Re: Cygwin licensing and redistribution, GPLv2, GPLv3

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

On Thu, Jan 27, 2011 at 05:13:21PM -0800, tom honermann wrote:
>On 1/27/2011 4:14 PM, Eric Blake wrote:
>> On 01/27/2011 04:57 PM, tom honermann wrote:
>>> I've been looking into Cygwin licensing and redistribution regarding the
>>> Cygwin DLL and various GNU utilities.  The current Cygwin license
>>> (http://cygwin.com/licensing.html) states (and I'm paraphrasing) that
>>> programs that use the Cygwin DLL do not need to be licensed under GPLv2
>>> (or compatible) so long as they are distributed with a license that
>>> meets the OSI's open source definition AND that the cygwin DLL is not
>>> distributed with the program.  With the release of the GPLv3 license and
>>> subsequent re-licensing, some of the GNU utilities included with the
>>> Cygwin distribution are now GPLv3 (or later).  The GPLv2 and GPLv3
>>> licenses are not compatible
>>> (http://www.gnu.org/licenses/gpl-faq.html#v2v3Compatibility).
>> Wrong list.  Ask on cygwin-licensing.
>Thanks Eric.  Copying cygwin-licensing instead now...
>>> The way I interpret this, this effectively means that no entity other than RedHat
>>> can distribute GPLv3 GNU utilities dynamically linked with the Cygwin
>>> DLL and include the Cygwin DLL with the GNU utilities (without
>>> additional permissions by RedHat).  This also means that no entity other
>>> than RedHat can redistribute the RedHat Cygwin distribution or build
>>> their own Cygwin distribution unless all programs are linked with a
>>> static version of the Cygwin library (again, without additional
>>> permissions by RedHat).  Does this sound right?  If so, is this an
>>> intentional property of the Cygwin license?
>> Short answer - wrong interpretation.  The cygwin license exception
>> specifically states that a GPLv3 program (by virtue of being an OSI
>> approved license) can be linked against cygwin and distributed as though
>> the GPLv2 of cygwin were not present.  Therefore, the GPLv2-only nature
>> of cygwin does not interfere with the GPLv3 license of the program.
>
>The exception posted at http://cygwin.com/licensing.html explicitly
>states "Note that this does not apply to the Cygwin???  DLL itself.  If
>you distribute the Cygwin???  DLL, either in its original form or in a
>form modified by you, you must adhere to the terms of the GPL".
>
>I've been reading this as requiring that distribution of programs that
>use the Cygwin DLL either must not distribute the Cygwin DLL (ie, the
>program must be installed and used with an existing Cygwin
>installation), or, if the distribution does include the Cygwin DLL,
>then uses of the Cygwin DLL must be in accordance with the GPL(v2).
>Perhaps this statement is only meant to indicate that changes to the
>Cygwin DLL itself must be licensed in accordance with the GPL(v2)?  As
>stated, it isn't clear that the open source licensing exception applies
>to copies of the Cygwin DLL distributed by entities other than Red Hat.

The sole intent of that paragraph is to underscore the fact that if you
distribute a binary Cygwin DLL you must provide sources for the DLL.
There is no override to the GPLv2 license under which the Cygwin DLL and
its assocated utilities are provided.

So, again:  if your distribution contains cygwin1.dll or mount.exe or
any of the binaries which are built from the winsup source directory
used to build the core of Cygwin then you must adhere to the GPL and
provide the sources too.