Currently I have Nagios up and running and it notifies me by email of events.
I would like to know the configuration change that I have to make, so that I will only be notified 1 time of a server going down and then only another email when it is up again.
At the moment when I server is down, I get an email every 30 minutes telling me that it is down, and I am only interested in knowing when it is up again (recovery).
I would like to know the change that I have to make in the configuration files manually. I don't use and don't want to use a fancy front-end.
In your host definition, set notification_interval to 0:
You can see the available configuration options for a host here: http://nagios.sourceforge.net/docs/3_0/objectdefinitions.html#host
You should log into the nagios interface and acknowledge the outage this should stop subsequent alerts, remembering to clear this once service has been restored, alternatively if this is scheduled maintenance, place the service / server in scheduled downtime.
Setting the alert me only once, is not what I would call best practice, as you are telling the system to assume you got the first alert, and not to send subsequent alerts, which is a perfect world would be fine, however this is not always the case such as a failed email send due to temporary smtp outage or temporary sms gateway outage.