Had this issue on Ubuntu/Debian linux:
$ sudo /etc/init.d/apache2 reload
* Reloading web server config apache2
apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1 for ServerName
Fix is pretty trivial:
$ sudo sh -c 'echo "ServerName localhost.localdomain" > /etc/apache2/conf.d/server_name'
$ sudo /etc/init.d/apache2 reload
* Reloading web server config apache2 [ OK ]