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Scenario: you distribute your program in binary format, and it uses a GPL or LGPL library. In addition to the required conditions on your part of the application, you must offer a way to obtain the source code of the library.

Can you fulfill that with a link to the download page of the original library's author? Of course you have to be confident that the link will be valid for the required number of years, but many sites keep archives with all the previous releases of their software.

Or does it violate the license condition that you must provide such a service to the recipient?

  • Why do you not want to host the sources? Is this to save storage costs? – Brandin Aug 7 at 12:11
  • It's right, usually it's not a problem, but sometimes you may have not a page to download the software, or the library sources can be very big. – m.alessandrini Aug 7 at 14:50
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For the GPL version 3, if you provide a binary only distribution (a "Non-Source Form" according to the license), you need to provide the corresponding source "from the same place" -- if you merely link to the project download page or a site containing archives of several versions of the source code (one of which corresponds to the version you used), that is not sufficient.

One reason is that the GPL specifically requires you provide the "Corresponding Source" -- for example if you use library version 1.2.3 to build your product, you need to provide the exact same version in your source code distribution (not 1.2.4, not 1.2.2, not 1.2.3a, etc.). If all you do is link to an archive page where I can download (say) 10 different source code releases, how would I know which one corresponds to the one that your binary distribution uses?

However, if you provide a single page which provides multiple download links together -- one to your binary version and then one or more separate (direct) download links to the corresponding source(s), and it is made clear which source code corresponds to which binary release, I would consider that "the same place" and I believe it would satisfy the license, even if some links went to different servers.

The relevant information is from the GPL version 3, section 6 (Conveying Non-Source Forms). It gives the rules you must follow when distributing binaries:

You may convey a covered work in object code form under the terms of sections 4 and 5, provided that you also convey the machine-readable Corresponding Source under the terms of this License, in one of these ways:

[...]

d) Convey the object code by offering access from a designated place (gratis or for a charge), and offer equivalent access to the Corresponding Source in the same way through the same place at no further charge. [...] If the place to copy the object code is a network server, the Corresponding Source may be on a different server (operated by you or a third party) that supports equivalent copying facilities, provided you maintain clear directions next to the object code saying where to find the Corresponding Source. Regardless of what server hosts the Corresponding Source, you remain obligated to ensure that it is available for as long as needed to satisfy these requirements.

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

I added bolding to the parts you need to pay attention to. In particular, if you go with this option, you need to ensure the link to download the corresponding source is valid as long as you are distributing the binary.

  • So "through the same place" seems to be the key, but it's curious that it allows an exception only if the software is downloaded from a server. For example if you distribute the binary on a physical medium, it seems like you cannot use a link to a "server operated by a third party", as you can do on a web page. Am I interpreting correctly? – m.alessandrini Aug 7 at 14:56
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    @m.alessandrini In that case you should look at section 6 and see the option for supplying a "Written Offer" instead. This applies if you distribute a binary on a physical medium. – Brandin Aug 7 at 17:20

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