Appendix B. Quick intro into building metapackages

This howto describes the building of metapackages by using the blends-dev package. It is perfectly possible to build a metapackage as any other normal Debian package but this HOWTO has the only purpose to describe the profit you might gain by using these tools.

~> cp -a /usr/share/doc/blends-dev/examples/tasks .
~> cat tasks/README
~> edit tasks/task1
Description: short description
 long description as in any debian/control file

Depends: dependency1, dependency2, ...

For each metapackage this skeleton of a debian/control entry is needed. All necessary information is available in the directory /usr/share/doc/blends-dev/examples/tasks.

To build any Debian package you always need a directory named debian, which contains a certain set of files. The package blends-dev provides a complete set of example files that only have to be copied and after editing some place holders are ready to use.

~> cp -a /usr/share/doc/blends-dev/examples/debian .
~> cat debian/README
~> edit debian/control.stub

Now the variables in the file control.stub change the variables named _BLEND_, _MAINTAINER_ etc. to match the names of the Debian Pure Blend to be built. Please note that the file debian/control is and has to be a symbolic link to control.stub to let the blends-dev tools work.

~> edit debian/rules

Also in the debian/rules the name of the Blend has to be inserted where the template contains _BLEND_. Depending from the way the sources.list should be scanned the options for the gen-control call can be adjusted.

You have to build the tarball using the command

~> make -f debian/rules get-orig-source

For your comfort you might like to create a file Makefile containing

#!/usr/bin/make -f 
include /usr/share/blends-dev/Makefile

which enables you to simply use

~> make dist

to build the source tarball. This tarball has to be moved to a location where the metapackages will be built. Unpack the tarball there and start the build process using for instance

~> debuild

That's all for the very simple case when the metapackages should not contain user menus. Even if user menus are suggested they are not necessary. The following paragraphs describe how to use the blends-dev tools to support these menus.

The creation of a common package is optional, but suggested, because it adds some special features like menus, user groups, and probably more in the future. It is automatically built by blend-install-helper, which is called in debian/rules, if the common directory exists. The easiest way to create this is as follows:

~> cp -a /usr/share/doc/blends-dev/examples/common .
~> cat common/README
~> edit common/conf common/control common/common.1

The variables (_BLEND_) in these three files have to be adjusted to the name of the Debian Pure Blend in question. This blend-config cares for the initialisation of the role based menu system and might contain adjustments of the general configuration inside the blends-common.

If the metapackage blend-config will be created according to these rules all other metapackages will depend automatically from this common package. For the friends of auto-apt, a helper /usr/bin/<metapackage-name> will be installed as well, which just prints some information about the meta package. All in all, the usage of the common package is strongly suggested to have a common registry for stuff like user roles and possibly other things that will be implemented in the future.

As explained in Section 6.3.1, “User menu tools” the metapackages can contain user menus. This optional feature can be implemented easily by using the template from the blends-dev in the following way:

~> cp -a /usr/share/doc/blends-dev/examples/menu .
~> cat menu/README
~> edit menu/task1
 Edit the example to legal menu entries of the
 dependencies of this metapackage
~> cp menu/task1 menu/<metapackage name>

A menu file for each task should be created containing valid menu entries for each dependent package. The easiest way to obtain those menu entries is to simply copy the original menu entry files that are contained in the packages on which the metapackage will depend. The only thing that has to be changed in these menu entries is the package field, which has to be changed from <dependent package> to blend-task. All other entries might remain unchanged. This is a good point to check whether the menu entries of the packages you depend from are formatted nicely and print the necessary information (for instance make use of "hints"). Here the metapackage maintainer has a good chance for quality assurance work, which is also part of the Debian Pure Blends issue.

In principle these menu items could be created automatically either at metapackage build time or even better in the postinst script of the metapackage because it is granted that the needed menu files are installed on the system, which is not really necessary on the metapackage build machine. This might be implemented in later versions of blends-dev. Currently the policy is that we like to have a little bit of control about the menu entries for the quality assurance issue mentioned above. Last, but not least, there are packages that do not provide a menu entry. If this is the case because the package maintainer just forgot it a bug report should be filed. On the other hand, there are packages with programs that provide a command line interface that does not allow a reasonable menu entry. A solution for this case is provided in the next paragraph.

The idea of the metapackage menu is to provide the user with easily viewable traces of any installed package that helps solving everyday tasks. So if there are packages that do not contain a menu, a screen with relevant documentation should be provided in a viewer by the creator of the metapackage. Such documentation can be created using the following templates:

~> cp -a /usr/share/doc/blends-dev/examples/docs .
~> cat docs/README
~> edit docs/task1/dep1
 Provide information about a package <dep1> that is
 a dependency of the metapackage <task1>, but does not
 contain a useful menu entry.
~> cp docs/task1/dep1 docs/task1/<dependent pkg>
~> cp -a docs/task1 docs/<metapackage name>

This ensures that our users become aware of all interesting packages on their system. The documentation files should contain hints to man pages to read, URLs that should be visited to learn more about the package or some short introduction how to get started.