ORA-12537: TNS:connection closed – When Nothing Else Works!

When you’re sure all the TNS listener (SID_LIST_LISTENER in this case) services and db_domain are fine, but you still face the ORA-12537: TNS:connection closed error when trying to remotely access an open database, what can you do next?

[oracle@pythiansrv admin]$ sqlplus sys/******@MYDB as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Wed Feb 3 17:45:29 2021

Copyright (c) 1982, 2013, Oracle. All rights reserved.

ERROR:
ORA-12537: TNS:connection closed

Here’s a quick tip — if you’ve been an Oracle DBA for long enough, you’ll know this workaround solves a variety of issues:

[oracle@pythiansrv admin]$ cd $ORACLE_HOME/bin
[oracle@pythiansrv bin]$ ls -lrt oracle
-rwxr-x--x. 1 oracle oinstall 242993632 Dec 18 19:20 oracle
[oracle@pythiansrv bin]$ chmod 6751 oracle
[oracle@pythiansrv bin]$ ls -lrt oracle
-rwsr-s--x. 1 oracle oinstall 242993632 Dec 18 19:20 oracle

As you can see, the CHMOD 6751 did it again!

The reason this happened to me is, somehow, these permissions were wrong in my LOCAL host (the one I was trying to use the SQLPlus* from).

I hope my experience helps you. If you have any questions or anything to add, please leave me a comment.