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<hr>

<h1>
<code>dbconfig-common</code> documentation
 Chapter 3 - Using <code>dbconfig-common</code> in your packages
</h1>

<hr>

<h2 id="s-quickndirty">3.1 Quick and dirty: what to do</h2>

There are three things you will have to do as a package maintainer if you want
to use <code>dbconfig-common</code>: provide the database code/scripts to setup
the data base, source the maintainer script libraries and launch
<code>dbconfig-common</code>. <code>dbconfig-common</code> will take care of
everything else, including all debconf related questions,
database/database-user creation, upgrade/remove/purge logic, etc. After all,
the goal of <code>dbconfig-common</code> is to make life easier for both the
local admin and the package maintainer :)

<hr>

<h3 id="s-depends">3.1.1 Update package dependencies</h3>

If your package just supports a single database type supported by
dbconfig-common, your package needs to depend on the matching
<code>dbconfig-&lt;database-type&gt;</code> package as well as have the
<code>dbconfig-no-thanks</code> as an alternative to that. E.g. packages that
need a PostgreSQL database must have the following in their Depends field:

<pre>
 Depends: dbconfig-pgsql | dbconfig-no-thanks
</pre>

Packages that support multiple database types (see more about that in the <a
href="#s-multidbtype">Packages that support multiple types of databases,
Section 3.2.4</a>) must alternatively depend on all the matching
<code>dbconfig-&lt;database-type&gt;</code> packages as well as have
<code>dbconfig-no-thanks</code> as an alternative to that. E.g. packages that
need a PostgreSQL or SQLite3 database must have the following in their Depends
field:

<pre>
 Depends: dbconfig-pgsql | dbconfig-sqlite3 | dbconfig-no-thanks
</pre>

<hr>

<h3 id="s-hooks">3.1.2 Putting hooks into the maintainer scripts</h3>

In the <var>config</var>, <var>postinst</var>, <var>prerm</var>, and
<var>postrm</var> scripts for your package, you will need to source the
libraries which perform most of the work for you (you do not need to do so in
your <var>preinst</var> script). If you are not currently using debconf in
your package, you will be now, and the debconf libraries need to be sourced
first. You will need to use dh_installdebconf or otherwise install your
<var>config</var> script into your deb file if you're not already doing so.
For example, here's what it might look like in a <var>config</var> script for
an imaginary <code>foo-mysql</code> package:

<pre>
 #!/bin/sh
 # config maintainer script for foo-mysql
 
 # source debconf stuff
 . /usr/share/debconf/confmodule
 # source dbconfig-common shell library, and call the hook function
 if [ -f /usr/share/dbconfig-common/dpkg/config.mysql ]; then
 . /usr/share/dbconfig-common/dpkg/config.mysql
 dbc_go foo-mysql &quot;$@&quot;
 fi
 
 # ... rest of your code ...
</pre>

<var>dbc_go</var> is a function defined in every maintainer script hook to
execute the appropriate code based on which maintainer script is being run.
Note that it is passed two arguments. <code>foo-mysql</code>, the name of the
package (there's sadly no clean way to figure this out automatically), and
<var>$@</var> (the arguments which were passed to the maintainer script).

NOTE: you do not need to conditionally test for the existance of the
shell library in the <var>postinst</var> and <var>prerm</var> scripts, but to
stay compliant with Policy section 7.2 you do need to do so at least in your
<var>config</var> and <var>postrm</var> scripts.

Note that if your package does not use debconf, you will need to explicitly
install the <var>config</var> script in your package. The easiest way to do so
is to call dh_installdebconf from <code>debian/rules</code>.

<hr>

<h3 id="s-bootstrap">3.1.3 Supplying the data/code for your database</h3>

There are three locations in which you can place code for installing the
databases of your package:

<ul>
<li>

<code>/usr/share/dbconfig-common/data/PACKAGE/install/DBTYPE</code>

</li>
</ul>
<ul>
<li>

<code>/usr/share/dbconfig-common/data/PACKAGE/install-dbadmin/DBTYPE</code>

</li>
</ul>
<ul>
<li>

<code>/usr/share/dbconfig-common/scripts/PACKAGE/install/DBTYPE</code>

</li>
</ul>

where <var>PACKAGE</var> is the name of the package, <var>DBTYPE</var> is the
type of data (mysql, pgsql, etc). The full location should be a file
containing the proper data.

The first location is for the majority of situations, in which the database can
be constructed from it's native language (SQL for MySQL/PostgreSQL, for
example). The data will be fed to the underlying database using the
credentials of the database user. The second location is like the first
location, but will be run using the credentials of the database administrator.
Warning: use of this second location should only be done when there
are excerpts of database code that must be run as the database
administrator (such as some language constructs in postgresql) and should
otherwise be avoided. The third location is for databases that require a more
robust solution, in which executable programs (shell/perl/python scripts, or
anything else) can be placed.

This code will only be executed on new installs and reconfiguration of failed
installs. In the case of SQL databases, in the data directory you would find
the simple create and insert statements needed to create tables and populate
the database. You do not need to create the underlying database, only
populate it. The scripts directory contains shell/perl/python/whatever
scripts, which are passed the same arguments as <var>dbc_go</var>. If you need
database connection information (username, password, etc) in your scripts, you
can source the <code>/bin/sh</code> format package config file, or you can
instruct <code>dbconfig-common</code> to generate one in your programming
language of choice (see the advanced tips section).

If files exist in both data and scripts, they will both be executed in an
unspecified order.

That's it! The rest of what needs to be done is handled by
<code>dbconfig-common</code>, which should keep all the work (and bugs) in one
place. Happy packaging! Of course, it's recommended you take a quick look
through the rest of the document, just to get an idea of other things that
<code>dbconfig-common</code> can do for you in case you have special needs.

<hr>

<h2 id="s-advanced">3.2 Advanced usage.</h2>

<hr>

<h3 id="s-genconfig">3.2.1 Generating custom configuration files with database information</h3>

Your database application will probably require a username and password in
order to function. Every package that uses <code>dbconfig-common</code>
already has a /bin/sh includable format config file, but it may be more
convenient to have something in the native language of the package. For
example, packaging a php/MySQL web app would be a lot easier if there were
already a file existing with all the information in php includable format.

Using <code>dbconfig-common</code>, you can do this with little effort. In
your <var>postinst</var> script, define the variable
<var>dbc_generate_include</var> to a value that follows the form
<var>format:location</var> where <var>format</var> is one of the supported
output formats of <var>dbconfig-generate-include</var> (list them with -h) and
location is the absolute location where you want your config file to go. There
are also some extra variables <var>dbc_generate_include_owner</var>,
<var>dbc_generate_include_perms</var>, and <var>dbc_generate_include_args</var>
which do what you would expect them to. Note: you will be responsible for
removing this file in your <var>postrm</var> script. Note2: the
ownership and permissions will only be used when creating the file, so don't
rely on this feature if your packages wants to change existing ownership and/or
permissions. When your scripts are run, this environment variable will be
exported to your scripts, as well as a variable <var>dbc_config_include</var>
which has the same value, but with the leading <var>format:</var> stripped away
for convenience. NOTE if you use this feature, you should also ensure
that the generated file is properly removed in the <var>postrm</var> script.
dbconfig-common can not handle this itself, unfortunately, because it may be
possible that it is purged before your package is purged. therefore, you
should do the following in your <var>postrm</var> script:

<pre>
 if [ &quot;$1&quot; = &quot;purge&quot; ]; then
 rm -f yourconfigfile
 if command -v ucf &gt;/dev/null; then
 ucf --purge yourconfigfile
 ucfr --purge yourpackage yourconfigfile
 fi
 fi
</pre>

<hr>

<h3 id="s-import">3.2.2 Importing <code>dbconfig-common</code> into an existing package</h3>

If your package is already part of debian, <code>dbconfig-common</code>
provides some support to load pre-existing settings from a specified config by
setting two variables: <var>dbc_first_version</var> and
<var>dbc_load_include</var>.

<var>dbc_load_include</var> should be specified in the <var>config</var> script
and be of the format <var>format:inputfile</var>. <var>format</var> is one of
the languages understood by <var>dbconfig-load-include</var>, and
<var>inputfile</var> is either the config file in <var>format</var> language,
or a script file in <var>format</var> language that otherwise determines the
values and sets them.

<var>dbc_first_version</var> should be specified in both the <var>config</var>
and <var>postinst</var> scripts, and should contain the first version
in which <code>dbconfig-common</code> was introduced. When the package is
installed, if it is being upgraded from a version less than this value it will
attempt to bootstrap itself with the values.

<hr>

<h3 id="s-updates">3.2.3 Database changes in new versions of your package</h3>

Occasionally, the upstream authors will modify the underlying databases between
versions of their software. For example, in MySQL applications column names
may change, move to new tables, or the data itself may need to be modified in
newer upstream versions of a package.

In order to cope with this, a second set of file locations exists for providing
packagers ways to modify the databases during package upgrades:

<ul>
<li>

<code>/usr/share/dbconfig-common/data/PACKAGE/upgrade/DBTYPE/VERSION</code>

</li>
</ul>
<ul>
<li>

<code>/usr/share/dbconfig-common/data/PACKAGE/upgrade-dbadmin/DBTYPE/VERSION</code>

</li>
</ul>
<ul>
<li>

<code>/usr/share/dbconfig-common/scripts/PACKAGE/upgrade/DBTYPE/VERSION</code>

</li>
</ul>

where <var>VERSION</var> is the version at which the upgrade should be applied,
and the respective path contains the upgrade code/data. When a package upgrade
occurs, all instances of <var>VERSION</var> which are newer than the previously
installed version will be applied, in order. There is also an automatically
included set of safeguards and behavior provided by
<code>dbconfig-common</code>, so as the packager you shouldn't need to worry
about most of the error-handling.

As with installation, scripts will be passed the same cmdline arguments as were
passed to dbc_go.

<hr>

<h3 id="s-multidbtype">3.2.4 Packages that support multiple types of databases</h3>

Sometimes, a particular package may support multiple database types. This is
common with perl or php based web applications, which frequently use some form
of database abstraction layer (pear DB for php, the DBD family for perl).

<code>dbconfig-common</code> provides support for such applications in a
relatively straightforward fashion, allowing the local admin to select which
database type to use when configuring a database for a package

To take advantage of this feature, you will want to use the &quot;generic&quot;
maintainer script hooks, and additionally hint the debconf <var>config</var>
script with the types of databases your package supports. For example, the
<var>postinst</var> script would now look like this:

<pre>
 #!/bin/sh
 # postinst maintainer script for foo-mysql
 
 # source debconf stuff
 . /usr/share/debconf/confmodule
 # source dbconfig-common stuff
 . /usr/share/dbconfig-common/dpkg/postinst
 dbc_go foo-mysql &quot;$@&quot;
 
 # ... rest of your code ...
</pre>

Unfortunately, specifying the proper dependencies on the right
<code>dbconfig-&lt;database-type&gt;</code> packages, as discussed earlier, is
not enough for dbconfig-common to figure out which database types your package
supports. Therefore you need to let dbconfig-common know via the
<var>config</var> script. It needs to contain an additional variable called
&quot;dbc_dbtypes&quot;, which is a comma-separated list of supported database
types:

<pre>
 #!/bin/sh
 # config maintainer script for foo-mysql
 
 # source debconf stuff
 . /usr/share/debconf/confmodule
 if [ -f /usr/share/dbconfig-common/dpkg/config ]; then
 # we support mysql and pgsql
 dbc_dbtypes=&quot;mysql, pgsql&quot;
 
 # source dbconfig-common stuff
 . /usr/share/dbconfig-common/dpkg/config
 dbc_go foo-mysql &quot;$@&quot;
 fi
 
 # ... rest of your code ...
</pre>

<hr>

<h3 id="s-frontends">3.2.5 Packages that connect to but should not create databases (read-only frontends)</h3>

Some packages provide multiple frontend packages to a single backend package.
Furthermore, sometimes these frontend packages are installed on a seperate
system from the actual database application, and should not manage the
databases on their own.

For example, if the frontend were to be installed on multiple servers (perhaps
load balancing or similar), it would not be wise to attempt to install/upgrade
the database on each client. Instead, it would be wiser to simply prompt for
the information and leave the database management to the single central
package.

If the above scenario matches one of your packages, there are a seperate set of
maintainer hooks for you to use. For example, <code>frontend.config</code> or
<code>frontend.config.mysql</code>. Using these hooks,
<code>dbconfig-common</code> will know enough to not take any actions apart
from prompting the local administrator for the pertinent information.

<hr>

<h3 id="s-removal">3.2.6 Packages that require extra logic during removal</h3>

Sometimes, it may be that your install sql/scripts perform operations that
aren't automatically undone by package removal. For example, if your package
gives extra grants to a user (such as triggers) it's possible that grants will
not automatically be revoked, which could cause problems for later
installations as well as potential security concerns. For this and any other
use you may need it for, you can place files in the following locations for
&quot;removal&quot; maintainer code:

<ul>
<li>

<code>/usr/share/dbconfig-common/data/PACKAGE/remove/DBTYPE</code>

</li>
</ul>
<ul>
<li>

<code>/usr/share/dbconfig-common/scripts/PACKAGE/remove/DBTYPE</code>

</li>
</ul>

This works just like the install/upgrade code, only it always runs as the
dbadmin. This code is run by default, unless the local admin opts out of
deconfiguration assistance (note that this is seperate from database purging,
which does not happen by default). Note that if you need to perform template
substitution, you should set dbc_sql_substitutions to &quot;yes&quot; in your
prerm maintainer script as well.

<hr>

<h3 id="s-defaults">3.2.7 Hinting defaults and advanced control of configuration/installation</h3>

<code>dbconfig-common</code> has a set of pre-defined default values for most
of the questions with which it prompts the user, most of which are variations
on the name of the package. However, as a packager you can override some these
values and set defaults that you feel are more appropriate, as well as
otherwise modify the behavior of some parts of <code>dbconfig-common</code>.

The following table lists the variables you can hint in your <var>config</var>
script, as well as some other variables you can use to have a finer level of
control over <code>dbconfig-common</code>. You must use these variables
exactly (and only) where directed in this table.

<dl>
<dt>dbc_dbuser (used in: <var>config</var>)</dt>
<dd>

Name to use when connecting to database. (defaults to: package name)

</dd>
</dl>
<dl>
<dt>dbc_basepath (used in: <var>config</var>)</dt>
<dd>

Database storage directory for local (filesystem) based database types. Not
applicable for RDBMs like MySQL and postgres. (defaults to:
/var/lib/dbconfig-common)

</dd>
</dl>
<dl>
<dt>dbc_dbname (used in: <var>config</var>)</dt>
<dd>

Name of database resource to which to connect. (defaults to: package name)

</dd>
</dl>
<dl>
<dt>dbc_dbtypes (used in: <var>config</var>)</dt>
<dd>

Database types supported by the package, in order of maintainers' preference.
(defaults to: empty)

</dd>
</dl>
<dl>
<dt>dbc_dbfile_owner (used in: <var>postinst</var>)</dt>
<dd>

Set the owner:group for the generated database file. This option is only valid
for databases like SQLite that use a single file for storage and is not
prompted via debconf. (defaults to: root:root)

</dd>
</dl>
<dl>
<dt>dbc_dbfile_perms (used in: <var>postinst</var>)</dt>
<dd>

Set the permissions for the generated database file. This option is only valid
for databases like SQLite that use a single file for storage and is not
prompted via debconf. (defaults to: 0640)

</dd>
</dl>
<dl>
<dt>dbc_generate_include (used in: <var>postinst</var>)</dt>
<dd>

format:outputfile pair for an extra config to be generated by
<var>dbconfig-generate-include</var>. (defaults to: empty)

</dd>
</dl>
<dl>
<dt>dbc_generate_include_owner (used in: <var>postinst</var>)</dt>
<dd>

Set the owner:group of include files generated by
<var>dbconfig-generate-include</var>. (defaults to: empty)

</dd>
</dl>
<dl>
<dt>dbc_generate_include_perms (used in: <var>postinst</var>)</dt>
<dd>

Set the permissions of include files generated by
<var>dbconfig-generate-include</var>. (defaults to: empty)

</dd>
</dl>
<dl>
<dt>dbc_generate_include_args (used in: <var>postinst</var>)</dt>
<dd>

Arguments passed directly to <var>dbconfig-generate-include</var>. (defaults
to: empty)

</dd>
</dl>
<dl>
<dt>dbc_dgi_on_manual (used in: <var>postinst</var>)</dt>
<dd>

Control whether config files should be generated by
<var>dbconfig-generate-include</var> when the admin opts for manual
installation. (defaults to: true)

</dd>
</dl>
<dl>
<dt>dbc_first_version (used in: <var>config</var>,<var>postinst</var>)</dt>
<dd>

The first version in which <code>dbconfig-common</code> was introduced in the
package. (defaults to: empty)

</dd>
</dl>
<dl>
<dt>dbc_load_include (used in: <var>config</var>)</dt>
<dd>

format:includefile pair for a config to be read in by
<var>dbconfig-load-include</var>. (defaults to: empty)

</dd>
</dl>
<dl>
<dt>dbc_load_include_args (used in: <var>config</var>)</dt>
<dd>

Arguments passed directly to <var>dbconfig-load-include</var>. (defaults to:
empty)

</dd>
</dl>
<dl>
<dt>dbc_pgsql_createdb_encoding (used in: <var>postinst</var>)</dt>
<dd>

Specifies encoding for created postgres databases. (defaults to: empty/system
default)

</dd>
</dl>
<dl>
<dt>dbc_mysql_createdb_encoding (used in: <var>postinst</var>)</dt>
<dd>

Specifies encoding for created MySQL databases. (defaults to: empty/system
default)

</dd>
</dl>
<dl>
<dt>dbc_sql_substitutions (used in: <var>postinst</var>, sometimes <var>prerm</var>)</dt>
<dd>

If nonempty, specifies that sql files should be piped through a template
substitution filter (<var>dbconfig-generate-include -f template</var>) before
being executed. (defaults to: empty)

</dd>
</dl>
<dl>
<dt>dbc_authmethod_user (used in <var>config</var>)</dt>
<dd>

If set to &quot;ident&quot;, dbconfig-common will set the default postgres
authentication method for the package's database user to &quot;ident&quot;.
(defaults to: empty)

</dd>
</dl>
<dl>
<dt>dbc_config_allow_backup (used in <var>config</var>)</dt>
<dd>

If nonempty, dbconfig-common will allow its state machine to backup past the
beginning, such that packages allowing backup in there own config script to
work transparently.

</dd>
</dl>
<dl>
<dt>dbc_prio_low / dbc_prio_medium / dbc_prio_high / dbc_prio_critical (used everywhere)</dt>
<dd>

If nonempty, dbconfig-common will use the values of these variables to set the
priority of its debconf questions. You can use this if you think that the
default levels of dbconfig-common are not well defined for your package. Be
comforted thou that the priority will be raised automatically on errors and
that all error handling allows the sysadmin to be asked the questions again.

</dd>
</dl>
<dl>
<dt>dbc_authplugin (used in <var>config</var>)</dt>
<dd>

This option defines which MySQL authentication plugin should be set to default
whenever dbconfig-common creates a user in the database on behalf of the
package using it. Choices are:

<ul>
<li>

default: use the default auth plugin for installed MySQL server.

</li>
</ul>
<ul>
<li>

mysql_native_password: no MySQL authentication plugin is used.

</li>
</ul>
<ul>
<li>

sha256_password: more secure password encryption than native.

</li>
</ul>
<ul>
<li>

caching_sha2_password: in-memory authentication cache.

</li>
</ul>

dbc_authplugin should be set in .config file, right before calling dbc_go
function. It can also be configured by user during package installation, or
during dpkg-reconfigure, if debconf questions priority is set to low.

Be careful when changing this. There are some differences in between MySQL and
MariaDB and some options might not be available on one or another. As up to
MariaDB 10.4, its default authentication plugin is
&quot;mysql_native_password&quot; while, for MySQL 8.0, the new default
authentication plugin is the &quot;caching_sha2_password&quot;.

</dd>
</dl>

<hr>

<h3 id="s-debugging">3.2.8 Debugging problems with <code>dbconfig-common</code></h3>

In the event that your package is having trouble working with
<code>dbconfig-common</code>, the first thing you should try is to export and
set the shell variable <var>dbc_debug</var> to a nonempty value before
installing your package. This will provide a slightly larger amount of
information about what's going on.

In the event that this does not provide enough information, the next thing to
do will provide much, much, more information; enough that you will probably
want to redirect stderr into a temporary output file. In the file
<code>/usr/share/dbconfig-common/dpkg/common</code>, uncomment the <var>set
-x</var> line near the top of the file. This will show you all the shell
commands and logic as they are executed. If you have a good idea of where the
problem is occurring, you can also insert your own <var>set -x</var> lines
elsewhere followed by <var>set +x</var> lines to reduce the amount of input.

<hr>

<code>dbconfig-common</code> documentation

<address>
Sean Finney 
 
</address>
<hr>

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