Problem scenario
You are running "sudo yum install foobar" but it is not working. You are trying to install a package on a RHEL server, but it is not available from the configured repositories. You notice that many packages you normally install are not available. What should you do?
Solution
Run this command:
sudo yum-config-manager --enable rhui-REGION-rhel-server-extras rhui-REGION-rhel-server-optional
FFR
To find the number of packages available to you in the configured repository (or repositories), run this command:
sudo yum list available | nl | tail -n 1 | awk '{print $1}'
To learn more about yum commands, see this PDF that RedHat.com provides.