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The [http://www.gnu.org/copyleft/gpl.html '''GNU General Public License'''] ('''GNU GPL''' or simply '''GPL''') is a widely used free software licence, originally written by Richard Stallman for the GNU project. The GPL is the most popular and well-known example of the type of strong copyleft licence that requires derived works to be available under the same copyleft. Under this philosophy, the GPL is said to grant the recipients of a computer program the rights of the free software definition and uses copyleft to ensure the freedoms are preserved, even when the work is changed or added to. This is in distinction to permissive free software licences, of which the BSD licences are the standard examples.
The '''GNU General Public License''' ('''GNU GPL''' or simply '''GPL''') is a widely used open source software license, originally written by Richard Stallman for the GNU project. The GPL license grants the users irrevocable rights to use, modify and redistribute software (even commercially) under the condition that software or its derivatives retain the GPL license and that the source code is included or available to the user.


The GNU Lesser General Public Licence (LGPL) is a modified, more permissive, version of the GPL, originally intended for some software libraries. There is also a GNU Free Documentation Licence, which was originally intended for use with documentation for GNU software, but has also been adopted for other uses, such as the Wikipedia project.
FlightGear, many of the related projects and the text of this wiki are released under the {{cite web |url=http://www.gnu.org/licenses/gpl-2.0.html |title=GNU General Public License, version 2 (GNU GPLv2)}}


The Affero General Public Licence (GNU AGPL) is a similar licence with a focus on networking server software. The GNU AGPL is similar to the GNU General Public Licence, except that it additionally covers the use of the software over a computer network, requiring that the complete source code be made available to any network user of the AGPLed work, for example a web application. The Free Software Foundation recommends that this licence is considered for any software that will commonly be run over the network.
{{note|The word "software" will refer to many other things than that only in this article, for example text, textures, or aircraft packages.}}
{{tip|If you can read and understand English, consider taking some time some day to read through the license text and maybe even print it.}}


== FlightGear and GPL ==
== What is copyleft? ==
FlightGear is released under the GNU GPL, which means that everyone may edit, change, or use models, source and textures freely. Most planes and scenery are also released under GPL.  
The GPL is a ''copyleft'' license.  This term can be a bit confusing at first.  It might seem like free software is not or should not be copyrighted and in essence should be released to the public domain.  However that would allow redistributing it as proprietary software after minor modifications, in essence copyrighting it and reserving all rights. Its users could then very well have no rights and it would no longer be free software.


Contributors releasing their contributions under the terms of the GPL to the FlightGear project should keep in mind that such contributions are non-revocable, open-source projects in general, work such that GPL'ed contributions are usually not removed once a contributor abandons/leaves the project, be it temporarily or indefinitely. To clarify: It is very common for open source projects that contributors show up for a period of time and then take some hiatus from the project -sometimes even for years, thus it is extremely uncommon for contributions to be removed from the project, despite the fact that we've seen some of our most-talented contributors requesting their contributions be removed after some form public/private community debate or disagreement. However, requesting removal of contributions shows a misunderstanding of the GPL, and of FlightGear in particular: As a project, we cannot afford having contributors who may spend months (or even years) contributing to the project, only to see them pull their contributions once there's even the slightest form of community disagreement. Unfortunately, it is typical to see especially artwork contributors (aircraft, scenery, base package) making such requests - obviously, because the corresponding resources are usually much more self-contained than core contributions (source code).  
Copyleft software is copyrighted, but is released with a license that aims at preserving the rights of the users.  It is called "copyleft" because it is designed to do the opposite to what copyrighted proprietary software would do for the users rights.  The GPL is a ''strong copyleft'' license in the sense that any derivate or redistributed software ''must'' use the same license, thereby granting the users the same rights they originally had.
 
== Things to consider before contributing using the GPL ==
{{note|This relates to contributing to the wiki as well.}}
 
=== Commercial reuse ===
Many does not realize that the GPL allows commercial reuse.  It does.  "Free" is here rather "free as in speech" than "free as in beer".
 
{{cquote|You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.|{{cite web |url=http://www.gnu.org/licenses/gpl-2.0.html |title=GNU General Public License, version 2, section 1}}}}
 
{{cquote|When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.|{{cite web |url=http://www.gnu.org/licenses/gpl-2.0.html |title=GNU General Public License, version 2, Preamble}}}}
 
Something to keep in mind though is that the very same license conditions have to be met as when redistributing for free, for example that the source have to be included or available to the users, or that it still can be redistributed for free or with a fee.
 
This part of the GPL also affects what resources that can be used when creating content.  For example it can rule out a lot of resources when creating scenery.
 
=== Revoking contributions ===
You should consider that when something is published on the Internet, it will be spread.  There is no way you can revoke all available copies, and they will all have the license.  In addition many contributions can not simply be removed as other things depend on them.


Thus, please think about all the repercussions of contributing to FlightGear before causing community irritation by asking for your contributions to be removed at some point - what you get and see now when you download and install FlightGear is the result of over a decade of contributions from hundreds of contributors, no matter if it's source code, artwork, aircraft, scenery, documentation, wiki articles or tens of thousands of discussions in the archives.  
Thus, please think about all the repercussions of contributing to FlightGear before causing community irritation by asking for your contributions to be removed at some point - what you get and see now when you download and install FlightGear is the result of over a decade of contributions from hundreds of contributors, no matter if it's source code, artwork, aircraft, scenery, documentation, wiki articles or tens of thousands of discussions in the archives.  


We cannot afford having contributors who feel that they're entitled to pull their contributions from the project once there's even the slightest bit of community disagreement, no matter if it's removing aircraft, scenery, wiki articles or forum threads - for the sake of the project, please consider your GPL'ed contributions final - otherwise, the project will always be in danger, because some of our key contributors may decide to ask for significant contributions to be removed from the project.
We cannot afford having contributors who feel that they're entitled to pull their contributions from the project if there is a community disagreement, no matter if it's removing aircraft, scenery, wiki articles or forum threads – please consider your GPL'ed contributions final – otherwise, the project will always be in danger, because some of our key contributors may decide to ask for significant contributions to be removed from the project.
 
It has been causing lots of irritation in the community whenever key contributors have asked for their contributions to be removed - and while there are no legal grounds that justify complying with such requests, we've still been trying to accommodate them, simply for the sake of peace and out of respect for long-time community members.


Honestly, it's been causing lots of irritation in the community whenever key contributors have asked for their contributions to be removed - and while there are no legal grounds that justify complying with such requests, we've still been trying to accomodate them, simply for the sake of peace and out of respect for long-time community members.
== Contributing using the GPL ==
{{note|When contributing to the wiki, this is automatically taken care of.}}


Imagine just for a second that you were to download FlightGear 3.0, enjoy lots of neat features like advanced weather, Rembrandt or the c172p, but once you download FlightGear 3.2 six months later, you'll notice that it no longer provides support for the very same features, just because some contributor got fed up with the project and asked for his contributions to be removed.
=== Modifying GPL software ===
Any derivate software have to be released under the GPL and it must be possible to see what you have changed and when.


However, that's simply not how the project (and open source in general) works - if you think that you are entitled to ask for your contributions to be removed at some point, please contribute to another project, not FlightGear.
For details see primarily section 2 of the {{cite web |url = http://www.gnu.org/licenses/gpl-2.0.html |title = GNU GPLv2}}
 
=== Applying the GPL to new software ===
The Free Software Foundation have some recommendations of what to do when applying the GPL to new software.  There is a slight variation depending on if the project is one single file or multiple files.
 
In essence they recommend that you should claim copyright, for example "Copyright (c) 2019-1023 Tony Stark", and add a preamble to each of the files and include a file with the plain text version of the license text.  The preamble can be a bit shorter in all but one file in multiple file projects.
 
For details see {{cite web |url = http://www.gnu.org/licenses/gpl-howto.html |title = How to use GNU licenses for your own software}}
 
== Related licenses ==
The ''GNU Lesser General Public License'' (''LGPL'') is a modified, more permissive, version of the GPL, originally intended for some software libraries. There is also a GNU Free Documentation License, which was originally intended for use with documentation for GNU software, but has also been adopted for other uses, such as the Wikipedia project.
 
The ''Affero General Public License'' (''GNU AGPL'') is a similar license with a focus on networking server software. The GNU AGPL is similar to the GNU General Public License, except that it additionally covers the use of the software over a computer network, requiring that the complete source code be made available to any network user of the AGPLed work, for example a web application. The Free Software Foundation recommends that this license is considered for any software that will commonly be run over the network.


== Related content ==
== Related content ==
* [[Copyright Inquiry]]
* [[Copyright Inquiry]]
== External links ==
* {{wikipedia|GNU General Public License}}
=== The official license text ===
* {{cite web
| url = http://www.gnu.org/licenses/gpl-2.0.html
| title = GNU General Public License, version 2
| month = June
| year = 1991
| publisher = Free Software Foundation, Inc.
| accessdate = 6 September 2014
}}
* {{cite web
| url = http://www.gnu.org/licenses/gpl-2.0.txt
| title = GNU General Public License, version 2 (plain-text version)
| month = June
| year = 1991
| publisher = Free Software Foundation, Inc.
| accessdate = 6 September 2014
}}
=== Other Free Software Foundation resources ===
* {{cite web
| url = http://www.gnu.org/licenses/gpl-howto.html
| title = How to use GNU licenses for your own software
| date = 12 April 2014
| publisher = Free Software Foundation, Inc.
| accessdate = 6 September 2014
}}
* {{cite web
| url = http://www.gnu.org/licenses/old-licenses/gpl-2.0-faq.html
| title = Frequently Asked Questions about version 2 of the GNU GPL
| date = 12 April 2014
| publisher = Free Software Foundation, Inc.
| accessdate = 6 September 2014
}}
* {{cite web
| url = http://www.gnu.org/licenses/license-list.html
| title = Various Licenses and Comments about Them
| date = 27 July 2014
| publisher = Free Software Foundation, Inc.
| accessdate = 6 September 2014
}} – ''In essence a list of licenses and if they are compatibility with GNU GPL.''


[[Category:Licenses]]
[[Category:Licenses]]


[[es:Licencia General Pública GNU]]
[[es:Licencia General Pública GNU]]

Revision as of 12:26, 6 September 2014

The GNU General Public License (GNU GPL or simply GPL) is a widely used open source software license, originally written by Richard Stallman for the GNU project. The GPL license grants the users irrevocable rights to use, modify and redistribute software (even commercially) under the condition that software or its derivatives retain the GPL license and that the source code is included or available to the user.

FlightGear, many of the related projects and the text of this wiki are released under the GNU General Public License, version 2 (GNU GPLv2).

Note  The word "software" will refer to many other things than that only in this article, for example text, textures, or aircraft packages.
Tip  If you can read and understand English, consider taking some time some day to read through the license text and maybe even print it.

What is copyleft?

The GPL is a copyleft license. This term can be a bit confusing at first. It might seem like free software is not or should not be copyrighted and in essence should be released to the public domain. However that would allow redistributing it as proprietary software after minor modifications, in essence copyrighting it and reserving all rights. Its users could then very well have no rights and it would no longer be free software.

Copyleft software is copyrighted, but is released with a license that aims at preserving the rights of the users. It is called "copyleft" because it is designed to do the opposite to what copyrighted proprietary software would do for the users rights. The GPL is a strong copyleft license in the sense that any derivate or redistributed software must use the same license, thereby granting the users the same rights they originally had.

Things to consider before contributing using the GPL

Note  This relates to contributing to the wiki as well.

Commercial reuse

Many does not realize that the GPL allows commercial reuse. It does. "Free" is here rather "free as in speech" than "free as in beer".

Cquote1.png You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.
 Cquote2.png
Cquote1.png When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.
 Cquote2.png

Something to keep in mind though is that the very same license conditions have to be met as when redistributing for free, for example that the source have to be included or available to the users, or that it still can be redistributed for free or with a fee.

This part of the GPL also affects what resources that can be used when creating content. For example it can rule out a lot of resources when creating scenery.

Revoking contributions

You should consider that when something is published on the Internet, it will be spread. There is no way you can revoke all available copies, and they will all have the license. In addition many contributions can not simply be removed as other things depend on them.

Thus, please think about all the repercussions of contributing to FlightGear before causing community irritation by asking for your contributions to be removed at some point - what you get and see now when you download and install FlightGear is the result of over a decade of contributions from hundreds of contributors, no matter if it's source code, artwork, aircraft, scenery, documentation, wiki articles or tens of thousands of discussions in the archives.

We cannot afford having contributors who feel that they're entitled to pull their contributions from the project if there is a community disagreement, no matter if it's removing aircraft, scenery, wiki articles or forum threads – please consider your GPL'ed contributions final – otherwise, the project will always be in danger, because some of our key contributors may decide to ask for significant contributions to be removed from the project.

It has been causing lots of irritation in the community whenever key contributors have asked for their contributions to be removed - and while there are no legal grounds that justify complying with such requests, we've still been trying to accommodate them, simply for the sake of peace and out of respect for long-time community members.

Contributing using the GPL

Note  When contributing to the wiki, this is automatically taken care of.

Modifying GPL software

Any derivate software have to be released under the GPL and it must be possible to see what you have changed and when.

For details see primarily section 2 of the GNU GPLv2.

Applying the GPL to new software

The Free Software Foundation have some recommendations of what to do when applying the GPL to new software. There is a slight variation depending on if the project is one single file or multiple files.

In essence they recommend that you should claim copyright, for example "Copyright (c) 2019-1023 Tony Stark", and add a preamble to each of the files and include a file with the plain text version of the license text. The preamble can be a bit shorter in all but one file in multiple file projects.

For details see How to use GNU licenses for your own software.

Related licenses

The GNU Lesser General Public License (LGPL) is a modified, more permissive, version of the GPL, originally intended for some software libraries. There is also a GNU Free Documentation License, which was originally intended for use with documentation for GNU software, but has also been adopted for other uses, such as the Wikipedia project.

The Affero General Public License (GNU AGPL) is a similar license with a focus on networking server software. The GNU AGPL is similar to the GNU General Public License, except that it additionally covers the use of the software over a computer network, requiring that the complete source code be made available to any network user of the AGPLed work, for example a web application. The Free Software Foundation recommends that this license is considered for any software that will commonly be run over the network.

Related content

External links

The official license text

Other Free Software Foundation resources

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