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https://issues.apache.org/jira/browse/HADOOP-4313?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12635805#action_12635805
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Allen Wittenauer commented on HADOOP-4313:
------------------------------------------
I was playing around with setting up a single node HDFS. As part of this
experiment, I set the following in my hadoop-site.xml:
<property>
<name>hadoop.tmp.dir</name>
<value>/grid/3/tmp</value>
</property>
<property>
<name>dfs.name.dir</name>
<value>/grid/3/hadoop/var/hdfs/name</value>
</property>
<property>
<name>dfs.data.dir</name>
<value>/grid/3/hadoop/var/hdfs/data</value>
</property>
clearly forgetting to set fs.default.name and formatting the name node. Upon
running start-all.sh, i was greeted with:
2008-09-30 18:14:07,565 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode:
java.lang.NullPointerException
at org.apache.hadoop.net.NetUtils.createSocketAddr(NetUtils.java:132)
at
org.apache.hadoop.hdfs.server.namenode.NameNode.getAddress(NameNode.java:130)
at
org.apache.hadoop.hdfs.server.namenode.NameNode.getAddress(NameNode.java:134)
at
org.apache.hadoop.hdfs.server.datanode.DataNode.startDataNode(DataNode.java:235)
at
org.apache.hadoop.hdfs.server.datanode.DataNode.<init>(DataNode.java:205)
at
org.apache.hadoop.hdfs.server.datanode.DataNode.makeInstance(DataNode.java:1199)
at
org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(DataNode.java:1154)
at
org.apache.hadoop.hdfs.server.datanode.DataNode.createDataNode(DataNode.java:1162)
at
org.apache.hadoop.hdfs.server.datanode.DataNode.main(DataNode.java:1284
with a similar error in the name node log.
This particular NPE is extremely unhelpful in letting someone know they forgot
something in the config. Also, as a side note the description says:
<description>The name of the default file system. Either the
literal string "local" or a hdfs://host:port for NDFS.</description>
Actually using 'local' reports that it is deprecated. So we probably shouldn't
put that in the config file as an option. :)
> ease-of-use: missing fs.default.name should be caught and give a helpful
> message
> ---------------------------------------------------------------------------------
>
> Key: HADOOP-4313
> URL: https://issues.apache.org/jira/browse/HADOOP-4313
> Project: Hadoop Core
> Issue Type: Bug
> Components: dfs
> Reporter: Allen Wittenauer
> Priority: Trivial
>
> Start a new data node and name node with the default fs.default.name can
> trigger a null pointer exception with no helpful information as to why.
> Instead, it should suggest checking fs.default.name .
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