Python: Howto launch a full process not a child process and retrieve the PID

Question

I would like:

Launch a new process (myexe.exe arg1) from my process (myexe.exe arg0)
Retrieve the PID of this new process (os windows)
when I kill my first entity (myexe.exe arg0) with the TaskManager Windows Command "End process tree", I need that the new one (myexe.exe arg1) will not be killed...

I've played with subprocess.Popen, os.exec, os.spawn, os.system... without success.

Another way to explain the problem: How to protect myexe.exe (arg1) if someone kills the "process tree" of the myexe.exe (arg0)?

EDIT: same question (without answer) HERE

EDIT: the following command do not guarantee the Independence of the subprocess

subprocess.Popen(["myexe.exe",arg[1]],creationflags = DETACHED_PROCESS | CREATE_NEW_PROCESS_GROUP,close_fds = True)

related: Popen waiting for child process even when the immediate child has terminated — jfs
– jfs, Commented Feb 10, 2013 at 11:43
Possible duplicate of Launch a totally independent process from Python — jtpereyda
– jtpereyda, Commented Feb 28, 2017 at 3:21

rstackhouse · Accepted Answer · 2017-07-27 19:52:13Z

14

To start a child process that can continue to run after the parent process exits on Windows:

from subprocess import Popen, PIPE CREATE_NEW_PROCESS_GROUP = 0x00000200 DETACHED_PROCESS = 0x00000008 p = Popen(["myexe.exe", "arg1"], stdin=PIPE, stdout=PIPE, stderr=PIPE, creationflags=DETACHED_PROCESS | CREATE_NEW_PROCESS_GROUP) print(p.pid)

Windows process creation flags are here

A more portable version is here.

edited Jul 27, 2017 at 19:52

rstackhouse

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answered Feb 10, 2013 at 11:53

jfs

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12 Comments

baco Over a year ago

nice try! But when I kill the "myexe.exe" (arg0) through "End process tree" taskmanager command of windows, both myexe.exe were killed ! If I've done the same command on the "myexe.exe" (arg1) only this entity will be killed...

jfs Over a year ago

@baco: Use the option that kills only one process instead of "process tree".

nikola Over a year ago

Probably the process tree is traversed in both directions.

baco Over a year ago

@JF Sebastian: that the question => how to protect myexe.exe (arg1) if someone kill the "process tree" of the myexe.exe (arg0) (the solution seems to use os.startfile but I can't use args!)

djvg Over a year ago

The windows process creation flags are (now) also available as subprocess windows constants.

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sotapme · Accepted Answer · 2013-02-10 11:36:36Z

I did similar a couple of years ago on windows and my issue was wanting to kill the child process.

I presume you can run the subprocess using pid = Popen(["/bin/mycmd", "myarg"]).pid so I'm unsure what the real issue is, so I'm guessing it's when you kill the main process.

IIRC it was something to do with the flags.

I can't prove it as I'm not running Windows.

subprocess.CREATE_NEW_CONSOLE The new process has a new console, instead of inheriting its parent’s console (the default). This flag is always set when Popen is created with shell=True. subprocess.CREATE_NEW_PROCESS_GROUP A Popen creationflags parameter to specify that a new process group will be created. This flag is necessary for using os.kill() on the subprocess. This flag is ignored if CREATE_NEW_CONSOLE is specified.

Andreas Bunkahle · Accepted Answer · 2015-02-18 19:01:32Z

So if I understand you right the code should go like this:

from subprocess import Popen, PIPE script = "C:\myexe.exe" param = "-help" DETACHED_PROCESS = 0x00000008 CREATE_NEW_PROCESS_GROUP = 0x00000200 pid = Popen([script, param], shell=True, stdin=PIPE, stdout=PIPE, stderr=PIPE, creationflags=DETACHED_PROCESS | CREATE_NEW_PROCESS_GROUP)

At least I tried this one and worked for me.

Robert · Accepted Answer · 2023-04-15 06:01:31Z

I have tried all the proposed solutions for Windows 10 but all of them still open the new process as part of the original processes' process tree (either directly below the main process or with a cmd shell in between). The only solution that is working for me is to create a fully independent process/fork using the cmd.exe's start command:

import subprocess subprocess.Popen(["cmd.exe", "/C", "start notepad"])

This is actually even easier as it requires no mangling with stdin/out parameters. Obviously, since it is completely independent, you cannot communicate with it. But you can use psutil to retrieve it's PID to at least monitor or close it, if necessary:

import psutil for process in psutil.process_iter(): if process.name() == 'notepad.exe': print(process.pid)

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