`dbconfig-common' documentation
-------------------------------
Sean Finney
-------------------------------------------------------------------------------
Abstract
--------
`dbconfig-common' is an implementation of the "best practices for
database applications" draft, which provides debian packagers with an
easy, reliable, and consistent method for managing databases used by
debian packages.
Copyright Notice
----------------
Copyright (C) 2005 sean finney <seanius@debian.org> and 2015 Paul
Gevers <elbrus@debian.org>.
This document is licensed under the Academic Free License, Version 2.1
(https://spdx.org/licenses/AFL-2.1.html)
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Contents
--------
1. Introduction
2. Try it out!
3. Using `dbconfig-common' in your packages
3.1. Quick and dirty: what to do
3.1.1. Update package dependencies
3.1.2. Putting hooks into the maintainer scripts
3.1.3. Supplying the data/code for your database
3.2. Advanced usage.
3.2.1. Generating custom configuration files with database
information
3.2.2. Importing `dbconfig-common' into an existing package
3.2.3. Database changes in new versions of your package
3.2.4. Packages that support multiple types of databases
3.2.5. Packages that connect to but should not create
databases (read-only frontends)
3.2.6. Packages that require extra logic during removal
3.2.7. Hinting defaults and advanced control of
configuration/installation
3.2.8. Debugging problems with `dbconfig-common'
4. More Information (and how to help)
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1. Introduction
---------------
`dbconfig-common' can:
* support MySQL, PostgreSQL and SQLite based applications
* create databases and database users
* access local or remote databases
* upgrade/modify databases when upstream changes database structure
* remove databases and database users
* generate config files in many formats with the database info
* import configs from packages previously managing databases on
their own
* prompt users with a set of normalized, pre-translated questions
* handle failures gracefully, with an option to retry.
* do all the hard work automatically
* work for package maintainers with little effort on their part
* work for local admins with little effort on their part
* comply with an agreed upon set of standards for behavior
* do absolutely nothing if it is the whim of the local admin
* perform all operations from within the standard flow of debian
package maintenance (no additional skill is required of the local
admin)
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2. Try it out!
--------------
If you're interested in trying it out, go ahead and check out Chapter
3, `Using `dbconfig-common' in your packages', which will teach you
how to get your packages working with `dbconfig-common'.
If you'd like to see some basic examples of `dbconfig-common' in
action, check out the sample packages available in
`/usr/share/doc/dbconfig-common/examples'. In this directory you'll
find debian source directories to build the binary packages, so you
can see not only how the packages work when they are installed, but
also how they are built. Take a look at the README file in this
directory for more information.
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3. Using `dbconfig-common' in your packages
-------------------------------------------
3.1. Quick and dirty: what to do
--------------------------------
There are three things you will have to do as a package maintainer if
you want to use `dbconfig-common': provide the database code/scripts
to setup the data base, source the maintainer script libraries and
launch `dbconfig-common'. `dbconfig-common' 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 `dbconfig-common' is to make life easier for
both the local admin _and_ the package maintainer :)
3.1.1. Update package dependencies
----------------------------------
If your package just supports a single database type supported by
dbconfig-common, your package needs to depend on the matching
`dbconfig-<database-type>' package as well as have the
`dbconfig-no-thanks' as an alternative to that. E.g. packages that
need a PostgreSQL database must have the following in their Depends
field:
Depends: dbconfig-pgsql | dbconfig-no-thanks
Packages that support multiple database types (see more about that in
the Section 3.2.4, `Packages that support multiple types of
databases') must alternatively depend on all the matching
`dbconfig-<database-type>' packages as well as have
`dbconfig-no-thanks' as an alternative to that. E.g. packages that
need a PostgreSQL or SQLite3 database must have the following in their
Depends field:
Depends: dbconfig-pgsql | dbconfig-sqlite3 | dbconfig-no-thanks
3.1.2. Putting hooks into the maintainer scripts
------------------------------------------------
In the <config>, <postinst>, <prerm>, and <postrm> 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 <preinst> 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 <config>
script into your deb file if you're not already doing so. For
example, here's what it might look like in a <config> script for an
imaginary `foo-mysql' package:
#!/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 "$@"
fi
# ... rest of your code ...
<dbc_go> is a function defined in every maintainer script hook to
execute the appropriate code based on which maintainer script is being
run. Note that it is passed two arguments. `foo-mysql', the name of
the package (there's sadly no clean way to figure this out
automatically), and <$@> (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 <postinst> and <prerm> scripts, but to stay
compliant with Policy section 7.2 you do need to do so at least in
your <config> and <postrm> scripts.
Note that if your package does not use debconf, you will need to
explicitly install the <config> script in your package. The easiest
way to do so is to call dh_installdebconf from `debian/rules'.
3.1.3. Supplying the data/code for your database
------------------------------------------------
There are three locations in which you can place code for installing
the databases of your package:
* `/usr/share/dbconfig-common/data/PACKAGE/install/DBTYPE'
* `/usr/share/dbconfig-common/data/PACKAGE/install-dbadmin/DBTYPE'
* `/usr/share/dbconfig-common/scripts/PACKAGE/install/DBTYPE'
where <PACKAGE> is the name of the package, <DBTYPE> 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 <dbc_go>. If you need database connection information
(username, password, etc) in your scripts, you can source the
`/bin/sh' format package config file, or you can instruct
`dbconfig-common' 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
`dbconfig-common', 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 `dbconfig-common' can do for you in case you have special
needs.
3.2. Advanced usage.
--------------------
3.2.1. Generating custom configuration files with database information
----------------------------------------------------------------------
Your database application will probably require a username and
password in order to function. Every package that uses
`dbconfig-common' 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 `dbconfig-common', you can do this with little effort. In your
<postinst> script, define the variable <dbc_generate_include> to a
value that follows the form <format:location> where <format> is one of
the supported output formats of <dbconfig-generate-include> (list them
with -h) and location is the absolute location where you want your
config file to go. There are also some extra variables
<dbc_generate_include_owner>, <dbc_generate_include_perms>, and
<dbc_generate_include_args> which do what you would expect them to.
_Note: you will be responsible for removing this file in your <postrm>
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 <dbc_config_include> which has the same
value, but with the leading <format:> stripped away for convenience.
_NOTE_ if you use this feature, you should also ensure that the
generated file is properly removed in the <postrm> 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 <postrm> script:
if [ "$1" = "purge" ]; then
rm -f yourconfigfile
if command -v ucf >/dev/null; then
ucf --purge yourconfigfile
ucfr --purge yourpackage yourconfigfile
fi
fi
3.2.2. Importing `dbconfig-common' into an existing package
-----------------------------------------------------------
If your package is already part of debian, `dbconfig-common' provides
some support to load pre-existing settings from a specified config by
setting two variables: <dbc_first_version> and <dbc_load_include>.
<dbc_load_include> should be specified in the <config> script and be
of the format <format:inputfile>. <format> is one of the languages
understood by <dbconfig-load-include>, and <inputfile> is either the
config file in <format> language, or a script file in <format>
language that otherwise determines the values and sets them.
<dbc_first_version> should be specified in both the <config> _and_
<postinst> scripts, and should contain the first version in which
`dbconfig-common' 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.
3.2.3. Database changes in new versions of your package
-------------------------------------------------------
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:
* `/usr/share/dbconfig-common/data/PACKAGE/upgrade/DBTYPE/VERSION'
* `/usr/share/dbconfig-common/data/PACKAGE/upgrade-dbadmin/DBTYPE/VERSION'
* `/usr/share/dbconfig-common/scripts/PACKAGE/upgrade/DBTYPE/VERSION'
where <VERSION> 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 <VERSION> 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 `dbconfig-common', 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.
3.2.4. Packages that support multiple types of databases
--------------------------------------------------------
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).
`dbconfig-common' 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 "generic"
maintainer script hooks, and additionally hint the debconf <config>
script with the types of databases your package supports. For
example, the <postinst> script would now look like this:
#!/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 "$@"
# ... rest of your code ...
Unfortunately, specifying the proper dependencies on the right
`dbconfig-<database-type>' 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 <config> script. It needs to contain an additional variable
called "dbc_dbtypes", which is a comma-separated list of supported
database types:
#!/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="mysql, pgsql"
# source dbconfig-common stuff
. /usr/share/dbconfig-common/dpkg/config
dbc_go foo-mysql "$@"
fi
# ... rest of your code ...
3.2.5. Packages that connect to but should not create databases (read-only
frontends)
----------------------------------------------------------------------------
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,
`frontend.config' or `frontend.config.mysql'. Using these hooks,
`dbconfig-common' will know enough to not take any actions apart from
prompting the local administrator for the pertinent information.
3.2.6. Packages that require extra logic during removal
-------------------------------------------------------
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 "removal" maintainer code:
* `/usr/share/dbconfig-common/data/PACKAGE/remove/DBTYPE'
* `/usr/share/dbconfig-common/scripts/PACKAGE/remove/DBTYPE'
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 "yes" in your prerm maintainer script as
well.
3.2.7. Hinting defaults and advanced control of configuration/installation
--------------------------------------------------------------------------
`dbconfig-common' 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
`dbconfig-common'.
The following table lists the variables you can hint in your <config>
script, as well as some other variables you can use to have a finer
level of control over `dbconfig-common'. _You must use these
variables exactly (and only) where directed in this table_.
dbc_dbuser (used in: <config>)
Name to use when connecting to database. (defaults to: package
name)
dbc_basepath (used in: <config>)
Database storage directory for local (filesystem) based database
types. Not applicable for RDBMs like MySQL and postgres.
(defaults to: /var/lib/dbconfig-common)
dbc_dbname (used in: <config>)
Name of database resource to which to connect. (defaults to:
package name)
dbc_dbtypes (used in: <config>)
Database types supported by the package, in order of maintainers'
preference. (defaults to: empty)
dbc_dbfile_owner (used in: <postinst>)
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)
dbc_dbfile_perms (used in: <postinst>)
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)
dbc_generate_include (used in: <postinst>)
format:outputfile pair for an extra config to be generated by
<dbconfig-generate-include>. (defaults to: empty)
dbc_generate_include_owner (used in: <postinst>)
Set the owner:group of include files generated by
<dbconfig-generate-include>. (defaults to: empty)
dbc_generate_include_perms (used in: <postinst>)
Set the permissions of include files generated by
<dbconfig-generate-include>. (defaults to: empty)
dbc_generate_include_args (used in: <postinst>)
Arguments passed directly to <dbconfig-generate-include>.
(defaults to: empty)
dbc_dgi_on_manual (used in: <postinst>)
Control whether config files should be generated by
<dbconfig-generate-include> when the admin opts for manual
installation. (defaults to: true)
dbc_first_version (used in: <config>,<postinst>)
The first version in which `dbconfig-common' was introduced in
the package. (defaults to: empty)
dbc_load_include (used in: <config>)
format:includefile pair for a config to be read in by
<dbconfig-load-include>. (defaults to: empty)
dbc_load_include_args (used in: <config>)
Arguments passed directly to <dbconfig-load-include>. (defaults
to: empty)
dbc_pgsql_createdb_encoding (used in: <postinst>)
Specifies encoding for created postgres databases. (defaults to:
empty/system default)
dbc_mysql_createdb_encoding (used in: <postinst>)
Specifies encoding for created MySQL databases. (defaults to:
empty/system default)
dbc_sql_substitutions (used in: <postinst>, sometimes <prerm>)
If nonempty, specifies that sql files should be piped through a
template substitution filter (<dbconfig-generate-include -f
template>) before being executed. (defaults to: empty)
dbc_authmethod_user (used in <config>)
If set to "ident", dbconfig-common will set the default postgres
authentication method for the package's database user to "ident".
(defaults to: empty)
dbc_config_allow_backup (used in <config>)
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.
dbc_prio_low / dbc_prio_medium / dbc_prio_high / dbc_prio_critical
(used everywhere)
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.
dbc_authplugin (used in <config>)
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:
* default: use the default auth plugin for installed MySQL
server.
* mysql_native_password: no MySQL authentication plugin is
used.
* sha256_password: more secure password encryption than
native.
* caching_sha2_password: in-memory authentication cache.
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 "mysql_native_password" while, for MySQL
8.0, the new default authentication plugin is the
"caching_sha2_password".
3.2.8. Debugging problems with `dbconfig-common'
------------------------------------------------
In the event that your package is having trouble working with
`dbconfig-common', the first thing you should try is to export and set
the shell variable <dbc_debug> 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 `/usr/share/dbconfig-common/dpkg/common', uncomment the
<set -x> 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
<set -x> lines elsewhere followed by <set +x> lines to reduce the
amount of input.
-------------------------------------------------------------------------------
4. More Information (and how to help)
-------------------------------------
Currently, there's a fair amount of work left to be done:
* more translators/translations are needed for the templates
* developers are needed to volunteer their packages with
`dbconfig-common'
* volunteers are needed to test the new packages
* support for other database formats would be nice
* more scheduled features are listed in
`/usr/share/doc/dbconfig-common/TODO'
-------------------------------------------------------------------------------
`dbconfig-common' documentation
Sean Finney
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