I was recently working on a Redhat system that was unregistered in which I added CentOS repository config file into /etc/yum.repos.d/ (similar to this) to pull from for yum.

Even though I was using centos packages, I was still plagued with this message:

Loaded plugins: rhnplugin, security
This system is not registered with RHN.
RHN support will be disabled.


Here is how to remove it, or how I removed it:

Edit this file /etc/yum/pluginconf.d/rhnplugin.conf with your favorite editor.

Modify the main section so that it is disabled.

[main]
enabled = 0


You could probably also remove the plugin, but I left it intact so it can easily be re-added.