host_notification_options：
d = notify on DOWN host states,
u = notify on UNREACHABLE host states
r = notify on host recoveries (UP states)
f = notify when the host starts and stops flapping
s = send notifications when host or service scheduled downtime starts and ends
n (none) as an option, the contact will not receive any type of host notifications.
service_notification_options:
w = notify on WARNING service states
u = notify on UNKNOWN service states
c = notify on CRITICAL service states
r = notify on service recoveries (OK states)
f = notify when the service starts and stops flapping
n (none) as an option, the contact will not receive any type of service notifications.
常用的设置
host_notification_options：d,u,r
service_notification_options:w,u,c,r
转自http://ethan.heroempire.com/2011/09/nagios-notification-options/