Or use tasklist /m on running sqlplus.exe – check for missing 64-bit modules. file $ORACLE_HOME/bin/sqlplus Output: ELF 64-bit LSB executable, x86-64

Also test:

1. Introduction The Oracle Client is a set of libraries, tools, and binaries that allow a 64-bit machine to communicate with an Oracle Database instance. It is essential for applications like SQL*Plus, Oracle Data Provider for .NET (ODP.NET), Oracle Call Interface (OCI), Python cx_Oracle, PHP OCI8, and many other development and administration tools.