harperville harperville - 4 years ago 163
Python Question

Run background process in Python and do NOT wait

My goal is simple: kick off rsync and DO NOT WAIT.

I've tried every solution I could find but the solutions do not work for me.

Python 2.7.9 on Debian

Sample code:

rsync_cmd = "/usr/bin/rsync -a -e 'ssh -i /home/myuser/.ssh/id_rsa' {0}@{1}:'{2}' {3}".format(remote_user, remote_server, file1, file1)
rsync_cmd2 = "/usr/bin/rsync -a -e 'ssh -i /home/myuser/.ssh/id_rsa' {0}@{1}:'{2}' {3} &".format(remote_user, remote_server, file1, file1)
rsync_path = "/usr/bin/rsync"
rsync_args = shlex.split("-a -e 'ssh -i /home/mysuser/.ssh/id_rsa' {0}@{1}:'{2}' {3}".format(remote_user, remote_server, file1, file1))
#subprocess.call(rsync_cmd, shell=True) # This isn't supposed to work but I tried it
#subprocess.Popen(rsync_cmd, shell=True) # This is supposed to be the solution but not for me
#subprocess.Popen(rsync_cmd2, shell=True) # Adding my own shell "&" to background it, still fails
#subprocess.Popen(rsync_cmd, shell=True, stdin=None, stdout=None, stderr=None, close_fds=True) # This doesn't work
#subprocess.Popen(shlex.split(rsync_cmd)) # This doesn't work
#os.execv(rsync_path, rsync_args) # This doesn't work
#os.spawnv(os.P_NOWAIT, rsync_path, rsync_args) # This doesn't work
#os.system(rsync_cmd2) # This doesn't work
print "DONE"

(I've commented out the execution commands only because I'm actually keeping all of my trials in my code so that I know what I've done and what I haven't done. Obviously, I would run the script with the right line uncommented.)

What happens is this...I can watch the transfer on the server and when it's finished, then I get a "DONE" printed to the screen.

What I'd like to have happen is a "DONE" printed immediately after issuing the
command and for the transfer to start.

Seems very straight-forward. I've tried ALL of the suggestions offered up by the Interwebs and I have found NOTHING that works for me.

Thanks ahead of time.

(I am sure everybody is going to offer up "This is a duplicate" but every entry that I've found in the entire StackExchange community fails. If you have one you'd like me to try, please pass it along before you think this is a duplicate.)

Answer Source

Here is verified example for Python REPL:

>>> import subprocess
>>> import sys
>>> p = subprocess.Popen([sys.executable, '-c', 'import time; time.sleep(100)'], stdout=subprocess.PIPE, stderr=subprocess.STDOUT); print('finished')

How to verify that via another terminal window:

$ ps aux | grep python


user           32820   0.0  0.0  2447684   3972 s003  S+   10:11PM   0:00.01 /Users/user/venv/bin/python -c import time; time.sleep(100)
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