内核命令行参数¶

See also Documentation/input/joydev/joystick.rst

analog.map= [HW,JOY] Analog joystick and gamepad support

Specifies type or capabilities of an analog joystick

connected to one of 16 gameports

Format: ,,..

apc= [HW,SPARC]

Power management functions (SPARCstation-4/5 + deriv.)

Format: noidle

Disable APC CPU standby support. SPARCstation-Fox does

not play well with APC CPU idle - disable it if you have

APC and your system crashes randomly.

apic [APIC,X86-64] Use IO-APIC. Default.

apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller

Change the output verbosity while booting

Format: { quiet (default) | verbose | debug }

Change the amount of debugging information output

when initialising the APIC and IO-APIC components.

apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting

Format: { bsp (default) | all | none }

bsp: External NMI is delivered only to CPU 0

all: External NMIs are broadcast to all CPUs as a

backup of CPU 0

none: External NMI is masked for all CPUs. This is

useful so that a dump capture kernel won't be

shot down by NMI

apicpmtimer Do APIC timer calibration using the pmtimer. Implies

apicmaintimer. Useful when your PIT timer is totally

broken.

autoconf= [IPV6]

See Documentation/networking/ipv6.rst.

apm= [APM] Advanced Power Management

See header of arch/x86/kernel/apm_32.c.

apparmor= [APPARMOR] Disable or enable AppArmor at boot time

Format: { "0" | "1" }

See security/apparmor/Kconfig help text

0 -- disable.

1 -- enable.

Default value is set via kernel config option.

arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards

Format: ,,

arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of

32 bit applications.

arm64.nobti [ARM64] Unconditionally disable Branch Target

Identification support

arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack

support

arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory

Set instructions support

arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And

Monitoring support

arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension

support

arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication

support

arm64.nosme [ARM64] Unconditionally disable Scalable Matrix

Extension support

arm64.nosve [ARM64] Unconditionally disable Scalable Vector

Extension support

ataflop= [HW,M68k]

atarimouse= [HW,MOUSE] Atari Mouse

atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,

EzKey and similar keyboards

atkbd.reset= [HW] Reset keyboard during initialization

atkbd.set= [HW] Select keyboard code set

Format: (2 = AT (default), 3 = PS/2)

atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar

keyboards

atkbd.softraw= [HW] Choose between synthetic and real raw mode

Format: (0 = real, 1 = synthetic (default))

atkbd.softrepeat= [HW]

Use software keyboard repeat

audit= [KNL] Enable the audit sub-system

Format: { "0" | "1" | "off" | "on" }

0 | off - kernel audit is disabled and can not be

enabled until the next reboot

unset - kernel audit is initialized but disabled and

will be fully enabled by the userspace auditd.

1 | on - kernel audit is initialized and partially

enabled, storing at most audit_backlog_limit

messages in RAM until it is fully enabled by the

userspace auditd.

Default: unset

audit_backlog_limit= [KNL] Set the audit queue size limit.

Format: (must be >=0)

Default: 64

bau= [X86_UV] Enable the BAU on SGI UV. The default

behavior is to disable the BAU (i.e. bau=0).

Format: { "0" | "1" }

0 - Disable the BAU.

1 - Enable the BAU.

unset - Disable the BAU.

baycom_epp= [HW,AX25]

Format: ,

baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem

Format: ,

See header of drivers/net/hamradio/baycom_par.c.

baycom_ser_fdx= [HW,AX25]

BayCom Serial Port AX.25 Modem (Full Duplex Mode)

Format: ,,[,]

See header of drivers/net/hamradio/baycom_ser_fdx.c.

baycom_ser_hdx= [HW,AX25]

BayCom Serial Port AX.25 Modem (Half Duplex Mode)

Format: ,,

See header of drivers/net/hamradio/baycom_ser_hdx.c.

bdev_allow_write_mounted=

Format:

Control the ability to open a mounted block device

for writing, i.e., allow / disallow writes that bypass

the FS. This was implemented as a means to prevent

fuzzers from crashing the kernel by overwriting the

metadata underneath a mounted FS without its awareness.

This also prevents destructive formatting of mounted

filesystems by naive storage tooling that don't use

O_EXCL. Default is Y and can be changed through the

Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED.

bert_disable [ACPI]

Disable BERT OS support on buggy BIOSes.

bgrt_disable [ACPI,X86,EARLY]

Disable BGRT to avoid flickering OEM logo.

blkdevparts= Manual partition parsing of block device(s) for

embedded devices based on command line input.

See Documentation/block/cmdline-partition.rst

boot_delay= [KNL,EARLY]

Milliseconds to delay each printk during boot.

Only works if CONFIG_BOOT_PRINTK_DELAY is enabled,

and you may also have to specify "lpj=". Boot_delay

values larger than 10 seconds (10000) are assumed

erroneous and ignored.

Format: integer

bootconfig [KNL,EARLY]

Extended command line options can be added to an initrd

and this will cause the kernel to look for it.

See Documentation/admin-guide/bootconfig.rst

bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)

bttv.radio= Most important insmod options are available as

kernel args too.

bttv.pll= See Documentation/admin-guide/media/bttv.rst

bttv.tuner=

bulk_remove=off [PPC] This parameter disables the use of the pSeries

firmware feature for flushing multiple hpte entries

at a time.

c101= [NET] Moxa C101 synchronous serial card

cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.

Sometimes CPU hardware bugs make them report the cache

size incorrectly. The kernel will attempt work arounds

to fix known problems, but for some CPUs it is not

possible to determine what the correct size should be.

This option provides an override for these situations.

carrier_timeout=

[NET] Specifies amount of time (in seconds) that

the kernel should wait for a network carrier. By default

it waits 120 seconds.

ca_keys= [KEYS] This parameter identifies a specific key(s) on

the system trusted keyring to be used for certificate

trust validation.

format: { id: | builtin }

cca= [MIPS,EARLY] Override the kernel pages' cache coherency

algorithm. Accepted values range from 0 to 7

inclusive. See arch/mips/include/asm/pgtable-bits.h

for platform specific values (SB1, Loongson3 and

others).

ccw_timeout_log [S390]

See Documentation/arch/s390/common_io.rst for details.

cgroup_disable= [KNL] Disable a particular controller or optional feature

Format: {name of the controller(s) or feature(s) to disable}

The effects of cgroup_disable=foo are:

- foo isn't auto-mounted if you mount all cgroups in

a single hierarchy

- foo isn't visible as an individually mountable

subsystem

- if foo is an optional feature then the feature is

disabled and corresponding cgroup files are not

created

{Currently only "memory" controller deal with this and

cut the overhead, others just disable the usage. So

only cgroup_disable=memory is actually worthy}

Specifying "pressure" disables per-cgroup pressure

stall information accounting feature

cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1

Format: { { controller | "all" | "named" }

[,{ controller | "all" | "named" }...] }

Like cgroup_disable, but only applies to cgroup v1;

the blacklisted controllers remain available in cgroup2.

"all" blacklists all controllers and "named" disables

named mounts. Specifying both "all" and "named" disables

all v1 hierarchies.

cgroup_favordynmods= [KNL] Enable or Disable favordynmods.

Format: { "true" | "false" }

Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS.

cgroup.memory= [KNL] Pass options to the cgroup memory controller.

Format:

nosocket -- Disable socket memory accounting.

nokmem -- Disable kernel memory accounting.

nobpf -- Disable BPF memory accounting.

checkreqprot= [SELINUX] Set initial checkreqprot flag value.

Format: { "0" | "1" }

See security/selinux/Kconfig help text.

0 -- check protection applied by kernel (includes

any implied execute protection).

1 -- check protection requested by application.

Default value is set via a kernel config option.

Value can be changed at runtime via

/sys/fs/selinux/checkreqprot.

Setting checkreqprot to 1 is deprecated.

cio_ignore= [S390]

See Documentation/arch/s390/common_io.rst for details.

clearcpuid=X[,X...] [X86]

Disable CPUID feature X for the kernel. See

arch/x86/include/asm/cpufeatures.h for the valid bit

numbers X. Note the Linux-specific bits are not necessarily

stable over kernel options, but the vendor-specific

ones should be.

X can also be a string as appearing in the flags: line

in /proc/cpuinfo which does not have the above

instability issue. However, not all features have names

in /proc/cpuinfo.

Note that using this option will taint your kernel.

Also note that user programs calling CPUID directly

or using the feature without checking anything

will still see it. This just prevents it from

being used by the kernel or shown in /proc/cpuinfo.

Also note the kernel might malfunction if you disable

some critical bits.

clk_ignore_unused

[CLK]

Prevents the clock framework from automatically gating

clocks that have not been explicitly enabled by a Linux

device driver but are enabled in hardware at reset or

by the bootloader/firmware. Note that this does not

force such clocks to be always-on nor does it reserve

those clocks in any way. This parameter is useful for

debug and development, but should not be needed on a

platform with proper driver support. For more

information, see Documentation/driver-api/clk.rst.

clock= [BUGS=X86-32, HW] gettimeofday clocksource override.

[Deprecated]

Forces specified clocksource (if available) to be used

when calculating gettimeofday(). If specified

clocksource is not available, it defaults to PIT.

Format: { pit | tsc | cyclone | pmtmr }

clocksource= Override the default clocksource

Format:

Override the default clocksource and use the clocksource

with the name specified.

Some clocksource names to choose from, depending on

the platform:

[all] jiffies (this is the base, fallback clocksource)

[ACPI] acpi_pm

[ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,

pxa_timer,timer3,32k_counter,timer0_1

[X86-32] pit,hpet,tsc;

scx200_hrt on Geode; cyclone on IBM x440

[MIPS] MIPS

[PARISC] cr16

[S390] tod

[SH] SuperH

[SPARC64] tick

[X86-64] hpet,tsc

clocksource.arm_arch_timer.evtstrm=

[ARM,ARM64,EARLY]

Format:

Enable/disable the eventstream feature of the ARM

architected timer so that code using WFE-based polling

loops can be debugged more effectively on production

systems.

clocksource.verify_n_cpus= [KNL]

Limit the number of CPUs checked for clocksources

marked with CLOCK_SOURCE_VERIFY_PERCPU that

are marked unstable due to excessive skew.

A negative value says to check all CPUs, while

zero says not to check any. Values larger than

nr_cpu_ids are silently truncated to nr_cpu_ids.

The actual CPUs are chosen randomly, with

no replacement if the same CPU is chosen twice.

clocksource-wdtest.holdoff= [KNL]

Set the time in seconds that the clocksource

watchdog test waits before commencing its tests.

Defaults to zero when built as a module and to

10 seconds when built into the kernel.

cma=nn[MG]@[start[MG][-end[MG]]]

[KNL,CMA,EARLY]

Sets the size of kernel global memory area for

contiguous memory allocations and optionally the

placement constraint by the physical address range of

memory allocations. A value of 0 disables CMA

altogether. For more information, see

kernel/dma/contiguous.c

cma_pernuma=nn[MG]

[KNL,CMA,EARLY]

Sets the size of kernel per-numa memory area for

contiguous memory allocations. A value of 0 disables

per-numa CMA altogether. And If this option is not

specified, the default value is 0.

With per-numa CMA enabled, DMA users on node nid will

first try to allocate buffer from the pernuma area

which is located in node nid, if the allocation fails,

they will fallback to the global default memory area.

numa_cma=:nn[MG][,:nn[MG]]

[KNL,CMA,EARLY]

Sets the size of kernel numa memory area for

contiguous memory allocations. It will reserve CMA

area for the specified node.

With numa CMA enabled, DMA users on node nid will

first try to allocate buffer from the numa area

which is located in node nid, if the allocation fails,

they will fallback to the global default memory area.

cmo_free_hint= [PPC] Format: { yes | no }

Specify whether pages are marked as being inactive

when they are freed. This is used in CMO environments

to determine OS memory pressure for page stealing by

a hypervisor.

Default: yes

coherent_pool=nn[KMG] [ARM,KNL,EARLY]

Sets the size of memory pool for coherent, atomic dma

allocations, by default set to 256K.

com20020= [HW,NET] ARCnet - COM20020 chipset

Format:

[,[,[,[,[,]]]]]

com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)

Format: [,]

com90xx= [HW,NET]

ARCnet - COM90xx chipset (memory-mapped buffers)

Format: [,[,]]

condev= [HW,S390] console device

conmode=

con3215_drop= [S390,EARLY] 3215 console drop mode.

Format: y|n|Y|N|1|0

When set to true, drop data on the 3215 console when

the console buffer is full. In this case the

operator using a 3270 terminal emulator (for example

x3270) does not have to enter the clear key for the

console output to advance and the kernel to continue.

This leads to a much faster boot time when a 3270

terminal emulator is active. If no 3270 terminal

emulator is used, this parameter has no effect.

console= [KNL] Output console device and options.

tty Use the virtual console device .

ttyS[,options]

ttyUSB0[,options]

Use the specified serial port. The options are of

the form "bbbbpnf", where "bbbb" is the baud rate,

"p" is parity ("n", "o", or "e"), "n" is number of

bits, and "f" is flow control ("r" for RTS or

omit it). Default is "9600n8".

See Documentation/admin-guide/serial-console.rst for more

information. See

Documentation/networking/netconsole.rst for an

alternative.

:.[,options]

Use the specified serial port on the serial core bus.

The addressing uses DEVNAME of the physical serial port

device, followed by the serial core controller instance,

and the serial port instance. The options are the same

as documented for the ttyS addressing above.

The mapping of the serial ports to the tty instances

can be viewed with:

$ ls -d /sys/bus/serial-base/devices/*:*.*/tty/*

/sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0

In the above example, the console can be addressed with

console=00:04:0.0. Note that a console addressed this

way will only get added when the related device driver

is ready. The use of an earlycon parameter in addition to

the console may be desired for console output early on.

uart[8250],io,[,options]

uart[8250],mmio,[,options]

uart[8250],mmio16,[,options]

uart[8250],mmio32,[,options]

uart[8250],0x[,options]

Start an early, polled-mode console on the 8250/16550

UART at the specified I/O port or MMIO address,

switching to the matching ttyS device later.

MMIO inter-register address stride is either 8-bit

(mmio), 16-bit (mmio16), or 32-bit (mmio32).

If none of [io|mmio|mmio16|mmio32], is assumed

to be equivalent to 'mmio'. 'options' are specified in

the same format described for ttyS above; if unspecified,

the h/w is not re-initialized.

hvc Use the hypervisor console device . This is for

both Xen and PowerPC hypervisors.

{ null | "" }

Use to disable console output, i.e., to have kernel

console messages discarded.

This must be the only console= parameter used on the

kernel command line.

If the device connected to the port is not a TTY but a braille

device, prepend "brl," before the device type, for instance

console=brl,ttyS0

For now, only VisioBraille is supported.

console_msg_format=

[KNL] Change console messages format

default

By default we print messages on consoles in

"[time stamp] text\n" format (time stamp may not be

printed, depending on CONFIG_PRINTK_TIME or

`printk_time' param).

syslog

Switch to syslog format: "<%u>[time stamp] text\n"

IOW, each message will have a facility and loglevel

prefix. The format is similar to one used by syslog()

syscall, or to executing "dmesg -S --raw" or to reading

from /proc/kmsg.

consoleblank= [KNL] The console blank (screen saver) timeout in

seconds. A value of 0 disables the blank timer.

Defaults to 0.

coredump_filter=

[KNL] Change the default value for

/proc//coredump_filter.

See also Documentation/filesystems/proc.rst.

coresight_cpu_debug.enable

[ARM,ARM64]

Format:

Enable/disable the CPU sampling based debugging.

0: default value, disable debugging

1: enable debugging at boot time

cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver

Format:

,,,[,]

cpuidle.off=1 [CPU_IDLE]

disable the cpuidle sub-system

cpuidle.governor=

[CPU_IDLE] Name of the cpuidle governor to use.

cpufreq.off=1 [CPU_FREQ]

disable the cpufreq sub-system

cpufreq.default_governor=

[CPU_FREQ] Name of the default cpufreq governor or

policy to use. This governor must be registered in the

kernel before the cpufreq driver probes.

cpu_init_udelay=N

[X86,EARLY] Delay for N microsec between assert and de-assert

of APIC INIT to start processors. This delay occurs

on every CPU online, such as boot, and resume from suspend.

Default: 10000

cpuhp.parallel=

[SMP] Enable/disable parallel bringup of secondary CPUs

Format:

Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise

the parameter has no effect.

crash_kexec_post_notifiers

Only jump to kdump kernel after running the panic

notifiers and dumping kmsg. This option increases

the risks of a kdump failure, since some panic

notifiers can make the crashed kernel more unstable.

In configurations where kdump may not be reliable,

running the panic notifiers could allow collecting

more data on dmesg, like stack traces from other CPUS

or extra data dumped by panic_print. Note that some

configurations enable this option unconditionally,

like Hyper-V, PowerPC (fadump) and AMD SEV-SNP.

crashkernel=size[KMG][@offset[KMG]]

[KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel'

upon panic. This parameter reserves the physical

memory region [offset, offset + size] for that kernel

image. If '@offset' is omitted, then a suitable offset

is selected automatically.

[KNL, X86-64, ARM64, RISCV, LoongArch] Select a region

under 4G first, and fall back to reserve region above

4G when '@offset' hasn't been specified.

See Documentation/admin-guide/kdump/kdump.rst for further details.

crashkernel=range1:size1[,range2:size2,...][@offset]

[KNL] Same as above, but depends on the memory

in the running system. The syntax of range is

start-[end] where start and end are both

a memory unit (amount[KMG]). See also

Documentation/admin-guide/kdump/kdump.rst for an example.

crashkernel=size[KMG],high

[KNL, X86-64, ARM64, RISCV, LoongArch] range could be

above 4G.

Allow kernel to allocate physical memory region from top,

so could be above 4G if system have more than 4G ram

installed. Otherwise memory region will be allocated

below 4G, if available.

It will be ignored if crashkernel=X is specified.

crashkernel=size[KMG],low

[KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G.

When crashkernel=X,high is passed, kernel could allocate

physical memory region above 4G, that cause second kernel

crash on system that require some amount of low memory,

e.g. swiotlb requires at least 64M+32K low memory, also

enough extra low memory is needed to make sure DMA buffers

for 32-bit devices won't run out. Kernel would try to allocate

default size of memory below 4G automatically. The default

size is platform dependent.

--> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB)

--> arm64: 128MiB

--> riscv: 128MiB

--> loongarch: 128MiB

This one lets the user specify own low range under 4G

for second kernel instead.

0: to disable low allocation.

It will be ignored when crashkernel=X,high is not used

or memory reserved is below 4G.

cryptomgr.notests

[KNL] Disable crypto self-tests

cs89x0_dma= [HW,NET]

Format:

cs89x0_media= [HW,NET]

Format: { rj45 | aui | bnc }

csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU

function call handling. When switched on,

additional debug data is printed to the console

in case a hanging CPU is detected, and that

CPU is pinged again in order to try to resolve

the hang situation. The default value of this

option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT

Kconfig option.

dasd= [HW,NET]

See header of drivers/s390/block/dasd_devmap.c.

db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port

(one device per port)

Format: ,

See also Documentation/input/devices/joystick-parport.rst

debug [KNL,EARLY] Enable kernel debugging (events log level).

debug_boot_weak_hash

[KNL,EARLY] Enable printing [hashed] pointers early in the

boot sequence. If enabled, we use a weak hash instead

of siphash to hash pointers. Use this option if you are

seeing instances of '(___ptrval___)') and need to see a

value (hashed pointer) instead. Cryptographically

insecure, please do not use on production kernels.

debug_locks_verbose=

[KNL] verbose locking self-tests

Format:

Print debugging info while doing the locking API

self-tests.

Bitmask for the various LOCKTYPE_ tests. Defaults to 0

(no extra messages), setting it to -1 (all bits set)

will print _a_lot_ more information - normally only

useful to lockdep developers.

debug_objects [KNL,EARLY] Enable object debugging

debug_guardpage_minorder=

[KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this

parameter allows control of the order of pages that will

be intentionally kept free (and hence protected) by the

buddy allocator. Bigger value increase the probability

of catching random memory corruption, but reduce the

amount of memory for normal system use. The maximum

possible value is MAX_PAGE_ORDER/2. Setting this

parameter to 1 or 2 should be enough to identify most

random memory corruption problems caused by bugs in

kernel or driver code when a CPU writes to (or reads

from) a random memory location. Note that there exists

a class of memory corruptions problems caused by buggy

H/W or F/W or by drivers badly programming DMA

(basically when memory is written at bus level and the

CPU MMU is bypassed) which are not detectable by

CONFIG_DEBUG_PAGEALLOC, hence this option will not

help tracking down these problems.

debug_pagealloc=

[KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter

enables the feature at boot time. By default, it is

disabled and the system will work mostly the same as a

kernel built without CONFIG_DEBUG_PAGEALLOC.

Note: to get most of debug_pagealloc error reports, it's

useful to also enable the page_owner functionality.

on: enable the feature

debugfs= [KNL,EARLY] This parameter enables what is exposed to

userspace and debugfs internal clients.

Format: { on, no-mount, off }

on: All functions are enabled.

no-mount:

Filesystem is not registered but kernel clients can

access APIs and a crashkernel can be used to read

its content. There is nothing to mount.

off: Filesystem is not registered and clients

get a -EPERM as result when trying to register files

or directories within debugfs.

This is equivalent of the runtime functionality if

debugfs was not enabled in the kernel at all.

Default value is set in build-time with a kernel configuration.

debugpat [X86] Enable PAT debugging

default_hugepagesz=

[HW] The size of the default HugeTLB page. This is

the size represented by the legacy /proc/ hugepages

APIs. In addition, this is the default hugetlb size

used for shmget(), mmap() and mounting hugetlbfs

filesystems. If not specified, defaults to the

architecture's default huge page size. Huge page

sizes are architecture dependent. See also

Documentation/admin-guide/mm/hugetlbpage.rst.

Format: size[KMG]

deferred_probe_timeout=

[KNL] Debugging option to set a timeout in seconds for

deferred probe to give up waiting on dependencies to

probe. Only specific dependencies (subsystems or

drivers) that have opted in will be ignored. A timeout

of 0 will timeout at the end of initcalls. If the time

out hasn't expired, it'll be restarted by each

successful driver registration. This option will also

dump out devices still on the deferred probe list after

retrying.

delayacct [KNL] Enable per-task delay accounting

dell_smm_hwmon.ignore_dmi=

[HW] Continue probing hardware even if DMI data

indicates that the driver is running on unsupported

hardware.

dell_smm_hwmon.force=

[HW] Activate driver even if SMM BIOS signature does

not match list of supported models and enable otherwise

blacklisted features.

dell_smm_hwmon.power_status=

[HW] Report power status in /proc/i8k

(disabled by default).

dell_smm_hwmon.restricted=

[HW] Allow controlling fans only if SYS_ADMIN

capability is set.

dell_smm_hwmon.fan_mult=

[HW] Factor to multiply fan speed with.

dell_smm_hwmon.fan_max=

[HW] Maximum configurable fan speed.

dfltcc= [HW,S390]

Format: { on | off | def_only | inf_only | always }

on: s390 zlib hardware support for compression on

level 1 and decompression (default)

off: No s390 zlib hardware support

def_only: s390 zlib hardware support for deflate

only (compression on level 1)

inf_only: s390 zlib hardware support for inflate

only (decompression)

always: Same as 'on' but ignores the selected compression

level always using hardware support (used for debugging)

dhash_entries= [KNL]

Set number of hash buckets for dentry cache.

disable_1tb_segments [PPC,EARLY]

Disables the use of 1TB hash page table segments. This

causes the kernel to fall back to 256MB segments which

can be useful when debugging issues that require an SLB

miss to occur.

disable= [IPV6]

See Documentation/networking/ipv6.rst.

disable_radix [PPC,EARLY]

Disable RADIX MMU mode on POWER9

disable_tlbie [PPC]

Disable TLBIE instruction. Currently does not work

with KVM, with HASH MMU, or with coherent accelerators.

disable_ddw [PPC/PSERIES,EARLY]

Disable Dynamic DMA Window support. Use this

to workaround buggy firmware.

disable_ipv6= [IPV6]

See Documentation/networking/ipv6.rst.

disable_mtrr_cleanup [X86,EARLY]

The kernel tries to adjust MTRR layout from continuous

to discrete, to make X server driver able to add WB

entry later. This parameter disables that.

disable_mtrr_trim [X86, Intel and AMD only,EARLY]

By default the kernel will trim any uncacheable

memory out of your available memory pool based on

MTRR settings. This parameter disables that behavior,

possibly causing your machine to run very slowly.

disable_timer_pin_1 [X86,EARLY]

Disable PIN 1 of APIC timer

Can be useful to work around chipset bugs.

dis_ucode_ldr [X86] Disable the microcode loader.

dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,

this option disables the debugging code at boot.

dma_debug_entries=

This option allows to tune the number of preallocated

entries for DMA-API debugging code. One entry is

required per DMA-API allocation. Use this if the

DMA-API debugging code disables itself because the

architectural default is too low.

dma_debug_driver=

With this option the DMA-API debugging driver

filter feature can be enabled at boot time. Just

pass the driver to filter for as the parameter.

The filter can be disabled or changed to another

driver later using sysfs.

reg_file_data_sampling=

[X86] Controls mitigation for Register File Data

Sampling (RFDS) vulnerability. RFDS is a CPU

vulnerability which may allow userspace to infer

kernel data values previously stored in floating point

registers, vector registers, or integer registers.

RFDS only affects Intel Atom processors.

on: Turns ON the mitigation.

off: Turns OFF the mitigation.

This parameter overrides the compile time default set

by CONFIG_MITIGATION_RFDS. Mitigation cannot be

disabled when other VERW based mitigations (like MDS)

are enabled. In order to disable RFDS mitigation all

VERW based mitigations need to be disabled.

For details see:

Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst

driver_async_probe= [KNL]

List of driver names to be probed asynchronously. *

matches with all driver names. If * is specified, the

rest of the listed driver names are those that will NOT

match the *.

Format: ,...

drm.edid_firmware=[:][,[:]]

Broken monitors, graphic adapters, KVMs and EDIDless

panels may send no or incorrect EDID data sets.

This parameter allows to specify an EDID data sets

in the /lib/firmware directory that are used instead.

An EDID data set will only be used for a particular

connector, if its name and a colon are prepended to

the EDID name. Each connector may use a unique EDID

data set by separating the files with a comma. An EDID

data set with no connector name will be used for

any connectors not explicitly specified.

dscc4.setup= [NET]

dt_cpu_ftrs= [PPC,EARLY]

Format: {"off" | "known"}

Control how the dt_cpu_ftrs device-tree binding is

used for CPU feature discovery and setup (if it

exists).

off: Do not use it, fall back to legacy cpu table.

known: Do not pass through unknown features to guests

or userspace, only those that the kernel is aware of.

dump_apple_properties [X86]

Dump name and content of EFI device properties on

x86 Macs. Useful for driver authors to determine

what data is available or for reverse-engineering.

dyndbg[="val"] [KNL,DYNAMIC_DEBUG]

.dyndbg[="val"]

Enable debug messages at boot time. See

Documentation/admin-guide/dynamic-debug-howto.rst

for details.

early_ioremap_debug [KNL,EARLY]

Enable debug messages in early_ioremap support. This

is useful for tracking down temporary early mappings

which are not unmapped.

earlycon= [KNL,EARLY] Output early console device and options.

When used with no options, the early console is

determined by stdout-path property in device tree's

chosen node or the ACPI SPCR table if supported by

the platform.

cdns,[,options]

Start an early, polled-mode console on a Cadence

(xuartps) serial port at the specified address. Only

supported option is baud rate. If baud rate is not

specified, the serial port must already be setup and

configured.

uart[8250],io,[,options[,uartclk]]

uart[8250],mmio,[,options[,uartclk]]

uart[8250],mmio32,[,options[,uartclk]]

uart[8250],mmio32be,[,options[,uartclk]]

uart[8250],0x[,options]

Start an early, polled-mode console on the 8250/16550

UART at the specified I/O port or MMIO address.

MMIO inter-register address stride is either 8-bit

(mmio) or 32-bit (mmio32 or mmio32be).

If none of [io|mmio|mmio32|mmio32be], is assumed

to be equivalent to 'mmio'. 'options' are specified

in the same format described for "console=ttyS"; if

unspecified, the h/w is not initialized. 'uartclk' is

the uart clock frequency; if unspecified, it is set

to 'BASE_BAUD' * 16.

pl011,

pl011,mmio32,

Start an early, polled-mode console on a pl011 serial

port at the specified address. The pl011 serial port

must already be setup and configured. Options are not

yet supported. If 'mmio32' is specified, then only

the driver will use only 32-bit accessors to read/write

the device registers.

liteuart,

Start an early console on a litex serial port at the

specified address. The serial port must already be

setup and configured. Options are not yet supported.

meson,

Start an early, polled-mode console on a meson serial

port at the specified address. The serial port must

already be setup and configured. Options are not yet

supported.

msm_serial,

Start an early, polled-mode console on an msm serial

port at the specified address. The serial port

must already be setup and configured. Options are not

yet supported.

msm_serial_dm,

Start an early, polled-mode console on an msm serial

dm port at the specified address. The serial port

must already be setup and configured. Options are not

yet supported.

owl,

Start an early, polled-mode console on a serial port

of an Actions Semi SoC, such as S500 or S900, at the

specified address. The serial port must already be

setup and configured. Options are not yet supported.

rda,

Start an early, polled-mode console on a serial port

of an RDA Micro SoC, such as RDA8810PL, at the

specified address. The serial port must already be

setup and configured. Options are not yet supported.

sbi

Use RISC-V SBI (Supervisor Binary Interface) for early

console.

smh Use ARM semihosting calls for early console.

s3c2410,

s3c2412,

s3c2440,

s3c6400,

s5pv210,

exynos4210,

Use early console provided by serial driver available

on Samsung SoCs, requires selecting proper type and

a correct base address of the selected UART port. The

serial port must already be setup and configured.

Options are not yet supported.

lantiq,

Start an early, polled-mode console on a lantiq serial

(lqasc) port at the specified address. The serial port

must already be setup and configured. Options are not

yet supported.

lpuart,

lpuart32,

Use early console provided by Freescale LP UART driver

found on Freescale Vybrid and QorIQ LS1021A processors.

A valid base address must be provided, and the serial

port must already be setup and configured.

ec_imx21,

ec_imx6q,

Start an early, polled-mode, output-only console on the

Freescale i.MX UART at the specified address. The UART

must already be setup and configured.

ar3700_uart,

Start an early, polled-mode console on the

Armada 3700 serial port at the specified

address. The serial port must already be setup

and configured. Options are not yet supported.

qcom_geni,

Start an early, polled-mode console on a Qualcomm

Generic Interface (GENI) based serial port at the

specified address. The serial port must already be

setup and configured. Options are not yet supported.

efifb,[options]

Start an early, unaccelerated console on the EFI

memory mapped framebuffer (if available). On cache

coherent non-x86 systems that use system memory for

the framebuffer, pass the 'ram' option so that it is

mapped with the correct attributes.

linflex,

Use early console provided by Freescale LINFlexD UART

serial driver for NXP S32V234 SoCs. A valid base

address must be provided, and the serial port must

already be setup and configured.

earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY]

earlyprintk=vga

earlyprintk=sclp

earlyprintk=xen

earlyprintk=serial[,ttySn[,baudrate]]

earlyprintk=serial[,0x...[,baudrate]]

earlyprintk=ttySn[,baudrate]

earlyprintk=dbgp[debugController#]

earlyprintk=mmio32,membase[,{nocfg|baudrate}]

earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}]

earlyprintk=xdbc[xhciController#]

earlyprintk=bios

earlyprintk is useful when the kernel crashes before

the normal console is initialized. It is not enabled by

default because it has some cosmetic problems.

Use "nocfg" to skip UART configuration, assume

BIOS/firmware has configured UART correctly.

Append ",keep" to not disable it when the real console

takes over.

Only one of vga, serial, or usb debug port can

be used at a time.

Currently only ttyS0 and ttyS1 may be specified by

name. Other I/O ports may be explicitly specified

on some architectures (x86 and arm at least) by

replacing ttySn with an I/O port address, like this:

earlyprintk=serial,0x1008,115200

You can find the port for a given device in

/proc/tty/driver/serial:

2: uart:ST16650V2 port:00001008 irq:18 ...

Interaction with the standard serial driver is not

very good.

The VGA output is eventually overwritten by

the real console.

The xen option can only be used in Xen domains.

The sclp output can only be used on s390.

The bios output can only be used on SuperH.

The optional "force" to "pciserial" enables use of a

PCI device even when its classcode is not of the

UART class.

edac_report= [HW,EDAC] Control how to report EDAC event

Format: {"on" | "off" | "force"}

on: enable EDAC to report H/W event. May be overridden

by other higher priority error reporting module.

off: disable H/W event reporting through EDAC.

force: enforce the use of EDAC to report H/W event.

default: on.

edd= [EDD]

Format: {"off" | "on" | "skip[mbr]"}

efi= [EFI,EARLY]

Format: { "debug", "disable_early_pci_dma",

"nochunk", "noruntime", "nosoftreserve",

"novamap", "no_disable_early_pci_dma" }

debug: enable misc debug output.

disable_early_pci_dma: disable the busmaster bit on all

PCI bridges while in the EFI boot stub.

nochunk: disable reading files in "chunks" in the EFI

boot stub, as chunking can cause problems with some

firmware implementations.

noruntime : disable EFI runtime services support

nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)

attribute may cause the kernel to reserve the

memory range for a memory mapping driver to

claim. Specify efi=nosoftreserve to disable this

reservation and treat the memory by its base type

(i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").

novamap: do not call SetVirtualAddressMap().

no_disable_early_pci_dma: Leave the busmaster bit set

on all PCI bridges while in the EFI boot stub

efi_no_storage_paranoia [EFI,X86,EARLY]

Using this parameter you can use more than 50% of

your efi variable storage. Use this parameter only if

you are really sure that your UEFI does sane gc and

fulfills the spec otherwise your board may brick.

efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT

that is to be dynamically loaded by Linux. If there are

multiple variables with the same name but with different

vendor GUIDs, all of them will be loaded. See

Documentation/admin-guide/acpi/ssdt-overlays.rst for details.

eisa_irq_edge= [PARISC,HW]

See header of drivers/parisc/eisa.c.

ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging

Format: ekgdboc=kbd

This is designed to be used in conjunction with

the boot argument: earlyprintk=vga

This parameter works in place of the kgdboc parameter

but can only be used if the backing tty is available

very early in the boot process. For early debugging

via a serial port see kgdboc_earlycon instead.

elanfreq= [X86-32]

See comment before function elanfreq_setup() in

arch/x86/kernel/cpu/cpufreq/elanfreq.c.

elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY]

Specifies physical address of start of kernel core

image elf header and optionally the size. Generally

kexec loader will pass this option to capture kernel.

See Documentation/admin-guide/kdump/kdump.rst for details.

enable_mtrr_cleanup [X86,EARLY]

The kernel tries to adjust MTRR layout from continuous

to discrete, to make X server driver able to add WB

entry later. This parameter enables that.

enable_timer_pin_1 [X86]

Enable PIN 1 of APIC timer

Can be useful to work around chipset bugs

(in particular on some ATI chipsets).

The kernel tries to set a reasonable default.

enforcing= [SELINUX] Set initial enforcing status.

Format: {"0" | "1"}

See security/selinux/Kconfig help text.

0 -- permissive (log only, no denials).

1 -- enforcing (deny and log).

Default value is 0.

Value can be changed at runtime via

/sys/fs/selinux/enforce.

erst_disable [ACPI]

Disable Error Record Serialization Table (ERST)

support.

ether= [HW,NET] Ethernet cards parameters

This option is obsoleted by the "netdev=" option, which

has equivalent usage. See its documentation for details.

evm= [EVM]

Format: { "fix" }

Permit 'security.evm' to be updated regardless of

current integrity status.

early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier

stages so cover more early boot allocations.

Please note that as side effect some optimizations

might be disabled to achieve that (e.g. parallelized

memory initialization is disabled) so the boot process

might take longer, especially on systems with a lot of

memory. Available with CONFIG_PAGE_EXTENSION=y.

failslab=

fail_usercopy=

fail_page_alloc=

fail_skb_realloc=

fail_make_request=[KNL]

General fault injection mechanism.

Format: ,,,

See also Documentation/fault-injection/.

fb_tunnels= [NET]

Format: { initns | none }

See Documentation/admin-guide/sysctl/net.rst for

fb_tunnels_only_for_init_ns

floppy= [HW]

See Documentation/admin-guide/blockdev/floppy.rst.

forcepae [X86-32]

Forcefully enable Physical Address Extension (PAE).

Many Pentium M systems disable PAE but may have a

functionally usable PAE implementation.

Warning: use of this parameter will taint the kernel

and may cause unknown problems.

fred= [X86-64]

Enable/disable Flexible Return and Event Delivery.

Format: { on | off }

on: enable FRED when it's present.

off: disable FRED, the default setting.

ftrace=[tracer]

[FTRACE] will set and start the specified tracer

as early as possible in order to facilitate early

boot debugging.

ftrace_boot_snapshot

[FTRACE] On boot up, a snapshot will be taken of the

ftrace ring buffer that can be read at:

/sys/kernel/tracing/snapshot.

This is useful if you need tracing information from kernel

boot up that is likely to be overridden by user space

start up functionality.

Optionally, the snapshot can also be defined for a tracing

instance that was created by the trace_instance= command

line parameter.

trace_instance=foo,sched_switch ftrace_boot_snapshot=foo

The above will cause the "foo" tracing instance to trigger

a snapshot at the end of boot up.

ftrace_dump_on_oops[=2(orig_cpu) | =][, |

,=2(orig_cpu)]

[FTRACE] will dump the trace buffers on oops.

If no parameter is passed, ftrace will dump global

buffers of all CPUs, if you pass 2 or orig_cpu, it

will dump only the buffer of the CPU that triggered

the oops, or the specific instance will be dumped if

its name is passed. Multiple instance dump is also

supported, and instances are separated by commas. Each

instance supports only dump on CPU that triggered the

oops by passing 2 or orig_cpu to it.

ftrace_dump_on_oops=foo=orig_cpu

The above will dump only the buffer of "foo" instance

on CPU that triggered the oops.

ftrace_dump_on_oops,foo,bar=orig_cpu

The above will dump global buffer on all CPUs, the

buffer of "foo" instance on all CPUs and the buffer

of "bar" instance on CPU that triggered the oops.

ftrace_filter=[function-list]

[FTRACE] Limit the functions traced by the function

tracer at boot up. function-list is a comma-separated

list of functions. This list can be changed at run

time by the set_ftrace_filter file in the debugfs

tracing directory.

ftrace_notrace=[function-list]

[FTRACE] Do not trace the functions specified in

function-list. This list can be changed at run time

by the set_ftrace_notrace file in the debugfs

tracing directory.

ftrace_graph_filter=[function-list]

[FTRACE] Limit the top level callers functions traced

by the function graph tracer at boot up.

function-list is a comma-separated list of functions

that can be changed at run time by the

set_graph_function file in the debugfs tracing directory.

ftrace_graph_notrace=[function-list]

[FTRACE] Do not trace from the functions specified in

function-list. This list is a comma-separated list of

functions that can be changed at run time by the

set_graph_notrace file in the debugfs tracing directory.

ftrace_graph_max_depth=

[FTRACE] Used with the function graph tracer. This is

the max depth it will trace into a function. This value

can be changed at run time by the max_graph_depth file

in the tracefs tracing directory. default: 0 (no limit)

fw_devlink= [KNL,EARLY] Create device links between consumer and supplier

devices by scanning the firmware to infer the

consumer/supplier relationships. This feature is

especially useful when drivers are loaded as modules as

it ensures proper ordering of tasks like device probing

(suppliers first, then consumers), supplier boot state

clean up (only after all consumers have probed),

suspend/resume & runtime PM (consumers first, then

suppliers).

Format: { off | permissive | on | rpm }

off -- Don't create device links from firmware info.

permissive -- Create device links from firmware info

but use it only for ordering boot state clean

up (sync_state() calls).

on -- Create device links from firmware info and use it

to enforce probe and suspend/resume ordering.

rpm -- Like "on", but also use to order runtime PM.

fw_devlink.strict=

[KNL,EARLY] Treat all inferred dependencies as mandatory

dependencies. This only applies for fw_devlink=on|rpm.

Format:

fw_devlink.sync_state =

[KNL,EARLY] When all devices that could probe have finished

probing, this parameter controls what to do with

devices that haven't yet received their sync_state()

calls.

Format: { strict | timeout }

strict -- Default. Continue waiting on consumers to

probe successfully.

timeout -- Give up waiting on consumers and call

sync_state() on any devices that haven't yet

received their sync_state() calls after

deferred_probe_timeout has expired or by

late_initcall() if !CONFIG_MODULES.

gamecon.map[2|3]=

[HW,JOY] Multisystem joystick and NES/SNES/PSX pad

support via parallel port (up to 5 devices per port)

Format: ,,,,,

See also Documentation/input/devices/joystick-parport.rst

gamma= [HW,DRM]

gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART

Format: off | on

default: on

gather_data_sampling=

[X86,INTEL,EARLY] Control the Gather Data Sampling (GDS)

mitigation.

Gather Data Sampling is a hardware vulnerability which

allows unprivileged speculative access to data which was

previously stored in vector registers.

This issue is mitigated by default in updated microcode.

The mitigation may have a performance impact but can be

disabled. On systems without the microcode mitigation

disabling AVX serves as a mitigation.

force: Disable AVX to mitigate systems without

microcode mitigation. No effect if the microcode

mitigation is present. Known to cause crashes in

userspace with buggy AVX enumeration.

off: Disable GDS mitigation.

gbpages [X86] Use GB pages for kernel direct mappings.

gcov_persist= [GCOV] When non-zero (default), profiling data for

kernel modules is saved and remains accessible via

debugfs, even when the module is unloaded/reloaded.

When zero, profiling data is discarded and associated

debugfs files are removed at module unload time.

goldfish [X86] Enable the goldfish android emulator platform.

Don't use this when you are not running on the

android emulator

gpio-mockup.gpio_mockup_ranges

[HW] Sets the ranges of gpiochip of for this device.

Format: ,,,...

gpio-mockup.gpio_mockup_named_lines

[HW] Let the driver know GPIO lines should be named.

gpt [EFI] Forces disk with valid GPT signature but

invalid Protective MBR to be treated as GPT. If the

primary GPT is corrupted, it enables the backup/alternate

GPT to be used instead.

grcan.enable0= [HW] Configuration of physical interface 0. Determines

the "Enable 0" bit of the configuration register.

Format: 0 | 1

Default: 0

grcan.enable1= [HW] Configuration of physical interface 1. Determines

the "Enable 0" bit of the configuration register.

Format: 0 | 1

Default: 0

grcan.select= [HW] Select which physical interface to use.

Format: 0 | 1

Default: 0

grcan.txsize= [HW] Sets the size of the tx buffer.

Format: such that (txsize & ~0x1fffc0) == 0.

Default: 1024

grcan.rxsize= [HW] Sets the size of the rx buffer.

Format: such that (rxsize & ~0x1fffc0) == 0.

Default: 1024

hardened_usercopy=

[KNL] Under CONFIG_HARDENED_USERCOPY, whether

hardening is enabled for this boot. Hardened

usercopy checking is used to protect the kernel

from reading or writing beyond known memory

allocation boundaries as a proactive defense

against bounds-checking flaws in the kernel's

copy_to_user()/copy_from_user() interface.

The default is determined by

CONFIG_HARDENED_USERCOPY_DEFAULT_ON.

on Perform hardened usercopy checks.

off Disable hardened usercopy checks.

hardlockup_all_cpu_backtrace=

[KNL] Should the hard-lockup detector generate

backtraces on all cpus.

Format: 0 | 1

hashdist= [KNL,NUMA] Large hashes allocated during boot

are distributed across NUMA nodes. Defaults on

for 64-bit NUMA, off otherwise.

Format: 0 | 1 (for off | on)

hd= [EIDE] (E)IDE hard drive subsystem geometry

Format: ,,

hest_disable [ACPI]

Disable Hardware Error Source Table (HEST) support;

corresponding firmware-first mode error processing

logic will be disabled.

hibernate= [HIBERNATION]

noresume Don't check if there's a hibernation image

present during boot.

nocompress Don't compress/decompress hibernation images.

no Disable hibernation and resume.

protect_image Turn on image protection during restoration

(that will set all pages holding image data

during restoration read-only).

hibernate.compressor= [HIBERNATION] Compression algorithm to be

used with hibernation.

Format: { lzo | lz4 }

Default: lzo

lzo: Select LZO compression algorithm to

compress/decompress hibernation image.

lz4: Select LZ4 compression algorithm to

compress/decompress hibernation image.

hibernate.pm_test_delay=

[HIBERNATION]

Sets the number of seconds to remain in a hibernation test

mode before resuming the system (see

/sys/power/pm_test). Only available when CONFIG_PM_DEBUG

is set. Default value is 5.

highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact

size of . This works even on boxes that have no

highmem otherwise. This also works to reduce highmem

size on bigger boxes.

highres= [KNL] Enable/disable high resolution timer mode.

Valid parameters: "on", "off"

Default: "on"

hlt [BUGS=ARM,SH]

hostname= [KNL,EARLY] Set the hostname (aka UTS nodename).

Format:

This allows setting the system's hostname during early

startup. This sets the name returned by gethostname.

Using this parameter to set the hostname makes it

possible to ensure the hostname is correctly set before

any userspace processes run, avoiding the possibility

that a process may call gethostname before the hostname

has been explicitly set, resulting in the calling

process getting an incorrect result. The string must

not exceed the maximum allowed hostname length (usually

64 characters) and will be truncated otherwise.

hpet= [X86-32,HPET] option to control HPET usage

Format: { enable (default) | disable | force |

verbose }

disable: disable HPET and use PIT instead

force: allow force enabled of undocumented chips (ICH4,

VIA, nVidia)

verbose: show contents of HPET registers during setup

hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET

registers. Default set by CONFIG_HPET_MMAP_DEFAULT.

hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot.

If this follows hugepagesz (below), it specifies

the number of pages of hugepagesz to be allocated.

If this is the first HugeTLB parameter on the command

line, it specifies the number of pages to allocate for

the default huge page size. If using node format, the

number of pages to allocate per-node can be specified.

See also Documentation/admin-guide/mm/hugetlbpage.rst.

Format: or (node format)

:[,:]

hugepagesz=

[HW,EARLY] The size of the HugeTLB pages. This is

used in conjunction with hugepages (above) to

allocate huge pages of a specific size at boot. The

pair hugepagesz=X hugepages=Y can be specified once

for each supported huge page size. Huge page sizes

are architecture dependent. See also

Documentation/admin-guide/mm/hugetlbpage.rst.

Format: size[KMG]

hugepage_alloc_threads=

[HW] The number of threads that should be used to

allocate hugepages during boot. This option can be

used to improve system bootup time when allocating

a large amount of huge pages.

The default value is 25% of the available hardware threads.

Note that this parameter only applies to non-gigantic huge pages.

hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation

of gigantic hugepages. Or using node format, the size

of a CMA area per node can be specified.

Format: nn[KMGTPE] or (node format)

:nn[KMGTPE][,:nn[KMGTPE]]

Reserve a CMA area of given size and allocate gigantic

hugepages using the CMA allocator. If enabled, the

boot-time allocation of gigantic hugepages is skipped.

hugetlb_cma_only=

[HW,CMA,EARLY] When allocating new HugeTLB pages, only

try to allocate from the CMA areas.

This option does nothing if hugetlb_cma= is not also

specified.

hugetlb_free_vmemmap=

[KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP

enabled.

Control if HugeTLB Vmemmap Optimization (HVO) is enabled.

Allows heavy hugetlb users to free up some more

memory (7 * PAGE_SIZE for each 2MB hugetlb page).

Format: { on | off (default) }

on: enable HVO

off: disable HVO

Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,

the default is on.

Note that the vmemmap pages may be allocated from the added

memory block itself when memory_hotplug.memmap_on_memory is

enabled, those vmemmap pages cannot be optimized even if this

feature is enabled. Other vmemmap pages not allocated from

the added memory block itself do not be affected.

hung_task_panic=

[KNL] Should the hung task detector generate panics.

Format: 0 | 1

A value of 1 instructs the kernel to panic when a

hung task is detected. The default value is controlled

by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time

option. The value selected by this boot parameter can

be changed later by the kernel.hung_task_panic sysctl.

hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)

terminal devices. Valid values: 0..8

hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.

If specified, z/VM IUCV HVC accepts connections

from listed z/VM user IDs only.

hv_nopvspin [X86,HYPER_V,EARLY]

Disables the paravirt spinlock optimizations

which allow the hypervisor to 'idle' the guest

on lock contention.

hw_protection= [HW]

Format: reboot | shutdown

Hardware protection action taken on critical events like

overtemperature or imminent voltage loss.

i2c_bus= [HW] Override the default board specific I2C bus speed

or register an additional I2C bus that is not

registered from board initialization code.

Format:

,

i2c_touchscreen_props= [HW,ACPI,X86]

Set device-properties for ACPI-enumerated I2C-attached

touchscreen, to e.g. fix coordinates of upside-down

mounted touchscreens. If you need this option please

submit a drivers/platform/x86/touchscreen_dmi.c patch

adding a DMI quirk for this.

Format:

:=[:prop_name=val][:...]

Where is one of:

Omit "=" entirely Set a boolean device-property

Unsigned number Set a u32 device-property

Anything else Set a string device-property

Examples (split over multiple lines):

i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x:

touchscreen-inverted-y

i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920:

touchscreen-size-y=1080:touchscreen-inverted-y:

firmware-name=gsl1680-vendor-model.fw:silead,home-button

i8042.debug [HW] Toggle i8042 debug mode

i8042.unmask_kbd_data

[HW] Enable printing of interrupt data from the KBD port

(disabled by default, and as a pre-condition

requires that i8042.debug=1 be enabled)

i8042.direct [HW] Put keyboard port into non-translated mode

i8042.dumbkbd [HW] Pretend that controller can only read data from

keyboard and cannot control its state

(Don't attempt to blink the leds)

i8042.noaux [HW] Don't check for auxiliary (== mouse) port

i8042.nokbd [HW] Don't check/create keyboard port

i8042.noloop [HW] Disable the AUX Loopback command while probing

for the AUX port

i8042.nomux [HW] Don't check presence of an active multiplexing

controller

i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX

controllers

i8042.notimeout [HW] Ignore timeout condition signalled by controller

i8042.reset [HW] Reset the controller during init, cleanup and

suspend-to-ram transitions, only during s2r

transitions, or never reset

Format: { 1 | Y | y | 0 | N | n }

1, Y, y: always reset controller

0, N, n: don't ever reset controller

Default: only on s2r transitions on x86; most other

architectures force reset to be always executed

i8042.unlock [HW] Unlock (ignore) the keylock

i8042.kbdreset [HW] Reset device connected to KBD port

i8042.probe_defer

[HW] Allow deferred probing upon i8042 probe errors

i810= [HW,DRM]

i915.invert_brightness=

[DRM] Invert the sense of the variable that is used to

set the brightness of the panel backlight. Normally a

brightness value of 0 indicates backlight switched off,

and the maximum of the brightness value sets the backlight

to maximum brightness. If this parameter is set to 0

(default) and the machine requires it, or this parameter

is set to 1, a brightness value of 0 sets the backlight

to maximum brightness, and the maximum of the brightness

value switches the backlight off.

-1 -- never invert brightness

0 -- machine default

1 -- force brightness inversion

ia32_emulation= [X86-64]

Format:

When true, allows loading 32-bit programs and executing 32-bit

syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at

boot time. When false, unconditionally disables IA32 emulation.

icn= [HW,ISDN]

Format: [,[,[,]]]

idle= [X86,EARLY]

Format: idle=poll, idle=halt, idle=nomwait

idle=poll: Don't do power saving in the idle loop

using HLT, but poll for rescheduling event. This will

make the CPUs eat a lot more power, but may be useful

to get slightly better performance in multiprocessor

benchmarks. It also makes some profiling using

performance counters more accurate. Please note that

on systems with MONITOR/MWAIT support (like Intel

EM64T CPUs) this option has no performance advantage

over the normal idle loop. It may also interact badly

with hyperthreading.

idle=halt: Halt is forced to be used for CPU idle.

In such case C2/C3 won't be used again.

idle=nomwait: Disable mwait for CPU C-states

idxd.sva= [HW]

Format:

Allow force disabling of Shared Virtual Memory (SVA)

support for the idxd driver. By default it is set to

true (1).

idxd.tc_override= [HW]

Format:

Allow override of default traffic class configuration

for the device. By default it is set to false (0).

ieee754= [MIPS] Select IEEE Std 754 conformance mode

Format: { strict | legacy | 2008 | relaxed | emulated }

Default: strict

Choose which programs will be accepted for execution

based on the IEEE 754 NaN encoding(s) supported by

the FPU and the NaN encoding requested with the value

of an ELF file header flag individually set by each

binary. Hardware implementations are permitted to

support either or both of the legacy and the 2008 NaN

encoding mode.

Available settings are as follows:

strict accept binaries that request a NaN encoding

supported by the FPU

legacy only accept legacy-NaN binaries, if supported

by the FPU

2008 only accept 2008-NaN binaries, if supported

by the FPU

relaxed accept any binaries regardless of whether

supported by the FPU

emulated accept any binaries but enable FPU emulator

if binary mode is unsupported by the FPU.

The FPU emulator is always able to support both NaN

encodings, so if no FPU hardware is present or it has

been disabled with 'nofpu', then the settings of

'legacy' and '2008' strap the emulator accordingly,

'relaxed' straps the emulator for both legacy-NaN and

2008-NaN, whereas 'strict' enables legacy-NaN only on

legacy processors and both NaN encodings on MIPS32 or

MIPS64 CPUs.

The setting for ABS.fmt/NEG.fmt instruction execution

mode generally follows that for the NaN encoding,

except where unsupported by hardware.

ignore_loglevel [KNL,EARLY]

Ignore loglevel setting - this will print /all/

kernel messages to the console. Useful for debugging.

We also add it as printk module parameter, so users

could change it dynamically, usually by

/sys/module/printk/parameters/ignore_loglevel.

ignore_rlimit_data

Ignore RLIMIT_DATA setting for data mappings,

print warning at first misuse. Can be changed via

/sys/module/kernel/parameters/ignore_rlimit_data.

ihash_entries= [KNL]

Set number of hash buckets for inode cache.

ima_appraise= [IMA] appraise integrity measurements

Format: { "off" | "enforce" | "fix" | "log" }

default: "enforce"

ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.

The builtin appraise policy appraises all files

owned by uid=0.

ima_canonical_fmt [IMA]

Use the canonical format for the binary runtime

measurements, instead of host native format.

ima_hash= [IMA]

Format: { md5 | sha1 | rmd160 | sha256 | sha384

| sha512 | ... }

default: "sha1"

The list of supported hash algorithms is defined

in crypto/hash_info.h.

ima_policy= [IMA]

The builtin policies to load during IMA setup.

Format: "tcb | appraise_tcb | secure_boot |

fail_securely | critical_data"

The "tcb" policy measures all programs exec'd, files

mmap'd for exec, and all files opened with the read

mode bit set by either the effective uid (euid=0) or

uid=0.

The "appraise_tcb" policy appraises the integrity of

all files owned by root.

The "secure_boot" policy appraises the integrity

of files (eg. kexec kernel image, kernel modules,

firmware, policy, etc) based on file signatures.

The "fail_securely" policy forces file signature

verification failure also on privileged mounted

filesystems with the SB_I_UNVERIFIABLE_SIGNATURE

flag.

The "critical_data" policy measures kernel integrity

critical data.

ima_tcb [IMA] Deprecated. Use ima_policy= instead.

Load a policy which meets the needs of the Trusted

Computing Base. This means IMA will measure all

programs exec'd, files mmap'd for exec, and all files

opened for read by uid=0.

ima_template= [IMA]

Select one of defined IMA measurements template formats.

Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" |

"ima-sigv2" }

Default: "ima-ng"

ima_template_fmt=

[IMA] Define a custom template format.

Format: { "field1|...|fieldN" }

ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage

Format:

Set the minimal file size for using asynchronous hash.

If left unspecified, ahash usage is disabled.

ahash performance varies for different data sizes on

different crypto accelerators. This option can be used

to achieve the best performance for a particular HW.

ima.ahash_bufsize= [IMA] Asynchronous hash buffer size

Format:

Set hashing buffer size. Default: 4k.

ahash performance varies for different chunk sizes on

different crypto accelerators. This option can be used

to achieve best performance for particular HW.

indirect_target_selection= [X86,Intel] Mitigation control for Indirect

Target Selection(ITS) bug in Intel CPUs. Updated

microcode is also required for a fix in IBPB.

on: Enable mitigation (default).

off: Disable mitigation.

force: Force the ITS bug and deploy default

mitigation.

vmexit: Only deploy mitigation if CPU is affected by

guest/host isolation part of ITS.

stuff: Deploy RSB-fill mitigation when retpoline is

also deployed. Otherwise, deploy the default

mitigation.

For details see:

Documentation/admin-guide/hw-vuln/indirect-target-selection.rst

init= [KNL]

Format:

Run specified binary instead of /sbin/init as init

process.

initcall_debug [KNL] Trace initcalls as they are executed. Useful

for working out where the kernel is dying during

startup.

initcall_blacklist= [KNL] Do not execute a comma-separated list of

initcall functions. Useful for debugging built-in

modules and initcalls.

initramfs_async= [KNL]

Format:

Default: 1

This parameter controls whether the initramfs

image is unpacked asynchronously, concurrently

with devices being probed and

initialized. This should normally just work,

but as a debugging aid, one can get the

historical behaviour of the initramfs

unpacking being completed before device_ and

late_ initcalls.

initrd= [BOOT,EARLY] Specify the location of the initial ramdisk

initrdmem= [KNL,EARLY] Specify a physical address and size from which to

load the initrd. If an initrd is compiled in or

specified in the bootparams, it takes priority over this

setting.

Format: ss[KMG],nn[KMG]

Default is 0, 0

init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with

zeroes.

Format: 0 | 1

Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.

init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes.

Format: 0 | 1

Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.

init_pkru= [X86] Specify the default memory protection keys rights

register contents for all processes. 0x55555554 by

default (disallow access to all but pkey 0). Can

override in debugfs after boot.

inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver

Format:

int_pln_enable [X86] Enable power limit notification interrupt

integrity_audit=[IMA]

Format: { "0" | "1" }

0 -- basic integrity auditing messages. (Default)

1 -- additional integrity auditing messages.

intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option

on

Enable intel iommu driver.

off

Disable intel iommu driver.

igfx_off [Default Off]

By default, gfx is mapped as normal device. If a gfx

device has a dedicated DMAR unit, the DMAR unit is

bypassed by not enabling DMAR with this option. In

this case, gfx device will use physical address for

DMA.

strict [Default Off]

Deprecated, equivalent to iommu.strict=1.

sp_off [Default Off]

By default, super page will be supported if Intel IOMMU

has the capability. With this option, super page will

not be supported.

sm_on

Enable the Intel IOMMU scalable mode if the hardware

advertises that it has support for the scalable mode

translation.

sm_off

Disallow use of the Intel IOMMU scalable mode.

tboot_noforce [Default Off]

Do not force the Intel IOMMU enabled under tboot.

By default, tboot will force Intel IOMMU on, which

could harm performance of some high-throughput

devices like 40GBit network cards, even if identity

mapping is enabled.

Note that using this option lowers the security

provided by tboot because it makes the system

vulnerable to DMA attacks.

intel_idle.max_cstate= [KNL,HW,ACPI,X86]

0 disables intel_idle and fall back on acpi_idle.

1 to 9 specify maximum depth of C-state.

intel_pstate= [X86,EARLY]

disable

Do not enable intel_pstate as the default

scaling driver for the supported processors

active

Use intel_pstate driver to bypass the scaling

governors layer of cpufreq and provides it own

algorithms for p-state selection. There are two

P-state selection algorithms provided by

intel_pstate in the active mode: powersave and

performance. The way they both operate depends

on whether or not the hardware managed P-states

(HWP) feature has been enabled in the processor

and possibly on the processor model.

passive

Use intel_pstate as a scaling driver, but configure it

to work with generic cpufreq governors (instead of

enabling its internal governor). This mode cannot be

used along with the hardware-managed P-states (HWP)

feature.

force

Enable intel_pstate on systems that prohibit it by default

in favor of acpi-cpufreq. Forcing the intel_pstate driver

instead of acpi-cpufreq may disable platform features, such

as thermal controls and power capping, that rely on ACPI

P-States information being indicated to OSPM and therefore

should be used with caution. This option does not work with

processors that aren't supported by the intel_pstate driver

or on platforms that use pcc-cpufreq instead of acpi-cpufreq.

no_hwp

Do not enable hardware P state control (HWP)

if available.

hwp_only

Only load intel_pstate on systems which support

hardware P state control (HWP) if available.

support_acpi_ppc

Enforce ACPI _PPC performance limits. If the Fixed ACPI

Description Table, specifies preferred power management

profile as "Enterprise Server" or "Performance Server",

then this feature is turned on by default.

per_cpu_perf_limits

Allow per-logical-CPU P-State performance control limits using

cpufreq sysfs interface

no_cas

Do not enable capacity-aware scheduling (CAS) on

hybrid systems

intremap= [X86-64,Intel-IOMMU,EARLY]

on enable Interrupt Remapping (default)

off disable Interrupt Remapping

nosid disable Source ID checking

no_x2apic_optout

BIOS x2APIC opt-out request will be ignored

nopost disable Interrupt Posting

posted_msi

enable MSIs delivered as posted interrupts

iomem= Disable strict checking of access to MMIO memory

strict regions from userspace.

relaxed

iommu= [X86,EARLY]

off

Don't initialize and use any kind of IOMMU.

force

Force the use of the hardware IOMMU even when

it is not actually needed (e.g. because < 3 GB

memory).

noforce

Don't force hardware IOMMU usage when it is not

needed. (default).

biomerge

panic

nopanic

merge

nomerge

soft

Use software bounce buffering (SWIOTLB) (default for

Intel machines). This can be used to prevent the usage

of an available hardware IOMMU.

[X86]

pt

[X86]

nopt

[PPC/POWERNV]

nobypass

Disable IOMMU bypass, using IOMMU for PCI devices.

[X86]

AMD Gart HW IOMMU-specific options:

Set the size of the remapping area in bytes.

allowed

Overwrite iommu off workarounds for specific chipsets

fullflush

Flush IOMMU on each allocation (default).

nofullflush

Don't use IOMMU fullflush.

memaper[=]

Allocate an own aperture over RAM with size

32MB<

merge

Do scatter-gather (SG) merging. Implies "force"

(experimental).

nomerge

Don't do scatter-gather (SG) merging.

noaperture

Ask the IOMMU not to touch the aperture for AGP.

noagp

Don't initialize the AGP driver and use full aperture.

panic

Always panic when IOMMU overflows.

iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices.

Format: { "0" | "1" }

0 - Try to allocate a 32-bit DMA address first, before

falling back to the full range if needed.

1 - Allocate directly from the full usable range,

forcing Dual Address Cycle for PCI cards supporting

greater than 32-bit addressing.

iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour

Format: { "0" | "1" }

0 - Lazy mode.

Request that DMA unmap operations use deferred

invalidation of hardware TLBs, for increased

throughput at the cost of reduced device isolation.

Will fall back to strict mode if not supported by

the relevant IOMMU driver.

1 - Strict mode.

DMA unmap operations invalidate IOMMU hardware TLBs

synchronously.

unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.

Note: on x86, strict mode specified via one of the

legacy driver-specific options takes precedence.

iommu.passthrough=

[ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default.

Format: { "0" | "1" }

0 - Use IOMMU translation for DMA.

1 - Bypass the IOMMU for DMA.

unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.

io7= [HW] IO7 for Marvel-based Alpha systems

See comment before marvel_specify_io7 in

arch/alpha/kernel/core_marvel.c.

io_delay= [X86,EARLY] I/O delay method

0x80

Standard port 0x80 based delay

0xed

Alternate port 0xed based delay (needed on some systems)

udelay

Simple two microseconds delay

none

No delay

ip= [IP_PNP]

See Documentation/admin-guide/nfs/nfsroot.rst.

ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V

IPC identifiers from 32,768 to 16,777,216.

ipe.enforce= [IPE]

Format:

Determine whether IPE starts in permissive (0) or

enforce (1) mode. The default is enforce.

ipe.success_audit=

[IPE]

Format:

Start IPE with success auditing enabled, emitting

an audit event when a binary is allowed. The default

is 0.

irqaffinity= [SMP] Set the default irq affinity mask

The argument is a cpu list, as described above.

irqchip.gicv2_force_probe=

[ARM,ARM64,EARLY]

Format:

Force the kernel to look for the second 4kB page

of a GICv2 controller even if the memory range

exposed by the device tree is too small.

irqchip.gicv3_nolpi=

[ARM,ARM64,EARLY]

Force the kernel to ignore the availability of

LPIs (and by consequence ITSs). Intended for system

that use the kernel as a bootloader, and thus want

to let secondary kernels in charge of setting up

LPIs.

irqchip.gicv3_pseudo_nmi= [ARM64,EARLY]

Enables support for pseudo-NMIs in the kernel. This

requires the kernel to be built with

CONFIG_ARM64_PSEUDO_NMI.

irqfixup [HW]

When an interrupt is not handled search all handlers

for it. Intended to get systems with badly broken

firmware running.

irqpoll [HW]

When an interrupt is not handled search all handlers

for it. Also check all handlers each timer

interrupt. Intended to get systems with badly broken

firmware running.

isapnp= [ISAPNP]

Format: ,,,

isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.

[Deprecated - use cpusets instead]

Format: [flag-list,]

Specify one or more CPUs to isolate from disturbances

specified in the flag list (default: domain):

nohz

Disable the tick when a single task runs as well as

disabling other kernel noises like having RCU callbacks

offloaded. This is equivalent to the nohz_full parameter.

A residual 1Hz tick is offloaded to workqueues, which you

need to affine to housekeeping through the global

workqueue's affinity configured via the

/sys/devices/virtual/workqueue/cpumask sysfs file, or

by using the 'domain' flag described below.

NOTE: by default the global workqueue runs on all CPUs,

so to protect individual CPUs the 'cpumask' file has to

be configured manually after bootup.

domain

Isolate from the general SMP balancing and scheduling

algorithms. Note that performing domain isolation this way

is irreversible: it's not possible to bring back a CPU to

the domains once isolated through isolcpus. It's strongly

advised to use cpusets instead to disable scheduler load

balancing through the "cpuset.sched_load_balance" file.

It offers a much more flexible interface where CPUs can

move in and out of an isolated set anytime.

You can move a process onto or off an "isolated" CPU via

the CPU affinity syscalls or cpuset.

begins at 0 and the maximum value is

"number of CPUs in system - 1".

managed_irq

Isolate from being targeted by managed interrupts

which have an interrupt mask containing isolated

CPUs. The affinity of managed interrupts is

handled by the kernel and cannot be changed via

the /proc/irq/* interfaces.

This isolation is best effort and only effective

if the automatically assigned interrupt mask of a

device queue contains isolated and housekeeping

CPUs. If housekeeping CPUs are online then such

interrupts are directed to the housekeeping CPU

so that IO submitted on the housekeeping CPU

cannot disturb the isolated CPU.

If a queue's affinity mask contains only isolated

CPUs then this parameter has no effect on the

interrupt routing decision, though interrupts are

only delivered when tasks running on those

isolated CPUs submit IO. IO submitted on

housekeeping CPUs has no influence on those

queues.

The format of is described above.

iucv= [HW,NET]

ivrs_ioapic [HW,X86-64]

Provide an override to the IOAPIC-ID<->DEVICE-ID

mapping provided in the IVRS ACPI table.

By default, PCI segment is 0, and can be omitted.

For example, to map IOAPIC-ID decimal 10 to

PCI segment 0x1 and PCI device 00:14.0,

write the parameter as:

ivrs_ioapic=10@0001:00:14.0

Deprecated formats:

* To map IOAPIC-ID decimal 10 to PCI device 00:14.0

write the parameter as:

ivrs_ioapic[10]=00:14.0

* To map IOAPIC-ID decimal 10 to PCI segment 0x1 and

PCI device 00:14.0 write the parameter as:

ivrs_ioapic[10]=0001:00:14.0

ivrs_hpet [HW,X86-64]

Provide an override to the HPET-ID<->DEVICE-ID

mapping provided in the IVRS ACPI table.

By default, PCI segment is 0, and can be omitted.

For example, to map HPET-ID decimal 10 to

PCI segment 0x1 and PCI device 00:14.0,

write the parameter as:

ivrs_hpet=10@0001:00:14.0

Deprecated formats:

* To map HPET-ID decimal 0 to PCI device 00:14.0

write the parameter as:

ivrs_hpet[0]=00:14.0

* To map HPET-ID decimal 10 to PCI segment 0x1 and

PCI device 00:14.0 write the parameter as:

ivrs_ioapic[10]=0001:00:14.0

ivrs_acpihid [HW,X86-64]

Provide an override to the ACPI-HID:UID<->DEVICE-ID

mapping provided in the IVRS ACPI table.

By default, PCI segment is 0, and can be omitted.

For example, to map UART-HID:UID AMD0020:0 to

PCI segment 0x1 and PCI device ID 00:14.5,

write the parameter as:

ivrs_acpihid=AMD0020:0@0001:00:14.5

Deprecated formats:

* To map UART-HID:UID AMD0020:0 to PCI segment is 0,

PCI device ID 00:14.5, write the parameter as:

ivrs_acpihid[00:14.5]=AMD0020:0

* To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and

PCI device ID 00:14.5, write the parameter as:

ivrs_acpihid[0001:00:14.5]=AMD0020:0

js= [HW,JOY] Analog joystick

See Documentation/input/joydev/joystick.rst.

kasan_multi_shot

[KNL] Enforce KASAN (Kernel Address Sanitizer) to print

report on every invalid memory access. Without this

parameter KASAN will print report only for the first

invalid access.

keep_bootcon [KNL,EARLY]

Do not unregister boot console at start. This is only

useful for debugging when something happens in the window

between unregistering the boot console and initializing

the real console.

keepinitrd [HW,ARM] See retain_initrd.

kernelcore= [KNL,X86,PPC,EARLY]

Format: nn[KMGTPE] | nn% | "mirror"

This parameter specifies the amount of memory usable by

the kernel for non-movable allocations. The requested

amount is spread evenly throughout all nodes in the

system as ZONE_NORMAL. The remaining memory is used for

movable memory in its own zone, ZONE_MOVABLE. In the

event, a node is too small to have both ZONE_NORMAL and

ZONE_MOVABLE, kernelcore memory will take priority and

other nodes will have a larger ZONE_MOVABLE.

ZONE_MOVABLE is used for the allocation of pages that

may be reclaimed or moved by the page migration

subsystem. Note that allocations like PTEs-from-HighMem

still use the HighMem zone if it exists, and the Normal

zone if it does not.

It is possible to specify the exact amount of memory in

the form of "nn[KMGTPE]", a percentage of total system

memory in the form of "nn%", or "mirror". If "mirror"

option is specified, mirrored (reliable) memory is used

for non-movable allocations and remaining memory is used

for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"

are exclusive, so you cannot specify multiple forms.

kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port.

Format: [,poll interval]

The controller # is the number of the ehci usb debug

port as it is probed via PCI. The poll interval is

optional and is the number seconds in between

each poll cycle to the debug port in case you need

the functionality for interrupting the kernel with

gdb or control-c on the dbgp connection. When

not using this parameter you use sysrq-g to break into

the kernel debugger.

kgdboc= [KGDB,HW] kgdb over consoles.

Requires a tty driver that supports console polling,

or a supported polling keyboard driver (non-usb).

Serial only format: [,baud]

keyboard only format: kbd

keyboard and serial format: kbd,[,baud]

Optional Kernel mode setting:

kms, kbd format: kms,kbd

kms, kbd and serial format: kms,kbd,[,baud]

kgdboc_earlycon= [KGDB,HW,EARLY]

If the boot console provides the ability to read

characters and can work in polling mode, you can use

this parameter to tell kgdb to use it as a backend

until the normal console is registered. Intended to

be used together with the kgdboc parameter which

specifies the normal console to transition to.

The name of the early console should be specified

as the value of this parameter. Note that the name of

the early console might be different than the tty

name passed to kgdboc. It's OK to leave the value

blank and the first boot console that implements

read() will be picked.

kgdbwait [KGDB,EARLY] Stop kernel execution and enter the

kernel debugger at the earliest opportunity.

kho= [KEXEC,EARLY]

Format: { "0" | "1" | "off" | "on" | "y" | "n" }

Enables or disables Kexec HandOver.

"0" | "off" | "n" - kexec handover is disabled

"1" | "on" | "y" - kexec handover is enabled

kho_scratch= [KEXEC,EARLY]

Format: ll[KMG],mm[KMG],nn[KMG] | nn%

Defines the size of the KHO scratch region. The KHO

scratch regions are physically contiguous memory

ranges that can only be used for non-kernel

allocations. That way, even when memory is heavily

fragmented with handed over memory, the kexeced

kernel will always have enough contiguous ranges to

bootstrap itself.

It is possible to specify the exact amount of

memory in the form of "ll[KMG],mm[KMG],nn[KMG]"

where the first parameter defines the size of a low

memory scratch area, the second parameter defines

the size of a global scratch area and the third

parameter defines the size of additional per-node

scratch areas. The form "nn%" defines scale factor

(in percents) of memory that was used during boot.

kmac= [MIPS] Korina ethernet MAC address.

Configure the RouterBoard 532 series on-chip

Ethernet adapter MAC address.

kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable

Valid arguments: on, off

Default: on

Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,

the default is off.

kprobe_event=[probe-list]

[FTRACE] Add kprobe events and enable at boot time.

The probe-list is a semicolon delimited list of probe

definitions. Each definition is same as kprobe_events

interface, but the parameters are comma delimited.

For example, to add a kprobe event on vfs_read with

arg1 and arg2, add to the command line;

kprobe_event=p,vfs_read,$arg1,$arg2

See also Documentation/trace/kprobetrace.rst "Kernel

Boot Parameter" section.

kpti= [ARM64,EARLY] Control page table isolation of

user and kernel address spaces.

Default: enabled on cores which need mitigation.

0: force disabled

1: force enabled

kunit.enable= [KUNIT] Enable executing KUnit tests. Requires

CONFIG_KUNIT to be set to be fully enabled. The

default value can be overridden via

KUNIT_DEFAULT_ENABLED.

Default is 1 (enabled)

kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.

Default is 0 (don't ignore, but inject #GP)

kvm.eager_page_split=

[KVM,X86] Controls whether or not KVM will try to

proactively split all huge pages during dirty logging.

Eager page splitting reduces interruptions to vCPU

execution by eliminating the write-protection faults

and MMU lock contention that would otherwise be

required to split huge pages lazily.

VM workloads that rarely perform writes or that write

only to a small region of VM memory may benefit from

disabling eager page splitting to allow huge pages to

still be used for reads.

The behavior of eager page splitting depends on whether

KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If

disabled, all huge pages in a memslot will be eagerly

split when dirty logging is enabled on that memslot. If

enabled, eager page splitting will be performed during

the KVM_CLEAR_DIRTY ioctl, and only for the pages being

cleared.

Eager page splitting is only supported when kvm.tdp_mmu=Y.

Default is Y (on).

kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86]

If enabled, KVM will enable virtualization in hardware

when KVM is loaded, and disable virtualization when KVM

is unloaded (if KVM is built as a module).

If disabled, KVM will dynamically enable and disable

virtualization on-demand when creating and destroying

VMs, i.e. on the 0=>1 and 1=>0 transitions of the

number of VMs.

Enabling virtualization at module load avoids potential

latency for creation of the 0=>1 VM, as KVM serializes

virtualization enabling across all online CPUs. The

"cost" of enabling virtualization when KVM is loaded,

is that doing so may interfere with using out-of-tree

hypervisors that want to "own" virtualization hardware.

kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.

Default is false (don't support).

kvm.nx_huge_pages=

[KVM] Controls the software workaround for the

X86_BUG_ITLB_MULTIHIT bug.

force : Always deploy workaround.

off : Never deploy workaround.

auto : Deploy workaround based on the presence of

X86_BUG_ITLB_MULTIHIT.

Default is 'auto'.

If the software workaround is enabled for the host,

guests do need not to enable it for nested guests.

kvm.nx_huge_pages_recovery_ratio=

[KVM] Controls how many 4KiB pages are periodically zapped

back to huge pages. 0 disables the recovery, otherwise if

the value is N KVM will zap 1/Nth of the 4KiB pages every

period (see below). The default is 60.

kvm.nx_huge_pages_recovery_period_ms=

[KVM] Controls the time period at which KVM zaps 4KiB pages

back to huge pages. If the value is a non-zero N, KVM will

zap a portion (see ratio above) of the pages every N msecs.

If the value is 0 (the default), KVM will pick a period based

on the ratio, such that a page is zapped after 1 hour on average.

kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in

KVM/SVM. Default is 1 (enabled).

kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables,

a.k.a. Two-Dimensional Page Tables. Default is 1

(enabled). Disable by KVM if hardware lacks support

for NPT.

kvm-arm.mode=

[KVM,ARM,EARLY] Select one of KVM/arm64's modes of

operation.

none: Forcefully disable KVM.

nvhe: Standard nVHE-based mode, without support for

protected guests.

protected: Mode with support for guests whose state is

kept private from the host, using VHE or

nVHE depending on HW support.

nested: VHE-based mode with support for nested

virtualization. Requires at least ARMv8.4

hardware (with FEAT_NV2).

Defaults to VHE/nVHE based on hardware support. Setting

mode to "protected" will disable kexec and hibernation

for the host. To force nVHE on VHE hardware, add

"arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the

command-line.

"nested" is experimental and should be used with

extreme caution.

kvm-arm.vgic_v3_group0_trap=

[KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0

system registers

kvm-arm.vgic_v3_group1_trap=

[KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1

system registers

kvm-arm.vgic_v3_common_trap=

[KVM,ARM,EARLY] Trap guest accesses to GICv3 common

system registers

kvm-arm.vgic_v4_enable=

[KVM,ARM,EARLY] Allow use of GICv4 for direct

injection of LPIs.

kvm-arm.wfe_trap_policy=

[KVM,ARM] Control when to set WFE instruction trap for

KVM VMs. Traps are allowed but not guaranteed by the

CPU architecture.

trap: set WFE instruction trap

notrap: clear WFE instruction trap

kvm-arm.wfi_trap_policy=

[KVM,ARM] Control when to set WFI instruction trap for

KVM VMs. Traps are allowed but not guaranteed by the

CPU architecture.

trap: set WFI instruction trap

notrap: clear WFI instruction trap

kvm_cma_resv_ratio=n [PPC,EARLY]

Reserves given percentage from system memory area for

contiguous memory allocation for KVM hash pagetable

allocation.

By default it reserves 5% of total system memory.

Format:

Default: 5

kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables,

a.k.a. Two-Dimensional Page Tables. Default is 1

(enabled). Disable by KVM if hardware lacks support

for EPT.

kvm-intel.emulate_invalid_guest_state=

[KVM,Intel] Control whether to emulate invalid guest

state. Ignored if kvm-intel.enable_unrestricted_guest=1,

as guest state is never invalid for unrestricted

guests. This param doesn't apply to nested guests (L2),

as KVM never emulates invalid L2 guest state.

Default is 1 (enabled).

kvm-intel.flexpriority=

[KVM,Intel] Control KVM's use of FlexPriority feature

(TPR shadow). Default is 1 (enabled). Disable by KVM if

hardware lacks support for it.

kvm-intel.nested=

[KVM,Intel] Control nested virtualization feature in

KVM/VMX. Default is 1 (enabled).

kvm-intel.unrestricted_guest=

[KVM,Intel] Control KVM's use of unrestricted guest

feature (virtualized real and unpaged mode). Default

is 1 (enabled). Disable by KVM if EPT is disabled or

hardware lacks support for it.

kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault

CVE-2018-3620.

Valid arguments: never, cond, always

always: L1D cache flush on every VMENTER.

cond: Flush L1D on VMENTER only when the code between

VMEXIT and VMENTER can leak host memory.

never: Disables the mitigation

Default is cond (do L1 cache flush in specific instances)

kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor

Identification feature (tagged TLBs). Default is 1

(enabled). Disable by KVM if hardware lacks support

for it.

l1d_flush= [X86,INTEL,EARLY]

Control mitigation for L1D based snooping vulnerability.

Certain CPUs are vulnerable to an exploit against CPU

internal buffers which can forward information to a

disclosure gadget under certain conditions.

In vulnerable processors, the speculatively

forwarded data can be used in a cache side channel

attack, to access data to which the attacker does

not have direct access.

This parameter controls the mitigation. The

options are:

on - enable the interface for the mitigation

l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on

affected CPUs

The kernel PTE inversion protection is unconditionally

enabled and cannot be disabled.

full

Provides all available mitigations for the

L1TF vulnerability. Disables SMT and

enables all mitigations in the

hypervisors, i.e. unconditional L1D flush.

SMT control and L1D flush control via the

sysfs interface is still possible after

boot. Hypervisors will issue a warning

when the first VM is started in a

potentially insecure configuration,

i.e. SMT enabled or L1D flush disabled.

full,force

Same as 'full', but disables SMT and L1D

flush runtime control. Implies the

'nosmt=force' command line option.

(i.e. sysfs control of SMT is disabled.)

flush

Leaves SMT enabled and enables the default

hypervisor mitigation, i.e. conditional

L1D flush.

SMT control and L1D flush control via the

sysfs interface is still possible after

boot. Hypervisors will issue a warning

when the first VM is started in a

potentially insecure configuration,

i.e. SMT enabled or L1D flush disabled.

flush,nosmt

Disables SMT and enables the default

hypervisor mitigation.

SMT control and L1D flush control via the

sysfs interface is still possible after

boot. Hypervisors will issue a warning

when the first VM is started in a

potentially insecure configuration,

i.e. SMT enabled or L1D flush disabled.

flush,nowarn

Same as 'flush', but hypervisors will not

warn when a VM is started in a potentially

insecure configuration.

off

Disables hypervisor mitigations and doesn't

emit any warnings.

It also drops the swap size and available

RAM limit restriction on both hypervisor and

bare metal.

Default is 'flush'.

For details see: Documentation/admin-guide/hw-vuln/l1tf.rst

l2cr= [PPC]

l3cr= [PPC]

lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS

disabled it.

lapic= [X86,APIC] Do not use TSC deadline

value for LAPIC timer one-shot implementation. Default

back to the programmable timer unit in the LAPIC.

Format: notscdeadline

lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer

in C2 power state.

libata.dma= [LIBATA] DMA control

libata.dma=0 Disable all PATA and SATA DMA

libata.dma=1 PATA and SATA Disk DMA only

libata.dma=2 ATAPI (CDROM) DMA only

libata.dma=4 Compact Flash DMA only

Combinations also work, so libata.dma=3 enables DMA

for disks and CDROMs, but not CFs.

libata.ignore_hpa= [LIBATA] Ignore HPA limit

libata.ignore_hpa=0 keep BIOS limits (default)

libata.ignore_hpa=1 ignore limits, using full disk

libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume

when set.

Format:

libata.force= [LIBATA] Force configurations. The format is a comma-

separated list of "[ID:]VAL" where ID is PORT[.DEVICE].

PORT and DEVICE are decimal numbers matching port, link

or device. Basically, it matches the ATA ID string

printed on console by libata. If the whole ID part is

omitted, the last PORT and DEVICE values are used. If

ID hasn't been specified yet, the configuration applies

to all ports, links and devices.

If only DEVICE is omitted, the parameter applies to

the port and all links and devices behind it. DEVICE

number of 0 either selects the first device or the

first fan-out link behind PMP device. It does not

select the host link. DEVICE number of 15 selects the

host link and device attached to it.

The VAL specifies the configuration to force. As long

as there is no ambiguity, shortcut notation is allowed.

For example, both 1.5 and 1.5G would work for 1.5Gbps.

The following configurations can be forced.

* Cable type: 40c, 80c, short40c, unk, ign or sata.

Any ID with matching PORT is used.

* SATA link speed limit: 1.5Gbps or 3.0Gbps.

* Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].

udma[/][16,25,33,44,66,100,133] notation is also

allowed.

* nohrst, nosrst, norst: suppress hard, soft and both

resets.

* rstonce: only attempt one reset during hot-unplug

link recovery.

* [no]dbdelay: Enable or disable the extra 200ms delay

before debouncing a link PHY and device presence

detection.

* [no]ncq: Turn on or off NCQ.

* [no]ncqtrim: Enable or disable queued DSM TRIM.

* [no]ncqati: Enable or disable NCQ trim on ATI chipset.

* [no]trim: Enable or disable (unqueued) TRIM.

* trim_zero: Indicate that TRIM command zeroes data.

* max_trim_128m: Set 128M maximum trim size limit.

* [no]dma: Turn on or off DMA transfers.

* atapi_dmadir: Enable ATAPI DMADIR bridge support.

* atapi_mod16_dma: Enable the use of ATAPI DMA for

commands that are not a multiple of 16 bytes.

* [no]dmalog: Enable or disable the use of the

READ LOG DMA EXT command to access logs.

* [no]iddevlog: Enable or disable access to the

identify device data log.

* [no]logdir: Enable or disable access to the general

purpose log directory.

* max_sec_128: Set transfer size limit to 128 sectors.

* max_sec_1024: Set or clear transfer size limit to

1024 sectors.

* max_sec_lba48: Set or clear transfer size limit to

65535 sectors.

* external: Mark port as external (hotplug-capable).

* [no]lpm: Enable or disable link power management.

* [no]setxfer: Indicate if transfer speed mode setting

should be skipped.

* [no]fua: Disable or enable FUA (Force Unit Access)

support for devices supporting this feature.

* dump_id: Dump IDENTIFY data.

* disable: Disable this device.

If there are multiple matching configurations changing

the same attribute, the last one is used.

load_ramdisk= [RAM] [Deprecated]

lockd.nlm_grace_period=P [NFS] Assign grace period.

Format:

lockd.nlm_tcpport=N [NFS] Assign TCP port.

Format:

lockd.nlm_timeout=T [NFS] Assign timeout value.

Format:

lockd.nlm_udpport=M [NFS] Assign UDP port.

Format:

lockdown= [SECURITY,EARLY]

{ integrity | confidentiality }

Enable the kernel lockdown feature. If set to

integrity, kernel features that allow userland to

modify the running kernel are disabled. If set to

confidentiality, kernel features that allow userland

to extract confidential information from the kernel

are also disabled.

locktorture.acq_writer_lim= [KNL]

Set the time limit in jiffies for a lock

acquisition. Acquisitions exceeding this limit

will result in a splat once they do complete.

locktorture.bind_readers= [KNL]

Specify the list of CPUs to which the readers are

to be bound.

locktorture.bind_writers= [KNL]

Specify the list of CPUs to which the writers are

to be bound.

locktorture.call_rcu_chains= [KNL]

Specify the number of self-propagating call_rcu()

chains to set up. These are used to ensure that

there is a high probability of an RCU grace period

in progress at any given time. Defaults to 0,

which disables these call_rcu() chains.

locktorture.long_hold= [KNL]

Specify the duration in milliseconds for the

occasional long-duration lock hold time. Defaults

to 100 milliseconds. Select 0 to disable.

locktorture.nested_locks= [KNL]

Specify the maximum lock nesting depth that

locktorture is to exercise, up to a limit of 8

(MAX_NESTED_LOCKS). Specify zero to disable.

Note that this parameter is ineffective on types

of locks that do not support nested acquisition.

locktorture.nreaders_stress= [KNL]

Set the number of locking read-acquisition kthreads.

Defaults to being automatically set based on the

number of online CPUs.

locktorture.nwriters_stress= [KNL]

Set the number of locking write-acquisition kthreads.

locktorture.onoff_holdoff= [KNL]

Set time (s) after boot for CPU-hotplug testing.

locktorture.onoff_interval= [KNL]

Set time (s) between CPU-hotplug operations, or

zero to disable CPU-hotplug testing.

locktorture.rt_boost= [KNL]

Do periodic testing of real-time lock priority

boosting. Select 0 to disable, 1 to boost

only rt_mutex, and 2 to boost unconditionally.

Defaults to 2, which might seem to be an

odd choice, but which should be harmless for

non-real-time spinlocks, due to their disabling

of preemption. Note that non-realtime mutexes

disable boosting.

locktorture.rt_boost_factor= [KNL]

Number that determines how often and for how

long priority boosting is exercised. This is

scaled down by the number of writers, so that the

number of boosts per unit time remains roughly

constant as the number of writers increases.

On the other hand, the duration of each boost

increases with the number of writers.

locktorture.shuffle_interval= [KNL]

Set task-shuffle interval (jiffies). Shuffling

tasks allows some CPUs to go into dyntick-idle

mode during the locktorture test.

locktorture.shutdown_secs= [KNL]

Set time (s) after boot system shutdown. This

is useful for hands-off automated testing.

locktorture.stat_interval= [KNL]

Time (s) between statistics printk()s.

locktorture.stutter= [KNL]

Time (s) to stutter testing, for example,

specifying five seconds causes the test to run for

five seconds, wait for five seconds, and so on.

This tests the locking primitive's ability to

transition abruptly to and from idle.

locktorture.torture_type= [KNL]

Specify the locking implementation to test.

locktorture.verbose= [KNL]

Enable additional printk() statements.

locktorture.writer_fifo= [KNL]

Run the write-side locktorture kthreads at

sched_set_fifo() real-time priority.

logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver

Format:

loglevel= [KNL,EARLY]

All Kernel Messages with a loglevel smaller than the

console loglevel will be printed to the console. It can

also be changed with klogd or other programs. The

loglevels are defined as follows:

0 (KERN_EMERG) system is unusable

1 (KERN_ALERT) action must be taken immediately

2 (KERN_CRIT) critical conditions

3 (KERN_ERR) error conditions

4 (KERN_WARNING) warning conditions

5 (KERN_NOTICE) normal but significant condition

6 (KERN_INFO) informational

7 (KERN_DEBUG) debug-level messages

log_buf_len=n[KMG] [KNL,EARLY]

Sets the size of the printk ring buffer, in bytes.

n must be a power of two and greater than the

minimal size. The minimal size is defined by

LOG_BUF_SHIFT kernel config parameter. There

is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config

parameter that allows to increase the default size

depending on the number of CPUs. See init/Kconfig

for more details.

logo.nologo [FB] Disables display of the built-in Linux logo.

This may be used to provide more screen space for

kernel log messages and is useful when debugging

kernel boot problems.

lp=0 [LP] Specify parallel ports to use, e.g,

lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses

lp=reset first parallel port). 'lp=0' disables the

lp=auto printer driver. 'lp=reset' (which can be

specified in addition to the ports) causes

attached printers to be reset. Using

lp=port1,port2,... specifies the parallel ports

to associate lp devices with, starting with

lp0. A port specification may be 'none' to skip

that lp device, or a parport name such as

'parport0'. Specifying 'lp=auto' instead of a

port specification list means that device IDs

from each port should be examined, to see if

an IEEE 1284-compliant printer is attached; if

so, the driver will manage that printer.

See also header of drivers/char/lp.c.

lpj=n [KNL]

Sets loops_per_jiffy to given constant, thus avoiding

time-consuming boot-time autodetection (up to 250 ms per

CPU). 0 enables autodetection (default). To determine

the correct value for your kernel, boot with normal

autodetection and see what value is printed. Note that

on SMP systems the preset will be applied to all CPUs,

which is likely to cause problems if your CPUs need

significantly divergent settings. An incorrect value

will cause delays in the kernel to be wrong, leading to

unpredictable I/O errors and other breakage. Although

unlikely, in the extreme case this might damage your

hardware.

lsm.debug [SECURITY] Enable LSM initialization debugging output.

lsm=lsm1,...,lsmN

[SECURITY] Choose order of LSM initialization. This

overrides CONFIG_LSM, and the "security=" parameter.

machtype= [Loongson] Share the same kernel image file between

different yeeloong laptops.

Example: machtype=lemote-yeeloong-2f-7inch

maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel

will bring up during bootup. maxcpus=n : n >= 0 limits

the kernel to bring up 'n' processors. Surely after

bootup you can bring up the other plugged cpu by executing

"echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus

only takes effect during system bootup.

While n=0 is a special case, it is equivalent to "nosmp",

which also disables the IO APIC.

max_loop= [LOOP] The number of loop block devices that get

(loop.max_loop) unconditionally pre-created at init time. The default

number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead

of statically allocating a predefined number, loop

devices can be requested on-demand with the

/dev/loop-control interface.

mce= [X86-{32,64}]

Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables.

off

disable machine check

no_cmci

disable CMCI(Corrected Machine Check Interrupt) that

Intel processor supports. Usually this disablement is

not recommended, but it might be handy if your

hardware is misbehaving.

Note that you'll get more problems without CMCI than

with due to the shared banks, i.e. you might get

duplicated error logs.

dont_log_ce

don't make logs for corrected errors. All events

reported as corrected are silently cleared by OS. This

option will be useful if you have no interest in any

of corrected errors.

ignore_ce

disable features for corrected errors, e.g.

polling timer and CMCI. All events reported as

corrected are not cleared by OS and remained in its

error banks.

Usually this disablement is not recommended, however

if there is an agent checking/clearing corrected

errors (e.g. BIOS or hardware monitoring

applications), conflicting with OS's error handling,

and you cannot deactivate the agent, then this option

will be a help.

no_lmce

do not opt-in to Local MCE delivery. Use legacy method

to broadcast MCEs.

bootlog

enable logging of machine checks left over from

booting. Disabled by default on AMD Fam10h and older

because some BIOS leave bogus ones.

If your BIOS doesn't do that it's a good idea to

enable though to make sure you log even machine check

events that result in a reboot. On Intel systems it is

enabled by default.

nobootlog

disable boot machine check logging.

monarchtimeout (number)

sets the time in us to wait for other CPUs on machine

checks. 0 to disable.

bios_cmci_threshold

don't overwrite the bios-set CMCI threshold. This boot

option prevents Linux from overwriting the CMCI

threshold set by the bios. Without this option, Linux

always sets the CMCI threshold to 1. Enabling this may

make memory predictive failure analysis less effective

if the bios sets thresholds for memory errors since we

will not see details for all errors.

recovery

force-enable recoverable machine check code paths

Everything else is in sysfs now.

md= [HW] RAID subsystems devices and level

See Documentation/admin-guide/md.rst.

mdacon= [MDA]

Format: ,

Specifies range of consoles to be captured by the MDA.

mds= [X86,INTEL,EARLY]

Control mitigation for the Micro-architectural Data

Sampling (MDS) vulnerability.

Certain CPUs are vulnerable to an exploit against CPU

internal buffers which can forward information to a

disclosure gadget under certain conditions.

In vulnerable processors, the speculatively

forwarded data can be used in a cache side channel

attack, to access data to which the attacker does

not have direct access.

This parameter controls the MDS mitigation. The

options are:

full - Enable MDS mitigation on vulnerable CPUs

full,nosmt - Enable MDS mitigation and disable

SMT on vulnerable CPUs

off - Unconditionally disable MDS mitigation

On TAA-affected machines, mds=off can be prevented by

an active TAA mitigation as both vulnerabilities are

mitigated with the same mechanism so in order to disable

this mitigation, you need to specify tsx_async_abort=off

too.

Not specifying this option is equivalent to

mds=full.

For details see: Documentation/admin-guide/hw-vuln/mds.rst

mem=nn[KMG] [HEXAGON,EARLY] Set the memory size.

Must be specified, otherwise memory size will be 0.

mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount

of memory Amount of memory to be used in cases

as follows:

1 for test;

2 when the kernel is not able to see the whole system memory;

3 memory that lies after 'mem=' boundary is excluded from

the hypervisor, then assigned to KVM guests.

4 to limit the memory available for kdump kernel.

[ARC,MICROBLAZE] - the limit applies only to low memory,

high memory is not affected.

[ARM64] - only limits memory covered by the linear

mapping. The NOMAP regions are not affected.

[X86] Work as limiting max address. Use together

with memmap= to avoid physical address space collisions.

Without memmap= PCI devices could be placed at addresses

belonging to unused RAM.

Note that this only takes effects during boot time since

in above case 3, memory may need be hot added after boot

if system memory of hypervisor is not sufficient.

mem=nn[KMG]@ss[KMG]

[ARM,MIPS,EARLY] - override the memory layout

reported by firmware.

Define a memory region of size nn[KMG] starting at

ss[KMG].

Multiple different regions can be specified with

multiple mem= parameters on the command line.

mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel

memory.

memblock=debug [KNL,EARLY] Enable memblock debug messages.

memchunk=nn[KMG]

[KNL,SH] Allow user to override the default size for

per-device physically contiguous DMA buffers.

memhp_default_state=online/offline/online_kernel/online_movable

[KNL] Set the initial state for the memory hotplug

onlining policy. If not specified, the default value is

set according to the

CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config

options.

See Documentation/admin-guide/mm/memory-hotplug.rst.

memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact

E820 memory map, as specified by the user.

Such memmap=exactmap lines can be constructed based on

BIOS output or other requirements. See the memmap=nn@ss

option description.

memmap=nn[KMG]@ss[KMG]

[KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory.

Region of memory to be used is from ss to ss+nn.

If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],

which limits max address to nn[KMG].

Multiple different regions can be specified,

comma delimited.

Example:

memmap=100M@2G,100M#3G,1G!1024G

memmap=nn[KMG]#ss[KMG]

[KNL,ACPI,EARLY] Mark specific memory as ACPI data.

Region of memory to be marked is from ss to ss+nn.

memmap=nn[KMG]$ss[KMG]

[KNL,ACPI,EARLY] Mark specific memory as reserved.

Region of memory to be reserved is from ss to ss+nn.

Example: Exclude memory from 0x18690000-0x1869ffff

memmap=64K$0x18690000

or

memmap=0x10000$0x18690000

Some bootloaders may need an escape character before '$',

like Grub2, otherwise '$' and the following number

will be eaten.

memmap=nn[KMG]!ss[KMG,EARLY]

[KNL,X86] Mark specific memory as protected.

Region of memory to be used, from ss to ss+nn.

The memory region may be marked as e820 type 12 (0xc)

and is NVDIMM or ADR memory.

memmap=%-+

[KNL,ACPI,EARLY] Convert memory within the specified region

from to . If "-" is left

out, the whole region will be marked as ,

even if previously unavailable. If "+" is left

out, matching memory will be removed. Types are

specified as e820 types, e.g., 1 = RAM, 2 = reserved,

3 = ACPI, 12 = PRAM.

memory_corruption_check=0/1 [X86,EARLY]

Some BIOSes seem to corrupt the first 64k of

memory when doing things like suspend/resume.

Setting this option will scan the memory

looking for corruption. Enabling this will

both detect corruption and prevent the kernel

from using the memory being corrupted.

However, its intended as a diagnostic tool; if

repeatable BIOS-originated corruption always

affects the same memory, you can use memmap=

to prevent the kernel from using that memory.

memory_corruption_check_size=size [X86,EARLY]

By default it checks for corruption in the low

64k, making this memory unavailable for normal

use. Use this parameter to scan for

corruption in more or less memory.

memory_corruption_check_period=seconds [X86,EARLY]

By default it checks for corruption every 60

seconds. Use this parameter to check at some

other rate. 0 disables periodic checking.

memory_hotplug.memmap_on_memory

[KNL,X86,ARM] Boolean flag to enable this feature.

Format: {on | off (default)}

When enabled, runtime hotplugged memory will

allocate its internal metadata (struct pages,

those vmemmap pages cannot be optimized even

if hugetlb_free_vmemmap is enabled) from the

hotadded memory which will allow to hotadd a

lot of memory without requiring additional

memory to do so.

This feature is disabled by default because it

has some implication on large (e.g. GB)

allocations in some configurations (e.g. small

memory blocks).

The state of the flag can be read in

/sys/module/memory_hotplug/parameters/memmap_on_memory.

Note that even when enabled, there are a few cases where

the feature is not effective.

memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest

Format:

default : 0

Specifies the number of memtest passes to be

performed. Each pass selects another test

pattern from a given set of patterns. Memtest

fills the memory with this pattern, validates

memory contents and reserves bad memory

regions that are detected.

mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control

Valid arguments: on, off

Default: off

mem_encrypt=on: Activate SME

mem_encrypt=off: Do not activate SME

Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst

for details on when memory encryption can be activated.

mem_sleep_default= [SUSPEND] Default system suspend mode:

s2idle - Suspend-To-Idle

shallow - Power-On Suspend or equivalent (if supported)

deep - Suspend-To-RAM or equivalent (if supported)

See Documentation/admin-guide/pm/sleep-states.rst.

mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when

the BIOS has incorrectly applied a workaround. TinyBIOS

version 0.98 is known to be affected, 0.99 fixes the

problem by letting the user disable the workaround.

mga= [HW,DRM]

microcode.force_minrev= [X86]

Format:

Enable or disable the microcode minimal revision

enforcement for the runtime microcode loader.

mini2440= [ARM,HW,KNL]

Format:[0..2][b][c][t]

Default: "0tb"

MINI2440 configuration specification:

0 - The attached screen is the 3.5" TFT

1 - The attached screen is the 7" TFT

2 - The VGA Shield is attached (1024x768)

Leaving out the screen size parameter will not load

the TFT driver, and the framebuffer will be left

unconfigured.

b - Enable backlight. The TFT backlight pin will be

linked to the kernel VESA blanking code and a GPIO

LED. This parameter is not necessary when using the

VGA shield.

c - Enable the s3c camera interface.

t - Reserved for enabling touchscreen support. The

touchscreen support is not enabled in the mainstream

kernel as of 2.6.30, a preliminary port can be found

in the "bleeding edge" mini2440 support kernel at

https://repo.or.cz/w/linux-2.6/mini2440.git

mitigations=

[X86,PPC,S390,ARM64,EARLY] Control optional mitigations for

CPU vulnerabilities. This is a set of curated,

arch-independent options, each of which is an

aggregation of existing arch-specific options.

Note, "mitigations" is supported if and only if the

kernel was built with CPU_MITIGATIONS=y.

off

Disable all optional CPU mitigations. This

improves system performance, but it may also

expose users to several CPU vulnerabilities.

Equivalent to: if nokaslr then kpti=0 [ARM64]

gather_data_sampling=off [X86]

indirect_target_selection=off [X86]

kvm.nx_huge_pages=off [X86]

l1tf=off [X86]

mds=off [X86]

mmio_stale_data=off [X86]

no_entry_flush [PPC]

no_uaccess_flush [PPC]

nobp=0 [S390]

nopti [X86,PPC]

nospectre_bhb [ARM64]

nospectre_v1 [X86,PPC]

nospectre_v2 [X86,PPC,S390,ARM64]

reg_file_data_sampling=off [X86]

retbleed=off [X86]

spec_rstack_overflow=off [X86]

spec_store_bypass_disable=off [X86,PPC]

spectre_bhi=off [X86]

spectre_v2_user=off [X86]

srbds=off [X86,INTEL]

ssbd=force-off [ARM64]

tsx_async_abort=off [X86]

Exceptions:

This does not have any effect on

kvm.nx_huge_pages when

kvm.nx_huge_pages=force.

auto (default)

Mitigate all CPU vulnerabilities, but leave SMT

enabled, even if it's vulnerable. This is for

users who don't want to be surprised by SMT

getting disabled across kernel upgrades, or who

have other ways of avoiding SMT-based attacks.

Equivalent to: (default behavior)

auto,nosmt

Mitigate all CPU vulnerabilities, disabling SMT

if needed. This is for users who always want to

be fully mitigated, even if it means losing SMT.

Equivalent to: l1tf=flush,nosmt [X86]

mds=full,nosmt [X86]

tsx_async_abort=full,nosmt [X86]

mmio_stale_data=full,nosmt [X86]

retbleed=auto,nosmt [X86]

mminit_loglevel=

[KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this

parameter allows control of the logging verbosity for

the additional memory initialisation checks. A value

of 0 disables mminit logging and a level of 4 will

log everything. Information is printed at KERN_DEBUG

so loglevel=8 may also need to be specified.

mmio_stale_data=

[X86,INTEL,EARLY] Control mitigation for the Processor

MMIO Stale Data vulnerabilities.

Processor MMIO Stale Data is a class of

vulnerabilities that may expose data after an MMIO

operation. Exposed data could originate or end in

the same CPU buffers as affected by MDS and TAA.

Therefore, similar to MDS and TAA, the mitigation

is to clear the affected CPU buffers.

This parameter controls the mitigation. The

options are:

full - Enable mitigation on vulnerable CPUs

full,nosmt - Enable mitigation and disable SMT on

vulnerable CPUs.

off - Unconditionally disable mitigation

On MDS or TAA affected machines,

mmio_stale_data=off can be prevented by an active

MDS or TAA mitigation as these vulnerabilities are

mitigated with the same mechanism so in order to

disable this mitigation, you need to specify

mds=off and tsx_async_abort=off too.

Not specifying this option is equivalent to

mmio_stale_data=full.

For details see:

Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst

.async_probe[=] [KNL]

If no value is specified or if the value

specified is not a valid , enable asynchronous

probe on this module. Otherwise, enable/disable

asynchronous probe on this module as indicated by the

value. See also: module.async_probe

module.async_probe=

[KNL] When set to true, modules will use async probing

by default. To enable/disable async probing for a

specific module, use the module specific control that

is documented under .async_probe. When both

module.async_probe and .async_probe are

specified, .async_probe takes precedence for

the specific module.

module.enable_dups_trace

[KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set,

this means that duplicate request_module() calls will

trigger a WARN_ON() instead of a pr_warn(). Note that

if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s

will always be issued and this option does nothing.

module.sig_enforce

[KNL] When CONFIG_MODULE_SIG is set, this means that

modules without (valid) signatures will fail to load.

Note that if CONFIG_MODULE_SIG_FORCE is set, that

is always true, so this option does nothing.

module_blacklist= [KNL] Do not load a comma-separated list of

modules. Useful for debugging problem modules.

mousedev.tap_time=

[MOUSE] Maximum time between finger touching and

leaving touchpad surface for touch to be considered

a tap and be reported as a left button click (for

touchpads working in absolute mode only).

Format:

mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices

reporting absolute coordinates, such as tablets

mousedev.yres= [MOUSE] Vertical screen resolution, used for devices

reporting absolute coordinates, such as tablets

movablecore= [KNL,X86,PPC,EARLY]

Format: nn[KMGTPE] | nn%

This parameter is the complement to kernelcore=, it

specifies the amount of memory used for migratable

allocations. If both kernelcore and movablecore is

specified, then kernelcore will be at *least* the

specified value but may be more. If movablecore on its

own is specified, the administrator must be careful

that the amount of memory usable for all allocations

is not too small.

movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory

NUMA nodes to be movable. This means that the memory

of such nodes will be usable only for movable

allocations which rules out almost all kernel

allocations. Use with caution!

MTD_Partition= [MTD]

Format: ,,,

MTD_Region= [MTD] Format:

,[,,,,]

mtdparts= [MTD]

See drivers/mtd/parsers/cmdlinepart.c

mtouchusb.raw_coordinates=

[HW] Make the MicroTouch USB driver use raw coordinates

('y', default) or cooked coordinates ('n')

mtrr=debug [X86,EARLY]

Enable printing debug information related to MTRR

registers at boot time.

mtrr_chunk_size=nn[KMG,X86,EARLY]

used for mtrr cleanup. It is largest continuous chunk

that could hold holes aka. UC entries.

mtrr_gran_size=nn[KMG,X86,EARLY]

Used for mtrr cleanup. It is granularity of mtrr block.

Default is 1.

Large value could prevent small alignment from

using up MTRRs.

mtrr_spare_reg_nr=n [X86,EARLY]

Format:

Range: 0,7 : spare reg number

Default : 1

Used for mtrr cleanup. It is spare mtrr entries number.

Set to 2 or more if your graphical card needs more.

multitce=off [PPC] This parameter disables the use of the pSeries

firmware feature for updating multiple TCE entries

at a time.

n2= [NET] SDL Inc. RISCom/N2 synchronous serial card

netdev= [NET] Network devices parameters

Format: ,,,,

Note that mem_start is often overloaded to mean

something different and driver-specific.

This usage is only documented in each driver source

file if at all.

netpoll.carrier_timeout=

[NET] Specifies amount of time (in seconds) that

netpoll should wait for a carrier. By default netpoll

waits 4 seconds.

nf_conntrack.acct=

[NETFILTER] Enable connection tracking flow accounting

0 to disable accounting

1 to enable accounting

Default value is 0.

nfs.cache_getent=

[NFS] sets the pathname to the program which is used

to update the NFS client cache entries.

nfs.cache_getent_timeout=

[NFS] sets the timeout after which an attempt to

update a cache entry is deemed to have failed.

nfs.callback_nr_threads=

[NFSv4] set the total number of threads that the

NFS client will assign to service NFSv4 callback

requests.

nfs.callback_tcpport=

[NFS] set the TCP port on which the NFSv4 callback

channel should listen.

nfs.delay_retrans=

[NFS] specifies the number of times the NFSv4 client

retries the request before returning an EAGAIN error,

after a reply of NFS4ERR_DELAY from the server.

Only applies if the softerr mount option is enabled,

and the specified value is >= 0.

nfs.enable_ino64=

[NFS] enable 64-bit inode numbers.

If zero, the NFS client will fake up a 32-bit inode

number for the readdir() and stat() syscalls instead

of returning the full 64-bit number.

The default is to return 64-bit inode numbers.

nfs.idmap_cache_timeout=

[NFS] set the maximum lifetime for idmapper cache

entries.

nfs.max_session_cb_slots=

[NFSv4.1] Sets the maximum number of session

slots the client will assign to the callback

channel. This determines the maximum number of

callbacks the client will process in parallel for

a particular server.

nfs.max_session_slots=

[NFSv4.1] Sets the maximum number of session slots

the client will attempt to negotiate with the server.

This limits the number of simultaneous RPC requests

that the client can send to the NFSv4.1 server.

Note that there is little point in setting this

value higher than the max_tcp_slot_table_limit.

nfs.nfs4_disable_idmapping=

[NFSv4] When set to the default of '1', this option

ensures that both the RPC level authentication

scheme and the NFS level operations agree to use

numeric uids/gids if the mount is using the

'sec=sys' security flavour. In effect it is

disabling idmapping, which can make migration from

legacy NFSv2/v3 systems to NFSv4 easier.

Servers that do not support this mode of operation

will be autodetected by the client, and it will fall

back to using the idmapper.

To turn off this behaviour, set the value to '0'.

nfs.nfs4_unique_id=

[NFS4] Specify an additional fixed unique ident-

ification string that NFSv4 clients can insert into

their nfs_client_id4 string. This is typically a

UUID that is generated at system install time.

nfs.recover_lost_locks=

[NFSv4] Attempt to recover locks that were lost due

to a lease timeout on the server. Please note that

doing this risks data corruption, since there are

no guarantees that the file will remain unchanged

after the locks are lost.

If you want to enable the kernel legacy behaviour of

attempting to recover these locks, then set this

parameter to '1'.

The default parameter value of '0' causes the kernel

not to attempt recovery of lost locks.

nfs.send_implementation_id=

[NFSv4.1] Send client implementation identification

information in exchange_id requests.

If zero, no implementation identification information

will be sent.

The default is to send the implementation identification

information.

nfs4.layoutstats_timer=

[NFSv4.2] Change the rate at which the kernel sends

layoutstats to the pNFS metadata server.

Setting this to value to 0 causes the kernel to use

whatever value is the default set by the layout

driver. A non-zero value sets the minimum interval

in seconds between layoutstats transmissions.

nfsd.inter_copy_offload_enable=

[NFSv4.2] When set to 1, the server will support

server-to-server copies for which this server is

the destination of the copy.

nfsd.nfs4_disable_idmapping=

[NFSv4] When set to the default of '1', the NFSv4

server will return only numeric uids and gids to

clients using auth_sys, and will accept numeric uids

and gids from such clients. This is intended to ease

migration from NFSv2/v3.

nfsd.nfsd4_ssc_umount_timeout=

[NFSv4.2] When used as the destination of a

server-to-server copy, knfsd temporarily mounts

the source server. It caches the mount in case

it will be needed again, and discards it if not

used for the number of milliseconds specified by

this parameter.

nfsaddrs= [NFS] Deprecated. Use ip= instead.

See Documentation/admin-guide/nfs/nfsroot.rst.

nfsroot= [NFS] nfs root filesystem for disk-less boxes.

See Documentation/admin-guide/nfs/nfsroot.rst.

nfsrootdebug [NFS] enable nfsroot debugging messages.

See Documentation/admin-guide/nfs/nfsroot.rst.

nmi_backtrace.backtrace_idle [KNL]

Dump stacks even of idle CPUs in response to an

NMI stack-backtrace request.

nmi_debug= [KNL,SH] Specify one or more actions to take

when a NMI is triggered.

Format: [state][,regs][,debounce][,die]

nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels

Format: [panic,][nopanic,][rNNN,][num]

Valid num: 0 or 1

0 - turn hardlockup detector in nmi_watchdog off

1 - turn hardlockup detector in nmi_watchdog on

rNNN - configure the watchdog with raw perf event 0xNNN

When panic is specified, panic when an NMI watchdog

timeout occurs (or 'nopanic' to not panic on an NMI

watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)

To disable both hard and soft lockup detectors,

please see 'nowatchdog'.

This is useful when you use a panic=... timeout and

need the box quickly up again.

These settings can be accessed at runtime via

the nmi_watchdog and hardlockup_panic sysctls.

no387 [BUGS=X86-32] Tells the kernel to use the 387 maths

emulation library even if a 387 maths coprocessor

is present.

no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes.

Forces kernel to use 3-level paging instead.

no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces

kernel to use 4-level paging instead.

noalign [KNL,ARM]

noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any

IOAPICs that may be present in the system.

noapictimer [APIC,X86] Don't set up the APIC timer

noautogroup Disable scheduler automatic task group creation.

nocache [ARM,EARLY]

no_console_suspend

[HW] Never suspend the console

Disable suspending of consoles during suspend and

hibernate operations. Once disabled, debugging

messages can reach various consoles while the rest

of the system is being put to sleep (ie, while

debugging driver suspend/resume hooks). This may

not work reliably with all consoles, but is known

to work with serial and VGA consoles.

To facilitate more flexible debugging, we also add

console_suspend, a printk module parameter to control

it. Users could use console_suspend (usually

/sys/module/printk/parameters/console_suspend) to

turn on/off it dynamically.

no_debug_objects

[KNL,EARLY] Disable object debugging

nodsp [SH] Disable hardware DSP at boot time.

noefi [EFI,EARLY] Disable EFI runtime services support.

no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel.

noexec32 [X86-64]

This affects only 32-bit executables.

noexec32=on: enable non-executable mappings (default)

read doesn't imply executable mappings

noexec32=off: disable non-executable mappings

read implies executable mappings

no_file_caps Tells the kernel not to honor file capabilities. The

only way then for a file to be executed with privilege

is to be setuid root or executed by root.

nofpu [MIPS,SH] Disable hardware FPU at boot time.

nofsgsbase [X86] Disables FSGSBASE instructions.

nofxsr [BUGS=X86-32] Disables x86 floating point extended

register save and restore. The kernel will only save

legacy floating-point registers on task switch.

nogbpages [X86] Do not use GB pages for kernel direct mappings.

no_hash_pointers

[KNL,EARLY]

Force pointers printed to the console or buffers to be

unhashed. By default, when a pointer is printed via %p

format string, that pointer is "hashed", i.e. obscured

by hashing the pointer value. This is a security feature

that hides actual kernel addresses from unprivileged

users, but it also makes debugging the kernel more

difficult since unequal pointers can no longer be

compared. However, if this command-line option is

specified, then all normal pointers will have their true

value printed. This option should only be specified when

debugging the kernel. Please do not use on production

kernels.

nohibernate [HIBERNATION] Disable hibernation and resume.

nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to

busy wait in do_idle() and not use the arch_cpu_idle()

implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP

to be effective. This is useful on platforms where the

sleep(SH) or wfi(ARM,ARM64) instructions do not work

correctly or when doing power measurements to evaluate

the impact of the sleep instructions. This is also

useful when using JTAG debugger.

nohpet [X86] Don't use the HPET timer.

nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings.

nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings.

nohz= [KNL] Boottime enable/disable dynamic ticks

Valid arguments: on, off

Default: on

nohz_full= [KNL,BOOT,SMP,ISOL]

The argument is a cpu list, as described above.

In kernels built with CONFIG_NO_HZ_FULL=y, set

the specified list of CPUs whose tick will be stopped

whenever possible. The boot CPU will be forced outside

the range to maintain the timekeeping. Any CPUs

in this list will have their RCU callbacks offloaded,

just as if they had also been called out in the

rcu_nocbs= boot parameter.

Note that this argument takes precedence over

the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.

noinitrd [RAM] Tells the kernel not to load any configured

initial RAM disk.

nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt

remapping.

[Deprecated - use intremap=off]

noinvpcid [X86,EARLY] Disable the INVPCID cpu feature.

noiotrap [SH] Disables trapped I/O port accesses.

noirqdebug [X86-32] Disables the code which attempts to detect and

disable unhandled interrupt sources.

noisapnp [ISAPNP] Disables ISA PnP code.

nokaslr [KNL,EARLY]

When CONFIG_RANDOMIZE_BASE is set, this disables

kernel and module base offset ASLR (Address Space

Layout Randomization).

no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page

fault handling.

no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver

nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC.

nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer.

nomce [X86-32] Disable Machine Check Exception

nomfgpt [X86-32] Disable Multi-Function General Purpose

Timer usage (for AMD Geode machines).

nomodeset Disable kernel modesetting. Most systems' firmware

sets up a display mode and provides framebuffer memory

for output. With nomodeset, DRM and fbdev drivers will

not load if they could possibly displace the pre-

initialized output. Only the system framebuffer will

be available for use. The respective drivers will not

perform display-mode changes or accelerated rendering.

Useful as error fallback, or for testing and debugging.

nomodule Disable module load

nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to

shutdown the other cpus. Instead use the REBOOT_VECTOR

irq.

nopat [X86,EARLY] Disable PAT (page attribute table extension of

pagetables) support.

nopcid [X86-64,EARLY] Disable the PCID cpu feature.

nopku [X86] Disable Memory Protection Keys CPU feature found

in some Intel CPUs.

nopti [X86-64,EARLY]

Equivalent to pti=off

nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY]

Disables the PV optimizations forcing the guest to run

as generic guest with no PV drivers. Currently support

XEN HVM, KVM, HYPER_V and VMWARE guest.

nopvspin [X86,XEN,KVM,EARLY]

Disables the qspinlock slow path using PV optimizations

which allow the hypervisor to 'idle' the guest on lock

contention.

norandmaps Don't use address space randomization. Equivalent to

echo 0 > /proc/sys/kernel/randomize_va_space

noreplace-smp [X86-32,SMP] Don't replace SMP instructions

with UP alternatives

noresume [SWSUSP] Disables resume and restores original swap

space.

no-scroll [VGA] Disables scrollback.

This is required for the Braillex ib80-piezo Braille

reader made by F.H. Papenmeier (Germany).

nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support.

nosmap [PPC,EARLY]

Disable SMAP (Supervisor Mode Access Prevention)

even if it is supported by processor.

nosmep [PPC64s,EARLY]

Disable SMEP (Supervisor Mode Execution Prevention)

even if it is supported by processor.

nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel,

and disable the IO APIC. legacy for "maxcpus=0".

nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT).

Equivalent to smt=1.

[KNL,X86,PPC,S390] Disable symmetric multithreading (SMT).

nosmt=force: Force disable SMT, cannot be undone

via the sysfs control file.

nosoftlockup [KNL] Disable the soft-lockup detector.

nospec_store_bypass_disable

[HW,EARLY] Disable all mitigations for the Speculative

Store Bypass vulnerability

nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch

history injection) vulnerability. System may allow data leaks

with this option.

nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1

(bounds check bypass). With this option data leaks are

possible in the system.

nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations

for the Spectre variant 2 (indirect branch

prediction) vulnerability. System may allow data

leaks with this option.

no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY]

Disable paravirtualized steal time accounting. steal time

is computed, but won't influence scheduler behaviour

nosync [HW,M68K] Disables sync negotiation for all devices.

no_timer_check [X86,APIC] Disables the code which tests for broken

timer IRQ sources, i.e., the IO-APIC timer. This can

work around problems with incorrect timer

initialization on some boards.

no_uaccess_flush

[PPC,EARLY] Don't flush the L1-D cache after accessing user data.

novmcoredd [KNL,KDUMP]

Disable device dump. Device dump allows drivers to

append dump data to vmcore so you can collect driver

specified debug info. Drivers can append the data

without any limit and this data is stored in memory,

so this may cause significant memory stress. Disabling

device dump can help save memory but the driver debug

data will be no longer available. This parameter

is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP

is set.

no-vmw-sched-clock

[X86,PV_OPS,EARLY] Disable paravirtualized VMware

scheduler clock and use the default one.

nowatchdog [KNL] Disable both lockup detectors, i.e.

soft-lockup and NMI watchdog (hard-lockup).

nowb [ARM,EARLY]

nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode.

NOTE: this parameter will be ignored on systems with the

LEGACY_XAPIC_DISABLED bit set in the

IA32_XAPIC_DISABLE_STATUS MSR.

noxsave [BUGS=X86] Disables x86 extended register state save

and restore using xsave. The kernel will fallback to

enabling legacy floating-point and sse state.

noxsaveopt [X86] Disables xsaveopt used in saving x86 extended

register states. The kernel will fall back to use

xsave to save the states. By using this parameter,

performance of saving the states is degraded because

xsave doesn't support modified optimization while

xsaveopt supports it on xsaveopt enabled systems.

noxsaves [X86] Disables xsaves and xrstors used in saving and

restoring x86 extended register state in compacted

form of xsave area. The kernel will fall back to use

xsaveopt and xrstor to save and restore the states

in standard form of xsave area. By using this

parameter, xsave area per process might occupy more

memory on xsaves enabled systems.

nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel

could support. nr_cpus=n : n >= 1 limits the kernel to

support 'n' processors. It could be larger than the

number of already plugged CPU during bootup, later in

runtime you can physically add extra cpu until it reaches

n. So during boot up some boot time memory for per-cpu

variables need be pre-allocated for later physical cpu

hot plugging.

nr_uarts= [SERIAL] maximum number of UARTs to be registered.

numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY]

Disable NUMA, Only set up a single NUMA node

spanning all memory.

numa=fake=[MG]

[KNL, ARM64, RISCV, X86, EARLY]

If given as a memory unit, fills all system RAM with

nodes of size interleaved over physical nodes.

numa=fake=

[KNL, ARM64, RISCV, X86, EARLY]

If given as an integer, fills all system RAM with N

fake nodes interleaved over physical nodes.

numa=fake=U

[KNL, ARM64, RISCV, X86, EARLY]

If given as an integer followed by 'U', it will

divide each physical node into N emulated nodes.

numa=noacpi [X86] Don't parse the SRAT table for NUMA setup

numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or

soft-reserved memory partitioning.

numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic

NUMA balancing.

Allowed values are enable and disable

numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.

'node', 'default' can be specified

This can be set from sysctl after boot.

See Documentation/admin-guide/sysctl/vm.rst for details.

ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver.

See Documentation/core-api/debugging-via-ohci1394.rst for more

info.

olpc_ec_timeout= [OLPC] ms delay when issuing EC commands

Rather than timing out after 20 ms if an EC

command is not properly ACKed, override the length

of the timeout. We have interrupts disabled while

waiting for the ACK, so if this is set too high

interrupts *may* be lost!

omap_mux= [OMAP] Override bootloader pin multiplexing.

Format: ...

For example, to override I2C bus2:

omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100

onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration

Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]

boundary - index of last SLC block on Flex-OneNAND.

The remaining blocks are configured as MLC blocks.

lock - Configure if Flex-OneNAND boundary should be locked.

Once locked, the boundary cannot be changed.

1 indicates lock status, 0 indicates unlock status.

oops=panic [KNL,EARLY]

Always panic on oopses. Default is to just kill the

process, but there is a small probability of

deadlocking the machine.

This will also cause panics on machine check exceptions.

Useful together with panic=30 to trigger a reboot.

page_alloc.shuffle=

[KNL] Boolean flag to control whether the page allocator

should randomize its free lists. This parameter can be

used to enable/disable page randomization. The state of

the flag can be read from sysfs at:

/sys/module/page_alloc/parameters/shuffle.

This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y.

page_owner= [KNL,EARLY] Boot-time page_owner enabling option.

Storage of the information about who allocated

each page is disabled in default. With this switch,

we can turn it on.

on: enable the feature

page_poison= [KNL,EARLY] Boot-time parameter changing the state of

poisoning on the buddy allocator, available with

CONFIG_PAGE_POISONING=y.

off: turn off poisoning (default)

on: turn on poisoning

page_reporting.page_reporting_order=

[KNL] Minimal page reporting order

Format:

Adjust the minimal page reporting order. The page

reporting is disabled when it exceeds MAX_PAGE_ORDER.

panic= [KNL] Kernel behaviour on panic: delay

timeout > 0: seconds before rebooting

timeout = 0: wait forever

timeout < 0: reboot immediately

Format:

panic_on_taint= [KNL,EARLY]

Bitmask for conditionally calling panic() in add_taint()

Format: [,nousertaint]

Hexadecimal bitmask representing the set of TAINT flags

that will cause the kernel to panic when add_taint() is

called with any of the flags in this set.

The optional switch "nousertaint" can be utilized to

prevent userspace forced crashes by writing to sysctl

/proc/sys/kernel/tainted any flagset matching with the

bitmask set on panic_on_taint.

See Documentation/admin-guide/tainted-kernels.rst for

extra details on the taint flags that users can pick

to compose the bitmask to assign to panic_on_taint.

panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump

on a WARN().

panic_print= Bitmask for printing system info when panic happens.

User can chose combination of the following bits:

bit 0: print all tasks info

bit 1: print system memory info

bit 2: print timer info

bit 3: print locks info if CONFIG_LOCKDEP is on

bit 4: print ftrace buffer

bit 5: print all printk messages in buffer

bit 6: print all CPUs backtrace (if available in the arch)

bit 7: print only tasks in uninterruptible (blocked) state

*Be aware* that this option may print a _lot_ of lines,

so there are risks of losing older messages in the log.

Use this option carefully, maybe worth to setup a

bigger log buffer with "log_buf_len" along with this.

parkbd.port= [HW] Parallel port number the keyboard adapter is

connected to, default is 0.

Format:

parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,

0 for XT, 1 for AT (default is AT).

Format:

parport= [HW,PPT] Specify parallel ports. 0 disables.

Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }

Use 'auto' to force the driver to use any

IRQ/DMA settings detected (the default is to

ignore detected IRQ/DMA settings because of

possible conflicts). You can specify the base

address, IRQ, and DMA settings; IRQ and DMA

should be numbers, or 'auto' (for using detected

settings on that particular port), or 'nofifo'

(to avoid using a FIFO even if it is detected).

Parallel ports are assigned in the order they

are specified on the command line, starting

with parport0.

parport_init_mode= [HW,PPT]

Configure VIA parallel port to operate in

a specific mode. This is necessary on Pegasos

computer where firmware has no options for setting

up parallel port mode and sets it to spp.

Currently this function knows 686a and 8231 chips.

Format: [spp|ps2|epp|ecp|ecpepp]

pata_legacy.all= [HW,LIBATA]

Format:

Set to non-zero to probe primary and secondary ISA

port ranges on PCI systems where no PCI PATA device

has been found at either range. Disabled by default.

pata_legacy.autospeed= [HW,LIBATA]

Format:

Set to non-zero if a chip is present that snoops speed

changes. Disabled by default.

pata_legacy.ht6560a= [HW,LIBATA]

Format:

Set to 1, 2, or 3 for HT 6560A on the primary channel,

the secondary channel, or both channels respectively.

Disabled by default.

pata_legacy.ht6560b= [HW,LIBATA]

Format:

Set to 1, 2, or 3 for HT 6560B on the primary channel,

the secondary channel, or both channels respectively.

Disabled by default.

pata_legacy.iordy_mask= [HW,LIBATA]

Format:

IORDY enable mask. Set individual bits to allow IORDY

for the respective channel. Bit 0 is for the first

legacy channel handled by this driver, bit 1 is for

the second channel, and so on. The sequence will often

correspond to the primary legacy channel, the secondary

legacy channel, and so on, but the handling of a PCI

bus and the use of other driver options may interfere

with the sequence. By default IORDY is allowed across

all channels.

pata_legacy.opti82c46x= [HW,LIBATA]

Format:

Set to 1, 2, or 3 for Opti 82c611A on the primary

channel, the secondary channel, or both channels

respectively. Disabled by default.

pata_legacy.opti82c611a= [HW,LIBATA]

Format:

Set to 1, 2, or 3 for Opti 82c465MV on the primary

channel, the secondary channel, or both channels

respectively. Disabled by default.

pata_legacy.pio_mask= [HW,LIBATA]

Format:

PIO mode mask for autospeed devices. Set individual

bits to allow the use of the respective PIO modes.

Bit 0 is for mode 0, bit 1 is for mode 1, and so on.

All modes allowed by default.

pata_legacy.probe_all= [HW,LIBATA]

Format:

Set to non-zero to probe tertiary and further ISA

port ranges on PCI systems. Disabled by default.

pata_legacy.probe_mask= [HW,LIBATA]

Format:

Probe mask for legacy ISA PATA ports. Depending on

platform configuration and the use of other driver

options up to 6 legacy ports are supported: 0x1f0,

0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing

of individual ports can be disabled by setting the

corresponding bits in the mask to 1. Bit 0 is for

the first port in the list above (0x1f0), and so on.

By default all supported ports are probed.

pata_legacy.qdi= [HW,LIBATA]

Format:

Set to non-zero to probe QDI controllers. By default

set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.

pata_legacy.winbond= [HW,LIBATA]

Format:

Set to non-zero to probe Winbond controllers. Use

the standard I/O port (0x130) if 1, otherwise the

value given is the I/O port to use (typically 0x1b0).

By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,

0 otherwise.

pata_platform.pio_mask= [HW,LIBATA]

Format:

Supported PIO mode mask. Set individual bits to allow

the use of the respective PIO modes. Bit 0 is for

mode 0, bit 1 is for mode 1, and so on. Mode 0 only

allowed by default.

pause_on_oops=

Halt all CPUs after the first oops has been printed for

the specified number of seconds. This is to be used if

your oopses keep scrolling off the screen.

pcbit= [HW,ISDN]

pci=option[,option...] [PCI,EARLY] various PCI subsystem options.

Some options herein operate on a specific device

or a set of devices (). These are

specified in one of the following formats:

[:]:.[/.]*

pci::[::]

Note: the first format specifies a PCI

bus/device/function address which may change

if new hardware is inserted, if motherboard

firmware changes, or due to changes caused

by other kernel parameters. If the

domain is left unspecified, it is

taken to be zero. Optionally, a path

to a device through multiple device/function

addresses can be specified after the base

address (this is more robust against

renumbering issues). The second format

selects devices using IDs from the

configuration space which may match multiple

devices in the system.

earlydump dump PCI config space before the kernel

changes anything

off [X86] don't probe for the PCI bus

bios [X86-32] force use of PCI BIOS, don't access

the hardware directly. Use this if your machine

has a non-standard PCI host bridge.

nobios [X86-32] disallow use of PCI BIOS, only direct

hardware access methods are allowed. Use this

if you experience crashes upon bootup and you

suspect they are caused by the BIOS.

conf1 [X86] Force use of PCI Configuration Access

Mechanism 1 (config address in IO port 0xCF8,

data in IO port 0xCFC, both 32-bit).

conf2 [X86] Force use of PCI Configuration Access

Mechanism 2 (IO port 0xCF8 is an 8-bit port for

the function, IO port 0xCFA, also 8-bit, sets

bus number. The config space is then accessed

through ports 0xC000-0xCFFF).

See http://wiki.osdev.org/PCI for more info

on the configuration access mechanisms.

noaer [PCIE] If the PCIEAER kernel config parameter is

enabled, this kernel boot option can be used to

disable the use of PCIE advanced error reporting.

nodomains [PCI] Disable support for multiple PCI

root domains (aka PCI segments, in ACPI-speak).

nommconf [X86] Disable use of MMCONFIG for PCI

Configuration

check_enable_amd_mmconf [X86] check for and enable

properly configured MMIO access to PCI

config space on AMD family 10h CPU

nomsi [MSI] If the PCI_MSI kernel config parameter is

enabled, this kernel boot option can be used to

disable the use of MSI interrupts system-wide.

noioapicquirk [APIC] Disable all boot interrupt quirks.

Safety option to keep boot IRQs enabled. This

should never be necessary.

ioapicreroute [APIC] Enable rerouting of boot IRQs to the

primary IO-APIC for bridges that cannot disable

boot IRQs. This fixes a source of spurious IRQs

when the system masks IRQs.

noioapicreroute [APIC] Disable workaround that uses the

boot IRQ equivalent of an IRQ that connects to

a chipset where boot IRQs cannot be disabled.

The opposite of ioapicreroute.

biosirq [X86-32] Use PCI BIOS calls to get the interrupt

routing table. These calls are known to be buggy

on several machines and they hang the machine

when used, but on other computers it's the only

way to get the interrupt routing table. Try

this option if the kernel is unable to allocate

IRQs or discover secondary PCI buses on your

motherboard.

rom [X86] Assign address space to expansion ROMs.

Use with caution as certain devices share

address decoders between ROMs and other

resources.

norom [X86] Do not assign address space to

expansion ROMs that do not already have

BIOS assigned address ranges.

nobar [X86] Do not assign address space to the

BARs that weren't assigned by the BIOS.

irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be

assigned automatically to PCI devices. You can

make the kernel exclude IRQs of your ISA cards

this way.

pirqaddr=0xAAAAA [X86] Specify the physical address

of the PIRQ table (normally generated

by the BIOS) if it is outside the

F0000h-100000h range.

lastbus=N [X86] Scan all buses thru bus #N. Can be

useful if the kernel is unable to find your

secondary buses and you want to tell it

explicitly which ones they are.

assign-busses [X86] Always assign all PCI bus

numbers ourselves, overriding

whatever the firmware may have done.

usepirqmask [X86] Honor the possible IRQ mask stored

in the BIOS $PIR table. This is needed on

some systems with broken BIOSes, notably

some HP Pavilion N5400 and Omnibook XE3

notebooks. This will have no effect if ACPI

IRQ routing is enabled.

noacpi [X86] Do not use ACPI for IRQ routing

or for PCI scanning.

use_crs [X86] Use PCI host bridge window information

from ACPI. On BIOSes from 2008 or later, this

is enabled by default. If you need to use this,

please report a bug.

nocrs [X86] Ignore PCI host bridge windows from ACPI.

If you need to use this, please report a bug.

use_e820 [X86] Use E820 reservations to exclude parts of

PCI host bridge windows. This is a workaround

for BIOS defects in host bridge _CRS methods.

If you need to use this, please report a bug to

.

no_e820 [X86] Ignore E820 reservations for PCI host

bridge windows. This is the default on modern

hardware. If you need to use this, please report

a bug to .

routeirq Do IRQ routing for all PCI devices.

This is normally done in pci_enable_device(),

so this option is a temporary workaround

for broken drivers that don't call it.

skip_isa_align [X86] do not align io start addr, so can

handle more pci cards

noearly [X86] Don't do any early type 1 scanning.

This might help on some broken boards which

machine check when some devices' config space

is read. But various workarounds are disabled

and some IOMMU drivers will not work.

bfsort Sort PCI devices into breadth-first order.

This sorting is done to get a device

order compatible with older (<= 2.4) kernels.

nobfsort Don't sort PCI devices into breadth-first order.

pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)

tuning and use the BIOS-configured MPS defaults.

pcie_bus_safe Set every device's MPS to the largest value

supported by all devices below the root complex.

pcie_bus_perf Set device MPS to the largest allowable MPS

based on its parent bus. Also set MRRS (Max

Read Request Size) to the largest supported

value (no larger than the MPS that the device

or bus can support) for best performance.

pcie_bus_peer2peer Set every device's MPS to 128B, which

every device is guaranteed to support. This

configuration allows peer-to-peer DMA between

any pair of devices, possibly at the cost of

reduced performance. This also guarantees

that hot-added devices will work.

cbiosize=nn[KMG] The fixed amount of bus space which is

reserved for the CardBus bridge's IO window.

The default value is 256 bytes.

cbmemsize=nn[KMG] The fixed amount of bus space which is

reserved for the CardBus bridge's memory

window. The default value is 64 megabytes.

resource_alignment=

Format:

[@][; ...]

Specifies alignment and device to reassign

aligned memory resources. How to

specify the device is described above.

If is not specified,

PAGE_SIZE is used as alignment.

A PCI-PCI bridge can be specified if resource

windows need to be expanded.

To specify the alignment for several

instances of a device, the PCI vendor,

device, subvendor, and subdevice may be

specified, e.g., 12@pci:8086:9c22:103c:198f

for 4096-byte alignment.

ecrc= Enable/disable PCIe ECRC (transaction layer

end-to-end CRC checking). Only effective if

OS has native AER control (either granted by

ACPI _OSC or forced via "pcie_ports=native")

bios: Use BIOS/firmware settings. This is the

the default.

off: Turn ECRC off

on: Turn ECRC on.

hpiosize=nn[KMG] The fixed amount of bus space which is

reserved for hotplug bridge's IO window.

Default size is 256 bytes.

hpmmiosize=nn[KMG] The fixed amount of bus space which is

reserved for hotplug bridge's MMIO window.

Default size is 2 megabytes.

hpmmioprefsize=nn[KMG] The fixed amount of bus space which is

reserved for hotplug bridge's MMIO_PREF window.

Default size is 2 megabytes.

hpmemsize=nn[KMG] The fixed amount of bus space which is

reserved for hotplug bridge's MMIO and

MMIO_PREF window.

Default size is 2 megabytes.

hpbussize=nn The minimum amount of additional bus numbers

reserved for buses below a hotplug bridge.

Default is 1.

realloc= Enable/disable reallocating PCI bridge resources

if allocations done by BIOS are too small to

accommodate resources required by all child

devices.

off: Turn realloc off

on: Turn realloc on

realloc same as realloc=on

noari do not use PCIe ARI.

noats [PCIE, Intel-IOMMU, AMD-IOMMU]

do not use PCIe ATS (and IOMMU device IOTLB).

pcie_scan_all Scan all possible PCIe devices. Otherwise we

only look for one device below a PCIe downstream

port.

big_root_window Try to add a big 64bit memory window to the PCIe

root complex on AMD CPUs. Some GFX hardware

can resize a BAR to allow access to all VRAM.

Adding the window is slightly risky (it may

conflict with unreported devices), so this

taints the kernel.

disable_acs_redir=[; ...]

Specify one or more PCI devices (in the format

specified above) separated by semicolons.

Each device specified will have the PCI ACS

redirect capabilities forced off which will

allow P2P traffic between devices through

bridges without forcing it upstream. Note:

this removes isolation between devices and

may put more devices in an IOMMU group.

config_acs=

Format:

@[; ...]

Specify one or more PCI devices (in the format

specified above) optionally prepended with flags

and separated by semicolons. The respective

capabilities will be enabled, disabled or

unchanged based on what is specified in

flags.

ACS Flags is defined as follows:

bit-0 : ACS Source Validation

bit-1 : ACS Translation Blocking

bit-2 : ACS P2P Request Redirect

bit-3 : ACS P2P Completion Redirect

bit-4 : ACS Upstream Forwarding

bit-5 : ACS P2P Egress Control

bit-6 : ACS Direct Translated P2P

Each bit can be marked as:

'0' – force disabled

'1' – force enabled

'x' – unchanged

For example,

pci=config_acs=10x@pci:0:0

would configure all devices that support

ACS to enable P2P Request Redirect, disable

Translation Blocking, and leave Source

Validation unchanged from whatever power-up

or firmware set it to.

Note: this may remove isolation between devices

and may put more devices in an IOMMU group.

force_floating [S390] Force usage of floating interrupts.

nomio [S390] Do not use MIO instructions.

norid [S390] ignore the RID field and force use of

one PCI domain per PCI function

notph [PCIE] If the PCIE_TPH kernel config parameter

is enabled, this kernel boot option can be used

to disable PCIe TLP Processing Hints support

system-wide.

pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power

Management.

off Don't touch ASPM configuration at all. Leave any

configuration done by firmware unchanged.

force Enable ASPM even on devices that claim not to support it.

WARNING: Forcing ASPM on may cause system lockups.

pcie_ports= [PCIE] PCIe port services handling:

native Use native PCIe services (PME, AER, DPC, PCIe hotplug)

even if the platform doesn't give the OS permission to

use them. This may cause conflicts if the platform

also tries to use these services.

dpc-native Use native PCIe service for DPC only. May

cause conflicts if firmware uses AER or DPC.

compat Disable native PCIe services (PME, AER, DPC, PCIe

hotplug).

pcie_port_pm= [PCIE] PCIe port power management handling:

off Disable power management of all PCIe ports

force Forcibly enable power management of all PCIe ports

pcie_pme= [PCIE,PM] Native PCIe PME signaling options:

nomsi Do not use MSI for native PCIe PME signaling (this makes

all PCIe root ports use INTx for all services).

pcmv= [HW,PCMCIA] BadgePAD 4

pd_ignore_unused

[PM]

Keep all power-domains already enabled by bootloader on,

even if no driver has claimed them. This is useful

for debug and development, but should not be

needed on a platform with proper driver support.

pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at

boot time.

Format: { 0 | 1 }

See arch/parisc/kernel/pdc_chassis.c

percpu_alloc= [MM,EARLY]

Select which percpu first chunk allocator to use.

Currently supported values are "embed" and "page".

Archs may support subset or none of the selections.

See comments in mm/percpu.c for details on each

allocator. This parameter is primarily for debugging

and performance comparison.

pirq= [SMP,APIC] Manual mp-table setup

See Documentation/arch/x86/i386/IO-APIC.rst.

plip= [PPT,NET] Parallel port network link

Format: { parport | timid | 0 }

See also Documentation/admin-guide/parport.rst.

pmtmr= [X86] Manual setup of pmtmr I/O Port.

Override pmtimer IOPort with a hex value.

e.g. pmtmr=0x508

pmu_override= [PPC] Override the PMU.

This option takes over the PMU facility, so it is no

longer usable by perf. Setting this option starts the

PMU counters by setting MMCR0 to 0 (the FC bit is

cleared). If a number is given, then MMCR1 is set to

that number, otherwise (e.g., 'pmu_override=on'), MMCR1

remains 0.

pm_debug_messages [SUSPEND,KNL]

Enable suspend/resume debug messages during boot up.

pnp.debug=1 [PNP]

Enable PNP debug messages (depends on the

CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time

via /sys/module/pnp/parameters/debug. We always show

current resource usage; turning this on also shows

possible settings and some assignment information.

pnpacpi= [ACPI]

{ off }

pnpbios= [ISAPNP]

{ on | off | curr | res | no-curr | no-res }

pnp_reserve_irq=

[ISAPNP] Exclude IRQs for the autoconfiguration

pnp_reserve_dma=

[ISAPNP] Exclude DMAs for the autoconfiguration

pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration

Ranges are in pairs (I/O port base and size).

pnp_reserve_mem=

[ISAPNP] Exclude memory regions for the

autoconfiguration.

Ranges are in pairs (memory base and size).

ports= [IP_VS_FTP] IPVS ftp helper module

Default is 21.

Up to 8 (IP_VS_APP_MAX_PORTS) ports

may be specified.

Format: ,....

possible_cpus= [SMP,S390,X86]

Format:

Set the number of possible CPUs, overriding the

regular discovery mechanisms (such as ACPI/FW, etc).

powersave=off [PPC] This option disables power saving features.

It specifically disables cpuidle and sets the

platform machine description specific power_save

function to NULL. On Idle the CPU just reduces

execution priority.

ppc_strict_facility_enable

[PPC,ENABLE] This option catches any kernel floating point,

Altivec, VSX and SPE outside of regions specifically

allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).

There is some performance impact when enabling this.

ppc_tm= [PPC,EARLY]

Format: {"off"}

Disable Hardware Transactional Memory

preempt= [KNL]

Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC

none - Limited to cond_resched() calls

voluntary - Limited to cond_resched() and might_sleep() calls

full - Any section that isn't explicitly preempt disabled

can be preempted anytime. Tasks will also yield

contended spinlocks (if the critical section isn't

explicitly preempt disabled beyond the lock itself).

lazy - Scheduler controlled. Similar to full but instead

of preempting the task immediately, the task gets

one HZ tick time to yield itself before the

preemption will be forced. One preemption is when the

task returns to user space.

print-fatal-signals=

[KNL] debug: print fatal signals

If enabled, warn about various signal handling

related application anomalies: too many signals,

too many POSIX.1 timers, fatal signals causing a

coredump - etc.

If you hit the warning due to signal overflow,

you might want to try "ulimit -i unlimited".

default: off.

printk.always_kmsg_dump=

Trigger kmsg_dump for cases other than kernel oops or

panics

Format: (1/Y/y=enable, 0/N/n=disable)

default: disabled

printk.console_no_auto_verbose=

Disable console loglevel raise on oops, panic

or lockdep-detected issues (only if lock debug is on).

With an exception to setups with low baudrate on

serial console, keeping this 0 is a good choice

in order to provide more debug information.

Format:

default: 0 (auto_verbose is enabled)

printk.debug_non_panic_cpus=

Allows storing messages from non-panic CPUs into

the printk log buffer during panic(). They are

flushed to consoles by the panic-CPU on

a best-effort basis.

Format: (1/Y/y=enable, 0/N/n=disable)

Default: disabled

printk.devkmsg={on,off,ratelimit}

Control writing to /dev/kmsg.

on - unlimited logging to /dev/kmsg from userspace

off - logging to /dev/kmsg disabled

ratelimit - ratelimit the logging

Default: ratelimit

printk.time= Show timing data prefixed to each printk message line

Format: (1/Y/y=enable, 0/N/n=disable)

proc_mem.force_override= [KNL]

Format: {always | ptrace | never}

Traditionally /proc/pid/mem allows memory permissions to be

overridden without restrictions. This option may be set to

restrict that. Can be one of:

- 'always': traditional behavior always allows mem overrides.

- 'ptrace': only allow mem overrides for active ptracers.

- 'never': never allow mem overrides.

If not specified, default is the CONFIG_PROC_MEM_* choice.

processor.max_cstate= [HW,ACPI]

Limit processor to maximum C-state

max_cstate=9 overrides any DMI blacklist limit.

processor.nocst [HW,ACPI]

Ignore the _CST method to determine C-states,

instead using the legacy FADT method

profile= [KNL] Enable kernel profiling via /proc/profile

Format: [,]

Param: : "schedule" or "kvm"

[defaults to kernel profiling]

Param: "schedule" - profile schedule points.

Param: "kvm" - profile VM exits.

Param: - step/bucket size as a power of 2 for

statistical time based profiling.

prompt_ramdisk= [RAM] [Deprecated]

prot_virt= [S390] enable hosting protected virtual machines

isolated from the hypervisor (if hardware supports

that). If enabled, the default kernel base address

might be overridden even when Kernel Address Space

Layout Randomization is disabled.

Format:

psi= [KNL] Enable or disable pressure stall information

tracking.

Format:

psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to

probe for; one of (bare|imps|exps|lifebook|any).

psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports

per second.

psmouse.resetafter= [HW,MOUSE]

Try to reset the device after so many bad packets

(0 = never).

psmouse.resolution=

[HW,MOUSE] Set desired mouse resolution, in dpi.

psmouse.smartscroll=

[HW,MOUSE] Controls Logitech smartscroll autorepeat.

0 = disabled, 1 = enabled (default).

pstore.backend= Specify the name of the pstore backend to use

pti= [X86-64] Control Page Table Isolation of user and

kernel address spaces. Disabling this feature

removes hardening, but improves performance of

system calls and interrupts.

on - unconditionally enable

off - unconditionally disable

auto - kernel detects whether your CPU model is

vulnerable to issues that PTI mitigates

Not specifying this option is equivalent to pti=auto.

pty.legacy_count=

[KNL] Number of legacy pty's. Overwrites compiled-in

default number.

quiet [KNL,EARLY] Disable most log messages

r128= [HW,DRM]

radix_hcall_invalidate=on [PPC/PSERIES]

Disable RADIX GTSE feature and use hcall for TLB

invalidate.

raid= [HW,RAID]

See Documentation/admin-guide/md.rst.

ramdisk_size= [RAM] Sizes of RAM disks in kilobytes

See Documentation/admin-guide/blockdev/ramdisk.rst.

ramdisk_start= [RAM] RAM disk image start address

random.trust_cpu=off

[KNL,EARLY] Disable trusting the use of the CPU's

random number generator (if available) to

initialize the kernel's RNG.

random.trust_bootloader=off

[KNL,EARLY] Disable trusting the use of the a seed

passed by the bootloader (if available) to

initialize the kernel's RNG.

randomize_kstack_offset=

[KNL,EARLY] Enable or disable kernel stack offset

randomization, which provides roughly 5 bits of

entropy, frustrating memory corruption attacks

that depend on stack address determinism or

cross-syscall address exposures. This is only

available on architectures that have defined

CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.

Format: (1/Y/y=enable, 0/N/n=disable)

Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.

ras=option[,option,...] [KNL] RAS-specific options

cec_disable [X86]

Disable the Correctable Errors Collector,

see CONFIG_RAS_CEC help text.

rcu_nocbs[=cpu-list]

[KNL] The optional argument is a cpu list,

as described above.

In kernels built with CONFIG_RCU_NOCB_CPU=y,

enable the no-callback CPU mode, which prevents

such CPUs' callbacks from being invoked in

softirq context. Invocation of such CPUs' RCU

callbacks will instead be offloaded to "rcuox/N"

kthreads created for that purpose, where "x" is

"p" for RCU-preempt, "s" for RCU-sched, and "g"

for the kthreads that mediate grace periods; and

"N" is the CPU number. This reduces OS jitter on

the offloaded CPUs, which can be useful for HPC

and real-time workloads. It can also improve

energy efficiency for asymmetric multiprocessors.

If a cpulist is passed as an argument, the specified

list of CPUs is set to no-callback mode from boot.

Otherwise, if the '=' sign and the cpulist

arguments are omitted, no CPU will be set to

no-callback mode from boot but the mode may be

toggled at runtime via cpusets.

Note that this argument takes precedence over

the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.

rcu_nocb_poll [KNL]

Rather than requiring that offloaded CPUs

(specified by rcu_nocbs= above) explicitly

awaken the corresponding "rcuoN" kthreads,

make these kthreads poll for callbacks.

This improves the real-time response for the

offloaded CPUs by relieving them of the need to

wake up the corresponding kthread, but degrades

energy efficiency by requiring that the kthreads

periodically wake up to do the polling.

rcutree.blimit= [KNL]

Set maximum number of finished RCU callbacks to

process in one batch.

rcutree.csd_lock_suppress_rcu_stall= [KNL]

Do only a one-line RCU CPU stall warning when

there is an ongoing too-long CSD-lock wait.

rcutree.do_rcu_barrier= [KNL]

Request a call to rcu_barrier(). This is

throttled so that userspace tests can safely

hammer on the sysfs variable if they so choose.

If triggered before the RCU grace-period machinery

is fully active, this will error out with EAGAIN.

rcutree.dump_tree= [KNL]

Dump the structure of the rcu_node combining tree

out at early boot. This is used for diagnostic

purposes, to verify correct tree setup.

rcutree.gp_cleanup_delay= [KNL]

Set the number of jiffies to delay each step of

RCU grace-period cleanup.

rcutree.gp_init_delay= [KNL]

Set the number of jiffies to delay each step of

RCU grace-period initialization.

rcutree.gp_preinit_delay= [KNL]

Set the number of jiffies to delay each step of

RCU grace-period pre-initialization, that is,

the propagation of recent CPU-hotplug changes up

the rcu_node combining tree.

rcutree.jiffies_till_first_fqs= [KNL]

Set delay from grace-period initialization to

first attempt to force quiescent states.

Units are jiffies, minimum value is zero,

and maximum value is HZ.

rcutree.jiffies_till_next_fqs= [KNL]

Set delay between subsequent attempts to force

quiescent states. Units are jiffies, minimum

value is one, and maximum value is HZ.

rcutree.jiffies_till_sched_qs= [KNL]

Set required age in jiffies for a

given grace period before RCU starts

soliciting quiescent-state help from

rcu_note_context_switch() and cond_resched().

If not specified, the kernel will calculate

a value based on the most recent settings

of rcutree.jiffies_till_first_fqs

and rcutree.jiffies_till_next_fqs.

This calculated value may be viewed in

rcutree.jiffies_to_sched_qs. Any attempt to set

rcutree.jiffies_to_sched_qs will be cheerfully

overwritten.

rcutree.kthread_prio= [KNL,BOOT]

Set the SCHED_FIFO priority of the RCU per-CPU

kthreads (rcuc/N). This value is also used for

the priority of the RCU boost threads (rcub/N)

and for the RCU grace-period kthreads (rcu_bh,

rcu_preempt, and rcu_sched). If RCU_BOOST is

set, valid values are 1-99 and the default is 1

(the least-favored priority). Otherwise, when

RCU_BOOST is not set, valid values are 0-99 and

the default is zero (non-realtime operation).

When RCU_NOCB_CPU is set, also adjust the

priority of NOCB callback kthreads.

rcutree.nocb_nobypass_lim_per_jiffy= [KNL]

On callback-offloaded (rcu_nocbs) CPUs,

RCU reduces the lock contention that would

otherwise be caused by callback floods through

use of the ->nocb_bypass list. However, in the

common non-flooded case, RCU queues directly to

the main ->cblist in order to avoid the extra

overhead of the ->nocb_bypass list and its lock.

But if there are too many callbacks queued during

a single jiffy, RCU pre-queues the callbacks into

the ->nocb_bypass queue. The definition of "too

many" is supplied by this kernel boot parameter.

rcutree.nohz_full_patience_delay= [KNL]

On callback-offloaded (rcu_nocbs) CPUs, avoid

disturbing RCU unless the grace period has

reached the specified age in milliseconds.

Defaults to zero. Large values will be capped

at five seconds. All values will be rounded down

to the nearest value representable by jiffies.

rcutree.qhimark= [KNL]

Set threshold of queued RCU callbacks beyond which

batch limiting is disabled.

rcutree.qlowmark= [KNL]

Set threshold of queued RCU callbacks below which

batch limiting is re-enabled.

rcutree.qovld= [KNL]

Set threshold of queued RCU callbacks beyond which

RCU's force-quiescent-state scan will aggressively

enlist help from cond_resched() and sched IPIs to

help CPUs more quickly reach quiescent states.

Set to less than zero to make this be set based

on rcutree.qhimark at boot time and to zero to

disable more aggressive help enlistment.

rcutree.rcu_delay_page_cache_fill_msec= [KNL]

Set the page-cache refill delay (in milliseconds)

in response to low-memory conditions. The range

of permitted values is in the range 0:100000.

rcutree.rcu_divisor= [KNL]

Set the shift-right count to use to compute

the callback-invocation batch limit bl from

the number of callbacks queued on this CPU.

The result will be bounded below by the value of

the rcutree.blimit kernel parameter. Every bl

callbacks, the softirq handler will exit in

order to allow the CPU to do other work.

Please note that this callback-invocation batch

limit applies only to non-offloaded callback

invocation. Offloaded callbacks are instead

invoked in the context of an rcuoc kthread, which

scheduler will preempt as it does any other task.

rcutree.rcu_fanout_exact= [KNL]

Disable autobalancing of the rcu_node combining

tree. This is used by rcutorture, and might

possibly be useful for architectures having high

cache-to-cache transfer latencies.

rcutree.rcu_fanout_leaf= [KNL]

Change the number of CPUs assigned to each

leaf rcu_node structure. Useful for very

large systems, which will choose the value 64,

and for NUMA systems with large remote-access

latencies, which will choose a value aligned

with the appropriate hardware boundaries.

rcutree.rcu_min_cached_objs= [KNL]

Minimum number of objects which are cached and

maintained per one CPU. Object size is equal

to PAGE_SIZE. The cache allows to reduce the

pressure to page allocator, also it makes the

whole algorithm to behave better in low memory

condition.

rcutree.rcu_nocb_gp_stride= [KNL]

Set the number of NOCB callback kthreads in

each group, which defaults to the square root

of the number of CPUs. Larger numbers reduce

the wakeup overhead on the global grace-period

kthread, but increases that same overhead on

each group's NOCB grace-period kthread.

rcutree.rcu_kick_kthreads= [KNL]

Cause the grace-period kthread to get an extra

wake_up() if it sleeps three times longer than

it should at force-quiescent-state time.

This wake_up() will be accompanied by a

WARN_ONCE() splat and an ftrace_dump().

rcutree.rcu_resched_ns= [KNL]

Limit the time spend invoking a batch of RCU

callbacks to the specified number of nanoseconds.

By default, this limit is checked only once

every 32 callbacks in order to limit the pain

inflicted by local_clock() overhead.

rcutree.rcu_unlock_delay= [KNL]

In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,

this specifies an rcu_read_unlock()-time delay

in microseconds. This defaults to zero.

Larger delays increase the probability of

catching RCU pointer leaks, that is, buggy use

of RCU-protected pointers after the relevant

rcu_read_unlock() has completed.

rcutree.sysrq_rcu= [KNL]

Commandeer a sysrq key to dump out Tree RCU's

rcu_node tree with an eye towards determining

why a new grace period has not yet started.

rcutree.use_softirq= [KNL]

If set to zero, move all RCU_SOFTIRQ processing to

per-CPU rcuc kthreads. Defaults to a non-zero

value, meaning that RCU_SOFTIRQ is used by default.

Specify rcutree.use_softirq=0 to use rcuc kthreads.

But note that CONFIG_PREEMPT_RT=y kernels disable

this kernel boot parameter, forcibly setting it

to zero.

rcutree.enable_rcu_lazy= [KNL]

To save power, batch RCU callbacks and flush after

delay, memory pressure or callback list growing too

big.

rcutree.rcu_normal_wake_from_gp= [KNL]

Reduces a latency of synchronize_rcu() call. This approach

maintains its own track of synchronize_rcu() callers, so it

does not interact with regular callbacks because it does not

use a call_rcu[_hurry]() path. Please note, this is for a

normal grace period.

How to enable it:

echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp

or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1"

Default is 0.

rcuscale.gp_async= [KNL]

Measure performance of asynchronous

grace-period primitives such as call_rcu().

rcuscale.gp_async_max= [KNL]

Specify the maximum number of outstanding

callbacks per writer thread. When a writer

thread exceeds this limit, it invokes the

corresponding flavor of rcu_barrier() to allow

previously posted callbacks to drain.

rcuscale.gp_exp= [KNL]

Measure performance of expedited synchronous

grace-period primitives.

rcuscale.holdoff= [KNL]

Set test-start holdoff period. The purpose of

this parameter is to delay the start of the

test until boot completes in order to avoid

interference.

rcuscale.kfree_by_call_rcu= [KNL]

In kernels built with CONFIG_RCU_LAZY=y, test

call_rcu() instead of kfree_rcu().

rcuscale.kfree_mult= [KNL]

Instead of allocating an object of size kfree_obj,

allocate one of kfree_mult * sizeof(kfree_obj).

Defaults to 1.

rcuscale.kfree_rcu_test= [KNL]

Set to measure performance of kfree_rcu() flooding.

rcuscale.kfree_rcu_test_double= [KNL]

Test the double-argument variant of kfree_rcu().

If this parameter has the same value as

rcuscale.kfree_rcu_test_single, both the single-

and double-argument variants are tested.

rcuscale.kfree_rcu_test_single= [KNL]

Test the single-argument variant of kfree_rcu().

If this parameter has the same value as

rcuscale.kfree_rcu_test_double, both the single-

and double-argument variants are tested.

rcuscale.kfree_nthreads= [KNL]

The number of threads running loops of kfree_rcu().

rcuscale.kfree_alloc_num= [KNL]

Number of allocations and frees done in an iteration.

rcuscale.kfree_loops= [KNL]

Number of loops doing rcuscale.kfree_alloc_num number

of allocations and frees.

rcuscale.minruntime= [KNL]

Set the minimum test run time in seconds. This

does not affect the data-collection interval,

but instead allows better measurement of things

like CPU consumption.

rcuscale.nreaders= [KNL]

Set number of RCU readers. The value -1 selects

N, where N is the number of CPUs. A value

"n" less than -1 selects N-n+1, where N is again

the number of CPUs. For example, -2 selects N

(the number of CPUs), -3 selects N+1, and so on.

A value of "n" less than or equal to -N selects

a single reader.

rcuscale.nwriters= [KNL]

Set number of RCU writers. The values operate

the same as for rcuscale.nreaders.

N, where N is the number of CPUs

rcuscale.scale_type= [KNL]

Specify the RCU implementation to test.

rcuscale.shutdown= [KNL]

Shut the system down after performance tests

complete. This is useful for hands-off automated

testing.

rcuscale.verbose= [KNL]

Enable additional printk() statements.

rcuscale.writer_holdoff= [KNL]

Write-side holdoff between grace periods,

in microseconds. The default of zero says

no holdoff.

rcuscale.writer_holdoff_jiffies= [KNL]

Additional write-side holdoff between grace

periods, but in jiffies. The default of zero

says no holdoff.

rcutorture.fqs_duration= [KNL]

Set duration of force_quiescent_state bursts

in microseconds.

rcutorture.fqs_holdoff= [KNL]

Set holdoff time within force_quiescent_state bursts

in microseconds.

rcutorture.fqs_stutter= [KNL]

Set wait time between force_quiescent_state bursts

in seconds.

rcutorture.fwd_progress= [KNL]

Specifies the number of kthreads to be used

for RCU grace-period forward-progress testing

for the types of RCU supporting this notion.

Defaults to 1 kthread, values less than zero or

greater than the number of CPUs cause the number

of CPUs to be used.

rcutorture.fwd_progress_div= [KNL]

Specify the fraction of a CPU-stall-warning

period to do tight-loop forward-progress testing.

rcutorture.fwd_progress_holdoff= [KNL]

Number of seconds to wait between successive

forward-progress tests.

rcutorture.fwd_progress_need_resched= [KNL]

Enclose cond_resched() calls within checks for

need_resched() during tight-loop forward-progress

testing.

rcutorture.gp_cond= [KNL]

Use conditional/asynchronous update-side

normal-grace-period primitives, if available.

rcutorture.gp_cond_exp= [KNL]

Use conditional/asynchronous update-side

expedited-grace-period primitives, if available.

rcutorture.gp_cond_full= [KNL]

Use conditional/asynchronous update-side

normal-grace-period primitives that also take

concurrent expedited grace periods into account,

if available.

rcutorture.gp_cond_exp_full= [KNL]

Use conditional/asynchronous update-side

expedited-grace-period primitives that also take

concurrent normal grace periods into account,

if available.

rcutorture.gp_cond_wi= [KNL]

Nominal wait interval for normal conditional

grace periods (specified by rcutorture's

gp_cond and gp_cond_full module parameters),

in microseconds. The actual wait interval will

be randomly selected to nanosecond granularity up

to this wait interval. Defaults to 16 jiffies,

for example, 16,000 microseconds on a system

with HZ=1000.

rcutorture.gp_cond_wi_exp= [KNL]

Nominal wait interval for expedited conditional

grace periods (specified by rcutorture's

gp_cond_exp and gp_cond_exp_full module

parameters), in microseconds. The actual wait

interval will be randomly selected to nanosecond

granularity up to this wait interval. Defaults to

128 microseconds.

rcutorture.gp_exp= [KNL]

Use expedited update-side primitives, if available.

rcutorture.gp_normal= [KNL]

Use normal (non-expedited) asynchronous

update-side primitives, if available.

rcutorture.gp_poll= [KNL]

Use polled update-side normal-grace-period

primitives, if available.

rcutorture.gp_poll_exp= [KNL]

Use polled update-side expedited-grace-period

primitives, if available.

rcutorture.gp_poll_full= [KNL]

Use polled update-side normal-grace-period

primitives that also take concurrent expedited

grace periods into account, if available.

rcutorture.gp_poll_exp_full= [KNL]

Use polled update-side expedited-grace-period

primitives that also take concurrent normal

grace periods into account, if available.

rcutorture.gp_poll_wi= [KNL]

Nominal wait interval for normal conditional

grace periods (specified by rcutorture's

gp_poll and gp_poll_full module parameters),

in microseconds. The actual wait interval will

be randomly selected to nanosecond granularity up

to this wait interval. Defaults to 16 jiffies,

for example, 16,000 microseconds on a system

with HZ=1000.

rcutorture.gp_poll_wi_exp= [KNL]

Nominal wait interval for expedited conditional

grace periods (specified by rcutorture's

gp_poll_exp and gp_poll_exp_full module

parameters), in microseconds. The actual wait

interval will be randomly selected to nanosecond

granularity up to this wait interval. Defaults to

128 microseconds.

rcutorture.gp_sync= [KNL]

Use normal (non-expedited) synchronous

update-side primitives, if available. If all

of rcutorture.gp_cond=, rcutorture.gp_exp=,

rcutorture.gp_normal=, and rcutorture.gp_sync=

are zero, rcutorture acts as if is interpreted

they are all non-zero.

rcutorture.gpwrap_lag= [KNL]

Enable grace-period wrap lag testing. Setting

to false prevents the gpwrap lag test from

running. Default is true.

rcutorture.gpwrap_lag_gps= [KNL]

Set the value for grace-period wrap lag during

active lag testing periods. This controls how many

grace periods differences we tolerate between

rdp and rnp's gp_seq before setting overflow flag.

The default is always set to 8.

rcutorture.gpwrap_lag_cycle_mins= [KNL]

Set the total cycle duration for gpwrap lag

testing in minutes. This is the total time for

one complete cycle of active and inactive

testing periods. Default is 30 minutes.

rcutorture.gpwrap_lag_active_mins= [KNL]

Set the duration for which gpwrap lag is active

within each cycle, in minutes. During this time,

the grace-period wrap lag will be set to the

value specified by gpwrap_lag_gps. Default is

5 minutes.

rcutorture.irqreader= [KNL]

Run RCU readers from irq handlers, or, more

accurately, from a timer handler. Not all RCU

flavors take kindly to this sort of thing.

rcutorture.leakpointer= [KNL]

Leak an RCU-protected pointer out of the reader.

This can of course result in splats, and is

intended to test the ability of things like

CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect

such leaks.

rcutorture.n_barrier_cbs= [KNL]

Set callbacks/threads for rcu_barrier() testing.

rcutorture.nfakewriters= [KNL]

Set number of concurrent RCU writers. These just

stress RCU, they don't participate in the actual

test, hence the "fake".

rcutorture.nocbs_nthreads= [KNL]

Set number of RCU callback-offload togglers.

Zero (the default) disables toggling.

rcutorture.nocbs_toggle= [KNL]

Set the delay in milliseconds between successive

callback-offload toggling attempts.

rcutorture.nreaders= [KNL]

Set number of RCU readers. The value -1 selects

N-1, where N is the number of CPUs. A value

"n" less than -1 selects N-n-2, where N is again

the number of CPUs. For example, -2 selects N

(the number of CPUs), -3 selects N+1, and so on.

rcutorture.object_debug= [KNL]

Enable debug-object double-call_rcu() testing.

rcutorture.onoff_holdoff= [KNL]

Set time (s) after boot for CPU-hotplug testing.

rcutorture.onoff_interval= [KNL]

Set time (jiffies) between CPU-hotplug operations,

or zero to disable CPU-hotplug testing.

rcutorture.preempt_duration= [KNL]

Set duration (in milliseconds) of preemptions

by a high-priority FIFO real-time task. Set to

zero (the default) to disable. The CPUs to

preempt are selected randomly from the set that

are online at a given point in time. Races with

CPUs going offline are ignored, with that attempt

at preemption skipped.

rcutorture.preempt_interval= [KNL]

Set interval (in milliseconds, defaulting to one

second) between preemptions by a high-priority

FIFO real-time task. This delay is mediated

by an hrtimer and is further fuzzed to avoid

inadvertent synchronizations.

rcutorture.read_exit_burst= [KNL]

The number of times in a given read-then-exit

episode that a set of read-then-exit kthreads

is spawned.

rcutorture.read_exit_delay= [KNL]

The delay, in seconds, between successive

read-then-exit testing episodes.

rcutorture.reader_flavor= [KNL]

A bit mask indicating which readers to use.

If there is more than one bit set, the readers

are entered from low-order bit up, and are

exited in the opposite order. For SRCU, the

0x1 bit is normal readers, 0x2 NMI-safe readers,

and 0x4 light-weight readers.

rcutorture.shuffle_interval= [KNL]

Set task-shuffle interval (s). Shuffling tasks

allows some CPUs to go into dyntick-idle mode

during the rcutorture test.

rcutorture.shutdown_secs= [KNL]

Set time (s) after boot system shutdown. This

is useful for hands-off automated testing.

rcutorture.stall_cpu= [KNL]

Duration of CPU stall (s) to test RCU CPU stall

warnings, zero to disable.

rcutorture.stall_cpu_block= [KNL]

Sleep while stalling if set. This will result

in warnings from preemptible RCU in addition to

any other stall-related activity. Note that

in kernels built with CONFIG_PREEMPTION=n and

CONFIG_PREEMPT_COUNT=y, this parameter will

cause the CPU to pass through a quiescent state.

Given CONFIG_PREEMPTION=n, this will suppress

RCU CPU stall warnings, but will instead result

in scheduling-while-atomic splats.

Use of this module parameter results in splats.

rcutorture.stall_cpu_holdoff= [KNL]

Time to wait (s) after boot before inducing stall.

rcutorture.stall_cpu_irqsoff= [KNL]

Disable interrupts while stalling if set, but only

on the first stall in the set.

rcutorture.stall_cpu_repeat= [KNL]

Number of times to repeat the stall sequence,

so that rcutorture.stall_cpu_repeat=3 will result

in four stall sequences.

rcutorture.stall_gp_kthread= [KNL]

Duration (s) of forced sleep within RCU

grace-period kthread to test RCU CPU stall

warnings, zero to disable. If both stall_cpu

and stall_gp_kthread are specified, the

kthread is starved first, then the CPU.

rcutorture.stat_interval= [KNL]

Time (s) between statistics printk()s.

rcutorture.stutter= [KNL]

Time (s) to stutter testing, for example, specifying

five seconds causes the test to run for five seconds,

wait for five seconds, and so on. This tests RCU's

ability to transition abruptly to and from idle.

rcutorture.test_boost= [KNL]

Test RCU priority boosting? 0=no, 1=maybe, 2=yes.

"Maybe" means test if the RCU implementation

under test support RCU priority boosting.

rcutorture.test_boost_duration= [KNL]

Duration (s) of each individual boost test.

rcutorture.test_boost_holdoff= [KNL]

Holdoff time (s) from start of test to the start

of RCU priority-boost testing. Defaults to zero,

that is, no holdoff.

rcutorture.test_boost_interval= [KNL]

Interval (s) between each boost test.

rcutorture.test_no_idle_hz= [KNL]

Test RCU's dyntick-idle handling. See also the

rcutorture.shuffle_interval parameter.

rcutorture.torture_type= [KNL]

Specify the RCU implementation to test.

rcutorture.verbose= [KNL]

Enable additional printk() statements.

rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]

Dump ftrace buffer after reporting RCU CPU

stall warning.

rcupdate.rcu_cpu_stall_notifiers= [KNL]

Provide RCU CPU stall notifiers, but see the

warnings in the RCU_CPU_STALL_NOTIFIER Kconfig

option's help text. TL;DR: You almost certainly

do not want rcupdate.rcu_cpu_stall_notifiers.

rcupdate.rcu_cpu_stall_suppress= [KNL]

Suppress RCU CPU stall warning messages.

rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]

Suppress RCU CPU stall warning messages and

rcutorture writer stall warnings that occur

during early boot, that is, during the time

before the init task is spawned.

rcupdate.rcu_cpu_stall_timeout= [KNL]

Set timeout for RCU CPU stall warning messages.

The value is in seconds and the maximum allowed

value is 300 seconds.

rcupdate.rcu_exp_cpu_stall_timeout= [KNL]

Set timeout for expedited RCU CPU stall warning

messages. The value is in milliseconds

and the maximum allowed value is 21000

milliseconds. Please note that this value is

adjusted to an arch timer tick resolution.

Setting this to zero causes the value from

rcupdate.rcu_cpu_stall_timeout to be used (after

conversion from seconds to milliseconds).

rcupdate.rcu_cpu_stall_cputime= [KNL]

Provide statistics on the cputime and count of

interrupts and tasks during the sampling period. For

multiple continuous RCU stalls, all sampling periods

begin at half of the first RCU stall timeout.

rcupdate.rcu_exp_stall_task_details= [KNL]

Print stack dumps of any tasks blocking the

current expedited RCU grace period during an

expedited RCU CPU stall warning.

rcupdate.rcu_expedited= [KNL]

Use expedited grace-period primitives, for

example, synchronize_rcu_expedited() instead

of synchronize_rcu(). This reduces latency,

but can increase CPU utilization, degrade

real-time latency, and degrade energy efficiency.

No effect on CONFIG_TINY_RCU kernels.

rcupdate.rcu_normal= [KNL]

Use only normal grace-period primitives,

for example, synchronize_rcu() instead of

synchronize_rcu_expedited(). This improves

real-time latency, CPU utilization, and

energy efficiency, but can expose users to

increased grace-period latency. This parameter

overrides rcupdate.rcu_expedited. No effect on

CONFIG_TINY_RCU kernels.

rcupdate.rcu_normal_after_boot= [KNL]

Once boot has completed (that is, after

rcu_end_inkernel_boot() has been invoked), use

only normal grace-period primitives. No effect

on CONFIG_TINY_RCU kernels.

But note that CONFIG_PREEMPT_RT=y kernels enables

this kernel boot parameter, forcibly setting

it to the value one, that is, converting any

post-boot attempt at an expedited RCU grace

period to instead use normal non-expedited

grace-period processing.

rcupdate.rcu_task_collapse_lim= [KNL]

Set the maximum number of callbacks present

at the beginning of a grace period that allows

the RCU Tasks flavors to collapse back to using

a single callback queue. This switching only

occurs when rcupdate.rcu_task_enqueue_lim is

set to the default value of -1.

rcupdate.rcu_task_contend_lim= [KNL]

Set the minimum number of callback-queuing-time

lock-contention events per jiffy required to

cause the RCU Tasks flavors to switch to per-CPU

callback queuing. This switching only occurs

when rcupdate.rcu_task_enqueue_lim is set to

the default value of -1.

rcupdate.rcu_task_enqueue_lim= [KNL]

Set the number of callback queues to use for the

RCU Tasks family of RCU flavors. The default

of -1 allows this to be automatically (and

dynamically) adjusted. This parameter is intended

for use in testing.

rcupdate.rcu_task_ipi_delay= [KNL]

Set time in jiffies during which RCU tasks will

avoid sending IPIs, starting with the beginning

of a given grace period. Setting a large

number avoids disturbing real-time workloads,

but lengthens grace periods.

rcupdate.rcu_task_lazy_lim= [KNL]

Number of callbacks on a given CPU that will

cancel laziness on that CPU. Use -1 to disable

cancellation of laziness, but be advised that

doing so increases the danger of OOM due to

callback flooding.

rcupdate.rcu_task_stall_info= [KNL]

Set initial timeout in jiffies for RCU task stall

informational messages, which give some indication

of the problem for those not patient enough to

wait for ten minutes. Informational messages are

only printed prior to the stall-warning message

for a given grace period. Disable with a value

less than or equal to zero. Defaults to ten

seconds. A change in value does not take effect

until the beginning of the next grace period.

rcupdate.rcu_task_stall_info_mult= [KNL]

Multiplier for time interval between successive

RCU task stall informational messages for a given

RCU tasks grace period. This value is clamped

to one through ten, inclusive. It defaults to

the value three, so that the first informational

message is printed 10 seconds into the grace

period, the second at 40 seconds, the third at

160 seconds, and then the stall warning at 600

seconds would prevent a fourth at 640 seconds.

rcupdate.rcu_task_stall_timeout= [KNL]

Set timeout in jiffies for RCU task stall

warning messages. Disable with a value less

than or equal to zero. Defaults to ten minutes.

A change in value does not take effect until

the beginning of the next grace period.

rcupdate.rcu_tasks_lazy_ms= [KNL]

Set timeout in milliseconds RCU Tasks asynchronous

callback batching for call_rcu_tasks().

A negative value will take the default. A value

of zero will disable batching. Batching is

always disabled for synchronize_rcu_tasks().

rcupdate.rcu_tasks_trace_lazy_ms= [KNL]

Set timeout in milliseconds RCU Tasks

Trace asynchronous callback batching for

call_rcu_tasks_trace(). A negative value

will take the default. A value of zero will

disable batching. Batching is always disabled

for synchronize_rcu_tasks_trace().

rcupdate.rcu_self_test= [KNL]

Run the RCU early boot self tests

rdinit= [KNL]

Format:

Run specified binary instead of /init from the ramdisk,

used for early userspace startup. See initrd.

rdrand= [X86,EARLY]

force - Override the decision by the kernel to hide the

advertisement of RDRAND support (this affects

certain AMD processors because of buggy BIOS

support, specifically around the suspend/resume

path).

rdt= [HW,X86,RDT]

Turn on/off individual RDT features. List is:

cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,

mba, smba, bmec.

E.g. to turn on cmt and turn off mba use:

rdt=cmt,!mba

reboot= [KNL]

Format (x86 or x86_64):

[w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \

[[,]s[mp]#### \

[[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \

[[,]f[orce]

Where reboot_mode is one of warm (soft) or cold (hard) or gpio

(prefix with 'panic_' to set mode for panic

reboot only),

reboot_type is one of bios, acpi, kbd, triple, efi, or pci,

reboot_force is either force or not specified,

reboot_cpu is s[mp]#### with #### being the processor

to be used for rebooting.

acpi

Use the ACPI RESET_REG in the FADT. If ACPI is not

configured or the ACPI reset does not work, the reboot

path attempts the reset using the keyboard controller.

bios

Use the CPU reboot vector for warm reset

cold

Set the cold reboot flag

default

There are some built-in platform specific "quirks"

- you may see: "reboot: series board detected.

Selecting for reboots." In the case where you

think the quirk is in error (e.g. you have newer BIOS,

or newer board) using this option will ignore the

built-in quirk table, and use the generic default

reboot actions.

efi

Use efi reset_system runtime service. If EFI is not

configured or the EFI reset does not work, the reboot

path attempts the reset using the keyboard controller.

force

Don't stop other CPUs on reboot. This can make reboot

more reliable in some cases.

kbd

Use the keyboard controller. cold reset (default)

pci

Use a write to the PCI config space register 0xcf9 to

trigger reboot.

triple

Force a triple fault (init)

warm

Don't set the cold reboot flag

Using warm reset will be much faster especially on big

memory systems because the BIOS will not go through

the memory check. Disadvantage is that not all

hardware will be completely reinitialized on reboot so

there may be boot problems on some systems.

refscale.holdoff= [KNL]

Set test-start holdoff period. The purpose of

this parameter is to delay the start of the

test until boot completes in order to avoid

interference.

refscale.lookup_instances= [KNL]

Number of data elements to use for the forms of

SLAB_TYPESAFE_BY_RCU testing. A negative number

is negated and multiplied by nr_cpu_ids, while

zero specifies nr_cpu_ids.

refscale.loops= [KNL]

Set the number of loops over the synchronization

primitive under test. Increasing this number

reduces noise due to loop start/end overhead,

but the default has already reduced the per-pass

noise to a handful of picoseconds on ca. 2020

x86 laptops.

refscale.nreaders= [KNL]

Set number of readers. The default value of -1

selects N, where N is roughly 75% of the number

of CPUs. A value of zero is an interesting choice.

refscale.nruns= [KNL]

Set number of runs, each of which is dumped onto

the console log.

refscale.readdelay= [KNL]

Set the read-side critical-section duration,

measured in microseconds.

refscale.scale_type= [KNL]

Specify the read-protection implementation to test.

refscale.shutdown= [KNL]

Shut down the system at the end of the performance

test. This defaults to 1 (shut it down) when

refscale is built into the kernel and to 0 (leave

it running) when refscale is built as a module.

refscale.verbose= [KNL]

Enable additional printk() statements.

refscale.verbose_batched= [KNL]

Batch the additional printk() statements. If zero

(the default) or negative, print everything. Otherwise,

print every Nth verbose statement, where N is the value

specified.

regulator_ignore_unused

[REGULATOR]

Prevents regulator framework from disabling regulators

that are unused, due no driver claiming them. This may

be useful for debug and development, but should not be

needed on a platform with proper driver support.

relax_domain_level=

[KNL, SMP] Set scheduler's default relax_domain_level.

See Documentation/admin-guide/cgroup-v1/cpusets.rst.

reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory

Format: ,[,,,...]

Reserve I/O ports or memory so the kernel won't use

them. If is less than 0x10000, the region

is assumed to be I/O ports; otherwise it is memory.

reserve_mem= [RAM]

Format: nn[KMG]::

Reserve physical memory and label it with a name that

other subsystems can use to access it. This is typically

used for systems that do not wipe the RAM, and this command

line will try to reserve the same physical memory on

soft reboots. Note, it is not guaranteed to be the same

location. For example, if anything about the system changes

or if booting a different kernel. It can also fail if KASLR

places the kernel at the location of where the RAM reservation

was from a previous boot, the new reservation will be at a

different location.

Any subsystem using this feature must add a way to verify

that the contents of the physical memory is from a previous

boot, as there may be cases where the memory will not be

located at the same location.

The format is size:align:label for example, to request

12 megabytes of 4096 alignment for ramoops:

reserve_mem=12M:4096:oops ramoops.mem_name=oops

reservetop= [X86-32,EARLY]

Format: nn[KMG]

Reserves a hole at the top of the kernel virtual

address space.

reset_devices [KNL] Force drivers to reset the underlying device

during initialization.

resume= [SWSUSP]

Specify the partition device for software suspend

Format:

{/dev/ | PARTUUID= | : | }

resume_offset= [SWSUSP]

Specify the offset from the beginning of the partition

given by "resume=" at which the swap header is located,

in units (needed only for swap files).

See Documentation/power/swsusp-and-swap-files.rst

resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to

read the resume files

resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.

Useful for devices that are detected asynchronously

(e.g. USB and MMC devices).

retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will

be accessible via /sys/firmware/initrd.

retbleed= [X86] Control mitigation of RETBleed (Arbitrary

Speculative Code Execution with Return Instructions)

vulnerability.

AMD-based UNRET and IBPB mitigations alone do not stop

sibling threads from influencing the predictions of other

sibling threads. For that reason, STIBP is used on pro-

cessors that support it, and mitigate SMT on processors

that don't.

off - no mitigation

auto - automatically select a migitation

auto,nosmt - automatically select a mitigation,

disabling SMT if necessary for

the full mitigation (only on Zen1

and older without STIBP).

ibpb - On AMD, mitigate short speculation

windows on basic block boundaries too.

Safe, highest perf impact. It also

enables STIBP if present. Not suitable

on Intel.

ibpb,nosmt - Like "ibpb" above but will disable SMT

when STIBP is not available. This is

the alternative for systems which do not

have STIBP.

unret - Force enable untrained return thunks,

only effective on AMD f15h-f17h based

systems.

unret,nosmt - Like unret, but will disable SMT when STIBP

is not available. This is the alternative for

systems which do not have STIBP.

Selecting 'auto' will choose a mitigation method at run

time according to the CPU.

Not specifying this option is equivalent to retbleed=auto.

rfkill.default_state=

0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,

etc. communication is blocked by default.

1 Unblocked.

rfkill.master_switch_mode=

0 The "airplane mode" button does nothing.

1 The "airplane mode" button toggles between everything

blocked and the previous configuration.

2 The "airplane mode" button toggles between everything

blocked and everything unblocked.

ring3mwait=disable

[KNL] Disable ring 3 MONITOR/MWAIT feature on supported

CPUs.

riscv_isa_fallback [RISCV,EARLY]

When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit

falling back to detecting extension support by parsing

"riscv,isa" property on devicetree systems when the

replacement properties are not found. See the Kconfig

entry for RISCV_ISA_FALLBACK.

ro [KNL] Mount root device read-only on boot

rodata= [KNL,EARLY]

on Mark read-only kernel memory as read-only (default).

off Leave read-only kernel memory writable for debugging.

full Mark read-only kernel memory and aliases as read-only

[arm64]

rockchip.usb_uart

[EARLY]

Enable the uart passthrough on the designated usb port

on Rockchip SoCs. When active, the signals of the

debug-uart get routed to the D+ and D- pins of the usb

port and the regular usb controller gets disabled.

root= [KNL] Root filesystem

Usually this is a block device specifier of some kind,

see the early_lookup_bdev comment in

block/early-lookup.c for details.

Alternatively this can be "ram" for the legacy initial

ramdisk, "nfs" and "cifs" for root on a network file

system, or "mtd" and "ubi" for mounting from raw flash.

rootdelay= [KNL] Delay (in seconds) to pause before attempting to

mount the root filesystem

rootflags= [KNL] Set root filesystem mount option string

rootfstype= [KNL] Set root filesystem type

rootwait [KNL] Wait (indefinitely) for root device to show up.

Useful for devices that are detected asynchronously

(e.g. USB and MMC devices).

rootwait= [KNL] Maximum time (in seconds) to wait for root device

to show up before attempting to mount the root

filesystem.

rproc_mem=nn[KMG][@address]

[KNL,ARM,CMA] Remoteproc physical memory block.

Memory area to be used by remote processor image,

managed by CMA.

rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling

when CONFIG_RT_GROUP_SCHED=y. Defaults to

!CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED.

Format:

rw [KNL] Mount root device read-write on boot

S [KNL] Run init in single mode

s390_iommu= [HW,S390]

Set s390 IOTLB flushing mode

strict

With strict flushing every unmap operation will result

in an IOTLB flush. Default is lazy flushing before

reuse, which is faster. Deprecated, equivalent to

iommu.strict=1.

s390_iommu_aperture= [KNL,S390]

Specifies the size of the per device DMA address space

accessible through the DMA and IOMMU APIs as a decimal

factor of the size of main memory.

The default is 1 meaning that one can concurrently use

as many DMA addresses as physical memory is installed,

if supported by hardware, and thus map all of memory

once. With a value of 2 one can map all of memory twice

and so on. As a special case a factor of 0 imposes no

restrictions other than those given by hardware at the

cost of significant additional memory use for tables.

sa1100ir [NET]

See drivers/net/irda/sa1100_ir.c.

sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages.

schedstats= [KNL,X86] Enable or disable scheduled statistics.

Allowed values are enable and disable. This feature

incurs a small amount of overhead in the scheduler

but is useful for debugging and performance tuning.

sched_thermal_decay_shift=

[Deprecated]

[KNL, SMP] Set a decay shift for scheduler thermal

pressure signal. Thermal pressure signal follows the

default decay period of other scheduler pelt

signals(usually 32 ms but configurable). Setting

sched_thermal_decay_shift will left shift the decay

period for the thermal pressure signal by the shift

value.

i.e. with the default pelt decay period of 32 ms

sched_thermal_decay_shift thermal pressure decay pr

1 64 ms

2 128 ms

and so on.

Format: integer between 0 and 10

Default is 0.

scftorture.holdoff= [KNL]

Number of seconds to hold off before starting

test. Defaults to zero for module insertion and

to 10 seconds for built-in smp_call_function()

tests.

scftorture.longwait= [KNL]

Request ridiculously long waits randomly selected

up to the chosen limit in seconds. Zero (the

default) disables this feature. Please note

that requesting even small non-zero numbers of

seconds can result in RCU CPU stall warnings,

softlockup complaints, and so on.

scftorture.nthreads= [KNL]

Number of kthreads to spawn to invoke the

smp_call_function() family of functions.

The default of -1 specifies a number of kthreads

equal to the number of CPUs.

scftorture.onoff_holdoff= [KNL]

Number seconds to wait after the start of the

test before initiating CPU-hotplug operations.

scftorture.onoff_interval= [KNL]

Number seconds to wait between successive

CPU-hotplug operations. Specifying zero (which

is the default) disables CPU-hotplug operations.

scftorture.shutdown_secs= [KNL]

The number of seconds following the start of the

test after which to shut down the system. The

default of zero avoids shutting down the system.

Non-zero values are useful for automated tests.

scftorture.stat_interval= [KNL]

The number of seconds between outputting the

current test statistics to the console. A value

of zero disables statistics output.

scftorture.stutter_cpus= [KNL]

The number of jiffies to wait between each change

to the set of CPUs under test.

scftorture.use_cpus_read_lock= [KNL]

Use use_cpus_read_lock() instead of the default

preempt_disable() to disable CPU hotplug

while invoking one of the smp_call_function*()

functions.

scftorture.verbose= [KNL]

Enable additional printk() statements.

scftorture.weight_single= [KNL]

The probability weighting to use for the

smp_call_function_single() function with a zero

"wait" parameter. A value of -1 selects the

default if all other weights are -1. However,

if at least one weight has some other value, a

value of -1 will instead select a weight of zero.

scftorture.weight_single_wait= [KNL]

The probability weighting to use for the

smp_call_function_single() function with a

non-zero "wait" parameter. See weight_single.

scftorture.weight_many= [KNL]

The probability weighting to use for the

smp_call_function_many() function with a zero

"wait" parameter. See weight_single.

Note well that setting a high probability for

this weighting can place serious IPI load

on the system.

scftorture.weight_many_wait= [KNL]

The probability weighting to use for the

smp_call_function_many() function with a

non-zero "wait" parameter. See weight_single

and weight_many.

scftorture.weight_all= [KNL]

The probability weighting to use for the

smp_call_function_all() function with a zero

"wait" parameter. See weight_single and

weight_many.

scftorture.weight_all_wait= [KNL]

The probability weighting to use for the

smp_call_function_all() function with a

non-zero "wait" parameter. See weight_single

and weight_many.

sdw_mclk_divider=[SDW]

Specify the MCLK divider for Intel SoundWire buses in

case the BIOS does not provide the clock rate properly.

skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate

xtime_lock contention on larger systems, and/or RCU lock

contention on all systems with CONFIG_MAXSMP set.

Format: { "0" | "1" }

0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"

1 -- enable.

Note: increases power consumption, thus should only be

enabled if running jitter sensitive (HPC/RT) workloads.

security= [SECURITY] Choose a legacy "major" security module to

enable at boot. This has been deprecated by the

"lsm=" parameter.

selinux= [SELINUX] Disable or enable SELinux at boot time.

Format: { "0" | "1" }

See security/selinux/Kconfig help text.

0 -- disable.

1 -- enable.

Default value is 1.

serialnumber [BUGS=X86-32]

sev=option[,option...] [X86-64]

debug

Enable debug messages.

nosnp

Do not enable SEV-SNP (applies to host/hypervisor

only). Setting 'nosnp' avoids the RMP check overhead

in memory accesses when users do not want to run

SEV-SNP guests.

shapers= [NET]

Maximal number of shapers.

show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller

Limit apic dumping. The parameter defines the maximal

number of local apics being dumped. Also it is possible

to set it to "all" by meaning -- no limit here.

Format: { 1 (default) | 2 | ... | all }.

The parameter valid if only apic=debug or

apic=verbose is specified.

Example: apic=debug show_lapic=all

slab_debug[=options[,slabs][;[options[,slabs]]...] [MM]

Enabling slab_debug allows one to determine the

culprit if slab objects become corrupted. Enabling

slab_debug can create guard zones around objects and

may poison objects when not in use. Also tracks the

last alloc / free. For more information see

Documentation/mm/slub.rst.

(slub_debug legacy name also accepted for now)

slab_max_order= [MM]

Determines the maximum allowed order for slabs.

A high setting may cause OOMs due to memory

fragmentation. For more information see

Documentation/mm/slub.rst.

(slub_max_order legacy name also accepted for now)

slab_merge [MM]

Enable merging of slabs with similar size when the

kernel is built without CONFIG_SLAB_MERGE_DEFAULT.

(slub_merge legacy name also accepted for now)

slab_min_objects= [MM]

The minimum number of objects per slab. SLUB will

increase the slab order up to slab_max_order to

generate a sufficiently large slab able to contain

the number of objects indicated. The higher the number

of objects the smaller the overhead of tracking slabs

and the less frequently locks need to be acquired.

For more information see Documentation/mm/slub.rst.

(slub_min_objects legacy name also accepted for now)

slab_min_order= [MM]

Determines the minimum page order for slabs. Must be

lower or equal to slab_max_order. For more information see

Documentation/mm/slub.rst.

(slub_min_order legacy name also accepted for now)

slab_nomerge [MM]

Disable merging of slabs with similar size. May be

necessary if there is some reason to distinguish

allocs to different slabs, especially in hardened

environments where the risk of heap overflows and

layout control by attackers can usually be

frustrated by disabling merging. This will reduce

most of the exposure of a heap attack to a single

cache (risks via metadata attacks are mostly

unchanged). Debug options disable merging on their

own.

For more information see Documentation/mm/slub.rst.

(slub_nomerge legacy name also accepted for now)

slab_strict_numa [MM]

Support memory policies on a per object level

in the slab allocator. The default is for memory

policies to be applied at the folio level when

a new folio is needed or a partial folio is

retrieved from the lists. Increases overhead

in the slab fastpaths but gains more accurate

NUMA kernel object placement which helps with slow

interconnects in NUMA systems.

slram= [HW,MTD]

smart2= [HW]

Format: [,[,...,]]

smp.csd_lock_timeout= [KNL]

Specify the period of time in milliseconds

that smp_call_function() and friends will wait

for a CPU to release the CSD lock. This is

useful when diagnosing bugs involving CPUs

disabling interrupts for extended periods

of time. Defaults to 5,000 milliseconds, and

setting a value of zero disables this feature.

This feature may be more efficiently disabled

using the csdlock_debug- kernel parameter.

smp.panic_on_ipistall= [KNL]

If a csd_lock_timeout extends for more than

the specified number of milliseconds, panic the

system. By default, let CSD-lock acquisition

take as long as they take. Specifying 300,000

for this value provides a 5-minute timeout.

smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices

smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port

smsc-ircc2.ircc_sir= [HW] SIR base I/O port

smsc-ircc2.ircc_fir= [HW] FIR base I/O port

smsc-ircc2.ircc_irq= [HW] IRQ line

smsc-ircc2.ircc_dma= [HW] DMA channel

smsc-ircc2.ircc_transceiver= [HW] Transceiver type:

0: Toshiba Satellite 1800 (GP data pin select)

1: Fast pin select (default)

2: ATC IRMode

smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads

(logical CPUs) to use per physical CPU on systems

capable of symmetric multithreading (SMT). Will

be capped to the actual hardware limit.

Format:

Default: -1 (no limit)

softlockup_panic=

[KNL] Should the soft-lockup detector generate panics.

Format: 0 | 1

A value of 1 instructs the soft-lockup detector

to panic the machine when a soft-lockup occurs. It is

also controlled by the kernel.softlockup_panic sysctl

and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the

respective build-time switch to that functionality.

softlockup_all_cpu_backtrace=

[KNL] Should the soft-lockup detector generate

backtraces on all cpus.

Format: 0 | 1

sonypi.*= [HW] Sony Programmable I/O Control Device driver

See Documentation/admin-guide/laptops/sonypi.rst

spectre_bhi= [X86] Control mitigation of Branch History Injection

(BHI) vulnerability. This setting affects the

deployment of the HW BHI control and the SW BHB

clearing sequence.

on - (default) Enable the HW or SW mitigation as

needed. This protects the kernel from

both syscalls and VMs.

vmexit - On systems which don't have the HW mitigation

available, enable the SW mitigation on vmexit

ONLY. On such systems, the host kernel is

protected from VM-originated BHI attacks, but

may still be vulnerable to syscall attacks.

off - Disable the mitigation.

spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2

(indirect branch speculation) vulnerability.

The default operation protects the kernel from

user space attacks.

on - unconditionally enable, implies

spectre_v2_user=on

off - unconditionally disable, implies

spectre_v2_user=off

auto - kernel detects whether your CPU model is

vulnerable

Selecting 'on' will, and 'auto' may, choose a

mitigation method at run time according to the

CPU, the available microcode, the setting of the

CONFIG_MITIGATION_RETPOLINE configuration option,

and the compiler with which the kernel was built.

Selecting 'on' will also enable the mitigation

against user space to user space task attacks.

Selecting specific mitigation does not force enable

user mitigations.

Selecting 'off' will disable both the kernel and

the user space protections.

Specific mitigations can also be selected manually:

retpoline - replace indirect branches

retpoline,generic - Retpolines

retpoline,lfence - LFENCE; indirect branch

retpoline,amd - alias for retpoline,lfence

eibrs - Enhanced/Auto IBRS

eibrs,retpoline - Enhanced/Auto IBRS + Retpolines

eibrs,lfence - Enhanced/Auto IBRS + LFENCE

ibrs - use IBRS to protect kernel

Not specifying this option is equivalent to

spectre_v2=auto.

spectre_v2_user=

[X86] Control mitigation of Spectre variant 2

(indirect branch speculation) vulnerability between

user space tasks

on - Unconditionally enable mitigations. Is

enforced by spectre_v2=on

off - Unconditionally disable mitigations. Is

enforced by spectre_v2=off

prctl - Indirect branch speculation is enabled,

but mitigation can be enabled via prctl

per thread. The mitigation control state

is inherited on fork.

prctl,ibpb

- Like "prctl" above, but only STIBP is

controlled per thread. IBPB is issued

always when switching between different user

space processes.

seccomp

- Same as "prctl" above, but all seccomp

threads will enable the mitigation unless

they explicitly opt out.

seccomp,ibpb

- Like "seccomp" above, but only STIBP is

controlled per thread. IBPB is issued

always when switching between different

user space processes.

auto - Kernel selects the mitigation depending on

the available CPU features and vulnerability.

Default mitigation: "prctl"

Not specifying this option is equivalent to

spectre_v2_user=auto.

spec_rstack_overflow=

[X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs

off - Disable mitigation

microcode - Enable microcode mitigation only

safe-ret - Enable sw-only safe RET mitigation (default)

ibpb - Enable mitigation by issuing IBPB on

kernel entry

ibpb-vmexit - Issue IBPB only on VMEXIT

(cloud-specific mitigation)

spec_store_bypass_disable=

[HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation

(Speculative Store Bypass vulnerability)

Certain CPUs are vulnerable to an exploit against a

a common industry wide performance optimization known

as "Speculative Store Bypass" in which recent stores

to the same memory location may not be observed by

later loads during speculative execution. The idea

is that such stores are unlikely and that they can

be detected prior to instruction retirement at the

end of a particular speculation execution window.

In vulnerable processors, the speculatively forwarded

store can be used in a cache side channel attack, for

example to read memory to which the attacker does not

directly have access (e.g. inside sandboxed code).

This parameter controls whether the Speculative Store

Bypass optimization is used.

On x86 the options are:

on - Unconditionally disable Speculative Store Bypass

off - Unconditionally enable Speculative Store Bypass

auto - Kernel detects whether the CPU model contains an

implementation of Speculative Store Bypass and

picks the most appropriate mitigation. If the

CPU is not vulnerable, "off" is selected. If the

CPU is vulnerable the default mitigation is

architecture and Kconfig dependent. See below.

prctl - Control Speculative Store Bypass per thread

via prctl. Speculative Store Bypass is enabled

for a process by default. The state of the control

is inherited on fork.

seccomp - Same as "prctl" above, but all seccomp threads

will disable SSB unless they explicitly opt out.

Default mitigations:

X86: "prctl"

On powerpc the options are:

on,auto - On Power8 and Power9 insert a store-forwarding

barrier on kernel entry and exit. On Power7

perform a software flush on kernel entry and

exit.

off - No action.

Not specifying this option is equivalent to

spec_store_bypass_disable=auto.

split_lock_detect=

[X86] Enable split lock detection or bus lock detection

When enabled (and if hardware support is present), atomic

instructions that access data across cache line

boundaries will result in an alignment check exception

for split lock detection or a debug exception for

bus lock detection.

off - not enabled

warn - the kernel will emit rate-limited warnings

about applications triggering the #AC

exception or the #DB exception. This mode is

the default on CPUs that support split lock

detection or bus lock detection. Default

behavior is by #AC if both features are

enabled in hardware.

fatal - the kernel will send SIGBUS to applications

that trigger the #AC exception or the #DB

exception. Default behavior is by #AC if

both features are enabled in hardware.

ratelimit:N -

Set system wide rate limit to N bus locks

per second for bus lock detection.

0 < N <= 1000.

N/A for split lock detection.

If an #AC exception is hit in the kernel or in

firmware (i.e. not while executing in user mode)

the kernel will oops in either "warn" or "fatal"

mode.

#DB exception for bus lock is triggered only when

CPL > 0.

srbds= [X86,INTEL,EARLY]

Control the Special Register Buffer Data Sampling

(SRBDS) mitigation.

Certain CPUs are vulnerable to an MDS-like

exploit which can leak bits from the random

number generator.

By default, this issue is mitigated by

microcode. However, the microcode fix can cause

the RDRAND and RDSEED instructions to become

much slower. Among other effects, this will

result in reduced throughput from /dev/urandom.

The microcode mitigation can be disabled with

the following option:

off: Disable mitigation and remove

performance impact to RDRAND and RDSEED

srcutree.big_cpu_lim [KNL]

Specifies the number of CPUs constituting a

large system, such that srcu_struct structures

should immediately allocate an srcu_node array.

This kernel-boot parameter defaults to 128,

but takes effect only when the low-order four

bits of srcutree.convert_to_big is equal to 3

(decide at boot).

srcutree.convert_to_big [KNL]

Specifies under what conditions an SRCU tree

srcu_struct structure will be converted to big

form, that is, with an rcu_node tree:

0: Never.

1: At init_srcu_struct() time.

2: When rcutorture decides to.

3: Decide at boot time (default).

0x1X: Above plus if high contention.

Either way, the srcu_node tree will be sized based

on the actual runtime number of CPUs (nr_cpu_ids)

instead of the compile-time CONFIG_NR_CPUS.

srcutree.counter_wrap_check [KNL]

Specifies how frequently to check for

grace-period sequence counter wrap for the

srcu_data structure's ->srcu_gp_seq_needed field.

The greater the number of bits set in this kernel

parameter, the less frequently counter wrap will

be checked for. Note that the bottom two bits

are ignored.

srcutree.exp_holdoff [KNL]

Specifies how many nanoseconds must elapse

since the end of the last SRCU grace period for

a given srcu_struct until the next normal SRCU

grace period will be considered for automatic

expediting. Set to zero to disable automatic

expediting.

srcutree.srcu_max_nodelay [KNL]

Specifies the number of no-delay instances

per jiffy for which the SRCU grace period

worker thread will be rescheduled with zero

delay. Beyond this limit, worker thread will

be rescheduled with a sleep delay of one jiffy.

srcutree.srcu_max_nodelay_phase [KNL]

Specifies the per-grace-period phase, number of

non-sleeping polls of readers. Beyond this limit,

grace period worker thread will be rescheduled

with a sleep delay of one jiffy, between each

rescan of the readers, for a grace period phase.

srcutree.srcu_retry_check_delay [KNL]

Specifies number of microseconds of non-sleeping

delay between each non-sleeping poll of readers.

srcutree.small_contention_lim [KNL]

Specifies the number of update-side contention

events per jiffy will be tolerated before

initiating a conversion of an srcu_struct

structure to big form. Note that the value of

srcutree.convert_to_big must have the 0x10 bit

set for contention-based conversions to occur.

ssbd= [ARM64,HW,EARLY]

Speculative Store Bypass Disable control

On CPUs that are vulnerable to the Speculative

Store Bypass vulnerability and offer a

firmware based mitigation, this parameter

indicates how the mitigation should be used:

force-on: Unconditionally enable mitigation for

for both kernel and userspace

force-off: Unconditionally disable mitigation for

for both kernel and userspace

kernel: Always enable mitigation in the

kernel, and offer a prctl interface

to allow userspace to register its

interest in being mitigated too.

stack_guard_gap= [MM]

override the default stack gap protection. The value

is in page units and it defines how many pages prior

to (for stacks growing down) resp. after (for stacks

growing up) the main stack are reserved for no other

mapping. Default value is 256 pages.

stack_depot_disable= [KNL,EARLY]

Setting this to true through kernel command line will

disable the stack depot thereby saving the static memory

consumed by the stack hash table. By default this is set

to false.

stacktrace [FTRACE]

Enabled the stack tracer on boot up.

stacktrace_filter=[function-list]

[FTRACE] Limit the functions that the stack tracer

will trace at boot up. function-list is a comma-separated

list of functions. This list can be changed at run

time by the stack_trace_filter file in the debugfs

tracing directory. Note, this enables stack tracing

and the stacktrace above is not needed.

sti= [PARISC,HW]

Format:

Set the STI (builtin display/keyboard on the HP-PARISC

machines) console (graphic card) which should be used

as the initial boot-console.

See also comment in drivers/video/console/sticore.c.

sti_font= [HW]

See comment in drivers/video/console/sticore.c.

stifb= [HW]

Format: bpp:[:[:...]]

strict_sas_size=

[X86]

Format:

Enable or disable strict sigaltstack size checks

against the required signal frame size which

depends on the supported FPU features. This can

be used to filter out binaries which have

not yet been made aware of AT_MINSIGSTKSZ.

stress_hpt [PPC,EARLY]

Limits the number of kernel HPT entries in the hash

page table to increase the rate of hash page table

faults on kernel addresses.

stress_slb [PPC,EARLY]

Limits the number of kernel SLB entries, and flushes

them frequently to increase the rate of SLB faults

on kernel addresses.

sunrpc.min_resvport=

sunrpc.max_resvport=

[NFS,SUNRPC]

SunRPC servers often require that client requests

originate from a privileged port (i.e. a port in the

range 0 < portnr < 1024).

An administrator who wishes to reserve some of these

ports for other uses may adjust the range that the

kernel's sunrpc client considers to be privileged

using these two parameters to set the minimum and

maximum port values.

sunrpc.svc_rpc_per_connection_limit=

[NFS,SUNRPC]

Limit the number of requests that the server will

process in parallel from a single connection.

The default value is 0 (no limit).

sunrpc.pool_mode=

[NFS]

Control how the NFS server code allocates CPUs to

service thread pools. Depending on how many NICs

you have and where their interrupts are bound, this

option will affect which CPUs will do NFS serving.

Note: this parameter cannot be changed while the

NFS server is running.

auto the server chooses an appropriate mode

automatically using heuristics

global a single global pool contains all CPUs

percpu one pool for each CPU

pernode one pool for each NUMA node (equivalent

to global on non-NUMA machines)

sunrpc.tcp_slot_table_entries=

sunrpc.udp_slot_table_entries=

[NFS,SUNRPC]

Sets the upper limit on the number of simultaneous

RPC calls that can be sent from the client to a

server. Increasing these values may allow you to

improve throughput, but will also increase the

amount of memory reserved for use by the client.

suspend.pm_test_delay=

[SUSPEND]

Sets the number of seconds to remain in a suspend test

mode before resuming the system (see

/sys/power/pm_test). Only available when CONFIG_PM_DEBUG

is set. Default value is 5.

svm= [PPC]

Format: { on | off | y | n | 1 | 0 }

This parameter controls use of the Protected

Execution Facility on pSeries.

swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY]

Format: { [,] | force | noforce }

-- Number of I/O TLB slabs

-- Second integer after comma. Number of swiotlb

areas with their own lock. Will be rounded up

to a power of 2.

force -- force using of bounce buffers even if they

wouldn't be automatically used by the kernel

noforce -- Never use bounce buffers (for debugging)

switches= [HW,M68k,EARLY]

sysctl.*= [KNL]

Set a sysctl parameter, right before loading the init

process, as if the value was written to the respective

/proc/sys/... file. Both '.' and '/' are recognized as

separators. Unrecognized parameters and invalid values

are reported in the kernel log. Sysctls registered

later by a loaded module cannot be set this way.

Example: sysctl.vm.swappiness=40

sysrq_always_enabled

[KNL]

Ignore sysrq setting - this boot parameter will

neutralize any effect of /proc/sys/kernel/sysrq.

Useful for debugging.

tcpmhash_entries= [KNL,NET]

Set the number of tcp_metrics_hash slots.

Default value is 8192 or 16384 depending on total

ram pages. This is used to specify the TCP metrics

cache size. See Documentation/networking/ip-sysctl.rst

"tcp_no_metrics_save" section for more details.

tdfx= [HW,DRM]

test_suspend= [SUSPEND]

Format: { "mem" | "standby" | "freeze" }[,N]

Specify "mem" (for Suspend-to-RAM) or "standby" (for

standby suspend) or "freeze" (for suspend type freeze)

as the system sleep state during system startup with

the optional capability to repeat N number of times.

The system is woken from this state using a

wakeup-capable RTC alarm.

thash_entries= [KNL,NET]

Set number of hash buckets for TCP connection

thermal.act= [HW,ACPI]

-1: disable all active trip points in all thermal zones

: override all lowest active trip points

thermal.crt= [HW,ACPI]

-1: disable all critical trip points in all thermal zones

: override all critical trip points

thermal.off= [HW,ACPI]

1: disable ACPI thermal control

thermal.psv= [HW,ACPI]

-1: disable all passive trip points

: override all passive trip points to this

value

thermal.tzp= [HW,ACPI]

Specify global default ACPI thermal zone polling rate

: poll all this frequency

0: no polling (default)

thp_anon= [KNL]

Format: [KMG],[KMG]:;[KMG]-[KMG]:

state is one of "always", "madvise", "never" or "inherit".

Control the default behavior of the system with respect

to anonymous transparent hugepages.

Can be used multiple times for multiple anon THP sizes.

See Documentation/admin-guide/mm/transhuge.rst for more

details.

threadirqs [KNL,EARLY]

Force threading of all interrupt handlers except those

marked explicitly IRQF_NO_THREAD.

thp_shmem= [KNL]

Format: [KMG],[KMG]:;[KMG]-[KMG]:

Control the default policy of each hugepage size for the

internal shmem mount. is one of policies available

for the shmem mount ("always", "inherit", "never", "within_size",

and "advise").

It can be used multiple times for multiple shmem THP sizes.

See Documentation/admin-guide/mm/transhuge.rst for more

details.

topology= [S390,EARLY]

Format: {off | on}

Specify if the kernel should make use of the cpu

topology information if the hardware supports this.

The scheduler will make use of this information and

e.g. base its process migration decisions on it.

Default is on.

torture.disable_onoff_at_boot= [KNL]

Prevent the CPU-hotplug component of torturing

until after init has spawned.

torture.ftrace_dump_at_shutdown= [KNL]

Dump the ftrace buffer at torture-test shutdown,

even if there were no errors. This can be a

very costly operation when many torture tests

are running concurrently, especially on systems

with rotating-rust storage.

torture.verbose_sleep_frequency= [KNL]

Specifies how many verbose printk()s should be

emitted between each sleep. The default of zero

disables verbose-printk() sleeping.

torture.verbose_sleep_duration= [KNL]

Duration of each verbose-printk() sleep in jiffies.

tpm.disable_pcr_integrity= [HW,TPM]

Do not protect PCR registers from unintended physical

access, or interposers in the bus by the means of

having an integrity protected session wrapped around

TPM2_PCR_Extend command. Consider this in a situation

where TPM is heavily utilized by IMA, thus protection

causing a major performance hit, and the space where

machines are deployed is by other means guarded.

tpm_suspend_pcr=[HW,TPM]

Format: integer pcr id

Specify that at suspend time, the tpm driver

should extend the specified pcr with zeros,

as a workaround for some chips which fail to

flush the last written pcr on TPM_SaveState.

This will guarantee that all the other pcrs

are saved.

tpm_tis.interrupts= [HW,TPM]

Enable interrupts for the MMIO based physical layer

for the FIFO interface. By default it is set to false

(0). For more information about TPM hardware interfaces

defined by Trusted Computing Group (TCG) see

https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/

tp_printk [FTRACE]

Have the tracepoints sent to printk as well as the

tracing ring buffer. This is useful for early boot up

where the system hangs or reboots and does not give the

option for reading the tracing buffer or performing a

ftrace_dump_on_oops.

To turn off having tracepoints sent to printk,

echo 0 > /proc/sys/kernel/tracepoint_printk

Note, echoing 1 into this file without the

tp_printk kernel cmdline option has no effect.

The tp_printk_stop_on_boot (see below) can also be used

to stop the printing of events to console at

late_initcall_sync.

** CAUTION **

Having tracepoints sent to printk() and activating high

frequency tracepoints such as irq or sched, can cause

the system to live lock.

tp_printk_stop_on_boot [FTRACE]

When tp_printk (above) is set, it can cause a lot of noise

on the console. It may be useful to only include the

printing of events during boot up, as user space may

make the system inoperable.

This command line option will stop the printing of events

to console at the late_initcall_sync() time frame.

trace_buf_size=nn[KMG]

[FTRACE] will set tracing buffer size on each cpu.

trace_clock= [FTRACE] Set the clock used for tracing events

at boot up.

local - Use the per CPU time stamp counter

(converted into nanoseconds). Fast, but

depending on the architecture, may not be

in sync between CPUs.

global - Event time stamps are synchronize across

CPUs. May be slower than the local clock,

but better for some race conditions.

counter - Simple counting of events (1, 2, ..)

note, some counts may be skipped due to the

infrastructure grabbing the clock more than

once per event.

uptime - Use jiffies as the time stamp.

perf - Use the same clock that perf uses.

mono - Use ktime_get_mono_fast_ns() for time stamps.

mono_raw - Use ktime_get_raw_fast_ns() for time

stamps.

boot - Use ktime_get_boot_fast_ns() for time stamps.

Architectures may add more clocks. See

Documentation/trace/ftrace.rst for more details.

trace_event=[event-list]

[FTRACE] Set and start specified trace events in order

to facilitate early boot debugging. The event-list is a

comma-separated list of trace events to enable. See

also Documentation/trace/events.rst

To enable modules, use :mod: keyword:

trace_event=:mod:

The value before :mod: will only enable specific events

that are part of the module. See the above mentioned

document for more information.

trace_instance=[instance-info]

[FTRACE] Create a ring buffer instance early in boot up.

This will be listed in:

/sys/kernel/tracing/instances

Events can be enabled at the time the instance is created

via:

trace_instance=,:,:

Note, the ":" portion is optional if the event is

unique.

trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall

will enable the "sched_switch" event (note, the "sched:" is optional, and

the same thing would happen if it was left off). The irq_handler_entry

event, and all events under the "initcall" system.

Flags can be added to the instance to modify its behavior when it is

created. The flags are separated by '^'.

The available flags are:

traceoff - Have the tracing instance tracing disabled after it is created.

traceprintk - Have trace_printk() write into this trace instance

(note, "printk" and "trace_printk" can also be used)

trace_instance=foo^traceoff^traceprintk,sched,irq

The flags must come before the defined events.

If memory has been reserved (see memmap for x86), the instance

can use that memory:

memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M

The above will create a "boot_map" instance that uses the physical

memory at 0x284500000 that is 12Megs. The per CPU buffers of that

instance will be split up accordingly.

Alternatively, the memory can be reserved by the reserve_mem option:

reserve_mem=12M:4096:trace trace_instance=boot_map@trace

This will reserve 12 megabytes at boot up with a 4096 byte alignment

and place the ring buffer in this memory. Note that due to KASLR, the

memory may not be the same location each time, which will not preserve

the buffer content.

Also note that the layout of the ring buffer data may change between

kernel versions where the validator will fail and reset the ring buffer

if the layout is not the same as the previous kernel.

If the ring buffer is used for persistent bootups and has events enabled,

it is recommend to disable tracing so that events from a previous boot do not

mix with events of the current boot (unless you are debugging a random crash

at boot up).

reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq

Note, saving the trace buffer across reboots does require that the system

is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION

can force a memory reset on boot which will clear any trace that was stored.

This is just one of many ways that can clear memory. Make sure your system

keeps the content of memory across reboots before relying on this option.

NB: Both the mapped address and size must be page aligned for the architecture.

See also Documentation/trace/debugging.rst

trace_options=[option-list]

[FTRACE] Enable or disable tracer options at boot.

The option-list is a comma delimited list of options

that can be enabled or disabled just as if you were

to echo the option name into

/sys/kernel/tracing/trace_options

For example, to enable stacktrace option (to dump the

stack trace of each event), add to the command line:

trace_options=stacktrace

See also Documentation/trace/ftrace.rst "trace options"

section.

trace_trigger=[trigger-list]

[FTRACE] Add a event trigger on specific events.

Set a trigger on top of a specific event, with an optional

filter.

The format is is "trace_trigger=.[ if ],..."

Where more than one trigger may be specified that are comma deliminated.

For example:

trace_trigger="sched_switch.stacktrace if prev_state == 2"

The above will enable the "stacktrace" trigger on the "sched_switch"

event but only trigger it if the "prev_state" of the "sched_switch"

event is "2" (TASK_UNINTERUPTIBLE).

See also "Event triggers" in Documentation/trace/events.rst

traceoff_after_boot

[FTRACE] Sometimes tracing is used to debug issues

during the boot process. Since the trace buffer has a

limited amount of storage, it may be prudent to

disable tracing after the boot is finished, otherwise

the critical information may be overwritten. With this

option, the main tracing buffer will be turned off at

the end of the boot process.

traceoff_on_warning

[FTRACE] enable this option to disable tracing when a

warning is hit. This turns off "tracing_on". Tracing can

be enabled again by echoing '1' into the "tracing_on"

file located in /sys/kernel/tracing/

This option is useful, as it disables the trace before

the WARNING dump is called, which prevents the trace to

be filled with content caused by the warning output.

This option can also be set at run time via the sysctl

option: kernel/traceoff_on_warning

transparent_hugepage=

[KNL]

Format: [always|madvise|never]

Can be used to control the default behavior of the system

with respect to transparent hugepages.

See Documentation/admin-guide/mm/transhuge.rst

for more details.

transparent_hugepage_shmem= [KNL]

Format: [always|within_size|advise|never|deny|force]

Can be used to control the hugepage allocation policy for

the internal shmem mount.

See Documentation/admin-guide/mm/transhuge.rst

for more details.

transparent_hugepage_tmpfs= [KNL]

Format: [always|within_size|advise|never]

Can be used to control the default hugepage allocation policy

for the tmpfs mount.

See Documentation/admin-guide/mm/transhuge.rst

for more details.

trusted.source= [KEYS]

Format:

This parameter identifies the trust source as a backend

for trusted keys implementation. Supported trust

sources:

- "tpm"

- "tee"

- "caam"

- "dcp"

If not specified then it defaults to iterating through

the trust source list starting with TPM and assigns the

first trust source as a backend which is initialized

successfully during iteration.

trusted.rng= [KEYS]

Format:

The RNG used to generate key material for trusted keys.

Can be one of:

- "kernel"

- the same value as trusted.source: "tpm" or "tee"

- "default"

If not specified, "default" is used. In this case,

the RNG's choice is left to each individual trust source.

trusted.dcp_use_otp_key

This is intended to be used in combination with

trusted.source=dcp and will select the DCP OTP key

instead of the DCP UNIQUE key blob encryption.

trusted.dcp_skip_zk_test

This is intended to be used in combination with

trusted.source=dcp and will disable the check if the

blob key is all zeros. This is helpful for situations where

having this key zero'ed is acceptable. E.g. in testing

scenarios.

tsc= Disable clocksource stability checks for TSC.

Format:

[x86] reliable: mark tsc clocksource as reliable, this

disables clocksource verification at runtime, as well

as the stability checks done at bootup. Used to enable

high-resolution timer mode on older hardware, and in

virtualized environment.

[x86] noirqtime: Do not use TSC to do irq accounting.

Used to run time disable IRQ_TIME_ACCOUNTING on any

platforms where RDTSC is slow and this accounting

can add overhead.

[x86] unstable: mark the TSC clocksource as unstable, this

marks the TSC unconditionally unstable at bootup and

avoids any further wobbles once the TSC watchdog notices.

[x86] nowatchdog: disable clocksource watchdog. Used

in situations with strict latency requirements (where

interruptions from clocksource watchdog are not

acceptable).

[x86] recalibrate: force recalibration against a HW timer

(HPET or PM timer) on systems whose TSC frequency was

obtained from HW or FW using either an MSR or CPUID(0x15).

Warn if the difference is more than 500 ppm.

[x86] watchdog: Use TSC as the watchdog clocksource with

which to check other HW timers (HPET or PM timer), but

only on systems where TSC has been deemed trustworthy.

This will be suppressed by an earlier tsc=nowatchdog and

can be overridden by a later tsc=nowatchdog. A console

message will flag any such suppression or overriding.

tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given

value instead. Useful when the early TSC frequency discovery

procedure is not reliable, such as on overclocked systems

with CPUID.16h support and partial CPUID.15h support.

Format:

tsx= [X86] Control Transactional Synchronization

Extensions (TSX) feature in Intel processors that

support TSX control.

This parameter controls the TSX feature. The options are:

on - Enable TSX on the system. Although there are

mitigations for all known security vulnerabilities,

TSX has been known to be an accelerator for

several previous speculation-related CVEs, and

so there may be unknown security risks associated

with leaving it enabled.

off - Disable TSX on the system. (Note that this

option takes effect only on newer CPUs which are

not vulnerable to MDS, i.e., have

MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get

the new IA32_TSX_CTRL MSR through a microcode

update. This new MSR allows for the reliable

deactivation of the TSX functionality.)

auto - Disable TSX if X86_BUG_TAA is present,

otherwise enable TSX on the system.

Not specifying this option is equivalent to tsx=off.

See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst

for more details.

tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async

Abort (TAA) vulnerability.

Similar to Micro-architectural Data Sampling (MDS)

certain CPUs that support Transactional

Synchronization Extensions (TSX) are vulnerable to an

exploit against CPU internal buffers which can forward

information to a disclosure gadget under certain

conditions.

In vulnerable processors, the speculatively forwarded

data can be used in a cache side channel attack, to

access data to which the attacker does not have direct

access.

This parameter controls the TAA mitigation. The

options are:

full - Enable TAA mitigation on vulnerable CPUs

if TSX is enabled.

full,nosmt - Enable TAA mitigation and disable SMT on

vulnerable CPUs. If TSX is disabled, SMT

is not disabled because CPU is not

vulnerable to cross-thread TAA attacks.

off - Unconditionally disable TAA mitigation

On MDS-affected machines, tsx_async_abort=off can be

prevented by an active MDS mitigation as both vulnerabilities

are mitigated with the same mechanism so in order to disable

this mitigation, you need to specify mds=off too.

Not specifying this option is equivalent to

tsx_async_abort=full. On CPUs which are MDS affected

and deploy MDS mitigation, TAA mitigation is not

required and doesn't provide any additional

mitigation.

For details see:

Documentation/admin-guide/hw-vuln/tsx_async_abort.rst

turbografx.map[2|3]= [HW,JOY]

TurboGraFX parallel port interface

Format:

,,,,,,,

See also Documentation/input/devices/joystick-parport.rst

udbg-immortal [PPC] When debugging early kernel crashes that

happen after console_init() and before a proper

console driver takes over, this boot options might

help "seeing" what's going on.

uhash_entries= [KNL,NET]

Set number of hash buckets for UDP/UDP-Lite connections

uhci-hcd.ignore_oc=

[USB] Ignore overcurrent events (default N).

Some badly-designed motherboards generate lots of

bogus events, for ports that aren't wired to

anything. Set this parameter to avoid log spamming.

Note that genuine overcurrent events won't be

reported either.

unaligned_scalar_speed=

[RISCV]

Format: {slow | fast | unsupported}

Allow skipping scalar unaligned access speed tests. This

is useful for testing alternative code paths and to skip

the tests in environments where they run too slowly. All

CPUs must have the same scalar unaligned access speed.

unaligned_vector_speed=

[RISCV]

Format: {slow | fast | unsupported}

Allow skipping vector unaligned access speed tests. This

is useful for testing alternative code paths and to skip

the tests in environments where they run too slowly. All

CPUs must have the same vector unaligned access speed.

unknown_nmi_panic

[X86] Cause panic on unknown NMI.

unwind_debug [X86-64,EARLY]

Enable unwinder debug output. This can be

useful for debugging certain unwinder error

conditions, including corrupt stacks and

bad/missing unwinder metadata.

usbcore.authorized_default=

[USB] Default USB device authorization:

(default -1 = authorized (same as 1),

0 = not authorized, 1 = authorized, 2 = authorized

if device connected to internal port)

usbcore.autosuspend=

[USB] The autosuspend time delay (in seconds) used

for newly-detected USB devices (default 2). This

is the time required before an idle device will be

autosuspended. Devices for which the delay is set

to a negative value won't be autosuspended at all.

usbcore.usbfs_snoop=

[USB] Set to log all usbfs traffic (default 0 = off).

usbcore.usbfs_snoop_max=

[USB] Maximum number of bytes to snoop in each URB

(default = 65536).

usbcore.blinkenlights=

[USB] Set to cycle leds on hubs (default 0 = off).

usbcore.old_scheme_first=

[USB] Start with the old device initialization

scheme (default 0 = off).

usbcore.usbfs_memory_mb=

[USB] Memory limit (in MB) for buffers allocated by

usbfs (default = 16, 0 = max = 2047).

usbcore.use_both_schemes=

[USB] Try the other device initialization scheme

if the first one fails (default 1 = enabled).

usbcore.initial_descriptor_timeout=

[USB] Specifies timeout for the initial 64-byte

USB_REQ_GET_DESCRIPTOR request in milliseconds

(default 5000 = 5.0 seconds).

usbcore.nousb [USB] Disable the USB subsystem

usbcore.quirks=

[USB] A list of quirk entries to augment the built-in

usb core quirk list. List entries are separated by

commas. Each entry has the form

VendorID:ProductID:Flags. The IDs are 4-digit hex

numbers and Flags is a set of letters. Each letter

will change the built-in quirk; setting it if it is

clear and clearing it if it is set. The letters have

the following meanings:

a = USB_QUIRK_STRING_FETCH_255 (string

descriptors must not be fetched using

a 255-byte read);

b = USB_QUIRK_RESET_RESUME (device can't resume

correctly so reset it instead);

c = USB_QUIRK_NO_SET_INTF (device can't handle

Set-Interface requests);

d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't

handle its Configuration or Interface

strings);

e = USB_QUIRK_RESET (device can't be reset

(e.g morph devices), don't use reset);

f = USB_QUIRK_HONOR_BNUMINTERFACES (device has

more interface descriptions than the

bNumInterfaces count, and can't handle

talking to these interfaces);

g = USB_QUIRK_DELAY_INIT (device needs a pause

during initialization, after we read

the device descriptor);

h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For

high speed and super speed interrupt

endpoints, the USB 2.0 and USB 3.0 spec

require the interval in microframes (1

microframe = 125 microseconds) to be

calculated as interval = 2 ^

(bInterval-1).

Devices with this quirk report their

bInterval as the result of this

calculation instead of the exponent

variable used in the calculation);

i = USB_QUIRK_DEVICE_QUALIFIER (device can't

handle device_qualifier descriptor

requests);

j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device

generates spurious wakeup, ignore

remote wakeup capability);

k = USB_QUIRK_NO_LPM (device can't handle Link

Power Management);

l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL

(Device reports its bInterval as linear

frames instead of the USB 2.0

calculation);

m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs

to be disconnected before suspend to

prevent spurious wakeup);

n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a

pause after every control message);

o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra

delay after resetting its port);

p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT

(Reduce timeout of the SET_ADDRESS

request from 5000 ms to 500 ms);

Example: quirks=0781:5580:bk,0a5c:5834:gij

usbhid.mousepoll=

[USBHID] The interval which mice are to be polled at.

usbhid.jspoll=

[USBHID] The interval which joysticks are to be polled at.

usbhid.kbpoll=

[USBHID] The interval which keyboards are to be polled at.

usb-storage.delay_use=

[UMS] The delay in seconds before a new device is

scanned for Logical Units (default 1).

Optionally the delay in milliseconds if the value has

suffix with "ms".

Example: delay_use=2567ms

usb-storage.quirks=

[UMS] A list of quirks entries to supplement or

override the built-in unusual_devs list. List

entries are separated by commas. Each entry has

the form VID:PID:Flags where VID and PID are Vendor

and Product ID values (4-digit hex numbers) and

Flags is a set of characters, each corresponding

to a common usb-storage quirk flag as follows:

a = SANE_SENSE (collect more than 18 bytes

of sense data, not on uas);

b = BAD_SENSE (don't collect more than 18

bytes of sense data, not on uas);

c = FIX_CAPACITY (decrease the reported

device capacity by one sector);

d = NO_READ_DISC_INFO (don't use

READ_DISC_INFO command, not on uas);

e = NO_READ_CAPACITY_16 (don't use

READ_CAPACITY_16 command);

f = NO_REPORT_OPCODES (don't use report opcodes

command, uas only);

g = MAX_SECTORS_240 (don't transfer more than

240 sectors at a time, uas only);

h = CAPACITY_HEURISTICS (decrease the

reported device capacity by one

sector if the number is odd);

i = IGNORE_DEVICE (don't bind to this

device);

j = NO_REPORT_LUNS (don't use report luns

command, uas only);

k = NO_SAME (do not use WRITE_SAME, uas only)

l = NOT_LOCKABLE (don't try to lock and

unlock ejectable media, not on uas);

m = MAX_SECTORS_64 (don't transfer more

than 64 sectors = 32 KB at a time,

not on uas);

n = INITIAL_READ10 (force a retry of the

initial READ(10) command, not on uas);

o = CAPACITY_OK (accept the capacity

reported by the device, not on uas);

p = WRITE_CACHE (the device cache is ON

by default, not on uas);

r = IGNORE_RESIDUE (the device reports

bogus residue values, not on uas);

s = SINGLE_LUN (the device has only one

Logical Unit);

t = NO_ATA_1X (don't allow ATA(12) and ATA(16)

commands, uas only);

u = IGNORE_UAS (don't bind to the uas driver);

w = NO_WP_DETECT (don't test whether the

medium is write-protected).

y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE

even if the device claims no cache,

not on uas)

Example: quirks=0419:aaf5:rl,0421:0433:rc

user_debug= [KNL,ARM]

Format:

See arch/arm/Kconfig.debug help text.

1 - undefined instruction events

2 - system calls

4 - invalid data aborts

8 - SIGSEGV faults

16 - SIGBUS faults

Example: user_debug=31

vdso= [X86,SH,SPARC]

On X86_32, this is an alias for vdso32=. Otherwise:

vdso=1: enable VDSO (the default)

vdso=0: disable VDSO mapping

vdso32= [X86] Control the 32-bit vDSO

vdso32=1: enable 32-bit VDSO

vdso32=0 or vdso32=2: disable 32-bit VDSO

See the help text for CONFIG_COMPAT_VDSO for more

details. If CONFIG_COMPAT_VDSO is set, the default is

vdso32=0; otherwise, the default is vdso32=1.

For compatibility with older kernels, vdso32=2 is an

alias for vdso32=0.

Try vdso32=0 if you encounter an error that says:

dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!

video= [FB,EARLY] Frame buffer configuration

See Documentation/fb/modedb.rst.

video.brightness_switch_enabled= [ACPI]

Format: [0|1]

If set to 1, on receiving an ACPI notify event

generated by hotkey, video driver will adjust brightness

level and then send out the event to user space through

the allocated input device. If set to 0, video driver

will only send out the event without touching backlight

brightness level.

default: 1

virtio_mmio.device=

[VMMIO] Memory mapped virtio (platform) device.

@:[:]

where:

:= size (can use standard suffixes

like K, M and G)

:= physical base address

:= interrupt number (as passed to

request_irq())

:= (optional) platform device id

example:

virtio_mmio.device=1K@0x100b0000:48:7

Can be used multiple times for multiple devices.

vga= [BOOT,X86-32] Select a particular video mode

See Documentation/arch/x86/boot.rst and

Documentation/admin-guide/svga.rst.

Use vga=ask for menu.

This is actually a boot loader parameter; the value is

passed to the kernel using a special protocol.

vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.

May slow down system boot speed, especially when

enabled on systems with a large amount of memory.

All options are enabled by default, and this

interface is meant to allow for selectively

enabling or disabling specific virtual memory

debugging features.

Available options are:

P Enable page structure init time poisoning

- Disable all of the above options

vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an

exact size of . This can be used to increase

the minimum size (128MB on x86, arm32 platforms).

It can also be used to decrease the size and leave more room

for directly mapped kernel RAM. Note that this parameter does

not exist on many other platforms (including arm64, alpha,

loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc,

parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc).

vmcp_cma=nn[MG] [KNL,S390,EARLY]

Sets the memory size reserved for contiguous memory

allocations for the vmcp device driver.

vmhalt= [KNL,S390] Perform z/VM CP command after system halt.

Format:

vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.

Format:

vmpoff= [KNL,S390] Perform z/VM CP command after power off.

Format:

vsyscall= [X86-64,EARLY]

Controls the behavior of vsyscalls (i.e. calls to

fixed addresses of 0xffffffffff600x00 from legacy

code). Most statically-linked binaries and older

versions of glibc use these calls. Because these

functions are at fixed addresses, they make nice

targets for exploits that can control RIP.

emulate Vsyscalls turn into traps and are emulated

reasonably safely. The vsyscall page is

readable.

xonly [default] Vsyscalls turn into traps and are

emulated reasonably safely. The vsyscall

page is not readable.

none Vsyscalls don't work at all. This makes

them quite hard to use for exploits but

might break your system.

vt.color= [VT] Default text color.

Format: 0xYX, X = foreground, Y = background.

Default: 0x07 = light gray on black.

vt.cur_default= [VT] Default cursor shape.

Format: 0xCCBBAA, where AA, BB, and CC are the same as

the parameters of the [?A;B;Cc escape sequence;

see vga-softcursor.rst. Default: 2 = underline.

vt.default_blu= [VT]

Format: ,,,...,

Change the default blue palette of the console.

This is a 16-member array composed of values

ranging from 0-255.

vt.default_grn= [VT]

Format: ,,,...,

Change the default green palette of the console.

This is a 16-member array composed of values

ranging from 0-255.

vt.default_red= [VT]

Format: ,,,...,

Change the default red palette of the console.

This is a 16-member array composed of values

ranging from 0-255.

vt.default_utf8=

[VT]

Format=<0|1>

Set system-wide default UTF-8 mode for all tty's.

Default is 1, i.e. UTF-8 mode is enabled for all

newly opened terminals.

vt.global_cursor_default=

[VT]

Format=<-1|0|1>

Set system-wide default for whether a cursor

is shown on new VTs. Default is -1,

i.e. cursors will be created by default unless

overridden by individual drivers. 0 will hide

cursors, 1 will display them.

vt.italic= [VT] Default color for italic text; 0-15.

Default: 2 = green.

vt.underline= [VT] Default color for underlined text; 0-15.

Default: 3 = cyan.

watchdog timers [HW,WDT] For information on watchdog timers,

see Documentation/watchdog/watchdog-parameters.rst

or other driver-specific files in the

Documentation/watchdog/ directory.

watchdog_thresh=

[KNL]

Set the hard lockup detector stall duration

threshold in seconds. The soft lockup detector

threshold is set to twice the value. A value of 0

disables both lockup detectors. Default is 10

seconds.

workqueue.unbound_cpus=

[KNL,SMP] Specify to constrain one or some CPUs

to use in unbound workqueues.

Format:

By default, all online CPUs are available for

unbound workqueues.

workqueue.watchdog_thresh=

If CONFIG_WQ_WATCHDOG is configured, workqueue can

warn stall conditions and dump internal state to

help debugging. 0 disables workqueue stall

detection; otherwise, it's the stall threshold

duration in seconds. The default value is 30 and

it can be updated at runtime by writing to the

corresponding sysfs file.

workqueue.panic_on_stall=

Panic when workqueue stall is detected by

CONFIG_WQ_WATCHDOG. It sets the number times of the

stall to trigger panic.

The default is 0, which disables the panic on stall.

workqueue.cpu_intensive_thresh_us=

Per-cpu work items which run for longer than this

threshold are automatically considered CPU intensive

and excluded from concurrency management to prevent

them from noticeably delaying other per-cpu work

items. Default is 10000 (10ms).

If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel

will report the work functions which violate this

threshold repeatedly. They are likely good

candidates for using WQ_UNBOUND workqueues instead.

workqueue.cpu_intensive_warning_thresh=

If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel

will report the work functions which violate the

intensive_threshold_us repeatedly. In order to prevent

spurious warnings, start printing only after a work

function has violated this threshold number of times.

The default is 4 times. 0 disables the warning.

workqueue.power_efficient

Per-cpu workqueues are generally preferred because

they show better performance thanks to cache

locality; unfortunately, per-cpu workqueues tend to

be more power hungry than unbound workqueues.

Enabling this makes the per-cpu workqueues which

were observed to contribute significantly to power

consumption unbound, leading to measurably lower

power usage at the cost of small performance

overhead.

The default value of this parameter is determined by

the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.

workqueue.default_affinity_scope=

Select the default affinity scope to use for unbound

workqueues. Can be one of "cpu", "smt", "cache",

"numa" and "system". Default is "cache". For more

information, see the Affinity Scopes section in

Documentation/core-api/workqueue.rst.

This can be changed after boot by writing to the

matching /sys/module/workqueue/parameters file. All

workqueues with the "default" affinity scope will be

updated accordingly.

workqueue.debug_force_rr_cpu

Workqueue used to implicitly guarantee that work

items queued without explicit CPU specified are put

on the local CPU. This guarantee is no longer true

and while local CPU is still preferred work items

may be put on foreign CPUs. This debug option

forces round-robin CPU selection to flush out

usages which depend on the now broken guarantee.

When enabled, memory and cache locality will be

impacted.

writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access

Type) of ioremap_wc().

on - Enable writecombine, use WUC for ioremap_wc()

off - Disable writecombine, use SUC for ioremap_wc()

x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of

default x2apic cluster mode on platforms

supporting x2apic.

xen_512gb_limit [KNL,X86-64,XEN]

Restricts the kernel running paravirtualized under Xen

to use only up to 512 GB of RAM. The reason to do so is

crash analysis tools and Xen tools for doing domain

save/restore/migration must be enabled to handle larger

domains.

xen_emul_unplug= [HW,X86,XEN,EARLY]

Unplug Xen emulated devices

Format: [unplug0,][unplug1]

ide-disks -- unplug primary master IDE devices

aux-ide-disks -- unplug non-primary-master IDE devices

nics -- unplug network devices

all -- unplug all emulated devices (NICs and IDE disks)

unnecessary -- unplugging emulated devices is

unnecessary even if the host did not respond to

the unplug protocol

never -- do not unplug even if version check succeeds

xen_legacy_crash [X86,XEN,EARLY]

Crash from Xen panic notifier, without executing late

panic() code such as dumping handler.

xen_mc_debug [X86,XEN,EARLY]

Enable multicall debugging when running as a Xen PV guest.

Enabling this feature will reduce performance a little

bit, so it should only be enabled for obtaining extended

debug data in case of multicall errors.

xen_msr_safe= [X86,XEN,EARLY]

Format:

Select whether to always use non-faulting (safe) MSR

access functions when running as Xen PV guest. The

default value is controlled by CONFIG_XEN_PV_MSR_SAFE.

xen_nopv [X86]

Disables the PV optimizations forcing the HVM guest to

run as generic HVM guest with no PV drivers.

This option is obsoleted by the "nopv" option, which

has equivalent effect for XEN platform.

xen_no_vector_callback

[KNL,X86,XEN,EARLY] Disable the vector callback for Xen

event channel interrupts.

xen_scrub_pages= [XEN]

Boolean option to control scrubbing pages before giving them back

to Xen, for use by other domains. Can be also changed at runtime

with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.

Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.

xen_timer_slop= [X86-64,XEN,EARLY]

Set the timer slop (in nanoseconds) for the virtual Xen

timers (default is 100000). This adjusts the minimum

delta of virtualized Xen timers, where lower values

improve timer resolution at the expense of processing

more timer interrupts.

xen.balloon_boot_timeout= [XEN]

The time (in seconds) to wait before giving up to boot

in case initial ballooning fails to free enough memory.

Applies only when running as HVM or PVH guest and

started with less memory configured than allowed at

max. Default is 180.

xen.event_eoi_delay= [XEN]

How long to delay EOI handling in case of event

storms (jiffies). Default is 10.

xen.event_loop_timeout= [XEN]

After which time (jiffies) the event handling loop

should start to delay EOI handling. Default is 2.

xen.fifo_events= [XEN]

Boolean parameter to disable using fifo event handling

even if available. Normally fifo event handling is

preferred over the 2-level event handling, as it is

fairer and the number of possible event channels is

much higher. Default is on (use fifo events).

xirc2ps_cs= [NET,PCMCIA]

Format:

,,,,,[,[,[,]]]

xive= [PPC]

By default on POWER9 and above, the kernel will

natively use the XIVE interrupt controller. This option

allows the fallback firmware mode to be used:

off Fallback to firmware control of XIVE interrupt

controller on both pseries and powernv

platforms. Only useful on POWER9 and above.

xive.store-eoi=off [PPC]

By default on POWER10 and above, the kernel will use

stores for EOI handling when the XIVE interrupt mode

is active. This option allows the XIVE driver to use

loads instead, as on POWER9.

xhci-hcd.quirks [USB,KNL]

A hex value specifying bitmask with supplemental xhci

host controller quirks. Meaning of each bit can be

consulted in header drivers/usb/host/xhci.h.

xmon [PPC,EARLY]

Format: { early | on | rw | ro | off }

Controls if xmon debugger is enabled. Default is off.

Passing only "xmon" is equivalent to "xmon=early".

early Call xmon as early as possible on boot; xmon

debugger is called from setup_arch().

on xmon debugger hooks will be installed so xmon

is only called on a kernel crash. Default mode,

i.e. either "ro" or "rw" mode, is controlled

with CONFIG_XMON_DEFAULT_RO_MODE.

rw xmon debugger hooks will be installed so xmon

is called only on a kernel crash, mode is write,

meaning SPR registers, memory and, other data

can be written using xmon commands.

ro same as "rw" option above but SPR registers,

memory, and other data can't be written using

xmon commands.

off xmon is disabled.