FreeBSD Release Engineering

Murray Stokely


$FreeBSD: doc/en_US.ISO8859-1/articles/releng/article.sgml,v 1.67 2005/03/18 03:00:47 murray Exp $

Legal Notice

This paper describes the approach used by the FreeBSD release engineering team to make production quality releases of the FreeBSD Operating System. It details the methodology used for the official FreeBSD releases and describes the tools available for those interested in producing customized FreeBSD releases for corporate rollouts or commercial productization.

Table of Contents
1 Introduction
2 Release Process
3 Release Building
4 Distribution
5 Extensibility
6 Lessons Learned from FreeBSD 4.4
7 Future Directions
8 Acknowledgements
9 References

1 Introduction

The development of FreeBSD is a very open process. FreeBSD is comprised of contributions from thousands of people around the world. The FreeBSD Project provides anonymous CVS[1] access to the general public so that others can have access to log messages, diffs (patches) between development branches, and other productivity enhancements that formal source code management provides. This has been a huge help in attracting more talented developers to FreeBSD. However, I think everyone would agree that chaos would soon manifest if write access was opened up to everyone on the Internet. Therefore only a “select” group of nearly 300 people are given write access to the CVS repository. These committers[6] are responsible for the bulk of FreeBSD development. An elected core-team[7] of very senior developers provides some level of direction over the project.

The rapid pace of FreeBSD development leaves little time for polishing the development system into a production quality release. To solve this dilemma, development continues on two parallel tracks. The main development branch is the HEAD or trunk of our CVS tree, known as “FreeBSD-CURRENT” or “-CURRENT” for short.

A more stable branch is maintained, known as “FreeBSD-STABLE” or “-STABLE” for short. Both branches live in a master CVS repository in California and are replicated via CVSup[2] to mirrors all over the world. FreeBSD-CURRENT[8] is the “bleeding-edge” of FreeBSD development where all new changes first enter the system. FreeBSD-STABLE is the development branch from which major releases are made. Changes go into this branch at a different pace, and with general assumption that they have first gone into FreeBSD-CURRENT and have been thoroughly tested by our user community.

In the interim period between releases, nightly snapshots are built automatically by the FreeBSD Project build machines and made available for download from The widespread availability of binary release snapshots, and the tendency of our user community to keep up with -STABLE development with CVSup and “make world”[8] helps to keep FreeBSD-STABLE in a very reliable condition even before the quality assurance activities ramp up pending a major release.

Bug reports and feature requests are continuously submitted by users throughout the release cycle. Problems reports are entered into our GNATS[9] database through email, the send-pr(1) application, or via the web interface provided at In addition to the multitude of different technical mailing lists about FreeBSD, the FreeBSD Quality Assurance mailing list provides a forum for discussing the finer points of “release-polishing”.

To service our most conservative users, individual release branches were introduced with FreeBSD 4.3. These release branches are created shortly before a final release is made. After the release goes out, only the most critical security fixes and additions are merged onto the release branch. In addition to source updates via CVS, binary patchkits are available to keep systems on the RELENG_X_Y branches updated.

Section 2 discusses the different phases of the release engineering process leading up to the actual system build and Section 3 describes the actual build process. Section 5 describes how the base release may be extended by third parties and Section 6 details some of the lessons learned through the release of FreeBSD 4.4. Finally, Section 7 presents future directions of development.

This, and other documents, can be downloaded from

For questions about FreeBSD, read the documentation before contacting <>.
For questions about this documentation, e-mail <>.

Hosting by: Hurra Communications Ltd.
Generated: 2007-01-26 17:58:40