Verifique se as entradas de /etc/hosts
(ou NIS) estão corretas.
Eu tentaria explicar isso, mas a manpage conta a história melhor:
THE FQDN
You can't change the FQDN (as returned by hostname --fqdn) or the DNS
domain name (as returned by dnsdomainname) with this command. The FQDN
of the system is the name that the resolver(3) returns for the host
name.
[..]
Therefore it depends on the configuration (usually in /etc/host.conf)
how you can change it. Usually (if the hosts file is parsed before DNS
or NIS) you can change it in /etc/hosts.