Linux implementation of groups uses a textfile (/etc/group) to define groups and map group names to GIDs.
The group file consist of four fields:
- Group name
- Password - Encrypted password, if empty no password required
- User list - Members of the group, separated by commas
To change the group ownership of a file or directory, use the chgrp command.
To add a new group, use the groupadd command.