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_EVENTS
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 AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_no_watchdog [HW,ACPI,WDT]
140 Ignore the ACPI-based watchdog interface (WDAT) and let
141 a native driver control the watchdog device instead.
143 acpi_rsdp= [ACPI,EFI,KEXEC]
144 Pass the RSDP address to the kernel, mostly used
145 on machines running EFI runtime service to boot the
146 second kernel for kdump.
148 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
149 Format: To spoof as Windows 98: ="Microsoft Windows"
151 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
152 of 2 which is mandated by ACPI 6) as the supported ACPI
153 specification revision (when using this switch, it may
154 be necessary to carry out a cold reboot _twice_ in a
155 row to make it take effect on the platform firmware).
157 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
158 acpi_osi="string1" # add string1
159 acpi_osi="!string2" # remove string2
160 acpi_osi=!* # remove all strings
161 acpi_osi=! # disable all built-in OS vendor
163 acpi_osi=!! # enable all built-in OS vendor
165 acpi_osi= # disable all strings
167 'acpi_osi=!' can be used in combination with single or
168 multiple 'acpi_osi="string1"' to support specific OS
169 vendor string(s). Note that such command can only
170 affect the default state of the OS vendor strings, thus
171 it cannot affect the default state of the feature group
172 strings and the current state of the OS vendor strings,
173 specifying it multiple times through kernel command line
174 is meaningless. This command is useful when one do not
175 care about the state of the feature group strings which
176 should be controlled by the OSPM.
178 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
179 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
180 can make '_OSI("Windows 2000")' TRUE.
182 'acpi_osi=' cannot be used in combination with other
183 'acpi_osi=' command lines, the _OSI method will not
184 exist in the ACPI namespace. NOTE that such command can
185 only affect the _OSI support state, thus specifying it
186 multiple times through kernel command line is also
189 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
192 'acpi_osi=!*' can be used in combination with single or
193 multiple 'acpi_osi="string1"' to support specific
194 string(s). Note that such command can affect the
195 current state of both the OS vendor strings and the
196 feature group strings, thus specifying it multiple times
197 through kernel command line is meaningful. But it may
198 still not able to affect the final state of a string if
199 there are quirks related to this string. This command
200 is useful when one want to control the state of the
201 feature group strings to debug BIOS issues related to
204 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
205 '_OSI("Module Device")' FALSE.
206 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
207 '_OSI("Module Device")' TRUE.
208 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
210 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
212 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
213 they all will make '_OSI("Windows 2000")' TRUE.
216 Override the pmtimer bug detection: force the kernel
217 to assume that this machine's pmtimer latches its value
218 and always returns good values.
220 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
221 Format: { level | edge | high | low }
223 acpi_skip_timer_override [HW,ACPI]
224 Recognize and ignore IRQ0/pin2 Interrupt Override.
225 For broken nForce2 BIOS resulting in XT-PIC timer.
227 acpi_sleep= [HW,ACPI] Sleep options
228 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
229 old_ordering, nonvs, sci_force_enable, nobl }
230 See Documentation/power/video.rst for information on
232 s3_beep is for debugging; it makes the PC's speaker beep
233 as soon as the kernel's real-mode entry point is called.
234 s4_nohwsig prevents ACPI hardware signature from being
235 used during resume from hibernation.
236 old_ordering causes the ACPI 1.0 ordering of the _PTS
237 control method, with respect to putting devices into
238 low power states, to be enforced (the ACPI 2.0 ordering
239 of _PTS is used by default).
240 nonvs prevents the kernel from saving/restoring the
241 ACPI NVS memory during suspend/hibernation and resume.
242 sci_force_enable causes the kernel to set SCI_EN directly
243 on resume from S1/S3 (which is against the ACPI spec,
244 but some broken systems don't work without it).
245 nobl causes the internal blacklist of systems known to
246 behave incorrectly in some ways with respect to system
247 suspend and resume to be ignored (use wisely).
249 acpi_use_timer_override [HW,ACPI]
250 Use timer override. For some broken Nvidia NF5 boards
251 that require a timer override, but don't have HPET
253 add_efi_memmap [EFI; X86] Include EFI memory map in
254 kernel's map of available physical RAM.
257 { off | try_unsupported }
258 off: disable AGP support
259 try_unsupported: try to drive unsupported chipsets
260 (may crash computer or cause data corruption)
263 See Documentation/sound/alsa-configuration.rst
266 Allow the default userspace alignment fault handler
267 behaviour to be specified. Bit 0 enables warnings,
268 bit 1 enables fixups, and bit 2 sends a segfault.
270 align_va_addr= [X86-64]
271 Align virtual addresses by clearing slice [14:12] when
272 allocating a VMA at process creation time. This option
273 gives you up to 3% performance improvement on AMD F15h
274 machines (where it is enabled by default) for a
275 CPU-intensive style benchmark, and it can vary highly in
276 a microbenchmark depending on workload and compiler.
278 32: only for 32-bit processes
279 64: only for 64-bit processes
280 on: enable for both 32- and 64-bit processes
281 off: disable for both 32- and 64-bit processes
283 alloc_snapshot [FTRACE]
284 Allocate the ftrace snapshot buffer on boot up when the
285 main buffer is allocated. This is handy if debugging
286 and you need to use tracing_snapshot() on boot up, and
287 do not want to use tracing_snapshot_alloc() as it needs
288 to be done where GFP_KERNEL allocations are allowed.
290 amd_iommu= [HW,X86-64]
291 Pass parameters to the AMD IOMMU driver in the system.
293 fullflush - enable flushing of IO/TLB entries when
294 they are unmapped. Otherwise they are
295 flushed before they will be reused, which
297 off - do not initialize any AMD IOMMU found in
299 force_isolation - Force device isolation for all
300 devices. The IOMMU driver is not
301 allowed anymore to lift isolation
302 requirements as needed. This option
303 does not override iommu=pt
305 amd_iommu_dump= [HW,X86-64]
306 Enable AMD IOMMU driver option to dump the ACPI table
307 for AMD IOMMU. With this option enabled, AMD IOMMU
308 driver will print ACPI tables for AMD IOMMU during
309 IOMMU initialization.
311 amd_iommu_intr= [HW,X86-64]
312 Specifies one of the following AMD IOMMU interrupt
314 legacy - Use legacy interrupt remapping mode.
315 vapic - Use virtual APIC mode, which allows IOMMU
316 to inject interrupts directly into guest.
317 This mode requires kvm-amd.avic=1.
318 (Default when IOMMU HW support is present.)
320 amijoy.map= [HW,JOY] Amiga joystick support
321 Map of devices attached to JOY0DAT and JOY1DAT
323 See also Documentation/input/joydev/joystick.rst
325 analog.map= [HW,JOY] Analog joystick and gamepad support
326 Specifies type or capabilities of an analog joystick
327 connected to one of 16 gameports
328 Format: <type1>,<type2>,..<type16>
331 Power management functions (SPARCstation-4/5 + deriv.)
333 Disable APC CPU standby support. SPARCstation-Fox does
334 not play well with APC CPU idle - disable it if you have
335 APC and your system crashes randomly.
337 apic= [APIC,X86] Advanced Programmable Interrupt Controller
338 Change the output verbosity while booting
339 Format: { quiet (default) | verbose | debug }
340 Change the amount of debugging information output
341 when initialising the APIC and IO-APIC components.
342 For X86-32, this can also be used to specify an APIC
344 Format: apic=driver_name
345 Examples: apic=bigsmp
347 apic_extnmi= [APIC,X86] External NMI delivery setting
348 Format: { bsp (default) | all | none }
349 bsp: External NMI is delivered only to CPU 0
350 all: External NMIs are broadcast to all CPUs as a
352 none: External NMI is masked for all CPUs. This is
353 useful so that a dump capture kernel won't be
357 See Documentation/networking/ipv6.rst.
359 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
360 Limit apic dumping. The parameter defines the maximal
361 number of local apics being dumped. Also it is possible
362 to set it to "all" by meaning -- no limit here.
363 Format: { 1 (default) | 2 | ... | all }.
364 The parameter valid if only apic=debug or
365 apic=verbose is specified.
366 Example: apic=debug show_lapic=all
368 apm= [APM] Advanced Power Management
369 See header of arch/x86/kernel/apm_32.c.
371 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
372 Format: <io>,<irq>,<nodeID>
374 arm64.nobti [ARM64] Unconditionally disable Branch Target
375 Identification support
377 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
382 atarimouse= [HW,MOUSE] Atari Mouse
384 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
385 EzKey and similar keyboards
387 atkbd.reset= [HW] Reset keyboard during initialization
389 atkbd.set= [HW] Select keyboard code set
390 Format: <int> (2 = AT (default), 3 = PS/2)
392 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
395 atkbd.softraw= [HW] Choose between synthetic and real raw mode
396 Format: <bool> (0 = real, 1 = synthetic (default))
398 atkbd.softrepeat= [HW]
399 Use software keyboard repeat
401 audit= [KNL] Enable the audit sub-system
402 Format: { "0" | "1" | "off" | "on" }
403 0 | off - kernel audit is disabled and can not be
404 enabled until the next reboot
405 unset - kernel audit is initialized but disabled and
406 will be fully enabled by the userspace auditd.
407 1 | on - kernel audit is initialized and partially
408 enabled, storing at most audit_backlog_limit
409 messages in RAM until it is fully enabled by the
413 audit_backlog_limit= [KNL] Set the audit queue size limit.
414 Format: <int> (must be >=0)
417 bau= [X86_UV] Enable the BAU on SGI UV. The default
418 behavior is to disable the BAU (i.e. bau=0).
419 Format: { "0" | "1" }
422 unset - Disable the BAU.
424 baycom_epp= [HW,AX25]
427 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
429 See header of drivers/net/hamradio/baycom_par.c.
431 baycom_ser_fdx= [HW,AX25]
432 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
433 Format: <io>,<irq>,<mode>[,<baud>]
434 See header of drivers/net/hamradio/baycom_ser_fdx.c.
436 baycom_ser_hdx= [HW,AX25]
437 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
438 Format: <io>,<irq>,<mode>
439 See header of drivers/net/hamradio/baycom_ser_hdx.c.
441 blkdevparts= Manual partition parsing of block device(s) for
442 embedded devices based on command line input.
443 See Documentation/block/cmdline-partition.rst
445 boot_delay= Milliseconds to delay each printk during boot.
446 Values larger than 10 seconds (10000) are changed to
451 Extended command line options can be added to an initrd
452 and this will cause the kernel to look for it.
454 See Documentation/admin-guide/bootconfig.rst
457 Disable BERT OS support on buggy BIOSes.
459 bgrt_disable [ACPI][X86]
460 Disable BGRT to avoid flickering OEM logo.
462 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
463 bttv.radio= Most important insmod options are available as
465 bttv.pll= See Documentation/admin-guide/media/bttv.rst
468 bulk_remove=off [PPC] This parameter disables the use of the pSeries
469 firmware feature for flushing multiple hpte entries
472 c101= [NET] Moxa C101 synchronous serial card
474 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
475 Sometimes CPU hardware bugs make them report the cache
476 size incorrectly. The kernel will attempt work arounds
477 to fix known problems, but for some CPUs it is not
478 possible to determine what the correct size should be.
479 This option provides an override for these situations.
482 [NET] Specifies amount of time (in seconds) that
483 the kernel should wait for a network carrier. By default
484 it waits 120 seconds.
486 ca_keys= [KEYS] This parameter identifies a specific key(s) on
487 the system trusted keyring to be used for certificate
489 format: { id:<keyid> | builtin }
491 cca= [MIPS] Override the kernel pages' cache coherency
492 algorithm. Accepted values range from 0 to 7
493 inclusive. See arch/mips/include/asm/pgtable-bits.h
494 for platform specific values (SB1, Loongson3 and
497 ccw_timeout_log [S390]
498 See Documentation/s390/common_io.rst for details.
500 cgroup_disable= [KNL] Disable a particular controller
501 Format: {name of the controller(s) to disable}
502 The effects of cgroup_disable=foo are:
503 - foo isn't auto-mounted if you mount all cgroups in
505 - foo isn't visible as an individually mountable
507 {Currently only "memory" controller deal with this and
508 cut the overhead, others just disable the usage. So
509 only cgroup_disable=memory is actually worthy}
511 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
512 Format: { { controller | "all" | "named" }
513 [,{ controller | "all" | "named" }...] }
514 Like cgroup_disable, but only applies to cgroup v1;
515 the blacklisted controllers remain available in cgroup2.
516 "all" blacklists all controllers and "named" disables
517 named mounts. Specifying both "all" and "named" disables
520 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
522 nosocket -- Disable socket memory accounting.
523 nokmem -- Disable kernel memory accounting.
525 checkreqprot [SELINUX] Set initial checkreqprot flag value.
526 Format: { "0" | "1" }
527 See security/selinux/Kconfig help text.
528 0 -- check protection applied by kernel (includes
529 any implied execute protection).
530 1 -- check protection requested by application.
531 Default value is set via a kernel config option.
532 Value can be changed at runtime via
533 /sys/fs/selinux/checkreqprot.
534 Setting checkreqprot to 1 is deprecated.
537 See Documentation/s390/common_io.rst for details.
540 Prevents the clock framework from automatically gating
541 clocks that have not been explicitly enabled by a Linux
542 device driver but are enabled in hardware at reset or
543 by the bootloader/firmware. Note that this does not
544 force such clocks to be always-on nor does it reserve
545 those clocks in any way. This parameter is useful for
546 debug and development, but should not be needed on a
547 platform with proper driver support. For more
548 information, see Documentation/driver-api/clk.rst.
550 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
552 Forces specified clocksource (if available) to be used
553 when calculating gettimeofday(). If specified
554 clocksource is not available, it defaults to PIT.
555 Format: { pit | tsc | cyclone | pmtmr }
557 clocksource= Override the default clocksource
559 Override the default clocksource and use the clocksource
560 with the name specified.
561 Some clocksource names to choose from, depending on
563 [all] jiffies (this is the base, fallback clocksource)
565 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
566 pxa_timer,timer3,32k_counter,timer0_1
567 [X86-32] pit,hpet,tsc;
568 scx200_hrt on Geode; cyclone on IBM x440
576 clocksource.arm_arch_timer.evtstrm=
579 Enable/disable the eventstream feature of the ARM
580 architected timer so that code using WFE-based polling
581 loops can be debugged more effectively on production
584 clearcpuid=BITNUM[,BITNUM...] [X86]
585 Disable CPUID feature X for the kernel. See
586 arch/x86/include/asm/cpufeatures.h for the valid bit
587 numbers. Note the Linux specific bits are not necessarily
588 stable over kernel options, but the vendor specific
590 Also note that user programs calling CPUID directly
591 or using the feature without checking anything
592 will still see it. This just prevents it from
593 being used by the kernel or shown in /proc/cpuinfo.
594 Also note the kernel might malfunction if you disable
597 cma=nn[MG]@[start[MG][-end[MG]]]
599 Sets the size of kernel global memory area for
600 contiguous memory allocations and optionally the
601 placement constraint by the physical address range of
602 memory allocations. A value of 0 disables CMA
603 altogether. For more information, see
604 kernel/dma/contiguous.c
608 Sets the size of kernel per-numa memory area for
609 contiguous memory allocations. A value of 0 disables
610 per-numa CMA altogether. And If this option is not
611 specificed, the default value is 0.
612 With per-numa CMA enabled, DMA users on node nid will
613 first try to allocate buffer from the pernuma area
614 which is located in node nid, if the allocation fails,
615 they will fallback to the global default memory area.
617 cmo_free_hint= [PPC] Format: { yes | no }
618 Specify whether pages are marked as being inactive
619 when they are freed. This is used in CMO environments
620 to determine OS memory pressure for page stealing by
624 coherent_pool=nn[KMG] [ARM,KNL]
625 Sets the size of memory pool for coherent, atomic dma
626 allocations, by default set to 256K.
628 com20020= [HW,NET] ARCnet - COM20020 chipset
630 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
632 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
636 ARCnet - COM90xx chipset (memory-mapped buffers)
637 Format: <io>[,<irq>[,<memstart>]]
639 condev= [HW,S390] console device
642 console= [KNL] Output console device and options.
644 tty<n> Use the virtual console device <n>.
648 Use the specified serial port. The options are of
649 the form "bbbbpnf", where "bbbb" is the baud rate,
650 "p" is parity ("n", "o", or "e"), "n" is number of
651 bits, and "f" is flow control ("r" for RTS or
652 omit it). Default is "9600n8".
654 See Documentation/admin-guide/serial-console.rst for more
656 Documentation/networking/netconsole.rst for an
659 uart[8250],io,<addr>[,options]
660 uart[8250],mmio,<addr>[,options]
661 uart[8250],mmio16,<addr>[,options]
662 uart[8250],mmio32,<addr>[,options]
663 uart[8250],0x<addr>[,options]
664 Start an early, polled-mode console on the 8250/16550
665 UART at the specified I/O port or MMIO address,
666 switching to the matching ttyS device later.
667 MMIO inter-register address stride is either 8-bit
668 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
669 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
670 to be equivalent to 'mmio'. 'options' are specified in
671 the same format described for ttyS above; if unspecified,
672 the h/w is not re-initialized.
674 hvc<n> Use the hypervisor console device <n>. This is for
675 both Xen and PowerPC hypervisors.
677 If the device connected to the port is not a TTY but a braille
678 device, prepend "brl," before the device type, for instance
680 For now, only VisioBraille is supported.
683 [KNL] Change console messages format
685 By default we print messages on consoles in
686 "[time stamp] text\n" format (time stamp may not be
687 printed, depending on CONFIG_PRINTK_TIME or
688 `printk_time' param).
690 Switch to syslog format: "<%u>[time stamp] text\n"
691 IOW, each message will have a facility and loglevel
692 prefix. The format is similar to one used by syslog()
693 syscall, or to executing "dmesg -S --raw" or to reading
696 consoleblank= [KNL] The console blank (screen saver) timeout in
697 seconds. A value of 0 disables the blank timer.
701 [KNL] Change the default value for
702 /proc/<pid>/coredump_filter.
703 See also Documentation/filesystems/proc.rst.
705 coresight_cpu_debug.enable
708 Enable/disable the CPU sampling based debugging.
709 0: default value, disable debugging
710 1: enable debugging at boot time
712 cpuidle.off=1 [CPU_IDLE]
713 disable the cpuidle sub-system
716 [CPU_IDLE] Name of the cpuidle governor to use.
718 cpufreq.off=1 [CPU_FREQ]
719 disable the cpufreq sub-system
721 cpufreq.default_governor=
722 [CPU_FREQ] Name of the default cpufreq governor or
723 policy to use. This governor must be registered in the
724 kernel before the cpufreq driver probes.
727 [X86] Delay for N microsec between assert and de-assert
728 of APIC INIT to start processors. This delay occurs
729 on every CPU online, such as boot, and resume from suspend.
732 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
734 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
736 crashkernel=size[KMG][@offset[KMG]]
737 [KNL] Using kexec, Linux can switch to a 'crash kernel'
738 upon panic. This parameter reserves the physical
739 memory region [offset, offset + size] for that kernel
740 image. If '@offset' is omitted, then a suitable offset
741 is selected automatically.
742 [KNL, X86-64] Select a region under 4G first, and
743 fall back to reserve region above 4G when '@offset'
744 hasn't been specified.
745 See Documentation/admin-guide/kdump/kdump.rst for further details.
747 crashkernel=range1:size1[,range2:size2,...][@offset]
748 [KNL] Same as above, but depends on the memory
749 in the running system. The syntax of range is
750 start-[end] where start and end are both
751 a memory unit (amount[KMG]). See also
752 Documentation/admin-guide/kdump/kdump.rst for an example.
754 crashkernel=size[KMG],high
755 [KNL, X86-64] range could be above 4G. Allow kernel
756 to allocate physical memory region from top, so could
757 be above 4G if system have more than 4G ram installed.
758 Otherwise memory region will be allocated below 4G, if
760 It will be ignored if crashkernel=X is specified.
761 crashkernel=size[KMG],low
762 [KNL, X86-64] range under 4G. When crashkernel=X,high
763 is passed, kernel could allocate physical memory region
764 above 4G, that cause second kernel crash on system
765 that require some amount of low memory, e.g. swiotlb
766 requires at least 64M+32K low memory, also enough extra
767 low memory is needed to make sure DMA buffers for 32-bit
768 devices won't run out. Kernel would try to allocate at
769 at least 256M below 4G automatically.
770 This one let user to specify own low range under 4G
771 for second kernel instead.
772 0: to disable low allocation.
773 It will be ignored when crashkernel=X,high is not used
774 or memory reserved is below 4G.
777 [KNL] Disable crypto self-tests
782 cs89x0_media= [HW,NET]
783 Format: { rj45 | aui | bnc }
785 csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call
786 handling. When switched on, additional debug data is
787 printed to the console in case a hanging CPU is
788 detected, and that CPU is pinged again in order to try
789 to resolve the hang situation.
790 0: disable csdlock debugging (default)
791 1: enable basic csdlock debugging (minor impact)
792 ext: enable extended csdlock debugging (more impact,
796 See header of drivers/s390/block/dasd_devmap.c.
798 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
799 (one device per port)
800 Format: <port#>,<type>
801 See also Documentation/input/devices/joystick-parport.rst
803 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
805 Documentation/admin-guide/dynamic-debug-howto.rst for
806 details. Deprecated, see dyndbg.
808 debug [KNL] Enable kernel debugging (events log level).
811 [KNL] Enable printing [hashed] pointers early in the
812 boot sequence. If enabled, we use a weak hash instead
813 of siphash to hash pointers. Use this option if you are
814 seeing instances of '(___ptrval___)') and need to see a
815 value (hashed pointer) instead. Cryptographically
816 insecure, please do not use on production kernels.
819 [KNL] verbose locking self-tests
821 Print debugging info while doing the locking API
823 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
824 (no extra messages), setting it to -1 (all bits set)
825 will print _a_lot_ more information - normally only
826 useful to lockdep developers.
828 debug_objects [KNL] Enable object debugging
831 [KNL] Disable object debugging
833 debug_guardpage_minorder=
834 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
835 parameter allows control of the order of pages that will
836 be intentionally kept free (and hence protected) by the
837 buddy allocator. Bigger value increase the probability
838 of catching random memory corruption, but reduce the
839 amount of memory for normal system use. The maximum
840 possible value is MAX_ORDER/2. Setting this parameter
841 to 1 or 2 should be enough to identify most random
842 memory corruption problems caused by bugs in kernel or
843 driver code when a CPU writes to (or reads from) a
844 random memory location. Note that there exists a class
845 of memory corruptions problems caused by buggy H/W or
846 F/W or by drivers badly programing DMA (basically when
847 memory is written at bus level and the CPU MMU is
848 bypassed) which are not detectable by
849 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
850 tracking down these problems.
853 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
854 enables the feature at boot time. By default, it is
855 disabled and the system will work mostly the same as a
856 kernel built without CONFIG_DEBUG_PAGEALLOC.
857 Note: to get most of debug_pagealloc error reports, it's
858 useful to also enable the page_owner functionality.
859 on: enable the feature
861 debugfs= [KNL] This parameter enables what is exposed to userspace
862 and debugfs internal clients.
863 Format: { on, no-mount, off }
864 on: All functions are enabled.
866 Filesystem is not registered but kernel clients can
867 access APIs and a crashkernel can be used to read
868 its content. There is nothing to mount.
869 off: Filesystem is not registered and clients
870 get a -EPERM as result when trying to register files
871 or directories within debugfs.
872 This is equivalent of the runtime functionality if
873 debugfs was not enabled in the kernel at all.
874 Default value is set in build-time with a kernel configuration.
876 debugpat [X86] Enable PAT debugging
878 decnet.addr= [HW,NET]
879 Format: <area>[,<node>]
880 See also Documentation/networking/decnet.rst.
883 [HW] The size of the default HugeTLB page. This is
884 the size represented by the legacy /proc/ hugepages
885 APIs. In addition, this is the default hugetlb size
886 used for shmget(), mmap() and mounting hugetlbfs
887 filesystems. If not specified, defaults to the
888 architecture's default huge page size. Huge page
889 sizes are architecture dependent. See also
890 Documentation/admin-guide/mm/hugetlbpage.rst.
893 deferred_probe_timeout=
894 [KNL] Debugging option to set a timeout in seconds for
895 deferred probe to give up waiting on dependencies to
896 probe. Only specific dependencies (subsystems or
897 drivers) that have opted in will be ignored. A timeout of 0
898 will timeout at the end of initcalls. This option will also
899 dump out devices still on the deferred probe list after
903 Format: { on | off | def_only | inf_only | always }
904 on: s390 zlib hardware support for compression on
905 level 1 and decompression (default)
906 off: No s390 zlib hardware support
907 def_only: s390 zlib hardware support for deflate
908 only (compression on level 1)
909 inf_only: s390 zlib hardware support for inflate
911 always: Same as 'on' but ignores the selected compression
912 level always using hardware support (used for debugging)
915 Set number of hash buckets for dentry cache.
917 disable_1tb_segments [PPC]
918 Disables the use of 1TB hash page table segments. This
919 causes the kernel to fall back to 256MB segments which
920 can be useful when debugging issues that require an SLB
924 Limits the number of kernel SLB entries, and flushes
925 them frequently to increase the rate of SLB faults
929 See Documentation/networking/ipv6.rst.
932 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
933 hardening is enabled for this boot. Hardened
934 usercopy checking is used to protect the kernel
935 from reading or writing beyond known memory
936 allocation boundaries as a proactive defense
937 against bounds-checking flaws in the kernel's
938 copy_to_user()/copy_from_user() interface.
939 on Perform hardened usercopy checks (default).
940 off Disable hardened usercopy checks.
943 Disable RADIX MMU mode on POWER9
945 radix_hcall_invalidate=on [PPC/PSERIES]
946 Disable RADIX GTSE feature and use hcall for TLB
950 Disable TLBIE instruction. Currently does not work
951 with KVM, with HASH MMU, or with coherent accelerators.
953 disable_cpu_apicid= [X86,APIC,SMP]
955 The number of initial APIC ID for the
956 corresponding CPU to be disabled at boot,
957 mostly used for the kdump 2nd kernel to
958 disable BSP to wake up multiple CPUs without
959 causing system reset or hang due to sending
962 disable_ddw [PPC/PSERIES]
963 Disable Dynamic DMA Window support. Use this
964 to workaround buggy firmware.
967 See Documentation/networking/ipv6.rst.
969 disable_mtrr_cleanup [X86]
970 The kernel tries to adjust MTRR layout from continuous
971 to discrete, to make X server driver able to add WB
972 entry later. This parameter disables that.
974 disable_mtrr_trim [X86, Intel and AMD only]
975 By default the kernel will trim any uncacheable
976 memory out of your available memory pool based on
977 MTRR settings. This parameter disables that behavior,
978 possibly causing your machine to run very slowly.
980 disable_timer_pin_1 [X86]
981 Disable PIN 1 of APIC timer
982 Can be useful to work around chipset bugs.
984 dis_ucode_ldr [X86] Disable the microcode loader.
986 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
987 this option disables the debugging code at boot.
989 dma_debug_entries=<number>
990 This option allows to tune the number of preallocated
991 entries for DMA-API debugging code. One entry is
992 required per DMA-API allocation. Use this if the
993 DMA-API debugging code disables itself because the
994 architectural default is too low.
996 dma_debug_driver=<driver_name>
997 With this option the DMA-API debugging driver
998 filter feature can be enabled at boot time. Just
999 pass the driver to filter for as the parameter.
1000 The filter can be disabled or changed to another
1001 driver later using sysfs.
1003 driver_async_probe= [KNL]
1004 List of driver names to be probed asynchronously.
1005 Format: <driver_name1>,<driver_name2>...
1007 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1008 Broken monitors, graphic adapters, KVMs and EDIDless
1009 panels may send no or incorrect EDID data sets.
1010 This parameter allows to specify an EDID data sets
1011 in the /lib/firmware directory that are used instead.
1012 Generic built-in EDID data sets are used, if one of
1013 edid/1024x768.bin, edid/1280x1024.bin,
1014 edid/1680x1050.bin, or edid/1920x1080.bin is given
1015 and no file with the same name exists. Details and
1016 instructions how to build your own EDID data are
1017 available in Documentation/admin-guide/edid.rst. An EDID
1018 data set will only be used for a particular connector,
1019 if its name and a colon are prepended to the EDID
1020 name. Each connector may use a unique EDID data
1021 set by separating the files with a comma. An EDID
1022 data set with no connector name will be used for
1023 any connectors not explicitly specified.
1028 Format: {"off" | "known"}
1029 Control how the dt_cpu_ftrs device-tree binding is
1030 used for CPU feature discovery and setup (if it
1032 off: Do not use it, fall back to legacy cpu table.
1033 known: Do not pass through unknown features to guests
1034 or userspace, only those that the kernel is aware of.
1036 dump_apple_properties [X86]
1037 Dump name and content of EFI device properties on
1038 x86 Macs. Useful for driver authors to determine
1039 what data is available or for reverse-engineering.
1041 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1042 <module>.dyndbg[="val"]
1043 Enable debug messages at boot time. See
1044 Documentation/admin-guide/dynamic-debug-howto.rst
1047 nopku [X86] Disable Memory Protection Keys CPU feature found
1050 <module>.async_probe [KNL]
1051 Enable asynchronous probe on this module.
1053 early_ioremap_debug [KNL]
1054 Enable debug messages in early_ioremap support. This
1055 is useful for tracking down temporary early mappings
1056 which are not unmapped.
1058 earlycon= [KNL] Output early console device and options.
1060 When used with no options, the early console is
1061 determined by stdout-path property in device tree's
1062 chosen node or the ACPI SPCR table if supported by
1065 cdns,<addr>[,options]
1066 Start an early, polled-mode console on a Cadence
1067 (xuartps) serial port at the specified address. Only
1068 supported option is baud rate. If baud rate is not
1069 specified, the serial port must already be setup and
1072 uart[8250],io,<addr>[,options]
1073 uart[8250],mmio,<addr>[,options]
1074 uart[8250],mmio32,<addr>[,options]
1075 uart[8250],mmio32be,<addr>[,options]
1076 uart[8250],0x<addr>[,options]
1077 Start an early, polled-mode console on the 8250/16550
1078 UART at the specified I/O port or MMIO address.
1079 MMIO inter-register address stride is either 8-bit
1080 (mmio) or 32-bit (mmio32 or mmio32be).
1081 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1082 to be equivalent to 'mmio'. 'options' are specified
1083 in the same format described for "console=ttyS<n>"; if
1084 unspecified, the h/w is not initialized.
1088 Start an early, polled-mode console on a pl011 serial
1089 port at the specified address. The pl011 serial port
1090 must already be setup and configured. Options are not
1091 yet supported. If 'mmio32' is specified, then only
1092 the driver will use only 32-bit accessors to read/write
1093 the device registers.
1096 Start an early, polled-mode console on a meson serial
1097 port at the specified address. The serial port must
1098 already be setup and configured. Options are not yet
1102 Start an early, polled-mode console on an msm serial
1103 port at the specified address. The serial port
1104 must already be setup and configured. Options are not
1107 msm_serial_dm,<addr>
1108 Start an early, polled-mode console on an msm serial
1109 dm port at the specified address. The serial port
1110 must already be setup and configured. Options are not
1114 Start an early, polled-mode console on a serial port
1115 of an Actions Semi SoC, such as S500 or S900, at the
1116 specified address. The serial port must already be
1117 setup and configured. Options are not yet supported.
1120 Start an early, polled-mode console on a serial port
1121 of an RDA Micro SoC, such as RDA8810PL, at the
1122 specified address. The serial port must already be
1123 setup and configured. Options are not yet supported.
1126 Use RISC-V SBI (Supervisor Binary Interface) for early
1129 smh Use ARM semihosting calls for early console.
1137 Use early console provided by serial driver available
1138 on Samsung SoCs, requires selecting proper type and
1139 a correct base address of the selected UART port. The
1140 serial port must already be setup and configured.
1141 Options are not yet supported.
1144 Start an early, polled-mode console on a lantiq serial
1145 (lqasc) port at the specified address. The serial port
1146 must already be setup and configured. Options are not
1151 Use early console provided by Freescale LP UART driver
1152 found on Freescale Vybrid and QorIQ LS1021A processors.
1153 A valid base address must be provided, and the serial
1154 port must already be setup and configured.
1158 Start an early, polled-mode, output-only console on the
1159 Freescale i.MX UART at the specified address. The UART
1160 must already be setup and configured.
1163 Start an early, polled-mode console on the
1164 Armada 3700 serial port at the specified
1165 address. The serial port must already be setup
1166 and configured. Options are not yet supported.
1169 Start an early, polled-mode console on a Qualcomm
1170 Generic Interface (GENI) based serial port at the
1171 specified address. The serial port must already be
1172 setup and configured. Options are not yet supported.
1175 Start an early, unaccelerated console on the EFI
1176 memory mapped framebuffer (if available). On cache
1177 coherent non-x86 systems that use system memory for
1178 the framebuffer, pass the 'ram' option so that it is
1179 mapped with the correct attributes.
1182 Use early console provided by Freescale LINFlexD UART
1183 serial driver for NXP S32V234 SoCs. A valid base
1184 address must be provided, and the serial port must
1185 already be setup and configured.
1187 earlyprintk= [X86,SH,ARM,M68k,S390]
1191 earlyprintk=serial[,ttySn[,baudrate]]
1192 earlyprintk=serial[,0x...[,baudrate]]
1193 earlyprintk=ttySn[,baudrate]
1194 earlyprintk=dbgp[debugController#]
1195 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1196 earlyprintk=xdbc[xhciController#]
1198 earlyprintk is useful when the kernel crashes before
1199 the normal console is initialized. It is not enabled by
1200 default because it has some cosmetic problems.
1202 Append ",keep" to not disable it when the real console
1205 Only one of vga, efi, serial, or usb debug port can
1208 Currently only ttyS0 and ttyS1 may be specified by
1209 name. Other I/O ports may be explicitly specified
1210 on some architectures (x86 and arm at least) by
1211 replacing ttySn with an I/O port address, like this:
1212 earlyprintk=serial,0x1008,115200
1213 You can find the port for a given device in
1214 /proc/tty/driver/serial:
1215 2: uart:ST16650V2 port:00001008 irq:18 ...
1217 Interaction with the standard serial driver is not
1220 The VGA and EFI output is eventually overwritten by
1223 The xen output can only be used by Xen PV guests.
1225 The sclp output can only be used on s390.
1227 The optional "force" to "pciserial" enables use of a
1228 PCI device even when its classcode is not of the
1231 edac_report= [HW,EDAC] Control how to report EDAC event
1232 Format: {"on" | "off" | "force"}
1233 on: enable EDAC to report H/W event. May be overridden
1234 by other higher priority error reporting module.
1235 off: disable H/W event reporting through EDAC.
1236 force: enforce the use of EDAC to report H/W event.
1239 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1242 This is designed to be used in conjunction with
1243 the boot argument: earlyprintk=vga
1245 This parameter works in place of the kgdboc parameter
1246 but can only be used if the backing tty is available
1247 very early in the boot process. For early debugging
1248 via a serial port see kgdboc_earlycon instead.
1251 Format: {"off" | "on" | "skip[mbr]"}
1254 Format: { "debug", "disable_early_pci_dma",
1255 "nochunk", "noruntime", "nosoftreserve",
1256 "novamap", "no_disable_early_pci_dma" }
1257 debug: enable misc debug output.
1258 disable_early_pci_dma: disable the busmaster bit on all
1259 PCI bridges while in the EFI boot stub.
1260 nochunk: disable reading files in "chunks" in the EFI
1261 boot stub, as chunking can cause problems with some
1262 firmware implementations.
1263 noruntime : disable EFI runtime services support
1264 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1265 attribute may cause the kernel to reserve the
1266 memory range for a memory mapping driver to
1267 claim. Specify efi=nosoftreserve to disable this
1268 reservation and treat the memory by its base type
1269 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1270 novamap: do not call SetVirtualAddressMap().
1271 no_disable_early_pci_dma: Leave the busmaster bit set
1272 on all PCI bridges while in the EFI boot stub
1274 efi_no_storage_paranoia [EFI; X86]
1275 Using this parameter you can use more than 50% of
1276 your efi variable storage. Use this parameter only if
1277 you are really sure that your UEFI does sane gc and
1278 fulfills the spec otherwise your board may brick.
1280 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1281 Add arbitrary attribute to specific memory range by
1282 updating original EFI memory map.
1283 Region of memory which aa attribute is added to is
1286 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1287 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1288 attribute is added to range 0x100000000-0x180000000 and
1289 0x10a0000000-0x1120000000.
1291 If efi_fake_mem=8G@9G:0x40000 is specified, the
1292 EFI_MEMORY_SP(0x40000) attribute is added to
1293 range 0x240000000-0x43fffffff.
1295 Using this parameter you can do debugging of EFI memmap
1296 related features. For example, you can do debugging of
1297 Address Range Mirroring feature even if your box
1298 doesn't support it, or mark specific memory as
1301 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1302 that is to be dynamically loaded by Linux. If there are
1303 multiple variables with the same name but with different
1304 vendor GUIDs, all of them will be loaded. See
1305 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1308 eisa_irq_edge= [PARISC,HW]
1309 See header of drivers/parisc/eisa.c.
1312 See comment before function elanfreq_setup() in
1313 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1315 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1316 Specifies physical address of start of kernel core
1317 image elf header and optionally the size. Generally
1318 kexec loader will pass this option to capture kernel.
1319 See Documentation/admin-guide/kdump/kdump.rst for details.
1321 enable_mtrr_cleanup [X86]
1322 The kernel tries to adjust MTRR layout from continuous
1323 to discrete, to make X server driver able to add WB
1324 entry later. This parameter enables that.
1326 enable_timer_pin_1 [X86]
1327 Enable PIN 1 of APIC timer
1328 Can be useful to work around chipset bugs
1329 (in particular on some ATI chipsets).
1330 The kernel tries to set a reasonable default.
1332 enforcing [SELINUX] Set initial enforcing status.
1334 See security/selinux/Kconfig help text.
1335 0 -- permissive (log only, no denials).
1336 1 -- enforcing (deny and log).
1338 Value can be changed at runtime via
1339 /sys/fs/selinux/enforce.
1342 Disable Error Record Serialization Table (ERST)
1345 ether= [HW,NET] Ethernet cards parameters
1346 This option is obsoleted by the "netdev=" option, which
1347 has equivalent usage. See its documentation for details.
1351 Permit 'security.evm' to be updated regardless of
1352 current integrity status.
1357 fail_make_request=[KNL]
1358 General fault injection mechanism.
1359 Format: <interval>,<probability>,<space>,<times>
1360 See also Documentation/fault-injection/.
1363 Format: { initns | none }
1364 See Documentation/admin-guide/sysctl/net.rst for
1365 fb_tunnels_only_for_init_ns
1368 See Documentation/admin-guide/blockdev/floppy.rst.
1370 force_pal_cache_flush
1371 [IA-64] Avoid check_sal_cache_flush which may hang on
1372 buggy SAL_CACHE_FLUSH implementations. Using this
1373 parameter will force ia64_sal_cache_flush to call
1374 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1377 Forcefully enable Physical Address Extension (PAE).
1378 Many Pentium M systems disable PAE but may have a
1379 functionally usable PAE implementation.
1380 Warning: use of this parameter will taint the kernel
1381 and may cause unknown problems.
1384 [FTRACE] will set and start the specified tracer
1385 as early as possible in order to facilitate early
1388 ftrace_dump_on_oops[=orig_cpu]
1389 [FTRACE] will dump the trace buffers on oops.
1390 If no parameter is passed, ftrace will dump
1391 buffers of all CPUs, but if you pass orig_cpu, it will
1392 dump only the buffer of the CPU that triggered the
1395 ftrace_filter=[function-list]
1396 [FTRACE] Limit the functions traced by the function
1397 tracer at boot up. function-list is a comma-separated
1398 list of functions. This list can be changed at run
1399 time by the set_ftrace_filter file in the debugfs
1402 ftrace_notrace=[function-list]
1403 [FTRACE] Do not trace the functions specified in
1404 function-list. This list can be changed at run time
1405 by the set_ftrace_notrace file in the debugfs
1408 ftrace_graph_filter=[function-list]
1409 [FTRACE] Limit the top level callers functions traced
1410 by the function graph tracer at boot up.
1411 function-list is a comma-separated list of functions
1412 that can be changed at run time by the
1413 set_graph_function file in the debugfs tracing directory.
1415 ftrace_graph_notrace=[function-list]
1416 [FTRACE] Do not trace from the functions specified in
1417 function-list. This list is a comma-separated list of
1418 functions that can be changed at run time by the
1419 set_graph_notrace file in the debugfs tracing directory.
1421 ftrace_graph_max_depth=<uint>
1422 [FTRACE] Used with the function graph tracer. This is
1423 the max depth it will trace into a function. This value
1424 can be changed at run time by the max_graph_depth file
1425 in the tracefs tracing directory. default: 0 (no limit)
1427 fw_devlink= [KNL] Create device links between consumer and supplier
1428 devices by scanning the firmware to infer the
1429 consumer/supplier relationships. This feature is
1430 especially useful when drivers are loaded as modules as
1431 it ensures proper ordering of tasks like device probing
1432 (suppliers first, then consumers), supplier boot state
1433 clean up (only after all consumers have probed),
1434 suspend/resume & runtime PM (consumers first, then
1436 Format: { off | permissive | on | rpm }
1437 off -- Don't create device links from firmware info.
1438 permissive -- Create device links from firmware info
1439 but use it only for ordering boot state clean
1440 up (sync_state() calls).
1441 on -- Create device links from firmware info and use it
1442 to enforce probe and suspend/resume ordering.
1443 rpm -- Like "on", but also use to order runtime PM.
1445 fw_devlink.strict=<bool>
1446 [KNL] Treat all inferred dependencies as mandatory
1447 dependencies. This only applies for fw_devlink=on|rpm.
1451 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1452 support via parallel port (up to 5 devices per port)
1453 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1454 See also Documentation/input/devices/joystick-parport.rst
1458 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART
1462 gcov_persist= [GCOV] When non-zero (default), profiling data for
1463 kernel modules is saved and remains accessible via
1464 debugfs, even when the module is unloaded/reloaded.
1465 When zero, profiling data is discarded and associated
1466 debugfs files are removed at module unload time.
1468 goldfish [X86] Enable the goldfish android emulator platform.
1469 Don't use this when you are not running on the
1472 gpt [EFI] Forces disk with valid GPT signature but
1473 invalid Protective MBR to be treated as GPT. If the
1474 primary GPT is corrupted, it enables the backup/alternate
1475 GPT to be used instead.
1477 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1478 the "Enable 0" bit of the configuration register.
1481 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1482 the "Enable 0" bit of the configuration register.
1485 grcan.select= [HW] Select which physical interface to use.
1488 grcan.txsize= [HW] Sets the size of the tx buffer.
1489 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1491 grcan.rxsize= [HW] Sets the size of the rx buffer.
1492 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1495 gpio-mockup.gpio_mockup_ranges
1496 [HW] Sets the ranges of gpiochip of for this device.
1497 Format: <start1>,<end1>,<start2>,<end2>...
1499 hardlockup_all_cpu_backtrace=
1500 [KNL] Should the hard-lockup detector generate
1501 backtraces on all cpus.
1504 hashdist= [KNL,NUMA] Large hashes allocated during boot
1505 are distributed across NUMA nodes. Defaults on
1506 for 64-bit NUMA, off otherwise.
1507 Format: 0 | 1 (for off | on)
1509 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1511 hd= [EIDE] (E)IDE hard drive subsystem geometry
1512 Format: <cyl>,<head>,<sect>
1515 Disable Hardware Error Source Table (HEST) support;
1516 corresponding firmware-first mode error processing
1517 logic will be disabled.
1519 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1520 size of <nn>. This works even on boxes that have no
1521 highmem otherwise. This also works to reduce highmem
1522 size on bigger boxes.
1524 highres= [KNL] Enable/disable high resolution timer mode.
1525 Valid parameters: "on", "off"
1530 hpet= [X86-32,HPET] option to control HPET usage
1531 Format: { enable (default) | disable | force |
1533 disable: disable HPET and use PIT instead
1534 force: allow force enabled of undocumented chips (ICH4,
1536 verbose: show contents of HPET registers during setup
1538 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1539 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1541 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation
1542 of gigantic hugepages.
1545 Reserve a CMA area of given size and allocate gigantic
1546 hugepages using the CMA allocator. If enabled, the
1547 boot-time allocation of gigantic hugepages is skipped.
1549 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1550 If this follows hugepagesz (below), it specifies
1551 the number of pages of hugepagesz to be allocated.
1552 If this is the first HugeTLB parameter on the command
1553 line, it specifies the number of pages to allocate for
1554 the default huge page size. See also
1555 Documentation/admin-guide/mm/hugetlbpage.rst.
1559 [HW] The size of the HugeTLB pages. This is used in
1560 conjunction with hugepages (above) to allocate huge
1561 pages of a specific size at boot. The pair
1562 hugepagesz=X hugepages=Y can be specified once for
1563 each supported huge page size. Huge page sizes are
1564 architecture dependent. See also
1565 Documentation/admin-guide/mm/hugetlbpage.rst.
1569 [KNL] Should the hung task detector generate panics.
1572 A value of 1 instructs the kernel to panic when a
1573 hung task is detected. The default value is controlled
1574 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1575 option. The value selected by this boot parameter can
1576 be changed later by the kernel.hung_task_panic sysctl.
1578 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1579 terminal devices. Valid values: 0..8
1580 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1581 If specified, z/VM IUCV HVC accepts connections
1582 from listed z/VM user IDs only.
1584 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1585 which allow the hypervisor to 'idle' the
1586 guest on lock contention.
1589 Do not unregister boot console at start. This is only
1590 useful for debugging when something happens in the window
1591 between unregistering the boot console and initializing
1594 i2c_bus= [HW] Override the default board specific I2C bus speed
1595 or register an additional I2C bus that is not
1596 registered from board initialization code.
1600 i8042.debug [HW] Toggle i8042 debug mode
1601 i8042.unmask_kbd_data
1602 [HW] Enable printing of interrupt data from the KBD port
1603 (disabled by default, and as a pre-condition
1604 requires that i8042.debug=1 be enabled)
1605 i8042.direct [HW] Put keyboard port into non-translated mode
1606 i8042.dumbkbd [HW] Pretend that controller can only read data from
1607 keyboard and cannot control its state
1608 (Don't attempt to blink the leds)
1609 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1610 i8042.nokbd [HW] Don't check/create keyboard port
1611 i8042.noloop [HW] Disable the AUX Loopback command while probing
1613 i8042.nomux [HW] Don't check presence of an active multiplexing
1615 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1617 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1618 i8042.reset [HW] Reset the controller during init, cleanup and
1619 suspend-to-ram transitions, only during s2r
1620 transitions, or never reset
1621 Format: { 1 | Y | y | 0 | N | n }
1622 1, Y, y: always reset controller
1623 0, N, n: don't ever reset controller
1624 Default: only on s2r transitions on x86; most other
1625 architectures force reset to be always executed
1626 i8042.unlock [HW] Unlock (ignore) the keylock
1627 i8042.kbdreset [HW] Reset device connected to KBD port
1631 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1632 indicates that the driver is running on unsupported
1634 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1635 does not match list of supported models.
1637 [HW] Report power status in /proc/i8k
1638 (disabled by default)
1639 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1642 i915.invert_brightness=
1643 [DRM] Invert the sense of the variable that is used to
1644 set the brightness of the panel backlight. Normally a
1645 brightness value of 0 indicates backlight switched off,
1646 and the maximum of the brightness value sets the backlight
1647 to maximum brightness. If this parameter is set to 0
1648 (default) and the machine requires it, or this parameter
1649 is set to 1, a brightness value of 0 sets the backlight
1650 to maximum brightness, and the maximum of the brightness
1651 value switches the backlight off.
1652 -1 -- never invert brightness
1653 0 -- machine default
1654 1 -- force brightness inversion
1657 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1659 ide-core.nodma= [HW] (E)IDE subsystem
1660 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1661 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1662 .cdrom .chs .ignore_cable are additional options
1663 See Documentation/ide/ide.rst.
1665 ide-generic.probe-mask= [HW] (E)IDE subsystem
1667 Probe mask for legacy ISA IDE ports. Depending on
1668 platform up to 6 ports are supported, enabled by
1669 setting corresponding bits in the mask to 1. The
1670 default value is 0x0, which has a special meaning.
1671 On systems that have PCI, it triggers scanning the
1672 PCI bus for the first and the second port, which
1673 are then probed. On systems without PCI the value
1674 of 0x0 enables probing the two first ports as if it
1677 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1678 Claim all unknown PCI IDE storage controllers.
1681 Format: idle=poll, idle=halt, idle=nomwait
1682 Poll forces a polling idle loop that can slightly
1683 improve the performance of waking up a idle CPU, but
1684 will use a lot of power and make the system run hot.
1686 idle=halt: Halt is forced to be used for CPU idle.
1687 In such case C2/C3 won't be used again.
1688 idle=nomwait: Disable mwait for CPU C-states
1692 Allow force disabling of Shared Virtual Memory (SVA)
1693 support for the idxd driver. By default it is set to
1696 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1697 Format: { strict | legacy | 2008 | relaxed }
1700 Choose which programs will be accepted for execution
1701 based on the IEEE 754 NaN encoding(s) supported by
1702 the FPU and the NaN encoding requested with the value
1703 of an ELF file header flag individually set by each
1704 binary. Hardware implementations are permitted to
1705 support either or both of the legacy and the 2008 NaN
1708 Available settings are as follows:
1709 strict accept binaries that request a NaN encoding
1710 supported by the FPU
1711 legacy only accept legacy-NaN binaries, if supported
1713 2008 only accept 2008-NaN binaries, if supported
1715 relaxed accept any binaries regardless of whether
1716 supported by the FPU
1718 The FPU emulator is always able to support both NaN
1719 encodings, so if no FPU hardware is present or it has
1720 been disabled with 'nofpu', then the settings of
1721 'legacy' and '2008' strap the emulator accordingly,
1722 'relaxed' straps the emulator for both legacy-NaN and
1723 2008-NaN, whereas 'strict' enables legacy-NaN only on
1724 legacy processors and both NaN encodings on MIPS32 or
1727 The setting for ABS.fmt/NEG.fmt instruction execution
1728 mode generally follows that for the NaN encoding,
1729 except where unsupported by hardware.
1731 ignore_loglevel [KNL]
1732 Ignore loglevel setting - this will print /all/
1733 kernel messages to the console. Useful for debugging.
1734 We also add it as printk module parameter, so users
1735 could change it dynamically, usually by
1736 /sys/module/printk/parameters/ignore_loglevel.
1739 Ignore RLIMIT_DATA setting for data mappings,
1740 print warning at first misuse. Can be changed via
1741 /sys/module/kernel/parameters/ignore_rlimit_data.
1743 ihash_entries= [KNL]
1744 Set number of hash buckets for inode cache.
1746 ima_appraise= [IMA] appraise integrity measurements
1747 Format: { "off" | "enforce" | "fix" | "log" }
1750 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1751 The builtin appraise policy appraises all files
1754 ima_canonical_fmt [IMA]
1755 Use the canonical format for the binary runtime
1756 measurements, instead of host native format.
1759 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1763 The list of supported hash algorithms is defined
1764 in crypto/hash_info.h.
1767 The builtin policies to load during IMA setup.
1768 Format: "tcb | appraise_tcb | secure_boot |
1769 fail_securely | critical_data"
1771 The "tcb" policy measures all programs exec'd, files
1772 mmap'd for exec, and all files opened with the read
1773 mode bit set by either the effective uid (euid=0) or
1776 The "appraise_tcb" policy appraises the integrity of
1777 all files owned by root.
1779 The "secure_boot" policy appraises the integrity
1780 of files (eg. kexec kernel image, kernel modules,
1781 firmware, policy, etc) based on file signatures.
1783 The "fail_securely" policy forces file signature
1784 verification failure also on privileged mounted
1785 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1788 The "critical_data" policy measures kernel integrity
1791 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1792 Load a policy which meets the needs of the Trusted
1793 Computing Base. This means IMA will measure all
1794 programs exec'd, files mmap'd for exec, and all files
1795 opened for read by uid=0.
1798 Select one of defined IMA measurements template formats.
1799 Formats: { "ima" | "ima-ng" | "ima-sig" }
1803 [IMA] Define a custom template format.
1804 Format: { "field1|...|fieldN" }
1806 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1807 Format: <min_file_size>
1808 Set the minimal file size for using asynchronous hash.
1809 If left unspecified, ahash usage is disabled.
1811 ahash performance varies for different data sizes on
1812 different crypto accelerators. This option can be used
1813 to achieve the best performance for a particular HW.
1815 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1817 Set hashing buffer size. Default: 4k.
1819 ahash performance varies for different chunk sizes on
1820 different crypto accelerators. This option can be used
1821 to achieve best performance for particular HW.
1825 Run specified binary instead of /sbin/init as init
1828 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1829 for working out where the kernel is dying during
1832 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1833 initcall functions. Useful for debugging built-in
1834 modules and initcalls.
1836 initrd= [BOOT] Specify the location of the initial ramdisk
1838 initrdmem= [KNL] Specify a physical address and size from which to
1839 load the initrd. If an initrd is compiled in or
1840 specified in the bootparams, it takes priority over this
1842 Format: ss[KMG],nn[KMG]
1845 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1848 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1850 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1852 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1854 init_pkru= [X86] Specify the default memory protection keys rights
1855 register contents for all processes. 0x55555554 by
1856 default (disallow access to all but pkey 0). Can
1857 override in debugfs after boot.
1859 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1862 int_pln_enable [X86] Enable power limit notification interrupt
1864 integrity_audit=[IMA]
1865 Format: { "0" | "1" }
1866 0 -- basic integrity auditing messages. (Default)
1867 1 -- additional integrity auditing messages.
1869 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1871 Enable intel iommu driver.
1873 Disable intel iommu driver.
1874 igfx_off [Default Off]
1875 By default, gfx is mapped as normal device. If a gfx
1876 device has a dedicated DMAR unit, the DMAR unit is
1877 bypassed by not enabling DMAR with this option. In
1878 this case, gfx device will use physical address for
1881 With this option iommu will not optimize to look
1882 for io virtual address below 32-bit forcing dual
1883 address cycle on pci bus for cards supporting greater
1884 than 32-bit addressing. The default is to look
1885 for translation below 32-bit and if not available
1886 then look in the higher range.
1887 strict [Default Off]
1888 With this option on every unmap_single operation will
1889 result in a hardware IOTLB flush operation as opposed
1890 to batching them for performance.
1891 sp_off [Default Off]
1892 By default, super page will be supported if Intel IOMMU
1893 has the capability. With this option, super page will
1896 By default, scalable mode will be disabled even if the
1897 hardware advertises that it has support for the scalable
1898 mode translation. With this option set, scalable mode
1899 will be used on hardware which claims to support it.
1900 tboot_noforce [Default Off]
1901 Do not force the Intel IOMMU enabled under tboot.
1902 By default, tboot will force Intel IOMMU on, which
1903 could harm performance of some high-throughput
1904 devices like 40GBit network cards, even if identity
1906 Note that using this option lowers the security
1907 provided by tboot because it makes the system
1908 vulnerable to DMA attacks.
1910 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1911 0 disables intel_idle and fall back on acpi_idle.
1912 1 to 9 specify maximum depth of C-state.
1916 Do not enable intel_pstate as the default
1917 scaling driver for the supported processors
1919 Use intel_pstate as a scaling driver, but configure it
1920 to work with generic cpufreq governors (instead of
1921 enabling its internal governor). This mode cannot be
1922 used along with the hardware-managed P-states (HWP)
1925 Enable intel_pstate on systems that prohibit it by default
1926 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1927 instead of acpi-cpufreq may disable platform features, such
1928 as thermal controls and power capping, that rely on ACPI
1929 P-States information being indicated to OSPM and therefore
1930 should be used with caution. This option does not work with
1931 processors that aren't supported by the intel_pstate driver
1932 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1934 Do not enable hardware P state control (HWP)
1937 Only load intel_pstate on systems which support
1938 hardware P state control (HWP) if available.
1940 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1941 Description Table, specifies preferred power management
1942 profile as "Enterprise Server" or "Performance Server",
1943 then this feature is turned on by default.
1945 Allow per-logical-CPU P-State performance control limits using
1946 cpufreq sysfs interface
1948 intremap= [X86-64, Intel-IOMMU]
1949 on enable Interrupt Remapping (default)
1950 off disable Interrupt Remapping
1951 nosid disable Source ID checking
1953 BIOS x2APIC opt-out request will be ignored
1954 nopost disable Interrupt Posting
1956 iomem= Disable strict checking of access to MMIO memory
1957 strict regions from userspace.
1972 nobypass [PPC/POWERNV]
1973 Disable IOMMU bypass, using IOMMU for PCI devices.
1975 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1976 Format: { "0" | "1" }
1978 Request that DMA unmap operations use deferred
1979 invalidation of hardware TLBs, for increased
1980 throughput at the cost of reduced device isolation.
1981 Will fall back to strict mode if not supported by
1982 the relevant IOMMU driver.
1983 1 - Strict mode (default).
1984 DMA unmap operations invalidate IOMMU hardware TLBs
1988 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
1989 Format: { "0" | "1" }
1990 0 - Use IOMMU translation for DMA.
1991 1 - Bypass the IOMMU for DMA.
1992 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1994 io7= [HW] IO7 for Marvel-based Alpha systems
1995 See comment before marvel_specify_io7 in
1996 arch/alpha/kernel/core_marvel.c.
1998 io_delay= [X86] I/O delay method
2000 Standard port 0x80 based delay
2002 Alternate port 0xed based delay (needed on some systems)
2004 Simple two microseconds delay
2009 See Documentation/admin-guide/nfs/nfsroot.rst.
2011 ipcmni_extend [KNL] Extend the maximum number of unique System V
2012 IPC identifiers from 32,768 to 16,777,216.
2014 irqaffinity= [SMP] Set the default irq affinity mask
2015 The argument is a cpu list, as described above.
2017 irqchip.gicv2_force_probe=
2020 Force the kernel to look for the second 4kB page
2021 of a GICv2 controller even if the memory range
2022 exposed by the device tree is too small.
2024 irqchip.gicv3_nolpi=
2026 Force the kernel to ignore the availability of
2027 LPIs (and by consequence ITSs). Intended for system
2028 that use the kernel as a bootloader, and thus want
2029 to let secondary kernels in charge of setting up
2032 irqchip.gicv3_pseudo_nmi= [ARM64]
2033 Enables support for pseudo-NMIs in the kernel. This
2034 requires the kernel to be built with
2035 CONFIG_ARM64_PSEUDO_NMI.
2038 When an interrupt is not handled search all handlers
2039 for it. Intended to get systems with badly broken
2043 When an interrupt is not handled search all handlers
2044 for it. Also check all handlers each timer
2045 interrupt. Intended to get systems with badly broken
2049 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2051 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2052 [Deprecated - use cpusets instead]
2053 Format: [flag-list,]<cpu-list>
2055 Specify one or more CPUs to isolate from disturbances
2056 specified in the flag list (default: domain):
2059 Disable the tick when a single task runs.
2061 A residual 1Hz tick is offloaded to workqueues, which you
2062 need to affine to housekeeping through the global
2063 workqueue's affinity configured via the
2064 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2065 by using the 'domain' flag described below.
2067 NOTE: by default the global workqueue runs on all CPUs,
2068 so to protect individual CPUs the 'cpumask' file has to
2069 be configured manually after bootup.
2072 Isolate from the general SMP balancing and scheduling
2073 algorithms. Note that performing domain isolation this way
2074 is irreversible: it's not possible to bring back a CPU to
2075 the domains once isolated through isolcpus. It's strongly
2076 advised to use cpusets instead to disable scheduler load
2077 balancing through the "cpuset.sched_load_balance" file.
2078 It offers a much more flexible interface where CPUs can
2079 move in and out of an isolated set anytime.
2081 You can move a process onto or off an "isolated" CPU via
2082 the CPU affinity syscalls or cpuset.
2083 <cpu number> begins at 0 and the maximum value is
2084 "number of CPUs in system - 1".
2088 Isolate from being targeted by managed interrupts
2089 which have an interrupt mask containing isolated
2090 CPUs. The affinity of managed interrupts is
2091 handled by the kernel and cannot be changed via
2092 the /proc/irq/* interfaces.
2094 This isolation is best effort and only effective
2095 if the automatically assigned interrupt mask of a
2096 device queue contains isolated and housekeeping
2097 CPUs. If housekeeping CPUs are online then such
2098 interrupts are directed to the housekeeping CPU
2099 so that IO submitted on the housekeeping CPU
2100 cannot disturb the isolated CPU.
2102 If a queue's affinity mask contains only isolated
2103 CPUs then this parameter has no effect on the
2104 interrupt routing decision, though interrupts are
2105 only delivered when tasks running on those
2106 isolated CPUs submit IO. IO submitted on
2107 housekeeping CPUs has no influence on those
2110 The format of <cpu-list> is described above.
2114 ivrs_ioapic [HW,X86-64]
2115 Provide an override to the IOAPIC-ID<->DEVICE-ID
2116 mapping provided in the IVRS ACPI table. For
2117 example, to map IOAPIC-ID decimal 10 to
2118 PCI device 00:14.0 write the parameter as:
2119 ivrs_ioapic[10]=00:14.0
2121 ivrs_hpet [HW,X86-64]
2122 Provide an override to the HPET-ID<->DEVICE-ID
2123 mapping provided in the IVRS ACPI table. For
2124 example, to map HPET-ID decimal 0 to
2125 PCI device 00:14.0 write the parameter as:
2126 ivrs_hpet[0]=00:14.0
2128 ivrs_acpihid [HW,X86-64]
2129 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2130 mapping provided in the IVRS ACPI table. For
2131 example, to map UART-HID:UID AMD0020:0 to
2132 PCI device 00:14.5 write the parameter as:
2133 ivrs_acpihid[00:14.5]=AMD0020:0
2135 js= [HW,JOY] Analog joystick
2136 See Documentation/input/joydev/joystick.rst.
2139 When CONFIG_RANDOMIZE_BASE is set, this disables
2140 kernel and module base offset ASLR (Address Space
2141 Layout Randomization).
2144 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2145 report on every invalid memory access. Without this
2146 parameter KASAN will print report only for the first
2151 kernelcore= [KNL,X86,IA-64,PPC]
2152 Format: nn[KMGTPE] | nn% | "mirror"
2153 This parameter specifies the amount of memory usable by
2154 the kernel for non-movable allocations. The requested
2155 amount is spread evenly throughout all nodes in the
2156 system as ZONE_NORMAL. The remaining memory is used for
2157 movable memory in its own zone, ZONE_MOVABLE. In the
2158 event, a node is too small to have both ZONE_NORMAL and
2159 ZONE_MOVABLE, kernelcore memory will take priority and
2160 other nodes will have a larger ZONE_MOVABLE.
2162 ZONE_MOVABLE is used for the allocation of pages that
2163 may be reclaimed or moved by the page migration
2164 subsystem. Note that allocations like PTEs-from-HighMem
2165 still use the HighMem zone if it exists, and the Normal
2166 zone if it does not.
2168 It is possible to specify the exact amount of memory in
2169 the form of "nn[KMGTPE]", a percentage of total system
2170 memory in the form of "nn%", or "mirror". If "mirror"
2171 option is specified, mirrored (reliable) memory is used
2172 for non-movable allocations and remaining memory is used
2173 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2174 are exclusive, so you cannot specify multiple forms.
2176 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2177 Format: <Controller#>[,poll interval]
2178 The controller # is the number of the ehci usb debug
2179 port as it is probed via PCI. The poll interval is
2180 optional and is the number seconds in between
2181 each poll cycle to the debug port in case you need
2182 the functionality for interrupting the kernel with
2183 gdb or control-c on the dbgp connection. When
2184 not using this parameter you use sysrq-g to break into
2185 the kernel debugger.
2187 kgdboc= [KGDB,HW] kgdb over consoles.
2188 Requires a tty driver that supports console polling,
2189 or a supported polling keyboard driver (non-usb).
2190 Serial only format: <serial_device>[,baud]
2191 keyboard only format: kbd
2192 keyboard and serial format: kbd,<serial_device>[,baud]
2193 Optional Kernel mode setting:
2194 kms, kbd format: kms,kbd
2195 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2197 kgdboc_earlycon= [KGDB,HW]
2198 If the boot console provides the ability to read
2199 characters and can work in polling mode, you can use
2200 this parameter to tell kgdb to use it as a backend
2201 until the normal console is registered. Intended to
2202 be used together with the kgdboc parameter which
2203 specifies the normal console to transition to.
2205 The name of the early console should be specified
2206 as the value of this parameter. Note that the name of
2207 the early console might be different than the tty
2208 name passed to kgdboc. It's OK to leave the value
2209 blank and the first boot console that implements
2210 read() will be picked.
2212 kgdbwait [KGDB] Stop kernel execution and enter the
2213 kernel debugger at the earliest opportunity.
2215 kmac= [MIPS] Korina ethernet MAC address.
2216 Configure the RouterBoard 532 series on-chip
2217 Ethernet adapter MAC address.
2219 kmemleak= [KNL] Boot-time kmemleak enable/disable
2220 Valid arguments: on, off
2222 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2225 kprobe_event=[probe-list]
2226 [FTRACE] Add kprobe events and enable at boot time.
2227 The probe-list is a semicolon delimited list of probe
2228 definitions. Each definition is same as kprobe_events
2229 interface, but the parameters are comma delimited.
2230 For example, to add a kprobe event on vfs_read with
2231 arg1 and arg2, add to the command line;
2233 kprobe_event=p,vfs_read,$arg1,$arg2
2235 See also Documentation/trace/kprobetrace.rst "Kernel
2236 Boot Parameter" section.
2238 kpti= [ARM64] Control page table isolation of user
2239 and kernel address spaces.
2240 Default: enabled on cores which need mitigation.
2244 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2245 Default is 0 (don't ignore, but inject #GP)
2247 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2248 Default is false (don't support).
2250 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2255 [KVM] Controls the software workaround for the
2256 X86_BUG_ITLB_MULTIHIT bug.
2257 force : Always deploy workaround.
2258 off : Never deploy workaround.
2259 auto : Deploy workaround based on the presence of
2260 X86_BUG_ITLB_MULTIHIT.
2264 If the software workaround is enabled for the host,
2265 guests do need not to enable it for nested guests.
2267 kvm.nx_huge_pages_recovery_ratio=
2268 [KVM] Controls how many 4KiB pages are periodically zapped
2269 back to huge pages. 0 disables the recovery, otherwise if
2270 the value is N KVM will zap 1/Nth of the 4KiB pages every
2271 minute. The default is 60.
2273 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2274 Default is 1 (enabled)
2276 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2278 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2281 [KVM,ARM] Select one of KVM/arm64's modes of operation.
2283 nvhe: Standard nVHE-based mode, without support for
2286 protected: nVHE-based mode with support for guests whose
2287 state is kept private from the host.
2288 Not valid if the kernel is running in EL2.
2290 Defaults to VHE/nVHE based on hardware support.
2292 kvm-arm.vgic_v3_group0_trap=
2293 [KVM,ARM] Trap guest accesses to GICv3 group-0
2296 kvm-arm.vgic_v3_group1_trap=
2297 [KVM,ARM] Trap guest accesses to GICv3 group-1
2300 kvm-arm.vgic_v3_common_trap=
2301 [KVM,ARM] Trap guest accesses to GICv3 common
2304 kvm-arm.vgic_v4_enable=
2305 [KVM,ARM] Allow use of GICv4 for direct injection of
2308 kvm_cma_resv_ratio=n [PPC]
2309 Reserves given percentage from system memory area for
2310 contiguous memory allocation for KVM hash pagetable
2312 By default it reserves 5% of total system memory.
2316 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2317 (virtualized MMU) support on capable Intel chips.
2318 Default is 1 (enabled)
2320 kvm-intel.emulate_invalid_guest_state=
2321 [KVM,Intel] Enable emulation of invalid guest states
2322 Default is 0 (disabled)
2324 kvm-intel.flexpriority=
2325 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2326 Default is 1 (enabled)
2329 [KVM,Intel] Enable VMX nesting (nVMX).
2330 Default is 0 (disabled)
2332 kvm-intel.unrestricted_guest=
2333 [KVM,Intel] Disable unrestricted guest feature
2334 (virtualized real and unpaged mode) on capable
2335 Intel chips. Default is 1 (enabled)
2337 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2340 Valid arguments: never, cond, always
2342 always: L1D cache flush on every VMENTER.
2343 cond: Flush L1D on VMENTER only when the code between
2344 VMEXIT and VMENTER can leak host memory.
2345 never: Disables the mitigation
2347 Default is cond (do L1 cache flush in specific instances)
2349 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2350 feature (tagged TLBs) on capable Intel chips.
2351 Default is 1 (enabled)
2353 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2356 The kernel PTE inversion protection is unconditionally
2357 enabled and cannot be disabled.
2360 Provides all available mitigations for the
2361 L1TF vulnerability. Disables SMT and
2362 enables all mitigations in the
2363 hypervisors, i.e. unconditional L1D flush.
2365 SMT control and L1D flush control via the
2366 sysfs interface is still possible after
2367 boot. Hypervisors will issue a warning
2368 when the first VM is started in a
2369 potentially insecure configuration,
2370 i.e. SMT enabled or L1D flush disabled.
2373 Same as 'full', but disables SMT and L1D
2374 flush runtime control. Implies the
2375 'nosmt=force' command line option.
2376 (i.e. sysfs control of SMT is disabled.)
2379 Leaves SMT enabled and enables the default
2380 hypervisor mitigation, i.e. conditional
2383 SMT control and L1D flush control via the
2384 sysfs interface is still possible after
2385 boot. Hypervisors will issue a warning
2386 when the first VM is started in a
2387 potentially insecure configuration,
2388 i.e. SMT enabled or L1D flush disabled.
2392 Disables SMT and enables the default
2393 hypervisor mitigation.
2395 SMT control and L1D flush control via the
2396 sysfs interface is still possible after
2397 boot. Hypervisors will issue a warning
2398 when the first VM is started in a
2399 potentially insecure configuration,
2400 i.e. SMT enabled or L1D flush disabled.
2403 Same as 'flush', but hypervisors will not
2404 warn when a VM is started in a potentially
2405 insecure configuration.
2408 Disables hypervisor mitigations and doesn't
2410 It also drops the swap size and available
2411 RAM limit restriction on both hypervisor and
2416 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2422 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2425 lapic= [X86,APIC] Do not use TSC deadline
2426 value for LAPIC timer one-shot implementation. Default
2427 back to the programmable timer unit in the LAPIC.
2428 Format: notscdeadline
2430 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2433 libata.dma= [LIBATA] DMA control
2434 libata.dma=0 Disable all PATA and SATA DMA
2435 libata.dma=1 PATA and SATA Disk DMA only
2436 libata.dma=2 ATAPI (CDROM) DMA only
2437 libata.dma=4 Compact Flash DMA only
2438 Combinations also work, so libata.dma=3 enables DMA
2439 for disks and CDROMs, but not CFs.
2441 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2442 libata.ignore_hpa=0 keep BIOS limits (default)
2443 libata.ignore_hpa=1 ignore limits, using full disk
2445 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2449 libata.force= [LIBATA] Force configurations. The format is comma-
2450 separated list of "[ID:]VAL" where ID is
2451 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2452 matching port, link or device. Basically, it matches
2453 the ATA ID string printed on console by libata. If
2454 the whole ID part is omitted, the last PORT and DEVICE
2455 values are used. If ID hasn't been specified yet, the
2456 configuration applies to all ports, links and devices.
2458 If only DEVICE is omitted, the parameter applies to
2459 the port and all links and devices behind it. DEVICE
2460 number of 0 either selects the first device or the
2461 first fan-out link behind PMP device. It does not
2462 select the host link. DEVICE number of 15 selects the
2463 host link and device attached to it.
2465 The VAL specifies the configuration to force. As long
2466 as there's no ambiguity shortcut notation is allowed.
2467 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2468 The following configurations can be forced.
2470 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2471 Any ID with matching PORT is used.
2473 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2475 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2476 udma[/][16,25,33,44,66,100,133] notation is also
2479 * [no]ncq: Turn on or off NCQ.
2481 * [no]ncqtrim: Turn off queued DSM TRIM.
2483 * nohrst, nosrst, norst: suppress hard, soft
2486 * rstonce: only attempt one reset during
2487 hot-unplug link recovery
2489 * dump_id: dump IDENTIFY data.
2491 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2493 * disable: Disable this device.
2495 If there are multiple matching configurations changing
2496 the same attribute, the last one is used.
2498 memblock=debug [KNL] Enable memblock debug messages.
2500 load_ramdisk= [RAM] [Deprecated]
2502 lockd.nlm_grace_period=P [NFS] Assign grace period.
2505 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2508 lockd.nlm_timeout=T [NFS] Assign timeout value.
2511 lockd.nlm_udpport=M [NFS] Assign UDP port.
2514 lockdown= [SECURITY]
2515 { integrity | confidentiality }
2516 Enable the kernel lockdown feature. If set to
2517 integrity, kernel features that allow userland to
2518 modify the running kernel are disabled. If set to
2519 confidentiality, kernel features that allow userland
2520 to extract confidential information from the kernel
2523 locktorture.nreaders_stress= [KNL]
2524 Set the number of locking read-acquisition kthreads.
2525 Defaults to being automatically set based on the
2526 number of online CPUs.
2528 locktorture.nwriters_stress= [KNL]
2529 Set the number of locking write-acquisition kthreads.
2531 locktorture.onoff_holdoff= [KNL]
2532 Set time (s) after boot for CPU-hotplug testing.
2534 locktorture.onoff_interval= [KNL]
2535 Set time (s) between CPU-hotplug operations, or
2536 zero to disable CPU-hotplug testing.
2538 locktorture.shuffle_interval= [KNL]
2539 Set task-shuffle interval (jiffies). Shuffling
2540 tasks allows some CPUs to go into dyntick-idle
2541 mode during the locktorture test.
2543 locktorture.shutdown_secs= [KNL]
2544 Set time (s) after boot system shutdown. This
2545 is useful for hands-off automated testing.
2547 locktorture.stat_interval= [KNL]
2548 Time (s) between statistics printk()s.
2550 locktorture.stutter= [KNL]
2551 Time (s) to stutter testing, for example,
2552 specifying five seconds causes the test to run for
2553 five seconds, wait for five seconds, and so on.
2554 This tests the locking primitive's ability to
2555 transition abruptly to and from idle.
2557 locktorture.torture_type= [KNL]
2558 Specify the locking implementation to test.
2560 locktorture.verbose= [KNL]
2561 Enable additional printk() statements.
2563 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2566 loglevel= All Kernel Messages with a loglevel smaller than the
2567 console loglevel will be printed to the console. It can
2568 also be changed with klogd or other programs. The
2569 loglevels are defined as follows:
2571 0 (KERN_EMERG) system is unusable
2572 1 (KERN_ALERT) action must be taken immediately
2573 2 (KERN_CRIT) critical conditions
2574 3 (KERN_ERR) error conditions
2575 4 (KERN_WARNING) warning conditions
2576 5 (KERN_NOTICE) normal but significant condition
2577 6 (KERN_INFO) informational
2578 7 (KERN_DEBUG) debug-level messages
2580 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2581 in bytes. n must be a power of two and greater
2582 than the minimal size. The minimal size is defined
2583 by LOG_BUF_SHIFT kernel config parameter. There is
2584 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2585 that allows to increase the default size depending on
2586 the number of CPUs. See init/Kconfig for more details.
2588 logo.nologo [FB] Disables display of the built-in Linux logo.
2589 This may be used to provide more screen space for
2590 kernel log messages and is useful when debugging
2591 kernel boot problems.
2593 lp=0 [LP] Specify parallel ports to use, e.g,
2594 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2595 lp=reset first parallel port). 'lp=0' disables the
2596 lp=auto printer driver. 'lp=reset' (which can be
2597 specified in addition to the ports) causes
2598 attached printers to be reset. Using
2599 lp=port1,port2,... specifies the parallel ports
2600 to associate lp devices with, starting with
2601 lp0. A port specification may be 'none' to skip
2602 that lp device, or a parport name such as
2603 'parport0'. Specifying 'lp=auto' instead of a
2604 port specification list means that device IDs
2605 from each port should be examined, to see if
2606 an IEEE 1284-compliant printer is attached; if
2607 so, the driver will manage that printer.
2608 See also header of drivers/char/lp.c.
2611 Sets loops_per_jiffy to given constant, thus avoiding
2612 time-consuming boot-time autodetection (up to 250 ms per
2613 CPU). 0 enables autodetection (default). To determine
2614 the correct value for your kernel, boot with normal
2615 autodetection and see what value is printed. Note that
2616 on SMP systems the preset will be applied to all CPUs,
2617 which is likely to cause problems if your CPUs need
2618 significantly divergent settings. An incorrect value
2619 will cause delays in the kernel to be wrong, leading to
2620 unpredictable I/O errors and other breakage. Although
2621 unlikely, in the extreme case this might damage your
2625 Format: <io>,<irq>,<dma>
2627 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2630 [SECURITY] Choose order of LSM initialization. This
2631 overrides CONFIG_LSM, and the "security=" parameter.
2633 machvec= [IA-64] Force the use of a particular machine-vector
2634 (machvec) in a generic kernel.
2635 Example: machvec=hpzx1
2637 machtype= [Loongson] Share the same kernel image file between
2638 different yeeloong laptops.
2639 Example: machtype=lemote-yeeloong-2f-7inch
2641 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2642 than or equal to this physical address is ignored.
2644 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2645 will bring up during bootup. maxcpus=n : n >= 0 limits
2646 the kernel to bring up 'n' processors. Surely after
2647 bootup you can bring up the other plugged cpu by executing
2648 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2649 only takes effect during system bootup.
2650 While n=0 is a special case, it is equivalent to "nosmp",
2651 which also disables the IO APIC.
2653 max_loop= [LOOP] The number of loop block devices that get
2654 (loop.max_loop) unconditionally pre-created at init time. The default
2655 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2656 of statically allocating a predefined number, loop
2657 devices can be requested on-demand with the
2658 /dev/loop-control interface.
2660 mce [X86-32] Machine Check Exception
2662 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2664 md= [HW] RAID subsystems devices and level
2665 See Documentation/admin-guide/md.rst.
2668 Format: <first>,<last>
2669 Specifies range of consoles to be captured by the MDA.
2672 Control mitigation for the Micro-architectural Data
2673 Sampling (MDS) vulnerability.
2675 Certain CPUs are vulnerable to an exploit against CPU
2676 internal buffers which can forward information to a
2677 disclosure gadget under certain conditions.
2679 In vulnerable processors, the speculatively
2680 forwarded data can be used in a cache side channel
2681 attack, to access data to which the attacker does
2682 not have direct access.
2684 This parameter controls the MDS mitigation. The
2687 full - Enable MDS mitigation on vulnerable CPUs
2688 full,nosmt - Enable MDS mitigation and disable
2689 SMT on vulnerable CPUs
2690 off - Unconditionally disable MDS mitigation
2692 On TAA-affected machines, mds=off can be prevented by
2693 an active TAA mitigation as both vulnerabilities are
2694 mitigated with the same mechanism so in order to disable
2695 this mitigation, you need to specify tsx_async_abort=off
2698 Not specifying this option is equivalent to
2701 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2703 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2704 Amount of memory to be used in cases as follows:
2707 2 when the kernel is not able to see the whole system memory;
2708 3 memory that lies after 'mem=' boundary is excluded from
2709 the hypervisor, then assigned to KVM guests.
2711 [X86] Work as limiting max address. Use together
2712 with memmap= to avoid physical address space collisions.
2713 Without memmap= PCI devices could be placed at addresses
2714 belonging to unused RAM.
2716 Note that this only takes effects during boot time since
2717 in above case 3, memory may need be hot added after boot
2718 if system memory of hypervisor is not sufficient.
2720 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2724 [KNL,SH] Allow user to override the default size for
2725 per-device physically contiguous DMA buffers.
2727 memhp_default_state=online/offline
2728 [KNL] Set the initial state for the memory hotplug
2729 onlining policy. If not specified, the default value is
2730 set according to the
2731 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2733 See Documentation/admin-guide/mm/memory-hotplug.rst.
2735 memmap=exactmap [KNL,X86] Enable setting of an exact
2736 E820 memory map, as specified by the user.
2737 Such memmap=exactmap lines can be constructed based on
2738 BIOS output or other requirements. See the memmap=nn@ss
2741 memmap=nn[KMG]@ss[KMG]
2742 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory.
2743 Region of memory to be used is from ss to ss+nn.
2744 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2745 which limits max address to nn[KMG].
2746 Multiple different regions can be specified,
2749 memmap=100M@2G,100M#3G,1G!1024G
2751 memmap=nn[KMG]#ss[KMG]
2752 [KNL,ACPI] Mark specific memory as ACPI data.
2753 Region of memory to be marked is from ss to ss+nn.
2755 memmap=nn[KMG]$ss[KMG]
2756 [KNL,ACPI] Mark specific memory as reserved.
2757 Region of memory to be reserved is from ss to ss+nn.
2758 Example: Exclude memory from 0x18690000-0x1869ffff
2759 memmap=64K$0x18690000
2761 memmap=0x10000$0x18690000
2762 Some bootloaders may need an escape character before '$',
2763 like Grub2, otherwise '$' and the following number
2766 memmap=nn[KMG]!ss[KMG]
2767 [KNL,X86] Mark specific memory as protected.
2768 Region of memory to be used, from ss to ss+nn.
2769 The memory region may be marked as e820 type 12 (0xc)
2770 and is NVDIMM or ADR memory.
2772 memmap=<size>%<offset>-<oldtype>+<newtype>
2773 [KNL,ACPI] Convert memory within the specified region
2774 from <oldtype> to <newtype>. If "-<oldtype>" is left
2775 out, the whole region will be marked as <newtype>,
2776 even if previously unavailable. If "+<newtype>" is left
2777 out, matching memory will be removed. Types are
2778 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2779 3 = ACPI, 12 = PRAM.
2781 memory_corruption_check=0/1 [X86]
2782 Some BIOSes seem to corrupt the first 64k of
2783 memory when doing things like suspend/resume.
2784 Setting this option will scan the memory
2785 looking for corruption. Enabling this will
2786 both detect corruption and prevent the kernel
2787 from using the memory being corrupted.
2788 However, its intended as a diagnostic tool; if
2789 repeatable BIOS-originated corruption always
2790 affects the same memory, you can use memmap=
2791 to prevent the kernel from using that memory.
2793 memory_corruption_check_size=size [X86]
2794 By default it checks for corruption in the low
2795 64k, making this memory unavailable for normal
2796 use. Use this parameter to scan for
2797 corruption in more or less memory.
2799 memory_corruption_check_period=seconds [X86]
2800 By default it checks for corruption every 60
2801 seconds. Use this parameter to check at some
2802 other rate. 0 disables periodic checking.
2804 memtest= [KNL,X86,ARM,PPC] Enable memtest
2806 default : 0 <disable>
2807 Specifies the number of memtest passes to be
2808 performed. Each pass selects another test
2809 pattern from a given set of patterns. Memtest
2810 fills the memory with this pattern, validates
2811 memory contents and reserves bad memory
2812 regions that are detected.
2814 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2815 Valid arguments: on, off
2816 Default (depends on kernel configuration option):
2817 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2818 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2819 mem_encrypt=on: Activate SME
2820 mem_encrypt=off: Do not activate SME
2822 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
2823 for details on when memory encryption can be activated.
2825 mem_sleep_default= [SUSPEND] Default system suspend mode:
2826 s2idle - Suspend-To-Idle
2827 shallow - Power-On Suspend or equivalent (if supported)
2828 deep - Suspend-To-RAM or equivalent (if supported)
2829 See Documentation/admin-guide/pm/sleep-states.rst.
2831 meye.*= [HW] Set MotionEye Camera parameters
2832 See Documentation/admin-guide/media/meye.rst.
2834 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2835 Multi-Function General Purpose Timers on AMD Geode
2838 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2839 the BIOS has incorrectly applied a workaround. TinyBIOS
2840 version 0.98 is known to be affected, 0.99 fixes the
2841 problem by letting the user disable the workaround.
2845 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2846 physical address is ignored.
2848 mini2440= [ARM,HW,KNL]
2849 Format:[0..2][b][c][t]
2851 MINI2440 configuration specification:
2852 0 - The attached screen is the 3.5" TFT
2853 1 - The attached screen is the 7" TFT
2854 2 - The VGA Shield is attached (1024x768)
2855 Leaving out the screen size parameter will not load
2856 the TFT driver, and the framebuffer will be left
2858 b - Enable backlight. The TFT backlight pin will be
2859 linked to the kernel VESA blanking code and a GPIO
2860 LED. This parameter is not necessary when using the
2862 c - Enable the s3c camera interface.
2863 t - Reserved for enabling touchscreen support. The
2864 touchscreen support is not enabled in the mainstream
2865 kernel as of 2.6.30, a preliminary port can be found
2866 in the "bleeding edge" mini2440 support kernel at
2867 https://repo.or.cz/w/linux-2.6/mini2440.git
2870 [X86,PPC,S390,ARM64] Control optional mitigations for
2871 CPU vulnerabilities. This is a set of curated,
2872 arch-independent options, each of which is an
2873 aggregation of existing arch-specific options.
2876 Disable all optional CPU mitigations. This
2877 improves system performance, but it may also
2878 expose users to several CPU vulnerabilities.
2879 Equivalent to: nopti [X86,PPC]
2881 nospectre_v1 [X86,PPC]
2883 nospectre_v2 [X86,PPC,S390,ARM64]
2884 spectre_v2_user=off [X86]
2885 spec_store_bypass_disable=off [X86,PPC]
2886 ssbd=force-off [ARM64]
2889 tsx_async_abort=off [X86]
2890 kvm.nx_huge_pages=off [X86]
2891 no_entry_flush [PPC]
2892 no_uaccess_flush [PPC]
2895 This does not have any effect on
2896 kvm.nx_huge_pages when
2897 kvm.nx_huge_pages=force.
2900 Mitigate all CPU vulnerabilities, but leave SMT
2901 enabled, even if it's vulnerable. This is for
2902 users who don't want to be surprised by SMT
2903 getting disabled across kernel upgrades, or who
2904 have other ways of avoiding SMT-based attacks.
2905 Equivalent to: (default behavior)
2908 Mitigate all CPU vulnerabilities, disabling SMT
2909 if needed. This is for users who always want to
2910 be fully mitigated, even if it means losing SMT.
2911 Equivalent to: l1tf=flush,nosmt [X86]
2912 mds=full,nosmt [X86]
2913 tsx_async_abort=full,nosmt [X86]
2916 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2917 parameter allows control of the logging verbosity for
2918 the additional memory initialisation checks. A value
2919 of 0 disables mminit logging and a level of 4 will
2920 log everything. Information is printed at KERN_DEBUG
2921 so loglevel=8 may also need to be specified.
2924 [KNL] When CONFIG_MODULE_SIG is set, this means that
2925 modules without (valid) signatures will fail to load.
2926 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2927 is always true, so this option does nothing.
2929 module_blacklist= [KNL] Do not load a comma-separated list of
2930 modules. Useful for debugging problem modules.
2933 [MOUSE] Maximum time between finger touching and
2934 leaving touchpad surface for touch to be considered
2935 a tap and be reported as a left button click (for
2936 touchpads working in absolute mode only).
2938 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2939 reporting absolute coordinates, such as tablets
2940 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2941 reporting absolute coordinates, such as tablets
2943 movablecore= [KNL,X86,IA-64,PPC]
2944 Format: nn[KMGTPE] | nn%
2945 This parameter is the complement to kernelcore=, it
2946 specifies the amount of memory used for migratable
2947 allocations. If both kernelcore and movablecore is
2948 specified, then kernelcore will be at *least* the
2949 specified value but may be more. If movablecore on its
2950 own is specified, the administrator must be careful
2951 that the amount of memory usable for all allocations
2954 movable_node [KNL] Boot-time switch to make hotplugable memory
2955 NUMA nodes to be movable. This means that the memory
2956 of such nodes will be usable only for movable
2957 allocations which rules out almost all kernel
2958 allocations. Use with caution!
2960 MTD_Partition= [MTD]
2961 Format: <name>,<region-number>,<size>,<offset>
2963 MTD_Region= [MTD] Format:
2964 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2967 See drivers/mtd/parsers/cmdlinepart.c
2969 multitce=off [PPC] This parameter disables the use of the pSeries
2970 firmware feature for updating multiple TCE entries
2973 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2975 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2977 boundary - index of last SLC block on Flex-OneNAND.
2978 The remaining blocks are configured as MLC blocks.
2979 lock - Configure if Flex-OneNAND boundary should be locked.
2980 Once locked, the boundary cannot be changed.
2981 1 indicates lock status, 0 indicates unlock status.
2984 ARM/S3C2412 JIVE boot control
2986 See arch/arm/mach-s3c/mach-jive.c
2988 mtouchusb.raw_coordinates=
2989 [HW] Make the MicroTouch USB driver use raw coordinates
2990 ('y', default) or cooked coordinates ('n')
2992 mtrr_chunk_size=nn[KMG] [X86]
2993 used for mtrr cleanup. It is largest continuous chunk
2994 that could hold holes aka. UC entries.
2996 mtrr_gran_size=nn[KMG] [X86]
2997 Used for mtrr cleanup. It is granularity of mtrr block.
2999 Large value could prevent small alignment from
3002 mtrr_spare_reg_nr=n [X86]
3004 Range: 0,7 : spare reg number
3006 Used for mtrr cleanup. It is spare mtrr entries number.
3007 Set to 2 or more if your graphical card needs more.
3009 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3011 netdev= [NET] Network devices parameters
3012 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3013 Note that mem_start is often overloaded to mean
3014 something different and driver-specific.
3015 This usage is only documented in each driver source
3019 [NETFILTER] Enable connection tracking flow accounting
3020 0 to disable accounting
3021 1 to enable accounting
3024 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3025 See Documentation/admin-guide/nfs/nfsroot.rst.
3027 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3028 See Documentation/admin-guide/nfs/nfsroot.rst.
3030 nfsrootdebug [NFS] enable nfsroot debugging messages.
3031 See Documentation/admin-guide/nfs/nfsroot.rst.
3033 nfs.callback_nr_threads=
3034 [NFSv4] set the total number of threads that the
3035 NFS client will assign to service NFSv4 callback
3038 nfs.callback_tcpport=
3039 [NFS] set the TCP port on which the NFSv4 callback
3040 channel should listen.
3043 [NFS] sets the pathname to the program which is used
3044 to update the NFS client cache entries.
3046 nfs.cache_getent_timeout=
3047 [NFS] sets the timeout after which an attempt to
3048 update a cache entry is deemed to have failed.
3050 nfs.idmap_cache_timeout=
3051 [NFS] set the maximum lifetime for idmapper cache
3055 [NFS] enable 64-bit inode numbers.
3056 If zero, the NFS client will fake up a 32-bit inode
3057 number for the readdir() and stat() syscalls instead
3058 of returning the full 64-bit number.
3059 The default is to return 64-bit inode numbers.
3061 nfs.max_session_cb_slots=
3062 [NFSv4.1] Sets the maximum number of session
3063 slots the client will assign to the callback
3064 channel. This determines the maximum number of
3065 callbacks the client will process in parallel for
3066 a particular server.
3068 nfs.max_session_slots=
3069 [NFSv4.1] Sets the maximum number of session slots
3070 the client will attempt to negotiate with the server.
3071 This limits the number of simultaneous RPC requests
3072 that the client can send to the NFSv4.1 server.
3073 Note that there is little point in setting this
3074 value higher than the max_tcp_slot_table_limit.
3076 nfs.nfs4_disable_idmapping=
3077 [NFSv4] When set to the default of '1', this option
3078 ensures that both the RPC level authentication
3079 scheme and the NFS level operations agree to use
3080 numeric uids/gids if the mount is using the
3081 'sec=sys' security flavour. In effect it is
3082 disabling idmapping, which can make migration from
3083 legacy NFSv2/v3 systems to NFSv4 easier.
3084 Servers that do not support this mode of operation
3085 will be autodetected by the client, and it will fall
3086 back to using the idmapper.
3087 To turn off this behaviour, set the value to '0'.
3089 [NFS4] Specify an additional fixed unique ident-
3090 ification string that NFSv4 clients can insert into
3091 their nfs_client_id4 string. This is typically a
3092 UUID that is generated at system install time.
3094 nfs.send_implementation_id =
3095 [NFSv4.1] Send client implementation identification
3096 information in exchange_id requests.
3097 If zero, no implementation identification information
3099 The default is to send the implementation identification
3102 nfs.recover_lost_locks =
3103 [NFSv4] Attempt to recover locks that were lost due
3104 to a lease timeout on the server. Please note that
3105 doing this risks data corruption, since there are
3106 no guarantees that the file will remain unchanged
3107 after the locks are lost.
3108 If you want to enable the kernel legacy behaviour of
3109 attempting to recover these locks, then set this
3111 The default parameter value of '0' causes the kernel
3112 not to attempt recovery of lost locks.
3114 nfs4.layoutstats_timer =
3115 [NFSv4.2] Change the rate at which the kernel sends
3116 layoutstats to the pNFS metadata server.
3118 Setting this to value to 0 causes the kernel to use
3119 whatever value is the default set by the layout
3120 driver. A non-zero value sets the minimum interval
3121 in seconds between layoutstats transmissions.
3123 nfsd.nfs4_disable_idmapping=
3124 [NFSv4] When set to the default of '1', the NFSv4
3125 server will return only numeric uids and gids to
3126 clients using auth_sys, and will accept numeric uids
3127 and gids from such clients. This is intended to ease
3128 migration from NFSv2/v3.
3130 nmi_backtrace.backtrace_idle [KNL]
3131 Dump stacks even of idle CPUs in response to an
3132 NMI stack-backtrace request.
3134 nmi_debug= [KNL,SH] Specify one or more actions to take
3135 when a NMI is triggered.
3136 Format: [state][,regs][,debounce][,die]
3138 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3139 Format: [panic,][nopanic,][num]
3141 0 - turn hardlockup detector in nmi_watchdog off
3142 1 - turn hardlockup detector in nmi_watchdog on
3143 When panic is specified, panic when an NMI watchdog
3144 timeout occurs (or 'nopanic' to not panic on an NMI
3145 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3146 To disable both hard and soft lockup detectors,
3147 please see 'nowatchdog'.
3148 This is useful when you use a panic=... timeout and
3149 need the box quickly up again.
3151 These settings can be accessed at runtime via
3152 the nmi_watchdog and hardlockup_panic sysctls.
3154 netpoll.carrier_timeout=
3155 [NET] Specifies amount of time (in seconds) that
3156 netpoll should wait for a carrier. By default netpoll
3159 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3160 emulation library even if a 387 maths coprocessor
3163 no5lvl [X86-64] Disable 5-level paging mode. Forces
3164 kernel to use 4-level paging instead.
3166 nofsgsbase [X86] Disables FSGSBASE instructions.
3169 [HW] Never suspend the console
3170 Disable suspending of consoles during suspend and
3171 hibernate operations. Once disabled, debugging
3172 messages can reach various consoles while the rest
3173 of the system is being put to sleep (ie, while
3174 debugging driver suspend/resume hooks). This may
3175 not work reliably with all consoles, but is known
3176 to work with serial and VGA consoles.
3177 To facilitate more flexible debugging, we also add
3178 console_suspend, a printk module parameter to control
3179 it. Users could use console_suspend (usually
3180 /sys/module/printk/parameters/console_suspend) to
3181 turn on/off it dynamically.
3183 novmcoredd [KNL,KDUMP]
3184 Disable device dump. Device dump allows drivers to
3185 append dump data to vmcore so you can collect driver
3186 specified debug info. Drivers can append the data
3187 without any limit and this data is stored in memory,
3188 so this may cause significant memory stress. Disabling
3189 device dump can help save memory but the driver debug
3190 data will be no longer available. This parameter
3191 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3194 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3195 caches in the slab allocator. Saves per-node memory,
3196 but will impact performance.
3200 noaltinstr [S390] Disables alternative instructions patching
3201 (CPU alternatives feature).
3203 noapic [SMP,APIC] Tells the kernel to not make use of any
3204 IOAPICs that may be present in the system.
3206 noautogroup Disable scheduler automatic task group creation.
3208 nobats [PPC] Do not use BATs for mapping kernel lowmem
3209 on "Classic" PPC cores.
3213 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
3215 nodelayacct [KNL] Disable per-task delay accounting
3217 nodsp [SH] Disable hardware DSP at boot time.
3219 noefi Disable EFI runtime services support.
3221 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
3226 On X86-32 available only on PAE configured kernels.
3227 noexec=on: enable non-executable mappings (default)
3228 noexec=off: disable non-executable mappings
3231 Disable SMAP (Supervisor Mode Access Prevention)
3232 even if it is supported by processor.
3235 Disable SMEP (Supervisor Mode Execution Prevention)
3236 even if it is supported by processor.
3239 This affects only 32-bit executables.
3240 noexec32=on: enable non-executable mappings (default)
3241 read doesn't imply executable mappings
3242 noexec32=off: disable non-executable mappings
3243 read implies executable mappings
3245 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3247 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3248 register save and restore. The kernel will only save
3249 legacy floating-point registers on task switch.
3251 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
3253 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3254 Equivalent to smt=1.
3256 [KNL,X86] Disable symmetric multithreading (SMT).
3257 nosmt=force: Force disable SMT, cannot be undone
3258 via the sysfs control file.
3260 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3261 (bounds check bypass). With this option data leaks are
3262 possible in the system.
3264 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3265 the Spectre variant 2 (indirect branch prediction)
3266 vulnerability. System may allow data leaks with this
3269 nospec_store_bypass_disable
3270 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3273 [PPC] Don't flush the L1-D cache after accessing user data.
3275 noxsave [BUGS=X86] Disables x86 extended register state save
3276 and restore using xsave. The kernel will fallback to
3277 enabling legacy floating-point and sse state.
3279 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3280 register states. The kernel will fall back to use
3281 xsave to save the states. By using this parameter,
3282 performance of saving the states is degraded because
3283 xsave doesn't support modified optimization while
3284 xsaveopt supports it on xsaveopt enabled systems.
3286 noxsaves [X86] Disables xsaves and xrstors used in saving and
3287 restoring x86 extended register state in compacted
3288 form of xsave area. The kernel will fall back to use
3289 xsaveopt and xrstor to save and restore the states
3290 in standard form of xsave area. By using this
3291 parameter, xsave area per process might occupy more
3292 memory on xsaves enabled systems.
3294 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait
3295 in do_idle() and not use the arch_cpu_idle()
3296 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3297 to be effective. This is useful on platforms where the
3298 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3299 correctly or when doing power measurements to evalute
3300 the impact of the sleep instructions. This is also
3301 useful when using JTAG debugger.
3303 no_file_caps Tells the kernel not to honor file capabilities. The
3304 only way then for a file to be executed with privilege
3305 is to be setuid root or executed by root.
3307 nohalt [IA-64] Tells the kernel not to use the power saving
3308 function PAL_HALT_LIGHT when idle. This increases
3309 power-consumption. On the positive side, it reduces
3310 interrupt wake-up latency, which may improve performance
3311 in certain environments such as networked servers or
3315 Force pointers printed to the console or buffers to be
3316 unhashed. By default, when a pointer is printed via %p
3317 format string, that pointer is "hashed", i.e. obscured
3318 by hashing the pointer value. This is a security feature
3319 that hides actual kernel addresses from unprivileged
3320 users, but it also makes debugging the kernel more
3321 difficult since unequal pointers can no longer be
3322 compared. However, if this command-line option is
3323 specified, then all normal pointers will have their true
3324 value printed. Pointers printed via %pK may still be
3325 hashed. This option should only be specified when
3326 debugging the kernel. Please do not use on production
3329 nohibernate [HIBERNATION] Disable hibernation and resume.
3331 nohz= [KNL] Boottime enable/disable dynamic ticks
3332 Valid arguments: on, off
3335 nohz_full= [KNL,BOOT,SMP,ISOL]
3336 The argument is a cpu list, as described above.
3337 In kernels built with CONFIG_NO_HZ_FULL=y, set
3338 the specified list of CPUs whose tick will be stopped
3339 whenever possible. The boot CPU will be forced outside
3340 the range to maintain the timekeeping. Any CPUs
3341 in this list will have their RCU callbacks offloaded,
3342 just as if they had also been called out in the
3343 rcu_nocbs= boot parameter.
3345 noiotrap [SH] Disables trapped I/O port accesses.
3347 noirqdebug [X86-32] Disables the code which attempts to detect and
3348 disable unhandled interrupt sources.
3350 no_timer_check [X86,APIC] Disables the code which tests for
3351 broken timer IRQ sources.
3353 noisapnp [ISAPNP] Disables ISA PnP code.
3355 noinitrd [RAM] Tells the kernel not to load any configured
3358 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3360 [Deprecated - use intremap=off]
3364 noinvpcid [X86] Disable the INVPCID cpu feature.
3366 nojitter [IA-64] Disables jitter checking for ITC timers.
3368 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3370 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3374 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3375 clock and use the default one.
3377 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
3378 accounting. steal time is computed, but won't
3379 influence scheduler behaviour
3381 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3383 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3385 noltlbs [PPC] Do not use large page/tlb entries for kernel
3386 lowmem mapping on PPC40x and PPC8xx
3388 nomca [IA-64] Disable machine check abort handling
3390 nomce [X86-32] Disable Machine Check Exception
3392 nomfgpt [X86-32] Disable Multi-Function General Purpose
3393 Timer usage (for AMD Geode machines).
3395 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3396 shutdown the other cpus. Instead use the REBOOT_VECTOR
3399 nomodule Disable module load
3401 nopat [X86] Disable PAT (page attribute table extension of
3402 pagetables) support.
3404 nopcid [X86-64] Disable the PCID cpu feature.
3406 norandmaps Don't use address space randomization. Equivalent to
3407 echo 0 > /proc/sys/kernel/randomize_va_space
3409 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3410 with UP alternatives
3412 nordrand [X86] Disable kernel use of the RDRAND and
3413 RDSEED instructions even if they are supported
3414 by the processor. RDRAND and RDSEED are still
3415 available to user space applications.
3417 noresume [SWSUSP] Disables resume and restores original swap
3420 no-scroll [VGA] Disables scrollback.
3421 This is required for the Braillex ib80-piezo Braille
3422 reader made by F.H. Papenmeier (Germany).
3426 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3428 nosgx [X86-64,SGX] Disables Intel SGX kernel support.
3430 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3431 and disable the IO APIC. legacy for "maxcpus=0".
3433 nosoftlockup [KNL] Disable the soft-lockup detector.
3435 nosync [HW,M68K] Disables sync negotiation for all devices.
3437 nowatchdog [KNL] Disable both lockup detectors, i.e.
3438 soft-lockup and NMI watchdog (hard-lockup).
3442 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3444 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3445 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3446 Some features depend on CPU0. Known dependencies are:
3447 1. Resume from suspend/hibernate depends on CPU0.
3448 Suspend/hibernate will fail if CPU0 is offline and you
3449 need to online CPU0 before suspend/hibernate.
3450 2. PIC interrupts also depend on CPU0. CPU0 can't be
3451 removed if a PIC interrupt is detected.
3452 It's said poweroff/reboot may depend on CPU0 on some
3453 machines although I haven't seen such issues so far
3454 after CPU0 is offline on a few tested machines.
3455 If the dependencies are under your control, you can
3456 turn on cpu0_hotplug.
3458 nps_mtm_hs_ctr= [KNL,ARC]
3459 This parameter sets the maximum duration, in
3460 cycles, each HW thread of the CTOP can run
3461 without interruptions, before HW switches it.
3462 The actual maximum duration is 16 times this
3464 Format: integer between 1 and 255
3467 nptcg= [IA-64] Override max number of concurrent global TLB
3468 purges which is reported from either PAL_VM_SUMMARY or
3471 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3472 could support. nr_cpus=n : n >= 1 limits the kernel to
3473 support 'n' processors. It could be larger than the
3474 number of already plugged CPU during bootup, later in
3475 runtime you can physically add extra cpu until it reaches
3476 n. So during boot up some boot time memory for per-cpu
3477 variables need be pre-allocated for later physical cpu
3480 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3482 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
3484 Allowed values are enable and disable
3486 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3487 'node', 'default' can be specified
3488 This can be set from sysctl after boot.
3489 See Documentation/admin-guide/sysctl/vm.rst for details.
3491 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3492 See Documentation/core-api/debugging-via-ohci1394.rst for more
3495 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3496 Rather than timing out after 20 ms if an EC
3497 command is not properly ACKed, override the length
3498 of the timeout. We have interrupts disabled while
3499 waiting for the ACK, so if this is set too high
3500 interrupts *may* be lost!
3502 omap_mux= [OMAP] Override bootloader pin multiplexing.
3503 Format: <mux_mode0.mode_name=value>...
3504 For example, to override I2C bus2:
3505 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3507 oops=panic Always panic on oopses. Default is to just kill the
3508 process, but there is a small probability of
3509 deadlocking the machine.
3510 This will also cause panics on machine check exceptions.
3511 Useful together with panic=30 to trigger a reboot.
3514 [KNL] Boolean flag to control whether the page allocator
3515 should randomize its free lists. The randomization may
3516 be automatically enabled if the kernel detects it is
3517 running on a platform with a direct-mapped memory-side
3518 cache, and this parameter can be used to
3519 override/disable that behavior. The state of the flag
3520 can be read from sysfs at:
3521 /sys/module/page_alloc/parameters/shuffle.
3523 page_owner= [KNL] Boot-time page_owner enabling option.
3524 Storage of the information about who allocated
3525 each page is disabled in default. With this switch,
3527 on: enable the feature
3529 page_poison= [KNL] Boot-time parameter changing the state of
3530 poisoning on the buddy allocator, available with
3531 CONFIG_PAGE_POISONING=y.
3532 off: turn off poisoning (default)
3533 on: turn on poisoning
3535 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3536 timeout > 0: seconds before rebooting
3537 timeout = 0: wait forever
3538 timeout < 0: reboot immediately
3541 panic_print= Bitmask for printing system info when panic happens.
3542 User can chose combination of the following bits:
3543 bit 0: print all tasks info
3544 bit 1: print system memory info
3545 bit 2: print timer info
3546 bit 3: print locks info if CONFIG_LOCKDEP is on
3547 bit 4: print ftrace buffer
3548 bit 5: print all printk messages in buffer
3550 panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
3551 Format: <hex>[,nousertaint]
3552 Hexadecimal bitmask representing the set of TAINT flags
3553 that will cause the kernel to panic when add_taint() is
3554 called with any of the flags in this set.
3555 The optional switch "nousertaint" can be utilized to
3556 prevent userspace forced crashes by writing to sysctl
3557 /proc/sys/kernel/tainted any flagset matching with the
3558 bitmask set on panic_on_taint.
3559 See Documentation/admin-guide/tainted-kernels.rst for
3560 extra details on the taint flags that users can pick
3561 to compose the bitmask to assign to panic_on_taint.
3563 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3566 crash_kexec_post_notifiers
3567 Run kdump after running panic-notifiers and dumping
3568 kmsg. This only for the users who doubt kdump always
3569 succeeds in any situation.
3570 Note that this also increases risks of kdump failure,
3571 because some panic notifiers can make the crashed
3572 kernel more unstable.
3574 parkbd.port= [HW] Parallel port number the keyboard adapter is
3575 connected to, default is 0.
3577 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3578 0 for XT, 1 for AT (default is AT).
3581 parport= [HW,PPT] Specify parallel ports. 0 disables.
3582 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3583 Use 'auto' to force the driver to use any
3584 IRQ/DMA settings detected (the default is to
3585 ignore detected IRQ/DMA settings because of
3586 possible conflicts). You can specify the base
3587 address, IRQ, and DMA settings; IRQ and DMA
3588 should be numbers, or 'auto' (for using detected
3589 settings on that particular port), or 'nofifo'
3590 (to avoid using a FIFO even if it is detected).
3591 Parallel ports are assigned in the order they
3592 are specified on the command line, starting
3595 parport_init_mode= [HW,PPT]
3596 Configure VIA parallel port to operate in
3597 a specific mode. This is necessary on Pegasos
3598 computer where firmware has no options for setting
3599 up parallel port mode and sets it to spp.
3600 Currently this function knows 686a and 8231 chips.
3601 Format: [spp|ps2|epp|ecp|ecpepp]
3603 pata_legacy.all= [HW,LIBATA]
3605 Set to non-zero to probe primary and secondary ISA
3606 port ranges on PCI systems where no PCI PATA device
3607 has been found at either range. Disabled by default.
3609 pata_legacy.autospeed= [HW,LIBATA]
3611 Set to non-zero if a chip is present that snoops speed
3612 changes. Disabled by default.
3614 pata_legacy.ht6560a= [HW,LIBATA]
3616 Set to 1, 2, or 3 for HT 6560A on the primary channel,
3617 the secondary channel, or both channels respectively.
3618 Disabled by default.
3620 pata_legacy.ht6560b= [HW,LIBATA]
3622 Set to 1, 2, or 3 for HT 6560B on the primary channel,
3623 the secondary channel, or both channels respectively.
3624 Disabled by default.
3626 pata_legacy.iordy_mask= [HW,LIBATA]
3628 IORDY enable mask. Set individual bits to allow IORDY
3629 for the respective channel. Bit 0 is for the first
3630 legacy channel handled by this driver, bit 1 is for
3631 the second channel, and so on. The sequence will often
3632 correspond to the primary legacy channel, the secondary
3633 legacy channel, and so on, but the handling of a PCI
3634 bus and the use of other driver options may interfere
3635 with the sequence. By default IORDY is allowed across
3638 pata_legacy.opti82c46x= [HW,LIBATA]
3640 Set to 1, 2, or 3 for Opti 82c611A on the primary
3641 channel, the secondary channel, or both channels
3642 respectively. Disabled by default.
3644 pata_legacy.opti82c611a= [HW,LIBATA]
3646 Set to 1, 2, or 3 for Opti 82c465MV on the primary
3647 channel, the secondary channel, or both channels
3648 respectively. Disabled by default.
3650 pata_legacy.pio_mask= [HW,LIBATA]
3652 PIO mode mask for autospeed devices. Set individual
3653 bits to allow the use of the respective PIO modes.
3654 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
3655 All modes allowed by default.
3657 pata_legacy.probe_all= [HW,LIBATA]
3659 Set to non-zero to probe tertiary and further ISA
3660 port ranges on PCI systems. Disabled by default.
3662 pata_legacy.probe_mask= [HW,LIBATA]
3664 Probe mask for legacy ISA PATA ports. Depending on
3665 platform configuration and the use of other driver
3666 options up to 6 legacy ports are supported: 0x1f0,
3667 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
3668 of individual ports can be disabled by setting the
3669 corresponding bits in the mask to 1. Bit 0 is for
3670 the first port in the list above (0x1f0), and so on.
3671 By default all supported ports are probed.
3673 pata_legacy.qdi= [HW,LIBATA]
3675 Set to non-zero to probe QDI controllers. By default
3676 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
3678 pata_legacy.winbond= [HW,LIBATA]
3680 Set to non-zero to probe Winbond controllers. Use
3681 the standard I/O port (0x130) if 1, otherwise the
3682 value given is the I/O port to use (typically 0x1b0).
3683 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
3686 pata_platform.pio_mask= [HW,LIBATA]
3688 Supported PIO mode mask. Set individual bits to allow
3689 the use of the respective PIO modes. Bit 0 is for
3690 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
3694 Halt all CPUs after the first oops has been printed for
3695 the specified number of seconds. This is to be used if
3696 your oopses keep scrolling off the screen.
3701 See header of drivers/block/paride/pcd.c.
3702 See also Documentation/admin-guide/blockdev/paride.rst.
3704 pci=option[,option...] [PCI] various PCI subsystem options.
3706 Some options herein operate on a specific device
3707 or a set of devices (<pci_dev>). These are
3708 specified in one of the following formats:
3710 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3711 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3713 Note: the first format specifies a PCI
3714 bus/device/function address which may change
3715 if new hardware is inserted, if motherboard
3716 firmware changes, or due to changes caused
3717 by other kernel parameters. If the
3718 domain is left unspecified, it is
3719 taken to be zero. Optionally, a path
3720 to a device through multiple device/function
3721 addresses can be specified after the base
3722 address (this is more robust against
3723 renumbering issues). The second format
3724 selects devices using IDs from the
3725 configuration space which may match multiple
3726 devices in the system.
3728 earlydump dump PCI config space before the kernel
3730 off [X86] don't probe for the PCI bus
3731 bios [X86-32] force use of PCI BIOS, don't access
3732 the hardware directly. Use this if your machine
3733 has a non-standard PCI host bridge.
3734 nobios [X86-32] disallow use of PCI BIOS, only direct
3735 hardware access methods are allowed. Use this
3736 if you experience crashes upon bootup and you
3737 suspect they are caused by the BIOS.
3738 conf1 [X86] Force use of PCI Configuration Access
3739 Mechanism 1 (config address in IO port 0xCF8,
3740 data in IO port 0xCFC, both 32-bit).
3741 conf2 [X86] Force use of PCI Configuration Access
3742 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3743 the function, IO port 0xCFA, also 8-bit, sets
3744 bus number. The config space is then accessed
3745 through ports 0xC000-0xCFFF).
3746 See http://wiki.osdev.org/PCI for more info
3747 on the configuration access mechanisms.
3748 noaer [PCIE] If the PCIEAER kernel config parameter is
3749 enabled, this kernel boot option can be used to
3750 disable the use of PCIE advanced error reporting.
3751 nodomains [PCI] Disable support for multiple PCI
3752 root domains (aka PCI segments, in ACPI-speak).
3753 nommconf [X86] Disable use of MMCONFIG for PCI
3755 check_enable_amd_mmconf [X86] check for and enable
3756 properly configured MMIO access to PCI
3757 config space on AMD family 10h CPU
3758 nomsi [MSI] If the PCI_MSI kernel config parameter is
3759 enabled, this kernel boot option can be used to
3760 disable the use of MSI interrupts system-wide.
3761 noioapicquirk [APIC] Disable all boot interrupt quirks.
3762 Safety option to keep boot IRQs enabled. This
3763 should never be necessary.
3764 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3765 primary IO-APIC for bridges that cannot disable
3766 boot IRQs. This fixes a source of spurious IRQs
3767 when the system masks IRQs.
3768 noioapicreroute [APIC] Disable workaround that uses the
3769 boot IRQ equivalent of an IRQ that connects to
3770 a chipset where boot IRQs cannot be disabled.
3771 The opposite of ioapicreroute.
3772 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3773 routing table. These calls are known to be buggy
3774 on several machines and they hang the machine
3775 when used, but on other computers it's the only
3776 way to get the interrupt routing table. Try
3777 this option if the kernel is unable to allocate
3778 IRQs or discover secondary PCI buses on your
3780 rom [X86] Assign address space to expansion ROMs.
3781 Use with caution as certain devices share
3782 address decoders between ROMs and other
3784 norom [X86] Do not assign address space to
3785 expansion ROMs that do not already have
3786 BIOS assigned address ranges.
3787 nobar [X86] Do not assign address space to the
3788 BARs that weren't assigned by the BIOS.
3789 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3790 assigned automatically to PCI devices. You can
3791 make the kernel exclude IRQs of your ISA cards
3793 pirqaddr=0xAAAAA [X86] Specify the physical address
3794 of the PIRQ table (normally generated
3795 by the BIOS) if it is outside the
3796 F0000h-100000h range.
3797 lastbus=N [X86] Scan all buses thru bus #N. Can be
3798 useful if the kernel is unable to find your
3799 secondary buses and you want to tell it
3800 explicitly which ones they are.
3801 assign-busses [X86] Always assign all PCI bus
3802 numbers ourselves, overriding
3803 whatever the firmware may have done.
3804 usepirqmask [X86] Honor the possible IRQ mask stored
3805 in the BIOS $PIR table. This is needed on
3806 some systems with broken BIOSes, notably
3807 some HP Pavilion N5400 and Omnibook XE3
3808 notebooks. This will have no effect if ACPI
3809 IRQ routing is enabled.
3810 noacpi [X86] Do not use ACPI for IRQ routing
3811 or for PCI scanning.
3812 use_crs [X86] Use PCI host bridge window information
3813 from ACPI. On BIOSes from 2008 or later, this
3814 is enabled by default. If you need to use this,
3815 please report a bug.
3816 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3817 If you need to use this, please report a bug.
3818 routeirq Do IRQ routing for all PCI devices.
3819 This is normally done in pci_enable_device(),
3820 so this option is a temporary workaround
3821 for broken drivers that don't call it.
3822 skip_isa_align [X86] do not align io start addr, so can
3823 handle more pci cards
3824 noearly [X86] Don't do any early type 1 scanning.
3825 This might help on some broken boards which
3826 machine check when some devices' config space
3827 is read. But various workarounds are disabled
3828 and some IOMMU drivers will not work.
3829 bfsort Sort PCI devices into breadth-first order.
3830 This sorting is done to get a device
3831 order compatible with older (<= 2.4) kernels.
3832 nobfsort Don't sort PCI devices into breadth-first order.
3833 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3834 tuning and use the BIOS-configured MPS defaults.
3835 pcie_bus_safe Set every device's MPS to the largest value
3836 supported by all devices below the root complex.
3837 pcie_bus_perf Set device MPS to the largest allowable MPS
3838 based on its parent bus. Also set MRRS (Max
3839 Read Request Size) to the largest supported
3840 value (no larger than the MPS that the device
3841 or bus can support) for best performance.
3842 pcie_bus_peer2peer Set every device's MPS to 128B, which
3843 every device is guaranteed to support. This
3844 configuration allows peer-to-peer DMA between
3845 any pair of devices, possibly at the cost of
3846 reduced performance. This also guarantees
3847 that hot-added devices will work.
3848 cbiosize=nn[KMG] The fixed amount of bus space which is
3849 reserved for the CardBus bridge's IO window.
3850 The default value is 256 bytes.
3851 cbmemsize=nn[KMG] The fixed amount of bus space which is
3852 reserved for the CardBus bridge's memory
3853 window. The default value is 64 megabytes.
3856 [<order of align>@]<pci_dev>[; ...]
3857 Specifies alignment and device to reassign
3858 aligned memory resources. How to
3859 specify the device is described above.
3860 If <order of align> is not specified,
3861 PAGE_SIZE is used as alignment.
3862 A PCI-PCI bridge can be specified if resource
3863 windows need to be expanded.
3864 To specify the alignment for several
3865 instances of a device, the PCI vendor,
3866 device, subvendor, and subdevice may be
3867 specified, e.g., 12@pci:8086:9c22:103c:198f
3868 for 4096-byte alignment.
3869 ecrc= Enable/disable PCIe ECRC (transaction layer
3870 end-to-end CRC checking).
3871 bios: Use BIOS/firmware settings. This is the
3875 hpiosize=nn[KMG] The fixed amount of bus space which is
3876 reserved for hotplug bridge's IO window.
3877 Default size is 256 bytes.
3878 hpmmiosize=nn[KMG] The fixed amount of bus space which is
3879 reserved for hotplug bridge's MMIO window.
3880 Default size is 2 megabytes.
3881 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
3882 reserved for hotplug bridge's MMIO_PREF window.
3883 Default size is 2 megabytes.
3884 hpmemsize=nn[KMG] The fixed amount of bus space which is
3885 reserved for hotplug bridge's MMIO and
3887 Default size is 2 megabytes.
3888 hpbussize=nn The minimum amount of additional bus numbers
3889 reserved for buses below a hotplug bridge.
3891 realloc= Enable/disable reallocating PCI bridge resources
3892 if allocations done by BIOS are too small to
3893 accommodate resources required by all child
3895 off: Turn realloc off
3897 realloc same as realloc=on
3898 noari do not use PCIe ARI.
3899 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3900 do not use PCIe ATS (and IOMMU device IOTLB).
3901 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3902 only look for one device below a PCIe downstream
3904 big_root_window Try to add a big 64bit memory window to the PCIe
3905 root complex on AMD CPUs. Some GFX hardware
3906 can resize a BAR to allow access to all VRAM.
3907 Adding the window is slightly risky (it may
3908 conflict with unreported devices), so this
3910 disable_acs_redir=<pci_dev>[; ...]
3911 Specify one or more PCI devices (in the format
3912 specified above) separated by semicolons.
3913 Each device specified will have the PCI ACS
3914 redirect capabilities forced off which will
3915 allow P2P traffic between devices through
3916 bridges without forcing it upstream. Note:
3917 this removes isolation between devices and
3918 may put more devices in an IOMMU group.
3919 force_floating [S390] Force usage of floating interrupts.
3920 nomio [S390] Do not use MIO instructions.
3921 norid [S390] ignore the RID field and force use of
3922 one PCI domain per PCI function
3924 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3927 force Enable ASPM even on devices that claim not to support it.
3928 WARNING: Forcing ASPM on may cause system lockups.
3930 pcie_ports= [PCIE] PCIe port services handling:
3931 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3932 even if the platform doesn't give the OS permission to
3933 use them. This may cause conflicts if the platform
3934 also tries to use these services.
3935 dpc-native Use native PCIe service for DPC only. May
3936 cause conflicts if firmware uses AER or DPC.
3937 compat Disable native PCIe services (PME, AER, DPC, PCIe
3940 pcie_port_pm= [PCIE] PCIe port power management handling:
3941 off Disable power management of all PCIe ports
3942 force Forcibly enable power management of all PCIe ports
3944 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3945 nomsi Do not use MSI for native PCIe PME signaling (this makes
3946 all PCIe root ports use INTx for all services).
3948 pcmv= [HW,PCMCIA] BadgePAD 4
3952 Keep all power-domains already enabled by bootloader on,
3953 even if no driver has claimed them. This is useful
3954 for debug and development, but should not be
3955 needed on a platform with proper driver support.
3958 See Documentation/admin-guide/blockdev/paride.rst.
3960 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3963 See arch/parisc/kernel/pdc_chassis.c
3965 percpu_alloc= Select which percpu first chunk allocator to use.
3966 Currently supported values are "embed" and "page".
3967 Archs may support subset or none of the selections.
3968 See comments in mm/percpu.c for details on each
3969 allocator. This parameter is primarily for debugging
3970 and performance comparison.
3973 See Documentation/admin-guide/blockdev/paride.rst.
3976 See Documentation/admin-guide/blockdev/paride.rst.
3978 pirq= [SMP,APIC] Manual mp-table setup
3979 See Documentation/x86/i386/IO-APIC.rst.
3981 plip= [PPT,NET] Parallel port network link
3982 Format: { parport<nr> | timid | 0 }
3983 See also Documentation/admin-guide/parport.rst.
3985 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3986 Override pmtimer IOPort with a hex value.
3989 pm_debug_messages [SUSPEND,KNL]
3990 Enable suspend/resume debug messages during boot up.
3993 Enable PNP debug messages (depends on the
3994 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3995 via /sys/module/pnp/parameters/debug. We always show
3996 current resource usage; turning this on also shows
3997 possible settings and some assignment information.
4003 { on | off | curr | res | no-curr | no-res }
4006 [ISAPNP] Exclude IRQs for the autoconfiguration
4009 [ISAPNP] Exclude DMAs for the autoconfiguration
4011 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4012 Ranges are in pairs (I/O port base and size).
4015 [ISAPNP] Exclude memory regions for the
4017 Ranges are in pairs (memory base and size).
4019 ports= [IP_VS_FTP] IPVS ftp helper module
4021 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4023 Format: <port>,<port>....
4025 powersave=off [PPC] This option disables power saving features.
4026 It specifically disables cpuidle and sets the
4027 platform machine description specific power_save
4028 function to NULL. On Idle the CPU just reduces
4031 ppc_strict_facility_enable
4032 [PPC] This option catches any kernel floating point,
4033 Altivec, VSX and SPE outside of regions specifically
4034 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4035 There is some performance impact when enabling this.
4039 Disable Hardware Transactional Memory
4042 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4043 none - Limited to cond_resched() calls
4044 voluntary - Limited to cond_resched() and might_sleep() calls
4045 full - Any section that isn't explicitly preempt disabled
4046 can be preempted anytime.
4048 print-fatal-signals=
4049 [KNL] debug: print fatal signals
4051 If enabled, warn about various signal handling
4052 related application anomalies: too many signals,
4053 too many POSIX.1 timers, fatal signals causing a
4056 If you hit the warning due to signal overflow,
4057 you might want to try "ulimit -i unlimited".
4061 printk.always_kmsg_dump=
4062 Trigger kmsg_dump for cases other than kernel oops or
4064 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4067 printk.devkmsg={on,off,ratelimit}
4068 Control writing to /dev/kmsg.
4069 on - unlimited logging to /dev/kmsg from userspace
4070 off - logging to /dev/kmsg disabled
4071 ratelimit - ratelimit the logging
4074 printk.time= Show timing data prefixed to each printk message line
4075 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4077 processor.max_cstate= [HW,ACPI]
4078 Limit processor to maximum C-state
4079 max_cstate=9 overrides any DMI blacklist limit.
4081 processor.nocst [HW,ACPI]
4082 Ignore the _CST method to determine C-states,
4083 instead using the legacy FADT method
4085 profile= [KNL] Enable kernel profiling via /proc/profile
4086 Format: [<profiletype>,]<number>
4087 Param: <profiletype>: "schedule", "sleep", or "kvm"
4088 [defaults to kernel profiling]
4089 Param: "schedule" - profile schedule points.
4090 Param: "sleep" - profile D-state sleeping (millisecs).
4091 Requires CONFIG_SCHEDSTATS
4092 Param: "kvm" - profile VM exits.
4093 Param: <number> - step/bucket size as a power of 2 for
4094 statistical time based profiling.
4096 prompt_ramdisk= [RAM] [Deprecated]
4098 prot_virt= [S390] enable hosting protected virtual machines
4099 isolated from the hypervisor (if hardware supports
4103 psi= [KNL] Enable or disable pressure stall information
4107 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4108 probe for; one of (bare|imps|exps|lifebook|any).
4109 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4111 psmouse.resetafter= [HW,MOUSE]
4112 Try to reset the device after so many bad packets
4115 [HW,MOUSE] Set desired mouse resolution, in dpi.
4116 psmouse.smartscroll=
4117 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4118 0 = disabled, 1 = enabled (default).
4120 pstore.backend= Specify the name of the pstore backend to use
4123 See Documentation/admin-guide/blockdev/paride.rst.
4125 pti= [X86-64] Control Page Table Isolation of user and
4126 kernel address spaces. Disabling this feature
4127 removes hardening, but improves performance of
4128 system calls and interrupts.
4130 on - unconditionally enable
4131 off - unconditionally disable
4132 auto - kernel detects whether your CPU model is
4133 vulnerable to issues that PTI mitigates
4135 Not specifying this option is equivalent to pti=auto.
4138 Equivalent to pti=off
4141 [KNL] Number of legacy pty's. Overwrites compiled-in
4144 quiet [KNL] Disable most log messages
4149 See Documentation/admin-guide/md.rst.
4151 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4152 See Documentation/admin-guide/blockdev/ramdisk.rst.
4154 ramdisk_start= [RAM] RAM disk image start address
4156 random.trust_cpu={on,off}
4157 [KNL] Enable or disable trusting the use of the
4158 CPU's random number generator (if available) to
4159 fully seed the kernel's CRNG. Default is controlled
4160 by CONFIG_RANDOM_TRUST_CPU.
4162 randomize_kstack_offset=
4163 [KNL] Enable or disable kernel stack offset
4164 randomization, which provides roughly 5 bits of
4165 entropy, frustrating memory corruption attacks
4166 that depend on stack address determinism or
4167 cross-syscall address exposures. This is only
4168 available on architectures that have defined
4169 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4170 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4171 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4173 ras=option[,option,...] [KNL] RAS-specific options
4176 Disable the Correctable Errors Collector,
4177 see CONFIG_RAS_CEC help text.
4180 The argument is a cpu list, as described above.
4182 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
4183 the specified list of CPUs to be no-callback CPUs.
4184 Invocation of these CPUs' RCU callbacks will be
4185 offloaded to "rcuox/N" kthreads created for that
4186 purpose, where "x" is "p" for RCU-preempt, and
4187 "s" for RCU-sched, and "N" is the CPU number.
4188 This reduces OS jitter on the offloaded CPUs,
4189 which can be useful for HPC and real-time
4190 workloads. It can also improve energy efficiency
4191 for asymmetric multiprocessors.
4194 Rather than requiring that offloaded CPUs
4195 (specified by rcu_nocbs= above) explicitly
4196 awaken the corresponding "rcuoN" kthreads,
4197 make these kthreads poll for callbacks.
4198 This improves the real-time response for the
4199 offloaded CPUs by relieving them of the need to
4200 wake up the corresponding kthread, but degrades
4201 energy efficiency by requiring that the kthreads
4202 periodically wake up to do the polling.
4204 rcutree.blimit= [KNL]
4205 Set maximum number of finished RCU callbacks to
4206 process in one batch.
4208 rcutree.dump_tree= [KNL]
4209 Dump the structure of the rcu_node combining tree
4210 out at early boot. This is used for diagnostic
4211 purposes, to verify correct tree setup.
4213 rcutree.gp_cleanup_delay= [KNL]
4214 Set the number of jiffies to delay each step of
4215 RCU grace-period cleanup.
4217 rcutree.gp_init_delay= [KNL]
4218 Set the number of jiffies to delay each step of
4219 RCU grace-period initialization.
4221 rcutree.gp_preinit_delay= [KNL]
4222 Set the number of jiffies to delay each step of
4223 RCU grace-period pre-initialization, that is,
4224 the propagation of recent CPU-hotplug changes up
4225 the rcu_node combining tree.
4227 rcutree.use_softirq= [KNL]
4228 If set to zero, move all RCU_SOFTIRQ processing to
4229 per-CPU rcuc kthreads. Defaults to a non-zero
4230 value, meaning that RCU_SOFTIRQ is used by default.
4231 Specify rcutree.use_softirq=0 to use rcuc kthreads.
4233 But note that CONFIG_PREEMPT_RT=y kernels disable
4234 this kernel boot parameter, forcibly setting it
4237 rcutree.rcu_fanout_exact= [KNL]
4238 Disable autobalancing of the rcu_node combining
4239 tree. This is used by rcutorture, and might
4240 possibly be useful for architectures having high
4241 cache-to-cache transfer latencies.
4243 rcutree.rcu_fanout_leaf= [KNL]
4244 Change the number of CPUs assigned to each
4245 leaf rcu_node structure. Useful for very
4246 large systems, which will choose the value 64,
4247 and for NUMA systems with large remote-access
4248 latencies, which will choose a value aligned
4249 with the appropriate hardware boundaries.
4251 rcutree.rcu_min_cached_objs= [KNL]
4252 Minimum number of objects which are cached and
4253 maintained per one CPU. Object size is equal
4254 to PAGE_SIZE. The cache allows to reduce the
4255 pressure to page allocator, also it makes the
4256 whole algorithm to behave better in low memory
4259 rcutree.jiffies_till_first_fqs= [KNL]
4260 Set delay from grace-period initialization to
4261 first attempt to force quiescent states.
4262 Units are jiffies, minimum value is zero,
4263 and maximum value is HZ.
4265 rcutree.jiffies_till_next_fqs= [KNL]
4266 Set delay between subsequent attempts to force
4267 quiescent states. Units are jiffies, minimum
4268 value is one, and maximum value is HZ.
4270 rcutree.jiffies_till_sched_qs= [KNL]
4271 Set required age in jiffies for a
4272 given grace period before RCU starts
4273 soliciting quiescent-state help from
4274 rcu_note_context_switch() and cond_resched().
4275 If not specified, the kernel will calculate
4276 a value based on the most recent settings
4277 of rcutree.jiffies_till_first_fqs
4278 and rcutree.jiffies_till_next_fqs.
4279 This calculated value may be viewed in
4280 rcutree.jiffies_to_sched_qs. Any attempt to set
4281 rcutree.jiffies_to_sched_qs will be cheerfully
4284 rcutree.kthread_prio= [KNL,BOOT]
4285 Set the SCHED_FIFO priority of the RCU per-CPU
4286 kthreads (rcuc/N). This value is also used for
4287 the priority of the RCU boost threads (rcub/N)
4288 and for the RCU grace-period kthreads (rcu_bh,
4289 rcu_preempt, and rcu_sched). If RCU_BOOST is
4290 set, valid values are 1-99 and the default is 1
4291 (the least-favored priority). Otherwise, when
4292 RCU_BOOST is not set, valid values are 0-99 and
4293 the default is zero (non-realtime operation).
4295 rcutree.rcu_nocb_gp_stride= [KNL]
4296 Set the number of NOCB callback kthreads in
4297 each group, which defaults to the square root
4298 of the number of CPUs. Larger numbers reduce
4299 the wakeup overhead on the global grace-period
4300 kthread, but increases that same overhead on
4301 each group's NOCB grace-period kthread.
4303 rcutree.qhimark= [KNL]
4304 Set threshold of queued RCU callbacks beyond which
4305 batch limiting is disabled.
4307 rcutree.qlowmark= [KNL]
4308 Set threshold of queued RCU callbacks below which
4309 batch limiting is re-enabled.
4311 rcutree.qovld= [KNL]
4312 Set threshold of queued RCU callbacks beyond which
4313 RCU's force-quiescent-state scan will aggressively
4314 enlist help from cond_resched() and sched IPIs to
4315 help CPUs more quickly reach quiescent states.
4316 Set to less than zero to make this be set based
4317 on rcutree.qhimark at boot time and to zero to
4318 disable more aggressive help enlistment.
4320 rcutree.rcu_idle_gp_delay= [KNL]
4321 Set wakeup interval for idle CPUs that have
4322 RCU callbacks (RCU_FAST_NO_HZ=y).
4324 rcutree.rcu_kick_kthreads= [KNL]
4325 Cause the grace-period kthread to get an extra
4326 wake_up() if it sleeps three times longer than
4327 it should at force-quiescent-state time.
4328 This wake_up() will be accompanied by a
4329 WARN_ONCE() splat and an ftrace_dump().
4331 rcutree.rcu_unlock_delay= [KNL]
4332 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
4333 this specifies an rcu_read_unlock()-time delay
4334 in microseconds. This defaults to zero.
4335 Larger delays increase the probability of
4336 catching RCU pointer leaks, that is, buggy use
4337 of RCU-protected pointers after the relevant
4338 rcu_read_unlock() has completed.
4340 rcutree.sysrq_rcu= [KNL]
4341 Commandeer a sysrq key to dump out Tree RCU's
4342 rcu_node tree with an eye towards determining
4343 why a new grace period has not yet started.
4345 rcuscale.gp_async= [KNL]
4346 Measure performance of asynchronous
4347 grace-period primitives such as call_rcu().
4349 rcuscale.gp_async_max= [KNL]
4350 Specify the maximum number of outstanding
4351 callbacks per writer thread. When a writer
4352 thread exceeds this limit, it invokes the
4353 corresponding flavor of rcu_barrier() to allow
4354 previously posted callbacks to drain.
4356 rcuscale.gp_exp= [KNL]
4357 Measure performance of expedited synchronous
4358 grace-period primitives.
4360 rcuscale.holdoff= [KNL]
4361 Set test-start holdoff period. The purpose of
4362 this parameter is to delay the start of the
4363 test until boot completes in order to avoid
4366 rcuscale.kfree_rcu_test= [KNL]
4367 Set to measure performance of kfree_rcu() flooding.
4369 rcuscale.kfree_rcu_test_double= [KNL]
4370 Test the double-argument variant of kfree_rcu().
4371 If this parameter has the same value as
4372 rcuscale.kfree_rcu_test_single, both the single-
4373 and double-argument variants are tested.
4375 rcuscale.kfree_rcu_test_single= [KNL]
4376 Test the single-argument variant of kfree_rcu().
4377 If this parameter has the same value as
4378 rcuscale.kfree_rcu_test_double, both the single-
4379 and double-argument variants are tested.
4381 rcuscale.kfree_nthreads= [KNL]
4382 The number of threads running loops of kfree_rcu().
4384 rcuscale.kfree_alloc_num= [KNL]
4385 Number of allocations and frees done in an iteration.
4387 rcuscale.kfree_loops= [KNL]
4388 Number of loops doing rcuscale.kfree_alloc_num number
4389 of allocations and frees.
4391 rcuscale.nreaders= [KNL]
4392 Set number of RCU readers. The value -1 selects
4393 N, where N is the number of CPUs. A value
4394 "n" less than -1 selects N-n+1, where N is again
4395 the number of CPUs. For example, -2 selects N
4396 (the number of CPUs), -3 selects N+1, and so on.
4397 A value of "n" less than or equal to -N selects
4400 rcuscale.nwriters= [KNL]
4401 Set number of RCU writers. The values operate
4402 the same as for rcuscale.nreaders.
4403 N, where N is the number of CPUs
4405 rcuscale.perf_type= [KNL]
4406 Specify the RCU implementation to test.
4408 rcuscale.shutdown= [KNL]
4409 Shut the system down after performance tests
4410 complete. This is useful for hands-off automated
4413 rcuscale.verbose= [KNL]
4414 Enable additional printk() statements.
4416 rcuscale.writer_holdoff= [KNL]
4417 Write-side holdoff between grace periods,
4418 in microseconds. The default of zero says
4421 rcutorture.fqs_duration= [KNL]
4422 Set duration of force_quiescent_state bursts
4425 rcutorture.fqs_holdoff= [KNL]
4426 Set holdoff time within force_quiescent_state bursts
4429 rcutorture.fqs_stutter= [KNL]
4430 Set wait time between force_quiescent_state bursts
4433 rcutorture.fwd_progress= [KNL]
4434 Enable RCU grace-period forward-progress testing
4435 for the types of RCU supporting this notion.
4437 rcutorture.fwd_progress_div= [KNL]
4438 Specify the fraction of a CPU-stall-warning
4439 period to do tight-loop forward-progress testing.
4441 rcutorture.fwd_progress_holdoff= [KNL]
4442 Number of seconds to wait between successive
4443 forward-progress tests.
4445 rcutorture.fwd_progress_need_resched= [KNL]
4446 Enclose cond_resched() calls within checks for
4447 need_resched() during tight-loop forward-progress
4450 rcutorture.gp_cond= [KNL]
4451 Use conditional/asynchronous update-side
4452 primitives, if available.
4454 rcutorture.gp_exp= [KNL]
4455 Use expedited update-side primitives, if available.
4457 rcutorture.gp_normal= [KNL]
4458 Use normal (non-expedited) asynchronous
4459 update-side primitives, if available.
4461 rcutorture.gp_sync= [KNL]
4462 Use normal (non-expedited) synchronous
4463 update-side primitives, if available. If all
4464 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4465 rcutorture.gp_normal=, and rcutorture.gp_sync=
4466 are zero, rcutorture acts as if is interpreted
4467 they are all non-zero.
4469 rcutorture.irqreader= [KNL]
4470 Run RCU readers from irq handlers, or, more
4471 accurately, from a timer handler. Not all RCU
4472 flavors take kindly to this sort of thing.
4474 rcutorture.leakpointer= [KNL]
4475 Leak an RCU-protected pointer out of the reader.
4476 This can of course result in splats, and is
4477 intended to test the ability of things like
4478 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
4481 rcutorture.n_barrier_cbs= [KNL]
4482 Set callbacks/threads for rcu_barrier() testing.
4484 rcutorture.nfakewriters= [KNL]
4485 Set number of concurrent RCU writers. These just
4486 stress RCU, they don't participate in the actual
4487 test, hence the "fake".
4489 rcutorture.nocbs_nthreads= [KNL]
4490 Set number of RCU callback-offload togglers.
4491 Zero (the default) disables toggling.
4493 rcutorture.nocbs_toggle= [KNL]
4494 Set the delay in milliseconds between successive
4495 callback-offload toggling attempts.
4497 rcutorture.nreaders= [KNL]
4498 Set number of RCU readers. The value -1 selects
4499 N-1, where N is the number of CPUs. A value
4500 "n" less than -1 selects N-n-2, where N is again
4501 the number of CPUs. For example, -2 selects N
4502 (the number of CPUs), -3 selects N+1, and so on.
4504 rcutorture.object_debug= [KNL]
4505 Enable debug-object double-call_rcu() testing.
4507 rcutorture.onoff_holdoff= [KNL]
4508 Set time (s) after boot for CPU-hotplug testing.
4510 rcutorture.onoff_interval= [KNL]
4511 Set time (jiffies) between CPU-hotplug operations,
4512 or zero to disable CPU-hotplug testing.
4514 rcutorture.read_exit= [KNL]
4515 Set the number of read-then-exit kthreads used
4516 to test the interaction of RCU updaters and
4517 task-exit processing.
4519 rcutorture.read_exit_burst= [KNL]
4520 The number of times in a given read-then-exit
4521 episode that a set of read-then-exit kthreads
4524 rcutorture.read_exit_delay= [KNL]
4525 The delay, in seconds, between successive
4526 read-then-exit testing episodes.
4528 rcutorture.shuffle_interval= [KNL]
4529 Set task-shuffle interval (s). Shuffling tasks
4530 allows some CPUs to go into dyntick-idle mode
4531 during the rcutorture test.
4533 rcutorture.shutdown_secs= [KNL]
4534 Set time (s) after boot system shutdown. This
4535 is useful for hands-off automated testing.
4537 rcutorture.stall_cpu= [KNL]
4538 Duration of CPU stall (s) to test RCU CPU stall
4539 warnings, zero to disable.
4541 rcutorture.stall_cpu_block= [KNL]
4542 Sleep while stalling if set. This will result
4543 in warnings from preemptible RCU in addition
4544 to any other stall-related activity.
4546 rcutorture.stall_cpu_holdoff= [KNL]
4547 Time to wait (s) after boot before inducing stall.
4549 rcutorture.stall_cpu_irqsoff= [KNL]
4550 Disable interrupts while stalling if set.
4552 rcutorture.stall_gp_kthread= [KNL]
4553 Duration (s) of forced sleep within RCU
4554 grace-period kthread to test RCU CPU stall
4555 warnings, zero to disable. If both stall_cpu
4556 and stall_gp_kthread are specified, the
4557 kthread is starved first, then the CPU.
4559 rcutorture.stat_interval= [KNL]
4560 Time (s) between statistics printk()s.
4562 rcutorture.stutter= [KNL]
4563 Time (s) to stutter testing, for example, specifying
4564 five seconds causes the test to run for five seconds,
4565 wait for five seconds, and so on. This tests RCU's
4566 ability to transition abruptly to and from idle.
4568 rcutorture.test_boost= [KNL]
4569 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4570 "Maybe" means test if the RCU implementation
4571 under test support RCU priority boosting.
4573 rcutorture.test_boost_duration= [KNL]
4574 Duration (s) of each individual boost test.
4576 rcutorture.test_boost_interval= [KNL]
4577 Interval (s) between each boost test.
4579 rcutorture.test_no_idle_hz= [KNL]
4580 Test RCU's dyntick-idle handling. See also the
4581 rcutorture.shuffle_interval parameter.
4583 rcutorture.torture_type= [KNL]
4584 Specify the RCU implementation to test.
4586 rcutorture.verbose= [KNL]
4587 Enable additional printk() statements.
4589 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4590 Dump ftrace buffer after reporting RCU CPU
4593 rcupdate.rcu_cpu_stall_suppress= [KNL]
4594 Suppress RCU CPU stall warning messages.
4596 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
4597 Suppress RCU CPU stall warning messages and
4598 rcutorture writer stall warnings that occur
4599 during early boot, that is, during the time
4600 before the init task is spawned.
4602 rcupdate.rcu_cpu_stall_timeout= [KNL]
4603 Set timeout for RCU CPU stall warning messages.
4605 rcupdate.rcu_expedited= [KNL]
4606 Use expedited grace-period primitives, for
4607 example, synchronize_rcu_expedited() instead
4608 of synchronize_rcu(). This reduces latency,
4609 but can increase CPU utilization, degrade
4610 real-time latency, and degrade energy efficiency.
4611 No effect on CONFIG_TINY_RCU kernels.
4613 rcupdate.rcu_normal= [KNL]
4614 Use only normal grace-period primitives,
4615 for example, synchronize_rcu() instead of
4616 synchronize_rcu_expedited(). This improves
4617 real-time latency, CPU utilization, and
4618 energy efficiency, but can expose users to
4619 increased grace-period latency. This parameter
4620 overrides rcupdate.rcu_expedited. No effect on
4621 CONFIG_TINY_RCU kernels.
4623 rcupdate.rcu_normal_after_boot= [KNL]
4624 Once boot has completed (that is, after
4625 rcu_end_inkernel_boot() has been invoked), use
4626 only normal grace-period primitives. No effect
4627 on CONFIG_TINY_RCU kernels.
4629 But note that CONFIG_PREEMPT_RT=y kernels enables
4630 this kernel boot parameter, forcibly setting
4631 it to the value one, that is, converting any
4632 post-boot attempt at an expedited RCU grace
4633 period to instead use normal non-expedited
4634 grace-period processing.
4636 rcupdate.rcu_task_ipi_delay= [KNL]
4637 Set time in jiffies during which RCU tasks will
4638 avoid sending IPIs, starting with the beginning
4639 of a given grace period. Setting a large
4640 number avoids disturbing real-time workloads,
4641 but lengthens grace periods.
4643 rcupdate.rcu_task_stall_timeout= [KNL]
4644 Set timeout in jiffies for RCU task stall warning
4645 messages. Disable with a value less than or equal
4648 rcupdate.rcu_self_test= [KNL]
4649 Run the RCU early boot self tests
4653 Run specified binary instead of /init from the ramdisk,
4654 used for early userspace startup. See initrd.
4657 force - Override the decision by the kernel to hide the
4658 advertisement of RDRAND support (this affects
4659 certain AMD processors because of buggy BIOS
4660 support, specifically around the suspend/resume
4664 Turn on/off individual RDT features. List is:
4665 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4667 E.g. to turn on cmt and turn off mba use:
4671 Format (x86 or x86_64):
4672 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4674 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4676 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4677 (prefix with 'panic_' to set mode for panic
4679 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4680 reboot_force is either force or not specified,
4681 reboot_cpu is s[mp]#### with #### being the processor
4682 to be used for rebooting.
4684 refscale.holdoff= [KNL]
4685 Set test-start holdoff period. The purpose of
4686 this parameter is to delay the start of the
4687 test until boot completes in order to avoid
4690 refscale.loops= [KNL]
4691 Set the number of loops over the synchronization
4692 primitive under test. Increasing this number
4693 reduces noise due to loop start/end overhead,
4694 but the default has already reduced the per-pass
4695 noise to a handful of picoseconds on ca. 2020
4698 refscale.nreaders= [KNL]
4699 Set number of readers. The default value of -1
4700 selects N, where N is roughly 75% of the number
4701 of CPUs. A value of zero is an interesting choice.
4703 refscale.nruns= [KNL]
4704 Set number of runs, each of which is dumped onto
4707 refscale.readdelay= [KNL]
4708 Set the read-side critical-section duration,
4709 measured in microseconds.
4711 refscale.scale_type= [KNL]
4712 Specify the read-protection implementation to test.
4714 refscale.shutdown= [KNL]
4715 Shut down the system at the end of the performance
4716 test. This defaults to 1 (shut it down) when
4717 refscale is built into the kernel and to 0 (leave
4718 it running) when refscale is built as a module.
4720 refscale.verbose= [KNL]
4721 Enable additional printk() statements.
4723 refscale.verbose_batched= [KNL]
4724 Batch the additional printk() statements. If zero
4725 (the default) or negative, print everything. Otherwise,
4726 print every Nth verbose statement, where N is the value
4730 [KNL, SMP] Set scheduler's default relax_domain_level.
4731 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4733 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4734 Format: <base1>,<size1>[,<base2>,<size2>,...]
4735 Reserve I/O ports or memory so the kernel won't use
4736 them. If <base> is less than 0x10000, the region
4737 is assumed to be I/O ports; otherwise it is memory.
4739 reservetop= [X86-32]
4741 Reserves a hole at the top of the kernel virtual
4746 Set the amount of memory to reserve for BIOS at
4747 the bottom of the address space.
4749 reset_devices [KNL] Force drivers to reset the underlying device
4750 during initialization.
4753 Specify the partition device for software suspend
4755 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4757 resume_offset= [SWSUSP]
4758 Specify the offset from the beginning of the partition
4759 given by "resume=" at which the swap header is located,
4760 in <PAGE_SIZE> units (needed only for swap files).
4761 See Documentation/power/swsusp-and-swap-files.rst
4763 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4764 read the resume files
4766 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4767 Useful for devices that are detected asynchronously
4768 (e.g. USB and MMC devices).
4770 hibernate= [HIBERNATION]
4771 noresume Don't check if there's a hibernation image
4772 present during boot.
4773 nocompress Don't compress/decompress hibernation images.
4774 no Disable hibernation and resume.
4775 protect_image Turn on image protection during restoration
4776 (that will set all pages holding image data
4777 during restoration read-only).
4779 retain_initrd [RAM] Keep initrd memory after extraction
4781 rfkill.default_state=
4782 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4783 etc. communication is blocked by default.
4786 rfkill.master_switch_mode=
4787 0 The "airplane mode" button does nothing.
4788 1 The "airplane mode" button toggles between everything
4789 blocked and the previous configuration.
4790 2 The "airplane mode" button toggles between everything
4791 blocked and everything unblocked.
4793 rhash_entries= [KNL,NET]
4794 Set number of hash buckets for route cache
4797 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4800 ro [KNL] Mount root device read-only on boot
4803 on Mark read-only kernel memory as read-only (default).
4804 off Leave read-only kernel memory writable for debugging.
4807 Enable the uart passthrough on the designated usb port
4808 on Rockchip SoCs. When active, the signals of the
4809 debug-uart get routed to the D+ and D- pins of the usb
4810 port and the regular usb controller gets disabled.
4812 root= [KNL] Root filesystem
4813 See name_to_dev_t comment in init/do_mounts.c.
4815 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4816 mount the root filesystem
4818 rootflags= [KNL] Set root filesystem mount option string
4820 rootfstype= [KNL] Set root filesystem type
4822 rootwait [KNL] Wait (indefinitely) for root device to show up.
4823 Useful for devices that are detected asynchronously
4824 (e.g. USB and MMC devices).
4826 rproc_mem=nn[KMG][@address]
4827 [KNL,ARM,CMA] Remoteproc physical memory block.
4828 Memory area to be used by remote processor image,
4831 rw [KNL] Mount root device read-write on boot
4833 S [KNL] Run init in single mode
4835 s390_iommu= [HW,S390]
4836 Set s390 IOTLB flushing mode
4838 With strict flushing every unmap operation will result in
4839 an IOTLB flush. Default is lazy flushing before reuse,
4843 See drivers/net/irda/sa1100_ir.c.
4845 sbni= [NET] Granch SBNI12 leased line adapter
4847 sched_verbose [KNL] Enables verbose scheduler debug messages.
4849 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4850 Allowed values are enable and disable. This feature
4851 incurs a small amount of overhead in the scheduler
4852 but is useful for debugging and performance tuning.
4854 sched_thermal_decay_shift=
4855 [KNL, SMP] Set a decay shift for scheduler thermal
4856 pressure signal. Thermal pressure signal follows the
4857 default decay period of other scheduler pelt
4858 signals(usually 32 ms but configurable). Setting
4859 sched_thermal_decay_shift will left shift the decay
4860 period for the thermal pressure signal by the shift
4862 i.e. with the default pelt decay period of 32 ms
4863 sched_thermal_decay_shift thermal pressure decay pr
4867 Format: integer between 0 and 10
4870 scftorture.holdoff= [KNL]
4871 Number of seconds to hold off before starting
4872 test. Defaults to zero for module insertion and
4873 to 10 seconds for built-in smp_call_function()
4876 scftorture.longwait= [KNL]
4877 Request ridiculously long waits randomly selected
4878 up to the chosen limit in seconds. Zero (the
4879 default) disables this feature. Please note
4880 that requesting even small non-zero numbers of
4881 seconds can result in RCU CPU stall warnings,
4882 softlockup complaints, and so on.
4884 scftorture.nthreads= [KNL]
4885 Number of kthreads to spawn to invoke the
4886 smp_call_function() family of functions.
4887 The default of -1 specifies a number of kthreads
4888 equal to the number of CPUs.
4890 scftorture.onoff_holdoff= [KNL]
4891 Number seconds to wait after the start of the
4892 test before initiating CPU-hotplug operations.
4894 scftorture.onoff_interval= [KNL]
4895 Number seconds to wait between successive
4896 CPU-hotplug operations. Specifying zero (which
4897 is the default) disables CPU-hotplug operations.
4899 scftorture.shutdown_secs= [KNL]
4900 The number of seconds following the start of the
4901 test after which to shut down the system. The
4902 default of zero avoids shutting down the system.
4903 Non-zero values are useful for automated tests.
4905 scftorture.stat_interval= [KNL]
4906 The number of seconds between outputting the
4907 current test statistics to the console. A value
4908 of zero disables statistics output.
4910 scftorture.stutter_cpus= [KNL]
4911 The number of jiffies to wait between each change
4912 to the set of CPUs under test.
4914 scftorture.use_cpus_read_lock= [KNL]
4915 Use use_cpus_read_lock() instead of the default
4916 preempt_disable() to disable CPU hotplug
4917 while invoking one of the smp_call_function*()
4920 scftorture.verbose= [KNL]
4921 Enable additional printk() statements.
4923 scftorture.weight_single= [KNL]
4924 The probability weighting to use for the
4925 smp_call_function_single() function with a zero
4926 "wait" parameter. A value of -1 selects the
4927 default if all other weights are -1. However,
4928 if at least one weight has some other value, a
4929 value of -1 will instead select a weight of zero.
4931 scftorture.weight_single_wait= [KNL]
4932 The probability weighting to use for the
4933 smp_call_function_single() function with a
4934 non-zero "wait" parameter. See weight_single.
4936 scftorture.weight_many= [KNL]
4937 The probability weighting to use for the
4938 smp_call_function_many() function with a zero
4939 "wait" parameter. See weight_single.
4940 Note well that setting a high probability for
4941 this weighting can place serious IPI load
4944 scftorture.weight_many_wait= [KNL]
4945 The probability weighting to use for the
4946 smp_call_function_many() function with a
4947 non-zero "wait" parameter. See weight_single
4950 scftorture.weight_all= [KNL]
4951 The probability weighting to use for the
4952 smp_call_function_all() function with a zero
4953 "wait" parameter. See weight_single and
4956 scftorture.weight_all_wait= [KNL]
4957 The probability weighting to use for the
4958 smp_call_function_all() function with a
4959 non-zero "wait" parameter. See weight_single
4962 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4963 xtime_lock contention on larger systems, and/or RCU lock
4964 contention on all systems with CONFIG_MAXSMP set.
4965 Format: { "0" | "1" }
4966 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4968 Note: increases power consumption, thus should only be
4969 enabled if running jitter sensitive (HPC/RT) workloads.
4971 security= [SECURITY] Choose a legacy "major" security module to
4972 enable at boot. This has been deprecated by the
4975 selinux= [SELINUX] Disable or enable SELinux at boot time.
4976 Format: { "0" | "1" }
4977 See security/selinux/Kconfig help text.
4982 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4983 Format: { "0" | "1" }
4984 See security/apparmor/Kconfig help text
4987 Default value is set via kernel config option.
4989 serialnumber [BUGS=X86-32]
4992 Maximal number of shapers.
5000 Disable merging of slabs with similar size. May be
5001 necessary if there is some reason to distinguish
5002 allocs to different slabs, especially in hardened
5003 environments where the risk of heap overflows and
5004 layout control by attackers can usually be
5005 frustrated by disabling merging. This will reduce
5006 most of the exposure of a heap attack to a single
5007 cache (risks via metadata attacks are mostly
5008 unchanged). Debug options disable merging on their
5010 For more information see Documentation/vm/slub.rst.
5012 slab_max_order= [MM, SLAB]
5013 Determines the maximum allowed order for slabs.
5014 A high setting may cause OOMs due to memory
5015 fragmentation. Defaults to 1 for systems with
5016 more than 32MB of RAM, 0 otherwise.
5018 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
5019 Enabling slub_debug allows one to determine the
5020 culprit if slab objects become corrupted. Enabling
5021 slub_debug can create guard zones around objects and
5022 may poison objects when not in use. Also tracks the
5023 last alloc / free. For more information see
5024 Documentation/vm/slub.rst.
5026 slub_max_order= [MM, SLUB]
5027 Determines the maximum allowed order for slabs.
5028 A high setting may cause OOMs due to memory
5029 fragmentation. For more information see
5030 Documentation/vm/slub.rst.
5032 slub_min_objects= [MM, SLUB]
5033 The minimum number of objects per slab. SLUB will
5034 increase the slab order up to slub_max_order to
5035 generate a sufficiently large slab able to contain
5036 the number of objects indicated. The higher the number
5037 of objects the smaller the overhead of tracking slabs
5038 and the less frequently locks need to be acquired.
5039 For more information see Documentation/vm/slub.rst.
5041 slub_min_order= [MM, SLUB]
5042 Determines the minimum page order for slabs. Must be
5043 lower than slub_max_order.
5044 For more information see Documentation/vm/slub.rst.
5046 slub_nomerge [MM, SLUB]
5047 Same with slab_nomerge. This is supported for legacy.
5048 See slab_nomerge for more information.
5051 Format: <io1>[,<io2>[,...,<io8>]]
5053 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
5054 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
5055 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
5056 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
5057 smsc-ircc2.ircc_irq= [HW] IRQ line
5058 smsc-ircc2.ircc_dma= [HW] DMA channel
5059 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
5060 0: Toshiba Satellite 1800 (GP data pin select)
5061 1: Fast pin select (default)
5064 smt [KNL,S390] Set the maximum number of threads (logical
5065 CPUs) to use per physical CPU on systems capable of
5066 symmetric multithreading (SMT). Will be capped to the
5067 actual hardware limit.
5069 Default: -1 (no limit)
5072 [KNL] Should the soft-lockup detector generate panics.
5075 A value of 1 instructs the soft-lockup detector
5076 to panic the machine when a soft-lockup occurs. It is
5077 also controlled by the kernel.softlockup_panic sysctl
5078 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
5079 respective build-time switch to that functionality.
5081 softlockup_all_cpu_backtrace=
5082 [KNL] Should the soft-lockup detector generate
5083 backtraces on all cpus.
5086 sonypi.*= [HW] Sony Programmable I/O Control Device driver
5087 See Documentation/admin-guide/laptops/sonypi.rst
5089 spectre_v2= [X86] Control mitigation of Spectre variant 2
5090 (indirect branch speculation) vulnerability.
5091 The default operation protects the kernel from
5094 on - unconditionally enable, implies
5096 off - unconditionally disable, implies
5098 auto - kernel detects whether your CPU model is
5101 Selecting 'on' will, and 'auto' may, choose a
5102 mitigation method at run time according to the
5103 CPU, the available microcode, the setting of the
5104 CONFIG_RETPOLINE configuration option, and the
5105 compiler with which the kernel was built.
5107 Selecting 'on' will also enable the mitigation
5108 against user space to user space task attacks.
5110 Selecting 'off' will disable both the kernel and
5111 the user space protections.
5113 Specific mitigations can also be selected manually:
5115 retpoline - replace indirect branches
5116 retpoline,generic - google's original retpoline
5117 retpoline,amd - AMD-specific minimal thunk
5119 Not specifying this option is equivalent to
5123 [X86] Control mitigation of Spectre variant 2
5124 (indirect branch speculation) vulnerability between
5127 on - Unconditionally enable mitigations. Is
5128 enforced by spectre_v2=on
5130 off - Unconditionally disable mitigations. Is
5131 enforced by spectre_v2=off
5133 prctl - Indirect branch speculation is enabled,
5134 but mitigation can be enabled via prctl
5135 per thread. The mitigation control state
5136 is inherited on fork.
5139 - Like "prctl" above, but only STIBP is
5140 controlled per thread. IBPB is issued
5141 always when switching between different user
5145 - Same as "prctl" above, but all seccomp
5146 threads will enable the mitigation unless
5147 they explicitly opt out.
5150 - Like "seccomp" above, but only STIBP is
5151 controlled per thread. IBPB is issued
5152 always when switching between different
5153 user space processes.
5155 auto - Kernel selects the mitigation depending on
5156 the available CPU features and vulnerability.
5159 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
5161 Not specifying this option is equivalent to
5162 spectre_v2_user=auto.
5164 spec_store_bypass_disable=
5165 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
5166 (Speculative Store Bypass vulnerability)
5168 Certain CPUs are vulnerable to an exploit against a
5169 a common industry wide performance optimization known
5170 as "Speculative Store Bypass" in which recent stores
5171 to the same memory location may not be observed by
5172 later loads during speculative execution. The idea
5173 is that such stores are unlikely and that they can
5174 be detected prior to instruction retirement at the
5175 end of a particular speculation execution window.
5177 In vulnerable processors, the speculatively forwarded
5178 store can be used in a cache side channel attack, for
5179 example to read memory to which the attacker does not
5180 directly have access (e.g. inside sandboxed code).
5182 This parameter controls whether the Speculative Store
5183 Bypass optimization is used.
5185 On x86 the options are:
5187 on - Unconditionally disable Speculative Store Bypass
5188 off - Unconditionally enable Speculative Store Bypass
5189 auto - Kernel detects whether the CPU model contains an
5190 implementation of Speculative Store Bypass and
5191 picks the most appropriate mitigation. If the
5192 CPU is not vulnerable, "off" is selected. If the
5193 CPU is vulnerable the default mitigation is
5194 architecture and Kconfig dependent. See below.
5195 prctl - Control Speculative Store Bypass per thread
5196 via prctl. Speculative Store Bypass is enabled
5197 for a process by default. The state of the control
5198 is inherited on fork.
5199 seccomp - Same as "prctl" above, but all seccomp threads
5200 will disable SSB unless they explicitly opt out.
5202 Default mitigations:
5203 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
5205 On powerpc the options are:
5207 on,auto - On Power8 and Power9 insert a store-forwarding
5208 barrier on kernel entry and exit. On Power7
5209 perform a software flush on kernel entry and
5213 Not specifying this option is equivalent to
5214 spec_store_bypass_disable=auto.
5216 spia_io_base= [HW,MTD]
5222 [X86] Enable split lock detection or bus lock detection
5224 When enabled (and if hardware support is present), atomic
5225 instructions that access data across cache line
5226 boundaries will result in an alignment check exception
5227 for split lock detection or a debug exception for
5232 warn - the kernel will emit rate-limited warnings
5233 about applications triggering the #AC
5234 exception or the #DB exception. This mode is
5235 the default on CPUs that support split lock
5236 detection or bus lock detection. Default
5237 behavior is by #AC if both features are
5238 enabled in hardware.
5240 fatal - the kernel will send SIGBUS to applications
5241 that trigger the #AC exception or the #DB
5242 exception. Default behavior is by #AC if
5243 both features are enabled in hardware.
5245 If an #AC exception is hit in the kernel or in
5246 firmware (i.e. not while executing in user mode)
5247 the kernel will oops in either "warn" or "fatal"
5250 #DB exception for bus lock is triggered only when
5254 Control the Special Register Buffer Data Sampling
5257 Certain CPUs are vulnerable to an MDS-like
5258 exploit which can leak bits from the random
5261 By default, this issue is mitigated by
5262 microcode. However, the microcode fix can cause
5263 the RDRAND and RDSEED instructions to become
5264 much slower. Among other effects, this will
5265 result in reduced throughput from /dev/urandom.
5267 The microcode mitigation can be disabled with
5268 the following option:
5270 off: Disable mitigation and remove
5271 performance impact to RDRAND and RDSEED
5273 srcutree.counter_wrap_check [KNL]
5274 Specifies how frequently to check for
5275 grace-period sequence counter wrap for the
5276 srcu_data structure's ->srcu_gp_seq_needed field.
5277 The greater the number of bits set in this kernel
5278 parameter, the less frequently counter wrap will
5279 be checked for. Note that the bottom two bits
5282 srcutree.exp_holdoff [KNL]
5283 Specifies how many nanoseconds must elapse
5284 since the end of the last SRCU grace period for
5285 a given srcu_struct until the next normal SRCU
5286 grace period will be considered for automatic
5287 expediting. Set to zero to disable automatic
5291 Speculative Store Bypass Disable control
5293 On CPUs that are vulnerable to the Speculative
5294 Store Bypass vulnerability and offer a
5295 firmware based mitigation, this parameter
5296 indicates how the mitigation should be used:
5298 force-on: Unconditionally enable mitigation for
5299 for both kernel and userspace
5300 force-off: Unconditionally disable mitigation for
5301 for both kernel and userspace
5302 kernel: Always enable mitigation in the
5303 kernel, and offer a prctl interface
5304 to allow userspace to register its
5305 interest in being mitigated too.
5307 stack_guard_gap= [MM]
5308 override the default stack gap protection. The value
5309 is in page units and it defines how many pages prior
5310 to (for stacks growing down) resp. after (for stacks
5311 growing up) the main stack are reserved for no other
5312 mapping. Default value is 256 pages.
5314 stack_depot_disable= [KNL]
5315 Setting this to true through kernel command line will
5316 disable the stack depot thereby saving the static memory
5317 consumed by the stack hash table. By default this is set
5321 Enabled the stack tracer on boot up.
5323 stacktrace_filter=[function-list]
5324 [FTRACE] Limit the functions that the stack tracer
5325 will trace at boot up. function-list is a comma-separated
5326 list of functions. This list can be changed at run
5327 time by the stack_trace_filter file in the debugfs
5328 tracing directory. Note, this enables stack tracing
5329 and the stacktrace above is not needed.
5333 Set the STI (builtin display/keyboard on the HP-PARISC
5334 machines) console (graphic card) which should be used
5335 as the initial boot-console.
5336 See also comment in drivers/video/console/sticore.c.
5339 See comment in drivers/video/console/sticore.c.
5342 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
5344 sunrpc.min_resvport=
5345 sunrpc.max_resvport=
5347 SunRPC servers often require that client requests
5348 originate from a privileged port (i.e. a port in the
5349 range 0 < portnr < 1024).
5350 An administrator who wishes to reserve some of these
5351 ports for other uses may adjust the range that the
5352 kernel's sunrpc client considers to be privileged
5353 using these two parameters to set the minimum and
5354 maximum port values.
5356 sunrpc.svc_rpc_per_connection_limit=
5358 Limit the number of requests that the server will
5359 process in parallel from a single connection.
5360 The default value is 0 (no limit).
5364 Control how the NFS server code allocates CPUs to
5365 service thread pools. Depending on how many NICs
5366 you have and where their interrupts are bound, this
5367 option will affect which CPUs will do NFS serving.
5368 Note: this parameter cannot be changed while the
5369 NFS server is running.
5371 auto the server chooses an appropriate mode
5372 automatically using heuristics
5373 global a single global pool contains all CPUs
5374 percpu one pool for each CPU
5375 pernode one pool for each NUMA node (equivalent
5376 to global on non-NUMA machines)
5378 sunrpc.tcp_slot_table_entries=
5379 sunrpc.udp_slot_table_entries=
5381 Sets the upper limit on the number of simultaneous
5382 RPC calls that can be sent from the client to a
5383 server. Increasing these values may allow you to
5384 improve throughput, but will also increase the
5385 amount of memory reserved for use by the client.
5387 suspend.pm_test_delay=
5389 Sets the number of seconds to remain in a suspend test
5390 mode before resuming the system (see
5391 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
5392 is set. Default value is 5.
5395 Format: { on | off | y | n | 1 | 0 }
5396 This parameter controls use of the Protected
5397 Execution Facility on pSeries.
5400 [KNL] Enable accounting of swap in memory resource
5401 controller if no parameter or 1 is given or disable
5402 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
5404 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
5405 Format: { <int> | force | noforce }
5406 <int> -- Number of I/O TLB slabs
5407 force -- force using of bounce buffers even if they
5408 wouldn't be automatically used by the kernel
5409 noforce -- Never use bounce buffers (for debugging)
5414 Set a sysctl parameter, right before loading the init
5415 process, as if the value was written to the respective
5416 /proc/sys/... file. Both '.' and '/' are recognized as
5417 separators. Unrecognized parameters and invalid values
5418 are reported in the kernel log. Sysctls registered
5419 later by a loaded module cannot be set this way.
5420 Example: sysctl.vm.swappiness=40
5422 sysfs.deprecated=0|1 [KNL]
5423 Enable/disable old style sysfs layout for old udev
5424 on older distributions. When this option is enabled
5425 very new udev will not work anymore. When this option
5426 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
5427 in older udev will not work anymore.
5428 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
5429 the kernel configuration.
5431 sysrq_always_enabled
5433 Ignore sysrq setting - this boot parameter will
5434 neutralize any effect of /proc/sys/kernel/sysrq.
5435 Useful for debugging.
5437 tcpmhash_entries= [KNL,NET]
5438 Set the number of tcp_metrics_hash slots.
5439 Default value is 8192 or 16384 depending on total
5440 ram pages. This is used to specify the TCP metrics
5441 cache size. See Documentation/networking/ip-sysctl.rst
5442 "tcp_no_metrics_save" section for more details.
5446 test_suspend= [SUSPEND][,N]
5447 Specify "mem" (for Suspend-to-RAM) or "standby" (for
5448 standby suspend) or "freeze" (for suspend type freeze)
5449 as the system sleep state during system startup with
5450 the optional capability to repeat N number of times.
5451 The system is woken from this state using a
5452 wakeup-capable RTC alarm.
5454 thash_entries= [KNL,NET]
5455 Set number of hash buckets for TCP connection
5457 thermal.act= [HW,ACPI]
5458 -1: disable all active trip points in all thermal zones
5459 <degrees C>: override all lowest active trip points
5461 thermal.crt= [HW,ACPI]
5462 -1: disable all critical trip points in all thermal zones
5463 <degrees C>: override all critical trip points
5465 thermal.nocrt= [HW,ACPI]
5466 Set to disable actions on ACPI thermal zone
5467 critical and hot trip points.
5469 thermal.off= [HW,ACPI]
5470 1: disable ACPI thermal control
5472 thermal.psv= [HW,ACPI]
5473 -1: disable all passive trip points
5474 <degrees C>: override all passive trip points to this
5477 thermal.tzp= [HW,ACPI]
5478 Specify global default ACPI thermal zone polling rate
5479 <deci-seconds>: poll all this frequency
5480 0: no polling (default)
5483 Force threading of all interrupt handlers except those
5484 marked explicitly IRQF_NO_THREAD.
5488 Specify if the kernel should make use of the cpu
5489 topology information if the hardware supports this.
5490 The scheduler will make use of this information and
5491 e.g. base its process migration decisions on it.
5494 topology_updates= [KNL, PPC, NUMA]
5496 Specify if the kernel should ignore (off)
5497 topology updates sent by the hypervisor to this
5500 torture.disable_onoff_at_boot= [KNL]
5501 Prevent the CPU-hotplug component of torturing
5502 until after init has spawned.
5504 torture.ftrace_dump_at_shutdown= [KNL]
5505 Dump the ftrace buffer at torture-test shutdown,
5506 even if there were no errors. This can be a
5507 very costly operation when many torture tests
5508 are running concurrently, especially on systems
5509 with rotating-rust storage.
5511 torture.verbose_sleep_frequency= [KNL]
5512 Specifies how many verbose printk()s should be
5513 emitted between each sleep. The default of zero
5514 disables verbose-printk() sleeping.
5516 torture.verbose_sleep_duration= [KNL]
5517 Duration of each verbose-printk() sleep in jiffies.
5521 tpm_suspend_pcr=[HW,TPM]
5522 Format: integer pcr id
5523 Specify that at suspend time, the tpm driver
5524 should extend the specified pcr with zeros,
5525 as a workaround for some chips which fail to
5526 flush the last written pcr on TPM_SaveState.
5527 This will guarantee that all the other pcrs
5530 trace_buf_size=nn[KMG]
5531 [FTRACE] will set tracing buffer size on each cpu.
5533 trace_event=[event-list]
5534 [FTRACE] Set and start specified trace events in order
5535 to facilitate early boot debugging. The event-list is a
5536 comma-separated list of trace events to enable. See
5537 also Documentation/trace/events.rst
5539 trace_options=[option-list]
5540 [FTRACE] Enable or disable tracer options at boot.
5541 The option-list is a comma delimited list of options
5542 that can be enabled or disabled just as if you were
5543 to echo the option name into
5545 /sys/kernel/debug/tracing/trace_options
5547 For example, to enable stacktrace option (to dump the
5548 stack trace of each event), add to the command line:
5550 trace_options=stacktrace
5552 See also Documentation/trace/ftrace.rst "trace options"
5556 Have the tracepoints sent to printk as well as the
5557 tracing ring buffer. This is useful for early boot up
5558 where the system hangs or reboots and does not give the
5559 option for reading the tracing buffer or performing a
5560 ftrace_dump_on_oops.
5562 To turn off having tracepoints sent to printk,
5563 echo 0 > /proc/sys/kernel/tracepoint_printk
5564 Note, echoing 1 into this file without the
5565 tracepoint_printk kernel cmdline option has no effect.
5569 Having tracepoints sent to printk() and activating high
5570 frequency tracepoints such as irq or sched, can cause
5571 the system to live lock.
5574 [FTRACE] enable this option to disable tracing when a
5575 warning is hit. This turns off "tracing_on". Tracing can
5576 be enabled again by echoing '1' into the "tracing_on"
5577 file located in /sys/kernel/debug/tracing/
5579 This option is useful, as it disables the trace before
5580 the WARNING dump is called, which prevents the trace to
5581 be filled with content caused by the warning output.
5583 This option can also be set at run time via the sysctl
5584 option: kernel/traceoff_on_warning
5586 transparent_hugepage=
5588 Format: [always|madvise|never]
5589 Can be used to control the default behavior of the system
5590 with respect to transparent hugepages.
5591 See Documentation/admin-guide/mm/transhuge.rst
5594 trusted.source= [KEYS]
5596 This parameter identifies the trust source as a backend
5597 for trusted keys implementation. Supported trust
5601 If not specified then it defaults to iterating through
5602 the trust source list starting with TPM and assigns the
5603 first trust source as a backend which is initialized
5604 successfully during iteration.
5606 tsc= Disable clocksource stability checks for TSC.
5608 [x86] reliable: mark tsc clocksource as reliable, this
5609 disables clocksource verification at runtime, as well
5610 as the stability checks done at bootup. Used to enable
5611 high-resolution timer mode on older hardware, and in
5612 virtualized environment.
5613 [x86] noirqtime: Do not use TSC to do irq accounting.
5614 Used to run time disable IRQ_TIME_ACCOUNTING on any
5615 platforms where RDTSC is slow and this accounting
5617 [x86] unstable: mark the TSC clocksource as unstable, this
5618 marks the TSC unconditionally unstable at bootup and
5619 avoids any further wobbles once the TSC watchdog notices.
5620 [x86] nowatchdog: disable clocksource watchdog. Used
5621 in situations with strict latency requirements (where
5622 interruptions from clocksource watchdog are not
5625 tsc_early_khz= [X86] Skip early TSC calibration and use the given
5626 value instead. Useful when the early TSC frequency discovery
5627 procedure is not reliable, such as on overclocked systems
5628 with CPUID.16h support and partial CPUID.15h support.
5629 Format: <unsigned int>
5631 tsx= [X86] Control Transactional Synchronization
5632 Extensions (TSX) feature in Intel processors that
5633 support TSX control.
5635 This parameter controls the TSX feature. The options are:
5637 on - Enable TSX on the system. Although there are
5638 mitigations for all known security vulnerabilities,
5639 TSX has been known to be an accelerator for
5640 several previous speculation-related CVEs, and
5641 so there may be unknown security risks associated
5642 with leaving it enabled.
5644 off - Disable TSX on the system. (Note that this
5645 option takes effect only on newer CPUs which are
5646 not vulnerable to MDS, i.e., have
5647 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
5648 the new IA32_TSX_CTRL MSR through a microcode
5649 update. This new MSR allows for the reliable
5650 deactivation of the TSX functionality.)
5652 auto - Disable TSX if X86_BUG_TAA is present,
5653 otherwise enable TSX on the system.
5655 Not specifying this option is equivalent to tsx=off.
5657 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5660 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
5661 Abort (TAA) vulnerability.
5663 Similar to Micro-architectural Data Sampling (MDS)
5664 certain CPUs that support Transactional
5665 Synchronization Extensions (TSX) are vulnerable to an
5666 exploit against CPU internal buffers which can forward
5667 information to a disclosure gadget under certain
5670 In vulnerable processors, the speculatively forwarded
5671 data can be used in a cache side channel attack, to
5672 access data to which the attacker does not have direct
5675 This parameter controls the TAA mitigation. The
5678 full - Enable TAA mitigation on vulnerable CPUs
5681 full,nosmt - Enable TAA mitigation and disable SMT on
5682 vulnerable CPUs. If TSX is disabled, SMT
5683 is not disabled because CPU is not
5684 vulnerable to cross-thread TAA attacks.
5685 off - Unconditionally disable TAA mitigation
5687 On MDS-affected machines, tsx_async_abort=off can be
5688 prevented by an active MDS mitigation as both vulnerabilities
5689 are mitigated with the same mechanism so in order to disable
5690 this mitigation, you need to specify mds=off too.
5692 Not specifying this option is equivalent to
5693 tsx_async_abort=full. On CPUs which are MDS affected
5694 and deploy MDS mitigation, TAA mitigation is not
5695 required and doesn't provide any additional
5699 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5701 turbografx.map[2|3]= [HW,JOY]
5702 TurboGraFX parallel port interface
5704 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
5705 See also Documentation/input/devices/joystick-parport.rst
5707 udbg-immortal [PPC] When debugging early kernel crashes that
5708 happen after console_init() and before a proper
5709 console driver takes over, this boot options might
5710 help "seeing" what's going on.
5712 uhash_entries= [KNL,NET]
5713 Set number of hash buckets for UDP/UDP-Lite connections
5716 [USB] Ignore overcurrent events (default N).
5717 Some badly-designed motherboards generate lots of
5718 bogus events, for ports that aren't wired to
5719 anything. Set this parameter to avoid log spamming.
5720 Note that genuine overcurrent events won't be
5724 [X86] Cause panic on unknown NMI.
5726 usbcore.authorized_default=
5727 [USB] Default USB device authorization:
5728 (default -1 = authorized except for wireless USB,
5729 0 = not authorized, 1 = authorized, 2 = authorized
5730 if device connected to internal port)
5732 usbcore.autosuspend=
5733 [USB] The autosuspend time delay (in seconds) used
5734 for newly-detected USB devices (default 2). This
5735 is the time required before an idle device will be
5736 autosuspended. Devices for which the delay is set
5737 to a negative value won't be autosuspended at all.
5739 usbcore.usbfs_snoop=
5740 [USB] Set to log all usbfs traffic (default 0 = off).
5742 usbcore.usbfs_snoop_max=
5743 [USB] Maximum number of bytes to snoop in each URB
5746 usbcore.blinkenlights=
5747 [USB] Set to cycle leds on hubs (default 0 = off).
5749 usbcore.old_scheme_first=
5750 [USB] Start with the old device initialization
5751 scheme (default 0 = off).
5753 usbcore.usbfs_memory_mb=
5754 [USB] Memory limit (in MB) for buffers allocated by
5755 usbfs (default = 16, 0 = max = 2047).
5757 usbcore.use_both_schemes=
5758 [USB] Try the other device initialization scheme
5759 if the first one fails (default 1 = enabled).
5761 usbcore.initial_descriptor_timeout=
5762 [USB] Specifies timeout for the initial 64-byte
5763 USB_REQ_GET_DESCRIPTOR request in milliseconds
5764 (default 5000 = 5.0 seconds).
5766 usbcore.nousb [USB] Disable the USB subsystem
5769 [USB] A list of quirk entries to augment the built-in
5770 usb core quirk list. List entries are separated by
5771 commas. Each entry has the form
5772 VendorID:ProductID:Flags. The IDs are 4-digit hex
5773 numbers and Flags is a set of letters. Each letter
5774 will change the built-in quirk; setting it if it is
5775 clear and clearing it if it is set. The letters have
5776 the following meanings:
5777 a = USB_QUIRK_STRING_FETCH_255 (string
5778 descriptors must not be fetched using
5780 b = USB_QUIRK_RESET_RESUME (device can't resume
5781 correctly so reset it instead);
5782 c = USB_QUIRK_NO_SET_INTF (device can't handle
5783 Set-Interface requests);
5784 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
5785 handle its Configuration or Interface
5787 e = USB_QUIRK_RESET (device can't be reset
5788 (e.g morph devices), don't use reset);
5789 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
5790 more interface descriptions than the
5791 bNumInterfaces count, and can't handle
5792 talking to these interfaces);
5793 g = USB_QUIRK_DELAY_INIT (device needs a pause
5794 during initialization, after we read
5795 the device descriptor);
5796 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
5797 high speed and super speed interrupt
5798 endpoints, the USB 2.0 and USB 3.0 spec
5799 require the interval in microframes (1
5800 microframe = 125 microseconds) to be
5801 calculated as interval = 2 ^
5803 Devices with this quirk report their
5804 bInterval as the result of this
5805 calculation instead of the exponent
5806 variable used in the calculation);
5807 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
5808 handle device_qualifier descriptor
5810 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
5811 generates spurious wakeup, ignore
5812 remote wakeup capability);
5813 k = USB_QUIRK_NO_LPM (device can't handle Link
5815 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
5816 (Device reports its bInterval as linear
5817 frames instead of the USB 2.0
5819 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
5820 to be disconnected before suspend to
5821 prevent spurious wakeup);
5822 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
5823 pause after every control message);
5824 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
5825 delay after resetting its port);
5826 Example: quirks=0781:5580:bk,0a5c:5834:gij
5829 [USBHID] The interval which mice are to be polled at.
5832 [USBHID] The interval which joysticks are to be polled at.
5835 [USBHID] The interval which keyboards are to be polled at.
5837 usb-storage.delay_use=
5838 [UMS] The delay in seconds before a new device is
5839 scanned for Logical Units (default 1).
5842 [UMS] A list of quirks entries to supplement or
5843 override the built-in unusual_devs list. List
5844 entries are separated by commas. Each entry has
5845 the form VID:PID:Flags where VID and PID are Vendor
5846 and Product ID values (4-digit hex numbers) and
5847 Flags is a set of characters, each corresponding
5848 to a common usb-storage quirk flag as follows:
5849 a = SANE_SENSE (collect more than 18 bytes
5850 of sense data, not on uas);
5851 b = BAD_SENSE (don't collect more than 18
5852 bytes of sense data, not on uas);
5853 c = FIX_CAPACITY (decrease the reported
5854 device capacity by one sector);
5855 d = NO_READ_DISC_INFO (don't use
5856 READ_DISC_INFO command, not on uas);
5857 e = NO_READ_CAPACITY_16 (don't use
5858 READ_CAPACITY_16 command);
5859 f = NO_REPORT_OPCODES (don't use report opcodes
5861 g = MAX_SECTORS_240 (don't transfer more than
5862 240 sectors at a time, uas only);
5863 h = CAPACITY_HEURISTICS (decrease the
5864 reported device capacity by one
5865 sector if the number is odd);
5866 i = IGNORE_DEVICE (don't bind to this
5868 j = NO_REPORT_LUNS (don't use report luns
5870 k = NO_SAME (do not use WRITE_SAME, uas only)
5871 l = NOT_LOCKABLE (don't try to lock and
5872 unlock ejectable media, not on uas);
5873 m = MAX_SECTORS_64 (don't transfer more
5874 than 64 sectors = 32 KB at a time,
5876 n = INITIAL_READ10 (force a retry of the
5877 initial READ(10) command, not on uas);
5878 o = CAPACITY_OK (accept the capacity
5879 reported by the device, not on uas);
5880 p = WRITE_CACHE (the device cache is ON
5881 by default, not on uas);
5882 r = IGNORE_RESIDUE (the device reports
5883 bogus residue values, not on uas);
5884 s = SINGLE_LUN (the device has only one
5886 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
5887 commands, uas only);
5888 u = IGNORE_UAS (don't bind to the uas driver);
5889 w = NO_WP_DETECT (don't test whether the
5890 medium is write-protected).
5891 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
5892 even if the device claims no cache,
5894 Example: quirks=0419:aaf5:rl,0421:0433:rc
5896 user_debug= [KNL,ARM]
5898 See arch/arm/Kconfig.debug help text.
5899 1 - undefined instruction events
5901 4 - invalid data aborts
5904 Example: user_debug=31
5907 [X86] Flags controlling user PTE allocations.
5909 nohigh = do not allocate PTE pages in
5910 HIGHMEM regardless of setting
5914 On X86_32, this is an alias for vdso32=. Otherwise:
5916 vdso=1: enable VDSO (the default)
5917 vdso=0: disable VDSO mapping
5919 vdso32= [X86] Control the 32-bit vDSO
5920 vdso32=1: enable 32-bit VDSO
5921 vdso32=0 or vdso32=2: disable 32-bit VDSO
5923 See the help text for CONFIG_COMPAT_VDSO for more
5924 details. If CONFIG_COMPAT_VDSO is set, the default is
5925 vdso32=0; otherwise, the default is vdso32=1.
5927 For compatibility with older kernels, vdso32=2 is an
5930 Try vdso32=0 if you encounter an error that says:
5931 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
5934 vector=percpu: enable percpu vector domain
5936 video= [FB] Frame buffer configuration
5937 See Documentation/fb/modedb.rst.
5939 video.brightness_switch_enabled= [0,1]
5940 If set to 1, on receiving an ACPI notify event
5941 generated by hotkey, video driver will adjust brightness
5942 level and then send out the event to user space through
5943 the allocated input device; If set to 0, video driver
5944 will only send out the event without touching backlight
5949 [VMMIO] Memory mapped virtio (platform) device.
5951 <size>@<baseaddr>:<irq>[:<id>]
5953 <size> := size (can use standard suffixes
5955 <baseaddr> := physical base address
5956 <irq> := interrupt number (as passed to
5958 <id> := (optional) platform device id
5960 virtio_mmio.device=1K@0x100b0000:48:7
5962 Can be used multiple times for multiple devices.
5964 vga= [BOOT,X86-32] Select a particular video mode
5965 See Documentation/x86/boot.rst and
5966 Documentation/admin-guide/svga.rst.
5967 Use vga=ask for menu.
5968 This is actually a boot loader parameter; the value is
5969 passed to the kernel using a special protocol.
5971 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
5972 May slow down system boot speed, especially when
5973 enabled on systems with a large amount of memory.
5974 All options are enabled by default, and this
5975 interface is meant to allow for selectively
5976 enabling or disabling specific virtual memory
5979 Available options are:
5980 P Enable page structure init time poisoning
5981 - Disable all of the above options
5983 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
5984 size of <nn>. This can be used to increase the
5985 minimum size (128MB on x86). It can also be used to
5986 decrease the size and leave more room for directly
5989 vmcp_cma=nn[MG] [KNL,S390]
5990 Sets the memory size reserved for contiguous memory
5991 allocations for the vmcp device driver.
5993 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5996 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5999 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
6003 Controls the behavior of vsyscalls (i.e. calls to
6004 fixed addresses of 0xffffffffff600x00 from legacy
6005 code). Most statically-linked binaries and older
6006 versions of glibc use these calls. Because these
6007 functions are at fixed addresses, they make nice
6008 targets for exploits that can control RIP.
6010 emulate [default] Vsyscalls turn into traps and are
6011 emulated reasonably safely. The vsyscall
6014 xonly Vsyscalls turn into traps and are
6015 emulated reasonably safely. The vsyscall
6016 page is not readable.
6018 none Vsyscalls don't work at all. This makes
6019 them quite hard to use for exploits but
6020 might break your system.
6022 vt.color= [VT] Default text color.
6023 Format: 0xYX, X = foreground, Y = background.
6024 Default: 0x07 = light gray on black.
6026 vt.cur_default= [VT] Default cursor shape.
6027 Format: 0xCCBBAA, where AA, BB, and CC are the same as
6028 the parameters of the <Esc>[?A;B;Cc escape sequence;
6029 see VGA-softcursor.txt. Default: 2 = underline.
6031 vt.default_blu= [VT]
6032 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
6033 Change the default blue palette of the console.
6034 This is a 16-member array composed of values
6037 vt.default_grn= [VT]
6038 Format: <green0>,<green1>,<green2>,...,<green15>
6039 Change the default green palette of the console.
6040 This is a 16-member array composed of values
6043 vt.default_red= [VT]
6044 Format: <red0>,<red1>,<red2>,...,<red15>
6045 Change the default red palette of the console.
6046 This is a 16-member array composed of values
6052 Set system-wide default UTF-8 mode for all tty's.
6053 Default is 1, i.e. UTF-8 mode is enabled for all
6054 newly opened terminals.
6056 vt.global_cursor_default=
6059 Set system-wide default for whether a cursor
6060 is shown on new VTs. Default is -1,
6061 i.e. cursors will be created by default unless
6062 overridden by individual drivers. 0 will hide
6063 cursors, 1 will display them.
6065 vt.italic= [VT] Default color for italic text; 0-15.
6068 vt.underline= [VT] Default color for underlined text; 0-15.
6071 watchdog timers [HW,WDT] For information on watchdog timers,
6072 see Documentation/watchdog/watchdog-parameters.rst
6073 or other driver-specific files in the
6074 Documentation/watchdog/ directory.
6078 Set the hard lockup detector stall duration
6079 threshold in seconds. The soft lockup detector
6080 threshold is set to twice the value. A value of 0
6081 disables both lockup detectors. Default is 10
6084 workqueue.watchdog_thresh=
6085 If CONFIG_WQ_WATCHDOG is configured, workqueue can
6086 warn stall conditions and dump internal state to
6087 help debugging. 0 disables workqueue stall
6088 detection; otherwise, it's the stall threshold
6089 duration in seconds. The default value is 30 and
6090 it can be updated at runtime by writing to the
6091 corresponding sysfs file.
6093 workqueue.disable_numa
6094 By default, all work items queued to unbound
6095 workqueues are affine to the NUMA nodes they're
6096 issued on, which results in better behavior in
6097 general. If NUMA affinity needs to be disabled for
6098 whatever reason, this option can be used. Note
6099 that this also can be controlled per-workqueue for
6100 workqueues visible under /sys/bus/workqueue/.
6102 workqueue.power_efficient
6103 Per-cpu workqueues are generally preferred because
6104 they show better performance thanks to cache
6105 locality; unfortunately, per-cpu workqueues tend to
6106 be more power hungry than unbound workqueues.
6108 Enabling this makes the per-cpu workqueues which
6109 were observed to contribute significantly to power
6110 consumption unbound, leading to measurably lower
6111 power usage at the cost of small performance
6114 The default value of this parameter is determined by
6115 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
6117 workqueue.debug_force_rr_cpu
6118 Workqueue used to implicitly guarantee that work
6119 items queued without explicit CPU specified are put
6120 on the local CPU. This guarantee is no longer true
6121 and while local CPU is still preferred work items
6122 may be put on foreign CPUs. This debug option
6123 forces round-robin CPU selection to flush out
6124 usages which depend on the now broken guarantee.
6125 When enabled, memory and cache locality will be
6128 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
6129 default x2apic cluster mode on platforms
6132 xen_512gb_limit [KNL,X86-64,XEN]
6133 Restricts the kernel running paravirtualized under Xen
6134 to use only up to 512 GB of RAM. The reason to do so is
6135 crash analysis tools and Xen tools for doing domain
6136 save/restore/migration must be enabled to handle larger
6139 xen_emul_unplug= [HW,X86,XEN]
6140 Unplug Xen emulated devices
6141 Format: [unplug0,][unplug1]
6142 ide-disks -- unplug primary master IDE devices
6143 aux-ide-disks -- unplug non-primary-master IDE devices
6144 nics -- unplug network devices
6145 all -- unplug all emulated devices (NICs and IDE disks)
6146 unnecessary -- unplugging emulated devices is
6147 unnecessary even if the host did not respond to
6149 never -- do not unplug even if version check succeeds
6151 xen_legacy_crash [X86,XEN]
6152 Crash from Xen panic notifier, without executing late
6153 panic() code such as dumping handler.
6155 xen_nopvspin [X86,XEN]
6156 Disables the qspinlock slowpath using Xen PV optimizations.
6157 This parameter is obsoleted by "nopvspin" parameter, which
6158 has equivalent effect for XEN platform.
6161 Disables the PV optimizations forcing the HVM guest to
6162 run as generic HVM guest with no PV drivers.
6163 This option is obsoleted by the "nopv" option, which
6164 has equivalent effect for XEN platform.
6166 xen_no_vector_callback
6167 [KNL,X86,XEN] Disable the vector callback for Xen
6168 event channel interrupts.
6170 xen_scrub_pages= [XEN]
6171 Boolean option to control scrubbing pages before giving them back
6172 to Xen, for use by other domains. Can be also changed at runtime
6173 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
6174 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
6176 xen_timer_slop= [X86-64,XEN]
6177 Set the timer slop (in nanoseconds) for the virtual Xen
6178 timers (default is 100000). This adjusts the minimum
6179 delta of virtualized Xen timers, where lower values
6180 improve timer resolution at the expense of processing
6181 more timer interrupts.
6183 xen.event_eoi_delay= [XEN]
6184 How long to delay EOI handling in case of event
6185 storms (jiffies). Default is 10.
6187 xen.event_loop_timeout= [XEN]
6188 After which time (jiffies) the event handling loop
6189 should start to delay EOI handling. Default is 2.
6191 xen.fifo_events= [XEN]
6192 Boolean parameter to disable using fifo event handling
6193 even if available. Normally fifo event handling is
6194 preferred over the 2-level event handling, as it is
6195 fairer and the number of possible event channels is
6196 much higher. Default is on (use fifo events).
6198 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
6199 Disables the PV optimizations forcing the guest to run
6200 as generic guest with no PV drivers. Currently support
6201 XEN HVM, KVM, HYPER_V and VMWARE guest.
6203 nopvspin [X86,XEN,KVM]
6204 Disables the qspinlock slow path using PV optimizations
6205 which allow the hypervisor to 'idle' the guest on lock
6208 xirc2ps_cs= [NET,PCMCIA]
6210 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
6213 By default on POWER9 and above, the kernel will
6214 natively use the XIVE interrupt controller. This option
6215 allows the fallback firmware mode to be used:
6217 off Fallback to firmware control of XIVE interrupt
6218 controller on both pseries and powernv
6219 platforms. Only useful on POWER9 and above.
6221 xhci-hcd.quirks [USB,KNL]
6222 A hex value specifying bitmask with supplemental xhci
6223 host controller quirks. Meaning of each bit can be
6224 consulted in header drivers/usb/host/xhci.h.
6227 Format: { early | on | rw | ro | off }
6228 Controls if xmon debugger is enabled. Default is off.
6229 Passing only "xmon" is equivalent to "xmon=early".
6230 early Call xmon as early as possible on boot; xmon
6231 debugger is called from setup_arch().
6232 on xmon debugger hooks will be installed so xmon
6233 is only called on a kernel crash. Default mode,
6234 i.e. either "ro" or "rw" mode, is controlled
6235 with CONFIG_XMON_DEFAULT_RO_MODE.
6236 rw xmon debugger hooks will be installed so xmon
6237 is called only on a kernel crash, mode is write,
6238 meaning SPR registers, memory and, other data
6239 can be written using xmon commands.
6240 ro same as "rw" option above but SPR registers,
6241 memory, and other data can't be written using
6243 off xmon is disabled.
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