oracle 12c gives ORA-01017: invalid username/password; logon denied while sqlplus / as sysdba

[oracle@localhost ~]$ sqlplus / as sysdba
SQL*Plus: Release 12.1.0.1.0 Production on Wed Jan 6 00:37:18 2016
Copyright (c) 1982, 2013, Oracle.  All rights reserved.
ERROR:
ORA-01017: invalid username/password; logon denied

Enter user-name: ^C
[oracle@localhost ~]$
[oracle@localhost ~]$
[oracle@localhost ~]$ sqlplus sys/oracle as sysdba
SQL*Plus: Release 12.1.0.1.0 Production on Wed Jan 6 00:37:30 2016
Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
PDB1@ORCL>
PDB1@ORCL> show con_name
CON_NAME
------------------------------
PDB1
PDB1@ORCL> Disconnected from Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
[oracle@localhost ~]$
[oracle@localhost ~]$
[oracle@localhost ~]$ echo $TWO_TASK
pdb1
[oracle@localhost ~]$ TWO_TASK=
[oracle@localhost ~]$ echo $TWO_TASK
[oracle@localhost ~]$
[oracle@localhost ~]$ sqlplus / as sysdba
SQL*Plus: Release 12.1.0.1.0 Production on Wed Jan 6 00:38:02 2016
Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
CDB$ROOT@ORCL> show con_name
CON_NAME
------------------------------
CDB$ROOT
CDB$ROOT@ORCL>