Expect for cryptsetup

theo@ubuntucy.org has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks,

I am trying to automate the decryption of a volume using Expext.pm I want to run this command automated:

# cryptsetup luksOpen /dev/VG/DATA dec-DATA
Enter passphrase for /dev/VG/DATA:
[download]

After you successfully give the passphrase you get /dev/mapper/dec-DATA which is the unencrypted volume I want to automate this using Expect.pm I came up with this code:

          
#!/usr/bin/perl

use strict;
use warnings;

use Expect;
use Getopt::Std;

$Expect::Debug = 0;
$Expect::Log_Stdout = 1;


my $command = "/sbin/cryptsetup";
my $timeout = 5;
my $exp = Expect->spawn( $command, 'luksOpen', 
                       '/dev/VG/DATA', 'dec-DATA' )
    or die "Cannot spawn $command: $!\n";

my $idx = $exp->expect($timeout,
        [qr/Enter\s+passphrase\s+for/, 
                sub { my $exp =shift; 
                        $exp->send("secret\n");
                }]
        );

$exp->soft_close();
[download]

Now I have the following peculiarity. When $Expect::Debug is set to 0 it does not work; when set to 1 it does!

Can you please enlight a perl newbie? Is this a bug or am I doing something fundamentally wrong?

I use perl v5.14.2 and Expect.pm is version 1.21.

Comment on Expect for cryptsetup Select or Download Code

Replies are listed 'Best First'.
Re: Expect for cryptsetup by kcott (Archbishop) on Aug 20, 2013 at 07:02 UTC
G'day theo@ubuntucy.org, Welcome to the monastery. "... it does not work ..." This is a totally inadequate error report. In what way doesn't it work: the script doesn't start; it functions incorrectly; your keyboard bursts into flames? Are there any warning or error messages? A better question will get you better answers: "How do I post a question effectively?" has guidelines for achieving this. -- Ken	[reply]
Re: Expect for cryptsetup by grondilu (Friar) on Aug 20, 2013 at 22:02 UTC
Do you really want/need to use Expect? Because that seems very complicated a solution, to me. There is certainly an option for cryptsetup that allows you to provide the passphrase on command-line or in a file. I've just looked at the cryptsetup man page, and I see there is a --key-file option.	[reply]
Re: Expect for cryptsetup by theo@ubuntucy.org (Initiate) on Aug 21, 2013 at 06:59 UTC
@kcott: Sorry for not clearing it out: "Works" translates to "creation of the decrypted device /dev/mapper/dec-DATA "Does not work" means no creation of decrypted device @grondilu: That will mean the keyfile will be available somewhere in the filesystem. We do not want that. The passphrase will be in fact entered by the user through a web interface to decrypt the volume. Anyway the CPAN guys figured it out. It was a race condition which is solved by a simple "sleep 1" after the $exp->send command. Thanks guys!	[reply]