Python Programming Language :: subprocess leaves child living


	subprocess leaves child living Hi, When I do a small program like from subprocess import Popen popen = Popen(["ping", "google.com"]) from time import sleep sleep(100) start it and kill it, the ping process lives on. Is there a way to ensure that the ping process is always killed when the python process is? I can't use atexit, as ping then isn't killed when python is killed "in the hard way" Thomas Dybdahl Ahle schrieb: > Hi, When I do a small program like > from subprocess import Popen > popen = Popen(["ping", "google.com"]) > from time import sleep > sleep(100) > start it and kill it, the ping process lives on. > Is there a way to ensure that the ping process is always killed when the > python process is? > I can't use atexit, as ping then isn't killed when python is killed "in > the hard way" Calling popen.close() perhaps ? You basically open a pipe, which spawns a shell and the command is then started in there. So, if your program quits, the spawned shell is still alive, only the pipe is dead. Den Tue, 05 Jun 2007 14:07:44 +0200 skrev Stefan Sonnenberg-Carstens: - Hide quoted text - > Thomas Dybdahl Ahle schrieb: >> Hi, When I do a small program like >> from subprocess import Popen >> popen = Popen(["ping", "google.com"]) from time import sleep >> sleep(100) >> start it and kill it, the ping process lives on. Is there a way to >> ensure that the ping process is always killed when the python process >> is? >> I can't use atexit, as ping then isn't killed when python is killed "in >> the hard way" > Calling popen.close() perhaps ? > You basically open a pipe, which spawns a shell and the command is then > started in there. > So, if your program quits, the spawned shell is still alive, only the > pipe is dead. Problem is - I can't do that when I get killed. Isn't it possible to open processes in such a way like terminals? If I kill the terminal, everything open in it will die too. Thomas Dybdahl Ahle wrote: > Problem is - I can't do that when I get killed. > Isn't it possible to open processes in such a way like terminals? If I > kill the terminal, everything open in it will die too. On POSIX platform you can use signals and ``os.kill`` function. Fo example: <code> import os, signal from subprocess import Popen from time import sleep def handler(signum, frame): print 'Signal handler called' raise KeyboardInterrupt signal.signal(signal.SIGTERM, handler) try: popen = Popen(["ping", "google.com"]) try: sleep(100) except KeyboardInterrupt: pass finally: if popen.poll() is None: print "killing process: %d" % popen.pid os.kill(popen.pid, signal.SIGTERM) </code> -- HTH, Rob Den Tue, 05 Jun 2007 07:06:15 -0700 skrev Rob Wolfe: - Hide quoted text - > Thomas Dybdahl Ahle wrote: >> Problem is - I can't do that when I get killed. Isn't it possible to >> open processes in such a way like terminals? If I kill the terminal, >> everything open in it will die too. > On POSIX platform you can use signals and ``os.kill`` function. Fo > example: > <code> > import os, signal > from subprocess import Popen > from time import sleep > def handler(signum, frame): > print 'Signal handler called' > raise KeyboardInterrupt > signal.signal(signal.SIGTERM, handler) > try: > popen = Popen(["ping", "google.com"]) try: > sleep(100) > except KeyboardInterrupt: > pass > finally: > if popen.poll() is None: > print "killing process: %d" % popen.pid os.kill(popen.pid, > signal.SIGTERM) > </code> But you can't ever catch sigkill. Isn't there a way to make sure the os kills the childprocess when the parrent dies? Thomas Dybdahl Ahle <lob@gmail.com> writes: > But you can't ever catch sigkill. There is no protection against sigkill. > Isn't there a way to make sure the os kills the childprocess when the > parrent dies? If the parent dies suddenly without any notification childprocesses become zombies and there is no way to avoid that. -- HTH, Rob On Jun 5, 2007, at 3:01 PM, Rob Wolfe wrote: > Thomas Dybdahl Ahle <lob@gmail.com> writes: >> But you can't ever catch sigkill. > There is no protection against sigkill. >> Isn't there a way to make sure the os kills the childprocess when the >> parrent dies? > If the parent dies suddenly without any notification childprocesses > become zombies and there is no way to avoid that. Apologies for picking nits... But actually that is an orphan process. When a parent process dies and the child continues to run, the child becomes an orphan and is adopted by init. Orphan processes can be cleaned up on most Unices with 'init q' (or something very similar). Zombies on the other hand, are those processes that have completed execution but still have an entry in the process table. The cause of zombies AFAIK, is a parent that has failed to call wait(2). To clean up zombies, you can send a SIGCHLD signal to the parent process -- probably with 'kill -17' (but use 'kill -l' to find out what it is on your system). hth, Michael --- "I would rather use Java than Perl. And I'd rather be eaten by a crocodile than use Java." Trouser Den Tue, 05 Jun 2007 22:01:44 +0200 skrev Rob Wolfe: > Thomas Dybdahl Ahle <lob@gmail.com> writes: >> But you can't ever catch sigkill. > There is no protection against sigkill. >> Isn't there a way to make sure the os kills the childprocess when the >> parrent dies? > If the parent dies suddenly without any notification childprocesses > become zombies and there is no way to avoid that. If I call "kill -9 pythonpid" on the python code you posted earlier, the terminal running the script will continue pinging forever. If it was a harder program like a chessengine or such, it would continue consuming 100% cpu time. Zombies would be fine to me. Den Tue, 05 Jun 2007 15:46:39 -0500 skrev Michael Bentley: > But actually that is an orphan process. When a parent process dies > and the child continues to run, the child becomes an orphan and is > adopted by init. Orphan processes can be cleaned up on most Unices with > 'init q' (or something very similar). Is it not possible to tell python that this process should not be adopted by init, but die with its parrent? Just like terminals seem to do it.. On Jun 5, 2007, at 4:17 PM, Thomas Dybdahl Ahle wrote: > Den Tue, 05 Jun 2007 15:46:39 -0500 skrev Michael Bentley: >> But actually that is an orphan process. When a parent process dies >> and the child continues to run, the child becomes an orphan and is >> adopted by init. Orphan processes can be cleaned up on most >> Unices with >> 'init q' (or something very similar). > Is it not possible to tell python that this process should not be > adopted > by init, but die with its parrent? > Just like terminals seem to do it.. Well, the way you posed the original question: > from subprocess import Popen > popen = Popen(["ping", "google.com"]) > from time import sleep > sleep(100) is really what adoption by init is designed to handle. Here you've created a child but have not waited for its return value. Like a good adoptive parent, init will wait(2) for the child. I think if you really looked into it you'd find that the terminal had called wait(2) before it was killed. Similarly, if you start a long- running subprocess in python and wait for it to return -- killing the parent will slaughter the child as well. hth, Michael --- Let the wookie win. On Jun 5, 2007, at 5:13 PM, Michael Bentley wrote: - Hide quoted text - > On Jun 5, 2007, at 4:17 PM, Thomas Dybdahl Ahle wrote: >> Den Tue, 05 Jun 2007 15:46:39 -0500 skrev Michael Bentley: >>> But actually that is an orphan process. When a parent process >>> dies >>> and the child continues to run, the child becomes an orphan and is >>> adopted by init. Orphan processes can be cleaned up on most >>> Unices with >>> 'init q' (or something very similar). >> Is it not possible to tell python that this process should not be >> adopted >> by init, but die with its parrent? >> Just like terminals seem to do it.. > Well, the way you posed the original question: >> from subprocess import Popen >> popen = Popen(["ping", "google.com"]) >> from time import sleep >> sleep(100) > is really what adoption by init is designed to handle. Here you've > created a child but have not waited for its return value. Like a > good adoptive parent, init will wait(2) for the child. > I think if you really looked into it you'd find that the terminal had > called wait(2) before it was killed. Similarly, if you start a long- > running subprocess in python and wait for it to return -- killing the > parent will slaughter the child as well. I guess I should have verified my suspicions before speaking up -- I was worng -- even if you are waiting for a return code, the child will persist as a child of init. regards, Michael --- The Rules of Optimization are simple. Rule 1: Don't do it. Rule 2 (for experts only): Don't do it yet. -Michael A. Jackson Thomas Dybdahl Ahle <lob@gmail.com> wrote: > But you can't ever catch sigkill. > Isn't there a way to make sure the os kills the childprocess when the > parrent dies? Not as far as I know. If you've got a pipe open to the child then killing the parent should deliver SIGPIPE to the child which may (or may not) kill it. At least it got some sort of notification. -- Nick Craig-Wood <n@craig-wood.com> -- http://www.craig-wood.com/nick Den Tue, 05 Jun 2007 17:41:47 -0500 skrev Michael Bentley: - Hide quoted text - > On Jun 5, 2007, at 5:13 PM, Michael Bentley wrote: >> On Jun 5, 2007, at 4:17 PM, Thomas Dybdahl Ahle wrote: >>> Den Tue, 05 Jun 2007 15:46:39 -0500 skrev Michael Bentley: >>>> But actually that is an orphan process. When a parent process dies >>>> and the child continues to run, the child becomes an orphan and is >>>> adopted by init. Orphan processes can be cleaned up on most Unices >>>> with >>>> 'init q' (or something very similar). >>> Is it not possible to tell python that this process should not be >>> adopted >>> by init, but die with its parrent? >>> Just like terminals seem to do it.. >> Well, the way you posed the original question: >>> from subprocess import Popen >>> popen = Popen(["ping", "google.com"]) from time import sleep >>> sleep(100) >> is really what adoption by init is designed to handle. Here you've >> created a child but have not waited for its return value. Like a good >> adoptive parent, init will wait(2) for the child. >> I think if you really looked into it you'd find that the terminal had >> called wait(2) before it was killed. Similarly, if you start a long- >> running subprocess in python and wait for it to return -- killing the >> parent will slaughter the child as well. > I guess I should have verified my suspicions before speaking up -- I was > worng -- even if you are waiting for a return code, the child will > persist as a child of init. Bugger. I know that if you use forkpty, the child get slaughtered, but using the subprocess module just seems much easier than forking. On Jun 6, 2007, at 7:11 AM, Thomas Dybdahl Ahle wrote: - Hide quoted text - > Den Tue, 05 Jun 2007 17:41:47 -0500 skrev Michael Bentley: >> On Jun 5, 2007, at 5:13 PM, Michael Bentley wrote: >>> On Jun 5, 2007, at 4:17 PM, Thomas Dybdahl Ahle wrote: >>>> Den Tue, 05 Jun 2007 15:46:39 -0500 skrev Michael Bentley: >>>>> But actually that is an orphan process. When a parent >>>>> process dies >>>>> and the child continues to run, the child becomes an orphan and is >>>>> adopted by init. Orphan processes can be cleaned up on most >>>>> Unices >>>>> with >>>>> 'init q' (or something very similar). >>>> Is it not possible to tell python that this process should not be >>>> adopted >>>> by init, but die with its parrent? >>>> Just like terminals seem to do it.. >>> Well, the way you posed the original question: >>>> from subprocess import Popen >>>> popen = Popen(["ping", "google.com"]) from time import sleep >>>> sleep(100) >>> is really what adoption by init is designed to handle. Here you've >>> created a child but have not waited for its return value. Like a >>> good >>> adoptive parent, init will wait(2) for the child. >>> I think if you really looked into it you'd find that the terminal >>> had >>> called wait(2) before it was killed. Similarly, if you start a >>> long- >>> running subprocess in python and wait for it to return -- killing >>> the >>> parent will slaughter the child as well. >> I guess I should have verified my suspicions before speaking up -- >> I was >> worng -- even if you are waiting for a return code, the child will >> persist as a child of init. > Bugger. > I know that if you use forkpty, the child get slaughtered, but > using the > subprocess module just seems much easier than forking. Yeah, and if there is some way (there may be, but I don't know) to make your python script the head of a process group (or session -- I'm not very clear on the distinction) -- children would be automatically slain. That's how a terminal session manages to get its children cleaned up I think... If it is important that children get terminated upon death of a parent, you probably do have to fork. g'luck! Michael --- "Neurons are far more valuable than disk space, screen lines, or CPU cycles." - Ben Finney On Jun 5, 7:58 am, Thomas Dybdahl Ahle <lob@gmail.com> wrote: > Hi, When I do a small program like > from subprocess import Popen > popen = Popen(["ping", "google.com"]) > from time import sleep > sleep(100) > start it and kill it, the ping process lives on. > Is there a way to ensure that the ping process is always killed when the > python process is? > I can't use atexit, as ping then isn't killed when python is killed "in > the hard way" pid = popen.pid pidfile = open('/usr/local/var/somefile.pid', 'w') pidfile.write('pid') pidfile.close() then you can check if it is still running when your ?program? restarts and can kill it. maybe not the perfect answer, but it answers an imperfect question. Den Thu, 07 Jun 2007 07:00:53 +0000 skrev reed: - Hide quoted text - > On Jun 5, 7:58 am, Thomas Dybdahl Ahle <lob@gmail.com> wrote: >> Hi, When I do a small program like >> from subprocess import Popen >> popen = Popen(["ping", "google.com"]) from time import sleep >> sleep(100) >> start it and kill it, the ping process lives on. Is there a way to >> ensure that the ping process is always killed when the python process >> is? >> I can't use atexit, as ping then isn't killed when python is killed "in >> the hard way" > pid = popen.pid > pidfile = open('/usr/local/var/somefile.pid', 'w') pidfile.write('pid') > pidfile.close() > then you can check if it is still running when your ?program? restarts > and can kill it. If it restarts yeah. > maybe not the perfect answer, but it answers an imperfect question. Any details you need?