启动数据库实例，分为两步：第一步，启动监听；第二步，启动数据库实例。
 
一、如何启动数据库实例
  1.进入到sqlplus启动实例
[root@localhost ~]# su - oracle                           ---------- --“切换到oracle用户”
[oracle@localhost ~]$ lsnrctl start                        -------------------“打开监听”

LSNRCTL for Linux: Version 11.2.0.1.0 - Production on 25-AUG-2008 06:02:59

Copyright (c) 1991, 2009, Oracle. All rights reserved.

Starting /opt/oracle/product/OraHome/bin/tnslsnr: please wait...

TNSLSNR for Linux: Version 11.2.0.1.0 - Production
System parameter file is /opt/oracle/product/OraHome/network/admin/listener.ora
Log messages written to /opt/oracle/diag/tnslsnr/localhost/listener/alert/log.xml
Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=localhost.localdomain)(PORT=1521)))

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost.localdomain)(PORT=1521)))
STATUS of the LISTENER
------------------------
Alias                    LISTENER
Version                  TNSLSNR for Linux: Version 11.2.0.1.0 - Production
Start Date               25-AUG-2008 06:03:00
Uptime                   0 days 0 hr. 0 min. 0 sec
Trace Level              off
Security                 ON: Local OS Authentication
SNMP                     OFF
Listener Parameter File  /opt/oracle/product/OraHome/network/admin/listener.ora
Listener Log File        /opt/oracle/diag/tnslsnr/localhost/listener/alert/log.xml
Listening Endpoints Summary...
 (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=localhost.localdomain)(PORT=1521)))
The listener supports no services
The command completed successfully
[oracle@localhost ~]$ sqlplus /nolog                                                ----“进入到sqlplus”

SQL*Plus: Release 11.2.0.1.0 Production on Mon Aug 25 06:03:53 2008

Copyright (c) 1982, 2009, Oracle. All rights reserved.

SQL> conn /as sysdba                                                                             --- --“连接到sysdba”
Connected to an idle instance.
SQL> startup                                                                                          ---------“启动数据库实例”
ORACLE instance started.
Total System Global Area 285212672 bytes
Fixed Size     1218968 bytes
Variable Size    88082024 bytes
Database Buffers  188743680 bytes
Redo Buffers     7168000 bytes
Database mounted.
Database opened.
SQL> shutdown immediate                                         --“关闭数据库实例”
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
[oracle@redhat ~]$ lsnrctl stop                                --“关闭监听”
LSNRCTL for Linux: Version 10.2.0.1.0 - Production on 14-OCT-2009 19:08:06
Copyright (c) 1991, 2005, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC2)))
The command completed successfully
 
  2.用dbstart和dbshut启动和关闭数据库实例
 
先启动监听 lsnrctl start
启动实例 dbstart
 
使用dbstart命令启动数据库比较方便，但是在linux上安装好oracle之后，第一次使用dbstart命令可能会报如下错误：
 
ORACLE_HOME_LISTNER is not SET, unable to auto-start Oracle Net Listener
Usage: /u01/app/oracle/oracle/product/10.2.0/db_1/bin/dbstart ORACLE_HOME

原因：
dbstart和dbshut脚本文件中ORACLE_HOME_LISTNER的设置有问题，分别打开两个文件找到：用vi编辑dbstart，ORACLE_HOME_LISTNER=$1,修改为
ORACLE_HOME_LISTNER=$ORACLE_HOME
 
 
然后保存退出，此时再运行dbstart，已经不报错了，但是没有任何反应，ps一下进程，没有oracle的进程，说明oracle实例没有正常启动。
 
此时的原因是在/etc/oratab的设置问题，我们vi一下，发现
zgz:/home/oracle/product/10g:N
最后设置的是"N"（我的环境中只有一个实例，因此只有一行配置语句），我们需要把“N”修改为“Y”。
 
以上的工作做好之后，dbstart就可以正常使用了：
 
[oracle@redhat bin]$ lsnrctl start                                  --“启动监听”
LSNRCTL for Linux: Version 10.2.0.1.0 - Production on 14-OCT-2009 19:44:53
Copyright (c) 1991, 2005, Oracle. All rights reserved.
Starting /home/oracle/product/10g/bin/tnslsnr: please wait...
TNSLSNR for Linux: Version 10.2.0.1.0 - Production
System parameter file is /home/oracle/product/10g/network/admin/listener.ora
Log messages written to /home/oracle/product/10g/network/log/listener.log
Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC2)))
Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=redhat)(PORT=1522)))
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC2)))
STATUS of the LISTENER
------------------------
Alias                    LISTENER
Version                  TNSLSNR for Linux: Version 10.2.0.1.0 - Production
Start Date               14-OCT-2009 19:44:53
Uptime                   0 days 0 hr. 0 min. 0 sec
Trace Level              off
Security                 ON: Local OS Authentication
SNMP                     OFF
Listener Parameter File  /home/oracle/product/10g/network/admin/listener.ora
Listener Log File        /home/oracle/product/10g/network/log/listener.log
Listening Endpoints Summary...
 (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC2)))
 (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=redhat)(PORT=1522)))
Services Summary...
Service "PLSExtProc" has 1 instance(s).
 Instance "PLSExtProc", status UNKNOWN, has 1 handler(s) for this service...
The command completed successfully
[oracle@redhat bin]$ dbstart                                  --“启动数据库实例”
Processing Database instance "zgz": log file /home/oracle/product/10g/startup.log
[oracle@redhat bin]$ dbshut                                   --“关闭数据库实例”
[oracle@redhat bin]$ lsnrctl stop                             --“关闭监听”
LSNRCTL for Linux: Version 10.2.0.1.0 - Production on 14-OCT-2009 19:45:33
Copyright (c) 1991, 2005, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC2)))
The command completed successfully
 
二、如何使数据库实例和linux系统一起启动
在/etc/rc.d/rc.local中加入如下语句即可实现同系统启动实例：
su - oracle -c "lsnrctl start"
su - oracle -c "dbstart"