Why Debian Rejected GFDL Invariant Sections

The friction between the GNU Free Documentation License (GFDL) and the Debian Project stemmed from a fundamental philosophical disagreement over whether documentation should be held to the same freedom standards as software code. While the Free Software Foundation (FSF) designed the GFDL with an option for "Invariant Sections" to preserve authors' political and philosophical viewpoints, the Debian Project concluded that these unmodifiable sections directly violated the Debian Free Software Guidelines (DFSG). This incompatibility forced Debian to remove significant amounts of GNU documentation from its core operating system and relegate it to its non-free repositories.

The GFDL was created by the FSF to license manuals, textbooks, and reference materials accompanying GNU software. A distinctive feature of this license is the option to mark secondary sections as "invariant." Invariant sections typically cover the author's relationship to the subject matter or explain philosophical justifications for free software, such as the GNU Manifesto. Under the terms of the GFDL, downstream distributors and users are strictly prohibited from modifying, condensing, or deleting any text designated as invariant, even when translating the manual or creating derived works.

This restriction came into direct conflict with DFSG Criterion 3, which explicitly demands that a free license must permit modifications and derived works, allowing them to be distributed under the same terms as the original software. Debian takes a unified stance on freedom: everything included in the official Debian distribution—whether executable binary code, artwork, audio, or documentation—must be entirely free for users to inspect, modify, fork, and reuse.

Debian developers identified several practical and ethical issues caused by invariant sections:

• Inability to Fork or Correct: If an invariant section contains outdated, offensive, or inaccurate information, future maintainers have no legal right to correct or remove it.
• Storage and Embedded System Constraints: In resource-constrained environments, such as embedded systems or minimal server images, administrators cannot strip out lengthy invariant essays to save disk space.
• Translation Barriers: Ambiguities in the GFDL left it unclear whether translating an invariant section into another language constituted an unauthorized modification, potentially hindering localization efforts.
• Hostile Content Addition: Debian highlighted a loophole where third parties creating derived works could add their own invariant sections, potentially turning technical manuals into bloated repositories of conflicting political commentary.

The dispute culminated in 2006 with Debian General Resolution 2006-001. The resolution determined that works licensed under the GFDL that contain invariant sections are non-free according to the DFSG. Consequently, Debian split packages containing such documentation, moving manuals for essential tools like GCC, Emacs, and Bash into the non-free archive, leaving only GFDL documentation without invariant sections in the main operating system repository.