今天在 CentOS 上安装完 Oracle 后，通过命令 “emctl start dbconsole” 启动管理控制台时，报了 “Environment variable ORACLE_UNQNAME not defined” 的错误。问题原因是因为 Oracle 总是获取不到正确的 IP 地址（安装 Oracle 时获取的 IP 地址就是错误的），导致 em 出现问题，只需重新配置 emca 即可。折腾了好久，最后终于把问题给解决了。
环境描述
操作系统： CentOS 6.5
IP： 192.168.132.41
域： mycompany.com.cn
主机名： hemw-pc
Oracle：11gR2，安装目录为 /opt/oracle/11g
问题分析
刚开始按照网上的解决方案使用命令“emca -config dbcontrol db -repos create” 重新创建 em，输入完对应的信息时，到最后确认时获取到的 IP 地址总是不正确（Local hostname 应该是 192.168.132.41 才对）：
----------------------------------------------------------------- You have specified the following settings Database ORACLE_HOME ................ /opt/oracle/11g Local hostname ................ 192.168.64.61 Listener ORACLE_HOME ................ /opt/oracle/11g Listener port number ................ 1521 Database SID ................ orcl Email address for notifications ............... Outgoing Mail (SMTP) server for notifications ............... -----------------------------------------------------------------
因为获取到的 hostname 值不正确，导致一直无法创建成功，提示如下错误
Could not complete the configuration. Refer to the log file at /opt/oracle/cfgtoollogs/emca/orcl/emca_2015_03_10_17_19_30.log for more details.
解决方案
经过各种尝试和折腾后，最终还是把问题给搞定了，步骤如下：
1. 停止监听器
$ lsnrctl stop
2. 停止 oracle 数据库
$ sqlplus "sys / as sysdba" SQL*Plus: Release 11.2.0.1.0 Production on Tue Mar 10 17:16:45 2015 Copyright (c) 1982, 2009, Oracle. All rights reserved. Enter password: Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production With the Partitioning, OLAP, Data Mining and Real Application Testing options SQL> shutdown
3. 修改 $ORACLE_HOME/network/admin/listener.ora，将文件内容中 HOST 的值改为正确的 IP（192.168.132.41），如：
LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.132.41)(PORT = 1521))
)
)
4. 修改 $ORACLE_HOME/network/admin/tnsnames.ora，将文件内容中 HOST 的值改为正确的 IP（192.168.132.41），如：
ORCL =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.132.41)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = orcl)
)
)
5. 修改 /etc/sysconfig/network，将文件内容改为：
NETWORKING=yes NETWORKING_IPV6=no HOSTNAME=hemw-pc
因为修改完这个文件后需要重启操作系统才会生效，所以在不重启操作系统的情况下需要同时执行一下：# hostname hemw-pc
6. 修改 /etc/hosts，在文件的最后新增如下内容：
192.168.132.41 hemw-pc hemw-pc.mycompany.com.cn
7. 启动数据库
SQL> startup
8. 启动监听
$ lsnrctl start
9. 删除早期DBCONSOLE创建的用户：
sql>drop role MGMT_USER; sql>drop user MGMT_VIEW cascade; sql>drop user sysman cascade;
10. 删除早期DBCONSOLE创建的对象：
sql>drop PUBLIC SYNONYM MGMT_TARGET_BLACKOUTS; sql>drop public synonym SETEMVIEWUSERCONTEXT;
11. 重新创建DBCONSOLE：（如果是在windows下，要先到注册表删除DBCONSOLE的服务，重启电脑）
$emca -config dbcontrol db -repos create
如果提示创建失败，输出类似 “Could not complete the configuration. Refer to the log file at /opt/oracle/cfgtoollogs/emca/orcl/emca_*.log for more details.” 的错误信息，请查看对应的日志文件， 日志文件的最后一行内容如果是 “ORA-00955: name is already used by an existing object”，如：
CREATE PUBLIC SYNONYM MGMT_AVAILABILITY FOR MGMT_AVAILABILITY
*
ERROR at line 1:
ORA-00955: name is already used by an existing object
则需要执行一次重建的命令：
$emca -config dbcontrol db -repos recreate
在执行上面命令的过程中需要根据提示输入对应的数据库信息及 SYS、DBSNMP 和 SYSMAN 的登录密码，最后输入 Y 进行确认，如：
STARTED EMCA at Mar 10, 2015 10:03:17 PM EM Configuration Assistant, Version 11.2.0.0.2 Production Copyright (c) 2003, 2005, Oracle. All rights reserved. Enter the following information: Database SID: orcl Listener port number: 1521 Listener ORACLE_HOME [ /opt/oracle/11g ]: Password for SYS user: Password for DBSNMP user: Password for SYSMAN user: Email address for notifications (optional): Outgoing Mail (SMTP) server for notifications (optional):
12. 检查 em 的状态
$ emctl status dbconsole Oracle Enterprise Manager 11g Database Control Release 11.2.0.1.0 Copyright (c) 1996, 2009 Oracle Corporation. All rights reserved. https://hemw-pc:1158/em/console/aboutApplication Oracle Enterprise Manager 11g is running. ------------------------------------------------------------------ Logs are generated in directory /opt/oracle/11g/hemw-pc_orcl/sysman/log
至此，问题已经解决完毕。
附：emca 常用命令
创建一个 em 资料库：emca -repos create
重建一个 em 资料库：emca -repos recreate
删除一个 em 资料库：emca -repos drop
配置数据库的 Database Control：emca -config dbcontrol db
删除数据库的 Database Control配置：emca -deconfig dbcontrol db
重新配置db control的端口，默认端口在1158
emca -reconfig ports
emca -reconfig ports -dbcontrol_http_port 1160
emca -reconfig ports -agent_port 3940
先设置 ORACLE_SID 环境变量后,启动 em console服务：emctl start dbconsole
先设置 ORACLE_SID 环境变量后,停止em console服务：emctl stop dbconsole
先设置 ORACLE_SID 环境变量后,查看 em console服务的状态：emctl status dbconsole
配置 dbconsole 的步骤
emca -repos create
emca -config dbcontrol db
emctl start dbconsole
重新配置 dbconsole 的步骤
emca -repos drop
emca -repos create
emca -config dbcontrol db
emctl start dbconsole
参考资料：
http://soulful.blog.51cto.com/468033/449934
http://czhwin.iteye.com/blog/1847366