5.1.1. Host down

This alert is configured for all nodes in the Hadoop cluster (Hadoop master and slave nodes) as well as the Nagios and Ganglia monitoring servers. By default, it uses the Nagios plugin check_ping to find the average round trip response (RTT) time and the packet loss percentage by pinging each cluster node.

This alert helps Ambari Web determine the number of cluster nodes that are up and down at a given time. A network outage may also result in a host down alert.

	Note
	The `hadoop-services.cfg` file does not define this alert explicitly. Instead, this alert is defined as a part of the generic host definition in the `templates.cfg` file using the `check-host-alive` plugin.

5.1.1.1. Possible causes

The host is actually down
There is a network outage and the Nagios server cannot access the host

5.1.1.2. Possible remedies

Check the host and restart if necessary
Check network connections

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