How to Compile the Linux Kernel
James Andrews
Saturday, May 29, 1999 01:36:47 PM
Introduction
RedHat is not Linux, it is a distribution based on the Linux kernel. 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.
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.
--
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