Create an init Script to make Oracle start automatically on system booting.
[1] Set environment variables for "oracle" user like follows.
[oracle@dlp ~]$ vim /etc/oratab
# end line: change
orcl:/u01/app/oracle/product/12.2.0/dbhome_1:Y

[oracle@dlp ~]$ vim ~/.bash_profile
# add follows to the end
export ORACLE_SID=orcl

[2] Create an init Script with the root user.
[root@dlp ~]# vim /etc/rc.d/init.d/oracle
# it's an example, edit it you like.
#!/bin/bash
# oracle: Start/Stop Oracle Database 12c R2
#
# chkconfig: 345 90 10
# description: The Oracle Database is an Object-Relational Database Management System.
#
# processname: oracle
. /etc/rc.d/init.d/functions
LOCKFILE=/var/lock/subsys/oracle
ORACLE_HOME=/u01/app/oracle/product/12.2.0/dbhome_1
ORACLE_USER=oracle

case "$1" in
'start')
if [ -f $LOCKFILE ]; then
echo $0 already running.
exit 1
fi
echo -n $"Starting Oracle Database:"
su - $ORACLE_USER -c "$ORACLE_HOME/bin/lsnrctl start"
su - $ORACLE_USER -c "$ORACLE_HOME/bin/dbstart $ORACLE_HOME"
touch $LOCKFILE
;;

'stop')
if [ ! -f $LOCKFILE ]; then
echo $0 already stopping.
exit 1
fi
echo -n $"Stopping Oracle Database:"
su - $ORACLE_USER -c "$ORACLE_HOME/bin/lsnrctl stop"
su - $ORACLE_USER -c "$ORACLE_HOME/bin/dbshut"
rm -f $LOCKFILE
;;

'restart')
$0 stop
$0 start
;;

'status')
if [ -f $LOCKFILE ]; then
echo $0 started.
else
echo $0 stopped.
fi
;;

*)
echo "Usage: $0 [start|stop|status]"
exit 1
esac
exit 0

[root@dlp ~]# chmod 755 /etc/init.d/oracle && chkconfig --add oracle && chkconfig oracle on