🚀 Complete Linux Interview Guide: From Basics to Advanced

🔹 Introduction

Welcome to the ultimate Linux interview guide! Whether you're a beginner or an advanced user, this guide covers everything you need to ace your Linux interview. You'll find essential commands, real-world scenarios, and practical examples. 💡

1) 🚀 What is Linux? and Explain Features of Linux

🔍 What is Linux?

Linux is a free, open-source, and highly secure operating system used on servers, desktops, and cloud platforms. It is known for its stability, flexibility, and performance, making it a top choice for DevOps, cloud engineers, and developers. 💻🚀

🔥 Key Features of Linux

🆓 1️⃣ Open-Source & Free

Linux is completely free to use, modify, and distribute, unlike Windows or macOS. You can customize it as per your needs.

👥 2️⃣ Multi-User Support

Multiple users can access the same system without interfering with each other’s files or processes.

⚙️ 3️⃣ Multi-Tasking

Linux efficiently handles multiple processes at the same time, making it perfect for servers and development.

🔒 4️⃣ High Security (🔑 Main Advantage!)

Linux is one of the most secure operating systems, making it less vulnerable to viruses and malware. Here's why:

✅ User Permissions & Role-Based Access – By default, Linux does not allow normal users to execute system-level changes, reducing the risk of malware infections.

✅ No Need for Antivirus (Unlike Windows!) – Linux doesn’t require traditional antivirus software because:

• 🛡️ Limited Root Access – Viruses cannot modify system files without admin permission.

• 🔄 Frequent Security Patches – The open-source community quickly fixes vulnerabilities.

• 🚫 Executable Restrictions – Files are not executable by default unless explicitly given permission.

• 🔍 Package Managers & Repositories – Software is installed from official, secure sources (like apt for Ubuntu), reducing the risk of malware.

✅ Firewall & Network Security – Linux has built-in firewall tools (iptables, ufw) to block unauthorized access and prevent cyber threats.

✅ Open-Source Advantage – Because the Linux code is public, security vulnerabilities are found and fixed faster than in proprietary systems like Windows.

🔹 Conclusion: Linux is inherently more secure than Windows due to strong user permissions, package management, and open-source security monitoring—so antivirus software is generally not needed! 🚀🔒

💻5️⃣Powerful Command-Line Interface (CLI)

Linux provides a robust terminal that supports automation, scripting, and DevOps tools.

👨‍💻 6️⃣Developer-Friendly

Supports multiple programming languages like Python, Java, C++, and Shell scripting, making it ideal for developers.

🤝 7️⃣ Active Community Support

A large, global community helps with troubleshooting, updates, and new features.

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2)🏗️ Linux Architecture (Explained in Simple Terms)

Linux follows a layered architecture, meaning each part has a specific role. Let’s break it down in the simplest way possible! 👇

🖥️ 1️⃣ Hardware Layer

This is the physical part of your computer, including:
🔹 CPU (Processor)
🔹 RAM (Memory)
🔹 Hard Disk (Storage)
🔹 Network & Other Devices

🧠 2️⃣ Kernel (The Brain of Linux!)

The kernel is the heart of Linux. It acts as a bridge between hardware and software. It does:
✅ Memory Management – Controls how much RAM a program can use.
✅ Process Management – Manages running applications and assigns CPU time.
✅ Device Management – Communicates with hardware like keyboards, mice, and printers.
✅ Security & Permissions – Controls who can access what in the system.

💻 3️⃣ Shell (Your Command Helper)

The shell is a translator between you and the kernel. When you type commands in the terminal, the shell sends those instructions to the kernel.
🔹 Examples of shells: Bash, Zsh, Fish

📌 Example:
When you type ls, the shell asks the kernel to list files, and the kernel fetches the result from storage.

🏢 4️⃣ User Applications (What You Use Daily)

This is where you interact with Linux! These are GUI or command-line programs like:
🖥️ Browsers – Firefox, Chrome
📂 File Managers – Dolphin, Nautilus
📄 Text Editors – Vim, Nano, VS Code
💻 Command-Line Tools – grep, awk, sed

Note: 🔄Let's understand how Linux processes a request from a user application to hardware using a step-by-step flow. This follows the User Application → Shell → Kernel → Hardware model.

→1️⃣ User Application Sends a Request The application (Terminal) ex. ls /home/user sends this request to Shell.

→ 2️⃣ Shell Processes the Request 📌 **Shell interprets the command (ls /home/user) and sends it to the Kernel for execution. ex . User → Shell: "Find files in /home/user"

→ 3️⃣ Kernel Communicates with Hardware

📌 Kernel checks storage (Hard Disk) and fetches the required data.

📌 Kernel sends the request to the hardware (Storage/Memory) to retrieve files.

→ 4️⃣ Hardware Responds to Kernel

📌 The hardware (Hard Disk) finds the data and returns it to the kernel.

→ 5️⃣ Kernel Sends Data Back to Shell

📌 Kernel processes the received data and passes it back to the Shell.

→ 6️⃣ Shell Displays Output in User Application

📌 Shell sends the result back to the terminal, and you see the file list on the screen.

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3)📌 Essential Linux Commands Cheat Sheet

Linux commands help you navigate, manage files, users, processes, networks, and storage efficiently. Here's a well-structured list to boost your Linux skills! 💡

📁 1. Basic File & Directory Commands

📝 These commands help you navigate and manage files.

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📂 2. File & Directory Management

📌 For advanced file operations, use these commands.

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👥 3. User & Permission Management

📌 Manage users, passwords, and permissions easily.

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⚙️ 4. Process Management

📌 Manage running processes and system performance.

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🌐 5. Networking in Linux

📌 Check network status, connections, and debugging.

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💾 6. Disk & Storage Management

📌 Monitor disk space, partitions, and mounting.

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🤖 7. Automation with Shell Scripting

💡 Automate repetitive tasks using shell scripts and cron jobs.

🔹 Basic Shell Script

A simple script to print a message:

#!/bin/bash
echo "Hello, Akshay! Welcome to Linux."

📌 Save it as script.sh, then run:

bash script.sh

🔹 Automate Tasks with Cron Jobs

Cron Jobs run tasks automatically at scheduled times.

📌 Example: Run a script daily at 2 AM

0 2 * * * /path/to/script.sh

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🔍 8. Advanced Linux Topics

📜 Log Management

Monitor system logs for errors and debugging.

✅ Use Case: Helps track system events and troubleshoot issues.

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📊 Performance Monitoring

Monitor system performance & resource usage.

✅ Use Case: Identify performance bottlenecks and optimize system resources.

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4)📂 Linux Directory Structure (19 Important Directories)

Below is a table format for a clear and structured view of the Linux directory system:

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5) 👤 System User (Root) vs Standard User in Linux

Linux has two main types of users:

🔥 1. System User (Root User) – The Super Boss!

✔ Full control over the system.
✔ Can install, modify, or delete anything.
✔ Can create and manage users.

👥 2. Standard User – The Safe Player!

✔ Limited access – Can use the system but can't modify core files.
✔ Can create, edit, and delete personal files.
✔ Cannot install software without root permission.
✔ Safer because mistakes won’t break the system.

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6)🌐 Types of Web Services – Explained Simply!

Web services help apps talk to each other over the internet. But how they are built matters a lot! Let’s explore the 4 main types of web service architectures.

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🏛 1. Monolithic Architecture – The One Big Block

💡 "All-in-One" System – Everything (UI, logic, database) is in one large codebase.
✔ Easy to develop initially but ❌ hard to scale & update.

🔥 Example: A traditional e-commerce website where all features run inside one big app.

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🔗 2. Microservices Architecture – The Flexible System

💡 "Break it Down" Approach – The app is split into small independent services.
✔ Scalable, Faster updates but ❌ needs good coordination.

🔥 Example: Netflix – Different services for movies, payments, and recommendations.

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🔥 3. Extended Architecture – Hybrid Power

💡 "Mix of Monolithic & Microservices" – Some parts remain monolithic, while others go microservices.
✔ Best of both worlds but ❌ can be complex to manage.

🔥 Example: A banking app where core functions (transactions) are monolithic, but extra features (chat, notifications) use microservices.

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☁️ 4. Serverless Architecture – No Server Worries!

💡 "Pay-as-you-go" Model – Code runs only when needed, no need to manage servers.
✔ Cost-efficient & auto-scales but ❌ depends on cloud providers.

🔥 Example: AWS Lambda-based apps – Runs only when a user logs in or uploads a file.

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🎯 Which One is Best?

✅ Monolithic – Best for small apps or startups.
✅ Microservices – Ideal for scalable, large applications.
✅ Extended – Good for migrating old systems.
✅ Serverless – Perfect for event-driven & cost-saving applications.

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7) 🌐 The OSI Model – Explained Simply! 🚀

Ever wondered how the internet works? How does a simple Google search or a WhatsApp message travel across the world? 🌎

Meet the OSI Model – a 7-layer system that helps devices communicate smoothly over networks! 📡

The OSI model is like a courier service 📦 – each layer handles a specific task to deliver your data safely!

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🔥 The 7 Layers of OSI Model & Their Purpose

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🕵️ How Data Travels in OSI Model?

🔹 When you send a message, it moves down all layers.
🔹 The receiver’s device moves it back up the layers to understand it.

🛠 Example:
1️⃣ You send a message on WhatsApp.
2️⃣ The OSI layers break it into packets & transmit it.
3️⃣ The receiver's phone reconstructs the message via OSI layers.

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8) 🖥️ Essential Linux Questions & Answers 🚀

🔎 1. How to Check Computer Name & Hostname in Linux?

Use the following commands:

hostname  # Displays the current hostname  
cat /etc/hostname  # Shows the system’s hostname file

📌 Tip: The hostnamectl command gives more details like OS and kernel version.

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📂 2. What is the Difference Between Relative and Absolute Path?

✅ Absolute Path: Full path starting from the root (/).
📌 Example: /home/akshay/docs/file.txt

✅ Relative Path: Path relative to the current location.
📌 Example: ./docs/file.txt (if you're in /home/akshay)

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🔐 3. How to Check File Permissions in Linux?

Run:

ls -l file.txt

Output:

-rwxr--r--  1 user user  1234  Jan 01 12:00  file.txt

📌 Tip: Use stat file.txt for detailed file permissions.

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🌐 4. How to Check the IP of Your Linux Server?

ip a   # Show all IP addresses  
hostname -I  # Show only the IP address

📌 Tip: Use ifconfig if ip a is not available.

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🔍 5. Which Command is Used to Find Files in Linux?

find / -name "file.txt"  # Search for a file by name  
locate file.txt  # Faster search (needs updatedb first)

📌 Tip: Use grep inside find to filter results.

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🔏 6. What are the Different Types of File Permissions in Linux?

📌 Tip: Change permissions using chmod and ownership using chown.

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7.🏗 Linux Skeleton Files Explained – .bashrc, .bash_profile, .bash_logout & More!

Ever wondered why your Linux terminal behaves a certain way every time you log in? The secret lies in skeleton files – hidden configuration files that control your environment settings, commands, and scripts when you start a session.

Let’s explore the most important skeleton files in Linux! 🚀

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📂 What are Skeleton Files?

Skeleton files are default configuration files that get copied to a new user’s home directory when the account is created. They help define the user environment, including shell behavior, aliases, and login/logout scripts.

🛠 Location of Skeleton Files:

/etc/skel/   # Default directory containing skeleton files

When a new user is created using useradd, these files are copied to /home/username/.

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📝 Important Skeleton Files in Linux

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