Port 9590 is a dummy listener on all NEMS 1.4.1+ servers.
This listener does nothing but reply to TCP requests when it is up. Its purpose is to provide a safe port to enable and disable while learning how to use the check command check_tcp.
To disable 9590 temporarily, open its process in Monit Service Monitor and choose “Stop service”. It will however resume normal operation at next reboot.
To disable 9590 permanently, first stop it with Monit (otherwise Monit will re-run the service once it detects it is not running). Then, open an SSH connection to your NEMS server and type:
sudo /usr/sbin/update-rc.d 9590 disable
To see how 9590 works, simply review the source code.