Linux

In short: A free, open-source, Unix-like operating system whose kernel was initiated by Linus Torvalds.

In more detail: Strictly speaking, “Linux” only refers to the kernel — the actual operating systems (“distributions” like Ubuntu, Debian, Arch) bundle the kernel with software around it. Dominates in the server and cloud space, as well as in embedded systems, thanks to free licensing, stability, and good scriptability via the shell.

In Depth

Kernel vs. distribution

The Linux kernel itself handles the basic functions of an operating system: process management, memory management, device drivers, file systems, the network stack. A “distribution” (distro for short) packages this kernel with a package manager, a standard selection of software, and often a graphical interface, into a complete, installable operating system — which is why Ubuntu, Debian, Arch or Fedora differ considerably in usability, update cadence and target audience, even though they all use the same kernel. Debian, for example, is considered especially stable and conservative (rare, well-tested updates), Arch a “rolling release” with always the newest software for users who want maximum control, Ubuntu a beginner-friendly compromise.

Origin

Linus Torvalds, a Finnish computer science student at the time, began developing his own kernel in 1991, inspired by (then not freely available) Unix. Combined with the already-existing GNU tools (Richard Stallman’s project for free Unix-compatible tools), this became a completely free operating system — which is why some purists correctly say “GNU/Linux” instead of just “Linux”. The open licence (GPL) allows anyone to view, modify and redistribute the source code, which led to one of the largest collaborative software developments in history.

Dominance in the server/cloud space

Linux dominates almost completely in the server/cloud space, for several reasons at once: free licensing (no licence costs per server, relevant with thousands of instances), high stability under long-term operation (servers often run for months or years without a restart), and a scriptability via the shell deeply rooted in the culture — practically every administrative task can be automated, which is essential for cloud infrastructure (managing many identical servers in an automated way). Docker and most cloud container technologies are built directly on Linux kernel features (namespaces, cgroups), which is why containers originally only ran natively on Linux — on Windows/macOS, Docker technically still runs in a hidden Linux VM in the background today.

Desktop usage

On the desktop, Linux remains a niche despite its server dominance (typically under 5% market share), often due to a lack of software compatibility (many commercial programs only come out for Windows/macOS) and inconsistent hardware driver support — an area where the situation has, however, noticeably improved in recent years, partly thanks to Steam’s “Proton” compatibility layer for games.

See also: Windows, Operating System, Shell, Docker