解决方案

找到hadoop主目录的bin文件夹下的hadoop文件，将倒数第二行

exec "$JAVA" $JAVA_HEAP_MAX $HADOOP_OPTS $CLASS "$@"

改成

exec "$JAVA" -classpath "$(cygpath -pw "$CLASSPATH")" $JAVA_HEAP_MAX $HADOOP_OPTS $CLASS "$@"

就可以了

ps:

我按这个方法解决了

http://*.com/questions/19363402/classpath-issue-in-hadoop-on-cygwin-while-running-hadoop-version-command