Exception in thread "main" while formatting namenode in hadoop - hadoop

Question

satya#ubuntu:~/hadoop/bin$ hadoop namenode -format
DEPRECATED: Use of this script to execute hdfs command is deprecated.
Instead use the hdfs command for it.
Exception in thread "main" java.lang.UnsupportedClassVersionError: org/apache/hadoop/hdfs/server/namenode/NameNode : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Could not find the main class: org.apache.hadoop.hdfs.server.namenode.NameNode. Program will exit.

Answer 1

This error (Unsupported major.minor version) generally appears because of using a higher JDK during compile time and lower JDK during runtime. In this case 51 corresponds to JDK 7 (for more version mappings visit this link), this indicates that
whatever the JVM 1.6 runtime loaded, it was meant for JVM 1.7. Try using JDK 1.7 and set that using JAVA_HOME environment variable in hadoop-env.sh.

Answer 2

The default java version and you Hadoop's java version should match. Do this:
java -version
Open hadoop-env.sh (can be found in hadoop config folder) and search for JAVA_HOME. This java version and the default java version should match.
NOTE: Set your JAVA_HOME to point to jdk folder and not your java's bin folder

Answer 3

It is better if you can show your Hadoop version... but for Hadoop 2, I think you can try the new format command
[hdfs]$ $HADOOP_PREFIX/bin/hdfs namenode -format [-clusterid cid] [-force] [-nonInteractive]
So in your case, type
satya#ubuntu:~/hadoop/bin$ hdfs namenode -format
(I'm referring to Hadoop 2.7.0 which should apply to your situation.)

Answer 4

I also met the question. And when I type:
$hadoop classpath
I find the classpath of hdfs is wrong. Then I did
vi ~/.bashrc
export HADOOP_HDFS_HOME=$HADOOP_HOME
It works, hope it helps.