I have Apache server running on my pi. I send a httprequest from my Java app to the server to turn the motor on and off by executing a pyhton script. PHP code on the server:

 echo "turning on";
 exec("python /home/pi/motor/on.py /dev/null/ 2>/dev/null/ &")

 echo "turning off";
 exec("python /home/pi/motor/off.py")

I think my problem is when turning the motor on, my application freezes as the exec call has not returned yet (because my python code is in a loop and can only exit when interrupt arrives). I want to be able to turn the motor on and off, but I can only turn it on. Any solutions for this problem or another way of achieving what I want to do?

exec("python /home/pi/motor/on.py /dev/null/ 2>/dev/null/ &")

There's a > missing. To redirect the standard output, it must read

exec("python /home/pi/motor/on.py >/dev/null/ 2>/dev/null/ &")

If you don't redirect both the standard output and standard error channels, php's exec() waits for completion, regardless of an &.

  • hmm this worked anyway. Thnaks. – Casper2210 Jan 30 '18 at 16:04
  • It's the same for you "off" script. You have to redirect standard output and standard error. – Janka Jan 30 '18 at 16:14

If you migrate your web server from php to flask, you can give the motor command natively. Make routes as @app.route('/motor-on') and ('/motor-off'), with their respective python commands, then trigger the motor control with ajax request on button click (java script). TIP: Use gpiozero library, it is super easy and effective.

  • The thing is it has to be a Java app controlling the motor. Can flask work with java? – Casper2210 Jan 30 '18 at 16:02
  • [speculative] yes i guess. – Abbas Kagdi Jan 31 '18 at 4:43
  • Assuming that you are using Java to read a web server response, then it is recommendable to simplify your setup to either Python or PHP. Partially, that is a matter of preference and skill. However, the Raspberry community is producing a lot of Python libraries which makes PHP a bit more difficult choice. To state in another way: Java sees web pages as text, so as long as your server produces text in a way understood by your Java app, the technology behind the curtain does not matter. – ferrix Feb 20 at 19:37

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