CentOS 4 has been EOL since March 2012. As there is no upgrade path from 4 to 5, many of you may still be running CentOS 4 systems.
At the time of the EOL announcement, the yum repository for CentOS 4 was shutdown. This meant that if you still needed to update packages that were recently updated in the repo, you were out of luck.
The CentOS 4 team announced that the repository has been re-enabled for people that absolutely need their CentOS 4 machine running (PLEASE UPGRADE IF YOU DON’T!). You can re-enable the repository by downloading this file here, placing it in your /etc/yum.repos.d/ directory, and replacing the one that exists there now.
Again, PLEASE UPGRADE TO CENTOS 5 or CENTOS 6 IF YOU DON’T NEED A CENTOS 4 MACHINE RUNNING. This news is great for people that are still migrating off of CentOS 4 or need that C4 machine as it contains many recent critical updates. For example, recent OpenSSL vulnerability patches.