Well, when you are sure all the TNS, listener (SID_LIST_LISTENER on this case), services, db_domain are fine but still facing this issue when trying to access remotely an open database… what to do?
[oracle@greporasrv admin]$ sqlplus sys/******@MYDB as sysdba SQL*Plus: Release 18.104.22.168.0 Production on Wed Feb 3 17:45:29 2021 Copyright (c) 1982, 2013, Oracle. All rights reserved. ERROR: ORA-12537: TNS:connection closed
My friend here is a quick tip that, if you are an Oracle DBA for time enough you know that solves several issues, maybe affecting this case again:
[oracle@greporasrv admin]$ cd $ORACLE_HOME/bin [oracle@greporasrv bin]$ ls -lrt oracle -rwxr-x--x. 1 oracle oinstall 242993632 Dec 18 19:20 oracle [oracle@greporasrv bin]$ chmod 6751 oracle [oracle@greporasrv bin]$ ls -lrt oracle -rwsr-s--x. 1 oracle oinstall 242993632 Dec 18 19:20 oracle
The CHMOD 6751 did it again!
It happened to me because, somehow, these permissions were wrong in my LOCAL host (the one I was trying to use the SQLPlus* from.
I hope it helps!