What Are Users and Groups?
In addition to a Red Hat Enterprise Linux system having a username for each user allowed access to a system, each system has user groups. A user group is a group of one or more users. A user can be a member of more than one group.
User groups can be any grouping of users on which you decide: groups of users in a functional department, groups in the same physical location, or groups based on security access. It is important to plan the user groups for your company carefully before implementing them because changing them means changing the groups associated with files, which can sometimes lead to incorrect group permissions if they are not changed correctly.