How to fix/suppress "apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1." warning message?

Warning message Before the fix:

"apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1. Set the 'ServerName' directive globally to suppress this message"


Fix: 
execute the following command in terminal

echo "ServerName localhost" | sudo tee -a /etc/apache2/apache2.conf

Now restart apache server by executing the following command

sudo /etc/init.d/apache2 restart


Message after the fix:
[ ok ] Restarting web server: apache2.