The instructions how to install Webmin on Debian (and thereby also Ubuntu) seem a bit outdated because edits to the file /etc/apt/sources.list should be replaced by adding a file to the directory /etc/apt/sources.list.d/.
So, instead of adding
deb https://download.webmin.com/download/repository sarge contrib
to the file
create a new file
with that content and possibly a comment why you added it.
The rest seems to be up to date:
“You should also fetch and install my GPG key with which the repository is signed, with the commands:”
cd /root wget http://www.webmin.com/jcameron-key.asc apt-key add jcameron-key.asc
“You will now be able to install with the commands:”
apt-get update apt-get install apt-transport-https apt-get install webmin
“All dependencies should be resolved automatically.”
The reason why I installed Webmin was that updating a server from Ubuntu 14.04 to 16.04 broke the Webmin installation. I kept getting the error “module proc does not exist”. Google did not turn up anything useful for this so I decided to simply uninstall Webmin:
apt remove webmin apt autoremove
And then I reinstalled it with the procedure described above. The error went away. I also got a new UI which will take a while to get used to.