How does one do off-line database backups?

Shut down the database from sqlplus or server manager. Backup all files to secondary storage (eg. tapes). Ensure that you backup all data files, all control files and all log files. When completed, restart your database.

Do the following queries to get a list of all files that needs to be backed up:

select name from sys.v_$datafile;
select member from sys.v_$logfile;
select name from sys.v_$controlfile;

Sometimes Oracle takes forever to shutdown with the "immediate" option. As workaround to this problem, shutdown using these commands:

alter system checkpoint;
shutdown abort
startup restrict
shutdown immediate

Note that if you database is in ARCHIVELOG mode, one can still use archived log files to roll forward from an offline backup. If you cannot take your database down for a cold (off-line) backup at a convenient time, switch your database into ARCHIVELOG mode and perform hot (on-line) backups.