Red Hat has released CentOS Stream 9, the first major version since the company badly shook its community by announcing it was ending traditional CentOS a year ago.
This is the second release of the new CentOS Stream distro, and presumably the IBM subsidiary hopes it will offer a more appealing migration path for CentOS users than for them to jump ship.
Notably, in CentOS Stream 8, RH's Application Streams – analogous to Fedora's "Modularity" – were mandatory, but they're optional in 9.
This is a big deal in the Red Hat world, but can be mysterious to the millions of non-Red Hat Linux users. Since it seems to please Red Hat to imagine that Red Hat is the entirety of the Linux world, its official materials don't really give you any context, so The Register will try to translate for you.
Executive historical summary
The original Red Hat Linux (RHL) was released in May 1995, making it one of the oldest distros, but the company killed it off after version 9 in 2003. RHL was replaced with Red Hat Enterprise Linux (RHEL), which became the company's only supported distro. The word supported is key here.
The pre-existing Fedora project, formerly a third-party repo for RHL add-ons, got promoted to being the free, unsupported, community distro: no paid support, updates for 13 months, a new version roughly twice a year, and upgrades from one version to the next could be tricky, although that's much better now.
Fedora tends to be pretty bleeding-edge compared to most regular-release-cycle distros – that's why the codeword "innovative" features heavily in the project's mission statement. The Reg has liked Fedora for a long time. The new shiny that works in Fedora, when it ends up boring and stable, goes into RHEL. As RH puts it, Fedora is "upstream" of RHEL.
RHEL, on the other hand, was and is commercial: you can only get RHEL by buying it, which in reality means buying a support contract. But it's still FOSS, meaning that RH is legally required to make the source code available. So anyone – not just customers – could download Red Hat's source code packages for each and every package in RHEL, free of charge, and recompile them all to build a free clone of RHEL.
Various third parties started doing this and producing independent distros which were RHEL-compatible, such as Scientific Linux (from FermiLab) and White Box Linux (from the Beauregard Public Library in Louisiana). The biggest of these, CentOS (Community Enterprise OS), started in 2004.
The idea of these distros is that they are basically identical to RHEL, but with the names changed. Not just the same commands, but the same versions of the same binaries, with the same config files, in the same directories, for perfect compatibility. Whatever fixes RHEL got, soon afterwards the rebuilds got too. You could learn using a freebie prototype and test on it, but deploy on the real thing. Theoretically, if you didn't want to pay for lots of RHEL licences, you could pay for one copy, get official support for it, but run all your other boxes on CentOS, and save a packet. You only get official support for one copy, but all the same methods and tools work on all of them.
Oh, and in 2006 that well-known friend of FOSS, Oracle, got into the game by making another such rebuild. This is often known by the name of its (paid, optional, and significantly cheaper than the official Red Hat Network) support service: Oracle Unbreakable Linux.
This was all fine, clear, and easy to understand. Sometimes, RH tried to make life difficult for the cloners, but they survived. Despite them, RHEL has been a huge success – by 2011 RH was the first billion-dollar Linux vendor.
The beginning of the end
Then in 2014 RH did something very strange: it brought CentOS in-house. So now the leading freebie was kinda-sorta officially sanctioned. Unsupported, but given the nod. Please pay for RHEL for your production boxes, but if you'd rather not, you could run CentOS Linux for nothing.
This was, obviously, very good for CentOS – but very bad for the other rebuilds, and as a result, most of them (except Oracle) shut down.
This left RH with an odd range of distro offerings. Before 2014, the positioning was clear: freeloaders got Fedora, and needed to upgrade regularly. If you wanted support, you paid for RHEL. After 2014: if you want stability and support, please buy RHEL; if you don't want to pay, well, there's our fast-moving, free community distro… or, you could have this nice stable distro that's identical to RHEL, and it's free, you just get no support. Effectively, the company offered a free product specifically designed to compete with its own commercial flagship.
Compare this to SUSE's easier-to-understand proposition: you can download a complete, fully functional evaluation version of any of its products, but you only get a 60-day trial period. After that, no more updates.
Or run the free openSUSE Leap, which has the same release cycle as SUSE Linux Enterprise. If you want support, for a price you can migrate from Leap direct to SUSE Linux Enterprise.
It took RH about five years, but eventually it appeared to realise this. In the company's terms, CentOS Linux was "downstream" of RHEL; although the word "community" is prominent on the CentOS site, there wasn't any way to contribute to it: it was a straightforward rebuild of RHEL.
The first visible result was a new direction for CentOS, with CentOS Linux 9 being cancelled and CentOS Linux itself being replaced by CentOS Stream in 2019.
Rather than duplicating RHEL's release cycle, the new Stream edition gets a continuous stream of updates. Critically, this means it's no longer a one-to-one exact duplicate of RHEL; from the sales point of view, it's no longer competing directly with its parent product.
For the company, this is all good. Presumably, it didn't tempt many CentOS Linux users to cross the Stream, because just five months later, the company announced that the end of life for CentOS Linux 8 was dropping from 2029 to 2021 – 36 months sooner than the version 7.
As is its wont, RH prefers to phrase this in terms of upstreams, downstreams, and communities. Before, RHEL was downstream of Fedora, and CentOS Linux was downstream of RHEL. Now, CentOS Stream is downstream of Fedora, and RHEL is downstream of CentOS Stream.
The company's Rich Bowen told us: "From my perspective as a community manager, CentOS Linux was not open source, was not a collaborative project, and was not really a community in any meaningful way. CentOS Stream gives us the opportunity to make CentOS into an actual community project, with an actual contributor/collaborator path".
Which is laudable and entirely understandable. In principle, migrating from CentOS Linux 8 to CentOS Stream 8 is as simple as two commands:
dnf swap centos-linux-repos centos-stream-repos
dnf distro-sync
