The Basics of the GPL

Filed as Features on July 7, 2009 4:40 pm

HeckertThere has been a lot of talk and a lot of confusion in blogging circles, especially among WordPress users, about the GNU General Public License or GPL as it is more commonly known.

When most people think of the GPL, they immediately think of Linux, Firefox (which actually uses several licenses, including the GPL) or other well-known programs that use it. However, several blogging platforms are also GPL including WordPress and Open Melody, a fork of Six Apart’s Open Movable Type project.

Over the next few weeks, we’re going to take a look at the GPL, what it is, what it means and, most importantly why it is important to bloggers and those who are running Web sites on open source platforms (including, for example, phpBB).

To start off, we’re going to talk about some of the basic premises of the GPL, what the actual license says and what your freedoms and rights are with GPLed software.

Open Source and The Two Kinds of Free

Open source software is a very broad term that describes software distributed under a license that, among other things, allows users to distribute the work, allows the creation of derivative works and allows access to the source code among other rights. The GPL is one of many different licenses classified by the Open Source Initiative as meeting their standards and is easily one of the most popular.

It is important to note that, in open source circles, there are two common definitions of the word “free”. The first is free as in “free beer”, which refers to the amount paid, and the other is free as in “freedom” or “free speech”, which refers to the rights that the user has over the software they acquire.

With open source software, it is the latter “free” that is protected. GPL and open source software, though often distributed at no cost, is not always free of cost. There are many Linux distributions, such as several Red Hat versions, that cost money though they are still licensed under the GPL.

The caveat to this is that any person who purchases a copy of the software must receive a copy of the source code and can redistribute the software without cost. Thus, every customer could, at least theoretically, turn around and give away your product for free without a license.

For this reason, many for-profit companies that distribute GPL software distribute the product for free, but sell service contracts and support.

But how does the GPL ensure these freedoms, especially over the long term? The answer lies within the license itself.

The Foundations of the GPL

The GPL is founded on four key principles, each of which are reflected in the license itself.

  • The freedom to use the software for any purpose,
  • The freedom to change the software to suit your needs,
  • The freedom to share the software with your friends and neighbors, and
  • The freedom to share the changes you make.

Any software licensed under terms that protect these four rights is considered “free”. The GPL protects these four rights through two very simple clauses contained within it, the first of which says:

You may convey verbatim copies of the Program’s source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice; keep intact all notices stating that this License and any non-permissive terms added in accord with section 7 apply to the code; keep intact all notices of the absence of any warranty; and give all recipients a copy of this License along with the Program.

This section deals with verbatim or exact copies of a GPL work, saying that you can distribute copies as you wish, including charging for them, so long as you keep intact all disclaimers and provide a copy of the license. If you distribute the work in a binary or other non-source code format, such as an exe file, you must also make the source available.

The second, and perhaps more important protection, is in the handling of modified versions of the source code, where the license says:

You may convey a work based on the Program, or the modifications to produce it from the Program, in the form of source code under the terms of section 4, provided that you also meet all of these conditions:

a) The work must carry prominent notices stating that you modified it, and giving a relevant date.

b) The work must carry prominent notices stating that it is released under this License and any conditions added under section 7. This requirement modifies the requirement in section 4 to “keep intact all notices”.

c) You must license the entire work, as a whole, under this License to anyone who comes into possession of a copy. This License will therefore apply, along with any applicable section 7 additional terms, to the whole of the work, and all its parts, regardless of how they are packaged. This License gives no permission to license the work in any other way, but it does not invalidate such permission if you have separately received it.

d) If the work has interactive user interfaces, each must display Appropriate Legal Notices; however, if the Program has interactive interfaces that do not display Appropriate Legal Notices, your work need not make them do so.

This allows others, without obtaining any additional license to make and distribute modified versions of the source code so long as their modifications are licensed under the same license. This prevents others from taking a GPLed work, writing some new code for it, and then licensing it under their own, more restrictive license.

This helps to ensure that the “free” software remains free, no matter who modifies it and for what reasons.

It is these protections that make GPL software so appealing to bloggers and other Webmasters. Even though many are lured in by the free price tag on most GPL content management systems, it is these GPL provisions that serve to ensure the longevity of these projects and that bloggers/Webmasters who depend on them will have built their sites on very solid ground.

Next Up: Why GPL Blogging Software is Important

Tags: , , , , ,

This post was written by

You can visit the for a short bio, more posts, and other information about the author.

Submissions & Subscriptions

Submit the post to Reddit, StumbleUpon, Digg or Del.icio.us.

Did you like it? Then subscribe to our RSS feed!



  1. By calendrier posted on July 7, 2009 at 6:14 pm
    Want an avatar? Get a gravatar! • You can link to this comment

    Very interesting.

    Reply

  2. By Ben Cook posted on July 7, 2009 at 8:28 pm
    Want an avatar? Get a gravatar! • You can link to this comment

    Wow, that’s probably the best explanation of the GPL that I’ve read to date.

    I’ve been mulling over the GPL use among WordPress theme developers quite a bit lately & this post helped solidify things for me.

    That one of the core principles is “The freedom to share the software with your friends and neighbors” is HUGE. While many theme developers SAY they’re GPL compliant, they certainly don’t seem to like or support this core principle.

    Reply

  3. By Byrne Reese posted on July 7, 2009 at 8:29 pm
    Want an avatar? Get a gravatar! • You can link to this comment

    I think it would be far more beneficial, rather than recapitulating the text of the GPL itself, to define for people what the GPL *can’t* do.

    The GPL for example cannot force anyone to change their license. It does not “infect” code. That is impossible. If I were to be in violation of the GPL, there are only two choices I have: a) stop distributing my software, or b) bring my software in compliance with the GPL license. Independent of those two choices are the damages one might seek for my having violated the license.

    So, if the claim that all proprietary, non-open source WordPress themes are in violation of the GPL, no one can rightfully claim that those themes are now open source as a result. Such a claim has absolutely no legal basis.

    But these are the things that people don’t understand and where more clarity needs to be provided. Here are some more topics to cover:

    * the definition of “dynamic linking” as it pertains to GPL’ed code.
    * the history of the GPL being challenged in court and what legal precedent actually exists.

    Reply

    Your words are your own, so be nice and helpful if you can. If this is the first time you're posting a comment, it might go into moderation. Don't worry, it's not lost, so there's no need to repost it! We accept clean XHTML in comments, but don't overdo it please.

    Current ye@r *