Min installtion jag gör för webmin

deb https://download.webmin.com/download/repository sarge contrib

You should also fetch and install my GPG key with which the repository is signed, with the commands : cd /root
wget https://download.webmin.com/jcameron-key.asc
apt-key add jcameron-key.asc
You will now be able to install with the commands : apt-get install apt-transport-https
apt-get update
apt-get install webmin