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. 
-- 
<:-)~MIKE~(-:>






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