The BSD License Problem
The two major categories of free software license are copyleft and
non-copyleft . Copyleft
licenses such as the GNU
GPL insist that modified versions of the program must be
free software as well. Non-copyleft licenses do not insist on this.
We recommend copyleft,
because it protects freedom for all users, but non-copylefted
software can still be free software, and useful to the free software
There are many variants of simple non-copyleft
free software licenses, such as the Expat license, FreeBSD license,
X10 license, the X11 license, and the two BSD (Berkeley Software
Distribution) licenses. Most of them are equivalent except for details
of wording, but the license used for BSD until 1999 had a special
problem: the “obnoxious BSD advertising clause”. It said that every
advertisement mentioning the software must include a particular
3. All advertising materials mentioning features or use of this software
must display the following acknowledgement:
This product includes software developed by the University of
California, Berkeley and its contributors.
Initially the obnoxious BSD advertising clause was used only in the
Berkeley Software Distribution. That did not cause any particular
problem, because including one sentence in an ad is not a great
If other developers who used BSD-like licenses had copied the BSD
advertising clause verbatim—including the sentence that refers to
the University of California—then they would not have made the
problem any bigger.
But, as you might expect, other developers did not copy the clause
verbatim. They changed it, replacing “University of California”
with their own institution or their own names. The result is a
plethora of licenses, requiring a plethora of different sentences.
When people put many such programs together in an operating system,
the result is a serious problem. Imagine if a software system
required 75 different sentences, each one naming a different author
or group of authors. To advertise that, you would need a full-page
This might seem like extrapolation ad absurdum, but it is actual
fact. In a 1997
version of NetBSD, I counted 75 of these sentences. (Fortunately
NetBSD has decided to stop adding them, and to remove those it could.)
To address this problem, in my “spare time” I talk with
developers who have used BSD-style licenses, asking them if they would
please remove the advertising clause. Around 1996 I spoke with the
developers of FreeBSD about this, and they decided to remove the
advertising clause from all of their own code. In May 1998 the developers
of Flick, at the University of Utah, removed this clause.
Dean Hal Varian at the University of California took up the cause,
and championed it with the administration. In June 1999, after two
years of discussions, the University of California removed this
clause from the license of BSD.
Thus, there is now a new BSD license which does not contain the
advertising clause. Unfortunately, this does not eliminate the
legacy of the advertising clause: similar clauses are still present
in the licenses of many packages which are not part of BSD. The
change in license for BSD has no effect on the other packages which
imitated the old BSD license; only the developers who made them can
But if they followed Berkeley's lead before, maybe Berkeley's
change in policy will convince some of them to change. It's worth
So if you have a favorite package which still uses the BSD license
with the advertising clause, please ask the maintainer to look at
this web page, and consider making the change.
And if you want to release a program as non-copylefted free
software, please don't use the advertising clause. Thus, instead of
copying the BSD license from some released package—which might
still have the old version of the license in it—please use one
of the other permissive licenses, such as Expat or FreeBSD.
You can also help spread awareness of the issue by not using the
term “BSD-style”, and not saying “the BSD license”
which implies there is only one. You see, when people refer to all
non-copyleft free software licenses as “BSD-style licenses”,
some new free software developer who wants to use a non-copyleft free
software license might take for granted that the place to get it is from
BSD. He or she might copy the license with the advertising clause, not by
specific intention, just by chance.
If you would like to cite one specific example of a non-copyleft
license, and you have no particular preference, please pick an
example which has no particular problem. For instance, if you talk
about “X11-style licenses”, you will encourage people to copy the
license from X11, which avoids the advertising clause for certain,
rather than take a risk by randomly choosing one of the BSD
Or you could mention the non-copyleft license
recommend over the other non-copyleft licenses: the Apache 2.0
license, which has a clause to prevent treachery with patents.
When you want to refer specifically to one of the BSD licenses,
please always state which one: the “original BSD license” or the
“revised BSD license”.
Later a third BSD license variant was introduced, with only the
first two of the original BSD license's four clauses. We call it
the “FreeBSD license.” It is a lax, noncopyleft free
license, compatible with the GNU GPL, much like the modified BSD