10.9.18 LDAP Services

The (gnu services authentication) module provides the nslcd-service-type, which can be used to authenticate against an LDAP server. In addition to configuring the service itself, you may want to add ldap as a name service to the Name Service Switch. See Name Service Switch for detailed information.

Here is a simple operating system declaration with a default configuration of the nslcd-service-type and a Name Service Switch configuration that consults the ldap name service last:

(use-service-modules authentication)
(use-modules (gnu system nss))
...
(operating-system
  ...
  (services
    (cons*
      (service nslcd-service-type)
      (service dhcp-client-service-type)
      %base-services))
  (name-service-switch
   (let ((services (list (name-service (name "db"))
                         (name-service (name "files"))
                         (name-service (name "ldap")))))
     (name-service-switch
      (inherit %mdns-host-lookup-nss)
      (password services)
      (shadow   services)
      (group    services)
      (netgroup services)
      (gshadow  services)))))

Available nslcd-configuration fields are:

nslcd-configuration parameter: package nss-pam-ldapd

The nss-pam-ldapd package to use.

nslcd-configuration parameter: maybe-number threads

The number of threads to start that can handle requests and perform LDAP queries. Each thread opens a separate connection to the LDAP server. The default is to start 5 threads.

Defaults to ‘disabled’.

nslcd-configuration parameter: string uid

This specifies the user id with which the daemon should be run.

Defaults to ‘"nslcd"’.

nslcd-configuration parameter: string gid

This specifies the group id with which the daemon should be run.

Defaults to ‘"nslcd"’.

nslcd-configuration parameter: log-option log

This option controls the way logging is done via a list containing SCHEME and LEVEL. The SCHEME argument may either be the symbols ‘none’ or ‘syslog’, or an absolute file name. The LEVEL argument is optional and specifies the log level. The log level may be one of the following symbols: ‘crit’, ‘error’, ‘warning’, ‘notice’, ‘info’ or ‘debug’. All messages with the specified log level or higher are logged.

Defaults to ‘("/var/log/nslcd" info)’.

nslcd-configuration parameter: list uri

The list of LDAP server URIs. Normally, only the first server will be used with the following servers as fall-back.

Defaults to ‘("ldap://localhost:389/")’.

nslcd-configuration parameter: maybe-string ldap-version

The version of the LDAP protocol to use. The default is to use the maximum version supported by the LDAP library.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string binddn

Specifies the distinguished name with which to bind to the directory server for lookups. The default is to bind anonymously.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string bindpw

Specifies the credentials with which to bind. This option is only applicable when used with binddn.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string rootpwmoddn

Specifies the distinguished name to use when the root user tries to modify a user’s password using the PAM module.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string rootpwmodpw

Specifies the credentials with which to bind if the root user tries to change a user’s password. This option is only applicable when used with rootpwmoddn

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string sasl-mech

Specifies the SASL mechanism to be used when performing SASL authentication.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string sasl-realm

Specifies the SASL realm to be used when performing SASL authentication.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string sasl-authcid

Specifies the authentication identity to be used when performing SASL authentication.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string sasl-authzid

Specifies the authorization identity to be used when performing SASL authentication.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-boolean sasl-canonicalize?

Determines whether the LDAP server host name should be canonicalised. If this is enabled the LDAP library will do a reverse host name lookup. By default, it is left up to the LDAP library whether this check is performed or not.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string krb5-ccname

Set the name for the GSS-API Kerberos credentials cache.

Defaults to ‘disabled’.

nslcd-configuration parameter: string base

The directory search base.

Defaults to ‘"dc=example,dc=com"’.

nslcd-configuration parameter: scope-option scope

Specifies the search scope (subtree, onelevel, base or children). The default scope is subtree; base scope is almost never useful for name service lookups; children scope is not supported on all servers.

Defaults to ‘(subtree)’.

nslcd-configuration parameter: maybe-deref-option deref

Specifies the policy for dereferencing aliases. The default policy is to never dereference aliases.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-boolean referrals

Specifies whether automatic referral chasing should be enabled. The default behaviour is to chase referrals.

Defaults to ‘disabled’.

nslcd-configuration parameter: list-of-map-entries maps

This option allows for custom attributes to be looked up instead of the default RFC 2307 attributes. It is a list of maps, each consisting of the name of a map, the RFC 2307 attribute to match and the query expression for the attribute as it is available in the directory.

Defaults to ‘()’.

nslcd-configuration parameter: list-of-filter-entries filters

A list of filters consisting of the name of a map to which the filter applies and an LDAP search filter expression.

Defaults to ‘()’.

nslcd-configuration parameter: maybe-number bind-timelimit

Specifies the time limit in seconds to use when connecting to the directory server. The default value is 10 seconds.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-number timelimit

Specifies the time limit (in seconds) to wait for a response from the LDAP server. A value of zero, which is the default, is to wait indefinitely for searches to be completed.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-number idle-timelimit

Specifies the period if inactivity (in seconds) after which the con‐ nection to the LDAP server will be closed. The default is not to time out connections.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-number reconnect-sleeptime

Specifies the number of seconds to sleep when connecting to all LDAP servers fails. By default one second is waited between the first failure and the first retry.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-number reconnect-retrytime

Specifies the time after which the LDAP server is considered to be permanently unavailable. Once this time is reached retries will be done only once per this time period. The default value is 10 seconds.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-ssl-option ssl

Specifies whether to use SSL/TLS or not (the default is not to). If ’start-tls is specified then StartTLS is used rather than raw LDAP over SSL.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-tls-reqcert-option tls-reqcert

Specifies what checks to perform on a server-supplied certificate. The meaning of the values is described in the ldap.conf(5) manual page.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string tls-cacertdir

Specifies the directory containing X.509 certificates for peer authen‐ tication. This parameter is ignored when using GnuTLS.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string tls-cacertfile

Specifies the path to the X.509 certificate for peer authentication.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string tls-randfile

Specifies the path to an entropy source. This parameter is ignored when using GnuTLS.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string tls-ciphers

Specifies the ciphers to use for TLS as a string.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string tls-cert

Specifies the path to the file containing the local certificate for client TLS authentication.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string tls-key

Specifies the path to the file containing the private key for client TLS authentication.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-number pagesize

Set this to a number greater than 0 to request paged results from the LDAP server in accordance with RFC2696. The default (0) is to not request paged results.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-ignore-users-option nss-initgroups-ignoreusers

This option prevents group membership lookups through LDAP for the specified users. Alternatively, the value ’all-local may be used. With that value nslcd builds a full list of non-LDAP users on startup.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-number nss-min-uid

This option ensures that LDAP users with a numeric user id lower than the specified value are ignored.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-number nss-uid-offset

This option specifies an offset that is added to all LDAP numeric user ids. This can be used to avoid user id collisions with local users.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-number nss-gid-offset

This option specifies an offset that is added to all LDAP numeric group ids. This can be used to avoid user id collisions with local groups.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-boolean nss-nested-groups

If this option is set, the member attribute of a group may point to another group. Members of nested groups are also returned in the higher level group and parent groups are returned when finding groups for a specific user. The default is not to perform extra searches for nested groups.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-boolean nss-getgrent-skipmembers

If this option is set, the group member list is not retrieved when looking up groups. Lookups for finding which groups a user belongs to will remain functional so the user will likely still get the correct groups assigned on login.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-boolean nss-disable-enumeration

If this option is set, functions which cause all user/group entries to be loaded from the directory will not succeed in doing so. This can dramatically reduce LDAP server load in situations where there are a great number of users and/or groups. This option is not recommended for most configurations.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string validnames

This option can be used to specify how user and group names are verified within the system. This pattern is used to check all user and group names that are requested and returned from LDAP.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-boolean ignorecase

This specifies whether or not to perform searches using case-insensitive matching. Enabling this could open up the system to authorization bypass vulnerabilities and introduce nscd cache poisoning vulnerabilities which allow denial of service.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-boolean pam-authc-ppolicy

This option specifies whether password policy controls are requested and handled from the LDAP server when performing user authentication.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string pam-authc-search

By default nslcd performs an LDAP search with the user’s credentials after BIND (authentication) to ensure that the BIND operation was successful. The default search is a simple check to see if the user’s DN exists. A search filter can be specified that will be used instead. It should return at least one entry.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string pam-authz-search

This option allows flexible fine tuning of the authorisation check that should be performed. The search filter specified is executed and if any entries match, access is granted, otherwise access is denied.

Defaults to ‘disabled’.

nslcd-configuration parameter: maybe-string pam-password-prohibit-message

If this option is set password modification using pam_ldap will be denied and the specified message will be presented to the user instead. The message can be used to direct the user to an alternative means of changing their password.

Defaults to ‘disabled’.

nslcd-configuration parameter: list pam-services

List of pam service names for which LDAP authentication should suffice.

Defaults to ‘()’.