If you've been put in charge of a system which was previously looked after by someone else, there are several files and commands with which it is a good idea to familiarize yourself, so that you can tell how the system has been set up.

Obviously, most of the files in the /etc directory fall into this category, specifically /etc/passwd and the associated /etc/shadow file, as well as /etc/group. On a Debian system, you should also familiarize yourself with a list of the currently installed packages and their versions; you can use the dpkg -list command to achieve this. This command is covered in more detail later.