这篇文章主要介绍sqlplus中prelim / as sysdba宕机且无法进入怎么办，文中介绍的非常详细，具有一定的参考价值，感兴趣的小伙伴们一定要看完！
遇到一个系统，数据库无法正常运行，查看数据库的进程发现数据库已宕，结果如下：
[oracle@xiaowu ~]$ ps -ef | grep ora_
oracle 6218 6161 0 09:39 pts/2 00:00:00 grep ora_
用超级管理员用户登录数据库时，系统报 ORA-00020 的错误，很奇怪，数据库未启动，还报进程数超上限的错误。
[oracle@xiaowu ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Wed Oct 23 10:48:12 2013
Copyright (c) 1982, 2009, Oracle. All rights reserved.
ERROR:
ORA-00020:maximum number of processes (500) exceeded
Enter user-name:
解决 ORA-00020 错误，加大processes的参数值即可，但是需要正常启动数据库并成功登陆后才能修改，但是现在数据库都无法正常启动，一时想不到解决方法，最后求助资深DBA解决，方法如下：
首先通过加参数 “-prelim” 成功登陆数据库
[oracle@xiaowu ~]$ sqlplus -prelim / as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Wed Oct 23 11:10:09 2013
Copyright (c) 1982, 2009, Oracle. All rights reserved.
SQL>
此时就可以正常关闭和开启数据库，安装如下命令操作解决问题：
shutdown immediate;
startup;
show parameter processes;
alter system set processes=1000 scope=spfile;
startup force;
show parameter processes;
exit;
************************************************************************************************
未完全关闭数据库导致ORA-01012: not logged的解决
首先使用SHUTDOWN NORMAL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
实验如下：
首先执行
SYS@bys1>shutdown
ORA-01013: user requested cancel of current operation
[oracle@bys001 ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Sat Sep 7 09:05:08 2013
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected.
ERROR:
ORA-01012: not logged on
Process ID: 0
Session ID: 0 Serial number: 0
SYS@bys1>startup
ORA-01012: not logged on
SYS@bys1>conn / as sysdba
Connected to an idle instance.
ERROR:
ORA-01012: not logged on
Process ID: 0
Session ID: 0 Serial number: 0
SYS@bys1>conn bys/bys
ERROR:
ORA-01090: shutdown in progress - connection is not permitted
Process ID: 0
Session ID: 0 Serial number: 0
Warning: You are no longer connected to ORACLE.
解决方法：
找到进程，kill掉就可以了。
[oracle@bys001 ~]$ ps -ef |grep ora_dbw0_
oracle 6519 1 0 Sep06 ? 00:00:15 ora_dbw0_bys1
oracle 20947 20924 0 09:08 pts/0 00:00:00 grep ora_dbw0_
[oracle@bys001 ~]$ kill -9 6519
[oracle@bys001 ~]$ ps -ef |grep ora_dbw0_
oracle 20949 20924 0 09:08 pts/0 00:00:00 grep ora_dbw0_
[oracle@bys001 ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Sat Sep 7 09:08:22 2013
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to an idle instance.
SYS@bys1>startup
ORACLE instance started.
Total System Global Area 631914496 bytes
Fixed Size 1338364 bytes
Variable Size 264242180 bytes
Database Buffers 360710144 bytes
Redo Buffers 5623808 bytes
Database mounted.
Database opened.
SYS@bys1>
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