DACSPASSWD(1) DACS Tools and Utilities DACSPASSWD(1)


dacspasswd — manage DACS accounts


dacspasswd [dacsoptions] [-p password] [-pf file] [-simple] [-vfs vfs_uri]
[op-spec] [--] [username]


This program is part of the DACS suite.

The dacspasswd command manages accounts that are used by the local_passwd_authenticate and local_simple_authenticate, authentication modules. This utility serves a similar purpose for these authentication modules that Apache's htpasswd(1) command does for its mod_auth_basic and mod_authn_dbm modules.

Apart from their use by local_passwd_authenticate and local_simple_authenticate, these accounts are completely separate from any other accounts and passwords.


Only lowercase usernames are permitted for these accounts.

The command allows arbitrary data to be associated with each account. This "private" data is opaque to DACS and is not used by DACS. Custom, account-specific information can be stored, retrieved, and deleted. Data that is not printable text must be encoded. The information is automatically deleted when its account is removed. Using this feature, account administration programs might be developed to store:

  • the last time a password was changed;

  • hashes of previous password values (so that they are not reused);

  • a note that the account's password must be changed;

  • a password reminder question and answer;

  • information for mutual authentication, such as a small image provided by the user that is displayed at login time;

  • an encrypted representation of the password for recovery purposes (when absolutely necessary)

  • several security questions (with answers), one of which might be selected at random and presented to the user at login time; or

  • user preferences.

Or instead, a pointer to any of this sort of information might be stored. There is no size limit for the data, but if relatively large amounts of data are being stored for a large number of accounts, the storage type should be chosen with care to ensure reasonable performance.

Passwords are accessed using the DACS virtual filestore through the passwds or simple item types. Each record in the file is keyed on the username. The information associated with each key consists of several fields separated by a "|" character, and includes a digest algorithm identifier, salt, the computed digest, and optional application data.

Use dacsauth(1) to validate (test) a password.


The password digest algorithm used depends on the PASSWORD_DIGEST directive in effect. The PASSWORD_SALT_PREFIX directive is also used.

Apart from using an authentication method stronger than one based on passwords, current best practice is to use a key derivation function like scrypt rather than a cryptographic digest for the PASSWORD_DIGEST. While in general doing so will provide additional protection if an attacker obtains the password file, it will not help if users are allowed to choose weak passwords.

Plaintext passwords are not stored by dacspasswd. This makes it more difficult for an attacker that gains access to the password file to discover plaintext passwords, but also means that forgotten passwords cannot be recovered (except by exhaustive search, which ought to be impractical).

The salted hash of the password is stored, assuming salting has not been disabled, rather than the hash of the password itself. This makes a stolen password file more difficult for an attacker to use (see rainbow tables).

Only a DACS administrator should be able to successfully run this program from the command line. Because DACS keys and configuration files, including the file used to store passwords, must be restricted to an administrator, this will normally be the case, but a careful administrator will set file permissions to deny access to all other users. An ordinary user is able to change his own password using the dacs_passwd(8) web service.


Even if the password file is stored as a plain text file, it is probably best to modify it only through this program or dacs_passwd. Corrupting a password file entry may prevent signing on to the corresponding account or even all accounts that require the password file.

It is good administrative practice to store accounts with passwords separately from those without.

This program is also available as a DACS web service, dacs_passwd(8).


By default, the program will prompt for a new password if one is required by the selected operation.

The dacspasswd command recognizes these command line flags:

-p password

Specify the password.


A password given on the command line may be visible to other users on the same system.


Delete the private data associated with username.


Get the private data associated with username and print it to the standard output.

-pds string

Set (or replace) string as private data associated with username.

-pdsf file

Set (or replace) the private data associated with username, reading it from file. If file is "-", then the data is read from the standard input. This flag and -pf cannot both be used to read from the standard input.

-pf file

Read the password to use from file. If file is "-", then the password is read from the standard input without prompting. This flag and -pdsf cannot both be used to read from the standard input.


Use the simple item type expected by local_simple_authenticate instead of the default. The program will not prompt for passwords because these accounts do not use them.

-vfs vfs_uri

Add vfs_uri as a VFS configuration directive. By specifying the item type passwds, a location for the password file can be given, overriding any configuration file value. This is particularly useful in conjunction with dacsauth(1).


The following operations are recognized. The -enable, -disable, -pdd, -pds, and -pdsf are the only operations that can be combined with another operation (for example, you can disable an account and set its private data at the same time).


Add username to the password file. The entry must not already exist. By default, the user will be prompted for the password, which must be retyped for confirmation. This is the default operation.


Delete username from the password file.


Disable the account for username so that authentication modules will not accept any password. If used with -a, -s, or -u, the account will also be disabled. The username may subsequently be enabled.


Re-enable the account for username, which is currently disabled. The authentication modules will once again accept the password. If used with -a, -s, or -u, the account will also be enabled.


Get the digest string for username and print it to the standard output. A script can validate a password by passing this digest string to password() along with the password obtained from the user.


List username if it appears in the password file. If no username is provided, list all usernames. A disabled account is indicated by a '*' (which is not a valid character in a username). The -long and -longlist variants display additional detail about each entry, such as the digest algorithm used.


Set or reset the password for username, which must already exist in the password file. The enabled/disabled status is preserved unless overridden by a flag.


Read the current password file (item type passwds) and copy it to the item type newpasswds. This will normally create an exact copy, but if there are applicable formatting changes, they are automatically applied to the input; that is, if the format of the input file is older than the format preferred by the current version of DACS, it will be updated in the output file to the extent possible. The output file should be carefully examined and tested before being used.

-test test-op

Test an entry for one of several attributes and report the outcome through the program's exit status. The test-op is one of the following keywords or abbreviated keywords:

  • enabled, ena, en

    Return an exit status of 0 if an account for username exists and is enabled, or 1 if it does not exist or is disabled.

  • exists, ex

    Return an exit status of 0 if an account for username exists, or 1 if it does not exist.

  • data

    Return an exit status of 0 if an account for username exists and has private data, or 1 if it does not exist or does not have private data. If an entry's private data is the empty string, it is considered to have private data.

  • disabled, dis

    Return an exit status of 0 if an account for username exists and is disabled, or 1 if it does not exist or is enabled.


Add username to the password file or update an existing entry for username. By default, the user will be prompted for the password, which must be retyped for confirmation. If the entry exists, the enabled/disabled status is preserved unless overridden by a flag.


This flag signals the end of the flag arguments; a username may follow, possibly beginning with a "-" character.

Since only the administrator is allowed to use this command, no restrictions are imposed on the length or quality of the passwords that the administrator supplies; a warning message will be emitted, however, if the password is considered to be weak based on the PASSWORD_CONSTRAINTS directive that is configured.


To list all of the accounts configured for the jurisdiction named EXAMPLE:

% dacspasswd -uj EXAMPLE -list

Note that the account for username bobo has been disabled.

To re-enable bobo's account:

% dacspasswd -uj EXAMPLE -ena bobo

To test if bobo's account is enabled:

% dacspasswd -uj EXAMPLE -test ena bobo
% echo $status

To test if there are accounts for usernames booboo and bob:

% dacspasswd -uj EXAMPLE -test exists booboo
% echo $status
% dacspasswd -uj EXAMPLE -test exists bob
% echo $status

To reset the password for username bobo interactively:

% dacspasswd -uj EXAMPLE -set bobo
New password for bobo?
Re-type new password for bobo?

Note that the password text is not displayed.

To reset the password for username bobo using the program's standard input:

% echo $newpasswd | dacspasswd -uj EXAMPLE -set -pf - bobo

To create a new, disabled account for username bob and store the private data "On vacation":

% dacspasswd -uj EXAMPLE -add -pf ./pwfile -dis -pds "On vacation" bob

The password is read from the file ./pwfile.

To get the private data for username bob:

% set x=`dacspasswd -uj EXAMPLE -pdg bob`
% echo "$x"
On vacation

To regenerate the current password file:

% dacspasswd -uj EXAMPLE -q -vfs "[newpasswds]dacs-kwv-fs:/usr/local/dacs/tmp/newpasswd?field_sep=:" -regen


The program exits 0 if everything was fine, and non-zero otherwise. A "false" outcome from the -test operation is reflected by an exit status of 1. An error condition is indicated by an exit status of 2.


That password information is not represented externally as an XML document tends to haunt your humble narrator. The password file format is subject to change.


dacs_passwd(8), dacsauth(1), dacs_authenticate(8), dacs_admin(8), dacs.conf(5)


Distributed Systems Software (www.dss.ca)


Copyright 2003-2016 Distributed Systems Software. See the LICENSE file that accompanies the distribution for licensing information.

DACS Version 1.4.38a 23-Nov-2016 DACSPASSWD(1)

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$Id: dacspasswd.1.xml 2903 2016-07-05 14:49:44Z brachman $