This is an error you may see from the Apache web server when the daemon starts up. To resolve this, you need to make sure that your server is assigned a fully qualified domain name [FQDN]. A fully qualified domain name is made up of the following parts:
[hostname].[domain].[top level domain]
Here's further explanation regarding FQDN's:
On my home network, I insure this by doing the following:
1) instruct my firewall/router to assign a domain name to all of the hosts on my local network. In this way, my web server running Apache will then be assigned a domain.
2) make sure you have a full domain name for the server listed in /etc/hosts. Here is the generic form of a proper host entry in the hosts file:
[IP address] [hostname.domain name.top level domain] [hostname]
192.168.0.3 computer.network.com computer
That will do it.
If the IP of the server is statically assigned, alternate methods are:
1) assign a domain in /etc/resolv.conf
2) assign a hostname in /etc/sysconfig/network
The two examples mentioned above are for Fedora and Red Hat. The network files may differ if you use another Linux distribution.
3) specify the ServerName parameter in Apache's httpd.conf file (usually located in /etc/httpd/conf/httpd.conf)
If interested, here's a recent thread with people talking about this subject:
Hope this helps.