reconfigure oracle-xe on ubuntu

To reconfigure an instance of oracle-xe on ubuntu, first edit this file

/etc/default$ more oracle-xe

change the CONFIGURE_RUN value to false

# ORACLE_DBENABLED:'true' means to load the Database at system boot.
ORACLE_DBENABLED=true

# LISTENER_PORT: Database listener
LISTENER_PORT=1521

# HTTP_PORT : HTTP port for Oracle Application Express
HTTP_PORT=8080

# Configuration : Check whether configure has been done or not
CONFIGURE_RUN=true

and then execute

/etc/initi.d/oracle-xe configure