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Script that installs itself to another location and runs from there [duplicate]

This question already has answers here:
Python spawn off a child subprocess, detach, and exit
(2 answers)
Closed 1 year ago.
I'm trying to create a Python script that can do two things:
Run normally if no args are present.
If install is passed as argument, install itself to a specific directory (/tmp), and run the installed version in the background, detached from the current process.
I've tried multiple combinations of subprocess.run, subprocess.Popen with the shell, close_fds and other options (even tried nohup), but since I do not have a good understanding of how process spawning works, I do not seem to be using the correct one.
What I'm looking for when I use the install argument is to see "Installing..." and that's it, the new process should be running in the background detached and my shell ready. But what I see is the child process still attached and my terminal busy outputting "Running..." just after the installing message.
How should this be done?
import subprocess
import sys
import time
import os
def installAndRun():
print('Installing...')
scriptPath = os.path.realpath(__file__)
scriptName = (__file__.split('/')[-1] if '/' in __file__ else __file__)
# Copy script to new location (installation)
subprocess.run(['cp', scriptPath, '/tmp'])
# Now run the installed script
subprocess.run(['python3', f'/tmp/{scriptName}'])
def run():
for _ in range(5):
print('Running...')
time.sleep(1)
if __name__=="__main__":
if 'install' in sys.argv:
installAndRun()
else:
run()
Edit: I've just realised that the process does not end when called like that.

Do not use "cp" to copy the script, but shutil.copy() instead.
Instead of "python3", use sys.executable to start the script with the same interpreter the original is started with.
subprocess.Popen() without anything else will work as long as the child process isn't writing anything to stdout and stderr, and isn't requesting any output. In general, the process is not started unless communicate() is not called or PIPEs being read/written to. You have to use os.fork() to detach from the parent (research how daemons are made), then use:
p = subprocess.Popen([sys.executable, new_path], stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
p.stdin.close() # If you do not need it
p.communicate()
or do not use subprocess.PIPE for stdin, stderr and stdout and make sure that the terminal is bound to the child when forking. After os.fork() you do with the parent what you want and with the child what you want. You can bind the child to whatever terminal you want or start a new shell e.g.:
pid = os.fork()
if pid==0: # Code in this if block is the child
<code to change the terminal and appropriately point sys.stdout, sys.stderr and sys.stdin>
subprocess.Popen([os.getenv("SHELL"), "-c", sys.executable, new_path]).communicate()
Note that you can point PIPEs to file-like objects using stdin, stderr and stdout arguments if you need.
To detach on Windows you can use os.startfile() or use subprocess.Popen(...).communicate() in a thread. If you then sys.exit() the parent, the child should stay opened. (that is how it worked on Windows XP with Python 2.x, I didn't try with Py3 nor on newer Win versions)

It seems like the correct combination was to use Popen + subprocess.PIPE for both stdout and stderr. The code now looks like this:
import subprocess
import sys
import time
import os
def installAndRun(scriptPath, scriptName):
print('Installing...')
# Copy script to new location (installation)
subprocess.run(['cp', scriptPath, '/tmp'])
# Now run the installed script
subprocess.Popen(['python3', f'/tmp/{scriptName}'],
stdout=subprocess.PIPE, stderr=subprocess.PIPE)
def run(scriptPath):
for _ in range(5):
print(f'Running... {scriptPath}')
time.sleep(1)
if __name__=="__main__":
scriptPath = os.path.realpath(__file__)
scriptName = (__file__.split('/')[-1] if '/' in __file__ else __file__)
if 'install' in sys.argv:
installAndRun(scriptPath, scriptName)
else:
run(scriptPath)

Python subprocess always waits for programm [duplicate]

I'm trying to port a shell script to the much more readable python version. The original shell script starts several processes (utilities, monitors, etc.) in the background with "&". How can I achieve the same effect in python? I'd like these processes not to die when the python scripts complete. I am sure it's related to the concept of a daemon somehow, but I couldn't find how to do this easily.

While jkp's solution works, the newer way of doing things (and the way the documentation recommends) is to use the subprocess module. For simple commands its equivalent, but it offers more options if you want to do something complicated.
Example for your case:
import subprocess
subprocess.Popen(["rm","-r","some.file"])
This will run rm -r some.file in the background. Note that calling .communicate() on the object returned from Popen will block until it completes, so don't do that if you want it to run in the background:
import subprocess
ls_output=subprocess.Popen(["sleep", "30"])
ls_output.communicate() # Will block for 30 seconds
See the documentation here.
Also, a point of clarification: "Background" as you use it here is purely a shell concept; technically, what you mean is that you want to spawn a process without blocking while you wait for it to complete. However, I've used "background" here to refer to shell-background-like behavior.

Note: This answer is less current than it was when posted in 2009. Using the subprocess module shown in other answers is now recommended in the docs
(Note that the subprocess module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using these functions.)
If you want your process to start in the background you can either use system() and call it in the same way your shell script did, or you can spawn it:
import os
os.spawnl(os.P_DETACH, 'some_long_running_command')
(or, alternatively, you may try the less portable os.P_NOWAIT flag).
See the documentation here.

You probably want the answer to "How to call an external command in Python".
The simplest approach is to use the os.system function, e.g.:
import os
os.system("some_command &")
Basically, whatever you pass to the system function will be executed the same as if you'd passed it to the shell in a script.

I found this here:
On windows (win xp), the parent process will not finish until the longtask.py has finished its work. It is not what you want in CGI-script. The problem is not specific to Python, in PHP community the problems are the same.
The solution is to pass DETACHED_PROCESS Process Creation Flag to the underlying CreateProcess function in win API. If you happen to have installed pywin32 you can import the flag from the win32process module, otherwise you should define it yourself:
DETACHED_PROCESS = 0x00000008
pid = subprocess.Popen([sys.executable, "longtask.py"],
creationflags=DETACHED_PROCESS).pid

Use subprocess.Popen() with the close_fds=True parameter, which will allow the spawned subprocess to be detached from the Python process itself and continue running even after Python exits.
https://gist.github.com/yinjimmy/d6ad0742d03d54518e9f
import os, time, sys, subprocess
if len(sys.argv) == 2:
time.sleep(5)
print 'track end'
if sys.platform == 'darwin':
subprocess.Popen(['say', 'hello'])
else:
print 'main begin'
subprocess.Popen(['python', os.path.realpath(__file__), '0'], close_fds=True)
print 'main end'

Both capture output and run on background with threading
As mentioned on this answer, if you capture the output with stdout= and then try to read(), then the process blocks.
However, there are cases where you need this. For example, I wanted to launch two processes that talk over a port between them, and save their stdout to a log file and stdout.
The threading module allows us to do that.
First, have a look at how to do the output redirection part alone in this question: Python Popen: Write to stdout AND log file simultaneously
Then:
main.py
#!/usr/bin/env python3
import os
import subprocess
import sys
import threading
def output_reader(proc, file):
while True:
byte = proc.stdout.read(1)
if byte:
sys.stdout.buffer.write(byte)
sys.stdout.flush()
file.buffer.write(byte)
else:
break
with subprocess.Popen(['./sleep.py', '0'], stdout=subprocess.PIPE, stderr=subprocess.PIPE) as proc1, \
subprocess.Popen(['./sleep.py', '10'], stdout=subprocess.PIPE, stderr=subprocess.PIPE) as proc2, \
open('log1.log', 'w') as file1, \
open('log2.log', 'w') as file2:
t1 = threading.Thread(target=output_reader, args=(proc1, file1))
t2 = threading.Thread(target=output_reader, args=(proc2, file2))
t1.start()
t2.start()
t1.join()
t2.join()
sleep.py
#!/usr/bin/env python3
import sys
import time
for i in range(4):
print(i + int(sys.argv[1]))
sys.stdout.flush()
time.sleep(0.5)
After running:
./main.py
stdout get updated every 0.5 seconds for every two lines to contain:
0
10
1
11
2
12
3
13
and each log file contains the respective log for a given process.
Inspired by: https://eli.thegreenplace.net/2017/interacting-with-a-long-running-child-process-in-python/
Tested on Ubuntu 18.04, Python 3.6.7.

You probably want to start investigating the os module for forking different threads (by opening an interactive session and issuing help(os)). The relevant functions are fork and any of the exec ones. To give you an idea on how to start, put something like this in a function that performs the fork (the function needs to take a list or tuple 'args' as an argument that contains the program's name and its parameters; you may also want to define stdin, out and err for the new thread):
try:
pid = os.fork()
except OSError, e:
## some debug output
sys.exit(1)
if pid == 0:
## eventually use os.putenv(..) to set environment variables
## os.execv strips of args[0] for the arguments
os.execv(args[0], args)

You can use
import os
pid = os.fork()
if pid == 0:
Continue to other code ...
This will make the python process run in background.

I haven't tried this yet but using .pyw files instead of .py files should help. pyw files dosen't have a console so in theory it should not appear and work like a background process.

Launch a completely independent process

I want to initiate a process from my python script main.py. Specifically, I want to run the below command:
`nohup python ./myfile.py &`
and the file myfile.py should continue running, even after the main.py script exits.
I also wish to get the pid of the new process.
I tried:
os.spawnl*
os.exec*
subprocess.Popen
and all are terminating the myfile.py when the main.py script exits.
Update: Can I use os.startfile with xdg-open? Is it the right approach?
Example
a = subprocess.Popen([sys.executable, "nohup /usr/bin/python25 /long_process.py &"],\
stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
print a.pid
If I check ps aux | grep long_process, there is no process running.
long_process.py which keeps on printing some text: no exit.
Am I doing anything wrong here?

You open your long-running process and keep a pipe to it. So you expect to talk to it. When yor launcher script exits, you can no longer talk to it. The long-running process receives a SIGPIPE and exits.
The following just worked for me (Linux, Python 2.7).
Create a long-running executable:
$ echo "sleep 100" > ~/tmp/sleeper.sh
Run Python REPL:
$ python
>>>
import subprocess
import os
p = subprocess.Popen(['/bin/sh', os.path.expanduser('~/tmp/sleeper.sh')])
# look ma, no pipes!
print p.pid
# prints 29893
Exit the REPL and see the process still running:
>>> ^D
$ ps ax | grep sleeper
29893 pts/0 S 0:00 /bin/sh .../tmp/sleeper.sh
29917 pts/0 S+ 0:00 grep --color=auto sleeper
If you want to first communicate to the started process and then leave it alone to run further, you have a few options:
Handle SIGPIPE in your long-running process, do not die on it. Live without stdin after the launcher process exits.
Pass whatever you wanted using arguments, environment, or a temporary file.
If you want bidirectional communication, consider using a named pipe (man mkfifo) or a socket, or writing a proper server.
Make the long-running process fork after the initial bi-direcional communication phase is done.

You can use os.fork().
import os
pid=os.fork()
if pid==0: # new process
os.system("nohup python ./myfile.py &")
exit()
# parent process continues

I could not see any process running.
You don't see any process running because the child python process exits immediately. The Popen arguments are incorrect as user4815162342 says in the comment.
To launch a completely independent process, you could use python-daemon package or use systemd/supervisord/etc:
#!/usr/bin/python25
import daemon
from long_process import main
with daemon.DaemonContext():
main()
Though it might be enough in your case, to start the child with correct Popen arguments:
with open(os.devnull, 'r+b', 0) as DEVNULL:
p = Popen(['/usr/bin/python25', '/path/to/long_process.py'],
stdin=DEVNULL, stdout=DEVNULL, stderr=STDOUT, close_fds=True)
time.sleep(1) # give it a second to launch
if p.poll(): # the process already finished and it has nonzero exit code
sys.exit(p.returncode)
If the child process doesn't require python2.5 then you could use sys.executable instead (to use the same Python version as the parent).
Note: the code closes DEVNULL in the parent without waiting for the child process to finish (it has no effect on the child).

Run a perl script from my python script, print the output and wait for it to finish

I have a python script which at one point is required to run a perl script, wait for it to finish, then continue.
As this case will only occur on a windows machine, I thought I could simply open a new cmd and run the perl script there, but I'm having difficulties doing so.
import os
os.system("start /wait cmd /c {timeout 10}")
should open a new cmd and sleep for 10 seconds, but it closes right away. I don't want to put the perl script in position of the timeout 10, as it is quite resource intensive.
Another idea was to use a subprocess with call or Popen and wait.
perl_script = subprocess.call(['script.pl', params])
But I'm not sure what would happen to the stdout of the perl script in such a case.
I know the location and the parameters of the perl script.
How can I run a perl script from my python script, print the output (a lot) and wait for it to finish?
edit:
As suggested by #rchang, I added the subprocess with communicate as following and it works just as intended.
import subprocess, sys
perl = "C:\\perl\\bin\\perl.exe"
perl_script "C:\\scripts\\perl\\flamethrower.pl"
params = " --mount-doom-hot"
pl_script = subprocess.Popen([perl, perl_script, params], stdout=sys.stdout)
pl_script.communicate()
These are my first lines of perl, just a quick copy/past script to test this.
print "Hello Perld!\n";
sleep 10;
print "Bye Perld!\n";

import subprocess
import sys
perl_script = subprocess.Popen(["script.pl", params], stdout=sys.stdout)
perl_script.communicate()
This should hook up the stdout of the subprocess to the stdout stream of the Python script, provided you won't actually need the Python script to output anything else meaningful during execution that may not be related to the subprocess output.

You could try:
perl_script = subprocess.check_output(["script.pl", params])
print perl_script

how to create and destroy non blocking sub process that are OS independent in python?

In a python script i want to spawn a process that runs a file in the same directory
I dont want the python script to be blocked by the new process
Then want to be able to close the spawned process from the script.
Ontop of it all i need it to be OS independant.
What is the best of doing this?

As #Keith suggested use subprocess module, but more specifically use Popen. For example, on Windows, this opens myfile.txt with notepad and then terminates it after a 20 seconds:
import subprocess
import time
command = "notepad myfile.txt"
pipe = subprocess.Popen(command, shell=False)
time.sleep(5)
pipe.poll()
print("%s" % pipe.returncode) #"None" when working fine
time.sleep(5)
pipe.terminate()
pipe.wait()
print("%s" % pipe.returncode) # 1 after termination