datanode runs but not detected - hadoop

Question

I configured hadoop on 2 machine. everything works fine. In the first one if I run the command jps I have
16406 NameNode
16774 ResourceManager
16619 SecondaryNameNode
17037 Jps
And in the second machine I have
2641 Jps
2445 NodeManager
2141 DataNode
but if I go in the browser master:50070 I see Live DataNodes 0(why?)
in fact if I try to put a file (hdfs dfs -put /input/file.txt)
I get this error
15/03/08 01:43:25 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
15/03/08 01:43:26 WARN hdfs.DFSClient: DataStreamer Exception
org.apache.hadoop.ipc.RemoteException(java.io.IOException): File /input/file.txt._COPYING_ could only be replicated to 0 nodes instead of minReplication (=1). There are 0 datanode(s) running and no node(s) are excluded in this operation.
at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget4NewBlock(BlockManager.java:1549)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:3200)
at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:641)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:482)
at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:619)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:962)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2039)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2035)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1628)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2033)
at org.apache.hadoop.ipc.Client.call(Client.java:1468)
at org.apache.hadoop.ipc.Client.call(Client.java:1399)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:232)
at com.sun.proxy.$Proxy9.addBlock(Unknown Source)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolTranslatorPB.addBlock(ClientNamenodeProtocolTranslatorPB.java:399)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:187)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:102)
at com.sun.proxy.$Proxy10.addBlock(Unknown Source)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.locateFollowingBlock(DFSOutputStream.java:1532)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:1349)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:588)
put: File /input/reduced.txt._COPYING_ could only be replicated to 0 nodes instead of minReplication (=1). There are 0 datanode(s) running and no node(s) are excluded in this operation.
Why it say me that there are no datanodes?
Instead if I run the command hdfs dfs -mkdir /input it works, why it behaves differently?

Answer 1

Your datanode is not able to connect to Namenode that is the reason for your datanode not being reflected namenode web UI. Please update the core-site.xml file present in both nodes along with datanode log.
Your core-site should have namenode address.
<property>
<name>fs.default.name</name>
<value>hdfs://$namenode.full.hostname:8020</value>
<description>Enter your NameNode hostname</description>
</property>

Answer 2

It seems the problem is in your hostname only. Use FULL COMPUTER NAME instead of hostname. If your system connected with a domain then you have to specify FCN which likes hostname.domainname
Then use FCN in all hadoop configuration files. FCN should be access/ping from all other machines. If you cannot ping it. Then edit /etc/hosts file and set the FCN for the specific ip address.
Some of the hadoop configuration to be set with FCN are listed below.
Core-site.xml
<property>
<name>fs.defaultFS</name>
<value>hdfs://FCN:8020</value>
</property>
Hdfs-site.xml
<property>
<name>dfs.namenode.http-address</name>
<value>FCN:50070</value>
</property>
Let me know if you have any further queries.

Answer 3

I had the same problem. Fixed it by ensuring all the slaves has "etc\hosts" file updated with the current ip.