Common Development and Distribution License
| Company type | Public |
|---|---|
| Industry | Computer software |
| Founded | February 24, 1982 |
| Founder | Vinod Khosla, Andy Bechtolsheim, Scott McNealy, Bill Joy |
| Fate | Acquired by Oracle Corporation in 2010 |
| Successor | Oracle Corporation |
| Headquarters | Santa Clara, California , United States |
The Common Development and Distribution License (CDDL) is an open-source and free software license created by Sun Microsystems, which is based on the Mozilla Public License (MPL). It allows the combination of files under the CDDL with those governed by other licenses, including proprietary ones. The Open Source Initiative approved it in 2005, and the Free Software Foundation recognizes it as a free software license; however, it remains incompatible with the GNU General Public License (GPL).
Terms
Derived from MPL version 1.1, the CDDL was designed to overcome certain limitations found in the MPL. It is classified as a weak copyleft license, occupying a middle ground between strong copyleft licenses like the GPL and permissive licenses such as BSD or MIT. The license mandates that only source files covered by CDDL must be maintained under this license.
Unlike strong copyleft licenses, the CDDL permits CDDL-licensed source code to be combined with other licensed code without requiring relicensing. Executable binaries may be distributed under different licenses provided that the original source code remains accessible under CDDL terms, facilitating commercial models preferred by Sun.
Additionally, the license includes a patent grant often referred to as "patent peace" from contributors; however, this grant is revoked if modifications are made to patented code. This mechanism aims to balance innovation protection with safeguarding contributors’ rights.
History
Prior to the CDDL, Sun Microsystems utilized the Sun Public License (SPL), which itself was derived from the Mozilla Public License. The Common Development and Distribution License is regarded by Sun (now part of Oracle) as essentially SPL version 2—a refined iteration of the Mozilla license.
The creation of CDDL was led by a team at Sun including Solaris kernel engineer Andrew Tucker and Claire Giordano, building upon MPL 1.1. The license was submitted to the Open Source Initiative on December 1, 2004, and received approval as an open source license in January 2005. A subsequent proposal in early 2005 addressed concerns about compliance with European copyright laws and enabled individual developers to adopt the CDDL.
In 2006, the OSI's license proliferation committee listed CDDL among nine favored licenses due to its widespread acceptance and robust community backing.
While recognized by the Free Software Foundation as a free software license, the FSF has pointed out its incompatibility with the GNU General Public License (GPL).
GPL compatibility
From 2004 through 2006, discussions within the free software community centered on whether CDDL was compatible with GPL licensing. The Free Software Foundation officially declared CDDL incompatible with GPL only in 2016.
This incompatibility stems from CDDL’s inheritance of MPL 1.1’s complex provisions and conflicts arising from GPL’s viral licensing nature. Consequently, it is not possible to combine code licensed under CDDL directly with GPL-licensed code within a single executable. Some have suggested that Sun deliberately crafted CDDL to avoid compatibility with GPL. Danese Cooper, who contributed to drafting CDDL, mentioned that the Mozilla license’s incompatibility with GPL influenced this decision, reflecting Solaris engineers’ preference for a license that would not align with GPL terms.
Simon Phipps, who served as Sun’s Chief Open Source Officer during that period and introduced Cooper as a co-author of CDDL, partially disagreed with her interpretation. He noted a significant preference among Solaris developers for a BSD-style license, which conflicted with Sun’s inclination toward copyleft licensing and legal delays caused by releasing code under GPLv3. Later, Phipps strongly refuted Cooper’s claims, underscoring internal disagreements and an urgent need to release code without waiting for GPLv3 or other licensing updates.
Bryan Cantrill, involved in publishing software under CDDL at Sun, remarked in 2015 that they anticipated swift adoption of CDDL-licensed projects within Linux environments and did not expect licensing issues to impede progress. However, retrospective analysis revealed that resistance within parts of the community—driven by licensing concerns and "not invented here" sentiments—slowed integration into Linux ecosystems.
cdrtools dispute
The controversy over GPL compatibility emerged when cdrtools was partly relicensed from the GPL to the CDDL. In 2006, the Debian project determined that cdrtools could not be legally distributed because its build system fell under the CDDL license.
Jörg Schilling, the author, maintained that smake is a separate entity and does not infringe on the GPLv3. He contended that although the GPL mandates build scripts to be openly licensed, they are not required to be licensed under the GPL itself, thereby avoiding any license conflicts.
Schilling further asserted that in cases of "combined works"—which differ from "derived works"—the GPL and CDDL licenses can coexist compatibly. Nevertheless, legal counsel at Red Hat prevented cdrtools from being included in both Fedora and Red Hat Enterprise Linux, citing disagreement with Schilling’s atypical interpretation of copyright.
ZFS integration in the Linux kernel
The debate over CDDL and GPL compatibility reemerged in 2015 when Ubuntu announced it would ship OpenZFS by default. After conducting a legal assessment in 2016, Ubuntu concluded that deploying ZFS as a binary kernel module rather than embedding it directly into the kernel image was legally permissible.
Following this approach, authorities such as James E. J. Bottomley argued that there was no substantial legal risk demonstrated, making enforcement improbable. Eben Moglen, co-author of the GPLv3 and founder of the SFLC, noted that although there may be a technical breach of the GPL’s terms, the fundamental intent behind both licenses remains preserved—a critical factor in legal judgment.
The SFLC also referenced precedent set by the Andrew File System kernel module, which Linux kernel maintainers do not regard as a derivative work.
On the other hand, Bradley M. Kuhn and attorney Karen M. Sandler from the Software Freedom Conservancy argued that distributing ZFS as a binary module violates both licenses since it effectively constitutes a derivative work of the Linux kernel. Despite this contention, Ubuntu 16.04 LTS included the CDDL-licensed ZFS on Linux.
Adoption
Significant projects distributed under the CDDL encompass:
- OpenSolaris, incorporating technologies like DTrace and ZFS
- illumos, which continues development of OpenSolaris OS/Net and its various distributions
- OpenZFS, an open source volume manager and file system available across multiple platforms
- The NetBeans Integrated Development Environment (IDE) and Rich Client Platform (RCP)
- GlassFish
- The JWSDP
- Project DReaM
- cdrtools
- OpenDJ