In Linux or Unix platform, installed SQL*Plus in database server can be executed by anyone.
We just need to make the tnsnames.ora file readable by others.
TNSNAMES Readable
[oracle@test ~]$ chmod o+r $ORACLE_HOME/network/admin/tnsnames.ora
After this just login to the user you want to login the database and set the environment by .oraenv and providing the SID.
[root@sql ~]# su - test Last login: Tue Aug 22 11:53:14 UTC 2023 on pts/0 [test@sql ~]$ [test@sql ~]$ [test@sql ~]$ [test@sql ~]$ . oraenv ORACLE_SID = [test] ? ORACLE_BASE environment variable is not being set since this information is not available for the current user ID test. You can set ORACLE_BASE manually if it is required. Resetting ORACLE_BASE to its previous value or ORACLE_HOME The Oracle base has been set to /u01/app/oracle/product/19.3/db_home [test@sql ~]$ [test@sql ~]$ [test@sql ~]$ sqlplus SQL*Plus: Release 19.0.0.0.0 - Production on Tue Aug 22 11:53:47 2023 Version 19.20.0.0.0 Copyright (c) 1982, 2022, Oracle. All rights reserved. Enter user-name: system Enter password: Last Successful login time: Tue Aug 22 2023 09:04:05 +00:00 Connected to: Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production Version 19.20.0.0.0 SQL>