I have an EC2 Amazon Linux Ami instance running PHP server version 5.6.22, also PostgreSQL 9.4.6 installed.
Doing an echo phpinfo(); it give the following value for PDO_PGSQL library:
PostgreSQL(libpq) Version 8.4.20
This is causing that the app server throws error while trying to connect to the RDS instance with Postgres 9.5 due to the missmatching versions.
I have been looking to make that version to be 9.4 or 9.5. Until now, I had done severals reinstall, trying dealing with repositories, but without results.
EDIT: The reported version for psql command is: psql (PostgreSQL) 9.4.6