I installed the Oracle database following the steps mentioned in this blog.

1. Downloaded 11g express edition

2. Created a new user oracle under the group dba. Following steps are executed using this.

3. Unzipped oracle-xe-11.2.0-1.0.x86_64.rpm.zip and then converted the rpm to the Ubuntu package by running:

   sudo alien --scripts -d oracle-xe-11.2.0-1.0.x86_64.rpm
   

4. Created /sbin/chkconfig file and added the entries as specified there.

5. Created /etc/sysctl.d/60-oracle.conf and added the entries as specified in the same link as above.

6. Running the commands:

   ln -s /usr/bin/awk /bin/awk
   mkdir /var/lock/subsys
   touch /var/lock/subsys/listener
   

7. .deb generated in step 3:

   sudo dpkg --install oracle-xe_11.2.0-2_amd64.deb
   

8. Left the default values as it is:

   sudo /etc/init.d/oracle-xe configure
   

9. Set the following env variables in ~/.bashrc file:

   export ORACLE_HOME=/u01/app/oracle/product/11.2.0/xe
   export ORACLE_SID=XE
   export NLS_LANG=`$ORACLE_HOME/bin/nls_lang.sh`
   export ORACLE_BASE=/u01/app/oracle
   export LD_LIBRARY_PATH=$ORACLE_HOME/lib:$LD_LIBRARY_PATH
   export PATH=$ORACLE_HOME/bin:$PATH
   

10. Running the commands:

    chown -R oracle:dba /var/tmp/.oracle
    chmod -R 755 /var/tmp/.oracle
    chown -R oracle:dba /tmp/.oracle
    chmod -R 755 /tmp/.oracle
    

11. Starting Oracle Database 11g Express Edition instance:

    sudo service oracle-xe start 
    

12. sqlplus / as sysdba and got the following:

    SQL*Plus: Release 11.2.0.2.0 Production on Thu Jan 3 09:41:58 2013
    
    Copyright (c) 1982, 2011, Oracle. All rights reserved.
    
    Connected to an idle instance.
    

Now when exectuting any SQL statements on SQLplus, I end up with the following error:

SQL> select * from dual;
select * from dual
*
ERROR at line 1:
ORA-01034: ORACLE not available
Process ID: 0
Session ID: 0 Serial number: 0

I have increased the swap memory as specified here

$ free -m
total used free shared buffers cached
Mem: 3901 3428 473 0 182 1988
-/+ buffers/cache: 1258 2643
Swap: 5066 0 5066