Install Oracle Client 12c -

Create $TNS_ADMIN/tnsnames.ora:

LEGACYDB =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = 10.2.1.100)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = ORCL)
    )
  )

Then test:

tnsping LEGACYDB  # Should show "OK (20 msec)"

The Windows installation is GUI-driven and straightforward for most users. install oracle client 12c

The modern dynamic linker (ld.so) needs to know about non-standard library paths. Many guides tell you to set LD_LIBRARY_PATH—that’s fragile and breaks containerization. Use ldconfig:

Create a configuration file:

echo "/opt/oracle/instantclient_12_2" | sudo tee /etc/ld.so.conf.d/oracle-instantclient.conf
sudo ldconfig

Verify:

ldconfig -p | grep clntsh
# Output should show libclntsh.so.12.1

Why this matters: Without ldconfig, Python’s cx_Oracle or PHP’s oci8 will throw ImportError: libclntsh.so.12.1: cannot open shared object file. Create $TNS_ADMIN/tnsnames

This often happens with locale settings. Unset it:

unset LANG LC_ALL
export NLS_LANG=AMERICAN_AMERICA.US7ASCII