@PRIMARY

SQL> select DB_UNIQUE_NAME,OPEN_MODE,DATABASE_ROLE from v$database;

DB_UNIQUE_NAME OPEN_MODE DATABASE_ROLE
------------------------------ -------------------- ----------------
PRIM READ WRITE PRIMARY
@ STANDBY
SQL> select name,OPEN_MODE,DATABASE_ROLE from v$database;

NAME OPEN_MODE DATABASE_ROLE
--------- -------------------- ----------------
STANDBY READ ONLY WITH APPLY PHYSICAL STANDBY

SQL> recover managed standby database cancel;
Media recovery complete.

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.

Total System Global Area 1.3935E+10 bytes
Fixed Size 6002112 bytes
Variable Size 4630514240 bytes
Database Buffers 9193914368 bytes
Redo Buffers 104153088 bytes
Database mounted.

rman target /

Recovery Manager: Release 12.1.0.1.0 - Production on Tue Oct 18 18:04:15 2016

Copyright (c) 1982, 2013, Oracle and/or its affiliates. All rights reserved.

connected to target database: STANDBY (DBID=599956155, not open)

RMAN> restore datafile 4 from service PRIM;

Starting restore at 18-OCT-16
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=705 device type=DISK

channel ORA_DISK_1: starting datafile backup set restore
channel ORA_DISK_1: using network backup set from service PRIM
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
channel ORA_DISK_1: restoring datafile 00004 to /archive/PRIM/PRIM/users01.dbf
channel ORA_DISK_1: restore complete, elapsed time: 00:00:01
Finished restore at 18-OCT-16

SQL> recover managed standby database using current logfile disconnect from session;
Media recovery complete.

SQL> recover managed standby database cancel;
Media recovery complete.
SQL> shutdown immediate;
ORA-01109: database not open


Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 1.3935E+10 bytes
Fixed Size 6002112 bytes
Variable Size 4630514240 bytes
Database Buffers 9193914368 bytes
Redo Buffers 104153088 bytes
Database mounted.
Database opened.

SQL> recover managed standby database using current logfile disconnect from session;
Media recovery complete.
Now all datafiles are online :
SQL> select file_name from dba_data_files;

FILE_NAME
--------------------------------------------------------------------------------
/archive/PRIM/PRIM/system01.dbf
/archive/PRIM/PRIM/sysaux01.dbf
/archive/PRIM/PRIM/undotbs01.dbf
/archive/PRIM/PRIM/users01.dbf