用php解决Shell_exec问题

I got a small issue with shell_exec function. What I'm trying to do is restart linux server by clicking on a button. I can't, however, seem to get the command to work.

This is the command I'm trying to use:

shell_exec('sudo sbin/shutdown -r now');

I've been reading about this issue for some hours now and tried all I could find but to no avail.

So here's what I've tried: First of all, I checked that there's no line in php.ini to prevent me from using the command. Secondly, I added this line to /etc/sudoers

%www-data ALL=NOPASSWD: /sbin/shutdown

When that didn't work either, I also created a new file to etc/sudoers.d/ and wrote this there: %users ALL=NOPASSWD: /sbin/shutdown

Also I don't know if that's relevant or not but when I tried to run another shell_exec in that very same place, it works fine (returns www-data) as

echo shell_exec("whoami");

But shows nothing when I add sudo:

echo shell_exec("sudo whoami");

So yeah, if there's anyone who can tell me what else to try, I would appreciate that. Thanks in advance. PS, It's linux wheezy that I'm trying to get this to work on if that's of any help.

Edit: even nobody ALL=NOPASSWD: ALL in sudoers file doesn't seem to make my shell_exec work with sudo.

I think it is a typo maybe.

It should be shell_exec('sudo /sbin/shutdown -r now');, using relative paths won't work everytime.