Various Licenses and Comments about Them

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Table of Contents

Introduction

We classify a license according to certain key questions:

If you want help choosing a license, evaluating a license, or have any other questions about licenses, you can email us at <licensing@gnu.org>.

By the way, if you believe you have found a violation of one of our copyleft licenses, please refer to our license violation page.

Software Licenses

The following licenses do qualify as free software licenses, and are compatible with the GNU GPL:

GPL-Compatible, Free Software Licenses

The GNU General Public License, or GNU GPL for short.
This is a free software license, and a copyleft license. We recommend it for most software packages.

The GNU Lesser General Public License, or GNU LGPL for short.
This is a free software license, but not a strong copyleft license, because it permits linking with non-free modules. It is compatible with the GNU GPL. We recommend it for special circumstances only.

Between version 2 and 2.1, the GNU LGPL was renamed from the GNU Library General Public License to the GNU Lesser General Public License to better reflect its actual purpose. Namely, it is not just for libraries, and the GNU GPL is sometimes more appropriate for libraries.

The license of Guile.
This consists of the GNU GPL plus a special statement giving blanket permission to link with non-free software. As a result, it is not a strong copyleft, and it is compatible with the GNU GPL. We recommend it for special circumstances only--much the same circumstances where you might consider using the LGPL.

The license of the run-time units of the GNU Ada compiler.
This is much like that of Guile.

The X11 license.
This is a simple, permissive non-copyleft free software license, compatible with the GNU GPL. XFree86 uses the same license.

Expat license.
This is a simple, permissive non-copyleft free software license, compatible with the GNU GPL. It is sometime ambiguously referred to as the MIT License.

Standard ML of New Jersey Copyright License.
This is a simple, permissive non-copyleft free software license, compatible with the GNU GPL.
The Cryptix General License.
This is a simple, permissive non-copyleft free software license, compatible with the GNU GPL. It is very similar to the X11 license.

The 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.

The license of ZLib.
This is a free software license, and compatible with the GPL.

The license of the iMatix Standard Function Library.
This is a free software license and is GPL compatible.

The W3C Software Notice and License.
This is a free software license and is GPL compatible.

The Berkeley Database License (aka the Sleepycat Software Product License).
This is a free software license and is compatible with the GNU GPL.

The License of Python 1.6a2 and earlier versions.
This is a free software license and is compatible with the GNU GPL. Please note, however, that newer versions of Python are under other licenses (see below).
The License of Python 2.0.1, 2.1.1, and newer versions.
This is a free software license and is compatible with the GNU GPL. Please note, however, that intermediate versions of Python (1.6b1, through 2.0 and 2.1) are under a different license (see below).

The license of Perl.
This license is the disjunction of the Artistic License and the GNU GPL--in other words, you can choose either of those two licenses. It qualifies as a free software license, but it may not be a real copyleft. It is compatible with the GNU GPL because the GNU GPL is one of the alternatives.

We recommend you use this license for any Perl package you write, to promote coherence and uniformity in Perl programming. Outside of Perl, we urge you not to use this license; it is better to use just the GNU GPL.

The Clarified Artistic License (used by NcFTP).
This license is a free software license, compatible with the GPL. It corrects the vagueness of the Original Artistic License.

The license of Netscape Javascript.
This is the disjunction of the Netscape Public License and the GNU GPL. Because of that, it is a free software license, compatible with the GNU GPL, but not a strong copyleft.

This disjunctive license is a good choice if you want to make your package GPL-compatible and MPL-compatible. However you can also accomplish that by using the LGPL or the Guile license.

Such a disjunctive license might be a good choice if you have been using the MPL, and want to change to a GPL-compatible license without subtracting any permission you have given for previous versions.

GPL-Incompatible, Free Software Licenses

The following licenses are free software licenses, but are not compatible with the GNU GPL:

The Arphic Public License.
This is a copyleft free software license, incompatible with the GPL. Its normal use is for fonts, and in that use, the incompatibility does not cause a problem.

The original BSD license.
(Note: on the preceding link, the original BSD license is listed in the "UCB/LBL" section.) 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.

The Apache License, Version 1.0.
This is a simple, permissive non-copyleft free software license with practical problems like those of the original BSD license, including incompatibility with the GNU GPL.

The Apache License, Version 1.1.
This is a permissive non-copyleft free software license with a few requirements that render it incompatible with the GNU GPL.

We urge you not to use the Apache licenses for software you write. However, there is no reason to avoid running programs that have been released under this license, such as Apache.

The Zope Public License.
This is a simple, fairly permissive non-copyleft free software license with practical problems like those of the original BSD license, including incompatibility with the GNU GPL.

We urge you not to use the license of Zope for software you write. However, there is no reason to avoid running programs that have been released under this license, such as Zope.

The license of xinetd
This is a copyleft free software license, incompatible with the GPL. It is incompatible because it places extra restrictions on redistribution of modified versions that contradict the redistribution requirements in the GPL.

The License of Python 1.6b1 and later versions, through 2.0 and 2.1.
This is a free software license but is incompatible with the GNU GPL. The primary incompatibility is that this Python license is governed by the laws of the State of Virginia, in the USA, and the GPL does not permit this.

The OpenLDAP License, Version 2.3.
This is a permissive non-copyleft free software license with a few requirements (in sections 4 and 5) that render it incompatible with the GNU GPL.

We urge you not to use the OpenLDAP license for software you write. However, there is no reason to avoid running programs that have been released under this license, such as OpenLDAP.

IBM Public License, Version 1.0
This is a free software license but it is incompatible with the GPL.

The IBM Public License is incompatible with the GPL because it has various specific requirements that are not in the GPL.

For example, it requires certain patent licenses be given that the GPL does not require. (We don't think those patent license requirements are inherently a bad idea, but nonetheless they are incompatible with the GNU GPL.)

The Phorum License, Version 1.2
This is a free software license but it is incompatible with the GPL. For example, the terms in section 3 and 4 make the license incompatible with the GPL.

The LaTeX Project Public License.
This license is an incomplete statement of the distribution terms for LaTeX. As far as it goes, it is a free software license, but incompatible with the GPL because it has many requirements that are not in the GPL.

This license contains complex and annoying restrictions on how to publish a modified version, including one requirement that falls just barely on the good side of the line of what is acceptable: that any modified file must have a new name.

The reason this requirement is acceptable for LaTeX is that LaTeX has a facility to allow you to map file names, to specify ``use file bar when file foo is requested''. With this facility, the requirement is merely annoying; without the facility, the same requirement would be a serious obstacle, and we would have to conclude it makes the program non-free.

The LPPL says that some files, in certain versions of LaTeX, may have additional restrictions, which could render them non-free. For this reason, it may take some careful checking to produce a version of LaTeX that is free software.

The LPPL makes the controversial claim that simply having files on a machine where a few other people could log in and access them in itself constitutes distribution. We believe courts would not uphold this claim, but it is not good for people to start making the claim.

Please do not use this license for any other project.

Note: These comments are based on version 1.2 (3 Sep 1999) of the LPPL.

The Mozilla Public License (MPL).
This is a free software license which is not a strong copyleft; unlike the X11 license, it has some complex restrictions that make it incompatible with the GNU GPL. That is, a module covered by the GPL and a module covered by the MPL cannot legally be linked together. We urge you not to use the MPL for this reason.

However, MPL 1.1 has a provision (section 13) that allows a program (or parts of it) to offer a choice of another license as well. If part of a program allows the GNU GPL as an alternate choice, or any other GPL-compatible license as an alternate choice, that part of the program has a GPL-compatible license.

The Netizen Open Source License (NOSL), Version 1.0.
This is a free software license that is essentially the same as the Mozilla Public License, Version 1.1. Like the MPL, the NOSL has some complex restrictions that make it incompatible with the GNU GPL. That is, a module covered by the GPL and a module covered by the NOSL cannot legally be linked together. We urge you not to use the NOSL for this reason.

The Interbase Public License, Version 1.0.
This is a free software license that is essentially the same as the Mozilla Public License, Version 1.1. Like the MPL, the IPL has some complex restrictions that make it incompatible with the GNU GPL. That is, a module covered by the GPL and a module covered by the IPL cannot legally be linked together. We urge you not to use the IPL for this reason.

The Sun Public License.
This is essentially the same as the Mozilla Public License: a free software license incompatible with the GNU GPL. Please do not confuse this with the Sun Community Source License which is not a free software license.

The Nokia Open Source License.
This is similar to the Mozilla Public License: a free software license incompatible with the GNU GPL.

The Netscape Public License (NPL)
This is a free software license, not a strong copyleft, and incompatible with the GNU GPL. It consists of the Mozilla Public License with an added clause that permits Netscape to use your added code even in their proprietary versions of the program. Of course, they do not give you permission to use their code in the analogous way. We urge you not to use the NPL.

The Jabber Open Source License, Version 1.0
The license is a free software license, incompatible with the GPL. It permits relicensing under a certain class of licenses, those which include all the requirements of the Jabber license. The GPL is not a member of that class, so the Jabber license does not permit relicensing under the GPL. Therefore, it is not compatible.
The Sun Industry Standards Source License 1.0
This is a free software license, not a strong copyleft, which is incompatible with the GNU GPL because of details rather than any major policy.

The Qt Public License (QPL).
This is a non-copyleft free software license which is incompatible with the GNU GPL. It also causes major practical inconvenience, because modified sources can only be distributed as patches.

We recommend that you avoid using the QPL for anything that you write, and use QPL-covered software packages only when absolutely necessary. However, this no avoidance longer applies to Qt itself, since Qt is now also released under the GNU GPL.

Since the QPL is incompatible with the GNU GPL, you cannot take a GPL-covered program and QPL-covered program and link them together, no matter how.

However, if you have written a program that uses QPL-covered library (called FOO), and you want to release your program under the GNU GPL, you can easily do that. You can resolve the conflict for your program by adding a notice like this to it: 

  As a special exception, you have permission to link this program
  with the FOO library and distribute executables, as long as you
  follow the requirements of the GNU GPL in regard to all of the
  software in the executable aside from FOO.
You can do this, legally, if you are the copyright holder for the program. Add it in the source files, after the notice that says the program is covered by the GNU GPL.

The FreeType license
The FreeType license is a non-copyleft free software license which is incompatible with the GPL for technical reasons.

The Open Compatibility License
This is a free software license with major drawbacks: it grants special privileges to the original developer, and it is incompatible with the GPL.

The PHP License, Version 2.02.
This license is used by most of PHP4, but one important part of PHP4, the Zend optimizer, uses a different and worse license: the QPL.

This is a non-copyleft free software license with practical problems like those of the original BSD license, including incompatibility with the GNU GPL.

PHP3 is not under this license. PHP3 is disjunctively dual-licensed with the GNU GPL. Thus, while PHP4 (which is covered only by the PHP 2.02 License) is still free software, we encourage you to use and make improvements to only PHP3. That way, we can have an active version of PHP whose license is compatible with the GPL. If you are interested in helping maintain an active version of PHP3, please contact the GNU Volunteer Coordinators <gvc@gnu.org>.

Non-Free Software Licenses

The following licenses do not qualify as free software licenses. A non-free license is automatically incompatible with the GNU GPL.

Of course, we urge you to avoid using non-free software licenses, and to avoid non-free software in general.

There is no way we could list all the known non-free software licenses here; after all, every proprietary software company has their own. We focus here on licenses that are often mistaken for free software licenses but are, in fact, not free software licenses.

We have provided links to these packages when we can do so without violating our general policy: that we do not make links to sites that promote, encourage or facilitate the use of non-free software packages. The last thing we want to do is give any non-free program some gratis publicity that might encourage more people to use it. For the same reason, we have avoided naming the programs for which a license is used, unless we think that for specific reasons it won't backfire.

The (Original) Artistic License.
We cannot say that this is a free software license because it is too vague; some passages are too clever for their own good, and their meaning is not clear. We urge you to avoid using it, except as part of the disjunctive license of Perl.

The problems are matters of wording, not substance. There is a revised version of the Artistic License (dubbed "The Artistic License 2.0") which is clearly a free software license, and even compatible with the GNU GPL. This license is being considered for use in Perl 6. If you are thinking of releasing a program under the Artistic License, please write to licensing@gnu.org to ask for a copy of this revised version.

The Apple Public Source License (APSL).
This is not a free software license. Please don't use this license, and we urge you to avoid any software that has been released under it.

Further discussion on why the APSL is not a free software license is available.

The Sun Community Source License.
This is not a free software license; it lacks essential freedoms such as publication of modified versions. Please don't use this license, and we urge you to avoid any software that has been released under it.

The Plan 9 License
This is not a free software license; it lacks essential freedoms such as the right to make and use private changes. Please don't use this license, and we urge you to avoid any software that has been released under it. A detailed discussion of this license is also available.

Open Public License
This is not a free software license, because it requires sending every published modified version to a specific initial developer. There are also some other words in this license whose meaning we're not sure of that might also be problematic.

There is another site for the Open Public License. We are not sure which copy is the canonical one; these two differ only in a minor way that doesn't change our evaluation of the license.

The Sun Solaris Source Code (Foundation Release) License, Version 1.1
This is not a free software license. The license prohibits redistribution, prohibits commercial use of the software, and can be revoked.

The YaST License
This is not a free software license. The license prohibits distribiution for a fee, and that makes it impossible for the software to be included in the many CD-ROM free software collections that are sold by companies and by organizations such as the FSF.

There may be another problem in section 2a, but a word seems to be missing there, so it is hard to be sure what meaning is really intended.

Daniel Bernstein's licenses
These licenses are not free software licenses because they do not permit publication of modified versions.

Licenses For Documentation

The following licenses do qualify as free documentation licenses:

Free Documentation Licenses

The GNU Free Documentation License.
This is a license intended for use on copylefted free documentation. We plan to adopt it for all GNU manuals.

The FreeBSD Documentation License
This is a permissive non-copyleft Free Documentation license that is compatible with the GNU FDL.

The Apple's Common Documentation License, Version 1.0
This is a Free Documentation license that is incompatible with the GNU FDL. It is incompatible because Section (2c) says "You add no other terms or conditions to those of this License", and the GNU FDL has additional terms not accounted for in the Common Documentation License.

Open Publication License, Version 1.0.
This license can be used as a free documentation license. It is a copyleft free documentation license provided the copyright holder does not exercise any of the "LICENSE OPTIONS" listed in Section VI of the license. But if either of the options is invoked, the license becomes non-free.

This creates a practical pitfall in using or recommending this license: if you recommend ``Use the Open Publication License, Version 1.0 but don't enable the options'', it would be easy for the second half of that recommendation to get forgotten; someone might use the license with the options, making a manual non-free, and yet think he is following your advice.

Likewise, if you use this license without either of the options to make your manual free, someone else might decide to imitate you, then change his mind about the options thinking that that is just a detail; the result would be that his manual is non-free.

Thus, while manuals published under this license do qualify as free documentation if neither license option was used, it is better to use the GNU Free Documentation License and avoid the risk of leading someone else astray.

Please note that this license is not the same as the Open Content License. These two licenses are frequently confused, as the Open Content License is often referred to as the "OPL". For clarity, it is better not to use the abbreviation ``OPL'' for either license. It is worth spelling their names in full to make sure people understand what you say.

Non-Free Documentation Licenses

The following licenses do not qualify as free documentation licenses:

The Open Content License, Version 1.0.
This license does not qualify as free, because there are restrictions on charging money for copies. We recommend you not use this license.

Please note that this license is not the same as the Open Publication License. The practice of abbreviating ``Open Content License'' as ``OPL'' leads to confusion between them. For clarity, it is better not to use the abbreviation ``OPL'' for either license. It is worth spelling their names in full to make sure people understand what you say.

The Open Directory License (aka The dmoz.org License).
This is not a free documentation license. The primary problems are that your right to redistribute any given version is not permanent and that it requires the user to keep checking back at that site, which is too restrictive of the user's freedom.

Licenses For Works Besides Software and Documentation

The Design Science License
This is a free and copyleft license meant for general data, not particularly for software.

Note, though, that the GNU GPL can be used for general data which is not software, as long as one can determine what the definition of "source code" refers to in the particular case. As it turns out, the DSL also requires that you determine what the "source code" is, using approximately the same definition that the GPL uses.

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Copyright (C) 1999,2000,2001 Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111, USA

Verbatim copying and distribution of this entire article is permitted in any medium, provided this notice is preserved.

Updated: $Date: 2001/09/19 03:29:31 $ $Author: brett $