Managing users and groups is one of the key tasks of the system administrator. It is important to know intimately how these work to maintain control of your system. Their study also touches on the very important topic of authentication, or how a user's identity is confirmed at login and who confirms it. A complete study of authentication is beyond the scope of this course (and beyond my expertise) but we will introduce it in this section.

Creating and initializing users involves a series of steps that are configurable. Although the procedure is no longer performed by hand, understanding the steps is necessary to troubleshoot the process and, as with any automated system, the automation itself adds complexity.

We will begin with a study of several of the most important files on a Unix system: the passwd, group and shadow files.