[LAU] GPL vs GPLv3

[Chris Cannam]

On Thu, Jun 10, 2010 at 10:19 AM, Atte André Jensen <atte at email.dk> wrote:
> I write a little code from time to time. I just discovered that at least
> some of it is still under GPL. Now I'm thinking about changing that to
> GPLv3.
>
> 1) Can I Just Do It, simply by stating on the webpage and/or in the software
> that it's under GPLv3.

If you own the copyright, and it doesn't use any GPLv2-only libraries,
then yes.  Though it won't affect any copies previously distributed.

> 2) Is it (as I understand from
> http://www.gnu.org/licenses/rms-why-gplv3.html) recommended to change to
> GPLv3? What are the main advantages (both for the community and me) with
> GPLv3 and are there any drawbacks?

I think the practical drawbacks are:

 * it is not compatible with GPLv2, so you can't mix v2-only and
v3-only code (you can mix v2-or-later and v3 code, but the result is
plain v3)

 * the licence is quite complex (although I have read and understood
the whole of GPLv2, I can't say the same for v3)

As a consequence of this second point, I can't say with real
confidence what the advantages of v3 are.  I _think_ that the main
ones are to disallow distributors from using technical means to
prevent users from running modified code, and to be more specific
about how any patents associated with the code must be licensed.

I'm sticking with v2 for my code at the moment, but there is some
complexity because some projects I work on have the "or later" clause
and some do not.  I do worry that at some point, someone will change
to v3-only a library required by a v2-only application, and so make
the application illegal to distribute with newer versions of the
library.  Indeed, it's not impossible that this has already happened
and I just haven't noticed it.


Chris