Oracle11g RAC + DG 搭建过程中，在备库进行 duplicate时报错如下：
[oracle@xxxx-dg:/u01/app/oracle/11.2/db_1/dbs]$rman target sys/password@racdb auxiliary sys/password@racdg nocatalog
Recovery Manager: Release 11.2.0.4.0 - Production on Fri Abc 21 17:33:01 xxxx
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.
connected to target database: RACDB (DBID=938466123)
using target database control file instead of recovery catalog
connected to auxiliary database (not started)
RMAN> duplicate target database for standby from active database nofilenamecheck;
Starting Duplicate Db at xxxx-xx-21 17:33:04
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of Duplicate Db command at xx/21/xxxx 17:33:05
RMAN-05501: aborting duplication of target database
RMAN-06403: could not obtain a fully authorized session
RMAN-04006: error from auxiliary database: ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux-x86_64 Error: 2: No such file or directory
RMAN> exit通过
RMAN-04006: error from auxiliary database: ORA-01034: ORACLE not availableORA-27101: shared memory realm does not exist
Linux-x86_64 Error: 2: No such file or directory可看到，由于连接数据库失败导致的，回头发现，之前通过Rman连接数据库时，备库已经是启动到nomount状态了，但是当进行
RMAN> duplicate target database for standby from active database nofilenamecheck;时，备库不知由于什么原因down掉了，查看alert日志，发现确实在RMAN连接上之后，备库nomount启动之后，数据库进行过shutdown immediate操作，重新将数据库启动至nomount状态，startup nomount。再次进行
duplicate未报同样错误
