OctoPi webcam on/off - script permissions errors

Does anyone know how I can toggle the webcam off using octopi? (Octoprint v 1.3.6 from the octopi image and standard Raspberry Pi webcam, rather than a USB camera)

I'm running it on a pi zero and getting a few performance issues when streaming is on, but generally I don't want streaming on all the time. If I disable the webcamd service, performance drastically improves.

From the command line, 'sudo service webcamd stop' will happily start and stop the service, so using visudo, I tried putting the following into my sudoers file:

pi    ALL=(ALL) NOPASSWD: /usr/sbin/service webcamd stop
pi    ALL=NOPASSWD: /bin/systemctl stop webcamd

I tried making a button using the custom control editor plugin, which placed the following in my config.yaml:

  - name: WebCam Off
    script: /usr/sbin/service webcamd stop
  - name: WebCam Off2
    script: /bin/systemctl stop webcamd

Both fail and all I get in octoprint.log is:
2018-03-18 16:22:47,936 - tornado.access - WARNING - 404 POST /api/printer/command ( 1518.94ms

After struggling for some time, I tried making a C program, setting it suid and putting it in /home/pi/bin. This worked from the command line but not from the custom button, giving the same tornado.access error.

Finally just to see if it would execute any script at all, I tried a short bash script:

date >> /tmp/t.log
whoami >> /tmp/t.log
echo Args=$0 >> /tmp/t.log

then I called that with a button:

  - name: WebCam Off
    script: /home/pi/bin/doIrun wemcam_off

Still the same tornado.access error. It looks like octoprint can not execute any command or script. Is there any way I can enable this or get any form of useful debugging output to see why the called scripts are failing. Or, taking a step back, is there a better way to allow the toggling of the webcam?

I fixed the problem, it was my understanding of the 'script:' directive. This is not a path to a shell script, this is only a GCODE script. The correct way of doing this is putting something in the system menu via config.yaml:

  - name: Webcam Off
    action: CamOff
    command: /home/pi/bin/octoRootHelp webcam_off
  - name: Webcam On
    action: CamOn
    command: /home/pi/bin/octoRootHelp webcam_on

octoRootHelp is a small SUID C program I did. I suspect if I try again now I should also be able to use 'service webcamd stop'. The nice thing about this solution, it also allows the commands to be called from the API, with the URL /api/system/commands/custom/CamOff