The Following script is very much helpful to generate script for DB Links created in the server.
SELECT 'create '||DECODE(U.NAME,'PUBLIC','public ')||'database link '||CHR(10)
||DECODE(U.NAME,'PUBLIC',Null, U.NAME||'.')|| L.NAME||chr(10)
||'connect to ' || L.USERID || ' identified by '
||L.PASSWORD||' using ''' || L.host || ''''
||chr(10)||';' TEXT
FROM sys.link$ L, sys.user$ U
WHERE L.OWNER# = U.USER#;