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dbconfig-commonin your packages
there are three things you will have to do as a package maintainer if you want
dbconfig-common: provide the database code/scripts to setup
the data base, source the maintainer script libraries and launch
dbconfig-common will take care of
everything else, include all debconf related questions, database/database-user
creation, upgrade/remove/purge logic, et c. after all, the goal of
dbconfig-common is to make life easier for both the local admin
and the package maintainer :)
Your package needs to depend on
dbconfig-common. Also you should
add Recommends for the command line client packages of the database types you
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 an what it might look like in a config script
for an imaginary
#!/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. XXX: add a note
about how to ignore the lintian warnings about missing templates files.
There are three locations in which you can place code for installing the databases of your package:
where PACKAGE is the name of the package, DBTYPE is the type of data (mysql, pgsql, et c). 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
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.
your database application will probably require a username and password in
order to function. every package that uses
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.
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. 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
if [ "$1" = "purge" ]; then rm -f yourconfigfile if which ucf >/dev/null 2>&1; then ucf --purge yourconfigfile fi fi
dbconfig-commoninto an existing package
If your package is already part of debian,
provides some support to load pre-existing settings from a specified config by
setting two variables: dbc_first_version and
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
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.
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 directories exists for providing packagers ways to modify the databases during package upgrades:
where VERSION is the version at which the upgrade should be applied.
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.
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 ...
The config script would 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 ...
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.mysql. using these hooks,
dbconfig-common will know enough to not take any actions apart
from prompting the local administrator for the pertinent information.
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:
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.
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
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
dbconfig-common. you must use these variables
exactly (and only) where directed in this table.
name to use when connecting to database (defaults to: package name)
database storage directory for local (filesystem) based database types. Not applicable for RDBMs like mysql and postgres. (defaults to: /var/lib/dbconfig-common)
name of database resource to which to connect (defaults to: package name)
database types supported by the package, in order of maintainers' preference (defaults to: empty)
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)
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)
format:outputfile pair for an extra config to be generated by dbconfig-generate-include. (defaults to: empty)
set the owner:group of include files generated by dbconfig-generate-include (defaults to: empty)
set the permissions of include files generated by dbconfig-generate-include (defaults to: empty)
arguments passed directly to dbconfig-generate-include (defaults to: empty)
the first version in which
dbconfig-common was introduced in the
package (defaults to: empty)
format:includefile pair for a config to be read in by dbconfig-load-include (defaults to: empty)
arguments passed directly to dbconfig-load-include (defaults to: empty)
specifies encoding for created postgres databases (defaults to: empty/system default)
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)
if set to "password", dbconfig-common will set the default postgres authentication method for the package's database user to "password" (defaults to: empty)
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.
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