+=head1 NOTIFICATION DATA FORMAT
+
+The notification executables receive values rather than providing them. In
+fact, after the program is started C<STDOUT> is connected to C</dev/null>.
+
+The data is passed to the executables over C<STDIN> in a format very similar to
+HTTP: At first there is a "header" with one line per field. Every line consists
+of a field name, ended by a colon, and the associated value until end-of-line.
+The "header" is ended by two newlines immediately following another,
+i.e. an empty line. The rest, basically the "body", is the message of the
+notification.
+
+The following is an example notification passed to a program:
+
+ Severity: FAILURE
+ Time: 1200928930.515
+ Host: myhost.mydomain.org
+ \n
+ This is a test notification to demonstrate the format
+
+The following header files are currently used. Please note, however, that you
+should ignore unknown header files to be as forward-compatible as possible.
+
+=over 4
+
+=item B<Severity>
+
+Severity of the notification. May either be B<FAILURE>, B<WARNING>, or B<OKAY>.
+
+=item B<Time>
+
+The time in epoch, i.e. as seconds since 1970-01-01 00:00:00 UTC. The value
+currently has millisecond precision (i.e. three decimal places), but scripts
+should accept arbitrary numbers of decimal places, including no decimal places.
+
+=item B<Host>
+
+=item B<Plugin>
+
+=item B<PluginInstance>
+
+=item B<Type>
+
+=item B<TypeInstance>
+
+Identification of the performance data this notification is associated with.
+All of these fields are optional because notifications do not B<need> to be
+associated with a certain value.
+
+=back
+
+=head1 ENVIRONMENT
+
+The following environment variables are set by the plugin before calling
+I<exec>:
+
+=over 4
+
+=item COLLECTD_INTERVAL
+
+Value of the global interval setting.
+
+=item COLLECTD_HOSTNAME
+
+Hostname used by I<collectd> to dispatch local values.
+
+=back
+
+=head1 USING NAGIOS PLUGINS
+
+Though the interface is far from perfect, there are tons of plugins for Nagios.
+You can use these plugins with collectd by using a simple transition layer,
+C<exec-nagios.px>, which is shipped with the collectd distribution in the
+C<contrib/> directory. It is a simple Perl script that comes with embedded
+documentation. To see it, run the following command:
+
+ perldoc exec-nagios.px
+
+This script expects a configuration file, C<exec-nagios.conf>. You can find an
+example in the C<contrib/> directory, too.
+
+Even a simple mechanism to submit "performance data" to collectd is
+implemented. If you need a more sophisticated setup, please rewrite the plugin
+to make use of collectd's more powerful interface.
+