The announcement—which clearly stated "CentOS Stream is not a replacement for CentOS Linux"—left thousands of CentOS users stunned and bewildered. In many cases, CentOS users had migrated to CentOS 8—which they expected to receive support until 2029—only to find out that their "until-2029" distro had become an "until-2021" distro just a few months after they'd installed it in the first place.
I can't pretend this is good news for CentOS users, but I can offer some good news: CentOS might be dead, but it's far from your only option for a "rebuild" distro that's binary-compatible with RHEL. Let's take a look at a few of the most likely options below.
I know, I know—put the pitchforks down! Many now-former CentOS users are much too mad at Red Hat to consider migrating to CentOS Linux's "not-replacement," CentOS Stream. But despite Red Hat CTO Jim Wright's bald-faced declaration that Stream is not a replacement for CentOS Linux... for an awful lot of users, it very easily could be.
Before this week, the relationship between CentOS Linux and Red Hat Enterprise Linux was, effectively, "it's the same thing, but without the branding and the support." In a lot of ways, that relationship will continue to be true. CentOS Stream and Red Hat Enterprise Linux will still track very closely to one another. The new relationship works like this:
* RHEL version x.0 forks from Fedora
* CentOS Stream version x forks from RHEL version x.0
* Development work for RHEL x.1 is done in CentOS Stream version x repos
* RHEL x.1 forks from CentOS Stream version x
* RHEL version y.0 forks from Fedora
* CentOS Stream version y forks from RHEL y.0
* Development work for RHEL x.2 is done in CentOS Stream version x repos
* Development work for RHEL y.1 is done in CentOS Stream version y repos
* RHEL x.2 forks from CentOS Stream x
* RHEL y.1 forks from CentOS Stream y
And so forth. So, while CentOS Stream is something of a rolling release, it's a limited one—it rolls from one minor version to the next, but its major version is stable and tracks Fedora's. A CentOS Stream 8 user won't be forced to dogfood RHEL 9 code any earlier than a CentOS Linux 8 user would have.
What's lost here is the ability to control when you perform a minor version upgrade on your system. A user on RHEL 8.x can decide when they're ready to upgrade to RHEL 8.y, whereas a CentOS Stream 8 user will seamlessly and automatically flow through the states that are frozen to become RHEL minor releases.
If you're the type who would pull the trigger on a CentOS minor release on the day it launches, this is a no-brainer—just migrate to Stream and be done with it. It will effectively be the same experience you're used to, with less work. You won't need to do the minor-release upgrades at all any more, they just happen automatically.
If you need minor-release control as well as major—or you're just too mad at Red Hat to want to continue using a product under their direct control and are determined to move downstream—read on. I've got more options for you. Some of them are even good!
Yes, Oracle. Here we go with the pitchforks again, right? Well, Oracle Linux is 100 percent application binary compatible with Red Hat Enterprise Linux. It's a "rebuild distro" based on RHEL's sources and not much else, just like CentOS Linux was.
If all you need or want is a free-as-in-beer distro that tracks RHEL precisely, Oracle Linux might be your new home. The distro has been around for a while, and it's got the backing of one of the world's biggest IT companies. Then again, moving to Oracle because you found Red Hat's governance arbitrary and oppressive is a pretty odd flex.
Oracle Linux as a replacement for CentOS probably makes the most sense for shops which already have a large Oracle presence.
CloudLinux OS is a RHEL rebuild distro designed for shared hosting providers. CloudLinux OS itself probably isn't the free replacement for CentOS anyone is looking for—it's more akin to RHEL itself, with subscription fees necessary for production use.
However, the CloudLinux OS maintainers have announced that they'll be releasing a 1:1 replacement for CentOS in Q1 2021. The new fork will be a "separate, totally free OS that is fully compatible with RHEL 8 and future versions."
There are a few upsides to this upcoming fork. CloudLinux OS has been around for a while, and it has a pretty solid reputation. The new fork they're announcing won't be a big challenge for Cloud—they're already forking RHEL regularly and tracking changes to maintain the full CloudLinux OS. All they really need to do is make certain they separate out their own branding and additional, license-only premium features.
This should also be a very easy upgrade for CentOS 8 users—there's already a very easy one-script migration path from CentOS to the full CloudLinux OS. Converting from CentOS to "the new fork" should be just as simple, and without the registration step necessary for the full Cloud Linux.
I've seen a lot of folks mistakenly recommending the deceased Scientific Linux distro as a CentOS replacement—that won't work, because Scientific Linux itself was deprecated in favor of CentOS. However, Springdale Linux is very similar—like Scientific Linux, it's a RHEL rebuild distro made by and for the academic scientific community. Unlike Scientific Linux, it's still actively maintained!
Springdale Linux is maintained and made available by Princeton and Rutgers universities, who use it for their HPC projects. It's been around for quite a long time. One Springdale Linux user from Carnegie Mellon describes their own experience with Springdale (formerly PUIAS—Princeton University Institute for Advanced Study) as a 10 year ride.
Theresa Arzadon-Labajo, one of Springdale Linux's maintainers, gave a pretty good seat-of-the-pants overview in a recent mailing list discussion:
"The School of Mathematics at the Institute for Advanced Study has been using Springdale (formerly PUIAS, then PU_IAS) since its inception. All of our *nix servers and workstations (yes, workstations) are running Springdale. On the server side, everything "just works", as is expected from a RHEL clone. On the workstation side, most of the issues we run into have to do with NVIDIA drivers, and glibc compatibility issues (e.g Chrome, Dropbox, Skype, etc), but most issues have been resolved or have a workaround in place.
... Springdale is a community project, and [it] mostly comes down to the hours (mostly Josko) that we can volunteer to the project. The way people utilize Springdale varies. Some are like us and use the whole thing. Others use a different OS and use Springdale just for its computational repositories."
Springdale Linux should be a natural fit for universities and scientists looking for a CentOS replacement. It will likely work for most anyone who needs it—but its relatively small community and firm roots in academia will probably make it the most comfortable for those with similar needs and environments.
I need to be very clear, here: for the moment, Rocky Linux is a concept, not an actual distribution. CentOS co-founder Greg Kurtzer reacted almost immediately to Red Hat's discontinuation of CentOS Linux by announcing his intention to effectively recreate it under a different name:
"I was just as shocked as the rest of the community with the news from Red Hat. When I started CentOS 16 years ago, I never imagined the incredible reach and impact it would have around the world on individuals and companies who rely on CentOS for Linux distribution.
In response to this unexpected shift, I am proud to announce the launch of a new project, Rocky Linux, in honor of my late CentOS co-founder Rocky McGough. I’ve started calling on participation from the global community and quickly assembling a team to further our founding commitment of ensuring seamless continuity of business operations for companies running CentOS 8 far beyond 2021. In just one day, we’ve seen an overwhelming response from thousands of supporters eager to join the project."
When we first reported on Rocky Linux yesterday, the project's Github repo only consisted of two commits—the initial commit, and a very barebones README.md. Today, there's still only a README.md there, but it's considerably more fleshed out. Now you can find links to discussion communities, infrastructure email addresses for the new project, and major supporters.
There is no real timeline for Rocky Linux to become a real distro yet, but I broadly expect it to happen sometime in 2021. The more interesting question is how much mindshare it accretes along the way. On the one hand, Kurtzer's is a big name and adds gravitas... but on the other, Rocky Linux will be a brand new distribution in and of itself, competing with other RHEL rebuilds with more direct history.
The last of the RHEL downstreams up for discussion today is Hewlett Packard Enterprise's in-house distro, ClearOS. Hewlett Packard makes ClearOS available as a preinstalled option on its ProLiant server line, and the company offers a free Community version to all comers.
"ClearOS is an open source software platform that leverages the open source model to deliver a simplified, low cost hybrid IT experience for SMBs. The value of ClearOS is the integration of free open source technologies making it easier to use. By not charging for open source, ClearOS focuses on the value SMBs gain from the integration so SMBs only pay for the products and services they need and value."
ClearOS is mostly notable here for its association with industry giant HPE and its availability as an OEM distro on ProLiant servers. It seems to be a bit behind the times—the most recent version is ClearOS 7.x, which is in turn based on RHEL 7. In addition to being a bit outdated compared with other options, it also appears to be a rolling release itself—more comparable to CentOS Stream itself, than to the CentOS Linux which came before it.
ClearOS is probably most interesting to small business types who might consider buying ProLiant servers with RHEL-compatible OEM linux pre-installed later.