http://www.linuxquestions.org/questi...n-name-870439/
http://stackoverflow.com/questions/9...domain-name-us
http://askubuntu.com/questions/25601...ed-domain-name
http://linuxamination.blogspot.com/2...e-servers.html
http://blog.depicus.com/index.php/20...or-servername/

yes i get this all the time using various operating systems.
there does not seem to be an answer.
it is just trial and error until the thing works.
add to apache2.conf or httpd.conf or wherever
lines like:-
ServerName fred.com
Listen 80
Servername localhost
ServerName localhost:80
then restart apache2 or the machine.
you may find that apache2 starts working
but still works when you remove the lines you have added
fiddle fiddle fiddle

while this is an old thread it has many visitors so obviously the question remains.

This works for all Debian derived distros
 

In the terminal:
echo "ServerName localhost" | sudo gedit /etc/apache2/conf-available/fqdn.conf
<enter>
sudo a2enconf fqdn
<enter>
HTH