Karan Rajpoot Oracle DBA Blog's

         TNS-12547: TNS:lost contact TNS-12560: TNS:protocol adapter error TNS-00517: Lost contact Error: - "TNS-12547: TNS: lost contact TNS-12560: TNS: protocol adapter error TNS-00517: Lost contact" Cause: - This error occurs when loopback entries have been missed in the /etc/hosts file. Solution: - To resolve this error you need to put the loopback entries in the /etc/hosts file. Example: -  [oracle@prod bin]$ lsnrctl start LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 14-APR-2019 22:08:16 Copyright (c) 1991, 2013, Oracle.  All rights reserved. Starting /u02/app/oracle/product/11.2.0/db_1/bin/tnslsnr: please wait... TNSLSNR for Linux: Version 11.2.0.4.0 - Production System parameter file is /u02/app/oracle/product/11.2.0/db_1/network/admin/listener.ora Log messages written to /u02/app/oracle/diag/tnslsnr/prod/listener/alert/log.xml Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=prod.radical.com)(PORT=1521))) C

To resolve "TNS-12541: TNS: no listener" error we need to check whether our listener is up and running. Step 1) To check whether our listener is up or running, we need to run below command Command : - ps -ef | grep tns Example: - Note: - In this case, my listener is not started,  So I need to start my listener Step 2) To start the listener, we need to run below command Command : - lsnrctl start Example: - Step 3) Now again check the status of listener whether it is up and running, It should be up and running Command: - ps -ef | grep tns Example: - Note: - Now my listener is up and running properly