How to delete all nagios availability history data?

According to the Nagios Support Forum here: Clear state, logs, etc. What is the best way?

Shut down the nagios service and remove the retention file:

service nagios stop
rm /usr/local/nagios/var/retention.dat
service nagios start

Delete the archived nagios.log files: /usr/local/nagios/var/archives/

That said, I've never actually done either of these in any Nagios environment...so make sure you backup the folders/files first somewhere and then try it and verify it did what was intended.