use warnings;
use strict;
use Net::SSH::Perl;
use Parallel::ForkManager;

### Add your own.
my $p_host = '';
my $d_host = '';
my $ssh_key_file = '';

### For command execution.
my @cmds = (
	'ls',
	'ls -l',
	'ls -1',
);
my ($out, $exit);

### Establish two connections. Works fine.
my $p_ssh = Net::SSH::Perl->new(
	$p_host,
	identity_files => [$ssh_key_file],
);
$p_ssh->login && print "$p_host connected.\n";

my $d_ssh = Net::SSH::Perl->new(
	$d_host,
	identity_files => [$ssh_key_file],
);
$d_ssh->login && print "$d_host connected.\n";

### Try the commands on each host. Works fine.
for my $cmd (@cmds) {
	print "Trying '$cmd'...\n";
	print '=' x 20, "\n";
	for my $server ($d_ssh, $p_ssh) {
		($out, undef, $exit) = $server->cmd($cmd);
		print "$out\n\n";
		die if $exit;
	}
}

### Now attempt the same thing in a fork. Bad news.
for my $cmd (@cmds) {
	print "Trying '$cmd'...\n";
	print '=' x 20, "\n";
	my $pfm = new Parallel::ForkManager(2);
	for my $host ($d_ssh, $p_ssh) {
		my $pid = $pfm->start and next;
		
		($out, undef, $exit) = $host->cmd($cmd);
		print "$out\n\n";
		die if $exit;
		
		$pfm->finish;
	}
	$pfm->wait_all_children;
}


##</code><code>##

host1 connected.
host2 connected.
Trying 'ls'...
====================
...listing from host1...

...listing from host2...

Trying 'ls -l'...
====================
...listing from host1...

...listing from host2...

Trying 'ls -1'...
====================
...listing from host1...

...listing from host2...

Trying 'ls'...
====================
...listing from host1...

...listing from host2...

Trying 'ls -l'...
====================
Bad packet length 3032450590 at /usr/local/lib/perl5/site_perl/5.10.0/Net/SSH/Perl/Packet.pm line 175
Bad packet length 629981479 at /usr/local/lib/perl5/site_perl/5.10.0/Net/SSH/Perl/Packet.pm line 175

Trying 'ls -1'...
====================
Use of uninitialized value $out in concatenation (.) or string at ./tmp.pl line 53.
Connection failed: Connection reset by peer
 at ./tmp.pl line 52