Nagios Client (NRPE) installation in Linux

i. Create Account Information
Become the root user. You may have to use sudo -s on Ubuntu and other distros.
su -l
Create a new nagios user account and give it a password.
/usr/sbin/useradd nagios
passwd nagios

ii. Install the Nagios Plugins
Create a directory for storing the downloads.
mkdir ~/downloads
cd ~/downloads

Download the source code tarball of the Nagios plugins (visit http://www.nagios.org/download/ for links to the latest versions).
wget http://osdn.dl.sourceforge.net/sourceforge/nagiosplug/nagios-plugins-1.4.6.tar.gz
Extract the Nagios plugins source code tarball.
tar xzf nagios-plugins-1.4.6.tar.gz
cd nagios-plugins-1.4.6
Compile and install the plugins.
./configure
make
make install
The permissions on the plugin directory and the plugins will need to be fixed at this point, so run the following
commands.
chown nagios.nagios /usr/local/nagios
chown -R nagios.nagios /usr/local/nagios/libexec

iii. Install xinetd
yum install xinetd

iv. Install the NRPE daemon
Download the source code tarball of the NRPE addon (visit http://www.nagios.org/download/ for links to the latest versions).
cd ~/downloads
wget http://osdn.dl.sourceforge.net/sourceforge/nagios/nrpe-2.8.tar.gz
Extract the NRPE source code tarball.
tar xzf nrpe-2.8.tar.gz
cd nrpe-2.8
Compile the NRPE addon.
./configure
make all
Install the NRPE plugin (for testing), daemon, and sample daemon config file.
make install-plugin
make install-daemon
make install-daemon-config
Install the NRPE daemon as a service under xinetd.
make install-xinetd

Edit the /etc/xinetd.d/nrpe file and add the IP address of the monitoring server to the only_from directive.
only_from = 127.0.0.1 <nagios_ip_address>
Add the following entry for the NRPE daemon to the /etc/services file.
nrpe 5666/tcp # NRPE
Restart the xinetd service.
service xinetd restart

v. Test the NRPE daemon locally
Its time to see if things are working properly...
Make sure the nrpe daemon is running under xinetd.
netstat -at | grep nrpe
The output out this command should show something like this:
tcp 0 0 *:nrpe *:* LISTEN
If it does, great! If it doesn't, make sure of the following:
– You added the nrpe entry to your /etc/services file
– The only_from directive in the /etc/xinetd.d/nrpe file contains an entry for "127.0.0.1"
– xinetd is installed and started
– Check the system log files for references about xinetd or nrpe and fix any problems that are reported
Next, check to make sure the NRPE daemon is functioning properly. To do this, run the check_nrpe plugin that
was installed for testing purposes.
/usr/local/nagios/libexec/check_nrpe -H localhost
You should get a string back that tells you what version of NRPE is installed, like this:
NRPE v2.8

vi. Open firewall rules
Port for NRPE is 5666, so open this port on your linux machine.

vii. Customize NRPE commands
The sample NRPE config file that got installed contains several command definitions that you'll likely use to
monitor this machine. The command definitions are used to define commands that the NRPE daemon
will run to monitor local resources and services. You can edit the command definitions, add new commands, etc, by editing the NRPE config file:
vi /usr/local/nagios/etc/nrpe.cfg