As you manage packages on your server, you'll eventually run into a situation where you'll have packages on your system that are installed, but not needed by anything. This occurs either when removing a package that has dependencies, or the dependencies on an installed package change. As you'll remember, when you install a package that requires other packages, those dependencies are also installed. But if you remove the package that required them, the dependencies will not be removed automatically.
To illustrate this situation, if I remove the apache2 package from one of my servers, I will see the following extra information if I then try to install something else:
In this example, I removed apache2 (that was done before the screenshot was taken) then I went on to install mariadb-server. The...
