Comment 2 for bug 1914875

From the log, looks like this hit a bug in debconf. Same issue appears to crop up for other packages (e.g. LP: #1914964).

 Setting up libpam-sss:amd64 (2.3.1-3ubuntu3) ...
 Use of uninitialized value $ret in string eq at /usr/share/perl5/Debconf/FrontEnd/Passthrough.pm line 134.

The code in question is:

sub capb
{
        my $this=shift;
        my $ret;
 return $this->{capb} if exists $this->{capb};

        ($ret, $this->{capb}) = $this->talk('CAPB');
 return $this->{capb} if $ret eq '0';
}

So apparently whatever $this->talk('CAPB') resolves to returned an undefined value for $ret. A paper-over fix might be something like:

 return $this->{capb} if defined $ret and $ret eq '0';

However, would be better to know what triggers the error condition since there could be a deeper problem involved.

Anyway, thanks for reporting this defect in Ubuntu, hopefully there's enough info for the debconf maintainers to take it from here.