hadoop 2.7.1 single node cluster

root@hadoop-master:/myhadoop# export JAVA_HOME=/usr/lib/jvm/java-8-oracle/
root@hadoop-master:/myhadoop# export HADOOP\_PREFIX=/myhadoop/hadoop-2.7.1
root@hadoop-master:/myhadoop# export HADOOP_CONF_DIR=$HADOOP_PREFIX/etc/hadoop

root@hadoop-master:~# vim /myhadoop/hadoop-2.7.1/etc/hadoop/hadoop-env.sh

#export JAVA_HOME=${JAVA_HOME}

export JAVA_HOME=/usr/lib/jvm/java-8-oracle/

If you want to change it globally and at system level;

root@hadoop-master:~# vim /etc/environment

PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games"

export JAVA_HOME=/usr/lib/jvm/java-8-oracle/