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

I tried to restart my Apache server on CentOS 5.0 and got this message:

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

Here is the /etc/hosts file:

127.0.0.1    server4-245    server4-245.com    localhost.localdomain localhost
::1        localhost6.localdomain6 localhost6

Here is the /etc/sysconfig/network file:

NETWORKING=yes
NETWORKING_IPV6=no
HOSTNAME=server4-245

I also have this in the Apache httpd.conf file:

ServerName localhost

However, I still get the first error message when I restart Apache.

If you don't have httpd.conf in folder /etc/apache2, you should have apache2.conf - simply add:

ServerName localhost

Then restart the apache2 service.

Your hosts file does not include a valid FQDN, nor is localhost an FQDN. An FQDN must include a hostname part, as well as a domain name part. For example, the following is a valid FQDN:

host.server4-245.com

Choose an FQDN and include it both in your /etc/hosts file on both the IPv4 and IPv6 addresses you are using (in your case, localhost or 127.0.0.1), and change your ServerName in your httpd configuration to match.

/etc/hosts:

127.0.0.1    localhost.localdomain localhost host.server4-245.com
::1          localhost.localdomain localhost host.server4-245.com

httpd.conf:

ServerName host.server4-245.com

After the initial install of Apache server, I got the following error while restarting the Apache service on Ubuntu 12.04 (Precise Pangolin)

The solution is really simple. Just add the ServerName directive to /etc/apache2/httpd.conf:

sudo nano /etc/apache2/httpd.conf

Add: ServerName localhost

Finally restart the Apache server:

sudo /etc/init.d/apache2 restart

Make sure you're editing the right httpd.conf file, then the error about unreliable server's domain name should be gone (this is the most common mistake).

To locate your httpd.conf Apache configuration file, run:

apachectl -t -D DUMP_INCLUDES

Then edit the file and uncomment or change ServerName line into:

ServerName localhost

Then restart your apache by: sudo apachectl restart