The Linux kernel is a complex program which provides
the underlying services to the rest of a Linux distribution. But it is easy to
add new features or improvments to it as, unlike commercial operating systems
like Windows 95 or MacOS, the source code is freely available. It is common
practice with a Linux based operating system to recompile the kernel from source
and much effort has been put in to make this a realitively user-friendly
experience.
Why Compile a New Kernel?
You may be thinking "But why recompile it? It
works fine as it is." There are three reasons for a recompile. Firstly, you
may have some hardware that is so new that there's no kernel module for it in on
your distribution CD. Secondly, you may have come across some kind of bug which
is fixed in a revision of the operating system. Lastly, you may have some new
software which requires a newer version of the operating system.
Getting the Kernel Sources
The most recent releases of the kernel sources are
available on ftp.kernel.org. This site is
mirrored worldwide so there is probably a fast copy of it somewhere near you.
Locate the file for the latest version of the operating system and download it
to /usr/src. Then issue the tar zxf command to unpack it.
Alternatively, if you already have the
kernel sources and only need to upgrade one version number (from 2.2.1
to 2.2.2 for instance) then download the patch file to /usr/src
and then use the command:
gzip -dc patch-2.2.2.gz |patch -p0
to upgrade your old kernel sources. Patch
files are much smaller to download than the whole thing.
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If you do not need the very latest version, then
installing a kernel source package from your distribution CD may be an easier
way to proceed.
Configuring For a Build
Change directory to /usr/src/Linux and issue the
command:
make menuconfig
This will build a few programs and then quickly
pop up a window. The window menu lets you alter many aspects of kernel
configuration.
After you have made any necessary changes, save
the configuration and follow these instructions--do a
make dep; make clean
The first of these commands builds the tree of
interdependencies in the kernel sources. These dependencies may have been
affected by the options you have choosen in the configure step. The make clean
purges any now-unwanted files left from previous builds of the kernel.
Then you are ready to go! Issue this command:
make zImage
and then, if you are on a machine slower than a
Pentium 200, go and make a cup of tea. This takes about 20 minutes on a Pentium
90...the kernel has a lot of source code as you may have noticed when
downloading it. When this is complete do a:
make modules
This will not take as long.
Installing a New Kernel
Phew, finally! The last step is installing the new
kernel. On an Intel-based system the kernel is installed to the right place in
/boot with the command
cp /usr/Linux/src/arch/i386/boot/zImage
/boot/newkernel
then
make modules_install
This will install the modules in /lib/modules.
Next, edit /etc/lilo.conf to add a section like this
image = /boot/newkernel
label = new
read-only
At the next reboot, select the kernel 'new' in
lilo, and it will load the new kernel. If it works fine, move it to the first
position in the lilo.conf so it will boot every time by default.
Summary
Compiling the kernel is a relatively simple
operation- if you have done it before! At first it can seem daunting. There are
many Web sites dedicated to the kernel; at the left are just a few.
Good Luck :)
