Clear rules about how free software licenses are displayed-or not-are surprisingly complex, and developers are often left wondering what’s allowed. The GNU General Public License (GPL) aims to balance user freedom with recognizing the work of developers, but interpreting its clauses regarding notices can be tricky.
Software freedom is strengthened by clear licensing practices, including informing users of their rights, which aids in enforcing those rights if a violation occurs. Recognizing the hard work of free software developers by displaying authorship and license details is also highly valued.The obligation to preserve these legal notices was intentionally included in the GNU GPL to prevent its misuse in limiting software freedom, though the specific wording differs between the GNU GPLv2 and the GNU GPLv3.
For users, clear authorship and license information is essential to ensure they are using free software, understand their rights, and know who granted them. The Free Software Foundation (FSF) recommends including these notices in the headers of all source code files and having interactive programs display them upon startup-such as, a brief copyright and copying permissions notice when a program launches.
The FSF’s Licensing and Compliance lab frequently receives questions about how the GPL’s notice clauses apply to web applications. Specifically,GPLv2’s Sec. 2(c) and GPLv3’s Sec. 5(d) and Sec. 7(b) are often the subject of inquiry. A common scenario involves a website operator wanting to remove attribution from a page generated by the application, or disagreement over whether such removal is permissible. Some developers also ask if requiring modification retainment of links or logos is acceptable as a license condition.
Understanding GPL Versions and Notices
The GNU GPLv2 Sec.2(c) requires those modifying interactive programs released under that license to display legal notices, but allows versatility in how and where those notices are displayed, as long as they are displayed in some form. The license includes an exception:
“if the Program itself is interactive but dose not normally print such an announcement, your work based on the Program is not required to print an announcement”.
The GNU GPLv3 handles notices similarly, introducing the term “Appropriate Legal Notices” (ALNs). These are notices displayed in an interactive user interface that include the copyright notice, which must contain the word “copyright” (or the (C) symbol), the year of first publication, and the name of the copyright holder. ALNs may also include information about the lack of warranty and how to view a copy of the license.
GPLv3 Sec. 7(b) previously contained a clause requiring verbatim preservation of attribution notices, but this was problematic. Richard M. Stallman successfully convinced the University of California to remove this clause from BSD releases, leading to the license’s disappearance.
Similarly, requiring verbatim preservation of an attribution, even after modification or combination with other programs, could create legal issues. Preserving the attribution might led to claims of misattribution, while modifying or removing it could lead to claims of violating the additional term.
Using GPLv3 Sec. 7(e) for Attribution
If a licensor aims to preserve links or logos, GNU GPLv3 Sec. 7(e) is the appropriate avenue. This section allows licensors to decline granting rights under trademark law for the use of trade names,trademarks,or service marks.
Including trademarked links or logos and explicitly declining a trademark license allows the trademark holder to protect their reputation while giving users the option to remove the trademarks for free modification and distribution. This approach aligns with the GPLv3’s goal of protecting software freedom, allowing modifiers flexibility in displaying ALNs without external restrictions.
