如何查看Oracle是否启动？
Oracle数据库系统是业界知名的关系型数据库管理系统。它具有高性能、高可靠、高安全等特点。在生产环境中，Oracle数据库是企业级应用的重要组成部分，因此，必须确认Oracle数据库是否启动。下面，我们将详细介绍如何检查Oracle是否启动。
1.使用SQL*Plus工具检查Oracle启动状态
Oracle提供了一个命令行工具SQL*Plus，可以使用它来检查Oracle启动状态。该工具在Oracle的客户端安装包中，可以在命令行中输入以下命令来启动SQL*Plus：
sqlplus / as sysdba
这条命令中，/ 表示以本机认证方式连接数据库，as sysdba 表示以 SYS 连接，以 SYSDBA 角色登录。当然，如果你知道其他用户的用户名和密码，也可以使用其他用户来登录。
如果Oracle已启动，将会出现以下提示：
SQL*Plus: Release 11.2.0.2.0 Production on Wed May 12 14:58:17 2021
Copyright (c) 1982, 2010, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL>
如果Oracle未启动，将会出现以下提示：
SQL*Plus: Release 11.2.0.2.0 Production on Wed May 12 14:59:09 2021
Copyright (c) 1982, 2010, Oracle. All rights reserved.
ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux-x86_64 Error: 2: No such file or directory
Process ID: 0
Session ID: 0 Serial number: 0
在提示符下，可以执行各种SQL命令，并查看Oracle数据库的状态。例如，可以查询Oracle实例的状态：
SELECT instance_name, status, database_status FROM v$instance;
执行以上语句，如果Oracle已启动，将会输出类似以下结果：
INSTANCE_NAME STATUS DATABASE_STATUS
---------------- ------------ -----------------
orcl OPEN ACTIVE
其中，INSTANCE_NAME 表示实例名，STATUS 表示实例状态，DATABASE_STATUS 表示数据库状态。
如果Oracle未启动，则会出现以下提示：
SQL> SELECT instance_name, status, database_status FROM v$instance;
SELECT instance_name, status, database_status FROM v$instance
*
ERROR at line 1:
ORA-01034: ORACLE not available
Process ID: 0
Session ID: 0 Serial number: 0
2.查看Oracle后台进程
Oracle在启动时，会启动多个进程。这些进程可以通过操作系统的进程管理器进行查看。例如，在Linux系统下，可以使用 ps 命令查看Oracle进程：
ps -ef | grep ora_
如果Oracle已启动，将会输出一组以 ora_ 开头的进程：
oracle 2652 1 0 16:07 ? 00:00:32 ora_dbw0_orcl
oracle 2654 1 0 16:07 ? 00:00:00 ora_psp0_orcl
oracle 2656 1 0 16:07 ? 00:00:03 ora_lgwr_orcl
oracle 2658 1 0 16:07 ? 00:00:49 ora_ckpt_orcl
oracle 2660 1 0 16:07 ? 00:00:00 ora_smon_orcl
oracle 2662 1 0 16:07 ? 00:00:00 ora_reco_orcl
oracle 2664 1 0 16:07 ? 00:00:02 ora_mmon_orcl
oracle 2666 1 0 16:07 ? 00:00:00 ora_mmnl_orcl
oracle 2668 1 0 16:07 ? 00:00:00 ora_d000_orcl
oracle 2670 1 0 16:07 ? 00:00:00 ora_s000_orcl
oracle 2672 1 0 16:07 ? 00:00:00 ora_s001_orcl
oracle 2674 1 0 16:07 ? 00:00:00 ora_s002_orcl
oracle 2676 1 0 16:07 ? 00:00:00 ora_s003_orcl
oracle 2678 1 0 16:07 ? 00:00:00 ora_s004_orcl
oracle 2680 1 0 16:07 ? 00:00:00 ora_s005_orcl
oracle 2682 1 0 16:07 ? 00:00:00 ora_qmnc_orcl
oracle 2684 1 0 16:07 ? 00:00:01 ora_cjq0_orcl
oracle 2686 1 0 16:07 ? 00:00:00 ora_dbrm_orcl
oracle 2688 1 0 16:07 ? 00:00:00 ora_p000_orcl
oracle 2690 1 0 16:07 ? 00:00:00 ora_p001_orcl
oracle 2692 1 0 16:07 ? 00:00:00 ora_p002_orcl
oracle 2694 1 0 16:07 ? 00:00:00 ora_p003_orcl
oracle 2696 1 0 16:07 ? 00:00:00 ora_p004_orcl
oracle 2698 1 0 16:07 ? 00:00:00 ora_p005_orcl
oracle 2700 1 0 16:07 ? 00:00:00 ora_p006_orcl
oracle 2702 1 0 16:07 ? 00:00:00 ora_p007_orcl
oracle 2704 1 0 16:07 ? 00:00:00 ora_p008_orcl
oracle 2706 1 0 16:07 ? 00:00:00 ora_p009_orcl
oracle 2708 1 0 16:07 ? 00:00:00 ora_p010_orcl
oracle 2710 1 0 16:07 ? 00:00:00 ora_p011_orcl
oracle 2712 1 0 16:07 ? 00:00:00 ora_p012_orcl
oracle 2714 1 0 16:07 ? 00:00:00 ora_p013_orcl
oracle 2716 1 0 16:07 ? 00:00:00 ora_p014_orcl
oracle 2718 1 0 16:07 ? 00:00:00 ora_p015_orcl
oracle 2720 1 0 16:07 ? 00:00:00 ora_p016_orcl
oracle 2722 1 0 16:07 ? 00:00:00 ora_p017_orcl
oracle 2724 1 0 16:07 ? 00:00:00 ora_p018_orcl
oracle 2726 1 0 16:07 ? 00:00:00 ora_p019_orcl
oracle 2728 1 0 16:07 ? 00:00:00 ora_p020_orcl
oracle 2730 1 0 16:07 ? 00:00:00 ora_p021_orcl
oracle 2732 1 0 16:07 ? 00:00:00 ora_p022_orcl
oracle 2734 1 0 16:07 ? 00:00:00 ora_p023_orcl
oracle 2736 1 0 16:07 ? 00:00:00 ora_p024_orcl
oracle 2738 1 0 16:07 ? 00:00:00 ora_p025_orcl
oracle 2740 1 0 16:07 ? 00:00:00 ora_p026_orcl
oracle 2742 1 0 16:07 ? 00:00:00 ora_p027_orcl
oracle 2744 1 0 16:07 ? 00:00:00 ora_p028_orcl
oracle 2746 1 0 16:07 ? 00:00:00 ora_p029_orcl
如果Oracle未启动，则不会输出任何进程。
3.查看Oracle监听器状态
Oracle监听器是一个网络服务，用于管理Oracle客户端和服务器之间的通信。在Oracle未启动时，监听器服务将无法启动。因此，我们可以通过检查监听器状态来了解Oracle是否已启动。可以使用 lsnrctl 工具来管理监听器。以下是一个检查监听器状态的例子：
lsnrctl status
如果Oracle已启动，将会输出以下信息：
LSNRCTL for Linux: Version 11.2.0.2.0 - Production on 12-MAY-2021 14:05:29
Copyright (c) 1991, 2010, Oracle. All rights reserved.
Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521))
STATUS of the LISTENER
------------------------
Alias LISTENER
Version TNSLSNR for Linux: Version 11.2.0.2.0 - Production
Start Date 12-MAY-2021 13:49:37
Uptime 0 days 0 hr. 15 min. 52 sec
Trace Level off
Security ON: Local OS Authentication
SNMP OFF
Listener Parameter File /u01/app/oracle/product/11.2.0/db_1/network/admin/listener.ora
Listener Log File /u01/app/oracle/diag/tnslsnr/db11g/listener/alert/log.xml
Listening Endpoints Summary...
(DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=127.0.0.1)(PORT=1521)))
Services Summary...
Service "orcl" has 1 instance(s).
Instance "orcl", status READY, has 1 handler(s) for this service...
Service "orclXDB" has 1 instance(s).
Instance "orcl", status READY, has 1 handler(s) for this service...
The command completed successfully
如果Oracle未启动，则会提示无法连接到监听器：
LSNRCTL for Linux: Version 11.2.0.2.0 - Production on 12-MAY-2021 14:22:01
Copyright (c) 1991, 2010, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC1521)))
TNS-12541: TNS:no listener
TNS-12560: TNS:protocol adapter error
TNS-00511: No listener
Linux Error: 111: Connection refused
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=127.0.0.1)(PORT=1521)))
TNS-12541: TNS:no listener
TNS-12560: TNS:protocol adapter error
TNS-00511: No listener
Linux Error: 111: Connection refused
总结
通过以上介绍，我们可以了解如何检查Oracle是否启动。可以使用SQL*Plus工具、查看Oracle后台进程、查看Oracle监听器状态等方法来验证Oracle的状态。在实际使用中，我们需要及时检查Oracle的状态，以确保其可以正常工作。