HDFS_NAMENODE_USER, HDFS_DATANODE_USER & HDFS_SECONDARYNAMENODE_USER not defined

I am new to hadoop.
I'm trying to install hadoop in my laptop in Pseudo-Distributed mode.
I am running it with root user, but I'm getting the error below.

root@debdutta-Lenovo-G50-80:~# $HADOOP_PREFIX/sbin/start-dfs.sh
WARNING: HADOOP_PREFIX has been replaced by HADOOP_HOME. Using value of HADOOP_PREFIX.
Starting namenodes on [localhost]
ERROR: Attempting to operate on hdfs namenode as root
ERROR: but there is no HDFS_NAMENODE_USER defined. 
Aborting operation.
Starting datanodes
ERROR: Attempting to operate on hdfs datanode as root
ERROR: but there is no HDFS_DATANODE_USER defined. 
Aborting operation.
Starting secondary namenodes [debdutta-Lenovo-G50-80]
ERROR: Attempting to operate on hdfs secondarynamenode as root
ERROR: but there is no HDFS_SECONDARYNAMENODE_USER defined. Aborting operation.
WARNING: HADOOP_PREFIX has been replaced by  HADOOP_HOME. Using value of HADOOP_PREFIX.

Also, I have to run hadoop in root user as hadoop is not able to access ssh service with other user.
How to fix the same?

just do what it asks you:

export HDFS_NAMENODE_USER="root"
export HDFS_DATANODE_USER="root"
export HDFS_SECONDARYNAMENODE_USER="root"
export YARN_RESOURCEMANAGER_USER="root"
export YARN_NODEMANAGER_USER="root"