path: root/README

   nss-ldapd - NSS library for name lookups using LDAP

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

   Copyright (C) 1997-2006 Luke Howard
   Copyright (C) 2006, 2007 West Consulting
   Copyright (C) 2006, 2007, 2008, 2009 Arthur de Jong

   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-ldapd library which is an NSS module to do name lookups to an
LDAP directory server. This library was forked from nss_ldap as provided by
Luke Howard of PADL Software Pty Ltd.

The 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.

This library consists of a thin NSS part that communicates with a local daemon
that handles the LDAP lookups. This simplifies the architecture and fixes some
scalability and locking problems in the original design.

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).

With nss-ldapd a number of refactoring steps were taken 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 of nss-ldapd 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 it's 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 NSS requests
from 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.

supported C libraries
---------------------

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 in due time 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 it's own method for getting the
maps from LDAP.

Although aliases is exposed through NSS, most mailservers parse /etc/aliases
by themselves and getting aliases from LDAP requires some configuration in the
mailserver.

The publickey, bootparams and netmasks are currently also 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 LDAP libraries
------------------------

The current version of nss-ldapd has been developed with OpenLDAP 2.4 but
adding support for other LDAP libraries with similar interfaces should not be
too hard.

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

Since nss-ldapd was forked from nss_ldap most of the features that came with
nss_ldap are available. However, not all features have extensively tested yet
and may cause problems.
- attribute value defaults and overrides have been removed (but may reappear
  some day if requested)
- the configuration file formats are not fully compatible
- nested groups are currently unsupported
- rootbinddn/rootbindpw support is removed and is not likely to return

In general, the focus is to have the functionality that is present be well
tested and supported.


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

The nss-ldapd library uses autoconf and automake for building. Installing
nss-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.* file 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 to run the nslcd daemon as.
Configure this user in /etc/nss-ldapd.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. Also, the nss-ldapd configuration file (specified at configure time)
needs to be modified to contain to the correct LDAP configuration.

Editing nsswitch.conf 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

Furthermore a configuration file (by default /etc/nss-ldapd.conf) needs to be
made. The location of this file can be specified with configure. See the
shipped manual page for details on the format and options. It should at 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-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-ldapd supports a wide range of possible LDAP schema configurations.
Furthermore 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 changeging the nss-ldapd.conf
configuration file. See the nss-ldapd.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
  ipNetmaskNumber   - network netmask
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 nss-ldapd.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 amount of lookups). This attributes 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 holds on to DN to uid translations for 15 minutes (see
DN2UID_CACHE_TIMEOUT in nslcd/passwd.c).

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"). Values in an LDAP database are
however cosidered case-insensitive. nss-ldapd tries to solve this problem by
adding an extra filtering layer and 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 member the
username matching is done case-insensitive. Note that in all cases the
case-use in the LDAP directory is returned.

Note however 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
  arthur@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).