[FigBug]

You absolutely can't use GPL libraries like this. If you use a GPL library you are required to release your entire application source code under a GPL compatible license.

With LGPL libraries I find a lot of developers aren't aware of the relinking requirement, but it does get enforced. That's why you won't find LGPL libraries being used in the iOS App Store and why you need to buy a commercial license for Qt for mobile.

Of course none of this applies to server apps since they aren't distributed to users. You can use all the GPL code you want.

[ronjouch]

"If you use a GPL library you are required to release your entire application source code under a GPL compatible license."

Thanks for contradicting. I almost swore nonsense, but I'm so unsure about everything when it comes to licensing that I thought I'd read about it first, and you're right. I'm flabbergasted; never understood this, and never met anyone confident enough about their understanding of GPL to contradict my (wrong) understanding.

But then, does this mean anyone can ask for the source of closed-source software that use GPL code, like the ones below? (I just dug two random examples).

- AutoDesk software. Uses GPL components at http://www.autodesk.com/company/legal-notices-trademarks/ope... -- EDIT: alright these are all _L_GPL libs, which means just distributing the (potentially modified) lib sources is okay as long as you don't link statically. Right?

- HipChat Enterprise. Server-side, but distributed, to be run by enterprises on their own servers. Uses GPL components at http://sources.hipchat.com/ -- EDIT: in this case, all the GPL components seem to be basic GNU utilities, used by calling binaries rather than being coupled to the commercial software by a linking / shared object mechanism. Right?

[lmm]

> But then, does this mean anyone can ask for the source of closed-source software that use GPL code, like the ones below? (I just dug two random examples).

If their software is a derivative work of someone else's code then they can't distribute their software without a license from the copyright holder of that code. In the case of the GPL, that licenses them only to distribute their code under the GPL. If they are distributing their software other than under the GPL, then that is copyright infringement (in the same way as if they had made a derived work of some non-GPL code and distributed that), they lose their license, and any holder of a copyright on the code that their software was a derivative work of could sue them for copyright infringement. (In theory they sue for damages; in practice the copyright holder of GPLed code they made a derivative of will usually settle for compliance and an agreement to have their future releases audited).

What constitutes a derivative work is a question for the courts. It's generally accepted that any program that uses a library is a derivative work of that library, and a program that invokes another program at arms length or via a standard interface is probably not a derivative work of that program. The exact boundary is unclear; there's a case to be made that a program that is tightly coupled to another program and invokes it via piped commands might still be a derivative work even though it's not shared objects.

The LGPL is an entirely different license from the GPL.

[FigBug]

I didn't look at all the LGPL/GPL code they are using, but your understanding seems correct.