🐧 DevOps Day 6 — Linux Fundamentals and Shell Scripting Basics

 

🚀 Introduction

Welcome to Day 6 of the DevOps series!

Linux is the foundation of modern DevOps infrastructure — from cloud servers to CI/CD pipelines and containers, nearly every DevOps tool runs on Linux.

As a DevOps engineer, mastering Linux and shell scripting helps you:

• Automate manual tasks

• Manage servers efficiently

• Understand logs, permissions, and system resources

• Integrate scripts into CI/CD pipelines

Today, we’ll explore Linux fundamentals, essential shell commands, and scripting basics that every DevOps professional should know.

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🧩 What is Linux?

Linux is a free and open-source operating system based on UNIX.

It is known for its stability, security, and flexibility.

💡 Why Linux in DevOps?

• Most cloud servers (AWS EC2, Azure VM, GCP Compute) use Linux distributions like Ubuntu, CentOS, or Amazon Linux.

• Tools like Docker, Kubernetes, Ansible, and Jenkins run best on Linux.

• You can easily automate infrastructure setup using shell scripts.

🧠 Common Linux Distributions

• Ubuntu / Debian — popular for DevOps and CI/CD servers

• CentOS / Red Hat (RHEL) — common in enterprise infrastructure

• Amazon Linux 2 — AWS-optimized version for EC2

• Alpine Linux — lightweight and used in Docker containers

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⚙️ The Linux Architecture

Linux is made up of several layers working together:

1. Hardware — CPU, RAM, storage, network

2. Kernel — core of the system; manages hardware communication

3. Shell — interface for users to execute commands

4. User Space — applications and utilities

When you run a command like:

cat file.txt

→ The shell interprets it → passes it to the kernel → retrieves data from the disk → displays the output.

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💻 Navigating the Linux File System

📂 Basic Commands

Task	Command	Description
Show current directory	pwd	Displays full path of current location
List files	ls	Lists files and folders
Detailed list	ls -l	Shows file permissions, owner, and size
Include hidden files	ls -a	Shows hidden files (those starting with .)
Change directory	cd /path	Move to a specific folder
Move up one level	cd ..	Goes one directory up
Go to home directory	cd ~	Returns to your home folder

💡 Tip: Combine commands with logical operators, for example:

cd /var/log && ls -l

This moves into /var/log and lists all files if the first command succeeds.

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🧱 Working with Files and Directories

📄 Create, Move, Copy, Delete Files

touch newfile.txt        # Create a new file
cp file.txt /tmp/         # Copy file to /tmp
mv file.txt docs/         # Move file to docs directory
rm oldfile.txt            # Delete a file

📁 Directory Operations

mkdir backups             # Create a new folder
rmdir emptydir            # Remove empty folder
rm -rf old_project        # Remove folder with contents (force)

💡 Be cautious with rm -rf — it permanently deletes files.

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🖋️ Viewing and Editing Files

🧩 View File Contents

cat filename.txt          # View entire file
head -n 10 filename.txt   # Show first 10 lines
tail -n 10 filename.txt   # Show last 10 lines
less filename.txt         # Scroll through long files
grep "error" logfile.txt  # Search for specific text

🧑‍💻 Create or Edit with VI Editor

vi notes.txt

Inside VI:

• Press i → Insert mode

• Type your content

• Press Esc → Type :wq → Save and quit

💡 Shortcut: To quit without saving → :q!

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📊 File Permissions and Ownership

Every file has permissions (read, write, execute) and an owner.

🔍 Check Permissions

ls -l

Example output:

-rwxr-xr--  1 user group  512 Oct 10 script.sh

Meaning:

• rwx (owner can read, write, execute)

• r-x (group can read, execute)

• r-- (others can read only)

🔧 Change Permissions

chmod 755 script.sh

🧑 Change Owner

sudo chown ubuntu:ubuntu script.sh

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🧠 Resource Monitoring and Management

🧩 System Information

uname -a              # Kernel and OS info
hostnamectl           # System hostname details
whoami                # Shows logged-in user

💾 Disk Usage

df -h                 # Human-readable disk usage
du -sh *              # Folder sizes in current directory

🧮 Memory and CPU

free -h               # Display RAM usage
top                   # Real-time CPU and memory stats
htop                  # (if installed) Interactive system monitor

🕒 System Uptime

uptime

Displays how long the system has been running and load averages.

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🧰 Shell Scripting Basics

Shell scripting is about automating repetitive tasks — deployment, backups, monitoring, or system setup.

Example:

#!/bin/bash
echo "System Report"
date
echo "Current user: $(whoami)"
echo "Disk usage:"
df -h | grep '/dev/'

Run Your Script:

chmod +x system_report.sh
./system_report.sh

💡 Tip:

• Use variables to store reusable values

• Use loops and conditionals for logic

• Combine multiple Linux commands with pipes (|) and redirection (>, >>)

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🧭 Commonly Used Linux Shortcuts and Tricks

Shortcut	Function
Ctrl + C	Stop a running command
Ctrl + L	Clear the terminal
Ctrl + R	Search command history
!!	Run the previous command
history	Show command history
alias ll='ls -alF'	Create a shortcut command

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⚙️ DevOps Use Cases for Linux

• CI/CD Servers: Jenkins and GitLab runners run on Linux hosts

• Containers: Docker containers use Linux namespaces and cgroups

• Infrastructure: Ansible, Terraform, and Kubernetes rely on Linux command execution

• Monitoring: Shell scripts automate log checks and alerts

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🌟 Conclusion

Linux isn’t just an operating system — it’s the command center of DevOps.

By mastering file management, permissions, resource monitoring, and shell scripting, you gain control over automation and cloud infrastructure.

“In DevOps, Linux isn’t a skill — it’s a language every engineer must speak fluently.”