2023-07-26
There's more than one reason that people used (or use) CentOS
The news of the time interval is that Red Hat has stopped making Red Hat Enterprise Linux source code generally available, although just as with the switch to 'CentOS Stream' from CentOS their article doesn't put it that way. This created difficulties for at least two CentOS replacement distributions, forcing AlmaLinux to change what they are. I don't have much to say on this specific topic, but it has sparked a series of exchanges about, for example, the history of RHEL rebuilds (via). As it happens, I have some views on why people would want to use a free 'clone' (rebuild) of RHEL, as CentOS was before it became CentOS Stream, partly based on personal experience.
Here are some major reasons people could want or need CentOS, at least back in the era of CentOS, before CentOS Stream became your only option from RHEL 8 onward:
- They want significantly more than the (maximum) five years of free
security updates and maybe bugfixes you can get elsewhere. I have
negative views on old zombie distribution version, but for a fixed function machine that
sits quietly in a corner, this is tempting; we have some of them
ourselves (our console server
and our central syslog server).
(We used to have more such machines.)
- They need something that is fully compatible with a Linux that
some commercial vendor's software works on, and the best option
the vendor has is Red Hat Enterprise Linux (for as long as that
lasts).
Possibly they want something that is essentially guaranteed to
properly run any software that runs on RHEL, so they don't
have to worry about how specific software behaves.
- They need something that is actively supported by a vendor for
some piece of commercial software, and the vendor will only qualify
and support exact duplicates of RHEL.
We used to run a piece of commercial software for which the best options listed and supported by the vendor were 'RHEL/CentOS 7'.
- They want a free Red Hat Enterprise Linux.
(CentOS Stream is suitable for a different group of people, also.)
The first reason doesn't need either 1:1 equivalence or ABI compatibility. All our syslog server and console server need is security updates.
The second reason needs at least ABI compatibility, but hopefully not 1:1 equivalence unless the software you're trying to run is extremely picky. The less guarantees of ABI compatibility you have, the riskier it is to use anything other than RHEL.
The third reason needs whatever the commercial vendor will support, but typically the vendor is trying to minimize its costs and doesn't want to test and qualify something that would be 'another Linux distribution'. The vendor might accept ABI compatibility as good enough, or it might decide that only 1:1 equivalence was low enough risk to let it provide official support.
One might argue that people should be willing to pay for RHEL (or another Linux distribution with long term security updates) in some or all of these situations. I'm in a somewhat unusual situation, but in general 'free' means that you don't need to get approval for things. If it costs your organization something every time someone adds a new Linux server or virtual machine running <distribution>, possibly even if it's a temporary one, then there is far more friction than if such a machine is free (for whatever reason, including a site license).
To mildly react to a bit of Ben Cotton's Ended, the clone wars have?, my view is that people who want the middle two reasons would still want a 'CentOS' even in a world where RHEL development started off in the new CentOS Stream model. It's possible that the new model CentOS Stream would provide sufficient ABI compatibility and so on for vendor software to work on it and even for vendors to support it, but Red Hat doesn't seem to have promised that and I'm dubious about it (even apart from the as far as I know open question of CentOS Stream security updates).
(And to the extent that some updates to CentOS Stream would be rolled back or superseded before they appeared in RHEL, I think there definitely would be people interested in 'CentOS Stream updates but only once they've appeared in RHEL'.)