Develop Reference

Run multiple shell scripts from one and do something at each finish

I am trying to write a python daemon
which will run multiple shell scripts at a same time on some conditions
and do something on each task finish
import time
import schedule
import subprocess
def spawn(name, count):
cmd = 'some long lived shell process'
proc = subprocess.Popen(cmd, shell=True, stdin=DEVNULL, stdout=DEVNULL, stderr=DEVNULL, close_fds=True)
consumers_dictionary[name] = proc
def thread_task():
if someconditions
spawn(name, count)
consumers_dictionary = {}
schedule.every(1).seconds.do(thread_task)
while 1:
schedule.run_pending()
time.sleep(1)
How can I control proc status and do something when process is finished?
Think I need something like promises, or check each my dictionary proc object on status?
P.S. Daemon should be able to work(run and track status) with up to 500 processes

To check whether a child process has terminated, you can use the poll() function of the Popen class. If it returns something other than None, the child process has terminated. In your while 1 loop with the one-second sleep, you could run through the dictionary of processes and poll each one and decide what to do when one has terminated.
From the way you wrote the question, I am guessing that this is what you want. If you want to get some kind of interrupt when a child process terminates, it looks like that may be possible, but may be platform-dependent.

To wait for a process opened with popen, use wait. Here's a code sample based on your skeleton:
def spawn(name, count):
processes = []
cmd = 'ls -l ; sleep 2'
for _ in range(count):
proc = subprocess.Popen(cmd, shell=True, stdin=DEVNULL, stdout=DEVNULL, stderr=DEVNULL, close_fds=True)
processes.append(proc)
for proc in processes:
res = proc.wait()
print(f"process with pid {proc.pid} returned {res}")
def thread_task():
if True:
spawn(name = "dummy", count = 5)
schedule.every(1).seconds.do(thread_task)
while 1:
schedule.run_pending()
time.sleep(1)
The result looks like:
process with pid 7784 returned 0
process with pid 7801 returned 0
process with pid 7802 returned 0
process with pid 7803 returned 0
process with pid 7805 returned 0
process with pid 7807 returned 0
...
Note, that you can also use poll to check on the status of a process without waiting for it to complete. (documentation)

Python 3 Stopping subprocess by sending Ctrl C

I have some GPU test software i'm trying to automate using python3, The test would normally be run for 3 minutes then cancelled by a user using ctrl+c generating the following output
After exiting with ctrl+c the test can then be run again with no issue
When trying to automate this with subprocess popen and sending SIGINT or SIGTERM i'm not getting the same as if keyboard entry was used. The script exits abruptly and on subsequent runs cant find the gpus (assume its not unloading the driver properly)
from subprocess import Popen, PIPE
from signal import SIGINT
from time import time
def check_subproc_alive(subproc):
return subproc.poll() is None
def print_subproc(subproc, timer=True):
start_time = time()
while check_subproc_alive(subproc):
line = subproc.stdout.readline().decode('utf-8')
print(line, end="")
if timer and (time() - start_time) > 10:
break
subproc = Popen(['./gpu_test.sh', '-t', '1'], stdin=PIPE, stdout=PIPE, stderr=PIPE, shell=False)
print_subproc(subproc)
subproc.send_signal(SIGINT)
print_subproc(subproc, False)
How can I send ctrl+c to a subprocess as if a user typed it?
**UPDATE
import subprocess
def start(executable_file):
return subprocess.Popen(
executable_file,
stdin=subprocess.PIPE,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE
)
def read(process):
return process.stdout.readline().decode("utf-8").strip()
def write(process):
process.stdin.write('\x03'.encode())
process.stdin.flush()
def terminate(process):
process.stdin.close()
process.terminate()
process.wait(timeout=0.2)
process = start("./test.sh")
write(process)
for x in range(100):
print(read(process))
terminate(process)
Tried the above code and can get characters to register with dummy sh script however sending the \x03 command just sends an empty char and doesn't end script

I think you can probably use something like this:
import signal
try:
p=subprocess...
except KeyboardInterrupt:
p.send_signal(signal.SIGINT)

The following solution is the only one I could find that works for windows and is the closest resemblance to sending a Ctrl+C event.
import signal
os.kill(self.p.pid, signal.CTRL_C_EVENT)

Python: Using popen poll on background process

I am running a long process (actually another python script) in the background. I need to know when it has finished. I have found that Popen.poll() always returns 0 for a background process. Is there another way to do this?
p = subprocess.Popen("sleep 30 &", shell=True,
stdout=subprocess.PIPE, stderr=subprocess.PIPE)
a = p.poll()
print(a)
Above code never prints None.

You don't need to use the shell backgrounding & syntax, as subprocess will run the process in the background by itself
Just run the command normally, then wait until Popen.poll returns not None
import time
import subprocess
p = subprocess.Popen("sleep 30", shell=True)
# Better: p = subprocess.Popen(["sleep", "30"])
# Wait until process terminates
while p.poll() is None:
time.sleep(0.5)
# It's done
print("Process ended, ret code:", p.returncode)

I think you want either the popen.wait() or popen.communicate() commands. Communicate will grab the stdout and stderr data which you've put into PIPE. If the other item is a Python script I would avoid running a shell=True call by doing something like:
p = subprocess.Popen([python.call, "my", params, (go, here)], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
(stdout, stderr) = p.communicate()
print(stdout)
print(stderr)
Of course these hold the main thread and wait for the other process to complete, which might be bad. If you want to busy wait then you could simply wrap your original code in a loop. (Your original code did print "None" for me, btw)
Example of the wrapping in a loop solution:
p = subprocess.Popen([python.call, "my", params, (go, here)], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
while p.poll() == None:
# We can do other things here while we wait
time.sleep(.5)
p.poll()
(results, errors) = p.communicate()
if errors == '':
return results
else:
raise My_Exception(errors)

You shouldn't run your script with ampersand at the end. Because shell forks your process and returns 0 exit code.

How to terminate a python subprocess launched with shell=True

I'm launching a subprocess with the following command:
p = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True)
However, when I try to kill using:
p.terminate()
or
p.kill()
The command keeps running in the background, so I was wondering how can I actually terminate the process.
Note that when I run the command with:
p = subprocess.Popen(cmd.split(), stdout=subprocess.PIPE)
It does terminate successfully when issuing the p.terminate().

Use a process group so as to enable sending a signal to all the process in the groups. For that, you should attach a session id to the parent process of the spawned/child processes, which is a shell in your case. This will make it the group leader of the processes. So now, when a signal is sent to the process group leader, it's transmitted to all of the child processes of this group.
Here's the code:
import os
import signal
import subprocess
# The os.setsid() is passed in the argument preexec_fn so
# it's run after the fork() and before exec() to run the shell.
pro = subprocess.Popen(cmd, stdout=subprocess.PIPE,
shell=True, preexec_fn=os.setsid)
os.killpg(os.getpgid(pro.pid), signal.SIGTERM) # Send the signal to all the process groups

p = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True)
p.kill()
p.kill() ends up killing the shell process and cmd is still running.
I found a convenient fix this by:
p = subprocess.Popen("exec " + cmd, stdout=subprocess.PIPE, shell=True)
This will cause cmd to inherit the shell process, instead of having the shell launch a child process, which does not get killed. p.pid will be the id of your cmd process then.
p.kill() should work.
I don't know what effect this will have on your pipe though.

If you can use psutil, then this works perfectly:
import subprocess
import psutil
def kill(proc_pid):
process = psutil.Process(proc_pid)
for proc in process.children(recursive=True):
proc.kill()
process.kill()
proc = subprocess.Popen(["infinite_app", "param"], shell=True)
try:
proc.wait(timeout=3)
except subprocess.TimeoutExpired:
kill(proc.pid)

I could do it using
from subprocess import Popen
process = Popen(command, shell=True)
Popen("TASKKILL /F /PID {pid} /T".format(pid=process.pid))
it killed the cmd.exe and the program that i gave the command for.
(On Windows)

When shell=True the shell is the child process, and the commands are its children. So any SIGTERM or SIGKILL will kill the shell but not its child processes, and I don't remember a good way to do it.
The best way I can think of is to use shell=False, otherwise when you kill the parent shell process, it will leave a defunct shell process.

None of these answers worked for me so Im leaving the code that did work. In my case even after killing the process with .kill() and getting a .poll() return code the process didn't terminate.
Following the subprocess.Popen documentation:
"...in order to cleanup properly a well-behaved application should kill the child process and finish communication..."
proc = subprocess.Popen(...)
try:
outs, errs = proc.communicate(timeout=15)
except TimeoutExpired:
proc.kill()
outs, errs = proc.communicate()
In my case I was missing the proc.communicate() after calling proc.kill(). This cleans the process stdin, stdout ... and does terminate the process.

As Sai said, the shell is the child, so signals are intercepted by it -- best way I've found is to use shell=False and use shlex to split the command line:
if isinstance(command, unicode):
cmd = command.encode('utf8')
args = shlex.split(cmd)
p = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
Then p.kill() and p.terminate() should work how you expect.

Send the signal to all the processes in group
self.proc = Popen(commands,
stdout=PIPE,
stderr=STDOUT,
universal_newlines=True,
preexec_fn=os.setsid)
os.killpg(os.getpgid(self.proc.pid), signal.SIGHUP)
os.killpg(os.getpgid(self.proc.pid), signal.SIGTERM)

There is a very simple way for Python 3.5 or + (Actually tested on Python 3.8)
import subprocess, signal, time
p = subprocess.Popen(['cmd'], shell=True)
time.sleep(5) #Wait 5 secs before killing
p.send_signal(signal.CTRL_C_EVENT)
Then, your code may crash at some point if you have a keyboard input detection, or sth like this. In this case, on the line of code/function where the error is given, just use:
try:
FailingCode #here goes the code which is raising KeyboardInterrupt
except KeyboardInterrupt:
pass
What this code is doing is just sending a "CTRL+C" signal to the running process, what will cause the process to get killed.

Solution that worked for me
if os.name == 'nt': # windows
subprocess.Popen("TASKKILL /F /PID {pid} /T".format(pid=process.pid))
else:
os.kill(process.pid, signal.SIGTERM)

Full blown solution that will kill running process (including subtree) on timeout reached or specific conditions via a callback function.
Works both on windows & Linux, from Python 2.7 up to 3.10 as of this writing.
Install with pip install command_runner
Example for timeout:
from command_runner import command_runner
# Kills ping after 2 seconds
exit_code, output = command_runner('ping 127.0.0.1', shell=True, timeout=2)
Example for specific condition:
Here we'll stop ping if current system time seconds digit is > 5
from time import time
from command_runner import command_runner
def my_condition():
# Arbitrary condition for demo
return True if int(str(int(time()))[-1]) > 5
# Calls my_condition() every second (check_interval) and kills ping if my_condition() returns True
exit_code, output = command_runner('ping 127.0.0.1', shell=True, stop_on=my_condition, check_interval=1)

How to limit program's execution time when using subprocess?

I want to use subprocess to run a program and I need to limit the execution time. For example, I want to kill it if it runs for more than 2 seconds.
For common programs, kill() works well. But if I try to run /usr/bin/time something, kill() can’t really kill the program.
My code below seems doesn’t work well. The program is still running.
import subprocess
import time
exec_proc = subprocess.Popen("/usr/bin/time -f \"%e\\n%M\" ./son > /dev/null", stdout = subprocess.PIPE, stderr = subprocess.STDOUT, shell = True)
max_time = 1
cur_time = 0.0
return_code = 0
while cur_time <= max_time:
if exec_proc.poll() != None:
return_code = exec_proc.poll()
break
time.sleep(0.1)
cur_time += 0.1
if cur_time > max_time:
exec_proc.kill()

If you're using Python 2.6 or later, you can use the multiprocessing module.
from multiprocessing import Process
def f():
# Stuff to run your process here
p = Process(target=f)
p.start()
p.join(timeout)
if p.is_alive():
p.terminate()
Actually, multiprocessing is the wrong module for this task since it is just a way to control how long a thread runs. You have no control over any children the thread may run. As singularity suggests, using signal.alarm is the normal approach.
import signal
import subprocess
def handle_alarm(signum, frame):
# If the alarm is triggered, we're still in the exec_proc.communicate()
# call, so use exec_proc.kill() to end the process.
frame.f_locals['self'].kill()
max_time = ...
stdout = stderr = None
signal.signal(signal.SIGALRM, handle_alarm)
exec_proc = subprocess.Popen(['time', 'ping', '-c', '5', 'google.com'],
stdin=None, stdout=subprocess.PIPE,
stderr=subprocess.STDOUT)
signal.alarm(max_time)
try:
(stdout, stderr) = exec_proc.communicate()
except IOError:
# process was killed due to exceeding the alarm
finally:
signal.alarm(0)
# do stuff with stdout/stderr if they're not None

do it like so in your command line:
perl -e 'alarm shift #ARGV; exec #ARGV' <timeout> <your_command>
this will run the command <your_command> and terminate it in <timeout> second.
a dummy example :
# set time out to 5, so that the command will be killed after 5 second
command = ['perl', '-e', "'alarm shift #ARGV; exec #ARGV'", "5"]
command += ["ping", "www.google.com"]
exec_proc = subprocess.Popen(command)
or you can use the signal.alarm() if you want it with python but it's the same.

I use os.kill() but am not sure if it works on all OSes.
Pseudo code follows, and see Doug Hellman's page.
proc = subprocess.Popen(['google-chrome'])
os.kill(proc.pid, signal.SIGUSR1)</code>