I am trying to clone the database using RMAN backup from Standby database(readonly) but i am facing with below issue. I tried without nofilenamecheck also.
RMAN> duplicate target database to oas nofilenamecheck;
Starting Duplicate Db at 26-OCT-12
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
database mounted
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of Duplicate Db command at 10/26/2012 13:28:51
RMAN-05501: aborting duplication of target database
RMAN-05001: auxiliary file name /oracle/app/oradata/oas/oas.dbf conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/oradata/oas/users01.dbf conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/oradata/oas/undotbs01.dbf conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/oradata/oas/sysaux01.dbf conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/oradata/oas/system01.dbf conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/flash_recovery_area/OAS_REP/onlinelog/o1_mf_10_7xgyw7gg_.log conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/flash_recovery_area/OAS_REP/onlinelog/o1_mf_9_7xgyw6h6_.log conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/flash_recovery_area/OAS_REP/onlinelog/o1_mf_8_7xgyw5hl_.log conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/flash_recovery_area/OAS_REP/onlinelog/o1_mf_7_7xgyw4jj_.log conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/flash_recovery_area/OAS_REP/onlinelog/o1_mf_6_7xgyw3kt_.log conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/flash_recovery_area/OAS_REP/onlinelog/o1_mf_5_7xgyw2kn_.log conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/flash_recovery_area/OAS_REP/onlinelog/o1_mf_4_7xgyw1o6_.log conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/oradata/oas/redo03.log conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/oradata/oas/redo02.log conflicts with a file used by the target database
RMAN-05001: auxiliary file name /oracle/app/oradata/oas/redo01.log conflicts with a file used by the target database
>>RMAN-05001: auxiliary file name /oracle/app/oradata/oas/redo01.log conflicts with a file used by the target database
Above error indicates that you are using cloning on same host or target host already has same files present. Most likely oas db is in open mode while you are trying to clone it again