Appendix C. Source packages (from old Packaging Manual)

Table of Contents

C.1. Tools for processing source packages
C.1.1. dpkg-source - packs and unpacks Debian source packages
C.1.2. dpkg-buildpackage - overall package-building control script
C.1.3. dpkg-gencontrol - generates binary package control files
C.1.4. dpkg-shlibdeps - calculates shared library dependencies
C.1.5. dpkg-distaddfile - adds a file to debian/files
C.1.6. dpkg-genchanges - generates a .changes upload control file
C.1.7. dpkg-parsechangelog - produces parsed representation of a changelog
C.1.8. dpkg-architecture - information about the build and host system
C.2. The Debian package source tree
C.2.1. debian/rules - the main building script
C.2.2. debian/substvars and variable substitutions
C.2.3. debian/files
C.2.4. debian/tmp
C.3. Source packages as archives
C.4. Unpacking a Debian source package without dpkg-source
C.4.1. Restrictions on objects in source packages

The Debian binary packages in the distribution are generated from Debian sources, which are in a special format to assist the easy and automatic building of binaries.

C.1. Tools for processing source packages

Various tools are provided for manipulating source packages; they pack and unpack sources and help build of binary packages and help manage the distribution of new versions.

They are introduced and typical uses described here; see dpkg-source(1) for full documentation about their arguments and operation.

For examples of how to construct a Debian source package, and how to use those utilities that are used by Debian source packages, please see the hello example package.

C.1.1.  dpkg-source - packs and unpacks Debian source packages

This program is frequently used by hand, and is also called from package-independent automated building scripts such as dpkg-buildpackage.

To unpack a package it is typically invoked with

dpkg-source -x .../path/to/filename.dsc

with the filename.tar.gz and filename.diff.gz (if applicable) in the same directory. It unpacks into package-version, and if applicable package-version.orig, in the current directory.

To create a packed source archive it is typically invoked:

dpkg-source -b package-version

This will create the .dsc, .tar.gz and .diff.gz (if appropriate) in the current directory. dpkg-source does not clean the source tree first - this must be done separately if it is required.

See also Section C.3, “Source packages as archives”.

C.1.2.  dpkg-buildpackage - overall package-building control script

See dpkg-buildpackage(1).

C.1.3.  dpkg-gencontrol - generates binary package control files

This program is usually called from debian/rules (see Section C.2, “The Debian package source tree”) in the top level of the source tree.

This is usually done just before the files and directories in the temporary directory tree where the package is being built have their permissions and ownerships set and the package is constructed using dpkg-deb/. [119]

dpkg-gencontrol must be called after all the files which are to go into the package have been placed in the temporary build directory, so that its calculation of the installed size of a package is correct.

It is also necessary for dpkg-gencontrol to be run after dpkg-shlibdeps so that the variable substitutions created by dpkg-shlibdeps in debian/substvars are available.

For a package which generates only one binary package, and which builds it in debian/tmp relative to the top of the source package, it is usually sufficient to call dpkg-gencontrol.

Sources which build several binaries will typically need something like:

dpkg-gencontrol -Pdebian/pkg -ppackage

The -P tells dpkg-gencontrol that the package is being built in a non-default directory, and the -p tells it which package's control file should be generated.

dpkg-gencontrol also adds information to the list of files in debian/files, for the benefit of (for example) a future invocation of dpkg-genchanges.

C.1.4.  dpkg-shlibdeps - calculates shared library dependencies

See dpkg-shlibdeps(1).

C.1.5.  dpkg-distaddfile - adds a file to debian/files

Some packages' uploads need to include files other than the source and binary package files.

dpkg-distaddfile adds a file to the debian/files file so that it will be included in the .changes file when dpkg-genchanges is run.

It is usually invoked from the binary target of debian/rules:

dpkg-distaddfile filename section priority

The filename is relative to the directory where dpkg-genchanges will expect to find it - this is usually the directory above the top level of the source tree. The debian/rules target should put the file there just before or just after calling dpkg-distaddfile.

The section and priority are passed unchanged into the resulting .changes file.

C.1.6.  dpkg-genchanges - generates a .changes upload control file

See dpkg-genchanges(1).

C.1.7.  dpkg-parsechangelog - produces parsed representation of a changelog

See dpkg-parsechangelog(1).

C.1.8.  dpkg-architecture - information about the build and host system

See dpkg-architecture(1).

C.2. The Debian package source tree

The source archive scheme described later is intended to allow a Debian package source tree with some associated control information to be reproduced and transported easily. The Debian package source tree is a version of the original program with certain files added for the benefit of the packaging process, and with any other changes required made to the rest of the source code and installation scripts.

The extra files created for Debian are in the subdirectory debian of the top level of the Debian package source tree. They are described below.

C.2.1.  debian/rules - the main building script

See Section 4.9, “Main building script: debian/rules.

C.2.2.  debian/substvars and variable substitutions

See Section 4.10, “ Variable substitutions: debian/substvars.

C.2.4. debian/tmp

This is the default temporary location for the construction of binary packages by the binary target. The directory tmp serves as the root of the file system tree as it is being constructed (for example, by using the package's upstream makefiles install targets and redirecting the output there), and it also contains the DEBIAN subdirectory. See Section B.1, “Creating package files - dpkg-deb.

This is only a default and can be easily overridden. Most packaging tools no longer use debian/tmp, instead preferring debian/pkg for the common case of a source package building only one binary package. Such tools usually only use debian/tmp as a temporary staging area for built files and do not construct packages from it.

If several binary packages are generated from the same source tree, it is usual to use a separate debian/pkg directory for each binary package as the temporary construction locations.

Whatever temporary directories are created and used by the binary target must of course be removed by the clean target.

C.3. Source packages as archives

As it exists on the FTP site, a Debian source package consists of three related files. You must have the right versions of all three to be able to use them.

Debian source control file - .dsc

This file is a control file used by dpkg-source to extract a source package. See Section 5.4, “Debian source control files -- .dsc.

Original source archive - package_upstream-version.orig.tar.gz

This is a compressed (with gzip -9) tar file containing the source code from the upstream authors of the program.

Debian package diff - package_upstream_version-revision.diff.gz

This is a unified context diff (diff -u) giving the changes which are required to turn the original source into the Debian source. These changes may only include editing and creating plain files. The permissions of files, the targets of symbolic links and the characteristics of special files or pipes may not be changed and no files may be removed or renamed.

All the directories in the diff must exist, except the debian subdirectory of the top of the source tree, which will be created by dpkg-source if necessary when unpacking.

The dpkg-source program will automatically make the debian/rules file executable (see below).

If there is no original source code - for example, if the package is specially prepared for Debian or the Debian maintainer is the same as the upstream maintainer - the format is slightly different: then there is no diff, and the tarfile is named package_version.tar.gz, and preferably contains a directory named package-version.

C.4.  Unpacking a Debian source package without dpkg-source

dpkg-source -x is the recommended way to unpack a Debian source package. However, if it is not available it is possible to unpack a Debian source archive as follows:

  1. Untar the tarfile, which will create a .orig directory.

  2. Rename the .orig directory to package-version.

  3. Create the subdirectory debian at the top of the source tree.

  4. Apply the diff using patch -p0.

  5. Untar the tarfile again if you want a copy of the original source code alongside the Debian version.

It is not possible to generate a valid Debian source archive without using dpkg-source. In particular, attempting to use diff directly to generate the .diff.gz file will not work.

C.4.1. Restrictions on objects in source packages

The source package may not contain any hard links, [120] [121] device special files, sockets or setuid or setgid files. [122]

The source packaging tools manage the changes between the original and Debian source using diff and patch. Turning the original source tree as included in the .orig.tar.gz into the Debian package source must not involve any changes which cannot be handled by these tools. Problematic changes which cause dpkg-source to halt with an error when building the source package are:

  • Adding or removing symbolic links, sockets or pipes.

  • Changing the targets of symbolic links.

  • Creating directories, other than debian.

  • Changes to the contents of binary files.

Changes which cause dpkg-source to print a warning but continue anyway are:

  • Removing files, directories or symlinks. [123]

  • Changed text files which are missing the usual final newline (either in the original or the modified source tree).

Changes which are not represented, but which are not detected by dpkg-source, are:

  • Changing the permissions of files (other than debian/rules) and directories.

The debian directory and debian/rules are handled specially by dpkg-source - before applying the changes it will create the debian directory, and afterwards it will make debian/rules world-executable.

[119] This is so that the control file which is produced has the right permissions

[120] This is not currently detected when building source packages, but only when extracting them.

[121] Hard links may be permitted at some point in the future, but would require a fair amount of work.

[122] Setgid directories are allowed.

[123] Renaming a file is not treated specially - it is seen as the removal of the old file (which generates a warning, but is otherwise ignored), and the creation of the new one.