passthru

On the server itself (to which I have root access) I type: someProgram arg1 arg2 arg3 and it runs properly, returning the proper output to standard output (the screen). I can do this from anywhere on the server (for example, from the same directory where my php scripts are located, /var/www/html/blah), and I can do it as the same user that apache runs as ('apache'). BUT, when I try: <?php passthru("someProgram arg1 arg2 arg3"); ?> it fails. I get no output at all. I can check that everything else is ok by doing something like <?php passthru("someProgram arg1 arg2 arg3"); passthru("echo 'finished'"); ?> which then returns just the word 'finished' to the browser. I CAN do other things via passthru, for example, <?php passthru("man tar"); ?>, and <?php passthru("ls -al"); ?> and so on. I am running php as an apache module. I am NOT running php in 'safe mode'. Any ideas what is going wrong here? Thanks, Michael Dickson