Users and Groups - User Management

In any multi-user operating system, managing users and groups is a fundamental concept. This is a core part of the basics of linux, designed for access control and permissions. When a process runs, it does so as the user who started it. Likewise, file access and ownership are dependent on permissions, preventing one user from accessing another's private documents.

The Basics of Linux Users and Groups

Every user on a Linux system is assigned a personal home directory, typically located at /home/username. This directory is where their user-specific files and configurations are stored, though the exact path can vary between Linux distributions.

The system identifies users with a User ID (UID) and groups with a Group ID (GID). While we use human-readable usernames, the operating system relies on these unique numerical IDs for all permission-related tasks. Groups are simply collections of users, making it easier to manage permissions for multiple accounts at once.

The Superuser and the Sudo Command

Within the hierarchy of linux users and groups, one user stands above all others: root, also known as the superuser. The root user has unlimited power, capable of accessing any file and managing any process. Operating as root continuously is risky, as a simple mistake could damage the system.

To mitigate this risk, authorized users can execute commands with root privileges using the sudo (superuser do) command. This allows for administrative tasks without logging in as the root user. Understanding how to properly use sudo is essential for anyone seeking the quickest way to linux advanced administration skills.

Let's try to view a protected file, such as /etc/shadow, which stores encrypted user passwords.

cat /etc/shadow

You will receive a "Permission denied" error. Let's examine the file's permissions:

$ ls -la /etc/shadow

-rw-r----- 1 root shadow 1134 Dec 1 11:45 /etc/shadow

While we will cover permissions in detail later, this output shows that only the root user and members of the shadow group can read this file. Now, run the command again with sudo:

sudo cat /etc/shadow

This time, you will be prompted for your password and, upon successful authentication, the contents of the file will be displayed.

While many apps to learn linux exist, hands-on practice is essential. Here are some labs to reinforce your understanding of Linux users, groups, and sudo:

Manage Linux User Accounts with useradd, usermod, and userdel - Practice the complete lifecycle of user administration, from creating and securing new accounts to modifying and deleting them.
Manage Linux Groups with groupadd, usermod, and groupdel - Gain hands-on experience with core command-line utilities for group administration, including creating new groups, modifying user memberships, and removing groups.
Configure User Accounts and Sudo Privileges in Linux - Learn essential techniques for managing user accounts and sudo privileges to enhance the security of a Linux system, including granting administrative permissions.

These labs will help you apply the concepts of user and group management, and the use of sudo, in real scenarios and build confidence with Linux system administration.

1. Users and Groups

The Basics of Linux Users and Groups

The Superuser and the Sudo Command

Exercises

Quiz

What command allows you to run a single command with `root` privileges? (Please answer in English, using only lowercase letters).