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http://www.gnu.org/licenses/license-list.html

FreeBSD Documentation License

This is a permissive non-copyleft free documentation license that is compatible with the GNU FDL.

http://www.freebsd.org/copyright/freebsd-doc-license.html

Modified BSD license

(Note: on the preceding link, the modified BSD license is listed in the General section.)

This is the original BSD license, modified by removal of the advertising clause. It is a simple, permissive non-copyleft free software license, compatible with the GNU GPL.

If you want a simple, permissive non-copyleft free software license, the modified BSD license is a reasonable choice. However, it is risky to recommend use of “the BSD license”, because confusion could easily occur and lead to use of the flawed original BSD license. To avoid this risk, you can suggest the X11 license instead. The X11 license and the revised BSD license are more or less equivalent.

This license is sometimes referred to as the 3-clause BSD license.

http://www.xfree86.org/3.3.6/COPYRIGHT2.html#5

Original BSD license

(Note: on the preceding link, the original BSD license is listed in the UCB/LBL section. This license is also sometimes called the “4-clause BSD license”.)

This is a simple, permissive non-copyleft free software license with a serious flaw: the “obnoxious BSD advertising clause”. The flaw is not fatal; that is, it does not render the software non-free. But it does cause practical problems, including incompatibility with the GNU GPL.

We urge you not to use the original BSD license for software you write. If you want to use a simple, permissive non-copyleft free software license, it is much better to use the modified BSD license or the X11 license. However, there is no reason not to use programs that have been released under the original BSD license.

http://www.xfree86.org/3.3.6/COPYRIGHT2.html#6
http://www.gnu.org/philosophy/bsd.html

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 community.

There are many variants of simple non-copyleft free software licenses, including the X10 license, the X11 license, the FreeBSD 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 sentence:

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 practical difficulty.

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 ad.

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 change them.

But if they followed Berkeley's lead before, maybe Berkeley's change in policy will convince some of them to change. It's worth asking.

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. Instead of copying the BSD license from some released package—which might still have the old version of the license in it—please copy the license from X11.

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 chosing one of the two BSD licenses.

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”.

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Updated: $Date: 2008/07/10 20:00:55 $

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