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https://issues.apache.org/jira/browse/HDFS-10986?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15572511#comment-15572511
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Hudson commented on HDFS-10986:
-------------------------------

SUCCESS: Integrated in Jenkins build Hadoop-trunk-Commit #10602 (See 
[https://builds.apache.org/job/Hadoop-trunk-Commit/10602/])
HDFS-10986. DFSAdmin should log detailed error message if any. (brahma: rev 
129125404244f35ee63b8f0491a095371685e9ba)
* (edit) 
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DFSAdmin.java
* (edit) 
hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/tools/TestDFSAdmin.java


> DFSAdmin should log detailed error message if any
> -------------------------------------------------
>
>                 Key: HDFS-10986
>                 URL: https://issues.apache.org/jira/browse/HDFS-10986
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: tools
>            Reporter: Mingliang Liu
>            Assignee: Mingliang Liu
>         Attachments: HDFS-10986-branch-2.8.002.patch, 
> HDFS-10986-branch-2.8.003.patch, HDFS-10986-branch-2.8.004.patch, 
> HDFS-10986.000.patch, HDFS-10986.001.patch, HDFS-10986.002.patch, 
> HDFS-10986.003.patch
>
>
> There are some subcommands in {{DFSAdmin}} that swallow IOException and give 
> very limited error message, if any, to the stderr.
> {code}
> $ hdfs dfsadmin -getBalancerBandwidth 127.0.0.1:9866
> Datanode unreachable.
> $ hdfs dfsadmin -getDatanodeInfo localhost:9866
> Datanode unreachable.
> $ hdfs dfsadmin -evictWriters 127.0.0.1:9866
> $ echo $?
> -1
> {code}
> User is not able to get the exception stack even the LOG level is DEBUG. This 
> is not very user friendly. Fortunately, if the port number is not accessible 
> (say 9999), users can infer the detailed error message by IPC logs:
> {code}
> $ hdfs dfsadmin -getBalancerBandwidth 127.0.0.1:9999
> 2016-10-07 18:01:35,115 WARN util.NativeCodeLoader: Unable to load 
> native-hadoop library for your platform... using builtin-java classes where 
> applicable
> 2016-10-07 18:01:36,335 INFO ipc.Client: Retrying connect to server: 
> localhost/127.0.0.1:9999. Already tried 0 time(s); retry policy is 
> RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000 
> MILLISECONDS)
> .....
> 2016-10-07 18:01:45,361 INFO ipc.Client: Retrying connect to server: 
> localhost/127.0.0.1:9999. Already tried 9 time(s); retry policy is 
> RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000 
> MILLISECONDS)
> 2016-10-07 18:01:45,362 WARN ipc.Client: Failed to connect to server: 
> localhost/127.0.0.1:9999: retries get failed due to exceeded maximum allowed 
> retries number: 10
> java.net.ConnectException: Connection refused
>       at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
>       at 
> sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
>         ...
>       at org.apache.hadoop.hdfs.tools.DFSAdmin.run(DFSAdmin.java:2073)
>       at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:76)
>       at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:90)
>       at org.apache.hadoop.hdfs.tools.DFSAdmin.main(DFSAdmin.java:2225)
> Datanode unreachable.
> {code}
> We should fix this by providing detailed error message. Actually, the 
> {{DFSAdmin#run}} already handles exception carefully, including:
> # set the exit ret value to -1
> # print the error message
> # log the exception stack trace (in DEBUG level)
> All we need to do is to not swallow exceptions without good reason.



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