Chapter 5.

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 logical users, meaning accounts

which exist for specific applications to use. Both types of users have a unique User ID (UID) and

Group ID (GID).

Groups are logical expressions of organization. Groups tie users together, giving them permissions to

read, write, or execute files.

When a file is created it is assigned a user and group. It is also assigned separate read, write, and

execute permissions for the file's owner, group, and everyone else. The user and group of a particular

file, as well as the access permissions on the file, can be changed by root 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 in the course of his duties.

5.1. Tools for User and Group Creation

Managing users and groups can be a tedious task, but Red Hat Linux provides a few tools and con 

ventions to make management easier for administrators.

You can use tools like

useradd

or

groupadd

to create new users and groups from the shell prompt.

But an easier way to manage users and groups is through the graphical application, User Manager.

For more information on User Manager, refer to the Official Red Hat Linux Customization Guide.

In Section 5.4 further discuss file permission concepts and will walk through command line steps for

managing users.

5.2. Standard Users

In Table 5 1, you will find the standard users set up by the installation process in the

/etc/passwd

file. The Group ID (GID) in this table is the primary group for the user. See Section 5.3 for a listing

of standard groups.

User

UID

GID

Home Directory

Shell

root

0

0

/root

/bin/bash

bin

1

1

/bin

/sbin/nologin

daemon

2

2

/sbin

/sbin/nologin

adm

3

4

/var/adm

/sbin/nologin

lp

4

7

/var/spool/lpd

/sbin/nologin

sync

5

0

/sbin

/bin/sync

shutdown

6

0

/sbin

/sbin/shutdown

halt

7

0

/sbin

/sbin/halt