Which free license for textbooks?

Posted Mar 28, 2007 10:23 UTC (Wed) by sanjoy (subscriber, #5026) [Link]

why does the GPLv2 require you to include an offer for machine readable physical media? why wouldn't a printed URL in the back of the book be just as good?

Here is Section 3 of the GPLv2:

You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following:

1. Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,
2. Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,
3. [an option valid only for "occasional, noncommercial" distribution]

If you as the distributor take option 3(a), then you include a CDROM or floppy in the back of the book. If you take option 3(b), then you need to include a written offer to provide the source on a "medium customarily used for software interchange." My understanding is that "medium" in this context means a physical medium such as a CDROM. Of course, you can also just give a URL as well, and hopefully everyone will take it from there instead of asking you for a CDROM. I ran into RMS on a street in Cambridge a few months ago and asked him about the GPL vs the GFDL for textbooks, and he confirmed the above understanding of source distribution. Here is the official FSF explanation.

Of course, what matters in court is the intention of the licensor rather than the explanation from the FSF (if the licensor is not the FSF). But most often, the licensor is a also licensee of upstream GPL code, in which case it's the intention of the original licensor(s) that matter.

One of the Ubuntu developers told me Ubuntu's experience with this clause. They have shipped millons of CDROMs, which also tell people where online to get the source. Despite the huge number shipped, Ubuntu has got only a handful (maybe two or three but I forget the exact number) of requests for a physical medium. It is one reason that the FSF agreed to the Internet-distribution option in the GPLv3 draft.

after all that works for people shipping binaries of GPL software in physical devices (be it Tivo or Linksys or anyone else)

The printed URL is useful, but they also need to include a written offer for people to get a physical medium. I think the requirement is overly strict today, and I hope that the final GPLv3 contains a more modern option.