pam_unix(su:session) opened for user postgres every 5 minutes

Every 5 minutes I get this:

Aug 24 17:05:55 islamorada su: pam_unix(su:session): session opened for user postgres by (uid=0) Aug 24 17:05:55 islamorada su: pam_unix(su:session): session closed for user postgres

ran crontab -e and it looks like only /etc/webmin/status/monitor.pl is running every 5 minutes, and postgres is not running at all on my server.

Looked at monitor.pl and not don't see anything obvious that would make this call.

Just curious, what's it doing?

Thanks!