sudo su - hdfs
hdfs dfs -mkdir /user/root
hdfs dfs -chown root:hdfs /user/root
got the answer as well from another thread
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sudo -u hdfs hdfs dfs -mkdir /user/root
sudo -u hdfs hdfs dfs -chown -R root:hdfs /user/root
You have to ssh to the machine using terminal. There is no hdfs user in Ambari that can create directory as superuser.