Oracle XE 12c won't configure - getting the "port 5,500 in use" error message
I found the solution with the assistance of our DBA team.

The problem was I using a fully qualified hostname in the /etc/hosts file. I had interpreted the solutions I found that cited "hostnames must match" to include the domain name as well.

If your hostname is xxxx.yyyy.zzzz, then you add just "xxxx" to /etc/hosts, per the instructions provided:

127.0.0.1    xxxx.yyyy.zzzz    anything-else   xxxx

In my case, I added just "iv4x" to the loopback line.