--关闭数据库，需要将数据库打开到mount状态才能开启闪回功能：

SQL> shutdown immediate

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> show user

USER is "SYS"

SQL> exit

Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production

With the Partitioning, OLAP and Data Mining options

[lubinsu@localhost oracle]$ sqlplus sys/lubinsu as sysdba

SQL*Plus: Release 10.2.0.1.0 - Production on Sat Mar 23 20:14:38 2013

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> show parameter database

ORA-01034: ORACLE not available