* Add "links" to Build-Depends list

[debian/debian-policy.git] / policy.sgml

<!doctype debiandoc system [
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<debiandoc>
  <!--
  Debian GNU/Linux Policy Manual.
  Copyright (C)1996,1997,1998 Ian Jackson and Christian Schwarz;
  released under the terms of the GNU
  General Public License, version 2 or (at your option) any later.
  Initial version 1996, Ian Jackson, ijackson@gnu.ai.mit.edu
  Revised November 27, 1996, David A. Morris, bweaver@debian.org
  New sections March 15, 1997, Christian Schwarz, schwarz@debian.org
  Reworked/Restructured April-July 1997, Christian Schwarz, schwarz@debian.org
  Maintainer since 1997, Christian Schwarz, schwarz@debian.org
  Christoph Lameter contributed the "Web Standard"
  The debian-policy mailing list has taken responsibility for the
  contents of this document since September 1998, with the package
  maintainers responsible for packaging administrivia only.
  -->

  <book>
    <titlepag>
      <title>Debian Policy Manual</title>
      <author>
        <name>Ian Jackson </name>
        <email>ijackson@gnu.ai.mit.edu</email>
      </author>
      <author>
        <name>Christian Schwarz</name>
        <email>schwarz@debian.org</email>
      </author>
      <author>
        <name>revised: David A. Morris</name>
        <email>bweaver@debian.org</email>
      </author>
      <author>
        <name>The Debian Policy mailing List</name>
        <email>debian-policy@lists.debian.org</email>
      </author>
      <version>version &version;, &date;</version>

      <abstract>
        This manual describes the policy requirements for the Debian
        GNU/Linux distribution. This includes the structure and
        contents of the Debian archive, several design issues of the
        operating system, as well as technical requirements that each
        package must satisfy to be included in the distribution. The
        policy package itself is maintained by a group of maintainers
        that have no editorial powers. At the moment, the list of
        maintainers is:
        <enumlist>
          <item>
            <p>Michael Alan Dorman <email>mdorman@debian.org</email></p>
          </item>
          <item>
            <p>Philip Hands <email>phil@hands.com</email></p>
          </item>
          <item>
            <p>Julian Gilbey <email>J.D.Gilbey@qmw.ac.uk</email></p>
          </item>
          <item>
            <p>Manoj Srivastava <email>srivasta@debian.org</email></p>
          </item>
        </enumlist>
      </abstract>


      <copyright>
        <copyrightsummary>
          Copyright &copy;1996,1997,1998 Ian Jackson
          and Christian Schwarz.
        </copyrightsummary>
        <p>
          This manual is free software; you may 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, or (at your option) any later version.
        </p>

        <p>
          This is distributed in the hope that it will be useful, but
          <em>without any warranty</em>; without even the implied
          warranty of merchantability or fitness for a particular
          purpose.  See the GNU General Public License for more
          details.
        </p>

        <p>
          A copy of the GNU General Public License is available as
          <tt>/usr/share/common-licences/GPL</tt> in the Debian GNU/Linux
          distribution or on the World Wide Web at
          <url id="http://www.gnu.org/copyleft/gpl.html"
               name="The GNU Public Licence">. You can also obtain it by writing to the
          Free Software Foundation, Inc., 59 Temple Place - Suite 330,
          Boston, MA 02111-1307, USA.
        </p>
      </copyright>
    </titlepag>

    <toc detail="sect">

    <chapt id="scope">
      <heading>About this manual</heading>
      <sect>
        <heading>Scope</heading>
        <p>
          This manual describes the policy requirements for the Debian
          GNU/Linux distribution. This includes the structure and
          contents of the Debian archive, several design issues of the
          operating system, as well as technical requirements that
          each package must satisfy to be included in the
          distribution.
        </p>


        <p>
          This manual also describes Debian policy as it relates to
          creating Debian packages. It is not a tutorial on how to build
          packages, nor is it exhaustive where it comes to describing
          the behavior of the packaging system. Instead, this manual
          attempts to define the interface to the package management
          system that the developers have to be conversant with.
          <footnote>
            <p>
              Informally, the criteria used for inclusion is that the
              material meet one of the following requirements:
              <taglist>
                <tag>Standard interfaces</tag>
                <item>
                  <p>
                    The material presented represents an interface to
                    the packaging system that is mandated for use, and
                    is used by, a significant number of packages, and
                    should not be changed without peer review. Package
                    maintainers can then rely on this interfaces not
                    changing, and the package management software
                    authors need to ensure compatibility with these
                    interface definitions. (control file and and
                    changelog file formats are one example)
                  </p>
                </item>
                <tag>Chosen Convention</tag>
                <item>
                  <p>
                    If there are a number of technically viable choices
                    that can be made, but one needs to select one of
                    these options for inter-operability. The version
                    number format is one example.
                  </p>
                </item>
              </taglist>
              Please note that these are not mutually exclusive;
              selected conventions often become parts of standard
              interfaces.
            </p>
          </footnote>
        </p>

        <p>
          Please note that the footnotes present in this manual are
          merely informative, and are not part of Debian policy itself.
        </p>


        <p>
          In this manual, the words <em>must</em>, <em>should</em> and
          <em>may</em>, and the adjectives <em>required</em>,
          <em>recommended</em> and <em>optional</em>, are used to
          distinguish the significance of the various guidelines in
          this policy document. Packages that do not conform the the
          guidelines denoted by <em>must</em> (or <em>required</em>)
          will generally not be considered acceptable for the Debian
          distribution. Non-conformance with guidelines denoted by
          <em>should</em> (or <em>recommended</em>) will generally be
          considered a bug, but will not necessarily render a package
          unsuitable for distribution. Guidelines denoted by
          <em>may</em> (or <em>optional</em>) are truly optional and
          adherence is left to the maintainer's discretion.
        </p>
        <p>
          These classifications are roughly equivalent to the bug
          severities <em>important</em> (for <em>must</em> or
          <em>required</em> directive violations), <em>normal</em>
          (for <em>should</em> or <em>recommended</em> directive
          violations) and <em>wishlist</em> (for <em>optional</em>
          items). <footnote>
            <p>Also see RFC 2119.</p>
          </footnote>
        </p>
        <p>
          Much of the information presented in this manual will be
          useful even when building a package which is to be
          distributed in some other way or is for local use.
        </p>
      </sect>
      <sect>
        <heading>New versions of this document</heading>
        <p>
          The current version of this document is always accessible from the
          Debian FTP server <ftpsite>ftp.debian.org</ftpsite> at
          <ftppath>/debian/doc/package-developer/debian-policy.html.tar.gz</ftppath>
          or from the Debian WWW server at
          <url id="http://www.debian.org/doc/debian-policy/"
               name="The Debian Policy Manual">.</p>

        <p>
          In addition, this manual is distributed via the Debian package
          <tt>debian-policy</tt>.
        </p>
      </sect>
      <sect>
        <heading>Feedback</heading>

        <p>
          As the Debian GNU/Linux system is continuously evolving this
          manual is changed from time to time.
        </p>
        <p>
          While the authors of this document tried hard not to include
          any typos or other errors these still occur. If you discover
          an error in this manual or if you want to tell us any
          comments, suggestions, or critics please send an email to
          the Debian Policy List,
          <email>debian-policy@lists.debian.org</email>, or submit a
          bug report against the <tt>debian-policy</tt> package.
        </p>
      </sect>
    </chapt>
    <chapt>
      <heading>The Debian Archive</heading>
      <p>
        The Debian GNU/Linux system is maintained and distributed as a
        collection of <em>packages</em>. Since there are so many of them (over
        5000) they are split into <em>sections</em> and <em>priorities</em> to
        simplify handling of them.
      </p>
      <p>
        The effort of the Debian project is to build a free operating
        system, but not every package we want to make accessible is
        <em>free</em> in our sense (see Debian Free Software
        Guidelines, below), or may be imported/exported without
        restrictions. Thus, the archive is split into the sections
        <em>main</em>, <em>non-free</em>, <em>contrib</em>,
        <em>non-US/main</em>, <em>non-US/non-free</em>, and
        <em>non-US/contrib</em>.</p>

      <p>
        The <em>main</em> and the <em>non-US/main</em> sections form
        the <em>Debian GNU/Linux distribution</em>.
      </p>

      <p>
        Packages in the other sections are not considered as part of
        the Debian distribution, though we support their use, and we
        provide infrastructure for them (such as our bug-tracking
        system and mailing lists). This Debian Policy Manual applies
        to these packages as well.</p>

      <sect id="pkgcopyright">
        <heading>Package copyright and sections</heading>
        <p>
          The aims of this policy are:

          <list compact="compact">
            <item>
              <p>We want to make as much software available as we
                can.</p>
            </item>
            <item>
              <p>We want to encourage everyone to write free software.</p>
            </item>
            <item>
              <p> We want to make it easy for people to produce
                CD-ROMs of our system without violating any licenses,
                import/export restrictions, or any other laws.</p>
            </item>
          </list>
        </p>
        <sect1>
          <heading>The Debian Free Software Guidelines</heading>
          <p>
            The Debian Free Software Guidelines (DFSG) is our
            definition of `free' software.
            <taglist>
              <tag>Free Redistribution
              </tag>
              <item>
                <p>
                  The license of a Debian component may not restrict any
                  party from selling or giving away the software as a
                  component of an aggregate software distribution
                  containing programs from several different
                  sources. The license may not require a royalty or
                  other fee for such sale.
                </p>
              </item>
              <tag>Source Code
              </tag>
              <item>
                <p>
                  The program must include source code, and must allow
                  distribution in source code as well as compiled form.
                </p>
              </item>
              <tag>Derived Works
              </tag>
              <item>
                <p>
                  The license must allow modifications and derived
                  works, and must allow them to be distributed under the
                  same terms as the license of the original software.
                </p>
              </item>
              <tag>Integrity of The Author's Source Code
              </tag>
              <item>
                <p>
                  The license may restrict source-code from being
                  distributed in modified form <em>only</em> if the
                  license allows the distribution of ``patch files''
                  with the source code for the purpose of modifying the
                  program at build time. The license must explicitly
                  permit distribution of software built from modified
                  source code. The license may require derived works to
                  carry a different name or version number from the
                  original software.  (This is a compromise. The Debian
                  group encourages all authors to not restrict any
                  files, source or binary, from being modified.)
                </p>
              </item>
              <tag>No Discrimination Against Persons or Groups
              </tag>
              <item>
                <p>
                  The license must not discriminate against any person
                  or group of persons.
                </p>
              </item>
              <tag>No Discrimination Against Fields of Endeavor
              </tag>
              <item>
                <p>
                  The license must not restrict anyone from making use
                  of the program in a specific field of endeavor. For
                  example, it may not restrict the program from being
                  used in a business, or from being used for genetic
                  research.
                </p>
              </item>
              <tag>Distribution of License
              </tag>
              <item>
                <p>
                  The rights attached to the program must apply to all
                  to whom the program is redistributed without the need
                  for execution of an additional license by those
                  parties.
                </p>
              </item>
              <tag>License Must Not Be Specific to Debian
              </tag>
              <item>
                <p>
                  The rights attached to the program must not depend on
                  the program's being part of a Debian system. If the
                  program is extracted from Debian and used or
                  distributed without Debian but otherwise within the
                  terms of the program's license, all parties to whom
                  the program is redistributed must have the same
                  rights as those that are granted in conjunction with
                  the Debian system.
                </p>
              </item>
              <tag>License Must Not Contaminate Other Software
              </tag>
              <item>
                <p>
                  The license must not place restrictions on other
                  software that is distributed along with the licensed
                  software. For example, the license must not insist
                  that all other programs distributed on the same medium
                  must be free software.
                </p>
              </item>
              <tag>Example Licenses
              </tag>
              <item>
                <p>
                  The ``GPL,'' ``BSD,'' and ``Artistic'' licenses are
                  examples of licenses that we consider <em>free</em>.
                </p>
              </item>
            </taglist>
          </p>
        </sect1>
        <sect1>
          <heading>The main section</heading>
          <p>
            Every package in "main"  and "non-US/main" must comply with
            the DFSG (Debian  Free Software Guidelines).</p>

          <p>
            In addition, the packages in "main"
            <list compact="compact">
              <item>
                <p>
                  must not require a package outside of "main" for
                  compilation or execution (thus, the package must not
                  declare a "Depends", "Recommends", or
                  "Build-Depends" relationship on a non-main package),
                </p>
              </item>
              <item>
                <p>
                  must not be so buggy that we refuse to support them,
                </p>
              </item>
              <item>
                <p>
                  must meet all policy requirements presented in this
                  manual.
                </p>
              </item>
            </list>
          </p>
          <p>
            Similarly, the packages in "non-US/main"
            <list compact="compact">
              <item>
                <p>
                   must not require a package outside of "main" or
                   "non-US/main" for compilation or execution,
                </p>
              </item>
              <item>
                <p>
                  must not be so buggy that we refuse to support them,
                </p>
              </item>
              <item>
                <p>
                  must meet all policy requirements presented in this
                  manual.
                </p>
              </item>
            </list>
          </p>
        </sect1>
        <sect1>
          <heading>The contrib section</heading>
          <p>
            Every package in "contrib"  and "non-US/contrib" must
            comply with the DFSG.
          </p>

          <p>
            Examples of packages which would be included in "contrib"
            or "non-US/contrib" are
            <list compact="compact">
              <item>
                <p>
                  free packages which require "contrib", "non-free"
                  packages or packages which are not in our
                  archive at all for compilation or execution,
                </p>
              </item>
              <item>
                <p>
                  wrapper packages or other sorts of free accessories for
                  non-free programs,
                </p>
              </item>
            </list>
          </p>
        </sect1>
        <sect1>
          <heading>The non-free section and non-US/non-free </heading>
          <p>
            Packages must be placed in "non-free" or "non-US/non-free"
            if they are not compliant with the DFSG or are encumbered
            by patents or other legal issues that make their
            distribution problematic.
          </p>
        </sect1>
        <sect1>
          <heading>The non-US sections</heading>
          <p>
            Some programs with cryptographic program code need to be stored
            on the "non-US" server because of export restrictions of the
            U.S. Such programs must be distributed in the appropriate
            non-US section, either non-US/main, non-US/contrib or
            non-US/non-free. </p>
          <p>
            This applies only to packages which contain cryptographic
            code. A package containing a program with an interface to a
            cryptographic program or a program that's dynamically linked
            against a cryptographic library should not be distributed
            via the non-us server if it is capable of running without the
            cryptography library or program.
          </p>
        </sect1>
        <sect1>
          <heading>Further copyright considerations</heading>
          <p>
            Every package must be accompanied by a verbatim copy of its
            copyright and distribution license in the file
            /usr/share/doc/&lt;package-name&gt;/copyright (see
            <ref id="copyrightfile"> for details).</p>
          <p>
            We reserve the right to restrict files from being included
            anywhere in our archives if
            <list compact="compact">
              <item>
                <p>
                  their use or distribution would break a law,
                </p>
              </item>
              <item>
                <p>
                  there is an ethical conflict in their distribution or
                  use,
                </p>
              </item>
              <item>
                <p>
                  we would have to sign a license for them, or
                </p>
              </item>
              <item>
                <p>
                  their distribution would conflict with other project
                  policies.
                </p>
              </item>
            </list>
          </p>

          <p>
            Programs whose authors encourage the user to make donations
            are fine for the main distribution, provided that the
            authors do not claim that not donating is immoral,
            unethical, illegal or something similar; otherwise they must
            go in non-free.</p>

          <p>
            Packages whose copyright permission notices (or patent
            problems) do not allow redistribution even of only binaries,
            and where no special permission has been obtained, must not be
            placed on the Debian FTP site and its mirrors at all.</p>

          <p>
            Note, that under international copyright law (this applies
            in the United States, too) <em>no</em> distribution or
            modification of a work is allowed without an explicit notice
            saying so.  Therefore a program without a copyright notice
            <em>is</em> copyrighted and you may not do anything to it
            without risking being sued! Likewise if a program has a
            copyright notice but no statement saying what is permitted
            then nothing is permitted.</p>

          <p>
            Many authors are unaware of the problems that restrictive
            copyrights (or lack of copyright notices) can cause for the
            users of their supposedly-free software.  It is often
            worthwhile contacting such authors diplomatically to ask
            them to modify their license terms. However, this is a
            politically difficult thing to do and you should ask for
            advice on <tt>debian-legal</tt> first.</p>

          <p>
            When in doubt, send mail to
            <email>debian-legal@lists.debian.org</email>.  Be prepared
            to provide us with the copyright statement.  Software
            covered by the GPL, public domain software and BSD-like
            copyrights are safe; be wary of the phrases `commercial use
            prohibited' and `distribution restricted'.</p>
        </sect1>
        <sect1>
          <heading>Subsections</heading>

          <p>
            The packages in all the sections (<em>main</em>,
            <em>contrib</em>, <em>non-US/main</em>, <em>non-free</em>,
            <em>non-US/contrib</em>, and <em>non-US/non-free</em>) are
            grouped further into <em>subsections</em> to simplify
            handling.</p>

          <p>
            The section for each package should be specified in the
            package's <em>control record</em>. However, the maintainer of
            the Debian archive may override this selection to assure the
            consistency of the Debian distribution. </p>

          <p>
            Please check the current Debian distribution to see which
            sections are available.</p>
        </sect1>
      <sect>
        <heading>Priorities</heading>

        <p>
          Each package should have a <em>priority</em> value,
          which is included in the package's <em>control
            record</em>. This information is used in the Debian package
          management tool to separate high-priority packages from
          less-important packages.</p>

        <p>
          The following <em>priority levels</em> are supported by the
          Debian package management system, <prgn>dpkg</prgn>.
          <taglist>
            <tag><tt>required</tt></tag>
            <item>
              <p>
                <tt>required</tt> packages are necessary for the
                proper functioning of the system.  You must not remove
                these packages or your system may become totally
                broken and you may not even be able to use
                <prgn>dpkg</prgn> to put things back.  Systems with
                only the <tt>required</tt> packages are probably
                unusable, but they do have enough functionality to
                allow the sysadmin to boot and install more
                software.</p>
            </item>
            <tag><tt>important</tt></tag>
            <item>
              <p>
                Important programs, including those which one would
                expect to find on any Unix-like system.  If the
                expectation is that an experienced Unix person who
                found it missing would say `What the F*!@&lt;+ is
                going on, where is <prgn>foo</prgn>', it must be in
                <tt>important</tt>.  This is an important criterion
                because we are trying to produce, amongst other
                things, a free Unix.  Other packages without which the
                system will not run well or be usable must also be
                here.  This does <em>not</em> include Emacs, the X
                Window System, TeX or any other large applications.
                The <tt>important</tt> packages are just a bare
                minimum of commonly-expected and necessary tools.</p>
            </item>
            <tag><tt>standard</tt></tag>
            <item>
              <p>
                These packages provide a reasonably small but not too
                limited character-mode system.  This is what will
                install by default if the user doesn't select anything
                else.  It doesn't include many large applications, but
                it does include Emacs (this is more of a piece of
                infrastructure than an application) and a reasonable
                subset of TeX and LaTeX (if this is possible without
                X).</p>
            </item>
            <tag><tt>optional</tt></tag>
            <item>
              <p>
                (In a sense everything is optional that isn't
                required, but that's not what is meant here.) This is
                all the software that you might reasonably want to
                install if you didn't know what it was or don't have
                specialized requirements. This is a much larger system
                and includes the X Window System, a full TeX distribution,
                and many applications. Note that optional packages should
                not conflict with each other.
              </p>
            </item>
            <tag><tt>extra</tt></tag>
            <item>
              <p>
                This contains all packages that conflict with others
                with required, important, standard or optional
                priorities, or are only likely to be useful if you
                already know what they are or have specialised
                requirements.
              </p>
            </item>
          </taglist></p>

        <p>
          Packages must not depend on packages with lower priority
          values (excluding build-time dependencies).  In order to
          ensure this, the priorities of one or more packages must
          be adjusted.
        </p>
      </sect>

      <sect>
        <heading>Binary packages</heading>

        <p>
          The Debian GNU/Linux distribution is based on the Debian
          package management system, called <prgn>dpkg</prgn>. Thus,
          all packages in the Debian distribution must be provided
          in the <tt>.deb</tt> file format.</p>


        <sect1>
          <heading>The package name</heading>

          <p>
            Every package must have a name that's unique within the Debian
            archive.</p>

          <p>
            Package names must only consist of lower case letters, digits (0-9),
            plus (+) or minus (-) signs, and periods (.).</p>

          <p>
            The package name is part of the file name of the
            <tt>.deb</tt> file and is included in the control field
            information.
          </p>
        </sect1>

        <sect1>
          <heading>The maintainer of a package</heading>
         <p>
            Every package must have a maintainer (the maintainer may
            be one person or a group of people reachable from a common
            email address, such as a mailing list).  The maintainer is
            responsible for ensuring that the  package is placed in
            the appropriate distribution
          </p>

          <p>
            The maintainer must be specified in the
            <tt>Maintainer</tt> control field with the correct name
            and a working email address for the Debian maintainer of
            the package.  If one person maintains several packages
            he/she should try to avoid having different forms of their
            name and email address in different <tt>Maintainer</tt>
            fields.</p>

          <p>
            If the maintainer of a package quits from the Debian
            project the Debian QA Group
            <email>debian-qa@lists.debian.org</email> takes over the
            maintainership of the package until someone else
            volunteers for that task. These packages are called
            <em>orphaned packages</em>.
          </p>
        </sect1>


        <sect1>
          <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.</p>

          <p>
            The description should be written so that it tells the user
            what they need to know to decide whether to install the
            package. This description should not just be copied from
            the blurb for the program.  Instructions for configuring
            or using the package should not be included -- that is what
            installation scripts, manual pages, Info files, etc. are
            for.  Copyright statements and other administrivia should
            not be included -- that is what the copyright file is
            for.</p>
        </sect1>


        <sect1>
          <heading>Dependencies</heading>

          <p>
            Every package must specify the dependency information
            about other packages that are required for the first to
            work correctly.</p>

          <p>
            For example, a dependency entry must be provided for any
            shared libraries required by a dynamically-linked executable
            binary in a package.</p>

          <p>
            Packages are not required to declare any dependencies they
            have on other packages which are marked <tt>Essential</tt>
            (see below), and should not do so unless they depend on a
            particular version of that package.</p>

          <p>
            Sometimes, a package requires another package to be installed
            <em>and</em> configured before it can be installed. In this
            case, you must specify a <tt>Pre-Depends</tt> entry for
            the package.</p>

          <p>
            You should not specify a <tt>Pre-Depends</tt> entry for a
            package before this has been discussed on the
            <tt>debian-devel</tt> mailing list and a consensus about
            doing that has been reached.</p></sect1>


        <sect1>
          <heading>Virtual packages</heading>

          <p>
            Sometimes, there are several packages doing more-or-less
            the same job. In this case, it's useful to define a
            <em>virtual package</em> whose name describes the function
            the packages have. (The virtual packages just exist
            logically, not physically--that's why they are called
            <em>virtual</em>.) The packages with this particular
            function will then <em>provide</em> the virtual
            package. Thus, any other package requiring that function
            can simply depend on the virtual package without having to
            specify all possible packages individually.</p>

          <p>
            All packages should use virtual package names where
            appropriate, and arrange to create new ones if necessary.
            They should not use virtual package names (except privately,
            amongst a cooperating group of packages) unless they have
            been agreed upon and appear in the list of virtual package
            names.</p>

          <p>
            The latest version of the authoritative list of virtual
            package names can be found on
            <ftpsite>ftp.debian.org</ftpsite> in
            <ftppath>/debian/doc/package-developer/virtual-package-names-list.text</ftppath>
            or your local mirror. In addition, it is included in the
            <tt>debian-policy</tt> package. The procedure for updating
            the list is described at the top of the file.</p></sect1>


        <sect1>
          <heading>Base packages</heading>

          <p>
            The packages included in the <tt>base</tt> section have a
            special function. They form a minimum subset of the Debian
            GNU/Linux system that is installed before everything else
            on a new system. Thus, only very few packages are allowed
            to go into the <tt>base</tt> section to keep the required
            disk usage very small.</p>

          <p>
            Most of these packages will have the priority value
            <tt>required</tt> or at least <tt>important</tt>, and many
            of them will be tagged <tt>essential</tt> (see below).</p>

          <p>
            You must not place any packages into the <tt>base</tt>
            section before this has been discussed on the
            <tt>debian-devel</tt> mailing list and a consensus about
            doing that has been reached.</p></sect1>


        <sect1>
          <heading>Essential packages</heading>

          <p>
            Some packages are tagged <tt>essential</tt>. (They have
            <tt>Essential: yes</tt> in their package control record.)
            This flag is used for packages that are <em>essential</em>
            for a system.</p>

          <p>
            Since these packages can not easily be removed (you'll
            have to specify an extra <em>force option</em> to
            <prgn>dpkg</prgn>) this flag must not be used unless
            absolutely necessary.  A shared library package must not
            be tagged <tt>essential</tt>--the dependencies will
            prevent its premature removal, and we need to be able to
            remove it when it has been superseded.
          </p>

          <p>
            Since dpkg will not prevent upgrading of other packages
            while an <tt>essential</tt> package is in an unconfigured
            state, all <tt>essential</tt> packages must supply all
            their core functionality even when unconfigured. If the
            package cannot satisfy this requirement it must not be
            tagged as essential, and any packages depending on this
            package must instead have explicit dependency fields as
            appropriate.
          </p>

          <p>
            You must not tag any packages <tt>essential</tt> before
            this has been discussed on the <tt>debian-devel</tt>
            mailing and a consensus about doing that has been
            reached.</p></sect1>


        <sect1>
          <heading>Maintainer scripts</heading>

          <p>
            The package installation scripts should avoid producing
            output which it is unnecessary for the user to see and
            should rely on <prgn>dpkg</prgn> to stave off boredom on
            the part of a user installing many packages.  This means,
            amongst other things, using the <tt>--quiet</tt> option on
            <prgn>install-info</prgn>.</p>

          <p>
            Errors which occur during the execution of an installation
            script must be checked and the installation must not
            continue after an error.
          </p>

          <p>
            Note, that <ref id="scripts">, in general applies to package
            maintainer scripts, too.
          </p>

          <p>
            You should not use <tt>dpkg-divert</tt> on a file
            belonging to another package without consulting the
            maintainer of that package first.
          </p>
          <p>
            All packages which supply an instance of a common command
            name (or, in general, filename) should generally use
            <prgn>update-alternatives</prgn>, so that they may be
            installed together.  If <prgn>update-alternatives</prgn>
            is not used, then each package must use
            <var>Conflicts</var> to ensure that other packages are
            de-installed.  (In this case, it may be appropriate to
            specify a conflict against earlier versions of something
            that previously did not use
            <prgn>update-alternatives</prgn> - this is an exception to
            the usual rule that this not allowed).
          </p>


          <sect2>
            <heading>Prompting in maintainer scripts</heading>
            <p>
              Package maintainer scripts may prompt the user if
              necessary. Prompting may be accomplished by hand, or by
              communicating with a program, such as
              <prgn>debconf</prgn>, which conforms to the Debian
              Configuration management specification, version 2 or
              higher. (Included in the
              <file>debconf_specification</file> files in the
              <package>debian-policy</package> package.)
              You may also find this file on the FTP site
              <ftpsite>ftp.debian.org</ftpsite> in
              <ftppath>/debian/doc/package-developer/debconf_specification.txt.gz</ftppath>
              or your local mirror.
              <footnote>
                <p>
                  2.5% of Debian packages
                  [<url id="http://kitenet.net/programs/debconf/stats/">]
                  use debconf to prompt the user at install time, and
                  this number is growing daily. The benefits of using
                  debconf are briefly explained at
                  <url id="http://kitenet.net/doc/debconf-doc/introduction.html">;
                  they include preconfiguration, (mostly)
                  noninteractive installation, elimination of
                  redundant prompting, consistency of user interface,
                  etc.
                </p>
                <p>
                  With this increasing number of packages using
                  debconf, plus the existance of a nascent second
                  implementation of the Debian configuration
                  management system (<package>cdebconf</package>), and
                  the stabalization of the protocol these things use,
                  the time has finally come to reflect the use of
                  these things in policy.

                </p>
              </footnote>
            </p>
            <p>
              Packages which use the Debian Configuration management
              specification may contain an additional
              <file>config</file> script and a <file>templates</file>
              file in their control archive. The <prgn>config</prgn>
              script can be run before the preinst, and before the
              package is unpacked or any of its dependancies or
              pre-dependancies are satisfied, so it must work using
              only the tools present in the <em>Essential</em>
              packages.
              <footnote>
                <p>
                  Debconf or another tool that implements the Debian
                  Configuration management specification will also be
                  installed, and any versioned dependancies on it will
                  be satisfied before preconfiguration begins.
                </p>
              </footnote>
            </p>

            <p>
              Packages should try to minimize the amount of prompting
              they need to do, and they should ensure that the user
              will only ever be asked each question once.  This means
              that packages should try to use appropriate shared
              configuration files (such as <tt>/etc/papersize</tt> and
              <tt>/etc/news/server</tt>), and shared debconf variables
              rather than each prompting for their own list of
              required pieces of information.
            </p>

            <p>
            It also means that an upgrade should not ask the same
            questions again, unless the user has used <tt>dpkg
              --purge</tt> to remove the package's configuration.  The
            answers to configuration questions should be stored in an
            appropriate place in <tt>/etc</tt> so that the user can
            modify them, and how this has been done should be
            documented.</p>

          <p>
              If a package has a vitally important piece of
              information to pass to the user (such as "don't run me
              as I am, you must edit the following configuration files
              first or you risk your system emitting badly-formatted
              messages"), it should display this in the
              <prgn>config</prgn> or <prgn>postinst</prgn> script and
              prompt the user to hit return to acknowledge the
              message.  Copyright messages do not count as vitally
              important (they belong in
              <tt>/usr/share/doc/<var>package</var>/copyright</tt>);
              neither do instructions on how to use a program (these
              should be in on line documentation, where all the users
              can see them).</p>

          <p>
            Any necessary prompting should almost always be confined
            to the <prgn>config</prgn> or <prgn>postinst</prgn>
            script. If it is done in the <prgn>postinst</prgn>, it
            should be protected with a conditional so that unnecessary
            prompting doesn't happen if a package's installation fails
            and the <prgn>postinst</prgn> is called with
            <tt>abort-upgrade</tt>, <tt>abort-remove</tt> or
            <tt>abort-deconfigure</tt>.</p>

        </sect1>
      </sect>
      <sect>
        <heading>Source packages</heading>

        <sect1>
          <heading>Standards conformance</heading>

          <p>
            You should specify the most recent version of the
            packaging standards with which your package complies in
            the source package's <tt>Standards-Version</tt> field.</p>

          <p>
            This value will be used to file bug reports automatically
            if your package becomes too much out of date.</p>

          <p>
            The value corresponds to a version of the Debian manuals,
            as can be found on the title page or page headers and
            footers (depending on the format).</p>

          <p>
            The version number has four components--major and minor
            number and major and minor patch level.  When the
            standards change in a way that requires every package to
            change the major number will be changed.  Significant
            changes that will require work in many packages will be
            signaled by a change to the minor number.  The major patch
            level will be changed for any change to the meaning of the
            standards, however small; the minor patch level will be
            changed when only cosmetic, typographical or other edits
            which do not change the meaning are made, or changes which
            do not affect the contents of packages.</p>

          <p>
            For package maintainers, only the first 3 digits of the
            manual version are significant in representing the
            <em>Standards-Version</em>, and either these 3 digits or
            the complete 4 digits may be specified.
            <footnote>
              <p>
                In the past, people specified 4 digits in the
                Standards-Version field, like `2.3.0.0'.  Since any
                `patch-level changes' don't introduce new policy, it
                was thought it would be better to relax policy and
                only require that the first 3 digits are specified. (4
                digits may still be used if someone wants to do so.)
              </p>
            </footnote>
          </p>

          <p>
            You should regularly, and especially if your package has
            become out of date, check for the newest Policy Manual
            available and update your package, if necessary. When your
            package complies with the new standards you should update the
            <tt>Standards-Version</tt> source package field and
            release it.</p></sect1>


        <sect1>
          <heading>Package relationships</heading>

          <p>
            Source packages should specify which binary packages they
            require to be installed or not to be installed in order to
            build correctly.  For example, if building a package
            requires a certain compiler, then the compiler should be
            specified as a build-time dependency.
          </p>

          <p>
            It is not necessary to explicitly specify build-time
            relationships on a minimal set of packages that are always
            needed to compile, link and put in a Debian package a
            standard "Hello World!" program written in C or C++.  The
            required packages are called <em>build-essential</em>, and
            an informational list can be found in
            <tt>/usr/share/doc/build-essential/list</tt> (which is
            contained in the <tt>build-essential</tt>
            package).
            <footnote>
              <p>Rationale:
                <list>
                  <item>
                    <p>This allows maintaining the list separately
                      from the policy documents (the list does not
                      need the kind of control that the policy
                      documents do)
                    </p>
                  </item>
                  <item>
                    <p>
                      Having a separate package allows one to install
                      the build essential packages on a machine, as
                      well as allowing other packages (think task
                      packages) to bring in the build-essential
                      packages using the depends relation
                    </p>
                  </item>
                  <item>
                    <p>
                      The separate package allows bug reports against
                      the package to be categorized separately from
                      the policy management process that uses the BTS
                    </p>
                  </item>
                </list>
              </p>

            </footnote>
          </p>

          <p>
            When specifying the set of build-time dependencies, one
            should list only those packages explicitly required by the
            build.  It is not necessary to list packages which are
            required merely because some other package in the list of
            build-time dependencies depends on them.  The reason is
            that dependencies change, and you should list only those
            <em>you</em> need.  What others need is their business.
          </p>

          <p>
            If build-time dependencies are specified, it must be
            possible to build the package and produce working binaries
            on a system with the build-essential packages installed
            and satisfying the build-time relationships (including any
            implied relationships).  This
            means in particular that version clauses should be used
            rigorously in build-time relationships so that one cannot
            produce bad or inconsistently configured packages when the
            relationships are properly satisfied.
          </p>

        <sect1>
          <heading>Changes to the upstream sources</heading>

          <p>
            If changes to the source code are made that are generally
            applicable, they should be sent to the upstream authors
            in whatever form they prefer so as to be included in the
            upstream version of the package.</p>

          <p>
            If you need to configure the package differently for
            Debian or for Linux, and the upstream source doesn't
            provide a way to configure it the way you need to, you
            should add such configuration facilities (for example, a new
            <prgn>autoconf</prgn> test or <tt>#define</tt>) and send
            the patch to the upstream authors, with the default set to
            the way they originally had it.  You can then easily
            override the default in your <tt>debian/rules</tt> or
            wherever is appropriate.</p>

          <p>
            You should make sure that the <prgn>configure</prgn> utility
            detects the correct architecture specification string
            (refer to <ref id="arch-spec"> for details).</p>

          <p>
            If you need to edit a <prgn>Makefile</prgn> where
            GNU-style <prgn>configure</prgn> scripts are used, you
            should edit the <tt>.in</tt> files rather than editing the
            <prgn>Makefile</prgn> directly.  This allows the user to
            reconfigure the package if necessary.  You should
            <em>not</em> configure the package and edit the generated
            <prgn>Makefile</prgn>!  This makes it impossible for
            someone else to later reconfigure the package.</p></sect1>


        <sect1>
          <heading>Documenting your changes</heading>

          <p>
            You should document your changes and updates to the source
            package properly in the <tt>debian/changelog</tt> file. (Note
            that mistakes in changelogs are usually best rectified by
            making  a new changelog entry rather than "rewriting history"
            by editing old changelog entries)</p>

          <p>
            In non-experimental packages you must only use a format for
            <tt>debian/changelog</tt> which is supported by the most
            recent released version of <prgn>dpkg</prgn>.  If your
            format is not supported and there is general support for
            it you should contact the <prgn>dpkg</prgn> maintainer to
            have the parser script for your format included in the
            <prgn>dpkg</prgn> package. (You will need to agree that
            the parser and its manpage may be distributed under the
            GNU GPL, just as the rest of <prgn>dpkg</prgn>
            is.)</p></sect1>


        <sect1>
          <heading>Error trapping in makefiles</heading>

          <p>
            When <prgn>make</prgn> invokes a command in a makefile
            (including your package's upstream makefiles and the
            <tt>debian/rules</tt>) it does so using <tt>sh</tt>.  This
            means that <tt>sh</tt>'s usual bad error handling
            properties apply: if you include a miniature script as one
            of the commands in your makefile you'll find that if you
            don't do anything about it then errors are not detected
            and <prgn>make</prgn> will blithely continue after
            problems.</p>

          <p>
            Every time you put more than one shell command (this
            includes using a loop) in a makefile command you
            must make sure that errors are trapped.  For
            simple compound commands, such as changing directory and
            then running a program, using <tt>&amp;&amp;</tt> rather
            than semicolon as a command separator is sufficient.  For
            more complex commands including most loops and
            conditionals you should include a separate <tt>set -e</tt>
            command at the start of every makefile command that's
            actually one of these miniature shell scripts.</p></sect1>


        <sect1>
          <heading>Obsolete constructs and libraries</heading>

          <p>
            The include file <prgn>&lt;varargs.h&gt;</prgn> is
            provided to support end-users compiling very old software;
            the library <tt>libtermcap</tt> is provided to support the
            execution of software which has been linked against it
            (either old programs or those such as Netscape which are
            only available in binary form).</p>

          <p>
            Debian packages should be ported to include
            <prgn>&lt;stdarg.h&gt;</prgn> and <tt>ncurses</tt> when
            they are built.</p>
        </sect1>
      </sect>
    </chapt>

    <chapt id="controlfields"><heading>Control files and their fields</heading>

      <p>
        Many of the tools in the package management suite manipulate
        data in a common format, known as control files.  Binary and
        source packages have control data as do the <tt>.changes</tt>
        files which control the installation of uploaded files, and
        <prgn>dpkg</prgn>'s internal databases are in a similar
        format.
      </p>

      <sect><heading>Syntax of control files</heading>

        <p>
          A file consists of one or more paragraphs of fields.  The
          paragraphs are separated by blank lines.  Some control files
          only allow one paragraph; others allow several, in which
          case each paragraph often refers to a different package.
        </p>

        <p>
          Each paragraph is a series of fields and values; each field
          consists of a name, followed by a colon and the value.  It
          ends at the end of the line.  Horizontal whitespace (spaces
          and tabs) may occur immediately before or after the value
          and is ignored there; it is conventional to put a single
          space after the colon.
        </p>

        <p>
          Some fields' values may span several lines; in this case
          each continuation line <em>must</em> start with a space or
          tab.  Any trailing spaces or tabs at the end of individual
          lines of a field value are ignored.
        </p>

        <p>
          Except where otherwise stated only a single line of data is
          allowed and whitespace is not significant in a field body.
          Whitespace may never appear inside names (of packages,
          architectures, files or anything else), version numbers or
          in between the characters of multi-character version
          relationships.
        </p>

        <p>
          Field names are not case-sensitive, but it is usual to
          capitalize the field names using mixed case as shown below.
        </p>

        <p>
          Blank lines, or lines consisting only of spaces and tabs,
          are not allowed within field values or between fields - that
          would mean a new paragraph.
        </p>

        <p>
          It is important to note that there are several fields which
          are optional as far as <prgn>dpkg</prgn> and the related
          tools are concerned, but which must appear in every Debian
          package, or whose omission may cause problems.  When writing
          the control files for Debian packages you <em>must</em> read
          the Debian policy manual in conjunction with the details
          below and the list of fields for the particular file.</p>
      </sect>

      <sect><heading>List of fields</heading>
        <p>
          This list here is not supposed to be exhaustive. Most fields
          are dealt with elsewhere in this document and in the
          packaging manual.
        </p>
        <sect1 id="f-Package"><heading><tt>Package</tt>
          </heading>

          <p>
            The name of the binary package.  Package names consist of
            the alphanumerics and <tt>+</tt> <tt>-</tt> <tt>.</tt>
            (plus, minus and full stop).
          </p>

          <p>
            They must be at least two characters long and must start
            with an alphanumeric character.  The use of lowercase
            package names is strongly recommended unless the package
            you're building (or referring to, in other fields) is
            already using uppercase.</p>
        </sect1>

        <sect1 id="f-Version"><heading><tt>Version</tt>
          </heading>

          <p>
            This lists the source or binary package's version number -
            see <ref id="versions">.
          </p>

        </sect1>

        <sect1
               id="f-Standards-Version"><heading><tt>Standards-Version</tt>
          </heading>

          <p>
            The most recent version of the standards (the policy
            manual and associated texts) with which the package
            complies.  This is updated manually when editing the
            source package to conform to newer standards; it can
            sometimes be used to tell when a package needs attention.
          </p>

          <p>
            Its format is the same as that of a version number except
            that no epoch or Debian revision is allowed - see <ref
                                                                   id="versions">.</p>
        </sect1>


        <sect1 id="f-Distribution"><heading><tt>Distribution</tt>
          </heading>

          <p>
            In a <tt>.changes</tt> file or parsed changelog output
            this contains the (space-separated) name(s) of the
            distribution(s) where this version of the package should
            be or was installed.  Distribution names follow the rules
            for package names.  (See <ref id="f-Package">).
          </p>

          <p>
            <footnote>
                Current distribution values are:
                <taglist>
                  <tag><em>stable</em></tag>
                  <item>
                    <p>
                      This is the current `released' version of Debian
                      GNU/Linux.  Once the
                      distribution is <em>stable</em> only major bug fixes
                      are allowed. When changes are made to this
                      distribution, the release number is increased
                      (for example: 1.2r1 becomes 1.2r2 then 1.2r3, etc).
                    </p>
                  </item>

                  <tag><em>unstable</em></tag>
                  <item>
                    <p>
                      This distribution value refers to the
                      <em>developmental</em> part of the Debian
                      distribution tree. New packages, new upstream
                      versions of packages and bug fixes go into the
                      <em>unstable</em> directory tree. Download from
                      this distribution at your own risk.
                    </p>
                  </item>

                  <tag><em>frozen</em></tag>
                  <item>
                    <p>
                      From time to time, the <em>unstable</em>
                      distribution enters a state of `code-freeze' in
                      anticipation of release as a <em>stable</em>
                      version. During this period of testing only
                      fixes for existing or newly-discovered bugs will
                      be allowed.
                    </p>
                  </item>

                  <tag><em>experimental</em></tag>
                  <item>
                    <p>
                      The packages with this distribution value are deemed
                      by their maintainers to be high risk. Oftentimes they
                      represent early beta or developmental packages from
                      various sources that the maintainers want people to
                      try, but are not ready to be a part of the other parts
                      of the Debian distribution tree. Download at your own
                      risk.
                    </p>
                  </item>
                </taglist>
                There are several sections in each
                distribution. Currently, these sections are:

                <taglist>
                  <tag><em>main</em></tag>
                  <item>
                    <p>
                      The packages in this section are those in the
                      main Debian distribution.  They are all free
                      (according to the Debian free software
                      guidelines) and meet any other criteria for
                      inclusion described in this manual.</p>
                  </item>

                  <tag><em>contrib</em></tag>
                  <item>
                    <p>
                      The packages in this section do not meet the
                      criteria for inclusion in the main Debian
                      distribution as defined by this manual, but are
                      otherwise free, as defined by the Debian free
                      software guidelines.</p>
                  </item>

                  <tag><em>non-free</em></tag>
                  <item>
                    <p>
                      Packages in <em>non-free</em> do not meet the
                      criteria of free software, as defined by the
                      Debian free software guidelines. Again, use your
                      best judgment in downloading from this
                      Distribution.</p>
                  </item>

                </taglist> You should list <em>all</em> distributions that
                the package should be installed into. Except in unusual
                circumstances, installations to <em>stable</em> should also
                go into <em>frozen</em> (if it exists) and
                <em>unstable</em>. Likewise, installations into
                <em>frozen</em> should also go into <em>unstable</em>.
            </footnote>
          </p>
        </sect1>


      </sect>
    </chapt>

    <chapt id="versions"><heading>Version numbering    </heading>

      <p>
        Every package has a version number, in its <tt>Version</tt>
        control file field.
      </p>

      <p>
        The package management system imposes an ordering on version
        numbers, so that it can tell whether packages are being up- or
        downgraded and so that package system front end applications
        can tell whether a package it finds available is newer than
        the one installed on the system.  The version number format
        has the most significant parts (as far as comparison is
        concerned) at the beginning.
      </p>

      <p>
        The version number format is:
        &lsqb<var>epoch</var><tt>:</tt>&rsqb;<var>upstream-version</var>&lsqb;<tt>-</tt><var>debian-revision</var>&rsqb;
      </p>

      <p>
        The three components here are:
        <taglist>
          <tag><var>epoch</var></tag>
          <item>

            <p>
              This is a single (generally small) unsigned integer.  It
              may be omitted, in which case zero is assumed.  If it is
              omitted then the <var>upstream-version</var> may not
              contain any colons.
            </p>

            <p>
              It is provided to allow mistakes in the version numbers
              of older versions of a package, and also a package's
              previous version numbering schemes, to be left behind.
            </p>

          </item>

          <tag><var>upstream-version</var></tag>
          <item>

            <p>
              This is the main part of the version.  It is usually the
              version number of the original (`upstream') package from
              which the <tt>.deb</tt> file has been made, if this is
              applicable.  Usually this will be in the same format as
              that specified by the upstream author(s); however, it
              may need to be reformatted to fit into the package
              management system's format and comparison scheme.
            </p>

            <p>
              The comparison behavior of the package management system
              with respect to the <var>upstream-version</var> is
              described below.  The <var>upstream-version</var>
              portion of the version number is mandatory.
            </p>

            <p>
              The <var>upstream-version</var> may contain only
              alphanumerics and the characters <tt>.</tt> <tt>+</tt>
              <tt>-</tt> <tt>:</tt> (full stop, plus, hyphen, colon)
              and should start with a digit.  If there is no
              <var>debian-revision</var> then hyphens are not allowed;
              if there is no <var>epoch</var> then colons are not
              allowed.</p>
          </item>

          <tag><var>debian-revision</var></tag>
          <item>

            <p>
              This part of the version represents the version of the
              modifications that were made to the package to make it a
              Debian binary package.  It is in the same format as the
              <var>upstream-version</var> and is compared in the same
              way.
            </p>

            <p>
              It is optional; if it isn't present then the
              <var>upstream-version</var> may not contain a hyphen.
              This format represents the case where a piece of
              software was written specifically to be turned into a
              Debian binary package, and so there is only one
              `debianization' of it and therefore no revision
              indication is required.
            </p>

            <p>
              It is conventional to restart the
              <var>debian-revision</var> at <tt>1</tt> each time the
              <var>upstream-version</var> is increased.
            </p>

            <p>
              The package management system will break the
              <var>upstream-version</var> and
              <var>debian-revision</var> apart at the last hyphen in
              the string.  The absence of a <var>debian-revision</var>
              compares earlier than the presence of one (but note that
              the <var>debian-revision</var> is the least significant
              part of the version number).
            </p>

            <p>
              The <var>debian-revision</var> may contain only
              alphanumerics and the characters <tt>+</tt> and
              <tt>.</tt> (plus and full stop).
            </p>
          </item>
        </taglist>
        The <var>upstream-version</var> and <var>debian-revision</var>
        parts are compared by the package management system using the
        same algorithm:
      </p>

      <p>
        The strings are compared from left to right.
      </p>

      <p>
        First the initial part of each string consisting entirely of
        non-digit characters is determined.  These two parts (one of
        which may be empty) are compared lexically.  If a difference
        is found it is returned.  The lexical comparison is a
        comparison of ASCII values modified so that all the letters
        sort earlier than all the non-letters.
      </p>

      <p>
        Then the initial part of the remainder of each string which
        consists entirely of digit characters is determined.  The
        numerical values of these two parts are compared, and any
        difference found is returned as the result of the comparison.
        For these purposes an empty string (which can only occur at
        the end of one or both version strings being compared) counts
        as zero.
      </p>

      <p>
        These two steps are repeated (chopping initial non-digit
        strings and initial digit strings off from the start) until a
        difference is found or both strings are exhausted.
      </p>

      <p>
        Note that the purpose of epochs is to allow us to leave behind
        mistakes in version numbering, and to cope with situations
        where the version numbering changes.  It is <em>not</em> there
        to cope with version numbers containing strings of letters
        which the package management system cannot interpret (such as
        <tt>ALPHA</tt> or <tt>pre-</tt>), or with silly orderings (the
        author of this manual has heard of a package whose versions
        went <tt>1.1</tt>, <tt>1.2</tt>, <tt>1.3</tt>, <tt>1</tt>,
        <tt>2.1</tt>, <tt>2.2</tt>, <tt>2</tt> and so forth).
      </p>

      <p>
        If an upstream package has problematic version numbers they
        should be converted to a sane form for use in the
        <tt>Version</tt> field.
      </p>

      <sect>
        <heading>Version numbers based on dates</heading>
        <p>
          In general, Debian packages should use the same version
          numbers as the upstream sources.</p>

        <p>
          However, in some cases where the upstream version number is
          based on a date (e.g., a development `snapshot' release) the
          package management system cannot handle these version
          numbers without epochs. For example, dpkg will consider
          `96May01' to be greater than `96Dec24'.</p>

        <p>
          To prevent having to use epochs for every new upstream
          version, the version number should be changed to the
          following format in such cases: `19960501', `19961224'. It
          is up to the maintainer whether he/she wants to bother the
          upstream maintainer to change the version numbers upstream,
          too.</p>

        <p>
          Note, that other version formats based on dates which are
          parsed correctly by the package management system should
          <em>not</em> be changed.</p>

        <p>
          Native Debian packages (i.e., packages which have been
          written especially for Debian) whose version numbers include
          dates should always use the `YYYYMMDD' format.</p>
      </sect>
    </chapt>

    <chapt id="miscellaneous"><heading>Packaging Considerations</heading>

      <sect id="timestamps"><heading>Time Stamps</heading>
        <p>
          Maintainers are encouraged to preserve the modification
          times of the upstream source files in a package, as far as
          is reasonably possible. Even though this is optional, this
          is still a good idea.
          <footnote>
            <p>
              The rationale is that there is some information conveyed
              by knowing the age of the file, for example, you could
              recognize that some documentation is very old by looking
              at the modification time, so it would be nice if the
              modification time of the upstream source would be
              preserved.
            </p>
          </footnote>
        </p>
      </sect>

      <sect id="debianrules"><heading><tt>debian/rules</tt> - the
          main building script    </heading>

        <p>
          This file must be an executable makefile, and contains the
          package-specific recipes for compiling the package and
          building binary package(s) out of the source.
        </p>

        <p>
          It must start with the line <tt>#!/usr/bin/make -f</tt>,
          so that it can be invoked by saying its name rather than
          invoking <prgn>make</prgn> explicitly.
        </p>

        <p>
          Since an interactive <tt>debian/rules</tt> script makes it
          impossible to auto-compile that package and also makes it
          hard for other people to reproduce the same binary
          package, all <strong>required targets</strong> MUST be
          non-interactive. At a minimum, required targets are the
          ones called by <prgn>dpkg-buildpackage</prgn>, namely,
          <em>clean</em>, <em>binary</em>, <em>binary-arch</em>,
          <em>binary-indep</em>, and <em>build</em>. It also follows
          that any target that these targets depend on must also be
          non-interactive.
        </p>

        <p>
          The targets which must be present are:
          <taglist>
            <tag><tt>build</tt></tag>
            <item>
              <p>
                This should perform all non-interactive
                configuration and compilation of the package.  If a
                package has an interactive pre-build configuration
                routine, the Debianised source package should be
                built after this has taken place, so that it can be
                built without rerunning the configuration.
              </p>

              <p>
                For some packages, notably ones where the same
                source tree is compiled in different ways to produce
                two binary packages, the <prgn>build</prgn> target
                does not make much sense.  For these packages it is
                good enough to provide two (or more) targets
                (<tt>build-a</tt> and <tt>build-b</tt> or whatever)
                for each of the ways of building the package, and a
                <prgn>build</prgn> target that does nothing.  The
                <prgn>binary</prgn> target will have to build the
                package in each of the possible ways and make the
                binary package out of each.
              </p>

              <p>
                The <prgn>build</prgn> target must not do anything
                that might require root privilege.
              </p>

              <p>
                The <prgn>build</prgn> target may need to run
                <prgn>clean</prgn> first - see below.
              </p>

              <p>
                When a package has a configuration routine that
                takes a long time, or when the makefiles are poorly
                designed, or when <prgn>build</prgn> needs to run
                <prgn>clean</prgn> first, it is a good idea to
                <tt>touch build</tt> when the build process is
                complete.  This will ensure that if <tt>debian/rules
                  build</tt> is run again it will not rebuild the
                whole program.
              </p>
            </item>

            <tag><tt>binary</tt>, <tt>binary-arch</tt>,
              <tt>binary-indep</tt>
            </tag>
            <item>
              <p>
                The <prgn>binary</prgn> target must be all that is
                necessary for the user to build the binary
                package. All these targets are required to be
                non-interactive.  It is split into two parts:
                <prgn>binary-arch</prgn> builds the packages' output
                files which are specific to a particular
                architecture, and <prgn>binary-indep</prgn> builds
                those which are not.
              </p>

              <p>
                <prgn>binary</prgn> may be (and commonly is) a target
                with no commands which simply depends on
                <prgn>binary-arch</prgn> and
                <prgn>binary-indep</prgn>.
              </p>

              <p>
                Both <prgn>binary-*</prgn> targets should depend on
                the <prgn>build</prgn> target, above, so that the
                package is built if it has not been already.  It
                should then create the relevant binary package(s),
                using <prgn>dpkg-gencontrol</prgn> to make their
                control files and <prgn>dpkg-deb</prgn> to build
                them and place them in the parent of the top level
                directory.
              </p>

              <p>
                If one of the <prgn>binary-*</prgn> targets has
                nothing to do (this will be always be the case if
                the source generates only a single binary package,
                whether architecture-dependent or not) it
                <em>must</em> still exist, and must always
                succeed.
              </p>

              <p>
                The <prgn>binary</prgn> targets must be invoked as
                root.
              </p>
            </item>

            <tag><tt>clean</tt></tag>
            <item>

              <p>
                This must undo any effects that the
                <prgn>build</prgn> and <prgn>binary</prgn> targets
                may have had, except that it should leave alone any
                output files created in the parent directory by a
                run of <prgn>binary</prgn>. This target must be
                non-interactive.
              </p>

              <p>
                If a <prgn>build</prgn> file is touched at the end
                of the <prgn>build</prgn> target, as suggested
                above, it should be removed as the first thing that
                <prgn>clean</prgn> does, so that running
                <prgn>build</prgn> again after an interrupted
                <prgn>clean</prgn> doesn't think that everything is
                already done.
              </p>

              <p>
                The <prgn>clean</prgn> target may need to be
                invoked as root if <prgn>binary</prgn> has been
                invoked since the last <prgn>clean</prgn>, or if
                <prgn>build</prgn> has been invoked as root (since
                <prgn>build</prgn> may create directories, for
                example).
              </p>
            </item>

            <tag><tt>get-orig-source</tt> (optional)</tag>
            <item>

              <p>
                This target fetches the most recent version of the
                original source package from a canonical archive site
                (via FTP or WWW, for example), does any necessary
                rearrangement to turn it into the original source
                tar file format described below, and leaves it in the
                current directory.
              </p>

              <p>
                This target may be invoked in any directory, and
                should take care to clean up any temporary files it
                may have left.
              </p>

              <p>
                This target is optional, but providing it if
                possible is a good idea.
              </p>
            </item>
          </taglist>

        <p>
          The <prgn>build</prgn>, <prgn>binary</prgn> and
          <prgn>clean</prgn> targets must be invoked with a current
          directory of the package's top-level directory.
        </p>


        <p>
          Additional targets may exist in <tt>debian/rules</tt>,
          either as published or undocumented interfaces or for the
          package's internal use.
        </p>

        <p>
          The architecture we build on and build for is determined by
          make variables via dpkg-architecture. You can get the Debian
          architecture and the GNU style architecture specification
          string for the build machine as well as the host
          machine. Here is a list of supported make variables:
          <list compact="compact">
            <item>
              <p><tt>DEB_*_ARCH</tt> (the Debian architecture)</p>
            </item>
            <item>
              <p><tt>DEB_*_GNU_TYPE</tt> (the GNU style architecture
                specification string)</p>
            </item>
            <item>
              <p><tt>DEB_*_GNU_CPU</tt> (the CPU part of DEB_*_GNU_TYPE)</p>
            </item>
            <item>
              <p><tt>DEB_*_GNU_SYSTEM</tt> (the System part of
                DEB_*_GNU_TYPE)</p>
          </list>
        </p>

        <p>
          where <tt>*</tt> is either <tt>BUILD</tt> for specification of
          the build machine or <tt>HOST</tt> for specification of the machine
          we build for.
        </p>

        <p>
          Backward compatibility can be provided in the rules file
          by setting the needed variables to suitable default
          values, please refer to the documentation of
          dpkg-architecture for details.
        </p>

        <p>
          It is important to understand that the <tt>DEB_*_ARCH</tt>
          string only determines which Debian architecture we are
          building on or for. It should not be used to get the CPU
          or system information; the GNU style variables should be
          used for that.
        </p>
      </sect>

      <sect id="dpkgchangelog"><heading><tt>debian/changelog</tt>
        </heading>

        <p>
          This file records the changes to the Debian-specific parts of the
          package
          <footnote>
            <p>
              Though there is nothing stopping an author who is also
              the Debian maintainer from using it for all their
              changes, it will have to be renamed if the Debian and
              upstream maintainers become different
              people.
            </p>
          </footnote>.
        </p>

        <p>
          It has a special format which allows the package building
          tools to discover which version of the package is being
          built and find out other release-specific information.
        </p>

        <p>
          That format is a series of entries like this:
          <example>
            <var>package</var> (<var>version</var>) <var>distribution(s)</var>; urgency=<var>urgency</var>

            * <var>change details</var>
            <var>more change details</var>
            * <var>even more change details</var>

            -- <var>maintainer name and email address</var>  <var>date</var>
          </example>
        </p>

        <p>
          <var>package</var> and <var>version</var> are the source
          package name and version number.
        </p>

        <p>
          <var>distribution(s)</var> lists the distributions where
          this version should be installed when it is uploaded - it
          is copied to the <tt>Distribution</tt> field in the
          <tt>.changes</tt> file.  See <ref id="f-Distribution">.
        </p>

        <p>
          <var>urgency</var> is the value for the <tt>Urgency</tt>
          field in the <tt>.changes</tt> file for the upload. It is
          not possible to specify an urgency containing commas; commas
          are used to separate
          <tt><var>keyword</var>=<var>value</var></tt> settings in the
          <prgn>dpkg</prgn> changelog format (though there is
          currently only one useful <var>keyword</var>,
          <tt>urgency</tt>).
        </p>

        <p>
          The change details may in fact be any series of lines
          starting with at least two spaces, but conventionally each
          change starts with an asterisk and a separating space and
          continuation lines are indented so as to bring them in
          line with the start of the text above.  Blank lines may be
          used here to separate groups of changes, if desired.
        </p>

        <p>
          The maintainer name and email address need <em>not</em>
          necessarily be those of the usual package maintainer.
          They should be the details of the person doing
          <em>this</em> version.  The information here will be
          copied to the <tt>.changes</tt> file, and then later used
          to send an acknowledgement when the upload has been
          installed.
        </p>

        <p>
          The <var>date</var> should be in RFC822 format
          <footnote>
            <p>
              This is generated by the <prgn>822-date</prgn>
              program.
            </p>
          </footnote>; it should include the time zone specified
          numerically, with the time zone name or abbreviation
          optionally present as a comment.
        </p>

        <p>
          The first `title' line with the package name should start
          at the left hand margin; the `trailer' line with the
          maintainer and date details should be preceded by exactly
          one space.  The maintainer details and the date must be
          separated by exactly two spaces.
        </p>

        <sect1><heading>Defining alternative changelog formats</heading>

          <p>
            It is possible to use a different format to the standard
            one, by providing a parser for the format you wish to
            use.
          </p>
          <p>
            A changelog parser must not interact with the user at
            all.
          </p>
        </sect1>
      </sect>

      <sect id="srcsubstvars"><heading><tt>debian/substvars</tt>
          and variable substitutions      </heading>

        <p>
          When <prgn>dpkg-gencontrol</prgn>,
          <prgn>dpkg-genchanges</prgn> and <prgn>dpkg-source</prgn>
          generate control files they do variable substitutions on
          their output just before writing it.  Variable
          substitutions have the form
          <tt>${<var>variable-name</var>}</tt>.  The optional file
          <tt>debian/substvars</tt> contains variable substitutions
          to be used; variables can also be set directly from
          <tt>debian/rules</tt> using the <tt>-V</tt> option to the
          source packaging commands, and certain predefined
          variables are available.
        </p>

        <p>
          The is usually generated and modified dynamically by
          <tt>debian/rules</tt> targets; in this case it must be
          removed by the <prgn>clean</prgn> target.
        </p>

        <p>
          See <manref name="dpkg-source" section="1"> for full
          details about source variable substitutions, including the
          format of <tt>debian/substvars</tt>.</p>
      </sect>

      <sect id="debianfiles"><heading><tt>debian/files</tt>
        </heading>

        <p>
          This file is not a permanent part of the source tree; it
          is used while building packages to record which files are
          being generated.  <prgn>dpkg-genchanges</prgn> uses it
          when it generates a <tt>.changes</tt> file.
        </p>

        <p>
          It should not exist in a shipped source package, and so it
          (and any backup files or temporary files such as
          <tt>files.new</tt>
          <footnote>
            <p>
              <tt>files.new</tt> is used as a temporary file by
              <prgn>dpkg-gencontrol</prgn> and
              <prgn>dpkg-distaddfile</prgn> - they write a new
              version of <tt>files</tt> here before renaming it,
              to avoid leaving a corrupted copy if an error
              occurs
            </p>
          </footnote>) should be removed by the
          <prgn>clean</prgn> target.  It may also be wise to
          ensure a fresh start by emptying or removing it at the
          start of the <prgn>binary</prgn> target.
        </p>

        <p>
          <prgn>dpkg-gencontrol</prgn> adds an entry to this file
          for the <tt>.deb</tt> file that will be created by
          <prgn>dpkg-deb</prgn> from the control file that it
          generates, so for most packages all that needs to be done
          with this file is to delete it in <prgn>clean</prgn>.
        </p>

        <p>
          If a package upload includes files besides the source
          package and any binary packages whose control files were
          made with <prgn>dpkg-gencontrol</prgn> then they should be
          placed in the parent of the package's top-level directory
          and <prgn>dpkg-distaddfile</prgn> should be called to add
          the file to the list in <tt>debian/files</tt>.</p>
      </sect>

      <sect id="restrictions"><heading>Restrictions on objects in source packages
        </heading>

        <p>
          The source package may not contain any hard links
          <footnote>
            <p>
              This is not currently detected when building source
              packages, but only when extracting
              them.
            </p>
          </footnote>
          <footnote>
            <p>
              Hard links may be permitted at some point in the
              future, but would require a fair amount of
              work.
            </p>
          </footnote>, device special files, sockets or setuid or
          setgid files.
          <footnote>
            <p>
              Setgid directories are allowed.
            </p>
          </footnote>
        </p>
      </sect>
      <sect id="descriptions"><heading>Descriptions of packages - the
          <tt>Description</tt> field </heading>

        <p>
          The description is intended to describe the program to a user
          who has never met it before so that they know whether they
          want to install it.  It should also give information about the
          significant dependencies and conflicts between this package
          and others, so that the user knows why these dependencies and
          conflicts have been declared.
        </p>

        <sect1><heading>Notes about writing descriptions
          </heading>

          <p>
            The single line synopsis should be kept brief - certainly
            under 80 characters.
          </p>

          <p>
            Do not include the package name in the synopsis line.  The
            display software knows how to display this already, and you
            do not need to state it.  Remember that in many situations
            the user may only see the synopsis line - make it as
            informative as you can.
          </p>

          <p>
            Do not try to continue the single line synopsis into the
            extended description.  This will not work correctly when
            the full description is displayed, and makes no sense
            where only the summary (the single line synopsis) is
            available.
          </p>

          <p>
            The extended description should describe what the package
            does and how it relates to the rest of the system (in terms
            of, for example, which subsystem it is which part of).
          </p>

          <p>
            The description field needs to make sense to anyone, even
            people who have no idea about any of the things the
            package deals with.
            <footnote>
              <p>
                The blurb that comes with a program in its
                announcements and/or <prgn>README</prgn> files is
                rarely suitable for use in a description.  It is
                usually aimed at people who are already in the
                community where the package is used.
              </p>
            </footnote>
          </p>

          <p>
            Put important information first, both in the synopsis and
            extended description.  Sometimes only the first part of the
            synopsis or of the description will be displayed.  You can
            assume that there will usually be a way to see the whole
            extended description.
          </p>

          <p>
            You may include information about dependencies and so forth
            in the extended description, if you wish.
          </p>

          <p>
            Do not use tab characters.  Their effect is not predictable.
          </p>

        </sect1>
      </sect>
    </chapt>


    <chapt id="maintainerscripts"><heading>Package maintainer scripts
        and installation procedure
      </heading>

      <sect><heading>Introduction to package maintainer scripts
        </heading>

        <p>
          It is possible to supply scripts as part of a package which
          the package management system will run for you when your
          package is installed, upgraded or removed.
        </p>

        <p>
          These scripts should be the files <tt>preinst</tt>,
          <tt>postinst</tt>, <tt>prerm</tt> and <tt>postrm</tt> 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 executable by anyone, and not world-writable.
        </p>

        <p>
          The package management system looks at the exit status from
          these scripts.  It is important that they exit with a
          non-zero status if there is an error, so that the package
          management system can stop its processing.  For shell
          scripts this means that you <em>almost always</em> need to
          use <tt>set -e</tt> (this is usually true when writing shell
          scripts, in fact).  It is also important, of course, that
          they don't exit with a non-zero status if everything went
          well.
        </p>

        <p>
          It is necessary for the error recovery procedures that the
          scripts be idempotent: i.e., invoking the same script several
          times in the same situation should do no harm.  If the first
          call failed, or aborted half way through for some reason,
          the second call should merely do the things that were left
          undone the first time, if any, and exit with a success
          status.
        </p>

        <p>
          When a package is upgraded a combination of the scripts from
          the old and new packages is called in amongst the other
          steps of the upgrade procedure.  If your scripts are going
          to be at all complicated you need to be aware of this, and
          may need to check the arguments to your scripts.
        </p>

        <p>
          Broadly speaking the <prgn>preinst</prgn> is called before
          (a particular version of) a package is installed, and the
          <prgn>postinst</prgn> afterwards; the <prgn>prerm</prgn>
          before (a version of) a package is removed and the
          <prgn>postrm</prgn> afterwards.
        </p>

        <p> Programs called from maintainer scripts should not
          normally have a path prepended to them. Before installation
          is started the package management system checks to see if
          the programs <prgn>ldconfig</prgn>,
          <prgn>start-stop-daemon</prgn>, <prgn>install-info</prgn>,
          and <prgn>update-rc.d</prgn> can be found via the
          <tt>PATH</tt> environment variable. Those programs, and any
          other program that one would expect to on the <tt>PATH</tt>,
          should thus be invoked without an absolute
          pathname. Maintainer scripts should also not reset the
          <tt>PATH</tt>, though they might choose to modify it by pre-
          or appending package-specific directories. These
          considerations really apply to all shell scripts.</p>
      </sect>
      <sect>
        <heading>Maintainer scripts Idempotency</heading>

        <p>
          It is very important to make maintainer scripts
          idempotent.
          <footnote>
            <p>
              That means that if it runs successfully or fails
              and then you call it again it doesn't bomb out,
              but just ensures that everything is the way it
              ought to be.
            </p>
          </footnote> This is so that if an error occurs, the
          user interrupts <prgn>dpkg</prgn> or some other
          unforeseen circumstance happens you don't leave the
          user with a badly-broken package.
        </p>
      </sect>
      <sect>
        <heading>Controlling terminal for maintainer scripts</heading>

        <p>
          The maintainer scripts are guaranteed to run with a
          controlling terminal and can interact with the user.
          If they need to prompt for passwords, do full-screen
          interaction or something similar you should do these
          things to and from <tt>/dev/tty</tt>, since
          <prgn>dpkg</prgn> will at some point redirect scripts'
          standard input and output so that it can log the
          installation process.  Likewise, because these scripts
          may be executed with standard output redirected into a
          pipe for logging purposes, Perl scripts should set
          unbuffered output by setting <tt>$|=1</tt> so that the
          output is printed immediately rather than being
          buffered.
        </p>

        <p>
          Each script should return a zero exit status for
          success, or a nonzero one for failure.
        </p>
      </sect>

      <sect id="mscriptsinstact"><heading>Summary of ways maintainer
          scripts are called
        </heading>

        <p>
          <list compact="compact">
            <item>
              <p><var>new-preinst</var> <tt>install</tt></p>
            </item>
            <item>
              <p><var>new-preinst</var> <tt>install</tt>
                <var>old-version</var></p>
            </item>
            <item>
              <p><var>new-preinst</var> <tt>upgrade</tt>
                <var>old-version</var></p>
            </item>
            <item>
              <p><var>old-preinst</var> <tt>abort-upgrade</tt>
                <var>new-version</var>
              </p>
            </item>
          </list>

        <p>
          <list compact="compact">
            <item>
              <p><var>postinst</var> <tt>configure</tt>
                <var>most-recently-configured-version</var></p>
            </item>
            <item>
              <p><var>old-postinst</var> <tt>abort-upgrade</tt>
                <var>new version</var></p>
            </item>
            <item>
              <p><var>conflictor's-postinst</var> <tt>abort-remove</tt>
                <tt>in-favour</tt> <var>package</var>
                <var>new-version</var></p>
            </item>
            <item>
              <p>
                <var>deconfigured's-postinst</var>
                <tt>abort-deconfigure</tt> <tt>in-favour</tt>
                <var>failed-install-package</var> <var>version</var>
                <tt>removing</tt> <var>conflicting-package</var>
                <var>version</var>
              </p>
            </item>
          </list>

        <p>
          <list compact="compact">
            <item>
              <p><var>prerm</var> <tt>remove</tt></p>
            </item>
            <item>
              <p><var>old-prerm</var> <tt>upgrade</tt>
                <var>new-version</var></p>
            </item>
            <item>
              <p><var>new-prerm</var> <tt>failed-upgrade</tt>
                <var>old-version</var></p>
            </item>
            <item>
              <p><var>conflictor's-prerm</var> <tt>remove</tt>
                <tt>in-favour</tt> <var>package</var>
                <var>new-version</var></p>
            </item>
            <item>
              <p>
                <var>deconfigured's-prerm</var> <tt>deconfigure</tt>
                <tt>in-favour</tt> <var>package-being-installed</var>
                <var>version</var> <tt>removing</tt>
                <var>conflicting-package</var>
                <var>version</var>
              </p>
            </item>
          </list>

        <p>
          <list compact="compact">
            <item>
              <p><var>postrm</var> <tt>remove</tt></p>
            </item>
            <item>
              <p><var>postrm</var> <tt>purge</tt></p>
            </item>
            <item>
              <p>
                <var>old-postrm</var> <tt>upgrade</tt>
                <var>new-version</var></p>
            </item>
            <item>
              <p><var>new-postrm</var> <tt>failed-upgrade</tt>
                <var>old-version</var></p>
            </item>
            <item>
              <p><var>new-postrm</var> <tt>abort-install</tt></p>
            </item>
            <item>
              <p><var>new-postrm</var> <tt>abort-install</tt>
                <var>old-version</var></p>
            </item>
            <item>
              <p><var>new-postrm</var> <tt>abort-upgrade</tt>
                <var>old-version</var></p>
            </item>
            <item>
              <p>
                <var>disappearer's-postrm</var> <tt>disappear</tt>
                <var>overwriter</var>
                <var>overwriter-version</var></p></item>
          </list>
        </p>


      <sect id="unpackphase"><heading>Details of unpack phase of
          installation or upgrade
        </heading>

        <p>
          The procedure on installation/upgrade/overwrite/disappear
          (i.e., when running <tt>dpkg --unpack</tt>, or the unpack
          stage of <tt>dpkg --install</tt>) is as follows.  In each
          case if an error occurs the actions are, in general, run
          backwards - this means that the maintainer scripts are run
          with different arguments in reverse order.  These are the
          `error unwind' calls listed below.

          <enumlist>
            <item>
              <p>
                <enumlist>
                  <item>
                    <p>If a version of the package is already
                      installed, call
                      <example>
                        <var>old-prerm</var> upgrade <var>new-version</var>
                      </example></p>
                  </item>
                  <item>
                    <p>
                      If the script runs but exits with a non-zero
                      exit status, <prgn>dpkg</prgn> will attempt:
                      <example>
                        <var>new-prerm</var> failed-upgrade <var>old-version</var>
                      </example>
                      Error unwind, for both the above cases:
                      <example>
                        <var>old-postinst</var> abort-upgrade <var>new-version</var>
                      </example>
                    </p>
                  </item>
                </enumlist>
              </p>
            </item>
            <item>
              <p>If a `conflicting' package is being removed at the same time:
                <enumlist>
                  <item>
                    <p>
                      If any packages depended on that conflicting
                      package and <tt>--auto-deconfigure</tt> is
                      specified, call, for each such package:
                      <example>
                        <var>deconfigured's-prerm</var> deconfigure \
                        in-favour <var>package-being-installed</var> <var>version</var> \
                        removing <var>conflicting-package</var> <var>version</var>
                      </example>
                      Error unwind:
                      <example>
                        <var>deconfigured's-postinst</var> abort-deconfigure \
                        in-favour <var>package-being-installed-but-failed</var> <var>version</var> \
                        removing <var>conflicting-package</var> <var>version</var>
                      </example>
                      The deconfigured packages are marked as
                      requiring configuration, so that if
                      <tt>--install</tt> is used they will be
                      configured again if possible.</p>
                  </item>
                  <item>
                    <p>To prepare for removal of the conflicting package, call:
                      <example>
                        <var>conflictor's-prerm</var> remove in-favour <var>package</var> <var>new-version</var>
                      </example>
                      Error unwind:
                      <example>
                        <var>conflictor's-postinst</var> abort-remove \
                        in-favour <var>package</var> <var>new-version</var>
                      </example>
                    </p>
                  </item>
                </enumlist>
              </p>
            </item>
            <item>
              <p>
                <enumlist>
                  <item>
                    <p>If the package is being upgraded, call:
                      <example>
                        <var>new-preinst</var> upgrade <var>old-version</var>
                      </example></p>
                  </item>
                  <item>
                    <p>
                      Otherwise, if the package had some configuration
                      files from a previous version installed (i.e., it
                      is in the `configuration files only' state):
                      <example>
                        <var>new-preinst</var> install <var>old-version</var>
                      </example></p>

                  <item>
                    <p>Otherwise (i.e., the package was completely purged):
                      <example>
                        <var>new-preinst</var> install
                      </example>
                      Error unwind versions, respectively:
                      <example>
                        <var>new-postrm</var> abort-upgrade <var>old-version</var>
                        <var>new-postrm</var> abort-install <var>old-version</var>
                        <var>new-postrm</var> abort-install
                      </example>
                    </p>
                  </item>
                </enumlist>
              </p>
            </item>
            <item>

              <p>
                The new package's files are unpacked, overwriting any
                that may be on the system already, for example any
                from the old version of the same package or from
                another package (backups of the old files are left
                around, and if anything goes wrong the package
                management system will attempt to put them back as
                part of the error unwind).
              </p>

              <p>
                It is an error for a package to contains files which
                are on the system in another package, unless
                <tt>Replaces</tt> is used (see <ref id="replaces">).
                Currently the <tt>--force-overwrite</tt> flag is
                enabled, downgrading it to a warning, but this may not
                always be the case.
              </p>

              <p>
                It is a more serious error for a package to contain a
                plain file or other kind of non-directory where another
                package has a directory (again, unless
                <tt>Replaces</tt> is used).  This error can be
                overridden if desired using
                <tt>--force-overwrite-dir</tt>, but this is not
                advisable.
              </p>

              <p>
                Packages which overwrite each other's files produce
                behavior which though deterministic is hard for the
                system administrator to understand.  It can easily
                lead to `missing' programs if, for example, a package
                is installed which overwrites a file from another
                package, and is then removed again.
                <footnote>
                  <p>
                    Part of the problem is due to what is arguably a
                    bug in <prgn>dpkg</prgn>.
                  </p>
                </footnote>
              </p>

              <p>
                A directory will never be replaced by a symbolic links
                to a directory or vice versa; instead, the existing
                state (symlink or not) will be left alone and
                <prgn>dpkg</prgn> will follow the symlink if there is
                one.</p>
            </item>

            <item>

              <p><enumlist>
                  <item>
                    <p>If the package is being upgraded, call
                      <example>
                        <var>old-postrm</var> upgrade <var>new-version</var>
                      </example></p>
                  </item>
                  <item>
                    <p>If this fails, <prgn>dpkg</prgn> will attempt:
                      <example>
                        <var>new-postrm</var> failed-upgrade <var>old-version</var>
                      </example>
                      Error unwind, for both cases:
                      <example>
                        <var>old-preinst</var> abort-upgrade <var>new-version</var>
                      </example>
                    </p>
                  </item>
                </enumlist>
              <p>
                This is the point of no return - if
                <prgn>dpkg</prgn> gets this far, it won't back off
                past this point if an error occurs.  This will
                leave the package in a fairly bad state, which
                will require a successful re-installation to clear
                up, but it's when <prgn>dpkg</prgn> starts doing
                things that are irreversible.
              </p>
            </item>
            <item>
              <p>
                Any files which were in the old version of the package
                but not in the new are removed.</p>
            </item>
            <item>
              <p>The new file list replaces the old.</p>
            </item>
            <item>
              <p>The new maintainer scripts replace the old.</p>
            </item>

            <item>
              <p>Any packages all of whose files have been overwritten during the
                installation, and which aren't required for
                dependencies, are considered to have been removed.
                For each such package,
                <enumlist>
                  <item>
                    <p><prgn>dpkg</prgn> calls:
                      <example>
                        <var>disappearer's-postrm</var> disappear \
                        <var>overwriter</var> <var>overwriter-version</var>
                      </example>
                    </p>
                  </item>
                  <item>
                    <p>The package's maintainer scripts are removed.
                    </p>
                  </item>
                  <item>
                    <p>
                      It is noted in the status database as being in a
                      sane state, namely not installed (any conffiles
                      it may have are ignored, rather than being
                      removed by <prgn>dpkg</prgn>).  Note that
                      disappearing packages do not have their prerm
                      called, because <prgn>dpkg</prgn> doesn't know
                      in advance that the package is going to
                      vanish.
                    </p>
                  </item>
                </enumlist>
              </p>
            </item>
            <item>
              <p>
                Any files in the package we're unpacking that are also
                listed in the file lists of other packages are removed
                from those lists.  (This will lobotomize the file list
                of the `conflicting' package if there is one.)
              </p>
            </item>
            <item>
              <p>
                The backup files made during installation, above, are
                deleted.
              </p>
            </item>

            <item>
              <p>
                The new package's status is now sane, and recorded as
                `unpacked'.  Here is another point of no return - if
                the conflicting package's removal fails we do not
                unwind the rest of the installation; the conflicting
                package is left in a half-removed limbo.
              </p>
            </item>
            <item>
              <p>
                If there was a conflicting package we go and do the
                removal actions (described below), starting with the
                removal of the conflicting package's files (any that
                are also in the package being installed have already
                been removed from the conflicting package's file list,
                and so do not get removed now).
              </p>
            </item>
          </enumlist>
        </p>
      </sect>

      <sect><heading>Details of configuration</heading>

        <p>
          When we configure a package (this happens with <tt>dpkg
            --install</tt>, or with <tt>--configure</tt>), we first
          update the conffiles and then call:
          <example>
            <var>postinst</var> configure <var>most-recently-configured-version</var>
          </example>
        </p>

        <p>
          No attempt is made to unwind after errors during
          configuration.
        </p>

        <p>
          If there is no most recently configured version
          <prgn>dpkg</prgn> will pass a null argument; older versions
          of dpkg may pass <tt>&lt;unknown&gt;</tt> (including the
          angle brackets) in this case.  Even older ones do not pass a
          second argument at all, under any circumstances.
        </p>
      </sect>

      <sect><heading>Details of removal and/or configuration purging
        </heading>

        <p>
          <enumlist>
            <item>
              <p>
                <example>
                  <var>prerm</var> remove
                </example>
              </p>
            </item>
            <item>
              <p>
                The package's files are removed (except conffiles).
              </p>
            </item>
            <item>
              <p><example>
                  <var>postrm</var> remove
                </example></p>
            </item>
            <item>
              <p>All the maintainer scripts except the postrm are removed.
              </p>

              <p>
                If we aren't purging the package we stop here.  Note
                that packages which have no postrm and no conffiles
                are automatically purged when removed, as there is no
                difference except for the <prgn>dpkg</prgn>
                status.</p>
            </item>
            <item>
              <p>
                The conffiles and any backup files (<tt>~</tt>-files,
                <tt>#*#</tt> files, <tt>%</tt>-files,
                <tt>.dpkg-{old,new,tmp}</tt>, etc.) are removed.</p>
            </item>
            <item>
              <p><example>
                  <var>postrm</var> purge
                </example></p>
            </item>
            <item>
              <p>The package's file list is removed.</p>
            </item>
          </enumlist>
          No attempt is made to unwind after errors during
          removal.</p>
      </sect>
    </chapt>


    <chapt id="relationships"><heading>Declaring relationships between
        packages      </heading>

      <p>
        Packages can declare in their control file that they have
        certain relationships to other packages - for example, that
        they may not be installed at the same time as certain other
        packages, and/or that they depend on the presence of others,
        or that they should overwrite files in certain other packages
        if present.
      </p>

      <p>
        This is done using the <tt>Depends</tt>, <tt>Recommends</tt>,
        <tt>Suggests</tt>, <tt>Enhances</tt>, <tt>Conflicts</tt>,
        <tt>Provides</tt> and <tt>Replaces</tt> control file fields.
      </p>

      <p>
        Source packages may declare relationships to binary packages,
        saying that they require certain binary packages to be
        installed or absent at the time of building the package.
      </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>

      <sect id="depsyntax"><heading>Syntax of relationship fields
        </heading>

        <p>
          These fields all have a uniform syntax.  They are a list of
          package names separated by commas.
        </p>

        <p>
          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
          dependencies on other packages, the package names listed may
          also include lists of alternative package names, separated
          by vertical bar symbols <tt>|</tt> (pipe symbols).  In such
          a case, the presence of any one of the alternative packages
          is installed, that part of the dependency is considered to
          be satisfied.
        </p>

        <p>
          All the fields except <tt>Provides</tt> may restrict their
          applicability to particular versions of each named package.
          This is done in parentheses after each individual package
          name; the parentheses should contain a relation from the
          list below followed by a version number, in the format
          described in <ref id="versions">.
        </p>

        <p>
          The relations allowed are <tt>&lt;&lt;</tt>, <tt>&lt;=</tt>,
          <tt>=</tt>, <tt>&gt;=</tt> and <tt>&gt;&gt;</tt> for
          strictly earlier, earlier or equal, exactly equal, later or
          equal and strictly later, respectively.  The forms
          <tt>&lt;</tt> and <tt>&gt;</tt> were used to mean
          earlier/later or equal, rather than strictly earlier/later,
          so they should not appear in new packages (though
          <prgn>dpkg</prgn> still supports them).
        </p>

        <p>
          Whitespace may appear at any point in the version
          specification, and must appear where it's necessary to
          disambiguate; it is not otherwise significant.  For
          consistency and in case of future changes to
          <prgn>dpkg</prgn> it is recommended that a single space be
          used after a version relationship and before a version
          number; it is usual also to put a single space after each
          comma, on either side of each vertical bar, and before each
          open parenthesis.
        </p>

        <p>
          For example:
          <example>
            Package: metamail
            Version: 2.7-3
            Depends: libc5 (>= 5.2.18-4), mime-support, csh | tcsh
          </example>
        </p>

        <p>
          All fields that specify build-time relationships
          (<tt>Build-Depends</tt>, <tt>Build-Depends-Indep</tt>,
          <tt>Build-Conflicts</tt> and <tt>Build-Conflicts-Indep</tt>)
          may be restricted to a certain set of architectures.  This
          is done in brackets after each individual package name and
          the optional version specification.  The brackets enclose a
          list of Debian architecture names separated by whitespace.
          An exclamation mark may be prepended to each name. If the
          current Debian host architecture is not in this list and
          there are no exclamation marks in the list, or it is in the
          list with a prepended exclamation mark, the package name and
          the associated version specification are ignored completely
          for the purposes of defining the relationships.
        </p>

        <p>
          For example:
          <example>
            Source: glibc
            Build-Depends-Indep: texinfo
            Build-Depends: kernel-headers-2.2.10 [!hurd-i386],
            hurd-dev [hurd-i386], gnumach-dev [hurd-i386]
          </example>
        </p>
      </sect>

      <sect>
        <heading>Binary Dependencies - <tt>Depends</tt>,
          <tt>Recommends</tt>, <tt>Suggests</tt>, <tt>Enhances</tt>,
          <tt>Pre-Depends</tt>
        </heading>

        <p>
          These five fields are used to declare a dependency
          relationship by one package on another.  They appear in the
          depending package's control file.
        </p>

        <p>
          All but <tt>Pre-Depends</tt> and <tt>Conflicts</tt>
          (discussed below) take effect <em>only</em> when a package
          is to be configured.  They do not prevent a package being on
          the system in an unconfigured state while its dependencies
          are unsatisfied, and it is possible to replace a package
          whose dependencies are satisfied and which is properly
          installed with a different version whose dependencies are
          not and cannot be satisfied; when this is done the depending
          package will be left unconfigured (since attempts to
          configure it will give errors) and will not function
          properly.
        </p>

        <p>
          For this reason packages in an installation run are usually
          all unpacked first and all configured later; this gives
          later versions of packages with dependencies on later
          versions of other packages the opportunity to have their
          dependencies satisfied.
        </p>

        <p>
          Thus <tt>Depends</tt> allows package maintainers to impose
          an order in which packages should be configured.
          <taglist>
            <tag><tt>Depends</tt></tag>
            <item>

              <p>This declares an absolute dependency.
              </p>

              <p>
                The <tt>Depends</tt> field should be used if the
                depended-on package is required for the depending
                package to provide a significant amount of
                functionality.</p>
            </item>

            <tag><tt>Recommends</tt></tag>
            <item>
              <p>This declares a strong, but not absolute, dependency.
              </p>

              <p>
                The <tt>Recommends</tt> field should list packages
                that would be found together with this one in all but
                unusual installations.</p>
            </item>

            <tag><tt>Suggests</tt></tag>
            <item>

              <p>
                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.
              </p>
            </item>

            <tag><tt>Enhances</tt></tag>
            <item>
              <p>
                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.
              </p>
            </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.
              </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>
                When the package declaring it is being configured, a
                <tt>Pre-Dependency</tt> will be considered satisfied
                only if the depending package has been correctly
                configured, just as if an ordinary <tt>Depends</tt>
                had been used.
              </p>

              <p>
                However, when a package declaring a Pre-dependency is
                being unpacked the predependency can be satisfied even
                if 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>
            </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 id="conflicts"><heading>Alternative binary packages -
          <tt>Conflicts</tt> and <tt>Replaces</tt>
        </heading>

        <p>
          When one binary package declares a conflict with another
          <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 (<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 specifically doesn't work 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 something.
        </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>Build-Depends</tt>, <tt>Build-Depends-Indep</tt>,
          <tt>Recommends</tt>, <tt>Suggests</tt>, <tt>Conflicts</tt>,
          <tt>Build-Conflicts</tt> and <tt>Build-Conflicts-Indep</tt> may
          mention virtual packages.
        </p>

        <p>
          A virtual package 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.
        </p>

        <p>
          If there are both a real and a virtual package of the same
          name then the dependency may be satisfied (or the conflict
          caused) by either the real package or any of the virtual
          packages which provide it.  This is so that, for example,
          supposing we have
          <example>
            Package: vm
            Depends: emacs
          </example>
          and someone else releases an xemacs package they can say
          <example>
            Package: xemacs
            Provides: emacs
          </example> and all will work in the interim (until a purely
          virtual package name is decided on and the <tt>emacs</tt>
          and <tt>vm</tt> packages are changed to use it).
        </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.
        </p>
      </sect>


      <sect id="replaces"><heading><tt>Replaces</tt> - overwriting
          files and replacing packages
        </heading>

        <p>
          The <tt>Replaces</tt> control file field has two purposes,
          which come into play in different situations.
        </p>

        <p>
          Virtual packages (<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>

        <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, though currently the
            <tt>--force-overwrite</tt> flag is enabled by default,
            downgrading the error to a warning,
          </p>

          <p>
            If the overwriting package declares that it replaces the
            one containing the file being overwritten then
            <prgn>dpkg</prgn> will proceed, and 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 conffiles details noted
            in the package will be ignored, as they will have been
            taken over by the replacing package(s).  The package's
            <prgn>postrm</prgn> script will be run to allow the
            package to do any final cleanup required.  See <ref
                                                                id="mscriptsinstact">.
          </p>

          <p>
            In the future <prgn>dpkg</prgn> will discard files which
            would overwrite those from an already installed package
            which declares that it replaces the package being
            installed.  This is so that you can install an older
            version of a package without problems.
          </p>

          <p>
            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 effects do not interfere with each other.
          </p>
        </sect1>
      </sect>

      <sect><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>
          A source package may declare a dependency or a conflict on a
          binary package.  This is done with the control file fields
          <tt>Build-Depends</tt>, <tt>Build-Depends-Indep</tt>,
          <tt>Build-Conflicts</tt>, and
          <tt>Build-Conflicts-Indep</tt>.  Their semantics are that
          the dependencies and conflicts they define must be satisfied
          (as defined earlier for binary packages), when one of the
          targets in <tt>debian/rules</tt> that the particular field
          applies to is invoked.

          <taglist>
            <tag><tt>Build-Depends</tt>, <tt>Build-Conflicts</tt></tag>
            <item>
              <p>
                The <tt>Build-Depends</tt> and
                <tt>Build-Conflicts</tt> fields apply to the targets
                <tt>build</tt>, <tt>binary</tt>, <tt>binary-arch</tt>
                and <tt>binary-indep</tt>.
              </p>
            </item>
            <tag><tt>Build-Depends-Indep</tt>, <tt>Build-Conflicts-Indep</tt></tag>
            <item>
              <p>
                The <tt>Build-Depends-Indep</tt> and
                <tt>Build-Conflicts-Indep</tt> fields apply to the
                targets <tt>binary</tt> and <tt>binary-indep</tt>.
              </p>
            </item>
          </taglist>

        </p>

      </sect>
    </chapt>


    <chapt id="conffiles"><heading>Configuration file handling
      </heading>

      <p>
        <prgn>dpkg</prgn> can do a certain amount of automatic
        handling of package configuration files.
      </p>

      <p>
        Whether this mechanism is appropriate depends on a number of
        factors, but basically there are two approaches to any
        particular configuration file.
      </p>

      <p>
        The easy method is to ship a best-effort configuration in the
        package, and use <prgn>dpkg</prgn>'s conffile mechanism to
        handle updates.  If the user is unlikely to want to edit the
        file, but you need them to be able to without losing their
        changes, and a new package with a changed version of the file
        is only released infrequently, this is a good approach.
      </p>

      <p>
        The hard method is to build the configuration file from
        scratch in the <prgn>postinst</prgn> script, and to take the
        responsibility for fixing any mistakes made in earlier
        versions of the package automatically.  This will be
        appropriate if the file is likely to need to be different on
        each system.
      </p>


    <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 libc.
      </p>

      <p>
        Firstly, your package should install the shared libraries
        under their normal names.  For example, the
        <prgn>libgdbm1</prgn> package should install
        <tt>libgdbm.so.1.7.3</tt> as
        <tt>/usr/lib/libgdbm.so.1.7.3</tt>.  The files should not be
        renamed or re-linked by any prerm or postrm 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>
        Secondly, your package should include the symlink that
        <prgn>ldconfig</prgn> would create for the shared libraries.
        For example, the <prgn>libgdbm1</prgn> package should include
        a symlink from <tt>/usr/lib/libgdbm.so.1</tt> to
        <tt>libgdbm.so.1.7.3</tt>.  This is needed so that
        <prgn>ld.so</prgn> can find the library in between the time
        <prgn>dpkg</prgn> installs it and <prgn>ldconfig</prgn> is run
        in the <prgn>postinst</prgn> script.  Furthermore, older
        versions of the package management system required the library
        must be placed before the symlink pointing to it in the
        <tt>.deb</tt> file.  This is so that by the time
        <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.
        Unfortunately, this was not not always possible, since it
        highly depends on the behavior of the file system. Some
        file systems (such as reiserfs) will reorder the files so it
        doesn't matter in what order you create them. Starting with
        release <tt>1.7.0</tt> <prgn>dpkg</prgn> will reorder the
        files itself when building a package.
      </p>

      <p>
        Thirdly, the development package should contain a symlink for
        the shared library without a version number.  For example, the
        <tt>libgdbm1-dev</tt> package should include a symlink from
        <tt>/usr/lib/libgdm.so</tt> to <tt>libgdm.so.1.7.3</tt>.  This
        symlink is needed by <prgn>ld</prgn> when compiling packages
        as it will only look for <tt>libgdm.so</tt> and
        <tt>libgdm.a</tt> when compiling dynamically or statically,
        respectively.
      </p>

      <p>
        Any package installing shared libraries in a directory that's listed
        in <tt>/etc/ld.so.conf</tt> or in one of the default library
        directories of <prgn>ld.so</prgn> (currently, these are <tt>/usr/lib</tt>
        and <tt>/lib</tt>) must call <prgn>ldconfig</prgn> in its <prgn>postinst</prgn>
        script if and only if the first argument is `configure'. However, it
        is important not to call <prgn>ldconfig</prgn> in the postrm or preinst
        scripts in the case where the package is being upgraded (see <ref
                                                                          id="unpackphase">), as <prgn>ldconfig</prgn> will see the temporary names
        that <prgn>dpkg</prgn> uses for the files while it is
        installing them and will make the shared library links point
        to them, just before <prgn>dpkg</prgn> continues the
        installation and removes the links!
      </p>

      <sect id="shlibs"><heading>The <tt>shlibs</tt> File Format
        </heading>

        <p>
          This file is for use by <prgn>dpkg-shlibdeps</prgn> and is
          required when your package provides shared libraries.
        </p>

        <p>
          Each line is of the form:
          <example>
            <var>library-name</var> <var>version-or-soname</var> <var>dependencies ...</var>
          </example>
        </p>

        <p>
          <var>library-name</var> is the name of the shared library,
          for example <tt>libc5</tt>.
        </p>

        <p>
          <var>version-or-soname</var> is the soname of the library -
          i.e., the thing that must exactly match for the library to be
          recognized by <prgn>ld.so</prgn>.  Usually this is the major
          version number of the library.
        </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 package(s) are required to satisfy a binary
          built against the version of the library contained in the
          package.  See <ref id="depsyntax">.
        </p>

        <p>
          For example, if the package <tt>foo</tt> contains
          <tt>libfoo.so.1.2.3</tt>, where the soname of the library is
          <tt>libfoo.so.1</tt>, and the first version of the package
          which contained a minor number of at least <tt>2.3</tt> was
          <var>1.2.3-1</var>, then the package's <var>shlibs</var>
          could say:
          <example>
            libfoo 1    foo (>= 1.2.3-1)
          </example>
        </p>

        <p>
          The version-specific dependency is to avoid warnings from
          <prgn>ld.so</prgn> about using older shared libraries with
          newer binaries.</p>
      </sect>

      <sect><heading>Further Technical information on
          <tt>shlibs</tt></heading>

        <sect1><heading><em>What</em> are the <tt>shlibs</tt> files?
          </heading>

          <p>
            The <tt>debian/shlibs</tt> file provides a way of checking
            for shared library dependencies on packaged binaries.
            They are intended to be used by package maintainers to
            make their lives easier.
          </p>

          <p>
            Other <tt>shlibs</tt> files that exist on a Debian system are
            <list>
              <item> <p><tt>/etc/dpkg/shlibs.default</tt></p></item>
              <item> <p><tt>/etc/dpkg/shlibs.override</tt></p></item>
              <item> <p><tt>/var/lib/dpkg/info/*.shlibs</tt></p></item>
              <item> <p><tt>debian/shlibs.local</tt></p></item>
            </list>
            These files are used by <prgn>dpkg-shlibdeps</prgn> when
            creating a binary package.</p>
        </sect1>

        <sect1><heading><em>How</em> does <prgn>dpkg-shlibdeps</prgn>
            work?
          </heading>
          <p>
            <prgn>dpkg-shlibdeps</prgn>
            determines the shared libraries directly
            <footnote>
              <p>
                It used to do this by calling <prgn>ldd</prgn>, but it
                now calls <prgn>objdump</prgn> to to this. This
                requires a couple of changes in the way that packages
                are built.
              </p>
              <p>
                A binary <tt>foo</tt> directly uses a library
                <tt>libbar</tt> if it is linked with that
                library. Other libraries that are needed by
                <tt>libbar</tt> are linked indirectly to <tt>foo</tt>,
                and the dynamic linker will load them automatically
                when it loads <tt>libbar</tt>. Running<prgn>ldd</prgn>
                lists all of the libraries used, both directly and
                indirectly; but <prgn>objdump</prgn> only lists the
                directly linked libraries. A package only needs to
                depend on the libraries it is directly linked to,
                since the dependencies for those libraries should
                automatically pull in the other libraries.
              </p>
              <p>
                This change does mean a change in the way packages are
                build though: currently <prgn>dpkg-shlibdeps</prgn> is
                only run on binaries. But since we will now rely on the
                libraries depending on the libraries they themselves
                need, the packages containing those libraries will
                need to run <prgn>dpkg-shlibdeps</prgn> on the
                libraries.
              </p>
              <p>
                A good example where this would help us is the current
                mess with multiple version of the <tt>mesa</tt>
                library. With the <prgn>ldd</prgn>-based system, every
                package that uses <tt>mesa</tt> needs to add a
                dependency on <tt>svgalib|svgalib-dummy</tt> in order
                to handle the glide <tt>mesa</tt> variant.  With an
                <prgn>objdump</prgn>-based system this isn't necessary
                anymore and would have saved everyone a lot of work.
              </p>
              <p>
                Another example: we could update <tt>libimlib</tt>
                with a new version that supports a new graphics format
                called dgf. If we use 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 wouldn't
                need to be updated.
              </p>
            </footnote>
            used by the compiled binaries and libraries passed through
            on its command line.
          </p>

          <p>
            For each shared library linked to,
            <prgn>dpkg-shlibdeps</prgn> needs to know
            <list compact="compact">
              <item><p>the package containing the library, and</p></item>
              <item><p>the library version number,</p></item>
            </list>
            and it scans the following files in this order:
            <enumlist compact="compact">
              <item><p><tt>debian/shlibs.local</tt></p></item>
              <item><p><tt>/etc/dpkg/shlibs.override</tt></p></item>
              <item><p><tt>/var/lib/dpkg/info/*.shlibs</tt></p></item>
              <item><p><tt>/etc/dpkg/shlibs.default</tt></p></item>
            </enumlist>
          </p>
        </sect1>

        <sect1><heading><em>Who</em> maintains the various
            <tt>shlibs</tt> files?
          </heading>

          <p>
            <list compact="compact">
              <item>
                <p><tt>/etc/dpkg/shlibs.default</tt> - the maintainer
                  of dpkg</p>
              </item>
              <item>
                <p>
                  <tt>/var/lib/dpkg/info/<var>package</var>.shlibs</tt>
                  - the maintainer of each package</p>
              </item>
              <item>
                <p>
                  <tt>/etc/dpkg/shlibs.override</tt> - the local
                  system administrator</p>
              </item>
              <item>
                <p><tt>debian/shlibs.local</tt> - the maintainer of
                  the package
                </p>
              </item>
            </list>
            The <tt>shlibs.default</tt> file is managed by
            <prgn>dpkg</prgn>. The entries in <tt>shlibs.default</tt>
            that are provided by <prgn>dpkg</prgn> are just there to
            fix things until the shared library packages all have
            <tt>shlibs</tt> files.
          </p>
        </sect1>

        <sect1><heading><em>How</em> to use <prgn>dpkg-shlibdeps</prgn> and
            the <tt>shlibs</tt> files
          </heading>

          <sect2><heading>If your package doesn't provide a shared
              library
            </heading>

            <p>
              Put a call to <prgn>dpkg-shlibdeps</prgn> into your
              <tt>debian/rules</tt> file.  If your package contains
              only binaries (e.g. no scripts) use:
              <example>
                dpkg-shlibdeps debian/tmp/usr/bin/* debian/tmp/usr/sbin/*
              </example>
              If <prgn>dpkg-shlibdeps</prgn> doesn't complain, you're
              done. If it does complain you might need to create your
              own <tt>debian/shlibs.local</tt> file.</p>
          </sect2>

          <sect2><heading>If your package provides a shared library
            </heading>

            <p>
              Create a <tt>debian/shlibs</tt> file and let
              <tt>debian/rules</tt> install it in the control area:
              <example>
                install -m644 debian/shlibs debian/tmp/DEBIAN
              </example>
              If your package contains additional binaries see above.
            </p>
          </sect2>
        </sect1>

        <sect1><heading><em>How</em> to write
            <tt>debian/shlibs.local</tt>
          </heading>

          <p>
            This file is intended only as a <em>temporary</em> fix if
            your binaries depend on a library which doesn't provide
            its own <tt>/var/lib/dpkg/info/*.shlibs</tt> file yet.
          </p>

          <p>
            Let's assume you are packaging a binary <tt>foo</tt>. Your
            output in building the package might look like this.
            <example>
              $ ldd foo
              libbar.so.1 => /usr/X11R6/lib/libbar.so.1.0 (0x4001e000)
              libX11.so.6 => /usr/X11R6/lib/libX11.so.6 (0x4002c000)
              libc.so.6 => /lib/libc.so.6 (0x40114000)
              /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)
            </example>
            And when you ran <prgn>dpkg-shlibdeps</prgn>
            <example>
              $ dpkg-shlibdeps -O foo
              dpkg-shlibdeps: warning: unable to find dependency information for shared library libbar
              (soname 1, path /usr/X11R6/lib/libbar.so.1.0, dependency field Depends)
              shlibs:Depends=libc6 (>= 2.2.1), xlibs (>= 4.0.1-11)
            </example>
            The <prgn>foo</prgn> binary depends on the
            <prgn>libbar</prgn> shared library, but no package seems
            to provide a <tt>*.shlibs</tt> file in
            <tt>/var/lib/dpkg/info/</tt>.  Let's determine the package
            responsible:
          </p>

          <p>
            <example>
              $ dpkg -S /usr/X11R6/lib/libbar.so.1.0
              bar1: /usr/X11R6/lib/libbar.so.1.0
              $ dpkg -s bar1 | grep Version
              Version: 1.0-1
            </example>
            This tells us that the <prgn>bar1</prgn> package, version
            1.0-1 is the one we are using. Now we can create our own
            <tt>debian/shlibs.local</tt> to temporarily fix the above
            problem. Include the following line into your
            <tt>debian/shlibs.local</tt> file.
            <example>
              libbar 1 bar1 (>= 1.0-1)
            </example>
            Now your package build should work. As soon as the
            maintainer of <prgn>libbar1</prgn> provides a
            <tt>shlibs</tt> file, you can remove your
            <tt>debian/shlibs.local</tt> file.
          </p>
        </sect1>
      </sect>
    </chapt>

    <chapt><heading>The Operating System</heading>


      <sect>
        <heading>File system hierarchy</heading>


        <sect1>
          <heading>Linux File system Structure</heading>

          <p>
            The location of all installed files and directories must
            comply  with the Linux File system Hierarchy Standard
            (FHS).  The latest version of this document can be found
            alongside this manual or on
            <url id="http://www.pathname.com/fhs/">.
            Specific questions about following the standard may be
            asked on <prgn>debian-devel</prgn>, or referred to Daniel
            Quinlan, the FHS coordinator, at
            <email>quinlan@pathname.com</email>.</p></sect1>


        <sect1>
          <heading>Site-specific programs</heading>

          <p>
            As mandated by the FHS, packages must not place any
            files in <tt>/usr/local</tt>, either by putting them in
            the file system archive to be unpacked by <prgn>dpkg</prgn>
            or by manipulating them in their maintainer scripts.</p>

          <p>
            However, the package may create empty directories below
            <tt>/usr/local</tt> so that the system administrator knows
            where to place site-specific files. These directories
            should be removed on package removal if they are
            empty.</p>

          <p>
            Note, that this applies only to directories <em>below</em>
            <tt>/usr/local</tt>, not <em>in</em>
            <tt>/usr/local</tt>. Packages must not create sub-directories
            in the directory <tt>/usr/local</tt> itself, except those listed in
            FHS, section 4.5. However, you may create directories
            below them as you wish. You must not remove any of the
            directories listed in 4.5, even if you created them.</p>

          <p>
            Since <tt>/usr/local</tt> can be mounted read-only from a
            remote server, these directories must be created and
            removed by the <tt>postinst</tt> and <tt>prerm</tt>
            maintainer scripts. These scripts must not fail if either
            of these operations fail. (In the future, it will be
            possible to tell <prgn>dpkg</prgn> not to unpack files
            matching certain patterns, so that the directories can be
            included in the <tt>.deb</tt> packages and system
            administrators who do not wish these directories in
            /usr/local do not need to have them.)</p>

          <p>
            For example, the <prgn>emacs</prgn> package will contain
            <example>
              mkdir -p /usr/local/lib/emacs/site-lisp || true
            </example>
            in the <tt>postinst</tt> script, and
            <example>
              rmdir /usr/local/lib/emacs/site-lisp || true
              rmdir /usr/local/lib/emacs || true
            </example>
            in the <tt>prerm</tt> script.</p>

          <p>
            If you do create a directory in <tt>/usr/local</tt> for
            local additions to a package, you should ensure that
            settings in <tt>/usr/local</tt> take precedence over the
            equivalents in <tt>/usr</tt>.</p>

          <p>
            However, because '/usr/local' and its contents are for
            exclusive use of the local administrator, a package must
            not rely on the presence or absence of files or
            directories in '/usr/local' for normal operation.</p>

          <p>
            The <tt>/usr/local</tt> directory itself and all the
            subdirectories created by the package should (by default) have
            permissions 2775 (group-writable and set-group-id) and be
            owned by <tt>root.staff</tt>.</p>
        </sect1>
      </sect>

      <sect>
        <heading>Users and groups</heading>

        <p>
          The Debian system can be configured to use either plain or
          shadow passwords.</p>

        <p>
          Some user ids (UIDs) and group ids (GIDs) are reserved
          globally for use by certain packages.  Because some packages
          need to include files which are owned by these users or
          groups, or need the ids compiled into binaries, these ids
          must be used on any Debian system only for the purpose for
          which they are allocated. This is a serious restriction, and
          we should avoid getting in the way of local administration
          policies. In particular, many sites allocate users and/or
          local system groups starting at 100.</p>

        <p>
          Apart from this we should have dynamically allocated ids,
          which should by default be arranged in some sensible
          order--but the behavior should be configurable.</p>

        <p>
          Packages other than <tt>base-passwd</tt> must not modify
          <tt>/etc/passwd</tt>, <tt>/etc/shadow</tt>,
          <tt>/etc/group</tt> or <tt>/etc/gshadow</tt>.</p>

        <p>
          The UID and GID ranges are as follows:
          <taglist>
            <tag>0-99:</tag>
            <item>
              <p>
                Globally allocated by the Debian project, the
                same on every Debian system.  These ids will appear in
                the <tt>passwd</tt> and <tt>group</tt> files of all
                Debian systems, new ids in this range being added
                automatically as the <tt>base-passwd</tt> package is
                updated.</p>

              <p>
                Packages which need a single statically allocated uid
                or gid should use one of these; their maintainers
                should ask the <tt>base-passwd</tt> maintainer for
                ids.</p>
            </item>

            <tag>100-999:</tag>
            <item>
              <p>
                Dynamically allocated system users and groups.
                Packages which need a user or group, but can have this
                user or group allocated dynamically and differently on
                each system, should use `<tt>adduser --system</tt>' to
                create the group and/or user.  <prgn>adduser</prgn>
                will check for the existence of the user or group, and
                if necessary choose an unused id based on the ranges
                specified in <tt>adduser.conf</tt>.</p></item>


            <tag>1000-29999:</tag>
            <item>
              <p>
                Dynamically allocated user accounts.  By default
                <prgn>adduser</prgn> will choose UIDs and GIDs for
                user accounts in this range, though
                <tt>adduser.conf</tt> may be used to modify this
                behavior.</p>
            </item>

            <tag>30000-59999:</tag>
            <item>
              <p>Reserved.</p></item>


            <tag>60000-64999:</tag>
            <item>
              <p>
                Globally allocated by the Debian project, but only
                created on demand. The ids are allocated centrally and
                statically, but the actual accounts are only created
                on users' systems on demand.</p>

              <p>
                These ids are for packages which are obscure or which
                require many statically-allocated ids.  These packages
                should check for and create the accounts in
                <tt>/etc/passwd</tt> or <tt>/etc/group</tt> (using
                <prgn>adduser</prgn> if it has this facility) if
                necessary.  Packages which are likely to require
                further allocations should have a `hole' left after
                them in the allocation, to give them room to
                grow.</p></item>


            <tag>65000-65533:</tag>
            <item>
              <p>Reserved.</p></item>


            <tag>65534:</tag>
            <item>
              <p>User `<tt>nobody</tt>.' The corresponding gid refers
              to the group  `<tt>nogroup</tt>.'</p></item>


            <tag>65535:</tag>
            <item>
              <p>
                <tt>(uid_t)(-1) == (gid_t)(-1)</tt>. NOT TO BE USED,
                because it is the error return sentinel value.</p>
            </item>
          </taglist>
        </p>
      </sect>
      <sect id="sysvinit">
        <heading>System run levels</heading>


        <sect1 id="/etc/init.d">
          <heading>Introduction</heading>

          <p>
            The <tt>/etc/init.d</tt> directory contains the scripts
            executed by <prgn>init</prgn> at boot time and when init
            state (or `runlevel') is changed (see <manref name="init"
                                                          section="8">).</p>

          <p>
            There are at least two different, yet functionally
            equivalent, ways of handling these scripts.  For the sake
            of simplicity, this document describes only the symbolic
            link method. However, it must not be assumed by maintainer
            scripts that this method is being used, and any automated
            manipulation of the various runlevel behaviours by
            maintainer scripts must be performed using `update-rc.d'
            as described below and not by manually installing or
            removing symlinks.  For  information on the
            implementation details of the other method, implemented in
            the <tt>file-rc</tt> package, please refer to the
            documentation of that package.</p>

          <p>
            These scripts are referenced by symbolic links in
            the <tt>/etc/rc<var>n</var>.d</tt> directories.  When
            changing runlevels, <prgn>init</prgn> looks in the
            directory <tt>/etc/rc<var>n</var>.d</tt> for the scripts
            it should execute, where <var>n</var> is the runlevel that
            is being changed to, or `S' for the boot-up scripts.</p>

          <p>
            The names of the links all have the form
            <tt>S<var>mm</var><var>script</var></tt> or
            <tt>K<var>mm</var><var>script</var></tt> where
            <var>mm</var> is a two-digit number and <var>script</var>
            is the name of the script (this should be the same as the
            name of the actual script in <tt>/etc/init.d</tt>.</p>

          <p>
            When <prgn>init</prgn> changes runlevel first the targets
            of the links whose names starting with a <tt>K</tt> are
            executed, each with the single argument <tt>stop</tt>,
            followed by the scripts prefixed with an <tt>S</tt>, each
            with the single argument <tt>start</tt>.  The <tt>K</tt>
            links are responsible for killing services and the
            <tt>S</tt> link for starting services upon entering the
            runlevel.</p>

          <p>
            For example, if we are changing from runlevel 2 to
            runlevel 3, init will first execute all of the <tt>K</tt>
            prefixed scripts it finds in <tt>/etc/rc3.d</tt>, and then
            all of the <tt>S</tt> prefixed scripts.  The links
            starting with <tt>K</tt> will cause the referred-to file
            to be executed with an argument of <tt>stop</tt>, and the
            <tt>S</tt> links with an argument of <tt>start</tt>.</p>

          <p>
            The two-digit number <var>mm</var> is used to decide which
            order to start and stop things in--low-numbered links have
            their scripts run first.  For example, the <tt>K20</tt>
            scripts will be executed before the <tt>K30</tt> scripts.
            This is used when a certain service must be started before
            another.  For example, the name server <prgn>bind</prgn>
            might need to be started before the news server
            <prgn>inn</prgn> so that <prgn>inn</prgn> can set up its
            access lists.  In this case, the script that starts
            <prgn>bind</prgn> would have a lower number than the
            script that starts <prgn>inn</prgn> so that it runs first:
            <example>
              /etc/rc2.d/S17bind
              /etc/rc2.d/S70inn
            </example>
          </p>
        </sect1>

        <sect1>
          <heading>Writing the scripts</heading>

          <p>
            Packages that include daemons for system services should
            place scripts in <tt>/etc/init.d</tt> to start or stop
            services at boot time or during a change of runlevel.
            These scripts should be named
            <tt>/etc/init.d/<var>package</var></tt>, and they should
            accept one argument, saying what to do:

            <taglist>
              <tag><tt>start</tt></tag>
              <item><p>start the service,</p></item>

              <tag><tt>stop</tt></tag>
              <item><p>stop the service,</p></item>

              <tag><tt>restart</tt></tag>
              <item><p>stop and restart the service,</p></item>

              <tag><tt>reload</tt></tag>
              <item><p>cause the configuration of the service to be
                  reloaded without actually stopping and restarting
                  the service,</p></item>

              <tag><tt>force-reload</tt></tag> <item><p>cause the
                  configuration to be reloaded if the service supports
                  this, otherwise restart the service.</p></item>
            </taglist>

            The <tt>start</tt>, <tt>stop</tt>, <tt>restart</tt>, and
            <tt>force-reload</tt> options should be supported by all
            scripts in <tt>/etc/init.d</tt>, the <tt>reload</tt>
            option is optional.</p>

          <p>
            The <tt>init.d</tt> scripts should ensure that they will
            behave sensibly if invoked with <tt>start</tt> when the
            service is already running, or with <tt>stop</tt> when it
            isn't, and that they don't kill unfortunately-named user
            processes.  The best way to achieve this is usually to use
            <prgn>start-stop-daemon</prgn>.</p>

          <p>
            If a service reloads its configuration automatically (as
            in the case of <prgn>cron</prgn>, for example), the
            <tt>reload</tt> option of the <tt>init.d</tt> script
            should behave as if the configuration has been reloaded
            successfully.</p>

          <p>
            These scripts should not fail obscurely when the
            configuration files remain but the package has been
            removed, as configuration files remain on the system after
            the package has been removed. Only when <prgn>dpkg</prgn>
            is executed with the <tt>--purge</tt> option will
            configuration files be removed. In particular, the init
            script itself is usually a configuration file (see
            <ref id="init.d notes">), and will remain on the system if
            the package is removed but not purged. Therefore, you
            should include a <tt>test</tt> statement at the top of the
            script, like this:
            <example>
              test -f <var>program-executed-later-in-script</var> || exit 0
            </example></p>

          <p>
            Often there are some values in the `<tt>init.d</tt>'
            scripts that a system administrator will frequently want
            to change. While the scripts are frequently conffiles,
            modifying them requires that the administrator merge in
            their changes each time the package is upgraded and the
            conffile changes. To ease the burden on the system
            administrator, such configurable values should not be
            placed directly in the script.  Instead, they should be
            placed in a file in `<tt>/etc/default</tt>', which
            typically will have the same base name as the
            `<tt>init.d</tt>' script. This extra file can be sourced
            by the script when the script runs. It must contain only
            variable settings and comments.
          </p>

          <p>
            To ensure that vital configurable values are always
            available, the `<tt>init.d</tt>' script should set default
            values for each of the shell variables it uses before
            sourcing the <tt>/etc/default/</tt> file. Also, since the
            `<tt>/etc/default/</tt>' file is often a conffile, the
            `<tt>init.d</tt>' script must behave sensibly without
            failing if it is deleted.
          </p>

        </sect1>

        <sect1>
          <heading>Managing the links</heading>

          <p>
            The program <prgn>update-rc.d</prgn> is provided to make
            it easier for package maintainers to arrange for the
            proper creation and removal of
            <tt>/etc/rc<var>n</var>.d</tt> symbolic links, or their
            functional equivalent if another method is being used.
            This may be used by maintainers in their packages'
            <tt>postinst</tt> and <tt>postrm</tt> scripts.</p>

          <p>
            You must use this script to make changes to
            <tt>/etc/rc<var>n</var>.d</tt> and <em>never</em> either
            include any <tt>/etc/rc<var>n</var>.d</tt> symbolic links
            in the actual archive or manually create or remove the
            symbolic links in maintainer scripts.  (The latter will
            fail if an alternative method of maintaining runlevel
            information is being used.)</p>

          <p>
            By default <prgn>update-rc.d</prgn> will start services in
            each of the multi-user state runlevels (2, 3, 4, and 5)
            and stop them in the halt runlevel (0), the single-user
            runlevel (1) and the reboot runlevel (6).  The system
            administrator will have the opportunity to customize
            runlevels by either running <prgn>update-rc.d</prgn>, by
            simply adding, moving, or removing the symbolic links in
            <tt>/etc/rc<var>n</var>.d</tt> if symbolic links are being
            used, or by modifying <tt>/etc/runlevel.conf</tt> if the
            <tt>file-rc</tt> method is being used.</p>

          <p>
            To get the default behavior for your package, put in your
            <tt>postinst</tt> script
            <example>
              update-rc.d <var>package</var> defaults &gt;/dev/null
            </example>
            and in your <tt>postrm</tt>
            <example>
              if [ purge = "$1" ]; then
              update-rc.d <var>package</var> remove &gt;/dev/null
              fi
            </example></p>

          <p>
            This will use a default sequence number of 20.  If it does
            not matter when or in which order the script is run, use
            this default.  If it does, then you should talk to the
            maintainer of the <prgn>sysvinit</prgn> package or post to
            <tt>debian-devel</tt>, and they will help you choose a
            number.</p>

          <p>
            For more information about using <tt>update-rc.d</tt>,
            please consult its manpage <manref name="update-rc.d"
                                               section="8">.</p></sect1>


        <sect1>
          <heading>Boot-time initialization</heading>

          <p>
            There used to be another directory, <tt>/etc/rc.boot</tt>,
            which contained scripts which were run once per machine
            boot. This has been deprecated in favour of links from
            <tt>/etc/rcS.d</tt> to files in <tt>/etc/init.d</tt> as
            described in <ref id="/etc/init.d">.  Packages must not
            place files in <tt>/etc/rc.boot</tt>.</p>

        <sect1 id="init.d notes">
          <heading>Notes</heading>

          <p>
            <em>Do not</em> include the
            <tt>/etc/rc<var>n</var>.d/*</tt> symbolic links in the
            <tt>.deb</tt> file system archive!  <em>This will cause
              problems!</em> You must create them with
            <prgn>update-rc.d</prgn>, as above.</p>

          <p>
            <em>Do not</em> include the
            <tt>/etc/rc<var>n</var>.d/*</tt> symbolic links in
            <prgn>dpkg</prgn>'s conffiles list!  <em>This will cause
              problems!</em> You should, however, treat the
            <tt>/etc/init.d</tt> scripts as configuration files,
            either by marking them as conffiles or managing them
            correctly in the maintainer scripts (see
            <ref id="config files">). (This is important since we want
            to give the local system administrator the chance to adapt
            the scripts to the local system--e.g., to disable a
            service without de-installing the package, or to specify
            some special command line options when starting a
            service--while making sure her changes aren't lost during
            the next package upgrade.)</p>
        </sect1>

        <sect1>
          <heading>Example</heading>

          <p>
            The <prgn>bind</prgn> DNS (nameserver) package wants to
            make sure that the nameserver is running in multiuser
            runlevels, and is properly shut down with the system.  It
            puts a script in <tt>/etc/init.d</tt>, naming the script
            appropriately <tt>bind</tt>.  As you can see, the script
            interprets the argument <tt>reload</tt> to send the
            nameserver a <tt>HUP</tt> signal (causing it to reload its
            configuration); this way the user can say
            <tt>/etc/init.d/bind reload</tt> to reload the name
            server.  The script has one configurable value, which can
            be used to pass parameters to the named program at
            startup.
          </p>

          <p>
            <example>
              #!/bin/sh
              #
              # Original version by Robert Leslie
              # &lt;rob@mars.org&gt;, edited by iwj and cs

              test -x /usr/sbin/named || exit 0

              # Source defaults file.
              PARAMS=''
              if [ -f /etc/default/bind ]; then
                . /etc/default/bind
              fi


              case "$1" in
              start)
              echo -n "Starting domain name service: named"
              start-stop-daemon --start --quiet --exec /usr/sbin/named \
                                -- $PARAMS
              echo "."
              ;;
              stop)
              echo -n "Stopping domain name service: named"
              start-stop-daemon --stop --quiet  \
              --pidfile /var/run/named.pid --exec /usr/sbin/named
              echo "."
              ;;
              restart)
              echo -n "Restarting domain name service: named"
              start-stop-daemon --stop --quiet  \
              --pidfile /var/run/named.pid --exec /usr/sbin/named
              start-stop-daemon --start --verbose --exec /usr/sbin/named \
                                -- $PARAMS
              echo "."
              ;;
              force-reload|reload)
              echo -n "Reloading configuration of domain name service: named"
              start-stop-daemon --stop --signal 1 --quiet  \
              --pidfile /var/run/named.pid --exec /usr/sbin/named
              echo "."
              ;;
              *)
              echo "Usage: /etc/init.d/bind {start|stop|restart|reload|force-reload}" >&2
              exit 1
              ;;
              esac

              exit 0
            </example>
          </p>

          <p>
            Complementing the above init script is a file
            '<tt>/etc/default/bind</tt>', which contains configurable
            parameters used by the script.
          </p>
          <p>
            <example>
              # Specified parameters to pass to named. See named(8).
              # You may uncomment the following line, and edit to taste.
              #PARAMS="-u nobody"
            </example>
          </p>

          <p>
            Another example on which to base your <tt>/etc/init.d</tt>
            scripts is in <tt>/etc/init.d/skeleton</tt>.</p>

          <p>
            If this package is happy with the default setup from
            <prgn>update-rc.d</prgn>, namely an ordering number of 20
            and having named running in all runlevels, it can say in
            its <tt>postinst</tt>:
            <example>
              update-rc.d bind defaults >/dev/null
            </example>
            And in its <tt>postrm</tt>, to remove the links when the
            package is purged:
            <example>
              if [ purge = "$1" ]; then
              update-rc.d bind remove >/dev/null
              fi
            </example></p>
        </sect1></sect>

      <sect>
        <heading>Cron jobs</heading>

        <p>
          Packages must not modify the configuration file
          <tt>/etc/crontab</tt>, and they must not modify the files in
          <tt>/var/spool/cron/crontabs</tt>.</p>

        <p>
          If a package wants to install a job that has to be executed
          via cron, it should place a file with the name of the
          package in one of the following directories:
          <example>
            /etc/cron.daily
            /etc/cron.weekly
            /etc/cron.monthly
          </example>
          As these directory names imply, the files within them are
          executed on a daily, weekly, or monthly basis,
          respectively. The exact times are listed in
          <tt>/etc/crontab</tt>.</p>

        <p>
          All files installed in any of these directories must be
          scripts (shell scripts, Perl scripts, etc.) so that they can
          easily be modified by the local system administrator. In
          addition, they should be treated as configuration files.</p>

        <p>
          If a certain job has to be executed more frequently than
          daily, the package should install a file
          <tt>/etc/cron.d/<var>package-name</var></tt>. This file uses
          the same syntax as <tt>/etc/crontab</tt> and is processed by
          <prgn>cron</prgn> automatically. The file must also be
          treated as a configuration file. (Note, that entries in the
          <tt>/etc/cron.d</tt> directory are not handled by
          <prgn>anacron</prgn>. Thus, you should only use this
          directory for jobs which may be skipped if the system is not
          running.)</p>

        <p>
          The scripts or crontab entries in these directories should
          check if all necessary programs are installed before they
          try to execute them. Otherwise, problems will arise when a
          package was removed but not purged since configuration files
          are kept on the system in this situation.</p>
      </sect>

      <sect>
        <heading>Console messages</heading>

        <p>
          This section describes different formats for messages
          written to standard output by the <tt>/etc/init.d</tt>
          scripts. The intent is to improve the consistency of
          Debian's startup and shutdown look and feel.</p>

        <p>
          Please look very careful at the details. We want to get the
          messages to look exactly the same way concerning spaces,
          punctuation, and case of letters.</p>

        <p>
          Here is a list of overall rules that you should use when you
          create output messages. They can be useful if you have a
          non-standard message that isn't covered in the sections
          below.</p>

        <p>
          <list>
            <item>
              <p>
                Every message should cover one line, start with a
                capital letter and end with a period `.'.</p></item>


            <item>
              <p>
                If you want to express that the computer is working on
                something (performing a specific task, not starting or
                stopping a program), we use an ``ellipsis'', namely
                three dots `...'. Note that we don't insert spaces in
                front of or behind the dots.  If the task has been
                completed we write `done.' and a line feed.</p></item>


            <item>
              <p>
                Design your messages as if the computer is telling you
                what he is doing (let him be polite :-) but don't
                mention ``him'' directly.  For example, if you think
                of saying
                <example>
                  I'm starting network daemons: nfsd mountd.
                </example>
                just say
                <example>
                  Starting network daemons: nfsd mountd.
                </example></p></item>
          </list></p>

        <p>
          The following formats should be used</p>

        <p>
          <list>
            <item>
              <p>when daemons get started.</p>

              <p>
                Use this format if your script starts one or more
                daemons.  The output should look like this (a single
                line, no leading spaces):
                <example>
                  Starting &lt;description&gt;: &lt;daemon-1&gt; &lt;daemon-2&gt; &lt;...&gt; &lt;daemon-n&gt;.
                </example>
                The &lt;description&gt; should describe the subsystem
                the daemon or set of daemons are part of, while
                &lt;daemon-1&gt; up to &lt;daemon-n&gt; denote each
                daemon's name (typically the file name of the
                program).</p>

              <p>
                For example, the output of /etc/init.d/lpd would look like:
                <example>
                  Starting printer spooler: lpd.
                </example></p>

              <p>
                This can be achieved by saying
                <example>
                  echo -n "Starting printer spooler: lpd"
                  start-stop-daemon --start --quiet lpd
                  echo "."
                </example>
                in the script. If you have more than one daemon to
                start, you should do the following:
                <example>
                  echo -n "Starting remote file system services:"
                  echo -n " nfsd"; start-stop-daemon --start --quiet nfsd
                  echo -n " mountd"; start-stop-daemon --start --quiet mountd
                  echo -n " ugidd"; start-stop-daemon --start --quiet ugidd
                  echo "."
                </example>
                This makes it possible for the user to see what takes
                so long and when the final daemon has been
                started. You should be careful where to put spaces: In the
                example above the system administrator can easily
                comment out a line if he don't wants to start a
                specific daemon, while the displayed message still
                looks good.</p></item>


            <item>
              <p>when something needs to be configured.</p>

              <p>
                If you have to set up different parameters of the
                system upon boot up, you should use this format:
                <example>
                  Setting &lt;parameter&gt; to `&lt;value&gt;'.
                </example></p>

              <p>
                You can use the following echo statement to get the quotes right:
                <example>
                  echo "Setting DNS domainname to \`"value"'."
                </example></p>

              <p>
                Note that the left quotation mark (`) is different
                from the right (').</p></item>

            <item>
              <p>when a daemon is stopped.</p>

              <p>
                When you stop a daemon you should issue a message
                similar to the startup message, except that `Starting'
                is replaced with `Stopping'.</p>

              <p>
                So stopping the printer daemon will like like this:
                <example>
                  Stopping printer spooler: lpd.
                </example></p></item>

            <item>
              <p>when something is executed.</p>

              <p>
                There are several examples where you have to run a
                program at system startup or shutdown to perform a
                specific task. For example, setting the system's clock
                via `netdate' or killing all processes when the system
                comes down. Your message should like this:
                <example>
                  Doing something very useful...done.
                </example>
                You should print the `done.' right after the job has been completed,
                so that the user gets informed why he has to wait. You can get this
                behavior by saying
                <example>
                  echo -n "Doing something very useful..."
                  do_something
                  echo "done."
                </example>
                in your script.</p></item>

            <item>
              <p>when the configuration is reloaded.</p>

              <p>
                When a daemon is forced to reload its configuration
                files you should use the following format:
                <example>
                  Reloading &lt;daemon's-name&gt; configuration...done.
                </example></p></item>

            <item>
              <p>when none of the above rules apply.</p>

              <p>
                If you have to print a message that doesn't fit into
                the styles described above, you can use something
                appropriate, but please have a look at the overall
                rules listed above.</p></item>
          </list></p></sect>


      <sect>
        <heading>Menus</heading>

        <p>
          Menu entries should follow the current menu policy as
          defined in the file <ftpsite>ftp.debian.org</ftpsite> in
          <ftppath>/debian/doc/package-developer/menu-policy.text.gz</ftppath>
          or your local mirror. In addition, it is included in the
          <tt>debian-policy</tt> package.
        </p>

        <p>
          The Debian <tt>menu</tt> packages provides a unique
          interface between packages providing applications and
          documents, and <em>menu programs</em> (either X window
          managers or text-based menu programs as
          <prgn>pdmenu</prgn>).</p>

        <p>
          All packages that provide applications that need not be
          passed any special command line arguments for normal
          operation should register a menu entry for those
          applications, so that users of the <tt>menu</tt> package
          will automatically get menu entries in their window
          managers, as well in shells like <tt>pdmenu</tt>.</p>

        <p>
          Please refer to the <em>Debian Menu System</em> document
          that comes with the <tt>menu</tt> package for information
          about how to register your applications and web
          documents.</p>
      </sect>


      <sect>
        <heading>Multimedia handlers</heading>

        <p>
          Packages which provide the ability to view/show/play,
          compose, edit or print MIME types should register themselves
          as such following the current MIME support policy as defined
          in the file found on <ftpsite>ftp.debian.org</ftpsite> in
          <ftppath>/debian/doc/package-developer/mime-policy.text.gz</ftppath>
          or your local mirror. In addition, it is included in the
          <tt>debian-policy</tt> package.
        </p>

        <p>
          MIME (Multipurpose Internet Mail Extensions, RFC 1521) is a
          mechanism for encoding files and data streams and providing
          meta-information about them, in particular their type (e.g.
          audio or video) and format (e.g. PNG, HTML, MP3).
        </p>

        <p>
          Registration of MIME type handlers allows programs like mail
          user agents and web browsers to to invoke these handlers to
          view, edit or display MIME types they don't support
          directly.
        </p>
      </sect>

      <sect>
        <heading>Keyboard configuration</heading>

        <p>
          To achieve a consistent keyboard configuration (i.e., all
          applications interpret a keyboard event the same way) all
          programs in the Debian distribution must be configured to
          comply with the following guidelines.</p>

        <p>
          Here is a list that contains certain keys and their interpretation:

          <taglist>
            <tag><tt>&lt;--</tt></tag>
            <item><p>delete the character to the left of the cursor</p></item>

            <tag><tt>Delete</tt></tag>
            <item><p>delete the character to the right of the cursor</p></item>

            <tag><tt>Control+H</tt></tag>
            <item><p>emacs: the help prefix</p></item>
          </taglist>

          The interpretation of any keyboard events should be independent
          of the terminal that's used, be it a virtual console, an X
          terminal emulator, an rlogin/telnet session, etc.</p>

        <p>
          The following list explains how the different programs
          should be set up to achieve this:</p>

        <p>
          <list compact="compact">
            <item><p>`<tt>&lt;--</tt>' generates KB_Backspace in
                X.</p></item>

            <item><p>`<tt>Delete</tt>' generates KB_Delete in X.</p></item>

            <item>
              <p>
                X translations are set up to make KB_Backspace
                generate ASCII DEL, and to make KB_Delete generate
                <tt>ESC [ 3 ~</tt> (this is the vt220 escape code for
                the `delete character' key).  This must be done by
                loading the resources using xrdb on all local X
                displays, not using the application defaults, so that
                the translation resources used correspond to the
                xmodmap settings.</p></item>

            <item>
              <p>
                The Linux console is configured to make
                `<tt>&lt;--</tt>' generate DEL, and `Delete' generate
                <tt>ESC [ 3 ~</tt> (this is the case at the
                moment).</p></item>

            <item><p>
                X applications are configured so that Backspace
                deletes left, and Delete deletes right.  Motif
                applications already work like this.</p></item>

            <item><p>stty erase <tt>^?</tt> .</p></item>

            <item><p>
                The `xterm' terminfo entry should have <tt>ESC [ 3
                  ~</tt> for kdch1, just like TERM=linux and
                TERM=vt220.</p></item>

            <item><p>
                Emacs is programmed to map KB_Backspace or the `stty
                erase' character to delete-backward-char, and
                KB_Delete or kdch1 to delete-forward-char, and
                <tt>^H</tt> to help as always.</p></item>

            <item><p>
                Other applications use the `stty erase' character and
                kdch1 for the two delete keys, with ASCII DEL being
                `delete previous character' and kdch1 being `delete
                character under cursor'.</p></item>
          </list></p>

        <p>
          This will solve the problem except for:</p>

        <p>
          <list compact="compact">
            <item><p>
                Some terminals have a <tt>&lt;--</tt> key that cannot
                be made to produce anything except <tt>^H</tt>.  On
                these terminals Emacs help will be unavailable on
                <tt>^H</tt> (assuming that the `stty erase' character
                takes precedence in Emacs, and has been set
                correctly).  M-x help or F1 (if available) can be used
                instead.</p></item>

            <item><p>
                Some operating systems use <tt>^H</tt> for stty erase.
                However, modern telnet versions and all rlogin
                versions propagate stty settings, and almost all UNIX
                versions honour stty erase.  Where the stty settings
                are not propagated correctly things can be made to
                work by using stty manually.</p></item>

            <item><p>
                Some systems (including previous Debian versions) use
                xmodmap to arrange for both <tt>&lt;--</tt> and Delete
                to generate KB_Delete.  We can change the behavior
                of their X clients via the same X resources that we
                use to do it for our own, or have our clients be
                configured via their resources when things are the
                other way around.  On displays configured like this
                Delete will not work, but <tt>&lt;--</tt>
                will.</p></item>

            <item><p>
                Some operating systems have different kdch1 settings
                in their terminfo for xterm and others.  On these
                systems the Delete key will not work correctly when
                you log in from a system conforming to our policy, but
                <tt>&lt;--</tt> will.</p></item>
          </list>
        </p>
      </sect>


      <sect>
        <heading>Environment variables</heading>

        <p>
          A program must not depend on environment variables to get
          reasonable defaults. (That's because these environment
          variables would have to be set in a system-wide
          configuration file like /etc/profile, which is not supported
          by all shells.)</p>

        <p>
          If a program usually depends on environment variables for its
          configuration, the program should be changed to fall back to
          a reasonable default configuration if these environment
          variables are not present. If this cannot be done easily
          (e.g., if the source code of a non-free program is not
          available), the program must be replaced by a small
          `wrapper' shell script which sets the environment variables
          if they are not already defined, and calls the original program.</p>

        <p>
          Here is an example of a wrapper script for this purpose:

          <example>
            #!/bin/sh
            BAR=${BAR:-/var/lib/fubar}
            export BAR
            exec /usr/lib/foo/foo "$@"
          </example></p>

        <p>
          Furthermore, as <tt>/etc/profile</tt> is a configuration
          file of the <prgn>base-files</prgn> package, other packages must not
          put any environment variables or other commands into that
          file.</p>
      </sect>
    </chapt>
    <chapt>
      <heading>Files</heading>


      <sect>
        <heading>Binaries</heading>

        <p>
          Two different packages must not install programs with
          different functionality but with the same filenames. (The
          case of two programs having the same functionality but
          different implementations is handled via `alternatives.')
          If this case happens, one of the programs must be
          renamed. The maintainers should report this to the
          developers' mailing and try to find a consensus about
          which package will have to be renamed.  If a consensus can
          not be reached, <em>both</em> programs must be
          renamed.</p>

        <p>
          Generally the following compilation parameters should be used:
          <example>
            CC = gcc
            CFLAGS = -O2 -Wall # sane warning options vary between programs
            LDFLAGS = # none
            install -s # (or use strip on the files in debian/tmp)
          </example></p>

        <p>
          Note that by default all installed binaries should be stripped,
          either by using the <tt>-s</tt> flag to
          <prgn>install</prgn>, or by calling <prgn>strip</prgn> on
          the binaries after they have been copied into
          <tt>debian/tmp</tt> but before the tree is made into a
          package.</p>

        <p>
          The <tt>-N</tt> flag should not be used.  On a.out systems
          it may have been useful for some very small binaries, but
          for ELF it has no good effect.</p>

        <p>
          Debugging symbols are useful for error diagnosis,
          investigation of core dumps (which may be submitted by users
          in bug reports), or testing and developing the
          software. Therefore it is recommended to support building
          the package with debugging information through the following
          interface: If the environment variable
          <tt>DEB_BUILD_OPTIONS</tt> contains the string
          <tt>debug</tt>, compile the software with debugging
          information (usually this involves adding the <tt>-g</tt>
          flag to <tt>CFLAGS</tt>). This allows the generation of a
          build tree with debugging information. If the environment
          variable <tt>DEB_BUILD_OPTIONS</tt> contains the string
          <tt>nostrip</tt>, do not strip the files at installation
          time. This allows one to generate a package with debugging
          information included. The following makefile snippet is only
          an example of how one may test for either condition:
          <footnote>
            <p>
              Rationale: Building by default with -g causes more
              wasted CPU cycles since the information is stripped away
              anyway. The package can by default build without -g if
              it also provides a mechanism to easily be rebuilt with
              debugging information. This can be done by providing a
              "build-debug" make target, or allowing the user to
              specify "DEB_BUILD_OPTIONS=debug" in the environment while
              compiling that package.
            </p>
            <p>Now this has several added benefits:
              <list>
                <item>
                  <p>
                    It is actually easier to build debugging bins and
                    libraries this way (no more editing debian/rules
                    or similar) since it provides a documented way of
                    getting this type of build.</p>
                </item>
                <item>
                  <p>
                    There will be much less wasted CPU time for the
                    autobuilders since not having debugging
                    information (and hence also not having to strip
                    it) will increase the speed of compiles. This
                    skips an entire pass of the compiler.
                  </p>
                </item>
              </list>
            </p>
          </footnote>


          <example>
            CFLAGS = -O2 -Wall
            INSTALL = install
            INSTALL_FILE    = $(INSTALL) -p    -o root -g root  -m  644
            INSTALL_PROGRAM = $(INSTALL) -p    -o root -g root  -m  755
            INSTALL_SCRIPT  = $(INSTALL) -p    -o root -g root  -m  755
            INSTALL_DIR     = $(INSTALL) -p -d -o root -g root  -m  755

            ifneq (,$(findstring debug,$(DEB_BUILD_OPTIONS)))
            CFLAGS += -g
            endif
            ifeq (,$(findstring nostrip,$(DEB_BUILD_OPTIONS)))
            INSTALL_PROGRAM += -s
            endif
          </example>

          Please note that the above example is merely informative,
          and is not a policy mandate. You may have to massage this
          example in order to make it work for your package.

        </p>

        <p>
          It is up to the package maintainer to decide what
          compilation options are best for the package.  Certain
          binaries (such as computationally-intensive programs) will
          function better with certain flags (<tt>-O3</tt>, for
          example); feel free to use them.  Please use good judgment
          here.  Don't use flags for the sake of it; only use them
          if there is good reason to do so.  Feel free to override
          the upstream author's ideas about which compilation
          options are best--they are often inappropriate for our
          environment.</p></sect>


      <sect>
        <heading>Libraries</heading>

        <p>
          All libraries must have a shared version in the lib
          package and a static version in the lib-dev package. The
          shared version must be compiled with <tt>-fPIC</tt>, and
          the static version must not be. In other words, each
          <tt>*.c</tt> file will need to be compiled twice.</p>

        <p>
          You must specify the gcc option <tt>-D_REENTRANT</tt>
          when building a library (either static or shared) to make
          the library compatible with LinuxThreads.</p>

        <p>
          Note that all installed shared libraries should be
          stripped with
          <example>
            strip --strip-unneeded &lt;your-lib&gt;
          </example>
          (The option `--strip-unneeded' makes <tt>strip</tt> remove
          only the symbols which aren't needed for relocation
          processing.)  Shared libraries can function perfectly well
          when stripped, since the symbols for dynamic linking are
          in a separate part of the ELF object file.</p>

        <p>
          Note that under some circumstances it may be useful to
          install a shared library unstripped, for example when
          building a separate package to support debugging.
        </p>

        <p>
          An ever increasing number of packages are using libtool to
          do their linking. The latest GNU libtools (>= 1.3a) can take
          advantage of the metadata in the installed libtool archive
          files (`*.la'). The main advantage of libtool's .la files is
          that it allows libtool to store and subsequently access
          metadata with respect to the libraries it builds.  libtool
          will search for those files, which contain a lot of useful
          information about a library (e.g. dependency libraries for
          static linking). Also, they're <em>essential</em> for
          programs using libltdl.
        </p>

        <p>
          Certainly libtool is fully capable of linking against shared
          libraries which don't have .la files, but being a mere shell
          script it can add considerably to the build time of a
          libtool using package if that shell-script has to derive all
          this information from first principles for each library every
          time it is linked. With the advent of libtool-1.4 (and to a
          lesser extent libtool-1.3), the .la files will also store
          information about inter-library dependencies which cannot
          necessarily be derived after the .la file is deleted.
        </p>

        <p>
          Packages that use libtool to create shared libraries should
          include the <em>.la</em> files in the <em>-dev</em>
          packages, with the exception that if the package relies on
          libtool's <em>libltdl</em> library, in which case the .la
          files must go in the run-time library package.  This is a
          good idea in general, and especially for static linking
          issues.
        </p>

        <p>
          You must make sure that you use only released versions of
          shared libraries to build your packages; otherwise other
          users will not be able to run your binaries
          properly. Producing source packages that depend on
          unreleased compilers is also usually a bad
          idea.
        </p>
      </sect>


      <sect>
        <heading>Shared libraries</heading>

        <p>
          Packages involving shared libraries should be split up
          into several binary packages.</p>

        <p>
          For a straightforward library which has a development
          environment and a runtime kit including just shared
          libraries you need to create two packages:
          <tt><var>libraryname</var><var>soname</var></tt>
          (<var>soname</var> is the shared object name of the shared
          library--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; usually the
          <var>soname</var> is the major number of the library) and
          <tt><var>libraryname</var><var>soname</var>-dev</tt>.</p>

        <p>
          If you prefer only to support one development version at a
          time you may name the development package
          <tt><var>libraryname</var>-dev</tt>; otherwise you may
          wish to use <prgn>dpkg</prgn>'s conflicts mechanism to
          ensure that the user only installs one development version
          at a time (after all, different development versions are
          likely to have the same header files in them, causing a
          filename clash if both are installed).  Typically the
          development version should  also have an exact version
          dependency on the runtime library, to make sure that
          compilation and linking happens correctly.</p>

        <p>
          Packages which use the shared library should have a
          dependency on the name of the shared library package,
          <tt><var>libraryname</var><var>soname</var></tt>.  When
          the <var>soname</var> changes you can have both versions
          of the library installed while moving from the old library
          to the new.</p>

        <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.  Instead, either create
          a third package for the runtime binaries (this package
          might typically be named
          <tt><var>libraryname</var>-runtime</tt>--note the absence
          of the <var>soname</var> in the package name) or if the
          development package is small include them in there.</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 their
          <var>soname</var>s 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>
          You should follow the directions in the <em>Debian Packaging
            Manual</em> for putting the shared library in its package,
          and you must include a <tt>shlibs</tt> control area
          file with details of the dependencies for packages which
          use the library.</p>

        <p>
          Shared libraries should not be installed
          executable, since <prgn>ld.so</prgn> does not require this
          and trying to execute a shared library results in a core
          dump.</p></sect>


      <sect id="scripts">
        <heading>Scripts</heading>

        <p>
          All command scripts, including the package maintainer
          scripts inside the package and used by <prgn>dpkg</prgn>,
          should have a <tt>#!</tt> line naming the shell to be used
          to interpret them.</p>

        <p>
          In the case of Perl scripts this should be
          <tt>#!/usr/bin/perl</tt>.</p>

        <p>
          Shell scripts (<prgn>sh</prgn> and <prgn>bash</prgn>)
          should almost certainly start with <tt>set -e</tt> so that
          errors are detected.  Every script should use
          <tt>set -e</tt> or check the exit status of <em>every</em>
          command.</p>

        <p>
          The standard shell interpreter `<tt>/bin/sh</tt>' can be a
          symbolic link to any POSIX compatible shell, if <tt>echo
            -n</tt> does not generate a newline.
          <footnote>
            <p>
              Debian policy specifies POSIX behavior for /bin/sh, but
              echo -n has widespread use in the Linux community
              (including especially debian policy, the linux kernel
              source, many debian scripts, etc.).  This echo -n
              mechanism is valid but not required under POSIX, hence
              this explicit addition. Also, rumour has it that this
              shall be mandated under the LSB anyway.
            </p>
          </footnote>
          Thus, shell scripts
          specifying `<tt>/bin/sh</tt>' as interpreter should only
          use POSIX features. If a script requires non-POSIX
          features from the shell interpreter, the appropriate shell
          must be specified in the first line of the script (e.g.,
          `<tt>#!/bin/bash</tt>') and the package must depend on the
          package providing the shell (unless the shell package is
          marked `Essential', e.g., in the case of
          <prgn>bash</prgn>).
        </p>

        <p>
          You may wish to restrict your script to POSIX features when possible so
          that it may use <tt>/bin/sh</tt> as its interpreter. If
          your script works with <prgn>ash</prgn>, it's probably
          POSIX compliant, but if you are in doubt, use
          <tt>/bin/bash</tt>.</p>

        <p>
          Perl scripts should check for errors when making any
          system calls, including <tt>open</tt>, <tt>print</tt>,
          <tt>close</tt>, <tt>rename</tt> and <tt>system</tt>.</p>

        <p>
          <prgn>csh</prgn> and <prgn>tcsh</prgn> should be avoided
          as scripting languages.  See <em>Csh Programming
            Considered Harmful</em>, one of the <tt>comp.unix.*</tt>
          FAQs.  It can be found on
          <url id="http://language.perl.com/versus/csh.whynot">, or
          <url id="http://www.cpan.org/doc/FMTEYEWTK/versus/csh.whynot">
          or even on <ftpsite>ftp.cpan.org</ftpsite>
          <ftppath>/pub/perl/CPAN/doc/FMTEYEWTK/versus/csh.whynot</ftppath>.
          If an upstream package comes with <prgn>csh</prgn> scripts
          then you must make sure that they start with
          <tt>#!/bin/csh</tt> and make your package depend on the
          <prgn>c-shell</prgn> virtual package.</p>

        <p>
          Any scripts which create files in world-writeable
          directories (e.g., in <tt>/tmp</tt>) must use a
          mechanism which will fail if a file with the same name
          already exists.</p>

        <p>
          The Debian base distribution provides the
          <prgn>tempfile</prgn> and <prgn>mktemp</prgn> utilities
          for use by scripts for this purpose.</p></sect>


      <sect>
        <heading>Symbolic links</heading>

        <p>
          In general, symbolic links within a top-level directory
          should be relative, and symbolic links pointing from one
          top-level directory into another should be absolute. (A
          top-level directory is a sub-directory of the root
          directory `/'.)</p>

        <p>
          In addition, symbolic links should be specified as short
          as possible, i.e., link targets like `foo/../bar' are
          deprecated.</p>

        <p>
          Note that when creating a relative link using
          <prgn>ln</prgn> it is not necessary for the target of the
          link to exist relative to the working directory you're
          running <prgn>ln</prgn> from; nor is it necessary to
          change directory to the directory where the link is to be
          made.  Simply include the string that should appear as the
          target of the link (this will be a pathname relative to
          the directory in which the link resides) as the first
          argument to <prgn>ln</prgn>.</p>

        <p>
          For example, in your <prgn>Makefile</prgn> or
          <tt>debian/rules</tt>, do things like:
          <example>
            ln -fs gcc $(prefix)/bin/cc
            ln -fs gcc debian/tmp/usr/bin/cc
            ln -fs ../sbin/sendmail $(prefix)/bin/runq
            ln -fs ../sbin/sendmail debian/tmp/usr/bin/runq
          </example></p>

        <p>
          A symbolic link pointing to a compressed file should
          always have the same file extension as the referenced
          file. (For example, if a file `<tt>foo.gz</tt>' is
          referenced by a symbolic link, the filename of the link
          has to end with `<tt>.gz</tt>' too, as in
          `bar.gz.')</p></sect>


      <sect>
        <heading>Device files</heading>

        <p>
          Packages must not include device files in the package file
          tree.</p>

        <p>
          If a package needs any special device files that are not
          included in the base system, it must call
          <prgn>MAKEDEV</prgn> in the <tt>postinst</tt> script,
          after asking the user for permission to do so.</p>

        <p>
          Packages must not remove any device files in the
          <tt>postrm</tt> or any other script. This is left to the
          system administrator.</p>

        <p>
          Debian uses the serial devices
          <tt>/dev/ttyS*</tt>. Programs using the old
          <tt>/dev/cu*</tt> devices should be changed to use
          <tt>/dev/ttyS*</tt>.</p>
      </sect>

      <sect id="config files">
        <heading>Configuration files</heading>
        <sect1>
          <heading>Definitions</heading>
          <p>
            <taglist>
              <tag>configuration file</tag>
              <item><p>
                  A file that affects the operation of program, or
                  provides site- or host-specific information, or
                  otherwise customizes the behavior of program.
                  Typically, configuration files are intended to be
                  modified by the system administrator (if needed or
                  desired) to conform to local policy or provide more
                  useful site-specific behavior.</p>
              </item>

              <tag><tt>conffile</tt></tag>
              <item><p>
                  A file listed in a package's <tt>conffiles</tt>
                  file, and is treated specially by <prgn>dpkg</prgn>
                  (see the <em>Debian Packaging Manual</em>).</p>
              </item>
            </taglist>
          </p>

          <p>
            The distinction between these two is important; they are
            not interchangeable concepts. Almost all
            <tt>conffiles</tt> are configuration files, but many
            configuration files are not <tt>conffiles</tt>.</p>

          <p>
            Note that a script that embeds configuration information
            (such as most of the files in <tt>/etc/init.d</tt> and
            <tt>/etc/cron.{daily,weekly,monthly}</tt>) is de-facto a
            configuration file and should be treated as such.</p>
        </sect1>

        <sect1>
          <heading>Location</heading>
          <p>
            Any configuration files created or used by your package
            must reside in <tt>/etc</tt>. If there are several you
            should consider creating a subdirectory of <tt>/etc</tt>
            named after your package.</p>

          <p>
            If your package creates or uses configuration files
            outside of <tt>/etc</tt>, and it is not feasible to modify
            the package to use the <tt>/etc</tt>, you should still put
            the files in <tt>/etc</tt> and create symbolic links to
            those files from the location that the package
            requires.</p>
        </sect1>

        <sect1>
          <heading>Behavior</heading>
          <p>
            Configuration file handling must conform to the following
            behavior:
            <list>
              <item>
                <p>local changes must be preserved during a package
                  upgrade</p>
              </item>
              <item>
                <p>configuration files must be preserved when the
                  package is removed, and only deleted when the
                  package is purged.</p>
              </item>
            </list></p>

          <p>
            The easy way to achieve this behavior is to make the
            configuration file a <tt>conffile</tt>. This is
            appropriate only if it is possible to distribute a default
            version that will work for most installations, although
            some system administrators may choose to modify it. This
            implies that the default version will be part of the
            package distribution, and must not be modified by the
            maintainer scripts during installation (or at any other
            time).
          </p>

          <p>
            In order to ensure that local changes are preserved
            correctly, no package may contain or make hard links to
            conffiles.
            <footnote>
              <p>
                Rationale: There are two problems with hard links.
                The first is that some editors break the link while
                editing one of the files, so that the two files may
                unwittingly become different.  The second is that
                <prgn>dpkg</prgn> might break the hard link while
                upgrading <tt>conffile</tt>s.
              </p>
            </footnote>

          <p>
            The other way to do it is via the maintainer scripts.
            In this case, the configuration file must not be listed as
            a <tt>conffile</tt> and must not be part of the package
            distribution. If the existence of a file is required for
            the package to be sensibly configured it is the
            responsibility of the package maintainer to write scripts
            which correctly create, update, maintain and
            remove-on-purge the file. These scripts must be idempotent
            (i.e., must work correctly if <prgn>dpkg</prgn> needs to
            re-run them due to errors during installation or removal),
            must cope with all the variety of ways <prgn>dpkg</prgn>
            can call maintainer scripts, must not overwrite or
            otherwise mangle the user's configuration without asking,
            must not ask unnecessary questions (particularly during
            upgrades), and otherwise be good citizens.</p>

          <p>
            The scripts are not required to configure every possible option for
            the package, but only those necessary to get the package
            running on a given system. Ideally the sysadmin should not
            have to do any configuration other than that done
            (semi-)automatically by the <tt>postinst</tt> script.</p>

          <p>
            A common practice is to create a script called
            <tt><var>package</var>-configure</tt> and have the
            package's <tt>postinst</tt> call it if and only if the
            configuration file does not already exist. In certain
            cases it is useful for there to be an example or template
            file which the maintainer scripts use. Such files should
            be in <tt>/usr/share/doc</tt> if they are examples or
            <tt>/usr/lib</tt> if they are templates, and should be
            perfectly ordinary <prgn>dpkg</prgn>-handled files
            (<em>not</em> <tt>conffiles</tt>).</p>

          <p>
            These two styles of configuration file handling must
            not be mixed, for that way lies madness:
            <prgn>dpkg</prgn> will ask about overwriting the file
            every time the package is upgraded.</p>

        </sect1>

        <sect1>
          <heading>Sharing configuration files</heading>
          <p>
            Packages which specify the same file as
            `<tt>conffile</tt>' must be tagged as <em>conflicting</em>
            with each other.
            </p>

          <p>
            The maintainer scripts must not alter the conffile of
            <em>any</em> package, including the one the scripts belong
            to.</p>

          <p>
            If two or more packages use the same configuration file
            and it is reasonable for both to be installed at the same
            time, one of these packages must be defined as
            <em>owner</em> of the configuration file, i.e., it will be
            the package to list that distributes the file and lists it
            as a <tt>conffile</tt>. Other packages that use the
            configuration file must depend on the owning package if
            they require the configuration file to operate. If the
            other package will use the configuration file if present,
            but is capable of operating without it, no dependency need
            be declared.</p>

          <p>
            If it is desirable for two or more related packages to
            share a configuration file <em>and</em> for all of the
            related packages to be able to modify that configuration
            file, then the following should be done:
            <enumlist>
              <item>
                <p>
                  have one of the related packages (the "core"
                  package) manage the configuration file with
                  maintainer scripts as described in the previous
                  section.</p>
              </item>
              <item><p>
                  the core package should also provide a program that
                  the other packages may use to modify the
                  configuration file.</p>
              </item>
              <item>
                <p>
                  the related packages must use the provided program
                  to make any modifications to the configuration file.
                  They should either depend on the core package to
                  guarantee that the configuration modifier program is
                  available or accept gracefully that they cannot
                  modify the configuration file if it is not.</p>
              </item>
            </enumlist></p>

          <p>
            Sometimes it's appropriate to create a new package which
            provides the basic infrastructure for the other packages
            and which manages the shared configuration files. (Check
            out the <tt>sgml-base</tt> package as an example.)</p>
        </sect1>

        <sect1>
          <heading>User configuration files ("dotfiles")</heading>

          <p>
            Files in <tt>/etc/skel</tt> will automatically be copied
            into new user accounts by <prgn>adduser</prgn>. They
            should not be referenced there by any program.</p>

          <p>
            Therefore, if a program needs a dotfile to exist in
            advance in <tt>$HOME</tt> to work sensibly, that dotfile
            should be installed in <tt>/etc/skel</tt> (and listed in
            conffiles, if it is not generated and modified dynamically
            by the package's installation scripts).</p>

          <p>
            However, programs that require dotfiles in order to
            operate sensibly (dotfiles that they do not create
            themselves automatically, that is) are a bad thing, and
            programs should be configured by the Debian default
            installation as close to normal as possible.</p>

          <p>
            Therefore, if a program in a Debian package needs to be
            configured in some way in order to operate sensibly that
            configuration should be done in a site-wide global
            configuration file elsewhere in <tt>/etc</tt>. Only if the
            program doesn't support a site-wide default configuration
            and the package maintainer doesn't have time to add it
            may a default per-user file be placed in
            <tt>/etc/skel</tt>.</p>

          <p>
            <tt>/etc/skel</tt> should be as empty as we can make it.
            This is particularly true because there is no easy
            mechanism for ensuring that the appropriate dotfiles are
            copied into the accounts of existing users when a package
            is installed.</p>
        </sect1>
      </sect>

      <sect>
        <heading>Log files</heading>
        <p>
          The traditional approach to log files has been to set up ad
          hoc log rotation schemes using simple shell scripts and
          cron. While this approach is highly customizable, it
          requires quite a lot of sysadmin work. Even though the
          original Debian system helped a little by automatically
          installing a system which can be used as a template, this
          was deemed not enough.
        </p>

        <p>
          A better scheme is to use logrotate, a GPL'd program
          developed by Red Hat, which centralizes log management. It
          has both a configuration file (<tt>/etc/logrotate.conf</tt>)
          and a directory where packages can drop logrotation info
          (<tt>/etc/logrotate.d</tt>).
        </p>

        <p>
          Log files should usually be named
          <tt>/var/log/<var>package</var>.log</tt>.  If you have many
          log files, or need a separate directory for permissions
          reasons (<tt>/var/log</tt> is writable only by
          <tt>root</tt>), you should usually create a directory named
          <tt>/var/log/<var>package</var></tt>.</p>

        <p>
          Log files must be rotated occasionally so
          that they don't grow indefinitely; the best way to do this
          is to drop a script into the directory
          <tt>/etc/logrotate.d</tt> and use the facilities provided by
          logrotate. Here is a good example for a logrotate config
          file (for more information see <manref name="logrotate"
                                                 section="8">):
          <example>
            /var/log/foo/* {
            rotate 12
            weekly
            compress
            postrotate
            /etc/init.d/foo force-reload
            endscript
            }
          </example>
          Which rotates all files under `/var/log/foo', saves 12
          compressed generations, and sends a HUP signal at the end of
          rotation.

        </p>

        <p>
          Log files should be removed when the package is
          purged (but not when it is only removed), by checking the
          argument to the <tt>postrm</tt> script (see the <em>Debian
            Packaging Manual</em> for details).</p>
      </sect>


      <sect>
        <heading>Permissions and owners</heading>

        <p>
          The rules in this section are guidelines for general use.
          If necessary you may deviate from the details below.
          However, if you do so you must make sure that what is done
          is secure and you should try to be as consistent as possible
          with the rest of the system.  You should probably also
          discuss it on <prgn>debian-devel</prgn> first.</p>

        <p>
          Files should be owned by <tt>root.root</tt>, and made
          writable only by the owner and universally readable (and
          executable, if appropriate).</p>

        <p>
          Directories should be mode 755 or (for group-writability)
          mode 2775.  The ownership of the directory should be
          consistent with its mode--if a directory is mode 2775, it
          should be owned by the group that needs write access to
          it.</p>

        <p>
          Setuid and setgid executables should be mode 4755 or 2755
          respectively, and owned by the appropriate user or group.
          They should not be made unreadable (modes like 4711 or
          2711 or even 4111); doing so achieves no extra security,
          because anyone can find the binary in the freely available
          Debian package--it is merely inconvenient.  For the same
          reason you should not restrict read or execute permissions
          on non-set-id executables.</p>

        <p>
          Some setuid programs need to be restricted to particular
          sets of users, using file permissions.  In this case they
          should be owned by the uid to which they are set-id, and
          by the group which should be allowed to execute them.
          They should have mode 4754; there is no point in making
          them unreadable to those users who must not be allowed to
          execute them.</p>

        <p>
          You must not arrange that the system administrator can only
          reconfigure the package to correspond to their local
          security policy by changing the permissions on a binary.
          Ordinary files installed by <prgn>dpkg</prgn> (as opposed
          to conffiles and other similar objects) have their
          permissions reset to the distributed permissions when the
          package is reinstalled.  Instead you should consider (for
          example) creating a group for people allowed to use the
          program(s) and making any setuid executables executable
          only by that group.</p>

        <p>
          If you need to create a new user or group for your package
          there are two possibilities.  Firstly, you may need to
          make some files in the binary package be owned by this
          user or group, or you may need to compile the user or
          group id (rather than just the name) into the binary
          (though this latter should be avoided if possible, as in
          this case you need a statically allocated id).</p>

        <p>
          If you need a statically allocated id, you must ask for a
          user or group id from the base system
          maintainer, and must not release the package until you
          have been allocated one.  Once you have been allocated one
          you must make the package depend on a version of the base
          system with the id present in <tt>/etc/passwd</tt> or
          <tt>/etc/group</tt>, or alternatively arrange for your
          package to create the user or group itself with the
          correct id (using <tt>adduser</tt>) in its pre- or
          post-installation script (the latter is to be preferred if
          it is possible).</p>

        <p>
          On the other hand, the program might be able to determine the
          uid or gid from the group name at runtime, so that a
          dynamic id can be used.  In this case you should choose an
          appropriate user or group name, discussing this on
          <prgn>debian-devel</prgn> and checking with the base
          system maintainer that it is unique and that they do not
          wish you to use a statically allocated id instead.  When
          this has been checked you must arrange for your package to
          create the user or group if necessary using
          <prgn>adduser</prgn> in the pre- or post-installation
          script (again, the latter is to be preferred if it is
          possible).</p>

        <p>
          Note that changing the numeric value of an id associated with a name
          is very difficult, and involves searching the file system for all
          appropriate files.  You need to think carefully whether a static or
          dynamic id is required, since changing your mind later will cause
          problems.</p>
      </sect>
    </chapt>

    <chapt>
      <heading>Customized programs</heading>

      <sect id="arch-spec">
        <heading>Architecture specification strings</heading>

        <p>
          If a program needs to specify an <em>architecture specification
            string</em> in some place, the following format should be used:
          <example>
            &lt;arch&gt;-&lt;os&gt;
          </example>
          where `&lt;arch&gt;' is one of the following: i386, alpha, arm, m68k,
          powerpc, sparc and `&lt;os&gt;' is one of: linux, gnu.  Use
          of <em>gnu</em> in this string is reserved for the GNU/Hurd
          operating system.</p>
        <p>
          Note, that we don't want to use `&lt;arch&gt;-debian-linux'
          to apply to the rule `architecture-vendor-os' since this
          would make our programs incompatible to other Linux
          distributions. Also note, that we don't use
          `&lt;arch&gt;-unknown-linux', since the `unknown' does not
          look very good.</p></sect>


      <sect>
        <heading>Daemons</heading>

        <p>
          The configuration files <tt>/etc/services</tt>,
          <tt>/etc/protocols</tt>, and <tt>/etc/rpc</tt> are managed
          by the <prgn>netbase</prgn> package and may not be modified
          by other packages.</p>

        <p>
          If a package requires a new entry in one of these files, the
          maintainer should get in contact with the
          <prgn>netbase</prgn> maintainer, who will add the entries
          and release a new version of the <prgn>netbase</prgn>
          package.</p>

        <p>
          The configuration file <tt>/etc/inetd.conf</tt> must not be
          modified by the package's scripts except via the
          <prgn>update-inetd</prgn> script or the
          <prgn>DebianNet.pm</prgn> Perl module.</p>

        <p>
          If a package wants to install an example entry into
          <tt>/etc/inetd.conf</tt>, the entry must be preceded with
          exactly one hash character (<tt>#</tt>). Such lines are
          treated as `commented out by user' by the
          <prgn>update-inetd</prgn> script and are not changed or
          activated during a package updates.</p></sect>


      <sect>
        <heading>Using pseudo-ttys and modifying wtmp, utmp and lastlog</heading>

        <p>
          Some programs need to create pseudo-ttys. This should be done
          using Unix98 ptys if the C library supports it. The resulting
          program must not be installed setuid root, unless that
          is required for other functionality.
        </p>

        <p>
          The files <tt>/var/run/utmp</tt>, <tt>/var/log/wtmp</tt> and
          <tt>/var/log/lastlog</tt> must be installed writeable by
          group utmp.  Programs who need to modify those files must
          be installed setgid utmp.
        </p>
      </sect>

      <sect>
        <heading>Editors and pagers</heading>

        <p>
          Some programs have the ability to launch an editor or pager
          program to edit or display a text document. Since there are
          lots of different editors and pagers available in the Debian
          distribution, the system administrator and each user should
          have the possibility to choose his/her preferred editor and
          pager.</p>

        <p>
          In addition, every program should choose a good default
          editor/pager if none is selected by the user or system
          administrator.</p>

        <p>
          Thus, every program that launches an editor or pager must
          use the EDITOR or PAGER environment variables to determine
          the editor/pager the user wants to get started. If these
          variables are not set, the programs <tt>/usr/bin/editor</tt>
          and <tt>/usr/bin/pager</tt> should be used, respectively.</p>

        <p>
          These two files are managed through `alternatives.' That is,
          every package providing an editor or pager must call the
          <prgn>update-alternatives</prgn> script to register these
          programs.</p>

        <p>
          If it is very hard to adapt a program to make us of the
          EDITOR and PAGER variables, that program may be configured
          to use <tt>/usr/bin/sensible-editor</tt> and
          <tt>/usr/bin/sensible-pager</tt> as editor or pager program,
          respectively. These are two scripts provided in the Debian
          base system that check the EDITOR and PAGER variables and
          launch the appropriate program or fall back to
          <tt>/usr/bin/editor</tt> and <tt>/usr/bin/pager</tt>,
          automatically.</p>

        <p>
          A program may also use the VISUAL environment variable to
          determine the user's choice of editor. If it exists, it
          should take precedence over EDITOR. This is in fact what
          <tt>/usr/bin/sensible-editor</tt> does.</p>

        <p>
          It is not required for a package to depend on
          `editor' and `pager', nor is it required for a package to
          provide such virtual packages.
          <footnote>
            <p>
              The Debian base system already provides an editor and
              a pager program,
            </p>
          </footnote>
        </p>

      </sect>


      <sect id="web-appl">
        <heading>Web servers and applications</heading>

        <p>
          This section describes the locations and URLs that should
          be used by all web servers and web application in the Debian
          system.</p>

        <p>
          <enumlist>
            <item>
              <p>Cgi-bin executable files are installed in the
                directory
                <example>
                  /usr/lib/cgi-bin/&lt;cgi-bin-name&gt;
                </example>
                and should be referred to as
                <example>
                  http://localhost/cgi-bin/&lt;cgi-bin-name&gt;
                </example></p></item>


            <item><p>Access to html documents</p>

              <p>
                Html documents for a package are stored in
                <tt>/usr/share/doc/<var>package</var></tt> but should
                be accessed via symlinks as
                <tt>/usr/doc/<var>package</var></tt><footnote> for
                    backward compatibility, see <ref id="usrdoc"></footnote>
                and can be referred to as
                <example>
                  http://localhost/doc/&lt;package&gt;/&lt;filename&gt;
                </example></p></item>


            <item><p>Web Document Root</p>

              <p>
                Web Applications should try to avoid storing files in
                the Web Document Root.  Instead they should use the
                /usr/share/doc/&lt;package&gt; directory for documents and
                register the Web Application via the menu package. If
                access to the web-root is unavoidable then use
                <example>
                  /var/www
                </example>
                as the Document Root. This might be just a
                symbolic link to the location where the sysadmin has
                put the real document root.</p>
            </item>

          </enumlist></p></sect>


      <sect>
        <heading>Mail transport, delivery and user agents</heading>

        <p>
          Debian packages which process electronic mail, whether
          mail-user-agents (MUAs) or mail-transport-agents (MTAs),
          must make sure that they are compatible with the
          configuration decisions below.  Failure to do this may
          result in lost mail, broken <tt>From:</tt> lines, and other
          serious brain damage!</p>

        <p>
          The mail spool is <tt>/var/spool/mail</tt> and the interface
          to send a mail message is <tt>/usr/sbin/sendmail</tt> (as
          per the FHS).  The mail spool is part of the base system
          and not part of the MTA package.</p>

        <p>
          All Debian MUAs, MTAs, MDAs and other mailbox accessing
          programs (like IMAP daemons) must lock the mailbox in an
          NFS-safe way. This means that <tt>fcntl()</tt> locking must
          be combined with dot locking.  To avoid deadlocks, a
          program should use <tt>fcntl()</tt> first and dot locking
          after this or alternatively implement the two locking
          methods in a non blocking way<footnote>
            <p>
              If it is not possible to establish both locks, the
              system shouldn't wait for the second lock to be
              established, but remove the first lock, wait a (random)
              time, and start over locking again.</p>
          </footnote>. Using the functions <tt>maillock</tt> and
          <tt>mailunlock</tt> provided by the
          <tt>liblockfile*</tt><footnote>
            <p>
              <tt>liblockfile</tt> version &gt;&gt;1.01</p>
          </footnote> packages is the recommended way to realize this.
        </p>

        <p>
          Mailboxes are generally 660 <tt><var>user</var>.mail</tt>
          unless the user has chosen otherwise.  A MUA may remove a
          mailbox (unless it has nonstandard permissions) in which
          case the MTA or another MUA must recreate it if needed.
          Mailboxes must be writable by group mail.</p>

        <p>
          The mail spool is 2775 <tt>root.mail</tt>, and MUAs should
          be setgid mail to do the locking mentioned above (and
          must obviously avoid accessing other users' mailboxes
          using this privilege).</p>

        <p>
          <tt>/etc/aliases</tt> is the source file for the system mail
          aliases (e.g., postmaster, usenet, etc.)--it is the one
          which the sysadmin and <tt>postinst</tt> scripts may edit.
          After <tt>/etc/aliases</tt> is edited the program or human
          editing it must call <prgn>newaliases</prgn>.  All MTA
          packages must come with a <prgn>newaliases</prgn> program,
          even if it does nothing, but older MTA packages do not do
          this so programs should not fail if <prgn>newaliases</prgn>
          cannot be found.</p>

        <p>
          The convention of writing <tt>forward to
            <var>address</var></tt> in the mailbox itself is not
          supported.  Use a <tt>.forward</tt> file instead.</p>

        <p>
          The <prgn>rmail</prgn> program used by UUCP
          for incoming mail should be  <tt>/usr/sbin/rmail</tt>.
          Likewise, <prgn>rsmtp</prgn>, for receiving
          batch-SMTP-over-UUCP, should be <tt>/usr/sbin/rsmtp</tt> if it
          is supported.</p>

        <p>
          If you need to know what name to use (for example) on
          outgoing news and mail messages which are generated locally,
          you should use the file <tt>/etc/mailname</tt>.  It will
          contain the portion after the username and <tt>@</tt> (at)
          sign for email addresses of users on the machine (followed
          by a newline).</p>

        <p>
          A package should check for the existence of this file.  If
          it exists it should use it without comment. (An MTA's
          prompting configuration script may wish to prompt the user
          even if it finds this file exists.) If it does not exist it
          should prompt the user for the value and store it in
          <tt>/etc/mailname</tt> as well as using it in the package's
          configuration.  The prompt should make it clear that the
          name will not just be used by that package.  For example, in
          this situation the INN package says:
          <example>
            Please enter the `mail name' of your system.  This is the
            hostname portion of the address to be shown on outgoing
            news and mail messages.  The default is
            <var>syshostname</var>, your system's host name.  Mail
            name [`<var>syshostname</var>']:
          </example>
          where <var>syshostname</var> is the output of <tt>hostname
            --fqdn</tt>.</p></sect>


      <sect>
        <heading>News system configuration</heading>

        <p>
          All the configuration files related to the NNTP (news)
          servers and clients should be located under
          <tt>/etc/news</tt>.</p>

        <p>
          There are some configuration issues that apply to a number
          of news clients and server packages on the machine. These
          are:

          <taglist>
            <tag>/etc/news/organization</tag>
            <item><p>A string which should appear as the
                organization header for all messages posted
                by NNTP clients on the machine</p></item>

            <tag>/etc/news/server</tag>
            <item><p>Contains the FQDN of the upstream NNTP
                server, or localhost if the local machine is
                an NNTP server.</p></item>
          </taglist>

          Other global files may be added as required for cross-package news
          configuration.</p></sect>


      <sect>
        <heading>Programs for the X Window System</heading>

        <p>
          <em>Programs that may be configured with support for the X Window
            System</em> must be configured to do so and must declare any
          package dependencies necessary to satisfy their runtime
          requirements when using the X Window System, unless the package
          in question is of standard or higher priority, in which case
          X-specific binaries may be split into a separate package, or
          alternative versions of the package with X support may be
          provided.
        </p>


        <p>
          <em>Packages which provide an X server</em> 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>
            <p>
              This implements current practice, and provides an actual
              policy for usage of the "xserver" virtual package which
              appears in the virtual packages list.  In a nutshell, X
              servers that interface directly with the display and input
              hardware or via another subsystem (e.g., GGI) should provide
              xserver.  Things like Xvfb, Xnest, and Xprt should not.
            </p>
          </footnote>
        </p>

        <p>
          <em>Packages that provide a terminal emulator</em> for the X
          Window System which support a terminal type with a terminfo
          description provided in the <tt>ncurses-base</tt> package
          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
          <tt>/usr/bin/x-terminal-emulator</tt>, with a priority of
          20.
        </p>

        <p>
          <em>Packages that provide window managers</em> 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 <tt>/usr/bin/x-window-manager</tt>, with a priority
          calculated as follows:
          <list>
            <item>Start with a priority of 20.</item>
            <item>If the window manager supports the Debian menu system,
                add 20 points if this support is available in the
                package's default configuration (i.e., no
                configuration files belonging to the system or user
                have to be edited to activate the feature); if
                configuration files must be modified, add only 10
                points.</item>
            <item>If the window manager permits the X session to be
                restarted using a <em>different</em> window manager
                (without killing the X server) in its default
                configuration, add 10 points; otherwise add
                none.</item>
          </list>
        </p>

        <p>
          <em>Packages that provide fonts for the X Window System</em>
          must do a number of things to ensure that they are both
          available without modification of the X or font server
          configuration, and that they do not corrupt files used by
          other font packages to register information about themselves.
          <enumlist>
            <item>
                Fonts of any type supported by the X Window System
                should be be in a separate binary package from any
                executables, libraries, or documentation (except that
                specific to the fonts shipped); if a program or
                library is <em>unusable</em> without one or more
                specific fonts, the package containing the program or
                library should declare a dependency on the package(s)
                containing the font(s) it requires.
            </item>
            <item>
                BDF fonts should be converted to PCF fonts with the
                <tt>bdftopcf</tt> utility (available in the
                <tt>xutils</tt> package, <tt>gzip</tt>ped, and
                placed in a directory that corresponds to their
                resolution:
                <list>
                  <item>
                      100 dpi fonts should be placed in
                      <tt>/usr/X11R6/lib/X11/fonts/100dpi/</tt>.
                  </item>
                  <item>
                      75 dpi fonts should be placed in
                      <tt>/usr/X11R6/lib/X11/fonts/75dpi/</tt>.
                  </item>
                  <item>
                      Character-cell fonts, cursor fonts, and other
                      low-resolution fonts should be placed in
                      <tt>/usr/X11R6/lib/X11/fonts/misc/</tt>.
                  </item>
                </list>
            </item>
            <item>
                Speedo fonts should be placed in
                <tt>/usr/X11R6/lib/X11/fonts/Speedo/</tt>.
            </item>
            <item>
                Type 1 fonts should be placed in
                <tt>/usr/X11R6/lib/X11/fonts/Type1/</tt>.  If font
                metric files are available, they may be placed here as
                well.
            </item>
            <item>
                Subdirectories of <tt>/usr/X11R6/lib/X11/fonts/</tt>
                other than those listed above should be neither created nor
                used.  (The <tt>PEX</tt> and <tt>cyrillic</tt> directories are
                excepted for historical reasons, but installation of files into
                these directories remains discouraged.)
            </item>
            <item>
                Font packages may, instead of placing files directly in
                the X font directories listed above, provide symbolic links in
                the font directory which point to the files' actual location
                in the filesystem.  Such a location should comply with the
                FHS.
            </item>
            <item>
                Font packages should not contain both 75dpi and 100dpi
                versions of a font.  If both are available, they should be
                provided in separate binary packages with "-75dpi" or "-100dpi"
                appended to the names of the packages containing the
                corresponding fonts.
            </item>
            <item>
                Fonts destined for the <tt>misc</tt> subdirectory should
                not be included in the same package as 75dpi or 100dpi fonts;
                instead, they should be provided in a separate package with
                "-misc" appended to its name.
            </item>
            <item>
                Font packages <em>must not</em> provide the files
                <tt>fonts.dir</tt>, <tt>fonts.alias</tt>, or
                <tt>fonts.scale</tt> in a font directory.
                <list>
                  <item>
                      <tt>fonts.dir</tt> files must not be provided at
                      all.
                  </item>
                  <item>
                      <tt>fonts.alias</tt> and <tt>fonts.scale</tt>
                      files, if needed, should be provided in the
                      directory
                      <tt>/etc/X11/fonts/<em>fontdir</em>/<em>package</em>.<em>extension</em></tt>,
                      where <em>fontdir</em> is the name of the
                      subdirectory of
                      <tt>/usr/X11R6/lib/X11/fonts/</tt> where the
                      package's corresponding fonts are stored (e.g.,
                      <tt>75dpi</tt> or <tt>misc</tt>),
                      <em>package</em> is the name of the package that
                      provides these fonts, and <em>extension</em> is
                      either <tt>scale</tt> or <tt>alias</tt>,
                      whichever corresponds to the file
                      contents.
                  </item>
                </list>
            </item>
            <item>
                Font packages must declare a dependency on
                <tt>xutils</tt> and, in the package
                post-installation and post-removal scripts, invoke the
                <tt>mkfontdir</tt> command on each directory into
                which they installed fonts.
            </item>
            <item>
                Font packages that provide one or more
                <tt>fonts.scale</tt> files as described above must declare a
                versioned dependency on <tt>xutils (&gt;=
                  4.0.2)</tt> and invoke <tt>update-fonts-scale</tt> on each
                directory into which they installed fonts
                <em>before</em> invoking <tt>mkfontdir</tt> on that
                directory.  This invocation must occur in both the
                post-installation and post-removal scripts.
            </item>
            <item>
                Font packages that provide one or more
                <tt>fonts.alias</tt> files as described above must
                declare a versioned dependency on <tt>xutils
                  (&gt;= 4.0.2)</tt> and, in the package
                post-installation and post-removal scripts, invoke
                <tt>update-fonts-alias</tt> on each directory into
                which they installed fonts.
            </item>
            <item>
                Font packages must not provide alias names for the
                fonts they include which collide with alias names already in
                use by fonts already packaged.
            </item>
            <item>
                Font packages must not provide fonts with the same XLFD
                registry name as another font already packaged.
            </item>
          </enumlist>
        </p>

        <p>
          <em>Application defaults</em> files must be installed in the
          directory <tt>/usr/X11R6/lib/X11/app-defaults/</tt>.
          <footnote>
            <p>Note: This shall change very shortly.</p>
          </footnote>
          They should not be registered as <em>conffile</em>s or
          otherwise treated as configuration files.  Customization of
          programs' X resources may be supported with the provision of
          a file with the same name as that of the package placed in
          the <tt>/etc/X11/Xresources/</tt> directory, which must
          registered as a <em>conffile</em>.  <em>Important:</em>
          packages that install files into the
          <tt>/etc/X11/Xresources/</tt> directory <em>must</em>
          declare a conflict with <tt>xbase (&lt;&lt;
            3.3.2.3a-2)</tt>; if this is not done it is possible for the
          installing package to destroy a previously-existing
          <tt>/etc/X11/Xresources</tt> <em>file</em> which had been
          customized by the system administrator.
          <footnote>
            <p>Rationale: clarifies the language to properly
              address the package maintainer, not the system
              administrator, as to how to manage
              /etc/X11/Xresources.</p>
          </footnote>
        </p>


        <p>
          <em>Packages using the X Window System should abide by the FHS
            standard whenever possible</em>; they should install binaries,
          libraries, manual pages, and other files in FHS-mandated
          locations wherever possible.  This means that files must
          not be installed into <tt>/usr/X11R6/bin/</tt>,
          <tt>/usr/X11R6/lib/</tt>, or <tt>/usr/X11R6/man/</tt> unless
          this is necessary for the package to operate properly.
          Configuration files for window managers and display managers
          should be placed in a subdirectory of <tt>/etc/X11/</tt>
          corresponding to the package name due to these programs'
          tight integration with the mechanisms of the X Window
          System.  Application-level programs should use the
          <tt>/etc/</tt> directory unless otherwise mandated by
          policy.  The installation of files into subdirectories of
          <tt>/usr/X11R6/include/X11/</tt> and
          <tt>/usr/X11R6/lib/X11/</tt> is permitted but discouraged;
          package maintainers should determine if subdirectories of
          <tt>/usr/lib/</tt> and <tt>/usr/share/</tt> can be used
          instead (symlinks from the X11R6 directories to
          FHS-compliant locations is encouraged if the program is not
          easily configured to look elsewhere for its files).
          Packages must not provide -- or install files into -- the
          directories <tt>/usr/bin/X11/</tt>,
          <tt>/usr/include/X11/</tt>, or <tt>/usr/lib/X11/</tt>.
          Files within a package should, however, make reference to
          these directories, rather than their X11R6-named
          counterparts <tt>/usr/X11R6/bin/</tt>,
          <tt>/usr/X11R6/include/X11/</tt>, and
          <tt>/usr/X11R6/lib/X11/</tt>, if the resources being
          referred to have not been moved to FHS-compliant locations.
        </p>

        <p>
          <em>Programs that require the non-DFSG-compliant OSF/Motif
            library</em> should be compiled against and tested with
          LessTif (a free re-implementation of Motif) instead.  If the
          maintainer judges that the program or programs do not work
          sufficiently well with LessTif to be distributed and
          supported, but do so when compiled against Motif, then two
          versions of the package should be created; one linked
          statically against Motif and with <tt>-smotif</tt> appended
          to the package name, and one linked dynamically against
          Motif and with <tt>-dmotif</tt> appended to the package
          name.  Both Motif-linked versions are dependent upon
          non-DFSG-compliant software and thus cannot be uploaded to
          the main distribution; if the software is itself
          DFSG-compliant it may be uploaded to the contrib
          distribution.  While known existing versions of OSF/Motif
          permit unlimited redistribution of binaries linked against
          the library (whether statically or dynamically), it is the
          package maintainer's responsibility to determine whether
          this is permitted by the license of the copy of OSF/Motif in
          his or her possession.
        </p>
      </sect>


      <sect>
        <heading>Emacs lisp programs</heading>

        <p>
          Please refer to the `Debian Emacs Policy' (documented in
          <tt>debian-emacs-policy.gz</tt> of the
          <prgn>emacsen-common</prgn> package) for details of how to
          package emacs lisp programs.</p></sect>


      <sect>
        <heading>Games</heading>

        <p>
          The permissions on /var/games are 755
          <tt>root.root</tt>.</p>

        <p>
          Each game decides on its own security policy.</p>

        <p>
          Games which require protected, privileged access to
          high-score files, savegames, etc., may be made
          set-<em>group</em>-id (mode 2755) and owned by
          <tt>root.games</tt>, and use files and directories with
          appropriate permissions (770 <tt>root.games</tt>, for
          example).  They must not be made
          set-<em>user</em>-id, as this causes security problems. (If
          an attacker can subvert any set-user-id game they can
          overwrite the executable of any other, causing other players
          of these games to run a Trojan horse program.  With a
          set-group-id game the attacker only gets access to less
          important game data, and if they can get at the other
          players' accounts at all it will take considerably more
          effort.)</p>

        <p>
          Some packages, for example some fortune cookie programs, are
          configured by the upstream authors to install with their
          data files or other static information made unreadable so
          that they can only be accessed through set-id programs
          provided.  You should not do this in a Debian package: anyone can
          download the <tt>.deb</tt> file and read the data from it,
          so there is no point making the files unreadable.  Not
          making the files unreadable also means that you don't have
          to make so many programs set-id, which reduces the risk of a
          security hole.</p>

        <p>
          As described in the FHS, binaries of games should be
          installed in the directory <tt>/usr/games</tt>. This also
          applies to games that use the X Window System. Manual pages
          for games (X and non-X games) should be installed in
          <tt>/usr/share/man/man6</tt>.</p>
      </sect>
    </chapt>

    <chapt><heading>Documentation</heading>


      <sect>
        <heading>Manual pages</heading>

        <p>
          You should install manual pages in <prgn>nroff</prgn> source
          form, in appropriate places under <tt>/usr/share/man</tt>.  You
          should only use sections 1 to 9 (see the FHS for more
          details).  You must not install a preformatted `cat
          page'.</p>

        <p>
          Each program, utility, and function should have an
          associated manpage included in the same package. It is
          suggested that all configuration files also have a manual
          page included as well.
        </p>

        <p>
          If no manual page is available for a particular program,
          utility, function or configuration file and this is reported as a bug on
          debian-bugs, a symbolic link from the requested manual page
          to the <manref name="undocumented" section="7"> manual page
          may be provided.  This symbolic link can be created from
          <tt>debian/rules</tt> like this:
          <example>
            ln -s ../man7/undocumented.7.gz \
            debian/tmp/usr/share/man/man[1-9]/the_requested_manpage.[1-9].gz
          </example>
          This manpage claims that the lack of a manpage has been
          reported as a bug, so you may only do this if it really has
          (you can report it yourself, if you like).  Do not close the
          bug report until a proper manpage is available.</p>

        <p>
          You may forward a complaint about a missing manpage to the
          upstream authors, and mark the bug as forwarded in the
          Debian bug tracking system.  Even though the GNU Project do
          not in general consider the lack of a manpage to be a bug,
          we do--if they tell you that they don't consider it a bug
          you should leave the bug in our bug tracking system open
          anyway.</p>

        <p>
          Manual pages should be installed compressed using <tt>gzip
            -9</tt>.</p>

        <p>
          If one manpage needs to be accessible via several names it
          is better to use a symbolic link than the <tt>.so</tt>
          feature, but there is no need to fiddle with the relevant
          parts of the upstream source to change from <tt>.so</tt> to
          symlinks--don't do it unless it's easy.  You should not create hard
          links in the manual page directories, nor put
          absolute filenames in <tt>.so</tt> directives.  The filename
          in a <tt>.so</tt> in a manpage should be relative to the
          base of the manpage tree (usually
          <tt>/usr/share/man</tt>).</p></sect>


      <sect>
        <heading>Info documents</heading>

        <p>
          Info documents should be installed in <tt>/usr/share/info</tt>.
          They should be compressed with <tt>gzip -9</tt>.</p>

        <p>
          Your package should call <prgn>install-info</prgn> to update the Info
          <tt>dir</tt>
          file, in its post-installation script:
          <example>
            install-info --quiet --section Development Development \
            /usr/share/info/foobar.info
          </example></p>

        <p>
          It is a good idea to specify a section for the location of
          your program; this is done with the <tt>--section</tt>
          switch.  To determine which section to use, you should look
          at <tt>/usr/share/info/dir</tt> on your system and choose the most
          relevant (or create a new section if none of the current
          sections are relevant).  Note that the <tt>--section</tt>
          flag takes two arguments; the first is a regular expression
          to match (case-insensitively) against an existing section,
          the second is used when creating a new one.</p>

        <p>
          You should remove the entries in the pre-removal script:
          <example>
            install-info --quiet --remove /usr/share/info/foobar.info
          </example></p>

        <p>
          If <prgn>install-info</prgn> cannot find a description entry
          in the Info file you must supply one.  See <manref
                                                             name="install-info" section="8"> for details.</p>
      </sect>

      <sect>
        <heading>Additional documentation</heading>

        <p>
          Any additional documentation that comes with the package may
          be installed at the discretion of the package maintainer.
          Text documentation should be installed in a directory
          <tt>/usr/share/doc/<var>package</var></tt>, where
          <var>package</var> is the name of the package, and
          compressed with <tt>gzip -9</tt> unless it is small.</p>

        <p>
          If a package comes with large amounts of documentation which
          many users of the package will not require you should create
          a separate binary package to contain it, so that it does not
          take up disk space on the machines of users who do not need
          or want it installed.</p>

        <p>
          It is often a good idea to put text information files
          (<tt>README</tt>s, changelogs, and so forth) that come with
          the source package in <tt>/usr/share/doc/<var>package</var></tt>
          in the binary package.  However, you don't need to install
          the instructions for building and installing the package, of
          course!</p>

        <p>
          Files in <tt>/usr/share/doc</tt> should not be referenced by
          any program, and the system administrator should be able to
          delete them without causing any programs to break. Any files
          that are referenced by programs but are also useful as
          standalone documentation should be installed under
          <tt>/usr/share/&lt;package&gt;/</tt> and symlinked in
          <tt>/usr/share/doc/&lt;package&gt;/</tt>.
        </p>

      </sect>

      <sect id="usrdoc">
        <heading>Accessing the documentation</heading>

        <p>
          Former Debian releases placed all additional documentation
          in <tt>/usr/doc/<var>package</var></tt>.  To realize a
          smooth migration to
          <tt>/usr/share/doc/<var>package</var></tt>, each package
          must maintain a symlink <tt>/usr/doc/<var>package</var></tt>
          that points to the new location of its documentation in
          <tt>/usr/share/doc/<var>package</var></tt><footnote>These
              symlinks will be removed in the future, but they have to be
              there for compatibility reasons until all packages have
              moved and the policy is changed accordingly.</footnote>.
          The symlink must be created when the package is installed;
          it cannot be contained in the package itself due to problems
          with <prgn>dpkg</prgn>. One reasonable way to accomplish
          this is to put the following in the package's
          <prgn>postinst</prgn>:
          <example>
            if [ "$1" = "configure" ]; then
            if [ -d /usr/doc -a ! -e /usr/doc/#PACKAGE# \
            -a -d /usr/share/doc/#PACKAGE# ]; then
            ln -sf ../share/doc/#PACKAGE# /usr/doc/#PACKAGE#
            fi
            fi
          </example>
          And the following in the package's <prgn>prerm</prgn>:
          <example>
            if [ \( "$1" = "upgrade" -o "$1" = "remove" \) \
            -a -L /usr/doc/#PACKAGE# ]; then
            rm -f /usr/doc/#PACKAGE#
            fi
          </example>
        </p>
      </sect>

      <sect>
        <heading>Preferred documentation formats</heading>

        <p>
          The unification of Debian documentation is being carried out
          via HTML.</p>

        <p>
          If your package comes with extensive documentation in a
          mark up format that can be converted to various other formats
          you should if possible ship HTML versions in a binary
          package, in the directory
          <tt>/usr/share/doc/<var>appropriate package</var></tt> or its
          subdirectories.
          <footnote>
            <p>The rationale: The important thing here is that HTML
              docs should be available in <em>some</em> package, not
              necessarily in the main binary package, though. </p>
          </footnote>
        </p>

        <p>
          Other formats such as PostScript may be provided at your
          option.</p>
      </sect>

      <sect id="copyrightfile">
        <heading>Copyright information</heading>

        <p>
          Every package must be accompanied by a verbatim copy of its
          copyright and distribution license in the file
          /usr/share/doc/&lt;package-name&gt;/copyright. This file must
          neither be compressed nor be a symbolic link.</p>

        <p>
          In addition, the copyright file must say where the upstream
          sources (if any) were obtained, and should explain briefly what
          modifications were made in the Debian version of the package
          compared to the upstream one.  It should name the original
          authors of the package and the Debian maintainer(s) who were
          involved with its creation.</p>

        <p>
          A copy of the file which will be installed in
          <tt>/usr/share/doc/<var>package</var>/copyright</tt> should be
          in <tt>debian/copyright</tt>.</p>


        <p>
          /usr/share/doc/&lt;package-name&gt; may be a symbolic link to a
          directory in /usr/share/doc only if two packages both come from
          the same source and the first package has a "Depends"
          relationship on the second.  These rules are important
          because copyrights must be extractable by mechanical
          means.</p>

        <p>
          Packages distributed under the UCB BSD license, the Artistic
          license, the GNU GPL, and the GNU LGPL should refer to the
          files /usr/share/common-licenses/BSD,
          /usr/share/common-licenses/Artistic,
          /usr/share/common-licenses/GPL, and
          /usr/share/common-licenses/LGPL.
          <footnote>
            <p>
              Why "licenses" and not "copyright"? Because
              <tt>/usr/doc/copyright</tt> used to contain all the
              copyright files, plus the four common licenses GPL,
              LGPL, Artistic and BSD. Now individual copyright files
              for packages are no longer in a common directory. Once
              <tt>/usr/doc/copyright</tt> is almost empty it makes
              sense to rename "copyright" to "licenses"
            </p>
            <p>
              Why "common-licenses" and not "licenses"? Because if I
              put just "licenses" I'm sure I will receive a bug report
              saying "license foo is not included in the licenses
              directory. They are not all the licenses, just a few
              common ones. I could use /usr/share/doc/common-licenses
              but I think this is too long, and, after all, the GPL
              does not "document" anything, it is merely a license.
            </p>
          </footnote>
        </p>

        <p>
          You should not use the copyright file as a general <tt>README</tt>
          file.  If your package has such a file it should be
          installed in <tt>/usr/share/doc/<var>package</var>/README</tt> or
          <tt>README.Debian</tt> or some other appropriate place.</p>
      </sect>

      <sect>
        <heading>Examples</heading>

        <p>
          Any examples (configurations, source files, whatever),
          should be installed in a directory
          <tt>/usr/share/doc/<var>package</var>/examples</tt>.  These
          files should not be referenced by any program--they're there
          for the benefit of the system administrator and users, as
          documentation only. Architecture-specific example files
          should be installed in a directory
          <tt>/usr/lib/<var>package</var>/examples</tt>, and files in
          <tt>/usr/share/doc/<var>package</var>/examples</tt> symlink
          to files in it. Or the latter directory may be a symlink to
          the former.</p>
      </sect>

      <sect id="instchangelog">
        <heading>Changelog files</heading>

        <p>
          Packages that are not Debian-native must contain a copy of
          <tt>debian/changelog</tt> file from the Debian source tree
          in <tt>/usr/share/doc/<var>package</var></tt> as
          <tt>changelog.Debian.gz</tt>. If an upstream changelog is
          available, it should be accessible as
          <tt>/usr/share/doc/<var>package</var>/changelog.gz</tt> in
          plain text. If the upstream changelog is distributed in
          HTML, it should be made available in that form as
          <tt>/usr/share/doc/<var>package</var>/changelog.html.gz</tt>
          and the <tt>changelog.gz</tt> should be generated using, eg,
          <tt>lynx -dump -nolist</tt>. If the upstream changelog files
          do not already conform to this naming convention, then this
          may be achieved either by renaming the files, or adding a
          symbolic link, at the maintainer's discretion.
          <footnote>
            <p>
              Rationale: People should not have to look into two
              places for upstream changelogs merely because they are
              in HTML format.
            </p>
          </footnote>
        </p>


        <p>
          All these files should be installed compressed using <tt>gzip -9</tt>,
          as they will become large with time even if they start out
          small.
        </p>

        <p>
          If the package has only one changelog which is used both as
          the Debian changelog and the upstream one because there is
          no separate upstream maintainer then that changelog should
          usually be installed as
          <tt>/usr/share/doc/<var>package</var>/changelog.gz</tt>; if
          there is a separate upstream maintainer, but no upstream
          changelog, then the Debian changelog should still be called
          <tt>changelog.Debian.gz</tt>.</p>
      </sect>
    </chapt>
  </book>
</debiandoc>