if you'd like to make a "socket_read" on a linux-system connected with a flash-client (v. 6.0 r81) you have to send a string to the connected port:
<?php
... //initialising communication
$string = "ready to get/send data\0";
socket_write($socket, $string);
//now you can read from...
$line = trim(socket_read($socket, MAXLINE));
... // do some stuff, finaly close connection
?>