方法一：
[oracle@odd-oelr4u8~]$ rman target sys/oracle@PROD1521 catalogcatalog_admin/catalog_admin@PROD21521

RecoveryManager: Release 10.2.0.1.0 - Production on Mon Jan 20 07:56:30 2014

Copyright(c) 1982, 2005, Oracle. All rightsreserved.

connectedto target database: PROD (DBID=248672105)
connectedto recovery catalog database
该方法指定catalog库并连接了target库，是一种CATALOG Mode

方法二：
[oracle@odd-oelr4u8~]$ rman target sys/oracle@PROD1521
RMAN>connect catalog catalog_admin/catalog_admin@PROD21521

connectedto recovery catalog database
该方法先连接target库，再指定catalog库，也是一种CATALOG Mode

方法三：
[oracle@odd-oelr4u8~]$rman
RMAN>connect target sys/oracle@PROD1521

connectedto target database: PROD (DBID=248672105)
RMAN>connect catalog catalog_admin/catalog_admin@PROD21521

connectedto recovery catalog database
该方法先连接rman，再指定连接target库，再指定catalog库，也是一种CATALOG Mode

方法四：
[oracle@odd-oelr4u8~]$ rman

RecoveryManager: Release 10.2.0.1.0 - Production on Mon Jan 20 07:59:21 2014

Copyright(c) 1982, 2005, Oracle. All rightsreserved.

RMAN>connect target sys/oracle@PROD1521

connectedto target database: PROD (DBID=248672105) --有dbid证明已连接到目标库

RMAN>show all;

using target database control file instead of recovery catalog --使用控制文件来代替恢复目录数据库存放rman元数据信息
RMANconfiguration parameters are:
CONFIGURERETENTION POLICY TO RECOVERY WINDOW OF 30 DAYS;
CONFIGUREBACKUP OPTIMIZATION ON;
CONFIGUREDEFAULT DEVICE TYPE TO DISK; # default
CONFIGURECONTROLFILE AUTOBACKUP ON;
CONFIGURECONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO'/home/oracle/backup/control/controlfile_%F';
CONFIGUREDEVICE TYPE DISK PARALLELISM 2 BACKUP TYPE TO BACKUPSET;
CONFIGUREDATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGUREARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURECHANNEL DEVICE TYPE DISK FORMAT '/home/oracle/backup/PROD_%U';
CONFIGUREMAXSETSIZE TO UNLIMITED; # default
CONFIGUREENCRYPTION FOR DATABASE OFF; # default
CONFIGUREENCRYPTION ALGORITHM 'AES128'; # default
CONFIGUREARCHIVELOG DELETION POLICY TO NONE; # default
CONFIGURESNAPSHOT CONTROLFILE NAME TO'/u01/app/oracle/product/10.2.0/db_1/dbs/snapcf_PROD.f'; # default

RMAN>connect catalog catalog_admin/catalog_admin@PROD21521

RMAN-00571:===========================================================
RMAN-00569:=============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571:===========================================================
RMAN-06445:cannot connect to recovery catalog after NOCATALOG has been used
这种情况是在连接target库之后，做了其他的非连接catalog库的动作，因此系统默认的是NO CATALOG MODE，系统已经默认使用controlfile作为知识库，再相连接catalog库就报错了
如果想再次使用catalog库，并将controlfile中的内容同步到catalog库中，则需要重新连接target和catalog，并作同步如下：
采用如上方法一、二、三中的任何一种方式连接target和catalog后，在rman中执行：
RMAN>resync catalog;

startingfull resync of recovery catalog
fullresync complete