Nagios NRPE: Unable to read output

3.25pm. Today I started looking into rolling out nagios monitoring over our *nix servers after the success of recently adding Windows Servers (via NSClient++) and our Core Switches (via SNMP).

Most of my servers are based on CentOS 5.5 so a quick search for nrpe (the linux alternative of nsclient++) on yum provided the required results:

nagios-plugins-nrpe.x86_64 : Provides nrpe plugin for Nagios
nrpe.x86_64 : Host/service/network monitoring agent for Nagios

Installing both packages went pretty well, adding the required nrpe user and service (just needed to 'chkconfig nrpe on' to ensure it started on boot). I then added the NetworkMonitor host IP to the nrpe.cfg file.

allowed_hosts=127.0.0.1,192.168.200.46

Annoyingly this is where I hit a road block, I was able to test communication from the Nagios/NetworkMonitor Box to the NRPE client:

# /usr/lib64/nagios/plugins/check_nrpe -H Sherpa
NRPE v2.12

However when it came to retrieving any useful data such as check_users or check_load I received the following error:

# /usr/lib64/nagios/plugins/check_nrpe -H sherpa -c check_users
NRPE: Unable to read output
# /usr/lib64/nagios/plugins/check_nrpe -H sherpa -c check_load
NRPE: Unable to read output

A quick in the NRPE plugins folder (/usr/lib64/nagios/plugins) provided the answer; it only contained the check_nrpe plugin (that I had installed earlier) and not a lot else. Sure enough I had only installed the nagios nrpe plugin (and not all the nrpe plugins that I first thought). Back to yum:

# yum search nagios-plugins-load
nagios-plugins-load.x86_64 : Nagios Plugin - check_load

So it looks like there is a plugin for each check, that's worth knowing! I can apply this logic to every item I now want to check on this host; or if I am feeling lazy install:

nagios-plugins-all.x86_64 : Nagios Plugins - All plugins

Which does the lot! Now to retest....

# /usr/lib64/nagios/plugins/check_nrpe -H sherpa -c check_users
USERS OK - 1 users currently logged in |users=1;5;10;0

# /usr/lib64/nagios/plugins/check_nrpe -H sherpa -c check_load
OK - load average: 0.00, 0.01, 0.00|load1=0.000;15.000;30.000;0; load5=0.010;10.000;25.000;0; load15=0.000;5.000;20.000;0;

Success!