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4.5 KiB
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121 lines
4.5 KiB
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================
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debconf concepts
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================
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This chapter explains how to use the Debian ``debconf`` and
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``dbconfig-common`` packages to configure OpenStack services. These
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packages enable users to perform configuration tasks. When users
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install OpenStack packages, ``debconf`` prompts the user for responses,
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which seed the contents of configuration files associated with that package.
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After package installation, users can update the configuration of a
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package by using the :command:`dpkg-reconfigure` program.
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If you are familiar with these packages and pre-seeding, you can proceed
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to :doc:`../keystone`.
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The Debian packages
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-------------------
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The rules described here are from the `Debian Policy
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Manual <http://www.debian.org/doc/debian-policy/>`__. If any rule
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described in this chapter is not respected, you have found a serious bug
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that must be fixed.
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When you install or upgrade a Debian package, all configuration file
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values are preserved. Using the ``debconf`` database as a registry is
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considered a bug in Debian. If you edit something in any OpenStack
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configuration file, the ``debconf`` package reads that value when it
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prepares to prompt the user. For example, to change the log in name for
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the RabbitMQ messaging queue for a service, you can edit its value in
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the corresponding configuration file.
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To opt out of using the ``debconf`` package, run the
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:command:`dpkg-reconfigure` command and select non-interactive mode:
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.. code-block:: console
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# dpkg-reconfigure -plow debconf
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Then, ``debconf`` does not prompt you.
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Another way to disable the ``debconf`` package is to prefix the
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:command:`apt` command with ``DEBIAN_FRONTEND=noninteractive``,
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as follows:
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.. code-block:: console
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# DEBIAN_FRONTEND=noninteractive apt-get install nova-api
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If you configure a package with ``debconf`` incorrectly, you can
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re-configure it, as follows:
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.. code-block:: console
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# dpkg-reconfigure PACKAGE-NAME
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This calls the post-installation script for the ``PACKAGE-NAME`` package
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after the user responds to all prompts. If you cannot install a Debian
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package in a non-interactive way, you have found a release-critical bug
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in Debian. Report it to the Debian bug tracking system.
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Generally, the ``-common`` packages install the configuration files. For
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example, the ``glance-common`` package installs the ``glance-api.conf``
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and ``glance-registry.conf`` files. So, for the Image service, you must
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re-configure the ``glance-common`` package. The same applies for
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``cinder-common``, ``nova-common``, and ``heat-common`` packages.
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In ``debconf``, the higher the priority for a screen, the greater the
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chance that the user sees that screen. If a ``debconf`` screen has
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``medium`` priority and you configure the Debian system to show only
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``critical`` prompts, which is the default in Debian, the user does not
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see that ``debconf`` screen. Instead, the default for the related package
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is used. In the Debian OpenStack packages, a number of ``debconf`` screens
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are set with ``medium`` priority. Consequently, if you want to respond to
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all ``debconf`` screens from the Debian OpenStack packages, you must run
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the following command and select the ``medium`` priority before you install
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any packages:
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.. code-block:: console
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# dpkg-reconfigure debconf
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.. note::
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The packages do not require pre-depends. If ``dbconfig-common`` is
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already installed on the system, the user sees all prompts. However,
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you cannot define the order in which the ``debconf`` screens appear.
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The user must make sense of it even if the prompts appear in an
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illogical order.
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Pre-seed debconf prompts
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------------------------
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You can pre-seed all ``debconf`` prompts. To pre-seed means to store
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responses in the ``debconf`` database so that ``debconf`` does not prompt
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the user for responses. Pre-seeding enables a hands-free installation for
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users. The package maintainer creates scripts that automatically
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configure the services.
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The following example shows how to pre-seed an automated MySQL Server
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installation:
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.. code-block:: bash
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MYSQL_PASSWORD=MYSQL_PASSWORD
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echo "mysql-server-5.5 mysql-server/root_password password ${MYSQL_PASSWORD}
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mysql-server-5.5 mysql-server/root_password seen true
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mysql-server-5.5 mysql-server/root_password_again password ${MYSQL_PASSWORD}
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mysql-server-5.5 mysql-server/root_password_again seen true
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" | debconf-set-selections
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DEBIAN_FRONTEND=noninteractive apt-get install -y --force-yes mysql-server
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The ``seen true`` option tells ``debconf`` that a specified screen was
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already seen by the user so do not show it again. This option is useful
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for upgrades.
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