Why JNRPE ?

You can use JNRPE everytime you need to write a Nagios plugin using the Java language and you don't want Nagios to start a new JVM every time your plugin(s) gets called.

Another reason you may want to get JNRPE, is that you want to control the internals of your application: JNRPE (as of version 2.0) can be easily embedded into your own application to give you the ability to answer to check_nrpe calls.

Last but not least, JNRPE and its plugins are pure JAVA: you can install and run JNRPE as soon as you have a JVM 1.5+.

How JNRPE works

Before we start configuring JNRPE, we must understand how it works. JNRPE makes a clear distinction between a plugin and a command: the plugin is an object that is able to execute some work, while the command is a configuration that says to the plugin what to execute (and how).

For example, suppose you are using MS Windows and want to check the free space of disk C and disk E.

In the example you want the following alerts:

• WARNING if less than 20% of space is available on disk C
• WARNING if less than 10% of space is available on disk E
• CRITICAL if less than 10% of space is available on disk C
• CRITICAL if less than 5% of space is available on disk E

You can perform such check using the CHECK_DISK plugin present in the plugin package. The plugin has the following command line:

     -p path -w WARNING_RANGE -c CRITICAL_RANGE

The range syntax is the following:

  [@]start:end
  Notes:

  start <= end

  start and ":" is not required if start=0

  if range is of format "start:" and end is not specified, assume end is infinity

  to specify negative infinity, use "~"

  if range starts with "@", then the range is negated (inclusive of endpoints)

In this example you will create the following command definition:

  check_disk_C : CHECK_DISK --path C: --warning :20 --critical :10 
  check_disk_E : CHECK_DISK --path E: --warning :10 --critical :5

A more advanced configuration would use the $ARG?$ macros to make the configuration dynamic:

  check_disk_C : CHECK_DISK --path C: --warning $ARG1$ --critical $ARG2$

JNRPE Server Configuration

While with the previous versions of JNRPE you were forced to configure JNRPE through an XML file, starting with JNRPE 2.0 you can now choose between two format:

• The new INI configuration file
• The old style XML configuration file

 
 [server]
 accept-params : true
 bind-address : 127.0.0.1:5666
 plugin-path : /usr/local/jnrpe/plugins
 allow-address : 127.0.0.1
   
 [commands]
 check_disk_C : CHECK_DISK --path C: --warning $ARG1$ --critical $ARG2$
 check_disk_E : CHECK_DISK --path E: --warning $ARG1$ --critical $ARG2$
 

 check_nrpe -n -H 127.0.0.1 -c check_disk_E -a ':10!:5'
 check_nrpe -n -H 127.0.0.1 -c check_disk_C -a ':20!:10'

  <?xml version="1.0" encoding="UTF-8"?>
  <config>
     <server accept-params="true">
        <bind address="127.0.0.1:5666" SSL="false"/>
        <allow ip="127.0.0.1"/>
        <plugin path="/usr/local/jnrpe/plugins"/>
     </server>
     <commands>
        <command name="check_disk_C" plugin_name="CHECK_DISK">
           <arg name="path"  value="C:" />
           <arg name="warning"  value="$ARG1$" />
           <arg name="critical"  value="$ARG2$" />
        </command>
        <command name="check_disk_E" plugin_name="CHECK_DISK">
           <arg name="path"  value="E:" />
           <arg name="warning"  value="$ARG1$" />
           <arg name="critical"  value="$ARG2$" />
        </command>
     </commands>
  </config>

 check_nrpe -n -H 127.0.0.1 -c check_disk_E -a ':10!:5'
 check_nrpe -n -H 127.0.0.1 -c check_disk_C -a ':20!:10'