Nameserver error "Listening on HTTP socket failed: While binding: Address already in use"

Symptoms

PowerDNS or BIND/named fails to listen on port 953. The following error is logged to /var/log/messages when using PowerDNS:

Listening on HTTP socket failed: While binding: Address already in use

Description 

The issue can be caused by the "portreserve" service which can be seen below:

# rpm -qa | grep portreserve
portreserve-0.0.4-11.el6.x86_64

# ls -lrt /etc/portreserve/named
-rw-r--r-- 1 root root 9 Nov  7 13:00 /etc/portreserve/named

Workaround

Remove the third-party portreserve service or the above "named" file and restart the nameserver. This should allow for the service to start on port 953.