4. Important exports ( if not setted )

# vi /etc/init.d/oracle-xe-18c
# DB defaults
export ORACLE_HOME=/opt/oracle/product/18c/dbhomeXE
export ORACLE_SID=XE
export TEMPLATE_NAME=XE_Database.dbc
export PDB_NAME=XEPDB1
export LISTENER_NAME=LISTENER
export NUMBER_OF_PDBS=1
export CREATE_AS_CDB=true
export PATH=$ORACLE_HOME/bin:$PATH