Linux kernel configuration
There are three basic methods to configure a Linux kernel (easiest to hardest methods):
- modifying tunable kernel configuration parameters
- by loading new drivers and modules on the fly
- building a kernel from scratch (by compiling it from the source code)
Tuning Linux kernel parameters
To increase kernel flexibility, special hooks allow parameters to be adjusted on the fly by the admin. There hooks are accessible through an interface represented by files in the
/proc filesystem (
You can view and set kernel options at runtime via special files in
$ ls /proc/sys abi crypto debug dev fs kernel net sunrpc user vm
For example, to change max number of files that system can have open at once, try sth like:
$ cat /proc/sys/fs/file-max 392792 $ echo 392700 > !:1 echo 392700 > /proc/sys/fs/file-max $ cat /proc/sys/fs/file-max 392700
!:1 gets the first argument from previous command
NOTE: above changes are not remembered across reboots
To save changes permanently, use
sysctl command or edit
/etc/sysctl.conf file which is read at boot time and its contents are used to set the initial values.
IPv4 & IPv6
Note there are two separate directories of
/proc/sys/net/ipv6. When you change a parameter for IPv4, you should also do the same thing to IPv6 – if you support both protocols – which you should.
Loading a Linux device driver
Device drivers are typically distributed on one of three forms:
- loadable kernel module
- an installation script that installs the driver
The most common form is installation script or package. There should be installation documentation which you should be able to follow.
In case where you have a patch, following command should do:
$ cd kernel_directory $ patch -p1 < patch_file
Building a custom kernel
First of all, be careful when a new release of some kind of software comes into play – is it as stable as current version? A rule of thumb is to upgrade or apply patches only when it’s worth the risk.
It’s unlikely that you need to build a kernel while using a distro that uses a stable kernel version (even number should indicate stable version – though double check that on kernel.org).
In most distributions kernel source files lies in
/usr/src/kernels. Main kernel configuration file lies in
/usr/src/kernels/4.14.287-215.504.amzn2.x86_64/.config but it’s not advisable to edit it straight away due to cryptic format and interdependent options. To make admin life easier there are a few
make files that help you configure the kernel through a CLI, eg
$ cat Kconfig # SPDX-License-Identifier: GPL-2.0 # # For a description of the syntax of this configuration file, # see Documentation/kbuild/kconfig-language.txt. # mainmenu "Linux/$ARCH $KERNELVERSION Kernel Configuration" config SRCARCH string option env="SRCARCH" source "arch/$SRCARCH/Kconfig"
Here’s an outline of the entire process:
- Change directory (cd) to the top level of the kernel source directory.
- Run make xconfig, make gconfig, or make menuconfig.
- Run make clean.
- Run make.
- Run make modules_install.
- Run make install.