ORA-20000: ORU-10027: buffer overflow, limit of 2000 bytes

Error:
ORA-20000: ORU-10027: buffer overflow, limit of 20000 bytes
ORA-06512: at “SYS.DBMS_OUTPUT”, line 32

Solution:

The default buffer sizes depend on the oracle version. In the above case the limit was 2000 bytes.
You can increase the buffer size up to 1,000,000.
Pl/SQL: DBMS_OUTPUT.ENABLE(100000)
SQL*Plus: set serveroutput on size 1000000

From Oracle 10g, it is possible to make the buffer size unlimited:
PL/SQL: DBMS_OUTPUT.ENABLE (buffer_size => NULL);
SQL*Plus: set serveroutput on size unlimited