.. _configuration/customobjectvars:

=======================
Custom Object Variables 
=======================


Introduction 
=============

Users often request that new variables be added to host, service, and contact definitions. These include variables for "SNMP" community, MAC address, AIM username, Skype number, and street address. The list is endless. The problem that I see with doing this is that it makes Nagios less generic and more infrastructure-specific. Nagios was intended to be flexible, which meant things needed to be designed in a generic manner. Host definitions in Nagios, for example, have a generic "address" variable that can contain anything from an IP address to human-readable driving directions - whatever is appropriate for the user's setup.

Still, there needs to be a method for admins to store information about their infrastructure components in their Nagios configuration without imposing a set of specific variables on others. Nagios attempts to solve this problem by allowing users to define custom variables in their object definitions. Custom variables allow users to define additional properties in their host, service, and contact definitions, and use their values in notifications, event handlers, and host and service checks.


Custom Variable Basics 
=======================

There are a few important things that you should note about custom variables:

  * Custom variable names must begin with an underscore (_) to prevent name collision with standard variables
  * Custom variable names are case-insensitive
  * Custom variables are :ref:`inherited <advanced/objectinheritance>` from object templates like normal variables
  * Scripts can reference custom variable values with :ref:`macros and environment variables <thebasics/macros>`


Examples 
=========

Here's an example of how custom variables can be defined in different types of object definitions:

::

  define host{
     host_name       linuxserver
     _mac_address    00:06:5B:A6:AD:AA ; <-- Custom MAC_ADDRESS variable
     _rack_number    R32               ; <-- Custom RACK_NUMBER variable
  ...
  }
  
  define service{
     host_name        linuxserver
     description      Memory Usage
     _SNMP_community  public         ; <-- Custom SNMP_COMMUNITY variable
     _TechContact     Jane Doe       ; <-- Custom TECHCONTACT variable
     ....
  }
  
  define contact{
     contact_name    john
     _AIM_username   john16        ; <-- Custom AIM_USERNAME variable
     _YahooID        john32        ; <-- Custom YAHOOID variable
     ...
  }


Custom Variables As Macros 
===========================

Custom variable values can be referenced in scripts and executables that Nagios runs for checks, notifications, etc. by using :ref:`macros <thebasics/macros>` or environment variables.

In order to prevent name collision among custom variables from different object types, Nagios prepends “_HOST", “_SERVICE", or “_CONTACT" to the beginning of custom host, service, or contact variables, respectively, in macro and environment variable names. The table below shows the corresponding macro and environment variable names for the custom variables that were defined in the example above.

=========== ============== ======================== =============================
Object Type Variable Name  Macro Name               Environment Variable         
Host        MAC_ADDRESS    $_HOSTMAC_ADDRESS$       NAGIOS__HOSTMAC_ADDRESS      
Host        RACK_NUMBER    $_HOSTRACK_NUMBER$       NAGIOS__HOSTRACK_NUMBER      
Service     SNMP_COMMUNITY $_SERVICESNMP_COMMUNITY$ NAGIOS__SERVICESNMP_COMMUNITY
Service     TECHCONTACT    $_SERVICETECHCONTACT$    NAGIOS__SERVICETECHCONTACT   
Contact     AIM_USERNAME   $_CONTACTAIM_USERNAME$   NAGIOS__CONTACTAIM_USERNAME  
Contact     YAHOOID        $_CONTACTYAHOOID$        NAGIOS__CONTACTYAHOOID       
=========== ============== ======================== =============================


Custom Variables And Inheritance 
=================================

Custom object variables are :ref:`inherited <advanced/objectinheritance>` just like standard host, service, or contact variables.