Xming appears to be a useful program for accessing and running your GNU/Linux applications remotely from a Windows computer. It is licensed under the GPLv2. But just how free is it, really?

Xming looks like a great tool for connecting Windows boxes to remote GNU/Linux computers to run applications. And, according to the license included with the software, it is released under the terms of the LGPLv2. Unfortunately, the developer's website includes a strange notice that poses a potentially confusing challenge for those who wish to redistribute the software. In addition to the GNU GPL license, the author requires that anyone desiring to redistribute the software must ask permission to do so.

According to the 3rd paragraph (displayed according to "fair use", as allowed by U.S. copyright law):

Xming is mostly a derivative work with many component licenses e.g. the zlib license, LGPLv2 for Pthreads, MIT/X11 for all PuTTY tools and the Pixman library, or Creative Commons by-nc-sa. Redistributing any part (or whole) of the Xming website, documentation, images, executables or installers, by the internet, other projects/products or via media such as CD's, without asking permission, attributing 'Colin Harrison' and providing links to http://StraightRunning.com/XmingNotes/ and SourceForge Project Xming will be regarded as a breach of copyright.

Note that the statement, as it currently reads, states quite clearly that the program is derived from several others, including software licensed under the GNU LGPLv2. The statement then refers to redistributing any part (or whole). Taken as is, the statement appears to cover the upstream code licensed under the terms of the LGPLv2 - in violation of that license's Section 10. Whether this is what Colin Harrison, the Xming developer intends is another question.

When Blue GNU contacted Harrison seeking clarification, his initial response was that if I don't like the license, I don't have to use the software. When I clarified that I was not attempting to engage in a debate, he replied that, "I don't have the time to explain my licensing at the moment. When the dust settles on the GPLv3 debate I will clarify the situation more in Xming." Meanwhile, the statement leads to possible confusion now, and downstream users need to be clear as to what is covered and what is not.

Harrison did take time to complain "that most of the software I have written in the past for free is now embedded in devices and products that I don't have source access to, or even change feedback or attribution." He did not specify whether he thought any of these uses were in violation of his license, or whether he has made any effort to enforce his license in such cases. He went on to further complain about "freeloaders" who do not give "attribution" without being more specific.

Harrison's e-mail ended with a question about whether FOSS might be devaluing the expertise of professional developers. Blue GNU has replied further saying that clarification of the statement on the website is needed, since Xming may be violating the LGPLv2 under which Pthreads is distributed by adding further restrictions on the software (section 10 of the LGPLv2) and failing to make the source code available. No source code for Pthreads is available from the Xming site, nor included in the distribution. Blue GNU also contacted the Win32 Pthreads developers and the FSF to find out if they agree there might be a violation.

Harrison's stipulation that redistributed copies of Xming must include links back to his own project appear hypocritical in view of the fact that he does not link back to the projects mentioned in the same paragraph. And, while it might withstand scrutiny in court, the stipulation amounts to a sort of advertising clause - something that has always been considered problematic. Perhaps this could have been better resolved through a trademark?

Neither Colin Harrison, the Pthreads developers, nor the FSF have had time to respond to the latest e-mails, so it remains to be seen how the issue will play out. However, the situation does raise some serious questions about how well developers understand Free Software licenses.

• How well do developers understand the various licenses they choose to use?
• Do they even bother to read them, or do they simply choose them because they're canned legalese?
• How well do people really understand that Free Software, according to the Free Software Definition and other documents, must be free to distribute and use commercially (for any purpose)?
• Do developers understand that a company, an individual - anyone - can modify Free Software in-house, and never give back so much as a comment, as long as they do not redistribute the modified version?
• Can a developer release something under a given license, and then still require explicit permission to redistribute it, or does meeting the license requirements satisfy copyright law?
• How does one define "attribution"? If all the copyright notices are intact, is that not attribution? Or must a project necessarily advertise for its upstream project(s) in order to be considered to be "attributing"?

Developers and others might modify and/or redistribute Free Software should always undertake to read and understand any licenses for code they choose to modify and/or redistribute, so they can ensure compliance. They also need to be clear when imposing additional stipulations that may involve code others have developed, as to exactly what is, and what is not, covered. While the issue can very likely be resolved fairly quickly and with little fanfare, developers could save themselves a little time and a lot of stress by doing some research and communicating clearly from the beginning.

Note: As of 14:25-14:30 GMT-5, the Xming site is returning a time-out error.

LGPL version 2