BACKUP DATABASE LINK IN ORACLE

Database links backup
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All DBlinks backup:
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set pages 0
set long 90000
set trimspool on
SELECT u.OWNER,DBMS_METADATA.GET_DDL('DB_LINK',u.DB_LINK,u.OWNER) FROM dba_db_links u;

For a specific DBlink backup:
---------------------------------
set pages 0
set long 90000
set trimspool on
SELECT DBMS_METADATA.GET_DDL('DB_LINK','&DB_LINK_NAME','&USER_NAME') FROM dba_db_links;