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]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/firmware-guide/acpi/debug.rst for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
159 acpi_osi=!! # enable all built-in OS vendor
161 acpi_osi= # disable all strings
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.rst for information on
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
259 See Documentation/sound/alsa-configuration.rst
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
293 off - do not initialize any AMD IOMMU found in
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
319 See also Documentation/input/joydev/joystick.rst
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
327 Power management functions (SPARCstation-4/5 + deriv.)
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity while booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.rst
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
465 [NET] Specifies amount of time (in seconds) that
466 the kernel should wait for a network carrier. By default
467 it waits 120 seconds.
469 ca_keys= [KEYS] This parameter identifies a specific key(s) on
470 the system trusted keyring to be used for certificate
472 format: { id:<keyid> | builtin }
474 cca= [MIPS] Override the kernel pages' cache coherency
475 algorithm. Accepted values range from 0 to 7
476 inclusive. See arch/mips/include/asm/pgtable-bits.h
477 for platform specific values (SB1, Loongson3 and
480 ccw_timeout_log [S390]
481 See Documentation/s390/common_io.rst for details.
483 cgroup_disable= [KNL] Disable a particular controller
484 Format: {name of the controller(s) to disable}
485 The effects of cgroup_disable=foo are:
486 - foo isn't auto-mounted if you mount all cgroups in
488 - foo isn't visible as an individually mountable
490 {Currently only "memory" controller deal with this and
491 cut the overhead, others just disable the usage. So
492 only cgroup_disable=memory is actually worthy}
494 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
495 Format: { { controller | "all" | "named" }
496 [,{ controller | "all" | "named" }...] }
497 Like cgroup_disable, but only applies to cgroup v1;
498 the blacklisted controllers remain available in cgroup2.
499 "all" blacklists all controllers and "named" disables
500 named mounts. Specifying both "all" and "named" disables
503 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
505 nosocket -- Disable socket memory accounting.
506 nokmem -- Disable kernel memory accounting.
508 checkreqprot [SELINUX] Set initial checkreqprot flag value.
509 Format: { "0" | "1" }
510 See security/selinux/Kconfig help text.
511 0 -- check protection applied by kernel (includes
512 any implied execute protection).
513 1 -- check protection requested by application.
514 Default value is set via a kernel config option.
515 Value can be changed at runtime via
516 /selinux/checkreqprot.
519 See Documentation/s390/common_io.rst for details.
522 Prevents the clock framework from automatically gating
523 clocks that have not been explicitly enabled by a Linux
524 device driver but are enabled in hardware at reset or
525 by the bootloader/firmware. Note that this does not
526 force such clocks to be always-on nor does it reserve
527 those clocks in any way. This parameter is useful for
528 debug and development, but should not be needed on a
529 platform with proper driver support. For more
530 information, see Documentation/driver-api/clk.rst.
532 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
534 Forces specified clocksource (if available) to be used
535 when calculating gettimeofday(). If specified
536 clocksource is not available, it defaults to PIT.
537 Format: { pit | tsc | cyclone | pmtmr }
539 clocksource= Override the default clocksource
541 Override the default clocksource and use the clocksource
542 with the name specified.
543 Some clocksource names to choose from, depending on
545 [all] jiffies (this is the base, fallback clocksource)
547 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
548 pxa_timer,timer3,32k_counter,timer0_1
549 [X86-32] pit,hpet,tsc;
550 scx200_hrt on Geode; cyclone on IBM x440
558 clocksource.arm_arch_timer.evtstrm=
561 Enable/disable the eventstream feature of the ARM
562 architected timer so that code using WFE-based polling
563 loops can be debugged more effectively on production
566 clearcpuid=BITNUM [X86]
567 Disable CPUID feature X for the kernel. See
568 arch/x86/include/asm/cpufeatures.h for the valid bit
569 numbers. Note the Linux specific bits are not necessarily
570 stable over kernel options, but the vendor specific
572 Also note that user programs calling CPUID directly
573 or using the feature without checking anything
574 will still see it. This just prevents it from
575 being used by the kernel or shown in /proc/cpuinfo.
576 Also note the kernel might malfunction if you disable
579 cma=nn[MG]@[start[MG][-end[MG]]]
581 Sets the size of kernel global memory area for
582 contiguous memory allocations and optionally the
583 placement constraint by the physical address range of
584 memory allocations. A value of 0 disables CMA
585 altogether. For more information, see
586 include/linux/dma-contiguous.h
588 cmo_free_hint= [PPC] Format: { yes | no }
589 Specify whether pages are marked as being inactive
590 when they are freed. This is used in CMO environments
591 to determine OS memory pressure for page stealing by
595 coherent_pool=nn[KMG] [ARM,KNL]
596 Sets the size of memory pool for coherent, atomic dma
597 allocations, by default set to 256K.
599 com20020= [HW,NET] ARCnet - COM20020 chipset
601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
607 ARCnet - COM90xx chipset (memory-mapped buffers)
608 Format: <io>[,<irq>[,<memstart>]]
610 condev= [HW,S390] console device
613 console= [KNL] Output console device and options.
615 tty<n> Use the virtual console device <n>.
619 Use the specified serial port. The options are of
620 the form "bbbbpnf", where "bbbb" is the baud rate,
621 "p" is parity ("n", "o", or "e"), "n" is number of
622 bits, and "f" is flow control ("r" for RTS or
623 omit it). Default is "9600n8".
625 See Documentation/admin-guide/serial-console.rst for more
627 Documentation/networking/netconsole.txt for an
630 uart[8250],io,<addr>[,options]
631 uart[8250],mmio,<addr>[,options]
632 uart[8250],mmio16,<addr>[,options]
633 uart[8250],mmio32,<addr>[,options]
634 uart[8250],0x<addr>[,options]
635 Start an early, polled-mode console on the 8250/16550
636 UART at the specified I/O port or MMIO address,
637 switching to the matching ttyS device later.
638 MMIO inter-register address stride is either 8-bit
639 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
640 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
641 to be equivalent to 'mmio'. 'options' are specified in
642 the same format described for ttyS above; if unspecified,
643 the h/w is not re-initialized.
645 hvc<n> Use the hypervisor console device <n>. This is for
646 both Xen and PowerPC hypervisors.
648 If the device connected to the port is not a TTY but a braille
649 device, prepend "brl," before the device type, for instance
651 For now, only VisioBraille is supported.
654 [KNL] Change console messages format
656 By default we print messages on consoles in
657 "[time stamp] text\n" format (time stamp may not be
658 printed, depending on CONFIG_PRINTK_TIME or
659 `printk_time' param).
661 Switch to syslog format: "<%u>[time stamp] text\n"
662 IOW, each message will have a facility and loglevel
663 prefix. The format is similar to one used by syslog()
664 syscall, or to executing "dmesg -S --raw" or to reading
667 consoleblank= [KNL] The console blank (screen saver) timeout in
668 seconds. A value of 0 disables the blank timer.
672 [KNL] Change the default value for
673 /proc/<pid>/coredump_filter.
674 See also Documentation/filesystems/proc.txt.
676 coresight_cpu_debug.enable
679 Enable/disable the CPU sampling based debugging.
680 0: default value, disable debugging
681 1: enable debugging at boot time
683 cpuidle.off=1 [CPU_IDLE]
684 disable the cpuidle sub-system
687 [CPU_IDLE] Name of the cpuidle governor to use.
689 cpufreq.off=1 [CPU_FREQ]
690 disable the cpufreq sub-system
693 [X86] Delay for N microsec between assert and de-assert
694 of APIC INIT to start processors. This delay occurs
695 on every CPU online, such as boot, and resume from suspend.
698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
700 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
702 crashkernel=size[KMG][@offset[KMG]]
703 [KNL] Using kexec, Linux can switch to a 'crash kernel'
704 upon panic. This parameter reserves the physical
705 memory region [offset, offset + size] for that kernel
706 image. If '@offset' is omitted, then a suitable offset
707 is selected automatically.
708 [KNL, x86_64] select a region under 4G first, and
709 fall back to reserve region above 4G when '@offset'
710 hasn't been specified.
711 See Documentation/admin-guide/kdump/kdump.rst for further details.
713 crashkernel=range1:size1[,range2:size2,...][@offset]
714 [KNL] Same as above, but depends on the memory
715 in the running system. The syntax of range is
716 start-[end] where start and end are both
717 a memory unit (amount[KMG]). See also
718 Documentation/admin-guide/kdump/kdump.rst for an example.
720 crashkernel=size[KMG],high
721 [KNL, x86_64] range could be above 4G. Allow kernel
722 to allocate physical memory region from top, so could
723 be above 4G if system have more than 4G ram installed.
724 Otherwise memory region will be allocated below 4G, if
726 It will be ignored if crashkernel=X is specified.
727 crashkernel=size[KMG],low
728 [KNL, x86_64] range under 4G. When crashkernel=X,high
729 is passed, kernel could allocate physical memory region
730 above 4G, that cause second kernel crash on system
731 that require some amount of low memory, e.g. swiotlb
732 requires at least 64M+32K low memory, also enough extra
733 low memory is needed to make sure DMA buffers for 32-bit
734 devices won't run out. Kernel would try to allocate at
735 at least 256M below 4G automatically.
736 This one let user to specify own low range under 4G
737 for second kernel instead.
738 0: to disable low allocation.
739 It will be ignored when crashkernel=X,high is not used
740 or memory reserved is below 4G.
743 [KNL] Disable crypto self-tests
748 cs89x0_media= [HW,NET]
749 Format: { rj45 | aui | bnc }
752 See header of drivers/s390/block/dasd_devmap.c.
754 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
755 (one device per port)
756 Format: <port#>,<type>
757 See also Documentation/input/devices/joystick-parport.rst
759 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
761 Documentation/admin-guide/dynamic-debug-howto.rst for
762 details. Deprecated, see dyndbg.
764 debug [KNL] Enable kernel debugging (events log level).
767 [KNL] Enable printing [hashed] pointers early in the
768 boot sequence. If enabled, we use a weak hash instead
769 of siphash to hash pointers. Use this option if you are
770 seeing instances of '(___ptrval___)') and need to see a
771 value (hashed pointer) instead. Cryptographically
772 insecure, please do not use on production kernels.
775 [KNL] verbose self-tests
777 Print debugging info while doing the locking API
779 We default to 0 (no extra messages), setting it to
780 1 will print _a lot_ more information - normally
781 only useful to kernel developers.
783 debug_objects [KNL] Enable object debugging
786 [KNL] Disable object debugging
788 debug_guardpage_minorder=
789 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
790 parameter allows control of the order of pages that will
791 be intentionally kept free (and hence protected) by the
792 buddy allocator. Bigger value increase the probability
793 of catching random memory corruption, but reduce the
794 amount of memory for normal system use. The maximum
795 possible value is MAX_ORDER/2. Setting this parameter
796 to 1 or 2 should be enough to identify most random
797 memory corruption problems caused by bugs in kernel or
798 driver code when a CPU writes to (or reads from) a
799 random memory location. Note that there exists a class
800 of memory corruptions problems caused by buggy H/W or
801 F/W or by drivers badly programing DMA (basically when
802 memory is written at bus level and the CPU MMU is
803 bypassed) which are not detectable by
804 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
805 tracking down these problems.
808 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
809 enables the feature at boot time. By default, it is
810 disabled and the system will work mostly the same as a
811 kernel built without CONFIG_DEBUG_PAGEALLOC.
812 Note: to get most of debug_pagealloc error reports, it's
813 useful to also enable the page_owner functionality.
814 on: enable the feature
816 debugpat [X86] Enable PAT debugging
818 decnet.addr= [HW,NET]
819 Format: <area>[,<node>]
820 See also Documentation/networking/decnet.txt.
823 [same as hugepagesz=] The size of the default
824 HugeTLB page size. This is the size represented by
825 the legacy /proc/ hugepages APIs, used for SHM, and
826 default size when mounting hugetlbfs filesystems.
827 Defaults to the default architecture's huge page size
830 deferred_probe_timeout=
831 [KNL] Debugging option to set a timeout in seconds for
832 deferred probe to give up waiting on dependencies to
833 probe. Only specific dependencies (subsystems or
834 drivers) that have opted in will be ignored. A timeout of 0
835 will timeout at the end of initcalls. This option will also
836 dump out devices still on the deferred probe list after
840 Set number of hash buckets for dentry cache.
842 disable_1tb_segments [PPC]
843 Disables the use of 1TB hash page table segments. This
844 causes the kernel to fall back to 256MB segments which
845 can be useful when debugging issues that require an SLB
849 See Documentation/networking/ipv6.txt.
852 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
853 hardening is enabled for this boot. Hardened
854 usercopy checking is used to protect the kernel
855 from reading or writing beyond known memory
856 allocation boundaries as a proactive defense
857 against bounds-checking flaws in the kernel's
858 copy_to_user()/copy_from_user() interface.
859 on Perform hardened usercopy checks (default).
860 off Disable hardened usercopy checks.
863 Disable RADIX MMU mode on POWER9
866 Disable TLBIE instruction. Currently does not work
867 with KVM, with HASH MMU, or with coherent accelerators.
869 disable_cpu_apicid= [X86,APIC,SMP]
871 The number of initial APIC ID for the
872 corresponding CPU to be disabled at boot,
873 mostly used for the kdump 2nd kernel to
874 disable BSP to wake up multiple CPUs without
875 causing system reset or hang due to sending
878 perf_v4_pmi= [X86,INTEL]
880 Disable Intel PMU counter freezing feature.
881 The feature only exists starting from
882 Arch Perfmon v4 (Skylake and newer).
884 disable_ddw [PPC/PSERIES]
885 Disable Dynamic DMA Window support. Use this if
886 to workaround buggy firmware.
889 See Documentation/networking/ipv6.txt.
891 disable_mtrr_cleanup [X86]
892 The kernel tries to adjust MTRR layout from continuous
893 to discrete, to make X server driver able to add WB
894 entry later. This parameter disables that.
896 disable_mtrr_trim [X86, Intel and AMD only]
897 By default the kernel will trim any uncacheable
898 memory out of your available memory pool based on
899 MTRR settings. This parameter disables that behavior,
900 possibly causing your machine to run very slowly.
902 disable_timer_pin_1 [X86]
903 Disable PIN 1 of APIC timer
904 Can be useful to work around chipset bugs.
906 dis_ucode_ldr [X86] Disable the microcode loader.
908 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
909 this option disables the debugging code at boot.
911 dma_debug_entries=<number>
912 This option allows to tune the number of preallocated
913 entries for DMA-API debugging code. One entry is
914 required per DMA-API allocation. Use this if the
915 DMA-API debugging code disables itself because the
916 architectural default is too low.
918 dma_debug_driver=<driver_name>
919 With this option the DMA-API debugging driver
920 filter feature can be enabled at boot time. Just
921 pass the driver to filter for as the parameter.
922 The filter can be disabled or changed to another
923 driver later using sysfs.
925 driver_async_probe= [KNL]
926 List of driver names to be probed asynchronously.
927 Format: <driver_name1>,<driver_name2>...
929 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
930 Broken monitors, graphic adapters, KVMs and EDIDless
931 panels may send no or incorrect EDID data sets.
932 This parameter allows to specify an EDID data sets
933 in the /lib/firmware directory that are used instead.
934 Generic built-in EDID data sets are used, if one of
935 edid/1024x768.bin, edid/1280x1024.bin,
936 edid/1680x1050.bin, or edid/1920x1080.bin is given
937 and no file with the same name exists. Details and
938 instructions how to build your own EDID data are
939 available in Documentation/driver-api/edid.rst. An EDID
940 data set will only be used for a particular connector,
941 if its name and a colon are prepended to the EDID
942 name. Each connector may use a unique EDID data
943 set by separating the files with a comma. An EDID
944 data set with no connector name will be used for
945 any connectors not explicitly specified.
950 Format: {"off" | "known"}
951 Control how the dt_cpu_ftrs device-tree binding is
952 used for CPU feature discovery and setup (if it
954 off: Do not use it, fall back to legacy cpu table.
955 known: Do not pass through unknown features to guests
956 or userspace, only those that the kernel is aware of.
958 dump_apple_properties [X86]
959 Dump name and content of EFI device properties on
960 x86 Macs. Useful for driver authors to determine
961 what data is available or for reverse-engineering.
963 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
964 module.dyndbg[="val"]
965 Enable debug messages at boot time. See
966 Documentation/admin-guide/dynamic-debug-howto.rst
969 nompx [X86] Disables Intel Memory Protection Extensions.
970 See Documentation/x86/intel_mpx.rst for more
971 information about the feature.
973 nopku [X86] Disable Memory Protection Keys CPU feature found
976 module.async_probe [KNL]
977 Enable asynchronous probe on this module.
979 early_ioremap_debug [KNL]
980 Enable debug messages in early_ioremap support. This
981 is useful for tracking down temporary early mappings
982 which are not unmapped.
984 earlycon= [KNL] Output early console device and options.
986 [ARM64] The early console is determined by the
987 stdout-path property in device tree's chosen node,
988 or determined by the ACPI SPCR table.
990 [X86] When used with no options the early console is
991 determined by the ACPI SPCR table.
993 cdns,<addr>[,options]
994 Start an early, polled-mode console on a Cadence
995 (xuartps) serial port at the specified address. Only
996 supported option is baud rate. If baud rate is not
997 specified, the serial port must already be setup and
1000 uart[8250],io,<addr>[,options]
1001 uart[8250],mmio,<addr>[,options]
1002 uart[8250],mmio32,<addr>[,options]
1003 uart[8250],mmio32be,<addr>[,options]
1004 uart[8250],0x<addr>[,options]
1005 Start an early, polled-mode console on the 8250/16550
1006 UART at the specified I/O port or MMIO address.
1007 MMIO inter-register address stride is either 8-bit
1008 (mmio) or 32-bit (mmio32 or mmio32be).
1009 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1010 to be equivalent to 'mmio'. 'options' are specified
1011 in the same format described for "console=ttyS<n>"; if
1012 unspecified, the h/w is not initialized.
1016 Start an early, polled-mode console on a pl011 serial
1017 port at the specified address. The pl011 serial port
1018 must already be setup and configured. Options are not
1019 yet supported. If 'mmio32' is specified, then only
1020 the driver will use only 32-bit accessors to read/write
1021 the device registers.
1024 Start an early, polled-mode console on a meson serial
1025 port at the specified address. The serial port must
1026 already be setup and configured. Options are not yet
1030 Start an early, polled-mode console on an msm serial
1031 port at the specified address. The serial port
1032 must already be setup and configured. Options are not
1035 msm_serial_dm,<addr>
1036 Start an early, polled-mode console on an msm serial
1037 dm port at the specified address. The serial port
1038 must already be setup and configured. Options are not
1042 Start an early, polled-mode console on a serial port
1043 of an Actions Semi SoC, such as S500 or S900, at the
1044 specified address. The serial port must already be
1045 setup and configured. Options are not yet supported.
1048 Start an early, polled-mode console on a serial port
1049 of an RDA Micro SoC, such as RDA8810PL, at the
1050 specified address. The serial port must already be
1051 setup and configured. Options are not yet supported.
1054 Use RISC-V SBI (Supervisor Binary Interface) for early
1057 smh Use ARM semihosting calls for early console.
1065 Use early console provided by serial driver available
1066 on Samsung SoCs, requires selecting proper type and
1067 a correct base address of the selected UART port. The
1068 serial port must already be setup and configured.
1069 Options are not yet supported.
1072 Start an early, polled-mode console on a lantiq serial
1073 (lqasc) port at the specified address. The serial port
1074 must already be setup and configured. Options are not
1079 Use early console provided by Freescale LP UART driver
1080 found on Freescale Vybrid and QorIQ LS1021A processors.
1081 A valid base address must be provided, and the serial
1082 port must already be setup and configured.
1085 Start an early, polled-mode console on the
1086 Armada 3700 serial port at the specified
1087 address. The serial port must already be setup
1088 and configured. Options are not yet supported.
1091 Start an early, polled-mode console on a Qualcomm
1092 Generic Interface (GENI) based serial port at the
1093 specified address. The serial port must already be
1094 setup and configured. Options are not yet supported.
1097 Start an early, unaccelerated console on the EFI
1098 memory mapped framebuffer (if available). On cache
1099 coherent non-x86 systems that use system memory for
1100 the framebuffer, pass the 'ram' option so that it is
1101 mapped with the correct attributes.
1104 Use early console provided by Freescale LinFlex UART
1105 serial driver for NXP S32V234 SoCs. A valid base
1106 address must be provided, and the serial port must
1107 already be setup and configured.
1109 earlyprintk= [X86,SH,ARM,M68k,S390]
1113 earlyprintk=serial[,ttySn[,baudrate]]
1114 earlyprintk=serial[,0x...[,baudrate]]
1115 earlyprintk=ttySn[,baudrate]
1116 earlyprintk=dbgp[debugController#]
1117 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1118 earlyprintk=xdbc[xhciController#]
1120 earlyprintk is useful when the kernel crashes before
1121 the normal console is initialized. It is not enabled by
1122 default because it has some cosmetic problems.
1124 Append ",keep" to not disable it when the real console
1127 Only one of vga, efi, serial, or usb debug port can
1130 Currently only ttyS0 and ttyS1 may be specified by
1131 name. Other I/O ports may be explicitly specified
1132 on some architectures (x86 and arm at least) by
1133 replacing ttySn with an I/O port address, like this:
1134 earlyprintk=serial,0x1008,115200
1135 You can find the port for a given device in
1136 /proc/tty/driver/serial:
1137 2: uart:ST16650V2 port:00001008 irq:18 ...
1139 Interaction with the standard serial driver is not
1142 The VGA and EFI output is eventually overwritten by
1145 The xen output can only be used by Xen PV guests.
1147 The sclp output can only be used on s390.
1149 The optional "force" to "pciserial" enables use of a
1150 PCI device even when its classcode is not of the
1153 edac_report= [HW,EDAC] Control how to report EDAC event
1154 Format: {"on" | "off" | "force"}
1155 on: enable EDAC to report H/W event. May be overridden
1156 by other higher priority error reporting module.
1157 off: disable H/W event reporting through EDAC.
1158 force: enforce the use of EDAC to report H/W event.
1161 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1164 This is designed to be used in conjunction with
1165 the boot argument: earlyprintk=vga
1168 Format: {"off" | "on" | "skip[mbr]"}
1171 Format: { "old_map", "nochunk", "noruntime", "debug",
1173 old_map [X86-64]: switch to the old ioremap-based EFI
1174 runtime services mapping. 32-bit still uses this one by
1176 nochunk: disable reading files in "chunks" in the EFI
1177 boot stub, as chunking can cause problems with some
1178 firmware implementations.
1179 noruntime : disable EFI runtime services support
1180 debug: enable misc debug output
1181 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1182 attribute may cause the kernel to reserve the
1183 memory range for a memory mapping driver to
1184 claim. Specify efi=nosoftreserve to disable this
1185 reservation and treat the memory by its base type
1186 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1188 efi_no_storage_paranoia [EFI; X86]
1189 Using this parameter you can use more than 50% of
1190 your efi variable storage. Use this parameter only if
1191 you are really sure that your UEFI does sane gc and
1192 fulfills the spec otherwise your board may brick.
1194 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1195 Add arbitrary attribute to specific memory range by
1196 updating original EFI memory map.
1197 Region of memory which aa attribute is added to is
1200 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1201 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1202 attribute is added to range 0x100000000-0x180000000 and
1203 0x10a0000000-0x1120000000.
1205 If efi_fake_mem=8G@9G:0x40000 is specified, the
1206 EFI_MEMORY_SP(0x40000) attribute is added to
1207 range 0x240000000-0x43fffffff.
1209 Using this parameter you can do debugging of EFI memmap
1210 related features. For example, you can do debugging of
1211 Address Range Mirroring feature even if your box
1212 doesn't support it, or mark specific memory as
1215 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1216 that is to be dynamically loaded by Linux. If there are
1217 multiple variables with the same name but with different
1218 vendor GUIDs, all of them will be loaded. See
1219 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1222 eisa_irq_edge= [PARISC,HW]
1223 See header of drivers/parisc/eisa.c.
1226 See comment before function elanfreq_setup() in
1227 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1229 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1230 Specifies physical address of start of kernel core
1231 image elf header and optionally the size. Generally
1232 kexec loader will pass this option to capture kernel.
1233 See Documentation/admin-guide/kdump/kdump.rst for details.
1235 enable_mtrr_cleanup [X86]
1236 The kernel tries to adjust MTRR layout from continuous
1237 to discrete, to make X server driver able to add WB
1238 entry later. This parameter enables that.
1240 enable_timer_pin_1 [X86]
1241 Enable PIN 1 of APIC timer
1242 Can be useful to work around chipset bugs
1243 (in particular on some ATI chipsets).
1244 The kernel tries to set a reasonable default.
1246 enforcing [SELINUX] Set initial enforcing status.
1248 See security/selinux/Kconfig help text.
1249 0 -- permissive (log only, no denials).
1250 1 -- enforcing (deny and log).
1252 Value can be changed at runtime via /selinux/enforce.
1255 Disable Error Record Serialization Table (ERST)
1258 ether= [HW,NET] Ethernet cards parameters
1259 This option is obsoleted by the "netdev=" option, which
1260 has equivalent usage. See its documentation for details.
1264 Permit 'security.evm' to be updated regardless of
1265 current integrity status.
1269 fail_make_request=[KNL]
1270 General fault injection mechanism.
1271 Format: <interval>,<probability>,<space>,<times>
1272 See also Documentation/fault-injection/.
1275 See Documentation/admin-guide/blockdev/floppy.rst.
1277 force_pal_cache_flush
1278 [IA-64] Avoid check_sal_cache_flush which may hang on
1279 buggy SAL_CACHE_FLUSH implementations. Using this
1280 parameter will force ia64_sal_cache_flush to call
1281 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1284 Forcefully enable Physical Address Extension (PAE).
1285 Many Pentium M systems disable PAE but may have a
1286 functionally usable PAE implementation.
1287 Warning: use of this parameter will taint the kernel
1288 and may cause unknown problems.
1291 [FTRACE] will set and start the specified tracer
1292 as early as possible in order to facilitate early
1295 ftrace_dump_on_oops[=orig_cpu]
1296 [FTRACE] will dump the trace buffers on oops.
1297 If no parameter is passed, ftrace will dump
1298 buffers of all CPUs, but if you pass orig_cpu, it will
1299 dump only the buffer of the CPU that triggered the
1302 ftrace_filter=[function-list]
1303 [FTRACE] Limit the functions traced by the function
1304 tracer at boot up. function-list is a comma separated
1305 list of functions. This list can be changed at run
1306 time by the set_ftrace_filter file in the debugfs
1309 ftrace_notrace=[function-list]
1310 [FTRACE] Do not trace the functions specified in
1311 function-list. This list can be changed at run time
1312 by the set_ftrace_notrace file in the debugfs
1315 ftrace_graph_filter=[function-list]
1316 [FTRACE] Limit the top level callers functions traced
1317 by the function graph tracer at boot up.
1318 function-list is a comma separated list of functions
1319 that can be changed at run time by the
1320 set_graph_function file in the debugfs tracing directory.
1322 ftrace_graph_notrace=[function-list]
1323 [FTRACE] Do not trace from the functions specified in
1324 function-list. This list is a comma separated list of
1325 functions that can be changed at run time by the
1326 set_graph_notrace file in the debugfs tracing directory.
1328 ftrace_graph_max_depth=<uint>
1329 [FTRACE] Used with the function graph tracer. This is
1330 the max depth it will trace into a function. This value
1331 can be changed at run time by the max_graph_depth file
1332 in the tracefs tracing directory. default: 0 (no limit)
1335 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1336 support via parallel port (up to 5 devices per port)
1337 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1338 See also Documentation/input/devices/joystick-parport.rst
1342 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1346 gcov_persist= [GCOV] When non-zero (default), profiling data for
1347 kernel modules is saved and remains accessible via
1348 debugfs, even when the module is unloaded/reloaded.
1349 When zero, profiling data is discarded and associated
1350 debugfs files are removed at module unload time.
1352 goldfish [X86] Enable the goldfish android emulator platform.
1353 Don't use this when you are not running on the
1356 gpt [EFI] Forces disk with valid GPT signature but
1357 invalid Protective MBR to be treated as GPT. If the
1358 primary GPT is corrupted, it enables the backup/alternate
1359 GPT to be used instead.
1361 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1362 the "Enable 0" bit of the configuration register.
1365 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1366 the "Enable 0" bit of the configuration register.
1369 grcan.select= [HW] Select which physical interface to use.
1372 grcan.txsize= [HW] Sets the size of the tx buffer.
1373 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1375 grcan.rxsize= [HW] Sets the size of the rx buffer.
1376 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1379 gpio-mockup.gpio_mockup_ranges
1380 [HW] Sets the ranges of gpiochip of for this device.
1381 Format: <start1>,<end1>,<start2>,<end2>...
1383 hardlockup_all_cpu_backtrace=
1384 [KNL] Should the hard-lockup detector generate
1385 backtraces on all cpus.
1388 hashdist= [KNL,NUMA] Large hashes allocated during boot
1389 are distributed across NUMA nodes. Defaults on
1390 for 64-bit NUMA, off otherwise.
1391 Format: 0 | 1 (for off | on)
1393 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1395 hd= [EIDE] (E)IDE hard drive subsystem geometry
1396 Format: <cyl>,<head>,<sect>
1399 Disable Hardware Error Source Table (HEST) support;
1400 corresponding firmware-first mode error processing
1401 logic will be disabled.
1403 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1404 size of <nn>. This works even on boxes that have no
1405 highmem otherwise. This also works to reduce highmem
1406 size on bigger boxes.
1408 highres= [KNL] Enable/disable high resolution timer mode.
1409 Valid parameters: "on", "off"
1414 hpet= [X86-32,HPET] option to control HPET usage
1415 Format: { enable (default) | disable | force |
1417 disable: disable HPET and use PIT instead
1418 force: allow force enabled of undocumented chips (ICH4,
1420 verbose: show contents of HPET registers during setup
1422 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1423 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1425 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1426 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1427 On x86-64 and powerpc, this option can be specified
1428 multiple times interleaved with hugepages= to reserve
1429 huge pages of different sizes. Valid pages sizes on
1430 x86-64 are 2M (when the CPU supports "pse") and 1G
1431 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1434 [KNL] Should the hung task detector generate panics.
1437 A nonzero value instructs the kernel to panic when a
1438 hung task is detected. The default value is controlled
1439 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1440 option. The value selected by this boot parameter can
1441 be changed later by the kernel.hung_task_panic sysctl.
1443 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1444 terminal devices. Valid values: 0..8
1445 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1446 If specified, z/VM IUCV HVC accepts connections
1447 from listed z/VM user IDs only.
1449 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1450 which allow the hypervisor to 'idle' the
1451 guest on lock contention.
1454 Do not unregister boot console at start. This is only
1455 useful for debugging when something happens in the window
1456 between unregistering the boot console and initializing
1459 i2c_bus= [HW] Override the default board specific I2C bus speed
1460 or register an additional I2C bus that is not
1461 registered from board initialization code.
1465 i8042.debug [HW] Toggle i8042 debug mode
1466 i8042.unmask_kbd_data
1467 [HW] Enable printing of interrupt data from the KBD port
1468 (disabled by default, and as a pre-condition
1469 requires that i8042.debug=1 be enabled)
1470 i8042.direct [HW] Put keyboard port into non-translated mode
1471 i8042.dumbkbd [HW] Pretend that controller can only read data from
1472 keyboard and cannot control its state
1473 (Don't attempt to blink the leds)
1474 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1475 i8042.nokbd [HW] Don't check/create keyboard port
1476 i8042.noloop [HW] Disable the AUX Loopback command while probing
1478 i8042.nomux [HW] Don't check presence of an active multiplexing
1480 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1482 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1483 i8042.reset [HW] Reset the controller during init, cleanup and
1484 suspend-to-ram transitions, only during s2r
1485 transitions, or never reset
1486 Format: { 1 | Y | y | 0 | N | n }
1487 1, Y, y: always reset controller
1488 0, N, n: don't ever reset controller
1489 Default: only on s2r transitions on x86; most other
1490 architectures force reset to be always executed
1491 i8042.unlock [HW] Unlock (ignore) the keylock
1492 i8042.kbdreset [HW] Reset device connected to KBD port
1496 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1497 indicates that the driver is running on unsupported
1499 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1500 does not match list of supported models.
1502 [HW] Report power status in /proc/i8k
1503 (disabled by default)
1504 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1507 i915.invert_brightness=
1508 [DRM] Invert the sense of the variable that is used to
1509 set the brightness of the panel backlight. Normally a
1510 brightness value of 0 indicates backlight switched off,
1511 and the maximum of the brightness value sets the backlight
1512 to maximum brightness. If this parameter is set to 0
1513 (default) and the machine requires it, or this parameter
1514 is set to 1, a brightness value of 0 sets the backlight
1515 to maximum brightness, and the maximum of the brightness
1516 value switches the backlight off.
1517 -1 -- never invert brightness
1518 0 -- machine default
1519 1 -- force brightness inversion
1522 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1524 ide-core.nodma= [HW] (E)IDE subsystem
1525 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1526 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1527 .cdrom .chs .ignore_cable are additional options
1528 See Documentation/ide/ide.rst.
1530 ide-generic.probe-mask= [HW] (E)IDE subsystem
1532 Probe mask for legacy ISA IDE ports. Depending on
1533 platform up to 6 ports are supported, enabled by
1534 setting corresponding bits in the mask to 1. The
1535 default value is 0x0, which has a special meaning.
1536 On systems that have PCI, it triggers scanning the
1537 PCI bus for the first and the second port, which
1538 are then probed. On systems without PCI the value
1539 of 0x0 enables probing the two first ports as if it
1542 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1543 Claim all unknown PCI IDE storage controllers.
1546 Format: idle=poll, idle=halt, idle=nomwait
1547 Poll forces a polling idle loop that can slightly
1548 improve the performance of waking up a idle CPU, but
1549 will use a lot of power and make the system run hot.
1551 idle=halt: Halt is forced to be used for CPU idle.
1552 In such case C2/C3 won't be used again.
1553 idle=nomwait: Disable mwait for CPU C-states
1555 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1556 Format: { strict | legacy | 2008 | relaxed }
1559 Choose which programs will be accepted for execution
1560 based on the IEEE 754 NaN encoding(s) supported by
1561 the FPU and the NaN encoding requested with the value
1562 of an ELF file header flag individually set by each
1563 binary. Hardware implementations are permitted to
1564 support either or both of the legacy and the 2008 NaN
1567 Available settings are as follows:
1568 strict accept binaries that request a NaN encoding
1569 supported by the FPU
1570 legacy only accept legacy-NaN binaries, if supported
1572 2008 only accept 2008-NaN binaries, if supported
1574 relaxed accept any binaries regardless of whether
1575 supported by the FPU
1577 The FPU emulator is always able to support both NaN
1578 encodings, so if no FPU hardware is present or it has
1579 been disabled with 'nofpu', then the settings of
1580 'legacy' and '2008' strap the emulator accordingly,
1581 'relaxed' straps the emulator for both legacy-NaN and
1582 2008-NaN, whereas 'strict' enables legacy-NaN only on
1583 legacy processors and both NaN encodings on MIPS32 or
1586 The setting for ABS.fmt/NEG.fmt instruction execution
1587 mode generally follows that for the NaN encoding,
1588 except where unsupported by hardware.
1590 ignore_loglevel [KNL]
1591 Ignore loglevel setting - this will print /all/
1592 kernel messages to the console. Useful for debugging.
1593 We also add it as printk module parameter, so users
1594 could change it dynamically, usually by
1595 /sys/module/printk/parameters/ignore_loglevel.
1598 Ignore RLIMIT_DATA setting for data mappings,
1599 print warning at first misuse. Can be changed via
1600 /sys/module/kernel/parameters/ignore_rlimit_data.
1602 ihash_entries= [KNL]
1603 Set number of hash buckets for inode cache.
1605 ima_appraise= [IMA] appraise integrity measurements
1606 Format: { "off" | "enforce" | "fix" | "log" }
1609 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1610 The builtin appraise policy appraises all files
1613 ima_canonical_fmt [IMA]
1614 Use the canonical format for the binary runtime
1615 measurements, instead of host native format.
1618 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1622 The list of supported hash algorithms is defined
1623 in crypto/hash_info.h.
1626 The builtin policies to load during IMA setup.
1627 Format: "tcb | appraise_tcb | secure_boot |
1630 The "tcb" policy measures all programs exec'd, files
1631 mmap'd for exec, and all files opened with the read
1632 mode bit set by either the effective uid (euid=0) or
1635 The "appraise_tcb" policy appraises the integrity of
1636 all files owned by root.
1638 The "secure_boot" policy appraises the integrity
1639 of files (eg. kexec kernel image, kernel modules,
1640 firmware, policy, etc) based on file signatures.
1642 The "fail_securely" policy forces file signature
1643 verification failure also on privileged mounted
1644 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1647 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1648 Load a policy which meets the needs of the Trusted
1649 Computing Base. This means IMA will measure all
1650 programs exec'd, files mmap'd for exec, and all files
1651 opened for read by uid=0.
1654 Select one of defined IMA measurements template formats.
1655 Formats: { "ima" | "ima-ng" | "ima-sig" }
1659 [IMA] Define a custom template format.
1660 Format: { "field1|...|fieldN" }
1662 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1663 Format: <min_file_size>
1664 Set the minimal file size for using asynchronous hash.
1665 If left unspecified, ahash usage is disabled.
1667 ahash performance varies for different data sizes on
1668 different crypto accelerators. This option can be used
1669 to achieve the best performance for a particular HW.
1671 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1673 Set hashing buffer size. Default: 4k.
1675 ahash performance varies for different chunk sizes on
1676 different crypto accelerators. This option can be used
1677 to achieve best performance for particular HW.
1681 Run specified binary instead of /sbin/init as init
1684 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1685 for working out where the kernel is dying during
1688 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1689 initcall functions. Useful for debugging built-in
1690 modules and initcalls.
1692 initrd= [BOOT] Specify the location of the initial ramdisk
1694 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1697 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1699 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1701 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1703 init_pkru= [x86] Specify the default memory protection keys rights
1704 register contents for all processes. 0x55555554 by
1705 default (disallow access to all but pkey 0). Can
1706 override in debugfs after boot.
1708 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1711 int_pln_enable [x86] Enable power limit notification interrupt
1713 integrity_audit=[IMA]
1714 Format: { "0" | "1" }
1715 0 -- basic integrity auditing messages. (Default)
1716 1 -- additional integrity auditing messages.
1718 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1720 Enable intel iommu driver.
1722 Disable intel iommu driver.
1723 igfx_off [Default Off]
1724 By default, gfx is mapped as normal device. If a gfx
1725 device has a dedicated DMAR unit, the DMAR unit is
1726 bypassed by not enabling DMAR with this option. In
1727 this case, gfx device will use physical address for
1730 With this option iommu will not optimize to look
1731 for io virtual address below 32-bit forcing dual
1732 address cycle on pci bus for cards supporting greater
1733 than 32-bit addressing. The default is to look
1734 for translation below 32-bit and if not available
1735 then look in the higher range.
1736 strict [Default Off]
1737 With this option on every unmap_single operation will
1738 result in a hardware IOTLB flush operation as opposed
1739 to batching them for performance.
1740 sp_off [Default Off]
1741 By default, super page will be supported if Intel IOMMU
1742 has the capability. With this option, super page will
1745 By default, scalable mode will be disabled even if the
1746 hardware advertises that it has support for the scalable
1747 mode translation. With this option set, scalable mode
1748 will be used on hardware which claims to support it.
1749 tboot_noforce [Default Off]
1750 Do not force the Intel IOMMU enabled under tboot.
1751 By default, tboot will force Intel IOMMU on, which
1752 could harm performance of some high-throughput
1753 devices like 40GBit network cards, even if identity
1755 Note that using this option lowers the security
1756 provided by tboot because it makes the system
1757 vulnerable to DMA attacks.
1758 nobounce [Default off]
1759 Disable bounce buffer for unstrusted devices such as
1760 the Thunderbolt devices. This will treat the untrusted
1761 devices as the trusted ones, hence might expose security
1762 risks of DMA attacks.
1764 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1765 0 disables intel_idle and fall back on acpi_idle.
1766 1 to 9 specify maximum depth of C-state.
1770 Do not enable intel_pstate as the default
1771 scaling driver for the supported processors
1773 Use intel_pstate as a scaling driver, but configure it
1774 to work with generic cpufreq governors (instead of
1775 enabling its internal governor). This mode cannot be
1776 used along with the hardware-managed P-states (HWP)
1779 Enable intel_pstate on systems that prohibit it by default
1780 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1781 instead of acpi-cpufreq may disable platform features, such
1782 as thermal controls and power capping, that rely on ACPI
1783 P-States information being indicated to OSPM and therefore
1784 should be used with caution. This option does not work with
1785 processors that aren't supported by the intel_pstate driver
1786 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1788 Do not enable hardware P state control (HWP)
1791 Only load intel_pstate on systems which support
1792 hardware P state control (HWP) if available.
1794 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1795 Description Table, specifies preferred power management
1796 profile as "Enterprise Server" or "Performance Server",
1797 then this feature is turned on by default.
1799 Allow per-logical-CPU P-State performance control limits using
1800 cpufreq sysfs interface
1802 intremap= [X86-64, Intel-IOMMU]
1803 on enable Interrupt Remapping (default)
1804 off disable Interrupt Remapping
1805 nosid disable Source ID checking
1807 BIOS x2APIC opt-out request will be ignored
1808 nopost disable Interrupt Posting
1810 iomem= Disable strict checking of access to MMIO memory
1811 strict regions from userspace.
1826 nobypass [PPC/POWERNV]
1827 Disable IOMMU bypass, using IOMMU for PCI devices.
1829 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1830 Format: { "0" | "1" }
1832 Request that DMA unmap operations use deferred
1833 invalidation of hardware TLBs, for increased
1834 throughput at the cost of reduced device isolation.
1835 Will fall back to strict mode if not supported by
1836 the relevant IOMMU driver.
1837 1 - Strict mode (default).
1838 DMA unmap operations invalidate IOMMU hardware TLBs
1842 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
1843 Format: { "0" | "1" }
1844 0 - Use IOMMU translation for DMA.
1845 1 - Bypass the IOMMU for DMA.
1846 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1848 io7= [HW] IO7 for Marvel based alpha systems
1849 See comment before marvel_specify_io7 in
1850 arch/alpha/kernel/core_marvel.c.
1852 io_delay= [X86] I/O delay method
1854 Standard port 0x80 based delay
1856 Alternate port 0xed based delay (needed on some systems)
1858 Simple two microseconds delay
1863 See Documentation/filesystems/nfs/nfsroot.txt.
1865 ipcmni_extend [KNL] Extend the maximum number of unique System V
1866 IPC identifiers from 32,768 to 16,777,216.
1868 irqaffinity= [SMP] Set the default irq affinity mask
1869 The argument is a cpu list, as described above.
1871 irqchip.gicv2_force_probe=
1874 Force the kernel to look for the second 4kB page
1875 of a GICv2 controller even if the memory range
1876 exposed by the device tree is too small.
1878 irqchip.gicv3_nolpi=
1880 Force the kernel to ignore the availability of
1881 LPIs (and by consequence ITSs). Intended for system
1882 that use the kernel as a bootloader, and thus want
1883 to let secondary kernels in charge of setting up
1886 irqchip.gicv3_pseudo_nmi= [ARM64]
1887 Enables support for pseudo-NMIs in the kernel. This
1888 requires the kernel to be built with
1889 CONFIG_ARM64_PSEUDO_NMI.
1892 When an interrupt is not handled search all handlers
1893 for it. Intended to get systems with badly broken
1897 When an interrupt is not handled search all handlers
1898 for it. Also check all handlers each timer
1899 interrupt. Intended to get systems with badly broken
1903 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1905 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1906 [Deprecated - use cpusets instead]
1907 Format: [flag-list,]<cpu-list>
1909 Specify one or more CPUs to isolate from disturbances
1910 specified in the flag list (default: domain):
1913 Disable the tick when a single task runs.
1915 A residual 1Hz tick is offloaded to workqueues, which you
1916 need to affine to housekeeping through the global
1917 workqueue's affinity configured via the
1918 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1919 by using the 'domain' flag described below.
1921 NOTE: by default the global workqueue runs on all CPUs,
1922 so to protect individual CPUs the 'cpumask' file has to
1923 be configured manually after bootup.
1926 Isolate from the general SMP balancing and scheduling
1927 algorithms. Note that performing domain isolation this way
1928 is irreversible: it's not possible to bring back a CPU to
1929 the domains once isolated through isolcpus. It's strongly
1930 advised to use cpusets instead to disable scheduler load
1931 balancing through the "cpuset.sched_load_balance" file.
1932 It offers a much more flexible interface where CPUs can
1933 move in and out of an isolated set anytime.
1935 You can move a process onto or off an "isolated" CPU via
1936 the CPU affinity syscalls or cpuset.
1937 <cpu number> begins at 0 and the maximum value is
1938 "number of CPUs in system - 1".
1940 The format of <cpu-list> is described above.
1946 ivrs_ioapic [HW,X86_64]
1947 Provide an override to the IOAPIC-ID<->DEVICE-ID
1948 mapping provided in the IVRS ACPI table. For
1949 example, to map IOAPIC-ID decimal 10 to
1950 PCI device 00:14.0 write the parameter as:
1951 ivrs_ioapic[10]=00:14.0
1953 ivrs_hpet [HW,X86_64]
1954 Provide an override to the HPET-ID<->DEVICE-ID
1955 mapping provided in the IVRS ACPI table. For
1956 example, to map HPET-ID decimal 0 to
1957 PCI device 00:14.0 write the parameter as:
1958 ivrs_hpet[0]=00:14.0
1960 ivrs_acpihid [HW,X86_64]
1961 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1962 mapping provided in the IVRS ACPI table. For
1963 example, to map UART-HID:UID AMD0020:0 to
1964 PCI device 00:14.5 write the parameter as:
1965 ivrs_acpihid[00:14.5]=AMD0020:0
1967 js= [HW,JOY] Analog joystick
1968 See Documentation/input/joydev/joystick.rst.
1971 When CONFIG_RANDOMIZE_BASE is set, this disables
1972 kernel and module base offset ASLR (Address Space
1973 Layout Randomization).
1976 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1977 report on every invalid memory access. Without this
1978 parameter KASAN will print report only for the first
1983 kernelcore= [KNL,X86,IA-64,PPC]
1984 Format: nn[KMGTPE] | nn% | "mirror"
1985 This parameter specifies the amount of memory usable by
1986 the kernel for non-movable allocations. The requested
1987 amount is spread evenly throughout all nodes in the
1988 system as ZONE_NORMAL. The remaining memory is used for
1989 movable memory in its own zone, ZONE_MOVABLE. In the
1990 event, a node is too small to have both ZONE_NORMAL and
1991 ZONE_MOVABLE, kernelcore memory will take priority and
1992 other nodes will have a larger ZONE_MOVABLE.
1994 ZONE_MOVABLE is used for the allocation of pages that
1995 may be reclaimed or moved by the page migration
1996 subsystem. Note that allocations like PTEs-from-HighMem
1997 still use the HighMem zone if it exists, and the Normal
1998 zone if it does not.
2000 It is possible to specify the exact amount of memory in
2001 the form of "nn[KMGTPE]", a percentage of total system
2002 memory in the form of "nn%", or "mirror". If "mirror"
2003 option is specified, mirrored (reliable) memory is used
2004 for non-movable allocations and remaining memory is used
2005 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2006 are exclusive, so you cannot specify multiple forms.
2008 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2009 Format: <Controller#>[,poll interval]
2010 The controller # is the number of the ehci usb debug
2011 port as it is probed via PCI. The poll interval is
2012 optional and is the number seconds in between
2013 each poll cycle to the debug port in case you need
2014 the functionality for interrupting the kernel with
2015 gdb or control-c on the dbgp connection. When
2016 not using this parameter you use sysrq-g to break into
2017 the kernel debugger.
2019 kgdboc= [KGDB,HW] kgdb over consoles.
2020 Requires a tty driver that supports console polling,
2021 or a supported polling keyboard driver (non-usb).
2022 Serial only format: <serial_device>[,baud]
2023 keyboard only format: kbd
2024 keyboard and serial format: kbd,<serial_device>[,baud]
2025 Optional Kernel mode setting:
2026 kms, kbd format: kms,kbd
2027 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2029 kgdbwait [KGDB] Stop kernel execution and enter the
2030 kernel debugger at the earliest opportunity.
2032 kmac= [MIPS] korina ethernet MAC address.
2033 Configure the RouterBoard 532 series on-chip
2034 Ethernet adapter MAC address.
2036 kmemleak= [KNL] Boot-time kmemleak enable/disable
2037 Valid arguments: on, off
2039 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2042 kprobe_event=[probe-list]
2043 [FTRACE] Add kprobe events and enable at boot time.
2044 The probe-list is a semicolon delimited list of probe
2045 definitions. Each definition is same as kprobe_events
2046 interface, but the parameters are comma delimited.
2047 For example, to add a kprobe event on vfs_read with
2048 arg1 and arg2, add to the command line;
2050 kprobe_event=p,vfs_read,$arg1,$arg2
2052 See also Documentation/trace/kprobetrace.rst "Kernel
2053 Boot Parameter" section.
2055 kpti= [ARM64] Control page table isolation of user
2056 and kernel address spaces.
2057 Default: enabled on cores which need mitigation.
2061 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2062 Default is 0 (don't ignore, but inject #GP)
2064 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2065 Default is false (don't support).
2067 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2072 [KVM] Controls the software workaround for the
2073 X86_BUG_ITLB_MULTIHIT bug.
2074 force : Always deploy workaround.
2075 off : Never deploy workaround.
2076 auto : Deploy workaround based on the presence of
2077 X86_BUG_ITLB_MULTIHIT.
2081 If the software workaround is enabled for the host,
2082 guests do need not to enable it for nested guests.
2084 kvm.nx_huge_pages_recovery_ratio=
2085 [KVM] Controls how many 4KiB pages are periodically zapped
2086 back to huge pages. 0 disables the recovery, otherwise if
2087 the value is N KVM will zap 1/Nth of the 4KiB pages every
2088 minute. The default is 60.
2090 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2091 Default is 1 (enabled)
2093 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2095 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2097 kvm-arm.vgic_v3_group0_trap=
2098 [KVM,ARM] Trap guest accesses to GICv3 group-0
2101 kvm-arm.vgic_v3_group1_trap=
2102 [KVM,ARM] Trap guest accesses to GICv3 group-1
2105 kvm-arm.vgic_v3_common_trap=
2106 [KVM,ARM] Trap guest accesses to GICv3 common
2109 kvm-arm.vgic_v4_enable=
2110 [KVM,ARM] Allow use of GICv4 for direct injection of
2113 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2114 (virtualized MMU) support on capable Intel chips.
2115 Default is 1 (enabled)
2117 kvm-intel.emulate_invalid_guest_state=
2118 [KVM,Intel] Enable emulation of invalid guest states
2119 Default is 0 (disabled)
2121 kvm-intel.flexpriority=
2122 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2123 Default is 1 (enabled)
2126 [KVM,Intel] Enable VMX nesting (nVMX).
2127 Default is 0 (disabled)
2129 kvm-intel.unrestricted_guest=
2130 [KVM,Intel] Disable unrestricted guest feature
2131 (virtualized real and unpaged mode) on capable
2132 Intel chips. Default is 1 (enabled)
2134 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2137 Valid arguments: never, cond, always
2139 always: L1D cache flush on every VMENTER.
2140 cond: Flush L1D on VMENTER only when the code between
2141 VMEXIT and VMENTER can leak host memory.
2142 never: Disables the mitigation
2144 Default is cond (do L1 cache flush in specific instances)
2146 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2147 feature (tagged TLBs) on capable Intel chips.
2148 Default is 1 (enabled)
2150 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2153 The kernel PTE inversion protection is unconditionally
2154 enabled and cannot be disabled.
2157 Provides all available mitigations for the
2158 L1TF vulnerability. Disables SMT and
2159 enables all mitigations in the
2160 hypervisors, i.e. unconditional L1D flush.
2162 SMT control and L1D flush control via the
2163 sysfs interface is still possible after
2164 boot. Hypervisors will issue a warning
2165 when the first VM is started in a
2166 potentially insecure configuration,
2167 i.e. SMT enabled or L1D flush disabled.
2170 Same as 'full', but disables SMT and L1D
2171 flush runtime control. Implies the
2172 'nosmt=force' command line option.
2173 (i.e. sysfs control of SMT is disabled.)
2176 Leaves SMT enabled and enables the default
2177 hypervisor mitigation, i.e. conditional
2180 SMT control and L1D flush control via the
2181 sysfs interface is still possible after
2182 boot. Hypervisors will issue a warning
2183 when the first VM is started in a
2184 potentially insecure configuration,
2185 i.e. SMT enabled or L1D flush disabled.
2189 Disables SMT and enables the default
2190 hypervisor mitigation.
2192 SMT control and L1D flush control via the
2193 sysfs interface is still possible after
2194 boot. Hypervisors will issue a warning
2195 when the first VM is started in a
2196 potentially insecure configuration,
2197 i.e. SMT enabled or L1D flush disabled.
2200 Same as 'flush', but hypervisors will not
2201 warn when a VM is started in a potentially
2202 insecure configuration.
2205 Disables hypervisor mitigations and doesn't
2207 It also drops the swap size and available
2208 RAM limit restriction on both hypervisor and
2213 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2219 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2222 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2223 value for LAPIC timer one-shot implementation. Default
2224 back to the programmable timer unit in the LAPIC.
2226 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2229 libata.dma= [LIBATA] DMA control
2230 libata.dma=0 Disable all PATA and SATA DMA
2231 libata.dma=1 PATA and SATA Disk DMA only
2232 libata.dma=2 ATAPI (CDROM) DMA only
2233 libata.dma=4 Compact Flash DMA only
2234 Combinations also work, so libata.dma=3 enables DMA
2235 for disks and CDROMs, but not CFs.
2237 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2238 libata.ignore_hpa=0 keep BIOS limits (default)
2239 libata.ignore_hpa=1 ignore limits, using full disk
2241 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2245 libata.force= [LIBATA] Force configurations. The format is comma
2246 separated list of "[ID:]VAL" where ID is
2247 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2248 matching port, link or device. Basically, it matches
2249 the ATA ID string printed on console by libata. If
2250 the whole ID part is omitted, the last PORT and DEVICE
2251 values are used. If ID hasn't been specified yet, the
2252 configuration applies to all ports, links and devices.
2254 If only DEVICE is omitted, the parameter applies to
2255 the port and all links and devices behind it. DEVICE
2256 number of 0 either selects the first device or the
2257 first fan-out link behind PMP device. It does not
2258 select the host link. DEVICE number of 15 selects the
2259 host link and device attached to it.
2261 The VAL specifies the configuration to force. As long
2262 as there's no ambiguity shortcut notation is allowed.
2263 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2264 The following configurations can be forced.
2266 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2267 Any ID with matching PORT is used.
2269 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2271 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2272 udma[/][16,25,33,44,66,100,133] notation is also
2275 * [no]ncq: Turn on or off NCQ.
2277 * [no]ncqtrim: Turn off queued DSM TRIM.
2279 * nohrst, nosrst, norst: suppress hard, soft
2282 * rstonce: only attempt one reset during
2283 hot-unplug link recovery
2285 * dump_id: dump IDENTIFY data.
2287 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2289 * disable: Disable this device.
2291 If there are multiple matching configurations changing
2292 the same attribute, the last one is used.
2294 memblock=debug [KNL] Enable memblock debug messages.
2296 load_ramdisk= [RAM] List of ramdisks to load from floppy
2297 See Documentation/admin-guide/blockdev/ramdisk.rst.
2299 lockd.nlm_grace_period=P [NFS] Assign grace period.
2302 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2305 lockd.nlm_timeout=T [NFS] Assign timeout value.
2308 lockd.nlm_udpport=M [NFS] Assign UDP port.
2311 lockdown= [SECURITY]
2312 { integrity | confidentiality }
2313 Enable the kernel lockdown feature. If set to
2314 integrity, kernel features that allow userland to
2315 modify the running kernel are disabled. If set to
2316 confidentiality, kernel features that allow userland
2317 to extract confidential information from the kernel
2320 locktorture.nreaders_stress= [KNL]
2321 Set the number of locking read-acquisition kthreads.
2322 Defaults to being automatically set based on the
2323 number of online CPUs.
2325 locktorture.nwriters_stress= [KNL]
2326 Set the number of locking write-acquisition kthreads.
2328 locktorture.onoff_holdoff= [KNL]
2329 Set time (s) after boot for CPU-hotplug testing.
2331 locktorture.onoff_interval= [KNL]
2332 Set time (s) between CPU-hotplug operations, or
2333 zero to disable CPU-hotplug testing.
2335 locktorture.shuffle_interval= [KNL]
2336 Set task-shuffle interval (jiffies). Shuffling
2337 tasks allows some CPUs to go into dyntick-idle
2338 mode during the locktorture test.
2340 locktorture.shutdown_secs= [KNL]
2341 Set time (s) after boot system shutdown. This
2342 is useful for hands-off automated testing.
2344 locktorture.stat_interval= [KNL]
2345 Time (s) between statistics printk()s.
2347 locktorture.stutter= [KNL]
2348 Time (s) to stutter testing, for example,
2349 specifying five seconds causes the test to run for
2350 five seconds, wait for five seconds, and so on.
2351 This tests the locking primitive's ability to
2352 transition abruptly to and from idle.
2354 locktorture.torture_type= [KNL]
2355 Specify the locking implementation to test.
2357 locktorture.verbose= [KNL]
2358 Enable additional printk() statements.
2360 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2363 loglevel= All Kernel Messages with a loglevel smaller than the
2364 console loglevel will be printed to the console. It can
2365 also be changed with klogd or other programs. The
2366 loglevels are defined as follows:
2368 0 (KERN_EMERG) system is unusable
2369 1 (KERN_ALERT) action must be taken immediately
2370 2 (KERN_CRIT) critical conditions
2371 3 (KERN_ERR) error conditions
2372 4 (KERN_WARNING) warning conditions
2373 5 (KERN_NOTICE) normal but significant condition
2374 6 (KERN_INFO) informational
2375 7 (KERN_DEBUG) debug-level messages
2377 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2378 in bytes. n must be a power of two and greater
2379 than the minimal size. The minimal size is defined
2380 by LOG_BUF_SHIFT kernel config parameter. There is
2381 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2382 that allows to increase the default size depending on
2383 the number of CPUs. See init/Kconfig for more details.
2385 logo.nologo [FB] Disables display of the built-in Linux logo.
2386 This may be used to provide more screen space for
2387 kernel log messages and is useful when debugging
2388 kernel boot problems.
2390 lp=0 [LP] Specify parallel ports to use, e.g,
2391 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2392 lp=reset first parallel port). 'lp=0' disables the
2393 lp=auto printer driver. 'lp=reset' (which can be
2394 specified in addition to the ports) causes
2395 attached printers to be reset. Using
2396 lp=port1,port2,... specifies the parallel ports
2397 to associate lp devices with, starting with
2398 lp0. A port specification may be 'none' to skip
2399 that lp device, or a parport name such as
2400 'parport0'. Specifying 'lp=auto' instead of a
2401 port specification list means that device IDs
2402 from each port should be examined, to see if
2403 an IEEE 1284-compliant printer is attached; if
2404 so, the driver will manage that printer.
2405 See also header of drivers/char/lp.c.
2408 Sets loops_per_jiffy to given constant, thus avoiding
2409 time-consuming boot-time autodetection (up to 250 ms per
2410 CPU). 0 enables autodetection (default). To determine
2411 the correct value for your kernel, boot with normal
2412 autodetection and see what value is printed. Note that
2413 on SMP systems the preset will be applied to all CPUs,
2414 which is likely to cause problems if your CPUs need
2415 significantly divergent settings. An incorrect value
2416 will cause delays in the kernel to be wrong, leading to
2417 unpredictable I/O errors and other breakage. Although
2418 unlikely, in the extreme case this might damage your
2422 Format: <io>,<irq>,<dma>
2424 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2427 [SECURITY] Choose order of LSM initialization. This
2428 overrides CONFIG_LSM, and the "security=" parameter.
2430 machvec= [IA-64] Force the use of a particular machine-vector
2431 (machvec) in a generic kernel.
2432 Example: machvec=hpzx1
2434 machtype= [Loongson] Share the same kernel image file between different
2436 Example: machtype=lemote-yeeloong-2f-7inch
2438 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2439 than or equal to this physical address is ignored.
2441 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2442 will bring up during bootup. maxcpus=n : n >= 0 limits
2443 the kernel to bring up 'n' processors. Surely after
2444 bootup you can bring up the other plugged cpu by executing
2445 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2446 only takes effect during system bootup.
2447 While n=0 is a special case, it is equivalent to "nosmp",
2448 which also disables the IO APIC.
2450 max_loop= [LOOP] The number of loop block devices that get
2451 (loop.max_loop) unconditionally pre-created at init time. The default
2452 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2453 of statically allocating a predefined number, loop
2454 devices can be requested on-demand with the
2455 /dev/loop-control interface.
2457 mce [X86-32] Machine Check Exception
2459 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2461 md= [HW] RAID subsystems devices and level
2462 See Documentation/admin-guide/md.rst.
2465 Format: <first>,<last>
2466 Specifies range of consoles to be captured by the MDA.
2469 Control mitigation for the Micro-architectural Data
2470 Sampling (MDS) vulnerability.
2472 Certain CPUs are vulnerable to an exploit against CPU
2473 internal buffers which can forward information to a
2474 disclosure gadget under certain conditions.
2476 In vulnerable processors, the speculatively
2477 forwarded data can be used in a cache side channel
2478 attack, to access data to which the attacker does
2479 not have direct access.
2481 This parameter controls the MDS mitigation. The
2484 full - Enable MDS mitigation on vulnerable CPUs
2485 full,nosmt - Enable MDS mitigation and disable
2486 SMT on vulnerable CPUs
2487 off - Unconditionally disable MDS mitigation
2489 On TAA-affected machines, mds=off can be prevented by
2490 an active TAA mitigation as both vulnerabilities are
2491 mitigated with the same mechanism so in order to disable
2492 this mitigation, you need to specify tsx_async_abort=off
2495 Not specifying this option is equivalent to
2498 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2500 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2501 Amount of memory to be used when the kernel is not able
2502 to see the whole system memory or for test.
2503 [X86] Work as limiting max address. Use together
2504 with memmap= to avoid physical address space collisions.
2505 Without memmap= PCI devices could be placed at addresses
2506 belonging to unused RAM.
2508 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2512 [KNL,SH] Allow user to override the default size for
2513 per-device physically contiguous DMA buffers.
2515 memhp_default_state=online/offline
2516 [KNL] Set the initial state for the memory hotplug
2517 onlining policy. If not specified, the default value is
2518 set according to the
2519 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2521 See Documentation/admin-guide/mm/memory-hotplug.rst.
2523 memmap=exactmap [KNL,X86] Enable setting of an exact
2524 E820 memory map, as specified by the user.
2525 Such memmap=exactmap lines can be constructed based on
2526 BIOS output or other requirements. See the memmap=nn@ss
2529 memmap=nn[KMG]@ss[KMG]
2530 [KNL] Force usage of a specific region of memory.
2531 Region of memory to be used is from ss to ss+nn.
2532 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2533 which limits max address to nn[KMG].
2534 Multiple different regions can be specified,
2537 memmap=100M@2G,100M#3G,1G!1024G
2539 memmap=nn[KMG]#ss[KMG]
2540 [KNL,ACPI] Mark specific memory as ACPI data.
2541 Region of memory to be marked is from ss to ss+nn.
2543 memmap=nn[KMG]$ss[KMG]
2544 [KNL,ACPI] Mark specific memory as reserved.
2545 Region of memory to be reserved is from ss to ss+nn.
2546 Example: Exclude memory from 0x18690000-0x1869ffff
2547 memmap=64K$0x18690000
2549 memmap=0x10000$0x18690000
2550 Some bootloaders may need an escape character before '$',
2551 like Grub2, otherwise '$' and the following number
2554 memmap=nn[KMG]!ss[KMG]
2555 [KNL,X86] Mark specific memory as protected.
2556 Region of memory to be used, from ss to ss+nn.
2557 The memory region may be marked as e820 type 12 (0xc)
2558 and is NVDIMM or ADR memory.
2560 memmap=<size>%<offset>-<oldtype>+<newtype>
2561 [KNL,ACPI] Convert memory within the specified region
2562 from <oldtype> to <newtype>. If "-<oldtype>" is left
2563 out, the whole region will be marked as <newtype>,
2564 even if previously unavailable. If "+<newtype>" is left
2565 out, matching memory will be removed. Types are
2566 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2567 3 = ACPI, 12 = PRAM.
2569 memory_corruption_check=0/1 [X86]
2570 Some BIOSes seem to corrupt the first 64k of
2571 memory when doing things like suspend/resume.
2572 Setting this option will scan the memory
2573 looking for corruption. Enabling this will
2574 both detect corruption and prevent the kernel
2575 from using the memory being corrupted.
2576 However, its intended as a diagnostic tool; if
2577 repeatable BIOS-originated corruption always
2578 affects the same memory, you can use memmap=
2579 to prevent the kernel from using that memory.
2581 memory_corruption_check_size=size [X86]
2582 By default it checks for corruption in the low
2583 64k, making this memory unavailable for normal
2584 use. Use this parameter to scan for
2585 corruption in more or less memory.
2587 memory_corruption_check_period=seconds [X86]
2588 By default it checks for corruption every 60
2589 seconds. Use this parameter to check at some
2590 other rate. 0 disables periodic checking.
2592 memtest= [KNL,X86,ARM,PPC] Enable memtest
2594 default : 0 <disable>
2595 Specifies the number of memtest passes to be
2596 performed. Each pass selects another test
2597 pattern from a given set of patterns. Memtest
2598 fills the memory with this pattern, validates
2599 memory contents and reserves bad memory
2600 regions that are detected.
2602 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2603 Valid arguments: on, off
2604 Default (depends on kernel configuration option):
2605 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2606 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2607 mem_encrypt=on: Activate SME
2608 mem_encrypt=off: Do not activate SME
2610 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
2611 for details on when memory encryption can be activated.
2613 mem_sleep_default= [SUSPEND] Default system suspend mode:
2614 s2idle - Suspend-To-Idle
2615 shallow - Power-On Suspend or equivalent (if supported)
2616 deep - Suspend-To-RAM or equivalent (if supported)
2617 See Documentation/admin-guide/pm/sleep-states.rst.
2619 meye.*= [HW] Set MotionEye Camera parameters
2620 See Documentation/media/v4l-drivers/meye.rst.
2622 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2623 Multi-Function General Purpose Timers on AMD Geode
2626 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2627 the BIOS has incorrectly applied a workaround. TinyBIOS
2628 version 0.98 is known to be affected, 0.99 fixes the
2629 problem by letting the user disable the workaround.
2633 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2634 physical address is ignored.
2636 mini2440= [ARM,HW,KNL]
2637 Format:[0..2][b][c][t]
2639 MINI2440 configuration specification:
2640 0 - The attached screen is the 3.5" TFT
2641 1 - The attached screen is the 7" TFT
2642 2 - The VGA Shield is attached (1024x768)
2643 Leaving out the screen size parameter will not load
2644 the TFT driver, and the framebuffer will be left
2646 b - Enable backlight. The TFT backlight pin will be
2647 linked to the kernel VESA blanking code and a GPIO
2648 LED. This parameter is not necessary when using the
2650 c - Enable the s3c camera interface.
2651 t - Reserved for enabling touchscreen support. The
2652 touchscreen support is not enabled in the mainstream
2653 kernel as of 2.6.30, a preliminary port can be found
2654 in the "bleeding edge" mini2440 support kernel at
2655 http://repo.or.cz/w/linux-2.6/mini2440.git
2658 [X86,PPC,S390,ARM64] Control optional mitigations for
2659 CPU vulnerabilities. This is a set of curated,
2660 arch-independent options, each of which is an
2661 aggregation of existing arch-specific options.
2664 Disable all optional CPU mitigations. This
2665 improves system performance, but it may also
2666 expose users to several CPU vulnerabilities.
2667 Equivalent to: nopti [X86,PPC]
2669 nospectre_v1 [X86,PPC]
2671 nospectre_v2 [X86,PPC,S390,ARM64]
2672 spectre_v2_user=off [X86]
2673 spec_store_bypass_disable=off [X86,PPC]
2674 ssbd=force-off [ARM64]
2677 tsx_async_abort=off [X86]
2678 kvm.nx_huge_pages=off [X86]
2681 This does not have any effect on
2682 kvm.nx_huge_pages when
2683 kvm.nx_huge_pages=force.
2686 Mitigate all CPU vulnerabilities, but leave SMT
2687 enabled, even if it's vulnerable. This is for
2688 users who don't want to be surprised by SMT
2689 getting disabled across kernel upgrades, or who
2690 have other ways of avoiding SMT-based attacks.
2691 Equivalent to: (default behavior)
2694 Mitigate all CPU vulnerabilities, disabling SMT
2695 if needed. This is for users who always want to
2696 be fully mitigated, even if it means losing SMT.
2697 Equivalent to: l1tf=flush,nosmt [X86]
2698 mds=full,nosmt [X86]
2699 tsx_async_abort=full,nosmt [X86]
2702 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2703 parameter allows control of the logging verbosity for
2704 the additional memory initialisation checks. A value
2705 of 0 disables mminit logging and a level of 4 will
2706 log everything. Information is printed at KERN_DEBUG
2707 so loglevel=8 may also need to be specified.
2710 [KNL] When CONFIG_MODULE_SIG is set, this means that
2711 modules without (valid) signatures will fail to load.
2712 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2713 is always true, so this option does nothing.
2715 module_blacklist= [KNL] Do not load a comma-separated list of
2716 modules. Useful for debugging problem modules.
2719 [MOUSE] Maximum time between finger touching and
2720 leaving touchpad surface for touch to be considered
2721 a tap and be reported as a left button click (for
2722 touchpads working in absolute mode only).
2724 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2725 reporting absolute coordinates, such as tablets
2726 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2727 reporting absolute coordinates, such as tablets
2729 movablecore= [KNL,X86,IA-64,PPC]
2730 Format: nn[KMGTPE] | nn%
2731 This parameter is the complement to kernelcore=, it
2732 specifies the amount of memory used for migratable
2733 allocations. If both kernelcore and movablecore is
2734 specified, then kernelcore will be at *least* the
2735 specified value but may be more. If movablecore on its
2736 own is specified, the administrator must be careful
2737 that the amount of memory usable for all allocations
2740 movable_node [KNL] Boot-time switch to make hotplugable memory
2741 NUMA nodes to be movable. This means that the memory
2742 of such nodes will be usable only for movable
2743 allocations which rules out almost all kernel
2744 allocations. Use with caution!
2746 MTD_Partition= [MTD]
2747 Format: <name>,<region-number>,<size>,<offset>
2749 MTD_Region= [MTD] Format:
2750 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2753 See drivers/mtd/cmdlinepart.c.
2755 multitce=off [PPC] This parameter disables the use of the pSeries
2756 firmware feature for updating multiple TCE entries
2759 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2761 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2763 boundary - index of last SLC block on Flex-OneNAND.
2764 The remaining blocks are configured as MLC blocks.
2765 lock - Configure if Flex-OneNAND boundary should be locked.
2766 Once locked, the boundary cannot be changed.
2767 1 indicates lock status, 0 indicates unlock status.
2770 ARM/S3C2412 JIVE boot control
2772 See arch/arm/mach-s3c2412/mach-jive.c
2774 mtouchusb.raw_coordinates=
2775 [HW] Make the MicroTouch USB driver use raw coordinates
2776 ('y', default) or cooked coordinates ('n')
2778 mtrr_chunk_size=nn[KMG] [X86]
2779 used for mtrr cleanup. It is largest continuous chunk
2780 that could hold holes aka. UC entries.
2782 mtrr_gran_size=nn[KMG] [X86]
2783 Used for mtrr cleanup. It is granularity of mtrr block.
2785 Large value could prevent small alignment from
2788 mtrr_spare_reg_nr=n [X86]
2790 Range: 0,7 : spare reg number
2792 Used for mtrr cleanup. It is spare mtrr entries number.
2793 Set to 2 or more if your graphical card needs more.
2795 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2797 netdev= [NET] Network devices parameters
2798 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2799 Note that mem_start is often overloaded to mean
2800 something different and driver-specific.
2801 This usage is only documented in each driver source
2805 [NETFILTER] Enable connection tracking flow accounting
2806 0 to disable accounting
2807 1 to enable accounting
2810 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2811 See Documentation/filesystems/nfs/nfsroot.txt.
2813 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2814 See Documentation/filesystems/nfs/nfsroot.txt.
2816 nfsrootdebug [NFS] enable nfsroot debugging messages.
2817 See Documentation/filesystems/nfs/nfsroot.txt.
2819 nfs.callback_nr_threads=
2820 [NFSv4] set the total number of threads that the
2821 NFS client will assign to service NFSv4 callback
2824 nfs.callback_tcpport=
2825 [NFS] set the TCP port on which the NFSv4 callback
2826 channel should listen.
2829 [NFS] sets the pathname to the program which is used
2830 to update the NFS client cache entries.
2832 nfs.cache_getent_timeout=
2833 [NFS] sets the timeout after which an attempt to
2834 update a cache entry is deemed to have failed.
2836 nfs.idmap_cache_timeout=
2837 [NFS] set the maximum lifetime for idmapper cache
2841 [NFS] enable 64-bit inode numbers.
2842 If zero, the NFS client will fake up a 32-bit inode
2843 number for the readdir() and stat() syscalls instead
2844 of returning the full 64-bit number.
2845 The default is to return 64-bit inode numbers.
2847 nfs.max_session_cb_slots=
2848 [NFSv4.1] Sets the maximum number of session
2849 slots the client will assign to the callback
2850 channel. This determines the maximum number of
2851 callbacks the client will process in parallel for
2852 a particular server.
2854 nfs.max_session_slots=
2855 [NFSv4.1] Sets the maximum number of session slots
2856 the client will attempt to negotiate with the server.
2857 This limits the number of simultaneous RPC requests
2858 that the client can send to the NFSv4.1 server.
2859 Note that there is little point in setting this
2860 value higher than the max_tcp_slot_table_limit.
2862 nfs.nfs4_disable_idmapping=
2863 [NFSv4] When set to the default of '1', this option
2864 ensures that both the RPC level authentication
2865 scheme and the NFS level operations agree to use
2866 numeric uids/gids if the mount is using the
2867 'sec=sys' security flavour. In effect it is
2868 disabling idmapping, which can make migration from
2869 legacy NFSv2/v3 systems to NFSv4 easier.
2870 Servers that do not support this mode of operation
2871 will be autodetected by the client, and it will fall
2872 back to using the idmapper.
2873 To turn off this behaviour, set the value to '0'.
2875 [NFS4] Specify an additional fixed unique ident-
2876 ification string that NFSv4 clients can insert into
2877 their nfs_client_id4 string. This is typically a
2878 UUID that is generated at system install time.
2880 nfs.send_implementation_id =
2881 [NFSv4.1] Send client implementation identification
2882 information in exchange_id requests.
2883 If zero, no implementation identification information
2885 The default is to send the implementation identification
2888 nfs.recover_lost_locks =
2889 [NFSv4] Attempt to recover locks that were lost due
2890 to a lease timeout on the server. Please note that
2891 doing this risks data corruption, since there are
2892 no guarantees that the file will remain unchanged
2893 after the locks are lost.
2894 If you want to enable the kernel legacy behaviour of
2895 attempting to recover these locks, then set this
2897 The default parameter value of '0' causes the kernel
2898 not to attempt recovery of lost locks.
2900 nfs4.layoutstats_timer =
2901 [NFSv4.2] Change the rate at which the kernel sends
2902 layoutstats to the pNFS metadata server.
2904 Setting this to value to 0 causes the kernel to use
2905 whatever value is the default set by the layout
2906 driver. A non-zero value sets the minimum interval
2907 in seconds between layoutstats transmissions.
2909 nfsd.nfs4_disable_idmapping=
2910 [NFSv4] When set to the default of '1', the NFSv4
2911 server will return only numeric uids and gids to
2912 clients using auth_sys, and will accept numeric uids
2913 and gids from such clients. This is intended to ease
2914 migration from NFSv2/v3.
2916 nmi_debug= [KNL,SH] Specify one or more actions to take
2917 when a NMI is triggered.
2918 Format: [state][,regs][,debounce][,die]
2920 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2921 Format: [panic,][nopanic,][num]
2923 0 - turn hardlockup detector in nmi_watchdog off
2924 1 - turn hardlockup detector in nmi_watchdog on
2925 When panic is specified, panic when an NMI watchdog
2926 timeout occurs (or 'nopanic' to not panic on an NMI
2927 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
2928 To disable both hard and soft lockup detectors,
2929 please see 'nowatchdog'.
2930 This is useful when you use a panic=... timeout and
2931 need the box quickly up again.
2933 These settings can be accessed at runtime via
2934 the nmi_watchdog and hardlockup_panic sysctls.
2936 netpoll.carrier_timeout=
2937 [NET] Specifies amount of time (in seconds) that
2938 netpoll should wait for a carrier. By default netpoll
2941 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2942 emulation library even if a 387 maths coprocessor
2945 no5lvl [X86-64] Disable 5-level paging mode. Forces
2946 kernel to use 4-level paging instead.
2949 [HW] Never suspend the console
2950 Disable suspending of consoles during suspend and
2951 hibernate operations. Once disabled, debugging
2952 messages can reach various consoles while the rest
2953 of the system is being put to sleep (ie, while
2954 debugging driver suspend/resume hooks). This may
2955 not work reliably with all consoles, but is known
2956 to work with serial and VGA consoles.
2957 To facilitate more flexible debugging, we also add
2958 console_suspend, a printk module parameter to control
2959 it. Users could use console_suspend (usually
2960 /sys/module/printk/parameters/console_suspend) to
2961 turn on/off it dynamically.
2963 novmcoredd [KNL,KDUMP]
2964 Disable device dump. Device dump allows drivers to
2965 append dump data to vmcore so you can collect driver
2966 specified debug info. Drivers can append the data
2967 without any limit and this data is stored in memory,
2968 so this may cause significant memory stress. Disabling
2969 device dump can help save memory but the driver debug
2970 data will be no longer available. This parameter
2971 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
2974 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2975 caches in the slab allocator. Saves per-node memory,
2976 but will impact performance.
2980 noaltinstr [S390] Disables alternative instructions patching
2981 (CPU alternatives feature).
2983 noapic [SMP,APIC] Tells the kernel to not make use of any
2984 IOAPICs that may be present in the system.
2986 noautogroup Disable scheduler automatic task group creation.
2988 nobats [PPC] Do not use BATs for mapping kernel lowmem
2989 on "Classic" PPC cores.
2993 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2995 nodelayacct [KNL] Disable per-task delay accounting
2997 nodsp [SH] Disable hardware DSP at boot time.
2999 noefi Disable EFI runtime services support.
3004 On X86-32 available only on PAE configured kernels.
3005 noexec=on: enable non-executable mappings (default)
3006 noexec=off: disable non-executable mappings
3009 Disable SMAP (Supervisor Mode Access Prevention)
3010 even if it is supported by processor.
3013 Disable SMEP (Supervisor Mode Execution Prevention)
3014 even if it is supported by processor.
3017 This affects only 32-bit executables.
3018 noexec32=on: enable non-executable mappings (default)
3019 read doesn't imply executable mappings
3020 noexec32=off: disable non-executable mappings
3021 read implies executable mappings
3023 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3025 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3026 register save and restore. The kernel will only save
3027 legacy floating-point registers on task switch.
3029 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings.
3031 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3032 Equivalent to smt=1.
3034 [KNL,x86] Disable symmetric multithreading (SMT).
3035 nosmt=force: Force disable SMT, cannot be undone
3036 via the sysfs control file.
3038 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3039 (bounds check bypass). With this option data leaks are
3040 possible in the system.
3042 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3043 the Spectre variant 2 (indirect branch prediction)
3044 vulnerability. System may allow data leaks with this
3047 nospec_store_bypass_disable
3048 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3050 noxsave [BUGS=X86] Disables x86 extended register state save
3051 and restore using xsave. The kernel will fallback to
3052 enabling legacy floating-point and sse state.
3054 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3055 register states. The kernel will fall back to use
3056 xsave to save the states. By using this parameter,
3057 performance of saving the states is degraded because
3058 xsave doesn't support modified optimization while
3059 xsaveopt supports it on xsaveopt enabled systems.
3061 noxsaves [X86] Disables xsaves and xrstors used in saving and
3062 restoring x86 extended register state in compacted
3063 form of xsave area. The kernel will fall back to use
3064 xsaveopt and xrstor to save and restore the states
3065 in standard form of xsave area. By using this
3066 parameter, xsave area per process might occupy more
3067 memory on xsaves enabled systems.
3069 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
3070 wfi(ARM) instruction doesn't work correctly and not to
3071 use it. This is also useful when using JTAG debugger.
3073 no_file_caps Tells the kernel not to honor file capabilities. The
3074 only way then for a file to be executed with privilege
3075 is to be setuid root or executed by root.
3077 nohalt [IA-64] Tells the kernel not to use the power saving
3078 function PAL_HALT_LIGHT when idle. This increases
3079 power-consumption. On the positive side, it reduces
3080 interrupt wake-up latency, which may improve performance
3081 in certain environments such as networked servers or
3084 nohibernate [HIBERNATION] Disable hibernation and resume.
3086 nohz= [KNL] Boottime enable/disable dynamic ticks
3087 Valid arguments: on, off
3090 nohz_full= [KNL,BOOT,SMP,ISOL]
3091 The argument is a cpu list, as described above.
3092 In kernels built with CONFIG_NO_HZ_FULL=y, set
3093 the specified list of CPUs whose tick will be stopped
3094 whenever possible. The boot CPU will be forced outside
3095 the range to maintain the timekeeping. Any CPUs
3096 in this list will have their RCU callbacks offloaded,
3097 just as if they had also been called out in the
3098 rcu_nocbs= boot parameter.
3100 noiotrap [SH] Disables trapped I/O port accesses.
3102 noirqdebug [X86-32] Disables the code which attempts to detect and
3103 disable unhandled interrupt sources.
3105 no_timer_check [X86,APIC] Disables the code which tests for
3106 broken timer IRQ sources.
3108 noisapnp [ISAPNP] Disables ISA PnP code.
3110 noinitrd [RAM] Tells the kernel not to load any configured
3113 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3115 [Deprecated - use intremap=off]
3119 noinvpcid [X86] Disable the INVPCID cpu feature.
3121 nojitter [IA-64] Disables jitter checking for ITC timers.
3123 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3125 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3129 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3130 clock and use the default one.
3132 no-steal-acc [X86,KVM,ARM64] Disable paravirtualized steal time
3133 accounting. steal time is computed, but won't
3134 influence scheduler behaviour
3136 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3138 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3140 noltlbs [PPC] Do not use large page/tlb entries for kernel
3141 lowmem mapping on PPC40x and PPC8xx
3143 nomca [IA-64] Disable machine check abort handling
3145 nomce [X86-32] Disable Machine Check Exception
3147 nomfgpt [X86-32] Disable Multi-Function General Purpose
3148 Timer usage (for AMD Geode machines).
3150 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3151 shutdown the other cpus. Instead use the REBOOT_VECTOR
3154 nomodule Disable module load
3156 nopat [X86] Disable PAT (page attribute table extension of
3157 pagetables) support.
3159 nopcid [X86-64] Disable the PCID cpu feature.
3161 norandmaps Don't use address space randomization. Equivalent to
3162 echo 0 > /proc/sys/kernel/randomize_va_space
3164 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3165 with UP alternatives
3167 nordrand [X86] Disable kernel use of the RDRAND and
3168 RDSEED instructions even if they are supported
3169 by the processor. RDRAND and RDSEED are still
3170 available to user space applications.
3172 noresume [SWSUSP] Disables resume and restores original swap
3175 no-scroll [VGA] Disables scrollback.
3176 This is required for the Braillex ib80-piezo Braille
3177 reader made by F.H. Papenmeier (Germany).
3181 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3183 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3184 and disable the IO APIC. legacy for "maxcpus=0".
3186 nosoftlockup [KNL] Disable the soft-lockup detector.
3188 nosync [HW,M68K] Disables sync negotiation for all devices.
3190 nowatchdog [KNL] Disable both lockup detectors, i.e.
3191 soft-lockup and NMI watchdog (hard-lockup).
3195 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3197 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3198 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3199 Some features depend on CPU0. Known dependencies are:
3200 1. Resume from suspend/hibernate depends on CPU0.
3201 Suspend/hibernate will fail if CPU0 is offline and you
3202 need to online CPU0 before suspend/hibernate.
3203 2. PIC interrupts also depend on CPU0. CPU0 can't be
3204 removed if a PIC interrupt is detected.
3205 It's said poweroff/reboot may depend on CPU0 on some
3206 machines although I haven't seen such issues so far
3207 after CPU0 is offline on a few tested machines.
3208 If the dependencies are under your control, you can
3209 turn on cpu0_hotplug.
3211 nps_mtm_hs_ctr= [KNL,ARC]
3212 This parameter sets the maximum duration, in
3213 cycles, each HW thread of the CTOP can run
3214 without interruptions, before HW switches it.
3215 The actual maximum duration is 16 times this
3217 Format: integer between 1 and 255
3220 nptcg= [IA-64] Override max number of concurrent global TLB
3221 purges which is reported from either PAL_VM_SUMMARY or
3224 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3225 could support. nr_cpus=n : n >= 1 limits the kernel to
3226 support 'n' processors. It could be larger than the
3227 number of already plugged CPU during bootup, later in
3228 runtime you can physically add extra cpu until it reaches
3229 n. So during boot up some boot time memory for per-cpu
3230 variables need be pre-allocated for later physical cpu
3233 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3235 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3236 Allowed values are enable and disable
3238 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3239 'node', 'default' can be specified
3240 This can be set from sysctl after boot.
3241 See Documentation/admin-guide/sysctl/vm.rst for details.
3243 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3244 See Documentation/debugging-via-ohci1394.txt for more
3247 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3248 Rather than timing out after 20 ms if an EC
3249 command is not properly ACKed, override the length
3250 of the timeout. We have interrupts disabled while
3251 waiting for the ACK, so if this is set too high
3252 interrupts *may* be lost!
3254 omap_mux= [OMAP] Override bootloader pin multiplexing.
3255 Format: <mux_mode0.mode_name=value>...
3256 For example, to override I2C bus2:
3257 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3259 oprofile.timer= [HW]
3260 Use timer interrupt instead of performance counters
3262 oprofile.cpu_type= Force an oprofile cpu type
3263 This might be useful if you have an older oprofile
3264 userland or if you want common events.
3265 Format: { arch_perfmon }
3266 arch_perfmon: [X86] Force use of architectural
3267 perfmon on Intel CPUs instead of the
3268 CPU specific event set.
3269 timer: [X86] Force use of architectural NMI
3270 timer mode (see also oprofile.timer
3271 for generic hr timer mode)
3273 oops=panic Always panic on oopses. Default is to just kill the
3274 process, but there is a small probability of
3275 deadlocking the machine.
3276 This will also cause panics on machine check exceptions.
3277 Useful together with panic=30 to trigger a reboot.
3280 [KNL] Boolean flag to control whether the page allocator
3281 should randomize its free lists. The randomization may
3282 be automatically enabled if the kernel detects it is
3283 running on a platform with a direct-mapped memory-side
3284 cache, and this parameter can be used to
3285 override/disable that behavior. The state of the flag
3286 can be read from sysfs at:
3287 /sys/module/page_alloc/parameters/shuffle.
3289 page_owner= [KNL] Boot-time page_owner enabling option.
3290 Storage of the information about who allocated
3291 each page is disabled in default. With this switch,
3293 on: enable the feature
3295 page_poison= [KNL] Boot-time parameter changing the state of
3296 poisoning on the buddy allocator, available with
3297 CONFIG_PAGE_POISONING=y.
3298 off: turn off poisoning (default)
3299 on: turn on poisoning
3301 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3302 timeout > 0: seconds before rebooting
3303 timeout = 0: wait forever
3304 timeout < 0: reboot immediately
3307 panic_print= Bitmask for printing system info when panic happens.
3308 User can chose combination of the following bits:
3309 bit 0: print all tasks info
3310 bit 1: print system memory info
3311 bit 2: print timer info
3312 bit 3: print locks info if CONFIG_LOCKDEP is on
3313 bit 4: print ftrace buffer
3314 bit 5: print all printk messages in buffer
3316 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3319 crash_kexec_post_notifiers
3320 Run kdump after running panic-notifiers and dumping
3321 kmsg. This only for the users who doubt kdump always
3322 succeeds in any situation.
3323 Note that this also increases risks of kdump failure,
3324 because some panic notifiers can make the crashed
3325 kernel more unstable.
3327 parkbd.port= [HW] Parallel port number the keyboard adapter is
3328 connected to, default is 0.
3330 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3331 0 for XT, 1 for AT (default is AT).
3334 parport= [HW,PPT] Specify parallel ports. 0 disables.
3335 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3336 Use 'auto' to force the driver to use any
3337 IRQ/DMA settings detected (the default is to
3338 ignore detected IRQ/DMA settings because of
3339 possible conflicts). You can specify the base
3340 address, IRQ, and DMA settings; IRQ and DMA
3341 should be numbers, or 'auto' (for using detected
3342 settings on that particular port), or 'nofifo'
3343 (to avoid using a FIFO even if it is detected).
3344 Parallel ports are assigned in the order they
3345 are specified on the command line, starting
3348 parport_init_mode= [HW,PPT]
3349 Configure VIA parallel port to operate in
3350 a specific mode. This is necessary on Pegasos
3351 computer where firmware has no options for setting
3352 up parallel port mode and sets it to spp.
3353 Currently this function knows 686a and 8231 chips.
3354 Format: [spp|ps2|epp|ecp|ecpepp]
3357 Halt all CPUs after the first oops has been printed for
3358 the specified number of seconds. This is to be used if
3359 your oopses keep scrolling off the screen.
3364 See header of drivers/block/paride/pcd.c.
3365 See also Documentation/admin-guide/blockdev/paride.rst.
3367 pci=option[,option...] [PCI] various PCI subsystem options.
3369 Some options herein operate on a specific device
3370 or a set of devices (<pci_dev>). These are
3371 specified in one of the following formats:
3373 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3374 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3376 Note: the first format specifies a PCI
3377 bus/device/function address which may change
3378 if new hardware is inserted, if motherboard
3379 firmware changes, or due to changes caused
3380 by other kernel parameters. If the
3381 domain is left unspecified, it is
3382 taken to be zero. Optionally, a path
3383 to a device through multiple device/function
3384 addresses can be specified after the base
3385 address (this is more robust against
3386 renumbering issues). The second format
3387 selects devices using IDs from the
3388 configuration space which may match multiple
3389 devices in the system.
3391 earlydump dump PCI config space before the kernel
3393 off [X86] don't probe for the PCI bus
3394 bios [X86-32] force use of PCI BIOS, don't access
3395 the hardware directly. Use this if your machine
3396 has a non-standard PCI host bridge.
3397 nobios [X86-32] disallow use of PCI BIOS, only direct
3398 hardware access methods are allowed. Use this
3399 if you experience crashes upon bootup and you
3400 suspect they are caused by the BIOS.
3401 conf1 [X86] Force use of PCI Configuration Access
3402 Mechanism 1 (config address in IO port 0xCF8,
3403 data in IO port 0xCFC, both 32-bit).
3404 conf2 [X86] Force use of PCI Configuration Access
3405 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3406 the function, IO port 0xCFA, also 8-bit, sets
3407 bus number. The config space is then accessed
3408 through ports 0xC000-0xCFFF).
3409 See http://wiki.osdev.org/PCI for more info
3410 on the configuration access mechanisms.
3411 noaer [PCIE] If the PCIEAER kernel config parameter is
3412 enabled, this kernel boot option can be used to
3413 disable the use of PCIE advanced error reporting.
3414 nodomains [PCI] Disable support for multiple PCI
3415 root domains (aka PCI segments, in ACPI-speak).
3416 nommconf [X86] Disable use of MMCONFIG for PCI
3418 check_enable_amd_mmconf [X86] check for and enable
3419 properly configured MMIO access to PCI
3420 config space on AMD family 10h CPU
3421 nomsi [MSI] If the PCI_MSI kernel config parameter is
3422 enabled, this kernel boot option can be used to
3423 disable the use of MSI interrupts system-wide.
3424 noioapicquirk [APIC] Disable all boot interrupt quirks.
3425 Safety option to keep boot IRQs enabled. This
3426 should never be necessary.
3427 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3428 primary IO-APIC for bridges that cannot disable
3429 boot IRQs. This fixes a source of spurious IRQs
3430 when the system masks IRQs.
3431 noioapicreroute [APIC] Disable workaround that uses the
3432 boot IRQ equivalent of an IRQ that connects to
3433 a chipset where boot IRQs cannot be disabled.
3434 The opposite of ioapicreroute.
3435 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3436 routing table. These calls are known to be buggy
3437 on several machines and they hang the machine
3438 when used, but on other computers it's the only
3439 way to get the interrupt routing table. Try
3440 this option if the kernel is unable to allocate
3441 IRQs or discover secondary PCI buses on your
3443 rom [X86] Assign address space to expansion ROMs.
3444 Use with caution as certain devices share
3445 address decoders between ROMs and other
3447 norom [X86] Do not assign address space to
3448 expansion ROMs that do not already have
3449 BIOS assigned address ranges.
3450 nobar [X86] Do not assign address space to the
3451 BARs that weren't assigned by the BIOS.
3452 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3453 assigned automatically to PCI devices. You can
3454 make the kernel exclude IRQs of your ISA cards
3456 pirqaddr=0xAAAAA [X86] Specify the physical address
3457 of the PIRQ table (normally generated
3458 by the BIOS) if it is outside the
3459 F0000h-100000h range.
3460 lastbus=N [X86] Scan all buses thru bus #N. Can be
3461 useful if the kernel is unable to find your
3462 secondary buses and you want to tell it
3463 explicitly which ones they are.
3464 assign-busses [X86] Always assign all PCI bus
3465 numbers ourselves, overriding
3466 whatever the firmware may have done.
3467 usepirqmask [X86] Honor the possible IRQ mask stored
3468 in the BIOS $PIR table. This is needed on
3469 some systems with broken BIOSes, notably
3470 some HP Pavilion N5400 and Omnibook XE3
3471 notebooks. This will have no effect if ACPI
3472 IRQ routing is enabled.
3473 noacpi [X86] Do not use ACPI for IRQ routing
3474 or for PCI scanning.
3475 use_crs [X86] Use PCI host bridge window information
3476 from ACPI. On BIOSes from 2008 or later, this
3477 is enabled by default. If you need to use this,
3478 please report a bug.
3479 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3480 If you need to use this, please report a bug.
3481 routeirq Do IRQ routing for all PCI devices.
3482 This is normally done in pci_enable_device(),
3483 so this option is a temporary workaround
3484 for broken drivers that don't call it.
3485 skip_isa_align [X86] do not align io start addr, so can
3486 handle more pci cards
3487 noearly [X86] Don't do any early type 1 scanning.
3488 This might help on some broken boards which
3489 machine check when some devices' config space
3490 is read. But various workarounds are disabled
3491 and some IOMMU drivers will not work.
3492 bfsort Sort PCI devices into breadth-first order.
3493 This sorting is done to get a device
3494 order compatible with older (<= 2.4) kernels.
3495 nobfsort Don't sort PCI devices into breadth-first order.
3496 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3497 tuning and use the BIOS-configured MPS defaults.
3498 pcie_bus_safe Set every device's MPS to the largest value
3499 supported by all devices below the root complex.
3500 pcie_bus_perf Set device MPS to the largest allowable MPS
3501 based on its parent bus. Also set MRRS (Max
3502 Read Request Size) to the largest supported
3503 value (no larger than the MPS that the device
3504 or bus can support) for best performance.
3505 pcie_bus_peer2peer Set every device's MPS to 128B, which
3506 every device is guaranteed to support. This
3507 configuration allows peer-to-peer DMA between
3508 any pair of devices, possibly at the cost of
3509 reduced performance. This also guarantees
3510 that hot-added devices will work.
3511 cbiosize=nn[KMG] The fixed amount of bus space which is
3512 reserved for the CardBus bridge's IO window.
3513 The default value is 256 bytes.
3514 cbmemsize=nn[KMG] The fixed amount of bus space which is
3515 reserved for the CardBus bridge's memory
3516 window. The default value is 64 megabytes.
3519 [<order of align>@]<pci_dev>[; ...]
3520 Specifies alignment and device to reassign
3521 aligned memory resources. How to
3522 specify the device is described above.
3523 If <order of align> is not specified,
3524 PAGE_SIZE is used as alignment.
3525 A PCI-PCI bridge can be specified if resource
3526 windows need to be expanded.
3527 To specify the alignment for several
3528 instances of a device, the PCI vendor,
3529 device, subvendor, and subdevice may be
3530 specified, e.g., 12@pci:8086:9c22:103c:198f
3531 for 4096-byte alignment.
3532 ecrc= Enable/disable PCIe ECRC (transaction layer
3533 end-to-end CRC checking).
3534 bios: Use BIOS/firmware settings. This is the
3538 hpiosize=nn[KMG] The fixed amount of bus space which is
3539 reserved for hotplug bridge's IO window.
3540 Default size is 256 bytes.
3541 hpmemsize=nn[KMG] The fixed amount of bus space which is
3542 reserved for hotplug bridge's memory window.
3543 Default size is 2 megabytes.
3544 hpbussize=nn The minimum amount of additional bus numbers
3545 reserved for buses below a hotplug bridge.
3547 realloc= Enable/disable reallocating PCI bridge resources
3548 if allocations done by BIOS are too small to
3549 accommodate resources required by all child
3551 off: Turn realloc off
3553 realloc same as realloc=on
3554 noari do not use PCIe ARI.
3555 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3556 do not use PCIe ATS (and IOMMU device IOTLB).
3557 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3558 only look for one device below a PCIe downstream
3560 big_root_window Try to add a big 64bit memory window to the PCIe
3561 root complex on AMD CPUs. Some GFX hardware
3562 can resize a BAR to allow access to all VRAM.
3563 Adding the window is slightly risky (it may
3564 conflict with unreported devices), so this
3566 disable_acs_redir=<pci_dev>[; ...]
3567 Specify one or more PCI devices (in the format
3568 specified above) separated by semicolons.
3569 Each device specified will have the PCI ACS
3570 redirect capabilities forced off which will
3571 allow P2P traffic between devices through
3572 bridges without forcing it upstream. Note:
3573 this removes isolation between devices and
3574 may put more devices in an IOMMU group.
3575 force_floating [S390] Force usage of floating interrupts.
3576 nomio [S390] Do not use MIO instructions.
3578 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3581 force Enable ASPM even on devices that claim not to support it.
3582 WARNING: Forcing ASPM on may cause system lockups.
3584 pcie_ports= [PCIE] PCIe port services handling:
3585 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3586 even if the platform doesn't give the OS permission to
3587 use them. This may cause conflicts if the platform
3588 also tries to use these services.
3589 compat Disable native PCIe services (PME, AER, DPC, PCIe
3592 pcie_port_pm= [PCIE] PCIe port power management handling:
3593 off Disable power management of all PCIe ports
3594 force Forcibly enable power management of all PCIe ports
3596 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3597 nomsi Do not use MSI for native PCIe PME signaling (this makes
3598 all PCIe root ports use INTx for all services).
3600 pcmv= [HW,PCMCIA] BadgePAD 4
3604 Keep all power-domains already enabled by bootloader on,
3605 even if no driver has claimed them. This is useful
3606 for debug and development, but should not be
3607 needed on a platform with proper driver support.
3610 See Documentation/admin-guide/blockdev/paride.rst.
3612 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3615 See arch/parisc/kernel/pdc_chassis.c
3617 percpu_alloc= Select which percpu first chunk allocator to use.
3618 Currently supported values are "embed" and "page".
3619 Archs may support subset or none of the selections.
3620 See comments in mm/percpu.c for details on each
3621 allocator. This parameter is primarily for debugging
3622 and performance comparison.
3625 See Documentation/admin-guide/blockdev/paride.rst.
3628 See Documentation/admin-guide/blockdev/paride.rst.
3630 pirq= [SMP,APIC] Manual mp-table setup
3631 See Documentation/x86/i386/IO-APIC.rst.
3633 plip= [PPT,NET] Parallel port network link
3634 Format: { parport<nr> | timid | 0 }
3635 See also Documentation/admin-guide/parport.rst.
3637 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3638 Override pmtimer IOPort with a hex value.
3642 Enable PNP debug messages (depends on the
3643 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3644 via /sys/module/pnp/parameters/debug. We always show
3645 current resource usage; turning this on also shows
3646 possible settings and some assignment information.
3652 { on | off | curr | res | no-curr | no-res }
3655 [ISAPNP] Exclude IRQs for the autoconfiguration
3658 [ISAPNP] Exclude DMAs for the autoconfiguration
3660 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3661 Ranges are in pairs (I/O port base and size).
3664 [ISAPNP] Exclude memory regions for the
3666 Ranges are in pairs (memory base and size).
3668 ports= [IP_VS_FTP] IPVS ftp helper module
3670 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3672 Format: <port>,<port>....
3674 powersave=off [PPC] This option disables power saving features.
3675 It specifically disables cpuidle and sets the
3676 platform machine description specific power_save
3677 function to NULL. On Idle the CPU just reduces
3680 ppc_strict_facility_enable
3681 [PPC] This option catches any kernel floating point,
3682 Altivec, VSX and SPE outside of regions specifically
3683 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3684 There is some performance impact when enabling this.
3688 Disable Hardware Transactional Memory
3690 print-fatal-signals=
3691 [KNL] debug: print fatal signals
3693 If enabled, warn about various signal handling
3694 related application anomalies: too many signals,
3695 too many POSIX.1 timers, fatal signals causing a
3698 If you hit the warning due to signal overflow,
3699 you might want to try "ulimit -i unlimited".
3703 printk.always_kmsg_dump=
3704 Trigger kmsg_dump for cases other than kernel oops or
3706 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3709 printk.devkmsg={on,off,ratelimit}
3710 Control writing to /dev/kmsg.
3711 on - unlimited logging to /dev/kmsg from userspace
3712 off - logging to /dev/kmsg disabled
3713 ratelimit - ratelimit the logging
3716 printk.time= Show timing data prefixed to each printk message line
3717 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3719 processor.max_cstate= [HW,ACPI]
3720 Limit processor to maximum C-state
3721 max_cstate=9 overrides any DMI blacklist limit.
3723 processor.nocst [HW,ACPI]
3724 Ignore the _CST method to determine C-states,
3725 instead using the legacy FADT method
3727 profile= [KNL] Enable kernel profiling via /proc/profile
3728 Format: [<profiletype>,]<number>
3729 Param: <profiletype>: "schedule", "sleep", or "kvm"
3730 [defaults to kernel profiling]
3731 Param: "schedule" - profile schedule points.
3732 Param: "sleep" - profile D-state sleeping (millisecs).
3733 Requires CONFIG_SCHEDSTATS
3734 Param: "kvm" - profile VM exits.
3735 Param: <number> - step/bucket size as a power of 2 for
3736 statistical time based profiling.
3738 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3740 See Documentation/admin-guide/blockdev/ramdisk.rst.
3742 psi= [KNL] Enable or disable pressure stall information
3746 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3747 probe for; one of (bare|imps|exps|lifebook|any).
3748 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3750 psmouse.resetafter= [HW,MOUSE]
3751 Try to reset the device after so many bad packets
3754 [HW,MOUSE] Set desired mouse resolution, in dpi.
3755 psmouse.smartscroll=
3756 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3757 0 = disabled, 1 = enabled (default).
3759 pstore.backend= Specify the name of the pstore backend to use
3762 See Documentation/admin-guide/blockdev/paride.rst.
3764 pti= [X86_64] Control Page Table Isolation of user and
3765 kernel address spaces. Disabling this feature
3766 removes hardening, but improves performance of
3767 system calls and interrupts.
3769 on - unconditionally enable
3770 off - unconditionally disable
3771 auto - kernel detects whether your CPU model is
3772 vulnerable to issues that PTI mitigates
3774 Not specifying this option is equivalent to pti=auto.
3777 Equivalent to pti=off
3780 [KNL] Number of legacy pty's. Overwrites compiled-in
3783 quiet [KNL] Disable most log messages
3788 See Documentation/admin-guide/md.rst.
3790 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3791 See Documentation/admin-guide/blockdev/ramdisk.rst.
3793 random.trust_cpu={on,off}
3794 [KNL] Enable or disable trusting the use of the
3795 CPU's random number generator (if available) to
3796 fully seed the kernel's CRNG. Default is controlled
3797 by CONFIG_RANDOM_TRUST_CPU.
3799 ras=option[,option,...] [KNL] RAS-specific options
3802 Disable the Correctable Errors Collector,
3803 see CONFIG_RAS_CEC help text.
3806 The argument is a cpu list, as described above,
3807 except that the string "all" can be used to
3808 specify every CPU on the system.
3810 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3811 the specified list of CPUs to be no-callback CPUs.
3812 Invocation of these CPUs' RCU callbacks will be
3813 offloaded to "rcuox/N" kthreads created for that
3814 purpose, where "x" is "p" for RCU-preempt, and
3815 "s" for RCU-sched, and "N" is the CPU number.
3816 This reduces OS jitter on the offloaded CPUs,
3817 which can be useful for HPC and real-time
3818 workloads. It can also improve energy efficiency
3819 for asymmetric multiprocessors.
3822 Rather than requiring that offloaded CPUs
3823 (specified by rcu_nocbs= above) explicitly
3824 awaken the corresponding "rcuoN" kthreads,
3825 make these kthreads poll for callbacks.
3826 This improves the real-time response for the
3827 offloaded CPUs by relieving them of the need to
3828 wake up the corresponding kthread, but degrades
3829 energy efficiency by requiring that the kthreads
3830 periodically wake up to do the polling.
3832 rcutree.blimit= [KNL]
3833 Set maximum number of finished RCU callbacks to
3834 process in one batch.
3836 rcutree.dump_tree= [KNL]
3837 Dump the structure of the rcu_node combining tree
3838 out at early boot. This is used for diagnostic
3839 purposes, to verify correct tree setup.
3841 rcutree.gp_cleanup_delay= [KNL]
3842 Set the number of jiffies to delay each step of
3843 RCU grace-period cleanup.
3845 rcutree.gp_init_delay= [KNL]
3846 Set the number of jiffies to delay each step of
3847 RCU grace-period initialization.
3849 rcutree.gp_preinit_delay= [KNL]
3850 Set the number of jiffies to delay each step of
3851 RCU grace-period pre-initialization, that is,
3852 the propagation of recent CPU-hotplug changes up
3853 the rcu_node combining tree.
3855 rcutree.use_softirq= [KNL]
3856 If set to zero, move all RCU_SOFTIRQ processing to
3857 per-CPU rcuc kthreads. Defaults to a non-zero
3858 value, meaning that RCU_SOFTIRQ is used by default.
3859 Specify rcutree.use_softirq=0 to use rcuc kthreads.
3861 rcutree.rcu_fanout_exact= [KNL]
3862 Disable autobalancing of the rcu_node combining
3863 tree. This is used by rcutorture, and might
3864 possibly be useful for architectures having high
3865 cache-to-cache transfer latencies.
3867 rcutree.rcu_fanout_leaf= [KNL]
3868 Change the number of CPUs assigned to each
3869 leaf rcu_node structure. Useful for very
3870 large systems, which will choose the value 64,
3871 and for NUMA systems with large remote-access
3872 latencies, which will choose a value aligned
3873 with the appropriate hardware boundaries.
3875 rcutree.jiffies_till_first_fqs= [KNL]
3876 Set delay from grace-period initialization to
3877 first attempt to force quiescent states.
3878 Units are jiffies, minimum value is zero,
3879 and maximum value is HZ.
3881 rcutree.jiffies_till_next_fqs= [KNL]
3882 Set delay between subsequent attempts to force
3883 quiescent states. Units are jiffies, minimum
3884 value is one, and maximum value is HZ.
3886 rcutree.jiffies_till_sched_qs= [KNL]
3887 Set required age in jiffies for a
3888 given grace period before RCU starts
3889 soliciting quiescent-state help from
3890 rcu_note_context_switch() and cond_resched().
3891 If not specified, the kernel will calculate
3892 a value based on the most recent settings
3893 of rcutree.jiffies_till_first_fqs
3894 and rcutree.jiffies_till_next_fqs.
3895 This calculated value may be viewed in
3896 rcutree.jiffies_to_sched_qs. Any attempt to set
3897 rcutree.jiffies_to_sched_qs will be cheerfully
3900 rcutree.kthread_prio= [KNL,BOOT]
3901 Set the SCHED_FIFO priority of the RCU per-CPU
3902 kthreads (rcuc/N). This value is also used for
3903 the priority of the RCU boost threads (rcub/N)
3904 and for the RCU grace-period kthreads (rcu_bh,
3905 rcu_preempt, and rcu_sched). If RCU_BOOST is
3906 set, valid values are 1-99 and the default is 1
3907 (the least-favored priority). Otherwise, when
3908 RCU_BOOST is not set, valid values are 0-99 and
3909 the default is zero (non-realtime operation).
3911 rcutree.rcu_nocb_gp_stride= [KNL]
3912 Set the number of NOCB callback kthreads in
3913 each group, which defaults to the square root
3914 of the number of CPUs. Larger numbers reduce
3915 the wakeup overhead on the global grace-period
3916 kthread, but increases that same overhead on
3917 each group's NOCB grace-period kthread.
3919 rcutree.qhimark= [KNL]
3920 Set threshold of queued RCU callbacks beyond which
3921 batch limiting is disabled.
3923 rcutree.qlowmark= [KNL]
3924 Set threshold of queued RCU callbacks below which
3925 batch limiting is re-enabled.
3927 rcutree.rcu_idle_gp_delay= [KNL]
3928 Set wakeup interval for idle CPUs that have
3929 RCU callbacks (RCU_FAST_NO_HZ=y).
3931 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3932 Set wakeup interval for idle CPUs that have
3933 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3934 Lazy RCU callbacks are those which RCU can
3935 prove do nothing more than free memory.
3937 rcutree.rcu_kick_kthreads= [KNL]
3938 Cause the grace-period kthread to get an extra
3939 wake_up() if it sleeps three times longer than
3940 it should at force-quiescent-state time.
3941 This wake_up() will be accompanied by a
3942 WARN_ONCE() splat and an ftrace_dump().
3944 rcutree.sysrq_rcu= [KNL]
3945 Commandeer a sysrq key to dump out Tree RCU's
3946 rcu_node tree with an eye towards determining
3947 why a new grace period has not yet started.
3949 rcuperf.gp_async= [KNL]
3950 Measure performance of asynchronous
3951 grace-period primitives such as call_rcu().
3953 rcuperf.gp_async_max= [KNL]
3954 Specify the maximum number of outstanding
3955 callbacks per writer thread. When a writer
3956 thread exceeds this limit, it invokes the
3957 corresponding flavor of rcu_barrier() to allow
3958 previously posted callbacks to drain.
3960 rcuperf.gp_exp= [KNL]
3961 Measure performance of expedited synchronous
3962 grace-period primitives.
3964 rcuperf.holdoff= [KNL]
3965 Set test-start holdoff period. The purpose of
3966 this parameter is to delay the start of the
3967 test until boot completes in order to avoid
3970 rcuperf.nreaders= [KNL]
3971 Set number of RCU readers. The value -1 selects
3972 N, where N is the number of CPUs. A value
3973 "n" less than -1 selects N-n+1, where N is again
3974 the number of CPUs. For example, -2 selects N
3975 (the number of CPUs), -3 selects N+1, and so on.
3976 A value of "n" less than or equal to -N selects
3979 rcuperf.nwriters= [KNL]
3980 Set number of RCU writers. The values operate
3981 the same as for rcuperf.nreaders.
3982 N, where N is the number of CPUs
3984 rcuperf.perf_type= [KNL]
3985 Specify the RCU implementation to test.
3987 rcuperf.shutdown= [KNL]
3988 Shut the system down after performance tests
3989 complete. This is useful for hands-off automated
3992 rcuperf.verbose= [KNL]
3993 Enable additional printk() statements.
3995 rcuperf.writer_holdoff= [KNL]
3996 Write-side holdoff between grace periods,
3997 in microseconds. The default of zero says
4000 rcutorture.fqs_duration= [KNL]
4001 Set duration of force_quiescent_state bursts
4004 rcutorture.fqs_holdoff= [KNL]
4005 Set holdoff time within force_quiescent_state bursts
4008 rcutorture.fqs_stutter= [KNL]
4009 Set wait time between force_quiescent_state bursts
4012 rcutorture.fwd_progress= [KNL]
4013 Enable RCU grace-period forward-progress testing
4014 for the types of RCU supporting this notion.
4016 rcutorture.fwd_progress_div= [KNL]
4017 Specify the fraction of a CPU-stall-warning
4018 period to do tight-loop forward-progress testing.
4020 rcutorture.fwd_progress_holdoff= [KNL]
4021 Number of seconds to wait between successive
4022 forward-progress tests.
4024 rcutorture.fwd_progress_need_resched= [KNL]
4025 Enclose cond_resched() calls within checks for
4026 need_resched() during tight-loop forward-progress
4029 rcutorture.gp_cond= [KNL]
4030 Use conditional/asynchronous update-side
4031 primitives, if available.
4033 rcutorture.gp_exp= [KNL]
4034 Use expedited update-side primitives, if available.
4036 rcutorture.gp_normal= [KNL]
4037 Use normal (non-expedited) asynchronous
4038 update-side primitives, if available.
4040 rcutorture.gp_sync= [KNL]
4041 Use normal (non-expedited) synchronous
4042 update-side primitives, if available. If all
4043 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4044 rcutorture.gp_normal=, and rcutorture.gp_sync=
4045 are zero, rcutorture acts as if is interpreted
4046 they are all non-zero.
4048 rcutorture.n_barrier_cbs= [KNL]
4049 Set callbacks/threads for rcu_barrier() testing.
4051 rcutorture.nfakewriters= [KNL]
4052 Set number of concurrent RCU writers. These just
4053 stress RCU, they don't participate in the actual
4054 test, hence the "fake".
4056 rcutorture.nreaders= [KNL]
4057 Set number of RCU readers. The value -1 selects
4058 N-1, where N is the number of CPUs. A value
4059 "n" less than -1 selects N-n-2, where N is again
4060 the number of CPUs. For example, -2 selects N
4061 (the number of CPUs), -3 selects N+1, and so on.
4063 rcutorture.object_debug= [KNL]
4064 Enable debug-object double-call_rcu() testing.
4066 rcutorture.onoff_holdoff= [KNL]
4067 Set time (s) after boot for CPU-hotplug testing.
4069 rcutorture.onoff_interval= [KNL]
4070 Set time (jiffies) between CPU-hotplug operations,
4071 or zero to disable CPU-hotplug testing.
4073 rcutorture.shuffle_interval= [KNL]
4074 Set task-shuffle interval (s). Shuffling tasks
4075 allows some CPUs to go into dyntick-idle mode
4076 during the rcutorture test.
4078 rcutorture.shutdown_secs= [KNL]
4079 Set time (s) after boot system shutdown. This
4080 is useful for hands-off automated testing.
4082 rcutorture.stall_cpu= [KNL]
4083 Duration of CPU stall (s) to test RCU CPU stall
4084 warnings, zero to disable.
4086 rcutorture.stall_cpu_holdoff= [KNL]
4087 Time to wait (s) after boot before inducing stall.
4089 rcutorture.stall_cpu_irqsoff= [KNL]
4090 Disable interrupts while stalling if set.
4092 rcutorture.stat_interval= [KNL]
4093 Time (s) between statistics printk()s.
4095 rcutorture.stutter= [KNL]
4096 Time (s) to stutter testing, for example, specifying
4097 five seconds causes the test to run for five seconds,
4098 wait for five seconds, and so on. This tests RCU's
4099 ability to transition abruptly to and from idle.
4101 rcutorture.test_boost= [KNL]
4102 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4103 "Maybe" means test if the RCU implementation
4104 under test support RCU priority boosting.
4106 rcutorture.test_boost_duration= [KNL]
4107 Duration (s) of each individual boost test.
4109 rcutorture.test_boost_interval= [KNL]
4110 Interval (s) between each boost test.
4112 rcutorture.test_no_idle_hz= [KNL]
4113 Test RCU's dyntick-idle handling. See also the
4114 rcutorture.shuffle_interval parameter.
4116 rcutorture.torture_type= [KNL]
4117 Specify the RCU implementation to test.
4119 rcutorture.verbose= [KNL]
4120 Enable additional printk() statements.
4122 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4123 Dump ftrace buffer after reporting RCU CPU
4126 rcupdate.rcu_cpu_stall_suppress= [KNL]
4127 Suppress RCU CPU stall warning messages.
4129 rcupdate.rcu_cpu_stall_timeout= [KNL]
4130 Set timeout for RCU CPU stall warning messages.
4132 rcupdate.rcu_expedited= [KNL]
4133 Use expedited grace-period primitives, for
4134 example, synchronize_rcu_expedited() instead
4135 of synchronize_rcu(). This reduces latency,
4136 but can increase CPU utilization, degrade
4137 real-time latency, and degrade energy efficiency.
4138 No effect on CONFIG_TINY_RCU kernels.
4140 rcupdate.rcu_normal= [KNL]
4141 Use only normal grace-period primitives,
4142 for example, synchronize_rcu() instead of
4143 synchronize_rcu_expedited(). This improves
4144 real-time latency, CPU utilization, and
4145 energy efficiency, but can expose users to
4146 increased grace-period latency. This parameter
4147 overrides rcupdate.rcu_expedited. No effect on
4148 CONFIG_TINY_RCU kernels.
4150 rcupdate.rcu_normal_after_boot= [KNL]
4151 Once boot has completed (that is, after
4152 rcu_end_inkernel_boot() has been invoked), use
4153 only normal grace-period primitives. No effect
4154 on CONFIG_TINY_RCU kernels.
4156 rcupdate.rcu_task_stall_timeout= [KNL]
4157 Set timeout in jiffies for RCU task stall warning
4158 messages. Disable with a value less than or equal
4161 rcupdate.rcu_self_test= [KNL]
4162 Run the RCU early boot self tests
4166 Run specified binary instead of /init from the ramdisk,
4167 used for early userspace startup. See initrd.
4170 force - Override the decision by the kernel to hide the
4171 advertisement of RDRAND support (this affects
4172 certain AMD processors because of buggy BIOS
4173 support, specifically around the suspend/resume
4177 Turn on/off individual RDT features. List is:
4178 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4180 E.g. to turn on cmt and turn off mba use:
4184 Format (x86 or x86_64):
4185 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4187 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4189 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4190 (prefix with 'panic_' to set mode for panic
4192 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4193 reboot_force is either force or not specified,
4194 reboot_cpu is s[mp]#### with #### being the processor
4195 to be used for rebooting.
4198 [KNL, SMP] Set scheduler's default relax_domain_level.
4199 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4201 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4202 Format: <base1>,<size1>[,<base2>,<size2>,...]
4203 Reserve I/O ports or memory so the kernel won't use
4204 them. If <base> is less than 0x10000, the region
4205 is assumed to be I/O ports; otherwise it is memory.
4207 reservetop= [X86-32]
4209 Reserves a hole at the top of the kernel virtual
4214 Set the amount of memory to reserve for BIOS at
4215 the bottom of the address space.
4217 reset_devices [KNL] Force drivers to reset the underlying device
4218 during initialization.
4221 Specify the partition device for software suspend
4223 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4225 resume_offset= [SWSUSP]
4226 Specify the offset from the beginning of the partition
4227 given by "resume=" at which the swap header is located,
4228 in <PAGE_SIZE> units (needed only for swap files).
4229 See Documentation/power/swsusp-and-swap-files.rst
4231 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4232 read the resume files
4234 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4235 Useful for devices that are detected asynchronously
4236 (e.g. USB and MMC devices).
4238 hibernate= [HIBERNATION]
4239 noresume Don't check if there's a hibernation image
4240 present during boot.
4241 nocompress Don't compress/decompress hibernation images.
4242 no Disable hibernation and resume.
4243 protect_image Turn on image protection during restoration
4244 (that will set all pages holding image data
4245 during restoration read-only).
4247 retain_initrd [RAM] Keep initrd memory after extraction
4249 rfkill.default_state=
4250 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4251 etc. communication is blocked by default.
4254 rfkill.master_switch_mode=
4255 0 The "airplane mode" button does nothing.
4256 1 The "airplane mode" button toggles between everything
4257 blocked and the previous configuration.
4258 2 The "airplane mode" button toggles between everything
4259 blocked and everything unblocked.
4261 rhash_entries= [KNL,NET]
4262 Set number of hash buckets for route cache
4265 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4268 ro [KNL] Mount root device read-only on boot
4271 on Mark read-only kernel memory as read-only (default).
4272 off Leave read-only kernel memory writable for debugging.
4275 Enable the uart passthrough on the designated usb port
4276 on Rockchip SoCs. When active, the signals of the
4277 debug-uart get routed to the D+ and D- pins of the usb
4278 port and the regular usb controller gets disabled.
4280 root= [KNL] Root filesystem
4281 See name_to_dev_t comment in init/do_mounts.c.
4283 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4284 mount the root filesystem
4286 rootflags= [KNL] Set root filesystem mount option string
4288 rootfstype= [KNL] Set root filesystem type
4290 rootwait [KNL] Wait (indefinitely) for root device to show up.
4291 Useful for devices that are detected asynchronously
4292 (e.g. USB and MMC devices).
4294 rproc_mem=nn[KMG][@address]
4295 [KNL,ARM,CMA] Remoteproc physical memory block.
4296 Memory area to be used by remote processor image,
4299 rw [KNL] Mount root device read-write on boot
4301 S [KNL] Run init in single mode
4303 s390_iommu= [HW,S390]
4304 Set s390 IOTLB flushing mode
4306 With strict flushing every unmap operation will result in
4307 an IOTLB flush. Default is lazy flushing before reuse,
4311 See drivers/net/irda/sa1100_ir.c.
4313 sbni= [NET] Granch SBNI12 leased line adapter
4315 sched_debug [KNL] Enables verbose scheduler debug messages.
4317 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4318 Allowed values are enable and disable. This feature
4319 incurs a small amount of overhead in the scheduler
4320 but is useful for debugging and performance tuning.
4322 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4323 xtime_lock contention on larger systems, and/or RCU lock
4324 contention on all systems with CONFIG_MAXSMP set.
4325 Format: { "0" | "1" }
4326 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4328 Note: increases power consumption, thus should only be
4329 enabled if running jitter sensitive (HPC/RT) workloads.
4331 security= [SECURITY] Choose a legacy "major" security module to
4332 enable at boot. This has been deprecated by the
4335 selinux= [SELINUX] Disable or enable SELinux at boot time.
4336 Format: { "0" | "1" }
4337 See security/selinux/Kconfig help text.
4340 Default value is set via kernel config option.
4341 If enabled at boot time, /selinux/disable can be used
4342 later to disable prior to initial policy load.
4344 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4345 Format: { "0" | "1" }
4346 See security/apparmor/Kconfig help text
4349 Default value is set via kernel config option.
4351 serialnumber [BUGS=X86-32]
4354 Maximal number of shapers.
4362 Disable merging of slabs with similar size. May be
4363 necessary if there is some reason to distinguish
4364 allocs to different slabs, especially in hardened
4365 environments where the risk of heap overflows and
4366 layout control by attackers can usually be
4367 frustrated by disabling merging. This will reduce
4368 most of the exposure of a heap attack to a single
4369 cache (risks via metadata attacks are mostly
4370 unchanged). Debug options disable merging on their
4372 For more information see Documentation/vm/slub.rst.
4374 slab_max_order= [MM, SLAB]
4375 Determines the maximum allowed order for slabs.
4376 A high setting may cause OOMs due to memory
4377 fragmentation. Defaults to 1 for systems with
4378 more than 32MB of RAM, 0 otherwise.
4380 slub_debug[=options[,slabs]] [MM, SLUB]
4381 Enabling slub_debug allows one to determine the
4382 culprit if slab objects become corrupted. Enabling
4383 slub_debug can create guard zones around objects and
4384 may poison objects when not in use. Also tracks the
4385 last alloc / free. For more information see
4386 Documentation/vm/slub.rst.
4388 slub_memcg_sysfs= [MM, SLUB]
4389 Determines whether to enable sysfs directories for
4390 memory cgroup sub-caches. 1 to enable, 0 to disable.
4391 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4392 Enabling this can lead to a very high number of debug
4393 directories and files being created under
4396 slub_max_order= [MM, SLUB]
4397 Determines the maximum allowed order for slabs.
4398 A high setting may cause OOMs due to memory
4399 fragmentation. For more information see
4400 Documentation/vm/slub.rst.
4402 slub_min_objects= [MM, SLUB]
4403 The minimum number of objects per slab. SLUB will
4404 increase the slab order up to slub_max_order to
4405 generate a sufficiently large slab able to contain
4406 the number of objects indicated. The higher the number
4407 of objects the smaller the overhead of tracking slabs
4408 and the less frequently locks need to be acquired.
4409 For more information see Documentation/vm/slub.rst.
4411 slub_min_order= [MM, SLUB]
4412 Determines the minimum page order for slabs. Must be
4413 lower than slub_max_order.
4414 For more information see Documentation/vm/slub.rst.
4416 slub_nomerge [MM, SLUB]
4417 Same with slab_nomerge. This is supported for legacy.
4418 See slab_nomerge for more information.
4421 Format: <io1>[,<io2>[,...,<io8>]]
4423 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4424 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4425 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4426 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4427 smsc-ircc2.ircc_irq= [HW] IRQ line
4428 smsc-ircc2.ircc_dma= [HW] DMA channel
4429 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4430 0: Toshiba Satellite 1800 (GP data pin select)
4431 1: Fast pin select (default)
4434 smt [KNL,S390] Set the maximum number of threads (logical
4435 CPUs) to use per physical CPU on systems capable of
4436 symmetric multithreading (SMT). Will be capped to the
4437 actual hardware limit.
4439 Default: -1 (no limit)
4442 [KNL] Should the soft-lockup detector generate panics.
4445 A nonzero value instructs the soft-lockup detector
4446 to panic the machine when a soft-lockup occurs. This
4447 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4448 which is the respective build-time switch to that
4451 softlockup_all_cpu_backtrace=
4452 [KNL] Should the soft-lockup detector generate
4453 backtraces on all cpus.
4456 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4457 See Documentation/admin-guide/laptops/sonypi.rst
4459 spectre_v2= [X86] Control mitigation of Spectre variant 2
4460 (indirect branch speculation) vulnerability.
4461 The default operation protects the kernel from
4464 on - unconditionally enable, implies
4466 off - unconditionally disable, implies
4468 auto - kernel detects whether your CPU model is
4471 Selecting 'on' will, and 'auto' may, choose a
4472 mitigation method at run time according to the
4473 CPU, the available microcode, the setting of the
4474 CONFIG_RETPOLINE configuration option, and the
4475 compiler with which the kernel was built.
4477 Selecting 'on' will also enable the mitigation
4478 against user space to user space task attacks.
4480 Selecting 'off' will disable both the kernel and
4481 the user space protections.
4483 Specific mitigations can also be selected manually:
4485 retpoline - replace indirect branches
4486 retpoline,generic - google's original retpoline
4487 retpoline,amd - AMD-specific minimal thunk
4489 Not specifying this option is equivalent to
4493 [X86] Control mitigation of Spectre variant 2
4494 (indirect branch speculation) vulnerability between
4497 on - Unconditionally enable mitigations. Is
4498 enforced by spectre_v2=on
4500 off - Unconditionally disable mitigations. Is
4501 enforced by spectre_v2=off
4503 prctl - Indirect branch speculation is enabled,
4504 but mitigation can be enabled via prctl
4505 per thread. The mitigation control state
4506 is inherited on fork.
4509 - Like "prctl" above, but only STIBP is
4510 controlled per thread. IBPB is issued
4511 always when switching between different user
4515 - Same as "prctl" above, but all seccomp
4516 threads will enable the mitigation unless
4517 they explicitly opt out.
4520 - Like "seccomp" above, but only STIBP is
4521 controlled per thread. IBPB is issued
4522 always when switching between different
4523 user space processes.
4525 auto - Kernel selects the mitigation depending on
4526 the available CPU features and vulnerability.
4529 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4531 Not specifying this option is equivalent to
4532 spectre_v2_user=auto.
4534 spec_store_bypass_disable=
4535 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4536 (Speculative Store Bypass vulnerability)
4538 Certain CPUs are vulnerable to an exploit against a
4539 a common industry wide performance optimization known
4540 as "Speculative Store Bypass" in which recent stores
4541 to the same memory location may not be observed by
4542 later loads during speculative execution. The idea
4543 is that such stores are unlikely and that they can
4544 be detected prior to instruction retirement at the
4545 end of a particular speculation execution window.
4547 In vulnerable processors, the speculatively forwarded
4548 store can be used in a cache side channel attack, for
4549 example to read memory to which the attacker does not
4550 directly have access (e.g. inside sandboxed code).
4552 This parameter controls whether the Speculative Store
4553 Bypass optimization is used.
4555 On x86 the options are:
4557 on - Unconditionally disable Speculative Store Bypass
4558 off - Unconditionally enable Speculative Store Bypass
4559 auto - Kernel detects whether the CPU model contains an
4560 implementation of Speculative Store Bypass and
4561 picks the most appropriate mitigation. If the
4562 CPU is not vulnerable, "off" is selected. If the
4563 CPU is vulnerable the default mitigation is
4564 architecture and Kconfig dependent. See below.
4565 prctl - Control Speculative Store Bypass per thread
4566 via prctl. Speculative Store Bypass is enabled
4567 for a process by default. The state of the control
4568 is inherited on fork.
4569 seccomp - Same as "prctl" above, but all seccomp threads
4570 will disable SSB unless they explicitly opt out.
4572 Default mitigations:
4573 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4575 On powerpc the options are:
4577 on,auto - On Power8 and Power9 insert a store-forwarding
4578 barrier on kernel entry and exit. On Power7
4579 perform a software flush on kernel entry and
4583 Not specifying this option is equivalent to
4584 spec_store_bypass_disable=auto.
4586 spia_io_base= [HW,MTD]
4591 srcutree.counter_wrap_check [KNL]
4592 Specifies how frequently to check for
4593 grace-period sequence counter wrap for the
4594 srcu_data structure's ->srcu_gp_seq_needed field.
4595 The greater the number of bits set in this kernel
4596 parameter, the less frequently counter wrap will
4597 be checked for. Note that the bottom two bits
4600 srcutree.exp_holdoff [KNL]
4601 Specifies how many nanoseconds must elapse
4602 since the end of the last SRCU grace period for
4603 a given srcu_struct until the next normal SRCU
4604 grace period will be considered for automatic
4605 expediting. Set to zero to disable automatic
4609 Speculative Store Bypass Disable control
4611 On CPUs that are vulnerable to the Speculative
4612 Store Bypass vulnerability and offer a
4613 firmware based mitigation, this parameter
4614 indicates how the mitigation should be used:
4616 force-on: Unconditionally enable mitigation for
4617 for both kernel and userspace
4618 force-off: Unconditionally disable mitigation for
4619 for both kernel and userspace
4620 kernel: Always enable mitigation in the
4621 kernel, and offer a prctl interface
4622 to allow userspace to register its
4623 interest in being mitigated too.
4625 stack_guard_gap= [MM]
4626 override the default stack gap protection. The value
4627 is in page units and it defines how many pages prior
4628 to (for stacks growing down) resp. after (for stacks
4629 growing up) the main stack are reserved for no other
4630 mapping. Default value is 256 pages.
4633 Enabled the stack tracer on boot up.
4635 stacktrace_filter=[function-list]
4636 [FTRACE] Limit the functions that the stack tracer
4637 will trace at boot up. function-list is a comma separated
4638 list of functions. This list can be changed at run
4639 time by the stack_trace_filter file in the debugfs
4640 tracing directory. Note, this enables stack tracing
4641 and the stacktrace above is not needed.
4645 Set the STI (builtin display/keyboard on the HP-PARISC
4646 machines) console (graphic card) which should be used
4647 as the initial boot-console.
4648 See also comment in drivers/video/console/sticore.c.
4651 See comment in drivers/video/console/sticore.c.
4654 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4656 sunrpc.min_resvport=
4657 sunrpc.max_resvport=
4659 SunRPC servers often require that client requests
4660 originate from a privileged port (i.e. a port in the
4661 range 0 < portnr < 1024).
4662 An administrator who wishes to reserve some of these
4663 ports for other uses may adjust the range that the
4664 kernel's sunrpc client considers to be privileged
4665 using these two parameters to set the minimum and
4666 maximum port values.
4668 sunrpc.svc_rpc_per_connection_limit=
4670 Limit the number of requests that the server will
4671 process in parallel from a single connection.
4672 The default value is 0 (no limit).
4676 Control how the NFS server code allocates CPUs to
4677 service thread pools. Depending on how many NICs
4678 you have and where their interrupts are bound, this
4679 option will affect which CPUs will do NFS serving.
4680 Note: this parameter cannot be changed while the
4681 NFS server is running.
4683 auto the server chooses an appropriate mode
4684 automatically using heuristics
4685 global a single global pool contains all CPUs
4686 percpu one pool for each CPU
4687 pernode one pool for each NUMA node (equivalent
4688 to global on non-NUMA machines)
4690 sunrpc.tcp_slot_table_entries=
4691 sunrpc.udp_slot_table_entries=
4693 Sets the upper limit on the number of simultaneous
4694 RPC calls that can be sent from the client to a
4695 server. Increasing these values may allow you to
4696 improve throughput, but will also increase the
4697 amount of memory reserved for use by the client.
4699 suspend.pm_test_delay=
4701 Sets the number of seconds to remain in a suspend test
4702 mode before resuming the system (see
4703 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4704 is set. Default value is 5.
4707 Format: { on | off | y | n | 1 | 0 }
4708 This parameter controls use of the Protected
4709 Execution Facility on pSeries.
4712 [KNL] Enable accounting of swap in memory resource
4713 controller if no parameter or 1 is given or disable
4714 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
4716 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4717 Format: { <int> | force | noforce }
4718 <int> -- Number of I/O TLB slabs
4719 force -- force using of bounce buffers even if they
4720 wouldn't be automatically used by the kernel
4721 noforce -- Never use bounce buffers (for debugging)
4725 sysfs.deprecated=0|1 [KNL]
4726 Enable/disable old style sysfs layout for old udev
4727 on older distributions. When this option is enabled
4728 very new udev will not work anymore. When this option
4729 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4730 in older udev will not work anymore.
4731 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4732 the kernel configuration.
4734 sysrq_always_enabled
4736 Ignore sysrq setting - this boot parameter will
4737 neutralize any effect of /proc/sys/kernel/sysrq.
4738 Useful for debugging.
4740 tcpmhash_entries= [KNL,NET]
4741 Set the number of tcp_metrics_hash slots.
4742 Default value is 8192 or 16384 depending on total
4743 ram pages. This is used to specify the TCP metrics
4744 cache size. See Documentation/networking/ip-sysctl.txt
4745 "tcp_no_metrics_save" section for more details.
4749 test_suspend= [SUSPEND][,N]
4750 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4751 standby suspend) or "freeze" (for suspend type freeze)
4752 as the system sleep state during system startup with
4753 the optional capability to repeat N number of times.
4754 The system is woken from this state using a
4755 wakeup-capable RTC alarm.
4757 thash_entries= [KNL,NET]
4758 Set number of hash buckets for TCP connection
4760 thermal.act= [HW,ACPI]
4761 -1: disable all active trip points in all thermal zones
4762 <degrees C>: override all lowest active trip points
4764 thermal.crt= [HW,ACPI]
4765 -1: disable all critical trip points in all thermal zones
4766 <degrees C>: override all critical trip points
4768 thermal.nocrt= [HW,ACPI]
4769 Set to disable actions on ACPI thermal zone
4770 critical and hot trip points.
4772 thermal.off= [HW,ACPI]
4773 1: disable ACPI thermal control
4775 thermal.psv= [HW,ACPI]
4776 -1: disable all passive trip points
4777 <degrees C>: override all passive trip points to this
4780 thermal.tzp= [HW,ACPI]
4781 Specify global default ACPI thermal zone polling rate
4782 <deci-seconds>: poll all this frequency
4783 0: no polling (default)
4786 Force threading of all interrupt handlers except those
4787 marked explicitly IRQF_NO_THREAD.
4791 Specify if the kernel should make use of the cpu
4792 topology information if the hardware supports this.
4793 The scheduler will make use of this information and
4794 e.g. base its process migration decisions on it.
4797 topology_updates= [KNL, PPC, NUMA]
4799 Specify if the kernel should ignore (off)
4800 topology updates sent by the hypervisor to this
4805 tpm_suspend_pcr=[HW,TPM]
4806 Format: integer pcr id
4807 Specify that at suspend time, the tpm driver
4808 should extend the specified pcr with zeros,
4809 as a workaround for some chips which fail to
4810 flush the last written pcr on TPM_SaveState.
4811 This will guarantee that all the other pcrs
4814 trace_buf_size=nn[KMG]
4815 [FTRACE] will set tracing buffer size on each cpu.
4817 trace_event=[event-list]
4818 [FTRACE] Set and start specified trace events in order
4819 to facilitate early boot debugging. The event-list is a
4820 comma separated list of trace events to enable. See
4821 also Documentation/trace/events.rst
4823 trace_options=[option-list]
4824 [FTRACE] Enable or disable tracer options at boot.
4825 The option-list is a comma delimited list of options
4826 that can be enabled or disabled just as if you were
4827 to echo the option name into
4829 /sys/kernel/debug/tracing/trace_options
4831 For example, to enable stacktrace option (to dump the
4832 stack trace of each event), add to the command line:
4834 trace_options=stacktrace
4836 See also Documentation/trace/ftrace.rst "trace options"
4840 Have the tracepoints sent to printk as well as the
4841 tracing ring buffer. This is useful for early boot up
4842 where the system hangs or reboots and does not give the
4843 option for reading the tracing buffer or performing a
4844 ftrace_dump_on_oops.
4846 To turn off having tracepoints sent to printk,
4847 echo 0 > /proc/sys/kernel/tracepoint_printk
4848 Note, echoing 1 into this file without the
4849 tracepoint_printk kernel cmdline option has no effect.
4853 Having tracepoints sent to printk() and activating high
4854 frequency tracepoints such as irq or sched, can cause
4855 the system to live lock.
4858 [FTRACE] enable this option to disable tracing when a
4859 warning is hit. This turns off "tracing_on". Tracing can
4860 be enabled again by echoing '1' into the "tracing_on"
4861 file located in /sys/kernel/debug/tracing/
4863 This option is useful, as it disables the trace before
4864 the WARNING dump is called, which prevents the trace to
4865 be filled with content caused by the warning output.
4867 This option can also be set at run time via the sysctl
4868 option: kernel/traceoff_on_warning
4870 transparent_hugepage=
4872 Format: [always|madvise|never]
4873 Can be used to control the default behavior of the system
4874 with respect to transparent hugepages.
4875 See Documentation/admin-guide/mm/transhuge.rst
4878 tsc= Disable clocksource stability checks for TSC.
4880 [x86] reliable: mark tsc clocksource as reliable, this
4881 disables clocksource verification at runtime, as well
4882 as the stability checks done at bootup. Used to enable
4883 high-resolution timer mode on older hardware, and in
4884 virtualized environment.
4885 [x86] noirqtime: Do not use TSC to do irq accounting.
4886 Used to run time disable IRQ_TIME_ACCOUNTING on any
4887 platforms where RDTSC is slow and this accounting
4889 [x86] unstable: mark the TSC clocksource as unstable, this
4890 marks the TSC unconditionally unstable at bootup and
4891 avoids any further wobbles once the TSC watchdog notices.
4892 [x86] nowatchdog: disable clocksource watchdog. Used
4893 in situations with strict latency requirements (where
4894 interruptions from clocksource watchdog are not
4897 tsx= [X86] Control Transactional Synchronization
4898 Extensions (TSX) feature in Intel processors that
4899 support TSX control.
4901 This parameter controls the TSX feature. The options are:
4903 on - Enable TSX on the system. Although there are
4904 mitigations for all known security vulnerabilities,
4905 TSX has been known to be an accelerator for
4906 several previous speculation-related CVEs, and
4907 so there may be unknown security risks associated
4908 with leaving it enabled.
4910 off - Disable TSX on the system. (Note that this
4911 option takes effect only on newer CPUs which are
4912 not vulnerable to MDS, i.e., have
4913 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
4914 the new IA32_TSX_CTRL MSR through a microcode
4915 update. This new MSR allows for the reliable
4916 deactivation of the TSX functionality.)
4918 auto - Disable TSX if X86_BUG_TAA is present,
4919 otherwise enable TSX on the system.
4921 Not specifying this option is equivalent to tsx=off.
4923 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
4926 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
4927 Abort (TAA) vulnerability.
4929 Similar to Micro-architectural Data Sampling (MDS)
4930 certain CPUs that support Transactional
4931 Synchronization Extensions (TSX) are vulnerable to an
4932 exploit against CPU internal buffers which can forward
4933 information to a disclosure gadget under certain
4936 In vulnerable processors, the speculatively forwarded
4937 data can be used in a cache side channel attack, to
4938 access data to which the attacker does not have direct
4941 This parameter controls the TAA mitigation. The
4944 full - Enable TAA mitigation on vulnerable CPUs
4947 full,nosmt - Enable TAA mitigation and disable SMT on
4948 vulnerable CPUs. If TSX is disabled, SMT
4949 is not disabled because CPU is not
4950 vulnerable to cross-thread TAA attacks.
4951 off - Unconditionally disable TAA mitigation
4953 On MDS-affected machines, tsx_async_abort=off can be
4954 prevented by an active MDS mitigation as both vulnerabilities
4955 are mitigated with the same mechanism so in order to disable
4956 this mitigation, you need to specify mds=off too.
4958 Not specifying this option is equivalent to
4959 tsx_async_abort=full. On CPUs which are MDS affected
4960 and deploy MDS mitigation, TAA mitigation is not
4961 required and doesn't provide any additional
4965 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
4967 turbografx.map[2|3]= [HW,JOY]
4968 TurboGraFX parallel port interface
4970 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4971 See also Documentation/input/devices/joystick-parport.rst
4973 udbg-immortal [PPC] When debugging early kernel crashes that
4974 happen after console_init() and before a proper
4975 console driver takes over, this boot options might
4976 help "seeing" what's going on.
4978 uhash_entries= [KNL,NET]
4979 Set number of hash buckets for UDP/UDP-Lite connections
4982 [USB] Ignore overcurrent events (default N).
4983 Some badly-designed motherboards generate lots of
4984 bogus events, for ports that aren't wired to
4985 anything. Set this parameter to avoid log spamming.
4986 Note that genuine overcurrent events won't be
4990 [X86] Cause panic on unknown NMI.
4992 usbcore.authorized_default=
4993 [USB] Default USB device authorization:
4994 (default -1 = authorized except for wireless USB,
4995 0 = not authorized, 1 = authorized, 2 = authorized
4996 if device connected to internal port)
4998 usbcore.autosuspend=
4999 [USB] The autosuspend time delay (in seconds) used
5000 for newly-detected USB devices (default 2). This
5001 is the time required before an idle device will be
5002 autosuspended. Devices for which the delay is set
5003 to a negative value won't be autosuspended at all.
5005 usbcore.usbfs_snoop=
5006 [USB] Set to log all usbfs traffic (default 0 = off).
5008 usbcore.usbfs_snoop_max=
5009 [USB] Maximum number of bytes to snoop in each URB
5012 usbcore.blinkenlights=
5013 [USB] Set to cycle leds on hubs (default 0 = off).
5015 usbcore.old_scheme_first=
5016 [USB] Start with the old device initialization
5017 scheme, applies only to low and full-speed devices
5020 usbcore.usbfs_memory_mb=
5021 [USB] Memory limit (in MB) for buffers allocated by
5022 usbfs (default = 16, 0 = max = 2047).
5024 usbcore.use_both_schemes=
5025 [USB] Try the other device initialization scheme
5026 if the first one fails (default 1 = enabled).
5028 usbcore.initial_descriptor_timeout=
5029 [USB] Specifies timeout for the initial 64-byte
5030 USB_REQ_GET_DESCRIPTOR request in milliseconds
5031 (default 5000 = 5.0 seconds).
5033 usbcore.nousb [USB] Disable the USB subsystem
5036 [USB] A list of quirk entries to augment the built-in
5037 usb core quirk list. List entries are separated by
5038 commas. Each entry has the form
5039 VendorID:ProductID:Flags. The IDs are 4-digit hex
5040 numbers and Flags is a set of letters. Each letter
5041 will change the built-in quirk; setting it if it is
5042 clear and clearing it if it is set. The letters have
5043 the following meanings:
5044 a = USB_QUIRK_STRING_FETCH_255 (string
5045 descriptors must not be fetched using
5047 b = USB_QUIRK_RESET_RESUME (device can't resume
5048 correctly so reset it instead);
5049 c = USB_QUIRK_NO_SET_INTF (device can't handle
5050 Set-Interface requests);
5051 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
5052 handle its Configuration or Interface
5054 e = USB_QUIRK_RESET (device can't be reset
5055 (e.g morph devices), don't use reset);
5056 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
5057 more interface descriptions than the
5058 bNumInterfaces count, and can't handle
5059 talking to these interfaces);
5060 g = USB_QUIRK_DELAY_INIT (device needs a pause
5061 during initialization, after we read
5062 the device descriptor);
5063 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
5064 high speed and super speed interrupt
5065 endpoints, the USB 2.0 and USB 3.0 spec
5066 require the interval in microframes (1
5067 microframe = 125 microseconds) to be
5068 calculated as interval = 2 ^
5070 Devices with this quirk report their
5071 bInterval as the result of this
5072 calculation instead of the exponent
5073 variable used in the calculation);
5074 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
5075 handle device_qualifier descriptor
5077 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
5078 generates spurious wakeup, ignore
5079 remote wakeup capability);
5080 k = USB_QUIRK_NO_LPM (device can't handle Link
5082 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
5083 (Device reports its bInterval as linear
5084 frames instead of the USB 2.0
5086 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
5087 to be disconnected before suspend to
5088 prevent spurious wakeup);
5089 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
5090 pause after every control message);
5091 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
5092 delay after resetting its port);
5093 Example: quirks=0781:5580:bk,0a5c:5834:gij
5096 [USBHID] The interval which mice are to be polled at.
5099 [USBHID] The interval which joysticks are to be polled at.
5102 [USBHID] The interval which keyboards are to be polled at.
5104 usb-storage.delay_use=
5105 [UMS] The delay in seconds before a new device is
5106 scanned for Logical Units (default 1).
5109 [UMS] A list of quirks entries to supplement or
5110 override the built-in unusual_devs list. List
5111 entries are separated by commas. Each entry has
5112 the form VID:PID:Flags where VID and PID are Vendor
5113 and Product ID values (4-digit hex numbers) and
5114 Flags is a set of characters, each corresponding
5115 to a common usb-storage quirk flag as follows:
5116 a = SANE_SENSE (collect more than 18 bytes
5118 b = BAD_SENSE (don't collect more than 18
5119 bytes of sense data);
5120 c = FIX_CAPACITY (decrease the reported
5121 device capacity by one sector);
5122 d = NO_READ_DISC_INFO (don't use
5123 READ_DISC_INFO command);
5124 e = NO_READ_CAPACITY_16 (don't use
5125 READ_CAPACITY_16 command);
5126 f = NO_REPORT_OPCODES (don't use report opcodes
5128 g = MAX_SECTORS_240 (don't transfer more than
5129 240 sectors at a time, uas only);
5130 h = CAPACITY_HEURISTICS (decrease the
5131 reported device capacity by one
5132 sector if the number is odd);
5133 i = IGNORE_DEVICE (don't bind to this
5135 j = NO_REPORT_LUNS (don't use report luns
5137 l = NOT_LOCKABLE (don't try to lock and
5138 unlock ejectable media);
5139 m = MAX_SECTORS_64 (don't transfer more
5140 than 64 sectors = 32 KB at a time);
5141 n = INITIAL_READ10 (force a retry of the
5142 initial READ(10) command);
5143 o = CAPACITY_OK (accept the capacity
5144 reported by the device);
5145 p = WRITE_CACHE (the device cache is ON
5147 r = IGNORE_RESIDUE (the device reports
5148 bogus residue values);
5149 s = SINGLE_LUN (the device has only one
5151 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
5152 commands, uas only);
5153 u = IGNORE_UAS (don't bind to the uas driver);
5154 w = NO_WP_DETECT (don't test whether the
5155 medium is write-protected).
5156 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
5157 even if the device claims no cache)
5158 Example: quirks=0419:aaf5:rl,0421:0433:rc
5160 user_debug= [KNL,ARM]
5162 See arch/arm/Kconfig.debug help text.
5163 1 - undefined instruction events
5165 4 - invalid data aborts
5168 Example: user_debug=31
5171 [X86] Flags controlling user PTE allocations.
5173 nohigh = do not allocate PTE pages in
5174 HIGHMEM regardless of setting
5178 On X86_32, this is an alias for vdso32=. Otherwise:
5180 vdso=1: enable VDSO (the default)
5181 vdso=0: disable VDSO mapping
5183 vdso32= [X86] Control the 32-bit vDSO
5184 vdso32=1: enable 32-bit VDSO
5185 vdso32=0 or vdso32=2: disable 32-bit VDSO
5187 See the help text for CONFIG_COMPAT_VDSO for more
5188 details. If CONFIG_COMPAT_VDSO is set, the default is
5189 vdso32=0; otherwise, the default is vdso32=1.
5191 For compatibility with older kernels, vdso32=2 is an
5194 Try vdso32=0 if you encounter an error that says:
5195 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
5198 vector=percpu: enable percpu vector domain
5200 video= [FB] Frame buffer configuration
5201 See Documentation/fb/modedb.rst.
5203 video.brightness_switch_enabled= [0,1]
5204 If set to 1, on receiving an ACPI notify event
5205 generated by hotkey, video driver will adjust brightness
5206 level and then send out the event to user space through
5207 the allocated input device; If set to 0, video driver
5208 will only send out the event without touching backlight
5213 [VMMIO] Memory mapped virtio (platform) device.
5215 <size>@<baseaddr>:<irq>[:<id>]
5217 <size> := size (can use standard suffixes
5219 <baseaddr> := physical base address
5220 <irq> := interrupt number (as passed to
5222 <id> := (optional) platform device id
5224 virtio_mmio.device=1K@0x100b0000:48:7
5226 Can be used multiple times for multiple devices.
5228 vga= [BOOT,X86-32] Select a particular video mode
5229 See Documentation/x86/boot.rst and
5230 Documentation/admin-guide/svga.rst.
5231 Use vga=ask for menu.
5232 This is actually a boot loader parameter; the value is
5233 passed to the kernel using a special protocol.
5235 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
5236 May slow down system boot speed, especially when
5237 enabled on systems with a large amount of memory.
5238 All options are enabled by default, and this
5239 interface is meant to allow for selectively
5240 enabling or disabling specific virtual memory
5243 Available options are:
5244 P Enable page structure init time poisoning
5245 - Disable all of the above options
5247 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
5248 size of <nn>. This can be used to increase the
5249 minimum size (128MB on x86). It can also be used to
5250 decrease the size and leave more room for directly
5253 vmcp_cma=nn[MG] [KNL,S390]
5254 Sets the memory size reserved for contiguous memory
5255 allocations for the vmcp device driver.
5257 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5260 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5263 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
5267 Controls the behavior of vsyscalls (i.e. calls to
5268 fixed addresses of 0xffffffffff600x00 from legacy
5269 code). Most statically-linked binaries and older
5270 versions of glibc use these calls. Because these
5271 functions are at fixed addresses, they make nice
5272 targets for exploits that can control RIP.
5274 emulate [default] Vsyscalls turn into traps and are
5275 emulated reasonably safely. The vsyscall
5278 xonly Vsyscalls turn into traps and are
5279 emulated reasonably safely. The vsyscall
5280 page is not readable.
5282 none Vsyscalls don't work at all. This makes
5283 them quite hard to use for exploits but
5284 might break your system.
5286 vt.color= [VT] Default text color.
5287 Format: 0xYX, X = foreground, Y = background.
5288 Default: 0x07 = light gray on black.
5290 vt.cur_default= [VT] Default cursor shape.
5291 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5292 the parameters of the <Esc>[?A;B;Cc escape sequence;
5293 see VGA-softcursor.txt. Default: 2 = underline.
5295 vt.default_blu= [VT]
5296 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5297 Change the default blue palette of the console.
5298 This is a 16-member array composed of values
5301 vt.default_grn= [VT]
5302 Format: <green0>,<green1>,<green2>,...,<green15>
5303 Change the default green palette of the console.
5304 This is a 16-member array composed of values
5307 vt.default_red= [VT]
5308 Format: <red0>,<red1>,<red2>,...,<red15>
5309 Change the default red palette of the console.
5310 This is a 16-member array composed of values
5316 Set system-wide default UTF-8 mode for all tty's.
5317 Default is 1, i.e. UTF-8 mode is enabled for all
5318 newly opened terminals.
5320 vt.global_cursor_default=
5323 Set system-wide default for whether a cursor
5324 is shown on new VTs. Default is -1,
5325 i.e. cursors will be created by default unless
5326 overridden by individual drivers. 0 will hide
5327 cursors, 1 will display them.
5329 vt.italic= [VT] Default color for italic text; 0-15.
5332 vt.underline= [VT] Default color for underlined text; 0-15.
5335 watchdog timers [HW,WDT] For information on watchdog timers,
5336 see Documentation/watchdog/watchdog-parameters.rst
5337 or other driver-specific files in the
5338 Documentation/watchdog/ directory.
5342 Set the hard lockup detector stall duration
5343 threshold in seconds. The soft lockup detector
5344 threshold is set to twice the value. A value of 0
5345 disables both lockup detectors. Default is 10
5348 workqueue.watchdog_thresh=
5349 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5350 warn stall conditions and dump internal state to
5351 help debugging. 0 disables workqueue stall
5352 detection; otherwise, it's the stall threshold
5353 duration in seconds. The default value is 30 and
5354 it can be updated at runtime by writing to the
5355 corresponding sysfs file.
5357 workqueue.disable_numa
5358 By default, all work items queued to unbound
5359 workqueues are affine to the NUMA nodes they're
5360 issued on, which results in better behavior in
5361 general. If NUMA affinity needs to be disabled for
5362 whatever reason, this option can be used. Note
5363 that this also can be controlled per-workqueue for
5364 workqueues visible under /sys/bus/workqueue/.
5366 workqueue.power_efficient
5367 Per-cpu workqueues are generally preferred because
5368 they show better performance thanks to cache
5369 locality; unfortunately, per-cpu workqueues tend to
5370 be more power hungry than unbound workqueues.
5372 Enabling this makes the per-cpu workqueues which
5373 were observed to contribute significantly to power
5374 consumption unbound, leading to measurably lower
5375 power usage at the cost of small performance
5378 The default value of this parameter is determined by
5379 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5381 workqueue.debug_force_rr_cpu
5382 Workqueue used to implicitly guarantee that work
5383 items queued without explicit CPU specified are put
5384 on the local CPU. This guarantee is no longer true
5385 and while local CPU is still preferred work items
5386 may be put on foreign CPUs. This debug option
5387 forces round-robin CPU selection to flush out
5388 usages which depend on the now broken guarantee.
5389 When enabled, memory and cache locality will be
5392 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5393 default x2apic cluster mode on platforms
5396 x86_intel_mid_timer= [X86-32,APBT]
5397 Choose timer option for x86 Intel MID platform.
5398 Two valid options are apbt timer only and lapic timer
5399 plus one apbt timer for broadcast timer.
5400 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5402 xen_512gb_limit [KNL,X86-64,XEN]
5403 Restricts the kernel running paravirtualized under Xen
5404 to use only up to 512 GB of RAM. The reason to do so is
5405 crash analysis tools and Xen tools for doing domain
5406 save/restore/migration must be enabled to handle larger
5409 xen_emul_unplug= [HW,X86,XEN]
5410 Unplug Xen emulated devices
5411 Format: [unplug0,][unplug1]
5412 ide-disks -- unplug primary master IDE devices
5413 aux-ide-disks -- unplug non-primary-master IDE devices
5414 nics -- unplug network devices
5415 all -- unplug all emulated devices (NICs and IDE disks)
5416 unnecessary -- unplugging emulated devices is
5417 unnecessary even if the host did not respond to
5419 never -- do not unplug even if version check succeeds
5421 xen_legacy_crash [X86,XEN]
5422 Crash from Xen panic notifier, without executing late
5423 panic() code such as dumping handler.
5425 xen_nopvspin [X86,XEN]
5426 Disables the ticketlock slowpath using Xen PV
5430 Disables the PV optimizations forcing the HVM guest to
5431 run as generic HVM guest with no PV drivers.
5432 This option is obsoleted by the "nopv" option, which
5433 has equivalent effect for XEN platform.
5435 xen_scrub_pages= [XEN]
5436 Boolean option to control scrubbing pages before giving them back
5437 to Xen, for use by other domains. Can be also changed at runtime
5438 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5439 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5441 xen_timer_slop= [X86-64,XEN]
5442 Set the timer slop (in nanoseconds) for the virtual Xen
5443 timers (default is 100000). This adjusts the minimum
5444 delta of virtualized Xen timers, where lower values
5445 improve timer resolution at the expense of processing
5446 more timer interrupts.
5448 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
5449 Disables the PV optimizations forcing the guest to run
5450 as generic guest with no PV drivers. Currently support
5451 XEN HVM, KVM, HYPER_V and VMWARE guest.
5453 xirc2ps_cs= [NET,PCMCIA]
5455 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5458 By default on POWER9 and above, the kernel will
5459 natively use the XIVE interrupt controller. This option
5460 allows the fallback firmware mode to be used:
5462 off Fallback to firmware control of XIVE interrupt
5463 controller on both pseries and powernv
5464 platforms. Only useful on POWER9 and above.
5466 xhci-hcd.quirks [USB,KNL]
5467 A hex value specifying bitmask with supplemental xhci
5468 host controller quirks. Meaning of each bit can be
5469 consulted in header drivers/usb/host/xhci.h.
5472 Format: { early | on | rw | ro | off }
5473 Controls if xmon debugger is enabled. Default is off.
5474 Passing only "xmon" is equivalent to "xmon=early".
5475 early Call xmon as early as possible on boot; xmon
5476 debugger is called from setup_arch().
5477 on xmon debugger hooks will be installed so xmon
5478 is only called on a kernel crash. Default mode,
5479 i.e. either "ro" or "rw" mode, is controlled
5480 with CONFIG_XMON_DEFAULT_RO_MODE.
5481 rw xmon debugger hooks will be installed so xmon
5482 is called only on a kernel crash, mode is write,
5483 meaning SPR registers, memory and, other data
5484 can be written using xmon commands.
5485 ro same as "rw" option above but SPR registers,
5486 memory, and other data can't be written using
5488 off xmon is disabled.
git.samba.org / sfrench / cifs-2.6.git / blob