How to properly handle and retain system shutdown (and SIGTERM) in order to finish its job in Python?

Question

Basic need : I've a Python daemon that's calling another program through os.system. My wish is to be able to properly to handle system shutdown or SIGTERM in order to let the called program return and then exiting.

What I've already tried: I've tried an approach using signal :

import signal, time

def handler(signum = None, frame = None):
    print 'Signal handler called with signal', signum
    time.sleep(3)
    #here check if process is done
    print 'Wait done'

signal.signal(signal.SIGTERM , handler)

while True:
    time.sleep(6)

The usage of time.sleep doesn't seems to work and the second print is never called.

I've read few words about atexit.register(handler) instead of signal.signal(signal.SIGTERM, handler) but nothing is called on kill.

I copied your code and it worked just fine. What version of python are you using, etc? — Derek Litz, Dec 23 '11 at 14:57
Your code seems to work. What's the output/behaviour you're getting? — Eduardo Ivanec, Dec 23 '11 at 14:59
Indeed ... it works, I refactored my code to put it there I've removed some lines I thought were causing problem ---> closing the question. Thank you however ! — AsTeR, Dec 23 '11 at 15:10
I think it's better to have an answer to this given point. Can one of you post this answer so that I can tick it. — AsTeR, Dec 23 '11 at 15:11

score 11 · Accepted Answer · answered Aug 08 '12 at 06:08

Your code does almost work, except you forgot to exit after cleaning up.

We often need to catch various other signals such as INT, HUP and QUIT, but not so much with daemons.

import sys, signal, time

def handler(signum = None, frame = None):
    print 'Signal handler called with signal', signum
    time.sleep(1)  #here check if process is done
    print 'Wait done'
    sys.exit(0)

for sig in [signal.SIGTERM, signal.SIGINT, signal.SIGHUP, signal.SIGQUIT]:
    signal.signal(sig, handler)

while True:
    time.sleep(6)

On many systems, ordinary processes don't have much time to clean up during shutdown. To be safe, you could write an init.d script to stop your daemon and wait for it.

Thanks for that interesting developed answer and leading to this init.d scripts documentation. — AsTeR, Aug 09 '12 at 12:33

How to properly handle and retain system shutdown (and SIGTERM) in order to finish its job in Python?

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