6. Univention Directory Listener

Replication of the directory data within a UCS domain is provided by the Univention Directory Listener/Notifier mechanism:

• The Univention Directory Listener service runs on all UCS systems.

• On the Primary Directory Node (and possibly existing Backup Directory Node systems) the Univention Directory Notifier service monitors changes in the LDAP directory and makes the selected changes available to the Univention Directory Listener services on all UCS systems joined into the domain.

The active Univention Directory Listener instances in the domain connect to a Univention Directory Notifier service. If an LDAP change is performed on the Primary Directory Node (all other LDAP servers in the domain are read-only), this is registered by the Univention Directory Notifier and reported to the listener instances.

Each Univention Directory Listener instance hosts a range of Univention Directory Listener modules. These modules are shipped by the installed applications; the print server package includes, for example, listener modules which generate the CUPS configuration.

Univention Directory Listener modules can be used to communicate domain changes to services which are not LDAP-aware. The print server CUPS is an example of this: The printer definitions are not read from the LDAP, but instead from the file /etc/cups/printers.conf. Now, if a printer is saved in the printer management of the Univention Management Console, it is stored in the LDAP directory. This change is detected by the Univention Directory Listener module cups-printers and an entry gets added to, modified in or deleted from /etc/cups/printers.conf based on the modification in the LDAP directory.

By default the Listener loads all modules from the directory /usr/lib/univention-directory-listener/system/. Other directories can be specified using the option -m when starting the univention-directory-listener daemon.

• 6.1. Structure of Listener Modules
  • name
  • get_name()
  • description
  • get_description()
  • filter
  • get_ldap_filter()
  • ldap_filter
  • attributes
  • get_attributes()
  • modrdn
  • handle_every_delete
  • priority
  • get_priority()
  • 6.1.1. Handle LDAP objects
  • 6.1.2. Initialize and clean
    • initialize()
    • clean()
  • 6.1.3. Suspend and resume
    • prerun()
    • postrun()
• 6.2. High-level Listener modules API
  • get_name()
  • name
  • get_description()
  • description
  • get_ldap_filter()
  • ldap_filter
  • get_attributes()
  • attributes
  • get_priority()
  • priority
  • get_listener_module_instance()
  • get_listener_module_class()
  • listener_module_class
  • get_active()
  • create()
  • modify()
  • remove()
  • initialize()
  • clean()
  • pre_run()
  • post_run()
  • as_root()
  • diff()
  • error_handler()
  • lo
  • po
  • logger
  • ucr
• 6.3. Low-level Listener module
  • filter
  • handler()
  • setdata()
• 6.4. Listener tasks and examples
  • 6.4.1. Listener API example
  • 6.4.2. Basic example
  • 6.4.3. Rename and move
  • 6.4.4. Full example with packaging
  • 6.4.5. A little bit more object oriented
• 6.5. Technical Details
  • 6.5.1. User-ID and Credentials
  • 6.5.2. Internal Cache
    • 6.5.2.1. univention-directory-listener-ctrl
    • 6.5.2.2. univention-directory-listener-dump
    • 6.5.2.3. univention-directory-listener-verify
    • 6.5.2.4. get_notifier_id.py
  • 6.5.3. Internal working
  • 6.5.4. LDAP Schema handling
  • 6.5.5. Python 3 migration