We've created a Hadoop cluster of two machines following these instructions: http://tecadmin.net/set-up-hadoop-multi-node-cluster-on-centos-6/with the machines set as follows:hadoop1 = master & slavehadoop2 = slaveWhen we start the services (bin/start-all.sh), all services (including datanode for hadoop2) initialize.  Everything is well.But when we check the DFS size (bin/hadoop dfsadmin -report), only one system (hadoop1) is detected.We've checked jps on both hosts. On hadoop1, all services are displayed, whereas on hadoop2 only jps is running.  This means the data node on the slave is not working even though the master shows that datanode is starting on hadoop2 as well.  When we check the logs, there is no datanode log for the hadoop2 slave.I've tried all possibles explanations including the namespaceID which we get from namename current VERSION and assign it to data node current VERSION.What could be the solution for this? I use centOS 7, and apache hadoop 1.2.1 
Datanode in slave isn't working : Hadoop in CentOS
centos;hadoop