# Quick intro into building metapackages

There are several descriptions available how to build Debian packages in general. The main resource might be the repository of Debian packaging manuals (especially developers reference chapter 6, best packaging practices). There are several external packaging HOWTOs for example the one from Joe 'Zonker' Brockmeier.

## Defining dependencies for 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`.

## The packaging directory

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 common metapackage

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 implementd in the future.

## The metapackage menus

As explained in 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 dependant 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 formated 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.

## Menu for any dependency

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.