The kernel’s command-line parameters
The following is a consolidated list of the kernel parameters as implemented by the __setup(), early_param(), core_param() and module_param() macros and sorted into English Dictionary order (defined as ignoring all punctuation and sorting digits before letters in a case insensitive manner), and with descriptions where known.
The kernel parses parameters from the kernel command line up to “--“; if it doesn’t recognize a parameter and it doesn’t contain a ‘.’, the parameter gets passed to init: parameters with ‘=’ go into init’s environment, others are passed as command line arguments to init. Everything after “--” is passed as an argument to init.
Module parameters can be specified in two ways: via the kernel command line with a module name prefix, or via modprobe, e.g.:
(kernel command line) usbcore.blinkenlights=1 (modprobe command line) modprobe usbcore blinkenlights=1
Parameters for modules which are built into the kernel need to be specified on the kernel command line. modprobe looks through the kernel command line (/proc/cmdline) and collects module parameters when it loads a module, so the kernel command line can be used for loadable modules too.
Hyphens (dashes) and underscores are equivalent in parameter names, so:
log_buf_len=1M print-fatal-signals=1
can also be entered as:
log-buf-len=1M print_fatal_signals=1
Double-quotes can be used to protect spaces in values, e.g.:
param="spaces in here"
cpu lists:
Some kernel parameters take a list of CPUs as a value, e.g. isolcpus, nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
<cpu number>,…,<cpu number>
or
<cpu number>-<cpu number> (must be a positive range in ascending order)
or a mixture
<cpu number>,…,<cpu number>-<cpu number>
Note that for the special case of a range one can split the range into equal sized groups and for each group use some amount from the beginning of that group:
<cpu number>-<cpu number>:<used size>/<group size>
For example one can add to the command line following parameter:
isolcpus=1,2,10-20,100-2000:2/25
where the final item represents CPUs 100,101,125,126,150,151,…
This document may not be entirely up to date and comprehensive. The command “modinfo -p ${modulename}” shows a current list of all parameters of a loadable module. Loadable modules, after being loaded into the running kernel, also reveal their parameters in /sys/module/${modulename}/parameters/. Some of these parameters may be changed at runtime by the command echo -n ${value} > /sys/module/${modulename}/parameters/${parm}.
The parameters listed below are only valid if certain kernel build options were enabled and if respective hardware is present. The text in square brackets at the beginning of each description states the restrictions within which a parameter is applicable:
ACPI ACPI support is enabled.
AGP AGP (Accelerated Graphics Port) is enabled.
ALSA ALSA sound support is enabled.
APIC APIC support is enabled.
APM Advanced Power Management support is enabled.
ARM ARM architecture is enabled.
ARM64 ARM64 architecture is enabled.
AX25 Appropriate AX.25 support is enabled.
CLK Common clock infrastructure is enabled.
CMA Contiguous Memory Area support is enabled.
DRM Direct Rendering Management support is enabled.
DYNAMIC_DEBUG Build in debug messages and enable them at runtime
EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
EFI EFI Partitioning (GPT) is enabled
EIDE EIDE/ATAPI support is enabled.
EVM Extended Verification Module
FB The frame buffer device is enabled.
FTRACE Function tracing enabled.
GCOV GCOV profiling is enabled.
HW Appropriate hardware is enabled.
IA-64 IA-64 architecture is enabled.
IMA Integrity measurement architecture is enabled.
IOSCHED More than one I/O scheduler is enabled.
IP_PNP IP DHCP, BOOTP, or RARP is enabled.
IPV6 IPv6 support is enabled.
ISAPNP ISA PnP code is enabled.
ISDN Appropriate ISDN support is enabled.
ISOL CPU Isolation is enabled.
JOY Appropriate joystick support is enabled.
KGDB Kernel debugger support is enabled.
KVM Kernel Virtual Machine support is enabled.
LIBATA Libata driver is enabled
LP Printer support is enabled.
LOOP Loopback device support is enabled.
M68k M68k architecture is enabled.
These options have more detailed description inside of
Documentation/m68k/kernel-options.rst.
MDA MDA console support is enabled.
MIPS MIPS architecture is enabled.
MOUSE Appropriate mouse support is enabled.
MSI Message Signaled Interrupts (PCI).
MTD MTD (Memory Technology Device) support is enabled.
NET Appropriate network support is enabled.
NUMA NUMA support is enabled.
NFS Appropriate NFS support is enabled.
OF Devicetree is enabled.
OSS OSS sound support is enabled.
PV_OPS A paravirtualized kernel is enabled.
PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
PARISC The PA-RISC architecture is enabled.
PCI PCI bus support is enabled.
PCIE PCI Express support is enabled.
PCMCIA The PCMCIA subsystem is enabled.
PNP Plug & Play support is enabled.
PPC PowerPC architecture is enabled.
PPT Parallel port support is enabled.
PS2 Appropriate PS/2 support is enabled.
RAM RAM disk support is enabled.
RDT Intel Resource Director Technology.
S390 S390 architecture is enabled.
SCSI Appropriate SCSI support is enabled.
A lot of drivers have their options described inside
the Documentation/scsi/ sub-directory.
SECURITY Different security models are enabled.
SELINUX SELinux support is enabled.
APPARMOR AppArmor support is enabled.
SERIAL Serial support is enabled.
SH SuperH architecture is enabled.
SMP The kernel is an SMP kernel.
SPARC Sparc architecture is enabled.
SWSUSP Software suspend (hibernation) is enabled.
SUSPEND System suspend states are enabled.
TPM TPM drivers are enabled.
TS Appropriate touchscreen support is enabled.
UMS USB Mass Storage support is enabled.
USB USB support is enabled.
USBHID USB Human Interface Device support is enabled.
V4L Video For Linux support is enabled.
VMMIO Driver for memory mapped virtio devices is enabled.
VGA The VGA console has been enabled.
VT Virtual terminal support is enabled.
WDT Watchdog support is enabled.
XT IBM PC/XT MFM hard disk support is enabled.
X86-32 X86-32, aka i386 architecture is enabled.
X86-64 X86-64 architecture is enabled.
More X86-64 boot options can be found in
Documentation/x86/x86_64/boot-options.rst.
X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
X86_UV SGI UV support is enabled.
XEN Xen support is enabled
XTENSA xtensa architecture is enabled.
In addition, the following text indicates that the option:
BUGS= Relates to possible processor bugs on the said processor. KNL Is a kernel start-up parameter. BOOT Is a boot loader parameter.
Parameters denoted with BOOT are actually interpreted by the boot loader, and have no meaning to the kernel directly. Do not modify the syntax of boot loader parameters without extreme need or coordination with <The Linux/x86 Boot Protocol>.
There are also arch-specific kernel-parameters not documented here. See for example <AMD64 Specific Boot Options>.
Note that ALL kernel parameters listed below are CASE SENSITIVE, and that a trailing = on the name of any parameter states that that parameter will be entered as an environment variable, whereas its absence indicates that it will appear as a kernel argument readable via /proc/cmdline by programs running once the system is up.
The number of kernel parameters is not limited, but the length of the complete command line (parameters including spaces etc.) is limited to a fixed number of characters. This limit depends on the architecture and is between 256 and 4096 characters. It is defined in the file ./include/asm/setup.h as COMMAND_LINE_SIZE.
Finally, the [KMG] suffix is commonly described after a number of kernel parameter values. These ‘K’, ‘M’, and ‘G’ letters represent the _binary_ multipliers ‘Kilo’, ‘Mega’, and ‘Giga’, equaling 2^10, 2^20, and 2^30 bytes respectively. Such letter suffixes can also be entirely omitted:
acpi= [HW,ACPI,X86,ARM64]
Advanced Configuration and Power Interface
Format: { force | on | off | strict | noirq | rsdt |
copy_dsdt }
force -- enable ACPI if default was off
on -- enable ACPI but allow fallback to DT [arm64]
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
For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
are available
See also Documentation/power/runtime_pm.rst, pci=noacpi
acpi_apic_instance= [ACPI, IOAPIC]
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
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_PCI_COMPONENT
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 PCI/PCI interrupt routing info messages:
acpi.debug_layer=0x400000
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]
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>
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]
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]
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] ACPI System Control Interrupt trigger mode
Format: { level | edge | high | low }
acpi_skip_timer_override [HW,ACPI]
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_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_nohwsig prevents ACPI hardware signature from being
used during resume from hibernation.
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]
Use timer override. For some broken Nvidia NF5 boards
that require a timer override, but don't have HPET
add_efi_memmap [EFI; X86] 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.
amd_iommu= [HW,X86-64]
Pass parameters to the AMD IOMMU driver in the system.
Possible values are:
fullflush - enable flushing of IO/TLB entries when
they are unmapped. Otherwise they are
flushed before they will be reused, which
is a lot of faster
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
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.)
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] 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] 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.
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
apm= [APM] Advanced Power Management
See header of arch/x86/kernel/apm_32.c.
arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
Format: <io>,<irq>,<nodeID>
arm64.nobti [ARM64] Unconditionally disable Branch Target
Identification support
arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
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.
blkdevparts= Manual partition parsing of block device(s) for
embedded devices based on command line input.
See Documentation/block/cmdline-partition.rst
boot_delay= Milliseconds to delay each printk during boot.
Values larger than 10 seconds (10000) are changed to
no delay (0).
Format: integer
bootconfig [KNL]
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
bert_disable [ACPI]
Disable BERT OS support on buggy BIOSes.
bgrt_disable [ACPI][X86]
Disable BGRT to avoid flickering OEM logo.
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] 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/s390/common_io.rst for details.
cgroup_disable= [KNL] Disable a particular controller
Format: {name of the controller(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
{Currently only "memory" controller deal with this and
cut the overhead, others just disable the usage. So
only cgroup_disable=memory is actually worthy}
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.memory= [KNL] Pass options to the cgroup memory controller.
Format: <string>
nosocket -- Disable socket memory accounting.
nokmem -- Disable kernel 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/s390/common_io.rst for details.
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]
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.
clearcpuid=BITNUM[,BITNUM...] [X86]
Disable CPUID feature X for the kernel. See
arch/x86/include/asm/cpufeatures.h for the valid bit
numbers. Note the Linux specific bits are not necessarily
stable over kernel options, but the vendor specific
ones should be.
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.
cma=nn[MG]@[start[MG][-end[MG]]]
[KNL,CMA]
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]
[ARM64,KNL,CMA]
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
specificed, 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.
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]
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=
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.
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.
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
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] 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
cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
Format:
<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
crashkernel=size[KMG][@offset[KMG]]
[KNL] 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] 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] 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] 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 at
at least 256M below 4G automatically.
This one let user to 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 }
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
ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
time. See
Documentation/admin-guide/dynamic-debug-howto.rst for
details. Deprecated, see dyndbg.
debug [KNL] Enable kernel debugging (events log level).
debug_boot_weak_hash
[KNL] 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] Enable object debugging
no_debug_objects
[KNL] Disable object debugging
debug_guardpage_minorder=
[KNL] 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_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 programing 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] 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] 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
decnet.addr= [HW,NET]
Format: <area>[,<node>]
See also Documentation/networking/decnet.rst.
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. This option will also
dump out devices still on the deferred probe list after
retrying.
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]
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.
stress_slb [PPC]
Limits the number of kernel SLB entries, and flushes
them frequently to increase the rate of SLB faults
on kernel addresses.
disable= [IPV6]
See Documentation/networking/ipv6.rst.
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.
disable_radix [PPC]
Disable RADIX MMU mode on POWER9
radix_hcall_invalidate=on [PPC/PSERIES]
Disable RADIX GTSE feature and use hcall for TLB
invalidate.
disable_tlbie [PPC]
Disable TLBIE instruction. Currently does not work
with KVM, with HASH MMU, or with coherent accelerators.
disable_cpu_apicid= [X86,APIC,SMP]
Format: <int>
The number of initial APIC ID for the
corresponding CPU to be disabled at boot,
mostly used for the kdump 2nd kernel to
disable BSP to wake up multiple CPUs without
causing system reset or hang due to sending
INIT from AP to BSP.
disable_ddw [PPC/PSERIES]
Disable Dynamic DMA Window support. Use this
to workaround buggy firmware.
disable_ipv6= [IPV6]
See Documentation/networking/ipv6.rst.
disable_mtrr_cleanup [X86]
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]
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]
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.
driver_async_probe= [KNL]
List of driver names to be probed asynchronously.
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.
Generic built-in EDID data sets are used, if one of
edid/1024x768.bin, edid/1280x1024.bin,
edid/1680x1050.bin, or edid/1920x1080.bin is given
and no file with the same name exists. Details and
instructions how to build your own EDID data are
available in Documentation/admin-guide/edid.rst. 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]
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.
nopku [X86] Disable Memory Protection Keys CPU feature found
in some Intel CPUs.
<module>.async_probe [KNL]
Enable asynchronous probe on this module.
early_ioremap_debug [KNL]
Enable debug messages in early_ioremap support. This
is useful for tracking down temporary early mappings
which are not unmapped.
earlycon= [KNL] 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]
uart[8250],mmio,<addr>[,options]
uart[8250],mmio32,<addr>[,options]
uart[8250],mmio32be,<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.
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.
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.
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]
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 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, efi, 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 and EFI output is eventually overwritten by
the real console.
The xen output can only be used by Xen PV guests.
The sclp output can only be used on s390.
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.
ekgdboc= [X86,KGDB] Allow early kernel console debugging
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.
edd= [EDD]
Format: {"off" | "on" | "skip[mbr]"}
efi= [EFI]
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]
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.
efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
Add arbitrary attribute to specific memory range by
updating original EFI memory map.
Region of memory which aa attribute is added to is
from ss to ss+nn.
If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
attribute is added to range 0x100000000-0x180000000 and
0x10a0000000-0x1120000000.
If efi_fake_mem=8G@9G:0x40000 is specified, the
EFI_MEMORY_SP(0x40000) attribute is added to
range 0x240000000-0x43fffffff.
Using this parameter you can do debugging of EFI memmap
related features. For example, you can do debugging of
Address Range Mirroring feature even if your box
doesn't support it, or mark specific memory as
"soft reserved".
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.
elanfreq= [X86-32]
See comment before function elanfreq_setup() in
arch/x86/kernel/cpu/cpufreq/elanfreq.c.
elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
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]
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.
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.
force_pal_cache_flush
[IA-64] Avoid check_sal_cache_flush which may hang on
buggy SAL_CACHE_FLUSH implementations. Using this
parameter will force ia64_sal_cache_flush to call
ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
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.
ftrace=[tracer]
[FTRACE] will set and start the specified tracer
as early as possible in order to facilitate early
boot debugging.
ftrace_dump_on_oops[=orig_cpu]
[FTRACE] will dump the trace buffers on oops.
If no parameter is passed, ftrace will dump
buffers of all CPUs, but if you pass orig_cpu, it will
dump only the buffer of the 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] 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] Treat all inferred dependencies as mandatory
dependencies. This only applies for fw_devlink=on|rpm.
Format: <bool>
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] disable the fix e820 for K8 GART
Format: off | on
default: on
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
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
gpio-mockup.gpio_mockup_ranges
[HW] Sets the ranges of gpiochip of for this device.
Format: <start1>,<end1>,<start2>,<end2>...
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)
hcl= [IA-64] SGI's Hardware Graph compatibility layer
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.
highmem=nn[KMG] [KNL,BOOT] 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]
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.
hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation
of gigantic hugepages.
Format: 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.
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. See also
Documentation/admin-guide/mm/hugetlbpage.rst.
Format: <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]
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] Disables the paravirt spinlock optimizations
which allow the hypervisor to 'idle' the
guest on lock contention.
keep_bootcon [KNL]
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.
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>
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
i810= [HW,DRM]
i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
indicates that the driver is running on unsupported
hardware.
i8k.force [HW] Activate i8k driver even if SMM BIOS signature
does not match list of supported models.
i8k.power_status
[HW] Report power status in /proc/i8k
(disabled by default)
i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
capability is set.
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
icn= [HW,ISDN]
Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
ide-core.nodma= [HW] (E)IDE subsystem
Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
.vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
.cdrom .chs .ignore_cable are additional options
See Documentation/ide/ide.rst.
ide-generic.probe-mask= [HW] (E)IDE subsystem
Format: <int>
Probe mask for legacy ISA IDE ports. Depending on
platform up to 6 ports are supported, enabled by
setting corresponding bits in the mask to 1. The
default value is 0x0, which has a special meaning.
On systems that have PCI, it triggers scanning the
PCI bus for the first and the second port, which
are then probed. On systems without PCI the value
of 0x0 enables probing the two first ports as if it
was 0x3.
ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
Claim all unknown PCI IDE storage controllers.
idle= [X86]
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).
ieee754= [MIPS] Select IEEE Std 754 conformance mode
Format: { strict | legacy | 2008 | relaxed }
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
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]
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-sig" }
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.
initrd= [BOOT] Specify the location of the initial ramdisk
initrdmem= [KNL] 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] 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] 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.
forcedac [X86-64]
With this option iommu will not optimize to look
for io virtual address below 32-bit forcing dual
address cycle on pci bus for cards supporting greater
than 32-bit addressing. The default is to look
for translation below 32-bit and if not available
then look in the higher range.
strict [Default Off]
With this option on every unmap_single operation will
result in a hardware IOTLB flush operation as opposed
to batching them for performance.
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 [Default Off]
By default, scalable mode will be disabled even if the
hardware advertises that it has support for the scalable
mode translation. With this option set, scalable mode
will be used on hardware which claims to support it.
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]
disable
Do not enable intel_pstate as the default
scaling driver for the supported processors
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]
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
iomem= Disable strict checking of access to MMIO memory
strict regions from userspace.
relaxed
iommu= [X86]
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.strict= [ARM64] 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 (default).
DMA unmap operations invalidate IOMMU hardware TLBs
synchronously.
iommu.passthrough=
[ARM64, X86] 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] 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] Extend the maximum number of unique System V
IPC identifiers from 32,768 to 16,777,216.
irqaffinity= [SMP] Set the default irq affinity mask
The argument is a cpu list, as described above.
irqchip.gicv2_force_probe=
[ARM, ARM64]
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]
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]
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. For
example, to map IOAPIC-ID decimal 10 to
PCI device 00:14.0 write the parameter as:
ivrs_ioapic[10]=00:14.0
ivrs_hpet [HW,X86-64]
Provide an override to the HPET-ID<->DEVICE-ID
mapping provided in the IVRS ACPI table. For
example, to map HPET-ID decimal 0 to
PCI device 00:14.0 write the parameter as:
ivrs_hpet[0]=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. For
example, to map UART-HID:UID AMD0020:0 to
PCI device 00:14.5 write the parameter as:
ivrs_acpihid[00:14.5]=AMD0020:0
js= [HW,JOY] Analog joystick
See Documentation/input/joydev/joystick.rst.
nokaslr [KNL]
When CONFIG_RANDOMIZE_BASE is set, this disables
kernel and module base offset ASLR (Address Space
Layout Randomization).
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.
keepinitrd [HW,ARM]
kernelcore= [KNL,X86,IA-64,PPC]
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] 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]
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] 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] 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] Control page table isolation of user
and kernel address spaces.
Default: enabled on cores which need mitigation.
0: force disabled
1: force enabled
kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
Default is 0 (don't ignore, but inject #GP)
kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
Default is false (don't support).
kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
KVM MMU at runtime.
Default is 0 (off)
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
minute. The default is 60.
kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
Default is 1 (enabled)
kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
for all guests.
Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
kvm-arm.mode=
[KVM,ARM] Select one of KVM/arm64's modes of operation.
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.
Not valid if the kernel is running in EL2.
Defaults to VHE/nVHE based on hardware support and
the value of CONFIG_ARM64_VHE.
kvm-arm.vgic_v3_group0_trap=
[KVM,ARM] Trap guest accesses to GICv3 group-0
system registers
kvm-arm.vgic_v3_group1_trap=
[KVM,ARM] Trap guest accesses to GICv3 group-1
system registers
kvm-arm.vgic_v3_common_trap=
[KVM,ARM] Trap guest accesses to GICv3 common
system registers
kvm-arm.vgic_v4_enable=
[KVM,ARM] Allow use of GICv4 for direct injection of
LPIs.
kvm_cma_resv_ratio=n [PPC]
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] Disable extended page tables
(virtualized MMU) support on capable Intel chips.
Default is 1 (enabled)
kvm-intel.emulate_invalid_guest_state=
[KVM,Intel] Enable emulation of invalid guest states
Default is 0 (disabled)
kvm-intel.flexpriority=
[KVM,Intel] Disable FlexPriority feature (TPR shadow).
Default is 1 (enabled)
kvm-intel.nested=
[KVM,Intel] Enable VMX nesting (nVMX).
Default is 0 (disabled)
kvm-intel.unrestricted_guest=
[KVM,Intel] Disable unrestricted guest feature
(virtualized real and unpaged mode) on capable
Intel chips. Default is 1 (enabled)
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] Disable Virtual Processor Identification
feature (tagged TLBs) on capable Intel chips.
Default is 1 (enabled)
l1tf= [X86] 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] 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] 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 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's 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.
* [no]ncq: Turn on or off NCQ.
* [no]ncqtrim: Turn off queued DSM TRIM.
* nohrst, nosrst, norst: suppress hard, soft
and both resets.
* rstonce: only attempt one reset during
hot-unplug link recovery
* dump_id: dump IDENTIFY data.
* atapi_dmadir: Enable ATAPI DMADIR bridge support
* disable: Disable this device.
If there are multiple matching configurations changing
the same attribute, the last one is used.