According to FSF, to use LGPL in my library, I have to include both the copy of GPL & LGPL. I understand that the reason being LGPL 3 is now written as additional permissions over GPL 3. However, as that's not the case for prior versions of LGPL, I understand that if I use LGPL 2.1 I only have to include a copy of LGPL 2.1. Is that correct?

And, as a side question, should I also include a copy of (L)GPL 3 too, given that it's now available, so that users can also know the additional rights (L)GPL 3 grants?


The LGPLv2 is a standalone license. You are not required to include the GPLv2 as well. That might even be confusing if someone contributes to the project and only intends to license their changes under GPLv2, which would not be compatible with the LGPLv2 project.

If you use the LGPLv2, then people who modify the software are already free to switch to the GPLv2 or later. This license change is an irreversible operation (for that copy of the software), and would replace any mention of the LGPL with the selected GPL version.

Ordinary users (that do not modify the software) cannot switch to LGPLv3 – unless you license the software under the LGPLv2 or any later version. Even if that is the case, I wouldn't include the LGPLv3 but merely link to it.

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