You then need to copy the snmp_informant_*.xml files to your <cacti_path>/resource/snmp_queries directory.
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Then select Import templates from the console menu. Select the data query you want to import via the browse button, and select the save button.
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The next screen will show the import results.
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Then select 'Devices' nad the device you which to monitor, at the bottom of this screen you'll see 'Associated data Queries'. Select the query you want to add and select the add button.
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If this is successful, you should see
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At this point you can select 'Create Graphs for this Host' as the top of this screen.
Select the Data Query you wish to graph, the graph type from the dropdown box, and select create.
That should do it.