ORA-01034: ORACLE not available ORA-01034ORA-27101 shared memory realm does not exist

[oracle@tsg root]$ sqlplus

SQL*Plus: Release 10.2.0.1.0 - Production on Tue May 17 18:55:37 2009

Copyright (c) 1982, 2005, Oracle. All rights reserved.
Enter user-name: sysman
Enter password:
ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux Error: 2: No such file or directory

=========================================

原因：数据库还没有启动。
         应该这样启动：

         sqlplus sys/sys_password as sysdba

         接下来输入
         startup

注意：sqlplus后的用户要具有sysdba的身份并且以此身份登录。