Error creating linked database to oracle
In a database link, you should use the net_service_name, i.e. the OPT string, instead of SERVICE_NAME identifier.

EDIT:

Example:

cat tnsnames.ora|grep TEST
TESTNS=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(Host=THE_HOST)(Port=THE_PORT)))(CONNECT_DATA=(SID=THE_SID)))

oracle@hostname&gt; export ORACLE_SID=ANOTHER_SID
oracle@hostname&gt; sqlplus username
Enter password: 
Connected to:
&lt;few lines of sqlplus banner&gt;
SQL&gt; create database link lll connect to &lt;the_username&gt; identified by &lt;the_password&gt; using 'testns';
Database link created.
SQL&gt; select * from global_name@lll;

GLOBAL_NAME
--------------------------------------------------------------------------------
&lt;the_global_name&gt;

SQL&gt;