Day 6: Linux & Shell Scripting Basics

When I first logged into a Linux server, I felt like I’d entered a different world.
No icons, no mouse clicks, no fancy windows. Just a blinking cursor.

And yet — this is the world where 90% of production systems live.
Amazon, Netflix, banking apps, SaaS platforms… all powered by Linux.

If you’re starting your DevOps journey, Linux and shell scripting aren’t just skills — they’re your bread and butter. Today, I’ll share the fundamentals I learned on Day 6 of my DevOps journey, with real examples you can try right now.

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1. What Exactly is an Operating System?

Think of an OS as the bridge between your apps and your hardware.

Flow looks like this:

👉 User → Application → Operating System → Hardware
👉 Hardware → Operating System → Application → User

When you open Chrome, it isn’t “talking” directly to your CPU. It’s asking the OS to handle that job.

Key takeaway: Without the OS, software and hardware wouldn’t understand each other.

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2. Why Linux Rules the DevOps World

While Windows dominates our laptops, Linux is king in servers and DevOps environments. Here’s why:

• Free & Open Source → No licenses needed. Anyone can build a Linux flavor.

• Secure by default → No constant antivirus alerts.

• Fast & Stable → Handles millions of requests without crashing.

• Flexible → Distributions like Ubuntu, CentOS, Red Hat, Alpine, Debian fit different needs.

💡 Fun fact: ~90% of servers you test & deploy apps on will run Linux.

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3. Linux OS Architecture (Simplified)

At its core:

• Kernel → The “heart” of Linux, managing memory, processes, devices.

• System Libraries → Tools apps use to request services from the kernel (e.g., libc).

• User Processes & Compilers → Your applications, code, system software.

Think of the kernel as the traffic controller, ensuring cars (apps) and roads (hardware) move smoothly without chaos.

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4. Shell Scripting: Talking to Linux

Servers rarely have a Graphical User Interface (GUI) — because it’s heavy and slows things down. Instead, we talk to Linux using the shell (command-line).

The most popular shell is Bash. Let’s explore some must-know commands, with real examples.

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4.1 Navigating the File System

1. PWD – Present Working Directory

pwd

Output:

/home/ubuntu

👉 Shows where you are in the server. Always run this right after logging in.

2. LS – List Files

ls

Output:

file1.txt  scripts  logs

👉 Lists files & folders.

3. CD – Change Directory

cd scripts
pwd

Output:

/home/ubuntu/scripts

👉 Moves into the scripts folder.

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4.2 Creating & Editing Files

4. TOUCH – Create File

touch hello.txt
ls

Output:

hello.txt

👉 Creates an empty file.

5. VI – Edit File

vi hello.txt

Inside vi:

• Press i → type: Welcome to DevOps!

• Press Esc :wq → save & quit

6. CAT – View File Content

cat hello.txt

Output:

Welcome to DevOps!

👉 Displays file contents.

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4.3 Organizing Files

7. MKDIR – Create Directory

mkdir projects
ls

Output:

projects/

8. RM – Remove File

rm hello.txt

9. RM -R – Remove Directory

rm -r projects

👉 Powerful but dangerous — it will delete everything inside!

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4.4 Monitoring the System

As a DevOps engineer, you need to constantly check server health.

10. FREE – Check Memory

free -mh

Output:

              total   used   free
Mem:          1.9G   512M   1.4G

11. NPROC – CPU Cores

nproc

Output:

2

12. DF – Disk Usage

df -h

Output:

Filesystem   Size  Used  Avail
/dev/xvda1    30G   10G   20G

13. TOP – Running Processes

top

Live output: CPU %, memory %, running processes.
👉 Interview favorite: “How do you check server load in Linux?” → Answer: top.

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5. Why Shell Scripting Matters

Every click in a GUI = a command behind the scenes.
With shell scripting, you can:

• Automate repetitive tasks

• Run batch jobs

• Manage deployments

• Monitor systems

This is why Linux + Bash is a must for every DevOps engineer.

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✅ My Key Takeaways from Day 6

1. Linux isn’t just another OS — it’s the foundation of modern DevOps.

2. The shell is how you “talk” to Linux.

3. Mastering even 10–15 commands can make you 10x faster.

4. Every command you learn is a building block toward automation.

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💬 Question for you:
👉 What was the first Linux command you ever learned? (Mine was ls 🙈)

Drop yours in comments below 👇

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