Automatically start oracle database on linux after server reboot

Here I'll show you how to configure system for automatically start oracle database after server reboot.
oracle database 11g --- Oracle Linux 6.3
First of all, you need to make sure that any database instances you want to auto start are set to "Y" in the /etc/oratab file

#
# This file is used by ORACLE utilities.  It is created by root.sh
# and updated by either Database Configuration Assistant while creating
# a database or ASM Configuration Assistant while creating ASM instance.

# A colon, ':', is used as the field terminator.  A new line terminates
# the entry.  Lines beginning with a pound sign, '#', are comments.
#
# Entries are of the form:
#   $ORACLE_SID:$ORACLE_HOME::
#
# The first and second fields are the system identifier and home
# directory of the database respectively.  The third filed indicates
# to the dbstart utility that the database should , "Y", or should not,
# "N", be brought up at system boot time.
#
# Multiple entries with the same $ORACLE_SID are not allowed.
#
#
orcl:/u0/app/oracle/product/11.2.0/dbhome_1:Y

Oracle 11g includes 2 scripts which can be used to start or shut down Oracle databases on Linux. Both scripts are in $ORACLE_HOME/bin and called dbstart and dbshut. We can add some more actions for example start enterprise manager if we create our scripts. Let's make two scripts db_start.sh and db_stop.sh
vi /u0/app/oracle/db_start.sh

# script to start the Oracle database, listener and dbconsole
. ~/.bash_profile
# start the listener and the database
$ORACLE_HOME/bin/dbstart $ORACLE_HOME
# start the Enterprise Manager db console
$ORACLE_HOME/bin/emctl start dbconsole
exit 0

vi /u0/app/oracle/db_stop.sh

# script to stop the Oracle database, listener and dbconsole
. ~/.bash_profile
# stop the Enterprise Manager db console
$ORACLE_HOME/bin/emctl stop dbconsole
# stop the listener and the database
$ORACLE_HOME/bin/dbshut $ORACLE_HOME
exit 0

inside script we are calling the .bash_profile file of the user "oracle" for export environment variables, we need it for $ORACLE_HOME.
give execute right:
chmod u+x db_start.sh db_stop.sh
With user root, create a file called "oracle" under /etc/init.d
vi /etc/init.d/oracle

ORA_OWNER=oracle
RETVAL=0
 
case "$1" in
    'start')
        # Start the Oracle databases:
        su - $ORA_OWNER -c "/u0/app/oracle/db_start.sh"
        touch /var/lock/subsys/oracle
        ;;
    'stop')
        # Stop the Oracle databases:
        su - $ORA_OWNER -c "/u0/app/oracle/db_stop.sh"
        rm -f /var/lock/subsys/oracle
        ;;
    *)
        echo $"Usage: $0 {start|stop}"
        RETVAL=1
esac
exit $RETVAL

change permission for /etc/init.d/oracle file:
chmod 750 /etc/init.d/oracle
to create service of this script:

chkconfig --add oracle

and now we can start and stop database with:

service oracle stop
service oracle start

Now it's time to test our automatically startup procedure, for this reboot your server and check if your database starts automatically after reboot.