TNS-12547: TNS:lost contact , Linux Error: 104: Connection reset by peer

TNS-12547: TNS:lost contact 

  TNS-12560: TNS:protocol adapter error 
    TNS-00517: Lost contact 
      Linux Error: 104: Connection reset by peer

TNS-12537: TNS:connection closed 
  TNS-12560: TNS:proto adapter error 
    TNS-00507: Connection closed 
      Linux Error: 29: Illegal seek



Make sure the following loop back entries exist in /etc/hosts file. If the Operating system configured with IPV6 then you need to add second line as well. Start the listener after adding the following entries.  For more information please check Doc ID 960152.1 from Oracle Support. localhost.localdomain localhost 

   ::1 localhost6.localdomain localhost6