View Current Kernel Configuration¶
The Linux kernel stores running kernel information in two places via special filesystems: (A summary of them)
- The older procfs which mounts
/proc
(verify viamount -l -t proc
) - The newer sysfs which mounts
/sys
(verify viamount -l -t sysfs
)
Warning
Be cautious if examining the files mentioned here, altering them can change the behavior of the actual running kernel!
These two interfaces allow you to view and change the parameters of the currently running kernel.
Note that if you do an ls -l
on some of these files, they will show as "0" length, but if you cat
them out they actually contain data. Most of them are ASCII and editable, however some are binary. In either case commands like file
or stat
will typically just return "empty file" or "0" for lengths, although they will show you other information.
The preferred and standard programs for interacting with these functions are lsmod
, modinfo
, and sysctl
, among others.
sysctl -a | grep -i <keyword>
lsmod | grep -i <keyword>
modinfo <module>
See what your currently running "kernel release" version is with:
uname -r
and substitute its return value in commands by using $(uname -r)
RHEL and derivative distributions (Fedora, CentOS Stream, Scientific Linux, RockyLinux, AlmaLinux, et. al.)
also store the configuration used for bootable installed kernels in the /boot
directory used by Grub2 as ASCII files:
/boot/config-<kernel-release>
To check the currently running kernel configuration for a particular value:
cat /boot/config-$(uname -r) | grep -i <keyword>
Results will show:
=m
if compiled in as a kernel module=y
if compiled statically into the kernelis not set
if that setting was commented out- a numeric value
- a quoted string value
Some distributions, like Gentoo and Arch, use the configs
kernel module to provide /proc/config.gz
by default instead:
zcat /proc/config.gz | grep -i <keyword>
zgrep <keyword> /proc/config.gz
For any distribution, if your running kernel has set both CONFIG_IKCONFIG
and CONFIG_IKCONFIG_PROC
and if
ls -lh /sys/module/configs
exists and is executable (searchable in the case of a dir) then you can create /proc/config.gz
with this command if it is not present:
modprobe configs
Enabled Repos
This document does not currently cover kernel packages that might have come from non-default repos such as:
appstream-debug, appstream-source, baseos-debug, baseos-source, or devel
The kernel-devel
packages install the config file used to compile each installed standard kernel package as an ASCII file in the following location:
/usr/src/kernels/<kernel-release>/.config
This file is more commonly accessed by a symlinked path provided by the kernel-core
packages:
/lib/modules/<kernel-release>/build/ -> /usr/src/kernels/<kernel-release>/
If you have kernel-debug-devel
packages installed, you will also have this directory:
/usr/src/kernels/<kernel-release>+debug/
You can look in any of the following for details on the config values used to build an installed kernel:
/lib/modules/<kernel-release>/config
/lib/modules/<kernel-release>/build/.config
/usr/src/kernels/<kernel-release>/.config
/usr/src/kernels/<kernel-release>+debug/.config
Configured modules for the currently running kernel, whether compiled as builtin (i.e., statically into the kernel itself) or a loadable module, are listed by sub directories named as the module name in:
/sys/module/
For each installed kernel-release you can examine these files to see what values were compiled into that kernel, and what version of GCC was used to compile it:
cat /lib/modules/$(uname -r)/config | grep -i <keyword>
cat /lib/modules/$(uname -r)/build/.config | grep -i <keyword>
cat /usr/src/kernels/$(uname -r)/.config | grep -i <keyword>
cat /usr/src/kernels/$(uname -r)+debug/.config | grep -i <keyword>
ls -lh /sys/module/ | grep -i <keyword>
You can check for kernel module dependencies in the file:
/lib/modules/<kernel-release>/modules.dep
but it is easier to read or parse the output of the "Used-by" field in lsmod
.
Reference¶
depmod, ls, lsmod, modinfo, modprobe, modules.dep, namespaces, procfs, sysctl, sysfs, uname
Author: David Hensley
Contributors: Steven Spencer