
3502 bitmask set on panic_on_taint.
3503 See Documentation/admin-guide/tainted-kernels.rst for
3504 extra details on the taint flags that users can pick
3505 to compose the bitmask to assign to panic_on_taint.
3507 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3510 crash_kexec_post_notifiers
3511 Run kdump after running panic-notifiers and dumping
3512 kmsg. This only for the users who doubt kdump always
3513 succeeds in any situation.
3514 Note that this also increases risks of kdump failure,
3515 because some panic notifiers can make the crashed
3516 kernel more unstable.
3518 parkbd.port= [HW] Parallel port number the keyboard adapter is
3519 connected to, default is 0.
3521 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3522 0 for XT, 1 for AT (default is AT).
3525 parport= [HW,PPT] Specify parallel ports. 0 disables.
3526 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3527 Use 'auto' to force the driver to use any
3528 IRQ/DMA settings detected (the default is to
3529 ignore detected IRQ/DMA settings because of
3530 possible conflicts). You can specify the base
3531 address, IRQ, and DMA settings; IRQ and DMA
3532 should be numbers, or 'auto' (for using detected
3533 settings on that particular port), or 'nofifo'
3534 (to avoid using a FIFO even if it is detected).
3535 Parallel ports are assigned in the order they
3536 are specified on the command line, starting
3539 parport_init_mode= [HW,PPT]
3540 Configure VIA parallel port to operate in
3541 a specific mode. This is necessary on Pegasos
3542 computer where firmware has no options for setting
3543 up parallel port mode and sets it to spp.
3544 Currently this function knows 686a and 8231 chips.
3545 Format: [spp|ps2|epp|ecp|ecpepp]
3548 Halt all CPUs after the first oops has been printed for
3549 the specified number of seconds. This is to be used if
3550 your oopses keep scrolling off the screen.
3555 See header of drivers/block/paride/pcd.c.
3556 See also Documentation/admin-guide/blockdev/paride.rst.
3558 pci=option[,option...] [PCI] various PCI subsystem options.
3560 Some options herein operate on a specific device
3561 or a set of devices (<pci_dev>). These are
3562 specified in one of the following formats:
3564 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3565 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3567 Note: the first format specifies a PCI
3568 bus/device/function address which may change
3569 if new hardware is inserted, if motherboard
3570 firmware changes, or due to changes caused
3571 by other kernel parameters. If the
3572 domain is left unspecified, it is
3573 taken to be zero. Optionally, a path
3574 to a device through multiple device/function
3575 addresses can be specified after the base
3576 address (this is more robust against
3577 renumbering issues). The second format
3578 selects devices using IDs from the
3579 configuration space which may match multiple
3580 devices in the system.
3582 earlydump dump PCI config space before the kernel
3584 off [X86] don't probe for the PCI bus
3585 bios [X86-32] force use of PCI BIOS, don't access
3586 the hardware directly. Use this if your machine
3587 has a non-standard PCI host bridge.
3588 nobios [X86-32] disallow use of PCI BIOS, only direct
3589 hardware access methods are allowed. Use this
3590 if you experience crashes upon bootup and you
3591 suspect they are caused by the BIOS.
3592 conf1 [X86] Force use of PCI Configuration Access
3593 Mechanism 1 (config address in IO port 0xCF8,
3594 data in IO port 0xCFC, both 32-bit).
3595 conf2 [X86] Force use of PCI Configuration Access
3596 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3597 the function, IO port 0xCFA, also 8-bit, sets
3598 bus number. The config space is then accessed
3599 through ports 0xC000-0xCFFF).
3600 See http://wiki.osdev.org/PCI for more info
3601 on the configuration access mechanisms.
3602 noaer [PCIE] If the PCIEAER kernel config parameter is
3603 enabled, this kernel boot option can be used to
3604 disable the use of PCIE advanced error reporting.
3605 nodomains [PCI] Disable support for multiple PCI
3606 root domains (aka PCI segments, in ACPI-speak).
3607 nommconf [X86] Disable use of MMCONFIG for PCI
3609 check_enable_amd_mmconf [X86] check for and enable
3610 properly configured MMIO access to PCI
3611 config space on AMD family 10h CPU
3612 nomsi [MSI] If the PCI_MSI kernel config parameter is
3613 enabled, this kernel boot option can be used to
3614 disable the use of MSI interrupts system-wide.
3615 noioapicquirk [APIC] Disable all boot interrupt quirks.
3616 Safety option to keep boot IRQs enabled. This
3617 should never be necessary.
3618 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3619 primary IO-APIC for bridges that cannot disable
3620 boot IRQs. This fixes a source of spurious IRQs
3621 when the system masks IRQs.
3622 noioapicreroute [APIC] Disable workaround that uses the
3623 boot IRQ equivalent of an IRQ that connects to
3624 a chipset where boot IRQs cannot be disabled.
3625 The opposite of ioapicreroute.
3626 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3627 routing table. These calls are known to be buggy
3628 on several machines and they hang the machine
3629 when used, but on other computers it's the only
3630 way to get the interrupt routing table. Try
3631 this option if the kernel is unable to allocate
3632 IRQs or discover secondary PCI buses on your
3634 rom [X86] Assign address space to expansion ROMs.
3635 Use with caution as certain devices share
3636 address decoders between ROMs and other
3638 norom [X86] Do not assign address space to
3639 expansion ROMs that do not already have
3640 BIOS assigned address ranges.
3641 nobar [X86] Do not assign address space to the
3642 BARs that weren't assigned by the BIOS.
3643 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3644 assigned automatically to PCI devices. You can
3645 make the kernel exclude IRQs of your ISA cards
3647 pirqaddr=0xAAAAA [X86] Specify the physical address
3648 of the PIRQ table (normally generated
3649 by the BIOS) if it is outside the
3650 F0000h-100000h range.
3651 lastbus=N [X86] Scan all buses thru bus #N. Can be
3652 useful if the kernel is unable to find your
3653 secondary buses and you want to tell it
3654 explicitly which ones they are.
3655 assign-busses [X86] Always assign all PCI bus
3656 numbers ourselves, overriding
3657 whatever the firmware may have done.
3658 usepirqmask [X86] Honor the possible IRQ mask stored
3659 in the BIOS $PIR table. This is needed on
3660 some systems with broken BIOSes, notably
3661 some HP Pavilion N5400 and Omnibook XE3
3662 notebooks. This will have no effect if ACPI
3663 IRQ routing is enabled.
3664 noacpi [X86] Do not use ACPI for IRQ routing
3665 or for PCI scanning.
3666 use_crs [X86] Use PCI host bridge window information
3667 from ACPI. On BIOSes from 2008 or later, this
3668 is enabled by default. If you need to use this,
3669 please report a bug.
3670 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3671 If you need to use this, please report a bug.
3672 routeirq Do IRQ routing for all PCI devices.
3673 This is normally done in pci_enable_device(),
3674 so this option is a temporary workaround
3675 for broken drivers that don't call it.
3676 skip_isa_align [X86] do not align io start addr, so can
3677 handle more pci cards
3678 noearly [X86] Don't do any early type 1 scanning.
3679 This might help on some broken boards which
3680 machine check when some devices' config space
3681 is read. But various workarounds are disabled
3682 and some IOMMU drivers will not work.
3683 bfsort Sort PCI devices into breadth-first order.
3684 This sorting is done to get a device
3685 order compatible with older (<= 2.4) kernels.
3686 nobfsort Don't sort PCI devices into breadth-first order.
3687 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3688 tuning and use the BIOS-configured MPS defaults.
3689 pcie_bus_safe Set every device's MPS to the largest value
3690 supported by all devices below the root complex.
3691 pcie_bus_perf Set device MPS to the largest allowable MPS
3692 based on its parent bus. Also set MRRS (Max
3693 Read Request Size) to the largest supported
3694 value (no larger than the MPS that the device
3695 or bus can support) for best performance.
3696 pcie_bus_peer2peer Set every device's MPS to 128B, which
3697 every device is guaranteed to support. This
3698 configuration allows peer-to-peer DMA between
3699 any pair of devices, possibly at the cost of
3700 reduced performance. This also guarantees
3701 that hot-added devices will work.
3702 cbiosize=nn[KMG] The fixed amount of bus space which is
3703 reserved for the CardBus bridge's IO window.
3704 The default value is 256 bytes.
3705 cbmemsize=nn[KMG] The fixed amount of bus space which is
3706 reserved for the CardBus bridge's memory
3707 window. The default value is 64 megabytes.
3710 [<order of align>@]<pci_dev>[; ...]
3711 Specifies alignment and device to reassign
3712 aligned memory resources. How to
3713 specify the device is described above.
3714 If <order of align> is not specified,
3715 PAGE_SIZE is used as alignment.
3716 A PCI-PCI bridge can be specified if resource
3717 windows need to be expanded.
3718 To specify the alignment for several
3719 instances of a device, the PCI vendor,
3720 device, subvendor, and subdevice may be
3721 specified, e.g., 12@pci:8086:9c22:103c:198f
3722 for 4096-byte alignment.
3723 ecrc= Enable/disable PCIe ECRC (transaction layer
3724 end-to-end CRC checking).
3725 bios: Use BIOS/firmware settings. This is the
3729 hpiosize=nn[KMG] The fixed amount of bus space which is
3730 reserved for hotplug bridge's IO window.
3731 Default size is 256 bytes.
3732 hpmmiosize=nn[KMG] The fixed amount of bus space which is
3733 reserved for hotplug bridge's MMIO window.
3734 Default size is 2 megabytes.
3735 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
3736 reserved for hotplug bridge's MMIO_PREF window.
3737 Default size is 2 megabytes.
3738 hpmemsize=nn[KMG] The fixed amount of bus space which is
3739 reserved for hotplug bridge's MMIO and
3741 Default size is 2 megabytes.
3742 hpbussize=nn The minimum amount of additional bus numbers
3743 reserved for buses below a hotplug bridge.
3745 realloc= Enable/disable reallocating PCI bridge resources
3746 if allocations done by BIOS are too small to
3747 accommodate resources required by all child
3749 off: Turn realloc off
3751 realloc same as realloc=on
3752 noari do not use PCIe ARI.
3753 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3754 do not use PCIe ATS (and IOMMU device IOTLB).
3755 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3756 only look for one device below a PCIe downstream
3758 big_root_window Try to add a big 64bit memory window to the PCIe
3759 root complex on AMD CPUs. Some GFX hardware
3760 can resize a BAR to allow access to all VRAM.
3761 Adding the window is slightly risky (it may
3762 conflict with unreported devices), so this
3764 disable_acs_redir=<pci_dev>[; ...]
3765 Specify one or more PCI devices (in the format
3766 specified above) separated by semicolons.
3767 Each device specified will have the PCI ACS
3768 redirect capabilities forced off which will
3769 allow P2P traffic between devices through
3770 bridges without forcing it upstream. Note:
3771 this removes isolation between devices and
3772 may put more devices in an IOMMU group.
3773 force_floating [S390] Force usage of floating interrupts.
3774 nomio [S390] Do not use MIO instructions.
3775 norid [S390] ignore the RID field and force use of
3776 one PCI domain per PCI function
3778 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3781 force Enable ASPM even on devices that claim not to support it.
3782 WARNING: Forcing ASPM on may cause system lockups.
3784 pcie_ports= [PCIE] PCIe port services handling:
3785 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3786 even if the platform doesn't give the OS permission to
3787 use them. This may cause conflicts if the platform
3788 also tries to use these services.
3789 dpc-native Use native PCIe service for DPC only. May
3790 cause conflicts if firmware uses AER or DPC.
3791 compat Disable native PCIe services (PME, AER, DPC, PCIe
3794 pcie_port_pm= [PCIE] PCIe port power management handling:
3795 off Disable power management of all PCIe ports
3796 force Forcibly enable power management of all PCIe ports
3798 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3799 nomsi Do not use MSI for native PCIe PME signaling (this makes
3800 all PCIe root ports use INTx for all services).
3802 pcmv= [HW,PCMCIA] BadgePAD 4
3806 Keep all power-domains already enabled by bootloader on,
3807 even if no driver has claimed them. This is useful
3808 for debug and development, but should not be
3809 needed on a platform with proper driver support.
3812 See Documentation/admin-guide/blockdev/paride.rst.
3814 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3817 See arch/parisc/kernel/pdc_chassis.c
3819 percpu_alloc= Select which percpu first chunk allocator to use.
3820 Currently supported values are "embed" and "page".
3821 Archs may support subset or none of the selections.
3822 See comments in mm/percpu.c for details on each
3823 allocator. This parameter is primarily for debugging
3824 and performance comparison.
3827 See Documentation/admin-guide/blockdev/paride.rst.
3830 See Documentation/admin-guide/blockdev/paride.rst.
3832 pirq= [SMP,APIC] Manual mp-table setup
3833 See Documentation/x86/i386/IO-APIC.rst.
3835 plip= [PPT,NET] Parallel port network link
3836 Format: { parport<nr> | timid | 0 }
3837 See also Documentation/admin-guide/parport.rst.
3839 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3840 Override pmtimer IOPort with a hex value.
3843 pm_debug_messages [SUSPEND,KNL]
3844 Enable suspend/resume debug messages during boot up.
3847 Enable PNP debug messages (depends on the
3848 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3849 via /sys/module/pnp/parameters/debug. We always show
3850 current resource usage; turning this on also shows
3851 possible settings and some assignment information.
3857 { on | off | curr | res | no-curr | no-res }
3860 [ISAPNP] Exclude IRQs for the autoconfiguration
3863 [ISAPNP] Exclude DMAs for the autoconfiguration
3865 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3866 Ranges are in pairs (I/O port base and size).
3869 [ISAPNP] Exclude memory regions for the
3871 Ranges are in pairs (memory base and size).
3873 ports= [IP_VS_FTP] IPVS ftp helper module
3875 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3877 Format: <port>,<port>....
3879 powersave=off [PPC] This option disables power saving features.
3880 It specifically disables cpuidle and sets the
3881 platform machine description specific power_save
3882 function to NULL. On Idle the CPU just reduces
3885 ppc_strict_facility_enable
3886 [PPC] This option catches any kernel floating point,
3887 Altivec, VSX and SPE outside of regions specifically
3888 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3889 There is some performance impact when enabling this.
3893 Disable Hardware Transactional Memory
3895 print-fatal-signals=
3896 [KNL] debug: print fatal signals
3898 If enabled, warn about various signal handling
3899 related application anomalies: too many signals,
3900 too many POSIX.1 timers, fatal signals causing a
3903 If you hit the warning due to signal overflow,
3904 you might want to try "ulimit -i unlimited".
3908 printk.always_kmsg_dump=
3909 Trigger kmsg_dump for cases other than kernel oops or
3911 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3914 printk.devkmsg={on,off,ratelimit}
3915 Control writing to /dev/kmsg.
3916 on - unlimited logging to /dev/kmsg from userspace
3917 off - logging to /dev/kmsg disabled
3918 ratelimit - ratelimit the logging
3921 printk.time= Show timing data prefixed to each printk message line
3922 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3924 processor.max_cstate= [HW,ACPI]
3925 Limit processor to maximum C-state
3926 max_cstate=9 overrides any DMI blacklist limit.
3928 processor.nocst [HW,ACPI]
3929 Ignore the _CST method to determine C-states,
3930 instead using the legacy FADT method
3932 profile= [KNL] Enable kernel profiling via /proc/profile
3933 Format: [<profiletype>,]<number>
3934 Param: <profiletype>: "schedule", "sleep", or "kvm"
3935 [defaults to kernel profiling]
3936 Param: "schedule" - profile schedule points.
3937 Param: "sleep" - profile D-state sleeping (millisecs).
3938 Requires CONFIG_SCHEDSTATS
3939 Param: "kvm" - profile VM exits.
3940 Param: <number> - step/bucket size as a power of 2 for
3941 statistical time based profiling.
3943 prompt_ramdisk= [RAM] [Deprecated]
3945 prot_virt= [S390] enable hosting protected virtual machines
3946 isolated from the hypervisor (if hardware supports
3950 psi= [KNL] Enable or disable pressure stall information
3954 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3955 probe for; one of (bare|imps|exps|lifebook|any).
3956 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3958 psmouse.resetafter= [HW,MOUSE]
3959 Try to reset the device after so many bad packets
3962 [HW,MOUSE] Set desired mouse resolution, in dpi.
3963 psmouse.smartscroll=
3964 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3965 0 = disabled, 1 = enabled (default).
3967 pstore.backend= Specify the name of the pstore backend to use
3970 See Documentation/admin-guide/blockdev/paride.rst.
3972 pti= [X86-64] Control Page Table Isolation of user and
3973 kernel address spaces. Disabling this feature
3974 removes hardening, but improves performance of
3975 system calls and interrupts.
3977 on - unconditionally enable
3978 off - unconditionally disable
3979 auto - kernel detects whether your CPU model is
3980 vulnerable to issues that PTI mitigates
3982 Not specifying this option is equivalent to pti=auto.
3985 Equivalent to pti=off
3988 [KNL] Number of legacy pty's. Overwrites compiled-in
3991 quiet [KNL] Disable most log messages
3996 See Documentation/admin-guide/md.rst.
3998 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3999 See Documentation/admin-guide/blockdev/ramdisk.rst.
4001 ramdisk_start= [RAM] RAM disk image start address
4003 random.trust_cpu={on,off}
4004 [KNL] Enable or disable trusting the use of the
4005 CPU's random number generator (if available) to
4006 fully seed the kernel's CRNG. Default is controlled
4007 by CONFIG_RANDOM_TRUST_CPU.
4009 ras=option[,option,...] [KNL] RAS-specific options
4012 Disable the Correctable Errors Collector,
4013 see CONFIG_RAS_CEC help text.
4016 The argument is a cpu list, as described above,
4017 except that the string "all" can be used to
4018 specify every CPU on the system.
4020 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
4021 the specified list of CPUs to be no-callback CPUs.
4022 Invocation of these CPUs' RCU callbacks will be
4023 offloaded to "rcuox/N" kthreads created for that
4024 purpose, where "x" is "p" for RCU-preempt, and
4025 "s" for RCU-sched, and "N" is the CPU number.
4026 This reduces OS jitter on the offloaded CPUs,
4027 which can be useful for HPC and real-time
4028 workloads. It can also improve energy efficiency
4029 for asymmetric multiprocessors.
4032 Rather than requiring that offloaded CPUs
4033 (specified by rcu_nocbs= above) explicitly
4034 awaken the corresponding "rcuoN" kthreads,
4035 make these kthreads poll for callbacks.
4036 This improves the real-time response for the
4037 offloaded CPUs by relieving them of the need to
4038 wake up the corresponding kthread, but degrades
4039 energy efficiency by requiring that the kthreads
4040 periodically wake up to do the polling.
4042 rcutree.blimit= [KNL]
4043 Set maximum number of finished RCU callbacks to
4044 process in one batch.
4046 rcutree.dump_tree= [KNL]
4047 Dump the structure of the rcu_node combining tree
4048 out at early boot. This is used for diagnostic
4049 purposes, to verify correct tree setup.
4051 rcutree.gp_cleanup_delay= [KNL]
4052 Set the number of jiffies to delay each step of
4053 RCU grace-period cleanup.
4055 rcutree.gp_init_delay= [KNL]
4056 Set the number of jiffies to delay each step of
4057 RCU grace-period initialization.
4059 rcutree.gp_preinit_delay= [KNL]
4060 Set the number of jiffies to delay each step of
4061 RCU grace-period pre-initialization, that is,
4062 the propagation of recent CPU-hotplug changes up
4063 the rcu_node combining tree.
4065 rcutree.use_softirq= [KNL]
4066 If set to zero, move all RCU_SOFTIRQ processing to
4067 per-CPU rcuc kthreads. Defaults to a non-zero
4068 value, meaning that RCU_SOFTIRQ is used by default.
4069 Specify rcutree.use_softirq=0 to use rcuc kthreads.
4071 rcutree.rcu_fanout_exact= [KNL]
4072 Disable autobalancing of the rcu_node combining
4073 tree. This is used by rcutorture, and might
4074 possibly be useful for architectures having high
4075 cache-to-cache transfer latencies.
4077 rcutree.rcu_fanout_leaf= [KNL]
4078 Change the number of CPUs assigned to each
4079 leaf rcu_node structure. Useful for very
4080 large systems, which will choose the value 64,
4081 and for NUMA systems with large remote-access
4082 latencies, which will choose a value aligned
4083 with the appropriate hardware boundaries.
4085 rcutree.rcu_min_cached_objs= [KNL]
4086 Minimum number of objects which are cached and
4087 maintained per one CPU. Object size is equal
4088 to PAGE_SIZE. The cache allows to reduce the
4089 pressure to page allocator, also it makes the
4090 whole algorithm to behave better in low memory
4093 rcutree.jiffies_till_first_fqs= [KNL]
4094 Set delay from grace-period initialization to
4095 first attempt to force quiescent states.
4096 Units are jiffies, minimum value is zero,
4097 and maximum value is HZ.
4099 rcutree.jiffies_till_next_fqs= [KNL]
4100 Set delay between subsequent attempts to force
4101 quiescent states. Units are jiffies, minimum
4102 value is one, and maximum value is HZ.
4104 rcutree.jiffies_till_sched_qs= [KNL]
4105 Set required age in jiffies for a
4106 given grace period before RCU starts
4107 soliciting quiescent-state help from
4108 rcu_note_context_switch() and cond_resched().
4109 If not specified, the kernel will calculate
4110 a value based on the most recent settings
4111 of rcutree.jiffies_till_first_fqs
4112 and rcutree.jiffies_till_next_fqs.
4113 This calculated value may be viewed in
4114 rcutree.jiffies_to_sched_qs. Any attempt to set
4115 rcutree.jiffies_to_sched_qs will be cheerfully
4118 rcutree.kthread_prio= [KNL,BOOT]
4119 Set the SCHED_FIFO priority of the RCU per-CPU
4120 kthreads (rcuc/N). This value is also used for
4121 the priority of the RCU boost threads (rcub/N)
4122 and for the RCU grace-period kthreads (rcu_bh,
4123 rcu_preempt, and rcu_sched). If RCU_BOOST is
4124 set, valid values are 1-99 and the default is 1
4125 (the least-favored priority). Otherwise, when
4126 RCU_BOOST is not set, valid values are 0-99 and
4127 the default is zero (non-realtime operation).
4129 rcutree.rcu_nocb_gp_stride= [KNL]
4130 Set the number of NOCB callback kthreads in
4131 each group, which defaults to the square root
4132 of the number of CPUs. Larger numbers reduce
4133 the wakeup overhead on the global grace-period
4134 kthread, but increases that same overhead on
4135 each group's NOCB grace-period kthread.
4137 rcutree.qhimark= [KNL]
4138 Set threshold of queued RCU callbacks beyond which
4139 batch limiting is disabled.
4141 rcutree.qlowmark= [KNL]
4142 Set threshold of queued RCU callbacks below which
4143 batch limiting is re-enabled.
4145 rcutree.qovld= [KNL]
4146 Set threshold of queued RCU callbacks beyond which
4147 RCU's force-quiescent-state scan will aggressively
4148 enlist help from cond_resched() and sched IPIs to
4149 help CPUs more quickly reach quiescent states.
4150 Set to less than zero to make this be set based
4151 on rcutree.qhimark at boot time and to zero to
4152 disable more aggressive help enlistment.
4154 rcutree.rcu_idle_gp_delay= [KNL]
4155 Set wakeup interval for idle CPUs that have
4156 RCU callbacks (RCU_FAST_NO_HZ=y).
4158 rcutree.rcu_idle_lazy_gp_delay= [KNL]
4159 Set wakeup interval for idle CPUs that have
4160 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
4161 Lazy RCU callbacks are those which RCU can
4162 prove do nothing more than free memory.
4164 rcutree.rcu_kick_kthreads= [KNL]
4165 Cause the grace-period kthread to get an extra
4166 wake_up() if it sleeps three times longer than
4167 it should at force-quiescent-state time.
4168 This wake_up() will be accompanied by a
4169 WARN_ONCE() splat and an ftrace_dump().
4171 rcutree.sysrq_rcu= [KNL]
4172 Commandeer a sysrq key to dump out Tree RCU's
4173 rcu_node tree with an eye towards determining
4174 why a new grace period has not yet started.
4176 rcuperf.gp_async= [KNL]
4177 Measure performance of asynchronous
4178 grace-period primitives such as call_rcu().
4180 rcuperf.gp_async_max= [KNL]
4181 Specify the maximum number of outstanding
4182 callbacks per writer thread. When a writer
4183 thread exceeds this limit, it invokes the
4184 corresponding flavor of rcu_barrier() to allow
4185 previously posted callbacks to drain.
4187 rcuperf.gp_exp= [KNL]
4188 Measure performance of expedited synchronous
4189 grace-period primitives.
4191 rcuperf.holdoff= [KNL]
4192 Set test-start holdoff period. The purpose of
4193 this parameter is to delay the start of the
4194 test until boot completes in order to avoid
4197 rcuperf.kfree_rcu_test= [KNL]
4198 Set to measure performance of kfree_rcu() flooding.
4200 rcuperf.kfree_nthreads= [KNL]
4201 The number of threads running loops of kfree_rcu().
4203 rcuperf.kfree_alloc_num= [KNL]
4204 Number of allocations and frees done in an iteration.
4206 rcuperf.kfree_loops= [KNL]
4207 Number of loops doing rcuperf.kfree_alloc_num number
4208 of allocations and frees.
4210 rcuperf.nreaders= [KNL]
4211 Set number of RCU readers. The value -1 selects
4212 N, where N is the number of CPUs. A value
4213 "n" less than -1 selects N-n+1, where N is again
4214 the number of CPUs. For example, -2 selects N
4215 (the number of CPUs), -3 selects N+1, and so on.
4216 A value of "n" less than or equal to -N selects
4219 rcuperf.nwriters= [KNL]
4220 Set number of RCU writers. The values operate
4221 the same as for rcuperf.nreaders.
4222 N, where N is the number of CPUs
4224 rcuperf.perf_type= [KNL]
4225 Specify the RCU implementation to test.
4227 rcuperf.shutdown= [KNL]
4228 Shut the system down after performance tests
4229 complete. This is useful for hands-off automated
4232 rcuperf.verbose= [KNL]
4233 Enable additional printk() statements.
4235 rcuperf.writer_holdoff= [KNL]
4236 Write-side holdoff between grace periods,
4237 in microseconds. The default of zero says
4240 rcutorture.fqs_duration= [KNL]
4241 Set duration of force_quiescent_state bursts
4244 rcutorture.fqs_holdoff= [KNL]
4245 Set holdoff time within force_quiescent_state bursts
4248 rcutorture.fqs_stutter= [KNL]
4249 Set wait time between force_quiescent_state bursts
4252 rcutorture.fwd_progress= [KNL]
4253 Enable RCU grace-period forward-progress testing
4254 for the types of RCU supporting this notion.
4256 rcutorture.fwd_progress_div= [KNL]
4257 Specify the fraction of a CPU-stall-warning
4258 period to do tight-loop forward-progress testing.
4260 rcutorture.fwd_progress_holdoff= [KNL]
4261 Number of seconds to wait between successive
4262 forward-progress tests.
4264 rcutorture.fwd_progress_need_resched= [KNL]
4265 Enclose cond_resched() calls within checks for
4266 need_resched() during tight-loop forward-progress
4269 rcutorture.gp_cond= [KNL]
4270 Use conditional/asynchronous update-side
4271 primitives, if available.
4273 rcutorture.gp_exp= [KNL]
4274 Use expedited update-side primitives, if available.
4276 rcutorture.gp_normal= [KNL]
4277 Use normal (non-expedited) asynchronous
4278 update-side primitives, if available.
4280 rcutorture.gp_sync= [KNL]
4281 Use normal (non-expedited) synchronous
4282 update-side primitives, if available. If all
4283 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4284 rcutorture.gp_normal=, and rcutorture.gp_sync=
4285 are zero, rcutorture acts as if is interpreted
4286 they are all non-zero.
4288 rcutorture.n_barrier_cbs= [KNL]
4289 Set callbacks/threads for rcu_barrier() testing.
4291 rcutorture.nfakewriters= [KNL]
4292 Set number of concurrent RCU writers. These just
4293 stress RCU, they don't participate in the actual
4294 test, hence the "fake".
4296 rcutorture.nreaders= [KNL]
4297 Set number of RCU readers. The value -1 selects
4298 N-1, where N is the number of CPUs. A value
4299 "n" less than -1 selects N-n-2, where N is again
4300 the number of CPUs. For example, -2 selects N
4301 (the number of CPUs), -3 selects N+1, and so on.
4303 rcutorture.object_debug= [KNL]
4304 Enable debug-object double-call_rcu() testing.
4306 rcutorture.onoff_holdoff= [KNL]
4307 Set time (s) after boot for CPU-hotplug testing.
4309 rcutorture.onoff_interval= [KNL]
4310 Set time (jiffies) between CPU-hotplug operations,
4311 or zero to disable CPU-hotplug testing.
4313 rcutorture.read_exit= [KNL]
4314 Set the number of read-then-exit kthreads used
4315 to test the interaction of RCU updaters and
4316 task-exit processing.
4318 rcutorture.read_exit_burst= [KNL]
4319 The number of times in a given read-then-exit
4320 episode that a set of read-then-exit kthreads
4323 rcutorture.read_exit_delay= [KNL]
4324 The delay, in seconds, between successive
4325 read-then-exit testing episodes.
4327 rcutorture.shuffle_interval= [KNL]
4328 Set task-shuffle interval (s). Shuffling tasks
4329 allows some CPUs to go into dyntick-idle mode
4330 during the rcutorture test.
4332 rcutorture.shutdown_secs= [KNL]
4333 Set time (s) after boot system shutdown. This
4334 is useful for hands-off automated testing.
4336 rcutorture.stall_cpu= [KNL]
4337 Duration of CPU stall (s) to test RCU CPU stall
4338 warnings, zero to disable.
4340 rcutorture.stall_cpu_block= [KNL]
4341 Sleep while stalling if set. This will result
4342 in warnings from preemptible RCU in addition
4343 to any other stall-related activity.
4345 rcutorture.stall_cpu_holdoff= [KNL]
4346 Time to wait (s) after boot before inducing stall.
4348 rcutorture.stall_cpu_irqsoff= [KNL]
4349 Disable interrupts while stalling if set.
4351 rcutorture.stall_gp_kthread= [KNL]
4352 Duration (s) of forced sleep within RCU
4353 grace-period kthread to test RCU CPU stall
4354 warnings, zero to disable. If both stall_cpu
4355 and stall_gp_kthread are specified, the
4356 kthread is starved first, then the CPU.
4358 rcutorture.stat_interval= [KNL]
4359 Time (s) between statistics printk()s.
4361 rcutorture.stutter= [KNL]
4362 Time (s) to stutter testing, for example, specifying
4363 five seconds causes the test to run for five seconds,
4364 wait for five seconds, and so on. This tests RCU's
4365 ability to transition abruptly to and from idle.
4367 rcutorture.test_boost= [KNL]
4368 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4369 "Maybe" means test if the RCU implementation
4370 under test support RCU priority boosting.
4372 rcutorture.test_boost_duration= [KNL]
4373 Duration (s) of each individual boost test.
4375 rcutorture.test_boost_interval= [KNL]
4376 Interval (s) between each boost test.
4378 rcutorture.test_no_idle_hz= [KNL]
4379 Test RCU's dyntick-idle handling. See also the
4380 rcutorture.shuffle_interval parameter.
4382 rcutorture.torture_type= [KNL]
4383 Specify the RCU implementation to test.
4385 rcutorture.verbose= [KNL]
4386 Enable additional printk() statements.
4388 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4389 Dump ftrace buffer after reporting RCU CPU
4392 rcupdate.rcu_cpu_stall_suppress= [KNL]
4393 Suppress RCU CPU stall warning messages.
4395 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
4396 Suppress RCU CPU stall warning messages and
4397 rcutorture writer stall warnings that occur
4398 during early boot, that is, during the time
4399 before the init task is spawned.
4401 rcupdate.rcu_cpu_stall_timeout= [KNL]
4402 Set timeout for RCU CPU stall warning messages.
4404 rcupdate.rcu_expedited= [KNL]
4405 Use expedited grace-period primitives, for
4406 example, synchronize_rcu_expedited() instead
4407 of synchronize_rcu(). This reduces latency,
4408 but can increase CPU utilization, degrade
4409 real-time latency, and degrade energy efficiency.
4410 No effect on CONFIG_TINY_RCU kernels.
4412 rcupdate.rcu_normal= [KNL]
4413 Use only normal grace-period primitives,
4414 for example, synchronize_rcu() instead of
4415 synchronize_rcu_expedited(). This improves
4416 real-time latency, CPU utilization, and
4417 energy efficiency, but can expose users to
4418 increased grace-period latency. This parameter
4419 overrides rcupdate.rcu_expedited. No effect on
4420 CONFIG_TINY_RCU kernels.
4422 rcupdate.rcu_normal_after_boot= [KNL]
4423 Once boot has completed (that is, after
4424 rcu_end_inkernel_boot() has been invoked), use
4425 only normal grace-period primitives. No effect
4426 on CONFIG_TINY_RCU kernels.
4428 rcupdate.rcu_task_ipi_delay= [KNL]
4429 Set time in jiffies during which RCU tasks will
4430 avoid sending IPIs, starting with the beginning
4431 of a given grace period. Setting a large
4432 number avoids disturbing real-time workloads,
4433 but lengthens grace periods.
4435 rcupdate.rcu_task_stall_timeout= [KNL]
4436 Set timeout in jiffies for RCU task stall warning
4437 messages. Disable with a value less than or equal
4440 rcupdate.rcu_self_test= [KNL]
4441 Run the RCU early boot self tests
4445 Run specified binary instead of /init from the ramdisk,
4446 used for early userspace startup. See initrd.
4449 force - Override the decision by the kernel to hide the
4450 advertisement of RDRAND support (this affects
4451 certain AMD processors because of buggy BIOS
4452 support, specifically around the suspend/resume
4456 Turn on/off individual RDT features. List is:
4457 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4459 E.g. to turn on cmt and turn off mba use:
4463 Format (x86 or x86_64):
4464 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4466 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4468 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4469 (prefix with 'panic_' to set mode for panic
4471 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4472 reboot_force is either force or not specified,
4473 reboot_cpu is s[mp]#### with #### being the processor
4474 to be used for rebooting.
4476 refscale.holdoff= [KNL]
4477 Set test-start holdoff period. The purpose of
4478 this parameter is to delay the start of the
4479 test until boot completes in order to avoid
4482 refscale.loops= [KNL]
4483 Set the number of loops over the synchronization
4484 primitive under test. Increasing this number
4485 reduces noise due to loop start/end overhead,
4486 but the default has already reduced the per-pass
4487 noise to a handful of picoseconds on ca. 2020
4490 refscale.nreaders= [KNL]
4491 Set number of readers. The default value of -1
4492 selects N, where N is roughly 75% of the number
4493 of CPUs. A value of zero is an interesting choice.
4495 refscale.nruns= [KNL]
4496 Set number of runs, each of which is dumped onto
4499 refscale.readdelay= [KNL]
4500 Set the read-side critical-section duration,
4501 measured in microseconds.
4503 refscale.scale_type= [KNL]
4504 Specify the read-protection implementation to test.
4506 refscale.shutdown= [KNL]
4507 Shut down the system at the end of the performance
4508 test. This defaults to 1 (shut it down) when
4509 rcuperf is built into the kernel and to 0 (leave
4510 it running) when rcuperf is built as a module.
4512 refscale.verbose= [KNL]
4513 Enable additional printk() statements.
4516 [KNL, SMP] Set scheduler's default relax_domain_level.
4517 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4519 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4520 Format: <base1>,<size1>[,<base2>,<size2>,...]
4521 Reserve I/O ports or memory so the kernel won't use
4522 them. If <base> is less than 0x10000, the region
4523 is assumed to be I/O ports; otherwise it is memory.
4525 reservetop= [X86-32]
4527 Reserves a hole at the top of the kernel virtual
4532 Set the amount of memory to reserve for BIOS at
4533 the bottom of the address space.
4535 reset_devices [KNL] Force drivers to reset the underlying device
4536 during initialization.
4539 Specify the partition device for software suspend
4541 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4543 resume_offset= [SWSUSP]
4544 Specify the offset from the beginning of the partition
4545 given by "resume=" at which the swap header is located,
4546 in <PAGE_SIZE> units (needed only for swap files).
4547 See Documentation/power/swsusp-and-swap-files.rst
4549 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4550 read the resume files
4552 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4553 Useful for devices that are detected asynchronously
4554 (e.g. USB and MMC devices).
4556 hibernate= [HIBERNATION]
4557 noresume Don't check if there's a hibernation image
4558 present during boot.
4559 nocompress Don't compress/decompress hibernation images.
4560 no Disable hibernation and resume.
4561 protect_image Turn on image protection during restoration
4562 (that will set all pages holding image data
4563 during restoration read-only).
4565 retain_initrd [RAM] Keep initrd memory after extraction
4567 rfkill.default_state=
4568 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4569 etc. communication is blocked by default.
4572 rfkill.master_switch_mode=
4573 0 The "airplane mode" button does nothing.
4574 1 The "airplane mode" button toggles between everything
4575 blocked and the previous configuration.
4576 2 The "airplane mode" button toggles between everything
4577 blocked and everything unblocked.
4579 rhash_entries= [KNL,NET]
4580 Set number of hash buckets for route cache
4583 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4586 ro [KNL] Mount root device read-only on boot
4589 on Mark read-only kernel memory as read-only (default).
4590 off Leave read-only kernel memory writable for debugging.
4593 Enable the uart passthrough on the designated usb port
4594 on Rockchip SoCs. When active, the signals of the
4595 debug-uart get routed to the D+ and D- pins of the usb
4596 port and the regular usb controller gets disabled.
4598 root= [KNL] Root filesystem
4599 See name_to_dev_t comment in init/do_mounts.c.
4601 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4602 mount the root filesystem
4604 rootflags= [KNL] Set root filesystem mount option string
4606 rootfstype= [KNL] Set root filesystem type
4608 rootwait [KNL] Wait (indefinitely) for root device to show up.
4609 Useful for devices that are detected asynchronously
4610 (e.g. USB and MMC devices).
4612 rproc_mem=nn[KMG][@address]
4613 [KNL,ARM,CMA] Remoteproc physical memory block.
4614 Memory area to be used by remote processor image,
4617 rw [KNL] Mount root device read-write on boot
4619 S [KNL] Run init in single mode
4621 s390_iommu= [HW,S390]
4622 Set s390 IOTLB flushing mode
4624 With strict flushing every unmap operation will result in
4625 an IOTLB flush. Default is lazy flushing before reuse,
4629 See drivers/net/irda/sa1100_ir.c.
4631 sbni= [NET] Granch SBNI12 leased line adapter
4633 sched_debug [KNL] Enables verbose scheduler debug messages.
4635 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4636 Allowed values are enable and disable. This feature
4637 incurs a small amount of overhead in the scheduler
4638 but is useful for debugging and performance tuning.
4640 sched_thermal_decay_shift=
4641 [KNL, SMP] Set a decay shift for scheduler thermal
4642 pressure signal. Thermal pressure signal follows the
4643 default decay period of other scheduler pelt
4644 signals(usually 32 ms but configurable). Setting
4645 sched_thermal_decay_shift will left shift the decay
4646 period for the thermal pressure signal by the shift
4648 i.e. with the default pelt decay period of 32 ms
4649 sched_thermal_decay_shift thermal pressure decay pr
4653 Format: integer between 0 and 10
4656 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4657 xtime_lock contention on larger systems, and/or RCU lock
4658 contention on all systems with CONFIG_MAXSMP set.
4659 Format: { "0" | "1" }
4660 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4662 Note: increases power consumption, thus should only be
4663 enabled if running jitter sensitive (HPC/RT) workloads.
4665 security= [SECURITY] Choose a legacy "major" security module to
4666 enable at boot. This has been deprecated by the
4669 selinux= [SELINUX] Disable or enable SELinux at boot time.
4670 Format: { "0" | "1" }
4671 See security/selinux/Kconfig help text.
4676 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4677 Format: { "0" | "1" }
4678 See security/apparmor/Kconfig help text
4681 Default value is set via kernel config option.
4683 serialnumber [BUGS=X86-32]
4686 Maximal number of shapers.
4694 Disable merging of slabs with similar size. May be
4695 necessary if there is some reason to distinguish
4696 allocs to different slabs, especially in hardened
4697 environments where the risk of heap overflows and
4698 layout control by attackers can usually be
4699 frustrated by disabling merging. This will reduce
4700 most of the exposure of a heap attack to a single
4701 cache (risks via metadata attacks are mostly
4702 unchanged). Debug options disable merging on their
4704 For more information see Documentation/vm/slub.rst.
4706 slab_max_order= [MM, SLAB]
4707 Determines the maximum allowed order for slabs.
4708 A high setting may cause OOMs due to memory
4709 fragmentation. Defaults to 1 for systems with
4710 more than 32MB of RAM, 0 otherwise.
4712 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
4713 Enabling slub_debug allows one to determine the
4714 culprit if slab objects become corrupted. Enabling
4715 slub_debug can create guard zones around objects and
4716 may poison objects when not in use. Also tracks the
4717 last alloc / free. For more information see
4718 Documentation/vm/slub.rst.
4720 slub_memcg_sysfs= [MM, SLUB]
4721 Determines whether to enable sysfs directories for
4722 memory cgroup sub-caches. 1 to enable, 0 to disable.
4723 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4724 Enabling this can lead to a very high number of debug
4725 directories and files being created under
4728 slub_max_order= [MM, SLUB]
4729 Determines the maximum allowed order for slabs.
4730 A high setting may cause OOMs due to memory
4731 fragmentation. For more information see
4732 Documentation/vm/slub.rst.
4734 slub_min_objects= [MM, SLUB]
4735 The minimum number of objects per slab. SLUB will
4736 increase the slab order up to slub_max_order to
4737 generate a sufficiently large slab able to contain
4738 the number of objects indicated. The higher the number
4739 of objects the smaller the overhead of tracking slabs
4740 and the less frequently locks need to be acquired.
4741 For more information see Documentation/vm/slub.rst.
4743 slub_min_order= [MM, SLUB]
4744 Determines the minimum page order for slabs. Must be
4745 lower than slub_max_order.
4746 For more information see Documentation/vm/slub.rst.
4748 slub_nomerge [MM, SLUB]
4749 Same with slab_nomerge. This is supported for legacy.
4750 See slab_nomerge for more information.
4753 Format: <io1>[,<io2>[,...,<io8>]]
4755 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4756 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4757 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4758 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4759 smsc-ircc2.ircc_irq= [HW] IRQ line
4760 smsc-ircc2.ircc_dma= [HW] DMA channel
4761 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4762 0: Toshiba Satellite 1800 (GP data pin select)
4763 1: Fast pin select (default)
4766 smt [KNL,S390] Set the maximum number of threads (logical
4767 CPUs) to use per physical CPU on systems capable of
4768 symmetric multithreading (SMT). Will be capped to the
4769 actual hardware limit.
4771 Default: -1 (no limit)
4774 [KNL] Should the soft-lockup detector generate panics.
4777 A value of 1 instructs the soft-lockup detector
4778 to panic the machine when a soft-lockup occurs. It is
4779 also controlled by the kernel.softlockup_panic sysctl
4780 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
4781 respective build-time switch to that functionality.
4783 softlockup_all_cpu_backtrace=
4784 [KNL] Should the soft-lockup detector generate
4785 backtraces on all cpus.
4788 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4789 See Documentation/admin-guide/laptops/sonypi.rst
4791 spectre_v2= [X86] Control mitigation of Spectre variant 2
4792 (indirect branch speculation) vulnerability.
4793 The default operation protects the kernel from
4796 on - unconditionally enable, implies
4798 off - unconditionally disable, implies
4800 auto - kernel detects whether your CPU model is
4803 Selecting 'on' will, and 'auto' may, choose a
4804 mitigation method at run time according to the
4805 CPU, the available microcode, the setting of the
4806 CONFIG_RETPOLINE configuration option, and the
4807 compiler with which the kernel was built.
4809 Selecting 'on' will also enable the mitigation
4810 against user space to user space task attacks.
4812 Selecting 'off' will disable both the kernel and
4813 the user space protections.
4815 Specific mitigations can also be selected manually:
4817 retpoline - replace indirect branches
4818 retpoline,generic - google's original retpoline
4819 retpoline,amd - AMD-specific minimal thunk
4821 Not specifying this option is equivalent to
4825 [X86] Control mitigation of Spectre variant 2
4826 (indirect branch speculation) vulnerability between
4829 on - Unconditionally enable mitigations. Is
4830 enforced by spectre_v2=on
4832 off - Unconditionally disable mitigations. Is
4833 enforced by spectre_v2=off
4835 prctl - Indirect branch speculation is enabled,
4836 but mitigation can be enabled via prctl
4837 per thread. The mitigation control state
4838 is inherited on fork.
4841 - Like "prctl" above, but only STIBP is
4842 controlled per thread. IBPB is issued
4843 always when switching between different user
4847 - Same as "prctl" above, but all seccomp
4848 threads will enable the mitigation unless
4849 they explicitly opt out.
4852 - Like "seccomp" above, but only STIBP is
4853 controlled per thread. IBPB is issued
4854 always when switching between different
4855 user space processes.
4857 auto - Kernel selects the mitigation depending on
4858 the available CPU features and vulnerability.
4861 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4863 Not specifying this option is equivalent to
4864 spectre_v2_user=auto.
4866 spec_store_bypass_disable=
4867 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4868 (Speculative Store Bypass vulnerability)
4870 Certain CPUs are vulnerable to an exploit against a
4871 a common industry wide performance optimization known
4872 as "Speculative Store Bypass" in which recent stores
4873 to the same memory location may not be observed by
4874 later loads during speculative execution. The idea
4875 is that such stores are unlikely and that they can
4876 be detected prior to instruction retirement at the
4877 end of a particular speculation execution window.
4879 In vulnerable processors, the speculatively forwarded
4880 store can be used in a cache side channel attack, for
4881 example to read memory to which the attacker does not
4882 directly have access (e.g. inside sandboxed code).
4884 This parameter controls whether the Speculative Store
4885 Bypass optimization is used.
4887 On x86 the options are:
4889 on - Unconditionally disable Speculative Store Bypass
4890 off - Unconditionally enable Speculative Store Bypass
4891 auto - Kernel detects whether the CPU model contains an
4892 implementation of Speculative Store Bypass and
4893 picks the most appropriate mitigation. If the
4894 CPU is not vulnerable, "off" is selected. If the
4895 CPU is vulnerable the default mitigation is
4896 architecture and Kconfig dependent. See below.
4897 prctl - Control Speculative Store Bypass per thread
4898 via prctl. Speculative Store Bypass is enabled
4899 for a process by default. The state of the control
4900 is inherited on fork.
4901 seccomp - Same as "prctl" above, but all seccomp threads
4902 will disable SSB unless they explicitly opt out.
4904 Default mitigations:
4905 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4907 On powerpc the options are:
4909 on,auto - On Power8 and Power9 insert a store-forwarding
4910 barrier on kernel entry and exit. On Power7
4911 perform a software flush on kernel entry and
4915 Not specifying this option is equivalent to
4916 spec_store_bypass_disable=auto.
4918 spia_io_base= [HW,MTD]
4924 [X86] Enable split lock detection
4926 When enabled (and if hardware support is present), atomic
4927 instructions that access data across cache line
4928 boundaries will result in an alignment check exception.
4932 warn - the kernel will emit rate limited warnings
4933 about applications triggering the #AC
4934 exception. This mode is the default on CPUs
4935 that supports split lock detection.
4937 fatal - the kernel will send SIGBUS to applications
4938 that trigger the #AC exception.
4940 If an #AC exception is hit in the kernel or in
4941 firmware (i.e. not while executing in user mode)
4942 the kernel will oops in either "warn" or "fatal"
4946 Control the Special Register Buffer Data Sampling
4949 Certain CPUs are vulnerable to an MDS-like
4950 exploit which can leak bits from the random
4953 By default, this issue is mitigated by
4954 microcode. However, the microcode fix can cause
4955 the RDRAND and RDSEED instructions to become
4956 much slower. Among other effects, this will
4957 result in reduced throughput from /dev/urandom.
4959 The microcode mitigation can be disabled with
4960 the following option:
4962 off: Disable mitigation and remove
4963 performance impact to RDRAND and RDSEED
4965 srcutree.counter_wrap_check [KNL]
4966 Specifies how frequently to check for
4967 grace-period sequence counter wrap for the
4968 srcu_data structure's ->srcu_gp_seq_needed field.
4969 The greater the number of bits set in this kernel
4970 parameter, the less frequently counter wrap will
4971 be checked for. Note that the bottom two bits
4974 srcutree.exp_holdoff [KNL]
4975 Specifies how many nanoseconds must elapse
4976 since the end of the last SRCU grace period for
4977 a given srcu_struct until the next normal SRCU
4978 grace period will be considered for automatic
4979 expediting. Set to zero to disable automatic
4983 Speculative Store Bypass Disable control
4985 On CPUs that are vulnerable to the Speculative
4986 Store Bypass vulnerability and offer a
4987 firmware based mitigation, this parameter
4988 indicates how the mitigation should be used:
4990 force-on: Unconditionally enable mitigation for
4991 for both kernel and userspace
4992 force-off: Unconditionally disable mitigation for
4993 for both kernel and userspace
4994 kernel: Always enable mitigation in the
4995 kernel, and offer a prctl interface
4996 to allow userspace to register its
4997 interest in being mitigated too.
4999 stack_guard_gap= [MM]
5000 override the default stack gap protection. The value
5001 is in page units and it defines how many pages prior
5002 to (for stacks growing down) resp. after (for stacks
5003 growing up) the main stack are reserved for no other
5004 mapping. Default value is 256 pages.
5007 Enabled the stack tracer on boot up.
5009 stacktrace_filter=[function-list]
5010 [FTRACE] Limit the functions that the stack tracer
5011 will trace at boot up. function-list is a comma separated
5012 list of functions. This list can be changed at run
5013 time by the stack_trace_filter file in the debugfs
5014 tracing directory. Note, this enables stack tracing
5015 and the stacktrace above is not needed.
5019 Set the STI (builtin display/keyboard on the HP-PARISC
5020 machines) console (graphic card) which should be used
5021 as the initial boot-console.
5022 See also comment in drivers/video/console/sticore.c.
5025 See comment in drivers/video/console/sticore.c.
5028 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
5030 sunrpc.min_resvport=
5031 sunrpc.max_resvport=
5033 SunRPC servers often require that client requests
5034 originate from a privileged port (i.e. a port in the
5035 range 0 < portnr < 1024).
5036 An administrator who wishes to reserve some of these
5037 ports for other uses may adjust the range that the
5038 kernel's sunrpc client considers to be privileged
5039 using these two parameters to set the minimum and
5040 maximum port values.
5042 sunrpc.svc_rpc_per_connection_limit=
5044 Limit the number of requests that the server will
5045 process in parallel from a single connection.
5046 The default value is 0 (no limit).
5050 Control how the NFS server code allocates CPUs to
5051 service thread pools. Depending on how many NICs
5052 you have and where their interrupts are bound, this
5053 option will affect which CPUs will do NFS serving.
5054 Note: this parameter cannot be changed while the
5055 NFS server is running.
5057 auto the server chooses an appropriate mode
5058 automatically using heuristics
5059 global a single global pool contains all CPUs
5060 percpu one pool for each CPU
5061 pernode one pool for each NUMA node (equivalent
5062 to global on non-NUMA machines)
5064 sunrpc.tcp_slot_table_entries=
5065 sunrpc.udp_slot_table_entries=
5067 Sets the upper limit on the number of simultaneous
5068 RPC calls that can be sent from the client to a
5069 server. Increasing these values may allow you to
5070 improve throughput, but will also increase the
5071 amount of memory reserved for use by the client.
5073 suspend.pm_test_delay=
5075 Sets the number of seconds to remain in a suspend test
5076 mode before resuming the system (see
5077 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
5078 is set. Default value is 5.
5081 Format: { on | off | y | n | 1 | 0 }
5082 This parameter controls use of the Protected
5083 Execution Facility on pSeries.
5086 [KNL] Enable accounting of swap in memory resource
5087 controller if no parameter or 1 is given or disable
5088 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
5090 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
5091 Format: { <int> | force | noforce }
5092 <int> -- Number of I/O TLB slabs
5093 force -- force using of bounce buffers even if they
5094 wouldn't be automatically used by the kernel
5095 noforce -- Never use bounce buffers (for debugging)
5100 Set a sysctl parameter, right before loading the init
5101 process, as if the value was written to the respective
5102 /proc/sys/... file. Both '.' and '/' are recognized as
5103 separators. Unrecognized parameters and invalid values
5104 are reported in the kernel log. Sysctls registered
5105 later by a loaded module cannot be set this way.
5106 Example: sysctl.vm.swappiness=40
5108 sysfs.deprecated=0|1 [KNL]
5109 Enable/disable old style sysfs layout for old udev
5110 on older distributions. When this option is enabled
5111 very new udev will not work anymore. When this option
5112 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
5113 in older udev will not work anymore.
5114 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
5115 the kernel configuration.
5117 sysrq_always_enabled
5119 Ignore sysrq setting - this boot parameter will
5120 neutralize any effect of /proc/sys/kernel/sysrq.
5121 Useful for debugging.
5123 tcpmhash_entries= [KNL,NET]
5124 Set the number of tcp_metrics_hash slots.
5125 Default value is 8192 or 16384 depending on total
5126 ram pages. This is used to specify the TCP metrics
5127 cache size. See Documentation/networking/ip-sysctl.rst
5128 "tcp_no_metrics_save" section for more details.
5132 test_suspend= [SUSPEND][,N]
5133 Specify "mem" (for Suspend-to-RAM) or "standby" (for
5134 standby suspend) or "freeze" (for suspend type freeze)
5135 as the system sleep state during system startup with
5136 the optional capability to repeat N number of times.
5137 The system is woken from this state using a
5138 wakeup-capable RTC alarm.
5140 thash_entries= [KNL,NET]
5141 Set number of hash buckets for TCP connection
5143 thermal.act= [HW,ACPI]
5144 -1: disable all active trip points in all thermal zones
5145 <degrees C>: override all lowest active trip points
5147 thermal.crt= [HW,ACPI]
5148 -1: disable all critical trip points in all thermal zones
5149 <degrees C>: override all critical trip points
5151 thermal.nocrt= [HW,ACPI]
5152 Set to disable actions on ACPI thermal zone
5153 critical and hot trip points.
5155 thermal.off= [HW,ACPI]
5156 1: disable ACPI thermal control
5158 thermal.psv= [HW,ACPI]
5159 -1: disable all passive trip points
5160 <degrees C>: override all passive trip points to this
5163 thermal.tzp= [HW,ACPI]
5164 Specify global default ACPI thermal zone polling rate
5165 <deci-seconds>: poll all this frequency
5166 0: no polling (default)
5169 Force threading of all interrupt handlers except those
5170 marked explicitly IRQF_NO_THREAD.
5174 Specify if the kernel should make use of the cpu
5175 topology information if the hardware supports this.
5176 The scheduler will make use of this information and
5177 e.g. base its process migration decisions on it.
5180 topology_updates= [KNL, PPC, NUMA]
5182 Specify if the kernel should ignore (off)
5183 topology updates sent by the hypervisor to this
5186 torture.disable_onoff_at_boot= [KNL]
5187 Prevent the CPU-hotplug component of torturing
5188 until after init has spawned.
5190 torture.ftrace_dump_at_shutdown= [KNL]
5191 Dump the ftrace buffer at torture-test shutdown,
5192 even if there were no errors. This can be a
5193 very costly operation when many torture tests
5194 are running concurrently, especially on systems
5195 with rotating-rust storage.
5199 tpm_suspend_pcr=[HW,TPM]
5200 Format: integer pcr id
5201 Specify that at suspend time, the tpm driver
5202 should extend the specified pcr with zeros,
5203 as a workaround for some chips which fail to
5204 flush the last written pcr on TPM_SaveState.
5205 This will guarantee that all the other pcrs
5208 trace_buf_size=nn[KMG]
5209 [FTRACE] will set tracing buffer size on each cpu.
5211 trace_event=[event-list]
5212 [FTRACE] Set and start specified trace events in order
5213 to facilitate early boot debugging. The event-list is a
5214 comma separated list of trace events to enable. See
5215 also Documentation/trace/events.rst
5217 trace_options=[option-list]
5218 [FTRACE] Enable or disable tracer options at boot.
5219 The option-list is a comma delimited list of options
5220 that can be enabled or disabled just as if you were
5221 to echo the option name into
5223 /sys/kernel/debug/tracing/trace_options
5225 For example, to enable stacktrace option (to dump the
5226 stack trace of each event), add to the command line:
5228 trace_options=stacktrace
5230 See also Documentation/trace/ftrace.rst "trace options"
5234 Have the tracepoints sent to printk as well as the
5235 tracing ring buffer. This is useful for early boot up
5236 where the system hangs or reboots and does not give the
5237 option for reading the tracing buffer or performing a
5238 ftrace_dump_on_oops.
5240 To turn off having tracepoints sent to printk,
5241 echo 0 > /proc/sys/kernel/tracepoint_printk
5242 Note, echoing 1 into this file without the
5243 tracepoint_printk kernel cmdline option has no effect.
5247 Having tracepoints sent to printk() and activating high
5248 frequency tracepoints such as irq or sched, can cause
5249 the system to live lock.
5252 [FTRACE] enable this option to disable tracing when a
5253 warning is hit. This turns off "tracing_on". Tracing can
5254 be enabled again by echoing '1' into the "tracing_on"
5255 file located in /sys/kernel/debug/tracing/
5257 This option is useful, as it disables the trace before
5258 the WARNING dump is called, which prevents the trace to
5259 be filled with content caused by the warning output.
5261 This option can also be set at run time via the sysctl
5262 option: kernel/traceoff_on_warning
5264 transparent_hugepage=
5266 Format: [always|madvise|never]
5267 Can be used to control the default behavior of the system
5268 with respect to transparent hugepages.
5269 See Documentation/admin-guide/mm/transhuge.rst
5272 tsc= Disable clocksource stability checks for TSC.
5274 [x86] reliable: mark tsc clocksource as reliable, this
5275 disables clocksource verification at runtime, as well
5276 as the stability checks done at bootup. Used to enable
5277 high-resolution timer mode on older hardware, and in
5278 virtualized environment.
5279 [x86] noirqtime: Do not use TSC to do irq accounting.
5280 Used to run time disable IRQ_TIME_ACCOUNTING on any
5281 platforms where RDTSC is slow and this accounting
5283 [x86] unstable: mark the TSC clocksource as unstable, this
5284 marks the TSC unconditionally unstable at bootup and
5285 avoids any further wobbles once the TSC watchdog notices.
5286 [x86] nowatchdog: disable clocksource watchdog. Used
5287 in situations with strict latency requirements (where
5288 interruptions from clocksource watchdog are not
5291 tsc_early_khz= [X86] Skip early TSC calibration and use the given
5292 value instead. Useful when the early TSC frequency discovery
5293 procedure is not reliable, such as on overclocked systems
5294 with CPUID.16h support and partial CPUID.15h support.
5295 Format: <unsigned int>
5297 tsx= [X86] Control Transactional Synchronization
5298 Extensions (TSX) feature in Intel processors that
5299 support TSX control.
5301 This parameter controls the TSX feature. The options are:
5303 on - Enable TSX on the system. Although there are
5304 mitigations for all known security vulnerabilities,
5305 TSX has been known to be an accelerator for
5306 several previous speculation-related CVEs, and
5307 so there may be unknown security risks associated
5308 with leaving it enabled.
5310 off - Disable TSX on the system. (Note that this
5311 option takes effect only on newer CPUs which are
5312 not vulnerable to MDS, i.e., have
5313 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
5314 the new IA32_TSX_CTRL MSR through a microcode
5315 update. This new MSR allows for the reliable
5316 deactivation of the TSX functionality.)
5318 auto - Disable TSX if X86_BUG_TAA is present,
5319 otherwise enable TSX on the system.
5321 Not specifying this option is equivalent to tsx=off.
5323 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5326 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
5327 Abort (TAA) vulnerability.
5329 Similar to Micro-architectural Data Sampling (MDS)
5330 certain CPUs that support Transactional
5331 Synchronization Extensions (TSX) are vulnerable to an
5332 exploit against CPU internal buffers which can forward
5333 information to a disclosure gadget under certain
5336 In vulnerable processors, the speculatively forwarded
5337 data can be used in a cache side channel attack, to
5338 access data to which the attacker does not have direct
5341 This parameter controls the TAA mitigation. The
5344 full - Enable TAA mitigation on vulnerable CPUs
5347 full,nosmt - Enable TAA mitigation and disable SMT on
5348 vulnerable CPUs. If TSX is disabled, SMT
5349 is not disabled because CPU is not
5350 vulnerable to cross-thread TAA attacks.
5351 off - Unconditionally disable TAA mitigation
5353 On MDS-affected machines, tsx_async_abort=off can be
5354 prevented by an active MDS mitigation as both vulnerabilities
5355 are mitigated with the same mechanism so in order to disable
5356 this mitigation, you need to specify mds=off too.
5358 Not specifying this option is equivalent to
5359 tsx_async_abort=full. On CPUs which are MDS affected
5360 and deploy MDS mitigation, TAA mitigation is not
5361 required and doesn't provide any additional
5365 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5367 turbografx.map[2|3]= [HW,JOY]
5368 TurboGraFX parallel port interface
5370 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
5371 See also Documentation/input/devices/joystick-parport.rst
5373 udbg-immortal [PPC] When debugging early kernel crashes that
5374 happen after console_init() and before a proper
5375 console driver takes over, this boot options might
5376 help "seeing" what's going on.
5378 uhash_entries= [KNL,NET]
5379 Set number of hash buckets for UDP/UDP-Lite connections
5382 [USB] Ignore overcurrent events (default N).
5383 Some badly-designed motherboards generate lots of
5384 bogus events, for ports that aren't wired to
5385 anything. Set this parameter to avoid log spamming.
5386 Note that genuine overcurrent events won't be
5390 [X86] Cause panic on unknown NMI.
5392 usbcore.authorized_default=
5393 [USB] Default USB device authorization:
5394 (default -1 = authorized except for wireless USB,
5395 0 = not authorized, 1 = authorized, 2 = authorized
5396 if device connected to internal port)
5398 usbcore.autosuspend=
5399 [USB] The autosuspend time delay (in seconds) used
5400 for newly-detected USB devices (default 2). This
5401 is the time required before an idle device will be
5402 autosuspended. Devices for which the delay is set
5403 to a negative value won't be autosuspended at all.
5405 usbcore.usbfs_snoop=
5406 [USB] Set to log all usbfs traffic (default 0 = off).
5408 usbcore.usbfs_snoop_max=
5409 [USB] Maximum number of bytes to snoop in each URB
5412 usbcore.blinkenlights=
5413 [USB] Set to cycle leds on hubs (default 0 = off).
5415 usbcore.old_scheme_first=
5416 [USB] Start with the old device initialization
5417 scheme (default 0 = off).
5419 usbcore.usbfs_memory_mb=
5420 [USB] Memory limit (in MB) for buffers allocated by
5421 usbfs (default = 16, 0 = max = 2047).
5423 usbcore.use_both_schemes=
5424 [USB] Try the other device initialization scheme
5425 if the first one fails (default 1 = enabled).
5427 usbcore.initial_descriptor_timeout=
5428 [USB] Specifies timeout for the initial 64-byte
5429 USB_REQ_GET_DESCRIPTOR request in milliseconds
5430 (default 5000 = 5.0 seconds).
5432 usbcore.nousb [USB] Disable the USB subsystem
5435 [USB] A list of quirk entries to augment the built-in
5436 usb core quirk list. List entries are separated by
5437 commas. Each entry has the form
5438 VendorID:ProductID:Flags. The IDs are 4-digit hex
5439 numbers and Flags is a set of letters. Each letter
5440 will change the built-in quirk; setting it if it is
5441 clear and clearing it if it is set. The letters have
5442 the following meanings:
5443 a = USB_QUIRK_STRING_FETCH_255 (string
5444 descriptors must not be fetched using
5446 b = USB_QUIRK_RESET_RESUME (device can't resume
5447 correctly so reset it instead);
5448 c = USB_QUIRK_NO_SET_INTF (device can't handle
5449 Set-Interface requests);
5450 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
5451 handle its Configuration or Interface
5453 e = USB_QUIRK_RESET (device can't be reset
5454 (e.g morph devices), don't use reset);
5455 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
5456 more interface descriptions than the
5457 bNumInterfaces count, and can't handle
5458 talking to these interfaces);
5459 g = USB_QUIRK_DELAY_INIT (device needs a pause
5460 during initialization, after we read
5461 the device descriptor);
5462 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
5463 high speed and super speed interrupt
5464 endpoints, the USB 2.0 and USB 3.0 spec
5465 require the interval in microframes (1
5466 microframe = 125 microseconds) to be
5467 calculated as interval = 2 ^
5469 Devices with this quirk report their
5470 bInterval as the result of this
5471 calculation instead of the exponent
5472 variable used in the calculation);
5473 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
5474 handle device_qualifier descriptor
5476 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
5477 generates spurious wakeup, ignore
5478 remote wakeup capability);
5479 k = USB_QUIRK_NO_LPM (device can't handle Link
5481 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
5482 (Device reports its bInterval as linear
5483 frames instead of the USB 2.0
5485 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
5486 to be disconnected before suspend to
5487 prevent spurious wakeup);
5488 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
5489 pause after every control message);
5490 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
5491 delay after resetting its port);
5492 Example: quirks=0781:5580:bk,0a5c:5834:gij
5495 [USBHID] The interval which mice are to be polled at.
5498 [USBHID] The interval which joysticks are to be polled at.
5501 [USBHID] The interval which keyboards are to be polled at.
5503 usb-storage.delay_use=
5504 [UMS] The delay in seconds before a new device is
5505 scanned for Logical Units (default 1).
5508 [UMS] A list of quirks entries to supplement or
5509 override the built-in unusual_devs list. List
5510 entries are separated by commas. Each entry has
5511 the form VID:PID:Flags where VID and PID are Vendor
5512 and Product ID values (4-digit hex numbers) and
5513 Flags is a set of characters, each corresponding
5514 to a common usb-storage quirk flag as follows:
5515 a = SANE_SENSE (collect more than 18 bytes
5516 of sense data, not on uas);
5517 b = BAD_SENSE (don't collect more than 18
5518 bytes of sense data, not on uas);
5519 c = FIX_CAPACITY (decrease the reported
5520 device capacity by one sector);
5521 d = NO_READ_DISC_INFO (don't use
5522 READ_DISC_INFO command, not on uas);
5523 e = NO_READ_CAPACITY_16 (don't use
5524 READ_CAPACITY_16 command);
5525 f = NO_REPORT_OPCODES (don't use report opcodes
5527 g = MAX_SECTORS_240 (don't transfer more than
5528 240 sectors at a time, uas only);
5529 h = CAPACITY_HEURISTICS (decrease the
5530 reported device capacity by one
5531 sector if the number is odd);
5532 i = IGNORE_DEVICE (don't bind to this
5534 j = NO_REPORT_LUNS (don't use report luns
5536 l = NOT_LOCKABLE (don't try to lock and
5537 unlock ejectable media, not on uas);
5538 m = MAX_SECTORS_64 (don't transfer more
5539 than 64 sectors = 32 KB at a time,
5541 n = INITIAL_READ10 (force a retry of the
5542 initial READ(10) command, not on uas);
5543 o = CAPACITY_OK (accept the capacity
5544 reported by the device, not on uas);
5545 p = WRITE_CACHE (the device cache is ON
5546 by default, not on uas);
5547 r = IGNORE_RESIDUE (the device reports
5548 bogus residue values, not on uas);
5549 s = SINGLE_LUN (the device has only one
5551 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
5552 commands, uas only);
5553 u = IGNORE_UAS (don't bind to the uas driver);
5554 w = NO_WP_DETECT (don't test whether the
5555 medium is write-protected).
5556 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
5557 even if the device claims no cache,
5559 Example: quirks=0419:aaf5:rl,0421:0433:rc
5561 user_debug= [KNL,ARM]
5563 See arch/arm/Kconfig.debug help text.
5564 1 - undefined instruction events
5566 4 - invalid data aborts
5569 Example: user_debug=31
5572 [X86] Flags controlling user PTE allocations.
5574 nohigh = do not allocate PTE pages in
5575 HIGHMEM regardless of setting
5579 On X86_32, this is an alias for vdso32=. Otherwise:
5581 vdso=1: enable VDSO (the default)
5582 vdso=0: disable VDSO mapping
5584 vdso32= [X86] Control the 32-bit vDSO
5585 vdso32=1: enable 32-bit VDSO
5586 vdso32=0 or vdso32=2: disable 32-bit VDSO
5588 See the help text for CONFIG_COMPAT_VDSO for more
5589 details. If CONFIG_COMPAT_VDSO is set, the default is
5590 vdso32=0; otherwise, the default is vdso32=1.
5592 For compatibility with older kernels, vdso32=2 is an
5595 Try vdso32=0 if you encounter an error that says:
5596 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
5599 vector=percpu: enable percpu vector domain
5601 video= [FB] Frame buffer configuration
5602 See Documentation/fb/modedb.rst.
5604 video.brightness_switch_enabled= [0,1]
5605 If set to 1, on receiving an ACPI notify event
5606 generated by hotkey, video driver will adjust brightness
5607 level and then send out the event to user space through
5608 the allocated input device; If set to 0, video driver
5609 will only send out the event without touching backlight
5614 [VMMIO] Memory mapped virtio (platform) device.
5616 <size>@<baseaddr>:<irq>[:<id>]
5618 <size> := size (can use standard suffixes
5620 <baseaddr> := physical base address
5621 <irq> := interrupt number (as passed to
5623 <id> := (optional) platform device id
5625 virtio_mmio.device=1K@0x100b0000:48:7
5627 Can be used multiple times for multiple devices.
5629 vga= [BOOT,X86-32] Select a particular video mode
5630 See Documentation/x86/boot.rst and
5631 Documentation/admin-guide/svga.rst.
5632 Use vga=ask for menu.
5633 This is actually a boot loader parameter; the value is
5634 passed to the kernel using a special protocol.
5636 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
5637 May slow down system boot speed, especially when
5638 enabled on systems with a large amount of memory.
5639 All options are enabled by default, and this
5640 interface is meant to allow for selectively
5641 enabling or disabling specific virtual memory
5644 Available options are:
5645 P Enable page structure init time poisoning
5646 - Disable all of the above options
5648 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
5649 size of <nn>. This can be used to increase the
5650 minimum size (128MB on x86). It can also be used to
5651 decrease the size and leave more room for directly
5654 vmcp_cma=nn[MG] [KNL,S390]
5655 Sets the memory size reserved for contiguous memory
5656 allocations for the vmcp device driver.
5658 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5661 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5664 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
5668 Controls the behavior of vsyscalls (i.e. calls to
5669 fixed addresses of 0xffffffffff600x00 from legacy
5670 code). Most statically-linked binaries and older
5671 versions of glibc use these calls. Because these
5672 functions are at fixed addresses, they make nice
5673 targets for exploits that can control RIP.
5675 emulate [default] Vsyscalls turn into traps and are
5676 emulated reasonably safely. The vsyscall
5679 xonly Vsyscalls turn into traps and are
5680 emulated reasonably safely. The vsyscall
5681 page is not readable.
5683 none Vsyscalls don't work at all. This makes
5684 them quite hard to use for exploits but
5685 might break your system.
5687 vt.color= [VT] Default text color.
5688 Format: 0xYX, X = foreground, Y = background.
5689 Default: 0x07 = light gray on black.
5691 vt.cur_default= [VT] Default cursor shape.
5692 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5693 the parameters of the <Esc>[?A;B;Cc escape sequence;
5694 see VGA-softcursor.txt. Default: 2 = underline.
5696 vt.default_blu= [VT]
5697 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5698 Change the default blue palette of the console.
5699 This is a 16-member array composed of values
5702 vt.default_grn= [VT]
5703 Format: <green0>,<green1>,<green2>,...,<green15>
5704 Change the default green palette of the console.
5705 This is a 16-member array composed of values
5708 vt.default_red= [VT]
5709 Format: <red0>,<red1>,<red2>,...,<red15>
5710 Change the default red palette of the console.
5711 This is a 16-member array composed of values
5717 Set system-wide default UTF-8 mode for all tty's.
5718 Default is 1, i.e. UTF-8 mode is enabled for all
5719 newly opened terminals.
5721 vt.global_cursor_default=
5724 Set system-wide default for whether a cursor
5725 is shown on new VTs. Default is -1,
5726 i.e. cursors will be created by default unless
5727 overridden by individual drivers. 0 will hide
5728 cursors, 1 will display them.
5730 vt.italic= [VT] Default color for italic text; 0-15.
5733 vt.underline= [VT] Default color for underlined text; 0-15.
5736 watchdog timers [HW,WDT] For information on watchdog timers,
5737 see Documentation/watchdog/watchdog-parameters.rst
5738 or other driver-specific files in the
5739 Documentation/watchdog/ directory.
5743 Set the hard lockup detector stall duration
5744 threshold in seconds. The soft lockup detector
5745 threshold is set to twice the value. A value of 0
5746 disables both lockup detectors. Default is 10
5749 workqueue.watchdog_thresh=
5750 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5751 warn stall conditions and dump internal state to
5752 help debugging. 0 disables workqueue stall
5753 detection; otherwise, it's the stall threshold
5754 duration in seconds. The default value is 30 and
5755 it can be updated at runtime by writing to the
5756 corresponding sysfs file.
5758 workqueue.disable_numa
5759 By default, all work items queued to unbound
5760 workqueues are affine to the NUMA nodes they're
5761 issued on, which results in better behavior in
5762 general. If NUMA affinity needs to be disabled for
5763 whatever reason, this option can be used. Note
5764 that this also can be controlled per-workqueue for
5765 workqueues visible under /sys/bus/workqueue/.
5767 workqueue.power_efficient
5768 Per-cpu workqueues are generally preferred because
5769 they show better performance thanks to cache
5770 locality; unfortunately, per-cpu workqueues tend to
5771 be more power hungry than unbound workqueues.
5773 Enabling this makes the per-cpu workqueues which
5774 were observed to contribute significantly to power
5775 consumption unbound, leading to measurably lower
5776 power usage at the cost of small performance
5779 The default value of this parameter is determined by
5780 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5782 workqueue.debug_force_rr_cpu
5783 Workqueue used to implicitly guarantee that work
5784 items queued without explicit CPU specified are put
5785 on the local CPU. This guarantee is no longer true
5786 and while local CPU is still preferred work items
5787 may be put on foreign CPUs. This debug option
5788 forces round-robin CPU selection to flush out
5789 usages which depend on the now broken guarantee.
5790 When enabled, memory and cache locality will be
5793 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5794 default x2apic cluster mode on platforms
5797 x86_intel_mid_timer= [X86-32,APBT]
5798 Choose timer option for x86 Intel MID platform.
5799 Two valid options are apbt timer only and lapic timer
5800 plus one apbt timer for broadcast timer.
5801 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5803 xen_512gb_limit [KNL,X86-64,XEN]
5804 Restricts the kernel running paravirtualized under Xen
5805 to use only up to 512 GB of RAM. The reason to do so is
5806 crash analysis tools and Xen tools for doing domain
5807 save/restore/migration must be enabled to handle larger
5810 xen_emul_unplug= [HW,X86,XEN]
5811 Unplug Xen emulated devices
5812 Format: [unplug0,][unplug1]
5813 ide-disks -- unplug primary master IDE devices
5814 aux-ide-disks -- unplug non-primary-master IDE devices
5815 nics -- unplug network devices
5816 all -- unplug all emulated devices (NICs and IDE disks)
5817 unnecessary -- unplugging emulated devices is
5818 unnecessary even if the host did not respond to
5820 never -- do not unplug even if version check succeeds
5822 xen_legacy_crash [X86,XEN]
5823 Crash from Xen panic notifier, without executing late
5824 panic() code such as dumping handler.
5826 xen_nopvspin [X86,XEN]
5827 Disables the qspinlock slowpath using Xen PV optimizations.
5828 This parameter is obsoleted by "nopvspin" parameter, which
5829 has equivalent effect for XEN platform.
5832 Disables the PV optimizations forcing the HVM guest to
5833 run as generic HVM guest with no PV drivers.
5834 This option is obsoleted by the "nopv" option, which
5835 has equivalent effect for XEN platform.
5837 xen_scrub_pages= [XEN]
5838 Boolean option to control scrubbing pages before giving them back
5839 to Xen, for use by other domains. Can be also changed at runtime
5840 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5841 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5843 xen_timer_slop= [X86-64,XEN]
5844 Set the timer slop (in nanoseconds) for the virtual Xen
5845 timers (default is 100000). This adjusts the minimum
5846 delta of virtualized Xen timers, where lower values
5847 improve timer resolution at the expense of processing
5848 more timer interrupts.
5850 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
5851 Disables the PV optimizations forcing the guest to run
5852 as generic guest with no PV drivers. Currently support
5853 XEN HVM, KVM, HYPER_V and VMWARE guest.
5855 nopvspin [X86,XEN,KVM]
5856 Disables the qspinlock slow path using PV optimizations
5857 which allow the hypervisor to 'idle' the guest on lock
5860 xirc2ps_cs= [NET,PCMCIA]
5862 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5865 By default on POWER9 and above, the kernel will
5866 natively use the XIVE interrupt controller. This option
5867 allows the fallback firmware mode to be used:
5869 off Fallback to firmware control of XIVE interrupt
5870 controller on both pseries and powernv
5871 platforms. Only useful on POWER9 and above.
5873 xhci-hcd.quirks [USB,KNL]
5874 A hex value specifying bitmask with supplemental xhci
5875 host controller quirks. Meaning of each bit can be
5876 consulted in header drivers/usb/host/xhci.h.
5879 Format: { early | on | rw | ro | off }
5880 Controls if xmon debugger is enabled. Default is off.
5881 Passing only "xmon" is equivalent to "xmon=early".
5882 early Call xmon as early as possible on boot; xmon
5883 debugger is called from setup_arch().
5884 on xmon debugger hooks will be installed so xmon
5885 is only called on a kernel crash. Default mode,
5886 i.e. either "ro" or "rw" mode, is controlled
5887 with CONFIG_XMON_DEFAULT_RO_MODE.
5888 rw xmon debugger hooks will be installed so xmon
5889 is called only on a kernel crash, mode is write,
5890 meaning SPR registers, memory and, other data
5891 can be written using xmon commands.
5892 ro same as "rw" option above but SPR registers,
5893 memory, and other data can't be written using
5895 off xmon is disabled.
projects / linux-2.6-microblaze.git / blob