Fully Qualified Domain Name on Debian Squeeze

Debian uses a simple FQDN approach by getting the values from hosts file.So, if you would like to set up ns1.example.com as a FQDN for your server, then modify /etc/hosts file so it looks like

127.0.0.1 localhost
127.0.1.1 ns1.example.com ns1

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

Other values may depend on your system.