Has anyone ever tried to mass replace installed RedHat RPMS with their equivalent CentOS versions or vice versa? I was thinking of generating a list of all packages and then running RPM or yum with a 'replace' option. The reason for doing this: Years ago I was tasked with building a RHEL4 system. Budgeting, time constraints, the lunar cycle, etc.., prevented the purchase of an equivalent development environment. So CentOS was used for the development/test system. It sufficed for several years. Now I need to make them as close to identical as possible which means registering the development system in RHN and making it "standard". I've seen posts that RHEL -> CentOS is at least possible. That is, take a RHEL system and get it to update via YUM and CentOS repositories. I have not seen the reverse, however.