Do not re-create repositories after updating - unix

Question

We manage systems and thus manage repositories. We remove repositories which we do not use, present in /etc/yum.repos.d/<file>
Our problem is: after an update/upgrade of the system, CentOS automatically re-creates the repositories which were removed, which is an issue for us.
Question: Is there a command / method to ensure repositories are not re-created after an upgrade on CentOS 7 systems.

Answer 1

Those repositories are created by someone, the OS doesn't recreate them.
Either they are restored by an update of a RPM package such as centos-release or by an automatic script you setup/run (ansible?).
I'm not aware of an automatic method to delete a repo; I see a couple of solutions:
Exclude centos-release from the upgradable packages, by adding
exclude=centos-release
to /etc/yum.conf (space separated list), but this could break some updates;
Disable them with:
# yum-config-manager --disable base,updates,extras,centosplus,epel,whatever
(this can be easily scripted and put in a cron or in your ansible playbook)
Write a small script and place it in /etc/cron.hourly/, e.g. /etc/cron.hourly/wipe_repos, containing:
#!/usr/bin/env bash
rm -f /etc/yum.repos.d/CentOS-Base.repo
or, better:
#!/usr/bin/env bash
yum-config-manager --disable base,updates,extras,centosplus,epel,whatever
I would suggest to use solution 2, since the repo files aren't overwritten by updates, but the new versions are placed along the old in .rpmnew files.
This is guaranteed by the flag %config(noreplace) in the source rpm of centos-release, applied to all files in /etc/yum.repos.d/.
You can check this by downloading the .src.rpm and opening the centos-release.spec file.
$ mkdir test && cd test
$ yumdownloader --source centos-release
$ rpm2cpio centos-release*.rpm | cpio -idmv
$ cat centos-release.spec
(or search for the package online and download the src.rpm)
Then scroll down to section %files and you'll notice:
%config(noreplace) /etc/yum.repos.d/*
%config(noreplace) means that all those files are not replaced with new files from an update, but the files from the new rpm are saved with the extension .rpmnew, so you'll have:
$ ls /etc/yum.repos.d/
CentOS-Base.repo <-- here you set them as disabled
CentOS-Base.repo.rpmnew <-- this comes from the update, but yum will ignore it
For reference, see http://people.ds.cam.ac.uk/jw35/docs/rpm_config.html or https://serverfault.com/a/48819/.

Answer 2

As I already said in the comments below the question, the reason why those repositories keep reappearing after an update is quite simple: the files defining the system repositories are owned by the package centos-release and whenever this package gets updated or reinstalled, the repositories reappear.
The package centos-release is a very basic package, it provides the capabilities redhat-release and system-release, and a number of other basic packages depend on it.
[local ~]$ rpm -q --provides centos-release
centos-release = 7-6.1810.2.el7.centos
centos-release(upstream) = 7.6
centos-release(x86-64) = 7-6.1810.2.el7.centos
config(centos-release) = 7-6.1810.2.el7.centos
redhat-release = 7.6-1
system-release = 7.6-1
system-release(releasever) = 7
[local ~]$ rpm -q --whatrequires system-release
setup-2.8.71-10.el7.noarch
grubby-8.28-25.el7.x86_64
[local ~]$ rpm -q --whatrequires redhat-release
initscripts-9.49.46-1.el7.x86_64
systemd-219-62.el7_6.5.x86_64
There is no easy way out of this.
But one possible solution might be to create a customized RPM package to replace centos-release. It should contain the pointers to your own repositories and of course needs to provide the capabilities redhat-release and system-release.
Please be aware that I have no idea if this is actually going to work, it's just something that came to my mind while thinking about the problem. It might save you the work of creating a full custom distribution derived from CentOS, which is the only other way I can think of to achieve what you seem to want.

Answer 3

My solution doesn't exactly solve the problem you request ("how do I delete default repository config files forever?"), but it does stabilize your config changes. If you zero out the files instead of deleting them, then system updates will leave your 'edited' versions unchanged.
I do feel that this is a 'hack', leaving named ghost files, but it's one I can live with. No need to disable or customize redhat-release or system-release.
My problem was slightly different than yours - I maintained different configs for the same repositories for different situations, indicated by filename. On updates the original files would return, leaving me with redundant and incorrect definitions. Now they don't.