troubleshooting hadoop 2.7.1 - hadoop

Question

I am trying to setup a 3-workers 1 master hadoop cluster using 2.7.1. When I start the cluster, the master has the following daemons running:
2792 NameNode
3611 NodeManager
4362 Jps
3346 ResourceManager
2962 DataNode
3169 SecondaryNameNode
And in the three worker nodes,
2163 NodeManager
2030 DataNode
2303 Jps
Problem is when I look at the web UI, the cluster does not recognize the 3 workers. It says 1 live data node and that is the master itself. Please have a look here:
http://master:50070/dfshealth.html#tab-overview
Question is, what are the daemon processes that are suppose to be running on workers node? I tried to look at the log files and didnt find anything helpful because it contains log only related to running daemons and the log files does not have any errors or Fatal errors.
I thought secondary namenode should be running in workers and ports are not letting it to communicate. So I tried to open up Port 9000 and 9001 in master by
sudo iptables -I INPUT -p tcp --dport 9000 -j ACCEPT
sudo iptables -I INPUT -p tcp --dport 9001 -j ACCEPT
iptables-save
but this didnt help much. Still facing the same problem. Log files in workers are not helpful either.
Appreicate your help in fixing this.
Edit 1:
The following is my configuration at core-site.xml:
<configuration>
<property>
<name>fs.defaultFS</name>
<value>hdfs://master:9001</value> <!-- slave1, 2 & 3 in position of master -->
</property>
</configuration>
This is my /etc/hosts file:
127.0.0.1 localhost math2
127.0.1.1 math2
192.168.1.2 master
192.168.1.3 worker1
192.168.1.7 worker5
192.168.1.8 worker6
This is my configuration at /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback
address 192.168.1.2 (3,5,6 instead of 2 for slaves)
netmask 255.255.255.0
gateway 192.168.1.1
broadcast 192.168.1.255
Here is the log output for one of the datanodes:
2016-02-05 17:54:12,655 FATAL org.apache.hadoop.hdfs.server.datanode.DataNode: Exception in secureMain
java.net.BindException: Problem binding to [0.0.0.0:50010] java.net.BindException: Address already in use; For more details see: http://wiki.apache.org/hadoop/BindException

Answer 1

Did you put the ip-address of all the nodes in /etc/hosts. The /etc/hosts file of all nodes(master and slaves) should contain the ip-address of all the nodes in your cluster.
For example if we have three data nodes and a master node the /etc/hosts file should be:
192.168.0.1 master
192.168.0.2 datanode1
192.168.0.3 datanode2
192.168.0.4 datanode33

Answer 2

On Datanode you can see below process when you run jps command
19728 DataNode
19819 Jps
and when you run ps -aef |grep -i datanode on Datanode, it should show the two process one with root user and another with HDFS user