orclz>
orclz> alter user system grant connect through scott;

User altered.

orclz> create database link l1 connect to "SCOTT[SYSTEM]" identified by tiger using 'orclz';

Database link created.

orclz>
orclz> select * from global_name@l1;
select * from global_name@l1
                          *
ERROR at line 1:
ORA-01017: invalid username/password; logon denied
ORA-02063: preceding line from L1


orclz> alter session set events '19191702 level 1';

Session altered.

orclz> select * from global_name@l1;
select * from global_name@l1
                          *
ERROR at line 1:
ORA-01017: invalid username/password; logon denied
ORA-02063: preceding line from L1


orclz>