Catching SIGTERM in Python

20 Feb 2016

I needed a very simple SIGTERM handler in a script I was working on. It is very simple to do so in Python, add a handler method and ‘register’ it.

First define a handler method:

def sigterm_handler(signal, frame):
    # this method defines the handler i.e. what to do
    # when you receive a SIGTERM
    pass

And register the handler:

# Register the handler and let the process know that 
# there is a handler for SIGTERM
signal.signal(signal.SIGTERM, sigterm_handler)

Here’s a simple script, if it receives kill then it saves current state and exits gracefully. Here’s a full working code:

import signal
import sys
import time


def sigterm_handler(signal, frame):
    # save the state here or do whatever you want
    print('booyah! bye bye')
    sys.exit(0)

signal.signal(signal.SIGTERM, sigterm_handler)


def main():
    for i in range(100):
        print(i)
        time.sleep(i)


if __name__ == '__main__':
    main()

Run the above script and send KILL, like

$ kill <PID here>

it will print 'booyah! bye bye' in terminal.

References

Python 3 docs on signal - link