7-Zip Open Source License Explained

7-Zip is a widely used, free file archiver known for its high compression ratios and broad format support. At its core, 7-Zip operates under a multi-license open-source model primarily governed by the GNU Lesser General Public License (LGPL). This licensing framework allows users to utilize the software for both personal and commercial purposes at no cost, while also granting software developers the freedom to integrate its code into proprietary applications under specific legal terms.

The Primary License: GNU LGPL

The majority of the 7-Zip source code is distributed under the GNU Lesser General Public License (LGPL). Unlike the standard GNU General Public License (GPL), which requires any derivative work or statically linked project to also adopt the GPL, the LGPL is more permissive. It permits developers to link 7-Zip libraries—such as its dynamic link libraries (DLLs)—into proprietary, closed-source software without being forced to open-source the parent application. However, if a developer directly modifies the 7-Zip source code itself, those modifications must remain open under the LGPL and be made available to the public.

The LZMA SDK: Public Domain

A critical component of 7-Zip's ecosystem is the Lempel-Ziv-Markov chain algorithm (LZMA) Software Development Kit (SDK). Originally distributed under the LGPL, the author released the core LZMA SDK into the public domain. This means that developers can freely use, modify, and distribute the LZMA compression and decompression algorithms in any project—whether commercial, open-source, or proprietary—without attribution or licensing restrictions.

The unRAR Restriction

While 7-Zip is open-source, certain modules carry distinct conditions due to third-party rights. The code responsible for unpacking RAR archives includes code based on the unRAR license created by Alexander Roshal. Under this specific license:

• Developers may decompress RAR files using the provided source code.
• The source code cannot be used to recreate the RAR compression algorithm or to reverse-engineer proprietary RAR functionality.

Because of this restriction, the unRAR component is technically non-free under strict open-source definitions, though it is legally bundled to facilitate read-only support for RAR archives.

BSD Licenses and Other Components

Minor portions of the 7-Zip codebase are distributed under permissive BSD licenses (such as the BSD 3-Clause License). These segments require minimal compliance: retaining the original copyright notice, the list of conditions, and the disclaimer of warranty in derivative distributions.

What This Means for Users and Businesses

• For End Users: Anyone can install and use 7-Zip on any number of computers—including corporate, governmental, and commercial workstations—without paying license fees or registering the software.
• For Developers: You can embed 7-Zip binaries or dynamically link to its libraries in commercial software, provided you comply with the LGPL regarding modifications to the library source files. To completely avoid LGPL compliance obligations, developers can opt to use only the public-domain LZMA SDK.