It seems that I'm not connected to localhost:2333, how can I verify or just know what is my RPC?
I think you must unlocked that tcp (local host connection) first.
Try these following steps (and for security purpose) as root :
ufw status
if result "inactive", then type :
ufw enable
then type "Y".
Then type :
ufw allow 2333/tcp
then try restart your cpuminer