本次在测试环境上,在某客户端上连接到生产库报ORA-12537错误
在MOS找到如下Solution
The ORA-12537 is an information message and means that the connection has been closed. This can be caused by a number of reasons:
1. Database is shut down (maybe for nightly backup), but connection to database was kept by client.
2. A time-out occurred on the client-connection.
3. When firewall closes idle connections.
3. A configuration problem in sqlnet.ora or listener.ora
4.Check and correct permissions on $ORACLE_HOME/bin/oracle binary and make sure that it is set to 6751
5.Check and correct the permission on /var/tmp/.oracle directory. Permissions on this directory should be 777 with sticky bit set.

根据排查法，到第四条发现$ORACLE_HOME/bin/oracle文件有误
[oracle@s1-11g bin]$ ls -l oracle
-rwxr-x--x 1 oracle dba 239810821 Nov 23 14:25 oracle
[oracle@s1-11g bin]$ chown oracle:oinstall oracle
[oracle@s1-11g bin]$ chmod 6751 oracle
[oracle@s1-11g bin]$ ls -l oracle
-rwsr-s--x 1 oracle oinstall 239810821 Nov 23 14:25 oracle

记录：
[oracle@xuh admin]$ tnsping mrhua   #网络、tnsnames.ora配置无误
TNS Ping Utility for Linux: Version 10.2.0.5.0 - Production on 11-JAN-2016 21:12:43
Copyright (c) 1997,  2010, Oracle.  All rights reserved.
Used parameter files:
/oracle/app/product/10.2.0/db_1/network/admin/sqlnet.ora
Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = 172.16.10.16)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = mrhua)))
OK (10 msec)

[oracle@xuh admin]$ sqlplus system/oracle@mrhua
SQL*Plus: Release 10.2.0.5.0 - Production on Mon Jan 11 20:51:05 2016
Copyright (c) 1982, 2010, Oracle.  All Rights Reserved.
ERROR:
ORA-12537: TNS:connection closed
Enter user-name:

[oracle@xuh admin]$ sqlplus system/oracle@mrhua   #$ORACLE_HOME/bin/oracle文件权限纠正，连接正常
SQL*Plus: Release 10.2.0.5.0 - Production on Mon Jan 11 20:57:08 2016
Copyright (c) 1982, 2010, 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
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