linux平台如何查看OS上存在多少个数据库，查询方法主要有三种，下面分别进行介绍 

1、 通过lsnrctl status命令查看

通过该方法，可以查看已经注册到listener中的数据库实例，在一定程度可以说明OS上存在有命令结果中所列出来的数据库实例，当然未启动的和未注册进来的除外

命令：#su – Oracle

$lsnrctl status

[oracle@rac1 ~]$ lsnrctl status   LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 23-JUL-2016 09:14:36 Copyright (c) 1991, 2013, Oracle.  All rights reserved. Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521)) STATUS of the LISTENER ------------------------ Alias                     LISTENER Version                   TNSLSNR for Linux: Version 11.2.0.4.0 - Production Start Date                23-JUL-2016 08:47:22 Uptime                    0 days 0 hr. 27 min. 13 sec Trace Level               off Security                  ON: Local OS Authentication SNMP                      OFF Listener Parameter File   /u01/app/11.2.0/grid/network/admin/listener.ora Listener Log File         /u01/app/grid/diag/tnslsnr/rac1/listener/alert/log.xml Listening Endpoints Summary...   (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=LISTENER)))   (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.11.101)(PORT=1521)))   (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.11.103)(PORT=1521))) Services Summary... Service "+ASM" has 1 instance(s).   Instance "+ASM1", status READY, has 1 handler(s) for this service... Service "orcl" has 1 instance(s).   Instance "orcl1", status READY, has 1 handler(s) for this service... The command completed successfully

从上面表格结果集中，可以看到有一个 “orcl1”的数据库实例注册到了listener中来了，说明该OS上最少有一个名叫orcl1的数据库实例存在 

2、通过cat /etc/oratab方式查看

创建数据库或实例时，会在/etc/oratab文件中增加一行记录，哪怕是数据库实例没有启动，用此方法也可以查看得到。如下所示：

命令：#cat /etc/oratab

[oracle@rac1 ~]$ cat /etc/oratab #Backup file is  /u01/app/oracle/product/11.2.0/db_1/srvm/admin/oratab.bak.rac1 line added by Agent # # This file is used by ORACLE utilities.  It is created by root.sh # and updated by either Database Configuration Assistant while creating # a database or ASM Configuration Assistant while creating ASM instance. # A colon, ':', is used as the field terminator.  A new line terminates # the entry.  Lines beginning with a pound sign, '#', are comments. # # Entries are of the form: #   $ORACLE_SID:$ORACLE_HOME:<N|Y>: # # The first and second fields are the system identifier and home # directory of the database respectively.  The third filed indicates # to the dbstart utility that the database should , "Y", or should not, # "N", be brought up at system boot time. # # Multiple entries with the same $ORACLE_SID are not allowed. # # +ASM1:/u01/app/11.2.0/grid:N            # line added by Agent orcl:/u01/app/oracle/product/11.2.0/db_1:N              # line added by Agent

从上面表格中最后一行结果中，可以看出该OS上存在有一个叫orcl的数据库（包括实例） 

3、通过ps –ef |grep ora_pmon方式查看

如果数据库或实例已经启动至nomount模式，就会产生pmon进程，所以我们可以通过查看OS是否存在pmon进程的方式来查看有几个数据库实例存在，每一个实例都会有一个pmon进程，如果查到存在有多个pmon进程，就意味着OS上存在着多个数据库实例

命令：# ps -ef |grep pmon

[oracle@rac1 ~]$ ps -ef|grep pmon grid       5807      1  0 Jul21 ?        00:00:47 asm_pmon_+ASM1 oracle    14027   9142  0 09:18 pts/0    00:00:00 grep pmon oracle    39213      1  0 06:22 ?        00:00:03 ora_pmon_orcl1

从上面表格中的结果中可以看到，OS上运行着一个名叫“orcl1”的数据库实例