Chapter 6. Users and Groups
Control of users and groups
is a core element of Red Hat 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 have a unique numerical
identification number called a userid
(UID) and a groupid
(GID) respectively.
When a file is created, it is assigned a user and group owner. It is also
assigned separate read, write, and execute permissions for the owner,
the group, and everyone else. The user and the group to which a file
belongs, as well as the access permissions on the file, can be changed by
the root user or, in most cases, by the creator of the file.
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 Accounts and
Group in the Red Hat Linux System Administration Primer.
6.1. User and Group Management Tools
Managing users and groups can be a tedious task, but Red Hat 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). For more information on
User Manager, refer to the chapter titled
User and Group Configuration in the
Red Hat Linux Customization Guide.
The following command line tools can also be used to manage users and
groups:
useradd, usermod, and
userdel — Industry-standard methods of
adding, deleting and modifying user accounts.
groupadd, groupmod, and
groupdel — Industry-standard methods of
adding, deleting, and modifying user groups.
gpasswd — Industry-standard method of
administering the /etc/group file.
pwck, grpck —
Tools for the verification of the password, group, and associated shadow files.
pwconv, pwunconv —
Tools for the conversion to shadow passwords and back to standard
passwords.
For an overview of users and group management, see the
Red Hat Linux System Administration Primer. 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 Linux Customization Guide.
