I have upgraded a server from Debian 8 to Debian 9. The server was running Nagios 3 to do some checks but that has been discontinued. The natural replacement is Icinga (version 1).
I've installed it and copied and adjusted the configuration files. Most of it worked directly but the NRPE remote checks are not working.
First of all I was using the check_nrpe_1arg
command but that seems to have been changed to check_nrpe
to make it clear it doesn't accept arguments (the only argment is the remote command name).
That fixed the configuration for icinga to start. But all the NRPE checks are in unknown state with this message:
CHECK_NRPE: Receive header underflow - only -1 bytes received (4 expected).
I've ran the command from the bash prompt to check if it was working correctly and it seems so.
$ /usr/lib/nagios/plugins/check_nrpe -H 192.168.4.1 -c check_users
USERS OK - 0 users currently logged in |users=0;5;10;0
But somehow from Icinga the command is not working.