PHP, problem with exec...how do I make sure the execution is working?

I am uploading a video, which is supposed to generate three screenshot thumbnails. I have the same upload code running in both admin and front-end, but for some odd reason the thumb is only being generat开发者_运维百科ed when I upload from front end, and not from backend...

My directory structure root/convert.php (this is the file running through exec call) (the following two files are the upload files running in user-end and admin-end respectively)

root/upload.php
root/siteadmin/modules/videos/edit.php

I believe convert.php is not being run from admin-side for some reason. The command is something like:

$cmd = $cgi . $config['phppath']. ' ' .$config['BASE_DIR']. '/convert.php ' .$vdoname. ' ' .$vid. ' ' .$ff;echo $cmd;die;
                        exec($cmd. '>/dev/null &');

And echoing out the exec $cmd, I get this:

/usr/bin/php /home/testsite/public_html/dev/convert.php 1272.mp4 1272 /home/testsite/public_html/dev/video/1272.mp4

How do I make sure convert.php is being run?

EDIT: OK, now I am sure it is not being executed from admin-side, any ideas why?

http://php.net/manual/en/function.exec.php

"return_var" - If the return_var argument is present along with the output argument, then the return status of the executed command will be written to this variable.

Another way to determine if exec actually runs the convert.php file, add some debugging info in convert.php (e.g. write something to a file when the covert.php script starts).

Just an Idea

you could print "TRUE" in the convert script when it runs successfully. don't add >/dev/null & check the return value of exec

$value = exec($cmd);
if($value == 'TRUE')
  // did run sucessfully 
}

chmod 755 convet.php

you also make sure the first line of convert.php is:

#!/usr/bin/php

check the full path of php cli executable.

Also make sure convert.php las unix line ending ("\n")