View source for snmp-extend to run custom script

1) Create a script/command that monitors something on your system and output the result to stdout. 
<br>example 
<br>script: /usr/local/bin/check_everything.sh
<br>outputs either...
<br>STATUS: OK - everything good
<br>or
<br>STATUS: NOT OK!

2) Create entry in the SNMP config to monitor the script:
 # vi /etc/snmp/userDefinedSettings.conf

add a line...
 extend everything_status /bin/sh /usr/local/bin/check_everything.sh

3) restart snmpd
 from clish, run "set snmp agent off" then run "set snmp agent on"

4) test it 

with a walk

 $ snmpwalk -On -v2c -c mycomstring 192.168.1.1 NET-SNMP-EXTEND-MIB::nsExtendObjects
 .1.3.6.1.4.1.8072.1.3.2.1.0 = INTEGER: 1
 .1.3.6.1.4.1.8072.1.3.2.2.1.2.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115 = STRING: /bin/sh
 .1.3.6.1.4.1.8072.1.3.2.2.1.3.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115 = STRING: 
 /usr/local/bin/check_everything.sh
 .1.3.6.1.4.1.8072.1.3.2.2.1.4.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115 = STRING: 
 .1.3.6.1.4.1.8072.1.3.2.2.1.5.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115 = INTEGER: 5
 .1.3.6.1.4.1.8072.1.3.2.2.1.6.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115 = INTEGER: exec(1)
 .1.3.6.1.4.1.8072.1.3.2.2.1.7.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115 = INTEGER: run-on-read(1)
 .1.3.6.1.4.1.8072.1.3.2.2.1.20.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115 = INTEGER: permanent(4)
 .1.3.6.1.4.1.8072.1.3.2.2.1.21.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115 = INTEGER: active(1)
 .1.3.6.1.4.1.8072.1.3.2.3.1.1.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115 = STRING: STATUS: OK - everything good
 .1.3.6.1.4.1.8072.1.3.2.3.1.2.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115 = STRING: STATUS: OK - everything good
 .1.3.6.1.4.1.8072.1.3.2.3.1.3.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115 = INTEGER: 1
 .1.3.6.1.4.1.8072.1.3.2.3.1.4.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115 = INTEGER: 0
 .1.3.6.1.4.1.8072.1.3.2.4.1.2.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115.1 = STRING: STATUS: OK - everything good

with a get

 $ snmpget -v 2c -c mycomstring 192.168.1.1 
 .1.3.6.1.4.1.8072.1.3.2.4.1.2.15.102.119.112.111.108.105.99.121.95.115.116.97.116.117.115.1
 NET-SNMP-EXTEND-MIB::nsExtendOutLine."fwpolicy_status".1 = STRING: STATUS: OK - everything good