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


A system running Ubuntu 18.04 should have the following

  1. A user account with sudo privileges
  2. The System with ufw 
  3. The system with nrpe configuration


Step 1: SSH the server

$ ssh user@ip

Step 2: Check the ufw status

$ ufw status 

(i) If it is inactive, enable ufw as shown below

$ ufw enable

(ii) If it is active as mentioned below proceed to the next step

Step 3: Allow port number 5666 in the server 

$ ufw allow 5666

Step 4: Enable the nrpe module and start it 

$ sudo systemctl enable nrpe.service

$ sudo systemctl start nrpe.service

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