今天使用SQL Developer连接一台测试服务器数据库（ORACLE 11g）时，遇到了“ORA-12514, TNS:listener does not currently know of service requested in connect descriptor”错误，具体提示如下所示：
执行请求的操作时遇到错误:
Listener refused the connection with the following error:
ORA-12514, TNS:listener does not currently know of service requested in connect descriptor
供应商代码 12514
几年前写过一篇关于”ORA-12514: TNS: 监听程序当前无法识别连接描述符中请求的服务“的案例文章，现在看来当时写的比较肤浅和粗糙,当然案例也不一样，下面在总结一下如何处理ORA-12514这个错误吧。
Step 1： 首先检查客户端的tnsnames.ora里面的host、port、service_name等是否正确
myvm =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 10.20.57.15)(PORT = 1521))
)
(CONNECT_DATA =
(SERVER = SHARED)
(SERVICE_NAME = gsp.localdomain)
)
)
逐一仔细检查过后发现这些配置都是正确的。 其实前几天还是正常来的。测试服务器和tnsnames.ora都没有改动过。所以我们继续后面排查。
Step 2：检查确认数据库实例是否启动。
SQL> select status from v$instance;
STATUS
------------
OPEN
SQL>
如上所示，数据库实例正常，并没有关闭。当数据库实例异常关闭，也会出现ORA-12514错误，如下所示（如果我关闭一数据库实例，然后使用SQL*Plus测试连接数据库就会遇到这个错误）：
C:\Users>sqlplus system/123456@mydb
SQL*Plus: Release 11.2.0.1.0 Production on 星期三 4月 12 11:56
Copyright (c) 1982, 2010, Oracle. All rights reserved.
ERROR:
ORA-12514: TNS: 监听程序当前无法识别连接描述符中请求的服务
Step 3：检查网络是否正常，tnsping能否ping通
如下所示，ping 和tnsping 均都正常
监听服务也正常，没有问题
[oracle@DB-Server admin]$ lsnrctl status
LSNRCTL for Linux: Version 11.2.0.1.0 - Production on 12-APR-2017 10:36:40
Copyright (c) 1991, 2009, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC1521)))
STATUS of the LISTENER
------------------------
Alias LISTENER
Version TNSLSNR for Linux: Version 11.2.0.1.0 - Production
Start Date 12-APR-2017 10:31:20
Uptime 0 days 0 hr. 5 min. 20 sec
Trace Level off
Security ON: Local OS Authentication
SNMP OFF
Listener Parameter File /u01/app/oracle/product/11.1.0/dbhome_1/network/admin/listener.ora
Listener Log File /u01/app/oracle/diag/tnslsnr/DB-Server/listener/alert/log.xml
Listening Endpoints Summary...
(DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=DB-Server.localdomain)(PORT=1521)))
The listener supports no services
The command completed successfully
Step 4：检查$ORACLE_BASE/diag/tnslsnr/DB-Server/listener/alert下的日志，发现host_addr为10.20.34.76，实际IP地址不是这个。因为监听文件里面我使用的hostname DB-Server.localdomain，所以赶紧检查/etc/hosts的配置
[root@DB-Server ~]# ifconfig
eth0 Link encap:Ethernet HWaddr B0:83:FE:55:32:E5
inet addr:10.20.57.15 Bcast:10.20.57.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2363981 errors:0 dropped:0 overruns:0 frame:0
TX packets:180048 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:225925147 (215.4 MiB) TX bytes:14349633 (13.6 MiB)
Interrupt:233 Base address:0x4000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:3692 errors:0 dropped:0 overruns:0 frame:0
TX packets:3692 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:2982961 (2.8 MiB) TX bytes:2982961 (2.8 MiB)
[root@DB-Server ~]# more /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
10.20.34.76 DB-Server.localdomain DB-Server
127.0.0.1 localhost.localdomain localhost
::1 localhost6.localdomain6 localhost6
[root@DB-Server ~]#
果然发现/etc/hosts下配置为10.20.34.76， 具体原因是因为IT部门调换办公室，从三楼撤到二楼，将这台PC搬下来后，服务器IP地址变化了，修改/etc/hosts，然后重启监听服务，问题解决。