Mastering Linux for DevOps: A Comprehensive Guide for Beginners

1. Introduction

What is Linux?

Linux is an open-source operating system and a core foundation of modern DevOps. Its stability, flexibility, and security make it the go-to OS for DevOps engineers. Whether you’re automating infrastructure or managing services, Linux is the bedrock.

Why Learn Linux for DevOps?

Almost all cloud infrastructure and container-based tools (like Docker and Kubernetes) run on Linux. Mastering Linux commands and shell scripting will enhance your efficiency as a DevOps engineer.

2. Core Concepts

1. Linux Basics

• Distributions: Ubuntu, CentOS, Fedora
• Package Management: apt, yum, dnf
• File System Hierarchy: /home, /etc, /var, /usr
• Permissions: chmod, chown, umask

1. Common Linux Commands

• Navigating the File System:

cd /path/to/directory       # Change directory
ls -la                       # List files and directories with details
pwd                          # Print working directory

• File Manipulation:

touch file.txt               # Create a new file
cat file.txt                 # Display file contents
cp file1.txt file2.txt        # Copy file
mv file.txt /new/path        # Move/rename file

• File Permissions:

chmod 755 file.sh            # Change file permissions
chown user:group file.sh     # Change file ownership

1. Shell Scripting Basics

• Shell scripting is a way to automate tasks by writing a series of commands in a file.
• Example: Simple Backup Script

#!/bin/bash
src="/home/user/docs"
dest="/backup/docs"
cp -r $src $dest
echo "Backup completed!"

3. Hands-On Example

Scenario: Set up a simple web server on Linux using Apache.

1. Install Apache on Ubuntu:

sudo apt update
sudo apt install apache2

1. Start Apache and check status:

sudo systemctl start apache2
sudo systemctl status apache2

1. Access Web Server:

• Visit http://localhost on your browser. If everything is set up correctly, you should see the Apache welcome page.

1. Automate Web Server Setup: Create a shell script for quick setup.

#!/bin/bash
sudo apt update
sudo apt install apache2 -y
sudo systemctl start apache2
echo "Web server installed and started!"

4. Best Practices

• Regular Updates: Always keep your Linux server updated by running sudo apt update && sudo apt upgrade.
• Security: Use firewall tools like ufw and iptables to secure your Linux servers.
• Backup: Regularly backup critical files using rsync or automated scripts.

5. Interview Questions

• Q: What is the difference between chmod 755 and chmod 644? A: chmod 755 gives the owner full permissions (read, write, execute) and others read and execute permissions. chmod 644 gives the owner read and write permissions, while others can only read.
• Q: How do you find large files in a Linux system? A: Use the find command:

find / -type f -size +100M

• Q: What is a symbolic link in Linux? A: A symbolic link is a file that points to another file or directory. Use ln -s target linkname to create one.