I have Nagios Xi 4.3.2 installed on Red Hat Enterprise Linux 7.3 (Mapio) . Recently, I had an issue with my Nagios monitoring tool. It stopped monitoring my devices. When I checked further, I found out that NDO2DB service stopped working. Because of that, I could not see most recent status of any of the devices monitored by Nagios. I logged on to Read hat box and tried below command to check the status of the service: #systemctl status ndo2db You can also use following command to check any service status #Service ndo2db status I tried following commands to start/restart ndo2db service. #systemctl start ndo2db OR #systemctl restart ndo2db After applying above commands, I ran following command again to check status but it failed to start #systemctl status ndo2db After doing bit of searching on this issue, I found the solution. I entered following commands to start NDO2DB service. #service nagios stop #service ndo2db stop #rm -f /usr/