What is an operating system?
Every computer needs an operating system (OS). It is the main program that runs the computer: it starts other programs, saves your files, talks to the keyboard, screen and network, and keeps programs from getting in each other's way.
You already know some operating systems: Windows, macOS, Android and iOS. Linux is another one, and it is everywhere.
Linux is everywhere
- Servers: most websites you visit, including this one, run on Linux servers.
- Phones: Android is built on top of Linux.
- The cloud: almost every cloud machine at AWS, Google Cloud and Azure runs Linux.
- Cyber security: tools like Kali Linux, and most servers you will test or defend, run Linux.
- Tiny devices: routers, smart TVs, cars and even some fridges.
That is why learning Linux is one of the most useful skills for anyone going into IT, programming, cloud or cyber security.
Kernel and distributions
Strictly speaking, Linux is the kernel: the core of the system that talks to the hardware. To get a complete, usable system, the kernel is packaged together with tools, a shell and other programs. Such a package is called a distribution (or distro).
| Distribution | Known for |
|---|---|
| Ubuntu | Friendly and very popular, on desktops and servers |
| Debian | Rock-solid; Ubuntu is based on it |
| Fedora / Red Hat | Used by many companies |
| Kali Linux | Packed with security and penetration-testing tools |
| Alpine Linux | Tiny and fast; popular in Docker containers |
The good news: the terminal commands are almost the same on every distribution. What you learn here works on Ubuntu, Kali, a cloud server or a Raspberry Pi.
Think of it like this: The kernel is like a car's engine. A distribution is the whole car: engine, seats, steering wheel and radio. Different car makers use similar engines, and once you can drive one car you can drive them all.
Why the terminal?
Linux has graphical desktops too, but servers usually have no screen at all. You control them by typing commands in a terminal. Typing can feel slow at first, but it quickly becomes much faster than clicking, and it lets you do things no mouse can, like renaming 1,000 files with a single line.
How this course works
- Each module teaches one topic in short lessons with real examples.
- Every example was run on a real Linux machine, and you see exactly what it printed.
- Each lesson page has a practice terminal: press Try it on any example to run it yourself.
- Every module ends with labs: missions you complete on a real Linux machine that runs right inside your browser. Tasks tick themselves off as you complete them.
Remember: You can't break anything. The lab machine lives only in your browser tab. If something goes wrong, press Reset and you get a fresh machine in a second.