1. Back up Current Data

Stop the original Ambari Server.

ambari-server stop

Create a directory to hold the database backups.

cd /tmp
mkdir dbdumps
cd dbdumps/

Create the database backups.

pg_dump -U $AMBARI-SERVER USERNAME ambari > ambari.sql Password: $AMBARI-SERVER PASSWORD 
pg_dump -U $MAPRED USERNAME ambarirca > ambarirca.sql Password: $MAPRED PASSWORD

Where usernames and passwords reflect your particular installation. Defaults are ambari-server/bigdata and mapred/mapred.