# 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](Graph-a-Single-SNMP-OID.md), 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:

```console
extend test /bin/echo hello
```

The result will be here:

```console
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:

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

The result is an OID that we can use:

```console
.1.3.6.1.4.1.8072.1.3.2.3.1.1.4.116.101.115.116
```

## FreeBSD BSNMPD

Install bsnmp-ucd:

```console
pkg install bsnmp-ucd
```

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

```console
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:

```console
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
```

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