The Free Software Foundation (FSF) has been working for many months on version 3 of the GPL (General Public License), which is by far the most popular Open Source license. Currently over 65% of the 42,611 Open Source licensed software projects at the repository use the GPL. The wildly successful Linux operating system is, of course, among them. The Apache Software Foundation hosts several very important Open Source software projects, including Apache (web server), Lucene (search), Perl (programming language), Spam Assassin (spam filtering), and a variety of related tools. They all use the Apache license, which has a fraction of the GPL’s mindshare. However, Apache server software runs approximately 58% of the web servers on the Internet, and is more often than not running on Linux. If you’re doing business on the Web (and who isn’t?) the odds are good that you’re using both Apache and Linux. The Apache and GPL have a long and somewhat contentious history, despite the frequent symbiosis between GPL’d and Apache-licensed software. Whether the current versions of the Apache and GPL licenses are compatible depends on who is doing the interpreting. The FSF characterizes Apache 2.0thusly:

This is a free software license but it is incompatible with the GPL. The Apache License is incompatible with the GPL because it has a specific requirement that is not in the GPL: it has certain patent termination cases that the GPL does not require. (We don’t think those patent termination cases are inherently a bad idea, but nonetheless they are incompatible with the GNU GPL.)

The Apache Software Foundation counters


The Apache Software Foundation considers this issue to be in legal limbo, at least until we get a definitive answer regarding the survivability of implied patent licenses. We are still working with the FSF in order to resolve the issue, which may result in future changes to either or both of our licenses. In the mean time, the FSF requests that you do not consider the two licenses to be compatible. The Apache Software Foundation believes that you should always try to obey the constraints expressed by the copyright holder when redistributing their work, even when those constraints may be unclear. In the future, we hope that the FSF will find a way to express their license terms such that they are understandable by recipients of the license, rather than requiring interpretation of the people who wrote it.

So is v3 of the GPL clearing up the issue? Allison Randal recently tackled the question, and was dismayed to find that the FSF still thinks GPL/Apache compatibility is not achievable. She quotes the GPL v3 second draft rationale document:

We regret that we will not achieve compatibility of the Apache License, Version 2.0, with GPLv3, despite what we had previously promised.

It seems this time around the Apache license patent termination terms are not the issue; the disclaimer of warranty is the bone of contention. Under both licenses, developers disclaim warranty. However, under the current draft of GPL v3, developers may provide warranty protection for a fee. Randal asks:

Is the FSF saying that when a downstream company takes on the legal burden to indemnify a piece of GPL software, they expect the developers to also take on that legal burden? Or, in the case where the FSF is the copyright holder, that they intend to take the legal burden of indemnification themselves?

The comments are particularly interesting, since Open Source expert Lawrence Rosen (who formerly served as General Counsel for the Open Source Initiative, and has advised the Apache Software Foundation) weighs in with this interpretation:

The Rationale document reflects a misunderstanding of Apache license section 9. Nothing in the Apache license requires anyone–including people who distribute Apache’s software as part of a GPL program–to offer indemnity. But if any downstream distributor *does* offer indemnity, they must *also* indemnify, defend and hold harmless Apache and its contributors from any liability or claims asserted “by reason of your accepting any such waranty or additional liability.” As this lawyer sees it, the two licenses are compatible.

GPL v3 is a thorough rewrite, and it has brought in much broader involvement from a range of stakeholders. But given that the Apache Foundation and the FSF’s goals differ, it may be unrealistic to expect the FSF to issue a compatibility seal of approval for Apache by the time GPL v3 is finalized.