Why does the the Yum installer display a warning message on CentOS 6?

The yum installer displays a warning message on Centos 6 if you are not using the latest version update of CentOS or if the new GNU Privacy Guard (GPG) keys are not in place.

On the Centos system, the new GPG keys are generally sent as an update before the expiry of the old keys. You must perform the version update regularly to receive the new GPG keys.

To avoid the warning message, use the ''-nopgcheck option'' in the yum install command.

yum install --nogpgcheck teamforge