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From:	Ronald Otto Valentin Fischer <ashi DOT niwatori AT the-quickest DOT com>
To:	cygwin AT cygwin DOT com
MIME-Version:	1.0
Subject:	Killing-Process woes
Date:	Tue, 20 Jun 2017 08:23:55 +0200

I'm spawning processes in background, but have problems killing them.
Here is the setup:

My script (zsh) creates one or more processes in the background, and
waits until they are finished. I have also set up a trap for SIGINT,
with the intention that if I press Control-C, the background processes
should be killed. I have verified the setup so far, that upon Control-C,
the trap function is indeed invoked, and I have all the PIDs of the
background processes. The problem is with the actual killing, and here
is why:

The background processes are actually (zsh-) scripts, which do some
setup (basically setting various environment variables), and then invoke
a (Cygwin-)Ruby program which does the "real work". The program is
executed by something like

    ruby myprog.rb

(Note that this Ruby program is NOT invoked in background).

When my SIGINT trap is entered, I can see from ps indeed the
relationship between the processes involved, for instance

    10852    9296    6224      10536  cons3    3672028 08:05:10
    /usr/bin/ruby
     9296    6224    6224      11236  cons3    3672028 08:05:10
     /usr/bin/zsh

The PID of my background process - the zsh wrapper - in this concrete
case is 9296, and we can see that this is the parent of the Ruby
process, 10852. The problem is that if I just kill 9296, the Ruby
process keeps running, orphaned:

    10852       1    6224      10536  cons3    3672028 08:05:10
    /usr/bin/ruby

I've found on Stackoverflow the suggestion to treat this as a process
group and use negative PIDs. I tried this too, but it didn't work. Here
is a similar example:

     5548   10276    5812       2376  cons3    3672028 08:20:43
     /usr/bin/ruby
    10276    5812    5812      10312  cons3    3672028 08:20:43
    /usr/bin/zsh

If I do a

    kill -- -10276

I get the error message

     kill: -10276: No such process

This happens both with the zsh-builtin kill and with /usr/bin/kill Is
there a simple way to kill the zsh process in addition to the ruby
process, or do I have to analyze the output of the ps command to
manually find the PID of the Ruby process and kill it?

Ronald
-- 
Ronald Fischer <ronald DOT fischer AT fusshuhn DOT de>
http://www.fusshuhn.de/


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