Shared memory error while connecting to Oracle
Looks like there are some hoops with fire you need to jump thru for installing Oracle XE on Ubuntu. You may want to try following the article here: http://meandmyubuntulinux.blogspot.com/2012/05/installing-oracle-11g-r2-express.html

Oracle is very finicky when it comes to installing on particular OS's. It's very specific as to what they support. However, that doesn't mean you can't install it on any OS you want. You'll just need to jump thru a few hoops... Some with fire.

Hope it helps!