Instalando Postgresql no Ubuntu 12.04

sudo apt-get purge postgresql-9.1
sudo apt-get purge postgresql-9.1*
sudo apt-get purge postgresql-8.4
sudo apt-get purge postgresql-8.4*
sudo apt-get install postgresql-9.1
sudo apt-get install postgresql-client-9.1

Sources:

http://ubuntuforums.org/showthread.php?t=1862358

https://help.ubuntu.com/community/PostgreSQL

http://www.cyberciti.biz/faq/howto-add-postgresql-user-account/