I was building a cloud server for a client this morning when I encountered following error,

E: Unable to locate package webmin-virtualmin-nginx
E: Unable to locate package webmin-virtualmin-nginx-ssl

I was building the server with my Ubuntu 16.04 LEMP stack tutorial. And I was trying to install nginx modules for Virtualmin with following command,

apt-get install webmin-virtualmin-nginx webmin-virtualmin-nginx-ssl

This is the first time I came across this error although it had been reported on comments section on a previous tutorial. The main reason for this error is that Virtualmin packages are missing on the sources list of the server. Adding them to sources.list file will fix the problem. So open it with nano text editor.

nano /etc/apt/sources.list

Append the file with following,

deb  http://software.virtualmin.com/gpl/debian/  virtualmin-squeeze main
deb  http://software.virtualmin.com/gpl/debian/  virtualmin-universal main

Save (Ctrl + X) the file and update apt cache,

apt-get update

Now run the command to install modules again.

apt-get install webmin-virtualmin-nginx webmin-virtualmin-nginx-ssl

Issue should be fixed now.