If you receive the following error, when you try to reinstall Oracle XE on Ubuntu (My version was 11.04):

Executing Post-install steps...
/bin/chown: invalid user: 'oracle:dba'

 

Perform these steps:

sudo aptitude purge oracle-xe-universal
sudo /usr/sbin/groupadd dba
sudo /usr/sbin/useradd -M -g dba -d /usr/lib/oracle -s /bin/bash oracle
sudo apt-get install oracle-xe-universal