RMAN-03002 RMAN-05501 RMAN-03015 RMAN-03009 ORA-17629 ORA-17627 ORA-27101 ORA-17629 duplicate target database for standby from active database

In 12c , try to duplicate a standby database with below errors:

channel ORA_DISK_1: SID=158 device type=DISK
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of Duplicate Db command at 01/15/2019 18:35:32
RMAN-05501: aborting duplication of target database
RMAN-03015: error occurred in stored script Memory Script
RMAN-03009: failure of backup command on ORA_DISK_1 channel at 01/15/2019 18:35:32
ORA-17629: Cannot connect to the remote database server
ORA-17627: ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux-x86_64 Error: 2: No such file or directory
Additional information: 3651
Additional information: -603812709
ORA-17629: Cannot connect to the remote database server

WORKAROUND

In tnsnames.ora of both primary and standby database server, add  “(UR = A)” for the standby database entry :

TESTDBSTY =
(DESCRIPTION =
   (ADDRESS = (PROTOCOL = TCP)(HOST = hostname)(PORT = 1521))
   (CONNECT_DATA = (SERVICE_NAME = TESTDBSTY)(UR=A))
)