path: root/README

   nss-pam-ldapd - NSS and PAM library for name lookups and authentication
                   using LDAP

   nss-pam-ldapd started as nss-ldapd which was a fork from nss_ldap which was
   originally written by Luke Howard of PADL Software Pty Ltd.

   http://www.padl.com/OSS/nss_ldap.html

   In 2006 Arthur de Jong of West Consuling forked the library to split it
   into a thin NSS part and a server part. Most of the code was rewritten.

   The software was renamed to nss-pam-ldapd when PAM code contributed by
   Howard Chu for the OpenLDAP nssov module was integrated.

   http://arthurdejong.org/nss-pam-ldapd/

   Copyright (C) 1997-2006 Luke Howard
   Copyright (C) 2006, 2007 West Consulting
   Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Arthur de Jong
   Copyright (C) 2009 Howard Chu

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   This library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with this library; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
   02110-1301 USA


INTRODUCTION
============

This is the nss-pam-ldapd library which consists of an NSS module to do name
lookups to an LDAP directory server and a PAM module to do authentication to
an LDAP server. The NSS part of this library was forked from nss_ldap as
provided by Luke Howard of PADL Software Pty Ltd. The PAM module was mostly
provided by Howard Chu of the OpenLDAP project.

The NSS library allows distributing account, group, host and other
configuration information from a central LDAP server throughout an
organisation. Because LDAP is a hierarchical directory service, you can
distribute the information in a manner which reflects an organisational
structure. This contrasts with the flat, single domain policy of NIS. LDAP has
many of the advantages of NIS+ (security and scalability) without the
complexity. The system will work alongside your existing NIS, NIS+, DNS and
flat file name services.

The PAM library (module) can be used to perform authentication based on
information inside the LDAP directory.

Both libraries consist of a thin NSS or PAM part that communicates with a
local daemon (nslcd) that handles the LDAP lookups. This simplifies the
architecture and fixes some scalability and locking problems in the original
design of nss_ldap.

Also it is possible to use the thin NSS and PAM parts together with the nssov
overlay in the OpenLDAP server (slapd).

The three parts (NSS module, PAM module, and nslcd server) can be build
separately and are not tied together. This means that for instance you can
still use pam_ldap and use the NSS module from nss-pam-ldapd.

improvements over nss_ldap
--------------------------

The fork from nss_ldap was done to implement some major design changes to fix
some structural problems in the library.

The biggest of those problems were host name lookups through LDAP which could
cause deadlocks in most cases and some general name lookup problems during
booting (when the LDAP server was not started or not yet reachable).

A number of refactoring steps were done to simplify the code and improve
maintainability. Legacy code was removed and support for non-Linux operating
systems was initially removed to make the code more readable. Portability will
be re-added once the architecture stabilises.

The most practical improvements over nss_ldap are:
- the LDAP library is not loaded for every process doing LDAP lookups
- the number of connections to the LDAP server is limited, because not every
  process will open its own connection (this problem is also mitigated by
  using nscd)
- hostname lookups should now be deadlock-free because the LDAP server name is
  no longer looked up using the ldap method
- the setup is easier to debug because logging on the server component can be
  enabled without affecting "normal" processes

This package runs a local daemon that will be enabled during the boot process.
This daemon will handle connections to the LDAP server and accept requests
through a named socket (/var/run/nslcd/socket). The thin NSS library will
proxy requests to the daemon.

Note that the package currently cannot be used on the same system alongside
nss_ldap.

comparison to pam_ldap
----------------------

The PAM module that is currently implemented contains functionality for
authentication, account management, password management and session
management. The nslcd daemon currently implements authentication,
authorisation and password modification. The OpenLDAP nssov overlay also
implements session functionality.

supported C libraries (for NSS module)
--------------------------------------

This library currently only supports the GNU C Library. Support for other C
libraries has been removed in a refactoring step. Compatibility code and
support for other C libraries will be added upon request.

supported name databases
------------------------

Currently the following name databases are supported:

  aliases, ethers, group, hosts, netgroup, networks, passwd, protocols, rpc,
  services and shadow

Note that for when using IPv6 hosts entries, the addresses in the LDAP
directory must be in their preferred form. The same is true for mac addresses
for the ethers database. Otherwise the address to entry lookups will not work.
For more details on the preferred form see
  http://ldap.akbkhome.com/index.php/attribute/ipHostNumber.html
and
  http://ldap.akbkhome.com/index.php/attribute/macAddress.html

automounter map lookups (which are also defined in /etc/nsswitch.conf) are not
supported because the NSS interface is not used for these. The common autofs
implementation (on GNU/Linux) currently uses its own method for getting the
maps from LDAP.

Although aliases are exposed through NSS, most mail servers parse /etc/aliases
by themselves and getting aliases from LDAP requires some configuration in the
mail server.

The publickey, bootparams and netmasks are currently unsupported. Some
investigation should be done if these are needed for anything, which
interfaces should be exported and how the LDAP schema part should look like.

supported PAM implementation
----------------------------

The PAM module is currently only regularly tested on Linux PAM but other PAM
implementations should also work.

supported LDAP libraries
------------------------

The current version of nss-pam-ldapd has been developed with OpenLDAP 2.4 but
other LDAP libraries and older versions of OpenLDAP may also work.

unsupported features
--------------------

Since nss-pam-ldapd was forked from nss_ldap most of the features that came
with nss_ldap are available. The most important differences:
- the configuration file formats are not fully compatible
- nested groups are currently unsupported
- rootbinddn/rootbindpw support is removed and is not likely to return

For the PAM module some functionality is missing. Comparing it to pam_ldap:
- only BIND authentication is supported
- only LDAP password modify EXOP is supported as password changing mechanism

Some things work a little different in nss-pam-ldapd. For instance the
attribute defaults and overrides of nss_ldap are implemented with mapping
expressions and pam_ldap's pam_check_*_attr options can be implemented with
the pam_authz_search option.


INSTALLATION
============

The nss-pam-ldapd library uses autoconf and automake for building. Installing
nss-pam-ldapd should be as simple as:

  % ./configure
  % make
  % make install

That said, it is a good idea to go first through the options of configure by
running:

  % ./configure --help

The last step (make install) should install the libnss_ldap.so.* and
pam_ldap.so files and the daemon (nslcd). The boot process needs to be
manually modified to start the daemon at the right time.

Also, it is recommended to create a dedicated user for the nslcd daemon.
Configure this user in /etc/nslcd.conf using the uid and gid options.


CONFIGURATION
=============

After installation the name service switch configuration file
(/etc/nsswitch.conf) needs to be modified to do name lookups using the new
module. This consist mostly of adding ldap in the list of lookup methods in
the right place. See the nsswitch.conf(5) manual page for details on the
format. As an example the file could look a little like this:

  # the following contain normal unix user and group information
  passwd:         files ldap
  group:          files ldap
  shadow:         files ldap

  # hostname lookups through ldap before dns should work now
  hosts:          files ldap dns
  networks:       files ldap

  # normal flat-file definitions
  protocols:      files ldap
  services:       files ldap
  ethers:         files ldap
  rpc:            files ldap
  netgroup:       ldap

  # whether alias lookups really use NSS depends on the mail server
  aliases:        files ldap

Configuring PAM differs a little from platform to platform but this is a basic
set-up for files under /etc/pam.d:

auth   sufficient   pam_unix.so
auth   sufficient   pam_ldap.so use_first_pass
auth   required     pam_deny.so

account   required     pam_unix.so
account   sufficient   pam_ldap.so
account   required     pam_permit.so

session   required   pam_unix.so
session   optional   pam_ldap.so

password   sufficient   pam_unix.so nullok md5 shadow use_authtok
password   sufficient   pam_ldap.so try_first_pass
password   required     pam_deny.so

Lastly, a configuration file for nslcd (by default /etc/nslcd.conf) needs to
be made. See the shipped manual page for details on the format and options. It
should at the very least contain something like:

  # the location of LDAP server
  uri ldap://localhost/

  # search base for all queries.
  base dc=example,dc=net

service discovery through DNS
-----------------------------

nss-pam-ldapd supports looking up LDAP server names through DNS SRV records as
specified in RFC 2782. However, Priority and Weight are not considered
separately and a single list of servers in added as if they had been specified
with uri options in the configuration file.

To use this feature specify DNS as an uri in the configuration file and
include something like the following in your zone:

  _ldap._tcp  SRV  10 0  389  ldapserver


LDAP SCHEMA
===========

nss-pam-ldapd supports a wide range of possible LDAP schema configurations and
it can be customized heavily. The LDAP schema used is described in RFC 2307.
Groups with distinguished name members (instead of login names) (RFC 2307bis)
are also supported, although use of memberUid has much better performance (see
below for details).

default attributes
------------------

This paragraph describes the mapping between the NSS lookups and the LDAP
database. The mapping may be modified by changing the nslcd.conf configuration
file. See the nslcd.conf(5) manual page for details.

aliases (objectClass=nisMailAlias)
  cn                - alias name
  rfc822MailMember  - members of the alias (recipients)
ethers (objectClass=ieee802Device)
  cn                - host name
  macAddress        - ethernet address
group (objectClass=posixGroup)
  cn                - group name
  userPassword      - password
  gidNumber         - gid
  memberUid         - members (user names)
  uniqueMember      - members (DN values)
hosts (objectClass=ipHost)
  cn                - host name (and aliases)
  ipHostNumber      - addresses
netgroup (objectClass=nisNetgroup)
  cn                - netgroup name
  nisNetgroupTriple - triplets describing netgroup entries
  memberNisNetgroup - reference to other netgroup
networks (objectClass=ipNetwork)
  cn                - network name
  ipNetworkNumber   - network address
passwd (objectClass=posixAccount)
  uid               - account name
  userPassword      - password
  uidNumber         - uid
  gidNumber         - gid
  gecos             - gecos
  cn                - gecos (if gecos is unset)
  homeDirectory     - home directory
  loginShell        - shell
protocols (objectClass=ipProtocol)
  cn                - protocol name
  ipProtocolNumber  - protocol number
rpc (oncRpc)
  cn                - rpc name
  oncRpcNumber      - rpc number
services (objectClass=ipService)
  cn                - service name
  ipServicePort     - service port
  ipServiceProtocol - service protocol
shadow (objectClass=shadowAccount)
  uid               - use name
  userPassword      - password
  shadowLastChange  - last change of password
  shadowMax         - days before password may be changed
  shadowMin         - days after which password must be changed
  shadowWarning     - expiry warning
  shadowInactive    - account is disabled if no password is changed
  shadowExpire      - account expiration
  shadowFlag        - reserved field

using Microsoft Active Directory
--------------------------------

When using Microsoft Active Directory server (typically on Microsoft Windows
2000) some changes need to be made to the nslcd.conf configuration file. The
included sample configuration file has some commented out attribute mappings
for such a set-up.

group membership
----------------

Currently, two ways of specifying group membership are supported. The first,
by using the memberUid attribute, is the simplest and by far the fastest
(takes the least number of lookups). This attribute maps to user names with
the same values as the uid attribute would hold for posixAccount entries.

The second method is to use DN values in the uniqueMember attribute (attribute
names can be changed by using the attribute mapping options as described in
the manual page). This is potentially a lot slower because in the worst case
every DN has to be looked up in the LDAP server to find the proper value for
the uid attribute.

If the DN value already contains a uid value (e.g. uid=arthur, dc=example,
dc=com) the lookup is skipped and the value from the DN is used. A cache is
maintained that saves the DN to uid translations for 15 minutes.

In all cases, users that are specified as member multiple times are returned
only once.

Currently, having nested groups by uniqueMember values pointing to other
groups, as well as the memberOf attribute in posixAccount entries are
unsupported.

case sensitivity
----------------

Most values in the NSS databases are considered case-sensitive (e.g. the user
"Foo" is a different user from the user "foo"). Most values in an LDAP
database are however considered case-insensitive. nss-pam-ldapd tries to solve
this problem by adding an extra filtering layer to ensure that e.g. when
looking for the user "foo" it will not return a user "Foo" that is found in
LDAP.

For the group, netgroup, passwd, protocols, rpc, services and shadow maps the
matches will be checked case-sensitively and for aliases, ethers, hosts and
networks matches will be case-insensitive (this seems to be what Glibc is
doing currently with flat files). Only searching for groups by user is done
case-insensitive. In all cases the case-use in the LDAP directory is returned.

Note that having entries that only differ in case is a bad idea and will
likely get you in trouble. One example of such a problem is that the DN
uid=test,dc=example,dc=com is the same as uid=TEST,dc=example,dc=com.


REPORTING BUGS
==============

If you find any bugs or missing features please send email to
  nss-pam-ldapd-users@lists.arthurdejong.org
If you are using the Debian package you are encouraged to use the BTS. Please
include as much information as needed (platform, output of configure if
compilation fails, output of the failure, etc). Patches are more than welcome
(also see the file HACKING).