1. UNIX intrinsically supports multiple users. Each user has a personal home directory /home/<username> in which the user's files are stored, hidden from other users. So far you may have been using the machine as the root user, who is the system administrator and has complete access to every file on the system. The root is also called the superuser. The home directory of the root user is /root. Note that there is an ambiguity here: the root directory is the topmost directory, known as the / directory. The root user's home directory is /root and is called the home directory of root. Other than the superuser, every other user has limited access to files and directories. Always use your machine as a normal user. Log in as root only to do system administration. This practice will save you from the destructive power that the root user has. In this chapter we show how to manually and automatically create new users. Users are also divided into sets, called groups. A user can belong to several groups and there can be as many groups on the system as you like. Each group is defined by a list of users that are part of that set. In addition, each user may have a group of the same name (as the user's login name), to which only that user belongs. From Rute-Users-Guide