Run code in python script on shutdown signal

Question

I have a python script that runs in the background on startup. The starting method is a entry in a run.sh file which is called with /etc/rc.local. The exact entry would be \

Answer 1

shutdown sends the SIGTERM signal, which atexit does not handle. Nor will context managers, finally blocks, etc.

import signal

signal.getsignal(signal.SIGTERM)
Out[64]: 0 #i.e. nothing

Contrast this with, say ctrl-C:

signal.getsignal(signal.SIGINT)
Out[65]: <function signal.default_int_handler> #i.e. something

You can register your byebye function with signal to run instead of doing nothing (which leads to the interpreter eventually getting killed by the shell)

signal.signal(signal.SIGTERM,byebye)

If you do the above you'll need to do two things:

• change the signature of byebye to accept the two arguments that signal will pass to it.
• you should do something like call sys.exit() at the end of your byebye function to allow python to gracefully close up shop.

You could alternatively do some combination of signal and atexit:

import sys
signal.signal(signal.SIGTERM, lambda num, frame: sys.exit(0))

Which would drop right in to your current code. This ensures the atomicity of your cleanup operation (i.e. byebye is guaranteed to be the last I/O operation) at the cost of being a bit clunky.