When use RMAN duplicate command to create a copy of source database on a different host or a physical standby database, usually we specify the option “NOFILENAMECHECK” to avoid error messages.
However an interesting thing is that starting from Oracle 19c – 22.214.171.124.0, you will see a warning message
RMAN-05158: WARNING: auxiliary (datafile) file name <file name> conflicts with a file used by the target database
if “NOFILENAMECHECK” is used.
Apparently Oracle has thought the option is dangerous and wanted to give a warning so that users do the due diligence to make sure the target (source) database is safe.
So if the auxiliary database is on a different host, and there is NO shared volumes etc, the warning message can be ignored.