Apache2 web server will almost always display this information message :
"Could not reliably determine the server's fully qualified name"
when it is first started in Ubuntu and Debian server.
The reason behind this message is because the web server fails to find the suitable domain name in the system.
How to remove the message
First, you need to edit “/etc/hosts” file and put your server name of choice in the file. For example:
127.0.0.1 server.mylocal
Then you need to add “ServerName” directive in the “/etc/apache2/apache2.conf” file.
ServerName server.mylocal
Finally, restart the web server for the changes to take effect. You will notice that the information message is gone now.
$ sudo service apache2 restart