NRPE (Nagios Remote Plugin Executor) is a Nagios agent witch allows for remote  system monitoring by executing scripts on a remote system allowing monitoring of disk usage, system’s load or number of users currently logged in and much more. Normally Nagios can only monitor public services such as HTTP & FTP. This is great if you only want to monitor public servers, however I bet that most people want to monitor their own servers and have access to private information, that’s were NRPE comes in. It works on a client server basis, you install a daemon on the machine you  want to monitor, then setup your Nagios server to connect to the remote daemon to gather information

So how do we set this up, well first we need to be running a Nagios server.Once you have a Nagios server setup you’ll need to download and install the NRPE daemon on the remote machine.

So lets get started first SSH into your remote machine and enter:

/usr/sbin/useradd nagios
passwd nagios

this will setup a new Nagios user, now we need to install some plugins:

wget http://prdownloads.sourceforge.net/sourceforge/nagiosplug/nagios-plugins-1.4.14.tar.gz
tar -xzf nagios-plugins-1.4.14.tar.gz
cd nagios-plugins-1.4.14
sudo ./configure --with-nagios-user=nagios --with-nagios-group=nagios
sudo make
sudo make install

This will download and install the Nagios plugins required for NRPE to run, now we need to give the plugins access via the new Nagios user:

chown nagios.nagios /usr/local/nagios
chown -R nagios.nagios /usr/local/nagios/libexec

NRPE require you install xinetd and libssl-dev so we’ll do that now

apt-get install xinetd
sudo apt-get install libssl-dev

Now that done its time to install the NRPE daemon itself:

cd ~/
wget http://prdownloads.sourceforge.net/sourceforge/nagios/nrpe-2.12.tar.gz
tar xzf nrpe-2.12.tar.gz
cd nrpe-2.12
./configure
make all
make install-plugin
make install-daemon
make install-daemon-config
make install-xinetd

now we need to configure the daemon so it will talk to our Nagios server, well do this buy editing /etc/xinetd.d/nrpe and adding our monitoring servers address:

nano /etc/xinetd.d/nrpe
<em>Should Look Like:</em>
# default: on
# description: NRPE (Nagios Remote Plugin Executor)
service nrpe
{
        flags           = REUSE
        socket_type     = stream
        port            = 5666
        wait            = no
        user            = nagios
        group           = nagios
        server          = /usr/local/nagios/bin/nrpe
        server_args     = -c /usr/local/nagios/etc/nrpe.cfg --inetd
        log_on_failure  += USERID
        disable         = no
        only_from       = 127.0.0.1 <strong>[NAGIOS SERVER ADDRESS]</strong>
}

Then add “nrpe 5666/tcp # NRPE” to /etc/services:

nano /etc/services
<em>add:</em>
nrpe 5666/tcp # NRPE

you can check this all been configured probably by typing:

netstat -at | grep nrpe

this should show something like

(tcp        0      0 *:nrpe                  *:*                     LISTEN)

If that worked correctly its time to setup your Nagios server to monitor your remote host, so ssh into your Nagios server. Now we are going to add separate host file for the new host so we need to edit the nano “nagios.cfg” file:

nano /usr/local/nagios/etc/nagios.cfg
<em>add lines:</em>
cfg_file=/usr/local/nagios/etc/objects/host1.cfg

Now we need to create the Host1.cfg:

nano /usr/local/nagios/etc/objects/host1.cfg

and enter the following code:

define host{
        use linux-server ; Inherit default values from a template
        host_name remotehost ; The name we're giving to this server
        alias Fedora Core 6 ; A longer name for the server
        address the-tech-tutorial.com; IP address of the server
}

define service{
        use generic-service
        host_name remotehost
        service_description CPU Load
        check_command check_nrpe!check_load
}

define service{
        use generic-service
        host_name remotehost
        service_description Current Users
        check_command check_nrpe!check_users
}

define service{
        use generic-service
        host_name remotehost
        service_description /dev/hda1 Free Space
        check_command check_nrpe!check_sda1
}

define service{
        use generic-service
        host_name remotehost
        service_description Total Processes
        check_command check_nrpe!check_total_procs
}

define service{
        use generic-service
        host_name remotehost
        service_description Zombie Processes
        check_command check_nrpe!check_zombie_procs
}

Run the nagios config check then restart nagios:

/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
/etc/init.d/nagios restart

And hay presto you Nagios should now be monitoring your remote host, don’t worry if it says pending it can take up to 5 minutes for the information to come through.

If you want to add more hosts repeat the above steps and use host2.cfg instead of host1.cfg.

the critical in the above screen dump is because I had disabled ICMP on the remote server.