Chapter 6. Users and Groups
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 a group can
read, write, or execute files owned by that group.
Each user and group has a unique numerical
identification number called a userid
(UID) and a groupid
(GID) respectively.
A user who creates a file is also the owner and group owner of that
file. The file is assigned separate read, write, and execute permissions
for the owner, the group, and everyone else. The file owner can be changed
only by the root user as well as 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 as well as the 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 guide.
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
(system-config-users). For more information on
User Manager, refer to the chapter titled
User 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, 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 used for the verification of the password, group, and associated shadow files.
pwconv, pwunconv —
Tools used for the conversion of passwords to shadow passwords and
back 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 Administration Guide.
