HADOOP Command sbin/start-dfs.sh Start Error
Error: Cannot find configuration directory: /etc/hadoop
JAVA_HME is not set and could not be found

Solution:

Configure hadoop-env.sh file in hadoop-2.7.1/etc/hadoop. write your own jdk and hadoop paths.
export JAVA_HOME=/usr/jdk1.8.0_221
export HADOOP_CONF_DIR=/usr/hadoop-2.7.1/etc/hadoop/