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OpenBSD Logo with Puffy, the pufferfish.
"Free, Functional & Secure"
The OpenBSD Project
OS family: BSD
Source model: Open source
Latest stable release: 4.0 / November 1, 2006
Package manager: OpenBSD package tools and ports collection
Supported platforms: AMD64, Alpha, i386, MIPS, 68000, PowerPC, Sparc, Sparc64, VAX, Zaurus and others
Kernel type: Monolithic
Default user interface: modified pdksh, FVWM for X11
License: Mostly BSD
Working state: Current
Computer and operating system
Unix and Unix-like
Software licensing
Computer insecurity

OpenBSD is a freely available Unix-like computer operating system descended from Berkeley Software Distribution (BSD), a Unix derivative developed at the University of California, Berkeley. It was forked from NetBSD (the oldest of the three most popular BSD-based operating systems still active today, with FreeBSD being the other) by project leader Theo de Raadt in late 1995. The project is widely known for the developers' insistence on open source code and quality documentation; uncompromising position on software licensing; and focus on security and code correctness. The project is coordinated from de Raadt's home in Calgary, Alberta, Canada. Its logo and mascot is Puffy, a pufferfish.

OpenBSD includes a number of security features absent or optional in other operating systems and has a tradition of developers auditing the source code for software bugs and security problems. The project maintains strict policies on licensing and prefers the open source BSD licence and its variants—in the past this has led to a comprehensive licence audit and moves to remove or replace code under licences found less acceptable.

In common with most other BSD-based operating systems, the OpenBSD kernel and userland programs, such as the shell and common tools like cat and ps, are developed together in a single source repository. Third-party software is available as binary packages or may be built from source using the ports collection.

OpenBSD currently runs on 16 different hardware platforms, including the DEC Alpha, Intel i386, Hewlett-Packard PA-RISC, AMD AMD64 and Motorola 68000 processors, Apple's PowerPC machines, Sun SPARC and SPARC64-based computers, the VAX and the Sharp Zaurus.

History and popularity

The OpenBSD 2.3 CD cover with the original mascot, before Puffy appeared with release 2.7
The OpenBSD 2.3 CD cover with the original mascot, before Puffy appeared with release 2.7

In December 1994, NetBSD co-founder Theo de Raadt was asked to resign his position as a senior developer and member of the NetBSD core team, and his access to the source code repository was revoked. The reason for this is not wholly clear, although there are claims that it was due to personality clashes within the NetBSD project and on its mailing lists. De Raadt has been criticized for having a sometimes abrasive personality: in his book, Free For All, Peter Wayner claims that de Raadt "began to rub some people the wrong way" before the split from NetBSD; Linus Torvalds has described him as "difficult;" and an interviewer admits to being "apprehensive" before meeting him. Many have different feelings: the same interviewer describes de Raadt's "transformation" on founding OpenBSD and his "desire to take care of his team," some find his straightforwardness refreshing, and few deny he is a talented coder and security "guru."

Proportion of users of each BSD variant from a BSD usage survey. Each participant was permitted to indicate multiple BSD variants
Proportion of users of each BSD variant from a BSD usage survey. Each participant was permitted to indicate multiple BSD variants

In October 1995, de Raadt founded OpenBSD, a new project forked from NetBSD 1.0. The initial release, OpenBSD 1.2, was made in July 1996, followed in October of the same year by OpenBSD 2.0. Since then, the project has followed a schedule of a release every six months, each of which is maintained and supported for one year. The latest release, OpenBSD 4.0, appeared on November 1, 2006.

Just how widely OpenBSD is used is hard to ascertain: the developers do not collect and publish usage statistics and there are few other sources of information. The nascent BSD Certification project performed a usage survey which revealed that 32.8% of BSD users (1420 of 4330 respondents) were using OpenBSD, placing it second of the four major BSD variants, behind FreeBSD with 77.0% and ahead of NetBSD with 16.3%. The Distrowatch website, well-known in the Linux community and often used as a reference for popularity, publishes page hits for each of the Linux distributions and other operating systems it covers. As of August 13, 2006 it places OpenBSD in 48th place, but fairly close to the average with 114 hits per day. FreeBSD is in 12th place with 532 hits per day and a number of Linux distributions range between them. From these statistics, it is possible to conclude that OpenBSD is a substantial presence in the BSD world, with somewhere around a third of the userbase of FreeBSD, and is not unnoticed in the wider open source and free software operating system community.


OpenBSD 3.7 running X.Org with the JWM window manager
OpenBSD 3.7 running X.Org with the JWM window manager

A goal of the OpenBSD project is to "maintain the spirit of the original Berkeley Unix copyrights," which permitted a "relatively un-encumbered Unix source distribution." To this end, the Internet Systems Consortium (ISC) licence, a simplified version of the BSD licence with wording removed that is unnecessary under the Berne convention, is preferred for new code, but the MIT or BSD licences are accepted. The widely used GNU General Public License is considered overly restrictive in comparison with these: code licensed under it, and other licences the project sees as undesirable, is no longer accepted for addition to the base system. In addition, existing code under such licences is actively replaced or relicensed when possible, except in some cases, such as the GNU Compiler Collection (GCC), where there is no suitable replacement and creating one would be time-consuming and impractical. Despite this, OpenBSD has made some significant strides in this area: of particular note is the development of OpenSSH, based on the original SSH suite and developed further by the OpenBSD team. It first appeared in OpenBSD 2.6 and is now the single most popular SSH implementation, available as standard or as a package on many operating systems. Also worth mentioning is the development, after licence restrictions were imposed on IPFilter, of the PF packet filter, which first appeared in OpenBSD 3.0 and is now available in DragonFly BSD, NetBSD and FreeBSD; more recently, OpenBSD releases have seen the GPL licensed tools diff, grep, gzip, bc, dc, nm and size replaced with BSD licensed equivalents. OpenBSD developers are also behind OpenBGPD, OpenOSPFD, OpenNTPD and OpenCVS, BSD licensed alternatives to existing software.

In June of 2001, triggered by concerns over Darren Reed's modification of IPFilter's licence wording, a systematic licence audit of the OpenBSD ports and source trees was undertaken. Code in more than a hundred files throughout the system was found to be unlicensed, ambiguously licensed or in use against the terms of the licence. To ensure that all licences were properly adhered to, an attempt was made to contact all the relevant copyright holders: some pieces of code were removed, many were replaced, and others, including the multicast routing tools, mrinfo and map-mbone, which were licensed by Xerox for research only, were relicensed so that OpenBSD could continue to use them. Also of note during this audit was the removal of all software produced by Daniel J. Bernstein from the OpenBSD ports tree. At the time, Bernstein requested that all modified versions of his code be approved by him prior to redistribution, a requirement to which OpenBSD developers were unwilling to devote time or effort. The removal led to a clash with Bernstein who felt the removal of his software to be uncalled for and cited the Netscape web browser as much less free, accusing the OpenBSD developers of hypocrisy for permitting Netscape to remain while removing his software. The OpenBSD project's stance was that Netscape, although not open source, had licence conditions that were much easier to meet; they asserted that Bernstein's demand for control of derivatives would lead to a great deal of additional work and that removal was the most appropriate way to comply with his requirements. At present, Daniel J. Bernstein's software is still absent from the ports tree.

Security and code auditing

Shortly after OpenBSD's creation, Theo de Raadt was contacted by a local security software company named Secure Networks, Inc. or SNI. They were developing a "network security auditing tool" called Ballista (later renamed to Cybercop Scanner after SNI was purchased by Network Associates) which was intended to find and attempt to exploit possible software security flaws. This coincided well with de Raadt's own interest in security, so the two agreed to cooperate, a relationship that was of particular use leading up to the release of OpenBSD 2.3 and helped to form the focal point of the project: OpenBSD developers would attempt to do what was right, proper or secure, even at the cost of ease, speed or functionality. As bugs within OpenBSD became harder to find and exploit, the security company found that it was too difficult, or not cost effective, to handle such obscure problems. After years of cooperation, the two parties decided that their goals together had been met and parted ways.

Until June 2002, the OpenBSD website featured the slogan:

No remote computer hole in the default install, in nearly 6 years.

In June 2002, Mark Dowd of Internet Security Systems disclosed a bug in the OpenSSH code implementing challenge-response authentication. This was the first and, so far, only vulnerability discovered in the OpenBSD default installation allowing an attacker remote access to the root account—it was extremely serious, partly due to the widespread use of OpenSSH by that time: the bug affected a considerable number of other operating systems. This problem necessitated the adjustment of the slogan on the OpenBSD website to:

Only one remote hole in the default install, in more than 8 years.

This statement has been criticized because little is enabled in a default install of OpenBSD and releases have included software that was later found to have remote holes; however, the project maintains that the slogan is intended to refer to a default install and that it is correct by that measure. One of the fundamental ideas behind OpenBSD is a drive for systems to be simple, clean and secure by default. For example, OpenBSD's minimal defaults fit in with standard computer security practice of enabling as few services as possible on production machines, and the project uses open source and code auditing practices argued to be important elements of a security system.

OpenBSD 3.8-current booting. 3.8 saw security changes to the malloc function
OpenBSD 3.8-current booting. 3.8 saw security changes to the malloc function

OpenBSD includes a large number of specific features designed to improve security, including API and toolchain alterations, such as the strlcpy and strlcat functions and a static bounds checker; memory protection techniques to guard against invalid accesses, such as ProPolice, StackGhost, the W^X (W xor X) page protection features, as well as alterations to malloc; and cryptography and randomization features, including network stack enhancements and the addition of the Blowfish cipher for password encryption. To reduce the risk of a vulnerability or misconfiguration allowing privilege escalation, some programs have been written or adapted to make use of privilege separation, privilege revocation and chrooting. Privilege separation is a technique, pioneered on OpenBSD and inspired by the principle of least privilege, where a program is split into two or more parts, one of which performs privileged operations and the other—almost always the bulk of the code—runs without privilege. Privilege revocation is similar and involves a program performing any necessary operations with the privileges it starts with then dropping them, and chrooting involves restricting an application to one section of the file system, prohibiting it from accessing areas that contain private or system files. Developers have applied these features to OpenBSD versions of common applications, including tcpdump and the Apache web server, which, due to licensing issues with the later Apache 2 series, is a heavily patched 1.3 release.

The project has a policy of continually auditing code for security problems, work developer Marc Espie has described as "never finished … more a question of process than of a specific bug being hunted." He went on to list several typical steps once a bug is found, including examining the entire source tree for the same and similar issues, "try[ing] to find out whether the documentation ought to be amended," and investigating whether "it's possible to augment the compiler to warn against this specific problem." Along with DragonFly BSD, OpenBSD is one of the two open source operating systems with a policy of seeking out examples of classic, K&R C code and converting it to the more modern ANSI equivalent—this involves no functional change and is purely for readability and consistency reasons. A standard code style, the Kernel Normal Form, which dictates how code must look in order to be easily maintained and understood, must be applied to all code before it is considered for inclusion in the base operating system; existing code is actively updated to meet the style requirements.


OpenBSD's security enhancements, built-in cryptography and the PF firewall suit it for use in the security industry, particularly for firewalls, intrusion-detection systems and VPN gateways. It is also commonly used for servers which need to be resistant against cracking attempts and DoS attacks, and due to the inclusion of the spamd daemon, it occasionally sees use in mail filtering applications.

There are several proprietary systems which are based on OpenBSD, including Profense from Armorlogic ApS, various security appliances made by .vantronix GmbH, syswall from Syscall Network Solutions AG, GeNUGate and GeNUBox from GeNUA mbH, HIOBMessenger from topX and RTMX O/S from RTMX Inc. Of these, both RTMX and GeNUA have contributed back to OpenBSD: RTMX have sent patches to add further POSIX compliance to the system and GeNUA funded the development of SMP on the i386 platform. Several open source operating systems have also been derived from OpenBSD, notably Anonym.OS and MirOS BSD, as well as the now defunct ekkoBSD, MicroBSD and Gentoo/OpenBSD. In addition, code from many of the OpenBSD system tools has been used in recent versions of Microsoft's Services for UNIX, an extension to the Windows operating system which provides some Unix-like functionality, originally based on 4.4BSD-Lite. Core force, a security product for Windows, is based on OpenBSD's PF firewall. There have also been projects which use OpenBSD as part of images for embedded systems, including OpenSoekris and flashdist; together with tools like nsh, these allow Cisco-like embedded devices to be created.

OpenBSD 3.8 running X.Org with the default FVWM window manager
OpenBSD 3.8 running X.Org with the default FVWM window manager

OpenBSD ships with the X window system. Following the XFree86 licence change, it includes a recent X.Org release; an older XFree86 3.3 release is also available for legacy video cards. With these, it is possible to use OpenBSD as a desktop or workstation, making use of a desktop environment, window manager or both to give the X desktop a wide range of appearances. The OpenBSD ports tree contains many of the most popular tools for desktop use, including desktop environments GNOME, KDE, and Xfce; web browsers Mozilla Firefox and Opera; and multimedia programs. In addition, graphical software for many uses is available from both the ports tree and by compiling POSIX compliant software. Also available are compatibility layers, which allow binary code compiled for other operating systems, including Linux, FreeBSD, SunOS and HP-UX, to be run. However, since hardware providers such as graphics card manufacturers ATI and NVIDIA refuse to release open source drivers or documentation for the 3D capabilities of their hardware, OpenBSD lacks accelerated 3D graphics support.

OpenBSD's performance and usability is occasionally criticized. Performance and scalability tests, most famously Felix von Leitner's tests, often show OpenBSD to lag behind other operating systems. OpenBSD users and developers have countered this by asserting that although performance is certainly given consideration, security, reliability and correctness are seen as more important. OpenBSD is also a relatively small project, particularly when compared with FreeBSD and Linux, and developer time is sometimes seen as better spent on security enhancements than performance optimisations. Critics of usability often point out the lack of user-friendly configuration tools, the bare default installation, and "spartan" and "intimidating" installer. These see much the same rebuttals as performance: a preference for simplicity, reliability and security; as one reviewer admits, "running an ultra-secure operating system can be a bit of work."

Distribution and marketing

OpenBSD is available freely in various ways: the source can be retrieved by anonymous CVS or CVSup, and binary releases and development snapshots can be downloaded either by FTP or HTTP. Prepackaged CD sets can be ordered online for a small fee, complete with an assortment of stickers and a copy of the release's theme song. These, with their artwork and other bonuses, are one of the project's few sources of income, funding hardware, bandwidth and other expenses. To encourage the sale of the official CDs, OpenBSD makes only a small install ISO image available for download rather than provide full release ISOs.

In common with several other operating systems, OpenBSD uses ports and packages systems to allow for easy installation and management of programs which are not part of the base operating system. Originally based on the FreeBSD ports tree, the system is now quite distinct. Additionally, major changes have been made since the 3.6 release, including the replacement of the package tools, the tools available to the user to manipulate packages, by more capable versions, written in Perl by Marc Espie. In contrast to FreeBSD, the OpenBSD ports system is intended as a source used to create the end product, the packages: installing a port first creates a package and then installs it using the package tools. Packages are built in bulk by the OpenBSD team and provided for download with each release. OpenBSD is also unique among the BSDs in that the ports and base operating system are developed and released together for each version: this means that the ports or packages released with, for example, 3.7 are not suitable for use with 3.6 and vice versa, a policy which lends a great deal of stability to the development process, but means that the software in ports for the latest OpenBSD release can lag somewhat from the latest version available from the author.

Around the time of the OpenBSD 2.7 release, the original mascot, a BSD daemon with a trident and aureola, was replaced by Puffy, traditionally said to be a pufferfish. In fact pufferfish do not possess spikes and images of Puffy are closer to a similar species, the porcupinefish. Puffy was selected because of the Blowfish encryption algorithm used in OpenSSH and the strongly defensive image of the porcupinefish with its spikes to deter predators. He quickly became very popular, mainly because of the appealing image of the fish and his distinction from the BSD daemon, also used by FreeBSD, and the horde of daemons then used by NetBSD. Puffy made his first public appearance in OpenBSD 2.6 and, since then, has appeared in a number of guises on tee-shirts and posters. These have included Puffiana Jones, the famed hackologist and adventurer, seeking out the Lost RAID; Puffathy, a little Alberta girl, who must work with Taiwan to save the day; Sir Puffy of Ramsay, a freedom fighter who, with Little Bob of Beckley, took from the rich and gave to all; and Puff Daddy, famed rapper and political icon.

After a number of releases, OpenBSD has become notorious for its catchy songs and interesting and often comical artwork. The promotional material of early OpenBSD releases did not have a cohesive theme or design but, starting with OpenBSD 3.0, the CDs, release songs, posters and tee-shirts for each release have been produced with a single style and theme, sometimes contributed to by Ty Semaka of the Plaid Tongued Devils. At first they were done lightly and only intended to add humour but, as the concept has evolved, they have become a part of OpenBSD advocacy, with each release expanding a moral or political point important to the project, often through parody. Past themes have included: in OpenBSD 3.8, the Hackers of the Lost RAID, a parody of Indiana Jones linked to the new RAID tools featured as part of the release; The Wizard of OS, making its debut in OpenBSD 3.7, based on the work of Pink Floyd and a parody of The Wizard of Oz related to the project's recent wireless hacking; and OpenBSD 3.3's Puff the Barbarian, including an 80s rock-style song and parody of Conan the Barbarian, alluding to open documentation.

In addition to the slogans used on tee-shirts and posters for releases, the project occasionally produces other material: over the years, catchphrases have included "Sending script kiddies to /dev/null since 1995," "Functional, secure, free – choose 3," "Secure by default," and a few insider slogans, only available on tee-shirts made for developer gatherings, such as "World class security for much less than the price of a cruise missile" and a crufty old octopus proclaiming "Shut up and hack!"


A number of books on OpenBSD have been published, including:

  • Mastering FreeBSD and OpenBSD Security by Yanek Korff, Paco Hope and Bruce Potter. ISBN 0-596-00626-8.
  • Building Firewalls with OpenBSD and PF: Second Edition by Jacek Artymiak. ISBN 83-916651-1-9.
  • Secure Architectures with OpenBSD by Brandon Palmer and Jose Nazario. ISBN 0-321-19366-0.
  • Absolute OpenBSD, Unix for the Practical Paranoid by Michael W. Lucas. ISBN 1-886411-99-9.
  • Building Linux and OpenBSD Firewalls by Wes Sonnenreich and Tom Yates. ISBN 0-471-35366-3.
  • The OpenBSD PF Packet Filter Book: PF for NetBSD, FreeBSD, DragonFly and OpenBSD published by Reed Media Services. ISBN 0-9790342-0-5.

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