Users And Groups; User And Group Management Tools - Red Hat ENTERPRISE LINUX 3 Reference Manual

The control of users and groups is a core element of Red Hat Enterprise Linux system administration.
Users can be either people, meaning accounts tied to physical users, or accounts which exist for
specific applications to use.
Groups are logical expressions of organization, tying users together for a common purpose. Users
within the same group can read, write, or execute files owned by the group.
Each user and group has a unique numerical identification number called a userid (UID) and a groupid
(GID) respectively.
The user who creates a file is assigned as the owner and group owner. The file is also assigned separate
read, write, and execute permissions for the owner, the group, and everyone else. The owner of a file
can be changed only by the root user. The group to which a file belongs can be changed by root or by
the owner of the file if the owner is part of the group being added to the file. Access permissions can
be changed by both the root user and the owner of the file.
Red Hat Enterprise Linux supports access control lists (ACLs) for files and directories which allow
permissions for specific users outside of the owner to be set. For more information about using ACLs,
refer to the chapter titled Access Control Lists in the Red Hat Enterprise Linux System Administration
Guide.
Proper management of users and groups, and effective management of file permissions are among the
most important tasks a system administrator undertakes. For a detailed look at strategies for managing
users and groups, refer to the chapter titled Managing User Accounts and Resource Access in the Red
Hat Enterprise Linux Introduction to System Administration.

6.1. User and Group Management Tools

Managing users and groups can be a tedious task, but Red Hat Enterprise Linux provides tools and
conventions to make their management easier.
The easiest way to manage users and groups is through the graphical application, User Manager
(
redhat-config-users
and Group Configuration in the Red Hat Enterprise Linux System Administration Guide.
The following command line tools can also be used to manage users and groups:
,
• useradd usermod
ing user accounts.
,
• groupadd groupmod
ifying user groups.
— Industry-standard method of administering the
•
gpasswd
, — Tools used for the verification of the password, group, and associated shadow files.
• pwck grpck
,
• pwconv pwunconv
to standard passwords.
For an overview of users and group management, refer to the Red Hat Enterprise Linux Introduction
to System Administration. For a detailed look at command line tools for managing users and groups,
see the chapter titled User and Group Configuration in the Red Hat Enterprise Linux System Admin-
istration Guide.
). For more information on User Manager, refer to the chapter titled User
, and — Industry-standard methods of adding, deleting and modify-
userdel
, and — Industry-standard methods of adding, deleting, and mod-
groupdel
— Tools used for the conversion of passwords to shadow passwords and back
Chapter 6.

Users and Groups

file.
/etc/group