Ubuntu 16.04
Sponsored Link

Nagios : Add Monitoring Target Item
It's possible to add monitoring Target Items. There are many RPM packages for them or it's possible to create a plugin by yourself. And also there are many plugins provided by comunity below.
⇒ http://exchange.nagios.org/
[1] Many plugins are provided with packages like follows.
apt-get search nagios-plugins-

i   nagios-plugins-basic            - transitional dummy package
p   nagios-plugins-common           - transitional dummy package
p   nagios-plugins-contrib          - Plugins for nagios compatible monitoring s
p   nagios-plugins-contrib:i386     - Plugins for nagios compatible monitoring s
p   nagios-plugins-extra            - transitional dummy package
p   nagios-plugins-extra:i386       - transitional dummy package
p   nagios-plugins-rabbitmq         - Set of Nagios checks useful for monitoring
p   nagios-plugins-standard         - transitional dummy package
p   nordugrid-arc-nagios-plugins-do - HTML documentation for the ARC Nagios plug
p   nordugrid-arc-nagios-plugins-eg - EGI configuration and dependencies for the
[2] For example, add check_ntp plugin to monitor time difference between the system and NTP server.
vi /etc/nagios3/commands.cfg
# add follows to the end

define command{
        command_name    check_ntp_time
        command_line    $USER1$/check_ntp_time -H $ARG1$ -w $ARG2$ -c $ARG3$

vi /etc/nagios3/conf.d/localhost_nagios2.cfg
# add follows to the end ( Warning if it has 1 sec time difference, Critical if it has 2 sec )

define service{
        use                             generic-service
        host_name                       localhost
        service_description             NTP_TIME
        check_command                   check_ntp_time!ntp1.jst.mfeed.ad.jp!1!2

systemctl restart nagios3

[3] It's possible to view the status for a new plugin on the admin site.