Monitoring a Host in Nagios Using NRPE

This post will go over how to monitor a host in nagios using nrpe.  The nrpe is the "Nagios Remote Plugin Executor", and allows you to remotely execute commands on another machine and gather desired metrics.  The version of nrpe that was installed on the target centos machine does not allow for command line arguments from the nagios server, so all arguments and thresholds must be specified on the machine itself.  The puppetmaster server is the machine being added to nagios.

Step 1:
On the target machine, add the EPEL repository.

wget http://dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
rpm -ivh epel-release-6-8.noarch.rpm

Step 2:
Install nagios and necessary packages.

yum install nagios* xinetd

Step 3:
Add the service to xinetd.

/etc/xinetd.d/nrpe
service nrpe
{
flags = REUSE
type = UNLISTED
port = 5666
socket_type = stream
wait = no
user = nagios
group = nagios
server = /usr/sbin/nrpe
server_args = -c /etc/nagios/nrpe.cfg --inetd
log_on_failure += USERID
disable = no
only_from = 192.168.1.16
}

Restart, the service

service xinetd restart

chkconfig xinetd on 

Step 4:
Make any changes or modifications to the data you want to monitor on the host in /etc/nagios/nrpe.cfg.  In this scenario, the root partition, number of users, current load, and number of processes are being monitored.

Step 5:
Configure the nagios server.

/etc/nagios/objects/commands.cfg
define command{
        command_name check_nrpe
        command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
}

Add the host, service, and hostgroup definitions to the necessary config files in /etc/nagios.  The puppet server is being added to the "Linux Servers" hostgroup.

Restart the service

service nagios restart

Step 6:
Verify functionality.