Understanding the /etc/passwd and /etc/shadow files

Now that we know how to create (and delete) user accounts on our server, we are well on our way to being able to manage our users. But where exactly is this information stored? We know that users store their personal files in /home, but is there some kind of database somewhere that keeps track of which user accounts are on our system? Actually, user account information is stored in two special text files: /etc/passwd and /etc/shadow.

You can display the contents of each of those two files with the following commands. Take note that any user can look at the contents of /etc/passwd, while only root has access to /etc/shadow:

# cat /etc/passwd
# cat /etc/shadow

Go ahead and take a look at these two files (just don't make any changes), and I will help you understand them. First, let's go over the /etc/passwd file. What follows is example output from this file on my test server. For brevity, I limited the output to the last seven lines...