A Way To Create Another Database Instance In Oracle 8.1.6

There are a few ways of doing this, but this is the one I did most recently and now I know how to do it, it's easy enough. My assumptions for this procedure are:

Create a user

Login as root. Create a new Unix user that you will use to administer the instance:
useradd newuser
passwd newuser
cp /home/oracle/.bash_profile /home/newuser/.bash_profile.
vi /home/newuser/.bash_profile
Change the Oracle SID in this file to the SID of your new instance (Click here for help with vi).

Give the user access to Oracle

We're not oracle, so we need to change a few permissions to be able to run Oracle. You would've thought that being in the dba group, we could just set the group permissions, but this didn't work for me so I'm going for the whole 777. Log in as newuser to set your new environment variables, then:
chmod 777 $ORACLE_BASE/admin
chmod 777 $ORACLE_HOME/dbs
chmod 777 $ORACLE_BASE/oradata
chmod 777 /etc/oratab
You should now be newuser. In X Window, run dbassist (found in $ORACLE_HOME/bin) and follow your normal database creation procedure. Make sure you note the location of any datafiles, control files and redo logs. When you've finished, save to a script and exit X Window.

As root do a chmod 777 on the directories that your datafiles, control files and redo logs are in. Also

chown oracle:dba $ORACLE_HOME/dbs/orapwnewSID

Create the new database instance

Finally, as newuser run the script you saved and make yourself a brew.