Mrtg.cfg is the configuration file for polling SNMP enabled devices. The community string (often 'public') is found in the line starting with target:#Target[test]: 1.3.6.1.4.1.2021.10.1.5.1&1.3.6.1.4.1.2021.10.1.5.2:public@localhostRemember not all targets are SNMP devices. Users can monitor CPU info for example.