Last week I was creating a new testing database from a backup of our demo database, both under Oracle 188.8.131.52. I grabbed one of my old scripts to handle the duplicate function, which looked similar to this:
connect auxiliary /;
duplicate database to testdb
backup location '$BACKUPDIR'
One important difference between the demo database and this new test database is that the original demo database lives on a filesystem and the new database was to go onto ASM on a different host. I had copied the syntax from the old script and kicked it off. I made sure that the db_create_file_dest was set to the ASM diskgroup. However the restore would fail as RMAN tried to write to the filesystem path used by the original demo database, which didn't exist on this host, instead of the ASM diskgroup.