Tech Tutorial: Manage Users and Groups on Red Hat Enterprise Linux (RHEL) #
Introduction #
In this tutorial, we will delve into the essential task of managing users and groups on a Red Hat Enterprise Linux (RHEL) system, a fundamental skill for any Red Hat Certified System Administrator (RHCSA). Effective user and group management ensures proper security and accessibility controls are in place, which is critical for maintaining the integrity and functionality of the system.
We will cover how to create, modify, delete users and groups, and also how to configure file permissions associated with these users and groups to ensure secure access to system files and resources.
Step-by-Step Guide #
1. Managing Users #
a. Creating a New User #
To create a new user in RHEL, you use the useradd
command. Here’s the basic syntax:
useradd [options] username
Example:
useradd johndoe
This command creates a new user named johndoe
with default settings. To specify additional options such as the home directory or the shell, you can use:
useradd -d /home/johndoe -s /bin/bash johndoe
b. Modifying a User #
To modify an existing user, use the usermod
command. It is similar to useradd
but used for modifying the existing users.
Example:
usermod -s /bin/csh johndoe
This changes the default shell for johndoe
to C shell (/bin/csh
).
c. Deleting a User #
To delete a user, the userdel
command is used. You can also remove the home directory and mail spool by using the -r
option.
Example:
userdel -r johndoe
2. Managing Groups #
a. Creating a Group #
To create a new group, use the groupadd
command.
Example:
groupadd developers
This command creates a new group named developers
.
b. Modifying a Group #
To modify an existing group, you use the groupmod
command.
Example:
groupmod -n devteam developers
This renames the group from developers
to devteam
.
c. Deleting a Group #
To delete a group, use the groupdel
command.
Example:
groupdel devteam
3. Managing User and Group Relationships #
a. Adding a User to a Group #
To add a user to a group, use the usermod
command with the -G
option.
Example:
usermod -aG developers johndoe
This adds johndoe
to the developers
group.
b. Removing a User from a Group #
To remove a user from a group, you will need to edit the /etc/group
file manually or use a tool like gpasswd
.
Example:
gpasswd -d johndoe developers
This removes johndoe
from the developers
group.
4. Setting Permissions #
The chmod
(change mode) command is used to change the file access permissions.
a. Granting File Permissions #
To give read, write, and execute permissions to the user and group, while keeping read-only access for others:
Example:
chmod 774 example.txt
b. Changing File Ownership #
The chown
command changes the user and/or group ownership of a given file.
Example:
chown johndoe:developers example.txt
This changes the ownership of example.txt
to user johndoe
and group developers
.
Conclusion #
Managing users and groups is a critical task for system administrators. This guide provides you with the necessary commands and examples to effectively manage users and groups on a RHEL system. Mastery of these commands ensures you can maintain proper security and operational efficiency in your Linux environments.