今天在 CentOS 上安裝完 Oracle 後，通過命令 “emctl start dbconsole” 啟動管理控制台時，報了 “Environment variable ORACLE_UNQNAME not defined” 的錯誤。問題原因是因為 Oracle 總是獲取不到正確的 IP 地址（安裝 Oracle 時獲取的 IP 地址就是錯誤的），導致 em 出現問題，只需重新配置 emca 即可。折騰了好久，最後終於把問題給解決了。
操作系統： CentOS 6.5
IP： 192.168.132.41
域： mycompany.com.cn
主機名： hemw-pc
Oracle：11gR2，安裝目錄為 /opt/oracle/11g
剛開始按照網上的解決方案使用命令“emca -config dbcontrol db -repos create” 重新創建 em，輸入完對應的信息時，到最後確認時獲取到的 IP 地址總是不正確（Local hostname 應該是 192.168.132.41 才對）：
----------------------------------------------------------------- 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 ............... -----------------------------------------------------------------因為獲取到的 hostname 值不正確，導致一直無法創建成功，提示如下錯誤
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.
經過各種嘗試和折騰後，最終還是把問題給搞定了，步驟如下：
1. 停止監聽器
$ lsnrctl stop
2. 停止 oracle 數據庫
$ 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，將文件內容中 HOST 的值改為正確的 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，將文件內容中 HOST 的值改為正確的 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，將文件內容改為：NETWORKING=yes NETWORKING_IPV6=no HOSTNAME=hemw-pc
因為修改完這個文件後需要重啟操作系統才會生效，所以在不重啟操作系統的情況下需要同時執行一下：# hostname hemw-pc
6. 修改 /etc/hosts，在文件的最後新增如下內容：
192.168.132.41 hemw-pc hemw-pc.mycompany.com.cn
7. 啟動數據庫
SQL> startup
8. 啟動監聽
$ lsnrctl start9. 刪除早期DBCONSOLE創建的用戶：
sql>drop role MGMT_USER; sql>drop user MGMT_VIEW cascade; sql>drop user sysman cascade;10. 刪除早期DBCONSOLE創建的對象：
sql>drop PUBLIC SYNONYM MGMT_TARGET_BLACKOUTS; sql>drop public synonym SETEMVIEWUSERCONTEXT;11. 重新創建DBCONSOLE：（如果是在windows下，要先到注冊表刪除DBCONSOLE的服務，重啟電腦）
$emca -config dbcontrol db -repos create如果提示創建失敗，輸出類似 “Could not complete the configuration. Refer to the log file at /opt/oracle/cfgtoollogs/emca/orcl/emca_*.log for more details.” 的錯誤信息，請查看對應的日志文件， 日志文件的最後一行內容如果是 “ORA-00955: name is already used by an existing object”，如：
CREATE PUBLIC SYNONYM MGMT_AVAILABILITY FOR MGMT_AVAILABILITY
*
ERROR at line 1:
ORA-00955: name is already used by an existing object
則需要執行一次重建的命令：$emca -config dbcontrol db -repos recreate在執行上面命令的過程中需要根據提示輸入對應的數據庫信息及 SYS、DBSNMP 和 SYSMAN 的登錄密碼，最後輸入 Y 進行確認，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. 檢查 em 的狀態
$ 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，問題已經解決完畢。
emctl start dbconsole
