oracle ~ $ oerr TNS 12170
12170, 00000, "TNS:Connect timeout occurred"
// *Cause:  The server shut down because connection establishment or
// communication with a client failed to complete within the allotted time
// interval. This may be a result of network or system delays; or this may
// indicate that a malicious client is trying to cause a Denial of Service
// attack on the server.
// *Action: If the error occurred because of a slow network or system,
// reconfigure one or all of the parameters SQLNET.INBOUND_CONNECT_TIMEOUT,
// SQLNET.SEND_TIMEOUT, SQLNET.RECV_TIMEOUT in sqlnet.ora to larger values.
// If a malicious client is suspected, use the address in sqlnet.log to
// identify the source and restrict access. Note that logged addresses may
// not be reliable as they can be forged (e.g. in TCP/IP).

oracle ~ $ oerr TNS 12535
12535, 00000, "TNS:operation timed out"
// *Cause: The requested operation could not be completed within the time out
// period.
// *Action: Look at the documentation on the secondary errors for possible
// remedy. See SQLNET.LOG to find secondary error if not provided explicitly.
// Turn on tracing to gather more information.

oracle ~ $ oerr TNS 12560
12560, 00000, "TNS:protocol adapter error"
// *Cause: A generic protocol adapter error occurred.
// *Action: Check addresses used for proper protocol specification. Before
// reporting this error, look at the error stack and check for lower level
// transport errors. For further details, turn on tracing and reexecute the
// operation. Turn off tracing when the operation is complete.

oracle ~ $ oerr TNS 00505
00505, 00000, "Operation timed out"
// *Cause: The requested operation could not be completed within the timeout
// period.
// *Action: For further details, turn on tracing and reexecute the operation.

oracle ~ $ oerr TNS 110
00110, 00000, "Could not initialize network from file TNSNET.ORA"
// *Cause: Poorly formed network information in network file.
// *Action: Fix network configuration data to assure that at least one
// Interchange is defined in TNSNET.ORA.