A: I recently had this message showing after upgrading my apache server on my Debian and so I thought to share how I solved the problem with you guys.
anyhoo, go to apache2.conf file which is located in /etc/apache2 and then edit the file with your chosen editor and add the following line
ServerName 127.0.0.1
…finally restart apache
So here it is all put together
1./ Create a back up copy of your config file, your really do not have to do this however I do it cause I’m tiny bit paranoid about things going horribly wrong. So to do this open Applications > Accessories > Terminal. Type…
sudo cp /etc/apache2/apache2.conf /etc/apache2/apache2.conf.bck
2./ Chose your editor, in this case VIM
sudo vi /etc/apache2/apache2.conf
If your are using VIM, move your cursor using the arrow keys to a blank line to insert a line and then press “i” (off-course without the double quotes).
After that, this line…
ServerName 127.0.0.1
…then save the file pressing [Esc][Shift]:wq
3./ Test and restart apache
sudo apache2ctl configtest
…and then
sudo apache2ctl restart