SQL*Plus Connection fails with following error.
SQL> connect sys/welcome
ERROR: connection as SYS should be as SYSDBA or SYSOPER
The error description itself is clear.
If you try to connect as sys using SQL*plus it should be either SYSDBA or SYSOPER. From Oracle 9i onwards, this has been implemented in Oracle. All other users will work as normal with username and password.
SQL> connect sys as sysoper
SQL> connect sys as sysdba