SymptomsSMTP service goes away for a random amount of time and customers cannot send mail, /var/log/messages shows:
xinetd: Deactivating service smtp due to excessive incoming connections. Restarting in 30 seconds.
xinetd: Activating service smtp
CauseSuch messages are caused by xinetd access restrictions that are defined in the /etc/xinetd.conf. For example:
cps = 50 10
instances = 50
per_source = 10
'cps' value limits the rate of incoming connections. Takes two arguments. The first argument is the number of connections per second to handle. If the rate of incoming connections is higher than this, the service will be temporarily disabled. The second argument is the number of seconds to wait before re-enabling the service after it has been disabled. The default for this setting is 50 incoming connections and the interval is 10 seconds.
'instances' determines the number of servers that can be simultaneously active for a service.
'per_source' specifies the maximum number of instances of the service per source IP address.