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.
Each user on a Red Hat Enterprise Linux system is assigned a unique user identification number, also known as a UID. UIDs below 500 are reserved for system users such as the root user. System users also include those added for a specific service such as the nfsnobody, rpc, and rpcuser users for the NFS service.
By default in Red Hat Enterprise Linux, when a user is added, a private user group is created—meaning that a user group of the same name is created and that the new user is the sole user in that group.
Red Hat Enterprise Linux includes a graphical program for managing users and groups.
The system-config-users package is required to do so. Install it using the RHN website or YUM. Start the user and group tool from the System menu on the top panel of the desktop by selecting Administration, Users and Groups or execute the command system-config-users. If the program is run as a non-root user, enter the root password when prompted. all existing users are listed on the Users tab.
By default, system users are not shown in the list of users. To show system users in the list, select Edit, Preferences from the pull-down menu. In the Preferences dialog, unselect the Hide system users and group’s option, and click Close.