OpenBSD-current is the most recent development version of OpenBSD, containing code that is making its public debut. Developers test each other’s work and then get approval to commit code to the tree. Eventually, they must put their work out for the public to test, review, and debug.

OpenBSD-current is where the public can access the newest code. If a change would temporarily break web servers, games, database servers, or whatever is running on -current, but the change is for the long-term good, the change will go into -current. Those programs will probably work again before the next OpenBSD release, but there’s no requirement that every third-party program work perfectly at all times on -current.

With these caveats, why would you possibly want to run -current? One excellent reason is to test the new OpenBSD in your environment. If today’s -current panics under certain conditions, but last week’s didn’t, the OpenBSD folks want to know that.

(All the OpenBSD folks run -current on their laptops, and they run firewalls on -current.) If you can exercise -current in the real world, with a real workload, they want you to do so. Having real users run -current is the only way that OpenBSD can be tested before the official releases come out.

Every few days, the OpenBSD team uploads a release from the latest -current code to the mirror servers. This is an interim release called a snapshot, which is identified only by the date of its release. A snapshot is simply the state of -current at a particular time. While the developers try not to build a snapshot on a day that -current is notably fouled up, guess who’s in charge of the snapshot quality-assurance process. That’s you.

Snapshots are provided for installation and testing convenience. Installing and testing a snapshot is easier than building -current on your own. Also, if you can reproduce a bug on a specific snapshot, the developers know exactly which version of the code you are running. It’s much easier to identify a problem as appeared “in the July 15 2013 snapshot” than in a -current you built yourself from “code downloaded from server X at about 3:17 PM EST on July 15, 2013.”

You can get snapshots installation media from any mirror site, in the /pub/OpenBSD/snapshots directory. If you want to run -current, the recommended way to start is by installing the most recent snapshot you can get your hands on and upgrading from there.

Every six months, the pace of OpenBSD development is deliberately slowed. Developers spend time polishing new features, and Theo makes increasingly forceful requests for beta testers of the newest snapshots. When the OpenBSD team is satisfied that the software is of adequate quality, the source code tree is tagged, and a high-quality snapshot is built. This snapshot is called a release and is issued a number like 5.2, 5.3, and so on. This is almost certainly what you installed on your first OpenBSD machine. A new release appears every May and November.

OpenBSD numbers releases sequentially, starting with 2.0 and incrementing .1 with every release. Unlike most software products, a .0 release has no special meaning. It’s just another spot along a long path—a milestone hit every five years.

The release is the best-supported version of OpenBSD. Everything is expected to work, and the development team stands behind its releases. If a serious security problem is discovered in a release, OpenBSD will release a patch, or errata, for it.

OpenBSD-stable is an OpenBSD release with all errata and very minor patches included. The developers deliberately hold the number of changes to each -stable version to the absolute bare minimum. A stable version is referred to as its base release plus -stable, such as 5.4-stable, 5.5-stable, and so on.

What sort of changes are merged back into -stable? Security fixes and errata go in automatically. Other than security issues, any patches added to -stable must be simple, short, and obviously correct. Patches that dramatically affect a small number of users might go in. For example, if all systems with a specific network card panic at random intervals, a patch might go into -stable (accompanied by various developers asking why no one with that network card ran snapshots before the release).

You won’t get new functions in -stable. It won’t come with any new device drivers or packet-filtering features. The API will not change. In general, -stable is expected to never get worse.

The only way to get OpenBSD-stable is to update the system from source.

OpenBSD’s release system combines the best features of open source development and commercial releases. Users have access to both the bleeding-edge experimental code and the stable, polished releases. Look at your requirements and choose your poison.

Remember the limitations of your chosen branch. A release is a good place to start, but you can gradually upgrade your system to -stable, and then to -current, as your understanding expands. Many developers started out as interested hobbyists.