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I was to make a launcher application, I haven't found a way to detach a sub-process entirely from the spawning python process.

When I launch a program with my desktop's (cinnamon's) launcher the process tree goes:

/sbin/init -> mdm -> mdm -> cinnamon-session -> cinnamon -> the-app-i-launched

Of the threads I read, this one was the most insightful/helpful: Launch a completely independent process. But gets muddied answers as the OP is looking to run python code, which can often be achieved in many usually-preferred ways than by spawning an independent process.

From other posts from stack overflow that do not answer how to launch a detatched python process:

  • Running daemonalized python code: Applicable to running python code/module as a daemon, (not another process/application) detached from the python instance.
  • subprocess.call: Process spawns as a child of the python process.
  • os.system: Process spawns as a child of the python process.
  • close_fds: (Apparently) Windows(R)-only solution, need portable solution (primary target is Debian linux). Attempting to use close_fds=True on linux, process spawns as a child of the python process.
  • creationflags: Windows(R)-only solution. On linux raises: ValueError: creationflags is only supported on Windows platforms.
  • prefix launched process with nohup: Process spawns as a child of the python process. As far as I know, nohup or equivalent is not available on all platforms, making it a linux-only solution.
  • os.fork: Same as "Running daemonalized python code".
  • multiprocessing: Same problem as "Running daemonalized python code": useful only for running python code/module.
  • os.spawnl* + os.P_NOWAIT: Deprecated functions are undesirable to use for new code. In my testing I was not able to see my process actually spawned at all.
  • os.spawnl* + os.P_DETACH: Windows(R)-only, seemingly removed in current python 2.X versions: AttributeError: 'module' object has no attribute 'P_DETACH'.
  • os.system + shell fork: I was able to actually see my process run detatched from the python process with this, however I am woried that it has the faults:
    • Relies on running commands in a shell, which is more vulnerable to maliciousness, intentional or otherwise?.
    • Relies on non-portable? POSIX/shell? syntaxies that may not be interpenetrate on non-Linux platforms. Which I haven't dug up any good reference for portability on Partial Ref.
  • subprocess.Popen Alt: I still only observed the sub-process running as a child of the python process.
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  • i think the question i was trying to ask is "how to disown a process" and I'm not sure there is really a way to disown a process completely, at best it can maybe be owned by the spawning process's parent process. My objective was to run a process that could survive after the launching process closed, I think the only viable option is to host that process from a daemon meant to host other processes, i think most shells, including desktop shells, own this responsibility which is why "using bash" seemed like a viable option. albeit somewhat a confusing mess. Please let me know Commented Jun 16, 2021 at 4:00

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A working solution can be found in JonMc's answer here. I use it to open documents using 'xdg-open'.

You can change the stderr argument to stderr=open('/dev/null', 'w'), if you do not want a logfile.

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The only workable solution I have, and that may be non-portable Linux-only is to use shell evaluation with shell-detach-ampersand syntax. 

#!/usr/bin/env python2 import os os.system('{cmd} &'.format('firefox'))

This might go too-far up the process tree though, outside of the window manager session, potentially not-exiting with your desktop session.

/sbin/init -> firefox

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I think this way the process is not detached.

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