I am having this issue right now. Exact same.
sudo: unable to resolve host HOSTNAMEHERE: Name or service not known
Host file is stripped down to this after TinyCP install:
127.0.0.1 localhost.localdomain localhost
::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
I added the hostname entry back in just below the local host entry, and after reboot, gone again. This makes TinyCP unusable.
I have now verified this was the case. I updated the /etc/hosts file 3 times, rebooting after each, to find it had removed my host entry each time. I then updated the host file one last time and uninstalled TinyCP via:
apt-get purge tinycp
followed by:
apt-get autoremove
to clean up the rest of the package files. I then rebooted and checked the /etc/hosts file and it is now intact.
I really like this control panel, and I hope you guys can resolve the issues. It's got a great modern interface, great features, and is well laid out. TinyCP is honestly the best control panel I have used in a long time, but I can't have it trashing my hosts file every reboot, and I kinda need the features working. (see my other post about vsFTPd.)