Why You Shouldn't Use the GNU FDL

Created by Nathanael Nerode.

This page last modified September 24, 2003.

What's wrong with it?

If you're considering the GNU FDL, you probably want to write free, open-source documentation, to go with your free, open-source program. The Free Software Foundation promotes the GNU General Public License version 2 (GPL) for software, and the so-called GNU Free Documentation License (GFDL) for documentation.

But the GFDL is not a free license in the same sense as the GPL.

The FSF actually admits this. The stated view is that different freedoms are needed for documentation than for programs. I, like many people who appreciate the importance of documentation for programs, disagree strongly with this.

The over-broad DRM clause

In a previous version of this page, I wrote:

"If you use the GFDL but don't use Invariant Sections or Cover Texts, and don't include an "Acknowledgements" or "Dedications" section, this is free."

However, I have since been made aware of another issue. The GFDL says the following:

"You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute."

This was intended to attack DRM systems, but it is far too broad. It applies to private copies made and not distributed. "Technical measures" is not defined. The natural interpretation includes activities like encrypting a copy, storing it on an encrypted filesystem, or even storing it on a file-sharing system with non-world-readable permissions. This is evidently not free.

Hopefully the FSF will fix this some time -- in my opinion, replacing "make or distribute" with "make and distribute" would be a good start.

Invariant Sections and related problems

The other problems with freeness lie in the rules on "Invariant Sections", "Cover Texts", "Acknowledgements", and "Dedications". These are not modifiable, and not even removable. First of all, the Invariant Sections are clearly not freely modifiable themselves, which means that they are not free in the "free software" sense of the GPL. Since they are "Secondary Sections", off-topic by definition, some people may not care about that.

But Invariant Sections and Cover Texts constitute a restriction on the modifiability of the technical material -- the documentation -- in the GFDL-covered document, because they can't be removed, ever. The documentation is forever shackled to the Invariant Sections. This makes documentation licensed under the GFDL with Invariant Sections not free (in the sense of 'free software' as used in the GPL).

Clearly not all restrictions on modification make a work non-free; some are trivial. (The requirement to accompany any version of the work with accurate copyright notices and copies of the license, for instance, is a trivial restriction). But this is not a trivial restriction; it is a troublesome one for many reasons:

Because the GFDL with Invariant Sections or Cover Texts is non-free, the Debian project is removing all manuals under such licenses from Debian. So if you want your manual to make it into Debian, you shouldn't use the GFDL.

Beyond its non-free status, the GFDL has additional serious practical problems:

What should I do?

So the GFDL is a very poor license for manuals for free programs. I recommend that you use the same license as the program has; this prevents an awful lot of future problems.

Isn't the GFDL just like the GPL?

Some people ask, "Why doesn't the GPL cause the same problems? It puts restrictions on what sort of modifications can be redistributed." There are only two clauses of the GPL which are significant here:

It's not about misrepresentation!

Some people apparently think that Invariant Sections are needed just to prevent people from misrepresenting other people's opinions. They're not.

If you're still concerned about not being given credit, clauses requiring attribution are present in many free licenses, including the GPL, and are perfectly acceptable.

If you want to put in a statement with your license which says "This license shall not be construed to give anyone permission to misrepresent my opinion, or to commit fraud, or to deliberately mislead anyone," go ahead. That's perfectly free. It isn't actually an extra condition, so it could even be used with the GPL.

If you're still concerned about having your opinion misrepresented, you can put in a clause like this: All modified versions must prominently state that they do not necessarily represent the opinions of [original author]. This is perfectly acceptable and free.

The GFDL goes much, much further than that. Here's an example of something which should be allowed for a free essay, but isn't permitted for a GFDL Invariant Section such as the GNU Manifesto is for the Emacs manual:

The Foo Manifesto, by Mr. Foo

This is based on the GNU Manifesto, by Richard Stallman, but does not necessarily represent his opinions.

GFDL'ed invariant sections prohibit modification. You probably just want to require that modified versions don't pretend to be your version, and possibly that they credit you as the author of the original. This can be accomplished much more easily, with better, freer licenses.

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