BSD licenses

BSD licenses are a family of permissive free software licenses, imposing minimal restrictions on the redistribution of covered software. This is in contrast to copyleft licenses, which have reciprocity share-alike requirements. The original BSD license was used for its namesake, the Berkeley Software Distribution (BSD), a Unix-like operating system. The original version has since been revised and its descendants are more properly termed modified BSD licenses.

Two variants of the license, the New BSD License/Modified BSD License (3-clause),^[1] and the Simplified BSD License/FreeBSD License (2-clause)^[2] have been verified as GPL-compatible free software licenses by the Free Software Foundation, and have been vetted as open source licenses by the Open Source Initiative,^[3] while the original, 4-clause license has not been accepted as an open source license and, although the original is considered to be a free software license by the FSF, the FSF does not consider it to be compatible with the GPL due to the advertising clause.^[4]

Terms

Besides the original license used in BSD, there are several derivative licenses that are commonly referred to as a "BSD license". Today, the typical BSD license is the 3-clause version, which is revised from the original 4-clause version.

Note that: In all BSD licences as following, <organization> is the organization of the <copyright holder> or just the <copyright holder>, and <year> is the year of the copyright. As published in BSD, <copyright holder> is "Regents of the University of California", and <organization> is "University of California, Berkeley".

Previous license

Some releases of BSD prior to the adoption of the 4-clause BSD license used a license that is clearly ancestral to the 4-clause BSD license. These releases include 4.3BSD-Tahoe (1988) and Net/1 (1989). Though largely replaced by the 4-clause license, this license can be found in 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 <organization>.  The name of the
<organization> 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.

4-clause license (original "BSD License")

The original BSD license contained a clause not found in later licenses, known as the "advertising clause". This clause eventually became controversial, as it required authors of all works deriving from a BSD-licensed work to include an acknowledgment of the original source in all advertising material. This was clause number 3 in the original license text:^[8]

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 <organization>.
4. Neither the name of the <organization> 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.

This clause was objected to on the grounds that as people changed the license to reflect their name or organization it led to escalating advertising requirements when programs were combined together in a software distribution—every occurrence of the license with a different name required a separate acknowledgment. In arguing against it, Richard Stallman has stated that he counted 75 such acknowledgments in a 1997 version of NetBSD.^[9] In addition, the clause presented a legal problem for those wishing to publish BSD-licensed software which relies upon separate programs using the more-restrictive GNU GPL: the advertising clause is incompatible with the GPL, which does not allow the addition of restrictions beyond those it already imposes; because of this, the GPL's publisher, the Free Software Foundation, recommends developers not use the license, though it states there is no reason not to use software already using it.^[4]

Today, this original license is now sometimes called "BSD-old" or "4-clause BSD".

3-clause license ("Revised BSD License", "New BSD License", or "Modified BSD License")

The advertising clause was removed from the license text in the official BSD on 01999-07-2222 July 1999 by William Hoskins, Director of the Office of Technology Licensing for UC Berkeley.^[8] Other BSD distributions removed the clause, but many similar clauses remain in BSD-derived code from other sources, and unrelated code using a derived license.

While the original license is sometimes referred to as "BSD-old", the resulting 3-clause version is sometimes referred to by "BSD-new." Other names include "New BSD", "revised BSD", "BSD-3", or "3-clause BSD". This version has been vetted as an Open source license by the OSI as "The BSD License".^[3] The Free Software Foundation, which refers to the license as the "Modified BSD License", states that it is compatible with the GNU GPL. The FSF encourages users to be specific when referring to the license by name (i.e. not simply referring to it as "a BSD license" or "BSD-style") to avoid confusion with the original BSD license.^[1]

This version allows unlimited redistribution for any purpose as long as its copyright notices and the license's disclaimers of warranty are maintained. The license also contains a clause restricting use of the names of contributors for endorsement of a derived work without specific permission.

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:
    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * 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.
    * Neither the name of the <organization> 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 <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.

2-clause license ("Simplified BSD License" or "FreeBSD License")

An even more simplified version has come into use, primarily known for its usage in FreeBSD.^[10] The primary difference between it and the New BSD (3-clause) License is that it omits the non-endorsement clause. It also adds a further disclaimer about views and opinions expressed in the software. The Free Software Foundation, which refers to the license as the FreeBSD License, states that it is compatible with the GNU GPL. In addition, the FSF encourages users to be specific when referring to the license by name (i.e. not simply referring to it as "a BSD license" or "BSD-style"), as it does with the modified/new BSD license, to avoid confusion with the original BSD license.^[2]

Copyright (c) <YEAR>, <OWNER>
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. 

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.

The views and conclusions contained in the software and documentation are those
of the authors and should not be interpreted as representing official policies, 
either expressed or implied, of the FreeBSD Project.

Other projects, such as NetBSD, use a similar 2-clause license, but without the additional disclaimer.^[11] This version has been vetted as an Open source license by the OSI as the "Simplified BSD License."^[3]

Proprietary software licenses compatibility

The BSD License allows proprietary use and allows the software released under the license to be incorporated into proprietary products. Works based on the material may be released under a proprietary license as closed source software.^[12]

See also

• Permissive free software licence

References

External links

• Twenty Years of Berkeley Unix: From AT&T-Owned to Freely Redistributable, Marshall Kirk McKusick, in: Open Sources: Voices from the Open Source Revolution, O'Reilly 1999
• BSD License Definition – by The Linux Information Project (LINFO)