Python spawn off a child subprocess, detach, and exit

by

popen on Unix is done using fork. That means you’ll be safe with:

  1. you run Popen in your parent process
  2. immediately exit the parent process

When the parent process exits, the child process is inherited by the init process (launchd on OSX) and will still run in the background.

The first two lines of your python program are not needed, this perfectly works:

import subprocess
p = subprocess.Popen(['nc', '-l', '8888'],
                     cwd="https://stackoverflow.com/",
                     stdout=subprocess.PIPE,
                     stderr=subprocess.STDOUT)

I was reading about double-forks and not sure if this is necessary

This would be needed if your parent process keeps running and you need to protect your children from dying with the parent. This answer shows how this can be done.

How the double-fork works:

  1. create a child via os.fork()
  2. in this child call Popen() which launches the long running process
  3. exit child: Popen process is inherited by init and runs in the background

Why the parent has to immediately exit? What happens if it doesn’t exit immediately?

If you leave the parent running and the user stops the process e.g. via ctrl-C (SIGINT) or ctrl-\ (SIGQUIT) then it would kill both the parent process and the Popen process.

What if it exits one second after forking?

Then, during this 1s period your Popen process is vulnerable to ctrl-c etc. If you need to be 100% sure then use the double forking.

More Related Contents:

  1. Sub-process in Python execute two task? [closed]
  2. How to terminate a python subprocess launched with shell=True
  3. How to use `subprocess` command with pipes
  4. ImageMagick not authorized to convert PDF to an image
  5. How do I run Selenium in Xvfb?
  6. What is the simplest way to SSH using Python?
  7. Python: how to kill child process(es) when parent dies?
  8. How do you set your pythonpath in an already-created virtualenv?
  9. How to kill a python child process created with subprocess.check_output() when the parent dies?
  10. Cross-platform subprocess with hidden window
  11. In Python script, how do I set PYTHONPATH?
  12. How to get output from subprocess.Popen(). proc.stdout.readline() blocks, no data prints out
  13. ‘yes’ reporting error with subprocess communicate()
  14. How to make a python, command-line program autocomplete arbitrary things NOT interpreter
  15. Understanding python subprocess.check_output’s first argument and shell=True [duplicate]
  16. Sending a password over SSH or SCP with subprocess.Popen
  17. How to split a huge csv file based on content of first column?
  18. Fetching the output of a command executed through os.system() command [duplicate]
  19. How to use “/” (directory separator) in both Linux and Windows in Python?
  20. When using os.execlp, why `python` needs `python` as argv[0]
  21. How to install and import Python modules at runtime
  22. Dropping Root Permissions In Python
  23. How to find the mountpoint a file resides on?
  24. How do I hide the console when I use os.system() or subprocess.call()?
  25. How can I run an external command asynchronously from Python?
  26. How to get exit code when using Python subprocess communicate method?
  27. Python subprocess.Popen “OSError: [Errno 12] Cannot allocate memory”
  28. “OSError: [Errno 2] No such file or directory” while using python subprocess with command and arguments
  29. How do i use subprocesses to force python to release memory?
  30. Run subprocess and print output to logging

Leave a Comment