Hi The difference is, check_nrpe needs a daemon on the host you are monitoring. Your Nagios server connects with this host on port 5506 (arraund this number) an tell the host which script the host should run. The host will do it, if it is right configured and give the result back to the nagios server. Using check_by_ssh the nagios server logs on the host it should monitor with a shell and call a command or a script an gives back the result. So check_by_ssh needs less administrative work. But as a example for test on windows system you need check_nrpe. Greetings Markus