We will approach the resolution systematically from the most likely cause to the least.

If your environment variables are correct and the error persists, you may have a 32-bit/64-bit mismatch. You cannot run a 64-bit SQL*Plus binary on a 32-bit OS.

: Occasionally caused by insufficient system RAM or incorrectly configured memory allocations (SGA/PGA). Recommended Fixes 1. Verify Environment Variables

sudo yum install libaio

chmod +x $ORACLE_HOME chmod +x $ORACLE_HOME/lib

SQL*Plus looks for libraries relative to the ORACLE_HOME directory. If this variable is not set, the executable cannot find its dependencies.