use strict;

if (my $pid = fork)
{
   # parent
   setpgrp($pid, $pid);

   waitpid($pid, 0);
   while (waitpid(-$pid, 0) != -1) {}
   exit;
}
else
{
   # child
   if (!(my $pid = fork))
   {
      # grandchild
      sleep(1) while 1;
   }
}