Open Source: The GPL, Your CMS Project and You

By Dee-Ann LeBlanc (@deele) Apr 21, 2009

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As the best-known free software and open source license, the GNU General Public License, or GPL, has become both a rallying point for the free software and open source (FLOSS) communities and a focus of FUD (Fear, Uncertainty and Doubt) campaigns for those who fear that these movements will destroy their revenue streams.

Let's take a look at some of the issues and misunderstandings that get in the way.

Common Misunderstandings

Let's hit the easy stuff first. The GPL in no way prevents you from selling your software.

It also doesn't mean you have to give the source to anyone that asks, even people who aren't your customers and the GPL does not cover the program's output. If you want to license the output of something you can do so however you like — as long as part of the program's source isn't part of the output.

The GPL does state that if you sell your software to someone in binary form and they ask for the source, you have to give it to them for the reasonable cost of the materials (say, a CD) and shipping. Or, you can't charge a fee for downloading the source that's higher than you charged for downloading the binary.

Also, if you modify a GPL'd program for your own purposes in-house, you do not have to release that modification. However, if you distribute your changes, then you also have to make the modified source available.

The GPL and Versions

One clause you'll find in the license declarations from many popular open source Content Management Systems is the statement that the software is licensed under "GPLv2 or any later version of the GPL."

If you've never encountered this statement before, it can be jarring. Yet, this is the recommended approach from the Software Freedom Law Center, the entity that advises many of the major FLOSS CMS projects — Drupal and Joomla! for example.

According to footnote 9 in "A Practical Guide to GPL Compliance":

However, most so-called GPLv2 programs are actually distributed with permission to redistribute under GPLv2 or any later version of the GPL (“GPLv2-or-later”). In the latter cases, the redistributor can choose to redistribute under GPLv2, GPLv3, GPLv2-or-later or even GPLv3-or-later. Where the redistributor has chosen v2 explicitly, the v2 termination provision will always apply. If the redistributor has chosen v3, the v3 termination provision will always apply. If the redistributor has chosen GPLv2-or-later, then the redistributor may want to narrow to GPLv3-only upon violation, to take advantage of the termination provisions in v3.

Making Complicated More Complex?

Does using such language ultimately complicate already complex legal issues? Neither the Free Software Foundation nor the Software Freedom Law Center seem to think so.

According to Pamela Jones of Groklaw, this phrasing is designed to legally and administratively simplify things for FLOSS projects. "It also makes enforcement by FSF faster and quicker, for those parts of code that are given over to FSF to protect."

GPLv2 and GPLv3 Incompatibilities

Another issue the phrasing simplifies is the fact that the GPLv2 and GPLv3 are in some cases not compatible with one another. If you have a project that needs to use some code licensed under GPLv2 and some code licensed under GPLv3, adopting the "or later" language can help ensure license compatibility.

Joe Brockmeier, openSUSE Community Manager, says that he feels that the suggestion to use "or later" is a way of pushing people to adopt the most recent version of the GPL, version 3, which has not been adopted as broadly as version 2. Brockmeier says he prefers "specificity," as far as linking to the specific version of the license that's in use.