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Comparing Open Source Licenses: GPL vs. BSDL

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David Chisnall compares the two most popular software licenses in the free and open source software (F/OSS) communities: the GNU General Public License (GPL) and the Berkeley Software Distribution License (BSDL). Each has advantages, but the distinctions are sometimes quite subtle.
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Two Licenses for Two Philosophies

In the free and open source software (F/OSS) communities, there are two common free software licenses, originating from two very different philosophies:

  • The Berkeley Software Distribution License (BSDL) is a very simple license. It states that you may not claim that you wrote the software under the license, and that you must state somewhere who did write it, but apart from that you can do anything you like with the code—including distributing binary copies of it and any derived works.
  • The GNU General Public License (GPL) is based on the idea of copyleft—the philosophical opposite of copyright, built using existing copyright laws. This aspect of the GPL is sometimes referred to as "viral," since any derived work of a GPL’d product is covered under the GPL, including the parts not originally licensed under the GPL. For example, it’s possible to take the Linux kernel (GPL) and add some BSDL code to it. The result, as a whole, is licensed under the GPL; however, the BSDL component on its own is also still covered by the BSDL.

The reason the GPL exists is to enforce the four freedoms of the Free Software Foundation, which I’ve outlined in a previous article. These freedoms are expressly granted by the GPL. The copyleft nature of the GPL means that any derived work of GPL software must also respect the four freedoms—in effect, it says that if you want to benefit from free software, you must play by the rules of free software.

These two licenses are not the only ones used by F/OSS. Others licenses are similar:

  • The MIT license under which X11 is distributed is a slightly more lenient version of the BSD license, removing the requirement for attribution in binary-only distributions.
  • The Lesser GPL (LGPL) removes some of the constraints of the GPL, and is intended for libraries that might be used in non-libre software.
  • There are also a whole set with slightly differing terms, including some—such as Apple’s and Sun’s licenses—which expressly allow the inclusion of closed-source components.
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