/usr/local/nagios/libexec                       #Path to default checks (scripts)

Reload configuration:

/etc/init.d/nagios reload
rcnagios reload

nagios-test                                     #Execute to check syntax of scripts/ services/ checks

nagios:~ # postsuper -d ALL
postsuper: Deleted: 15 messages
nagios:~ # mailq
postqueue: warning: Mail system is down -- accessing queue directly
Mail queue is empty

See also: http://www.nagios-wiki.de