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Series: Introduction to Ubuntu Development Part 4

This is the fourth article in a series to explain the basics of Ubuntu Development in a way that does not require huge amounts of background and goes through concepts, tools, processes and infrastructure step by step. If you like the article or have questions or found bugs, please leave a comment.

Thanks a lot to the Ubuntu Packaging Guide team for their work on this!


Basic Overview of the debian/ Directory

This article will briefly explain the different files important to the packaging of Ubuntu packages which are contained in the debian/ directory. The most important of them are changelog, control, copyright, and rules. These are required for all packages. A number of additional files in the debian/ may be used in order to customize and configure the behavior of the package. Some of these files are discussed in this article, but this is not meant to be a complete list.

The changelog

This file is, as its name implies, a listing of the changes made in each version. It has a specific format that gives the package name, version, distribution, changes, and who made the changes at a given time. If you have a GPG key (see: Getting set up), make sure to use the same name and email address in changelog as you have in your key. The following is a template changelog:

package (version) distribution; urgency=urgency

 * change details
  - more change details
 * even more change details

-- maintainer name <email address>[two spaces]  date

The format (especially of the date) is important. The date should be in RFC 5322 format, which can be obtained by using the command date -R. For convenience, the command dch may be used to edit changelog. It will update the date automatically.

Minor bullet points are indicated by a dash “-”, while major points use an asterisk “*”.

If you are packaging from scratch, dch --create (dch is in the devscripts package) will create a standard debian/changelog for you.

Here is a sample changelog file for hello:

hello (2.6-0ubuntu1) natty; urgency=low

  * New upstream release with lots of bug fixes and feature improvements.

-- Jane Doe <packager@example.com>  Thu, 21 Apr 2011 11:12:00 -0400

Notice that the version has a -0ubuntu1 appended to it, this is the distro revision, used so that the packaging can be updated (to fix bugs for example) with new uploads within the same source release version.

Ubuntu and Debian have slightly different package versioning schemes to avoid conflicting packages with the same source version. If a Debian package has been changed in Ubuntu, it has ubuntuX (where X is the Ubuntu revision number) appended to the end of the Debian version. So if the Debian hello 2.6-1 package was changed by Ubuntu, the version string would be 2.6-1ubuntu1. If a package for the application does not exist in Debian, then the Debian revision is 0 (e.g. 2.6-0ubuntu1).

For further information, see the changelog section (Section 4.4) of the Debian Policy Manual.

The control file

The control file contains the information that the package manager (such as apt-get, synaptic, and adept) uses, build-time dependencies, maintainer information, and much more.

For the Ubuntu hello package, the control file looks something like:

Source: hello
Section: devel
Priority: optional
Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>
XSBC-Original-Maintainer: Jane Doe <packager@example.com>
Standards-Version: 3.9.1
Build-Depends: debhelper (>= 7)
Bzr-Vcs: lp:ubuntu/hello
Homepage: http://www.gnu.org/software/hello/

Package: hello
Architecture: any
Depends: ${shlibs:Depends}
Description: The classic greeting, and a good example
 The GNU hello program produces a familiar, friendly greeting. It
 allows non-programmers to use a classic computer science tool which
 would otherwise be unavailable to them. Seriously, though: this is
 an example of how to do a Debian package. It is the Debian version of
 the GNU Project's `hello world' program (which is itself an example
 for the GNU Project).

The first paragraph describes the source package including the list of packages required to build the package from source in the Build-Depends field. It also contains some meta-information such as the maintainer’s name, the version of Debian Policy that the package complies with, the location of the packaging version control repository, and the upstream home page.

Note that in Ubuntu, we set the Maintainer field to a general address because anyone can change any package (this differs from Debian where changing packages is usually restricted to an individual or a team). Packages in Ubuntu should generally have the Maintainer field set to Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>. If the Maintainer field is modified, the old value should be saved in the XSBC-Original-Maintainer field. This can be done automatically with the update-maintainer script available in the ubuntu-dev-tools package. For further information, see the Debian Maintainer Field spec on the Ubuntu wiki.

Each additional paragraph describes a binary package to be built.

For further information, see the control file section (Chapter 5) of the Debian Policy Manual.

The copyright file

This file gives the copyright information for both the upstream source and the packaging. Ubuntu and Debian Policy (Section 12.5) require that each package installs a verbatim copy of its copyright and license information to /usr/share/doc/$(package_name)/copyright.

Generally, copyright information is found in the COPYING file in the program’s source directory. This file should include such information as the names of the author and the packager, the URL from which the source came, a Copyright line with the year and copyright holder, and the text of the copyright itself. An example template would be:

Format: http://svn.debian.org/wsvn/dep/web/deps/dep5.mdwn?op=file&rev=166
Upstream-Name: Hello
Source: ftp://ftp.example.com/pub/games

Files: *
Copyright: Copyright 1998 John Doe <jdoe@example.com>
License: GPL-2+
 This program is free software; you can redistribute it
 and/or modify it under the terms of the GNU General Public
 License as published by the Free Software Foundation; either
 version 2 of the License, or (at your option) any later
 version.
 .
 This program is distributed in the hope that it will be
 useful, but WITHOUT ANY WARRANTY; without even the implied
 warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 PURPOSE.  See the GNU General Public License for more
 details.
 .
 You should have received a copy of the GNU General Public
 License along with this package; if not, write to the Free
 Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 Boston, MA  02110-1301 USA
 .
 On Debian systems, the full text of the GNU General Public
 License version 2 can be found in the file
 `/usr/share/common-licenses/GPL-2'.

Files: debian/*
Copyright: Copyright 1998 Jane Doe <packager@example.com>
License: GPL-2+

This example follows the DEP-5: Machine-parseable debian/copyright proposal. You are encouraged to use this format as well.

The rules file

The last file we need to look at is rules. This does all the work for creating our package. It is a Makefile with targets to compile and install the application, then create the .deb file from the installed files. It also has a target to clean up all the build files so you end up with just a source package again.

Here is a simplified version of the rules file created by dh_make (which can be found in the dh-make package):

#!/usr/bin/make -f
# -*- makefile -*-

# Uncomment this to turn on verbose mode.
#export DH_VERBOSE=1

%:
       dh  $@

Let us go through this file in some detail. What this does is pass every build target that debian/rules is called with as an argument to /usr/bin/dh, which itself will call all the necessary dh_* commands.

dh runs a sequence of debhelper commands. The supported sequences correspond to the targets of a debian/rules file: “build”, “clean”, “install”, “binary-arch”, “binary-indep”, and “binary”. In order to see what commands are run in each target, run:

$ dh binary-arch --no-act

Commands in the binary-indep sequence are passed the “-i” option to ensure they only work on binary independent packages, and commands in the binary-arch sequences are passed the “-a” option to ensure they only work on architecture dependent packages.

Each debhelper command will record when it’s successfully run in debian/package.debhelper.log. (Which dh_clean deletes.) So dh can tell which commands have already been run, for which packages, and skip running those commands again.

Each time dh is run, it examines the log, and finds the last logged command that is in the specified sequence. It then continues with the next command in the sequence. The --until, --before, --after, and --remaining options can override this behavior.

If debian/rules contains a target with a name like override_dh_command, then when it gets to that command in the sequence, dh will run that target from the rules file, rather than running the actual command. The override target can then run the command with additional options, or run entirely different commands instead. (Note that to use this feature, you should Build-Depend on debhelper 7.0.50 or above.)

Have a look at /usr/share/doc/debhelper/examples/ and man dh for more examples. Also see the rules section (Section 4.9) of the Debian Policy Manual.

Additional Files

The install file

The install file is used by dh_install to install files into the binary package. It has two standard use cases:

  • To install files into your package that are not handled by the upstream build system.
  • Splitting a single large source package into multiple binary packages.

In the first case, the install file should have one line per file installed, specifying both the the file and the installation directory. For example, the following install file would install the script foo in the source package’s root directory to usr/bin and a desktop file in the debian directory to usr/share/applications:

foo usr/bin
debian/bar.desktop usr/share/applications

When a source package is producing multiple binary packages dh will install the files into debian/tmp rather than directly into debian/<package>. Files installed into debian/tmp can then be moved into separate binary packages using multiple $package_name.install files. This is often done to split large amounts of architecture independent data out of architecture dependent packages and into Architecture: all packages. In this case, only the name of the files (or directories) to be installed are needed without the installation directory. For example, foo.install containing only the architecture dependent files might look like:

usr/bin/
usr/lib/foo/*.so

While foo-common.install containing only the architecture independent file might look like:

/usr/share/doc/
/usr/share/icons/
/usr/share/foo/
/usr/share/locale/

This would create two binary packages, foo and foo-common. Both would require their own paragraph in debian/control.

See man dh_install and the install file section (Section 5.11) of the Debian New Maintainers’ Guide for additional details.

The watch file

The debian/watch file allows us to check automatically for new upstream versions using the tool uscan found in the devscripts package. The first line of the watch file must be the format version (3, at the time of this writing), while the following lines contain any URLs to parse. For example:

version=3

http://ftp.gnu.org/gnu/hello/hello-(.*).tar.gz

Running uscan in the root source directory will now compare the upstream version number in debian/changelog with the latest available upstream version. If a new upstream version is found, it will be automatically downloaded. For example:

$ uscan
hello: Newer version (2.7) available on remote site:

http://ftp.gnu.org/gnu/hello/hello-2.7.tar.gz

  (local version is 2.6)
hello: Successfully downloaded updated package hello-2.7.tar.gz
    and symlinked hello_2.7.orig.tar.gz to it

For further information, see man uscan and the watch file section (Section 4.11) of the Debian Policy Manual.

For a list of packages where the watch file reports they are not in sync with upstream see Ubuntu External Health Status.

The source/format file

This file indicates the format of the source package. Currently, the package source format defaults to 1.0 if this file does not exist. You are encouraged to use the newer 3.0 source format. In this case, the file should contain a single line indicating the desired format:

  • 3.0 (native) for Debian native packages (no upstream version) or
  • 3.0 (quilt) for packages with a separate upstream tarball

If for some reason, you wish to keep using the old format, please create this file and put 1.0 in it to be explicit about the source package version. This allows for the future removal of the 1.0 default for the package source format.

http://wiki.debian.org/Projects/DebSrc3.0 summarizes information concerning and the benefits of the switch to the 3.0 source package formats.

See man dpkg-source and the source/format section (Section 5.21) of the Debian New Maintainers’ Guide for additional details.

Additional Resources

In addition to the links to the Debian Policy Manual in each section above, the Debian New Maintainers’ Guide has more detailed descriptions of each file. Chapter 4, “Required files under the debian directory” further discusses the control, changelog, copyright and rules files. Chapter 5, “Other files under the debian directory” discusses additional files that may be used.