The BSD family of operating systems

At OSHUG #46 I was given the opportunity to present the BSD’s to a group of open source hardware enthusiast & speak about why this family of operating systems would benefit the person running a flavour on their hardware. There was a recording made of the talk but it may be some time before it is made available online, so I thought I’d take the time to write something up to share in the meantime.

My slides.

BSD
This line of operating systems started out life as a series of patches to AT&T UNIX which was introduced to the University of Berkeley by Ken Thompson whilst on sabbatical in 1977.
From the 1BSD TAPE file included in the CSRG archive CD set

Berkeley UNIX Software Tape
Jan 16, 1978 TP 800BPI

The first release came with things such as the ex editor, ashell and Pascal compiler as an add-on for UNIX v7, running on a PDP-11. Over the life time of the CSRG they produced releases which included vi, csh, the IPv4 TCP/IP network stack, the virtual memory subsystem (the kernel being named vmunix, parodied by Linux as vmlinuz) and UFS.
The distribution tapes were only available to AT&T licensees; over time the code base of the distribution grew increasingly independent from AT&T UNIX. At the same time the cost of the AT&T license continued to increase as well. Starting out at a cost of $10000 and reaching north of $250000 in the late 80’s. According to Kirk McKusick there was pressure to release the independently developed components of the CSRG so the community could benefit from the use of things such as the network stack without purchasing a costly license. This resulted in several release, comprised mostly of the code developed outside of AT&T such as 4.3BSD-Net/1, Net/2, 4.4BSD-Lite & Lite2. “Mostly” in that with the release of Net/2 AT&T file a lawsuit against the University of California for alleged code copying and theft of trade secrets.
During its lifetime, BSD saw itself being run on several CPU architectures from the DEC PDP-11, VAX to the MIPS, HP 9000 and Motorola 68000 to name a few. These ports along with the  Power 6/32 helped to improve the portability of the code base. The code base was deemed to be 90% platform independent, the remaining 10% being mostly related to the VM subsystem which was platform specific. As with AT&T UNIX, portability & migration between different systems was part of the nature of the code base, from the beginning.

The 4.3BSD-Net/2 code base was used as the basis for a port to the Intel 386, resulting in 386BSD (free) & BSD386 (commercial) releases.

The Modern BSD variants
At the time of writing there are many BSD variants in existence, each with its own area of focus. Everything still leads back to 2 major variants.

NetBSD
NetBSD was the first of the modern variants that is still actively developed. It started out life as a fork of 386BSD. The focus of NetBSD is portability which not only makes porting to new hardware easier (currently supporting over 60 different ports across may CPU architectures).
Everything from a VAX, ARM & MIPS Windows CE based PDAs to a Sega Dreamcast and many other systems are supported and able to run the latest version of NetBSD. There’s even a toaster which run NetBSD
The focus on portability also makes reusing components on other operating systems easy. For example the packaging system (forked from FreeBSD (which we’ll talk about next)) supports over 20 operating systems.
This enables a consistent toolset to be used regardless of operating system.

Some of the highlights of NetBSD include ATF, unprivileged builds and portable build infrastructure using build.sh.

ATF, as the name suggests is used for automated tests of the source code to discover regression in the code base in an automated manner. Results can be found on the NetBSD release engineering page.

Unprivileged builds allow a user to not only build a copy of the operating systems without elevated privileged, but they can also build and install software from pkgsrc in a location they have write access to (by default, in a prefix under their home directory).

build.sh, the build framework, allows NetBSD to be built on any modern POSIX compliant operating system. Freeing the person to use a operating system of their choice to build releases.

FreeBSD
04/05/2016- Note Ollivier’s comment, I made a mistake when I was gathering info and looked at the source for head and checked the history for the COPYRIGHT file there, not noticing the repository started with v2.0.

Forked from the 4.4BSD Lite code base, 6 months after NetBSD was started. The focus of FreeBSD was performance on i386 systems. Over time support was added for the DEC Alpha as this meant porting the code base to a 64bit systems and addressing any bugs which would prevent the code base from running on a 64bit system. Many years later the project branched out and introduced support for additional platforms. Today the project boasts support for CPUs such as ARMv8, RISC-V and BERI.

OpenBSD
Forked from NetBSD, the focus of OpenBSD is security. The project is home to many components which see wider use outside of OpenBSD, such as OpenSSH, PF (firewall), LibreSSL and others.

DragonFlyBSD
Forked from FreeBSD, the focus of DragonFly BSD is scalability & performance. Taking the operating system in a new direction with regards to how SMP is implemented and from there, developing a new files system called HAMMER.

Documentation
No matter the flavour, documentation is a key part of the development process for the BSD’s.
Whether it is the Design & Implementation series which started with covering 4.3BSD in 1989 and more recently FreeBSD 10 in the fourth instalment of the series, or each projects own set of documentation. Documentation is important as it distinguishes intent & implementation as well as save a lot of question and answers emails.
FreeBSD has handbooks, NetBSD has guides, OpenBSD has FAQs and all projects make their man pages available online as web pages. There is even  a teaching course based around the  The Design and Implementation of the FreeBSD Operating System, 2nd edition.

Frameworks for building embedded images
Each operating system release is a complete, self contained bundle, containing the documentation and necessary toolchain required for building a copy of the operating system from source. release(7) on FreeBSD & NetBSD, release(8) on OpenBSD, nerelease(7) on DragonFlyBSD

For the purpose of embedding the operating system it may not be desirable to build a full blown release. Depending on the choice of variant, either the functionality is built in as standard or a project exists to assist with generating customised images with ease.

FreeBSD had PicoBSD which is now superseded by NanoBSD.
OpenBSD has flashrd and resflash.
NetBSD has a target for generating an image in build.sh, customisations controlled by variables set in mk.conf.
DragonFlyBSD has nrelase.

RetroBSD / LiteBSD
RetroBSD is a port of 2.11BSD (originally targeted for the PDP-11) to the MIPS M4K core found on the PIC32 micro-controllers. LiteBSD is a port of 4.4BSD to the PIC32MZ micro-controllers with a MIPS32 core. Due to the limited resources available, RetroBSD does not offer a network stack, Of the 128KB of RAM, 96KB are available for user space applications. A compiler, editor & various utilities come bundled with the OS so software could be developed on the PIC itself. Variants of common software titles are available to extend the system, such as an Emacs like editor.
LiteBSD is based on a more recent version of BSD, taking advantage of the availability of more RAM (512KB) and MMU on the targeted micro controller. It features a network stack.

Projects such as these take advantage of prior effort and offer the user a consistent environment from the microcontroller to desktop to server. With the extensive documentation and availability of source history, it is possible to realise at which stage in the evolution of the code base the currently running system is and if a desired feature is implemented.

Conclusion
The development of BSD is closely tied with that of the internet. BSD’s modern variants are some of the oldest communities who have collaborated over the internet to develop a software project. The workflow of the projects has transpired to become the standard way of developing open source software on the internet, whether it’s adhering to a style guide or developing with a publicly accessible source repository or holding a hackathon.

For a newcomer interested in an operating system to run on your hardware, it is a great opportunity to be a part of a tech savvy community working to evolve an idea started almost 40 years ago.

As a business, each project produces a mature and robust operating system that has seen many applications from running on devices such as game consoles, mobile phones, cars, satellites and the international space station. Nearly all projects are backed by a non-profit foundation which can act as a liaison for businesses and assist with enquiries regarding development.

3 thoughts on “The BSD family of operating systems

  1. Venture37 Post author

    Hello Jason,
    It has been a while! 🙂
    You’re not the first to mention this, it was highlighted during Q&A that I skipped the whole history of Bill Joy & Sun.
    The talk was meant to be about the appeal of a particular group of operating systems to use on a hardware project, so I skipped most of the historical background.

  2. Ollivier Robert

    Hello, slight correction: FreeBSD did start a few months after NetBSD but was based like it on Net/2 & 386BSD, not yet 4.4BSD-lite. That happened only after the [in]famous lawsuit between USL & BSDi then CSRG from Berkeley as well. After the settlement, the FreeBSD1 codebase was abandonned and 4.4BSD-lite was the basis of FreeBSD 2.0.

    Cheers,
    Ollivier aka @keltounet.

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