+ <tag><tt>Suggests</tt></tag>
+ <item>
+ This is used to declare that one package may be more
+ useful with one or more others. Using this field
+ tells the packaging system and the user that the
+ listed packages are related to this one and can
+ perhaps enhance its usefulness, but that installing
+ this one without them is perfectly reasonable.
+ </item>
+
+ <tag><tt>Enhances</tt></tag>
+ <item>
+ This field is similar to Suggests but works in the
+ opposite direction. It is used to declare that a
+ package can enhance the functionality of another
+ package.
+ </item>
+
+ <tag><tt>Pre-Depends</tt></tag>
+ <item>
+ <p>
+ This field is like <tt>Depends</tt>, except that it
+ also forces <prgn>dpkg</prgn> to complete installation
+ of the packages named before even starting the
+ installation of the package which declares the
+ pre-dependency, as follows:
+ </p>
+
+ <p>
+ When a package declaring a pre-dependency is about to
+ be <em>unpacked</em> the pre-dependency can be
+ satisfied if the depended-on package is either fully
+ configured, <em>or even if</em> the depended-on
+ package(s) are only unpacked or half-configured,
+ provided that they have been configured correctly at
+ some point in the past (and not removed or partially
+ removed since). In this case, both the
+ previously-configured and currently unpacked or
+ half-configured versions must satisfy any version
+ clause in the <tt>Pre-Depends</tt> field.
+ </p>
+
+ <p>
+ When the package declaring a pre-dependency is about
+ to be <em>configured</em>, the pre-dependency will be
+ treated as a normal <tt>Depends</tt>, that is, it will
+ be considered satisfied only if the depended-on
+ package has been correctly configured.
+ </p>
+
+ <p>
+ <tt>Pre-Depends</tt> should be used sparingly,
+ preferably only by packages whose premature upgrade or
+ installation would hamper the ability of the system to
+ continue with any upgrade that might be in progress.
+ </p>
+
+ <p>
+ <tt>Pre-Depends</tt> are also required if the
+ <prgn>preinst</prgn> script depends on the named
+ package. It is best to avoid this situation if
+ possible.
+ </p>
+ </item>
+ </taglist>
+ </p>
+
+ <p>
+ When selecting which level of dependency to use you should
+ consider how important the depended-on package is to the
+ functionality of the one declaring the dependency. Some
+ packages are composed of components of varying degrees of
+ importance. Such a package should list using
+ <tt>Depends</tt> the package(s) which are required by the
+ more important components. The other components'
+ requirements may be mentioned as Suggestions or
+ Recommendations, as appropriate to the components' relative
+ importance.
+ </p>
+ </sect>
+
+ <sect id="conflicts">
+ <heading>Conflicting binary packages - <tt>Conflicts</tt></heading>
+
+ <p>
+ When one binary package declares a conflict with another
+ using a <tt>Conflicts</tt> field, <prgn>dpkg</prgn> will
+ refuse to allow them to be installed on the system at the
+ same time.
+ </p>
+
+ <p>
+ If one package is to be installed, the other must be removed
+ first - if the package being installed is marked as
+ replacing (see <ref id="replaces">) the one on the system,
+ or the one on the system is marked as deselected, or both
+ packages are marked <tt>Essential</tt>, then
+ <prgn>dpkg</prgn> will automatically remove the package
+ which is causing the conflict, otherwise it will halt the
+ installation of the new package with an error. This
+ mechanism is specifically designed to produce an error when
+ the installed package is <tt>Essential</tt>, but the new
+ package is not.
+ </p>
+
+ <p>
+ A package will not cause a conflict merely because its
+ configuration files are still installed; it must be at least
+ half-installed.
+ </p>
+
+ <p>
+ A special exception is made for packages which declare a
+ conflict with their own package name, or with a virtual
+ package which they provide (see below): this does not
+ prevent their installation, and allows a package to conflict
+ with others providing a replacement for it. You use this
+ feature when you want the package in question to be the only
+ package providing some feature.
+ </p>
+
+ <p>
+ A <tt>Conflicts</tt> entry should almost never have an
+ "earlier than" version clause. This would prevent
+ <prgn>dpkg</prgn> from upgrading or installing the package
+ which declared such a conflict until the upgrade or removal
+ of the conflicted-with package had been completed.
+ </p>
+ </sect>
+
+ <sect id="virtual"><heading>Virtual packages - <tt>Provides</tt>
+ </heading>
+
+ <p>
+ As well as the names of actual ("concrete") packages, the
+ package relationship fields <tt>Depends</tt>,
+ <tt>Recommends</tt>, <tt>Suggests</tt>, <tt>Enhances</tt>,
+ <tt>Pre-Depends</tt>, <tt>Conflicts</tt>,
+ <tt>Build-Depends</tt>, <tt>Build-Depends-Indep</tt>,
+ <tt>Build-Conflicts</tt> and <tt>Build-Conflicts-Indep</tt>
+ may mention "virtual packages".
+ </p>
+
+ <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">)
+ </p>
+
+ <p>
+ If there are both concrete and virtual packages of the same
+ name, then the dependency may be satisfied (or the conflict
+ caused) by either the concrete package with the name in
+ question or any other concrete package which provides the
+ virtual package with the name in question. This is so that,
+ for example, supposing we have
+ <example compact="compact">
+Package: foo
+Depends: bar
+ </example>
+ and someone else releases an enhanced version of the
+ <tt>bar</tt> package (for example, a non-US variant), they
+ can say:
+ <example compact="compact">
+Package: bar-plus
+Provides: bar
+ </example>
+ and the <tt>bar-plus</tt> package will now also satisfy the
+ dependency for the <tt>foo</tt> package.
+ </p>
+
+ <p>
+ If a dependency or a conflict has a version number attached
+ then only real packages will be considered to see whether
+ the relationship is satisfied (or the prohibition violated,
+ for a conflict) - it is assumed that a real package which
+ provides the virtual package is not of the "right" version.
+ So, a <tt>Provides</tt> field may not contain version
+ numbers, and the version number of the concrete package
+ which provides a particular virtual package will not be
+ looked at when considering a dependency on or conflict with
+ the virtual package name.
+ </p>
+
+ <p>
+ It is likely that the ability will be added in a future
+ release of <prgn>dpkg</prgn> to specify a version number for
+ each virtual package it provides. This feature is not yet
+ present, however, and is expected to be used only
+ infrequently.
+ </p>
+
+ <p>
+ If you want to specify which of a set of real packages
+ should be the default to satisfy a particular dependency on
+ a virtual package, you should list the real package as an
+ alternative before the virtual one.
+ </p>
+ </sect>
+
+
+ <sect id="replaces"><heading>Overwriting files and replacing
+ packages - <tt>Replaces</tt></heading>
+
+ <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.
+ </p>
+
+ <sect1><heading>Overwriting files in other packages</heading>
+
+ <p>
+ Firstly, as mentioned before, it is usually an error for a
+ package to contain files which are on the system in
+ another package.
+ </p>
+
+ <p>
+ However, if the overwriting package declares that it
+ <tt>Replaces</tt> the one containing the file being
+ overwritten, then <prgn>dpkg</prgn> will replace the file
+ from the old package with that from the new. The file
+ will no longer be listed as "owned" by the old package.
+ </p>
+
+ <p>
+ If a package is completely replaced in this way, so that
+ <prgn>dpkg</prgn> does not know of any files it still
+ contains, it is considered to have "disappeared". It will
+ be marked as not wanted on the system (selected for
+ removal) and not installed. Any <tt>conffile</tt>s
+ details noted for the package will be ignored, as they
+ will have been taken over by the overwriting package. The
+ package's <prgn>postrm</prgn> script will be run with a
+ special argument to allow the package to do any final
+ cleanup required. See <ref id="mscriptsinstact">.
+ <footnote>
+ <p>
+ Replaces is a one way relationship -- you have to
+ install the replacing package after the replaced
+ package.
+ </p>
+ </footnote>
+ </p>
+
+ <p>
+ For this usage of <tt>Replaces</tt>, virtual packages (see
+ <ref id="virtual">) are not considered when looking at a
+ <tt>Replaces</tt> field - the packages declared as being
+ replaced must be mentioned by their real names.
+ </p>
+
+ <p>
+ Furthermore, this usage of <tt>Replaces</tt> only takes
+ effect when both packages are at least partially on the
+ system at once, so that it can only happen if they do not
+ conflict or if the conflict has been overridden.
+ </p>
+
+ </sect1>
+
+ <sect1><heading>Replacing whole packages, forcing their
+ removal</heading>
+
+ <p>
+ Secondly, <tt>Replaces</tt> allows the packaging system to
+ resolve which package should be removed when there is a
+ conflict - see <ref id="conflicts">. This usage only
+ takes effect when the two packages <em>do</em> conflict,
+ so that the two usages of this field do not interfere with
+ each other.
+ </p>
+
+ <p>
+ In this situation, the package declared as being replaced
+ can be a virtual package, so for example, all mail
+ transport agents (MTAs) would have the following fields in
+ their control files:
+ <example compact="compact">
+Provides: mail-transport-agent
+Conflicts: mail-transport-agent
+Replaces: mail-transport-agent
+ </example>
+ ensuring that only one MTA can be installed at any one
+ time.
+ </sect1>
+ </sect>
+
+ <sect id="sourcebinarydeps">
+ <heading>Relationships between source and binary packages -
+ <tt>Build-Depends</tt>, <tt>Build-Depends-Indep</tt>,
+ <tt>Build-Conflicts</tt>, <tt>Build-Conflicts-Indep</tt>
+ </heading>
+
+ <p>
+ Source packages that require certain binary packages to be
+ installed or absent at the time of building the package
+ can declare relationships to those binary packages.
+ </p>
+
+ <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.
+ </p>
+
+ <p>
+ Build-dependencies on "build-essential" binary packages can be
+ omitted. Please see <ref id="pkg-relations"> for more information.
+ </p>
+
+ <p>
+ The dependencies and conflicts they define must be satisfied
+ (as defined earlier for binary packages) in order to invoke
+ the targets in <tt>debian/rules</tt>, as follows:<footnote>
+ <p>
+ If you make "build-arch" or "binary-arch", you need
+ Build-Depends. If you make "build-indep" or
+ "binary-indep", you need Build-Depends and
+ Build-Depends-Indep. If you make "build" or "binary",
+ you need both.
+ </p>
+ <p>
+ There is no Build-Depends-Arch; the autobuilders will
+ only need the Build-Depends if they know how to build
+ only build-arch and binary-arch. Anyone building the
+ build-indep/binary-indep targets is basically assumed to
+ be building the whole package and so installs all build
+ dependencies.
+ </p>
+ <p>
+ The purpose of the original split, I recall, was so that
+ the autobuilders wouldn't need to install extra packages
+ needed only for the binary-indep targets. But without a
+ build-arch/build-indep split, this didn't work, since
+ most of the work is done in the build target, not in the
+ binary target.
+ </p>
+ </footnote>
+
+ <taglist>
+ <tag><tt>Build-Depends</tt>, <tt>Build-Conflicts</tt></tag>
+ <item>
+ The <tt>Build-Depends</tt> and
+ <tt>Build-Conflicts</tt> fields must be satisfied when
+ any of the following targets is invoked:
+ <tt>build</tt>, <tt>clean</tt>, <tt>binary</tt>,
+ <tt>binary-arch</tt>, <tt>build-arch</tt>,
+ <tt>build-indep</tt> and <tt>binary-indep</tt>.
+ </item>
+ <tag><tt>Build-Depends-Indep</tt>,
+ <tt>Build-Conflicts-Indep</tt></tag>
+ <item>
+ The <tt>Build-Depends-Indep</tt> and
+ <tt>Build-Conflicts-Indep</tt> fields must be
+ satisfied when any of the following targets is
+ invoked: <tt>build</tt>, <tt>build-indep</tt>,
+ <tt>binary</tt> and <tt>binary-indep</tt>.
+ </item>
+ </taglist>
+ </p>
+
+ </sect>
+
+ </chapt>
+
+
+ <chapt id="sharedlibs"><heading>Shared libraries</heading>
+
+ <p>
+ Packages containing shared libraries must be constructed with
+ a little care to make sure that the shared library is always
+ available. This is especially important for packages whose
+ shared libraries are vitally important, such as the C library
+ (currently <tt>libc6</tt>).
+ </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.
+ </p>
+
+ <sect id="sharedlibs-runtime">
+ <heading>Run-time shared libraries</heading>
+
+ <p>
+ The run-time shared library needs to be placed 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.
+ </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).
+ </p>
+
+ <p>
+ The package should install the shared libraries under
+ their normal names. For example, the <package>libgdbm3</package>
+ package should install <file>libgdbm.so.3.0.0</file> as
+ <file>/usr/lib/libgdbm.so.3.0.0</file>. The files should not be
+ renamed or re-linked by any <prgn>prerm</prgn> or
+ <prgn>postrm</prgn> scripts; <prgn>dpkg</prgn> will take care
+ of renaming things safely without affecting running programs,
+ and attempts to interfere with this are likely to lead to
+ problems.
+ </p>
+
+ <p>
+ Shared libraries should not be installed executable, since
+ the dynamic linker does not require this and trying to
+ execute a shared library usually results in a core dump.
+ </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
+ <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
+ time that <prgn>dpkg</prgn> installs it and the time that
+ <prgn>ldconfig</prgn> is run in the <prgn>postinst</prgn>
+ script.<footnote>
+ The package management system requires the library to be
+ placed before the symbolic link pointing to it in the
+ <file>.deb</file> file. This is so that when
+ <prgn>dpkg</prgn> comes to install the symlink
+ (overwriting the previous symlink pointing at an older
+ version of the library), the new shared library is already
+ in place. In the past, this was achieved by creating the
+ library in the temporary packaging directory before
+ creating the symlink. Unfortunately, this was not always
+ effective, since the building of the tar file in the
+ <file>.deb</file> depended on the behavior of the underlying
+ file system. Some file systems (such as reiserfs) reorder
+ the files so that the order of creation is forgotten.
+ Since version 1.7.0, <prgn>dpkg</prgn>
+ reorders the files itself as necessary when building a
+ package. Thus it is no longer important to concern
+ oneself with the order of file creation.
+ </footnote>
+ </p>
+
+ <sect1 id="ldconfig">
+ <heading><tt>ldconfig</tt></heading>
+
+ <p>
+ Any package installing shared libraries in one of the default
+ library directories of the dynamic linker (which are currently
+ <file>/usr/lib</file> and <file>/lib</file>) or a directory that is
+ listed in <file>/etc/ld.so.conf</file><footnote>
+ These are currently
+ <list compact="compact">
+ <item>/usr/X11R6/lib/Xaw3d</item>
+ <item>/usr/local/lib</item>
+ <item>/usr/lib/libc5-compat</item>
+ <item>/lib/libc5-compat</item>
+ <item>/usr/X11R6/lib</item>
+ </list>
+ </footnote>
+ must use <prgn>ldconfig</prgn> to update the shared library
+ system.
+ </p>
+
+ <p>
+ The package must call <prgn>ldconfig</prgn> in the
+ <prgn>postinst</prgn> script if the first argument is
+ <tt>configure</tt>; the <prgn>postinst</prgn> script may
+ optionally invoke <prgn>ldconfig</prgn> at other times. The
+ package should call <prgn>ldconfig</prgn> in the
+ <prgn>postrm</prgn> script if the first argument is
+ <tt>remove</tt>. The maintainer scripts must not invoke
+ <prgn>ldconfig</prgn> under any circumstances other than those
+ described in this paragraph.<footnote>
+ <p>
+ During install or upgrade, the preinst is called before
+ the new files are installed, so calling "ldconfig" is
+ pointless. The preinst of an existing package can also be
+ called if an upgrade fails. However, this happens during
+ the critical time when a shared libs may exist on-disk
+ under a temporary name. Thus, it is dangerous and
+ forbidden by current policy to call "ldconfig" at this
+ time.
+ </p>
+
+ <p>
+ When a package is installed or upgraded, "postinst
+ configure" runs after the new files are safely on-disk.
+ Since it is perfectly safe to invoke ldconfig
+ unconditionally in a postinst, it is OK for a package to
+ simply put ldconfig in its postinst without checking the
+ argument. The postinst can also be called to recover from
+ a failed upgrade. This happens before any new files are
+ unpacked, so there is no reason to call "ldconfig" at this
+ point.
+ </p>
+
+ <p>
+ For a package that is being removed, prerm is
+ called with all the files intact, so calling ldconfig is
+ useless. The other calls to "prerm" happen in the case of
+ upgrade at a time when all the files of the old package
+ are on-disk, so again calling "ldconfig" is pointless.
+ </p>
+
+ <p>
+ postrm, on the other hand, is called with the "remove"
+ argument just after the files are removed, so this is the
+ proper time to call "ldconfig" to notify the system of the
+ fact shared libraries from the package are removed.
+ The postrm can be called at several other times. At the
+ time of "postrm purge", "postrm abort-install", or "postrm
+ abort-upgrade", calling "ldconfig" is useless because the
+ shared lib files are not on-disk. However, when "postrm"
+ is invoked with arguments "upgrade", "failed-upgrade", or
+ "disappear", a shared lib may exist on-disk under a
+ temporary filename.
+ </p>
+ </footnote>
+ </p>
+ </sect1>
+
+ </sect>
+
+ <sect id="sharedlibs-runtime-progs">
+ <heading>Run-time support programs</heading>
+
+ <p>
+ If your package has some run-time support programs which use
+ the shared library you must not put them in the shared
+ library package. If you do that then you won't be able to
+ install several versions of the shared library without
+ getting filename clashes.
+ </p>
+
+ <p>
+ Instead, either create another package for the runtime binaries
+ (this package might typically be named
+ <package><var>libraryname</var>-runtime</package>; note the absence
+ of the <var>soversion</var> in the package name), or if the
+ development package is small, include them in there.
+ </p>
+ </sect>
+
+ <sect id="sharedlibs-static">
+ <heading>Static libraries</heading>
+
+ <p>
+ The static library (<file><var>libraryname.a</var></file>)
+ is usually provided in addition to the shared version.
+ It is placed into the development package (see below).
+ </p>
+
+ <p>
+ In some cases, it is acceptable for a library to be
+ available in static form only; these cases include:
+ <list>
+ <item>libraries for languages whose shared library support
+ is immature or unstable</item>
+ <item>libraries whose interfaces are in flux or under
+ development (commonly the case when the library's
+ major version number is zero, or where the ABI breaks
+ across patchlevels)</item>
+ <item>libraries which are explicitly intended to be
+ available only in static form by their upstream
+ author(s)</item>
+ </list>
+ </p>
+
+ <sect id="sharedlibs-dev">
+ <heading>Development files</heading>
+
+ <p>
+ The development files associated to a shared library need to be
+ placed in a package called
+ <package><var>libraryname</var><var>soversion</var>-dev</package>,
+ or if you prefer only to support one development version at a
+ time, <package><var>libraryname</var>-dev</package>.
+ </p>
+
+ <p>
+ In case several development versions of a library exist, you may
+ need to use <prgn>dpkg</prgn>'s Conflicts mechanism (see
+ <ref id="conflicts">) to ensure that the user only installs one
+ development version at a time (as different development versions are
+ likely to have the same header files in them, which would cause a
+ filename clash if both were installed).
+ </p>
+
+ <p>
+ The development package should contain a symlink for the associated
+ shared library without a version number. For example, the
+ <package>libgdbm-dev</package> package should include a symlink
+ from <file>/usr/lib/libgdbm.so</file> to
+ <file>libgdbm.so.3.0.0</file>. This symlink is needed by the linker
+ (<prgn>ld</prgn>) when compiling packages, as it will only look for
+ <file>libgdbm.so</file> when compiling dynamically.
+ </p>
+ </sect>
+
+ <sect id="sharedlibs-intradeps">
+ <heading>Dependencies between the packages of the same library</heading>
+
+ <p>
+ Typically the development version should have an exact
+ version dependency on the runtime library, to make sure that
+ compilation and linking happens correctly. The
+ <tt>${Source-Version}</tt> substitution variable can be
+ useful for this purpose.
+ </p>
+ </sect>
+
+ <sect id="sharedlibs-shlibdeps">
+ <heading>Dependencies between the library and other packages -
+ the <tt>shlibs</tt> system</heading>
+
+ <p>
+ If a package contains a binary or library which links to a
+ shared library, we must ensure that when the package is
+ installed on the system, all of the libraries needed are
+ also installed. This requirement led to the creation of the
+ <tt>shlibs</tt> system, which is very simple in its design:
+ any package which <em>provides</em> a shared library also
+ provides information on the package dependencies required to
+ ensure the presence of this library, and any package which
+ <em>uses</em> a shared library uses this information to
+ determine the dependencies it requires. The files which
+ contain the mapping from shared libraries to the necessary
+ dependency information are called <file>shlibs</file> files.
+ </p>
+
+ <p>
+ Thus, when a package is built which contains any shared
+ libraries, it must provide a <file>shlibs</file> file for other
+ packages to use, and when a package is built which contains
+ any shared libraries or compiled binaries, it must run
+ <prgn>dpkg-shlibdeps</prgn> on these to determine the
+ libraries used and hence the dependencies needed by this
+ package.<footnote>
+ <p>
+ In the past, the shared libraries linked to were
+ determined by calling <prgn>ldd</prgn>, but now
+ <prgn>objdump</prgn> is used to do this. The only
+ change this makes to package building is that
+ <prgn>dpkg-shlibdeps</prgn> must also be run on shared
+ libraries, whereas in the past this was unnecessary.
+ The rest of this footnote explains the advantage that
+ this method gives.
+ </p>
+
+ <p>
+ We say that a binary <tt>foo</tt> <em>directly</em> uses
+ a library <tt>libbar</tt> if it is explicitly linked
+ with that library (that is, it uses the flag
+ <tt>-lbar</tt> during the linking stage). Other
+ libraries that are needed by <tt>libbar</tt> are linked
+ <em>indirectly</em> to <tt>foo</tt>, and the dynamic
+ linker will load them automatically when it loads
+ <tt>libbar</tt>. A package should depend on
+ the libraries it directly uses, and the dependencies for
+ those libraries should automatically pull in the other
+ libraries.
+ </p>
+
+ <p>
+ Unfortunately, the <prgn>ldd</prgn> program shows both
+ the directly and indirectly used libraries, meaning that
+ the dependencies determined included both direct and
+ indirect dependencies. The use of <prgn>objdump</prgn>
+ avoids this problem by determining only the directly
+ used libraries.
+ </p>
+
+ <p>
+ A good example of where this helps is the following. We
+ could update <tt>libimlib</tt> with a new version that
+ supports a new graphics format called dgf (but retaining
+ the same major version number). If we used the old
+ <prgn>ldd</prgn> method, every package that uses
+ <tt>libimlib</tt> would need to be recompiled so it
+ would also depend on <tt>libdgf</tt> or it wouldn't run
+ due to missing symbols. However with the new system,
+ packages using <tt>libimlib</tt> can rely on
+ <tt>libimlib</tt> itself having the dependency on
+ <tt>libdgf</tt> and so they would not need rebuilding.
+ </p>
+ </footnote>
+ </p>
+
+ <p>
+ In the following sections, we will first describe where the
+ various <tt>shlibs</tt> files are to be found, then how to
+ use <prgn>dpkg-shlibdeps</prgn>, and finally the
+ <tt>shlibs</tt> file format and how to create them if your
+ package contains a shared library.
+ </p>
+
+ <sect1>
+ <heading>The <tt>shlibs</tt> files present on the system</heading>
+
+ <p>
+ There are several places where <tt>shlibs</tt> files are
+ found. The following list gives them in the order in which
+ they are read by <prgn>dpkg-shlibdeps</prgn>. (The first
+ one which gives the required information is used.)
+ </p>
+
+ <p>
+ <list>
+ <item>
+ <p><file>debian/shlibs.local</file></p>
+
+ <p>
+ This lists overrides for this package. Its use is
+ described below (see <ref id="shlibslocal">).
+ </p>
+ </item>
+
+ <item>
+ <p><file>/etc/dpkg/shlibs.override</file></p>
+
+ <p>
+ This lists global overrides. This list is normally
+ empty. It is maintained by the local system
+ administrator.
+ </p>
+ </item>
+
+ <item>
+ <p><file>DEBIAN/shlibs</file> files in the "build directory"</p>
+
+ <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
+ 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>. When building the binary
+ packages, the two packages are created in the
+ directories <file>debian/libfoo2</file> and
+ <file>debian/foo-runtime</file> respectively.
+ (<file>debian/tmp</file> could be used instead of one
+ of these.) Since <tt>libfoo2</tt> provides the
+ <tt>libfoo</tt> shared library, it will require a
+ <tt>shlibs</tt> file, which will be installed in
+ <file>debian/libfoo2/DEBIAN/shlibs</file>, eventually
+ to become
+ <file>/var/lib/dpkg/info/libfoo2.shlibs</file>. Then
+ when <prgn>dpkg-shlibdeps</prgn> is run on the
+ executable
+ <file>debian/foo-runtime/usr/bin/foo-prog</file>, it
+ will examine the
+ <file>debian/libfoo2/DEBIAN/shlibs</file> file to
+ determine whether <tt>foo-prog</tt>'s library
+ dependencies are satisfied by any of the libraries
+ provided by <tt>libfoo2</tt>. For this reason,
+ <prgn>dpkg-shlibdeps</prgn> must only be run once
+ all of the individual binary packages'
+ <tt>shlibs</tt> files have been installed into the
+ build directory.
+ </footnote>
+ </p>
+ </item>
+
+ <item>
+ <p><file>/var/lib/dpkg/info/*.shlibs</file></p>
+
+ <p>
+ These are the <file>shlibs</file> files corresponding to
+ all of the packages installed on the system, and are
+ maintained by the relevant package maintainers.
+ </p>
+ </item>
+
+ <item>
+ <p><file>/etc/dpkg/shlibs.default</file></p>
+
+ <p>
+ This file lists any shared libraries whose packages
+ have failed to provide correct <file>shlibs</file> files.
+ It was used when the <file>shlibs</file> setup was first
+ introduced, but it is now normally empty. It is
+ maintained by the <tt>dpkg</tt> maintainer.
+ </p>
+ </item>
+ </list>
+ </p>
+ </sect1>
+
+ <sect1>
+ <heading>How to use <prgn>dpkg-shlibdeps</prgn> and the
+ <file>shlibs</file> files</heading>
+
+ <p>
+ Put a call to <prgn>dpkg-shlibdeps</prgn> into your
+ <file>debian/rules</file> file. If your package contains only
+ compiled binaries and libraries (but no scripts), you can
+ use a command such as:
+ <example compact="compact">
+dpkg-shlibdeps debian/tmp/usr/bin/* debian/tmp/usr/sbin/* \
+ debian/tmp/usr/lib/*
+ </example>
+ Otherwise, you will need to explicitly list the compiled
+ binaries and libraries.<footnote>
+ If you are using <tt>debhelper</tt>, the
+ <prgn>dh_shlibdeps</prgn> program will do this work for
+ you. It will also correctly handle multi-binary
+ packages.
+ </footnote>
+ </p>
+
+ <p>
+ This command puts the dependency information into the
+ <file>debian/substvars</file> file, which is then used by
+ <prgn>dpkg-gencontrol</prgn>. You will need to place a
+ <tt>${shlib:Depends}</tt> variable in the <tt>Depends</tt>
+ field in the control file for this to work.
+ </p>
+
+ <p>
+ If <prgn>dpkg-shlibdeps</prgn> doesn't complain, you're
+ done. If it does complain you might need to create your own
+ <file>debian/shlibs.local</file> file, as explained below (see
+ <ref id="shlibslocal">).
+ </p>
+
+ <p>
+ If you have multiple binary packages, you will need to call
+ <prgn>dpkg-shlibdeps</prgn> on each one which contains
+ compiled libraries or binaries. In such a case, you will
+ need to use the <tt>-T</tt> option to the <tt>dpkg</tt>
+ utilities to specify a different <file>substvars</file> file.
+ For more details on this and other options, see <manref
+ name="dpkg-shlibdeps" section="1">.
+ </p>
+ </sect1>
+
+ <sect1 id="shlibs">
+ <heading>The <file>shlibs</file> File Format</heading>
+
+ <p>
+ Each <file>shlibs</file> file has the same format. Lines
+ beginning with <tt>#</tt> are considered to be comments and
+ are ignored. Each line is of the form:
+ <example compact="compact">
+<var>library-name</var> <var>soname-version-number</var> <var>dependencies ...</var>
+ </example>
+ </p>
+
+ <p>
+ We will explain this by reference to the example of the
+ <tt>zlib1g</tt> package, which (at the time of writing)
+ installs the shared library <file>/usr/lib/libz.so.1.1.3</file>.
+ </p>
+
+ <p>
+ <var>library-name</var> is the name of the shared library,
+ in this case <tt>libz</tt>. (This must match the name part
+ of the soname, see below.)
+ </p>
+
+ <p>
+ <var>soname-version-number</var> is the version part of the
+ soname of the library. The soname is the thing that must
+ exactly match for the library to be recognized by the
+ dynamic linker, and is usually of the form
+ <tt><var>name</var>.so.<var>major-version</var></tt>, in our
+ example, <tt>libz.so.1</tt>.<footnote>
+ This can be determined using the command
+ <example compact="compact">
+objdump -p /usr/lib/libz.so.1.1.3 | grep SONAME
+ </example>
+ </footnote>
+ The version part is the part which comes after
+ <tt>.so.</tt>, so in our case, it is <tt>1</tt>.
+ </p>
+
+ <p>
+ <var>dependencies</var> has the same syntax as a dependency
+ field in a binary package control file. It should give
+ details of which packages are required to satisfy a binary
+ built against the version of the library contained in the
+ package. See <ref id="depsyntax"> for details.
+ </p>
+
+ <p>
+ In our example, if the first version of the <tt>zlib1g</tt>
+ package which contained a minor number of at least
+ <tt>1.3</tt> was <var>1:1.1.3-1</var>, then the
+ <tt>shlibs</tt> entry for this library could say:
+ <example compact="compact">
+libz 1 zlib1g (>= 1:1.1.3)
+ </example>
+ The version-specific dependency is to avoid warnings from
+ the dynamic linker about using older shared libraries with
+ newer binaries.
+ </p>
+ </sect1>
+
+ <sect1>
+ <heading>Providing a <file>shlibs</file> file</heading>
+
+ <p>
+ If your package provides a shared library, you should create
+ a <file>shlibs</file> file following the format described above.
+ 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:
+ <example compact="compact">
+install -m644 debian/shlibs debian/tmp/DEBIAN
+ </example>
+ or, in the case of a multi-binary package:
+ <example compact="compact">
+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>
+ This is what <prgn>dh_makeshlibs</prgn> in the
+ <tt>debhelper</tt> suite does.
+ </footnote>
+ since the <file>debian/shlibs</file> file itself is ignored by
+ <prgn>dpkg-shlibdeps</prgn>.
+ </p>
+
+ <p>
+ As <prgn>dpkg-shlibdeps</prgn> reads the
+ <file>DEBIAN/shlibs</file> files in all of the binary packages
+ being built from this source package, all of the
+ <file>DEBIAN/shlibs</file> files should be installed before
+ <prgn>dpkg-shlibdeps</prgn> is called on any of the binary
+ packages.
+ </p>
+ </sect1>
+
+ <sect1 id="shlibslocal">
+ <heading>Writing the <file>debian/shlibs.local</file> file</heading>
+
+ <p>
+ This file is intended only as a <em>temporary</em> fix if
+ your binaries or libraries depend on a library whose package
+ does not yet provide a correct <file>shlibs</file> file.
+ </p>
+
+ <p>
+ We will assume that you are trying to package a binary
+ <tt>foo</tt>. When you try running
+ <prgn>dpkg-shlibdeps</prgn> you get the following error
+ message (<tt>-O</tt> displays the dependency information on
+ <tt>stdout</tt> instead of writing it to
+ <tt>debian/substvars</tt>, and the lines have been wrapped
+ for ease of reading):
+ <example compact="compact">
+$ dpkg-shlibdeps -O debian/tmp/usr/bin/foo
+dpkg-shlibdeps: warning: unable to find dependency
+ information for shared library libbar (soname 1,
+ path /usr/lib/libbar.so.1, dependency field Depends)
+shlibs:Depends=libc6 (>= 2.2.2-2)
+ </example>
+ You can then run <prgn>ldd</prgn> on the binary to find the
+ full location of the library concerned:
+ <example compact="compact">
+$ ldd foo
+libbar.so.1 => /usr/lib/libbar.so.1 (0x4001e000)
+libc.so.6 => /lib/libc.so.6 (0x40032000)
+/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)
+ </example>
+ So the <prgn>foo</prgn> binary depends on the
+ <prgn>libbar</prgn> shared library, but no package seems to
+ provide a <file>*.shlibs</file> file handling
+ <file>libbar.so.1</file> in <file>/var/lib/dpkg/info/</file>. Let's
+ determine the package responsible:
+ <example compact="compact">
+$ dpkg -S /usr/lib/libbar.so.1
+bar1: /usr/lib/libbar.so.1
+$ dpkg -s bar1 | grep Version
+Version: 1.0-1
+ </example>
+ This tells us that the <tt>bar1</tt> package, version 1.0-1,
+ is the one we are using. Now we can file a bug against the
+ <tt>bar1</tt> package and create our own
+ <file>debian/shlibs.local</file> to locally fix the problem.
+ Including the following line into your
+ <file>debian/shlibs.local</file> file:
+ <example compact="compact">
+libbar 1 bar1 (>= 1.0-1)
+ </example>
+ should allow the package build to work.
+ </p>
+
+ <p>
+ As soon as the maintainer of <tt>bar1</tt> provides a
+ correct <file>shlibs</file> file, you should remove this line
+ from your <file>debian/shlibs.local</file> file. (You should
+ probably also then have a versioned <tt>Build-Depends</tt>
+ on <tt>bar1</tt> to help ensure that others do not have the
+ same problem building your package.)
+ </p>
+ </sect1>
+
+ </sect>
+
+ </chapt>
+
+
+ <chapt id="opersys"><heading>The Operating System</heading>
+
+ <sect>
+ <heading>Filesystem hierarchy</heading>
+
+
+ <sect1 id="fhs">
+ <heading>Filesystem Structure</heading>
+
+ <p>
+ The location of all installed files and directories must
+ comply with the Filesystem Hierarchy Standard (FHS),
+ version 2.1, except where doing so would violate other
+ terms of Debian Policy. The version of this document
+ referred here can be found in the <tt>debian-policy</tt>
+ package or on
+ <url id="http://www.debian.org/doc/packaging-manuals/fhs/"
+ name="FHS (Debian copy)"> alongside this manual (or, if
+ you have the <package>debian-policy</package> installed,
+ you can try <url
+ id="file:///usr/share/doc/debian-policy/fhs/" name="FHS
+ (local copy)">). The
+ latest version, which may be a more recent version, may
+ be found on
+ <url id="http://www.pathname.com/fhs/" name="FHS (upstream)">.
+ Specific questions about following the standard may be
+ asked on the <tt>debian-devel</tt> mailing list, or
+ referred to the FHS mailing list (see the
+ <url id="http://www.pathname.com/fhs/" name="FHS web site"> for
+ more information).
+ </p>