nagios to cacti

[supapo]

is that mean that the nagios can check falls in the graphs and alet?
if so how can i do it?

[gandalf]

Cacti poller will print an error message (depending on logging level) in case a polled ressource returns invalid/no data. You should be able to watch the log file to detect this.
As this is an ugly method, it would be an option to add a custom plugin hook to the update function, that reads polled data in order to update rrd files. But I fear that this will not make you very happy; there are many reasons why such a polling may fail. And you may see too many failures ... But as already said, this can be done
R,