If you’ve ever seen this when starting Apache
apache2: Could not reliably determine the server's fully qualified domain name, using <IP address> for ServerName
then check is you have an entry in your /etc/hosts file for this IP address and that the FQDN comes first, then the hostname. If hostname is first, move that to the back and restart/reload Apache. Instead of fiddling with the hosts file a mapping from IP to name in DNS might do, but I have not tested that.