🐧 Linux Fundamentals & User Management

📌 Introduction to Linux Fundamentals

Linux is a powerful and flexible operating system widely used in enterprise environments, cloud platforms, and server management. Mastering Linux fundamentals is a key step toward becoming a Red Hat Certified System Administrator (RHCSA). This article will guide you through essential user and group management concepts, providing real-world examples to help solidify your understanding.

📖 What You’ll Learn in This Guide

🔹 How to create, modify, and delete users in Linux
🔹 Group management and access control
🔹 Setting up shared directories for collaboration
🔹 Understanding file permissions and security
🔹 Best practices for system administration

👤 Understanding User & Group Management in Linux

User and group management is fundamental to system security and resource allocation in Linux. Imagine you are an administrator managing a team of developers. You need to control access to shared resources while ensuring security policies are met.

🔹 Case Study: Setting Up a Development Team

You are managing a software development team with the following requirements:

• Three developers (Alice, Bob, Charlie)
• They need access to a shared /projects directory
• Each developer should have their own personal workspace in /home/
• Only Alice should have admin privileges

🚀 Step-by-Step Guide to User Management

Step 1: Creating User Accounts

Each team member gets a unique Linux user account:

sudo useradd -m -s /bin/bash alice
sudo useradd -m -s /bin/bash bob
sudo useradd -m -s /bin/bash charlie

• -m creates a home directory (/home/alice, /home/bob, etc.)
• -s /bin/bash sets the default shell to Bash

Step 2: Setting Up Passwords

Each user needs a secure password:

sudo passwd alice
sudo passwd bob
sudo passwd charlie

Linux will prompt you to set and confirm the password for each user.

🔑 Managing Groups & Access Control

To simplify access control, we create a developers group and add users:

sudo groupadd developers
sudo usermod -aG developers alice
sudo usermod -aG developers bob
sudo usermod -aG developers charlie

• groupadd developers creates a new group
• usermod -aG developers username adds a user to the group

Configuring Shared Access to /projects

To allow developers to collaborate on shared files, we set up /projects:

sudo mkdir /projects
sudo chown :developers /projects
sudo chmod 2775 /projects

• chown :developers /projects makes developers the group owner
• chmod 2775 ensures group members have full access while maintaining ownership inheritance

⚡ Advanced User Management: Granting Admin Privileges

Alice is the team lead and needs administrative rights. We grant her sudo privileges:

sudo usermod -aG sudo alice

To confirm, Alice runs:

sudo whoami

If it returns root, Alice has admin privileges.

🔐 Understanding File Permissions & Security

Every file and directory in Linux has permissions that define access control:

ls -l /projects

Example output:

drwxrwxr-x 2 root developers 4096 Jan 1 12:00 /projects

Breaking it down:

• d → Directory
• rwxrwxr-x → Owner: Read, Write, Execute (rwx)
  • Group: Read, Write, Execute (rwx)
  • Others: Read, Execute (r-x)
• developers → Group ownership

To modify permissions, use chmod:

chmod 750 /projects

• 750 → Owner has full access, group can read/execute, others denied

To change ownership, use chown:

chown alice:developers /projects

• Assigns alice as owner, developers as group

🔥 Essential Practice for RHCSA

✅ Create and manage users with different access levels
✅ Configure sudo privileges for administrative users
✅ Set file and directory permissions correctly
✅ Manage system groups and user access

📌 Next Article: File Systems & Storage Management

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