Nagios/Icinga Debian - CHECK_NRPE: Error - Could not complete SSL handshake.

Error: Nagios/Icinga (Debian Squeeze) - CHECK_NRPE: Error - Could not complete SSL handshake.

You try to connect from your Nagios/Icinga host to a remote Nagios NRPE server like this...

/usr/lib/nagios/plugins/check_nrpe -H 9.8.7.6

... and get the following error:

root@server1:/etc/nagios-plugins/config# /usr/lib/nagios/plugins/check_nrpe -H 9.8.7.6 
CHECK_NRPE: Error - Could not complete SSL handshake.
root@server1:/etc/nagios-plugins/config#

Solution

Open /etc/nagios/nrpe.cfg on the remote Nagios NRPE server...

vi /etc/nagios/nrpe.cfg

... and add the IP address of your Nagios/Icinga host (1.2.3.4 in this example) to the allowed_hosts line:

[...]
# ALLOWED HOST ADDRESSES
# This is an optional comma-delimited list of IP address or hostnames
# that are allowed to talk to the NRPE daemon.
#
# Note: The daemon only does rudimentary checking of the client's IP
# address.  I would highly recommend adding entries in your /etc/hosts.allow
# file to allow only the specified host to connect to the port
# you are running this daemon on.
#
# NOTE: This option is ignored if NRPE is running under either inetd or xinetd

allowed_hosts=127.0.0.1,1.2.3.4
[...]

Save the file and restart the NRPE server:

/etc/init.d/nagios-nrpe-server restart