# Introduction Before introducing you to Linux, let us first provide you with some background on Unix. ## Unix Unix is a multi-user, multitasking OS originally developed in the late 1960s at AT\&T Bell Labs by Ken Thompson, Dennis Ritchie, and others. Unlike Linux, which is open-source, Unix was proprietary and licensed to companies like IBM, Sun Microsystems, and HP. Popular Unix-based OSs include macOS, AIX, Solaris, and HP-UX. ## Here comes “Linux” Linux is an [open-source](https://github.com/torvalds/linux) operating system (OS) based on the Unix architecture. It was created by Linus Torvalds in 1991 and has since become one of the most widely used OSs, especially in servers, cybersecurity, programming, embedded systems, and ethical hacking (like Kali Linux, which we will use). Linux follows a monolithic kernel design, meaning the core of the OS (the kernel) manages everything, including hardware, processes, and system calls. It comes in various distributions (distros) such as Ubuntu, Debian, Fedora, Arch Linux, and Kali Linux. ## Linux Vs Unix | Unix | Linux | | -------------------------------------------------- | ------------------------------------------------------------------------------------- | | Developed in the 1970s by AT\&T Bell Labs | Developed in the 1990s by Linus Torvalds | | Proprietary (mostly closed-source) | Open-source and freely available | | Mainly used in enterprise, servers, and mainframes | Used in servers, desktops, embedded systems, and mobile devices | | Generally expensive, requires a license | Mostly free and open-source | | Typically runs on specific hardware | Can run on a wide range of hardware | | Monolithic and multi-user | Modular, customizable, and multi-user | | Used by companies like IBM, HP, and Oracle | Used by individuals, organizations, and companies like Google, Red Hat, and Canonical | | Slower updates and limited community support | Frequent updates and strong community support | ## Linux Distributions Linux distributions, often referred to as "distros," are operating systems built upon the Linux kernel. They serve a wide range of purposes, from powering servers and embedded devices to running desktop computers and mobile phones. While all Linux distributions share the same underlying components, architecture, and philosophy, each one is tailored to meet specific market needs or user preferences. These variations provide unique configurations, software packages, and tools, allowing users to customize their experience according to their requirements. Popular Linux distributions include Ubuntu, Fedora, CentOS, Debian, and Red Hat Enterprise Linux. For cybersecurity practitioners, there are several Linux distributions that are highly regarded for their security features and penetration testing tools. Some of the most commonly used distros include ParrotOS, Kali Linux, BlackArch, and Pentoo. Each of these distributions is designed to cater to specific cybersecurity needs, offering tools and utilities to support tasks such as vulnerability scanning, exploitation, and network analysis. In this book, we will primarily use Kali Linux for penetration testing. Kali is an excellent choice for beginners because it is easy to install in VirtualBox, and it comes preloaded with a comprehensive set of penetration testing tools. This means that you can start learning and practicing right away without the need to spend time setting up tools in a clean distro. While Kali Linux is recommended for its ease of use, you are free to experiment with other distributions such as ParrotOS if you prefer. However, if you're willing to take on the challenge of setting up and configuring tools manually, feel free to explore other distros. The goal is to dive into penetration testing, and whichever distribution you choose, the learning experience will be valuable. ## Why do hackers use Linux? Hackers prefer Linux for several reasons, the biggest being its open-source nature. Since Linux is open source, anyone can inspect, modify, and optimize the code, making it highly flexible for security professionals who need complete control over their operating system. Unlike closed-source systems like Windows, where much of the internal workings remain hidden, Linux is fully transparent, allowing hackers and penetration testers to understand exactly how the system operates, identify vulnerabilities, and customize it to their needs. Another major advantage is the level of granular control Linux provides. Users have full access to system resources, fine-tuned permissions, and deep customization options that are simply not possible in proprietary OSes. This level of control is essential for ethical hackers who need to manipulate network traffic, modify system behavior, and run specialized security tools. Speaking of tools, the majority of penetration testing and hacking tools—like Metasploit, Nmap, Wireshark, and John the Ripper—are developed specifically for Linux. Even if some tools are available for Windows, they often run more efficiently and with fewer restrictions on Linux. Beyond that, Unix-based systems, including Linux, are widely regarded as the future of computing. Most modern servers, cloud infrastructures, and even mobile devices (Android is based on Linux) run on Unix-like environments. This makes Linux an essential skill for anyone in cybersecurity because understanding it means understanding the backbone of modern digital infrastructure. Additionally, Linux is more secure than Windows by design, with better privilege management, fewer exploitable vulnerabilities, and a lower risk of malware infections—making it the preferred choice for both defenders and attackers in cybersecurity. Lastly, Linux offers powerful scripting and automation capabilities with Bash, Python, and Perl, which hackers use to automate attacks, scan networks, or exploit vulnerabilities. The ability to write and execute scripts efficiently is a must-have skill for anyone serious about penetration testing. Put simply, Linux isn't just a choice for hackers—it’s a necessity. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://handbook.ncateam.xyz/fundamentals/linux/introduction.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.