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pythonlinuxsubprocessos.system

How to determine pid of process started via os.system

I want to start several subprocesses with a programm, i.e. a module foo.py starts several instances of bar.py.

Since I sometimes have to terminate the process manually, I need the process id to perform a kill command.

Even though the whole setup is pretty “dirty”, is there a good pythonic way to obtain a process’ pid, if the process is started via os.system?

foo.py:

import os
import time
os.system("python bar.py \"{0}\ &".format(str(argument)))
time.sleep(3)
pid = ???
os.system("kill -9 {0}".format(pid))

bar.py:

import time
print("bla")
time.sleep(10) % within this time, the process should be killed
print("blubb")
Solution

  • os.system return exit code. It does not provide pid of the child process.

    Use subprocess module.

    import subprocess
import time
argument = '...'
proc = subprocess.Popen(['python', 'bar.py', argument], shell=True)
time.sleep(3) # <-- There's no time.wait, but time.sleep.
pid = proc.pid # <--- access `pid` attribute to get the pid of the child process.

    To terminate the process, you can use terminate method or kill. (No need to use external kill program)

    proc.terminate()