Unable to match Net::Telnet Prompt on CentOS. However, the same prompt works fine on FC20

[shoundic]

I've a script which works fine on FC20. But, when I try to execute the same script on CentOS(CentOS Linux release 7.5.1804 (Core)), it hangs. On further, investigation it was revealed that, it is not able to match the prompt given. Please note it is able to match host prompt but not application prompt. Here is a brief detail of the issue

Code of the wrapper function which is used to create object of Net::Telnet-

package api::Telnet;

use strict;
use warnings;
use Net::Telnet;
use Exporter;
use Carp;

our @ISA    = qw (Exporter);
our @EXPORT = qw (
    &open_pty
    &close_pty
);

# Constant global variables
use constant SSH_TIMEOUT => 1800;

sub spwan_pty 
{
    my (@cmd) = @_;
    my ($pid, $tty, $tty_fd);

    # Create a new pseudo terminal
    use IO::Pty ();
    my $pty = new IO::Pty or die $!;

    # Execute the program in another process
    # Child process
    unless ($pid = fork) {
        die "problem spawning program: $!\n" unless defined $pid;

        # Disassociate process from existing controlling terminal
        use POSIX ();
        POSIX::setsid
            or die "setsid failed: $!";

        # Associate process with new controlling terminal
        $pty->make_slave_controlling_terminal;
        $pty->set_raw();
        $tty = $pty->slave();
        $tty_fd = $tty->fileno;
        close $pty;

        # Make stdio use the new controlling terminal
        open STDIN, "<&$tty_fd" or die $!;
        open STDOUT, ">&$tty_fd" or die $!;
        open STDERR, ">&STDOUT" or die $!;
        close $tty;

        exec @cmd
            or die "problem executing $cmd[0]\n";
    } # end child process  

    $pty;
}

sub open_pty 
{
    my (%args) = @_;

    # Start ssh program.
    my $pty = &spwan_pty("ssh",
        "-l", $args{user_name},
        "-e", "none",
        "-F", "/dev/null",
        "-o", "PreferredAuthentications=password",
        "-o", "NumberOfPasswordPrompts=1",
        "-o", "StrictHostKeyChecking=no",
        "-o", "UserKnownHostsFile=/dev/null",
        $args{ip_addr}
    );

    # Create a Net::Telnet object to perform I/0 on ssh's tty
    my $ssh = new Net::Telnet (
        -fhopen          => $pty,
        -prompt          => $args{prompt},
        -telnetmode      => 0,
        -cmd_remove_mode => 1,
        -timeout         => SSH_TIMEOUT,
        -output_record_separator => "\r",
        #-errmode         => sub { print "Telnet FAIL\n"; }
    );

    # Wait for the password prompt and send password.
    $ssh->waitfor(-match => '/password: ?$/i', -errmode => "return")
        or die "problem connecting to \"$args{ip_addr}\": ", $ssh->las
+tline;

    $ssh->print($args{user_pswd});

    # Wait for the shell prompt.
    my (undef, $match) = $ssh->waitfor(
        -match => $ssh->prompt,
        -match => '/^Permission denied/m',
        -errmode => "return"
    ) or return $ssh->error("login failed: expected shell prompt ", "d
+oesn't match actual\n");

    return $ssh->error("login failed: bad login-name or password\n") i
+f $match =~ /^Permission denied/m;

    # logging 
    $ssh->input_log($args{log_file});
    $ssh->cmd("ifconfig");
    $ssh->cmd("date");
    return $ssh;
}

sub close_pty
{
    my ($tty) = shift;
    $tty->close();
}

1;

Once Net:Telnet object is obtained, it is used to spawn an interactive application. Here is the code snippet of the same-

 
my $host_prompt = '/[\$%#>] $/';
my $util_prompt = '/(\s)*Command: (\s)*/i';

my $owner = &open_pty (
                user_name     =>  "<user_name>",
                user_pswd     =>  "<password>",
                 ip_addr       =>  "127.0.0.1",
                prompt        =>  $host_prompt,
                log_file      =>  'Log/Owner'
            );

$owner->cmd ( String => "cd <navigate to application path>", Prompt =>
+ $host_prompt );
$owner->cmd ( String => "<Launch the application>", Prompt => $util_pr
+ompt );
$owner->cmd ( String => "<Execute command>", Prompt => $util_prompt );

The code successfully creates a Net::Telnet object and spawn the application, but it is unable to match the prompt of the application, due to which it hungs and the script is unable to proceed forward. Here is the log generated-

em1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet xxx.xxx.xxx.xxx  netmask 255.255.252.0  broadcast xxx.xxx
+.xxx.xxx
        inet6 xxxx::xxxx:xxxx:xxxx:xxxx  prefixlen 64  scopeid 0x20<li
+nk>
        ether xx:xx:xx:xx:xx:xx  txqueuelen 1000  (Ethernet)
        RX packets 393842  bytes 40650026 (38.7 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 138388  bytes 15595013 (14.8 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 16  memory 0x92f00000-92f20000  

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 5296  bytes 928222 (906.4 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 5296  bytes 928222 (906.4 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

virbr0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        inet xxx.xxx.xxx.xxx  netmask xxx.xxx.xxx.xxx  broadcast xxx.x
+xx.xxx.xxx
        ether xx:xx:xx:xx:xx:xx  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

[root@hyd1658 ~]# Wed Jan 16 15:29:54 IST 2019
.
.
.
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        Command:

Please Note: The same code works on FC20, but fails on CentOS

Could anyone please pinpoint the issue or suggest a remedy for the same

[VinsWorldcom]

You could set:

my $obj = Net::Telnet->new(
    ...
    dump_log => 'dump.log',
    ....
}

# or

$obj->dump_log('dump.log');

on your Net::Telnet object to get a "binary" log file showing all the hex characters of what's on the wire - then you could see any funky escape characters in the prompt as suggested by RMGir above.

[shoundic]

Thanks, by using dump_log I was able to solve the issue.

[RMGir]

Excellent! But now I'm curious: what was it? :)

[RMGir]

My guess would be that CentOS is sending you a colourized or otherwise escape-sequence-mangled prompt, but it's hard to tell.

Have you tried using wireshark to see what's actually being sent over the wire, to make sure the prompt you expect is what you're sent? Just using 'telnet' isn't really enough, since you might not be able to see anything that's not printable. (Edit: Actually, as suggested below, use the dump_log option - it sounds much simpler than wireshark).

[kschwab]

You could try copying the .bashrc and any other shell config scripts from the Fedora box to the Centos box. Make backups first.