OpenBSD is a security-focused, free and open-source operating system based on the Berkeley Software Distribution (BSD), a Unix derivative developed at the University of California, Berkeley. Theo de Raadt created OpenBSD in 1995 by forking the codebase from NetBSD.
Free, Functional, and Secure
OpenBSD 6.1 default desktop with various utilities: Top, Xterm, Xclock, Calculator, GlxGears
|Developer||The OpenBSD Project|
|Written in||C, assembly, Perl, Unix shell|
|OS family||Unix-like (BSD)|
|Initial release||1 October 1996|
|Latest release||6.4 (18 October 2018[±])|
|Package manager||OpenBSD package tools|
|Platforms||Alpha, x86-64, ARMv7, ARMv8 (64-bit), PA-RISC, IA-32, LANDISK, Omron LUNA-88K, MIPS64, PowerPC, SPARC64|
|Default user interface||Modified pdksh, X11 (FVWM)|
|License||BSD, ISC, other permissive licenses|
According to De Raadt, OpenBSD is a research operating system for developing security mitigations. Because of the project's emphasis on code quality, many components are reused in other software projects. Android uses its C standard library, LLVM uses its regular expression library, and Windows 10 uses OpenSSH with LibreSSL.
The system is intended to be secure by default, and many of its security features are either missing or optional in other operating systems. According to author Michael W. Lucas, OpenBSD is "widely regarded as the most secure operating system available anywhere, under any licensing terms.":xxix
De Raadt coordinates the project from his home in Calgary, Alberta, Canada. In addition to the operating system itself, the project maintains portable versions of many subsystems (such as OpenSSH), which are available as packages for other operating systems. Its logo and mascot is a pufferfish named Puffy.
In December 1994, Theo de Raadt was forced to resign from the NetBSD core team, and his access to the source repository was revoked. Fellow team members claimed it was due to personality clashes on the mailing lists.
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 by OpenBSD 2.0 in October of the same year. Since then, the project has issued a release every six months, each of which is supported for one year.
On 25 July 2007, OpenBSD developer Bob Beck announced the formation of the OpenBSD Foundation, a Canadian non-profit organization formed to "act as a single point of contact for persons and organizations requiring a legal entity to deal with when they wish to support OpenBSD."
It is hard to determine how widely OpenBSD is used, because the developers do not publish or collect usage statistics. In September 2005, the BSD Certification Group surveyed BSD users, showing that 33% used OpenBSD, behind FreeBSD with 77% and ahead of NetBSD with 16%.[n 1]
OpenBSD ships with Xenocara, an implementation of the X Window System, and is suitable for use as a workstation.:xl As of September 2018[update], OpenBSD includes approximately 8000 packages in its software repository, including desktop environments such as GNOME, Plasma 4 and Xfce, and web browsers such as Firefox and Chromium. The project also includes three window managers in the main distribution: cwm, FVWM (part of the default configuration for Xenocara), and twm.
Proprietary systems from several manufacturers are based on OpenBSD, including devices from Armorlogic (Profense web application firewall), Calyptix Security, GeNUA, RTMX, and .vantronix. Later versions of Microsoft's Services for UNIX, an extension to the Windows operating system providing Unix-like functionality, use large amounts of OpenBSD code.
Shortly after OpenBSD was created, De Raadt was contacted by a local security software company named Secure Networks (SNI). They were developing a "network security auditing tool" called Ballista,[n 2] which was intended to find and attempt to exploit possible software security flaws. This coincided with De Raadt's own interest in security, so for a time the two cooperated, a relationship that was of particular usefulness leading up to the release of OpenBSD 2.3 and helped to define security as the focal point of the project.
OpenBSD includes features designed to improve security, such as:
- secure alternatives to POSIX functions in the C standard library, such as
- toolchain alterations, including a static bounds checker
- memory protection techniques to guard against invalid accesses, such as ProPolice and the W^X page protection feature
- strong cryptography and randomization
To reduce the risk of a vulnerability or misconfiguration allowing privilege escalation, many 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. 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 enhancements to OpenBSD versions of many common applications, such as tcpdump, file, tmux, smtpd, and syslogd.
OpenBSD developers were instrumental in the creation and development of OpenSSH, which is developed in the OpenBSD CVS repositories. OpenSSH is based on the original SSH. It first appeared in OpenBSD 2.6 and is now by far the most popular SSH client and server, available on many operating systems.
The project has a policy of continually auditing source code for problems, work that 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."
The OpenBSD website features a prominent reference to the system's security record. Until June 2002, it read:
|“||Five years without a remote hole in the default install!||”|
In June 2002, Mark Dowd of Internet Security Systems disclosed a bug in the OpenSSH code implementing challenge-response authentication. This vulnerability in the OpenBSD default installation allowed an attacker remote access to the root account, which was extremely serious not only to OpenBSD, but also to the large number of other operating systems that were using OpenSSH by that time. This problem necessitated the adjustment of the slogan on the OpenBSD website to:
|“||One remote hole in the default install, in nearly 6 years!||”|
The quote remained unchanged as time passed, until on March 13, 2007 when Alfredo Ortega of Core Security Technologies disclosed a network-related remote vulnerability. The quote was subsequently changed to:
|“||Only two remote holes in the default install, in a heck of a long time!||”|
This statement has been criticized because the default install contains few running services, and many use cases require additional services. Also, because the ports tree contains unaudited third-party software, it is easy for users to compromise security by installing or improperly configuring packages. 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. The default install is quite minimal, which the project states is to ensure novice users "do not need to become security experts overnight", which fits with open-source and code auditing practices considered important elements of a security system.
On 11 December 2010, Gregory Perry, a former technical consultant for the Federal Bureau of Investigation (FBI), emailed De Raadt alleging that the FBI had paid some OpenBSD ex-developers 10 years previously to insert backdoors into the OpenBSD Cryptographic Framework. De Raadt made the email public on 14 December by forwarding it to the openbsd-tech mailing list and suggested an audit of the IPsec codebase. De Raadt's response was skeptical of the report and he invited all developers to independently review the relevant code. In the weeks that followed, bugs were fixed but no evidence of backdoors were found. De Raadt stated "I believe that NetSec was probably contracted to write backdoors as alleged. If those were written, I don't believe they made it into our tree. They might have been deployed as their own product."
Many open source projects started as components of OpenBSD, including:
- CARP, a free alternative to Cisco's patented HSRP/VRRP redundancy protocols
- cwm, a stacking window manager
- httpd, an HTTP server first included in the 5.6 release
- LibreSSL, an implementation of the SSL and TLS protocols, forked from OpenSSL 1.0.1g
- OpenBGPD, an implementation of BGP-4
- OpenIKED, an implementation of IKEv2
- OpenNTPD, a simpler alternative to ntp.org's NTP daemon
- OpenOSPFD, an implementation of OSPF
- OpenSMTPD, an SMTP daemon with IPv4/IPv6, PAM, Maildir and virtual domains support
- OpenSSH, an implementation of SSH
- PF, an IPv4/IPv6 stateful firewall with NAT, PAT, QoS and traffic normalization support
- pfsync, a firewall state synchronization protocol for PF with high availability support using CARP
- sndio, a compact audio and MIDI framework
- spamd, a spam filter with greylisting support designed to inter-operate with PF
- Xenocara, a customized X.Org build infrastructure
Linux administrator Carlos Fenollosa commented on moving from Linux to OpenBSD that the system is faithful to the Unix philosophy of small, simple tools that work together well: "Some base components are not as feature-rich, on purpose. Since 99% of the servers don't need the flexibility of Apache, OpenBSD's httpd will work fine, be more secure, and probably faster". He characterized the developer community's attitude to components as: "When the community decides that some module sucks, they develop a new one from scratch. OpenBSD has its own NTPd, SMTPd and, more recently, HTTPd. They work great". As a result, OpenBSD is relatively prolific in creating components that become widely reused by other systems.
OpenBSD includes a number of third-party components, many with OpenBSD-specific patches, such as Xorg, Clang (the default compiler on several architectures), GCC,[n 3] Perl, NSD, Unbound, ncurses, GNU binutils, GDB, and AWK.
OpenBSD formerly included a fork of Apache 1.3, later replaced by Nginx. In the 5.6 release, Nginx was replaced with httpd, an HTTP server with FastCGI and TLS support. As of May 2018[update], Apache and Nginx are still available as ports.
Development is continuous, and team management is open and tiered. Anyone with appropriate skills may contribute, with commit rights being awarded on merit and De Raadt acting as coordinator.:xxxv Two official releases are made per year, with the version number incremented by 0.1, and these are each supported for twelve months (two release cycles). Snapshot releases are also available at frequent intervals.
Maintenance patches for supported releases may be applied manually or by updating the system against the patch branch of the CVS repository for that release. Alternatively, a system administrator may opt to upgrade using a snapshot release and then regularly update the system against the -current branch of the CVS repository, in order to gain pre-release access to recently added features.
The generic OpenBSD kernel provided by default is strongly recommended for end users, in contrast to operating systems that recommend user kernel customization.
Packages outside the base system are maintained by CVS through a ports tree and are the responsibility of the individual maintainers, known as porters. As well as keeping the current branch up to date, porters are expected to apply appropriate bug-fixes and maintenance fixes to branches of their package for OpenBSD's supported releases. Ports are generally not subject to the same continuous auditing as the base system due to lack of manpower.
Binary packages are built centrally from the ports tree for each architecture. This process is applied for the current version, for each supported release, and for each snapshot. Administrators are recommended to use the package mechanism rather than build the package from the ports tree, unless they need to perform their own source changes.
Most new releases include a song.
Open source and open documentationEdit
When OpenBSD was created, De Raadt decided that the source code should be available for anyone to read. At the time, a small team of developers generally had access to a project's source code. Chuck Cranor and De Raadt concluded this practice was "counter to the open source philosophy" and inconvenient to potential contributors. Together, Cranor and De Raadt set up the first public, anonymous CVS server. De Raadt's decision allowed users to "take a more active role", and established the project's commitment to open access.
Since OpenBSD is based in Canada, no United States export restrictions on cryptography apply, allowing the distribution to make full use of modern algorithms for encryption. For example, the swap space is divided into small sections and each section is encrypted with its own key, ensuring that sensitive data does not leak into an insecure part of the system.
OpenBSD randomizes various behaviors of applications, making them less predictable and thus more difficult to attack. For example, PIDs are created and associated randomly to processes; the
bind system call uses random port numbers; files are created with random inode numbers; and IP datagrams have random identifiers. This approach also helps expose bugs in the kernel and in user space programs.
The OpenBSD policy on openness extends to hardware documentation: in the slides for a December 2006 presentation, De Raadt explained that without it "developers often make mistakes writing drivers", and pointed out that "the [oh my god, I got it to work] rush is harder to achieve, and some developers just give up." He went on to say that vendor-supplied binary drivers are unacceptable for inclusion in OpenBSD, that they have "no trust of vendor binaries running in our kernel" and that there is "no way to fix [them] ... when they break."
OpenBSD maintains a strict license policy, preferring the ISC license and other variants of the BSD license. The project attempts to "maintain the spirit of the original Berkeley Unix copyrights," which permitted a "relatively un-encumbered Unix source distribution." The widely used Apache License and GNU General Public License are considered overly restrictive.
In June 2001, triggered by concerns over Darren Reed's modification of IPFilter's license wording, a systematic license 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 license. To ensure that all licenses 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, such as the multicast routing tools mrinfo and map-mbone, were relicensed so that OpenBSD could continue to use them. Also removed during this audit was all software produced by Daniel J. Bernstein. 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.
Because of licensing concerns, the OpenBSD team has reimplemented software from scratch or adopted suitable existing software. For example, OpenBSD developers created the PF packet filter after unacceptable restrictions were imposed on IPFilter. PF first appeared in OpenBSD 3.0 and is now available in many other operating systems. OpenBSD developers have also replaced GPL-licensed tools (such as CVS, diff, grep and pkg-config) with permissively licensed equivalents.
Although the operating system and its portable components are used in commercial products, De Raadt says that little of the funding for the project comes from the industry: "traditionally all our funding has come from user donations and users buying our CDs (our other products don't really make us much money). Obviously, that has not been a lot of money."
For a two-year period in the early 2000s, the project received funding from DARPA, which "paid the salaries of 5 people to work completely full-time, bought about $30k in hardware, and paid for 3 hackathons", from the POSSE project.
In 2006, the OpenBSD project experienced financial difficulties. The Mozilla Foundation and GoDaddy are among the organizations that helped OpenBSD to survive. However, De Raadt expressed concern about the asymmetry of funding: "I think that contributions should have come first from the vendors, secondly from the corporate users, and thirdly from individual users. But the response has been almost entirely the opposite, with almost a 15-to-1 dollar ratio in favor of the little people. Thanks a lot, little people!"
On 14 January 2014, Bob Beck issued a request for funding to cover electrical costs. If sustainable funding was not found, Beck suggested the OpenBSD project would shut down. The project soon received a US$20,000 donation from Mircea Popescu, the Romanian creator of the MPEx bitcoin stock exchange, paid in bitcoins. The project raised US$150,000 in response to the appeal, enabling it to pay its bills and securing its short-term future. Since 2014, several large contributions to the OpenBSD Foundation have come from corporations such as Microsoft, Facebook, and Google as well as the Core Infrastructure Initiative.
OpenBSD is freely available in various ways: the source can be retrieved by anonymous CVS, and binary releases and development snapshots can be downloaded by FTP, HTTP, and rsync. Prepackaged CD-ROM sets through version 6.0 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, have been one of the project's few sources of income, funding hardware, Internet service, and other expenses. Beginning with version 6.1, CD-ROM sets are no longer released.
In common with other operating systems, OpenBSD provides a package management system for easy installation and management of programs which are not part of the base operating system. Packages are binary files which are extracted, managed and removed using the package tools. On OpenBSD, the source of packages is the ports system, a collection of Makefiles and other infrastructure required to create packages. In OpenBSD, 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, 4.6 are not suitable for use with 4.5 and vice versa.
Songs and artworkEdit
Initially, OpenBSD used a haloed version of the BSD daemon mascot drawn by Erick Green, who was asked by De Raadt to create the logo for the 2.3 and 2.4 versions of OpenBSD. Green planned to create a full daemon, including head and body, but only the head was completed in time for OpenBSD 2.3. The body as well as pitchfork and tail was completed for OpenBSD 2.4.
Subsequent releases used variations such as a police daemon by Ty Semaka, but eventually settled on a pufferfish named Puffy.[n 4] Since then, Puffy has appeared on OpenBSD promotional material and featured in release songs and artwork.
The promotional material of early OpenBSD releases did not have a cohesive theme or design, but later the CD-ROMs, 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. These have become a part of OpenBSD advocacy, with each release expounding a moral or political point important to the project, often through parody.
Themes have included Puff the Barbarian in OpenBSD 3.3, which included an 80s rock song and parody of Conan the Barbarian alluding to open documentation, The Wizard of OS in OpenBSD 3.7, related to the project's work on wireless drivers, and Hackers of the Lost RAID, a parody of Indiana Jones referencing the new RAID tools in OpenBSD 3.8.
- Multiple selections were permitted as a user may use multiple BSD variants side by side.
- Later renamed to Cybercop Scanner after SNI was purchased by Network Associates.
- As of OpenBSD 6.3[update], either Clang 5.0.1, GCC 4.2.1 or GCC 3.3.6 is shipped, depending on the platform.
- Pufferfish do not, in fact, possess spikes; images of Puffy are closer to a similar species, the porcupinefish.
- "Package Management". OpenBSD Frequently Asked Questions. Retrieved 1 June 2016.
- "Platforms". OpenBSD. Retrieved 3 September 2016.
- "Copyright Policy". OpenBSD. Retrieved 13 December 2011.
- "Pledge() - A New Mitigation Mechanism". Retrieved 8 October 2018.
- "Android's C Library Has 173 Files of Unchanged OpenBSD Code". Retrieved 8 October 2018.
- "LLVM Release License". Retrieved 8 October 2018.
- "OpenSSH for Windows". Retrieved 8 October 2018.
- "Security". OpenBSD. Retrieved 13 December 2011.
Secure by Default.
- Lucas, Michael W. (2013). Absolute OpenBSD: Unix for the practical paranoid (2nd ed.). San Francisco: No Starch Press. ISBN 978-1-59327-476-4.
- Grimes, Roger A. (29 December 2006). "New year's resolution No. 1: Get OpenBSD". InfoWorld.
- BSD Usage Survey (PDF) (Report). The BSD Certification Group. 31 October 2005. p. 9. Retrieved 16 September 2012.
- Glass, Adam (23 December 1994). "Theo De Raadt". netbsd-users (Mailing list).
- De Raadt, Theo (18 October 1996). "The OpenBSD 2.0 release". openbsd-announce (Mailing list).
- "Announcing – The OpenBSD Foundation". OpenBSD Journal. 26 July 2007.
- "About Xenocara". Xenocara. Retrieved 13 December 2011.
- Tzanidakis, Manolis (21 April 2006). "Using OpenBSD on the desktop". Linux.com. Retrieved 9 March 2012.
- Lucas, Michael W. (April 2013). Absolute OpenBSD: Unix for the Practical Paranoid (2nd ed.). San Francisco, California: No Starch Press. ISBN 978-1-59327-476-4.
- "OpenPorts.se Statistics". OpenPorts.se. Retrieved 8 February 2018.
- "OpenBSD 6.0". OpenBSD. Retrieved 1 November 2016.
- "The X Windows System". OpenBSD Frequently Asked Questions. Retrieved 22 May 2016.
OpenBSD ships with the cwm(1), fvwm(1) and twm(1) window managers, [...]
- McIntire, Tim (8 August 2006). "Take a closer look at OpenBSD". Developerworks. IBM. Retrieved 13 December 2011.
- "AccessEnforcer Model AE800". Calyptix Security. Retrieved 28 May 2016.
- "High Resistance Firewall genugate". GeNUA. Retrieved 29 May 2016.
- "RTMX O/S IEEE Real Time POSIX Operating Systems". RTMX. Retrieved 13 December 2011.
RTMX O/S is a product extension to OpenBSD Unix-like operating system with emphasis on embedded, dedicated applications.
- ".vantronix secure system". Compumatica secure networks. Archived from the original on 1 January 2012. Retrieved 13 December 2011.
The Next Generation Firewall is not a standalone device, it is a Router for operation in security critical environments with high requirements for availability, comprehensive support as well as reliable and trusted systems powered by OpenBSD.
- Dohnert, Roberto J. (21 January 2004). "Review of Windows Services for UNIX 3.5". OSNews. David Adams.
- Varghese, Sam (8 October 2004). "Staying on the cutting edge". The Age. Retrieved 13 December 2011.
- Laird, Cameron; Staplin, George Peter (17 July 2003). "The Essence of OpenBSD". ONLamp. Retrieved 13 December 2011.
- De Raadt, Theo (19 December 2005). "2.3 release announcement". openbsd-misc (Mailing list).
Without [SNI's] support at the right time, this release probably would not have happened.
- Wayner, Peter (13 July 2000). "18.3 Flames, Fights, and the Birth of OpenBSD". Free For All: How Linux and the Free Software Movement Undercut the High Tech Titans (1st ed.). HarperBusiness. ISBN 978-0-06-662050-3. Archived from the original on 14 January 2012. Retrieved 13 December 2011.
- Miller, Todd C.; De Raadt, Theo (6 June 1999). strlcpy and strlcat - Consistent, Safe, String Copy and Concatenation. USENIX Annual Technical Conference. Monterey, California. Retrieved 13 December 2011.
- "gcc-local – local modifications to gcc". OpenBSD manual pages. Retrieved 1 November 2016.
- De Raadt, Theo; Hallqvist, Niklas; Grabowski, Artur; Keromytis, Angelos D.; Provos, Niels (6 June 1999). Cryptography in OpenBSD: An Overview. USENIX Annual Technical Conference. Monterey, California. Retrieved 27 May 2016.
- Provos, Niels (9 August 2003). "Privilege Separated OpenSSH". Retrieved 13 December 2011.
- "Innovations". OpenBSD. Retrieved 18 May 2016.
Privilege separation: [...] The concept is now used in many OpenBSD programs, for example [...] etc.
- "Project History and Credits". OpenSSH. Retrieved 13 December 2011.
- "SSH usage profiling". OpenSSH. Retrieved 13 December 2011.
- Biancuzzi, Federico (18 March 2004). "An Interview with OpenBSD's Marc Espie". ONLamp. Retrieved 13 December 2011.
- Internet Security Systems. OpenSSH Remote Challenge Vulnerability, June 26, 2002. Visited December 17, 2005.
- A partial list of affected operating systems.
- Core Security Technologies' homepage.
- Core Security Technologies. OpenBSD's IPv6 mbufs remote kernel buffer overflow. March 13, 2007. Visited March 13, 2007.
- Brindle, Joshua (2008-03-30), "Secure doesn't mean anything", Security Blog, retrieved 2011-12-13
- Wheeler, David A. (3 March 2003). "2.4. Is Open Source Good for Security?". Secure Programming for Linux and Unix HOWTO. Retrieved 13 December 2011.
- De Raadt, Theo (14 December 2010). "Allegations regarding OpenBSD IPSEC". openbsd-tech (Mailing list). Retrieved 28 May 2016.
- Holwerda, Thom (14 December 2010). "FBI Added Secret Backdoors to OpenBSD IPSEC". OSNews. Retrieved 13 December 2011.
- Ryan, Paul (23 December 2010). "OpenBSD code audit uncovers bugs, but no evidence of backdoor". Ars Technica. Retrieved 9 January 2011.
- Mathew J. Schwartz (22 December 2010). "OpenBSD Founder Believes FBI Built IPsec Backdoor". InformationWeek: DARKreading. Archived from the original on 11 July 2017.
- "Contents of /stable/10/crypto/openssh/README". svnweb.freebsd.org. Retrieved 19 May 2016.
This is the port of OpenBSD's excellent OpenSSH to Linux and other Unices.
- "src/crypto/external/bsd/openssh/dist/README – view – 1.4". NetBSD CVS Repositories. Retrieved 19 May 2016.
- "dragonfly.git/blob – crypto/openssh/README". gitweb.dragonflybsd.org. Retrieved 19 May 2016.
This is the port of OpenBSD's excellent OpenSSH to Linux and other Unices.
- "Arch Linux – openssh 7.2p2-1 (x86_64)". Arch Linux. Retrieved 17 May 2016.
- "openssh". OpenSUSE. Retrieved 17 May 2016.
- "Debian – Details of package openssh-client in jessie". Debian. Retrieved 17 May 2016.
- de Raadt, Theo (18 June 2013). "An Internet Exchange for Calgary" (PDF). Retrieved 9 October 2018.
- "clang-local – OpenBSD-specific behavior of LLVM/clang". OpenBSD manual pages. Retrieved 2 February 2018.
- "httpd – HTTP daemon". OpenBSD manual pages. Retrieved 1 November 2016.
- "OpenBSD ports ∴ www/apache-httpd,-main". ports.su. Retrieved 13 May 2018.
- "OpenBSD ports ∴ www/nginx". ports.su. Retrieved 13 May 2018.
- Andrews, Jeremy (2 May 2006). "Interview: Theo de Raadt". KernelTrap. Archived from the original on 24 April 2013.
- "OpenBSD's flavors". OpenBSD Frequently Asked Questions. Retrieved 22 May 2016.
- "Applying patches in OpenBSD". OpenBSD Frequently Asked Questions. Retrieved 15 May 2016.
- "Migrating to OpenBSD". OpenBSD Frequently Asked Questions. Retrieved 4 January 2017.
- "Hackathons". OpenBSD. Retrieved 18 May 2016.
- "Interview: Theo de Raadt of OpenBSD". NewsForge. 28 March 2006. Retrieved 31 March 2016.
- "Release Songs". OpenBSD. Retrieved 22 May 2016.
- Beck, Bob (25 February 2014). "Google Summer of Code 2014". openbsd-misc (Mailing list). Retrieved 4 March 2014.
- "GSOC 2014 with the OpenBSD Foundation". Google Summer of Code 2014. Retrieved 4 March 2014.
- Chisnall, David (20 January 2006). "BSD: The Other Free UNIX Family". InformIT. Archived from the original on 14 March 2014.
- Smith, Jesse (18 November 2013). "OpenBSD 5.4: Puffy on the Desktop". Archived from the original on 30 April 2014.
- Cranor, Chuck D.; De Raadt, Theo (6 June 1999). Opening the Source Repository with Anonymous CVS. USENIX Annual Technical Conference. Monterey, California. Retrieved 13 December 2011.
- Cranor, Chuck D. "Chuck Cranor's Home Page". Retrieved 13 December 2011.
I also hosted and helped create the first Anonymous CVS server on the Internet (the original anoncvs
.openbsd .org [...]
- "Project Goals". OpenBSD. Retrieved 18 May 2016.
Integrate good code from any source with acceptable licenses. [...], NDAs are never acceptable.
- De Raadt, Theo; Hallqvist, Niklas; Grabowski, Artur; Keromytis, Angelos D.; Provos, Niels (6 June 1999). "Randomness Used Inside the Kernel". Cryptography in OpenBSD: An Overview. USENIX Annual Technical Conference. Monterey, California. Retrieved 1 February 2014.
- De Raadt, Theo (5 December 2006). "Presentation at OpenCON". OpenBSD. Retrieved 13 December 2011.
- Matzan, Jem (15 June 2005). "BSD cognoscenti on Linux". NewsForge. Linux.com. Retrieved 28 May 2016.
- Gasperson, Tina (6 June 2001). "OpenBSD and ipfilter still fighting over license disagreement". Linux.com. Archived from the original on 26 June 2008.
- "src/usr.sbin/mrinfo/mrinfo.c – view – 1.7". cvsweb.openbsd.org. 31 July 2001. Retrieved 24 May 2016.
New license from Xerox! This code is now FREE! Took a while and a lot of mails, but it is worth it.
- "src/usr.sbin/map-mbone/mapper.c – view – 1.5". cvsweb.openbsd.org. 31 July 2001. Retrieved 24 May 2016.
New license from Xerox! This code is now FREE! Took a while and a lot of mails, but it is worth it.
- De Raadt, Theo (24 August 2001). "Re: Why were all DJB's ports removed? No more qmail?". openbsd-misc (Mailing list). Archived from the original on 19 April 2016.
- Bernstein, Daniel J. (27 August 2001). "Re: Why were all DJB's ports removed? No more qmail?". openbsd-misc (Mailing list). Archived from the original on 4 February 2012.
- Espie, Marc (28 August 2001). "Re: Why were all DJB's ports removed? No more qmail?". openbsd-misc (Mailing list). Archived from the original on 19 April 2016.
- Hartmeier, Daniel (10 June 2002). Design and Performance of the OpenBSD Stateful Packet Filter (pf). USENIX Annual Technical Conference. Monterey, California. Retrieved 13 December 2011.
- The OpenBSD PF Packet Filter Book: PF for NetBSD, FreeBSD, DragonFly and OpenBSD. Reed Media Services. ISBN 0-9790342-0-5. Retrieved 19 May 2016.
- "New BSD licensed CVS replacement for OpenBSD". Retrieved 9 October 2018.
- "pkg-config(1)". Retrieved 9 October 2018.
- "OpenBSD Project in Financial Danger". Slashdot. 21 March 2006. Retrieved 12 December 2014.
- "Mozilla Foundation Donates $10K to OpenSSH". Slashdot. 4 April 2006. Retrieved 12 December 2014.
- "GoDaddy.com Donates $10K to Open Source Development Project". The Hosting News. 19 April 2006. Archived from the original on 11 November 2006.
- Beck, Bob (14 January 2014). "Request for Funding our Electricity". openbsd-misc (Mailing list). Retrieved 17 May 2016.
- Bright, Peter (20 January 2014). "OpenBSD rescued from unpowered oblivion by $20K bitcoin donation". Ars Technica. Retrieved 20 January 2014.
- "The OpenBSD Foundation 2014 Fundraising Campaign". OpenBSD Foundation. Retrieved 24 May 2014.
- McAllister, Neil (8 July 2015). "Microsoft rains cash on OpenBSD Foundation, becomes top 2015 donor". The Register. Retrieved 27 May 2016.
- "Contributors". OpenBSD Foundation. Retrieved 27 May 2016.
- "OpenBSD Donors".
- "Smartisan Makes Another Iridium Donation to the OpenBSD Foundation". Undeadly.
- "Anonymous CVS". OpenBSD. Retrieved 13 December 2011.
- "Mirrors". OpenBSD. Retrieved 22 May 2016.
- "Orders". OpenBSD. Retrieved 20 May 2016.
- "Packages and Ports". OpenBSD Frequently Asked Questions. Retrieved 22 May 2016.
- "OpenBSD". mckusick.com. Retrieved 12 December 2014.
- De Raadt, Theo (19 May 1999). "OpenBSD 2.5 Release Announcement". openbsd-announce (Mailing list). Archived from the original on 14 March 2014.
OpenBSD 2.5 introduces the new Cop daemon image done by cartoonist Ty Semeka.
- "OpenBSD 2.7". OpenBSD. Retrieved 22 May 2016.
- Matzan, Jem (1 December 2006). "OpenBSD 4.0 review". Software in Review. Retrieved 13 December 2011.
Each OpenBSD release has a graphical theme and a song that goes with it. The theme reflects a major concern that the OpenBSD programmers are addressing or bringing to light.