There is a database which is online, I have to duplicate this database in another computer. How can I do this? I cannot make a cold database backup because the system run 24 hours.

Steps  to duplicate database from A to B online

1. do a  consistent hot backup in A. This consistent hot backup will include the  hot backup data files,  and the archive log files which are done just after the hot backup fiinished, and the create controlfile  in text format.

2 .copy all the above to machine B. change the create control file  accordingly for B, then create controlfile,
then do a recover database using backup controlf file until cancel,
just recover the archive log file  in the backup set , then cancel,
finaly , alter database open resetlogs.

you can use rman to  duplicate  a database in another computer;