Ntp server is one of the important thing in the network, because all the clients and servers in your network get update & synced with NTP server to maintain uniformity in time. What if NTP server or service fails, think ?   every thing gets messed up especially services and your applications that depends on time. So no use of your nagios with out configuring it to monitor NTP server. Lets do it how to configure nagios to do it for you.

First copy and paste a sample or any other hosts .cfg file on the nagios server  and edit it for your new host, name and ip etc... Now just define ntp service in the .cfg file.  In my case my ntp server file is ntp.cfg.

[root@nagios]# cd /usr/local/nagios/etc/servers/ntp.cfg

define service {
     use                    generic-service
     host_name              ntp
     service-description    ntp
     check_command          check_nrpe!check_ntp
}

Now on the client side edit /etc/nagios/nrpe.cfg

[root@ntp]# vim /etc/nagios/nrpe.cfg

command[check_ntp]=/usr/local/nagios/libexec/check_ntp_peer  -H  192.168.85.111  -w 0.5 -c 1 -j -1:100 -k -1:200

gil ...