How to kill a python child process created with subprocess.check_output() when the parent dies?

Question

I am running on a linux machine a python script which creates a child process using subprocess.check_output() as it follows:

subprocess.check_output(["ls", "-l"], stderr=subprocess.STDOUT) 

The problem is that even if the parent process dies, the child is still running. Is there any way I can kill the child process as well when the parent dies?

Answer 1

Yes, you can achieve this by two methods. Both of them require you to use Popen instead of check_output. The first is a simpler method, using try..finally, as follows:

from contextlib import contextmanager  @contextmanager def run_and_terminate_process(*args, **kwargs): try:     p = subprocess.Popen(*args, **kwargs)     yield p         finally:     p.terminate() # send sigterm, or ...     p.kill()      # send sigkill  def main():     with run_and_terminate_process(args) as running_proc:         # Your code here, such as running_proc.stdout.readline() 

This will catch sigint (keyboard interrupt) and sigterm, but not sigkill (if you kill your script with -9).

The other method is a bit more complex, and uses ctypes' prctl PR_SET_PDEATHSIG. The system will send a signal to the child once the parent exits for any reason (even sigkill).

import signal import ctypes libc = ctypes.CDLL("libc.so.6") def set_pdeathsig(sig = signal.SIGTERM):     def callable():         return libc.prctl(1, sig)     return callable p = subprocess.Popen(args, preexec_fn = set_pdeathsig(signal.SIGTERM))