OK, first time accessing a client, and you have this question?
# RHEL:
[grepora-rhel-server]$ rpm -qf /etc/redhat-release redhat-release-server-6Server-6.9.0.4.el6.x86_64
# OEL:
[grepora-oel-server]$ rpm -qf /etc/redhat-release enterprise-release-5-0.0.2
You may also have some other options like:
[grepora-fedora-server]$ rpm -qf /etc/redhat-release fedora-release-20-3.noarch
Hope you enjoy it!
Cheers!