CONN / AS SYSDBA give ORA-01031 In windows, If you have such error: SQL> conn / as sysdba ERROR: ORA-01031: insufficient privileges Check the sqlnet.ora first SQLNET.AUTHENTICATION_SERVICES = (NTS) This allows any privileged user defined in the NT user group (named ORA_<sid>_DBA or ORA_DBA) to login to database without providing a password. To disable this, comment this line or change it to: SQLNET.AUTHENTICATION_SERVICES = (NONE) After solve this issue, open a new sqlplusw, you should able to see: SQL> conn / as sysdba Connected. SQL> Remarks: Following information can be found in the Application log with event viewer. Event Type: Information Event Source: Oracle.orcl Event Category: None Event ID: 34 Date: 8/8/2005 Time: 3:44:31 PM User: N/A Computer: AIX Description: The description for Event ID ( 34 ) in Source ( Oracle.orcl ) cannot be found. The local computer may not have the necessary registry information or message DLL files to display messages from a remote computer. You may be able to use the /AUXSOURCE= flag to retrieve this description; see Help and Support for details. The following information is part of the event: ACTION : 'CONNECT' DATABASE USER: '/' PRIVILEGE : NONE CLIENT USER: donghua CLIENT TERMINAL: AIX STATUS: 1031 .