I am so new to perl that "noob" is probably too generous a description. I am a Linux admin and have recently upgraded a server from Debian Lenny to Debian Jessie. The previous admin who built the Lenny server left behind some perl scripts, one of which I am unable to get running on new server. It says:

Can't locate Filesys/DiskUsage.pm in @INC (you may need to install the Filesys::DiskUsage module)

So I did some digging and found that I should install cpanminus and use it to install the the missing module. When I do so while logged in as root, it says:

cpan Filesys::DiskUsage
Reading '/root/.cpan/Metadata'
  Database was generated on Tue, 07 Feb 2017 01:53:38 GMT
Running install for module 'Filesys::DiskUsage'
Checksum for /root/.cpan/sources/authors/id/M/MA/MANWAR/Filesys-DiskUs
+age-0.10.tar.gz ok
'YAML' not installed, will not store persistent state
Configuring M/MA/MANWAR/Filesys-DiskUsage-0.10.tar.gz with Makefile.PL
Checking if your kit is complete...
Looks good
Generating a Unix-style Makefile
Writing Makefile for Filesys::DiskUsage
Writing MYMETA.yml and MYMETA.json
  MANWAR/Filesys-DiskUsage-0.10.tar.gz
  /usr/bin/perl Makefile.PL INSTALLDIRS=site -- OK
Running make for M/MA/MANWAR/Filesys-DiskUsage-0.10.tar.gz
cp lib/Filesys/DiskUsage.pm blib/lib/Filesys/DiskUsage.pm
cp fdu blib/script/fdu
/usr/bin/perl -MExtUtils::MY -e 'MY->fixin(shift)' -- blib/script/fdu
Manifying blib/man1/fdu.1p
Manifying blib/man3/Filesys::DiskUsage.3pm
  MANWAR/Filesys-DiskUsage-0.10.tar.gz
  /usr/bin/make -- OK
Running make test
PERL_DL_NONLAZY=1 PERL_USE_UNSAFE_INC=1 /usr/bin/perl "-MExtUtils::Com
+mand::MM" "-MTest::Harness" "-e" "undef *Test::Harness::Switches; tes
+t_harness(0, 'blib/lib', 'blib/arch')" t/*.t
t/00.load.t .......................... 1/1 # Testing Filesys::DiskUsag
+e 0.10
t/00.load.t .......................... ok
t/01.basic.t ......................... ok
t/02.warnings.t ...................... 1/2
#   Failed test 'warning for permission denied'
#   at t/02.warnings.t line 40.
# didn't find a warning
# expected to find warning: (?^:^could not open /tmp/b1jhnkInea/sub \(
+.+\)$)

#   Failed test 'size of one file'
#   at t/02.warnings.t line 42.
#          got: '10'
#     expected: '5'
# We run this again to see what are the various error messages in diff
+erent locales. There will be a warning next line:
# $ENV{LANG}: en_US.UTF-8
# Looks like you failed 2 tests of 2.
t/02.warnings.t ...................... Dubious, test returned 2 (wstat
+ 512, 0x200)
Failed 2/2 subtests
t/03.rmtree.t ........................ ok
t/71-version_numbers_are_the_same.t .. ok
t/pod-coverage.t ..................... skipped: Test::Pod::Coverage 1.
+04 required for testing POD coverage
t/pod.t .............................. skipped: Test::Pod 1.14 require
+d for testing POD

Test Summary Report
-------------------
t/02.warnings.t                    (Wstat: 512 Tests: 2 Failed: 2)
  Failed tests:  1-2
  Non-zero exit status: 2
Files=7, Tests=26,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.10 cusr
+  0.00 csys =  0.12 CPU)
Result: FAIL
Failed 1/7 test programs. 2/26 subtests failed.
Makefile:851: recipe for target 'test_dynamic' failed
make: *** [test_dynamic] Error 255
  MANWAR/Filesys-DiskUsage-0.10.tar.gz
  /usr/bin/make test -- NOT OK
//hint// to see the cpan-testers results for installing this module, t
+ry:
  reports MANWAR/Filesys-DiskUsage-0.10.tar.gz
[download]

And I have no idea what to do with that information. I've included the script here in case it might be helpful:

#!/usr/bin/perl

#PURPOSE - get each users inbox & imap storage sizes

use strict;
use warnings;
use FileHandle;

print "\n"x2;
inboxsize();
print "\n"x2;
mailboxsize();

my %hash;
my $version = '.93';
my %folderhash;

sub inboxsize{
my $dir = '/var/mail';
my $alert_size = '199.99';
my $alert_mark = '   <-----';

opendir my $dh, $dir or do {
  warn "Cannot open '$dir' $!";
};

my ($name, $size) = ( '', '' );
my $rounded;

while ( my $file = readdir $dh ) {
  $size = ( stat "$dir/$file" )[ 7 ] or do {
#  warn "Cannot stat '$dir/$file' $!";
#  last;
  };

($name, $size) = ($file, ($size / (1024*1024)));
$rounded = sprintf('%.2f', $size);
#if ($rounded >= $alert_size){$rounded=$rounded.$alert_mark};
if ($name =~ /^\./){next};
$hash{"$name"}="$rounded";
};

print "Mail Inbox sizes > $alert_size MB as of ". scalar (localtime) .
+"\n\n\n";
# sort by value, rather than key
foreach (sort {$hash{$a} <=> $hash{$b}} keys %hash) {
if ($hash{$_} >= $alert_size){write};

}
print '-'x41,"\n\n";
}

sub mailboxsize{
use Filesys::DiskUsage qw/du/;

#my $dir = '/Big-Drive/Fedora/';
my $dir = '/home/';
my $mdir = '/mail/';
my $alert_size = '499.99';

# get the usernames and put in @array
opendir(DIR,"$dir") or die "Couldn't open $dir directory!\n";
push (my @array, grep {!/^\./} readdir (DIR));
close (DIR);

foreach (@array){
  my $name = "$dir$_$mdir";
  if (-d "$name"){
    my $tot=du ({ 'sector-size' => 1024 }, qq'$name');
    my $totMB = sprintf('%.2f', ($tot / (1024*1024)));
    $hash{"$_"}="$totMB";
  }
}

print "Mail directory sizes > $alert_size MB as of ". scalar (localtim
+e) ."\n\n\n";
# sort by value, rather than key
foreach (sort {$hash{$a} <=> $hash{$b}} keys %hash) {
if ($hash{$_} >= $alert_size){
   STDOUT->format_name("STDOUT");
   write;  # mail directory total size
   # start getting folder sizes for each largemaildir user
   my $name = "$dir$_$mdir";  # /home/user/mail/
   opendir(DIR,"$name") or die "Couldn't open $name directory!\n";
   push (my @array, grep {!/^\./} readdir (DIR));  # get the folder na
+mes
   close (DIR);
   undef %folderhash;
   foreach (@array){  # get folder sizes and put in %folderhash
#      if (-f "$name$_"){
         my $tot=du ({ 'sector-size' => 1024 }, qq'$name$_');
         my $totMB = sprintf('%.2f', ($tot / (1024*1024)));
         $folderhash{"$_"}="$totMB";
#      };
   };
      # sort by value, rather than key
      STDOUT->format_name("MIDDLE");
      foreach (sort {$folderhash{$a} <=> $folderhash{$b}} keys %folder
+hash) {write}  # mail folder sizes
};
}
print '-'x41,"\n\n";
}
print "Printed by $0 version $version at ". scalar (localtime) ."\n";

format STDOUT =
@<<<<<<<<<<<<<<<<<<<<<<<<<<< @>>>>>>>>>>>
$_,                          $hash{$_}
.

format MIDDLE =
   @<<<<<<<<<<<<<<<<<<<<<<<<<<<     @>>>>>>>>>>>
   $_,                              $folderhash{$_}
.
[download]

Please be gentle and generous with your step by step advice on how I should proceed.