Performing Oracle Advanced Recovery - OCP: Oracle Database 12c Administrator Certified Professional - page 293

You can use the DUPLICATE command to exclude tablespaces, as shown here:
Duplicate target database to neworcl nofilenamecheck spfile skip tablespace users;
You can also define a restore point, as shown in this example:
Duplicate target database to neworcl nofilenamecheck spfile skip
tablespace users to restore point 'Test';
You can have Oracle open the duplicated database in restricted mode by adding the OPEN
RESTRICTED parameter, as follows:
Duplicate target database to neworcl nofilenamecheck spfile open restricted;
As with pretty much everything else Oracle, the DUPLICATE command
is well documented. We strongly recommend that you review the Oracle
Database Backup and Recovery Reference (Oracle part number B28273-02)
for more information on all RMAN-related commands.
Active Database Duplication
When you perform standard RMAN database duplication, the server where the new data-
base is going to be created must have access to the RMAN backup set files of the target
database. This can be problematic if the systems do not have a way to share storage or if
security restrictions make maintaining NFS mounts impractical. Also, if the target data-
base has not yet been backed up, then you would not be able to duplicate it (this is a much
less frequent situation).
In cases like this, you can use an RMAN feature called Active Database Duplication.
Active Database Duplication sources the duplicate database creation from the target data-
base itself rather than from RMAN backup sets. Active Database Duplication uses the
network to move the data from the target database to the duplicate database being created
(thus, a network connection must be able to be established between the servers where the
target and duplicated database reside).
Active database duplication is started by issuing the RMAN DUPLICATE DATABASE
command and including the FROM ACTIVE DATABASE parameter. Active database duplica-
tion is not the default.
When you perform active database duplication, Oracle will create the auxiliary channel to
the auxiliary database. An additional target-database RMAN channel will also be required.
If you have configured automated channels, this should be sufficient. If not, you will need to
allocate a channel manually with the ALLOCATE CHANNEL command.
Finally, the UNTIL and TO RESTORE POINT clauses are not valid when doing an active
database duplication. Here is an example of the RMAN DUPLICATE command performing
an active database duplication:
duplicate target database to neworcl from active database nofilenamecheck
spfile set control_files 'c:\oracle\oradata\neworcl\control01.ctl',