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.