How to run and cancel a Linux command using Flask Python API? - python-3.x

Question

I am working on a Flask based Python api. It has two api, run_cmd and stop_cmd. Run cmd will execute a command in the terminal. This command will keep on going until someone manually cancels it. So to cancel it, we have stop_cmd api. Below is the code:
from flask import Flask, jsonify, request
from threading import Thread
from subprocess import call
app = Flask(__name__)
def RunCmd():
call('while true; do echo "hello"; sleep 2s; done', shell=True)
#app.route('/run_cmd', methods=['GET'])
def run_cmd():
Thread(target=RunCmd).start()
return jsonify({"status": "ok"}), 200
#app.route('/stop_cmd', methods=['GET'])
def stop_cmd():
# This api will stop the cmd running in RunCmd
As you can see in the above code, if we hit the /run_cmd, it starts and keeps printing hello in the terminal. I wanted to know how can we cancel this ongoing session of the command so that we can write it in stop cmd api. Is this possible?

Answer 1

This is how I solved it
from flask import Flask, jsonify, request
from threading import Thread
import subprocess
import psutil
from subprocess import call
from command_runner import command_runner
app = Flask(__name__)
proc = ""
def kill(proc_pid):
process = psutil.Process(proc_pid)
for proc in process.children(recursive=True):
proc.kill()
process.kill()
def RunCmd():
global proc
proc = subprocess.Popen(['while true; do echo "hello"; sleep 2s; done'], shell=True)
#app.route('/run_cmd', methods=['GET'])
def run_cmd():
Thread(target=RunCmd).start()
return jsonify({"status": "ok"}), 200
#app.route('/stop_cmd', methods=['GET'])
def stop_cmd():
global proc
kill(proc.pid)
return jsonify({"status": True}), 200
if __name__ == '__main__':
app.run(host='127.0.0.1', port=5000)

Answer 2

Subprocess.call is a part of an older, deprecated API if I am informed correctly. Instead, you should probably use subprocess.Popen(). Then you could start your command by running
proc = subprocess.Popen(["somecommand", "-somearg", "somethingelse"])
This will return a Popen object which you can terminate by sending it a signal, for example proc.terminate() or proc.kill().