How to make Python script run as service?

Question

I want to run a python script in a CENTOS server:

#!/usr/bin/env python
import socket
try:    
    import thread 
except ImportError:
    import _thread as thread #Py3K changed it.
class Polserv(object):
    def __init__(self):
        self.numthreads = 0
        self.tidcount   = 0
        self.port       = 843
        self.sock       = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.sock.bind(('100.100.100.100', self.port))
        self.sock.listen(5)
    def run(self):
        while True:
            thread.start_new_thread(self.handle, self.sock.accept()) 
    def handle(self,conn,addr):
        self.numthreads += 1
        self.tidcount   += 1
        tid=self.tidcount
        while True:
            data=conn.recv(2048)
            if not data:
                conn.close()
                self.numthreads-=1
                break
            #if "<policy-file-request/>\0" in data:
            conn.sendall(b"<?xml version='1.0'?><cross-domain-policy><allow-access-from domain='*' to-ports='*'/></cross-domain-policy>")
            conn.close()
            self.numthreads-=1
            break
        #conn.sendall(b"[#%d (%d running)] %s" % (tid,self.numthreads,data) )
Polserv().run()

Im using $ python flashpolicyd.py and it works fine... The question is: How to keep this script running even after I close the ssh console?

Answer 1

I use this code to daemonize my applications. It allows you start/stop/restart the script using the following commands.

python myscript.py start
python myscript.py stop
python myscript.py restart

In addition to this I also have an init.d script for controlling my service. This allows you to automatically start the service when your operating system boots-up.

Here is a simple example to get your going. Simply move your code inside a class, and call it from the run function inside MyDeamon.

import sys
import time

from daemon import Daemon


class YourCode(object):
    def run(self):
        while True:
            time.sleep(1)


class MyDaemon(Daemon):
    def run(self):
        # Or simply merge your code with MyDaemon.
        your_code = YourCode()
        your_code.run()


if __name__ == "__main__":
    daemon = MyDaemon('/tmp/daemon-example.pid')
    if len(sys.argv) == 2:
        if 'start' == sys.argv[1]:
            daemon.start()
        elif 'stop' == sys.argv[1]:
            daemon.stop()
        elif 'restart' == sys.argv[1]:
            daemon.restart()
        else:
            print "Unknown command"
            sys.exit(2)
        sys.exit(0)
    else:
        print "usage: %s start|stop|restart" % sys.argv[0]
        sys.exit(2)

Upstart

If you are running an operating system that is using Upstart (e.g. CentOS 6) - you can also use Upstart to manage the service. If you use Upstart you can keep your script as is, and simply add something like this under /etc/init/my-service.conf

start on started sshd
stop on runlevel [!2345]

exec /usr/bin/python /opt/my_service.py
respawn

You can then use start/stop/restart to manage your service.

e.g.

start my-service
stop my-service
restart my-service

A more detailed example of working with upstart is available here.

Systemd

If you are running an operating system that uses Systemd (e.g. CentOS 7) you can take a look at the following Stackoverflow answer.