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Linux Basics: Managing Users and Groups using useradd usermod userdel

As a Linux system administrator, one of your main tasks involves user and group management. In this guide, we’ll explain how to add, modify, delete, and manage users and groups using commands such as useradd, usermod, userdel, groupadd, and groupdel.

Understanding User and Group Concepts

Every user on a Linux system has a unique user ID and belongs to at least one group. User information is stored in the /etc/passwd file, while group information is in the /etc/group file. Groups, denoted by unique group IDs, allow users with the same computing needs to be categorized for easier permission management.

Adding a User

Adding a user in Linux involves the useradd command. The syntax is straightforward – useradd followed by the username. For example, to add a user called ‘purevoltage’, you’d run:

sudo useradd purevoltage

You can also specify additional options such as the home directory (-d), login shell (-s), and more.

Modifying a User

Modifying user details can be achieved using the usermod command. For instance, to add a user to another group, you use the -aG options, which stands for append to group:

sudo usermod -aG sudo purevoltage

This command adds ‘purevoltage’ to the ‘sudo’ group, thus granting sudo privileges.

Deleting a User

The userdel command is used to remove a user:

sudo userdel purevoltage

By default, this doesn’t remove the user’s home directory. If you wish to delete it as well, use the -r option:

sudo userdel -r purevoltage

Adding a Group

Creating a new group involves the groupadd command. For example, to create a group named ‘developers’:

sudo groupadd developers

Deleting a Group

To delete a group, utilize the groupdel command:

sudo groupdel developers

This will remove the ‘developers’ group.

Understanding /etc/passwd and /etc/group

User and group information is stored in the /etc/passwd and /etc/group files respectively. You can view these files with a simple cat command:

cat /etc/passwd

cat /etc/group

Remember, effective user and group management is crucial in maintaining a secure and efficient Linux system. Keep practicing these commands to enhance your skillset. For more Linux essentials, visit our Linux Basics series.