proftpd-basic 1.3.5~rc3-2.1ubuntu2 / usr / sbin / ftpasswd

#!/usr/bin/env perl
# ---------------------------------------------------------------------------
# Copyright (C) 2000-2013 TJ Saunders <tj@castaglia.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA.
#
# Based on MacGuyver's genuser.pl script, this script generates password
# files suitable for use with proftpd's AuthUserFile directive, in passwd(5)
# format, or AuthGroupFile, in group(5) format.  The idea is somewhat similar
# to Apache's htpasswd program.
#
#  $Id: ftpasswd,v 1.18 2013/04/23 23:25:20 castaglia Exp $
# ---------------------------------------------------------------------------

use strict;

use File::Basename qw(basename);
use Getopt::Long;

# turn off auto abbreviation
$Getopt::Long::auto_abbrev = 0;

my $program = basename($0);
my $default_passwd_file = "./ftpd.passwd";
my $default_group_file = "./ftpd.group";
my $shell_file = "/etc/shells";
#my $default_cracklib_dict = "/usr/lib/cracklib_dict";
my $default_cracklib_dict = "/var/cache/cracklib";
my $cracklib_dict;
my $output_file;
my $version = "1.2.0";

my @data;

my %opts = ();
GetOptions(\%opts,
  'change-password',
  'delete-group',
  'delete-user',
  'des',
  'enable-group-passwd',
  'file=s',
  'F|force',
  'gecos=s',
  'gid=n',
  'group',
  'hash',
  'h|help',
  'home=s',
  'md5',
  'm|member=s@',
  'name=s',
  'not-previous-password',
  'not-system-password',
  'passwd',
  'sha256',
  'sha512',
  'shell=s',
  'stdin',
  'uid=n',
  'use-cracklib:s',
  'version',
);

usage() if (defined($opts{'h'}));

version() if (defined($opts{'version'}));

# check if "use-cracklib" was given as an option, and whether a path
# to other dictionary files was given.
if (defined($opts{'use-cracklib'})) {

  # make sure that Crypt::Cracklib is installed before trying to use
  # it later
  eval { require Crypt::Cracklib };
  die "$program: --use-cracklib requires Crypt::Cracklib to be installed\n" if $@;

  if ($opts{'use-cracklib'} ne "") {
    $cracklib_dict = $opts{'use-cracklib'};

  } else {
    $cracklib_dict = $default_cracklib_dict;
  }
}

# make sure that both passwd and group modes haven't been simultaneously
# requested

if ((exists($opts{'passwd'}) && exists($opts{'group'})) ||
    (exists($opts{'passwd'}) && exists($opts{'hash'})) ||
    (exists($opts{'group'}) && exists($opts{'hash'}))) {
  die "$program: please use *one*: --passwd, --group, or --hash\n";

} elsif (defined($opts{'passwd'})) {

  # determine to which file to write the passwd entry
  if (defined($opts{'file'})) {
    $output_file = $opts{'file'}; 
    print STDOUT "$program: using alternate file: $output_file\n"

  } else {
    $output_file = $default_passwd_file;
  } 

  # make sure that the required arguments are present
  die "$program: --passwd: missing required argument: --name\n"
    unless (defined($opts{'name'}));

  # check for and handle the --delete-user option.
  if (defined($opts{'delete-user'})) {
    open_output_file();

    my ($pass, $uid, $gid, $gecos, $home, $shell) = find_passwd_entry(name =>
      $opts{'name'});

    handle_passwd_entry(name => $opts{'name'}, uid => $uid, gid => $gid,
      gecos => $gecos, home => $home, shell => $shell,
      delete_user => $opts{'delete-user'});

    close_output_file();

    # done
    exit 0;
  }

  # now check for the --change-password option.  If present, lookup
  # the given name in the password file, and reuse all the information
  # except for the password
  if (defined($opts{'change-password'})) {
    open_output_file();

    my ($pass, $uid, $gid, $gecos, $home, $shell) = find_passwd_entry(name =>
      $opts{'name'});

    handle_passwd_entry(name => $opts{'name'}, uid => $uid, gid => $gid,
      gecos => $gecos, home => $home, shell => $shell);

    close_output_file();

    # done
    exit 0;
  }

  # check for the --not-system-password option.  If present, make sure that
  # a) the script is running with root privs, and b) perl on the system is
  # such that getpwnam() will return the system password
  if (defined($opts{'not-system-password'})) {
    die "$program: must be user root for system password check\n"
      unless ($> == 0);
  }

  die "$program: --passwd: missing required argument: --home\n"
    unless (defined($opts{'home'}));

  die "$program: --passwd: missing required argument: --shell\n"
    unless (defined($opts{'shell'}));

  die "$program: --passwd: missing required argument: --uid\n"
    unless (defined($opts{'uid'}));

  # As per Flying Hamster's suggestion, have $opts{'gid'} default to --uid
  # if none are specified on the command-line via --gid
  unless (defined($opts{'gid'})) {
    $opts{'gid'} = $opts{'uid'};
    warn "$program: --passwd: missing --gid argument: default gid set to uid\n";
  }

  open_output_file();

  handle_passwd_entry(name => $opts{'name'}, uid => $opts{'uid'},
    gid => $opts{'gid'}, gecos => $opts{'gecos'}, home => $opts{'home'},
    shell => $opts{'shell'}, delete_user => $opts{'delete-user'});

  close_output_file();

  # NOTE: if this process is not running as root, then the file generated
  # is not owned by root.  Issue a warning reminding the user to make the
  # generated file mode 0400, owned by root, before using it.

} elsif (defined($opts{'group'})) {

  # determine to which file to write the group entry
  if (defined($opts{'file'})) {
    $output_file = $opts{'file'};
    print STDOUT "$program: using alternate file: $output_file\n";

  } else {
    $output_file = $default_group_file;
  }

  # check for and handle the --delete-group option.
  if (defined($opts{'delete-group'})) {
    open_output_file();

    handle_group_entry(name => $opts{'name'},
      delete_group => $opts{'delete-group'});

    close_output_file();

    # done
    exit 0;
  }

  # make sure the required options are present
  die "$program: --group: missing required argument: --gid\n"
    unless (defined($opts{'gid'}));

  die "$program: --group: missing required argument: --name\n"
    unless (defined($opts{'name'}));

  open_output_file();

  handle_group_entry(gid => $opts{'gid'}, members => $opts{'m'},
    name => $opts{'name'}, delete_user => $opts{'delete-user'},
    delete_group => $opts{'delete-group'});

  close_output_file();

} elsif (defined($opts{'hash'})) {
  print STDOUT "$program: ", get_passwd(), "\n";

} else {
  die "$program: missing required --passwd or --group\n$program: use $program --help for details on usage\n\n";
}

# done
exit 0;

# ----------------------------------------------------------------------------
sub check_shell {
  my %args = @_;

  my $shell = $args{'shell'};
  my $result = 0;

  # check the given shell against the list in /etc/shells.  If not present
  # there, issue a message recognizing this, and suggesting that
  # RequireValidShell be set to off, and that any necessary PAM modules be
  # adjusted.

  unless (open(SHELLS, "< $shell_file")) {
    warn "$program: unable to open $shell_file: $!\n";
    warn "$program: skipping check of $shell_file\n";
    return;
  }

  while(my $line = <SHELLS>) {
    chomp($line);

    if ($line eq $shell) {
      $result = 1;
      last;
    } 
  }

  close(SHELLS);

  unless ($result) {
    print STDOUT "\n$program: $shell is not among the valid system shells.  Use of\n";
    print STDOUT "$program: \"RequireValidShell off\" may be required, and the PAM\n";
    print STDOUT "$program: module configuration may need to be adjusted.\n\n";
  }

  return $result;
}

# ----------------------------------------------------------------------------
sub close_output_file {
  my %args = @_;

  open(OUTPUT, "> $output_file") or
    die "$program: unable to open $output_file: $!\n";

  # flush the data to the file
  foreach my $line (@data) {
    print OUTPUT "$line\n";
  }

  # set the permissions appropriately, ie 0440, before closing the file
  unless (chmod(0440, $output_file)) {
    die("$program: unable to set permissions on $output_file: $!");
  }

  close(OUTPUT) or die "$program: unable to close $output_file: $!\n";
}

# ----------------------------------------------------------------------------
sub find_passwd_entry {
  my %args = @_;

  my $name = $args{'name'};
  my ($pass, $uid, $gid, $gecos, $home, $shell);
  my $found = 0;

  # given a name, find the corresponding entry in the passwd file
  foreach my $line (@data) {
    next unless $line =~ /^$name:/;

    my @fields = split(':', $line);

    $pass = $fields[1];
    $uid = $fields[2];
    $gid = $fields[3];
    $gecos = $fields[4];
    $home = $fields[5];
    $shell = $fields[6];

    $found = 1;

    last;
  }

  unless ($found) {
    print STDOUT "$program: error: no such user $name in $output_file\n";
    exit 1;
  }

  return ($pass, $uid, $gid, $gecos, $home, $shell);
}

# ----------------------------------------------------------------------------
sub get_salt {
  my $salt;

  # The determination of with encryption algorithm to use is done via
  # the salt.  The format and nature of the salt is how crypt(3) knows
  # how to do its thing.  By default, generate a salt that triggers MD5.

  if (defined($opts{'des'})) {
    # DES salt
    $salt = join '', ('.', '/', 0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64];

  } elsif (defined($opts{'sha256'})) {
    # SHA-256 salt (16 characters)
    $salt = join '', (0..9, 'A'..'Z', 'a'..'z')
      [rand 62, rand 62, rand 62, rand 62,
       rand 62, rand 62, rand 62, rand 62,
       rand 62, rand 62, rand 62, rand 62,
       rand 62, rand 62, rand 62, rand 62];
    $salt = '$5$' . $salt;

  } elsif (defined($opts{'sha512'})) {
    # SHA-512 salt (16 characters)
    $salt = join '', (0..9, 'A'..'Z', 'a'..'z')
      [rand 62, rand 62, rand 62, rand 62,
       rand 62, rand 62, rand 62, rand 62,
       rand 62, rand 62, rand 62, rand 62,
       rand 62, rand 62, rand 62, rand 62];
    $salt = '$6$' . $salt;

  } else {
    # MD5 salt (16 characters)
    $salt = join '', (0..9, 'A'..'Z', 'a'..'z')
      [rand 62, rand 62, rand 62, rand 62,
       rand 62, rand 62, rand 62, rand 62,
       rand 62, rand 62, rand 62, rand 62,
       rand 62, rand 62, rand 62, rand 62];
    $salt = '$1$' . $salt;
  }

  return $salt;
}

# ----------------------------------------------------------------------------
sub get_passwd {
  my %args = @_;
  my $name = $args{'name'};
  my ($passwd, $passwd2);

  # If using a DES salt, print an informative message about the 8 character
  # limit of relevant password characters.

  if (defined($opts{'des'}) && !defined($opts{'stdin'})) {
    print STDOUT "\nPlease be aware that only the first 8 characters of a DES password are\nrelevant.  Use the --md5, --sha256, or --sha512 options as they do not have\nthis limitation.\n";
  }

  if (defined($opts{'stdin'})) {

    # simply read in the password from stdin, as from a script
    chomp($passwd = <STDIN>);

  } else {

    # prompt for the password to be used
    system "stty -echo";
    print STDOUT "\nPassword: ";

    # open the tty for reading (is this portable?)
    open(TTY, "/dev/tty") or die "$program: unable to open /dev/tty: $!\n";
    chomp($passwd = <TTY>);
    print STDOUT "\n";
    system "stty echo";

    # prompt again, to make sure the user typed in the password correctly
    system "stty -echo";
    print STDOUT "Re-type password: ";
    chomp($passwd2 = <TTY>);
    print STDOUT "\n\n";
    system "stty echo";
    close(TTY);

    if ($passwd2 ne $passwd) {
      print STDOUT "Passwords do not match.  Please try again.\n";
      return get_passwd(name => $name);
    }
  }

  if (defined($name) && defined($opts{'change-password'})) {

    # retrieve the user's current password from the file and compare
    my ($curpasswd, @junk) = find_passwd_entry(name => $name);

    my $hash = crypt($passwd, $curpasswd);

    if ($hash eq $curpasswd) {

      if (defined($opts{'stdin'})) {

        # cannot prompt again if automated.  Simply print an error message
        # and exit.
        print STDOUT "$program: error: password matches current password\n";
        exit 2;

      } else {
        print STDOUT "Please use a password that is different from your current password.\n";
        return get_passwd(name => $name);
      }
    }
  }

  if (defined($name) && defined($opts{'not-previous-password'})) {
    # retrieve the user's current passwd and compare
    my ($currpasswd) = find_passwd_entry(name => $name);

    my $hash = crypt($passwd, $currpasswd);

    if (($hash && $currpasswd) && $hash eq $currpasswd) {
      if (defined($opts{'stdin'})) {

        # cannot prompt again if automated.  Simply print an error message
        # and exit.
        print STDOUT "$program: error: password matches previous password\n";
        exit 4;

      } else {
        print STDOUT "Please use a password that is different from your previous password.\n";
        return get_passwd(name => $name);
      }
    }
  }

  if (defined($name) && defined($opts{'not-system-password'})) {

    # retrieve the user's system passwd (from /etc/shadow) and compare
    my $syspasswd = get_syspasswd(user => $name);

    my $hash = crypt($passwd, $syspasswd);

    if (($hash && $syspasswd) && $hash eq $syspasswd) {

      if (defined($opts{'stdin'})) {

        # cannot prompt again if automated.  Simply print an error message
        # and exit.
        print STDOUT "$program: error: password matches system password\n";
        exit 4;

      } else {
        print STDOUT "Please use a password that is different from your system password.\n";
        return get_passwd(name => $name);
      }
    }
  }

  return "" if ($args{'allow_blank'} and $passwd eq "");

  # check for BAD passwords, BLANK passwords, etc, if requested
  if (defined($opts{'use-cracklib'})) {
    require Crypt::Cracklib;
    if (!Crypt::Cracklib::check($passwd, $cracklib_dict)) {
      print STDOUT "Bad password: ", Crypt::Cracklib::fascist_check($passwd,
        $cracklib_dict), "\n";
      return get_passwd(name => $name);
    }
  }

  my $salt = get_salt();

  my $hash = crypt($passwd, $salt);

  # Check that the crypt() implementation properly supports use of the MD5
  # (or other non-DES algorithm), if specified.
  if (!defined($opts{'des'})) {
    if (defined($opts{'md5'})) {
      # if the first three characters of the hash are not "$1$", the crypt()
      # implementation doesn't support MD5.  Some crypt()s will happily use
      # "$1" as a salt even though this is not a valid DES salt.  Humf.
      #
      # Perl doesn't treat strings as arrays of characters, so extracting the
      # first three characters is a little more convoluted (I'm accustomed to
      # C's strncmp(3) for this now).

      my @string = split('', $hash);
      my $prefix = $string[0] . $string[1] . $string[2];

      if ($prefix ne '$1$') { 
        print STDOUT "You requested MD5 passwords but your system does not support it.  Defaulting to DES passwords.\n\n";
      }

    } elsif (defined($opts{'sha256'})) {
      # if the first three characters of the hash are not "$5$", the crypt()
      # implementation doesn't support SHA-256.  Some crypt()s will happily use
      # "$5" as a salt even though this is not a valid DES salt.  Humf.
      #
      # Perl doesn't treat strings as arrays of characters, so extracting the
      # first three characters is a little more convoluted (I'm accustomed to
      # C's strncmp(3) for this now).

      my @string = split('', $hash);
      my $prefix = $string[0] . $string[1] . $string[2];

      if ($prefix ne '$5$') {
        print STDOUT "You requested SHA-256 passwords but your system does not support it.  Defaulting to DES passwords.\n\n";
      }

    } elsif (defined($opts{'sha512'})) {
      # if the first three characters of the hash are not "$6$", the crypt()
      # implementation doesn't support SHA-512.  Some crypt()s will happily use
      # "$6" as a salt even though this is not a valid DES salt.  Humf.
      #
      # Perl doesn't treat strings as arrays of characters, so extracting the
      # first three characters is a little more convoluted (I'm accustomed to
      # C's strncmp(3) for this now).

      my @string = split('', $hash);
      my $prefix = $string[0] . $string[1] . $string[2];

      if ($prefix ne '$6$') {
        print STDOUT "You requested SHA-512 passwords but your system does not support it.  Defaulting to DES passwords.\n\n";
      }
    }
  }

  return $hash;
}

# ----------------------------------------------------------------------------
sub get_syspasswd {
  my %args = @_;

  my $user = $args{'user'};

  # test the shadow password support on this system.  Some systems, such
  # as the BSDs, use "transparent shadowing", where the real passwd will
  # be returned via getpwnam() only if the process has root privs (effective
  # UID of zero).  That check has already been performed.  However, other
  # systems still may not return the password via getpwnam() (such as Linux).
  # These other systems use a shadow password library of functions, and require
  # other work to retrieve the password.  On these systems, the retrieved
  # password will be "x".

  my $syspasswd = (getpwnam($user))[1];

  if ($syspasswd eq "" || $syspasswd eq "x")  {

    # do the retrieval the hard way: open up /etc/shadow and iterate
    # through each line.  Yuck.  *sigh*.  Thanks to Micah Anderson
    # for working out this issue.

    open(SHADOW, "< /etc/shadow") or
      die "$program: unable to access shadow file: $!\n";

    while (chomp(my $line = <SHADOW>)) {
      next unless $line =~ /^$user/;
      $syspasswd = (split(':', $line))[1];
      last; 
    }
    close(SHADOW);

    # if the password is still "x", you have problems 
    if ($syspasswd eq "x") {
      die "$program: unable to retrieve shadow password.\nContact your system
administrator.\n";
    }
  } 

  return $syspasswd;
}

# ----------------------------------------------------------------------------
sub handle_group_entry {
  my %args = @_;

  my $gid = $args{'gid'};
  my $name = $args{'name'};
  my $delete_group = $args{'delete_group'};
  my $delete_user = $args{'delete_user'};
  my $passwd;

  my $members = "";
  $members = join(',', @{$args{'members'}}) if (defined($args{'members'}));

  # check to see whether we should update the fields for this group (because
  # it already exists), or to create a new entry

  my $found = 0;
  my $index = 0;
  for ($index = 0; $index <= $#data; $index++) {
    my @entry = split(':', $data[$index]);

    if ($name eq $entry[0]) {
      $found = 1;
      last;
    }
  }

  unless ($found) {
    print STDOUT "$program: creating group entry for group $name\n";

  } else {
    print STDOUT "$program: updating group entry for group $name\n";
  }

  # if present, add the members given to the group.  If none, just leave that
  # field blank

  # prompt for the group password, if requested
  if (defined($opts{'enable-group-passwd'})) {
    $passwd = get_passwd(name => $name, allow_blank => 1);

  } else {
    $passwd = "x";
  }

  # remove the entry to be updated
  splice(@data, $index, 1);

  if ($delete_group) {
    print STDOUT "$program: entry deleted\n";
    return;
  }

  # format: $name:$passwd:$gid:$members
  push(@data, "$name:$passwd:$gid:$members");

  # always sort by GIDs before printing out the file
  @data = map { $_->[0] }
          sort {
                $a->[3] <=> $b->[3]
               }
          map { [ $_, (split /:/)[0, 1, 2, 3] ] }
          @data;

  if ($delete_group) {
    print STDOUT "$program: entry deleted\n";

  } elsif ($found) {
    print STDOUT "$program: entry updated\n";

  } else {
    print STDOUT "$program: entry created\n";
  }
}

# ----------------------------------------------------------------------------
sub handle_passwd_entry {
  my %args = @_;

  my $name = $args{'name'};
  my $uid = $args{'uid'};
  my $gid = $args{'gid'};
  my $gecos = $args{'gecos'};
  my $home = $args{'home'};
  my $shell = $args{'shell'};
  my $delete_user = $args{'delete_user'};

  # Trim any trailing slashes in $home.
  $home =~ s/(.*)\/$/$1/ if ($home =~ /\/$/);

  # Make sure the given home directory is NOT a relative path (what a
  # horrible idea).
 
  unless ($home =~ /^\//) {
    print STDOUT "$program: error: relative path given for home directory\n";
    exit 8;
  }
  
  # check to see whether we should update the fields for this user (because
  # they already exist), or create a new entry

  my $found = 0;
  my $index = 0;
  for ($index = 0; $index <= $#data; $index++) {
    my @entry = split(':', $data[$index]);

    if ($name eq $entry[0]) {
      $found = 1;
      last;
    }
  }

  unless ($found) {
    print STDOUT "$program: creating passwd entry for user $name\n";

  } else {
    print STDOUT "$program: updating passwd entry for user $name\n";
  }

  my $passwd;
  unless ($delete_user) {
    # check the requested shell against the list in /etc/shells
    check_shell(shell => $shell);

    # prompt the user for the password
    $passwd = get_passwd(name => $name);
  }

  # remove the entry to be updated
  splice(@data, $index, 1);

  if ($delete_user) {
    print STDOUT "$program: entry deleted\n";
    return;
  }

  # format: $name:$passwd:$uid:$gid:$gecos:$home:$shell
  push(@data, "$name:$passwd:$uid:$gid:$gecos:$home:$shell");

  # always sort by UIDs before printing out the file
  @data = map { $_->[0] }
          sort {
                $a->[3] <=> $b->[3]
               }
          map { [ $_, (split /:/)[0, 1, 2, 3, 4, 5, 6] ] }
          @data;

  if ($delete_user) {
    print STDOUT "$program: entry deleted\n";

  } elsif ($found) {
    print STDOUT "$program: entry updated\n";

  } else {
    print STDOUT "$program: entry created\n";
  }
}

# ----------------------------------------------------------------------------
sub open_output_file {
  my %args = @_;

  # open $output_file, paying attention to the --force command-line option
  # If the file already exists, slurp up its contents for later updating.

  if (-f $output_file) {
    # make sure we can write/update the file first
    unless (chmod 0644, $output_file) {
      die "$program: unable to set permissions on $output_file to 0644: $!\n";
    }

    open(INPUT, "< $output_file") or
      die "$program: unable to open $output_file: $!\n";
    chomp(@data = <INPUT>);
    close(INPUT);
  }

  # if the --force option was given, just zero out any data that might have
  # been read in, effectively erasing whatever contents there were.  A new
  # file is generated, anyway -- it's just a question of what data goes into
  # it

  @data = () if (defined($opts{'F'}));
}

# ----------------------------------------------------------------------------
sub usage {

	print STDOUT <<END_OF_USAGE;

usage: $program [--help] [--hash|--group|--passwd]

  REQUIRED: --passwd, --group, or --hash.  These specify whether $program is to
  operate on a passwd(5) format file, on a group(5) format file, or simply
  to generate a password hash, respectively.

  If used with --passwd, $program creates a file in the passwd(5) format,
  suitable for use with proftpd's AuthUserFile configuration directive.
  You will be prompted for the password to use of the user, which will be
  encrypted, and written out as the encrypted string.  New entries are
  appended to the file by default.
 
  By default, using --passwd will write output to "$default_passwd_file".

  Error exit values:

  To make it easier for wrapper scripts to interact with $program, $program
  will exit with the following error values for the reasons described:

    1       no such user
    2       password matches current password
    4       password matches system password
    8       relative path given for home directory

  Options:

    --file      Write output to specified file, rather than "$default_passwd_file".

    -F          If the file to be used already exists, delete it and write a
    --force     new one.  By default, new entries will be appended to the file.

    --gecos     Descriptive string for the given user (usually the user's
                full name).

    --gid       Primary group ID for this user (optional, will default to
                given --uid value if absent).

    -h          Displays this message.
    --help

    --home      Home directory for the user (required).

    --des       Use the DES algorithm for encrypting passwords.  The default
                is the MD5 algorithm.

    --md5       Use the MD5 algorithm for encrypting passwords.  This is the
                default.

    --name      Name of the user account (required).  If the name does not
                exist in the specified output-file, an entry will be created
                for her.  Otherwise, the given fields will be updated.

    --shell     Shell for the user (required).  Recommended: /bin/false

    --uid       Numerical user ID (required)

    --change-password

                Update only the password field for a user.  This option
                requires that the --name and --passwd options be used, but
                no others.  This also double-checks the given password against
                the user's current password in the existing passwd file, and
                requests that a new password be given if the entered password
                is the same as the current password.

    --delete-user
 
                Remove the entry for the given user name from the file.

    --not-previous-password

                Double-checks the given password against the previous password
                for the user, and requests that a new password be given if
                the entered password is the same as the previous password.

    --not-system-password

                Double-checks the given password against the system password
                for the user, and requests that a new password be given if
                the entered password is the same as the system password.  This
                helps to enforce different passwords for different types of
                access.

    --sha256    Use the SHA-256 algorithm for encrypting passwords.

    --sha512    Use the SHA-512 algorithm for encrypting passwords.

    --stdin
                Read the password directly from standard in rather than
                prompting for it.  This is useful for writing scripts that
                automate use of $program.

    --use-cracklib

                Causes $program to use Alec Muffet's cracklib routines in
                order to determine and prevent the use of bad or weak
                passwords.  The optional path to this option specifies
                the path to the dictionary files to use -- default path
                is "$default_cracklib_dict".  This requires the Perl
                Crypt::Cracklib module to be installed on your system.

    --version
                Displays the version of $program.

  If used with --group, $program creates a file in the group(5) format,
  suitable for use with proftpd's AuthGroupFile configuration directive.

  By default, using --group will write output to "$default_group_file".

  Options:

    --delete-group

                Remove the entry for the given group name from the file.

    --enable-group-passwd

                Prompt for a group password.  This is disabled by default,
                as group passwords are not usually a good idea at all.

    --file      Write output to specified file, rather than "$default_group_file".

    -F          If the file be used already exists, delete it and write a new
    --force     one.  By default, new entries will be appended to the file.

    --gid       Numerical group ID (required).

    -h
    --help      Displays this message.

    -m
    --member    User name to be a member of the group.  This argument may be
                used multiple times to specify the full list of users to be
                members of this group.

    --des       Use the DES algorithm for encrypting passwords.  The default
                is the MD5 algorithm.

    --md5       Use the MD5 algorithm for encrypting passwords.  This is the
                default.

    --name      Name of the group (required).  If the name does not exist in
                the specified output-file, an entry will be created for them.
                Otherwise, the given fields will be updated.

    --sha256    Use the SHA-256 algorithm for encrypting passwords.

    --sha512    Use the SHA-512 algorithm for encrypting passwords.

    --stdin
                Read the password directly from standard in rather than
                prompting for it.  This is useful for writing scripts that
                automate use of $program.

    --use-cracklib

                Causes $program to use Alec Muffet's cracklib routines in
                order to determine and prevent the use of bad or weak
                passwords.  The optional path to this option specifies
                the path to the dictionary files to use -- default path
                is "$default_cracklib_dict".  This requires the Perl
                Crypt::Cracklib module to be installed on your system.

    --version
                Displays the version of $program.

  If used with --hash, $program generates a hash of a password, as would
  appear in an AuthUserFile.  The hash is written to standard out.
  This hash is suitable for use with proftpd's UserPassword directive.

  Options:

    --des       Use the DES algorithm for encrypting passwords.  The default
                is the MD5 algorithm.

    --md5       Use the MD5 algorithm for encrypting passwords.  This is the
                default.

    --sha256    Use the SHA-256 algorithm for encrypting passwords.

    --sha512    Use the SHA-512 algorithm for encrypting passwords.

    --stdin
                Read the password directly from standard in rather than
                prompting for it.  This is useful for writing scripts that
                automate use of $program.

    --use-cracklib

                Causes $program to use Alec Muffet's cracklib routines in
                order to determine and prevent the use of bad or weak
                passwords.  The optional path to this option specifies
                the path to the dictionary files to use -- default path
                is "$default_cracklib_dict".  This requires the Perl
                Crypt::Cracklib module to be installed on your system.

    --version
                Displays the version of $program.

END_OF_USAGE

  exit 0;
}

# ---------------------------------------------------------------------------
sub version {
  print STDOUT "$version\n";

  exit 0;
}

# ---------------------------------------------------------------------------