How open oracle DB Linux (After installation)
First edit your /etc/oratab changing N to Y like that:

orcl:/u01/app/oracle/product/11.2.0/dbhome_1:N


Must be change to Y:

orcl:/u01/app/oracle/product/11.2.0/dbhome_1:Y


Then to start you must use the dbstart script like that: 

export ORACLE_HOME=youroraclehome
su oracle -c "$ORACLE_HOME/bin/dbstart $ORACLE_HOME"


Where "oracle" in the "su" command is the name of the user you used to install oracle. 

This will up all oracle essential services including the https port 1158 (and you can put that in an auto-start script) 

And to stop it: 

export ORACLE_HOME=youroraclehome
su oracle -c "$ORACLE_HOME/bin/dbshut $ORACLE_HOME" 


And to backup it (dump) ;-)

export ORACLE_HOME=youroraclehome
$ORACLE_HOME/bin/exp file=mybackup.dmp full=y 


Remember to test your backup before thinking its working.