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According to this article, radvd is under BSD license, sourced with a link to the project mailing list where one of the maintainers claims "an old style BSD license". However, while radvd's licenece (as of v2.17) is similar to the old "four-clause" BSD license, it seems to diverge from all known forms of the BSD license, in particular by adding the clauses numbered "0." and "1.":

  The author(s) grant permission for redistribution and use in source and 
binary forms, with or without modification, of the software and documentation 
provided that the following conditions are met: 
 
0. If you receive a version of the software that is specifically labelled 
   as not being for redistribution (check the version message and/or README), 
   you are not permitted to redistribute that version of the software in any 
   way or form. 
1. All terms of all other applicable copyrights and licenses must be 
   followed. 
2. Redistributions of source code must retain the authors' copyright 
   notice(s), this list of conditions, and the following disclaimer. 
3. Redistributions in binary form must reproduce the authors' copyright 
   notice(s), this list of conditions, and the following disclaimer in the 
   documentation and/or other materials provided with the distribution. 
4. All advertising materials mentioning features or use of this software 
   must display the following acknowledgement with the name(s) of the 
   authors as specified in the copyright notice(s) substituted where 
   indicated: 
 
        This product includes software developed by the authors which are  
        mentioned at the start of the source files and other contributors. 
 
5. Neither the name(s) of the author(s) 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 ITS AUTHORS 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 AUTHORS 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.

-- Theoprakt ( talk) 15:25, 26 October 2017 (UTC) reply

Well, it's not exactly a BSD license but it doesn't in effect do anything a BSD license doesn't already do. You can turn BSD licensed stuff to proprietary software which is basically what clause 0 says. Just a useless vanity license. 2001:14BA:80D2:6F00:0:0:0:1EC ( talk) 17:03, 28 September 2018 (UTC) reply