Red Hat's source code for RHEL (Red Hat Enterprise Linux) was previously publicly accessible, even if you were not a customer. Now only customers may get access to the source code (which is allowed by the GPL since source code only has to be delivered to those who have received binaries generated from it). But there are Linux distributions who use Red Hat's publicly available sources to create RHEL "clones" (in quotation marks because they obviously don't pretend to be RHEL), except without providing the corporate support one would receive for being a RHEL customer. They do have community forums though.

The superficial issue is that those "clone"-distros would have to either purchase a RHEL license or apply to one of Red Hat's other programs to access the sources for their own distro. The actual issue is that Red Hat's terms for being a customer are that they'll kick you out if you use that code to redistribute your own versions of it (or, god forbid, even create a full distro from it).

Since CentOS proper was killed off years ago, many people who wanted a Red Hat compatible server distro but didn't want or need commercial support shifted their systems to the aforementioned other "clone"-distros, which are now in danger of disappearing because of that change.

Is Red Hat legally able to do it? Yes. Is it a dick move? Absolutely. Will it help spread the popularity of RHEL or other Red Hat distros? Absolutely not.

RedHat creates a product called RHEL (Red Hat Enterprise Linux) that is a paid support product, mostly targeted at businesses (and things like Academia/Laboratories/etc).

At one point, there was a Wholly seperate product, created outside the RedHat umbrella, called CentOS, that quite literally took the sources of RHEL, removed the RHEL branding, and rebuilt it, allowing folks to "mostly" be able to use RHEL, without paying RedHat for a support contract.

In 2014, the CentOS Project/Product was "purchased" by RedHat, and then in 2020, RedHat decided that CentOS would no longer just be a "rebuilt" RHEL, but instead would become the development space for RHEL, called CentOS Stream. This made many people very unhappy, and they decided to start the Rocky Linux and AlmaLinux projects to provide roughly the same product that prior versions of CentOS had provided.

Additionally (I don't actually know exactly when), at some point, Oracle started doing basically the same thing that CentOS had been doing, and rebuilding the RHEL sources, and selling it, as "Oracle Linux"

So net effect of what this means, is that RHEL sources will no longer be publicly available at git.centos.org, and will only be available to RedHat customers (i.e. you must have signed up for an account/license with RedHat for RHEL). This may make things more difficult for Rocky, Alma, and Oracle, to provide the same "Bug for Bug" compatible product to RHEL.

Most of what people are upset about, is because they're willfully misreading the GPL (GNU Public License) which covers an awful lot of the RHEL sources.

The GPL requires that if you distribute software, licensed under the GPL, that you also must provide the folks that you distribute that software to, with the sources you used. It doesn't specify how you have to provide them, you could make them available for download, you could mail folks a DVD with all the sources on it, (honestly, I think you might be able to just print them all out and send them on dead trees, and still be compliant).

What most of the folks are upset about, is there is a clause within the GPL, that says something about providing the sources "without restriction on redistribution" or some such. And they view that RedHat can choose to terminate your license to RHEL, if you redistribute RHEL sources/software as violating the GPL. But the GPL cannot dictate business relationships. Redhat cannot stop one of their customers from distributing sources that they are licensed to have. But they are well within their legal rights to terminate that license, and provide no further access, if you distribute them. (i.e. you have an RHEL license, and version 1.0 of a library is covered under that license, you redistribute that source, and RedHat must allow that, but they're under no obligation to continue that business relationship, and provide you continuing access to version 1.1)

That's a rough rundown on the history. What does this mean for the average linux user? Nothing, really. Unless you happen to use Rocky Linux, AlmaLinux, or Oracle Linux. It doesn't affect Debian, or Ubuntu, or openSUSE, or Arch, or anybody else. RedHat will continue to contribute back upstream to projects like the linux kernel, or GNOME, or what have you, they will continue to sponsor and hire developers, they just will no longer be providing free and open access to the RHEL Sources.

It's not a question of legality really, but more one of an ethical nature. It sort of depends on you, as to whether or not you're bothered by RedHat doing this or not.

I'd also like to know what people are using server side instead. Debian?

Jeff Geerling has a pretty good summary: https://www.youtube.com/watch?v=kF5pyVUQBH8