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 on: enable the feature
814 debugpat [X86] Enable PAT debugging
816 decnet.addr= [HW,NET]
817 Format: <area>[,<node>]
818 See also Documentation/networking/decnet.txt.
821 [same as hugepagesz=] The size of the default
822 HugeTLB page size. This is the size represented by
823 the legacy /proc/ hugepages APIs, used for SHM, and
824 default size when mounting hugetlbfs filesystems.
825 Defaults to the default architecture's huge page size
828 deferred_probe_timeout=
829 [KNL] Debugging option to set a timeout in seconds for
830 deferred probe to give up waiting on dependencies to
831 probe. Only specific dependencies (subsystems or
832 drivers) that have opted in will be ignored. A timeout of 0
833 will timeout at the end of initcalls. This option will also
834 dump out devices still on the deferred probe list after
838 Set number of hash buckets for dentry cache.
840 disable_1tb_segments [PPC]
841 Disables the use of 1TB hash page table segments. This
842 causes the kernel to fall back to 256MB segments which
843 can be useful when debugging issues that require an SLB
847 See Documentation/networking/ipv6.txt.
850 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
851 hardening is enabled for this boot. Hardened
852 usercopy checking is used to protect the kernel
853 from reading or writing beyond known memory
854 allocation boundaries as a proactive defense
855 against bounds-checking flaws in the kernel's
856 copy_to_user()/copy_from_user() interface.
857 on Perform hardened usercopy checks (default).
858 off Disable hardened usercopy checks.
861 Disable RADIX MMU mode on POWER9
863 disable_cpu_apicid= [X86,APIC,SMP]
865 The number of initial APIC ID for the
866 corresponding CPU to be disabled at boot,
867 mostly used for the kdump 2nd kernel to
868 disable BSP to wake up multiple CPUs without
869 causing system reset or hang due to sending
872 perf_v4_pmi= [X86,INTEL]
874 Disable Intel PMU counter freezing feature.
875 The feature only exists starting from
876 Arch Perfmon v4 (Skylake and newer).
878 disable_ddw [PPC/PSERIES]
879 Disable Dynamic DMA Window support. Use this if
880 to workaround buggy firmware.
883 See Documentation/networking/ipv6.txt.
885 disable_mtrr_cleanup [X86]
886 The kernel tries to adjust MTRR layout from continuous
887 to discrete, to make X server driver able to add WB
888 entry later. This parameter disables that.
890 disable_mtrr_trim [X86, Intel and AMD only]
891 By default the kernel will trim any uncacheable
892 memory out of your available memory pool based on
893 MTRR settings. This parameter disables that behavior,
894 possibly causing your machine to run very slowly.
896 disable_timer_pin_1 [X86]
897 Disable PIN 1 of APIC timer
898 Can be useful to work around chipset bugs.
900 dis_ucode_ldr [X86] Disable the microcode loader.
902 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
903 this option disables the debugging code at boot.
905 dma_debug_entries=<number>
906 This option allows to tune the number of preallocated
907 entries for DMA-API debugging code. One entry is
908 required per DMA-API allocation. Use this if the
909 DMA-API debugging code disables itself because the
910 architectural default is too low.
912 dma_debug_driver=<driver_name>
913 With this option the DMA-API debugging driver
914 filter feature can be enabled at boot time. Just
915 pass the driver to filter for as the parameter.
916 The filter can be disabled or changed to another
917 driver later using sysfs.
919 driver_async_probe= [KNL]
920 List of driver names to be probed asynchronously.
921 Format: <driver_name1>,<driver_name2>...
923 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
924 Broken monitors, graphic adapters, KVMs and EDIDless
925 panels may send no or incorrect EDID data sets.
926 This parameter allows to specify an EDID data sets
927 in the /lib/firmware directory that are used instead.
928 Generic built-in EDID data sets are used, if one of
929 edid/1024x768.bin, edid/1280x1024.bin,
930 edid/1680x1050.bin, or edid/1920x1080.bin is given
931 and no file with the same name exists. Details and
932 instructions how to build your own EDID data are
933 available in Documentation/driver-api/edid.rst. An EDID
934 data set will only be used for a particular connector,
935 if its name and a colon are prepended to the EDID
936 name. Each connector may use a unique EDID data
937 set by separating the files with a comma. An EDID
938 data set with no connector name will be used for
939 any connectors not explicitly specified.
944 Format: {"off" | "known"}
945 Control how the dt_cpu_ftrs device-tree binding is
946 used for CPU feature discovery and setup (if it
948 off: Do not use it, fall back to legacy cpu table.
949 known: Do not pass through unknown features to guests
950 or userspace, only those that the kernel is aware of.
952 dump_apple_properties [X86]
953 Dump name and content of EFI device properties on
954 x86 Macs. Useful for driver authors to determine
955 what data is available or for reverse-engineering.
957 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
958 module.dyndbg[="val"]
959 Enable debug messages at boot time. See
960 Documentation/admin-guide/dynamic-debug-howto.rst
963 nompx [X86] Disables Intel Memory Protection Extensions.
964 See Documentation/x86/intel_mpx.rst for more
965 information about the feature.
967 nopku [X86] Disable Memory Protection Keys CPU feature found
970 module.async_probe [KNL]
971 Enable asynchronous probe on this module.
973 early_ioremap_debug [KNL]
974 Enable debug messages in early_ioremap support. This
975 is useful for tracking down temporary early mappings
976 which are not unmapped.
978 earlycon= [KNL] Output early console device and options.
980 [ARM64] The early console is determined by the
981 stdout-path property in device tree's chosen node,
982 or determined by the ACPI SPCR table.
984 [X86] When used with no options the early console is
985 determined by the ACPI SPCR table.
987 cdns,<addr>[,options]
988 Start an early, polled-mode console on a Cadence
989 (xuartps) serial port at the specified address. Only
990 supported option is baud rate. If baud rate is not
991 specified, the serial port must already be setup and
994 uart[8250],io,<addr>[,options]
995 uart[8250],mmio,<addr>[,options]
996 uart[8250],mmio32,<addr>[,options]
997 uart[8250],mmio32be,<addr>[,options]
998 uart[8250],0x<addr>[,options]
999 Start an early, polled-mode console on the 8250/16550
1000 UART at the specified I/O port or MMIO address.
1001 MMIO inter-register address stride is either 8-bit
1002 (mmio) or 32-bit (mmio32 or mmio32be).
1003 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1004 to be equivalent to 'mmio'. 'options' are specified
1005 in the same format described for "console=ttyS<n>"; if
1006 unspecified, the h/w is not initialized.
1010 Start an early, polled-mode console on a pl011 serial
1011 port at the specified address. The pl011 serial port
1012 must already be setup and configured. Options are not
1013 yet supported. If 'mmio32' is specified, then only
1014 the driver will use only 32-bit accessors to read/write
1015 the device registers.
1018 Start an early, polled-mode console on a meson serial
1019 port at the specified address. The serial port must
1020 already be setup and configured. Options are not yet
1024 Start an early, polled-mode console on an msm serial
1025 port at the specified address. The serial port
1026 must already be setup and configured. Options are not
1029 msm_serial_dm,<addr>
1030 Start an early, polled-mode console on an msm serial
1031 dm port at the specified address. The serial port
1032 must already be setup and configured. Options are not
1036 Start an early, polled-mode console on a serial port
1037 of an Actions Semi SoC, such as S500 or S900, at the
1038 specified address. The serial port must already be
1039 setup and configured. Options are not yet supported.
1042 Start an early, polled-mode console on a serial port
1043 of an RDA Micro SoC, such as RDA8810PL, at the
1044 specified address. The serial port must already be
1045 setup and configured. Options are not yet supported.
1048 Use RISC-V SBI (Supervisor Binary Interface) for early
1051 smh Use ARM semihosting calls for early console.
1059 Use early console provided by serial driver available
1060 on Samsung SoCs, requires selecting proper type and
1061 a correct base address of the selected UART port. The
1062 serial port must already be setup and configured.
1063 Options are not yet supported.
1066 Start an early, polled-mode console on a lantiq serial
1067 (lqasc) port at the specified address. The serial port
1068 must already be setup and configured. Options are not
1073 Use early console provided by Freescale LP UART driver
1074 found on Freescale Vybrid and QorIQ LS1021A processors.
1075 A valid base address must be provided, and the serial
1076 port must already be setup and configured.
1079 Start an early, polled-mode console on the
1080 Armada 3700 serial port at the specified
1081 address. The serial port must already be setup
1082 and configured. Options are not yet supported.
1085 Start an early, polled-mode console on a Qualcomm
1086 Generic Interface (GENI) based serial port at the
1087 specified address. The serial port must already be
1088 setup and configured. Options are not yet supported.
1091 Start an early, unaccelerated console on the EFI
1092 memory mapped framebuffer (if available). On cache
1093 coherent non-x86 systems that use system memory for
1094 the framebuffer, pass the 'ram' option so that it is
1095 mapped with the correct attributes.
1097 earlyprintk= [X86,SH,ARM,M68k,S390]
1101 earlyprintk=serial[,ttySn[,baudrate]]
1102 earlyprintk=serial[,0x...[,baudrate]]
1103 earlyprintk=ttySn[,baudrate]
1104 earlyprintk=dbgp[debugController#]
1105 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1106 earlyprintk=xdbc[xhciController#]
1108 earlyprintk is useful when the kernel crashes before
1109 the normal console is initialized. It is not enabled by
1110 default because it has some cosmetic problems.
1112 Append ",keep" to not disable it when the real console
1115 Only one of vga, efi, serial, or usb debug port can
1118 Currently only ttyS0 and ttyS1 may be specified by
1119 name. Other I/O ports may be explicitly specified
1120 on some architectures (x86 and arm at least) by
1121 replacing ttySn with an I/O port address, like this:
1122 earlyprintk=serial,0x1008,115200
1123 You can find the port for a given device in
1124 /proc/tty/driver/serial:
1125 2: uart:ST16650V2 port:00001008 irq:18 ...
1127 Interaction with the standard serial driver is not
1130 The VGA and EFI output is eventually overwritten by
1133 The xen output can only be used by Xen PV guests.
1135 The sclp output can only be used on s390.
1137 The optional "force" to "pciserial" enables use of a
1138 PCI device even when its classcode is not of the
1141 edac_report= [HW,EDAC] Control how to report EDAC event
1142 Format: {"on" | "off" | "force"}
1143 on: enable EDAC to report H/W event. May be overridden
1144 by other higher priority error reporting module.
1145 off: disable H/W event reporting through EDAC.
1146 force: enforce the use of EDAC to report H/W event.
1149 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1152 This is designed to be used in conjunction with
1153 the boot argument: earlyprintk=vga
1156 Format: {"off" | "on" | "skip[mbr]"}
1159 Format: { "old_map", "nochunk", "noruntime", "debug" }
1160 old_map [X86-64]: switch to the old ioremap-based EFI
1161 runtime services mapping. 32-bit still uses this one by
1163 nochunk: disable reading files in "chunks" in the EFI
1164 boot stub, as chunking can cause problems with some
1165 firmware implementations.
1166 noruntime : disable EFI runtime services support
1167 debug: enable misc debug output
1169 efi_no_storage_paranoia [EFI; X86]
1170 Using this parameter you can use more than 50% of
1171 your efi variable storage. Use this parameter only if
1172 you are really sure that your UEFI does sane gc and
1173 fulfills the spec otherwise your board may brick.
1175 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1176 Add arbitrary attribute to specific memory range by
1177 updating original EFI memory map.
1178 Region of memory which aa attribute is added to is
1180 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1181 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1182 attribute is added to range 0x100000000-0x180000000 and
1183 0x10a0000000-0x1120000000.
1185 Using this parameter you can do debugging of EFI memmap
1186 related feature. For example, you can do debugging of
1187 Address Range Mirroring feature even if your box
1190 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1191 that is to be dynamically loaded by Linux. If there are
1192 multiple variables with the same name but with different
1193 vendor GUIDs, all of them will be loaded. See
1194 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1197 eisa_irq_edge= [PARISC,HW]
1198 See header of drivers/parisc/eisa.c.
1201 See comment before function elanfreq_setup() in
1202 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1205 Format: { "mq-deadline" | "kyber" | "bfq" }
1206 See Documentation/block/deadline-iosched.rst,
1207 Documentation/block/kyber-iosched.rst and
1208 Documentation/block/bfq-iosched.rst for details.
1210 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1211 Specifies physical address of start of kernel core
1212 image elf header and optionally the size. Generally
1213 kexec loader will pass this option to capture kernel.
1214 See Documentation/admin-guide/kdump/kdump.rst for details.
1216 enable_mtrr_cleanup [X86]
1217 The kernel tries to adjust MTRR layout from continuous
1218 to discrete, to make X server driver able to add WB
1219 entry later. This parameter enables that.
1221 enable_timer_pin_1 [X86]
1222 Enable PIN 1 of APIC timer
1223 Can be useful to work around chipset bugs
1224 (in particular on some ATI chipsets).
1225 The kernel tries to set a reasonable default.
1227 enforcing [SELINUX] Set initial enforcing status.
1229 See security/selinux/Kconfig help text.
1230 0 -- permissive (log only, no denials).
1231 1 -- enforcing (deny and log).
1233 Value can be changed at runtime via /selinux/enforce.
1236 Disable Error Record Serialization Table (ERST)
1239 ether= [HW,NET] Ethernet cards parameters
1240 This option is obsoleted by the "netdev=" option, which
1241 has equivalent usage. See its documentation for details.
1245 Permit 'security.evm' to be updated regardless of
1246 current integrity status.
1250 fail_make_request=[KNL]
1251 General fault injection mechanism.
1252 Format: <interval>,<probability>,<space>,<times>
1253 See also Documentation/fault-injection/.
1256 See Documentation/admin-guide/blockdev/floppy.rst.
1258 force_pal_cache_flush
1259 [IA-64] Avoid check_sal_cache_flush which may hang on
1260 buggy SAL_CACHE_FLUSH implementations. Using this
1261 parameter will force ia64_sal_cache_flush to call
1262 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1265 Forcefully enable Physical Address Extension (PAE).
1266 Many Pentium M systems disable PAE but may have a
1267 functionally usable PAE implementation.
1268 Warning: use of this parameter will taint the kernel
1269 and may cause unknown problems.
1272 [FTRACE] will set and start the specified tracer
1273 as early as possible in order to facilitate early
1276 ftrace_dump_on_oops[=orig_cpu]
1277 [FTRACE] will dump the trace buffers on oops.
1278 If no parameter is passed, ftrace will dump
1279 buffers of all CPUs, but if you pass orig_cpu, it will
1280 dump only the buffer of the CPU that triggered the
1283 ftrace_filter=[function-list]
1284 [FTRACE] Limit the functions traced by the function
1285 tracer at boot up. function-list is a comma separated
1286 list of functions. This list can be changed at run
1287 time by the set_ftrace_filter file in the debugfs
1290 ftrace_notrace=[function-list]
1291 [FTRACE] Do not trace the functions specified in
1292 function-list. This list can be changed at run time
1293 by the set_ftrace_notrace file in the debugfs
1296 ftrace_graph_filter=[function-list]
1297 [FTRACE] Limit the top level callers functions traced
1298 by the function graph tracer at boot up.
1299 function-list is a comma separated list of functions
1300 that can be changed at run time by the
1301 set_graph_function file in the debugfs tracing directory.
1303 ftrace_graph_notrace=[function-list]
1304 [FTRACE] Do not trace from the functions specified in
1305 function-list. This list is a comma separated list of
1306 functions that can be changed at run time by the
1307 set_graph_notrace file in the debugfs tracing directory.
1309 ftrace_graph_max_depth=<uint>
1310 [FTRACE] Used with the function graph tracer. This is
1311 the max depth it will trace into a function. This value
1312 can be changed at run time by the max_graph_depth file
1313 in the tracefs tracing directory. default: 0 (no limit)
1316 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1317 support via parallel port (up to 5 devices per port)
1318 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1319 See also Documentation/input/devices/joystick-parport.rst
1323 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1327 gcov_persist= [GCOV] When non-zero (default), profiling data for
1328 kernel modules is saved and remains accessible via
1329 debugfs, even when the module is unloaded/reloaded.
1330 When zero, profiling data is discarded and associated
1331 debugfs files are removed at module unload time.
1333 goldfish [X86] Enable the goldfish android emulator platform.
1334 Don't use this when you are not running on the
1337 gpt [EFI] Forces disk with valid GPT signature but
1338 invalid Protective MBR to be treated as GPT. If the
1339 primary GPT is corrupted, it enables the backup/alternate
1340 GPT to be used instead.
1342 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1343 the "Enable 0" bit of the configuration register.
1346 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1347 the "Enable 0" bit of the configuration register.
1350 grcan.select= [HW] Select which physical interface to use.
1353 grcan.txsize= [HW] Sets the size of the tx buffer.
1354 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1356 grcan.rxsize= [HW] Sets the size of the rx buffer.
1357 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1360 gpio-mockup.gpio_mockup_ranges
1361 [HW] Sets the ranges of gpiochip of for this device.
1362 Format: <start1>,<end1>,<start2>,<end2>...
1364 hardlockup_all_cpu_backtrace=
1365 [KNL] Should the hard-lockup detector generate
1366 backtraces on all cpus.
1369 hashdist= [KNL,NUMA] Large hashes allocated during boot
1370 are distributed across NUMA nodes. Defaults on
1371 for 64-bit NUMA, off otherwise.
1372 Format: 0 | 1 (for off | on)
1374 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1376 hd= [EIDE] (E)IDE hard drive subsystem geometry
1377 Format: <cyl>,<head>,<sect>
1380 Disable Hardware Error Source Table (HEST) support;
1381 corresponding firmware-first mode error processing
1382 logic will be disabled.
1384 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1385 size of <nn>. This works even on boxes that have no
1386 highmem otherwise. This also works to reduce highmem
1387 size on bigger boxes.
1389 highres= [KNL] Enable/disable high resolution timer mode.
1390 Valid parameters: "on", "off"
1395 hpet= [X86-32,HPET] option to control HPET usage
1396 Format: { enable (default) | disable | force |
1398 disable: disable HPET and use PIT instead
1399 force: allow force enabled of undocumented chips (ICH4,
1401 verbose: show contents of HPET registers during setup
1403 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1404 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1406 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1407 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1408 On x86-64 and powerpc, this option can be specified
1409 multiple times interleaved with hugepages= to reserve
1410 huge pages of different sizes. Valid pages sizes on
1411 x86-64 are 2M (when the CPU supports "pse") and 1G
1412 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1415 [KNL] Should the hung task detector generate panics.
1418 A nonzero value instructs the kernel to panic when a
1419 hung task is detected. The default value is controlled
1420 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1421 option. The value selected by this boot parameter can
1422 be changed later by the kernel.hung_task_panic sysctl.
1424 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1425 terminal devices. Valid values: 0..8
1426 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1427 If specified, z/VM IUCV HVC accepts connections
1428 from listed z/VM user IDs only.
1430 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1431 which allow the hypervisor to 'idle' the
1432 guest on lock contention.
1435 Do not unregister boot console at start. This is only
1436 useful for debugging when something happens in the window
1437 between unregistering the boot console and initializing
1440 i2c_bus= [HW] Override the default board specific I2C bus speed
1441 or register an additional I2C bus that is not
1442 registered from board initialization code.
1446 i8042.debug [HW] Toggle i8042 debug mode
1447 i8042.unmask_kbd_data
1448 [HW] Enable printing of interrupt data from the KBD port
1449 (disabled by default, and as a pre-condition
1450 requires that i8042.debug=1 be enabled)
1451 i8042.direct [HW] Put keyboard port into non-translated mode
1452 i8042.dumbkbd [HW] Pretend that controller can only read data from
1453 keyboard and cannot control its state
1454 (Don't attempt to blink the leds)
1455 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1456 i8042.nokbd [HW] Don't check/create keyboard port
1457 i8042.noloop [HW] Disable the AUX Loopback command while probing
1459 i8042.nomux [HW] Don't check presence of an active multiplexing
1461 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1463 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1464 i8042.reset [HW] Reset the controller during init, cleanup and
1465 suspend-to-ram transitions, only during s2r
1466 transitions, or never reset
1467 Format: { 1 | Y | y | 0 | N | n }
1468 1, Y, y: always reset controller
1469 0, N, n: don't ever reset controller
1470 Default: only on s2r transitions on x86; most other
1471 architectures force reset to be always executed
1472 i8042.unlock [HW] Unlock (ignore) the keylock
1473 i8042.kbdreset [HW] Reset device connected to KBD port
1477 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1478 indicates that the driver is running on unsupported
1480 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1481 does not match list of supported models.
1483 [HW] Report power status in /proc/i8k
1484 (disabled by default)
1485 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1488 i915.invert_brightness=
1489 [DRM] Invert the sense of the variable that is used to
1490 set the brightness of the panel backlight. Normally a
1491 brightness value of 0 indicates backlight switched off,
1492 and the maximum of the brightness value sets the backlight
1493 to maximum brightness. If this parameter is set to 0
1494 (default) and the machine requires it, or this parameter
1495 is set to 1, a brightness value of 0 sets the backlight
1496 to maximum brightness, and the maximum of the brightness
1497 value switches the backlight off.
1498 -1 -- never invert brightness
1499 0 -- machine default
1500 1 -- force brightness inversion
1503 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1505 ide-core.nodma= [HW] (E)IDE subsystem
1506 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1507 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1508 .cdrom .chs .ignore_cable are additional options
1509 See Documentation/ide/ide.rst.
1511 ide-generic.probe-mask= [HW] (E)IDE subsystem
1513 Probe mask for legacy ISA IDE ports. Depending on
1514 platform up to 6 ports are supported, enabled by
1515 setting corresponding bits in the mask to 1. The
1516 default value is 0x0, which has a special meaning.
1517 On systems that have PCI, it triggers scanning the
1518 PCI bus for the first and the second port, which
1519 are then probed. On systems without PCI the value
1520 of 0x0 enables probing the two first ports as if it
1523 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1524 Claim all unknown PCI IDE storage controllers.
1527 Format: idle=poll, idle=halt, idle=nomwait
1528 Poll forces a polling idle loop that can slightly
1529 improve the performance of waking up a idle CPU, but
1530 will use a lot of power and make the system run hot.
1532 idle=halt: Halt is forced to be used for CPU idle.
1533 In such case C2/C3 won't be used again.
1534 idle=nomwait: Disable mwait for CPU C-states
1536 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1537 Format: { strict | legacy | 2008 | relaxed }
1540 Choose which programs will be accepted for execution
1541 based on the IEEE 754 NaN encoding(s) supported by
1542 the FPU and the NaN encoding requested with the value
1543 of an ELF file header flag individually set by each
1544 binary. Hardware implementations are permitted to
1545 support either or both of the legacy and the 2008 NaN
1548 Available settings are as follows:
1549 strict accept binaries that request a NaN encoding
1550 supported by the FPU
1551 legacy only accept legacy-NaN binaries, if supported
1553 2008 only accept 2008-NaN binaries, if supported
1555 relaxed accept any binaries regardless of whether
1556 supported by the FPU
1558 The FPU emulator is always able to support both NaN
1559 encodings, so if no FPU hardware is present or it has
1560 been disabled with 'nofpu', then the settings of
1561 'legacy' and '2008' strap the emulator accordingly,
1562 'relaxed' straps the emulator for both legacy-NaN and
1563 2008-NaN, whereas 'strict' enables legacy-NaN only on
1564 legacy processors and both NaN encodings on MIPS32 or
1567 The setting for ABS.fmt/NEG.fmt instruction execution
1568 mode generally follows that for the NaN encoding,
1569 except where unsupported by hardware.
1571 ignore_loglevel [KNL]
1572 Ignore loglevel setting - this will print /all/
1573 kernel messages to the console. Useful for debugging.
1574 We also add it as printk module parameter, so users
1575 could change it dynamically, usually by
1576 /sys/module/printk/parameters/ignore_loglevel.
1579 Ignore RLIMIT_DATA setting for data mappings,
1580 print warning at first misuse. Can be changed via
1581 /sys/module/kernel/parameters/ignore_rlimit_data.
1583 ihash_entries= [KNL]
1584 Set number of hash buckets for inode cache.
1586 ima_appraise= [IMA] appraise integrity measurements
1587 Format: { "off" | "enforce" | "fix" | "log" }
1590 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1591 The builtin appraise policy appraises all files
1594 ima_canonical_fmt [IMA]
1595 Use the canonical format for the binary runtime
1596 measurements, instead of host native format.
1599 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1603 The list of supported hash algorithms is defined
1604 in crypto/hash_info.h.
1607 The builtin policies to load during IMA setup.
1608 Format: "tcb | appraise_tcb | secure_boot |
1611 The "tcb" policy measures all programs exec'd, files
1612 mmap'd for exec, and all files opened with the read
1613 mode bit set by either the effective uid (euid=0) or
1616 The "appraise_tcb" policy appraises the integrity of
1617 all files owned by root.
1619 The "secure_boot" policy appraises the integrity
1620 of files (eg. kexec kernel image, kernel modules,
1621 firmware, policy, etc) based on file signatures.
1623 The "fail_securely" policy forces file signature
1624 verification failure also on privileged mounted
1625 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1628 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1629 Load a policy which meets the needs of the Trusted
1630 Computing Base. This means IMA will measure all
1631 programs exec'd, files mmap'd for exec, and all files
1632 opened for read by uid=0.
1635 Select one of defined IMA measurements template formats.
1636 Formats: { "ima" | "ima-ng" | "ima-sig" }
1640 [IMA] Define a custom template format.
1641 Format: { "field1|...|fieldN" }
1643 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1644 Format: <min_file_size>
1645 Set the minimal file size for using asynchronous hash.
1646 If left unspecified, ahash usage is disabled.
1648 ahash performance varies for different data sizes on
1649 different crypto accelerators. This option can be used
1650 to achieve the best performance for a particular HW.
1652 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1654 Set hashing buffer size. Default: 4k.
1656 ahash performance varies for different chunk sizes on
1657 different crypto accelerators. This option can be used
1658 to achieve best performance for particular HW.
1662 Run specified binary instead of /sbin/init as init
1665 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1666 for working out where the kernel is dying during
1669 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1670 initcall functions. Useful for debugging built-in
1671 modules and initcalls.
1673 initrd= [BOOT] Specify the location of the initial ramdisk
1675 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1678 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1680 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1682 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1684 init_pkru= [x86] Specify the default memory protection keys rights
1685 register contents for all processes. 0x55555554 by
1686 default (disallow access to all but pkey 0). Can
1687 override in debugfs after boot.
1689 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1692 int_pln_enable [x86] Enable power limit notification interrupt
1694 integrity_audit=[IMA]
1695 Format: { "0" | "1" }
1696 0 -- basic integrity auditing messages. (Default)
1697 1 -- additional integrity auditing messages.
1699 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1701 Enable intel iommu driver.
1703 Disable intel iommu driver.
1704 igfx_off [Default Off]
1705 By default, gfx is mapped as normal device. If a gfx
1706 device has a dedicated DMAR unit, the DMAR unit is
1707 bypassed by not enabling DMAR with this option. In
1708 this case, gfx device will use physical address for
1711 With this option iommu will not optimize to look
1712 for io virtual address below 32-bit forcing dual
1713 address cycle on pci bus for cards supporting greater
1714 than 32-bit addressing. The default is to look
1715 for translation below 32-bit and if not available
1716 then look in the higher range.
1717 strict [Default Off]
1718 With this option on every unmap_single operation will
1719 result in a hardware IOTLB flush operation as opposed
1720 to batching them for performance.
1721 sp_off [Default Off]
1722 By default, super page will be supported if Intel IOMMU
1723 has the capability. With this option, super page will
1726 By default, scalable mode will be disabled even if the
1727 hardware advertises that it has support for the scalable
1728 mode translation. With this option set, scalable mode
1729 will be used on hardware which claims to support it.
1730 tboot_noforce [Default Off]
1731 Do not force the Intel IOMMU enabled under tboot.
1732 By default, tboot will force Intel IOMMU on, which
1733 could harm performance of some high-throughput
1734 devices like 40GBit network cards, even if identity
1736 Note that using this option lowers the security
1737 provided by tboot because it makes the system
1738 vulnerable to DMA attacks.
1740 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1741 0 disables intel_idle and fall back on acpi_idle.
1742 1 to 9 specify maximum depth of C-state.
1746 Do not enable intel_pstate as the default
1747 scaling driver for the supported processors
1749 Use intel_pstate as a scaling driver, but configure it
1750 to work with generic cpufreq governors (instead of
1751 enabling its internal governor). This mode cannot be
1752 used along with the hardware-managed P-states (HWP)
1755 Enable intel_pstate on systems that prohibit it by default
1756 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1757 instead of acpi-cpufreq may disable platform features, such
1758 as thermal controls and power capping, that rely on ACPI
1759 P-States information being indicated to OSPM and therefore
1760 should be used with caution. This option does not work with
1761 processors that aren't supported by the intel_pstate driver
1762 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1764 Do not enable hardware P state control (HWP)
1767 Only load intel_pstate on systems which support
1768 hardware P state control (HWP) if available.
1770 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1771 Description Table, specifies preferred power management
1772 profile as "Enterprise Server" or "Performance Server",
1773 then this feature is turned on by default.
1775 Allow per-logical-CPU P-State performance control limits using
1776 cpufreq sysfs interface
1778 intremap= [X86-64, Intel-IOMMU]
1779 on enable Interrupt Remapping (default)
1780 off disable Interrupt Remapping
1781 nosid disable Source ID checking
1783 BIOS x2APIC opt-out request will be ignored
1784 nopost disable Interrupt Posting
1786 iomem= Disable strict checking of access to MMIO memory
1787 strict regions from userspace.
1802 nobypass [PPC/POWERNV]
1803 Disable IOMMU bypass, using IOMMU for PCI devices.
1805 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1806 Format: { "0" | "1" }
1808 Request that DMA unmap operations use deferred
1809 invalidation of hardware TLBs, for increased
1810 throughput at the cost of reduced device isolation.
1811 Will fall back to strict mode if not supported by
1812 the relevant IOMMU driver.
1813 1 - Strict mode (default).
1814 DMA unmap operations invalidate IOMMU hardware TLBs
1818 [ARM64] Configure DMA to bypass the IOMMU by default.
1819 Format: { "0" | "1" }
1820 0 - Use IOMMU translation for DMA.
1821 1 - Bypass the IOMMU for DMA.
1822 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1824 io7= [HW] IO7 for Marvel based alpha systems
1825 See comment before marvel_specify_io7 in
1826 arch/alpha/kernel/core_marvel.c.
1828 io_delay= [X86] I/O delay method
1830 Standard port 0x80 based delay
1832 Alternate port 0xed based delay (needed on some systems)
1834 Simple two microseconds delay
1839 See Documentation/filesystems/nfs/nfsroot.txt.
1841 ipcmni_extend [KNL] Extend the maximum number of unique System V
1842 IPC identifiers from 32,768 to 16,777,216.
1844 irqaffinity= [SMP] Set the default irq affinity mask
1845 The argument is a cpu list, as described above.
1847 irqchip.gicv2_force_probe=
1850 Force the kernel to look for the second 4kB page
1851 of a GICv2 controller even if the memory range
1852 exposed by the device tree is too small.
1854 irqchip.gicv3_nolpi=
1856 Force the kernel to ignore the availability of
1857 LPIs (and by consequence ITSs). Intended for system
1858 that use the kernel as a bootloader, and thus want
1859 to let secondary kernels in charge of setting up
1862 irqchip.gicv3_pseudo_nmi= [ARM64]
1863 Enables support for pseudo-NMIs in the kernel. This
1864 requires the kernel to be built with
1865 CONFIG_ARM64_PSEUDO_NMI.
1868 When an interrupt is not handled search all handlers
1869 for it. Intended to get systems with badly broken
1873 When an interrupt is not handled search all handlers
1874 for it. Also check all handlers each timer
1875 interrupt. Intended to get systems with badly broken
1879 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1881 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1882 [Deprecated - use cpusets instead]
1883 Format: [flag-list,]<cpu-list>
1885 Specify one or more CPUs to isolate from disturbances
1886 specified in the flag list (default: domain):
1889 Disable the tick when a single task runs.
1891 A residual 1Hz tick is offloaded to workqueues, which you
1892 need to affine to housekeeping through the global
1893 workqueue's affinity configured via the
1894 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1895 by using the 'domain' flag described below.
1897 NOTE: by default the global workqueue runs on all CPUs,
1898 so to protect individual CPUs the 'cpumask' file has to
1899 be configured manually after bootup.
1902 Isolate from the general SMP balancing and scheduling
1903 algorithms. Note that performing domain isolation this way
1904 is irreversible: it's not possible to bring back a CPU to
1905 the domains once isolated through isolcpus. It's strongly
1906 advised to use cpusets instead to disable scheduler load
1907 balancing through the "cpuset.sched_load_balance" file.
1908 It offers a much more flexible interface where CPUs can
1909 move in and out of an isolated set anytime.
1911 You can move a process onto or off an "isolated" CPU via
1912 the CPU affinity syscalls or cpuset.
1913 <cpu number> begins at 0 and the maximum value is
1914 "number of CPUs in system - 1".
1916 The format of <cpu-list> is described above.
1922 ivrs_ioapic [HW,X86_64]
1923 Provide an override to the IOAPIC-ID<->DEVICE-ID
1924 mapping provided in the IVRS ACPI table. For
1925 example, to map IOAPIC-ID decimal 10 to
1926 PCI device 00:14.0 write the parameter as:
1927 ivrs_ioapic[10]=00:14.0
1929 ivrs_hpet [HW,X86_64]
1930 Provide an override to the HPET-ID<->DEVICE-ID
1931 mapping provided in the IVRS ACPI table. For
1932 example, to map HPET-ID decimal 0 to
1933 PCI device 00:14.0 write the parameter as:
1934 ivrs_hpet[0]=00:14.0
1936 ivrs_acpihid [HW,X86_64]
1937 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1938 mapping provided in the IVRS ACPI table. For
1939 example, to map UART-HID:UID AMD0020:0 to
1940 PCI device 00:14.5 write the parameter as:
1941 ivrs_acpihid[00:14.5]=AMD0020:0
1943 js= [HW,JOY] Analog joystick
1944 See Documentation/input/joydev/joystick.rst.
1947 When CONFIG_RANDOMIZE_BASE is set, this disables
1948 kernel and module base offset ASLR (Address Space
1949 Layout Randomization).
1952 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1953 report on every invalid memory access. Without this
1954 parameter KASAN will print report only for the first
1959 kernelcore= [KNL,X86,IA-64,PPC]
1960 Format: nn[KMGTPE] | nn% | "mirror"
1961 This parameter specifies the amount of memory usable by
1962 the kernel for non-movable allocations. The requested
1963 amount is spread evenly throughout all nodes in the
1964 system as ZONE_NORMAL. The remaining memory is used for
1965 movable memory in its own zone, ZONE_MOVABLE. In the
1966 event, a node is too small to have both ZONE_NORMAL and
1967 ZONE_MOVABLE, kernelcore memory will take priority and
1968 other nodes will have a larger ZONE_MOVABLE.
1970 ZONE_MOVABLE is used for the allocation of pages that
1971 may be reclaimed or moved by the page migration
1972 subsystem. Note that allocations like PTEs-from-HighMem
1973 still use the HighMem zone if it exists, and the Normal
1974 zone if it does not.
1976 It is possible to specify the exact amount of memory in
1977 the form of "nn[KMGTPE]", a percentage of total system
1978 memory in the form of "nn%", or "mirror". If "mirror"
1979 option is specified, mirrored (reliable) memory is used
1980 for non-movable allocations and remaining memory is used
1981 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1982 are exclusive, so you cannot specify multiple forms.
1984 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1985 Format: <Controller#>[,poll interval]
1986 The controller # is the number of the ehci usb debug
1987 port as it is probed via PCI. The poll interval is
1988 optional and is the number seconds in between
1989 each poll cycle to the debug port in case you need
1990 the functionality for interrupting the kernel with
1991 gdb or control-c on the dbgp connection. When
1992 not using this parameter you use sysrq-g to break into
1993 the kernel debugger.
1995 kgdboc= [KGDB,HW] kgdb over consoles.
1996 Requires a tty driver that supports console polling,
1997 or a supported polling keyboard driver (non-usb).
1998 Serial only format: <serial_device>[,baud]
1999 keyboard only format: kbd
2000 keyboard and serial format: kbd,<serial_device>[,baud]
2001 Optional Kernel mode setting:
2002 kms, kbd format: kms,kbd
2003 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2005 kgdbwait [KGDB] Stop kernel execution and enter the
2006 kernel debugger at the earliest opportunity.
2008 kmac= [MIPS] korina ethernet MAC address.
2009 Configure the RouterBoard 532 series on-chip
2010 Ethernet adapter MAC address.
2012 kmemleak= [KNL] Boot-time kmemleak enable/disable
2013 Valid arguments: on, off
2015 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2018 kprobe_event=[probe-list]
2019 [FTRACE] Add kprobe events and enable at boot time.
2020 The probe-list is a semicolon delimited list of probe
2021 definitions. Each definition is same as kprobe_events
2022 interface, but the parameters are comma delimited.
2023 For example, to add a kprobe event on vfs_read with
2024 arg1 and arg2, add to the command line;
2026 kprobe_event=p,vfs_read,$arg1,$arg2
2028 See also Documentation/trace/kprobetrace.rst "Kernel
2029 Boot Parameter" section.
2031 kpti= [ARM64] Control page table isolation of user
2032 and kernel address spaces.
2033 Default: enabled on cores which need mitigation.
2037 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2038 Default is 0 (don't ignore, but inject #GP)
2040 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2041 Default is false (don't support).
2043 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2047 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2048 Default is 1 (enabled)
2050 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2052 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2054 kvm-arm.vgic_v3_group0_trap=
2055 [KVM,ARM] Trap guest accesses to GICv3 group-0
2058 kvm-arm.vgic_v3_group1_trap=
2059 [KVM,ARM] Trap guest accesses to GICv3 group-1
2062 kvm-arm.vgic_v3_common_trap=
2063 [KVM,ARM] Trap guest accesses to GICv3 common
2066 kvm-arm.vgic_v4_enable=
2067 [KVM,ARM] Allow use of GICv4 for direct injection of
2070 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2071 (virtualized MMU) support on capable Intel chips.
2072 Default is 1 (enabled)
2074 kvm-intel.emulate_invalid_guest_state=
2075 [KVM,Intel] Enable emulation of invalid guest states
2076 Default is 0 (disabled)
2078 kvm-intel.flexpriority=
2079 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2080 Default is 1 (enabled)
2083 [KVM,Intel] Enable VMX nesting (nVMX).
2084 Default is 0 (disabled)
2086 kvm-intel.unrestricted_guest=
2087 [KVM,Intel] Disable unrestricted guest feature
2088 (virtualized real and unpaged mode) on capable
2089 Intel chips. Default is 1 (enabled)
2091 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2094 Valid arguments: never, cond, always
2096 always: L1D cache flush on every VMENTER.
2097 cond: Flush L1D on VMENTER only when the code between
2098 VMEXIT and VMENTER can leak host memory.
2099 never: Disables the mitigation
2101 Default is cond (do L1 cache flush in specific instances)
2103 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2104 feature (tagged TLBs) on capable Intel chips.
2105 Default is 1 (enabled)
2107 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2110 The kernel PTE inversion protection is unconditionally
2111 enabled and cannot be disabled.
2114 Provides all available mitigations for the
2115 L1TF vulnerability. Disables SMT and
2116 enables all mitigations in the
2117 hypervisors, i.e. unconditional L1D flush.
2119 SMT control and L1D flush control via the
2120 sysfs interface is still possible after
2121 boot. Hypervisors will issue a warning
2122 when the first VM is started in a
2123 potentially insecure configuration,
2124 i.e. SMT enabled or L1D flush disabled.
2127 Same as 'full', but disables SMT and L1D
2128 flush runtime control. Implies the
2129 'nosmt=force' command line option.
2130 (i.e. sysfs control of SMT is disabled.)
2133 Leaves SMT enabled and enables the default
2134 hypervisor mitigation, i.e. conditional
2137 SMT control and L1D flush control via the
2138 sysfs interface is still possible after
2139 boot. Hypervisors will issue a warning
2140 when the first VM is started in a
2141 potentially insecure configuration,
2142 i.e. SMT enabled or L1D flush disabled.
2146 Disables SMT and enables the default
2147 hypervisor mitigation.
2149 SMT control and L1D flush control via the
2150 sysfs interface is still possible after
2151 boot. Hypervisors will issue a warning
2152 when the first VM is started in a
2153 potentially insecure configuration,
2154 i.e. SMT enabled or L1D flush disabled.
2157 Same as 'flush', but hypervisors will not
2158 warn when a VM is started in a potentially
2159 insecure configuration.
2162 Disables hypervisor mitigations and doesn't
2164 It also drops the swap size and available
2165 RAM limit restriction on both hypervisor and
2170 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2176 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2179 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2180 value for LAPIC timer one-shot implementation. Default
2181 back to the programmable timer unit in the LAPIC.
2183 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2186 libata.dma= [LIBATA] DMA control
2187 libata.dma=0 Disable all PATA and SATA DMA
2188 libata.dma=1 PATA and SATA Disk DMA only
2189 libata.dma=2 ATAPI (CDROM) DMA only
2190 libata.dma=4 Compact Flash DMA only
2191 Combinations also work, so libata.dma=3 enables DMA
2192 for disks and CDROMs, but not CFs.
2194 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2195 libata.ignore_hpa=0 keep BIOS limits (default)
2196 libata.ignore_hpa=1 ignore limits, using full disk
2198 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2202 libata.force= [LIBATA] Force configurations. The format is comma
2203 separated list of "[ID:]VAL" where ID is
2204 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2205 matching port, link or device. Basically, it matches
2206 the ATA ID string printed on console by libata. If
2207 the whole ID part is omitted, the last PORT and DEVICE
2208 values are used. If ID hasn't been specified yet, the
2209 configuration applies to all ports, links and devices.
2211 If only DEVICE is omitted, the parameter applies to
2212 the port and all links and devices behind it. DEVICE
2213 number of 0 either selects the first device or the
2214 first fan-out link behind PMP device. It does not
2215 select the host link. DEVICE number of 15 selects the
2216 host link and device attached to it.
2218 The VAL specifies the configuration to force. As long
2219 as there's no ambiguity shortcut notation is allowed.
2220 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2221 The following configurations can be forced.
2223 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2224 Any ID with matching PORT is used.
2226 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2228 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2229 udma[/][16,25,33,44,66,100,133] notation is also
2232 * [no]ncq: Turn on or off NCQ.
2234 * [no]ncqtrim: Turn off queued DSM TRIM.
2236 * nohrst, nosrst, norst: suppress hard, soft
2239 * rstonce: only attempt one reset during
2240 hot-unplug link recovery
2242 * dump_id: dump IDENTIFY data.
2244 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2246 * disable: Disable this device.
2248 If there are multiple matching configurations changing
2249 the same attribute, the last one is used.
2251 memblock=debug [KNL] Enable memblock debug messages.
2253 load_ramdisk= [RAM] List of ramdisks to load from floppy
2254 See Documentation/admin-guide/blockdev/ramdisk.rst.
2256 lockd.nlm_grace_period=P [NFS] Assign grace period.
2259 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2262 lockd.nlm_timeout=T [NFS] Assign timeout value.
2265 lockd.nlm_udpport=M [NFS] Assign UDP port.
2268 locktorture.nreaders_stress= [KNL]
2269 Set the number of locking read-acquisition kthreads.
2270 Defaults to being automatically set based on the
2271 number of online CPUs.
2273 locktorture.nwriters_stress= [KNL]
2274 Set the number of locking write-acquisition kthreads.
2276 locktorture.onoff_holdoff= [KNL]
2277 Set time (s) after boot for CPU-hotplug testing.
2279 locktorture.onoff_interval= [KNL]
2280 Set time (s) between CPU-hotplug operations, or
2281 zero to disable CPU-hotplug testing.
2283 locktorture.shuffle_interval= [KNL]
2284 Set task-shuffle interval (jiffies). Shuffling
2285 tasks allows some CPUs to go into dyntick-idle
2286 mode during the locktorture test.
2288 locktorture.shutdown_secs= [KNL]
2289 Set time (s) after boot system shutdown. This
2290 is useful for hands-off automated testing.
2292 locktorture.stat_interval= [KNL]
2293 Time (s) between statistics printk()s.
2295 locktorture.stutter= [KNL]
2296 Time (s) to stutter testing, for example,
2297 specifying five seconds causes the test to run for
2298 five seconds, wait for five seconds, and so on.
2299 This tests the locking primitive's ability to
2300 transition abruptly to and from idle.
2302 locktorture.torture_type= [KNL]
2303 Specify the locking implementation to test.
2305 locktorture.verbose= [KNL]
2306 Enable additional printk() statements.
2308 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2311 loglevel= All Kernel Messages with a loglevel smaller than the
2312 console loglevel will be printed to the console. It can
2313 also be changed with klogd or other programs. The
2314 loglevels are defined as follows:
2316 0 (KERN_EMERG) system is unusable
2317 1 (KERN_ALERT) action must be taken immediately
2318 2 (KERN_CRIT) critical conditions
2319 3 (KERN_ERR) error conditions
2320 4 (KERN_WARNING) warning conditions
2321 5 (KERN_NOTICE) normal but significant condition
2322 6 (KERN_INFO) informational
2323 7 (KERN_DEBUG) debug-level messages
2325 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2326 in bytes. n must be a power of two and greater
2327 than the minimal size. The minimal size is defined
2328 by LOG_BUF_SHIFT kernel config parameter. There is
2329 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2330 that allows to increase the default size depending on
2331 the number of CPUs. See init/Kconfig for more details.
2333 logo.nologo [FB] Disables display of the built-in Linux logo.
2334 This may be used to provide more screen space for
2335 kernel log messages and is useful when debugging
2336 kernel boot problems.
2338 lp=0 [LP] Specify parallel ports to use, e.g,
2339 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2340 lp=reset first parallel port). 'lp=0' disables the
2341 lp=auto printer driver. 'lp=reset' (which can be
2342 specified in addition to the ports) causes
2343 attached printers to be reset. Using
2344 lp=port1,port2,... specifies the parallel ports
2345 to associate lp devices with, starting with
2346 lp0. A port specification may be 'none' to skip
2347 that lp device, or a parport name such as
2348 'parport0'. Specifying 'lp=auto' instead of a
2349 port specification list means that device IDs
2350 from each port should be examined, to see if
2351 an IEEE 1284-compliant printer is attached; if
2352 so, the driver will manage that printer.
2353 See also header of drivers/char/lp.c.
2356 Sets loops_per_jiffy to given constant, thus avoiding
2357 time-consuming boot-time autodetection (up to 250 ms per
2358 CPU). 0 enables autodetection (default). To determine
2359 the correct value for your kernel, boot with normal
2360 autodetection and see what value is printed. Note that
2361 on SMP systems the preset will be applied to all CPUs,
2362 which is likely to cause problems if your CPUs need
2363 significantly divergent settings. An incorrect value
2364 will cause delays in the kernel to be wrong, leading to
2365 unpredictable I/O errors and other breakage. Although
2366 unlikely, in the extreme case this might damage your
2370 Format: <io>,<irq>,<dma>
2372 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2375 [SECURITY] Choose order of LSM initialization. This
2376 overrides CONFIG_LSM, and the "security=" parameter.
2378 machvec= [IA-64] Force the use of a particular machine-vector
2379 (machvec) in a generic kernel.
2380 Example: machvec=hpzx1_swiotlb
2382 machtype= [Loongson] Share the same kernel image file between different
2384 Example: machtype=lemote-yeeloong-2f-7inch
2386 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2387 than or equal to this physical address is ignored.
2389 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2390 will bring up during bootup. maxcpus=n : n >= 0 limits
2391 the kernel to bring up 'n' processors. Surely after
2392 bootup you can bring up the other plugged cpu by executing
2393 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2394 only takes effect during system bootup.
2395 While n=0 is a special case, it is equivalent to "nosmp",
2396 which also disables the IO APIC.
2398 max_loop= [LOOP] The number of loop block devices that get
2399 (loop.max_loop) unconditionally pre-created at init time. The default
2400 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2401 of statically allocating a predefined number, loop
2402 devices can be requested on-demand with the
2403 /dev/loop-control interface.
2405 mce [X86-32] Machine Check Exception
2407 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2409 md= [HW] RAID subsystems devices and level
2410 See Documentation/admin-guide/md.rst.
2413 Format: <first>,<last>
2414 Specifies range of consoles to be captured by the MDA.
2417 Control mitigation for the Micro-architectural Data
2418 Sampling (MDS) vulnerability.
2420 Certain CPUs are vulnerable to an exploit against CPU
2421 internal buffers which can forward information to a
2422 disclosure gadget under certain conditions.
2424 In vulnerable processors, the speculatively
2425 forwarded data can be used in a cache side channel
2426 attack, to access data to which the attacker does
2427 not have direct access.
2429 This parameter controls the MDS mitigation. The
2432 full - Enable MDS mitigation on vulnerable CPUs
2433 full,nosmt - Enable MDS mitigation and disable
2434 SMT on vulnerable CPUs
2435 off - Unconditionally disable MDS mitigation
2437 Not specifying this option is equivalent to
2440 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2442 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2443 Amount of memory to be used when the kernel is not able
2444 to see the whole system memory or for test.
2445 [X86] Work as limiting max address. Use together
2446 with memmap= to avoid physical address space collisions.
2447 Without memmap= PCI devices could be placed at addresses
2448 belonging to unused RAM.
2450 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2454 [KNL,SH] Allow user to override the default size for
2455 per-device physically contiguous DMA buffers.
2457 memhp_default_state=online/offline
2458 [KNL] Set the initial state for the memory hotplug
2459 onlining policy. If not specified, the default value is
2460 set according to the
2461 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2463 See Documentation/admin-guide/mm/memory-hotplug.rst.
2465 memmap=exactmap [KNL,X86] Enable setting of an exact
2466 E820 memory map, as specified by the user.
2467 Such memmap=exactmap lines can be constructed based on
2468 BIOS output or other requirements. See the memmap=nn@ss
2471 memmap=nn[KMG]@ss[KMG]
2472 [KNL] Force usage of a specific region of memory.
2473 Region of memory to be used is from ss to ss+nn.
2474 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2475 which limits max address to nn[KMG].
2476 Multiple different regions can be specified,
2479 memmap=100M@2G,100M#3G,1G!1024G
2481 memmap=nn[KMG]#ss[KMG]
2482 [KNL,ACPI] Mark specific memory as ACPI data.
2483 Region of memory to be marked is from ss to ss+nn.
2485 memmap=nn[KMG]$ss[KMG]
2486 [KNL,ACPI] Mark specific memory as reserved.
2487 Region of memory to be reserved is from ss to ss+nn.
2488 Example: Exclude memory from 0x18690000-0x1869ffff
2489 memmap=64K$0x18690000
2491 memmap=0x10000$0x18690000
2492 Some bootloaders may need an escape character before '$',
2493 like Grub2, otherwise '$' and the following number
2496 memmap=nn[KMG]!ss[KMG]
2497 [KNL,X86] Mark specific memory as protected.
2498 Region of memory to be used, from ss to ss+nn.
2499 The memory region may be marked as e820 type 12 (0xc)
2500 and is NVDIMM or ADR memory.
2502 memmap=<size>%<offset>-<oldtype>+<newtype>
2503 [KNL,ACPI] Convert memory within the specified region
2504 from <oldtype> to <newtype>. If "-<oldtype>" is left
2505 out, the whole region will be marked as <newtype>,
2506 even if previously unavailable. If "+<newtype>" is left
2507 out, matching memory will be removed. Types are
2508 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2509 3 = ACPI, 12 = PRAM.
2511 memory_corruption_check=0/1 [X86]
2512 Some BIOSes seem to corrupt the first 64k of
2513 memory when doing things like suspend/resume.
2514 Setting this option will scan the memory
2515 looking for corruption. Enabling this will
2516 both detect corruption and prevent the kernel
2517 from using the memory being corrupted.
2518 However, its intended as a diagnostic tool; if
2519 repeatable BIOS-originated corruption always
2520 affects the same memory, you can use memmap=
2521 to prevent the kernel from using that memory.
2523 memory_corruption_check_size=size [X86]
2524 By default it checks for corruption in the low
2525 64k, making this memory unavailable for normal
2526 use. Use this parameter to scan for
2527 corruption in more or less memory.
2529 memory_corruption_check_period=seconds [X86]
2530 By default it checks for corruption every 60
2531 seconds. Use this parameter to check at some
2532 other rate. 0 disables periodic checking.
2534 memtest= [KNL,X86,ARM,PPC] Enable memtest
2536 default : 0 <disable>
2537 Specifies the number of memtest passes to be
2538 performed. Each pass selects another test
2539 pattern from a given set of patterns. Memtest
2540 fills the memory with this pattern, validates
2541 memory contents and reserves bad memory
2542 regions that are detected.
2544 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2545 Valid arguments: on, off
2546 Default (depends on kernel configuration option):
2547 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2548 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2549 mem_encrypt=on: Activate SME
2550 mem_encrypt=off: Do not activate SME
2552 Refer to Documentation/virtual/kvm/amd-memory-encryption.rst
2553 for details on when memory encryption can be activated.
2555 mem_sleep_default= [SUSPEND] Default system suspend mode:
2556 s2idle - Suspend-To-Idle
2557 shallow - Power-On Suspend or equivalent (if supported)
2558 deep - Suspend-To-RAM or equivalent (if supported)
2559 See Documentation/admin-guide/pm/sleep-states.rst.
2561 meye.*= [HW] Set MotionEye Camera parameters
2562 See Documentation/media/v4l-drivers/meye.rst.
2564 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2565 Multi-Function General Purpose Timers on AMD Geode
2568 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2569 the BIOS has incorrectly applied a workaround. TinyBIOS
2570 version 0.98 is known to be affected, 0.99 fixes the
2571 problem by letting the user disable the workaround.
2575 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2576 physical address is ignored.
2578 mini2440= [ARM,HW,KNL]
2579 Format:[0..2][b][c][t]
2581 MINI2440 configuration specification:
2582 0 - The attached screen is the 3.5" TFT
2583 1 - The attached screen is the 7" TFT
2584 2 - The VGA Shield is attached (1024x768)
2585 Leaving out the screen size parameter will not load
2586 the TFT driver, and the framebuffer will be left
2588 b - Enable backlight. The TFT backlight pin will be
2589 linked to the kernel VESA blanking code and a GPIO
2590 LED. This parameter is not necessary when using the
2592 c - Enable the s3c camera interface.
2593 t - Reserved for enabling touchscreen support. The
2594 touchscreen support is not enabled in the mainstream
2595 kernel as of 2.6.30, a preliminary port can be found
2596 in the "bleeding edge" mini2440 support kernel at
2597 http://repo.or.cz/w/linux-2.6/mini2440.git
2600 [X86,PPC,S390,ARM64] Control optional mitigations for
2601 CPU vulnerabilities. This is a set of curated,
2602 arch-independent options, each of which is an
2603 aggregation of existing arch-specific options.
2606 Disable all optional CPU mitigations. This
2607 improves system performance, but it may also
2608 expose users to several CPU vulnerabilities.
2609 Equivalent to: nopti [X86,PPC]
2613 nospectre_v2 [X86,PPC,S390,ARM64]
2614 spectre_v2_user=off [X86]
2615 spec_store_bypass_disable=off [X86,PPC]
2616 ssbd=force-off [ARM64]
2621 Mitigate all CPU vulnerabilities, but leave SMT
2622 enabled, even if it's vulnerable. This is for
2623 users who don't want to be surprised by SMT
2624 getting disabled across kernel upgrades, or who
2625 have other ways of avoiding SMT-based attacks.
2626 Equivalent to: (default behavior)
2629 Mitigate all CPU vulnerabilities, disabling SMT
2630 if needed. This is for users who always want to
2631 be fully mitigated, even if it means losing SMT.
2632 Equivalent to: l1tf=flush,nosmt [X86]
2633 mds=full,nosmt [X86]
2636 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2637 parameter allows control of the logging verbosity for
2638 the additional memory initialisation checks. A value
2639 of 0 disables mminit logging and a level of 4 will
2640 log everything. Information is printed at KERN_DEBUG
2641 so loglevel=8 may also need to be specified.
2644 [KNL] When CONFIG_MODULE_SIG is set, this means that
2645 modules without (valid) signatures will fail to load.
2646 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2647 is always true, so this option does nothing.
2649 module_blacklist= [KNL] Do not load a comma-separated list of
2650 modules. Useful for debugging problem modules.
2653 [MOUSE] Maximum time between finger touching and
2654 leaving touchpad surface for touch to be considered
2655 a tap and be reported as a left button click (for
2656 touchpads working in absolute mode only).
2658 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2659 reporting absolute coordinates, such as tablets
2660 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2661 reporting absolute coordinates, such as tablets
2663 movablecore= [KNL,X86,IA-64,PPC]
2664 Format: nn[KMGTPE] | nn%
2665 This parameter is the complement to kernelcore=, it
2666 specifies the amount of memory used for migratable
2667 allocations. If both kernelcore and movablecore is
2668 specified, then kernelcore will be at *least* the
2669 specified value but may be more. If movablecore on its
2670 own is specified, the administrator must be careful
2671 that the amount of memory usable for all allocations
2674 movable_node [KNL] Boot-time switch to make hotplugable memory
2675 NUMA nodes to be movable. This means that the memory
2676 of such nodes will be usable only for movable
2677 allocations which rules out almost all kernel
2678 allocations. Use with caution!
2680 MTD_Partition= [MTD]
2681 Format: <name>,<region-number>,<size>,<offset>
2683 MTD_Region= [MTD] Format:
2684 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2687 See drivers/mtd/cmdlinepart.c.
2689 multitce=off [PPC] This parameter disables the use of the pSeries
2690 firmware feature for updating multiple TCE entries
2693 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2695 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2697 boundary - index of last SLC block on Flex-OneNAND.
2698 The remaining blocks are configured as MLC blocks.
2699 lock - Configure if Flex-OneNAND boundary should be locked.
2700 Once locked, the boundary cannot be changed.
2701 1 indicates lock status, 0 indicates unlock status.
2704 ARM/S3C2412 JIVE boot control
2706 See arch/arm/mach-s3c2412/mach-jive.c
2708 mtouchusb.raw_coordinates=
2709 [HW] Make the MicroTouch USB driver use raw coordinates
2710 ('y', default) or cooked coordinates ('n')
2712 mtrr_chunk_size=nn[KMG] [X86]
2713 used for mtrr cleanup. It is largest continuous chunk
2714 that could hold holes aka. UC entries.
2716 mtrr_gran_size=nn[KMG] [X86]
2717 Used for mtrr cleanup. It is granularity of mtrr block.
2719 Large value could prevent small alignment from
2722 mtrr_spare_reg_nr=n [X86]
2724 Range: 0,7 : spare reg number
2726 Used for mtrr cleanup. It is spare mtrr entries number.
2727 Set to 2 or more if your graphical card needs more.
2729 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2731 netdev= [NET] Network devices parameters
2732 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2733 Note that mem_start is often overloaded to mean
2734 something different and driver-specific.
2735 This usage is only documented in each driver source
2739 [NETFILTER] Enable connection tracking flow accounting
2740 0 to disable accounting
2741 1 to enable accounting
2744 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2745 See Documentation/filesystems/nfs/nfsroot.txt.
2747 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2748 See Documentation/filesystems/nfs/nfsroot.txt.
2750 nfsrootdebug [NFS] enable nfsroot debugging messages.
2751 See Documentation/filesystems/nfs/nfsroot.txt.
2753 nfs.callback_nr_threads=
2754 [NFSv4] set the total number of threads that the
2755 NFS client will assign to service NFSv4 callback
2758 nfs.callback_tcpport=
2759 [NFS] set the TCP port on which the NFSv4 callback
2760 channel should listen.
2763 [NFS] sets the pathname to the program which is used
2764 to update the NFS client cache entries.
2766 nfs.cache_getent_timeout=
2767 [NFS] sets the timeout after which an attempt to
2768 update a cache entry is deemed to have failed.
2770 nfs.idmap_cache_timeout=
2771 [NFS] set the maximum lifetime for idmapper cache
2775 [NFS] enable 64-bit inode numbers.
2776 If zero, the NFS client will fake up a 32-bit inode
2777 number for the readdir() and stat() syscalls instead
2778 of returning the full 64-bit number.
2779 The default is to return 64-bit inode numbers.
2781 nfs.max_session_cb_slots=
2782 [NFSv4.1] Sets the maximum number of session
2783 slots the client will assign to the callback
2784 channel. This determines the maximum number of
2785 callbacks the client will process in parallel for
2786 a particular server.
2788 nfs.max_session_slots=
2789 [NFSv4.1] Sets the maximum number of session slots
2790 the client will attempt to negotiate with the server.
2791 This limits the number of simultaneous RPC requests
2792 that the client can send to the NFSv4.1 server.
2793 Note that there is little point in setting this
2794 value higher than the max_tcp_slot_table_limit.
2796 nfs.nfs4_disable_idmapping=
2797 [NFSv4] When set to the default of '1', this option
2798 ensures that both the RPC level authentication
2799 scheme and the NFS level operations agree to use
2800 numeric uids/gids if the mount is using the
2801 'sec=sys' security flavour. In effect it is
2802 disabling idmapping, which can make migration from
2803 legacy NFSv2/v3 systems to NFSv4 easier.
2804 Servers that do not support this mode of operation
2805 will be autodetected by the client, and it will fall
2806 back to using the idmapper.
2807 To turn off this behaviour, set the value to '0'.
2809 [NFS4] Specify an additional fixed unique ident-
2810 ification string that NFSv4 clients can insert into
2811 their nfs_client_id4 string. This is typically a
2812 UUID that is generated at system install time.
2814 nfs.send_implementation_id =
2815 [NFSv4.1] Send client implementation identification
2816 information in exchange_id requests.
2817 If zero, no implementation identification information
2819 The default is to send the implementation identification
2822 nfs.recover_lost_locks =
2823 [NFSv4] Attempt to recover locks that were lost due
2824 to a lease timeout on the server. Please note that
2825 doing this risks data corruption, since there are
2826 no guarantees that the file will remain unchanged
2827 after the locks are lost.
2828 If you want to enable the kernel legacy behaviour of
2829 attempting to recover these locks, then set this
2831 The default parameter value of '0' causes the kernel
2832 not to attempt recovery of lost locks.
2834 nfs4.layoutstats_timer =
2835 [NFSv4.2] Change the rate at which the kernel sends
2836 layoutstats to the pNFS metadata server.
2838 Setting this to value to 0 causes the kernel to use
2839 whatever value is the default set by the layout
2840 driver. A non-zero value sets the minimum interval
2841 in seconds between layoutstats transmissions.
2843 nfsd.nfs4_disable_idmapping=
2844 [NFSv4] When set to the default of '1', the NFSv4
2845 server will return only numeric uids and gids to
2846 clients using auth_sys, and will accept numeric uids
2847 and gids from such clients. This is intended to ease
2848 migration from NFSv2/v3.
2850 nmi_debug= [KNL,SH] Specify one or more actions to take
2851 when a NMI is triggered.
2852 Format: [state][,regs][,debounce][,die]
2854 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2855 Format: [panic,][nopanic,][num]
2857 0 - turn hardlockup detector in nmi_watchdog off
2858 1 - turn hardlockup detector in nmi_watchdog on
2859 When panic is specified, panic when an NMI watchdog
2860 timeout occurs (or 'nopanic' to not panic on an NMI
2861 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
2862 To disable both hard and soft lockup detectors,
2863 please see 'nowatchdog'.
2864 This is useful when you use a panic=... timeout and
2865 need the box quickly up again.
2867 These settings can be accessed at runtime via
2868 the nmi_watchdog and hardlockup_panic sysctls.
2870 netpoll.carrier_timeout=
2871 [NET] Specifies amount of time (in seconds) that
2872 netpoll should wait for a carrier. By default netpoll
2875 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2876 emulation library even if a 387 maths coprocessor
2879 no5lvl [X86-64] Disable 5-level paging mode. Forces
2880 kernel to use 4-level paging instead.
2883 [HW] Never suspend the console
2884 Disable suspending of consoles during suspend and
2885 hibernate operations. Once disabled, debugging
2886 messages can reach various consoles while the rest
2887 of the system is being put to sleep (ie, while
2888 debugging driver suspend/resume hooks). This may
2889 not work reliably with all consoles, but is known
2890 to work with serial and VGA consoles.
2891 To facilitate more flexible debugging, we also add
2892 console_suspend, a printk module parameter to control
2893 it. Users could use console_suspend (usually
2894 /sys/module/printk/parameters/console_suspend) to
2895 turn on/off it dynamically.
2897 novmcoredd [KNL,KDUMP]
2898 Disable device dump. Device dump allows drivers to
2899 append dump data to vmcore so you can collect driver
2900 specified debug info. Drivers can append the data
2901 without any limit and this data is stored in memory,
2902 so this may cause significant memory stress. Disabling
2903 device dump can help save memory but the driver debug
2904 data will be no longer available. This parameter
2905 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
2908 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2909 caches in the slab allocator. Saves per-node memory,
2910 but will impact performance.
2914 noaltinstr [S390] Disables alternative instructions patching
2915 (CPU alternatives feature).
2917 noapic [SMP,APIC] Tells the kernel to not make use of any
2918 IOAPICs that may be present in the system.
2920 noautogroup Disable scheduler automatic task group creation.
2922 nobats [PPC] Do not use BATs for mapping kernel lowmem
2923 on "Classic" PPC cores.
2927 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2929 nodelayacct [KNL] Disable per-task delay accounting
2931 nodsp [SH] Disable hardware DSP at boot time.
2933 noefi Disable EFI runtime services support.
2938 On X86-32 available only on PAE configured kernels.
2939 noexec=on: enable non-executable mappings (default)
2940 noexec=off: disable non-executable mappings
2943 Disable SMAP (Supervisor Mode Access Prevention)
2944 even if it is supported by processor.
2947 Disable SMEP (Supervisor Mode Execution Prevention)
2948 even if it is supported by processor.
2951 This affects only 32-bit executables.
2952 noexec32=on: enable non-executable mappings (default)
2953 read doesn't imply executable mappings
2954 noexec32=off: disable non-executable mappings
2955 read implies executable mappings
2957 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2959 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2960 register save and restore. The kernel will only save
2961 legacy floating-point registers on task switch.
2963 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings.
2965 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2966 Equivalent to smt=1.
2968 [KNL,x86] Disable symmetric multithreading (SMT).
2969 nosmt=force: Force disable SMT, cannot be undone
2970 via the sysfs control file.
2972 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2973 check bypass). With this option data leaks are possible
2976 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
2977 the Spectre variant 2 (indirect branch prediction)
2978 vulnerability. System may allow data leaks with this
2981 nospec_store_bypass_disable
2982 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2984 noxsave [BUGS=X86] Disables x86 extended register state save
2985 and restore using xsave. The kernel will fallback to
2986 enabling legacy floating-point and sse state.
2988 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2989 register states. The kernel will fall back to use
2990 xsave to save the states. By using this parameter,
2991 performance of saving the states is degraded because
2992 xsave doesn't support modified optimization while
2993 xsaveopt supports it on xsaveopt enabled systems.
2995 noxsaves [X86] Disables xsaves and xrstors used in saving and
2996 restoring x86 extended register state in compacted
2997 form of xsave area. The kernel will fall back to use
2998 xsaveopt and xrstor to save and restore the states
2999 in standard form of xsave area. By using this
3000 parameter, xsave area per process might occupy more
3001 memory on xsaves enabled systems.
3003 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
3004 wfi(ARM) instruction doesn't work correctly and not to
3005 use it. This is also useful when using JTAG debugger.
3007 no_file_caps Tells the kernel not to honor file capabilities. The
3008 only way then for a file to be executed with privilege
3009 is to be setuid root or executed by root.
3011 nohalt [IA-64] Tells the kernel not to use the power saving
3012 function PAL_HALT_LIGHT when idle. This increases
3013 power-consumption. On the positive side, it reduces
3014 interrupt wake-up latency, which may improve performance
3015 in certain environments such as networked servers or
3018 nohibernate [HIBERNATION] Disable hibernation and resume.
3020 nohz= [KNL] Boottime enable/disable dynamic ticks
3021 Valid arguments: on, off
3024 nohz_full= [KNL,BOOT,SMP,ISOL]
3025 The argument is a cpu list, as described above.
3026 In kernels built with CONFIG_NO_HZ_FULL=y, set
3027 the specified list of CPUs whose tick will be stopped
3028 whenever possible. The boot CPU will be forced outside
3029 the range to maintain the timekeeping. Any CPUs
3030 in this list will have their RCU callbacks offloaded,
3031 just as if they had also been called out in the
3032 rcu_nocbs= boot parameter.
3034 noiotrap [SH] Disables trapped I/O port accesses.
3036 noirqdebug [X86-32] Disables the code which attempts to detect and
3037 disable unhandled interrupt sources.
3039 no_timer_check [X86,APIC] Disables the code which tests for
3040 broken timer IRQ sources.
3042 noisapnp [ISAPNP] Disables ISA PnP code.
3044 noinitrd [RAM] Tells the kernel not to load any configured
3047 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3049 [Deprecated - use intremap=off]
3053 noinvpcid [X86] Disable the INVPCID cpu feature.
3055 nojitter [IA-64] Disables jitter checking for ITC timers.
3057 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3059 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3063 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3064 clock and use the default one.
3066 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
3067 steal time is computed, but won't influence scheduler
3070 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3072 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3074 noltlbs [PPC] Do not use large page/tlb entries for kernel
3075 lowmem mapping on PPC40x and PPC8xx
3077 nomca [IA-64] Disable machine check abort handling
3079 nomce [X86-32] Disable Machine Check Exception
3081 nomfgpt [X86-32] Disable Multi-Function General Purpose
3082 Timer usage (for AMD Geode machines).
3084 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3085 shutdown the other cpus. Instead use the REBOOT_VECTOR
3088 nomodule Disable module load
3090 nopat [X86] Disable PAT (page attribute table extension of
3091 pagetables) support.
3093 nopcid [X86-64] Disable the PCID cpu feature.
3095 norandmaps Don't use address space randomization. Equivalent to
3096 echo 0 > /proc/sys/kernel/randomize_va_space
3098 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3099 with UP alternatives
3101 nordrand [X86] Disable kernel use of the RDRAND and
3102 RDSEED instructions even if they are supported
3103 by the processor. RDRAND and RDSEED are still
3104 available to user space applications.
3106 noresume [SWSUSP] Disables resume and restores original swap
3109 no-scroll [VGA] Disables scrollback.
3110 This is required for the Braillex ib80-piezo Braille
3111 reader made by F.H. Papenmeier (Germany).
3115 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3117 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3118 and disable the IO APIC. legacy for "maxcpus=0".
3120 nosoftlockup [KNL] Disable the soft-lockup detector.
3122 nosync [HW,M68K] Disables sync negotiation for all devices.
3124 nowatchdog [KNL] Disable both lockup detectors, i.e.
3125 soft-lockup and NMI watchdog (hard-lockup).
3129 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3131 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3132 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3133 Some features depend on CPU0. Known dependencies are:
3134 1. Resume from suspend/hibernate depends on CPU0.
3135 Suspend/hibernate will fail if CPU0 is offline and you
3136 need to online CPU0 before suspend/hibernate.
3137 2. PIC interrupts also depend on CPU0. CPU0 can't be
3138 removed if a PIC interrupt is detected.
3139 It's said poweroff/reboot may depend on CPU0 on some
3140 machines although I haven't seen such issues so far
3141 after CPU0 is offline on a few tested machines.
3142 If the dependencies are under your control, you can
3143 turn on cpu0_hotplug.
3145 nps_mtm_hs_ctr= [KNL,ARC]
3146 This parameter sets the maximum duration, in
3147 cycles, each HW thread of the CTOP can run
3148 without interruptions, before HW switches it.
3149 The actual maximum duration is 16 times this
3151 Format: integer between 1 and 255
3154 nptcg= [IA-64] Override max number of concurrent global TLB
3155 purges which is reported from either PAL_VM_SUMMARY or
3158 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3159 could support. nr_cpus=n : n >= 1 limits the kernel to
3160 support 'n' processors. It could be larger than the
3161 number of already plugged CPU during bootup, later in
3162 runtime you can physically add extra cpu until it reaches
3163 n. So during boot up some boot time memory for per-cpu
3164 variables need be pre-allocated for later physical cpu
3167 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3169 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3170 Allowed values are enable and disable
3172 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3173 'node', 'default' can be specified
3174 This can be set from sysctl after boot.
3175 See Documentation/admin-guide/sysctl/vm.rst for details.
3177 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3178 See Documentation/debugging-via-ohci1394.txt for more
3181 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3182 Rather than timing out after 20 ms if an EC
3183 command is not properly ACKed, override the length
3184 of the timeout. We have interrupts disabled while
3185 waiting for the ACK, so if this is set too high
3186 interrupts *may* be lost!
3188 omap_mux= [OMAP] Override bootloader pin multiplexing.
3189 Format: <mux_mode0.mode_name=value>...
3190 For example, to override I2C bus2:
3191 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3193 oprofile.timer= [HW]
3194 Use timer interrupt instead of performance counters
3196 oprofile.cpu_type= Force an oprofile cpu type
3197 This might be useful if you have an older oprofile
3198 userland or if you want common events.
3199 Format: { arch_perfmon }
3200 arch_perfmon: [X86] Force use of architectural
3201 perfmon on Intel CPUs instead of the
3202 CPU specific event set.
3203 timer: [X86] Force use of architectural NMI
3204 timer mode (see also oprofile.timer
3205 for generic hr timer mode)
3207 oops=panic Always panic on oopses. Default is to just kill the
3208 process, but there is a small probability of
3209 deadlocking the machine.
3210 This will also cause panics on machine check exceptions.
3211 Useful together with panic=30 to trigger a reboot.
3214 [KNL] Boolean flag to control whether the page allocator
3215 should randomize its free lists. The randomization may
3216 be automatically enabled if the kernel detects it is
3217 running on a platform with a direct-mapped memory-side
3218 cache, and this parameter can be used to
3219 override/disable that behavior. The state of the flag
3220 can be read from sysfs at:
3221 /sys/module/page_alloc/parameters/shuffle.
3223 page_owner= [KNL] Boot-time page_owner enabling option.
3224 Storage of the information about who allocated
3225 each page is disabled in default. With this switch,
3227 on: enable the feature
3229 page_poison= [KNL] Boot-time parameter changing the state of
3230 poisoning on the buddy allocator, available with
3231 CONFIG_PAGE_POISONING=y.
3232 off: turn off poisoning (default)
3233 on: turn on poisoning
3235 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3236 timeout > 0: seconds before rebooting
3237 timeout = 0: wait forever
3238 timeout < 0: reboot immediately
3241 panic_print= Bitmask for printing system info when panic happens.
3242 User can chose combination of the following bits:
3243 bit 0: print all tasks info
3244 bit 1: print system memory info
3245 bit 2: print timer info
3246 bit 3: print locks info if CONFIG_LOCKDEP is on
3247 bit 4: print ftrace buffer
3248 bit 5: print all printk messages in buffer
3250 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3253 crash_kexec_post_notifiers
3254 Run kdump after running panic-notifiers and dumping
3255 kmsg. This only for the users who doubt kdump always
3256 succeeds in any situation.
3257 Note that this also increases risks of kdump failure,
3258 because some panic notifiers can make the crashed
3259 kernel more unstable.
3261 parkbd.port= [HW] Parallel port number the keyboard adapter is
3262 connected to, default is 0.
3264 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3265 0 for XT, 1 for AT (default is AT).
3268 parport= [HW,PPT] Specify parallel ports. 0 disables.
3269 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3270 Use 'auto' to force the driver to use any
3271 IRQ/DMA settings detected (the default is to
3272 ignore detected IRQ/DMA settings because of
3273 possible conflicts). You can specify the base
3274 address, IRQ, and DMA settings; IRQ and DMA
3275 should be numbers, or 'auto' (for using detected
3276 settings on that particular port), or 'nofifo'
3277 (to avoid using a FIFO even if it is detected).
3278 Parallel ports are assigned in the order they
3279 are specified on the command line, starting
3282 parport_init_mode= [HW,PPT]
3283 Configure VIA parallel port to operate in
3284 a specific mode. This is necessary on Pegasos
3285 computer where firmware has no options for setting
3286 up parallel port mode and sets it to spp.
3287 Currently this function knows 686a and 8231 chips.
3288 Format: [spp|ps2|epp|ecp|ecpepp]
3291 Halt all CPUs after the first oops has been printed for
3292 the specified number of seconds. This is to be used if
3293 your oopses keep scrolling off the screen.
3298 See header of drivers/block/paride/pcd.c.
3299 See also Documentation/admin-guide/blockdev/paride.rst.
3301 pci=option[,option...] [PCI] various PCI subsystem options.
3303 Some options herein operate on a specific device
3304 or a set of devices (<pci_dev>). These are
3305 specified in one of the following formats:
3307 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3308 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3310 Note: the first format specifies a PCI
3311 bus/device/function address which may change
3312 if new hardware is inserted, if motherboard
3313 firmware changes, or due to changes caused
3314 by other kernel parameters. If the
3315 domain is left unspecified, it is
3316 taken to be zero. Optionally, a path
3317 to a device through multiple device/function
3318 addresses can be specified after the base
3319 address (this is more robust against
3320 renumbering issues). The second format
3321 selects devices using IDs from the
3322 configuration space which may match multiple
3323 devices in the system.
3325 earlydump dump PCI config space before the kernel
3327 off [X86] don't probe for the PCI bus
3328 bios [X86-32] force use of PCI BIOS, don't access
3329 the hardware directly. Use this if your machine
3330 has a non-standard PCI host bridge.
3331 nobios [X86-32] disallow use of PCI BIOS, only direct
3332 hardware access methods are allowed. Use this
3333 if you experience crashes upon bootup and you
3334 suspect they are caused by the BIOS.
3335 conf1 [X86] Force use of PCI Configuration Access
3336 Mechanism 1 (config address in IO port 0xCF8,
3337 data in IO port 0xCFC, both 32-bit).
3338 conf2 [X86] Force use of PCI Configuration Access
3339 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3340 the function, IO port 0xCFA, also 8-bit, sets
3341 bus number. The config space is then accessed
3342 through ports 0xC000-0xCFFF).
3343 See http://wiki.osdev.org/PCI for more info
3344 on the configuration access mechanisms.
3345 noaer [PCIE] If the PCIEAER kernel config parameter is
3346 enabled, this kernel boot option can be used to
3347 disable the use of PCIE advanced error reporting.
3348 nodomains [PCI] Disable support for multiple PCI
3349 root domains (aka PCI segments, in ACPI-speak).
3350 nommconf [X86] Disable use of MMCONFIG for PCI
3352 check_enable_amd_mmconf [X86] check for and enable
3353 properly configured MMIO access to PCI
3354 config space on AMD family 10h CPU
3355 nomsi [MSI] If the PCI_MSI kernel config parameter is
3356 enabled, this kernel boot option can be used to
3357 disable the use of MSI interrupts system-wide.
3358 noioapicquirk [APIC] Disable all boot interrupt quirks.
3359 Safety option to keep boot IRQs enabled. This
3360 should never be necessary.
3361 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3362 primary IO-APIC for bridges that cannot disable
3363 boot IRQs. This fixes a source of spurious IRQs
3364 when the system masks IRQs.
3365 noioapicreroute [APIC] Disable workaround that uses the
3366 boot IRQ equivalent of an IRQ that connects to
3367 a chipset where boot IRQs cannot be disabled.
3368 The opposite of ioapicreroute.
3369 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3370 routing table. These calls are known to be buggy
3371 on several machines and they hang the machine
3372 when used, but on other computers it's the only
3373 way to get the interrupt routing table. Try
3374 this option if the kernel is unable to allocate
3375 IRQs or discover secondary PCI buses on your
3377 rom [X86] Assign address space to expansion ROMs.
3378 Use with caution as certain devices share
3379 address decoders between ROMs and other
3381 norom [X86] Do not assign address space to
3382 expansion ROMs that do not already have
3383 BIOS assigned address ranges.
3384 nobar [X86] Do not assign address space to the
3385 BARs that weren't assigned by the BIOS.
3386 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3387 assigned automatically to PCI devices. You can
3388 make the kernel exclude IRQs of your ISA cards
3390 pirqaddr=0xAAAAA [X86] Specify the physical address
3391 of the PIRQ table (normally generated
3392 by the BIOS) if it is outside the
3393 F0000h-100000h range.
3394 lastbus=N [X86] Scan all buses thru bus #N. Can be
3395 useful if the kernel is unable to find your
3396 secondary buses and you want to tell it
3397 explicitly which ones they are.
3398 assign-busses [X86] Always assign all PCI bus
3399 numbers ourselves, overriding
3400 whatever the firmware may have done.
3401 usepirqmask [X86] Honor the possible IRQ mask stored
3402 in the BIOS $PIR table. This is needed on
3403 some systems with broken BIOSes, notably
3404 some HP Pavilion N5400 and Omnibook XE3
3405 notebooks. This will have no effect if ACPI
3406 IRQ routing is enabled.
3407 noacpi [X86] Do not use ACPI for IRQ routing
3408 or for PCI scanning.
3409 use_crs [X86] Use PCI host bridge window information
3410 from ACPI. On BIOSes from 2008 or later, this
3411 is enabled by default. If you need to use this,
3412 please report a bug.
3413 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3414 If you need to use this, please report a bug.
3415 routeirq Do IRQ routing for all PCI devices.
3416 This is normally done in pci_enable_device(),
3417 so this option is a temporary workaround
3418 for broken drivers that don't call it.
3419 skip_isa_align [X86] do not align io start addr, so can
3420 handle more pci cards
3421 noearly [X86] Don't do any early type 1 scanning.
3422 This might help on some broken boards which
3423 machine check when some devices' config space
3424 is read. But various workarounds are disabled
3425 and some IOMMU drivers will not work.
3426 bfsort Sort PCI devices into breadth-first order.
3427 This sorting is done to get a device
3428 order compatible with older (<= 2.4) kernels.
3429 nobfsort Don't sort PCI devices into breadth-first order.
3430 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3431 tuning and use the BIOS-configured MPS defaults.
3432 pcie_bus_safe Set every device's MPS to the largest value
3433 supported by all devices below the root complex.
3434 pcie_bus_perf Set device MPS to the largest allowable MPS
3435 based on its parent bus. Also set MRRS (Max
3436 Read Request Size) to the largest supported
3437 value (no larger than the MPS that the device
3438 or bus can support) for best performance.
3439 pcie_bus_peer2peer Set every device's MPS to 128B, which
3440 every device is guaranteed to support. This
3441 configuration allows peer-to-peer DMA between
3442 any pair of devices, possibly at the cost of
3443 reduced performance. This also guarantees
3444 that hot-added devices will work.
3445 cbiosize=nn[KMG] The fixed amount of bus space which is
3446 reserved for the CardBus bridge's IO window.
3447 The default value is 256 bytes.
3448 cbmemsize=nn[KMG] The fixed amount of bus space which is
3449 reserved for the CardBus bridge's memory
3450 window. The default value is 64 megabytes.
3453 [<order of align>@]<pci_dev>[; ...]
3454 Specifies alignment and device to reassign
3455 aligned memory resources. How to
3456 specify the device is described above.
3457 If <order of align> is not specified,
3458 PAGE_SIZE is used as alignment.
3459 PCI-PCI bridge can be specified, if resource
3460 windows need to be expanded.
3461 To specify the alignment for several
3462 instances of a device, the PCI vendor,
3463 device, subvendor, and subdevice may be
3464 specified, e.g., 4096@pci:8086:9c22:103c:198f
3465 ecrc= Enable/disable PCIe ECRC (transaction layer
3466 end-to-end CRC checking).
3467 bios: Use BIOS/firmware settings. This is the
3471 hpiosize=nn[KMG] The fixed amount of bus space which is
3472 reserved for hotplug bridge's IO window.
3473 Default size is 256 bytes.
3474 hpmemsize=nn[KMG] The fixed amount of bus space which is
3475 reserved for hotplug bridge's memory window.
3476 Default size is 2 megabytes.
3477 hpbussize=nn The minimum amount of additional bus numbers
3478 reserved for buses below a hotplug bridge.
3480 realloc= Enable/disable reallocating PCI bridge resources
3481 if allocations done by BIOS are too small to
3482 accommodate resources required by all child
3484 off: Turn realloc off
3486 realloc same as realloc=on
3487 noari do not use PCIe ARI.
3488 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3489 do not use PCIe ATS (and IOMMU device IOTLB).
3490 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3491 only look for one device below a PCIe downstream
3493 big_root_window Try to add a big 64bit memory window to the PCIe
3494 root complex on AMD CPUs. Some GFX hardware
3495 can resize a BAR to allow access to all VRAM.
3496 Adding the window is slightly risky (it may
3497 conflict with unreported devices), so this
3499 disable_acs_redir=<pci_dev>[; ...]
3500 Specify one or more PCI devices (in the format
3501 specified above) separated by semicolons.
3502 Each device specified will have the PCI ACS
3503 redirect capabilities forced off which will
3504 allow P2P traffic between devices through
3505 bridges without forcing it upstream. Note:
3506 this removes isolation between devices and
3507 may put more devices in an IOMMU group.
3508 force_floating [S390] Force usage of floating interrupts.
3509 nomio [S390] Do not use MIO instructions.
3511 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3514 force Enable ASPM even on devices that claim not to support it.
3515 WARNING: Forcing ASPM on may cause system lockups.
3517 pcie_ports= [PCIE] PCIe port services handling:
3518 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3519 even if the platform doesn't give the OS permission to
3520 use them. This may cause conflicts if the platform
3521 also tries to use these services.
3522 compat Disable native PCIe services (PME, AER, DPC, PCIe
3525 pcie_port_pm= [PCIE] PCIe port power management handling:
3526 off Disable power management of all PCIe ports
3527 force Forcibly enable power management of all PCIe ports
3529 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3530 nomsi Do not use MSI for native PCIe PME signaling (this makes
3531 all PCIe root ports use INTx for all services).
3533 pcmv= [HW,PCMCIA] BadgePAD 4
3537 Keep all power-domains already enabled by bootloader on,
3538 even if no driver has claimed them. This is useful
3539 for debug and development, but should not be
3540 needed on a platform with proper driver support.
3543 See Documentation/admin-guide/blockdev/paride.rst.
3545 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3548 See arch/parisc/kernel/pdc_chassis.c
3550 percpu_alloc= Select which percpu first chunk allocator to use.
3551 Currently supported values are "embed" and "page".
3552 Archs may support subset or none of the selections.
3553 See comments in mm/percpu.c for details on each
3554 allocator. This parameter is primarily for debugging
3555 and performance comparison.
3558 See Documentation/admin-guide/blockdev/paride.rst.
3561 See Documentation/admin-guide/blockdev/paride.rst.
3563 pirq= [SMP,APIC] Manual mp-table setup
3564 See Documentation/x86/i386/IO-APIC.rst.
3566 plip= [PPT,NET] Parallel port network link
3567 Format: { parport<nr> | timid | 0 }
3568 See also Documentation/admin-guide/parport.rst.
3570 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3571 Override pmtimer IOPort with a hex value.
3575 Enable PNP debug messages (depends on the
3576 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3577 via /sys/module/pnp/parameters/debug. We always show
3578 current resource usage; turning this on also shows
3579 possible settings and some assignment information.
3585 { on | off | curr | res | no-curr | no-res }
3588 [ISAPNP] Exclude IRQs for the autoconfiguration
3591 [ISAPNP] Exclude DMAs for the autoconfiguration
3593 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3594 Ranges are in pairs (I/O port base and size).
3597 [ISAPNP] Exclude memory regions for the
3599 Ranges are in pairs (memory base and size).
3601 ports= [IP_VS_FTP] IPVS ftp helper module
3603 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3605 Format: <port>,<port>....
3607 powersave=off [PPC] This option disables power saving features.
3608 It specifically disables cpuidle and sets the
3609 platform machine description specific power_save
3610 function to NULL. On Idle the CPU just reduces
3613 ppc_strict_facility_enable
3614 [PPC] This option catches any kernel floating point,
3615 Altivec, VSX and SPE outside of regions specifically
3616 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3617 There is some performance impact when enabling this.
3621 Disable Hardware Transactional Memory
3623 print-fatal-signals=
3624 [KNL] debug: print fatal signals
3626 If enabled, warn about various signal handling
3627 related application anomalies: too many signals,
3628 too many POSIX.1 timers, fatal signals causing a
3631 If you hit the warning due to signal overflow,
3632 you might want to try "ulimit -i unlimited".
3636 printk.always_kmsg_dump=
3637 Trigger kmsg_dump for cases other than kernel oops or
3639 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3642 printk.devkmsg={on,off,ratelimit}
3643 Control writing to /dev/kmsg.
3644 on - unlimited logging to /dev/kmsg from userspace
3645 off - logging to /dev/kmsg disabled
3646 ratelimit - ratelimit the logging
3649 printk.time= Show timing data prefixed to each printk message line
3650 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3652 processor.max_cstate= [HW,ACPI]
3653 Limit processor to maximum C-state
3654 max_cstate=9 overrides any DMI blacklist limit.
3656 processor.nocst [HW,ACPI]
3657 Ignore the _CST method to determine C-states,
3658 instead using the legacy FADT method
3660 profile= [KNL] Enable kernel profiling via /proc/profile
3661 Format: [<profiletype>,]<number>
3662 Param: <profiletype>: "schedule", "sleep", or "kvm"
3663 [defaults to kernel profiling]
3664 Param: "schedule" - profile schedule points.
3665 Param: "sleep" - profile D-state sleeping (millisecs).
3666 Requires CONFIG_SCHEDSTATS
3667 Param: "kvm" - profile VM exits.
3668 Param: <number> - step/bucket size as a power of 2 for
3669 statistical time based profiling.
3671 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3673 See Documentation/admin-guide/blockdev/ramdisk.rst.
3675 psi= [KNL] Enable or disable pressure stall information
3679 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3680 probe for; one of (bare|imps|exps|lifebook|any).
3681 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3683 psmouse.resetafter= [HW,MOUSE]
3684 Try to reset the device after so many bad packets
3687 [HW,MOUSE] Set desired mouse resolution, in dpi.
3688 psmouse.smartscroll=
3689 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3690 0 = disabled, 1 = enabled (default).
3692 pstore.backend= Specify the name of the pstore backend to use
3695 See Documentation/admin-guide/blockdev/paride.rst.
3697 pti= [X86_64] Control Page Table Isolation of user and
3698 kernel address spaces. Disabling this feature
3699 removes hardening, but improves performance of
3700 system calls and interrupts.
3702 on - unconditionally enable
3703 off - unconditionally disable
3704 auto - kernel detects whether your CPU model is
3705 vulnerable to issues that PTI mitigates
3707 Not specifying this option is equivalent to pti=auto.
3710 Equivalent to pti=off
3713 [KNL] Number of legacy pty's. Overwrites compiled-in
3716 quiet [KNL] Disable most log messages
3721 See Documentation/admin-guide/md.rst.
3723 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3724 See Documentation/admin-guide/blockdev/ramdisk.rst.
3726 random.trust_cpu={on,off}
3727 [KNL] Enable or disable trusting the use of the
3728 CPU's random number generator (if available) to
3729 fully seed the kernel's CRNG. Default is controlled
3730 by CONFIG_RANDOM_TRUST_CPU.
3732 ras=option[,option,...] [KNL] RAS-specific options
3735 Disable the Correctable Errors Collector,
3736 see CONFIG_RAS_CEC help text.
3739 The argument is a cpu list, as described above,
3740 except that the string "all" can be used to
3741 specify every CPU on the system.
3743 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3744 the specified list of CPUs to be no-callback CPUs.
3745 Invocation of these CPUs' RCU callbacks will be
3746 offloaded to "rcuox/N" kthreads created for that
3747 purpose, where "x" is "p" for RCU-preempt, and
3748 "s" for RCU-sched, and "N" is the CPU number.
3749 This reduces OS jitter on the offloaded CPUs,
3750 which can be useful for HPC and real-time
3751 workloads. It can also improve energy efficiency
3752 for asymmetric multiprocessors.
3755 Rather than requiring that offloaded CPUs
3756 (specified by rcu_nocbs= above) explicitly
3757 awaken the corresponding "rcuoN" kthreads,
3758 make these kthreads poll for callbacks.
3759 This improves the real-time response for the
3760 offloaded CPUs by relieving them of the need to
3761 wake up the corresponding kthread, but degrades
3762 energy efficiency by requiring that the kthreads
3763 periodically wake up to do the polling.
3765 rcutree.blimit= [KNL]
3766 Set maximum number of finished RCU callbacks to
3767 process in one batch.
3769 rcutree.dump_tree= [KNL]
3770 Dump the structure of the rcu_node combining tree
3771 out at early boot. This is used for diagnostic
3772 purposes, to verify correct tree setup.
3774 rcutree.gp_cleanup_delay= [KNL]
3775 Set the number of jiffies to delay each step of
3776 RCU grace-period cleanup.
3778 rcutree.gp_init_delay= [KNL]
3779 Set the number of jiffies to delay each step of
3780 RCU grace-period initialization.
3782 rcutree.gp_preinit_delay= [KNL]
3783 Set the number of jiffies to delay each step of
3784 RCU grace-period pre-initialization, that is,
3785 the propagation of recent CPU-hotplug changes up
3786 the rcu_node combining tree.
3788 rcutree.use_softirq= [KNL]
3789 If set to zero, move all RCU_SOFTIRQ processing to
3790 per-CPU rcuc kthreads. Defaults to a non-zero
3791 value, meaning that RCU_SOFTIRQ is used by default.
3792 Specify rcutree.use_softirq=0 to use rcuc kthreads.
3794 rcutree.rcu_fanout_exact= [KNL]
3795 Disable autobalancing of the rcu_node combining
3796 tree. This is used by rcutorture, and might
3797 possibly be useful for architectures having high
3798 cache-to-cache transfer latencies.
3800 rcutree.rcu_fanout_leaf= [KNL]
3801 Change the number of CPUs assigned to each
3802 leaf rcu_node structure. Useful for very
3803 large systems, which will choose the value 64,
3804 and for NUMA systems with large remote-access
3805 latencies, which will choose a value aligned
3806 with the appropriate hardware boundaries.
3808 rcutree.jiffies_till_first_fqs= [KNL]
3809 Set delay from grace-period initialization to
3810 first attempt to force quiescent states.
3811 Units are jiffies, minimum value is zero,
3812 and maximum value is HZ.
3814 rcutree.jiffies_till_next_fqs= [KNL]
3815 Set delay between subsequent attempts to force
3816 quiescent states. Units are jiffies, minimum
3817 value is one, and maximum value is HZ.
3819 rcutree.jiffies_till_sched_qs= [KNL]
3820 Set required age in jiffies for a
3821 given grace period before RCU starts
3822 soliciting quiescent-state help from
3823 rcu_note_context_switch() and cond_resched().
3824 If not specified, the kernel will calculate
3825 a value based on the most recent settings
3826 of rcutree.jiffies_till_first_fqs
3827 and rcutree.jiffies_till_next_fqs.
3828 This calculated value may be viewed in
3829 rcutree.jiffies_to_sched_qs. Any attempt to set
3830 rcutree.jiffies_to_sched_qs will be cheerfully
3833 rcutree.kthread_prio= [KNL,BOOT]
3834 Set the SCHED_FIFO priority of the RCU per-CPU
3835 kthreads (rcuc/N). This value is also used for
3836 the priority of the RCU boost threads (rcub/N)
3837 and for the RCU grace-period kthreads (rcu_bh,
3838 rcu_preempt, and rcu_sched). If RCU_BOOST is
3839 set, valid values are 1-99 and the default is 1
3840 (the least-favored priority). Otherwise, when
3841 RCU_BOOST is not set, valid values are 0-99 and
3842 the default is zero (non-realtime operation).
3844 rcutree.rcu_nocb_leader_stride= [KNL]
3845 Set the number of NOCB kthread groups, which
3846 defaults to the square root of the number of
3847 CPUs. Larger numbers reduces the wakeup overhead
3848 on the per-CPU grace-period kthreads, but increases
3849 that same overhead on each group's leader.
3851 rcutree.qhimark= [KNL]
3852 Set threshold of queued RCU callbacks beyond which
3853 batch limiting is disabled.
3855 rcutree.qlowmark= [KNL]
3856 Set threshold of queued RCU callbacks below which
3857 batch limiting is re-enabled.
3859 rcutree.rcu_idle_gp_delay= [KNL]
3860 Set wakeup interval for idle CPUs that have
3861 RCU callbacks (RCU_FAST_NO_HZ=y).
3863 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3864 Set wakeup interval for idle CPUs that have
3865 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3866 Lazy RCU callbacks are those which RCU can
3867 prove do nothing more than free memory.
3869 rcutree.rcu_kick_kthreads= [KNL]
3870 Cause the grace-period kthread to get an extra
3871 wake_up() if it sleeps three times longer than
3872 it should at force-quiescent-state time.
3873 This wake_up() will be accompanied by a
3874 WARN_ONCE() splat and an ftrace_dump().
3876 rcutree.sysrq_rcu= [KNL]
3877 Commandeer a sysrq key to dump out Tree RCU's
3878 rcu_node tree with an eye towards determining
3879 why a new grace period has not yet started.
3881 rcuperf.gp_async= [KNL]
3882 Measure performance of asynchronous
3883 grace-period primitives such as call_rcu().
3885 rcuperf.gp_async_max= [KNL]
3886 Specify the maximum number of outstanding
3887 callbacks per writer thread. When a writer
3888 thread exceeds this limit, it invokes the
3889 corresponding flavor of rcu_barrier() to allow
3890 previously posted callbacks to drain.
3892 rcuperf.gp_exp= [KNL]
3893 Measure performance of expedited synchronous
3894 grace-period primitives.
3896 rcuperf.holdoff= [KNL]
3897 Set test-start holdoff period. The purpose of
3898 this parameter is to delay the start of the
3899 test until boot completes in order to avoid
3902 rcuperf.nreaders= [KNL]
3903 Set number of RCU readers. The value -1 selects
3904 N, where N is the number of CPUs. A value
3905 "n" less than -1 selects N-n+1, where N is again
3906 the number of CPUs. For example, -2 selects N
3907 (the number of CPUs), -3 selects N+1, and so on.
3908 A value of "n" less than or equal to -N selects
3911 rcuperf.nwriters= [KNL]
3912 Set number of RCU writers. The values operate
3913 the same as for rcuperf.nreaders.
3914 N, where N is the number of CPUs
3916 rcuperf.perf_type= [KNL]
3917 Specify the RCU implementation to test.
3919 rcuperf.shutdown= [KNL]
3920 Shut the system down after performance tests
3921 complete. This is useful for hands-off automated
3924 rcuperf.verbose= [KNL]
3925 Enable additional printk() statements.
3927 rcuperf.writer_holdoff= [KNL]
3928 Write-side holdoff between grace periods,
3929 in microseconds. The default of zero says
3932 rcutorture.fqs_duration= [KNL]
3933 Set duration of force_quiescent_state bursts
3936 rcutorture.fqs_holdoff= [KNL]
3937 Set holdoff time within force_quiescent_state bursts
3940 rcutorture.fqs_stutter= [KNL]
3941 Set wait time between force_quiescent_state bursts
3944 rcutorture.fwd_progress= [KNL]
3945 Enable RCU grace-period forward-progress testing
3946 for the types of RCU supporting this notion.
3948 rcutorture.fwd_progress_div= [KNL]
3949 Specify the fraction of a CPU-stall-warning
3950 period to do tight-loop forward-progress testing.
3952 rcutorture.fwd_progress_holdoff= [KNL]
3953 Number of seconds to wait between successive
3954 forward-progress tests.
3956 rcutorture.fwd_progress_need_resched= [KNL]
3957 Enclose cond_resched() calls within checks for
3958 need_resched() during tight-loop forward-progress
3961 rcutorture.gp_cond= [KNL]
3962 Use conditional/asynchronous update-side
3963 primitives, if available.
3965 rcutorture.gp_exp= [KNL]
3966 Use expedited update-side primitives, if available.
3968 rcutorture.gp_normal= [KNL]
3969 Use normal (non-expedited) asynchronous
3970 update-side primitives, if available.
3972 rcutorture.gp_sync= [KNL]
3973 Use normal (non-expedited) synchronous
3974 update-side primitives, if available. If all
3975 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3976 rcutorture.gp_normal=, and rcutorture.gp_sync=
3977 are zero, rcutorture acts as if is interpreted
3978 they are all non-zero.
3980 rcutorture.n_barrier_cbs= [KNL]
3981 Set callbacks/threads for rcu_barrier() testing.
3983 rcutorture.nfakewriters= [KNL]
3984 Set number of concurrent RCU writers. These just
3985 stress RCU, they don't participate in the actual
3986 test, hence the "fake".
3988 rcutorture.nreaders= [KNL]
3989 Set number of RCU readers. The value -1 selects
3990 N-1, where N is the number of CPUs. A value
3991 "n" less than -1 selects N-n-2, where N is again
3992 the number of CPUs. For example, -2 selects N
3993 (the number of CPUs), -3 selects N+1, and so on.
3995 rcutorture.object_debug= [KNL]
3996 Enable debug-object double-call_rcu() testing.
3998 rcutorture.onoff_holdoff= [KNL]
3999 Set time (s) after boot for CPU-hotplug testing.
4001 rcutorture.onoff_interval= [KNL]
4002 Set time (jiffies) between CPU-hotplug operations,
4003 or zero to disable CPU-hotplug testing.
4005 rcutorture.shuffle_interval= [KNL]
4006 Set task-shuffle interval (s). Shuffling tasks
4007 allows some CPUs to go into dyntick-idle mode
4008 during the rcutorture test.
4010 rcutorture.shutdown_secs= [KNL]
4011 Set time (s) after boot system shutdown. This
4012 is useful for hands-off automated testing.
4014 rcutorture.stall_cpu= [KNL]
4015 Duration of CPU stall (s) to test RCU CPU stall
4016 warnings, zero to disable.
4018 rcutorture.stall_cpu_holdoff= [KNL]
4019 Time to wait (s) after boot before inducing stall.
4021 rcutorture.stall_cpu_irqsoff= [KNL]
4022 Disable interrupts while stalling if set.
4024 rcutorture.stat_interval= [KNL]
4025 Time (s) between statistics printk()s.
4027 rcutorture.stutter= [KNL]
4028 Time (s) to stutter testing, for example, specifying
4029 five seconds causes the test to run for five seconds,
4030 wait for five seconds, and so on. This tests RCU's
4031 ability to transition abruptly to and from idle.
4033 rcutorture.test_boost= [KNL]
4034 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4035 "Maybe" means test if the RCU implementation
4036 under test support RCU priority boosting.
4038 rcutorture.test_boost_duration= [KNL]
4039 Duration (s) of each individual boost test.
4041 rcutorture.test_boost_interval= [KNL]
4042 Interval (s) between each boost test.
4044 rcutorture.test_no_idle_hz= [KNL]
4045 Test RCU's dyntick-idle handling. See also the
4046 rcutorture.shuffle_interval parameter.
4048 rcutorture.torture_type= [KNL]
4049 Specify the RCU implementation to test.
4051 rcutorture.verbose= [KNL]
4052 Enable additional printk() statements.
4054 rcupdate.rcu_cpu_stall_suppress= [KNL]
4055 Suppress RCU CPU stall warning messages.
4057 rcupdate.rcu_cpu_stall_timeout= [KNL]
4058 Set timeout for RCU CPU stall warning messages.
4060 rcupdate.rcu_expedited= [KNL]
4061 Use expedited grace-period primitives, for
4062 example, synchronize_rcu_expedited() instead
4063 of synchronize_rcu(). This reduces latency,
4064 but can increase CPU utilization, degrade
4065 real-time latency, and degrade energy efficiency.
4066 No effect on CONFIG_TINY_RCU kernels.
4068 rcupdate.rcu_normal= [KNL]
4069 Use only normal grace-period primitives,
4070 for example, synchronize_rcu() instead of
4071 synchronize_rcu_expedited(). This improves
4072 real-time latency, CPU utilization, and
4073 energy efficiency, but can expose users to
4074 increased grace-period latency. This parameter
4075 overrides rcupdate.rcu_expedited. No effect on
4076 CONFIG_TINY_RCU kernels.
4078 rcupdate.rcu_normal_after_boot= [KNL]
4079 Once boot has completed (that is, after
4080 rcu_end_inkernel_boot() has been invoked), use
4081 only normal grace-period primitives. No effect
4082 on CONFIG_TINY_RCU kernels.
4084 rcupdate.rcu_task_stall_timeout= [KNL]
4085 Set timeout in jiffies for RCU task stall warning
4086 messages. Disable with a value less than or equal
4089 rcupdate.rcu_self_test= [KNL]
4090 Run the RCU early boot self tests
4094 Run specified binary instead of /init from the ramdisk,
4095 used for early userspace startup. See initrd.
4098 Turn on/off individual RDT features. List is:
4099 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4101 E.g. to turn on cmt and turn off mba use:
4105 Format (x86 or x86_64):
4106 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4108 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4110 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4111 (prefix with 'panic_' to set mode for panic
4113 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4114 reboot_force is either force or not specified,
4115 reboot_cpu is s[mp]#### with #### being the processor
4116 to be used for rebooting.
4119 [KNL, SMP] Set scheduler's default relax_domain_level.
4120 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4122 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4123 Format: <base1>,<size1>[,<base2>,<size2>,...]
4124 Reserve I/O ports or memory so the kernel won't use
4125 them. If <base> is less than 0x10000, the region
4126 is assumed to be I/O ports; otherwise it is memory.
4128 reservetop= [X86-32]
4130 Reserves a hole at the top of the kernel virtual
4135 Set the amount of memory to reserve for BIOS at
4136 the bottom of the address space.
4138 reset_devices [KNL] Force drivers to reset the underlying device
4139 during initialization.
4142 Specify the partition device for software suspend
4144 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4146 resume_offset= [SWSUSP]
4147 Specify the offset from the beginning of the partition
4148 given by "resume=" at which the swap header is located,
4149 in <PAGE_SIZE> units (needed only for swap files).
4150 See Documentation/power/swsusp-and-swap-files.rst
4152 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4153 read the resume files
4155 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4156 Useful for devices that are detected asynchronously
4157 (e.g. USB and MMC devices).
4159 hibernate= [HIBERNATION]
4160 noresume Don't check if there's a hibernation image
4161 present during boot.
4162 nocompress Don't compress/decompress hibernation images.
4163 no Disable hibernation and resume.
4164 protect_image Turn on image protection during restoration
4165 (that will set all pages holding image data
4166 during restoration read-only).
4168 retain_initrd [RAM] Keep initrd memory after extraction
4170 rfkill.default_state=
4171 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4172 etc. communication is blocked by default.
4175 rfkill.master_switch_mode=
4176 0 The "airplane mode" button does nothing.
4177 1 The "airplane mode" button toggles between everything
4178 blocked and the previous configuration.
4179 2 The "airplane mode" button toggles between everything
4180 blocked and everything unblocked.
4182 rhash_entries= [KNL,NET]
4183 Set number of hash buckets for route cache
4186 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4189 ro [KNL] Mount root device read-only on boot
4192 on Mark read-only kernel memory as read-only (default).
4193 off Leave read-only kernel memory writable for debugging.
4196 Enable the uart passthrough on the designated usb port
4197 on Rockchip SoCs. When active, the signals of the
4198 debug-uart get routed to the D+ and D- pins of the usb
4199 port and the regular usb controller gets disabled.
4201 root= [KNL] Root filesystem
4202 See name_to_dev_t comment in init/do_mounts.c.
4204 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4205 mount the root filesystem
4207 rootflags= [KNL] Set root filesystem mount option string
4209 rootfstype= [KNL] Set root filesystem type
4211 rootwait [KNL] Wait (indefinitely) for root device to show up.
4212 Useful for devices that are detected asynchronously
4213 (e.g. USB and MMC devices).
4215 rproc_mem=nn[KMG][@address]
4216 [KNL,ARM,CMA] Remoteproc physical memory block.
4217 Memory area to be used by remote processor image,
4220 rw [KNL] Mount root device read-write on boot
4222 S [KNL] Run init in single mode
4224 s390_iommu= [HW,S390]
4225 Set s390 IOTLB flushing mode
4227 With strict flushing every unmap operation will result in
4228 an IOTLB flush. Default is lazy flushing before reuse,
4232 See drivers/net/irda/sa1100_ir.c.
4234 sbni= [NET] Granch SBNI12 leased line adapter
4236 sched_debug [KNL] Enables verbose scheduler debug messages.
4238 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4239 Allowed values are enable and disable. This feature
4240 incurs a small amount of overhead in the scheduler
4241 but is useful for debugging and performance tuning.
4243 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4244 xtime_lock contention on larger systems, and/or RCU lock
4245 contention on all systems with CONFIG_MAXSMP set.
4246 Format: { "0" | "1" }
4247 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4249 Note: increases power consumption, thus should only be
4250 enabled if running jitter sensitive (HPC/RT) workloads.
4252 security= [SECURITY] Choose a legacy "major" security module to
4253 enable at boot. This has been deprecated by the
4256 selinux= [SELINUX] Disable or enable SELinux at boot time.
4257 Format: { "0" | "1" }
4258 See security/selinux/Kconfig help text.
4261 Default value is set via kernel config option.
4262 If enabled at boot time, /selinux/disable can be used
4263 later to disable prior to initial policy load.
4265 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4266 Format: { "0" | "1" }
4267 See security/apparmor/Kconfig help text
4270 Default value is set via kernel config option.
4272 serialnumber [BUGS=X86-32]
4275 Maximal number of shapers.
4283 Disable merging of slabs with similar size. May be
4284 necessary if there is some reason to distinguish
4285 allocs to different slabs, especially in hardened
4286 environments where the risk of heap overflows and
4287 layout control by attackers can usually be
4288 frustrated by disabling merging. This will reduce
4289 most of the exposure of a heap attack to a single
4290 cache (risks via metadata attacks are mostly
4291 unchanged). Debug options disable merging on their
4293 For more information see Documentation/vm/slub.rst.
4295 slab_max_order= [MM, SLAB]
4296 Determines the maximum allowed order for slabs.
4297 A high setting may cause OOMs due to memory
4298 fragmentation. Defaults to 1 for systems with
4299 more than 32MB of RAM, 0 otherwise.
4301 slub_debug[=options[,slabs]] [MM, SLUB]
4302 Enabling slub_debug allows one to determine the
4303 culprit if slab objects become corrupted. Enabling
4304 slub_debug can create guard zones around objects and
4305 may poison objects when not in use. Also tracks the
4306 last alloc / free. For more information see
4307 Documentation/vm/slub.rst.
4309 slub_memcg_sysfs= [MM, SLUB]
4310 Determines whether to enable sysfs directories for
4311 memory cgroup sub-caches. 1 to enable, 0 to disable.
4312 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4313 Enabling this can lead to a very high number of debug
4314 directories and files being created under
4317 slub_max_order= [MM, SLUB]
4318 Determines the maximum allowed order for slabs.
4319 A high setting may cause OOMs due to memory
4320 fragmentation. For more information see
4321 Documentation/vm/slub.rst.
4323 slub_min_objects= [MM, SLUB]
4324 The minimum number of objects per slab. SLUB will
4325 increase the slab order up to slub_max_order to
4326 generate a sufficiently large slab able to contain
4327 the number of objects indicated. The higher the number
4328 of objects the smaller the overhead of tracking slabs
4329 and the less frequently locks need to be acquired.
4330 For more information see Documentation/vm/slub.rst.
4332 slub_min_order= [MM, SLUB]
4333 Determines the minimum page order for slabs. Must be
4334 lower than slub_max_order.
4335 For more information see Documentation/vm/slub.rst.
4337 slub_nomerge [MM, SLUB]
4338 Same with slab_nomerge. This is supported for legacy.
4339 See slab_nomerge for more information.
4342 Format: <io1>[,<io2>[,...,<io8>]]
4344 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4345 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4346 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4347 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4348 smsc-ircc2.ircc_irq= [HW] IRQ line
4349 smsc-ircc2.ircc_dma= [HW] DMA channel
4350 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4351 0: Toshiba Satellite 1800 (GP data pin select)
4352 1: Fast pin select (default)
4355 smt [KNL,S390] Set the maximum number of threads (logical
4356 CPUs) to use per physical CPU on systems capable of
4357 symmetric multithreading (SMT). Will be capped to the
4358 actual hardware limit.
4360 Default: -1 (no limit)
4363 [KNL] Should the soft-lockup detector generate panics.
4366 A nonzero value instructs the soft-lockup detector
4367 to panic the machine when a soft-lockup occurs. This
4368 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4369 which is the respective build-time switch to that
4372 softlockup_all_cpu_backtrace=
4373 [KNL] Should the soft-lockup detector generate
4374 backtraces on all cpus.
4377 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4378 See Documentation/admin-guide/laptops/sonypi.rst
4380 spectre_v2= [X86] Control mitigation of Spectre variant 2
4381 (indirect branch speculation) vulnerability.
4382 The default operation protects the kernel from
4385 on - unconditionally enable, implies
4387 off - unconditionally disable, implies
4389 auto - kernel detects whether your CPU model is
4392 Selecting 'on' will, and 'auto' may, choose a
4393 mitigation method at run time according to the
4394 CPU, the available microcode, the setting of the
4395 CONFIG_RETPOLINE configuration option, and the
4396 compiler with which the kernel was built.
4398 Selecting 'on' will also enable the mitigation
4399 against user space to user space task attacks.
4401 Selecting 'off' will disable both the kernel and
4402 the user space protections.
4404 Specific mitigations can also be selected manually:
4406 retpoline - replace indirect branches
4407 retpoline,generic - google's original retpoline
4408 retpoline,amd - AMD-specific minimal thunk
4410 Not specifying this option is equivalent to
4414 [X86] Control mitigation of Spectre variant 2
4415 (indirect branch speculation) vulnerability between
4418 on - Unconditionally enable mitigations. Is
4419 enforced by spectre_v2=on
4421 off - Unconditionally disable mitigations. Is
4422 enforced by spectre_v2=off
4424 prctl - Indirect branch speculation is enabled,
4425 but mitigation can be enabled via prctl
4426 per thread. The mitigation control state
4427 is inherited on fork.
4430 - Like "prctl" above, but only STIBP is
4431 controlled per thread. IBPB is issued
4432 always when switching between different user
4436 - Same as "prctl" above, but all seccomp
4437 threads will enable the mitigation unless
4438 they explicitly opt out.
4441 - Like "seccomp" above, but only STIBP is
4442 controlled per thread. IBPB is issued
4443 always when switching between different
4444 user space processes.
4446 auto - Kernel selects the mitigation depending on
4447 the available CPU features and vulnerability.
4450 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4452 Not specifying this option is equivalent to
4453 spectre_v2_user=auto.
4455 spec_store_bypass_disable=
4456 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4457 (Speculative Store Bypass vulnerability)
4459 Certain CPUs are vulnerable to an exploit against a
4460 a common industry wide performance optimization known
4461 as "Speculative Store Bypass" in which recent stores
4462 to the same memory location may not be observed by
4463 later loads during speculative execution. The idea
4464 is that such stores are unlikely and that they can
4465 be detected prior to instruction retirement at the
4466 end of a particular speculation execution window.
4468 In vulnerable processors, the speculatively forwarded
4469 store can be used in a cache side channel attack, for
4470 example to read memory to which the attacker does not
4471 directly have access (e.g. inside sandboxed code).
4473 This parameter controls whether the Speculative Store
4474 Bypass optimization is used.
4476 On x86 the options are:
4478 on - Unconditionally disable Speculative Store Bypass
4479 off - Unconditionally enable Speculative Store Bypass
4480 auto - Kernel detects whether the CPU model contains an
4481 implementation of Speculative Store Bypass and
4482 picks the most appropriate mitigation. If the
4483 CPU is not vulnerable, "off" is selected. If the
4484 CPU is vulnerable the default mitigation is
4485 architecture and Kconfig dependent. See below.
4486 prctl - Control Speculative Store Bypass per thread
4487 via prctl. Speculative Store Bypass is enabled
4488 for a process by default. The state of the control
4489 is inherited on fork.
4490 seccomp - Same as "prctl" above, but all seccomp threads
4491 will disable SSB unless they explicitly opt out.
4493 Default mitigations:
4494 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4496 On powerpc the options are:
4498 on,auto - On Power8 and Power9 insert a store-forwarding
4499 barrier on kernel entry and exit. On Power7
4500 perform a software flush on kernel entry and
4504 Not specifying this option is equivalent to
4505 spec_store_bypass_disable=auto.
4507 spia_io_base= [HW,MTD]
4512 srcutree.counter_wrap_check [KNL]
4513 Specifies how frequently to check for
4514 grace-period sequence counter wrap for the
4515 srcu_data structure's ->srcu_gp_seq_needed field.
4516 The greater the number of bits set in this kernel
4517 parameter, the less frequently counter wrap will
4518 be checked for. Note that the bottom two bits
4521 srcutree.exp_holdoff [KNL]
4522 Specifies how many nanoseconds must elapse
4523 since the end of the last SRCU grace period for
4524 a given srcu_struct until the next normal SRCU
4525 grace period will be considered for automatic
4526 expediting. Set to zero to disable automatic
4530 Speculative Store Bypass Disable control
4532 On CPUs that are vulnerable to the Speculative
4533 Store Bypass vulnerability and offer a
4534 firmware based mitigation, this parameter
4535 indicates how the mitigation should be used:
4537 force-on: Unconditionally enable mitigation for
4538 for both kernel and userspace
4539 force-off: Unconditionally disable mitigation for
4540 for both kernel and userspace
4541 kernel: Always enable mitigation in the
4542 kernel, and offer a prctl interface
4543 to allow userspace to register its
4544 interest in being mitigated too.
4546 stack_guard_gap= [MM]
4547 override the default stack gap protection. The value
4548 is in page units and it defines how many pages prior
4549 to (for stacks growing down) resp. after (for stacks
4550 growing up) the main stack are reserved for no other
4551 mapping. Default value is 256 pages.
4554 Enabled the stack tracer on boot up.
4556 stacktrace_filter=[function-list]
4557 [FTRACE] Limit the functions that the stack tracer
4558 will trace at boot up. function-list is a comma separated
4559 list of functions. This list can be changed at run
4560 time by the stack_trace_filter file in the debugfs
4561 tracing directory. Note, this enables stack tracing
4562 and the stacktrace above is not needed.
4566 Set the STI (builtin display/keyboard on the HP-PARISC
4567 machines) console (graphic card) which should be used
4568 as the initial boot-console.
4569 See also comment in drivers/video/console/sticore.c.
4572 See comment in drivers/video/console/sticore.c.
4575 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4577 sunrpc.min_resvport=
4578 sunrpc.max_resvport=
4580 SunRPC servers often require that client requests
4581 originate from a privileged port (i.e. a port in the
4582 range 0 < portnr < 1024).
4583 An administrator who wishes to reserve some of these
4584 ports for other uses may adjust the range that the
4585 kernel's sunrpc client considers to be privileged
4586 using these two parameters to set the minimum and
4587 maximum port values.
4589 sunrpc.svc_rpc_per_connection_limit=
4591 Limit the number of requests that the server will
4592 process in parallel from a single connection.
4593 The default value is 0 (no limit).
4597 Control how the NFS server code allocates CPUs to
4598 service thread pools. Depending on how many NICs
4599 you have and where their interrupts are bound, this
4600 option will affect which CPUs will do NFS serving.
4601 Note: this parameter cannot be changed while the
4602 NFS server is running.
4604 auto the server chooses an appropriate mode
4605 automatically using heuristics
4606 global a single global pool contains all CPUs
4607 percpu one pool for each CPU
4608 pernode one pool for each NUMA node (equivalent
4609 to global on non-NUMA machines)
4611 sunrpc.tcp_slot_table_entries=
4612 sunrpc.udp_slot_table_entries=
4614 Sets the upper limit on the number of simultaneous
4615 RPC calls that can be sent from the client to a
4616 server. Increasing these values may allow you to
4617 improve throughput, but will also increase the
4618 amount of memory reserved for use by the client.
4620 suspend.pm_test_delay=
4622 Sets the number of seconds to remain in a suspend test
4623 mode before resuming the system (see
4624 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4625 is set. Default value is 5.
4628 [KNL] Enable accounting of swap in memory resource
4629 controller if no parameter or 1 is given or disable
4630 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
4632 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4633 Format: { <int> | force | noforce }
4634 <int> -- Number of I/O TLB slabs
4635 force -- force using of bounce buffers even if they
4636 wouldn't be automatically used by the kernel
4637 noforce -- Never use bounce buffers (for debugging)
4641 sysfs.deprecated=0|1 [KNL]
4642 Enable/disable old style sysfs layout for old udev
4643 on older distributions. When this option is enabled
4644 very new udev will not work anymore. When this option
4645 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4646 in older udev will not work anymore.
4647 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4648 the kernel configuration.
4650 sysrq_always_enabled
4652 Ignore sysrq setting - this boot parameter will
4653 neutralize any effect of /proc/sys/kernel/sysrq.
4654 Useful for debugging.
4656 tcpmhash_entries= [KNL,NET]
4657 Set the number of tcp_metrics_hash slots.
4658 Default value is 8192 or 16384 depending on total
4659 ram pages. This is used to specify the TCP metrics
4660 cache size. See Documentation/networking/ip-sysctl.txt
4661 "tcp_no_metrics_save" section for more details.
4665 test_suspend= [SUSPEND][,N]
4666 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4667 standby suspend) or "freeze" (for suspend type freeze)
4668 as the system sleep state during system startup with
4669 the optional capability to repeat N number of times.
4670 The system is woken from this state using a
4671 wakeup-capable RTC alarm.
4673 thash_entries= [KNL,NET]
4674 Set number of hash buckets for TCP connection
4676 thermal.act= [HW,ACPI]
4677 -1: disable all active trip points in all thermal zones
4678 <degrees C>: override all lowest active trip points
4680 thermal.crt= [HW,ACPI]
4681 -1: disable all critical trip points in all thermal zones
4682 <degrees C>: override all critical trip points
4684 thermal.nocrt= [HW,ACPI]
4685 Set to disable actions on ACPI thermal zone
4686 critical and hot trip points.
4688 thermal.off= [HW,ACPI]
4689 1: disable ACPI thermal control
4691 thermal.psv= [HW,ACPI]
4692 -1: disable all passive trip points
4693 <degrees C>: override all passive trip points to this
4696 thermal.tzp= [HW,ACPI]
4697 Specify global default ACPI thermal zone polling rate
4698 <deci-seconds>: poll all this frequency
4699 0: no polling (default)
4702 Force threading of all interrupt handlers except those
4703 marked explicitly IRQF_NO_THREAD.
4707 Specify if the kernel should make use of the cpu
4708 topology information if the hardware supports this.
4709 The scheduler will make use of this information and
4710 e.g. base its process migration decisions on it.
4713 topology_updates= [KNL, PPC, NUMA]
4715 Specify if the kernel should ignore (off)
4716 topology updates sent by the hypervisor to this
4721 tpm_suspend_pcr=[HW,TPM]
4722 Format: integer pcr id
4723 Specify that at suspend time, the tpm driver
4724 should extend the specified pcr with zeros,
4725 as a workaround for some chips which fail to
4726 flush the last written pcr on TPM_SaveState.
4727 This will guarantee that all the other pcrs
4730 trace_buf_size=nn[KMG]
4731 [FTRACE] will set tracing buffer size on each cpu.
4733 trace_event=[event-list]
4734 [FTRACE] Set and start specified trace events in order
4735 to facilitate early boot debugging. The event-list is a
4736 comma separated list of trace events to enable. See
4737 also Documentation/trace/events.rst
4739 trace_options=[option-list]
4740 [FTRACE] Enable or disable tracer options at boot.
4741 The option-list is a comma delimited list of options
4742 that can be enabled or disabled just as if you were
4743 to echo the option name into
4745 /sys/kernel/debug/tracing/trace_options
4747 For example, to enable stacktrace option (to dump the
4748 stack trace of each event), add to the command line:
4750 trace_options=stacktrace
4752 See also Documentation/trace/ftrace.rst "trace options"
4756 Have the tracepoints sent to printk as well as the
4757 tracing ring buffer. This is useful for early boot up
4758 where the system hangs or reboots and does not give the
4759 option for reading the tracing buffer or performing a
4760 ftrace_dump_on_oops.
4762 To turn off having tracepoints sent to printk,
4763 echo 0 > /proc/sys/kernel/tracepoint_printk
4764 Note, echoing 1 into this file without the
4765 tracepoint_printk kernel cmdline option has no effect.
4769 Having tracepoints sent to printk() and activating high
4770 frequency tracepoints such as irq or sched, can cause
4771 the system to live lock.
4774 [FTRACE] enable this option to disable tracing when a
4775 warning is hit. This turns off "tracing_on". Tracing can
4776 be enabled again by echoing '1' into the "tracing_on"
4777 file located in /sys/kernel/debug/tracing/
4779 This option is useful, as it disables the trace before
4780 the WARNING dump is called, which prevents the trace to
4781 be filled with content caused by the warning output.
4783 This option can also be set at run time via the sysctl
4784 option: kernel/traceoff_on_warning
4786 transparent_hugepage=
4788 Format: [always|madvise|never]
4789 Can be used to control the default behavior of the system
4790 with respect to transparent hugepages.
4791 See Documentation/admin-guide/mm/transhuge.rst
4794 tsc= Disable clocksource stability checks for TSC.
4796 [x86] reliable: mark tsc clocksource as reliable, this
4797 disables clocksource verification at runtime, as well
4798 as the stability checks done at bootup. Used to enable
4799 high-resolution timer mode on older hardware, and in
4800 virtualized environment.
4801 [x86] noirqtime: Do not use TSC to do irq accounting.
4802 Used to run time disable IRQ_TIME_ACCOUNTING on any
4803 platforms where RDTSC is slow and this accounting
4805 [x86] unstable: mark the TSC clocksource as unstable, this
4806 marks the TSC unconditionally unstable at bootup and
4807 avoids any further wobbles once the TSC watchdog notices.
4808 [x86] nowatchdog: disable clocksource watchdog. Used
4809 in situations with strict latency requirements (where
4810 interruptions from clocksource watchdog are not
4813 turbografx.map[2|3]= [HW,JOY]
4814 TurboGraFX parallel port interface
4816 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4817 See also Documentation/input/devices/joystick-parport.rst
4819 udbg-immortal [PPC] When debugging early kernel crashes that
4820 happen after console_init() and before a proper
4821 console driver takes over, this boot options might
4822 help "seeing" what's going on.
4824 uhash_entries= [KNL,NET]
4825 Set number of hash buckets for UDP/UDP-Lite connections
4828 [USB] Ignore overcurrent events (default N).
4829 Some badly-designed motherboards generate lots of
4830 bogus events, for ports that aren't wired to
4831 anything. Set this parameter to avoid log spamming.
4832 Note that genuine overcurrent events won't be
4836 [X86] Cause panic on unknown NMI.
4838 usbcore.authorized_default=
4839 [USB] Default USB device authorization:
4840 (default -1 = authorized except for wireless USB,
4841 0 = not authorized, 1 = authorized, 2 = authorized
4842 if device connected to internal port)
4844 usbcore.autosuspend=
4845 [USB] The autosuspend time delay (in seconds) used
4846 for newly-detected USB devices (default 2). This
4847 is the time required before an idle device will be
4848 autosuspended. Devices for which the delay is set
4849 to a negative value won't be autosuspended at all.
4851 usbcore.usbfs_snoop=
4852 [USB] Set to log all usbfs traffic (default 0 = off).
4854 usbcore.usbfs_snoop_max=
4855 [USB] Maximum number of bytes to snoop in each URB
4858 usbcore.blinkenlights=
4859 [USB] Set to cycle leds on hubs (default 0 = off).
4861 usbcore.old_scheme_first=
4862 [USB] Start with the old device initialization
4863 scheme, applies only to low and full-speed devices
4866 usbcore.usbfs_memory_mb=
4867 [USB] Memory limit (in MB) for buffers allocated by
4868 usbfs (default = 16, 0 = max = 2047).
4870 usbcore.use_both_schemes=
4871 [USB] Try the other device initialization scheme
4872 if the first one fails (default 1 = enabled).
4874 usbcore.initial_descriptor_timeout=
4875 [USB] Specifies timeout for the initial 64-byte
4876 USB_REQ_GET_DESCRIPTOR request in milliseconds
4877 (default 5000 = 5.0 seconds).
4879 usbcore.nousb [USB] Disable the USB subsystem
4882 [USB] A list of quirk entries to augment the built-in
4883 usb core quirk list. List entries are separated by
4884 commas. Each entry has the form
4885 VendorID:ProductID:Flags. The IDs are 4-digit hex
4886 numbers and Flags is a set of letters. Each letter
4887 will change the built-in quirk; setting it if it is
4888 clear and clearing it if it is set. The letters have
4889 the following meanings:
4890 a = USB_QUIRK_STRING_FETCH_255 (string
4891 descriptors must not be fetched using
4893 b = USB_QUIRK_RESET_RESUME (device can't resume
4894 correctly so reset it instead);
4895 c = USB_QUIRK_NO_SET_INTF (device can't handle
4896 Set-Interface requests);
4897 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4898 handle its Configuration or Interface
4900 e = USB_QUIRK_RESET (device can't be reset
4901 (e.g morph devices), don't use reset);
4902 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4903 more interface descriptions than the
4904 bNumInterfaces count, and can't handle
4905 talking to these interfaces);
4906 g = USB_QUIRK_DELAY_INIT (device needs a pause
4907 during initialization, after we read
4908 the device descriptor);
4909 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4910 high speed and super speed interrupt
4911 endpoints, the USB 2.0 and USB 3.0 spec
4912 require the interval in microframes (1
4913 microframe = 125 microseconds) to be
4914 calculated as interval = 2 ^
4916 Devices with this quirk report their
4917 bInterval as the result of this
4918 calculation instead of the exponent
4919 variable used in the calculation);
4920 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4921 handle device_qualifier descriptor
4923 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4924 generates spurious wakeup, ignore
4925 remote wakeup capability);
4926 k = USB_QUIRK_NO_LPM (device can't handle Link
4928 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4929 (Device reports its bInterval as linear
4930 frames instead of the USB 2.0
4932 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4933 to be disconnected before suspend to
4934 prevent spurious wakeup);
4935 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4936 pause after every control message);
4937 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
4938 delay after resetting its port);
4939 Example: quirks=0781:5580:bk,0a5c:5834:gij
4942 [USBHID] The interval which mice are to be polled at.
4945 [USBHID] The interval which joysticks are to be polled at.
4948 [USBHID] The interval which keyboards are to be polled at.
4950 usb-storage.delay_use=
4951 [UMS] The delay in seconds before a new device is
4952 scanned for Logical Units (default 1).
4955 [UMS] A list of quirks entries to supplement or
4956 override the built-in unusual_devs list. List
4957 entries are separated by commas. Each entry has
4958 the form VID:PID:Flags where VID and PID are Vendor
4959 and Product ID values (4-digit hex numbers) and
4960 Flags is a set of characters, each corresponding
4961 to a common usb-storage quirk flag as follows:
4962 a = SANE_SENSE (collect more than 18 bytes
4964 b = BAD_SENSE (don't collect more than 18
4965 bytes of sense data);
4966 c = FIX_CAPACITY (decrease the reported
4967 device capacity by one sector);
4968 d = NO_READ_DISC_INFO (don't use
4969 READ_DISC_INFO command);
4970 e = NO_READ_CAPACITY_16 (don't use
4971 READ_CAPACITY_16 command);
4972 f = NO_REPORT_OPCODES (don't use report opcodes
4974 g = MAX_SECTORS_240 (don't transfer more than
4975 240 sectors at a time, uas only);
4976 h = CAPACITY_HEURISTICS (decrease the
4977 reported device capacity by one
4978 sector if the number is odd);
4979 i = IGNORE_DEVICE (don't bind to this
4981 j = NO_REPORT_LUNS (don't use report luns
4983 l = NOT_LOCKABLE (don't try to lock and
4984 unlock ejectable media);
4985 m = MAX_SECTORS_64 (don't transfer more
4986 than 64 sectors = 32 KB at a time);
4987 n = INITIAL_READ10 (force a retry of the
4988 initial READ(10) command);
4989 o = CAPACITY_OK (accept the capacity
4990 reported by the device);
4991 p = WRITE_CACHE (the device cache is ON
4993 r = IGNORE_RESIDUE (the device reports
4994 bogus residue values);
4995 s = SINGLE_LUN (the device has only one
4997 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4998 commands, uas only);
4999 u = IGNORE_UAS (don't bind to the uas driver);
5000 w = NO_WP_DETECT (don't test whether the
5001 medium is write-protected).
5002 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
5003 even if the device claims no cache)
5004 Example: quirks=0419:aaf5:rl,0421:0433:rc
5006 user_debug= [KNL,ARM]
5008 See arch/arm/Kconfig.debug help text.
5009 1 - undefined instruction events
5011 4 - invalid data aborts
5014 Example: user_debug=31
5017 [X86] Flags controlling user PTE allocations.
5019 nohigh = do not allocate PTE pages in
5020 HIGHMEM regardless of setting
5024 On X86_32, this is an alias for vdso32=. Otherwise:
5026 vdso=1: enable VDSO (the default)
5027 vdso=0: disable VDSO mapping
5029 vdso32= [X86] Control the 32-bit vDSO
5030 vdso32=1: enable 32-bit VDSO
5031 vdso32=0 or vdso32=2: disable 32-bit VDSO
5033 See the help text for CONFIG_COMPAT_VDSO for more
5034 details. If CONFIG_COMPAT_VDSO is set, the default is
5035 vdso32=0; otherwise, the default is vdso32=1.
5037 For compatibility with older kernels, vdso32=2 is an
5040 Try vdso32=0 if you encounter an error that says:
5041 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
5044 vector=percpu: enable percpu vector domain
5046 video= [FB] Frame buffer configuration
5047 See Documentation/fb/modedb.rst.
5049 video.brightness_switch_enabled= [0,1]
5050 If set to 1, on receiving an ACPI notify event
5051 generated by hotkey, video driver will adjust brightness
5052 level and then send out the event to user space through
5053 the allocated input device; If set to 0, video driver
5054 will only send out the event without touching backlight
5059 [VMMIO] Memory mapped virtio (platform) device.
5061 <size>@<baseaddr>:<irq>[:<id>]
5063 <size> := size (can use standard suffixes
5065 <baseaddr> := physical base address
5066 <irq> := interrupt number (as passed to
5068 <id> := (optional) platform device id
5070 virtio_mmio.device=1K@0x100b0000:48:7
5072 Can be used multiple times for multiple devices.
5074 vga= [BOOT,X86-32] Select a particular video mode
5075 See Documentation/x86/boot.rst and
5076 Documentation/admin-guide/svga.rst.
5077 Use vga=ask for menu.
5078 This is actually a boot loader parameter; the value is
5079 passed to the kernel using a special protocol.
5081 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
5082 May slow down system boot speed, especially when
5083 enabled on systems with a large amount of memory.
5084 All options are enabled by default, and this
5085 interface is meant to allow for selectively
5086 enabling or disabling specific virtual memory
5089 Available options are:
5090 P Enable page structure init time poisoning
5091 - Disable all of the above options
5093 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
5094 size of <nn>. This can be used to increase the
5095 minimum size (128MB on x86). It can also be used to
5096 decrease the size and leave more room for directly
5099 vmcp_cma=nn[MG] [KNL,S390]
5100 Sets the memory size reserved for contiguous memory
5101 allocations for the vmcp device driver.
5103 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5106 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5109 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
5113 Controls the behavior of vsyscalls (i.e. calls to
5114 fixed addresses of 0xffffffffff600x00 from legacy
5115 code). Most statically-linked binaries and older
5116 versions of glibc use these calls. Because these
5117 functions are at fixed addresses, they make nice
5118 targets for exploits that can control RIP.
5120 emulate [default] Vsyscalls turn into traps and are
5121 emulated reasonably safely. The vsyscall
5124 xonly Vsyscalls turn into traps and are
5125 emulated reasonably safely. The vsyscall
5126 page is not readable.
5128 none Vsyscalls don't work at all. This makes
5129 them quite hard to use for exploits but
5130 might break your system.
5132 vt.color= [VT] Default text color.
5133 Format: 0xYX, X = foreground, Y = background.
5134 Default: 0x07 = light gray on black.
5136 vt.cur_default= [VT] Default cursor shape.
5137 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5138 the parameters of the <Esc>[?A;B;Cc escape sequence;
5139 see VGA-softcursor.txt. Default: 2 = underline.
5141 vt.default_blu= [VT]
5142 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5143 Change the default blue palette of the console.
5144 This is a 16-member array composed of values
5147 vt.default_grn= [VT]
5148 Format: <green0>,<green1>,<green2>,...,<green15>
5149 Change the default green palette of the console.
5150 This is a 16-member array composed of values
5153 vt.default_red= [VT]
5154 Format: <red0>,<red1>,<red2>,...,<red15>
5155 Change the default red palette of the console.
5156 This is a 16-member array composed of values
5162 Set system-wide default UTF-8 mode for all tty's.
5163 Default is 1, i.e. UTF-8 mode is enabled for all
5164 newly opened terminals.
5166 vt.global_cursor_default=
5169 Set system-wide default for whether a cursor
5170 is shown on new VTs. Default is -1,
5171 i.e. cursors will be created by default unless
5172 overridden by individual drivers. 0 will hide
5173 cursors, 1 will display them.
5175 vt.italic= [VT] Default color for italic text; 0-15.
5178 vt.underline= [VT] Default color for underlined text; 0-15.
5181 watchdog timers [HW,WDT] For information on watchdog timers,
5182 see Documentation/watchdog/watchdog-parameters.rst
5183 or other driver-specific files in the
5184 Documentation/watchdog/ directory.
5188 Set the hard lockup detector stall duration
5189 threshold in seconds. The soft lockup detector
5190 threshold is set to twice the value. A value of 0
5191 disables both lockup detectors. Default is 10
5194 workqueue.watchdog_thresh=
5195 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5196 warn stall conditions and dump internal state to
5197 help debugging. 0 disables workqueue stall
5198 detection; otherwise, it's the stall threshold
5199 duration in seconds. The default value is 30 and
5200 it can be updated at runtime by writing to the
5201 corresponding sysfs file.
5203 workqueue.disable_numa
5204 By default, all work items queued to unbound
5205 workqueues are affine to the NUMA nodes they're
5206 issued on, which results in better behavior in
5207 general. If NUMA affinity needs to be disabled for
5208 whatever reason, this option can be used. Note
5209 that this also can be controlled per-workqueue for
5210 workqueues visible under /sys/bus/workqueue/.
5212 workqueue.power_efficient
5213 Per-cpu workqueues are generally preferred because
5214 they show better performance thanks to cache
5215 locality; unfortunately, per-cpu workqueues tend to
5216 be more power hungry than unbound workqueues.
5218 Enabling this makes the per-cpu workqueues which
5219 were observed to contribute significantly to power
5220 consumption unbound, leading to measurably lower
5221 power usage at the cost of small performance
5224 The default value of this parameter is determined by
5225 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5227 workqueue.debug_force_rr_cpu
5228 Workqueue used to implicitly guarantee that work
5229 items queued without explicit CPU specified are put
5230 on the local CPU. This guarantee is no longer true
5231 and while local CPU is still preferred work items
5232 may be put on foreign CPUs. This debug option
5233 forces round-robin CPU selection to flush out
5234 usages which depend on the now broken guarantee.
5235 When enabled, memory and cache locality will be
5238 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5239 default x2apic cluster mode on platforms
5242 x86_intel_mid_timer= [X86-32,APBT]
5243 Choose timer option for x86 Intel MID platform.
5244 Two valid options are apbt timer only and lapic timer
5245 plus one apbt timer for broadcast timer.
5246 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5248 xen_512gb_limit [KNL,X86-64,XEN]
5249 Restricts the kernel running paravirtualized under Xen
5250 to use only up to 512 GB of RAM. The reason to do so is
5251 crash analysis tools and Xen tools for doing domain
5252 save/restore/migration must be enabled to handle larger
5255 xen_emul_unplug= [HW,X86,XEN]
5256 Unplug Xen emulated devices
5257 Format: [unplug0,][unplug1]
5258 ide-disks -- unplug primary master IDE devices
5259 aux-ide-disks -- unplug non-primary-master IDE devices
5260 nics -- unplug network devices
5261 all -- unplug all emulated devices (NICs and IDE disks)
5262 unnecessary -- unplugging emulated devices is
5263 unnecessary even if the host did not respond to
5265 never -- do not unplug even if version check succeeds
5267 xen_nopvspin [X86,XEN]
5268 Disables the ticketlock slowpath using Xen PV
5272 Disables the PV optimizations forcing the HVM guest to
5273 run as generic HVM guest with no PV drivers.
5274 This option is obsoleted by the "nopv" option, which
5275 has equivalent effect for XEN platform.
5277 xen_scrub_pages= [XEN]
5278 Boolean option to control scrubbing pages before giving them back
5279 to Xen, for use by other domains. Can be also changed at runtime
5280 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5281 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5283 xen_timer_slop= [X86-64,XEN]
5284 Set the timer slop (in nanoseconds) for the virtual Xen
5285 timers (default is 100000). This adjusts the minimum
5286 delta of virtualized Xen timers, where lower values
5287 improve timer resolution at the expense of processing
5288 more timer interrupts.
5290 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
5291 Disables the PV optimizations forcing the guest to run
5292 as generic guest with no PV drivers. Currently support
5293 XEN HVM, KVM, HYPER_V and VMWARE guest.
5295 xirc2ps_cs= [NET,PCMCIA]
5297 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5300 By default on POWER9 and above, the kernel will
5301 natively use the XIVE interrupt controller. This option
5302 allows the fallback firmware mode to be used:
5304 off Fallback to firmware control of XIVE interrupt
5305 controller on both pseries and powernv
5306 platforms. Only useful on POWER9 and above.
5308 xhci-hcd.quirks [USB,KNL]
5309 A hex value specifying bitmask with supplemental xhci
5310 host controller quirks. Meaning of each bit can be
5311 consulted in header drivers/usb/host/xhci.h.
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