ORA-12537: TNS:connection closed
问题描述：
1、就在刚才，遇到了一个小问题，通过服务名怎么也连接不上数据库：
[oracle@rac1 ~]$ sqlplus system/oracle@rac
SQL*Plus: Release 11.2.0.4.0 Production on Mon Jun 5 13:31:17 2017
Copyright (c) 1982, 2013, Oracle. All rights reserved.
ERROR:
ORA-12537: TNS:connection closed
2、但是通过sqlplus / as sysdba是可以连接上的，于是乎检查监听，正常：
[oracle@rac1 ~]$ lsnrctl status
LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 05-JUN-2017 13:30:51
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 05-JUN-2017 13:19:05
Uptime 0 days 0 hr. 11 min. 45 sec
Trace Level off
Security ON: Local OS Authentication
SNMP OFF
Listener Parameter File /u01/grid/app/11.2.0/network/admin/listener.ora
Listener Log File /u01/grid/app/grid/diag/tnslsnr/rac1/listener/alert/log.xml
Listening Endpoints Summary...
(DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=LISTENER)))
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.56.101)(PORT=1521)))
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.56.201)(PORT=1521)))
Services Summary...
Service "+ASM" has 1 instance(s).
Instance "+ASM1", status READY, has 1 handler(s) for this service...
Service "rac" has 1 instance(s).
Instance "rac1", status READY, has 1 handler(s) for this service...
Service "racXDB" has 1 instance(s).
Instance "rac1", status READY, has 1 handler(s) for this service...
The command completed successfully
3、而且tnsping也是ok的：
[oracle@rac1 ~]$ tnsping rac
TNS Ping Utility for Linux: Version 11.2.0.4.0 - Production on 05-JUN-2017 13:31:48
Copyright (c) 1997, 2013, Oracle. All rights reserved.
Used parameter files:
Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.56.100)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = rac)))
OK (10 msec)
解决办法：
1、检查权限：
[oracle@rac1 ~]$ cd /u01/oracle/app/11.2.0/bin/
[oracle@rac1 bin]$ ls -lh oracle
-rwxr-x--x 1 oracle oinstall 229M Mar 22 09:52 oracle
2、修改权限为6751：
[oracle@rac1 bin]$ chmod 6751 oracle
[oracle@rac1 bin]$ ls -lh oracle
-rwsr-s--x 1 oracle oinstall 229M Mar 22 09:52 oracle
3、重新连接就可以连接上了：
[oracle@rac1 bin]$ sqlplus system/oracle@rac
SQL*Plus: Release 11.2.0.4.0 Production on Mon Jun 5 13:33:57 2017
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options
总结：
对于RAC环境，轻易不要修改安装目录下任何一个文件的权限，以免不必要的麻烦。
参考文章：
http://www.linuxidc.com/Linux/2016-01/126988.htm