Re: Re: Killing child process

I couldn't get that to work:

#!/usr/bin/perl -w

use strict;

$SIG{TERM}= sub { 
  print "TERM $$\n";
  exit(1);
};

if (my $kidpid = fork)
{
  # Parent
  sleep(1);
  print "\n";
  kill -15, $kidpid;
  sleep(5);
}
else
{
  print "CREATED CHILD $$\n";
  # Child
  for my $i (1..10)
  {
    if (!fork)
    {
      # Grandchild
      print "CREATED GRANDCHILD $$\n";
      sleep(5);
      exit(0);
    }
  }
  sleep(300);
}
[download]

Is there a bug in this code, or are things not working as documented?

Comment on Re: Re: Killing child process Download Code

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Re: Re: Re: Killing child process by Thelonius (Priest) on Oct 13, 2003 at 02:20 UTC
Oops, yeah, I forgot you need to set the process group for the process you want to be a group leader. To do this call `setpgrp(0,0);` after the fork. In your test program, do it right where you have `print "CREATED CHILD $$\n";` and don't do it in the grandchildren.	[reply] [d/l] [select]
Re: Re: Re: Re: Killing child process by sgifford (Prior) on Oct 13, 2003 at 03:31 UTC
Cool, that worked! Thanks, I've always wondered how process groups worked. Now, I wonder if this answered the OP's question?... :-)	[reply]
Re: Re: Re: Killing child process by pg (Canon) on Oct 12, 2003 at 17:02 UTC
Two points about OS: To send a signal to a process group, you have to be a super user; Most of OS's, if not all, does not let you capture SIGTERM for ordinary users. That's for a good reason, if some processes (intentionally or by mistake - bugs) decide to be alive forever, that will really be a nightmare.	[reply]
Re: Re: Re: Re: Killing child process by sgifford (Prior) on Oct 12, 2003 at 17:42 UTC
This program doesn't work when run as root either. I believe you're thinking of SIGKILL. SIGTERM is a perfectly normal signal. If I change the `kill` command to just send a normal signal to `$kidpid`, then the child process prints the TERM message, but not the grandchildren. Similarly, if you make the `sleep`s a little longer, you can send TERM signals by hand to individual grandchildren, and they print the message.	[reply] [d/l] [select]