After a recent upgrade of a server from CentOS 4.4 to 5.1 using yum, I ran into a bit of a problem with rpm. Pretty much any rpm command would result in the following error: rpmdb: Program version 4.3 doesn’t match environment version error: db4 error(-30974) from dbenv->open: DB_VERSION_MISMATCH: Database environment version mismatch error: cannot open Packages index using db3 - (-30974) error: cannot open Packages database in /var/lib/rpm

The solution as suggested on a Fedora forum was: rm /var/lib/rpm/__db.* rpm –rebuilddb Once this had finished, everything was back to normal.