You’re not in violation. If people download the binaries, and you offer the source code at the same download site, and they choose not to download the source code, that’s on them; you are off the hook.

I also did not mention (because it was not relevant to the parties being discussed) one other option: If you received the binaries from someone else, with a written offer for source code, and you are distributing the binaries non-commercially, you can simply forward a copy of the written offer of source code you received.

The section of the GPL 2 you want is section 3, and in GPL 3 it’s section 6.

This is covered in section 6 of the GPL(v3). See the text here: https://www.gnu.org/licenses/gpl-3.0.en.html

Note that there are some changes here compared to v2 of the GPL.

IANAL but my understanding/interpretation (simplified) is you have to either:

6a) Ship the binaries in a physical product with a copy of the source code accompanying

6b) Ship the binaries in a physical product along with an offer to provide the source code on request

6c) "occasionally and noncommercially" ship the binaries (not necessarily in a physical product) along with an offer to provide the source code on request

6d) Make the binaries available from somewhere (e.g. a website) which also offers the source code (e.g. GitHub would count)

6e) Ship the binaries via a P2P mechanism if you include a link to where you host the source code

Again, IANAL but if you hosted a GPLv3 binary somewhere without source code, it would technically be a violation of the GPL.

However, since you are the copyright holder in this case, you can ship it however you want - it would just prevent anyone else from then distributing it under the GPL since they wouldn't be able to comply with section 6, since they don't have the source code.

But this is not about distributing GPL code in a custom binary. Rather, a GPL binary library was linked against by a custom binary, and that GPL binary was distributed alongside the ”custom” binary. Do those license terms apply here?

Yes, linking to a GPL library means you need to follow the terms of the GPL.

Pardon the confusion, this was about LGPL, not GPL—and the former does allow linking.

There are terms you need to follow when you link to LGPL libraries, as well. You need to provide your compiled program in an object format such that users can link it against their own versions of the LGPL library you originally linked it against. The LGPLv3 also adds some anti-Tivoization clauses, too, that make those rights explicit.

Section 6 pretty much lets you choose between:

- Bundling the source with the program (a)

- Letting people download the source from the same place as they can download the program (d)

- A written offer to hand over the source on request (b, c, e)

https://www.gnu.org/licenses/gpl-3.0.en.html