In this article we are going to resolve the Nagios alert “(No output on stdout) stderr: connect to address IP port 5666: Connection refused” on ubuntu 18.04 Prerequisites A system running Ubuntu 18.04 should have the following A user account with sudo privileges The System with ufw  The system with… Continue Reading Nagios Alert: (No output on stdout) stderr: connect to address IP port 5666: Connection refused on Ubuntu 18.04