TNS-12547: TNS:lost contact
TNS-12560: TNS:protocol adapter error
TNS-00517: Lost contact
Linux Error: 104: Connection reset by peer
or
TNS-12537: TNS:connection closed
TNS-12560: TNS:proto adapter error
TNS-00507: Connection closed
Linux Error: 29: Illegal seek
Solution:
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.
127.0.0.1 localhost.localdomain localhost
::1 localhost6.localdomain localhost6