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GPL vs LGPL, in the context of adns
-----------------------------------
Several people have asked me to release GNU adns under the GNU Lesser
General Public Licence (LGPL, formerly the Library GPL) instead of the
`stronger' GPL. This file is intended to answer most of these
questions. If you still have questions or comments, please mail me at
<adns-maint@chiark.greenend.org.uk>.
Typically there are two or three kinds of situation where people make
this request: the first is where another free software project
currently using a GPL-incompatible licence, wishes to use adns. The
second case, which often overlaps with the first, is where a free
software project is currently using an MIT-like licence or the LGPL
and fear `GPL infection'. The third case is where someone is
developing a proprietary program and wishes to make use of adns but
doesn't wish to make their program free software
1. GPL-incompatible free software licences
------------------------------------------
Regrettably, there are a number of free software licences (and
semi-free licences) in existence which are not compatible with the
GPL. That is, they impose restrictions which are not present in the
GPL, and therefore distributing a whole work which contains both such
a program and a GPL'd program is not possible: either the combination
would have to be distributed under the GPL (violating the restrictions
made by the original author), or under the GPL-incompatible licence
(violating the GPL).
I may be prepared to make exceptions for such a licence. Please
contact me at <adns-maint@chiark.greenend.org.uk> with the full text
of the GPL-incompatible licence. However, I would usually prefer it
if you could use a GPL-compatible licence for your project instead.
2. GPL-avoiding projects (MIT licence, et al)
---------------------------------------------
Some free software projects prefer to avoid the GPL and other licences
which force the software always to be free. Instead they use
something like the MIT X licence, which allows proprietary versions of
their software, or the in the case of some free libraries, the LGPL,
which allows proprietary applications. I have to say that I think
these people are misguided, but that doesn't mean that they don't have
a perfect right to do that.
Some of these people think that merely writing to an interface
provided by GPL'd software will cause their program to become GPL'd
too, even if they don't distribute the GPL'd software. I don't think
this is the case. I'm perfectly happy for non-GPL'd but
GPL-compatible software to refer to adns in its source code. However,
I think that exectuables (or compiled libraries) which contain or are
dynamically linked against adns must be GPL'd; likewise executable
programs (whether compiled or in an interpreted language) which
require utilities from adns to function properly must be GPL'd.
So, you can distribute your non-GPL'd program source which needs adns
to compile (provided it's under a GPL-compatible licence), but people
who wish to distribute binaries must do so under the terms of the GNU
GPL. This may make sense for some GPL-avoiding free software
projects; people can still make proprietary programs from your code,
provided that they make some provision to replace adns with something
whose copyright allows proprietary versions.
However, this doesn't make much sense for the authors of LGPL'd
libraries. All I can say to them is to ask which is more important:
that their library be well-constructed and use all the best technology
available as free software, or whether it is worth degrading quality
of their library in order to allow proprietary programs to use it !
To help the case of LGPL'd libraries for which adns is not a vital
component - for example, a library which provides access to other
libraries so that programs which use it need only use certain parts,
I have released adns.h (just the public header file) under the LGPL as
well as the GPL. See the copyright notice in adns.h for details.
Note that this will not help you if it adns is essential to the
functioning of your library, because all programs using your library
must link against both your library and adns and so must be GPL'd.
For some information and views from the Free Software Foundation on
free software licensing, visit:
Various licenses and comments about them
at http://www.fsf.org/philosophy/license-list.html
Why you shouldn't use the Library GPL for your next library
at http://www.fsf.org/philosophy/why-not-lgpl.html
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