-- on new standby database

alter system set db_name='<primary_db_name>' scope=spfile sid='*';
alter system set db_unique_name='<standby_db_unique_name>' scope=spfile sid='*';

-- duplicate using RMAN
rman auxiliary /

run
{
  allocate auxiliary channel aux01 device type disk;
  allocate auxiliary channel aux02 device type disk;
  allocate auxiliary channel aux03 device type disk;
  allocate auxiliary channel aux04 device type disk;
  allocate auxiliary channel aux05 device type disk;
  allocate auxiliary channel aux06 device type disk;
  allocate auxiliary channel aux07 device type disk;
  allocate auxiliary channel aux08 device type disk;
  allocate auxiliary channel aux09 device type disk;
  allocate auxiliary channel aux10 device type disk;
  duplicate database '<primary_db_name>' for standby backup location '<local_copy_of_primary_db_backup>';
}