Apache2: apr_sockaddr_info_get() failed for HOSTNAME

If your apache2 outputs this warning when starting, read along how to fix it:

Problem is that Apache2 is told to use a hostname that the system can not resolve.
Simple solution is to put HOSTNAME to the /etc/hosts file, like this:

If you have the problem that your /etc/hosts is ignored, check this article:
Linux: /etc/hosts gets ignored