linux/Documentation/admin-guide/kernel-parameters.rst
Linus Torvalds 9ad55a67a7 soundwire updates for 6.13
- structure optimization of few bus structures and header updates
  - support for 2.0 disco spec
  - amd driver updates for acp revision, refactoring code and support for
    acp6.3
  - soft reset support for cadence driver
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Merge tag 'soundwire-6.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vkoul/soundwire

Pull soundwire updates from Vinod Koul:

 - structure optimization of few bus structures and header updates

 - support for 2.0 disco spec

 - amd driver updates for acp revision, refactoring code and support for
   acp6.3

 - soft reset support for cadence driver

* tag 'soundwire-6.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vkoul/soundwire: (24 commits)
  soundwire: Minor formatting fixups in sdw.h header
  soundwire: Update the includes on the sdw.h header
  soundwire: cadence: clear MCP BLOCK_WAKEUP in init
  soundwire: cadence: add soft-reset on startup
  soundwire: intel_auxdevice: add kernel parameter for mclk divider
  soundwire: mipi-disco: add support for DP0/DPn 'lane-list' property
  soundwire: mipi-disco: add new properties from 2.0 spec
  soundwire: mipi-disco: add comment on DP0-supported property
  soundwire: mipi-disco: add support for peripheral channelprepare timeout
  soundwire: mipi_disco: add support for clock-scales property
  soundwire: mipi-disco: add error handling for property array read
  soundwire: mipi-disco: remove DPn audio-modes
  soundwire: optimize sdw_dpn_prop
  soundwire: optimize sdw_dp0_prop
  soundwire: optimize sdw_slave_prop
  soundwire: optimize sdw_bus structure
  soundwire: optimize sdw_master_prop
  soundwire: optimize sdw_stream_runtime memory layout
  soundwire: mipi_disco: add MIPI-specific property_read_bool() helpers
  soundwire: Correct some typos in comments
  ...
2024-11-27 13:38:09 -08:00

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.. _kernelparameters:
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.
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}``.
Special handling
----------------
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,...
The value "N" can be used to represent the numerically last CPU on the system,
i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
Keep in mind that "N" is dynamic, so if system changes cause the bitmap width
to change, such as less cores in the CPU list, then N and any ranges using N
will also change. Use the same on a small 4 core system, and "16-N" becomes
"16-3" and now the same boot input will be flagged as invalid (start > end).
The special case-tolerant group name "all" has a meaning of selecting all CPUs,
so that "nohz_full=all" is the equivalent of "nohz_full=0-N".
The semantics of "N" and "all" is supported on a level of bitmaps and holds for
all users of bitmap_parselist().
Metric suffixes
~~~~~~~~~~~~~~~
The [KMG] suffix is commonly described after a number of kernel
parameter values. 'K', 'M', 'G', 'T', 'P', and 'E' suffixes are allowed.
These letters represent the _binary_ multipliers 'Kilo', 'Mega', 'Giga',
'Tera', 'Peta', and 'Exa', equaling 2^10, 2^20, 2^30, 2^40, 2^50, and
2^60 bytes respectively. Such letter suffixes can also be entirely omitted.
Kernel Build Options
--------------------
The parameters listed below are only valid if certain kernel build options
were enabled and if respective hardware is present. This list should be kept
in alphabetical order. 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.
APPARMOR AppArmor 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
EARLY Parameter processed too early to be embedded in initrd.
EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
EFI EFI Partitioning (GPT) is enabled
EVM Extended Verification Module
FB The frame buffer device is enabled.
FTRACE Function tracing enabled.
GCOV GCOV profiling is enabled.
HIBERNATION HIBERNATION is enabled.
HW Appropriate hardware is enabled.
HYPER_V HYPERV support is enabled.
IMA Integrity measurement architecture 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
LOONGARCH LoongArch architecture is enabled.
LOOP Loopback device support is enabled.
LP Printer support is enabled.
M68k M68k architecture is enabled.
These options have more detailed description inside of
Documentation/arch/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.
NFS Appropriate NFS support is enabled.
NUMA NUMA support is enabled.
OF Devicetree 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.
PV_OPS A paravirtualized kernel is enabled.
RAM RAM disk support is enabled.
RDT Intel Resource Director Technology.
RISCV RISCV architecture is enabled.
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.
SDW SoundWire support is enabled.
SECURITY Different security models are enabled.
SELINUX SELinux 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.
SUSPEND System suspend states are enabled.
SWSUSP Software suspend (hibernation) is enabled.
TPM TPM drivers are 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.
VGA The VGA console has been enabled.
VMMIO Driver for memory mapped virtio devices is enabled.
VT Virtual terminal support is enabled.
WDT Watchdog 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/arch/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::
BOOT Is a boot loader parameter.
BUGS= Relates to possible processor bugs on the said processor.
KNL Is a kernel start-up 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 <Documentation/arch/x86/boot.rst>.
There are also arch-specific kernel-parameters not documented here.
See for example <Documentation/arch/x86/x86_64/boot-options.rst>.
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/uapi/asm-generic/setup.h as COMMAND_LINE_SIZE.
.. include:: kernel-parameters.txt
:literal: