Im trying to understand why signals arent being passed properly under this setup.
Simple test, I have a python script that registers a sigterm handler and prints if it gets it. I have verified this works if i run it and send a TERM.

However, I happen to be running this as a python Subprocess with useShell = True. useShell launches the command with /bin/sh -c ...

If I do this, it actually works as well:

$/bin/sh -c "python ~/tmpcode/signal_test.py" &
[8] 6207
$ kill 6207
 signum 15

However, I have scripts that do chained commands, ie /foo/bar.sh; some_other_script.py. Under this scenario, the signal is not passed to the final script:

$ /bin/sh -c "echo foo; python ~/tmpcode/signal_test.py" &
[8] 8015
$ kill 8015

Same thing happens if I try && instead of ;
Im trying to understand whats going on here, and if there is a way to get the signal to chain through.
Side point: The main reason the script is running multi-chain commands is because the first command sets up some environment for the second one to use.

signal_test.py:

import time
import signal
import sys

def handler( signum, frame ):
 print( "signum %dn" % signum ) 
 sys.exit(signum)

signal.signal( signal.SIGTERM, handler )
time.sleep(60)

Let me explain the details.

The number bash returned is not pid, it is pgid (process group id)

When you run a command in the shell, shell will create a new process group. The group will contain all process in the command. And the pgid is the same as pid of the leader process.

A process group means task in the word multi-task, shell is able to switch between groups using bg(^Z)/fg. All signal (like ^C) generated by shell (acturaly pty, another story) will send to the entire group instead of leader process.

When shell creates multiple processes or single process ?

The answer is obviously, the shell will create multiple processes when the commands can't be handled by a single process.

In the first example

$/bin/sh -c "python ~/tmpcode/signal_test.py" &
[8] 6207

a single command is issued, so the sub-shell itself (/bin/sh) becomes python. Notes, even there is only one process, there still be a new process group containing the only process.

In the second example

$ /bin/sh -c "echo foo; python ~/tmpcode/signal_test.py" &
[8] 8015

two commands are issued, the task can't be achieved by a single process, so multiple process is needed:

/bin/sh
 echo
 python

A process group is created containing these three process.

How to send signals to process group ?

Use

kill <SIGNAL> -<pgid>

The minus sign in front of pgid is essential.