Here i got a nice article about starting oracle xe in ubuntu. here is the link: http://ivansnotebook.blogspot.com/2007/12/start-up-oracle-xe-in-ubuntu.html
Well, here is the main point:
There one problem in starting up oracle 10g in Ubuntu after you restart the computer, which is it wouldn’t start(if you didn’t enable the “Start Oracle on logon” option) unless you login as Oracle user account. One way I found out to start the listener and database, without login as Oracle, is to run the restart command.
sudo /etc/init.d/oracle-xe restart
I don’t know whether this is a security bug because firing the command start and stop doesn’t work using your own login.
Check the database status using the following code:
sudo /etc/init.d/oracle-xe status
Sometimes, the database won’t start after firing the restart command even the listener is active. Start the database using the menu path and check the status again.