9.3. The GPL and License Compatibility
By far the sharpest dividing line in licensing is that between proprietary-incompatible and proprietary-compatible licenses, that is, between the GNU General Public License and everything else. Because the primary goal of the GPL's authors is the promotion of free software, they deliberately crafted the license to make it
With these conditions, the GPL succeeds in making freedom contagious. Once a program is
The question of whether or not this is a good way to promote free software is one of the most persistent holy wars on the Internet (see Section 6.2.4 in Chapter 6), and we won't investigate it here. What's important for our purposes is that GPL compatibility is an important issue when choosing a license. The GPL is by far the most popular
Fortunately, the Free Software Foundation maintains a list showing which licenses are compatible with the GPL at http://www.gnu.org/licenses/license-list.html. All licenses discussed in this chapter are present on that list, on one side or the other.
9.4. Choosing a License
When choosing a license to apply to your project, if at all possible use an existing license instead of making up a new one. There are two reasons why existing licenses are better:
To apply one of these licenses to your project, see Section 2.3.3 in Chapter 2.
9.4.1. The MIT/X Window System License
If your goal is that your code be accessible by the greatest possible number of developers and derivative works, and you do not mind the code being used in proprietary programs, choose the MIT/X Window System license (so named because it is the license under which the Massachusetts Institute of Technology released the original X Window System code). This license's basic message is "You are free to use this code however you want." It is taken from http://www.opensource.org/licenses/mit-license.php; is compatible with the GNU GPL; and is short, simple, and easy to understand:
Copyright (c) <year> <copyright holders> Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
9.4.2. The GNU General Public License
If you prefer that your project's code not be used in proprietary programs, or if you at least don't care whether or not it can be used in proprietary programs, choose the GNU General Public License (http://www.fsf.org/licensing/licenses/gpl.html). The GPL is probably the most widely used free software license in the world today; this instant recognizability is itself one of the GPL's major advantages.
When writing a code library that is
220.127.116.11. Is the GPL free or not free?
One consequence of choosing the GPL is the possibilitysmall, but not infinitely smallof finding yourself or your project embroiled in a dispute about whether or not the GPL is truly "free," given that it places some restrictions on what you can do with the codenamely, the restriction that the code cannot be distributed under any other license. For some people, the existence of this restriction means the GPL is "less free" than more permissive licenses such as the MIT/X license. Where this argument usually goes, of course, is that since "more free" must be better than "less free" (after all, who's not in favor of freedom?), it
This debate is another popular holy war (see Section 6.2.4 in Chapter 6). Avoid participating in it, at least in project forums. Don't attempt to
Since this is a book and not a mailing list thread, however, I will admit that I've never
(Oh, and if you do get drawn into a debate about it, don't raise the stakes by making inflammatory
9.4.3. What About The BSD License?
A fair amount of
The presence of that clause not only made the original BSD license GPL-incompatible, it also set a dangerous precedent: as other organizations put similar advertising clauses into
free softwaresubstituting their own organization's
The result is the revised BSD license, which is simply the original BSD license with the advertising clause removed. However, this history makes the phrase "BSD license" a bit ambiguous: does it refer to the original, or the revised version? This is why I prefer the MIT/X license, which is
It's not clear that without such a clause, a recipient of the software would have had the right to use the
If you wish to use the revised BSD license, a template is available at http://www.opensource.org/licenses/bsd-license.php.