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How to save history of "Last Message" from SNMP Custom String Sensor



I have a custom sensor configured to capture a string value. It displays the result without issue. My problem is that I cannot see any history of the responses. My goal is to be able to be notified of the change (this is already working) and look at the sensor to see what the string value was previously. I'm not trying to graph it so I don't want to extract anything.

Is it possible to capture this value in a channel?

An example of how one could display it is using the SNMP Cisco ASA VPN Users sensor. It displays each value it has ever received as a new channel and then marks it as online or offline. I'm assuming this is based on a lookup table.

Is this possible?

channel custom-sensor prtg snmp string

Created on Mar 19, 2015 6:20:14 PM

6 Replies



Dear Greg

The sensor message itself cannot be stored. Only the current message is shown. However, you can configure an SNMP Custom String sensor to use a regex to extract a numerical value. This numeric value can be used for a value channel and is part of the historic data.

Created on Mar 20, 2015 10:25:23 AM by  Arne Seifert [Paessler Support]




Please advise how to do this?

I am currently receiving a last message value of "LTE" for a custom SNMP sensor.

How can i convert this to a numerical value?

Created on Sep 24, 2015 2:28:22 PM



Dear gurpswu

A pure string cannot be converted into a number that way. However, you can create a custom look-up table and use it in reverse with the SNMP Custom Lookup Sensor.

Created on Sep 24, 2015 3:11:01 PM by  Arne Seifert [Paessler Support]



Just another user with similar problem, but I think I found a suitable solution for now: It is possible to trigger a notification on change. This can be used to create a ticket which includes the new message returned by the sensor. Setup a PRTG user to assign these tickets to to help organize them, and you have a way to track the history of the returned string. It is not ideal, but is functional to track some strings that should not change often, such as configuration history for certain parameters. Useful for SNMP String sensor, for example, which otherwise only seems to provide the current message with no easy access to historical returned strings. Event-Log notifications might also be useful for this, but I think tickets allow better organizational options.

Created on Mar 31, 2016 11:02:47 PM



In reference to what Arne posted above:

To extract a number from the current message:

Configure an SNMP Custom String sensor (with the SNMP OID for the object e.g. for a Cisco loadbalancer - do a manual SNMPWalk or use the Paessler SNMP tool to get all the SNMP object IDs).

By default the SNMP Custom String sensor will only show "response time" and "status" (ok/down). Under the "Extended processing" part of the SNMP Custom String sensor, use the regex:


(- thanks wikipedia for this regex), to extract all numerical values.

You should then see a new channel in the SNMP Custom String sensor after a few refreshes, with the numerical value. (Channel 2 in my case).

This channel can then be added to similar results using a Factory Sensor, if you want to know all the Cisco loadbalancer current connections.

Created on Jan 9, 2018 8:47:53 AM

Last change on Jan 9, 2018 9:52:29 AM by  Luciano Lingnau [Paessler]



Thank you.

Some further options are described here.

Created on Jan 9, 2018 4:00:49 PM by  Arne Seifert [Paessler Support]

Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.