RMAN>
duplicate target database to clonedb from active database;

Starting
Duplicate Db at 28-JAN-16

RMAN-00571:
===========================================================

RMAN-00569:
=============== ERROR MESSAGE STACK FOLLOWS ===============

RMAN-00571:
===========================================================

RMAN-03002:
failure of Duplicate Db command at 01/28/2016 19:56:12

RMAN-06217: not connected to auxiliary database with a
net service name

RMAN>
quit

解决办法：

登录方式不对，为rman target sys/MANAGER@orcl auxiliary sys/MANAGER@clonedb 即可