If you get a message similar to this:

[username@localhost ~]$ sudo yum update
rpmdb: Thread/process 2402/139688794072832 failed: Thread died in Berkeley DB library
error: db4 error(-30974) from dbenv->failchk: DB_RUNRECOVERY: Fatal error, run database recovery
error: cannot open Packages index using db3 - (-30974)
error: cannot open Packages database in /var/lib/rpm

Error: rpmdb open failed


You can fix it by running the following 3 commands:

[username@localhost ~]$ sudo rm -f /var/lib/rpm/__db*
[username@localhost ~]$ sudo db_verify /var/lib/rpm/Packages
[username@localhost ~]$ sudo rpm --rebuilddb