On the new Apache2 instance that I have running Cacti, I ran into a problem where I get the error message:

apache2: Could not reliably determine the server’s fully qualified domain name, using 127.0.1.1 for ServerName

To fix this, I have to add the following line into the /etc/apache2/httpd.conf file:

ServerName nameofserver

Replace nameofserver with the actual name of the server that you want to have Apache configured under.