in the <tt>.deb</tt> file format.
</p>
+ <p>
+ A <tt>.deb</tt> package contains two sets of files: a set of files
+ to install on the system when the package is installed, and a set
+ of files that provide additional metadata about the package or
+ which are executed when the package is installed or removed. This
+ second set of files is called <em>control information files</em>.
+ Among those files are the package maintainer scripts
+ and <file>control</file>, the <qref id="binarycontrolfiles">binary
+ package control file</qref> that contains the control fields for
+ the package. Other control information files
+ include <qref id="sharedlibs-shlibdeps">the <file>shlibs</file>
+ file</qref> used to store shared library dependency information
+ and the <file>conffiles</file> file that lists the package's
+ configuration files (described in <ref id="config-files">).
+ </p>
+
+ <p>
+ There is unfortunately a collision of terminology here between
+ control information files and files in the Debian control file
+ format. Throughout this document, a <em>control file</em> refers
+ to a file in the Debian control file format. These files are
+ documented in <ref id="controlfields">. Only files referred to
+ specifically as <em>control information files</em> are the files
+ included in the control information file member of
+ the <file>.deb</file> file format used by binary packages. Most
+ control information files are not in the Debian control file
+ format.
+ </p>
+
<sect>
<heading>The package name</heading>
<heading>The description of a package</heading>
<p>
- Every Debian package must have an extended description
- stored in the appropriate field of the control record.
- The technical information about the format of the
+ Every Debian package must have a <tt>Description</tt> control
+ field which contains a synopsis and extended description of the
+ package. Technical information about the format of the
<tt>Description</tt> field is in <ref id="f-Description">.
</p>
must be available and usable on the system at all times, even
when packages are in an unconfigured (but unpacked) state.
Packages are tagged <tt>essential</tt> for a system using the
- <tt>Essential</tt> control file field. The format of the
+ <tt>Essential</tt> control field. The format of the
<tt>Essential</tt> control field is described in <ref
id="f-Essential">.
</p>
<p>
Packages which use the Debian Configuration Management
- Specification may contain an additional
- <prgn>config</prgn> script and a <tt>templates</tt>
- file in their control archive<footnote>
- The control.tar.gz inside the .deb.
- See <manref name="deb" section="5">.
- </footnote>.
- The <prgn>config</prgn> script might be run before the
- <prgn>preinst</prgn> script, and before the package is unpacked
- or any of its dependencies or pre-dependencies are satisfied.
- Therefore it must work using only the tools present in
- <em>essential</em> packages.<footnote>
+ Specification may contain the additional control information
+ files <file>config</file>
+ and <file>templates</file>. <file>config</file> is an
+ additional maintainer script used for package configuration,
+ and <file>templates</file> contains templates used for user
+ prompting. The <prgn>config</prgn> script might be run before
+ the <prgn>preinst</prgn> script and before the package is
+ unpacked or any of its dependencies or pre-dependencies are
+ satisfied. Therefore it must work using only the tools
+ present in <em>essential</em> packages.<footnote>
<package>Debconf</package> or another tool that
implements the Debian Configuration Management
Specification will also be installed, and any
<p>
When <prgn>dpkg-gencontrol</prgn>,
<prgn>dpkg-genchanges</prgn> and <prgn>dpkg-source</prgn>
- generate control files they perform variable substitutions
+ generate control files, they perform variable substitutions
on their output just before writing it. Variable
substitutions have the form <tt>${<var>variable</var>}</tt>.
The optional file <file>debian/substvars</file> contains
<heading>Optional upstream source location: <file>debian/watch</file></heading>
<p>
- This is an optional, recommended control file for the
- <tt>uscan</tt> utility which defines how to automatically
- scan ftp or http sites for newly available updates of the
- package. This is used by <url id="
- http://dehs.alioth.debian.org/"> and other Debian QA tools
- to help with quality control and maintenance of the
+ This is an optional, recommended configuration file for the
+ <tt>uscan</tt> utility which defines how to automatically scan
+ ftp or http sites for newly available updates of the
+ package. This is used
+ by <url id="http://dehs.alioth.debian.org/"> and other Debian QA
+ tools to help with quality control and maintenance of the
distribution as a whole.
</p>
</p>
<p>
- These scripts are the files <prgn>preinst</prgn>,
- <prgn>postinst</prgn>, <prgn>prerm</prgn> and
- <prgn>postrm</prgn> in the control area of the package.
- They must be proper executable files; if they are scripts
- (which is recommended), they must start with the usual
- <tt>#!</tt> convention. They should be readable and
+ These scripts are the control information
+ files <prgn>preinst</prgn>, <prgn>postinst</prgn>, <prgn>prerm</prgn>
+ and <prgn>postrm</prgn>. They must be proper executable files;
+ if they are scripts (which is recommended), they must start with
+ the usual <tt>#!</tt> convention. They should be readable and
executable by anyone, and must not be world-writable.
</p>
they exit with a zero status if everything went well.
</p>
- Additionally, packages interacting with users using
- <tt>debconf</tt> in the <prgn>postinst</prgn> script should
- install a <prgn>config</prgn> script in the control area,
- see <ref id="maintscriptprompt"> for details.
- </p>
+ <p>
+ Additionally, packages interacting with users
+ using <prgn>debconf</prgn> in the <prgn>postinst</prgn> script
+ should install a <prgn>config</prgn> script as a control
+ information file. See <ref id="maintscriptprompt"> for details.
+ </p>
<p>
When a package is upgraded a combination of the scripts from
In the <tt>Depends</tt>, <tt>Recommends</tt>,
<tt>Suggests</tt>, <tt>Pre-Depends</tt>,
<tt>Build-Depends</tt> and <tt>Build-Depends-Indep</tt>
- control file fields of the package, which declare
+ control fields of the package, which declare
dependencies on other packages, the package names listed may
also include lists of alternative package names, separated
by vertical bar (pipe) symbols <tt>|</tt>. In such a case,
<p>
This is done using the <tt>Depends</tt>, <tt>Pre-Depends</tt>,
<tt>Recommends</tt>, <tt>Suggests</tt>, <tt>Enhances</tt>,
- <tt>Breaks</tt> and <tt>Conflicts</tt> control file fields.
+ <tt>Breaks</tt> and <tt>Conflicts</tt> control fields.
<tt>Breaks</tt> is described in <ref id="breaks">, and
<tt>Conflicts</tt> is described in <ref id="conflicts">. The
rest are described below.
<p>
A <em>virtual package</em> is one which appears in the
- <tt>Provides</tt> control file field of another package.
- The effect is as if the package(s) which provide a
- particular virtual package name had been listed by name
- everywhere the virtual package name appears. (See also <ref
- id="virtual_pkg">)
+ <tt>Provides</tt> control field of another package. The effect
+ is as if the package(s) which provide a particular virtual
+ package name had been listed by name everywhere the virtual
+ package name appears. (See also <ref id="virtual_pkg">)
</p>
<p>
<p>
Packages can declare in their control file that they should
- overwrite files in certain other packages, or completely
- replace other packages. The <tt>Replaces</tt> control file
- field has these two distinct purposes.
+ overwrite files in certain other packages, or completely replace
+ other packages. The <tt>Replaces</tt> control field has these
+ two distinct purposes.
</p>
<sect1><heading>Overwriting files in other packages</heading>
<p>
This is done using the <tt>Build-Depends</tt>,
<tt>Build-Depends-Indep</tt>, <tt>Build-Conflicts</tt> and
- <tt>Build-Conflicts-Indep</tt> control file fields.
+ <tt>Build-Conflicts-Indep</tt> control fields.
</p>
<p>
</p>
<p>
- Packages involving shared libraries should be split up into
- several binary packages. This section mostly deals with how
- this separation is to be accomplished; rules for files within
- the shared library packages are in <ref id="libraries"> instead.
+ This section deals only with public shared libraries: shared
+ libraries that are placed in directories searched by the dynamic
+ linker by default or which are intended to be linked against
+ normally and possibly used by other, independent packages. Shared
+ libraries that are internal to a particular package or that are
+ only loaded as dynamic modules are not covered by this section and
+ are not subject to its requirements.
</p>
- <sect id="sharedlibs-runtime">
- <heading>Run-time shared libraries</heading>
+ <p>
+ A shared library is identified by the <tt>SONAME</tt> attribute
+ stored in its dynamic section. When a binary is linked against a
+ shared library, the <tt>SONAME</tt> of the shared library is
+ recorded in the binary's <tt>NEEDED</tt> section so that the
+ dynamic linker knows that library must be loaded at runtime. The
+ shared library file's full name (which usually contains additional
+ version information not needed in the <tt>SONAME</tt>) is
+ therefore normally not referenced directly. Instead, the shared
+ library is loaded by its <tt>SONAME</tt>, which exists on the file
+ system as a symlink pointing to the full name of the shared
+ library. This symlink must be provided by the
+ package. <ref id="sharedlibs-runtime"> describes how to do this.
+ <footnote>
+ This is a convention of shared library versioning, but not a
+ requirement. Some libraries use the <tt>SONAME</tt> as the full
+ library file name instead and therefore do not need a symlink.
+ Most, however, encode additional information about
+ backwards-compatible revisions as a minor version number in the
+ file name. The <tt>SONAME</tt> itself only changes when
+ binaries linked with the earlier version of the shared library
+ may no longer work, but the filename may change with each
+ release of the library. See <ref id="sharedlibs-runtime"> for
+ more information.
+ </footnote>
+ </p>
<p>
- The run-time shared library needs to be placed in a package
- whose name changes whenever the shared object version
- changes.<footnote>
- <p>
- Since it is common place to install several versions of a
- package that just provides shared libraries, it is a
- good idea that the library package should not
- contain any extraneous non-versioned files, unless they
- happen to be in versioned directories.</p>
- </footnote>
- The most common mechanism is to place it in a package
- called
- <package><var>libraryname</var><var>soversion</var></package>,
- where <file><var>soversion</var></file> is the version number
- in the soname of the shared library<footnote>
- The soname is the shared object name: it's the thing
- that has to match exactly between building an executable
- and running it for the dynamic linker to be able run the
- program. For example, if the soname of the library is
- <file>libfoo.so.6</file>, the library package would be
- called <file>libfoo6</file>.
- </footnote>.
- Alternatively, if it would be confusing to directly append
- <var>soversion</var> to <var>libraryname</var> (e.g. because
- <var>libraryname</var> itself ends in a number), you may use
- <package><var>libraryname</var>-<var>soversion</var></package> and
- <package><var>libraryname</var>-<var>soversion</var>-dev</package>
- instead.
+ When linking a binary or another shared library against a shared
+ library, the <tt>SONAME</tt> for that shared library is not yet
+ known. Instead, the shared library is found by looking for a file
+ matching the library name with <tt>.so</tt> appended. This file
+ exists on the file system as a symlink pointing to the shared
+ library.
</p>
<p>
- If you have several shared libraries built from the same
- source tree you may lump them all together into a single
- shared library package, provided that you change all of
- their sonames at once (so that you don't get filename
- clashes if you try to install different versions of the
- combined shared libraries package).
+ Shared libraries are normally split into several binary packages.
+ The <tt>SONAME</tt> symlink is installed by the runtime shared
+ library package, and the bare <tt>.so</tt> symlink is installed in
+ the development package since it's only used when linking binaries
+ or shared libraries. However, there are some exceptions for
+ unusual shared libraries or for shared libraries that are also
+ loaded as dynamic modules by other programs.
</p>
+ <p>
+ This section is primarily concerned with how the separation of
+ shared libraries into multiple packages should be done and how
+ dependencies on and between shared library binary packages are
+ managed in Debian. <ref id="libraries"> should be read in
+ conjunction with this section and contains additional rules for
+ the files contained in the shared library packages.
+ </p>
+
+ <sect id="sharedlibs-runtime">
+ <heading>Run-time shared libraries</heading>
+
+ <p>
+ The run-time shared library must be placed in a package
+ whose name changes whenever the <tt>SONAME</tt> of the shared
+ library changes. This allows several versions of the shared
+ library to be installed at the same time, allowing installation
+ of the new version of the shared library without immediately
+ breaking binaries that depend on the old version. Normally, the
+ run-time shared library and its <tt>SONAME</tt> symlink should
+ be placed in a package named
+ <package><var>libraryname</var><var>soversion</var></package>,
+ where <var>soversion</var> is the version number in
+ the <tt>SONAME</tt> of the shared library.
+ See <ref id="shlibs"> for detailed information on how to
+ determine this version. Alternatively, if it would be confusing
+ to directly append <var>soversion</var>
+ to <var>libraryname</var> (if, for example, <var>libraryname</var>
+ itself ends in a number), you should use
+ <package><var>libraryname</var>-<var>soversion</var></package>
+ instead.
+ </p>
+
+ <p>
+ If you have several shared libraries built from the same source
+ tree, you may lump them all together into a single shared
+ library package provided that all of their <tt>SONAME</tt>s will
+ always change together. Be aware that this is not normally the
+ case, and if the <tt>SONAME</tt>s do not change together,
+ upgrading such a merged shared library package will be
+ unnecessarily difficult because of file conflicts with the old
+ version of the package. When in doubt, always split shared
+ library packages so that each binary package installs a single
+ shared library.
+ </p>
+
+ <p>
+ Every time the shared library ABI changes in a way that may
+ break binaries linked against older versions of the shared
+ library, the <tt>SONAME</tt> of the library and the
+ corresponding name for the binary package containing the runtime
+ shared library should change. Normally, this means
+ the <tt>SONAME</tt> should change any time an interface is
+ removed from the shared library or the signature of an interface
+ (the number of parameters or the types of parameters that it
+ takes, for example) is changed. This practice is vital to
+ allowing clean upgrades from older versions of the package and
+ clean transitions between the old ABI and new ABI without having
+ to upgrade every affected package simultaneously.
+ </p>
+
+ <p>
+ The <tt>SONAME</tt> and binary package name need not, and indeed
+ normally should not, change if new interfaces are added but none
+ are removed or changed, since this will not break binaries
+ linked against the old shared library. Correct versioning of
+ dependencies on the newer shared library by binaries that use
+ the new interfaces is handled via
+ the <qref id="sharedlibs-shlibdeps"><tt>shlibs</tt>
+ system</qref> or via symbols files (see
+ <manref name="deb-symbols" section="5">).
+ </p>
+
<p>
The package should install the shared libraries under
their normal names. For example, the <package>libgdbm3</package>
</p>
<p>
- The run-time library package should include the symbolic link that
- <prgn>ldconfig</prgn> would create for the shared libraries.
- For example, the <package>libgdbm3</package> package should include
- a symbolic link from <file>/usr/lib/libgdbm.so.3</file> to
+ The run-time library package should include the symbolic link for
+ the <tt>SONAME</tt> that <prgn>ldconfig</prgn> would create for
+ the shared libraries. For example,
+ the <package>libgdbm3</package> package should include a symbolic
+ link from <file>/usr/lib/libgdbm.so.3</file> to
<file>libgdbm.so.3.0.0</file>. This is needed so that the dynamic
linker (for example <prgn>ld.so</prgn> or
<prgn>ld-linux.so.*</prgn>) can find the library between the
<p>
When packages are being built,
any <file>debian/shlibs</file> files are copied into the
- control file area of the temporary build directory and
- given the name <file>shlibs</file>. These files give
- details of any shared libraries included in the same
- package.<footnote>
+ control information file area of the temporary build
+ directory and given the name <file>shlibs</file>. These
+ files give details of any shared libraries included in the
+ same package.<footnote>
An example may help here. Let us say that the source
package <tt>foo</tt> generates two binary
packages, <tt>libfoo2</tt> and <tt>foo-runtime</tt>.
It is usual to call this file <file>debian/shlibs</file> (but if
you have multiple binary packages, you might want to call it
<file>debian/shlibs.<var>package</var></file> instead). Then
- let <file>debian/rules</file> install it in the control area:
+ let <file>debian/rules</file> install it in the control
+ information file area:
<example compact="compact">
install -m644 debian/shlibs debian/tmp/DEBIAN
</example>
install -m644 debian/shlibs.<var>package</var> debian/<var>package</var>/DEBIAN/shlibs
</example>
An alternative way of doing this is to create the
- <file>shlibs</file> file in the control area directly from
- <file>debian/rules</file> without using a <file>debian/shlibs</file>
- file at all,<footnote>
+ <file>shlibs</file> file in the control information file area
+ directly from <file>debian/rules</file> without using
+ a <file>debian/shlibs</file> file at all,<footnote>
This is what <prgn>dh_makeshlibs</prgn> in
the <package>debhelper</package> suite does. If your package
also has a udeb that provides a shared
this so programs should not fail if <prgn>newaliases</prgn>
cannot be found. Note that because of this, all MTA
packages must have <tt>Provides</tt>, <tt>Conflicts</tt> and
- <tt>Replaces: mail-transport-agent</tt> control file
- fields.
+ <tt>Replaces: mail-transport-agent</tt> control fields.
</p>
<p>
<p>
Packages that provide an X server that, directly or
indirectly, communicates with real input and display
- hardware should declare in their control data that they
- provide the virtual package <tt>xserver</tt>.<footnote>
+ hardware should declare in their <tt>Provides</tt> control
+ field that they provide the virtual
+ package <tt>xserver</tt>.<footnote>
This implements current practice, and provides an
actual policy for usage of the <tt>xserver</tt>
virtual package which appears in the virtual packages
<p>
Packages that provide a terminal emulator for the X Window
- System which meet the criteria listed below should declare
- in their control data that they provide the virtual
- package <tt>x-terminal-emulator</tt>. They should also
- register themselves as an alternative for
+ System which meet the criteria listed below should declare in
+ their <tt>Provides</tt> control field that they provide the
+ virtual package <tt>x-terminal-emulator</tt>. They should
+ also register themselves as an alternative for
<file>/usr/bin/x-terminal-emulator</file>, with a priority of
20. That alternative should have a slave alternative
for <file>/usr/share/man/man1/x-terminal-emulator.1.gz</file>
<p>
Packages that provide a window manager should declare in
- their control data that they provide the virtual package
- <tt>x-window-manager</tt>. They should also register
- themselves as an alternative for
+ their <tt>Provides</tt> control field that they provide the
+ virtual package <tt>x-window-manager</tt>. They should also
+ register themselves as an alternative for
<file>/usr/bin/x-window-manager</file>, with a priority
calculated as follows:
<list compact="compact">
<item>
Font packages must declare a dependency on
- <tt>xfonts-utils</tt> in their control
- data.
+ <tt>xfonts-utils</tt> in their <tt>Depends</tt>
+ or <tt>Pre-Depends</tt> control field.
</item>
<item>
<p>
It is possible to put other files in the package control
- area, but this is not generally a good idea (though they
- will largely be ignored).
+ information file area, but this is not generally a good idea
+ (though they will largely be ignored).
</p>
<p>
- Here is a brief list of the control info files supported by
- <prgn>dpkg</prgn> and a summary of what they're used for.
+ Here is a brief list of the control information files supported
+
by <prgn>dpkg</prgn> and a summary of what they're used for.
</p>
<p>
<tag><tt>Package_Revision</tt></tag>
<item>
The Debian revision part of the package version was
- at one point in a separate control file field. This
+ at one point in a separate control field. This
field went through several names.
</item>
</heading>
<p>
- A package may contain a control area file called
+ A package may contain a control information file called
<tt>conffiles</tt>. This file should be a list of filenames
of configuration files needing automatic handling, separated
by newlines. The filenames should be absolute pathnames,
projects / debian / debian-policy.git / commitdiff