serial port (ttyS0 / ttyUSB0) - Permission denied

Hello I need a simple script to read the information from a serial port (ttyS0 / ttyUSB0) using PHP on CentosLinux. I have tried th following code but the code hangs and no results are returned. <?php $myFile = "/dev/ttyUSB0"; $handle = fopen($myFile, 'rb+'); $Data = fread($handle, 15); fclose($handle); echo $Data; ?> Information from the serial port could come at anytime so there needs to be some sort of continuous polling waiting to receive the data from serial port. Warning: fopen(/dev/ttyUSB0): failed to open stream: Permission denied in /var/www/html/scripts/[login to view URL] on line 2