I don't use the oci functions, but I have set up connections/queries to a production Oracle database running under AIX. I'm using php3 (I can't get php4 to compile in the Oracle libs on AIX, isn't a problem under linux however).
This seems to work for me:
<?php
$conn = ora_logon("davs/david@cats");
if ($conn){
ora_logoff($conn);
echo "Connection successful";
}
else{
echo "Connection fails";
}
?>
Hope this helps a little.