PDO_INFORMIX DSN

$db = new PDO("informix:DSN=Infdrv33", "", "");

[ODBC Data Sources]
Infdrv33=INFORMIX 3.3 32-BIT

[Infdrv33]
Driver=/opt/informix/csdk_2.81.UC1G2/lib/cli/iclis09b.so
Description=INFORMIX 3.3 32-BIT
Database=common_db
LogonID=testuser
pwd=testpass
Servername=ids_server
DB_LOCALE=en_US.819
OPTIMIZEAUTOCOMMIT=1
ENABLESCROLLABLECURSORS=1

$db = new PDO("informix:host=host.domain.com; service=9800;
    database=common_db; server=ids_server; protocol=onsoctcp;
    EnableScrollableCursors=1", "testuser", "tespass");