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https://issues.apache.org/jira/browse/HDFS-17952?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18096720#comment-18096720
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Xiaoqiao He commented on HDFS-17952:
------------------------------------
Thanks [~Jepon] for your report. I think the main issue is that JVM can't find
the classpath file after you move jar file but not restart datanode. So it
throws NoClassDefFoundError. BTW, please send mail to maillist here
https://hadoop.apache.org/mailing_lists.html first.
Will close this ticket. Please feel free to reopen it if make sure this is one
issue. Thanks again.
> standby namenode restart,datanode failed to connect
> ----------------------------------------------------
>
> Key: HDFS-17952
> URL: https://issues.apache.org/jira/browse/HDFS-17952
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Affects Versions: 2.9.2
> Reporter: Jepon
> Priority: Major
>
> {*}{color:#4c9aff}Environment：{color}{*}1、Back up all nodes'
> $HADOOP_HOME/share/hadoop/hdfs/hadoop-hdfs-2.9.2.jar files directly to bak
> and upload the latest jar file.
> 2、Apache Hadoop 2.9.2 setup with two Namenode nodes (NN1 as standby, NN2 as
> active).
> *After restarting NN1, the system shows 83 DN nodes with 82 successfully
> registered DN links, but one DN node fails to establish a connection with
> NN1, triggering an error:*
> 2026-07-13 18:24:12,159 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: bdpprd01/10.1.1.1:9000. Already tried 0 time(s); retry policy is
> RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000
> MILLISECONDS)
> 2026-07-13 18:24:13,159 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: bdpprd01/10.1.1.1:9000. Already tried 1 time(s); retry policy is
> RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000
> MILLISECONDS)
> 2026-07-13 18:24:14,159 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: bdpprd01/10.1.1.1:9000. Already tried 2 time(s); retry policy is
> RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000
> MILLISECONDS)
> 2026-07-13 18:24:15,160 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: bdpprd01/10.1.1.1:9000. Already tried 3 time(s); retry policy is
> RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000
> MILLISECONDS)
> 2026-07-13 18:24:16,160 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: bdpprd01/10.1.1.1:9000. Already tried 4 time(s); retry policy is
> RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000
> MILLISECONDS)
> 2026-07-13 18:24:17,160 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: bdpprd01/10.1.1.1:9000. Already tried 5 time(s); retry policy is
> RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000
> MILLISECONDS)
> 2026-07-13 18:24:18,161 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: bdpprd01/10.1.1.1:9000. Already tried 6 time(s); retry policy is
> RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000
> MILLISECONDS)
> 2026-07-13 18:24:19,161 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: bdpprd01/10.1.1.1:9000. Already tried 7 time(s); retry policy is
> RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000
> MILLISECONDS)
> 2026-07-13 18:24:20,162 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: bdpprd01/10.1.1.1:9000. Already tried 8 time(s); retry policy is
> RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000
> MILLISECONDS)
> 2026-07-13 18:24:21,162 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: bdpprd01/10.1.1.1:9000. Already tried 9 time(s); retry policy is
> RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000
> MILLISECONDS)
> 2026-07-13 18:24:22,492 WARN org.apache.hadoop.hdfs.server.datanode.DataNode:
> Unexpected exception in block pool Block pool
> BP-383332234-10.1.1.1-1584640173217 (Datanode Uuid
> 213c4874-89c5-40d5-8a61-db4dbcd0439c) service to bdpprd01/10.1.1.1:9000
> {color:#de350b}java.lang.NoClassDefFoundError:
> org/apache/hadoop/hdfs/protocol/UnregisteredNodeException{color}
> at
> org.apache.hadoop.hdfs.server.datanode.BPServiceActor.offerService(BPServiceActor.java:717)
> at
> org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:841)
> at java.lang.Thread.run(Thread.java:748)
> 2026-07-13 18:24:22,492 WARN org.apache.hadoop.hdfs.server.datanode.DataNode:
> Ending block pool service for: Block pool BP-383332234-10.1.1.1-1584640173217
> (Datanode Uuid 213c4874-89c5-40d5-8a61-db4dbcd0439c) service to
> bdpprd01/10.1.1.1:9000
> But，Check the bak Jar's source code; this
> {color:#de350b}UnregisteredNodeException {color}class exists.
> Why?
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