Error: Nagios/Icinga (Debian Squeeze) - CHECK_NRPE: Received 0 bytes from daemon. Check the remote server logs for error messages.

You monitor a remote server with Nagios or Icinga and see the following error in your Nagios/Icinga web interface:

CHECK_NRPE: Received 0 bytes from daemon. Check the remote server logs for error messages.

In /var/log/syslog on the remote server you see these messages:

Aug 23 14:20:20 server2 nrpe[11496]: Error: Request contained command arguments, but argument option is not enabled!
Aug 23 14:20:20 server2 nrpe[11496]: Client request was invalid, bailing out...

Solution

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

vi /etc/nagios/nrpe.cfg

... and set dont_blame_nrpe to 1:

[...]
# COMMAND ARGUMENT PROCESSING
# This option determines whether or not the NRPE daemon will allow clients
# to specify arguments to commands that are executed.  This option only works
# if the daemon was configured with the --enable-command-args configure script
# option.
#
# *** ENABLING THIS OPTION IS A SECURITY RISK! ***
# Read the SECURITY file for information on some of the security implications
# of enabling this variable.
#
# Values: 0=do not allow arguments, 1=allow command arguments

dont_blame_nrpe=1
[...]

Save the file and restart the NRPE server:

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