When monitoring a remote Ubuntu server which Nagios XI I was receiving the below unknown message for the service status:
CHECK_NRPE: Received 0 bytes from daemon. Check the remote server logs for error messages.
Following investigation , I noticed the following entry in /var/log/syslog:
Nov 11 15:24:58 nrpe: Error: Request contained command arguments, but argument option is not enabled! Nov 11 15:24:58 nrpe: Client request was invalid, bailing out...
In order to resolve this issue I had to modify the Nagios configuration file (/etc/nagios/nrpe.cfg) on the remote server to allow command arguments:
dont_blame_nrpe = 1