A quick summary of what might go wrong when trying to connect to an Oracle database. Based on this excellent article. Read the whole thing, this is just a quick reference.
|ORA-12154||TNS:could not resolve the connect identifier specified||No entry with the requested name in tnsnames.ora|
|ORA-12545||Connect failed because target host or object does not exist||There is an entry in tnsnames.ora, but the hostname doesn’t resolve to an IP, or the IP is bad. The server can’t be reached|
|ORA-12541||TNS:no listener||All the above are OK, but there is no listener process running on the server we’re trying to connect to|
|ORA-12560||TNS:protocol adapter error||The connection to the server is OK, and there is a listener process on the target server, but it is running on a different port than that specified in the tnsnames.ora|
|ORA-12514||TNS:listener does not currently know of service requested in connect descriptor/td>||We got as far as connecting to the listener process on the server, but the service name in the tnsnames.ora is wrong|