Red Hat-based systems such as Fedora, RHEL, CentOS, and Scientific Linux have a prerequisite package that is not part of the included distribution repositories. To install Nagios, we need to add the Extra Packages for Enterprise Linux (EPEL) library. Red Hat systems can do this by obtaining the most recent EPEL package for their OS versions and architectures from the following URL:
https://fedoraproject.org/wiki/EPEL
Look for the package file that begins with epel-release and download it to the monitoring server. Once the package is downloaded, it can be installed with this command as a root-level user:
sudo rpm -ivh epel-release-*.rpm
