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             &