PAMD(8) DACS Web Services and CGI PAMD(8)


pamd — PAM transaction server


pamd [dacsoptions] [-daemon] [-fork] [-h hostname] [-http] [-inetd] [-nofork]
[-p portnum] [-policy name] [-secure] [-unsecure]


This program is part of the DACS suite.

The pamd server is required by the local_pam_authenticate authentication module. It acts as a proxy for local_pam_authenticate, calling PAM functions on its behalf. The pamd server may be started from inetd(8) or from the command line, but it must be running for DACS to perform PAM-based authentication.

Each pamd process is involved in an arbitrarily long "conversation" or "transaction" with one or more executions of local_pam_authenticate. For instance, pamd's initial response to local_pam_authenticate might be that it requires an account name; upon receiving the account name from local_pam_authenticate, pamd's response might be that it requires the password for the account; and upon receiving the password, pamd would indicate success or failure, depending on whether an acceptable username/password pair was received. The eventual outcome of a transaction is that authentication succeeds, fails, or could not be completed because an error occurs.

pamd must be run on the host where pam(3) processing is being performed, which is not necessarily the same host where local_pam_authenticate is executed.


  • pamd will usually be run as root so that it can access the files it needs to perform authentication.

  • pamd is not a DACS web service and is not protected by DACS.

  • The protocol between pamd and its client may include sensitive material, such as passwords. If both programs are run on the same host, this is probably not an issue. If there is any possibility of eavesdropping etc. by an attacker, however, communication should be secured through an SSL/TLS wrapper.

  • pamd should probably not be run on a world-accessible server, since it would offer a way for attackers to try to guess passwords.

The operating system's PAM policy file is consulted - see pam.conf(5). The default PAM service name is "dacs" (see pam_start(3)), which may be used by PAM to locate the appropriate policy file. A different policy name can be specified using the -policy flag.

The prompts that passed from PAM to pamd to local_pam_authenticate to dacs_authenticate (or dacsauth) are simply displayed to the user. The user must understand what the prompts mean (e.g., that "Login:" means to provide a Unix account name).

pamd can be used by non-DACS applications. The protocol, though simple, is not yet documented other than within the source code. A program called pamd-client is available for testing and debugging pamd; it is built when PAM support is required, but is neither installed nor documented (see the source code for basic instructions).


In addition to the standard dacsoptions, pamd recognizes these command line flags:


Wait for a connection, then service the request. Mutually exclusive with -inetd.


Create a new process to service each request. It implies the -daemon flag.

-h hostname

If pamd is running on a host with multiple IP addresses, this specifies the hostname (or IP address) to listen to for incoming requests. If not provided, the PAMD_HOST directive will be consulted; if unavailable, gethostname(3) will be used.


This flag is reserved for future use.


The server assumes it has been started by inetd(8) and therefore does not wait for a connection. It exits after servicing the request. This is the default behaviour and preferred way to configure pamd. This mode of operation assumes that an entry has been added to inetd.conf(5) that looks much like this:

dacs-pamd stream tcp nowait root /usr/local/dacs/sbin/pamd pamd -uj EXAMPLE -inetd


This flag, which implies the -daemon, causes the pamd server to exit after servicing one request (which is useful when debugging). This is the default behaviour of -daemon mode.

-p portnum

This specifies the port number to listen to, overriding any PAMD_PORT directive in effect. It can also be a service name. Any otherwise unassigned port number on the system from 49152 through 65535 (i.e., one in the dynamic and/or private range) ought to be acceptable.

If neither this flag nor a PAMD_PORT directive is provided, the program will try to find the port associated with the dacs-pamd service name in services(5). For example:

dacs-pamd       17000/tcp  # DACS pamd

-policy name

Use name as the PAM policy name instead of the default.


The client must supply valid DACS administrative credentials encapsulated within a DACS cookie. This is the default.


Administrative credentials are not required, but if they are provided they must be valid. This should probably be used only when testing or if client identification is not an issue or has been addressed in some other way.


When the -secure flag is in effect, pamd must be associated with a jurisdiction. Therefore, the DACS configuration files are read and the jurisdiction must be specified on the command line (e.g., using the -uj flag).


For testing purposes, or to better understand how pamd works, you can run it manually and interact with it using telnet(1), for example, which takes the place of local_pam_authenticate. You must have PAM authentication configured on the host where you run pamd and you will probably need to run it as root. This is best done using two windows; start pamd in the first window and then telnet to it from the second window.

An interaction to perform username/password authentication will look something like the following (substitute your jurisdiction's name for myjur, your jurisdiction's domain name or IP address for, and use a username and password pair that is recognized on your system). The first telnet connection receives a prompt for a username (labeled "Login:" and assigned the variable name AUTH_PROMPT_VAR1) from pamd, a transaction identifier (TRANSID) "" for this session, and port number to use for subsequent operations belonging to this transaction (62475). The second telnet connection provides the TRANSID and username (AUTH_PROMPT_VAR1="auggie"), and receives a prompt for a password ("Password:", assigned the variable name AUTH_PROMPT_VAR2). The third telnet connection provides the TRANSID and the password (AUTH_PROMPT_VAR2="doggy"), and receives the result of authentication ("Success").

# ./pamd -uj myjur -ll debug -daemon -unsecure -nofork
pamd[info]: Site config file is "/usr/local/dacs/federations/site.conf"
pamd[info]: Config file is "/usr/local/dacs/federations/dacs.conf"
pamd[info]: This is jurisdiction DSS::myjur
pamd[info]: Secure mode is off
pamd[debug]: Waiting for initial input block...
pamd[debug]: No username
pamd[debug]: Calling pam_authenticate
pamd[debug]: pamd_conv: reply to port 62475
pamd[debug]: TRANSID is ""
pamd[debug]:   type="text"
pamd[debug]:   label="Login:"
pamd[debug]:   varname="AUTH_PROMPT_VAR1"
pamd[debug]: pamd_conv: waiting 60 seconds for reply
pamd[debug]: pamd_conv: received connection
pamd[debug]: Reading reply...
pamd[debug]: pamd_conv: reply to port 62475
pamd[debug]: TRANSID is ""
pamd[debug]:   type="password"
pamd[debug]:   label="Password:"
pamd[debug]:   varname="AUTH_PROMPT_VAR2"
pamd[debug]: pamd_conv: waiting 60 seconds for reply
pamd[debug]: pamd_conv: received connection
pamd[debug]: Reading reply...
pamd[debug]: Success
pamd[debug]: result="ok"
pamd[debug]: username="auggie"

% telnet 17000
Connected to
Escape character is '^]'.

Connection closed by foreign host.
% telnet 62475
Connected to
Escape character is '^]'.

Connection closed by foreign host.
% telnet 62475
Connected to
Escape character is '^]'.

Connection closed by foreign host.


The program exits 0 if everything was fine, 1 if an error occurred.


The -daemon flag should cause the process to detach and put itself in the background unless overridden by another flag; at present it must be started in the background "manually".

The -http flag, which would allow a pamd session to be started with a web service request, is not implemented.


dacs_authenticate(8), dacsauth(1), pam(3), X/Open Single Sign-On Service (XSSO) preliminary specification


Distributed Systems Software (


Copyright 2003-2014 Distributed Systems Software. See the LICENSE file that accompanies the distribution for licensing information.

DACS Version 1.4.38a 23-Nov-2016 PAMD(8)

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$Id: pamd.8.xml 2792 2015-03-26 22:22:19Z brachman $