Theory
The system you will live on
When you log in to the campus lab server, or rent a server online, or look inside an Android phone, you are almost certainly using Linux. It runs the majority of the world's servers and supercomputers. This semester you will learn to work on it hands-on, typing commands at its shell.
You already met Linux at a concept level in your Operating Systems course: the kernel, processes, the file system. Now you go practical. But first, why is Linux everywhere? The answer is in its features, and this opening lesson lays them out.
Theory
What Linux actually is
Linux is an operating system: the software that manages a computer's hardware and runs your programs. Strictly, 'Linux' is the kernel, the core that talks to the hardware, and a full working system pairs it with the GNU utilities and other software, which is why you sometimes see it written GNU/Linux.
Its defining trait is that it is free and open source: the source code is public, and anyone may use, study, modify, and share it. That single fact shapes almost everything else about Linux, including why it is so widely trusted for servers.
At a glance
| Feature | What it means |
|---|---|
| Open source and free | The source code is public; anyone can use, study, and modify it |
| Multiuser | Many users can work on the same system at the same time |
| Multitasking | Many programs (processes) run at once |
| Portable | Runs on many kinds of hardware, from phones to supercomputers |
| Secure | User accounts and file permissions control who can do what |
| Stable and reliable | Runs for long periods without needing a restart |
Formula
Multiuser and multitasking are the big two
For a shared machine like the campus lab server, two features matter most. Multiuser means many students can be logged in and working at once, each with their own files and permissions, without stepping on each other. Multitasking means the system runs many programs simultaneously, your script, someone's compiler, the web server, all at the same time.
These are not add-ons bolted on later; Linux was designed this way from the start, which is why it handles shared, busy servers so well.
Quiz
Several students are logged into the campus Linux server at the same time, each editing their own files. Which Linux feature makes this possible?
- Portability, because it runs on different hardware
- Multiuser, because many users can use the system at once, each with their own account and files
- Open source, because the code is public
- It is not possible; Linux allows only one user at a time
Show the answer
Multiuser, because many users can use the system at once, each with their own account and files
Multiuser is the feature that lets many people use the same system simultaneously, each with a separate account, home directory, and permissions, exactly the shared-server situation described. Option A, portability, is about running on different hardware types, not about multiple simultaneous users. Option C, open source, is about the code being public and modifiable; it does not by itself provide multiple logins. Option D is simply false: multiuser support is a core Linux feature, which is why it dominates on shared servers. Multiuser (many people) and multitasking (many programs) are the traits that make Linux ideal for servers.
Think first
Why does open source make Linux more trusted, not less?
It might seem that public source code would make a system easier to attack. Why is the opposite generally argued? Then tap.
Show the answer
Because open source means the code can be inspected, tested, and fixed by anyone, so problems are found and corrected in the open rather than hidden. With Linux, thousands of developers and organisations worldwide can read the source, spot security flaws, and submit fixes, so bugs tend to be caught and patched quickly, and you are never dependent on a single company's goodwill or schedule. You are also free to run it without licence fees, modify it for your needs, and know exactly what it does, there are no secret parts. The security argument is that 'many eyes' scrutinising open code catches more problems than a small closed team, and indeed the most security-sensitive infrastructure on earth, banks, governments, the core of the internet, runs on Linux. Openness also prevents lock-in: because the system is free and modifiable, it has been adapted to run everywhere, from tiny devices to supercomputers. Transparency, community fixing, freedom from fees and lock-in: that is why open source is a strength.
Summary
Key takeaways
- Linux is a free, open-source operating system that runs most of the world's servers; you will learn it hands-on this semester.
- Strictly, Linux is the kernel; a full system pairs it with GNU utilities, hence GNU/Linux.
- Open source and free: the source code is public and anyone may use, study, and modify it.
- Multiuser: many users can work on one system at once, each with their own account and files.
- Multitasking: many programs run at the same time; both were designed in from the start.
- It is also portable (many hardware types), secure (users and permissions), and stable (long uptimes).
- Memory hook: free and open, multiuser and multitasking, the server's operating system.