On attempted installation of Webmin on Ubuntu 18.04 server, receiving the following:
webmin: Depends: libauthen-pam-perl but it is not installable
Depends: apt-show-versions but it is not installable
E: Unable to correct problems, you have held broken packages.
On ubuntu 18.04.1 the universe and multiverse repositories are disabled by default
to enable do:
sudo add-apt-repository universe
sudo add-apt-repository multiverse
Now you can resolve the webmin dependencies and install it.