Linux Essentials Preparation · lesson 1 of 23 · 25 min
What Is Linux?
Linux is a free, open-source operating system kernel created by Linus Torvalds in 1991. It is the foundation of countless operating systems (called distributions) used in servers, cloud infrastructure, embedded systems, Android phones, and supercomputers. Understanding Linux is essential for cybersecurity, networking, and cloud careers.
Linux powers over 90% of the world’s cloud servers, all of the top 500 supercomputers, and the majority of internet infrastructure. The Linux Essentials exam tests your understanding of the Linux ecosystem, open source concepts, and basic command-line skills.
Open Source Fundamentals
Copyleft vs Permissive
Copyleft (GPL): If you distribute a modified version, you must release the source under the same license. Ensures derivatives stay open.Permissive (MIT, Apache, BSD): You can use the code in proprietary software without releasing your source. More business-friendly.
Linux Architecture
Popular Linux Distributions
Worked Scenario: Choosing a Distribution
Scenario
A security team needs to set up a system for penetration testing. A developer needs a container base image. A company needs a stable enterprise server. Which Linux distribution is best for each?
Penetration testing → Kali Linux. Pre-loaded with hundreds of security tools (Metasploit, Nmap, Wireshark, Burp Suite). Debian-based, maintained by Offensive Security.
Container base image → Alpine Linux. At ~5MB, Alpine is the smallest Linux distribution — ideal for Docker containers where image size matters. Uses musl libc and busybox instead of glibc and GNU coreutils.
Enterprise server → RHEL or Rocky Linux. RHEL provides paid support and long-term stability. Rocky Linux is a free, community-supported RHEL-compatible alternative — popular since CentOS shifted to a rolling release model.
Flashcard Drill
Linux kernel Core of the OS created by Linus Torvalds in 1991 — manages hardware, memory, and processes. Open source Source code is publicly available — anyone can view, modify, and distribute. GPL (copyleft) GNU General Public License — derivatives must also be GPL. Ensures software stays open. MIT / Apache (permissive) Permissive licenses — can use in proprietary software without releasing source. Shell Command interpreter — translates user commands to kernel calls. Bash is most common. Daemon Background service process — runs without user interaction (sshd, httpd, cron). Ubuntu Most popular Linux distribution for beginners — Debian-based, uses apt. Kali Linux Debian-based penetration testing distribution — pre-loaded with security tools. Alpine Linux Extremely small (~5MB) Linux distribution — used in containers. RHEL / Rocky Linux Enterprise Linux — RHEL is paid, Rocky Linux is free RHEL-compatible. Package manager Installs/removes software — apt for Debian/Ubuntu, yum/dnf for RHEL/CentOS. Everything is a file Linux philosophy — devices, pipes, sockets, and directories are all represented as files.
Knowledge Check — 12 Questions
Linux & Open Source (Linux Essentials)
Who created the Linux kernel?
- Richard Stallman
- Linus Torvalds
- Dennis Ritchie
- Ken Thompson
Answer: Linus Torvalds
Linus Torvalds created the Linux kernel in 1991 as a free, open-source project.
Which license requires that derivatives also be released under the same license?
- MIT
- Apache
- GPL
- BSD
Answer: GPL
GPL (GNU General Public License) is copyleft — derivatives must also be GPL.
Which Linux distribution is pre-loaded with penetration testing tools?
- Ubuntu
- Fedora
- Kali Linux
- Alpine
Answer: Kali Linux
Kali Linux is a Debian-based distribution designed for penetration testing and security research.
A background service process in Linux is called a _____.
Answer: daemon
Daemons are background processes that run without user interaction — e.g. sshd, httpd, cron.
Which package manager is used on Debian/Ubuntu systems?
- yum
- dnf
- apt
- rpm
Answer: apt
apt (Advanced Package Tool) is the package manager for Debian-based systems including Ubuntu.
What is the role of the Linux kernel?
- Provide a GUI
- Manage hardware, memory, and processes
- Run web servers
- Interpret shell commands
Answer: Manage hardware, memory, and processes
The kernel is the core of the OS — it manages hardware resources, memory, and system calls.
Open source software is always free of charge.
- True
- False
Answer: False
Open source means the source code is available — it can still be sold. “Free” in FOSS refers to freedom, not price.
Which Linux distribution is known for its extremely small footprint and use in containers?
- Ubuntu
- Kali
- Fedora
- Alpine Linux
Answer: Alpine Linux
Alpine Linux is tiny (~5MB) — widely used as a base image for Docker containers.
The shell in Linux is:
- The kernel
- A command interpreter that translates user commands to kernel calls
- A GUI desktop environment
- A file system
- Answer: A command interpreter that translates user commands to kernel calls
The shell (bash, zsh, etc.) interprets commands and passes them to the kernel.
The package manager used on RHEL/CentOS systems is _____.
Answer: yum
yum (and its successor dnf) is the package manager for RHEL-based systems.
Which license allows use in proprietary software without releasing source code?
- GPL
- LGPL
- MIT
- AGPL
Answer: MIT
MIT is a permissive license — you can use it in proprietary software without releasing your source.
A company needs a free, enterprise-grade Linux server compatible with RHEL. Which should they use?
- Ubuntu
- Kali Linux
- Rocky Linux
- Alpine
Answer: Rocky Linux
Rocky Linux is a free, community-supported RHEL-compatible distribution — popular enterprise choice since CentOS changed its model.
Back to Linux Essentials Preparation
Next lesson: Linux distributions: Debian/Ubuntu, RHEL/CentOS/Rocky, Arch, Alpine; package managers