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From Steve Loughran <ste...@apache.org>
Subject Re: datanode can not connect to the namenode
Date Mon, 15 Feb 2010 10:53:37 GMT
Marc Sturlese wrote:
> Hey there I have a hadoop cluster build with 2 servers. One node (A) contains
> the namenode, a datanode, the jobtraker and a tasktraker.
> The other node(B) just has a datanode and a tasktraker.
> I set up correctly hdfs with ./start-hdfs.sh
> 
> When I try to set up MapReduce with ./start-mapred.sh the TaskTraker of node
> (B) can not connect to the namenode. The log will keep throwing:
> 
> INFO org.apache.hadoop.ipc.Client: Retrying connect to server:
> mynamenode/192.168.0.13:8021. Already tried 8 time(s)
> 
> I think maybe something is missing in /etc/hosts file or this hadoop
> property is not set correctly:
> <property>
>   <name>dfs.datanode.address</name>
>   <value>0.0.0.0:50010</value>
>   <description>
>     The address where the datanode server will listen to.
>     If the port is 0 then the server will start on a free port.
>   </description>
> </property>
> 
> I try on the namenode:
> telnet localhost 8021
> telnet 192.168.0.10 8021
> Both cases I get:
> telnet: Unable to connect to remote host: Connection refused
> 

That's the Namenode that isn't there, which should be on 192.168.0.13 at 
8021

You can see what ports really are open on the namenode by identifying 
the process (jps -v will do that) then netstat -a -p | grep PID , where 
PID= process ID of the namenode.

If you can telnet to port 8021 when logged in to the NN, but not 
remotely, it's your firewall or routing interfering

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