[CentOS] I broke "yum update" - C7

Wed Aug 28 20:36:11 UTC 2019
Gary Stainburn <gary.stainburn at ringways.co.uk>

This evening I decided to do some work on my development C7 system. As I have not touched it for a while, and wanted to install new services I thought I'd better yum update first.

I saw that it only did updates from Google and PHP, and none from the system repo's so I had a closer look. It showed certificate errors on a number of repo's.

[root at stan2 ~]# yum update
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
Could not get metalink https://mirrors.fedoraproject.org/metalink?repo=epel-7&arch=x86_64 error was
14: curl#60 - "Peer's Certificate issuer is not recognized."
 * base: mirrors.clouvider.net
 * epel: mirrors.coreix.net
 * extras: mirrors.clouvider.net
 * remi-php72: mirror.netweaver.uk
 * remi-safe: mirror.netweaver.uk
 * updates: mirrors.vooservers.com
https://rpm.nodesource.com/pub_6.x/el/7/x86_64/repodata/repomd.xml: [Errno 14] curl#60 - "Peer's Certificate issuer is not recognized."
Trying other mirror.
It was impossible to connect to the CentOS servers.
This could mean a connectivity issue in your environment, such as the requirement to configure a proxy,
or a transparent proxy that tampers with TLS security, or an incorrect system clock.
You can try to solve this issue by using the instructions on https://wiki.centos.org/yum-errors
If above article doesn't help to resolve this issue please use https://bugs.centos.org/.

https://download.postgresql.org/pub/repos/yum/10/redhat/rhel-7-x86_64/repodata/repomd.xml: [Errno 14] curl#60 - "Peer's Certificate issuer is not recognized."
Trying other mirror.
https://download.postgresql.org/pub/repos/yum/9.6/redhat/rhel-7-x86_64/repodata/repomd.xml: [Errno 14] curl#60 - "Peer's Certificate issuer is not recognized."
Trying other mirror.
No packages marked for update
[root at stan2 ~]#

I wrongly followed the instructions in https://wiki.centos.org/yum-errors hoping that it would resolve the problems but it's only made it worse.  Now all I get is:

[root at stan2 ~]# yum clean all
Loaded plugins: fastestmirror, langpacks
Cleaning repos: base epel extras google-chrome nodesource pgdg10 pgdg96 remi-php72 remi-safe updates
Cleaning up list of fastest mirrors
[root at stan2 ~]# rm -rf /var/cache/yum/*
[root at stan2 ~]# yum update
Loaded plugins: fastestmirror, langpacks
Determining fastest mirrors

 One of the configured repositories failed (Unknown),
 and yum doesn't have enough cached data to continue. At this point the only
 safe thing yum can do is fail. There are a few ways to work "fix" this:

     1. Contact the upstream for the repository and get them to fix the problem.

     2. Reconfigure the baseurl/etc. for the repository, to point to a working
        upstream. This is most often useful if you are using a newer
        distribution release than is supported by the repository (and the
        packages for the previous distribution release still work).

     3. Run the command with the repository temporarily disabled
            yum --disablerepo=<repoid> ...

     4. Disable the repository permanently, so yum won't use it by default. Yum
        will then just ignore the repository until you permanently enable it
        again or use --enablerepo for temporary usage:

            yum-config-manager --disable <repoid>
            subscription-manager repos --disable=<repoid>

     5. Configure the failing repository to be skipped, if it is unavailable.
        Note that yum will try to contact the repo. when it runs most commands,
        so will have to try and fail each time (and thus. yum will be be much
        slower). If it is a very temporary problem though, this is often a nice

            yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true

Cannot retrieve metalink for repository: epel/x86_64. Please verify its path and try again
[root at stan2 ~]# 

I removed and re-installed the epel-release RPM which made no difference.  I've also tried disabling each repo in turn, pgdg10, remi-php72, nodesource-el, pgdg96, google-chrome but still have no success.

Anyone got any suggestions?