How to detect if python script is being run as a background process

Question

Is there a way to tell whether my python script is running as a background process or not? I'm trying to differentiate between these two:

sudo ./myscript.py
sudo ./myscript.py &

Using sys.argv doesn't work - the ampersand doesn't count as an argument apparently. And what would be the effect of the following instead:

sudo python myscript.py
sudo python myscript.py &

I've had a look around, but everything seems to be about starting a background process from within a Python script, not whether the Python script itself is a background process. Thanks!

EDIT: The aim is to output a message (or not), i.e. "Press Ctrl+C to stop this script" if started normally, but don't display the message if started as a background process.

EDIT 2 I neglected to mention that this python script will be started by a script in /etc/init.d rather than from a terminal prompt. So the answer marked as correct does indeed answer the question as I phrased it and with the information given, but I thought I should point out that it doesn't work in the init.d scenario, to avoid any potential confusion in the future.

Thanks Aaron. I've added to the original request to clarify. — HaydnW
– HaydnW, Commented Jul 21, 2014 at 9:25
When the process is detached, reading from stdin will block it. Writing to stdout works, though. I don't know a way to check whether reading stdin would block, though. — Aaron Digulla
– Aaron Digulla, Commented Jul 21, 2014 at 9:30
possible duplicate of Checking for interactive shell in a Python script — Lie Ryan
– Lie Ryan, Commented Jul 21, 2014 at 10:00

Community · Accepted Answer · 2017-05-23 12:32:23Z

8

Based on the answer for C @AaronDigulla pointed to in a comment:

import os
import sys


def main():
    if os.getpgrp() == os.tcgetpgrp(sys.stdout.fileno()):
        print 'Running in foreground.'
    else:
        print 'Running in background.'


if __name__ == '__main__':
    main()

edited May 23, 2017 at 12:32

CommunityBot

11 silver badge

answered Jul 21, 2014 at 9:52

BlackJack

4,7231 gold badge22 silver badges26 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

HaydnW Over a year ago

Example given above worked perfectly, to a degree. :) I'm actually running the script using a script in /etc/init.d on Linux, rather than through a terminal. The example given works brilliantly when I start the Python script at a terminal prompt, but fails with OSError: [Errno 25] Inappropriate ioctl for device when run via the init.d script. I'll keep looking! :)

Ross Ridge Over a year ago

Wrap the call to os.tcgetpgrp in a try/except block and if throws an OSError then you know sys.stdout isn't a terminal. In that case it's probably safe to assume that no one is going to be able read the message. CTRL-C probably also won't work.

Pablo Over a year ago

Technically, calling "nohup python code.py > output_file.txt" is not running the code in background, but this answer tells me so.

Dunes · Accepted Answer · 2014-07-21 21:51:42Z

2

I saw the other solutions on other and decided to write a pure python solution. It reads from /proc/<pid>/stat rather than calling a subprocess.

from os import getpid

with open("/proc/{}/stat".format(getpid())) as f:
    data = f.read()

foreground_pid_of_group = data.rsplit(" ", 45)[1]
is_in_foreground = str(getpid()) == foreground_pid_of_group

The meanings of the columns of the stat file can be found here

answered Jul 21, 2014 at 21:51

Dunes

42.1k7 gold badges86 silver badges107 bronze badges

Comments

Community · Accepted Answer · 2017-04-13 12:36:31Z

1

Based on bash solution from this answer:

import os
import subprocess
pid = os.getpid()
if "+" in subprocess.check_output(["ps", "-o", "stat=", "-p", str(pid)]):
  print "Running in foreground"
else:
  print "Running in background"

edited Apr 13, 2017 at 12:36

CommunityBot

11 silver badge

answered Jul 21, 2014 at 9:49

RomanHotsiy

5,1482 gold badges30 silver badges37 bronze badges

1 Comment

Pablo Over a year ago

I get this error: TypeError: a bytes-like object is required, not 'str'

Collectives™ on Stack Overflow

How to detect if python script is being run as a background process

3 Answers 3

3 Comments

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related