Unfortunately, we do not have a guide for how to monitor temperatures on Linux. You may want to check if there are any OIDs with which you can retrieve the temperature, for more information about how to set up SNMP on Linux please see this article.
Alternatively, you could try to retrieve the temperature with a custom SSH script, which you could then use in a SSH Script Sensor.
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.