Develop Reference

Kill python script launched by a subprocess called by another script (Windows)

I'm trying to integrate ESA'2 sen2cor python-script into my workflow. To do this I create a subprocess with which I call the "L2A_Process.bat" file, which in turn calls the "L2A_Process.py" script.
I want to launch the sen2cor-script with a timeout since it gets stuck and freezes from time to time, so as to automatically re-launch it if it failed.
To launch it and catch a timeout I successfully used the following script:
import os, subprocess
from signal import CTRL_BREAK_EVENT
timeout = 3600 #1hour
l1c_safe_path = "path/to/my/input/file.SAFE" #product that I want to process
command = ["L2A_process.bat", l1c_safe_path]
p = subprocess.Popen(command,shell=False, creationflags=subprocess.CREATE_NEW_PROCESS_GROUP)
try:
p.wait(timeout)
except subprocess.TimeoutExpired:
os.kill(p.pid, CTRL_BREAK_EVENT)
This is as far as I got. It results in the sen2cor-script being paused giving the following output:
Terminate batch job (Y/N)
I'd like to know how I can properly terminate my subprocess "p" with all it own child-subprocesses (i.e. "L2A_Process.py").
Some observations:
This script needs to run on Windows;
I've tried to kill the subprocess without the creationflag I've used in the example above: this results in the subprocess being killed but the "L2A_Process.py" script deteaches an keeps running (which is the core of my problem);
I cannot use a CTRL_C_EVENT since I want to re-launch the failed "L2A_Process.py" in a loop until it succeeds.

This code works for me to monitor Sen2cor status while converting L1C to L2A for Sentinel 2 data. The Sen2cor process is time and cpu consuming so be patient. It took half an hour to create L2A with DEM, DDV, etc. Hope it helps
from subprocess import Popen, PIPE
import os
pathtoprodS1C = "path_to_L1C_product" // safe file
outdirS2A = "output_dir" // where L2A files will be placed
pathtoL2Process = "path_to_L2A_Process" //if not in path
pathtoGIPP = "path_to_your_GIPP/L2A_GIPP.xml"
procName = "./L2A_Process"
os.chdir(pathtoL2Process)
import shlex
pcall = "./{} {} --output_dir {} --tif --GIP_L2A {}".format(procName,
pathtoprodS1C,
pathtoprodS2A,
pathtoGIPP)
args = shlex.split(pcall)
print(args)
try:
p = Popen(args, stdout=PIPE)
eut = p.stdout.readline()
while eut:
eut = p.stdout.readline()
print(eut)
finally:
print('Sen2Cor is Done')
exit()

python-daemon to start an independent process but let the main application continue?

Okay I'm officially out of ideas after running each and every sample I could find on google up to 19th page. I have a "provider" script. The goal of this python script is to start up other services that run indefinitely even after this "provider" stopped running. Basically, start the process then forget about it but continue the script and not stopping it...
My problem: python-daemon... I have actions (web-service calls to start/stop/get status from the started services). I create the start commands on the fly and perform variable substitution on the config files as required.
Let's start from this point: I have a command to run (A bash script that executes a java process - a long running service that will be stopped sometime later).
def start(command, working_directory):
pidfile = os.path.join(working_directory, 'application.pid')
# I expect the pid of the started application to be here. The file is not created. Nothing is there.
context = daemon.DaemonContext(working_directory=working_directory,
pidfile=daemon.pidfile.PIDLockFile(pidfile))
with context:
psutil.Popen(command)
# This part never runs. Even if I put a simple print statement at this point, that never appears. Debugging in pycharms shows that my script returns with 0 on with context
with open(pidfile, 'r') as pf:
pid = pf.read()
return pid
From here on in my caller to this method I prepare a json object to return to the client which essentially contains an instance_id (don't mind it) and a pid (that'll be used to stop this process in another request.
What happens? After with context my application exits with status 0, nothing is returned, no json response gets created, no pidfile gets created only the executed psutil.Popen command runs. How can I achieve what I need? I need an independently running process and need to know its PID in order to stop it later on. The executed process must run even if the current python script stops for some reason. I can't get around the shell script as that application is not mine I have to use what I have.
Thanks for any tip!
#Edit:
I tried using simply the Popen from psutil/subprocess with somewhat more promising result.
def start(self, command):
import psutil/subprocess
proc = psutil.Popen(command)
return str(proc.pid)
Now If I debug the application and wait some undefined time on the return statement everything is working great! The service is running the pid is there, I can stop later on. Then I simply ran the provider without debugging. It returns the pid but the process is not running. Seems like Popen has no time to start the service because the whole provider stops faster.
#Update:
Using os.fork:
#staticmethod
def __start_process(command, working_directory):
pid = os.fork()
if pid == 0:
os.chdir(working_directory)
proc = psutil.Popen(command)
with open('application.pid', 'w') as pf:
pf.write(proc.pid)
def start(self):
...
__start_process(command, working_directory)
with open(os.path.join(working_directory, 'application.pid'), 'r') as pf:
pid = int(pf.read())
proc = psutil.Process(pid)
print("RUNNING" if proc.status() == psutil.STATUS_RUNNING else "...")
After running the above sample, RUNNING is written on console. After the main script exits because I'm not fast enough:
ps auxf | grep
No instances are running...
Checking the pidfile; sure it's there it was created
cat /application.pid
EMPTY 0bytes

From multiple partial tips i got, finally managed to get it working...
def start(command, working_directory):
pid = os.fork()
if pid == 0:
os.setsid()
os.umask(0) # I'm not sure about this, not on my notebook at the moment
os.execv(command[0], command) # This was strange as i needed to use the name of the shell script twice: command argv[0] [args]. Upon using ksh as command i got a nice error...
else:
with open(os.path.join(working_directory, 'application.pid'), 'w') as pf:
pf.write(str(pid))
return pid
That together solved the issue. The started process is not a child process of the running python script and won't stop when the script terminates.

Have you tried with os.fork()?
In a nutshell, os.fork() spawns a new process and returns the PID of that new process.
You could do something like this:
#!/usr/bin/env python
import os
import subprocess
import sys
import time
command = 'ls' # YOUR COMMAND
working_directory = '/etc' # YOUR WORKING DIRECTORY
def child(command, directory):
print "I'm the child process, will execute '%s' in '%s'" % (command, directory)
# Change working directory
os.chdir(directory)
# Execute command
cmd = subprocess.Popen(command
, shell=True
, stdout=subprocess.PIPE
, stderr=subprocess.PIPE
, stdin=subprocess.PIPE
)
# Retrieve output and error(s), if any
output = cmd.stdout.read() + cmd.stderr.read()
print output
# Exiting
print 'Child process ending now'
sys.exit(0)
def main():
print "I'm the main process"
pid = os.fork()
if pid == 0:
child(command, working_directory)
else:
print 'A subprocess was created with PID: %s' % pid
# Do stuff here ...
time.sleep(5)
print 'Main process ending now.'
sys.exit(0)
if __name__ == '__main__':
main()
Further info:
Documentation: https://docs.python.org/2/library/os.html#os.fork
Examples: http://www.python-course.eu/forking.php
Another related-question: Regarding The os.fork() Function In Python

Python SIGTERM not killing subprocess

I have a class which can start and close a process. However it seems not to close the process.
My python code, there are other methods but they work fine.:
class KismetInstance:
"""Creates a kismet_server instance"""
def __init__(self, value=False):
logging.basicConfig(format='%(asctime)-15s::: %(message)s')
self.logger = logging.getLogger('kismet_instance')
self.example = value
def __create_kismet_instance__(self):
"""
Create a kismet_server subprocess.
:return:
"""
shell = ['sudo', '/usr/local/bin/kismet_server']
self.logger.debug('Attempting to run: %s', " ".join(shell))
self.kismet = Popen(shell, stdin=PIPE, stdout=PIPE, stderr=PIPE, cwd=r'./logs', preexec_fn=os.setsid)
def __destroy_kismet_instance__(self):
"""
Kill the subprocess
:return:
"""
os.killpg(os.getpgid(self.kismet.pid), 15)
It can create the subprocess fine. But I get this error when I try to kill (no sudo)
OSError: [Errno 1] Operation not permitted
And if I run with sudo, the process is still running afterwards.
pi#raspberrypi ~/project $ ps -A | grep 'kismet'
2912 ? 00:00:00 kismet_server

I managed to fix this. Turns out the subprocess was respawning itself creating something weird which prevented python from keeping track of it.
So I had to do this to fix it, However this is not the most elegant solution, and rather dangerouddangerous.
Be careful if you use this, because if you enter a term more broad than mine ('kismet') then you could kill a lot of processes on your system.
def __destroy_kismet_instance__(self):
"""
Kill the subprocess
:return:
"""
sig = signal.SIGKILL # What signal to send
os.killpg(os.getpgid(self.kismet.pid), sig) # Kill one of them
p_list = subprocess.Popen(['ps', '-A'], stdout=subprocess.PIPE) # Get All processes on system
out, err = p_list.communicate()
for line in out.splitlines(): # For each line (or process)
if 'kismet' in line: # if 'kismet' appears in its name
pid = int(line.split(None, 1)[0]) # Get the process ID
self.logger.debug("Found: %d", pid)
os.killpg(os.getpgid(pid), sig) # Kill the process

How to control background process in linux

I need to write a script in Linux which can start a background process using one command and stop the process using another.
The specific application is to take userspace and kernel logs for android.
following command should start taking logs
$ mylogscript start
following command should stop the logging
$ mylogscript stop
Also, the commands should not block the terminal. For example, once I send the start command, the script run in background and I should be able to do other work on terminal.
Any pointers on how to implement this in perl or python would be helpful.
EDIT:
Solved: https://stackoverflow.com/a/14596380/443889

I got the solution to my problem. Solution essentially includes starting a subprocess in python and sending a signal to kill the process when done.
Here is the code for reference:
#!/usr/bin/python
import subprocess
import sys
import os
import signal
U_LOG_FILE_PATH = "u.log"
K_LOG_FILE_PATH = "k.log"
U_COMMAND = "adb logcat > " + U_LOG_FILE_PATH
K_COMMAND = "adb shell cat /proc/kmsg > " + K_LOG_FILE_PATH
LOG_PID_PATH="log-pid"
def start_log():
if(os.path.isfile(LOG_PID_PATH) == True):
print "log process already started, found file: ", LOG_PID_PATH
return
file = open(LOG_PID_PATH, "w")
print "starting log process: ", U_COMMAND
proc = subprocess.Popen(U_COMMAND,
stdout=subprocess.PIPE, stderr=subprocess.PIPE,
shell=True, preexec_fn=os.setsid)
print "log process1 id = ", proc.pid
file.write(str(proc.pid) + "\n")
print "starting log process: ", K_COMMAND
proc = subprocess.Popen(K_COMMAND,
stdout=subprocess.PIPE, stderr=subprocess.PIPE,
shell=True, preexec_fn=os.setsid)
print "log process2 id = ", proc.pid
file.write(str(proc.pid) + "\n")
file.close()
def stop_log():
if(os.path.isfile(LOG_PID_PATH) != True):
print "log process not started, can not find file: ", LOG_PID_PATH
return
print "terminating log processes"
file = open(LOG_PID_PATH, "r")
log_pid1 = int(file.readline())
log_pid2 = int(file.readline())
file.close()
print "log-pid1 = ", log_pid1
print "log-pid2 = ", log_pid2
os.killpg(log_pid1, signal.SIGTERM)
print "logprocess1 killed"
os.killpg(log_pid2, signal.SIGTERM)
print "logprocess2 killed"
subprocess.call("rm " + LOG_PID_PATH, shell=True)
def print_usage(str):
print "usage: ", str, "[start|stop]"
# Main script
if(len(sys.argv) != 2):
print_usage(sys.argv[0])
sys.exit(1)
if(sys.argv[1] == "start"):
start_log()
elif(sys.argv[1] == "stop"):
stop_log()
else:
print_usage(sys.argv[0])
sys.exit(1)
sys.exit(0)

There are a couple of different approaches you can take on this:
1. Signal - you use a signal handler, and use, typically "SIGHUP" to signal the process to restart ("start"), SIGTERM to stop it ("stop").
2. Use a named pipe or other IPC mechanism. The background process has a separate thread that simply reads from the pipe, and when something comes in, acts on it. This method relies on having a separate executable file that opens the pipe, and sends messages ("start", "stop", "set loglevel 1" or whatever you fancy).
I'm sorry, I haven't implemented either of these in Python [and perl I haven't really written anything in], but I doubt it's very hard - there's bound to be a ready-made set of python code to deal with named pipes.
Edit: Another method that just struck me is that you simply daemonise the program at start, and then let the "stop" version find your deamonized process [e.g. by reading the "pidfile" that you stashed somewhere suitable], and then sends a SIGTERM for it to terminate.

I don't know if this is the optimum way to do it in perl, but for example:
system("sleep 60 &")
This starts a background process that will sleep for 60 seconds without blocking the terminal. The ampersand in shell means to do something in the background.
A simple mechanism for telling the process when to stop is to have it periodically check for the existence of a certain file. If the file exists, it exits.

How can I run an external command asynchronously from Python?

I need to run a shell command asynchronously from a Python script. By this I mean that I want my Python script to continue running while the external command goes off and does whatever it needs to do.
I read this post:
Calling an external command in Python
I then went off and did some testing, and it looks like os.system() will do the job provided that I use & at the end of the command so that I don't have to wait for it to return. What I am wondering is if this is the proper way to accomplish such a thing? I tried commands.call() but it will not work for me because it blocks on the external command.
Please let me know if using os.system() for this is advisable or if I should try some other route.

subprocess.Popen does exactly what you want.
from subprocess import Popen
p = Popen(['watch', 'ls']) # something long running
# ... do other stuff while subprocess is running
p.terminate()
(Edit to complete the answer from comments)
The Popen instance can do various other things like you can poll() it to see if it is still running, and you can communicate() with it to send it data on stdin, and wait for it to terminate.

If you want to run many processes in parallel and then handle them when they yield results, you can use polling like in the following:
from subprocess import Popen, PIPE
import time
running_procs = [
Popen(['/usr/bin/my_cmd', '-i %s' % path], stdout=PIPE, stderr=PIPE)
for path in '/tmp/file0 /tmp/file1 /tmp/file2'.split()]
while running_procs:
for proc in running_procs:
retcode = proc.poll()
if retcode is not None: # Process finished.
running_procs.remove(proc)
break
else: # No process is done, wait a bit and check again.
time.sleep(.1)
continue
# Here, `proc` has finished with return code `retcode`
if retcode != 0:
"""Error handling."""
handle_results(proc.stdout)
The control flow there is a little bit convoluted because I'm trying to make it small -- you can refactor to your taste. :-)
This has the advantage of servicing the early-finishing requests first. If you call communicate on the first running process and that turns out to run the longest, the other running processes will have been sitting there idle when you could have been handling their results.

This is covered by Python 3 Subprocess Examples under "Wait for command to terminate asynchronously". Run this code using IPython or python -m asyncio:
import asyncio
proc = await asyncio.create_subprocess_exec(
'ls','-lha',
stdout=asyncio.subprocess.PIPE,
stderr=asyncio.subprocess.PIPE)
# do something else while ls is working
# if proc takes very long to complete, the CPUs are free to use cycles for
# other processes
stdout, stderr = await proc.communicate()
The process will start running as soon as the await asyncio.create_subprocess_exec(...) has completed. If it hasn't finished by the time you call await proc.communicate(), it will wait there in order to give you your output status. If it has finished, proc.communicate() will return immediately.
The gist here is similar to Terrels answer but I think Terrels answer appears to overcomplicate things.
See asyncio.create_subprocess_exec for more information.

What I am wondering is if this [os.system()] is the proper way to accomplish such a thing?
No. os.system() is not the proper way. That's why everyone says to use subprocess.
For more information, read http://docs.python.org/library/os.html#os.system
The subprocess module provides more
powerful facilities for spawning new
processes and retrieving their
results; using that module is
preferable to using this function. Use
the subprocess module. Check
especially the Replacing Older
Functions with the subprocess Module
section.

The accepted answer is very old.
I found a better modern answer here:
https://kevinmccarthy.org/2016/07/25/streaming-subprocess-stdin-and-stdout-with-asyncio-in-python/
and made some changes:
make it work on windows
make it work with multiple commands
import sys
import asyncio
if sys.platform == "win32":
asyncio.set_event_loop_policy(asyncio.WindowsProactorEventLoopPolicy())
async def _read_stream(stream, cb):
while True:
line = await stream.readline()
if line:
cb(line)
else:
break
async def _stream_subprocess(cmd, stdout_cb, stderr_cb):
try:
process = await asyncio.create_subprocess_exec(
*cmd, stdout=asyncio.subprocess.PIPE, stderr=asyncio.subprocess.PIPE
)
await asyncio.wait(
[
_read_stream(process.stdout, stdout_cb),
_read_stream(process.stderr, stderr_cb),
]
)
rc = await process.wait()
return process.pid, rc
except OSError as e:
# the program will hang if we let any exception propagate
return e
def execute(*aws):
""" run the given coroutines in an asyncio loop
returns a list containing the values returned from each coroutine.
"""
loop = asyncio.get_event_loop()
rc = loop.run_until_complete(asyncio.gather(*aws))
loop.close()
return rc
def printer(label):
def pr(*args, **kw):
print(label, *args, **kw)
return pr
def name_it(start=0, template="s{}"):
"""a simple generator for task names
"""
while True:
yield template.format(start)
start += 1
def runners(cmds):
"""
cmds is a list of commands to excecute as subprocesses
each item is a list appropriate for use by subprocess.call
"""
next_name = name_it().__next__
for cmd in cmds:
name = next_name()
out = printer(f"{name}.stdout")
err = printer(f"{name}.stderr")
yield _stream_subprocess(cmd, out, err)
if __name__ == "__main__":
cmds = (
[
"sh",
"-c",
"""echo "$SHELL"-stdout && sleep 1 && echo stderr 1>&2 && sleep 1 && echo done""",
],
[
"bash",
"-c",
"echo 'hello, Dave.' && sleep 1 && echo dave_err 1>&2 && sleep 1 && echo done",
],
[sys.executable, "-c", 'print("hello from python");import sys;sys.exit(2)'],
)
print(execute(*runners(cmds)))
It is unlikely that the example commands will work perfectly on your system, and it doesn't handle weird errors, but this code does demonstrate one way to run multiple subprocesses using asyncio and stream the output.

I've had good success with the asyncproc module, which deals nicely with the output from the processes. For example:
import os
from asynproc import Process
myProc = Process("myprogram.app")
while True:
# check to see if process has ended
poll = myProc.wait(os.WNOHANG)
if poll is not None:
break
# print any new output
out = myProc.read()
if out != "":
print out

Using pexpect with non-blocking readlines is another way to do this. Pexpect solves the deadlock problems, allows you to easily run the processes in the background, and gives easy ways to have callbacks when your process spits out predefined strings, and generally makes interacting with the process much easier.

Considering "I don't have to wait for it to return", one of the easiest solutions will be this:
subprocess.Popen( \
[path_to_executable, arg1, arg2, ... argN],
creationflags = subprocess.CREATE_NEW_CONSOLE,
).pid
But... From what I read this is not "the proper way to accomplish such a thing" because of security risks created by subprocess.CREATE_NEW_CONSOLE flag.
The key things that happen here is use of subprocess.CREATE_NEW_CONSOLE to create new console and .pid (returns process ID so that you could check program later on if you want to) so that not to wait for program to finish its job.

I have the same problem trying to connect to an 3270 terminal using the s3270 scripting software in Python. Now I'm solving the problem with an subclass of Process that I found here:
http://code.activestate.com/recipes/440554/
And here is the sample taken from file:
def recv_some(p, t=.1, e=1, tr=5, stderr=0):
if tr < 1:
tr = 1
x = time.time()+t
y = []
r = ''
pr = p.recv
if stderr:
pr = p.recv_err
while time.time() < x or r:
r = pr()
if r is None:
if e:
raise Exception(message)
else:
break
elif r:
y.append(r)
else:
time.sleep(max((x-time.time())/tr, 0))
return ''.join(y)
def send_all(p, data):
while len(data):
sent = p.send(data)
if sent is None:
raise Exception(message)
data = buffer(data, sent)
if __name__ == '__main__':
if sys.platform == 'win32':
shell, commands, tail = ('cmd', ('dir /w', 'echo HELLO WORLD'), '\r\n')
else:
shell, commands, tail = ('sh', ('ls', 'echo HELLO WORLD'), '\n')
a = Popen(shell, stdin=PIPE, stdout=PIPE)
print recv_some(a),
for cmd in commands:
send_all(a, cmd + tail)
print recv_some(a),
send_all(a, 'exit' + tail)
print recv_some(a, e=0)
a.wait()

There are several answers here but none of them satisfied my below requirements:
I don't want to wait for command to finish or pollute my terminal with subprocess outputs.
I want to run bash script with redirects.
I want to support piping within my bash script (for example find ... | tar ...).
The only combination that satiesfies above requirements is:
subprocess.Popen(['./my_script.sh "arg1" > "redirect/path/to"'],
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,
shell=True)