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Using yum to upgrade from Red Hat Linux 9 to CentOS 3.1

1. Update the subject system to the terminal updates of the prior release, probably using yum, and remove any unneeded packages. Package removal is beyond the scope of this document, but is done using the rpm -e (packagename) approach.
   
   Particularly watch for and remove unneeded or unused development packages. This is needed to address the fact that a RHEL derived base system will not have the rich range of '-devel' packages which RHL 9 carried.
   
   
2. Clear sufficient space in the filesystem, and get a local archive of the CentOS RPMs in place. This may be done by retrieval of the ISO images from a CentOS mirror, and then progressively mounting each of the images in turn on the loopback device and using:
   cp /path/to/mount/RedHat/RPM/* /path/to/local/copy/
   Again, lookback mounting and ISO usage are matters are beyond the scope of this document, but are more fully discussed in our discussion about the tools for PXE installs, which notes are also fully applicable for use with CentOS-31.
   
   
3. Pull and also copy in the updates from a CentOS mirror into that same local copy point. [Strictly speaking, this addition of the updates should not be immediately necessary, but the original CentOS 3.1 ISOs had an improper dependency on three perl modules, which is addressed in the updates, and fixed in later ISOs -- we mention it to avoid an issue which also discussed in the CentOS Build8 to final Release notes.]
   
   
4. Build a yum archive for that local RPM set:
   cd /path/to/local/copy/ yum-arch .
5. Import the CentOS GPG rpm-signing key (local copy), which is found on the ISO image, or at the mirror site, using, eg,:
   rpm --import http://mirror.caosity.org/centos-3/RPM-GPG-KEY-CentOS-3
6. Put together a minimal /etc/yum-upgrade.conf:
   [main] cachedir=/var/cache/yum debuglevel=2 logfile=/var/log/yum.log pkgpolicy=newest distroverpkg=redhat-release installonlypkgs=kernel kernel-smp kernel-hugemem kernel-enterprise kernel-debug kernel-unsupported kernel-smp-unsupported kernel-hugemem-unsupported tolerant=1 exactarch=1 [upgrade] name=Centos upgrade baseurl=file://localhost/path/to/local/copy/ # this may commented out when using the respin ISO # or with the [update] stanza below # [base] # name=CentOS-$releasever - Base # baseurl=http://mirror.centos.org/centos/3.1/os/$basearch/ #released updates [update] name=CentOS-$releasever - Updates baseurl=http://mirror.centos.org/centos/3.1/updates/$basearch/
7. Alternatively, for a 'wire' upgrade we could use:
   [main] cachedir=/var/cache/yum debuglevel=2 logfile=/var/log/yum.log pkgpolicy=newest distroverpkg=redhat-release installonlypkgs=kernel kernel-smp kernel-hugemem kernel-enterprise kernel-debug kernel-unsupported kernel-smp-unsupported kernel-hugemem-unsupported tolerant=1 exactarch=1 [base] name=CentOS-$releasever - Base baseurl=http://mirror.centos.org/centos/3.1/os/$basearch/ #released updates [update] name=CentOS-$releasever - Updates baseurl=http://mirror.centos.org/centos/3.1/updates/$basearch/
8. As a matter of safety, upgrade rpm, the kernel and their dependencies first:
   rpm -vv --rebuilddb yum -y -t -c /etc/yum-upgrade.conf upgrade rpm kernel rpm -vv --rebuilddb yum -y -t -c /etc/yum-upgrade.conf upgrade rpm kernel
   (yum, yum.conf and yum-arch each have excellent and current man pages for the curious), and then inspect the bootloader (hopefully grub at this time), and reboot, just to let any library updates take effect.
   
   
9. Then, let's do the rest:
   yum -y -t -c /etc/yum-upgrade.conf upgrade

Sample CentOS /etc/yum.conf

Acknowledgement