if (my $pid = fork()) {
    wait;
    
} elsif (defined $pid) {
    setpgrp;   # create new process group
    eval {
        local $SIG{ALRM} = sub { die "alarm\n" };
        alarm 5;
        system 'bash -c "cat; echo"';   # run something (several processes) that hangs
        alarm 0;
    };
    if ($@ eq "alarm\n") {
        kill 9, 0;    # kill current process group
    }
    exit;
}