#!/usr/bin/perl -T
use strict;
use warnings;
use POSIX 'setsid';


$ENV{'PATH'} = '/bin:/usr/bin:/usr/sbin';
delete @ENV{'IFS', 'CDPATH', 'ENV', 'BASH_ENV'};

my $p0f;
my $pid;

open($p0f, "p0f -l 'tcp dst port 25' 2>&1 | ") or die "Can't fork: $!";

daemonize();

while(<$p0f>) {
  print if /Linux/;
}


sub daemonize {
    chdir '/'  or die "Can't chdir to /: $!";
    open STDIN, '/dev/null' or die "Can't read /dev/null: $!";
    open STDOUT, '>/dev/null' or die "Can't write to /dev/null: $!";
    defined(my $pid = fork) or die "Can't fork: $!";
    exit if $pid;
    setsid or die "Can’t start a new session: $!";
    open STDERR, '>&STDOUT' or die "Can't dup stdout: $!";
}