How to install Nagios herald.

Nagios Herald can most simply be installed as a Ruby gem. Assuming you already have Ruby installed, just run:

gem install nagios-herald

When configuring Nagios, you’ll need to reference the full path to the nagios-herald command. This may differ based on how you’ve installed Ruby. You can find it by running:

which nagios-herald

In my case, that returns:

/usr/local/rvm/gems/ruby-2.2.1/bin/nagios-herald

So, my Nagios configuration looks like:

define command {
    command_name    notify-host-by-email
    command_line    /usr/local/rvm/gems/ruby-2.2.1/bin/nagios-herald --message-type email --formatter=$_HOSTMESSAGE_FORMATTER_NAME$ --nagios-cgi-url=http://nagios.example.com/nagios/cgi-bin/cmd.cgi --reply-to=nagios@example.com
}

To find more information on configuring nagios-herald see here.