Making this into a separate post. This is for the FREE DB build from the .ova image in Virtualbox. I needed to do some tweaking to get it to work properly, especially if you want to connect directly to the db (not via listener).
I found some issues with the FREE DB installed from the ova image on Virtualbox. The ORACLE_SID is really ‘FREE’ (uppercase) but some of the setup has it defined as ‘free’ (lowercase) which is causing issues if you try to connect directly since then your sqlplus client cannot find the SGA (causing ora-1034 etc.). Then there's the issue that there is a directory /home/oracle/LDLIB in PATH with scripts that wrap tools such as sqlplus first and set the ORACLE_SID and other values also to the lowercase ORACLE_SID. Also you need to ‘unset TWO_TASK’ to directly connect.
So a quick remedy is to edit /home/oracle/bin/dbenv and set
export ORACLE_SID=FREE
You can do the same with ~/.bashrc
The database runs from a service, if you run:
service oracle-free-26ai.service status
You can find the whole setup is initiated from /etc/rc.d/init.d/oracle-free-26ai