# 🐧 Linux Interview Questions Every DevOps Engineer Must Know

## 🔰 Beginner-Level Linux Interview Questions

### 1️⃣ What is Linux?

**Linux** is an **open-source, Unix-like operating system kernel** used to manage hardware resources and provide services to applications.

📌 Examples:

* Ubuntu
    
* CentOS
    
* Amazon Linux
    
* Red Hat Enterprise Linux (RHEL)
    

---

### 2️⃣ What is the Linux Kernel?

The **kernel** is the **core of the operating system** that:

* Manages CPU, memory, and devices
    
* Handles process scheduling
    
* Acts as a bridge between hardware and software
    

---

### 3️⃣ Difference between Linux and Unix?

| Linux | Unix |
| --- | --- |
| Open source | Mostly proprietary |
| Free | Paid |
| Community driven | Vendor controlled |
| Widely used in cloud | Limited usage |

---

### 4️⃣ What is a Shell?

A **shell** is a command-line interface that allows users to interact with the Linux OS.

Popular shells:

* bash
    
* zsh
    
* sh
    

---

### 5️⃣ Common Linux Commands

```plaintext
ls      # list files
pwd     # current directory
cd      # change directory
mkdir   # create directory
rm      # delete file
cp      # copy file
mv      # move/rename file
```

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## ⚙️ Intermediate-Level Linux Interview Questions

### 6️⃣ What is the difference between `rm` and `rm -r`?

* `rm file` → deletes a file
    
* `rm -r dir` → deletes a directory recursively
    

---

### 7️⃣ What are Linux file permissions?

Linux permissions are:

* **Read (r)** – 4
    
* **Write (w)** – 2
    
* **Execute (x)** – 1
    

Example:

```plaintext
chmod 754 file.sh
```

Meaning:

* Owner: rwx
    
* Group: r-x
    
* Others: r--
    

---

### 8️⃣ What is a process in Linux?

A **process** is a running instance of a program.

Commands:

```plaintext
ps
top
htop
kill
```

---

### 9️⃣ Difference between `ps` and `top`?

| ps | top |
| --- | --- |
| Static output | Real-time |
| Snapshot | Dynamic |
| Lightweight | Interactive |

---

### 🔟 What is a daemon?

A **daemon** is a background process that runs continuously.

Examples:

* `sshd`
    
* `cron`
    
* `systemd`
    

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## 🧠 Advanced Linux Interview Questions

### 1️⃣1️⃣ What is the difference between Soft link and Hard link?

| Hard Link | Soft Link |
| --- | --- |
| Same inode | Different inode |
| Cannot cross filesystem | Can cross filesystem |
| Works even if original deleted | Breaks if original deleted |

---

### 1️⃣2️⃣ What is inode?

An **inode** stores metadata about a file:

* File size
    
* Permissions
    
* Owner
    
* Disk location
    

📌 File name is **not stored** in inode.

---

### 1️⃣3️⃣ What is swap space?

**Swap** is disk space used as **virtual memory** when RAM is full.

Commands:

```plaintext
free -h
swapon -s
```

---

### 1️⃣4️⃣ What is cron?

`cron` is a **job scheduler** used to run tasks automatically.

Example:

```plaintext
0 2 * * * backup.sh
```

➡ Runs daily at 2 AM

---

### 1️⃣5️⃣ Explain booting process in Linux

1. BIOS/UEFI
    
2. Bootloader (GRUB)
    
3. Kernel
    
4. init/systemd
    
5. User space
    

---

## 🚀 Linux + DevOps Interview Questions

### 1️⃣6️⃣ How Linux is used in DevOps?

* Running Docker containers
    
* Managing Kubernetes nodes
    
* CI/CD pipelines
    
* Cloud servers (AWS EC2, GCP, Azure)
    

---

### 1️⃣7️⃣ Difference between `systemctl` and `service`?

| systemctl | service |
| --- | --- |
| Used in systemd | Used in SysVinit |
| Modern | Legacy |
| More control | Limited |

---

## 📝 Final Tips for Linux Interviews

✔ Practice commands daily  
✔ Understand **why**, not just **how**  
✔ Use real-world examples  
✔ Learn Linux from a DevOps perspective

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## 📌 Conclusion

Linux is not just an operating system — it’s a **core skill for DevOps engineers**. Mastering Linux fundamentals gives you confidence in **interviews and real production environments**.