The GNU Free Documentation License (GNU FDL or simply GFDL) is a copyleft license for free documentation, designed by the Free Software Foundation (FSF) for the GNU Project. It is similar to the GNU General Public License, giving readers the rights to copy, redistribute and modify a work and requires all copies and derivatives to be available under the same license. Copies may also be sold commercially, but, if produced in larger quantities (greater than 100), the original document or source code must be made available to the work's recipient.
The GFDL was designed for manuals, textbooks, other reference and instructional materials, and documentation which often accompanies GNU software. However, it can be used for any text-based work, regardless of subject matter. For example, the free online encyclopedia Wikipedia uses the GFDL for all of its text.
The FDL was released in draft form for feedback in late 1999. After revisions, version 1.1 was issued in March, year 2000, and version 1.2 in November 2002. The current state of the license is version 1.2.
The first discussion draft of the GNU Free Documentation License version 2 was released on September 26 2006, along with a draft of the new GNU Simpler Free Documentation License.
The new draft of the GNU FDL includes a number of improvements, such as new terms crafted during the GPLv3 process to improve internationalization, clarifications to help people applying the license to audio and video, and relaxed requirements for using an excerpt from a work.
The new proposed GNU Simpler Free Documentation License has no requirements to maintain Cover Texts and Invariant Sections. This will provide a simpler licensing option for authors who do not wish to use these features in the GNU FDL.
On December 1 2007, Jimmy Wales announced that a long period of discussion and negotiation between and amongst the Free Software Foundation, Creative Commons, the Wikimedia Foundation and others have produced a proposal supported by both the FSF and Creative Commons to modify the Free Documentation License in such a fashion as to allow the possibility for the Wikimedia Foundation to migrate the projects to CC-BY-SA.
Material licensed under the current version of the license can be used for any purpose, as long as the use meets certain conditions.
- All previous authors of the work must be attributed.
- All changes to the work must be logged.
- All derivative works must be licensed under the same license.
- The full text of the license, unmodified invariant sections as defined by the author if any, and any other added warranty disclaimers (such as a general disclaimer alerting readers that the document may not be accurate for example) and copyright notices from previous versions must be maintained.
- Technical measures such as DRM may not be used to control or obstruct distribution or editing of the document.
The license explicitly separates any kind of "Document" from "Secondary Sections", which may not be integrated with the Document, but exist as front-matter materials or appendices. Secondary sections can contain information regarding the author's or publisher's relationship to the subject matter, but not any subject matter itself. While the Document itself is wholly editable, and is essentially covered by a license equivalent to (but mutually incompatible with) the GNU General Public License
, some of the secondary sections have various restrictions designed primarily to deal with proper attribution to previous authors.
Specifically, the authors of prior versions have to be acknowledged and certain "invariant sections" specified by the original author and dealing with his or her relationship to the subject matter may not be changed. If the material is modified, its title has to be changed (unless the prior authors give permission to retain the title). The license also has provisions for the handling of front-cover and back-cover texts of books, as well as for "History", "Acknowledgements", "Dedications" and "Endorsements" sections.
The GFDL requires the ability to "copy and distribute the Document in any medium, either commercially or noncommercially" and therefore is incompatible with material that excludes commercial re-use. Material that restricts commercial re-use is incompatible with the license and cannot be incorporated into the work. However, incorporating such restricted material may be fair use
under United States copyright law and does not need to be licensed to fall within the GFDL if such fair use is covered by all potential subsequent uses. One example of such liberal and commercial fair use is parody
Wikipedia, the best-known user of the GFDL, has never taken anyone to court to enforce its license. A Dutch court has enforced a similar license - CC-BY-NC-SA
- against a commercial magazine that reprinted photos that had been uploaded to Flickr
Criticism of the GFDL
project and Nathanael Nerode
have raised objections. Debian developers eventually voted to consider works licensed under the GFDL to comply with their Debian Free Software Guidelines
provided the invariant section clauses are not used. These critics recommend the use of alternative licenses such as the share-alike Creative Commons licenses
, the BSD Documentation License
, or even the GNU GPL. They consider the GFDL a non-free license. The reasons for this are that the GFDL allows "invariant" text which cannot be modified or removed, and that its prohibition against digital rights management
(DRM) systems applies to valid usages, like for "private copies made and not distributed".
The GNU FDL contains the statement:
A criticism of this language is that it is too broad, because it applies to private copies made but not distributed. This means that a licensee is not allowed to save document copies "made" in a proprietary file format or using encryption.
In 2003, Richard Stallman said about the above sentence on the debian-legal mailing list:
A GNU FDL work can quickly be encumbered because a new, different, title must be given and a list of previous titles must be kept. This could lead to the situation where there are a whole series of title pages, and dedications, in each and every copy of the book if it has a long lineage. These pages cannot be removed until the work enters the public domain
Richard Stallman said about invariant sections on the debian-legal mailing list:
GPL incompatible in both directions
The GNU FDL is incompatible
in both directions with the GPL: that is GNU FDL material cannot be put into GPL code and GPL code cannot be put into a GNU FDL manual.
Because of this, code samples are often dual-licensed
so that they may appear in documentation and can be incorporated into a free software program.
At the June 22nd and 23rd 2006 international GPLv3 conference in Barcelona, Eben Moglen hinted that a future version of the GPL could be made suitable for documentation:
Burdens when printing
The GNU FDL requires that licensees, when printing a document covered by the license, must also include "this License, the copyright notices, and the license notice saying this License applies to the Document". This means that if a licensee prints out a copy of an article whose text is covered under the GNU FDL, he or she must also include a copyright notice and a physical printout of the GNU FDL, which is a significantly large document in itself. Worse, the same is required for the standalone use of just one (for example, Wikipedia) image.
The definition of a "transparent" format is complicated, and may be difficult to apply. For example, drawings are required to be in a format that allows them to be revised straightforwardly with "some widely available drawing editor." The definition of "widely available" may be difficult to interpret, and may change over time, since, e.g., the open-source Inkscape
editor is rapidly maturing, but has not yet reached version 1.0. This section, which was rewritten somewhat between versions 1.1 and 1.2 of the license, uses the terms "widely available" and "proprietary" inconsistently and without defining them. According to a strict interpretation of the license, the references to "generic text editors" could be interpreted as ruling out any non-human-readable format even if used by an open-source word-processor; according to a loose interpretation, however, Microsoft Word
.doc format could qualify as transparent, since a subset of .doc files can be edited perfectly using OpenOffice.org
, and the format therefore is not one "that can be read and edited only by proprietary word processors."
Other free content licenses
Some of these were developed independently of the GNU FDL, while others were developed in response to perceived flaws in the GNU FDL.
List of projects that use GFDL