License comparison
LGPL-2.1 vs LGPL-3.0: device requirements
Both LGPL versions can accommodate an application under other terms, provided you satisfy the library's source and replacement or relinking conditions. LGPL-3.0 is built on GPLv3 and adds Installation Information where its User Product conditions apply. For a device that restricts modified software, supplying library source alone may therefore be insufficient. LGPL-2.1 has no corresponding Installation Information clause.
Compare the permissions, limits and obligations recorded in each guide. Read the license text for the full conditions that apply to your release.
Permissions
LGPL-2.1-only
Commercial use
You may ship the code inside a paid product. The license does not restrict commercial use.
Modify
You may change the code, including keeping those changes private, unless a later obligation says otherwise.
Distribute
You may give copies to others. Distribution is what usually turns notice and source duties into real work.
Private use
Use inside your company, including internal forks, does not by itself trigger distribution duties.
Patent use
These licenses typically include a patent grant covering the licensed files. Read the grant before relying on it in a high-stakes deal.
LGPL-3.0-only
Commercial use
You may ship the code inside a paid product. The license does not restrict commercial use.
Modify
You may change the code, including keeping those changes private, unless a later obligation says otherwise.
Distribute
You may give copies to others. Distribution is what usually turns notice and source duties into real work.
Private use
Use inside your company, including internal forks, does not by itself trigger distribution duties.
Patent use
These licenses typically include a patent grant covering the licensed files. Read the grant before relying on it in a high-stakes deal.
Limits
LGPL-2.1-only
Hold liable
The authors disclaim warranty. Recipients cannot hold them liable for damages arising from the software, except where law forbids that disclaimer.
Use trademark
The license is not a trademark license. Names, logos and product marks stay with their owners unless a separate grant says otherwise.
Open your product
File- or library-scoped copyleft does not, on its face, force you to open your entire application. Reciprocity stays on the covered files.
Move to LGPL-3.0
LGPL-2.1-only pins version 2.1. Recipients cannot elect LGPL-3.0, so GPLv3 patent and Installation Information terms do not arrive through this grant.
LGPL-3.0-only
Hold liable
The authors disclaim warranty. Recipients cannot hold them liable for damages arising from the software, except where law forbids that disclaimer.
Use trademark
The license is not a trademark license. Names, logos and product marks stay with their owners unless a separate grant says otherwise.
Open your product
File- or library-scoped copyleft does not, on its face, force you to open your entire application. Reciprocity stays on the covered files.
Obligations
LGPL-2.1-only
Include copyright
Keep copyright notices on the covered files you distribute.
Include license
Keep the license text with the covered files, and say that those files are under this license.
Disclose source
Source for the library, including your modifications to it, has to be available to people who received a binary.
Keep replaceable
Recipients must be able to swap in their own build of the library. Dynamic linking is the usual path. Static linking means you also hand over a way to relink.
LGPL-3.0-only
Include copyright
Keep copyright notices on the covered files you distribute.
Include license
Keep the license text with the covered files, and say that those files are under this license.
Disclose source
Source for the library, including your modifications to it, has to be available to people who received a binary.
Keep replaceable
Recipients must be able to swap in their own build of the library. Dynamic linking is the usual path. Static linking means you also hand over a way to relink.
Installation Information
LGPL-3.0 rides on GPLv3, so a Combined Work in a User Product also owes Installation Information for a changed library.
License texts
Practical guidance for procurement review, not legal advice. Confirm high-stakes use with counsel.