First you will need to make sure SNMP is installed.

apt-get install snmpd snmp snmp-mibs-downloader

You’ll need to configure a new snmpd.conf file with

snmpconf

Run through the steps and when your done replace your current snmpd.conf file in /etc/snmp/ with the new one.

Now open up your new snmpd.conf file

vi /etc/snmp/snmpd.conf

and add the following to the bottom of the file.

extend myshscript /path/to/your.sh

Save and close the file and restart the snmpd service.

service snmpd restart

Now we need to find the OID of our new data point.  Do this by running

snmpwalk -v2c -c public localhost .1.3.6.1.4.1.8072.1.3.2

It should display something similar to the following.

root@localhost:/etc/snmp# snmpwalk -v2c -c public localhost .1.3.6.1.4.1.8072.1.3.2
iso.3.6.1.4.1.8072.1.3.2.1.0 = INTEGER: 1
iso.3.6.1.4.1.8072.1.3.2.2.1.2.4.118.111.108.116 = STRING: "/etc/snmp/volt.sh"
iso.3.6.1.4.1.8072.1.3.2.3.1.4.4.118.111.108.116 = INTEGER: 0
iso.3.6.1.4.1.8072.1.3.2.4.1.2.4.118.111.108.116.1 = STRING: "14.3"
root@localhost:/etc/snmp#

The OID we are interested in is the one on the last line.  If you run a snmpwalk command with the OID you should get your data point.

root@localhost:/etc/snmp# snmpwalk -v2c -c public localhost 1.3.6.1.4.1.8072.1.3.2.4.1.2.4.118.111.108.116.1
iso.3.6.1.4.1.8072.1.3.2.4.1.2.4.118.111.108.116.1 = STRING: "14.3"
root@localhost:/etc/snmp#

All that’s left is to add the OID to your SNMP monitor.  If You run into issues with your SNMP server not monitoring the OID, you might need do what I did in the above command, replace the beginning of the OID “iso.” with a “1”.