BSD licenses facts for kids

BSD licenses are a group of special rules that tell people how they can use, share, and change computer programs. These rules are very flexible and don't put many limits on what you can do with the software. This is different from other licenses, like copyleft licenses, which often require you to share any changes you make.

The first BSD license was used for a computer operating system called the Berkeley Software Distribution (BSD). This system was a lot like Unix. Over time, the original BSD license changed, and newer versions are now called "modified BSD licenses."

A "BSD license" can mean both a specific set of rules and a whole group of similar rules. The modified BSD license, which is used a lot today, is very much like the first one used for the BSD version of Unix. It's a simple license that mainly asks you to keep the original BSD license notice with the code if you share it. If you share the program in a ready-to-use form (not the code itself), you just need to include the notice. Unlike some other licenses, the BSD license doesn't force you to share the original code at all.

What Are the Different BSD Licenses?

The original BSD license had four main rules, or "clauses." Since then, several new versions have appeared, but they are all still called "BSD licenses." Today, the most common one has three clauses.

In all these BSD licenses, `<year>` means the year the copyright was made. The `<copyright holder>` is usually "Regents of the University of California," because they created the original BSD software.

Older BSD License Versions

Before the well-known 4-clause BSD license, some older versions of BSD software used a license that was clearly a first step towards it. This older license was found in parts of 4.3BSD-Tahoe (from 1988) and Net/1 (from 1989). Even though the 4-clause license mostly replaced it, you can still find this older license in some software like 4.3BSD-Reno, Net/2, and 4.4BSD-Alpha.

Copyright (c) <year> <copyright holder>.
All rights reserved.

Redistribution and use in source and binary forms are permitted provided that the above copyright notice and this paragraph are duplicated in all such forms and that any documentation, advertising materials, and other materials related to such distribution and use acknowledge that the software was developed by the <copyright holder>. The name of the <copyright holder> may not be used to endorse or promote products derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED `'AS IS″ AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

The Original 4-Clause BSD License

The first BSD license had a rule that isn't in newer versions. This rule was called the "advertising clause." It became a bit of a problem because it said that anyone who used software with this license had to mention the original creators in all their advertising. This was the third rule in the original license:

Copyright (c) <year>, <copyright holder>
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
   
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
   
3. All advertising materials mentioning features or use of this software must display the following acknowledgement: This product includes software developed by the <copyright holder>.
   
4. Neither the name of the <copyright holder> nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
   

THIS SOFTWARE IS PROVIDED BY <COPYRIGHT HOLDER> AS IS AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

People didn't like this rule because if you combined many programs, each with a different name in its license, you would end up with a huge list of acknowledgments in your advertising. For example, Richard Stallman once found 75 such acknowledgments in a version of NetBSD from 1997.

Also, this clause caused problems with other licenses, like the GNU GPL. The GPL doesn't allow extra rules like the advertising clause. Because of this, the Free Software Foundation, which publishes the GPL, suggests that developers avoid using the 4-clause BSD license for new projects. However, they say it's fine to use software that already has it.

The Modern 3-Clause BSD License

The "advertising clause" was officially removed from the BSD license on July 22, 1999. This change was made by William Hoskins, who worked for UC Berkeley. Later, in 2012, UC Berkeley confirmed that people no longer needed to include acknowledgments in advertising materials for software licensed under their BSD license. So, the third clause of the original 4-clause BSD license was completely taken out. Other BSD software projects also removed this clause, but you might still find similar clauses in older code from other sources.

The original license is sometimes called "BSD-old," and this newer 3-clause version is often called "BSD-new." Other names include "revised BSD," "BSD-3," or "3-clause BSD." This version is approved as an Open Source license by the OSI. The Free Software Foundation calls it the "Modified BSD License" and says it works well with the GNU GPL. They suggest being specific when you talk about this license to avoid confusing it with the older 4-clause version.

This 3-clause license lets you share and use the software for any reason, as long as you keep the copyright notices and the license's warnings about warranties. It also has a rule that says you can't use the names of the people who contributed to the software to promote your own work without their specific permission.

Copyright <year> <copyright holder>

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
   
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
   
3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
   

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

The Simple 2-Clause BSD License

An even simpler version of the BSD license is used a lot, especially by the FreeBSD project. It was used there as early as April 1999. The main difference between this 2-clause license and the 3-clause "New BSD" license is that it removes the rule about not using names for endorsement. The FreeBSD version of the license also adds a small extra note about opinions in the software, but other projects usually don't include that part.

The Free Software Foundation calls this the "FreeBSD License" and says it works with the GNU GPL. Like with the 3-clause license, they suggest being specific when you talk about this license to avoid confusion with the original BSD license.

Copyright (c) <year>, <copyright holder>

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
   
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
   

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Other projects, like NetBSD, also use a similar 2-clause license. The OSI has approved this version as the "Simplified BSD License."

The ISC license is very similar to this 2-clause license and is recommended by the OpenBSD project for new contributions.

The Super Simple 0-Clause BSD License

The BSD 0-clause license is even simpler than the 2-clause version. It removes all requirements to include the copyright notice, the license text, or any disclaimers, whether you're sharing the code or the ready-to-use program. This makes it very similar to putting software into the public domain. It's also known as "0BSD" or "Zero-Clause BSD." Rob Landley created it in 2013 for his Toybox project because he wasn't happy with the GNU General Public License he used for BusyBox.

Copyright (C) [year] by [copyright holder] <[email]>

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

Other Kinds of BSD Licenses

The SPDX License List has even more types of BSD licenses. Here are a couple of examples:

• BSD-1-Clause: This license only has the rule about keeping the source code notice. It was used by Berkeley Software Design in the 1990s and later by the Boost Software License. It has been approved by the OSI since 2020.
• BSD-2-Clause-Patent: This is like the 2-clause BSD license but also includes a special permission for patents. It has been approved by the OSI since 2017.

How BSD Licenses Work with Other Licenses

Working with Commercial Software

The FreeBSD project believes that BSD-style licenses are great for companies and for making commercial products. This is because they work well with private, closed-source licenses and are very flexible. They say BSD-style licenses only put "minimal restrictions" on what you can do later and are not "legal time-bombs" like some other licenses.

The BSD license allows companies to use the software in their own private products. Software based on BSD-licensed material can be released as closed-source, which means companies can use it for their usual business purposes.

Working with Free and Open-Source Software

The 3-clause BSD license, like most permissive licenses (licenses that allow a lot of freedom), works well with almost all free and open-source software (FOSS) licenses. It also works with private, closed-source licenses.

Two versions of the BSD license, the New BSD License (3-clause) and the Simplified BSD License (2-clause), have been checked and approved as GPL-compatible free software licenses by the Free Software Foundation. They are also approved as open source licenses by the Open Source Initiative.

However, the original, 4-clause BSD license has not been accepted as an open source license. Even though the Free Software Foundation considers it a free software license, they don't think it's compatible with the GPL because of that old "advertising clause."

See also

In Spanish: Licencia BSD para niños

• Comparison of free and open-source software licenses
• Software using the BSD license (category)