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Opens a process with Popen cant close it ( need to run Ros command in cmd)

I need to save some image files from my simulation at different times. So my idea was to open a subprocess save some image files and close it .
import subprocess
cmd = "rosrun pcl_ros pointcloud_to_pcd input:=camera/depth/points"
proc = subprocess.Popen(cmd, shell=True)
When it comes to closing I tried different things:
import os
import signal
import subprocess
cmd = "rosrun pcl_ros pointcloud_to_pcd input:=camera/depth/points"
pro = subprocess.Popen(cmd, stdout=subprocess.PIPE,
shell=True, preexec_fn=os.setsid)
os.killpg(os.getpgid(pro.pid), signal.SIGTERM)
command did not execute , so it doesn't work for me. I also tried a solution with psutil and it didn't work neither...

you probably don't need shell=True here, which is the cause of your problems. I suspect that when you kill the process group in your second snippet, the shell process is killed before the process you want to run has a chance to start...
Try to pass the parameters as a list of strings (so you don't need shell=True), wait a bit, and use terminate on the Popen object. You don't need process group, or psutil to kill the process & its children, just plain old terminate() on the process object does the trick.
cmd = ["rosrun","pcl_ros","pointcloud_to_pcd","input:=camera/depth/points"]
proc = subprocess.Popen(cmd)
time.sleep(1) # maybe needed to wait the process to do something useful
proc.terminate()
Note that proc.terminate() tries to exit gracefully where proc.kill() would have just killed the process (there's a difference under Un*x systems, not under Windows)
Another plea for "do not use shell=True unless forced at gunpoint".

python - subprocess.Popen().pid return the pid of the parent script

I am trying to run a Python script from another Python script, and getting its pid so I can kill it later.
I tried subprocess.Popen() with argument shell=True', but thepidattribute returns thepid` of the parent script, so when I try to kill the subprocess, it kills the parent.
Here is my code:
proc = subprocess.Popen(" python ./script.py", shell=True)
pid_ = proc.pid
.
.
.
# later in my code
os.system('kill -9 %s'%pid_)
#IT KILLS THE PARENT :(

shell=True starts a new shell process. proc.pid is the pid of that shell process. kill -9 kills the shell process making the grandchild python process into an orphan.
If the grandchild python script can spawn its own child processes and you want to kill the whole process tree then see How to terminate a python subprocess launched with shell=True:
#!/usr/bin/env python
import os
import signal
import subprocess
proc = subprocess.Popen("python script.py", shell=True, preexec_fn=os.setsid)
# ...
os.killpg(proc.pid, signal.SIGTERM)
If script.py does not spawn any processes then use #icktoofay suggestion: drop shell=True, use a list argument, and call proc.terminate() or proc.kill() -- the latter always works eventually:
#!/usr/bin/env python
import subprocess
proc = subprocess.Popen(["python", "script.py"])
# ...
proc.terminate()
If you want to run your parent script from a different directory; you might need get_script_dir() function.
Consider importing the python module and running its functions, using its object (perhaps via multiprocessing) instead of running it as a script. Here's code example that demonstrates get_script_dir() and multiprocessing usage.

So run it directly without a shell:
proc = subprocess.Popen(['python', './script.py'])
By the way, you may want to consider changing the hardcoded 'python' to sys.executable. Also, you can use proc.kill() to kill the process rather than extracting the PID and using that; furthermore, even if you did need to kill by PID, you could use os.kill to kill the process rather than spawning another command.

Python: Terminate subprocess = Success, but it's still running (?)

I have a simple script that calls another python script as a subprocess. I can confirm the subprocess is started and I can grab its PID.
When I attempt to terminate the subprocess (in win), I get the SUCCESS message against the correct PID, but Windows task manager shows the 2nd python.exe process to still be running.
Any suggestions to accomplish this task in Win? I'll be extending this to also work in OSX and Linux eventually:
Simplified:
#!/usr/bin/env python
import os, sys
import subprocess
from subprocess import Popen, PIPE, STDOUT, check_call
pyTivoPath="c:\pyTivo\pyTivo.py"
print "\nmyPID: %d" % os.getpid()
## Start pyTivo ##
py_process = subprocess.Popen(pyTivoPath, shell=True, stdout=PIPE, stderr=subprocess.STDOUT)
print "newPID: %s" % py_process.pid
## Terminate pyTivo ##
#py_process.terminate() - for nonWin (?)
py_kill = subprocess.Popen("TASKKILL /PID "+ str(py_process.pid) + " /f")
raw_input("\nPress Enter to continue...")
Note: Python2.7 required, psutils not available

In my implementation, the following actually creates TWO processes in Windows ("cmd.exe" and "python.exe").
py_process = subprocess.Popen(pyTivoPath, shell=True, stdout=PIPE, stderr=subprocess.STDOUT)
Noticing the "python.exe" process is a child of the "cmd.exe" process, I added the "/T" (tree kill) switch to my TASKKILL:
py_kill = subprocess.Popen("TASKKILL /PID "+ str(py_process.pid) + " /f /t")
This results in the desired effect to effectively KILL the python subprocess.

Two processes are created because you call Popen with shell=True. It looks like the only reason you need to use a shell is so you make use of the file association with the interpreter. To resolve your issue you could also try:
from subprocess Popen, PIPE, STDOUT
pyTivoPath = "c:\pyTivo\pyTivo.py"
cmd = r'c:\Python27\python.exe "{}"'.format(pyTivoPath)
# start process
py_process = Popen(cmd, stdout=PIPE, stderr=STDOUT)
# kill process
py_process.terminate()

Use the /F (Force) switch on the TASKKILL command. Lots of windows commands do not has useful return values. Don't recall if TASKKILL returns has a useful value.
Sorry, overlooked your /F
You could try calling the win32 api directly.
import win32api
win32api.TerminateProcess(int(process._handle), -1)
Found the ActiveState page for this. Documents a number of kill methods, including the Win32 approach above.
There are also a number of reasons why Windows will not allow you to terminate a process. Common reasons are permissions and buggy drivers that have pending I/O requests that don't response to the kill signal properly.
There are some programs, e.g. ProcessHacker, that are more enthusiastic about killing processes, but I don't know the technical details for certain, though I suspect forced closing of open file handles etc. and then calling Terminate are involved.
You can have similar issues on Linux, i.e., no permission to kill process or the process is ignoring the kill signal. Easier to resolve on Linux though, if kill -9 does not work, it can't be killed and it is a rarer condition because you have to ignore signal 9 explicitly in your code.
0) You could use TASKKILL /T to kill CMD and the Python interpreter.
1) If you change your process creation to create the python process directly (instead of invoking the .py and relying on cmd to launch) with the script name as command argument you will get the PID you expect when you create the process.
2) You could use TASKKILL /IM to kill the process by name, but the name will be the python interpreter and it could kill unintended processes.

Python: Check when a cmd command completes its job

When I execute a python script using subprocess.Popen(script, shell=True) in another python script, is it possible to alert python when the script completes running before executing other functions?
On a side note, can I get real-time output of the executed python script?
I can only get output from it doing command>output.txt but that's only after the whole process ends. stdout does not grep any ouput.

When you create a subprocess with Popen, it returns a subprocess.Popen object that has several methods for accessing subprocess status and data:
You can use poll() to determine whether a subprocess has finished. None indicates that the process has ended.
Output from a script while its running can be retrieved with communicate().
You can combine these two to create a script that monitors output from a subprocess and waits until its ready as follows:
import subprocess
p = subprocess.Popen((["python", "script.py"]), stdout=subprocess.PIPE)
while p.poll() is None:
(stdout, stderr) = p.communicate()
print stdout

You want to wait for the Popen to end? have you tried simply this:
popen = subprocess.Popen(script, shell=True)
popen.wait()
Have you considered using the external python script importing it as a module instead of spawning a subprocess?
As for the real-time output: try python -u ...

is there a way to start/stop linux processes with python?

I want to be able to start a process and then be able to kill it afterwards

Here's a little python script that starts a process, checks if it is running, waits a while, kills it, waits for it to terminate, then checks again. It uses the 'kill' command. Version 2.6 of python subprocess has a kill function. This was written on 2.5.
import subprocess
import time
proc = subprocess.Popen(["sleep", "60"], shell=False)
print 'poll =', proc.poll(), '("None" means process not terminated yet)'
time.sleep(3)
subprocess.call(["kill", "-9", "%d" % proc.pid])
proc.wait()
print 'poll =', proc.poll()
The timed output shows that it was terminated after about 3 seconds, and not 60 as the call to sleep suggests.
$ time python prockill.py
poll = None ("None" means process not terminated yet)
poll = -9
real 0m3.082s
user 0m0.055s
sys 0m0.029s

Have a look at the subprocess module.
You can also use low-level primitives like fork() via the os module.

http://docs.python.org/library/os.html#process-management

A simple function that uses subprocess module:
def CMD(cmd) :
p = subprocess.Popen(cmd, shell=True,
stdin=subprocess.PIPE,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,
close_fds=False)
return (p.stdin, p.stdout, p.stderr)

see docs for primitive fork() and modules subprocess, multiprocessing, multithreading

If you need to interact with the sub process at all, I recommend the pexpect module (link text). You can send input to the process, receive (or "expect") output in return, and you can close the process (with force=True to send SIGKILL).