GNU/Linux Desktop Survival Guide
by Graham Williams
Groups: Managing Access Permissions
Every file and folder in a GNU/Linux system belongs to a single group. Each user is also a member of one or more groups. Groups are used to control collections of users who may have access to particular files, folders, and services.
A Debian GNU/Linux system creates some standard groups and users. The system administrator can also create new users and may also create new groups. Groups can be managed using the Gnome users-admin tool, accessed from Applications-->System Tools-->Users and Groups. By default this shows only users, but you can access groups by selecting the More Options button. This allows you to add new groups and to add and remove users from groups.