Simple. Copyright law says you cannot copy the software.
The license grants an exception to that prohibition, so
you can copy the software under certain circumstances.
Two licenses grant two different exceptions, the
user/distributor gets to choose which exception to use.
Every distributor must decide which license they want
to distribute the program under. You pick one or the other.
So people who want to put the software in the Linux kernel
or want to link to GPLled software choose the GPL. They are
not allowed to distribute without source.
People who want to link to non-source software choose the
special license (eg. Perl's artistic license).
Note that there is not generally thought to be a conflict
between the XFree license and the GPL, so you can actually
conform to both at the same time. That is, both exceptions
to the copying prohibtions can apply simultaneously.
> If it is valid to do both, then both become pointless. Someone
> takes the "foo" sources, and modifies them. When sued, they say
> "Oh, I was using the GPL'd sources". Someone else takes the
Fine.
> sources, and modifies them, not releasing the modifications, and
> sells commercially. When sued by the GPL folk, they say "Oh, I
> was using the commercial copyright, and I've got permission from
> the author."
Also fine.
> If that is the case, then GPL is meaningless. Perhaps you could
Note that only the author(s) can issue the software under
two licenses, and all authors must agree. So if you have
a problem with the above scenario, you don't release under
both licenses.
So why might you want to use two license? Perhaps
your preferred license is incompatible with the GPL
(eg. Netscape's NPL or a license that allows non-source
distribution to noncommercial entities), but you want
users/distributors to be allowed to link to GPL software.
So that may be a reason to release under the GPL or a
license compatible with the GPL.
I am not a lawyer.
-- Erik Corry erik@arbat.com Ceterum censeo, Microsoftem esse delendam!- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/