exec() sytem() problem with starting ext. prg

Hello php-general, on a LAMP server I have the following problem: 1. playing around I tried to execute the linux df (diskfree) command with exec() or system() - no problem, works fine! 2. trying to start an application did not work! - the application which I am trying to start can be started by anyone, here are the user rights: -rwxrwxrwx 1 10575 21129 1052648 M?r 13 16:31 mldonkey - the application is normally (from the console, no gui) started like this: mldonkey > mldonkey.log & - for testing I configured the Apache (in httpd.conf) as a user - doing a little research (http://www.php.net/manual/en/ref.exec.php) I tried this: exec("php script.php parameters 2>dev/null >&- <&- >/dev/null &"); Where... ...php is the path to your php script executer (php has to be specifically complied to be to do this) ...script.php is the script ...parameters are none or more parameters ...2>dev/null redirects the stderr to a file ...<&- switches off the stdin ...>&- switches off the stdout ...>dev/null redirects all other output to the file dev/null ...& direct script to run in background - played a little with the parameters and... nothing happened! ;-( Help me please! Maybe anybody knows, if this has something to do with user rights (I think not)? What do I have to do, if I want to send e.g. 'kill PID' Linux command (no success here either)? Thank's a lot, Alex