8.3. Administration of local system configuration with Univention Configuration Registry#

Univention Configuration Registry is the central tool for managing the local system configuration of a UCS-based system. Direct editing of the configuration files is usually not necessary.

Settings are specified in a consistent format in a registry mechanism, the so-called Univention Configuration Registry variables. These variables are used to generate the configuration files used effectively by the services/programs from the configuration templates (the so-called Univention Configuration Registry templates).

This procedure offers a range of advantages:

  • It is not usually necessary to edit any configuration files manually. This avoids errors arising from invalid syntax of configuration settings or similar.

  • There is a uniform interface for editing the settings and the different syntax formats of the configuration files are hidden from the administrator.

  • Settings are decoupled from the actual configuration file, i.e., if a software uses a different configuration format in a new version, a new template in a new format is simply delivered instead of performing time-consuming and error-prone conversion of the file.

  • The variables used in a configuration file administrated with Univention Configuration Registry are registered internally. This ensures that when a UCR variable is changed, all the configuration files containing the changed variable are recreated.

Univention Configuration Registry variables can be configured in the command line using the univention-config-registry command (short form: ucr) or via the UMC module Univention Configuration Registry.

As the majority of packages perform their configuration via Univention Configuration Registry and the corresponding basic settings need to be set up during the installation, hundreds of Univention Configuration Registry variables are already set after the installation of a UCS system.

UCR variables can also be used efficiently in shell scripts for accessing current system settings.

The variables are named according to a tree structure with a forward slash being used to separate components of the name. For example, Univention Configuration Registry variables beginning with ldap are settings which apply to the local directory service.

A description is given for the majority of variables explaining their use.

If a configuration file is administrated by a UCR template and the required setting has not already been covered by an existing variable, the UCR template should be edited instead of the configuration file. If the configuration were directly adapted, the next time the file is regenerated - e.g., when a registered UCR variable is set - the local modification will be overwritten again. Adaptation of UCR templates is described in Modifying UCR templates.

Part of the settings configured in Univention Configuration Registry are system-specific (e.g., the computer name); many settings can, however, be used on more then one computer. The Univention Configuration Registry policy in the domain administration UMC modules can be used to compile variables and apply them on more than one computer.

The evaluation of the Univention Configuration Registry variables on a UCS system comprises four stages:

  • First the local Univention Configuration Registry variables are evaluated.

  • The local variables are overruled by policy variables which are usually sourced from the directory service

  • The --schedule option is used to set local variables which are only intended to apply for a certain period of time. This level of the Univention Configuration Registry is reserved for local settings which are automated by time-controlled mechanisms in Univention Corporate Server.

  • When the --force option is used in setting a local variable, settings adopted from the directory service and variables from the schedule level are overruled and the given value for the local system fixed instead. An example:

    $ univention-config-registry set --force mail/messagesizelimit=1000000
    

If a variable is set which is overwritten by a superordinate policy, a warning message is given.

The use of the Univention Configuration Registry policy is documented in the Policy-based configuration of UCR variables.

8.3.1. Using the Univention Management Console module#

The UMC module Univention Configuration Registry can be used to display and adjust the variables of a system. There is also the possibility of setting new variables using Add new variable.

A search mask is displayed on the start page. All variables are classified using a Category, for example all LDAP-specific settings.

The Search attribute can be entered as a filter in the search mask, which can refer to the variable name, value or description.

Following a successful search, the variables found are displayed in a table with the variable name and the value. A detailed description of the variable is displayed when moving the mouse cursor over the variable name.

A variable can be edited by clicking on its name. A variable can be deleted by right-clicking and selecting Delete.

8.3.2. Using the command line front end#

The command line interface of Univention Configuration Registry is run using the univention-config-registry command. Alternatively, the short form ucr can be used.

8.3.2.1. Querying a UCR variable#

get#

A single Univention Configuration Registry variable can be queried with the parameter get:

$ univention-config-registry get ldap/server/ip
dump#

The parameter dump can also be used to display all currently set variables:

$ univention-config-registry dump

8.3.2.2. Setting UCR variables#

set#

The parameter set is used to set a variable. The variable can be given any name consisting exclusively of letters, full stops, figures, hyphens and forward slashes.

$ univention-config-registry set VARIABLENAME=VALUE

If the variable already exists, the content is updated; otherwise, a new entry is created.

When setting a new value for a Univention Configuration Registry variable UCR runs checks to verify the compatibility of the value with the variable type. In case of incompatibility UCR displays a warning message. Moreover, the variable is not set to the new value if the Univention Configuration Registry variable ucr/check/type is true (default is false). If the --ignore-check option is used, the value is always set independent of type compatibility and setting of ucr/check/type.

When a variable changes, UCR rewrites all configuration files immediately for which the variable is registered. UCR outputs the paths of the updated files to the console.

In doing so it must be noted that although the configuration of a service is updated, the service in question is not restarted automatically! The restart must be performed manually.

It is also possible to perform simultaneous changes to several variables in one command line. If these refer to the same configuration file, the file is only rewritten once.

$ univention-config-registry set \
  dns/forwarder1=192.0.2.2 \
  sshd/xforwarding="no" \
  sshd/port=2222

A conditional setting is also possible. For example, if a value should only be saved in a Univention Configuration Registry variable when the variable does not yet exist, this can be done by entering a question mark (?) instead of the equals sign (=) when assigning values.

$ univention-config-registry set dns/forwarder1?192.0.2.2

8.3.2.3. Searching for variables and set values#

The parameter search can be used to search for a variable. This command searches for variable names which contain nscd and displays these with their current assignments:

$ univention-config-registry search nscd

Alternatively, searches can also be performed for set variable values. This request searches for all variables set to primary.example.com:

$ univention-config-registry search --value primary.example.com

Search templates in the form of regular expressions can also be used in the search. The complete format is documented at Regular expression operations in the Python 2 documentation.

8.3.2.4. Deleting UCR variables#

unset#

The parameter unset is used to delete a variable. The following example deletes the variable dns/forwarder2. It is also possible here to specify several variables to be deleted:

$ univention-config-registry unset dns/forwarder2

8.3.2.5. Regeneration of configuration files from their template#

commit#

The parameter commit is used to regenerate a configuration file from its template. The name of the configuration file is entered as a parameter, e.g.:

$ univention-config-registry commit /etc/samba/smb.conf

As UCR templates are generally regenerated automatically when UCR variables are edited, this is primarily used for tests.

If no filename is given when running ucr commit, all of the files managed by Univention Configuration Registry will be regenerated from the templates. It is, however, not generally necessary to regenerate all the configuration files.

8.3.2.6. Sourcing variables in shell scripts#

shell#

The parameter shell is used to display Univention Configuration Registry variables and their current assignments in a format that can be used in shell scripts.

$ univention-config-registry shell ldap/server/name

Different conversions are involved in this: forward slashes in variable names are replaced with underscores and characters in the values which have a particular significance in shell scripts are included in quotation marks to ensure they are not altered.

The Univention Configuration Registry output must be executed via the command eval for Univention Configuration Registry variables to be able to be read in a shell script as environment variables:

# eval "$(univention-config-registry shell ldap/server/name)"
# echo "$ldap_server_name"
primary.firma.de

8.3.3. Policy-based configuration of UCR variables#

Part of the settings configured in Univention Configuration Registry are system-specific (e.g., the computer name); many settings can, however, be used on more then one computer. The Univention Configuration Registry policy managed in the UMC module Policies can be used to compile variables and apply them on more than one computer.

Policy-based configuration of the Apache start page and forced HTTPS

Fig. 8.6 Policy-based configuration of the Apache start page and forced HTTPS#

Firstly, a Name must be set for the policy which is to be created, under which the variables will later be assigned to the individual computer objects.

In addition, at least one Variable must be configured and a Value assigned.

This policy can then be assigned to a computer object or a container or OU (see Applying policies). Note that the evaluation of configured values differs from other policies: The values are not forwarded directly to the computer, but rather written on the assigned computer by Univention Directory Policy. The time interval used for this is configured by the Univention Configuration Registry Variable ldap/policy/cron and is set to hourly as standard.

8.3.4. Modifying UCR templates#

In the simplest case, a Univention Configuration Registry template is a copy of the original configuration file in which the points at which the value of a variable are to be used contain a reference to the variable name.

Inline Python code can also be integrated for more complicated scenarios, which then also allows more complicated constructions such as conditional assignments.

Note

Univention Configuration Registry templates are included in the corresponding software packages as configuration files. When packages are updated, a check is performed for whether any changes have been made to the configuration files.

If configuration files are no longer there in the form in which they were delivered, they will not be overwritten. Instead a new version will be created in the same directory with the ending .debian.dpkg-new.

If changes are to be made on the Univention Configuration Registry templates, these templates are also not overwritten during the update and are instead re-saved in the same directory with the ending .dpkg-new or .dpkg-dist. Corresponding notes are written in the /var/log/univention/actualise.log log file. This only occurs if UCR templates have been locally modified.

The UCR templates are stored in the /etc/univention/templates/files/ directory. The path to the templates is the absolute path to the configuration file with the prefixed path to the template directory. For example, the template for the /etc/issue configuration file can be found under /etc/univention/templates/files/etc/issue.

For the configuration files to be processed correctly by Univention Configuration Registry they must be in UNIX format. If configuration files are edited in DOS or Windows, for example, control characters are inserted to indicate line breaks, which can disrupt the way Univention Configuration Registry uses the file.

8.3.4.1. Referencing of UCR variables in templates#

In the simplest case, a UCR variable can be directly referenced in the template. The variable name framed by the string @%@ represents the wildcard. As an example the option for the activation of X11 forwarding in the configuration file /etc/ssh/sshd_config of the OpenSSH server:

X11Forwarding @%@sshd/xforwarding@%@

Newly added references to UCR variables are automatically evaluated by templates; additional registration is only required with the use of inline Python code (see Integration of inline Python code in templates).

8.3.4.2. Integration of inline Python code in templates#

Any type of Python code can be embedded in UCR templates by entering a code block framed by the string @!@. For example, these blocks can be used to realize conditional requests so that when a parameter is changed via a variable, further dependent settings are automatically adopted in the configuration file. The following code sequence configures for example network settings using the Univention Configuration Registry settings:

@!@
if configRegistry.get('apache2/ssl/certificate'):
    print('SSLCertificateFile %s' %
        configRegistry['apache2/ssl/certificate'])
@!@

All the data output with the print function are written in the generated configuration file. The data saved in Univention Configuration Registry can be requested via the ConfigRegistry object, e.g.:

@!@
if configRegistry.get('version/version') and \
        configRegistry.get('version/patchlevel'):
    print('UCS %(version/version)s-%(version/patchlevel)s' %
        configRegistry)
@!@

In contrast to directly referenced UCR variables (see Referencing of UCR variables in templates), variables accessed in inline Python code must be explicitly registered.

The Univention Configuration Registry variables used in the configuration files are registered in info files in the /etc/univention/templates/info/ directory which are usually named after the package name with the file ending .info. If new Python code is entered into the templates or the existing code changed in such a way that it requires additional or different variables, one of the existing .info files will need to be modified or a new one added.

Following the changing of .info files, the ucr update command must be run.