Using the steps below one take cold backup using RMAN. As it’s a cold backup the database as the database is in mount stage the database doesn’t have to be archivelog so cold backup can taken for a database which is in noarchivelog mode too.

Step 1) Shutdown database

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.

Step 2) Start database in mount stage

SQL> startup mount;
ORACLE instance started.

Total System Global Area 167772160 bytes
Fixed Size 2019320 bytes
Variable Size 75497480 bytes
Database Buffers 88080384 bytes
Redo Buffers 2174976 bytes

Step 3) Run rman and connect to target database and run rman to backup database and connection to catalog if you are using one
$ $ORACLE_HOME/bin/rman target /

Recovery Manager: Release 10.2.0.1.0 – Production on Fri Apr 23 02:33:38 2010

Copyright (c) 1982, 2005, Oracle. All rights reserved.

connected to target database: TEST (DBID=1992878807, not open)

RMAN> backup database include current controlfile;

Starting backup at 23-APR-10
..
using target database control file instead of recovery catalog
released channel: ORA_DISK_1
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=35 devtype=DISK
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00003 name=/u01/oradata/TEST/sysaux_01.dbf
input datafile fno=00001 name=/u01/oradata/TEST/system_01.dbf
input datafile fno=00004 name=/u01/oradata/TEST/test_01.dbf
input datafile fno=00002 name=/u01/oradata/TEST/undo_01.dbf
…