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How to use GNU licenses for your own software

This is a brief explanation of how to place a program under the GNU General Public License, GNU Lesser General Public License, or GNU Affero General Public License. For the GNU Free Documentation License, we have a separate page.

For further information, see our list of frequently asked questions about our licenses.

If you are considering using the GNU Lesser General Public License, please read the article “Why you shouldn't use the LGPL for your next library” first. The article explains why it may be better to use the ordinary GPL instead, and how we would make the decision.

Here's a brief summary of what you need to do to release a program under one of our licenses:

This involves adding two elements to each source file of your program: a copyright notice (such as “Copyright 1999 Terry Jones”), and a statement of copying permission, saying that the program is distributed under the terms of the GNU General Public License (or the Lesser GPL, or the Affero GPL).

The copyright disclaimer

To avoid possible legal complications later, it's wise to ask your employer or school, if any, to sign a copyright disclaimer for your program, so it cannot later claim that the copyright belongs to it and that you had no right to release the program at all. This really has nothing to do with the GNU GPL—it applies no matter which free software license you use to release the program.

Here is a sample copyright disclaimer; just alter the names, title, and program description as appropriate:

Yoyodyne, Inc., hereby disclaims all copyright interest in the program “Woodpecker” (which deconstructs trees) written by James Hacker.

signature of Moe Ghoul 1 April 1989
Moe Ghoul, President of Vice

If you are a university student, we recommend you request the disclaimer at an early stage in writing the program to reduce resistance. If you are not a research assistant or teaching assistant, it could be that the university has no claim to copyright on your work, but ask a lawyer to make sure of that.

If you work, the best time to negotiate permission to release free software is when negotiating your employment agreement.

The copyright notice

The copyright notice should include the year in which you finished preparing the release (so if you finished it in 1998 but didn't post it until 1999, use 1998). You should add the proper year for each past release; for example, “Copyright 1998, 1999 Terry Jones” if some releases were finished in 1998 and some were finished in 1999. If several people helped write the code, use all their names.

For software with several releases over multiple years, it's okay to use a range (“2008-2010”) instead of listing individual years (“2008, 2009, 2010”) if and only if every year in the range, inclusive, really is a “copyrightable” year that would be listed individually; and you make an explicit statement in your documentation about this usage.

Always use the English word “Copyright”; by international convention, this is used worldwide, even for material in other languages. The copyright symbol “©” can be included if you wish (and your character set supports it), but it's not necessary. There is no legal significance to using the three-character sequence “(C)”, but it does no harm.

If you have copied code from other programs covered by the same license, copy their copyright notices too. Put all the copyright notices for a file together, right near the top of the file.

The license files

You should also include a copy of the license itself somewhere in the distribution of your program. All programs, whether they are released under the GPL or LGPL, should include the text version of the GPL. In GNU programs we conventionally put the license in a file called COPYING.

If you are releasing your program under the GNU AGPL, use the text version of the GNU AGPL instead of the GNU GPL.

If you are releasing your program under the Lesser GPL, you should also include the text version of the LGPL, usually in a file called COPYING.LESSER. Please note that, since the LGPL is a set of additional permissions on top of the GPL, it's crucial to include both licenses so users have all the materials they need to understand their rights.

The license notices

Each file's copying permission statement (also called the license notice) should come right after its copyright notices. For a one-file program, the statement (for the GPL) should look like this, to use GPL version 3 or later:

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.

For programs that are more than one file, it is better to replace “this program” with the name of the program, and begin the statement with a line saying “This file is part of NAME”. For instance,

    This file is part of Foobar.

    Foobar is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    Foobar is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with Foobar.  If not, see <http://www.gnu.org/licenses/>.

To use a different set of GPL versions, you would modify the end of the first long paragraph. For instance, to license under version 2 or later, you would replace “3” with “2”.

This statement should go near the beginning of every source file, close to the copyright notices. When using the Lesser GPL, insert the word “Lesser” before “General” in all three places. When using the GNU AGPL, insert the word “Affero” before “General” in all three places.

Why license notices?

The purpose of a free software license is to give certain rights to all users of a program. If it is not clear what rights you have given them, that defeats the purpose. Our practices are designed to avoid any uncertainty.

If a program has a copy of a license FOO alongside the source files, but doesn't have an explicit statement that “This program is released under license FOO,” that leaves room for uncertainty about whether the license FOO applies to the code of that program.

If a release has one statement that “This program is released under license FOO,” in a central place such as the README file, that makes the situation clear for that release. However, programmers often copy source files from one free program into another. If a source file contains no statement about what its license is, then moving it into another context eliminates all trace of that point. This invites confusion and error.

The startup notice

For interactive programs, it is usually a good idea to make the program display a brief notice about copyright and copying permission when it starts up. See the end of the GNU GPL for more information about this.

The Affero notice

If you are releasing your program under the GNU AGPL, and it can interact with users over a network, the program should offer its source to those users in some way. For example, if your program is a web application, its interface could display a “Source” link that leads users to an archive of the code. The GNU AGPL is flexible enough that you can choose a method that's suitable for your specific program—see section 13 for details.

Miscellaneous

It is very important for practical reasons to include contact information for how to reach you, perhaps in the README file, but this has nothing to do with the legal issues of applying the license.

There is no legal requirement to register your copyright with anyone; simply writing the program makes it copyrighted. However, for the US, it is a good idea to register the copyright with the US Registry of Copyrights, because that puts you in a stronger position against anyone who violates the license in the US. Most other countries have no system of copyright registration.

We would like to list all free software programs in the Free Software Directory, including all programs licensed under the GPL (any version). So please submit an entry for your program, when it has reached the point of being useful. Please see the Directory web page for information and an online submission form.

It is also possible to make your program a GNU package, a part of the GNU Project. If you might be interested in joining up with the GNU Project in this way, please see our GNU software evaluation page for more information and a short questionnaire. We will respond and discuss the matter with you.

You are welcome to use any of our licenses even if your program is not a GNU package; indeed, we hope you will. They're available to everyone. If you'd like to advertise your use of a particular license, feel free to use one of our logos.

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