What are the three main advantages of Linux as an operating system?

The three most-cited pillars are being open source, being fully controllable from the command line, and having a modular design.

These three are really one idea seen from three angles: Linux gives you control rather than hiding it. Open source gives control of the code, the CLI gives control of the running system, and modularity gives control of what the system even contains.

1. Open source — you can view, modify, and redistribute the source. Beyond ideology this means no vendor lock-in: if a maintainer disappears or makes a hostile change, anyone can fork and continue.

2. Command-line interface — every administrative task can be done by typing commands, not just clicking. That's what unlocks automation, scripting, and managing a thousand remote servers from one screen; a GUI-only OS can't be driven that way.

3. Modular design — components are independent and swappable, so the same base can be shrunk to a tiny embedded device or expanded into a full workstation. You're not forced to carry software you don't want.

Tip: GUIs come and go, but the CLI is the constant across every distro and every decade — investing in CLI skill is the highest-leverage thing a Linux admin can do.