LGPL

LGPL
Free Software Foundation · Public domain · source
Name	GNU Lesser General Public License
Abbreviation	LGPL
Author	Free Software Foundation
Initial release	1991
Latest release	2019 (version 3.0)
License type	Copyleft, Free software license
Website	Free Software Foundation

LGPL

The LGPL is a family of free software licenses that provides a hybrid of copyleft and permissive licensing approaches, developed by the Free Software Foundation and linked historically to the GNU Project and the work of Richard Stallman. It was created to enable wider use of libraries and components by allowing linking from proprietary programs while preserving freedoms for modifications to the licensed components themselves, a balance aimed at ecosystems evolving around Linux and other Unix-like systems. Policymakers, developers, and corporations such as Red Hat, Nokia, Google, and IBM have engaged with the license in productization, standards, and litigation contexts.

Overview and History

The LGPL originated as the "Librarian's" variant of the GNU General Public License in response to debates within the Free Software Foundation and the GNU Project community about reuse of software libraries in proprietary products. Early milestones include the 1991 designation for the first variant and the 1999 and 2007 revisions of broader GPL policy that influenced LGPL drafts. The 2007 era saw engagement with organizations like GCC maintainers and contributors associated with Debian and FSF Europe to clarify compatibility with dynamic linking on systems like GNU/Linux and distributions such as Debian GNU/Linux and Ubuntu. In 2007–2010, commercial actors including Nokia and Oracle Corporation weighed LGPL strategy in mobile and middleware stacks, while legal firms such as Morrison & Foerster and DLA Piper produced analyses for clients.

Key Provisions and Requirements

LGPL grants recipients rights to use, copy, modify, and redistribute covered library code while imposing obligations on distribution to preserve source availability for the library. Recipients must provide or offer source for modified library components, maintain license notices, and allow reverse engineering for debugging such as for interoperability with programs from vendors like Apple Inc., Microsoft, or Samsung. The license distinguishes between static and dynamic linking, referencing mechanisms familiar to POSIX-compliant environments and toolchains like GCC and GNU Make. Compliance often requires coordinated packaging practices used by projects like LibreOffice, GIMP, and FFmpeg, and is enforced via community norms and occasional litigation involving firms like Versata and SCO Group.

Compatibility and Derivative Works

LGPL's compatibility rules affect combination with code under other licenses. The license allows linking into programs under proprietary licenses provided the library remains separable and users can relink or replace the library; projects such as Mozilla Firefox and Chromium have navigated such constraints. When combined with GPL-licensed code, the sublicense can trigger conversion rules: some LGPL versions can be relicensed under GPL by the licensor, impacting projects like Drupal or MySQL historically subject to dual-licensing decisions by companies including Oracle Corporation and Sun Microsystems. Interoperability with permissive licenses such as the MIT License and the BSD license is common, but mixing requires legal attention as seen in guidance from the Open Source Initiative and counsel at firms like Eversheds Sutherland.

Versions and Notable Changes

Major versions include the original 2.0-era texts and the later clarifications culminating in LGPL version 2.1 and the 2019-de facto transitionary practice aligning with GPL version 3 semantics. Key changes addressed patent deals, tivoization-style restrictions highlighted by cases involving TiVo Inc. and device manufacturers, and compatibility with AGPL in networked contexts. The transition toward recommending use of "LGPLv3 or later" or preferring GPL-compatible library strategies influenced projects maintained by entities such as Canonical Ltd. and Red Hat. The evolution reflects responses to technological shifts in containerization with Docker, virtualization with VMware, and cloud distribution models used by Amazon Web Services.

Adoption and Use in Software Projects

LGPL is used widely for libraries and frameworks where authors seek broad adoption without forfeiting modification freedoms. Notable LGPL-licensed components include older releases of GTK+ used by GNOME, the zlib family in some contexts, and certain modules within OpenJDK-adjacent toolchains. Distributions of Debian and projects maintained by The Apache Software Foundation and Eclipse Foundation have made pragmatic licensing choices balancing LGPL components with permissively licensed parts. Companies such as Nokia (in its Maemo era), Intel Corporation (in some multimedia stacks), and smaller vendors in embedded markets have selected LGPL to enable device integration while preserving enhancement sharing.

Legal and Licensing Controversies

LGPL has been at the center of disputes over linking, static linking, and compliance in embedded devices and software-as-a-service contexts. Cases and debates involving TiVo Inc., Versata, and community enforcement actions by entities like the Software Freedom Conservancy have clarified obligations under different linking models. Corporate audits by firms such as Black Duck Software and enforcement letters from counsel have prompted remediation by companies including Google and Samsung in product stacks. Controversies also involve patent grant language and contributor agreements as seen in negotiations with organizations like Open Invention Network and the interaction of LGPL terms with trademark policies of bodies such as W3C and IETF.

Category:Free software licenses