Control of users and groups is a core element of Red Hat Linux system administration.
Users can be either people, meaning accounts tied to physical users, or logical users, meaning accounts which exist for specific applications to use. Both types of users have a unique User ID (UID) and Group ID (GID).
Groups are logical expressions of organization. Groups tie users together, giving them permissions to read, write, or execute files.
When a file is created it is assigned a user and group. It is also assigned separate read, write, and execute permissions for the file's owner, group, and everyone else. The user and group of a particular file, as well as the access permissions on the file, can be changed by root or, in most cases, by the creator of the file.
Proper management of users and groups and effective management of file permissions, are among the most important tasks a system administrator undertakes in the course of his duties.
Managing users and groups can be a tedious task, but Red Hat Linux provides a few tools and conventions to make management easier for administrators.
You can use tools like useradd or groupadd to create new users and groups from the shell prompt. But an easier way to manage users and groups is through the graphical application, User Manager. For more information on User Manager, refer to the Official Red Hat Linux Customization Guide.
In the Section called User Private Groups further discuss file permission concepts and will walk through command line steps for managing users.