Oracle Connection Error Messages

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.

Error Code Message Translation
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