/*************************************************************************************
 * sqlplus: no TNS_ADMIN => error
 */

$ ${ORACLE_HOME}/bin/sqlplus -L <user>@<servicename>
SQL*Plus: Release 19.0.0.0.0 - Production on Mon Jul 10 19:08:27 2023
Version 19.13.0.0.0
Copyright (c) 1982, 2021, Oracle.  All rights reserved.

ERROR:
ORA-12154: TNS:could not resolve the connect identifier specified

SP2-0751: Unable to connect to Oracle.  Exiting SQL*Plus

/*************************************************************************************
 * sqlplus: with TNS_ADMIN, TCPS using sqlnet.ora/wallet => error, wallet not accessible (permission denied)
 */

$ TNS_ADMIN=/app/tns ${ORACLE_HOME}/bin/sqlplus -L <user>@<servicename>
SQL*Plus: Release 19.0.0.0.0 - Production on Mon Jul 10 19:08:56 2023
Version 19.13.0.0.0
Copyright (c) 1982, 2021, Oracle.  All rights reserved.

ERROR:
ORA-28759: failure to open file

SP2-0751: Unable to connect to Oracle.  Exiting SQL*Plus

/*************************************************************************************
 * tnsping: with TNS_ADMIN, TCPS using sqlnet.ora/wallet => error, wallet not accessible (permission denied)
 */
$ TNS_ADMIN=/app/tns ${ORACLE_HOME}/bin/tnsping <servicename>
TNS Ping Utility for Linux: Version 19.0.0.0.0 - Production on 11-JUL-2023 08:18:34
Copyright (c) 1997, 2021, Oracle.  All rights reserved.

Used parameter files:
/app/tns/sqlnet.ora

Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION_LIST= (LOAD_BALANCE=off) (FAILOVER=off) (DESCRIPTION= (CONNECT_TIMEOUT=5) (TRANSPORT_CONNECT_TIMEOUT=3) (RETRY_COUNT=3) (ADDRESS_LIST= (LOAD_BALANCE=on) (ADDRESS= (PROTOCOL=TCPS) (HOST=<hostname>) (PORT=1522))) (CONNECT_DATA= (SERVICE_NAME=<servicename>))))

TNS-12560: TNS:protocol adapter error

/*************************************************************************************
 * tnsping: with TNS_ADMIN, TCP => ok
 */
$ TNS_ADMIN=/app/tns ${ORACLE_HOME}/bin/tnsping <servicename>

TNS Ping Utility for Linux: Version 19.0.0.0.0 - Production on 11-JUL-2023 09:52:39

Copyright (c) 1997, 2021, Oracle.  All rights reserved.

Used parameter files:
/app/tns/sqlnet.ora

Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION_LIST= (LOAD_BALANCE=off) (FAILOVER=off) (DESCRIPTION= (CONNECT_TIMEOUT=5) (TRANSPORT_CONNECT_TIMEOUT=3) (RETRY_COUNT=3) (ADDRESS_LIST= (LOAD_BALANCE=o) (ADDRESS= (PROTOCOL=TCP) (HOST=<hostname>) (PORT=1521))) (CONNECT_DATA= (SERVICE_NAME=<servicename>))))

OK (0 msec)

/*************************************************************************************
 * sqlplus: with TNS_ADMIN, TCP => ok
 */
$ TNS_ADMIN=/app/tns ${ORACLE_HOME}/bin/sqlplus <user>@<servicename>

SQL*Plus: Release 19.0.0.0.0 - Production on Tue Jul 11 09:52:48 2023
Version 19.13.0.0.0

Copyright (c) 1982, 2021, Oracle.  All rights reserved.

Enter password:
Last Successful login time: Tue Jul 11 2023 07:18:44 +02:00

Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.18.0.0.0

SQL> exit

NLS_LANG=American_America.WE8ISO8859P1
NLS_LANG=American_America.UTF8