You might probably faced the same following error while you were restarting the Apache server on Ubuntu.
To fix that problem, you need to edit the httpd.conf file. Open the terminal and type,
By default httpd.conf file will be blank. Now, simply add the following line to the file.
Save the file and exit from gEdit. Finally restart the server.
aslam@aslam:~$ sudo /etc/init.d/apache2 restart
* Restarting web server apache2 apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName
... waiting apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName
* Restarting web server apache2 apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName
... waiting apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName
sudo gedit /etc/apache2/httpd.conf
ServerName localhost
sudo /etc/init.d/apache2 restart