[root@sgyyhdb2 ~]# su - oracle
[oracle@sgyyhdb2 ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Fri Jan 30 03:27:38 2015

Copyright (c) 1982, 2013, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options

SQL> alter user system account unlock;

User altered.

SQL>