Unix has always supported the notion of multiple users working independently and simultaneously on the
same computer − right back to the earliest Unix operating systems, born at the end of the 1960s. Each user in
possession of a valid user account could log in to the computer (by supplying a username and a password) and
hence work with the desired applications. Users would access the system via a system console (which was
normally reserved for administrative tasks such as backups) or from one of a number of serial terminals
(these usually consisted of a keyboard and a monitor, or perhaps even a line printer). Even though networking
wasn't part of the original Unix design, it became available quite early, giving users the ability to interact with
a Unix system from anywhere: locally, via the telephone system and a modem, via a network connection.
Linux has inherited its multi−user nature from those first Unix systems, just as it has inherited a surprising
number of other capabilities, such as permissions and file protection. These features haven't changed much
over time. What has changed is the toolset − tasks like adding a new user account are now easier than they've
ever been. The traditional techniques (using command line tools, or even employing a text editor to alter the
relevant configuration files) have been enriched with graphical tools that greatly simplify our administrative
chores. Red Hat Linux is just one of a number of Linux distributions that have made developments in this
direction.
If you have a single machine that is meant mostly for exclusive use, and you're not planning to share its
resources with anyone else, then the world of administering user accounts and permissions may seem a little
irrelevant to you. However, the notion of multiple user accounts is quite important in Linux, as it is in many
other modern operating systems (such as Mac OS X, other Unix derivatives like the BSD family, and
Microsoft Windows NT, 2000, or XP).
Whether you share your machine with other users, or it's exclusively for your own personal use, each action
you request of it will be denied or allowed in accordance with specific policies. For example, some user
accounts will be allowed to install applications, execute certain programs, and access devices such as a
CD−ROM drive, while other accounts will not.
Understanding how to manage user accounts and control permissions is a definite advantage when learning
Linux. For example, it will allow you to share your computer with other people without compromising
privacy; it will help you to protect yourself from accidental damage (like accidental deletion of system files);
it will help you to avoid virus problems; and it will help you prevent secondary users from cluttering the
system with unnecessary software installations.