GNU, Copyleft, and Licenses
Ximena posts online a program she made to keep the accounts for her family's little corner store. Two months later, a company downloads it, adds features, sells it, and shares nothing about what it changed. Could it do that? It depends on the license Ximena chose. On this page you will see what licenses exist and what consequences each one has.
GNU and Linux: Two Pieces of One System
In 1983 Richard Stallman announced the GNU project: to create a complete operating system that would be free, meaning that anyone could use, study, modify, and share it. The name is a recursive pun: "GNU is Not Unix."
By 1990 GNU already had almost everything: a compiler, a text editor, a command interpreter, and many tools. It was missing one central piece, the kernel, which is the part of the operating system that talks directly to the hardware: memory, processor, disks.
In 1991 Linus Torvalds, a Finnish student, wrote a kernel and shared it under a free license. It was called Linux. Combining the Linux kernel with the GNU tools produced a complete, free operating system.
That is why many people say GNU/Linux: Linux is only the kernel; the complete system was built with the GNU tools and the kernel together. In everyday use people simply say "Linux," but the longer name acknowledges both contributions.
Explain in your own words the relationship between the GNU project (started in 1983 by Richard Stallman to create a free operating system) and the Linux kernel (written…
Explain in your own words the relationship between the GNU project (started in 1983 by Richard Stallman to create a free operating system) and the Linux kernel (written by Linus Torvalds in 1991), and why the complete system is usually called GNU/Linux. Also define what copyleft is using the analogy of a shared recipe that forces you to share its variations.
What Copyleft Is
Every program has copyright: by default, no one else can copy or modify it without permission. A license is the permission that the author grants to use their work and the conditions under which it may be used.
Stallman came up with a clever legal trick: using copyright to guarantee freedom instead of restricting it. This is called copyleft (a play on copyright).
Think of a shared recipe. Your grandmother gives you her mole recipe with one condition: you can change it and cook it however you like, but if you share your version, you must also share the recipe with the same permissions. That way, all the variations stay open.
The best-known copyleft license is the GPL (GNU General Public License). Linux and many GNU programs use the GPL.
Permissive Licenses
Not all free licenses require sharing improvements. Permissive licenses (MIT, BSD, Apache) impose very few conditions: usually they only ask that the notice of authorship be kept. They allow someone to take the code, improve it, and distribute it as proprietary software, with the code closed.
| Copyleft (GPL) | Permissive (MIT, BSD, Apache) | |
|---|---|---|
| Use and modify | Yes | Yes |
| Redistribute | Yes | Yes |
| Derivatives must have open code | Yes | No |
| Can be built into proprietary software | No | Yes |
Which is better? It depends on the goal. Copyleft protects knowledge so that it stays common property. Permissive licenses aim for the widest possible spread, even if someone closes it later.
Creative Commons for Non-Software Works
For texts, photos, music, or videos, Creative Commons (CC) licenses are used. The author combines conditions:
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BY (attribution): credit must be given to the author.
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NC (noncommercial): commercial use is not allowed.
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ND (no derivatives): the work may not be modified.
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SA (share alike): derivative works must use the same license. This is the equivalent of copyleft.
So a CC BY-SA license asks for credit and for derivatives to be shared alike (copyleft). CC BY asks only for credit, like a permissive license. With ND or NC, the author limits derivative works or commercial use.
What Happens If a License Is Broken
Imagine the case from the beginning with a GPL license: a company improves the program and sells the version without publishing its code.
A company takes a copyleft-licensed program, improves it and sells the improved version without publishing the code of its improvements. Explain whether it respects the…
A company takes a copyleft-licensed program, improves it and sells the improved version without publishing the code of its improvements. Explain whether it respects the license and why, what the program's community can do about it, and what would have changed if the original license had been a permissive one (for example, MIT or BSD), which does allow derivative works to be closed.
Summary
Go back to the beginning: if Ximena chose the GPL, the company must share its improvements; if she chose MIT, it can close them.