Converting your RHEL 5.x system to CentOS 5.x is relatively easy,
and will save you the pain of having to rebuild a system from the
ground up with a fresh install of CentOS. Updates and Conversions
Currently, RHEL is at release 5.2,
while CentOS is at release 5.1. If you have not yet updated to RHEL
5.2, do not do so before converting! If you have already
updated to RHEL 5.2, it is strongly suggested you wait until CentOS 5.2
is released before doing the conversion. Downloading Required Packages
To begin, you will need to
download the following packages. It's best to create a temporary
directory for the packages, and download them to that temporary
directory. Depending on which architecture your system is running, you will
need to download packages from a different directory on the CentOS
mirror:
- i386 (32-bit)
- ftp://mirror.ucsd.edu/centos/5/os/i386/CentOS/
- x86_64 (64-bit)
- ftp://mirror.ucsd.edu/centos/5/os/x86_64/CentOS/
- ia64 (Itanium)
- ftp://mirror.ucsd.edu/centos/5/os/ia64/CentOS/
From this directory, you will want to select these RPM packages:
- centos-release
- python-elementtree
- python-sqlite
- python-urlgrabber
- sqlite
- yum
- yum-metadata-parser
Removing RHEL Packages
Next, you have to remove some
specific packages from Red Hat. As root, run the following commands
on your system:
- rpm -e --nodeps redhat-release-notes redhat-release
- rpm -e yum-rhn-plugin
- service rhnsd stop
- rpm -e rhn-client-tools rhn-setup-gnome rhnlib rhn-setup
rhnsd rhn-check
Installing CentOS GPG Key
Now, we have to import the
CentOS 5 RPM GPG key, which is used to sign all the packages
provided by CentOS 5.
Installing CentOS Packages
Change into the temporary
directory you created for the packages you downloaded above (cd) and
run the following as root:
If you receive any warnings about a package already being installed,
or a newer version of a package already installed, simply delete the
downloaded package of the same name from your temporary directory,
and re-run the above command. The conversion will still work. Updating With CentOS Package
Once you've upgraded the
necessary packages from the set that you downloaded manually, you
can let yum take over and finish the job for you. Run the following
two command as root:
- yum clean all
- yum -y update
The "yum -y update" may or may not download anything, so
do not be alarmed if it doesn't do anything. That simply means your
system's packages are up to date with the latest available versions
provided by CentOS. Reboot
While not strictly necessary unless new kernel
packages are installed, it's strongly recommended that you now
reboot your system to fully activate all the system changes. You have now successfully completed your conversion from Red Hat
Enterprise Linux 5.x to CentOS 5.x.  | 
