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kernel/Documentation/admin-guide/kernel-parameters.txt

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accept_memory= [MM]
Format: { eager | lazy }
default: lazy
By default, unaccepted memory is accepted lazily to
avoid prolonged boot times. The lazy option will add
some runtime overhead until all memory is eventually
accepted. In most cases the overhead is negligible.
For some workloads or for debugging purposes
accept_memory=eager can be used to accept all memory
at once during boot.
acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY]
Advanced Configuration and Power Interface
Format: { force | on | off | strict | noirq | rsdt |
copy_dsdt | nospcr }
force -- enable ACPI if default was off
on -- enable ACPI but allow fallback to DT [arm64,riscv64]
off -- disable ACPI if default was on
noirq -- do not use ACPI for IRQ routing
strict -- Be less tolerant of platforms that are not
strictly ACPI specification compliant.
rsdt -- prefer RSDT over (default) XSDT
copy_dsdt -- copy DSDT to memory
nospcr -- disable console in ACPI SPCR table as
default _serial_ console on ARM64
For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or
"acpi=nospcr" are available
For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force"
are available
See also Documentation/power/runtime_pm.rst, pci=noacpi
acpi_apic_instance= [ACPI,IOAPIC,EARLY]
Format: <int>
2: use 2nd APIC table, if available
1,0: use 1st APIC table
default: 0
acpi_backlight= [HW,ACPI]
{ vendor | video | native | none }
If set to vendor, prefer vendor-specific driver
(e.g. thinkpad_acpi, sony_acpi, etc.) instead
of the ACPI video.ko driver.
If set to video, use the ACPI video.ko driver.
If set to native, use the device's native backlight mode.
If set to none, disable the ACPI backlight interface.
acpi_force_32bit_fadt_addr [ACPI,EARLY]
force FADT to use 32 bit addresses rather than the
64 bit X_* addresses. Some firmware have broken 64
bit addresses for force ACPI ignore these and use
the older legacy 32 bit addresses.
acpica_no_return_repair [HW, ACPI]
Disable AML predefined validation mechanism
This mechanism can repair the evaluation result to make
the return objects more ACPI specification compliant.
This option is useful for developers to identify the
root cause of an AML interpreter issue when the issue
has something to do with the repair mechanism.
acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
Format: <int>
CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
debug output. Bits in debug_layer correspond to a
_COMPONENT in an ACPI source file, e.g.,
#define _COMPONENT ACPI_EVENTS
Bits in debug_level correspond to a level in
ACPI_DEBUG_PRINT statements, e.g.,
ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
The debug_level mask defaults to "info". See
Documentation/firmware-guide/acpi/debug.rst for more information about
debug layers and levels.
Enable processor driver info messages:
acpi.debug_layer=0x20000000
Enable AML "Debug" output, i.e., stores to the Debug
object while interpreting AML:
acpi.debug_layer=0xffffffff acpi.debug_level=0x2
Enable all messages related to ACPI hardware:
acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
Some values produce so much output that the system is
unusable. The "log_buf_len" parameter may be useful
if you need to capture more output.
acpi_enforce_resources= [ACPI]
{ strict | lax | no }
Check for resource conflicts between native drivers
and ACPI OperationRegions (SystemIO and SystemMemory
only). IO ports and memory declared in ACPI might be
used by the ACPI subsystem in arbitrary AML code and
can interfere with legacy drivers.
strict (default): access to resources claimed by ACPI
is denied; legacy drivers trying to access reserved
resources will fail to bind to device using them.
lax: access to resources claimed by ACPI is allowed;
legacy drivers trying to access reserved resources
will bind successfully but a warning message is logged.
no: ACPI OperationRegions are not marked as reserved,
no further checks are performed.
acpi_force_table_verification [HW,ACPI,EARLY]
Enable table checksum verification during early stage.
By default, this is disabled due to x86 early mapping
size limitation.
acpi_irq_balance [HW,ACPI]
ACPI will balance active IRQs
default in APIC mode
acpi_irq_nobalance [HW,ACPI]
ACPI will not move active IRQs (default)
default in PIC mode
acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
Format: <irq>,<irq>...
acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
use by PCI
Format: <irq>,<irq>...
acpi_mask_gpe= [HW,ACPI]
Due to the existence of _Lxx/_Exx, some GPEs triggered
by unsupported hardware/firmware features can result in
GPE floodings that cannot be automatically disabled by
the GPE dispatcher.
This facility can be used to prevent such uncontrolled
GPE floodings.
Format: <byte> or <bitmap-list>
acpi_no_auto_serialize [HW,ACPI]
Disable auto-serialization of AML methods
AML control methods that contain the opcodes to create
named objects will be marked as "Serialized" by the
auto-serialization feature.
This feature is enabled by default.
This option allows to turn off the feature.
acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
kernels.
acpi_no_static_ssdt [HW,ACPI,EARLY]
Disable installation of static SSDTs at early boot time
By default, SSDTs contained in the RSDT/XSDT will be
installed automatically and they will appear under
/sys/firmware/acpi/tables.
This option turns off this feature.
Note that specifying this option does not affect
dynamic table installation which will install SSDT
tables to /sys/firmware/acpi/tables/dynamic.
acpi_no_watchdog [HW,ACPI,WDT]
Ignore the ACPI-based watchdog interface (WDAT) and let
a native driver control the watchdog device instead.
acpi_rsdp= [ACPI,EFI,KEXEC,EARLY]
Pass the RSDP address to the kernel, mostly used
on machines running EFI runtime service to boot the
second kernel for kdump.
acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
Format: To spoof as Windows 98: ="Microsoft Windows"
acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
of 2 which is mandated by ACPI 6) as the supported ACPI
specification revision (when using this switch, it may
be necessary to carry out a cold reboot _twice_ in a
row to make it take effect on the platform firmware).
acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
acpi_osi="string1" # add string1
acpi_osi="!string2" # remove string2
acpi_osi=!* # remove all strings
acpi_osi=! # disable all built-in OS vendor
strings
acpi_osi=!! # enable all built-in OS vendor
strings
acpi_osi= # disable all strings
'acpi_osi=!' can be used in combination with single or
multiple 'acpi_osi="string1"' to support specific OS
vendor string(s). Note that such command can only
affect the default state of the OS vendor strings, thus
it cannot affect the default state of the feature group
strings and the current state of the OS vendor strings,
specifying it multiple times through kernel command line
is meaningless. This command is useful when one do not
care about the state of the feature group strings which
should be controlled by the OSPM.
Examples:
1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
to 'acpi_osi="Windows 2000" acpi_osi=!', they all
can make '_OSI("Windows 2000")' TRUE.
'acpi_osi=' cannot be used in combination with other
'acpi_osi=' command lines, the _OSI method will not
exist in the ACPI namespace. NOTE that such command can
only affect the _OSI support state, thus specifying it
multiple times through kernel command line is also
meaningless.
Examples:
1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
FALSE.
'acpi_osi=!*' can be used in combination with single or
multiple 'acpi_osi="string1"' to support specific
string(s). Note that such command can affect the
current state of both the OS vendor strings and the
feature group strings, thus specifying it multiple times
through kernel command line is meaningful. But it may
still not able to affect the final state of a string if
there are quirks related to this string. This command
is useful when one want to control the state of the
feature group strings to debug BIOS issues related to
the OSPM features.
Examples:
1. 'acpi_osi="Module Device" acpi_osi=!*' can make
'_OSI("Module Device")' FALSE.
2. 'acpi_osi=!* acpi_osi="Module Device"' can make
'_OSI("Module Device")' TRUE.
3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
equivalent to
'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
and
'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
they all will make '_OSI("Windows 2000")' TRUE.
acpi_pm_good [X86]
Override the pmtimer bug detection: force the kernel
to assume that this machine's pmtimer latches its value
and always returns good values.
acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode
Format: { level | edge | high | low }
acpi_skip_timer_override [HW,ACPI,EARLY]
Recognize and ignore IRQ0/pin2 Interrupt Override.
For broken nForce2 BIOS resulting in XT-PIC timer.
acpi_sleep= [HW,ACPI] Sleep options
Format: { s3_bios, s3_mode, s3_beep, s4_hwsig,
s4_nohwsig, old_ordering, nonvs,
sci_force_enable, nobl }
See Documentation/power/video.rst for information on
s3_bios and s3_mode.
s3_beep is for debugging; it makes the PC's speaker beep
as soon as the kernel's real-mode entry point is called.
s4_hwsig causes the kernel to check the ACPI hardware
signature during resume from hibernation, and gracefully
refuse to resume if it has changed. This complies with
the ACPI specification but not with reality, since
Windows does not do this and many laptops do change it
on docking. So the default behaviour is to allow resume
and simply warn when the signature changes, unless the
s4_hwsig option is enabled.
s4_nohwsig prevents ACPI hardware signature from being
used (or even warned about) during resume.
old_ordering causes the ACPI 1.0 ordering of the _PTS
control method, with respect to putting devices into
low power states, to be enforced (the ACPI 2.0 ordering
of _PTS is used by default).
nonvs prevents the kernel from saving/restoring the
ACPI NVS memory during suspend/hibernation and resume.
sci_force_enable causes the kernel to set SCI_EN directly
on resume from S1/S3 (which is against the ACPI spec,
but some broken systems don't work without it).
nobl causes the internal blacklist of systems known to
behave incorrectly in some ways with respect to system
suspend and resume to be ignored (use wisely).
acpi_use_timer_override [HW,ACPI,EARLY]
Use timer override. For some broken Nvidia NF5 boards
that require a timer override, but don't have HPET
add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in
kernel's map of available physical RAM.
agp= [AGP]
{ off | try_unsupported }
off: disable AGP support
try_unsupported: try to drive unsupported chipsets
(may crash computer or cause data corruption)
ALSA [HW,ALSA]
See Documentation/sound/alsa-configuration.rst
alignment= [KNL,ARM]
Allow the default userspace alignment fault handler
behaviour to be specified. Bit 0 enables warnings,
bit 1 enables fixups, and bit 2 sends a segfault.
align_va_addr= [X86-64]
Align virtual addresses by clearing slice [14:12] when
allocating a VMA at process creation time. This option
gives you up to 3% performance improvement on AMD F15h
machines (where it is enabled by default) for a
CPU-intensive style benchmark, and it can vary highly in
a microbenchmark depending on workload and compiler.
32: only for 32-bit processes
64: only for 64-bit processes
on: enable for both 32- and 64-bit processes
off: disable for both 32- and 64-bit processes
alloc_snapshot [FTRACE]
Allocate the ftrace snapshot buffer on boot up when the
main buffer is allocated. This is handy if debugging
and you need to use tracing_snapshot() on boot up, and
do not want to use tracing_snapshot_alloc() as it needs
to be done where GFP_KERNEL allocations are allowed.
allow_mismatched_32bit_el0 [ARM64,EARLY]
Allow execve() of 32-bit applications and setting of the
PER_LINUX32 personality on systems where only a strict
subset of the CPUs support 32-bit EL0. When this
parameter is present, the set of CPUs supporting 32-bit
EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
and hot-unplug operations may be restricted.
See Documentation/arch/arm64/asymmetric-32bit.rst for more
information.
amd_iommu= [HW,X86-64]
Pass parameters to the AMD IOMMU driver in the system.
Possible values are:
fullflush - Deprecated, equivalent to iommu.strict=1
off - do not initialize any AMD IOMMU found in
the system
force_isolation - Force device isolation for all
devices. The IOMMU driver is not
allowed anymore to lift isolation
requirements as needed. This option
does not override iommu=pt
force_enable - Force enable the IOMMU on platforms known
to be buggy with IOMMU enabled. Use this
option with care.
pgtbl_v1 - Use v1 page table for DMA-API (Default).
pgtbl_v2 - Use v2 page table for DMA-API.
irtcachedis - Disable Interrupt Remapping Table (IRT) caching.
nohugepages - Limit page-sizes used for v1 page-tables
to 4 KiB.
v2_pgsizes_only - Limit page-sizes used for v1 page-tables
to 4KiB/2Mib/1GiB.
amd_iommu_dump= [HW,X86-64]
Enable AMD IOMMU driver option to dump the ACPI table
for AMD IOMMU. With this option enabled, AMD IOMMU
driver will print ACPI tables for AMD IOMMU during
IOMMU initialization.
amd_iommu_intr= [HW,X86-64]
Specifies one of the following AMD IOMMU interrupt
remapping modes:
legacy - Use legacy interrupt remapping mode.
vapic - Use virtual APIC mode, which allows IOMMU
to inject interrupts directly into guest.
This mode requires kvm-amd.avic=1.
(Default when IOMMU HW support is present.)
amd_pstate= [X86,EARLY]
disable
Do not enable amd_pstate as the default
scaling driver for the supported processors
passive
Use amd_pstate with passive mode as a scaling driver.
In this mode autonomous selection is disabled.
Driver requests a desired performance level and platform
tries to match the same performance level if it is
satisfied by guaranteed performance level.
active
Use amd_pstate_epp driver instance as the scaling driver,
driver provides a hint to the hardware if software wants
to bias toward performance (0x0) or energy efficiency (0xff)
to the CPPC firmware. then CPPC power algorithm will
calculate the runtime workload and adjust the realtime cores
frequency.
guided
Activate guided autonomous mode. Driver requests minimum and
maximum performance level and the platform autonomously
selects a performance level in this range and appropriate
to the current workload.
amd_prefcore=
[X86]
disable
Disable amd-pstate preferred core.
amijoy.map= [HW,JOY] Amiga joystick support
Map of devices attached to JOY0DAT and JOY1DAT
Format: <a>,<b>
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: <type1>,<type2>,..<type16>
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,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.
For X86-32, this can also be used to specify an APIC
driver name.
Format: apic=driver_name
Examples: apic=bigsmp
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
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: <io>,<irq>,<nodeID>
arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of
32 bit applications.
arm64.nobti [ARM64] Unconditionally disable Branch Target
Identification support
arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory
Set instructions 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: <int> (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: <bool> (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: <int> (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: <io>,<mode>
baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
Format: <io>,<mode>
See header of drivers/net/hamradio/baycom_par.c.
baycom_ser_fdx= [HW,AX25]
BayCom Serial Port AX.25 Modem (Full Duplex Mode)
Format: <io>,<irq>,<mode>[,<baud>]
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: <io>,<irq>,<mode>
See header of drivers/net/hamradio/baycom_ser_hdx.c.
bdev_allow_write_mounted=
Format: <bool>
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:<keyid> | 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: <string>
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: <string>
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: <bool>
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=<node>:nn[MG][,<node>: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:
<io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
Format: <io>[,<irq>]
com90xx= [HW,NET]
ARCnet - COM90xx chipset (memory-mapped buffers)
Format: <io>[,<irq>[,<memstart>]]
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<n> Use the virtual console device <n>.
ttyS<n>[,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.
<DEVNAME>:<n>.<n>[,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,<addr>[,options]
uart[8250],mmio,<addr>[,options]
uart[8250],mmio16,<addr>[,options]
uart[8250],mmio32,<addr>[,options]
uart[8250],0x<addr>[,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], <addr> 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<n> Use the hypervisor console device <n>. 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/<pid>/coredump_filter.
See also Documentation/filesystems/proc.rst.
coresight_cpu_debug.enable
[ARM,ARM64]
Format: <bool>
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:
<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
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: <bool>
Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise
the parameter has no effect.
crash_kexec_post_notifiers
Run kdump after running panic-notifiers and dumping
kmsg. This only for the users who doubt kdump always
succeeds in any situation.
Note that this also increases risks of kdump failure,
because some panic notifiers can make the crashed
kernel more unstable.
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: <dma>
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: <port#>,<type>
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: <int>
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=<number>
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=<driver_name>
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: <driver_name1>,<driver_name2>...
drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
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]
<module>.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,<addr>[,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,<addr>[,options[,uartclk]]
uart[8250],mmio,<addr>[,options[,uartclk]]
uart[8250],mmio32,<addr>[,options[,uartclk]]
uart[8250],mmio32be,<addr>[,options[,uartclk]]
uart[8250],0x<addr>[,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], <addr> is assumed
to be equivalent to 'mmio'. 'options' are specified
in the same format described for "console=ttyS<n>"; if
unspecified, the h/w is not initialized. 'uartclk' is
the uart clock frequency; if unspecified, it is set
to 'BASE_BAUD' * 16.
pl011,<addr>
pl011,mmio32,<addr>
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,<addr>
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,<addr>
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,<addr>
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,<addr>
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,<addr>
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,<addr>
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,<addr>
s3c2412,<addr>
s3c2440,<addr>
s3c6400,<addr>
s5pv210,<addr>
exynos4210,<addr>
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,<addr>
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,<addr>
lpuart32,<addr>
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,<addr>
ec_imx6q,<addr>
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,<addr>
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,<addr>
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,<addr>
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=pciserial[,force],bus:device.function[,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.
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_make_request=[KNL]
General fault injection mechanism.
Format: <interval>,<probability>,<space>,<times>
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) | =<instance>][,<instance> |
,<instance>=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=<uint>
[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=<bool>
[KNL,EARLY] Treat all inferred dependencies as mandatory
dependencies. This only applies for fw_devlink=on|rpm.
Format: <bool>
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: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
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.
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: <start1>,<end1>,<start2>,<end2>...
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: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
Default: 1024
grcan.rxsize= [HW] Sets the size of the rx buffer.
Format: <unsigned int> 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.
on Perform hardened usercopy checks (default).
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: <cyl>,<head>,<sect>
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.
highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact
size of <nn>. 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: <string>
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] 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: <integer> or (node format)
<node>:<integer>[,<node>:<integer>]
hugepagesz=
[HW] 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]
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)
<node>:nn[KMGTPE][,<node>: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_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.
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:
<bus_id>,<clkrate>
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:
<ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...]
Where <val> is one of:
Omit "=<val>" 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: <bool>
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: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
idle= [X86,EARLY]
Format: idle=poll, idle=halt, idle=nomwait
Poll forces a polling idle loop that can slightly
improve the performance of waking up a idle CPU, but
will use a lot of power and make the system run hot.
Not recommended.
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: <bool>
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: <bool>
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: <min_file_size>
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: <bufsize>
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.
init= [KNL]
Format: <full_path>
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: <bool>
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: <irq>
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
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
force
noforce
biomerge
panic
nopanic
merge
nomerge
soft
pt [X86]
nopt [X86]
nobypass [PPC/POWERNV]
Disable IOMMU bypass, using IOMMU for PCI devices.
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: <bool>
Determine whether IPE starts in permissive (0) or
enforce (1) mode. The default is enforce.
ipe.success_audit=
[IPE]
Format: <bool>
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: <bool>
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: <RDP>,<reset>,<pci_scan>,<verbosity>
isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
[Deprecated - use cpusets instead]
Format: [flag-list,]<cpu-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.
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.
<cpu number> 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 <cpu-list> 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: <Controller#>[,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: <serial_device>[,baud]
keyboard only format: kbd
keyboard and serial format: kbd,<serial_device>[,baud]
Optional Kernel mode setting:
kms, kbd format: kms,kbd
kms, kbd and serial format: kms,kbd,<ser_dev>[,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.
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 lode 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: nVHE-based mode with support for guests whose
state is kept private from the host.
nested: VHE-based mode with support for nested
virtualization. Requires at least ARMv8.3
hardware.
Defaults to VHE/nVHE based on hardware support. Setting
mode to "protected" will disable kexec and hibernation
for the host. "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: <integer>
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: <int>
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.
* [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: <integer>
lockd.nlm_tcpport=N [NFS] Assign TCP port.
Format: <integer>
lockd.nlm_timeout=T [NFS] Assign timeout value.
Format: <integer>
lockd.nlm_udpport=M [NFS] Assign UDP port.
Format: <integer>
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: <irq>
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] Machine Check Exception
mce=option [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst
md= [HW] RAID subsystems devices and level
See Documentation/admin-guide/md.rst.
mdacon= [MDA]
Format: <first>,<last>
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_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
option.
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=<size>%<offset>-<oldtype>+<newtype>
[KNL,ACPI,EARLY] Convert memory within the specified region
from <oldtype> to <newtype>. If "-<oldtype>" is left
out, the whole region will be marked as <newtype>,
even if previously unavailable. If "+<newtype>" 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: <integer>
default : 0 <disable>
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: <bool>
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]
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
<module>.async_probe[=<bool>] [KNL]
If no <bool> value is specified or if the value
specified is not a valid <bool>, enable asynchronous
probe on this module. Otherwise, enable/disable
asynchronous probe on this module as indicated by the
<bool> value. See also: module.async_probe
module.async_probe=<bool>
[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 <module>.async_probe. When both
module.async_probe and <module>.async_probe are
specified, <module>.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: <msecs>
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: <name>,<region-number>,<size>,<offset>
MTD_Region= [MTD] Format:
<name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
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: <integer>
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: <irq>,<io>,<mem_start>,<mem_end>,<name>
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.
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.
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.
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,S390,EARLY] Disable symmetric multithreading (SMT).
Equivalent to smt=1.
[KNL,X86,PPC] 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.
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=<size>[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=<N>
[KNL, ARM64, RISCV, X86, EARLY]
If given as an integer, fills all system RAM with N
fake nodes interleaved over physical nodes.
numa=fake=<N>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_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: <mux_mode0.mode_name=value>...
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: <integer>
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>
timeout > 0: seconds before rebooting
timeout = 0: wait forever
timeout < 0: reboot immediately
Format: <timeout>
panic_on_taint= [KNL,EARLY]
Bitmask for conditionally calling panic() in add_taint()
Format: <hex>[,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: <parport#>
parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
0 for XT, 1 for AT (default is AT).
Format: <mode>
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: <int>
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: <int>
Set to non-zero if a chip is present that snoops speed
changes. Disabled by default.
pata_legacy.ht6560a= [HW,LIBATA]
Format: <int>
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: <int>
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: <int>
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: <int>
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: <int>
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: <int>
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: <int>
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: <int>
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: <int>
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: <int>
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: <int>
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=<int>
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 (<pci_dev>). These are
specified in one of the following formats:
[<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
pci:<vendor>:<device>[:<subvendor>:<subdevice>]
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
<linux-pci@vger.kernel.org>.
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 <linux-pci@vger.kernel.org>.
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:
[<order of align>@]<pci_dev>[; ...]
Specifies alignment and device to reassign
aligned memory resources. How to
specify the device is described above.
If <order of align> 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=<pci_dev>[; ...]
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:
<ACS flags>@<pci_dev>[; ...]
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
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
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<nr> | 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: <port>,<port>....
possible_cpus= [SMP,S390,X86]
Format: <unsigned int>
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).
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: <bool> (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: <bool>
default: 0 (auto_verbose is enabled)
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: <bool> (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: [<profiletype>,]<number>
Param: <profiletype>: "schedule" or "kvm"
[defaults to kernel profiling]
Param: "schedule" - profile schedule points.
Param: "kvm" - profile VM exits.
Param: <number> - 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: <bool>
psi= [KNL] Enable or disable pressure stall information
tracking.
Format: <bool>
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: <bool> (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
primitives, if available.
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_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.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.read_exit= [KNL]
Set the number of read-then-exit kthreads used
to test the interaction of RCU updaters and
task-exit processing.
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.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_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: <full_path>
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.
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: <base1>,<size1>[,<base2>,<size2>,...]
Reserve I/O ports or memory so the kernel won't use
them. If <base> is less than 0x10000, the region
is assumed to be I/O ports; otherwise it is memory.
reserve_mem= [RAM]
Format: nn[KNG]:<align>:<label>
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/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
resume_offset= [SWSUSP]
Specify the offset from the beginning of the partition
given by "resume=" at which the swap header is located,
in <PAGE_SIZE> 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.
rh_waived=
Enable waived features in RHEL.
Waived features are disabled by default in RHEL, this parameter
provides support to enable such features, as needed.
Format: <feat-1>,<feat-2>...<feat-n>
Use 'rh_waived' to enable all waived features listed at
Documentation/admin-guide/rh-waived-features.rst
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 a 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.
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.
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] See Documentation/arch/x86/x86_64/boot-options.rst
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)
slram= [HW,MTD]
smart2= [HW]
Format: <io1>[,<io2>[,...,<io8>]]
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: <integer>
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 '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: <num>
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:<bpp1>[:<bpp2>[:<bpp3>...]]
strict_sas_size=
[X86]
Format: <bool>
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: { <int> [,<int>] | force | noforce }
<int> -- Number of I/O TLB slabs
<int> -- 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
<degrees C>: override all lowest active trip points
thermal.crt= [HW,ACPI]
-1: disable all critical trip points in all thermal zones
<degrees C>: override all critical trip points
thermal.off= [HW,ACPI]
1: disable ACPI thermal control
thermal.psv= [HW,ACPI]
-1: disable all passive trip points
<degrees C>: override all passive trip points to this
value
thermal.tzp= [HW,ACPI]
Specify global default ACPI thermal zone polling rate
<deci-seconds>: poll all this frequency
0: no polling (default)
thp_anon= [KNL]
Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state>
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.
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
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=<name>,<system1>:<event1>,<system2>:<event2>
Note, the "<system*>:" 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
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=<event>.<trigger>[ if <filter>],..."
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_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.
trusted.source= [KEYS]
Format: <string>
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: <string>
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: <string>
[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: <unsigned int>
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:
<port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
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.
unknown_nmi_panic
[X86] Cause panic on unknown NMI.
unprivileged_bpf_disabled=
Format: { "0" | "1" | "2" }
Sets the initial value of
kernel.unprivileged_bpf_disabled sysctl knob.
0 - unprivileged bpf() syscall access is enabled.
1 - unprivileged bpf() syscall access is disabled permanently.
2 - unprivileged bpf() syscall access is disabled.
Default value is 2.
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: <int>
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
userpte=
[X86,EARLY] Flags controlling user PTE allocations.
nohigh = do not allocate PTE pages in
HIGHMEM regardless of setting
of CONFIG_HIGHPTE.
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.
<size>@<baseaddr>:<irq>[:<id>]
where:
<size> := size (can use standard suffixes
like K, M and G)
<baseaddr> := physical base address
<irq> := interrupt number (as passed to
request_irq())
<id> := (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 <nn>. 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: <command>
vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
Format: <command>
vmpoff= [KNL,S390] Perform z/VM CP command after power off.
Format: <command>
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 <Esc>[?A;B;Cc escape sequence;
see VGA-softcursor.txt. Default: 2 = underline.
vt.default_blu= [VT]
Format: <blue0>,<blue1>,<blue2>,...,<blue15>
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: <green0>,<green1>,<green2>,...,<green15>
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: <red0>,<red1>,<red2>,...,<red15>
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: <cpu-list>
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=<uint>
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=<uint>
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: <bool>
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:
<irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
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.
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