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 bin]$ 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 bin]$ kill -9 11980
SQL> 已杀死
[oracle@oracle bin]$ ./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.

未完全关闭数据库导致ORA-01012: not logged的解决