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How to debug a NullPointerException on "hdfs dfs -cat /filename"

How to debug a NullPointerException on "hdfs dfs -cat /filename"

New Contributor

When executing a simple "hdfs dfs -cat" on a file, I get a NullPointerException (running on HDP 2.4.2):

hdfs --loglevel TRACE dfs -cat '/filename'
[...]
17/04/24 18:06:39 TRACE ipc.ProtobufRpcEngine: 1: Call -> prd-hmaster-01-tor/172.22.5.37:8020: getBlockLocations {src: "/filename" offset: 0 length: 1342177280}
17/04/24 18:06:39 DEBUG ipc.Client: IPC Client (1293677337) connection to prd-hmaster-01-tor/172.22.5.37:8020 from hdfs sending #1
17/04/24 18:06:39 DEBUG ipc.Client: IPC Client (1293677337) connection to prd-hmaster-01-tor/172.22.5.37:8020 from hdfs got value #1
17/04/24 18:06:39 TRACE ipc.ProtobufRpcEngine: 1: Exception <- prd-hmaster-01-tor/172.22.5.37:8020: getBlockLocations {org.apache.hadoop.ipc.RemoteException(java.lang.NullPointerException): java.lang.NullPointerException
}
cat: java.lang.NullPointerException
17/04/24 18:06:39 DEBUG ipc.Client: stopping client from cache: org.apache.hadoop.ipc.Client@62656be4
[...]

Unfortunately, the NameNode logs do not show a stack trace:

2017-04-24 18:06:39,199 WARN  ipc.Server (Server.java:logException(2292)) - IPC Server handler 99 on 8020, call org.apache.hadoop.hdfs.protocol.ClientProtocol.getBlockLocations from 172.22.5.39:17182 Call#1 Retry#0                      java.lang.NullPointerException

Any hints on how to debug this issue would be much appreciated.

Thanks a lot

Michael

1 REPLY 1
Highlighted

Re: How to debug a NullPointerException on "hdfs dfs -cat /filename"

Hi @Michael Häusler, this may be caused by HDFS-9958.

I see that HDFS-9958 is not fixed in HDP 2.4.2 but it was fixed in HDP 2.4.3. If you can see this consistently I'd recommend upgrading to check whether that fixes the problem. If you have a support contract we can provide you with a hotfix release.