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I am using a LGPL (GNU Lesser General Public License version 2.1) licensed library in my Java project I'm soon about to release. In order to solve a bug in this library I have copied a particular class from the source code, modified it, and made it a part of my project.

Breakdown:

  • Library A is available in binary form at central nexus repo. This library A is also available as source code and licensed with LGPL 2.1. Library A contains class B that is buggy.

  • Project C built in Java and Maven depends on library A. In order to solve the bug in class B, B is copied to a new class D and stored as a part of project C source code. The bug is then fixed in D.

  • Project C's source code is about to be released and available for others.

Question: What must project C contain, license-wise?

I am looking for another answer than answers like: "In order to follow LGPL 2.1, you must implement the things listed in license LGPL 2.1".

  • Under which license do you intend to release project C? – Mans Gunnarsson Feb 15 '17 at 19:44
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    Thats one of the things I would like to know. Is it enought to license it with the same one as the dependency (LGPL 2.1) ? In this case, and if I choose LGPL 2.1, what do I need to add to my project in terms of files, content. Do I need to comment my code in any way? – Stefan Vahlgren Feb 15 '17 at 19:49
  • That would definitely be enough, but perhaps not necessary. You do, in any event, need to release class D as LGPL 2.1 since it's an improvement of LGPL 2.1 class B. Regarding how to apply the license: gnu.org/licenses/gpl-howto.html – Mans Gunnarsson Feb 15 '17 at 19:53
  • Ok. But I still don't know how to actually do this. For example, if reading some other description of the license it says this: "Give prominent notice with each copy of your work that the LGPL'd software is being used." What does this mean? Am I supposed to create a text file named prominent_notice.txt and specify that the class D is a modified copy of the class B from the library A ? This is very unclear to me. – Stefan Vahlgren Feb 15 '17 at 19:58
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    If there's no UI then the documentation is a good place – Mans Gunnarsson Feb 15 '17 at 20:24
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The main thing to note is that the conditions for distributing modified copies are a hassle and basically amount to having to maintain your personal fork with carefully marked modification and a distribution channel for it. You want to get rid of that hassle as soon as possible, so you should try getting your bug fixes accepted upstream.

Apart from that advice, I don't think the gist of your request "what do I have to do to heed the conditions of the LPGL? Please don't ask me to read the conditions of the GPL" makes a lot of sense. You have to read through and understand a set of conditions anyway, so why not read the original rather than something regurgitated by someone whose reading is legally irrelevant?

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