apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1 for ServerName

Problem:

user@localhost:~$ sudo service apache2 restart

 * Restarting web server apache2                                              
apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1 for ServerName
 ... waiting apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1 for ServerName


Solution:

Open and edit your apache2.conf

      sudo gedit /etc/apache2/apache2.conf

Into the file write:

       ServerName localhost

Save the file.
Restart your apache.

    sudo service apache2 restart