After installing all Hadoop environment, I used DistCp to copy large files in distributed cluster. But it report error:

#hadoop distcp
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/hadoop/mapreduce/Job
        at java.lang.Class.getDeclaredMethods0(Native Method)
        at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
        at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
        at java.lang.Class.getMethod0(Class.java:3018)
        at java.lang.Class.getMethod(Class.java:1784)
        at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)
        at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.mapreduce.Job
        at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
        ... 7 more

Seems it can’t even find the basic MapReduce class. Then I checked CLASSPATH for Hadoop:

#hadoop classpath
/usr/lib/hadoop-2.6.0/etc/hadoop/:/usr/lib/hadoop-2.6.0/share/hadoop/common/lib/*:/usr/lib/hadoop-2.6.0/share/hadoop/common/*:/usr/lib/hadoop-2.6.0//share/hadoop/hdfs:/usr/lib/hadoop-2.6.0//share/hadoop/hdfs/lib/*:/usr/lib/hadoop-2.6.0//share/hadoop/hdfs/*:/usr/lib/hadoop-2.6.0/share/hadoop/yarn/lib/*:/usr/lib/hadoop-2.6.0/share/hadoop/yarn/*:/usr/lib/hadoop-mapreduce/share/hadoop/mapreduce/*

Pretty strange, the HADOOP_CLASSPATH contains ‘mapreduce’ directories. It supposed to be able to find ‘Job’ class, unless the MapReduce jar package is in other directories.
Finally, I found the real MapReduce jar is actually in other position. Therefore I add these directories into HADOOP_CLASSPATH: edit ~/.bashrc and add following line

#.bashrc
export HADOOP_CLASSPATH=${HADOOP_CLASSPATH}:/usr/lib/hadoop-2.6.0/share/hadoop/mapreduce/*:/usr/lib/hadoop-2.6.0/share/hadoop/mapreduce/lib/*

DistCp could work now.

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