How to make a Python script run like a service or

Question

I have written a Python script that checks a certain e-mail address and passes new e-mails to an external program. How can I get this script to execute 24/7, such as turning it into daemon or service in Linux. Would I also need a loop that never ends in the program, or can it be done by just having the code re executed multiple times?

Answer 1

how about using $nohup command on linux?

I use it for running my commands on my Bluehost server.

Please advice if I am wrong.

Answer 2

I would recommend this solution. You need to inherit and override method run.

import sys
import os
from signal import SIGTERM
from abc import ABCMeta, abstractmethod



class Daemon(object):
    __metaclass__ = ABCMeta


    def __init__(self, pidfile):
        self._pidfile = pidfile


    @abstractmethod
    def run(self):
        pass


    def _daemonize(self):
        # decouple threads
        pid = os.fork()

        # stop first thread
        if pid > 0:
            sys.exit(0)

        # write pid into a pidfile
        with open(self._pidfile, 'w') as f:
            print >> f, os.getpid()


    def start(self):
        # if daemon is started throw an error
        if os.path.exists(self._pidfile):
            raise Exception("Daemon is already started")

        # create and switch to daemon thread
        self._daemonize()

        # run the body of the daemon
        self.run()


    def stop(self):
        # check the pidfile existing
        if os.path.exists(self._pidfile):
            # read pid from the file
            with open(self._pidfile, 'r') as f:
                pid = int(f.read().strip())

            # remove the pidfile
            os.remove(self._pidfile)

            # kill daemon
            os.kill(pid, SIGTERM)

        else:
            raise Exception("Daemon is not started")


    def restart(self):
        self.stop()
        self.start()

Answer 3

A simple and supported version is Deamonize Install it from Python Package Index (PyPI):

$ pip install daemonize

and then use like:

...
import os, sys
from daemonize import Daemonize
...
def main()
      # your code here

if __name__ == '__main__':
        myname=os.path.basename(sys.argv[0])
        pidfile='/tmp/%s' % myname       # any name
        daemon = Daemonize(app=myname,pid=pidfile, action=main)
        daemon.start()

Answer 4

Use whatever service manager your system offers - for example under Ubuntu use upstart. This will handle all the details for you such as start on boot, restart on crash, etc.

Answer 5

First, read up on mail aliases. A mail alias will do this inside the mail system without you having to fool around with daemons or services or anything of the sort.

You can write a simple script that will be executed by sendmail each time a mail message is sent to a specific mailbox.

See http://www.feep.net/sendmail/tutorial/intro/aliases.html

If you really want to write a needlessly complex server, you can do this.

nohup python myscript.py &

That's all it takes. Your script simply loops and sleeps.

import time
def do_the_work():
    # one round of polling -- checking email, whatever.
while True:
    time.sleep( 600 ) # 10 min.
    try:
        do_the_work()
    except:
        pass

Answer 6

If you are using terminal(ssh or something) and you want to keep a long-time script working after you log out from the terminal, you can try this:

screen

apt-get install screen

create a virtual terminal inside( namely abc): screen -dmS abc

now we connect to abc: screen -r abc

So, now we can run python script: python Keep_sending_mail.py

from now on, you can directly close your terminal, however, the python script will keep running rather than being shut down

Since this Keep_sending_mail.py's PID belong to the virtual screen rather than the terminal(ssh)

If you want to go back check your script running status, you can use screen -r abc again