SQL> select open_mode from v$database;

OPEN_MODE
----------
READ WRITE

SQL> show user
USER is "SYS"
SQL> select table_name from dictionary where table_name like '%LINK%';

TABLE_NAME
------------------------------
USER_DB_LINKS
ALL_DB_LINKS
DBA_DB_LINKS
V$DBLINK
GV$DBLINK

SQL> select count(*) from DBA_DB_LINKS;
select count(*) from DBA_DB_LINKS
                     *
ERROR at line 1:
ORA-00942: table or view does not exist

SQL> grant dba to a identified by a;

Grant succeeded.

SQL> create database link db_link_a connect to a identified by a using 'CANADA';

Database link created.

SQL> select sysdate from dual@db_link_a;

SYSDATE
---------
03-JUL-06

SQL> select count(*) from dba_db_links;
select count(*) from dba_db_links
                     *
ERROR at line 1:
ORA-00942: table or view does not exist

SQL> select count(*) from all_db_links;

  COUNT(*)
----------
         1

SQL> select banner from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE    10.2.0.1.0      Production
TNS for 32-bit Windows: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production