mysqldump

I have created a PHP script that looks like: <?php $filename = "/var/www/html/db_backup_" . date("n-j-y").".sql"; exec('mysqldump -u ***** -p***** database > $filename'); ?> For some reason this doesnt work and I cant figure out why. There is no error that comes back. When I run the mysqldump command from the server console it produces the file fine. I have read a few other posts out there about this same thing which resulted in the location the file was being saved. But I have gone through my server and found nothing. Does anyone have any suggestions for regarding this. Thanks, Aaron