Launch a completely independent process

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You open your long-running process and keep a pipe to it. So you expect to talk to it. When yor launcher script exits, you can no longer talk to it. The long-running process receives a SIGPIPE and exits.

The following just worked for me (Linux, Python 2.7).

Create a long-running executable:

$ echo "sleep 100" > ~/tmp/sleeper.sh

Run Python REPL:

$ python
>>>

import subprocess
import os
p = subprocess.Popen(['/bin/sh', os.path.expanduser('~/tmp/sleeper.sh')])
# look ma, no pipes!
print p.pid
# prints 29893

Exit the REPL and see the process still running:

>>> ^D
$ ps ax | grep sleeper
29893 pts/0    S      0:00 /bin/sh .../tmp/sleeper.sh
29917 pts/0    S+     0:00 grep --color=auto sleeper

If you want to first communicate to the started process and then leave it alone to run further, you have a few options:

  • Handle SIGPIPE in your long-running process, do not die on it. Live without stdin after the launcher process exits.
  • Pass whatever you wanted using arguments, environment, or a temporary file.
  • If you want bidirectional communication, consider using a named pipe (man mkfifo) or a socket, or writing a proper server.
  • Make the long-running process fork after the initial bi-direcional communication phase is done.

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