FreeBSD legacy license with restrictions on copyright notice placement
I understand Debian includes the package libbsd in Debian main. This
package includes a man page with the following license (see
Redistribution and use in source and binary forms, with or without
modification, is permitted provided that the following conditions
1. Redistributions of source code must retain the above copyright
notice immediately at the beginning of the file, without modification,
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. This work was done expressly for inclusion into FreeBSD. Other use
is permitted provided this notation is included.
4. Absolutely no warranty of function or purpose is made by the author
5. Modifications may be freely made to this file providing the above
conditions are met.
I'm curious if there are opinions on why "must retain the above
copyright notice immediately at the beginning of the file" is
consistent with the DFSG. This is one of a variety of 1990s FreeBSD
3-clause BSD variants with such a feature.