The Ubuntu Core Documentation Project uses a dual license strategy for the documentation source-code. The documentation source-code licenses are the GNU Free Documentation License (GFDL) and the Creative Commons ShareAlike? 2.0 License (CC-BY-SA). All works produced as works for hire for Canonical will be released under both licenses.

Authors retain the right to release documents under a single license if they wish. That single can be either the CC-SA, the GFDL, or any other license. However, the following implication of this action should be noted.

Documents under a GFDL or CC-BY incompatible license will not be able to be combined with the core documents. Additionally, documents released under a single license (i.e., either GFDL or CC-BY-SA) are essentially forking from the duality regime of the documentation source-code base. Once released under a single license such works cannot be merged back under the dual license regime. As a result, such works will need to be excluded from any derivative works covered under the dual regime or the regime of the unused license. Unless expressly specified by the author, all document code-source contributions and their derivative works will be made available under the conditions of both licenses.

This provides all parties with maximum flexibility in the contribution of documentation works and any subsequent reuse thereafter. Dual licensing of the Ubuntu Documentation source code provides open and free access to compositions for the GNU Free Documentation License (GFDL) and for other developers and companies that cannot use the GFDL but are happier with the CC-BY-SA which many people consider to be a higher quality license and which is translated (both the language and the law) internationally as part of the iCommons project.

You are free to modify, extend, and improve the Ubuntu documentation source code. The only question is whether or not you must provide the source code and contribute modifications to the community. In this regard, the combination of GFDL and CC-BY-SA licenses provide different great flexibility. Ultimately, regardless of the license selected by an author, any and all incompatible changes must be published openly.

Copies of the licenses are available in XML format in the common/ directory of the repository and are included in the appendices section of all derived presentational formats. Online versions of these licenses can be found at the following URL's:

    * GNU Free Documentation License http://www.gnu.org/copyleft/fdl.html
    * Creative Commons ShareAlike? 2.0 License http://creativecommons.org/licenses/by-sa/2.0/
