ONLINE RMAN Backup ON STANDBY

If backup is scheduled from Standby and database is read only with apply 

nohup rman target / cmdfile=ABC_bkp.sh log=ABC_bkp.log &

vi ABC_bkp.sh
run
{
ALLOCATE CHANNEL D1 DEVICE TYPE DISK;
ALLOCATE CHANNEL D2 DEVICE TYPE DISK;
ALLOCATE CHANNEL D3 DEVICE TYPE DISK;
ALLOCATE CHANNEL D4 DEVICE TYPE DISK;
ALLOCATE CHANNEL D5 DEVICE TYPE DISK;
backup incremental level 0 tag backup_db_level_0 format '/rman_backup/ABC_RESTORE/CHG0013712/dblevel0_%d.%s_%p_%t' database;
backup archivelog all format '/rman_backup/ABC_RESTORE/CHG0013712/arch_%d.%s_%p_%t';
backup current controlfile format '/rman_backup/ABC_RESTORE/CHG0013712/ctlfile_%d.%s_%p_%t';
release channel D1;
release channel D2;
release channel D3;
release channel D4;
release channel D5;
}