Apache error "Could not reliably determine the server's fully qualified domain name"

13.04 and older

This is just a friendly warning and not really a problem (as in that something does not work).

If you go to:

/etc/apache2/apache2.conf

and insert:

ServerName localhost   

and then restart apache by typing into the terminal:

sudo systemctl reload apache2

the notice will disappear.

If you have a name inside /etc/hostname you can also use that name instead of localhost.

And it uses 127.0.1.1 if it is inside your /etc/hosts:

127.0.0.1 localhost
127.0.1.1 myhostname

Preferred method

Troubleshooting Apache

If you get this error:

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

then use a text editor such as "sudo nano" at the command line or "gksudo gedit" on the desktop to create a new file,

sudo nano /etc/apache2/conf.d/fqdn

or

gksu "gedit /etc/apache2/conf.d/fqdn"

then add

ServerName localhost

to the file and save. This can all be done in a single command with the following:

 echo "ServerName localhost" | sudo tee /etc/apache2/conf.d/fqdn

But on Ubuntu 14.04:

 echo "ServerName localhost" | sudo tee /etc/apache2/conf-available/fqdn.conf
 sudo a2enconf fqdn

Don't forget the ".conf" (without will not work).

13.10 or newer

As of Apache 2.4 - which is available by default as of 13.10 - you cannot use the method about adding a config file in the conf.d directory.

Apache no longer uses the conf.d directory. All the configuration files are stored inside /etc/apache2/conf-available directory and all the configuration files should now have a .conf extension.

In order to solve this message in Apache 2.4, we have to create a configuration file inside the conf-available directory. For example servername.conf.

sudo vi /etc/apache2/conf-available/servername.conf

And inside this we just need to add one line

ServerName localhost

You can combine the previous two commands in one with:

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

If you want to use a domain name or any other name depending on the requirement its fine, just replace localhost with whatever you need. Next you have to enable this configuration. For this, you need to run the following command:

sudo a2enconf servername

a2enconf is a command to enable a configuration file in Apaches 2.4. Also note that servername on the above command is from the name of the configuration file servername.conf. If your configuration file was ngenericserver.conf then you would have to write sudo a2enconf ngenericserver.

After this reload the server and the above message will no longer bug you.

sudo service apache2 reload

or

sudo apache2ctl graceful

Now after this you will see that the message will not be shown again and the problem will be fixed.