[oracle@vbgeneric backup]$ sqlplus /nolog
SQL*Plus: Release 12.1.0.2.0 Production on Mon Oct 17 17:11:37 2016
Copyright (c) 1982, 2014, Oracle. All rights reserved.
SQL> connect sys/oracle@localhost:1521/orcl12c as sysdba
Connected.
SQL> SHUTDOWN
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> STARTUP MOUNT
ORACLE instance started.
Total System Global Area 838860800 bytes
Fixed Size 2929936 bytes
Variable Size 608176880 bytes
Database Buffers 222298112 bytes
Redo Buffers 5455872 bytes
Database mounted.
SQL> ALTER DATABASE ARCHIVELOG;
Database altered.
SQL> ALTER DATABASE OPEN;
Database altered.
SQL> SELECT LOG_MODE FROM SYS.V$DATABASE;
LOG_MODE
————
ARCHIVELOG
SQL>