Armin Ronacher's Thoughts and Writings

Are you sure you want to use GPL?

written on Thursday, February 12, 2009

When I started using Linux I was totally sold to the concept of Open Source. I still am, but my view changed. The first code I released under an Open Source license was GPL licensed and I continued to do so for some time. The last code under the GPL license I actively developed was Zine until a few days before the release when I relicensed it under the modified BSD license.

The reason why I changed the license is a rather complex one and I want to share my experiences with the GPL and other Open Source licenses here for a moment. I suppose many people acted like me and chose the GPL because everyone else did but didn't know about all the implications it has.

Left versus Right

The GPL and BSD (and friends) licenses couldn't be more different. It starts with the length of the paper. The BSD license is two or three clauses of text plus a copyright information and no-warranty clause. The GPLv3 on the other hand has 600 lines of text. BSD restricts the rights, GPL permits. Restricting rights sounds bad, but it just means that you can do everything with it, except the stuff listed in the license. The GPL starts by explaining what you can do with it. The GPL is following the Copyleft principle, something the BSD license is not doing.

This has some very complex implications many GPL / BSD users don't know about but should.

What BSD means

Let's start with the BSD license, the license of my choice. The three clause version is very similar to the MIT license and the two clause version is basically the MIT license. What does it say?

Copyright (c) <year>, <copyright holder> All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
  • Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
  • Neither the name of the <organization> nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

Pretty simple. It allows the user to do everything with the application but removing the Copyright. The third clause means that derived works may not use the author's names for advertising. This clause is not in the 2 clause BSD and MIT licenses.

Now this of course means that someone can take your software, change the branding and sell it. The world is bad and you can be sure that this will happen if your application is worth it. We'll cover that part of the license a little bit later.

Let's see how the GPL works there.

What GPL means

The GPL license is too long to be quoted here, but I'll try to sum up the most important aspects of it:

  • Copies may be distributed free of charge or for money, but the source code has to be shipped or provided free of charge (or at cost price) on demand. The receiver of the source code has the same rights meaning he can share copies free of charge or resell.
  • The licensed material may be analysed or modified.
  • Modified material may be distributed under the same licensing terms but don't have to be distributed.

There is a lot more in the license, like how long source code has to be available and how to deal with that, but the essence is that. Like for the BSD license someone can take the application, rebrand it and sell it, however the license demands that the modified source is available under the same license.

However modifications only have to be made available to the public if distribution happens. So it's perfectly fine to take GPL code, modify it heavily and use it in a not distributed application / library. This is how companies like Google can run their own patched versions of Linux for example.

But what this also means is that non GPL code can't use GPL code which is also the main problem of it.

License Compatibilities

BSD is GPL compatible, but GPL does not permit the use of GPL licensed code in non-GPL code. This is especially annoying if important libraries users expect are GPL. For example the very popular readline library is GPL licensed. Users of OS X will know that, because interactive shells of Python and other non GPL applications sucks there. People tried to rewrite readline to get rid of the GPL problem but the alternatives are not as well maintained as the original one.

I guess this is also what Steve Ballmer referred to as “cancer”. Unfortunately he's not entirely wrong there. For example I tried to develop an interactive administration shell for Zine but without readline (which I cannot use as Zine is BSD licensed) the user experience is just meh. I would have to relicense the entire application to GPL just so that I can have an interactive shell with readline support.


Now this depends on how you define freedom. The people behind the GPL have a very communistic point of view in terms of freedom: free software should be available to everybody under the same terms. Unfortunately like communism it does not work out that well because it turns out humans are not really compatible to that way to look at things. On the other hand there are the permissive licenses like BSD that just give away all rights except the copyright and do not enforce freedom. You can take BSD code and re-license it under the GPL if you want to. That kind of freedom however is a one-way ticket. Once you made a GPL release of your code there will always be a GPL version of it. If not for future releases, at least for that one release as you can't revoke the license.

Making Money

Ultimately the goal of software development for many is to make money. Many people decide to utilize the GPL license for that by dual-licensing the code under the GPL and a proprietary license where the latter is only available to costumers. As a single developer it's arguable harder to sell code that is licensed under the BSD license. There the business model is probably more selling non-open-source extensions to paying costumers. If you open source all your code under the BSD you have to be really good so that you can make money out of it.

Many developers don't really care about that, have their fun developing it and BSD license it for others to start where they stopped. A good example of successful BSD / MIT code are Django and Ruby on Rails. Both projects developed by strong communities with supporting companies behind it. The company behind Rails creates very successful closed source applications based on Rails; Many of the developers working on Django are paid by individual companies that work with it.


Before you license your code under an Open Source license: Think about the license! Both types of licenses have their advantages and disadvantages and it would be stupid to use the GPL without thinking just because “everybody does”. Many just do because they haven't read the license either.

This entry was tagged licensing and rant