Comment 22 for bug 185209

I can confirm this bug in Hardy-Gnome. If a domain is added to the hostname in /etc/hosts, sudo does not work any more. In Gutsy that did not matter; sudo still worked even if a domain name was added: localhost [hostname].[domain]

I think, the problem is not, how the domain name has been added. It is rather how /etc/hosts is parsed.

A simple workaround to edit /etc/hosts without rebooting in recovery mode (as described above) is to open an administration terminal from the main menue. This is possible without any sudo command and does still work.