How-To-SNMP-Custom-Script.md

How To Extend snmpd with custom script/data

Some SNMP servers can be extended with custom scripts or programs. The output of the running script can then be read using the OID and can therefore be easily used in Cacti. An example is the thermometer on the USB port. In combination with Graph a Single SNMP OID, this is a very simple way to display such data.

We will show the procedure for the very extensive Net-SNMP and FreeBSD BSNMPD.

Linux Net-SNMP

Simply add a line to /etc/snmpd.conf and restart snmpd:

extend test /bin/echo hello

The result will be here:

snmpwalk -v2c -c testing 127.0.0.1 nsExtendOutput1
NET-SNMP-EXTEND-MIB::nsExtendOutput1Line."test" = STRING: hello
NET-SNMP-EXTEND-MIB::nsExtendOutputFull."test" = STRING: hello
NET-SNMP-EXTEND-MIB::nsExtendOutNumLines."test" = INTEGER: 1
NET-SNMP-EXTEND-MIB::nsExtendResult."test" = INTEGER: 0

For Cacti you need a numeric OID. Use snmptranslate:

snmptranslate -On NET-SNMP-EXTEND-MIB::nsExtendOutput1Line."test"

The result is an OID that we can use:

.1.3.6.1.4.1.8072.1.3.2.3.1.1.4.116.101.115.116

FreeBSD BSNMPD

Install bsnmp-ucd:

pkg install bsnmp-ucd

Add these lines to /etc/snmpd.config and restart bsnmpd:

begemotSnmpdModulePath."ucd" = "/usr/local/lib/snmp_ucd.so"
%ucd
extNames.0 = "first command"
extCommand.0 = "/path/to/script.sh"
extNames.1 = "second command"
extCommand.1 = "/path/to/script.sh param1"

The name and result of the first command share the same index:

snmpwalk -v2c -c testing 127.0.0.1 .1.3.6.1.4.1.2021.8.1.2.0
.1.3.6.1.4.1.2021.8.1.2.0 = STRING: first command

snmpwalk -v2c -c testing 127.0.0.1 .1.3.6.1.4.1.2021.8.1.101.0
.1.3.6.1.4.1.2021.8.1.101.0 = STRING: 15

---

Copyright (c) 2004-2026 The Cacti Group