linux/Documentation/admin-guide/kernel-parameters.rst
Linus Torvalds 9a45da9270 RCU changes for this cycle were:
- Bitmap support for "N" as alias for last bit
  - kvfree_rcu updates
  - mm_dump_obj() updates.  (One of these is to mm, but was suggested by Andrew Morton.)
  - RCU callback offloading update
  - Polling RCU grace-period interfaces
  - Realtime-related RCU updates
  - Tasks-RCU updates
  - Torture-test updates
  - Torture-test scripting updates
  - Miscellaneous fixes
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'core-rcu-2021-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU updates from Ingo Molnar:

 - Support for "N" as alias for last bit in bitmap parsing library (eg
   using syntax like "nohz_full=2-N")

 - kvfree_rcu updates

 - mm_dump_obj() updates. (One of these is to mm, but was suggested by
   Andrew Morton.)

 - RCU callback offloading update

 - Polling RCU grace-period interfaces

 - Realtime-related RCU updates

 - Tasks-RCU updates

 - Torture-test updates

 - Torture-test scripting updates

 - Miscellaneous fixes

* tag 'core-rcu-2021-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (77 commits)
  rcutorture: Test start_poll_synchronize_rcu() and poll_state_synchronize_rcu()
  rcu: Provide polling interfaces for Tiny RCU grace periods
  torture: Fix kvm.sh --datestamp regex check
  torture: Consolidate qemu-cmd duration editing into kvm-transform.sh
  torture: Print proper vmlinux path for kvm-again.sh runs
  torture: Make TORTURE_TRUST_MAKE available in kvm-again.sh environment
  torture: Make kvm-transform.sh update jitter commands
  torture: Add --duration argument to kvm-again.sh
  torture: Add kvm-again.sh to rerun a previous torture-test
  torture: Create a "batches" file for build reuse
  torture: De-capitalize TORTURE_SUITE
  torture: Make upper-case-only no-dot no-slash scenario names official
  torture: Rename SRCU-t and SRCU-u to avoid lowercase characters
  torture: Remove no-mpstat error message
  torture: Record kvm-test-1-run.sh and kvm-test-1-run-qemu.sh PIDs
  torture: Record jitter start/stop commands
  torture: Extract kvm-test-1-run-qemu.sh from kvm-test-1-run.sh
  torture: Record TORTURE_KCONFIG_GDB_ARG in qemu-cmd
  torture: Abstract jitter.sh start/stop into scripts
  rcu: Provide polling interfaces for Tree RCU grace periods
  ...
2021-04-28 12:00:13 -07:00

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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.
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).
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.
RISCV RISCV architecture 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 <Documentation/x86/boot.rst>.
There are also arch-specific kernel-parameters not documented here.
See for example <Documentation/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/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:
.. include:: kernel-parameters.txt
:literal:
Todo
----
Add more DRM drivers.