datanode[slave] running but connect namenode[master]

i can start hadoop sucess but datanode[slave] can’t connect namenode[master]

2016-11-09 16:00:15,953 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Problem connecting to server: master/192.168.1.101:9000
2016-11-09 16:00:21,957 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: master/192.168.1.101:9000. Already tried 0 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000 MILLISECONDS)
2016-11-09 16:00:22,965 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: master/192.168.1.101:9000. Already tried 1 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000 MILLISECONDS)

detail /etc/hosts

127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

192.168.1.101 master
192.168.1.102 slave1

core-site.xml

<configuration>
<property>
<name>fs.defaultFS</name>
<value>hdfs://master:9000</value>
</property>
</configuration>

and hdfs-site.xml

<property>
 <name>dfs.replication</name>
 <value>1</value>
</property>

<property>
<name>dfs.namenode.name.dir</name>
<value>file:///opt/volume/namenode</value>
</property>

<property>
<name>dfs.datanode.data.dir</name>
<value>file:///opt/volume/datanode</value>
</property>

Answer

1) check if firewall is restricting port

sudo iptables -L 

if so, flush it

To open 9000,

$ sudo iptables -A INPUT -p tcp -m tcp --dport 9000 -j ACCEPT
$ sudo /etc/init.d/iptables save

2) check namenode logs for any issues under /var/log/hadoop