On Mon, Jan 29, 2001 at 12:58:35PM +0000, Chris Withers wrote:
> And the reason I asked is 'cos, as I understand it, if I use a GPL-licensed
> product in a product/solution I provide, then I have to do that for free and
> open source it too, which often isn't an option :-(

Nope, that's wrong.

If you extend a GPL-licensed product by your own work, and if you want to
distribute this to somebody else, then you have to give this "somebody" the
right to re-distribute the complete product (including your own work) under
the terms of the GPL.

Therefore it's no problem to sell such a product... The important thing is,
though, that your customer could give away the result to everybody else for
free (and could do everything else with it that the GPL allows).

And in fact, yes, you'll have to make available the sources of your work,
too, for your customer--if he demands to see them.

So it's perfectly fine to use GPL software in a consulting work, and let the
customer pay for it--if you give him all the other rights granted in the

A very crucial point is the exact definition of "extending a
GPL-licensed product" (that's my own words for "derived work"). According to
the FSF, typical things of "deriving a work" from a GPL-licensed product are
probably modifying or extending the code, reusing portions of the code, but
also linking with it (be it statically or shared). In the field of
interpreted languages, it gets even more complicated.

It's completely clear on the other hand, that a mere aggregetion of the
product (e.g. distribution GNU emacs on a CD with proprietary software) is
no problem, and it's also no problem to use GNU tools to produce proprietary
output (e.g. using GCC to compile a proprietary program).

The GPL definitely is not contra selling software or services (one could
even argue that it's the perfect solution for specialized consulting
products, since it gives the customer a security that he'll be able to buy
support for a product even if the original author has lost interest).

Have a look at www.gnu.org, e.g. "Selling Free Software" by RMS
(http://www.gnu.org/philosophy/selling.html) is especially interesting.


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