How to run a script in the background even after I logout SSH?

Question

I have Python script bgservice.py and I want it to run all the time, because it is part of the web service I build. How can I make it run continuously even after I logout SSH?

Answer 1

Run nohup python bgservice.py & to get the script to ignore the hangup signal and keep running. Output will be put in nohup.out.

Ideally, you'd run your script with something like supervise so that it can be restarted if (when) it dies.

Answer 2

If you've already started the process, and don't want to kill it and restart under nohup, you can send it to the background, then disown it.

Ctrl+Z (suspend the process)

bg (restart the process in the background

disown %1 (assuming this is job #1, use jobs to determine)

Answer 3

Running a Python Script in the Background

First, you need to add a shebang line in the Python script which looks like the following:

#!/usr/bin/env python3

This path is necessary if you have multiple versions of Python installed and /usr/bin/env will ensure that the first Python interpreter in your $$PATH environment variable is taken. You can also hardcode the path of your Python interpreter (e.g. #!/usr/bin/python3), but this is not flexible and not portable on other machines. Next, you’ll need to set the permissions of the file to allow execution:

chmod +x test.py

Now you can run the script with nohup which ignores the hangup signal. This means that you can close the terminal without stopping the execution. Also, don’t forget to add & so the script runs in the background:

nohup /path/to/test.py &

If you did not add a shebang to the file you can instead run the script with this command:

nohup python /path/to/test.py &

The output will be saved in the nohup.out file, unless you specify the output file like here:

nohup /path/to/test.py > output.log &
nohup python /path/to/test.py > output.log &

If you have redirected the output of the command somewhere else - including /dev/null - that's where it goes instead.

# doesn't create nohup.out

nohup command >/dev/null 2>&1   

If you're using nohup, that probably means you want to run the command in the background by putting another & on the end of the whole thing:

# runs in background, still doesn't create nohup.out

 nohup command >/dev/null 2>&1 &  

You can find the process and its process ID with this command:

ps ax | grep test.py

# or
# list of running processes Python

ps -fA | grep python

ps stands for process status

If you want to stop the execution, you can kill it with the kill command:

kill PID

Answer 4

You could also use GNU screen which just about every Linux/Unix system should have.

If you are on Ubuntu/Debian, its enhanced variant byobu is rather nice too.

Answer 5

You might consider turning your python script into a proper python daemon, as described here.

python-daemon is a good tool that can be used to run python scripts as a background daemon process rather than a forever running script. You will need to modify existing code a bit but its plain and simple.

If you are facing problems with python-daemon, there is another utility supervisor that will do the same for you, but in this case you wont have to write any code (or modify existing) as this is a out of the box solution for daemonizing processes.

Answer 6

Alternate answer: tmux

• ssh into the remote machine
• type tmux into cmd
• start the process you want inside the tmux e.g. python3 main.py
• leaving the tmux session by Ctrl+b then d

It is now safe to exit the remote machine. When you come back use tmux attach to re-enter tmux session.

If you want to start multiple sessions, name each session using Ctrl+b then $. then type your session name.

to list all session use tmux list-sessions

to attach a running session use tmux attach-session -t <session-name>.

Answer 7

You can nohup it, but I prefer screen.

Answer 8

Here is a simple solution inside python using a decorator:

import os, time

def daemon(func):
    def wrapper(*args, **kwargs):
        if os.fork(): return
        func(*args, **kwargs)
        os._exit(os.EX_OK)
    return wrapper

@daemon
def my_func(count=10):    
  for i in range(0,count):
     print('parent pid: %d' % os.getppid())
     time.sleep(1)


my_func(count=10)
#still in parent thread
time.sleep(2)
#after 2 seconds the function my_func lives on is own

You can of course replace the content of your bgservice.py file in place of my_func.

Answer 9

Try this:

nohup python -u <your file name>.py >> <your log file>.log &

You can run above command in screen and come out of screen.

Now you can tail logs of your python script by: tail -f <your log file>.log

To kill you script, you can use ps -aux and kill commands.

Answer 10

The zsh shell has an option to make all background processes run with nohup.

In ~/.zshrc add the lines:

setopt nocheckjobs  #don't warn about bg processes on exit
setopt nohup        #don't kill bg processes on exit

Then you just need to run a process like so: python bgservice.py &, and you no longer need to use the nohup command.

I know not many people use zsh, but it's a really cool shell which I would recommend.

Answer 11

If what you need is that the process should run forever no matter whether you are logged in or not, consider running the process as a daemon.

supervisord is a great out of the box solution that can be used to daemonize any process. It has another controlling utility supervisorctl that can be used to monitor processes that are being run by supervisor.

You don't have to write any extra code or modify existing scripts to make this work. Moreover, verbose documentation makes this process much simpler.

After scratching my head for hours around python-daemon, supervisor is the solution that worked for me in minutes.

Hope this helps someone trying to make python-daemon work

Answer 12

You can also use Yapdi:

Basic usage:

import yapdi

daemon = yapdi.Daemon()
retcode = daemon.daemonize()

# This would run in daemon mode; output is not visible
if retcode == yapdi.OPERATION_SUCCESSFUL:
print('Hello Daemon')