Here is a scary exception thrown out when I started Hive.
org.datanucleus.store.rdbms.connectionpool.DatastoreDriverNotFoundException: The specified datastore driver (“com.mysql.jdbc.Driver”) was not found in the CLASSPATH. Please check your CLASSPATH specification, and the name of the driver.
I forgot to copy the mysql driver to hive lib folder. Here is the command to copy the same
cp /usr/share/java/mysql-connector-java-5.1.38.jar /opt/hadoop/hive/lib/