hdfs data node disconnected from namenode

Question

I get from time to time the following errors in cloudera manager:

This DataNode is not connected to one or more of its NameNode(s). 

and

Answer 1

If you're using Linux then please make sure that you have configured these properties correctly:

1. Disable SELINUX

type the command getenforce on CLI and if it shows enforcing, means it is enabled. Change it fro /etc/selinux/config file.

2. Disable Firewall

3. Make sure you have NTP service installed.

4. Make sure your server can SSH to all client nodes.

5. Make sure all the nodes have FQDN(Fully Qualified Domain Name) and have an entry in /etc/hosts with name and IP.

If these settings are right in the place then please attach the log of any of your datanode which got disconnected.