How to backup database in Oracle Server 10.10.10.10

How to backup database in Oracle Server 10.10.10.10
Step 1 : Login to the oracle server as root in 10.10.10.10

Step 2 : Then switch over as oracle user using below command
                #su - oracle

Step 3 : Then set oracle_sid to use the respective database
               # export ORACLE_SID=citialps

Step 4 : Then check whether oracle home directory has been set as below
               #echo $ORACLE_HOME
                  /opt/ora9/product/9.2

Step 5 : Then use the below command to backup the database.

Note : make sure atleast 5 GB space is available in the server

            #exp testuat/testuat file=testuat280812.dmp full=yes