How to detect remote machine os, while connecting?

[ckant8]

After i connect, i have to give username. There i need to know the OS type. Based on that i will give username.

[RonB]

You're not going to be able to determine the OS prior to login.

[RonB]

Here's an example demonstrating the fact that you won;t be able to accurately determine the OS.

#!/usr/bin/perl

use 5.10.1;
use strict;
use warnings;
use XML::Simple;
use Data::Dumper;

close STDERR;

foreach my $ip ( qw(10.100.0.130 10.100.0.119 10.100.0.118) ) {
    say "scanning $ip";
    say '-' x 21;
    my $nmap = `nmap -v -v -v -O  -oX - $ip`;
    my $nmap_xml = XMLin($nmap);
    say Dumper keys %{ $nmap_xml->{host}{os}{osmatch} };
}

Outputs:

scanning 10.100.0.130
---------------------
$VAR1 = 'name';
$VAR2 = 'accuracy';
$VAR3 = 'line';

scanning 10.100.0.119
---------------------

scanning 10.100.0.118
---------------------
$VAR1 = 'AXIS 211A Network Camera (Linux 2.6.20)';
$VAR2 = 'Linux 2.6.17 (Mandriva)';
$VAR3 = 'Linux 2.6.9 - 2.6.18';
$VAR4 = 'Linux 2.6.22 - 2.6.23';
$VAR5 = 'IBM System Storage DS4700 NAS device';
$VAR6 = 'Linux 2.6.9 - 2.6.27';
$VAR7 = 'Linux 2.6.9 - 2.6.28';
$VAR8 = 'Linux 2.6.28 (Gentoo)';
$VAR9 = 'AXIS 211A Network Camera (Linux 2.6)';
$VAR10 = 'Linux 2.6.18 (Centos 5.3)';

All 3 of those hosts are on the local network.

Can you tell me the OS for the first 2 and which one of those 10 results for the 3rd host is correct?