PHP exec无法通过crontab（cronjobs）工作，但通过控制台工作正常

I try to restart my LTE modem via cron. I have a PHP file (restart.php) with exec() function:

exec('usb_modeswitch -R -v 12d1 -p 1436');

It works fine if I type in console (as root):

php restart.php

But not works via crontab (for root):

*/10 * * * * php /var/www/html/modem/restart.php

I have 777 permissions for restart.php file and the path is ok.

What is wrong? And how I can fix it? Any ideas?

Please, help

I added a full path to usb_modeswitch and it solved my problem:

exec('/usr/sbin/usb_modeswitch -R -v 12d1 -p 1436');

Rob Ruchte, Thank u for solution

Try to use full path in crontab for php and in php script. You can find where is php binary by this command:

whereis php