[CentOS] Problems switching from RHEL 6 to Centos 6

Sun Jul 30 12:32:08 UTC 2017
Alois Treindl <alois at astro.ch>

I am trying to migratean existing RHEL 6 machine to Centos 6.

I followed the instructions in https://wiki.centos.org/HowTos/MigrationGuide

I run into problems:

when I run

yum upgrade

then yum tries to access a repository rhel-6-server-extras-rpms

and then fails.

What can I do that yum no longer tries to access this repository?