Week 2 - Day 1: Linux Introduction

📚 Learning Objectives

By the end of this session, you will be able to:

Understand what Linux is and why it's crucial for DevOps
Set up a Linux environment (VM or WSL)
Navigate the Linux file system hierarchy
Use basic navigation commands (cd, ls, pwd)
Understand file paths (absolute vs relative)

📖 Core Concepts (2 Hours)

What is Linux?

Linux is an open-source operating system kernel. Over 90% of servers run Linux. DevOps without Linux knowledge is impossible.

Open Source: Free to use, modify, distribute
Distributions: Ubuntu, CentOS, Debian, Red Hat, Amazon Linux
Why DevOps needs Linux: Servers, containers, automation all run on Linux

Setting Up Linux

                    
# Option 1: WSL (Windows Subsystem for Linux)
# Open PowerShell as Admin
wsl --install

# Option 2: VirtualBox + Ubuntu
# Download: virtualbox.org
# Download: ubuntu.com/download/desktop

# Option 3: Cloud VM (AWS EC2, Azure VM)
# Launch free tier instance

# Option 4: Already on Linux/Mac
# Open Terminal!
                    
                

Linux File System Hierarchy

                    
/                   # Root - everything starts here
├── bin/            # Essential user binaries (ls, cp, mv)
├── boot/           # Boot loader files
├── dev/            # Device files
├── etc/            # Configuration files (Very Important!)
├── home/           # User home directories
│   └── username/   # Your personal files
├── lib/            # System libraries
├── opt/            # Optional/third-party software
├── proc/           # Process information
├── root/           # Root user's home
├── tmp/            # Temporary files
├── usr/            # User programs and data
│   ├── bin/        # User binaries
│   └── local/      # Locally installed software
└── var/            # Variable data (logs, databases)
    └── log/        # Log files (Very Important!)
                    
                

Essential Navigation Commands

                    
# Print Working Directory - where am I?
pwd
# Output: /home/username

# Change Directory
cd /home           # Go to /home
cd ..              # Go up one level
cd ~               # Go to home directory
cd -               # Go to previous directory
cd /var/log        # Go to absolute path

# List files and directories
ls                 # List current directory
ls -l              # Long format (details)
ls -la             # Include hidden files
ls -lh             # Human readable sizes
ls /etc            # List specific directory

# Clear screen
clear              # or Ctrl + L
                    
                

Absolute vs Relative Paths

                    
# Absolute path - starts from /
/home/user/documents/file.txt

# Relative path - from current location
# If you're in /home/user:
documents/file.txt    # Relative
./documents/file.txt  # Same (. = current dir)
../other/file.txt     # Go up, then to other

# Special path symbols
.     # Current directory
..    # Parent directory
~     # Home directory
/     # Root directory
                    
                

🔬 Hands-on Lab (2.5 Hours)

Lab 1: Environment Setup

Install Linux (WSL, VM, or native)
Open terminal
Run whoami and hostname
Check Linux version: cat /etc/os-release

Lab 2: File System Exploration

Navigate to root: cd /
List all directories: ls -la
Explore each important directory
Find configuration files in /etc

                    
# Lab 2: Exploration Commands
cd /
ls -la

# Explore important directories
ls /etc          # Configuration files
ls /var/log      # Log files
ls /home         # User directories
ls /usr/bin      # User programs

# Check disk usage
df -h            # Disk free space
du -sh /var      # Directory size
                    
                

Lab 3: Navigation Challenge

Go to your home directory
Navigate to /var/log using relative path
Go back to home using ~
Create navigation shortcuts in your mind

                    
# Lab 3: Navigation Exercise
# Start from home
cd ~
pwd              # /home/username

# Navigate to /var/log using relative paths
cd ../..         # Go to /
cd var/log       # Enter var/log
pwd              # /var/log

# Go back home
cd ~

# Practice: Navigate between these directories
# /etc/ssh
# /var/log
# /usr/local/bin
# /tmp
# Your home directory
                    
                

📝 Practice Exercises

What is the difference between /bin and /usr/bin?
Where are log files typically stored?
Navigate to 5 different directories using both absolute and relative paths
List all hidden files in your home directory

💡 DevOps Relevance

Why this matters:

/etc: Where all configuration files live (nginx.conf, ssh_config)
/var/log: Troubleshooting and debugging
/opt: Where you'll install third-party tools
/tmp: Temporary files for scripts and builds

✅ Day 1 Checklist

Linux environment set up and working
Understand file system hierarchy
Can navigate using cd, ls, pwd
Understand absolute vs relative paths
Know where config and log files are