What is Linux?
Summary: contrary to popular belief, "Linux" is not an operating system in the usual sense of the term. It is a kernel — the heart of an operating system — around which hundreds of projects add everything needed to make a computer work. This lesson clarifies it all, with the history and the philosophy that come with it.
1. A fundamental distinction: the kernel ≠ the complete system
A complete operating system is three layers stacked on top of each other:
Linux, strictly speaking, is only the orange middle layer: the kernel. The rest (shell, tools, interface) comes from other projects, mainly the GNU project — hence the rigorous name "GNU/Linux" you sometimes hear.
In everyday language, we simply say "Linux" to refer to the whole. It is a convenient shortcut, not to be confused with the technical reality.
2. Born in 1991, in a student bedroom
The history of Linux fits in one sentence: a Finnish student, Linus Torvalds, published in August 1991 the message that would change everything.
Two brilliant choices by Linus Torvalds made it all possible:
- Publishing the source code from the start, under a free licence.
- Accepting outside contributions, with rigorous editorial control.
Result: more than 20,000 contributors have written Linux kernel code since 1991. No single company could have produced software of this quality. It is the striking demonstration that the open source model can produce industrial-grade critical software.
3. The kernel: what exactly does it do?
The kernel is the computer's invisible conductor. It does four essential things.
Every application (browser, database, game, Python script…) must go through the kernel to talk to the hardware. The kernel is the only program allowed to access the processor, memory and disks directly.
That centralization is what makes Linux stable and secure: a crashing application does not take the computer down with it, because it never had the keys to the hardware.
4. A distribution: the kernel + everything else
Nobody installs "Linux by itself". You install a distribution, which gathers:
- The Linux kernel (usually a stable, tested version).
- The shell (generally Bash, sometimes Zsh or Fish).
- The GNU tools (
ls,cp,grep,cat, etc.) to manipulate files and text. - A package manager (
apton Debian/Ubuntu,dnfon Fedora,apkon Alpine) to install software easily. - Sometimes a graphical interface (GNOME, KDE, XFCE…) and ready-to-use applications.
- An update policy and a clearly defined life cycle.
There are more than 500 active Linux distributions. Lesson 3 helps you pick the right one for your context.
5. The Unix philosophy: four simple rules
Linux inherits the Unix philosophy, formulated in the 1970s by the creators of Unix at Bell Labs. It fits in four rules that explain why Linux is so elegant to use once you understand the terminal.
| Rule | Concrete translation |
|---|---|
| Each program does one thing, and does it well | ls lists, grep filters, sort sorts. No tool mixes roles. |
| Programs cooperate | Tools are chained with pipes (|) to combine their power: ls | grep .txt | sort. |
| Everything is a file | A disk, a mouse, a process, a network connection: everything is represented as a file you can read or write. |
| Text is the universal format | Configurations, logs, exchanges between programs happen in readable text, never in a proprietary binary format. |
These four rules mean that every Linux command composes with all the others. That is what makes an experienced Linux user radically more productive than a Windows user on administration or analysis tasks.
6. Tux the penguin: why?
A small cultural detail. Linux's official mascot is a penguin named Tux, drawn in 1996 by Larry Ewing. Why a penguin?
- Linus Torvalds was bitten by a penguin at the Canberra zoo in 1993 (a genuine anecdote).
- He later said he liked this image of a penguin relaxed, yet able to swim very fast — a good metaphor for Linux: simple on the surface, formidable underneath.
No obligation to remember this anecdote, but it explains why you will see this penguin everywhere in the Linux ecosystem.
7. "Is Linux really free?"
Yes, twice yes.
- Free to install and use: no licence to buy, for personal, professional, educational or commercial use.
- Free to modify and redistribute, under conditions defined by the GPL (General Public License).
The business model of the companies living off Linux (Red Hat, Canonical, SUSE) relies on commercial support, not on selling the software: they sell service guarantees, certifications, training. It is a complete inversion of the Microsoft model — and it works, since Red Hat was bought by IBM in 2019 for 34 billion dollars.
Remember in 30 seconds
- Linux in the strict sense = a kernel, created by Linus Torvalds in 1991.
- In the everyday sense = a distribution = kernel + shell + tools + package manager.
- The kernel manages the processor, memory, disks and network. Nothing else touches them.
- The Unix philosophy (each tool does one thing, tools chain together, everything is a file, everything is text) explains the power of the terminal.
- Linux is free and open source; the companies living off it sell support, not software.