Try trapping the following signals:

HUP, INT, QUIT, KILL, TERM, STOP, ABRT

One of those will probably do it but I'm not sure which.

To trap a signal, use the following:

$SIG{KILL} = sub {
  print "This is my signal handling code.  Log messages here.\n";
};
[download]

BTW, you can get a list (in the form of a single string separated by single spaces) of all the signals your system supports like this:

use Config;
print "$Config{sig_name}\n";
[download]

HTH

bbfu
Seasons don't fear The Reaper.
Nor do the wind, the sun, and the rain.
We can be like they are.

You have forgotten PIPE which it most likely is.

Hrm. I intentionally didn't include PIPE because I didn't think it would be that causing. Thinking about it now, though, I see that it could well be the cause. Mea culpa.

bbfu
Seasons don't fear The Reaper.
Nor do the wind, the sun, and the rain.
We can be like they are.