Phase 2: Mastering Linux System Insight Commands for DevOps & SysAdmins

• Level: Beginner
• Estimated Time: ~20–25 minutes
• Tools Used: Linux Terminal / CLI
• Outcome: You'll gain visibility into your system's behavior, performance, and usage key for DevOps and DevSecOps work.

If you’ve nailed Phase 1: File and Directory Mastery, take a moment to celebrate 🎉. You’ve built your foundation. Now it's time to understand what your system is doing under the hood like checking your car’s dashboard while driving.

Welcome to Phase 2: System Insight Tools, where you’ll learn how to monitor system health, processes, and performance a must for every DevOps pro, SRE, or power user.

🚀 Why This Phase Matters

✅ Helps diagnose performance issues
✅ Core foundation for DevOps & sysadmin tasks
✅ Lets you observe, troubleshoot, and secure your system like a pro

🔍 What You’ll Learn

• Monitor disk usage and free space
• Understand RAM usage and availability
• Visualize directory structure
• List running processes and system activity
• Identify logged-in users and user permissions

✅ Start Here: Where Are You?

pwd

Always know where you're starting from especially when redirecting output.

🌳 tree –> Visualize Directory Structure

tree
tree -L 2

Get a visual map of your folders.

💡 -L 2 limits depth great for big folders.

⚠️ If not installed:

sudo apt install tree

💽 du -sh * –> Folder-by-Folder Disk Usage

du -sh *

• -s: summary only
• -h: human-readable sizes
• *: all items in the directory

🔎 Use this in your ~/Downloads or ~/Projects folder to spot heavy folders.

🧱 df -h – Disk Space on Mounted Devices

df -h

See total size, used, available, and usage % for your drives.

⚖️ Use du for per-folder size; use df for whole disk partitions.

🧠 free -h –> RAM & Swap Usage

free -h

Breaks down:

• Total / Used / Free RAM
• Swap memory usage

🚨 Useful to check before/after running heavy scripts.

🔍 ps aux –> All Running Processes

ps aux

See everything running in the background from apps to daemons.

🧠 Combine with grep:

ps aux | grep nginx

📈 top / htop –> Live System Monitor

top

htop  # If installed

• top: default, updates every few seconds
• htop: colorful, interactive (use arrow keys, F6 to sort)

✅ Install htop:

sudo apt install htop

👤 whoami –> Current User

whoami

See your current user crucial when working across user roles or sudo environments.

🆔 id –> User ID and Group Info

id

Displays:

• UID (User ID)
• GID (Group ID)
• All groups the user belongs to

🔐 Understanding permissions starts here.

⚙️ System Snapshot Script

Try running this full system snapshot in your terminal:

echo "--- System Health Check ---"
echo "Current Directory: $(pwd)"
echo ""
echo "--- Disk Usage (Current Folder) ---"
du -sh *
echo ""
echo "--- Overall Disk Space ---"
df -h
echo ""
echo "--- RAM Usage ---"
free -h
echo ""
echo "--- Top 5 CPU Processes ---"
ps aux --sort=-%cpu | head -n 6
echo ""
echo "--- Current User Info ---"
whoami
id
echo "--------------------------"

📊 Summary Table

🧪 Mini Challenge: Log Your System State

Try this workflow:

mkdir ~/sys-check
cd ~/sys-check

tree ~ > tree.txt
df -h > disk.txt
free -h > memory.txt
ps aux --sort=-%mem | head -n 10 > top-memory.txt

Then review the files using:

cat memory.txt
cat top-memory.txt

🔜 What’s Next: Text Manipulation & Permissions

In Phase 3, you'll learn to:

• View and edit text files
• Chain commands with pipes
• Manage file permissions (chmod, chown)
• Start scripting automation basics

This is where the shell becomes your superpower. 💪

Author: Abdulrahman A. Muhamad
🌐 Portfolio • GitHub • LinkedIn