首先使用SHUTDOWN 没加任何参数方式关闭数据库，在数据库未关闭时CTRL+Z停止执行，退出用SQLPLUS重登陆，出现报错：ORA-01012: not logged on
SQL> startup
ORA-01012: not logged on
解决 ：
SQL> shutdown abort
ORACLE instance shut down.
[oracle@oracle ~]$ ps -ef
le 11549 1 0 21:51 ? 00:00:00 /u01/app/oracle/product/11.2.0/d
root 11668 1 0 21:53 ? 00:00:00 su - oracle
oracle 11669 11668 0 21:53 ? 00:00:00 -bash
oracle 11853 1 0 22:05 ? 00:00:00 /u01/app/oracle/product/11.2.0/d
oracle 11980 10672 0 22:15 pts/0 00:00:00 ./sqlplus as sysdba
oracle 12006 11980 0 22:17 ? 00:00:00 oracleorcl2 (DESCRIPTION=(LOCAL=
root 12017 2627 0 22:18 ? 00:00:00 sleep 60
[oracle@oracle ~]$ kill -9 11980
SQL> 已杀死
[oracle@oracle ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Wed Mar 12 22:19:32 2014
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup
ORACLE instance started.
Total System Global Area 730714112 bytes
Fixed Size 2216944 bytes
Variable Size 452987920 bytes
Database Buffers 268435456 bytes
Redo Buffers 7073792 bytes
Database mounted.
Database opened.