Listener and service are up and running. In SQL Plus, if I connect with no login, and execute 'conn sys/pwd@host:port/sid as sysdba', connection is established successfully. But if I connect / as sysdba or with username and password , it always throws ORA-12560: TNS:protocol adapter error. What are the possible reasons for this ?

  • ORACLE_SID is not set properly. – Balazs Papp May 25 '20 at 21:32
  • Yeah, my mistake. ORACLE_SID was not available in registry – Aegon May 26 '20 at 11:26

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