dpkg/doc/guidelines.texi.beforeeric

\input texinfo @c -*-texinfo-*-
@setfilename guidelines.info

@set DATE 26th January 1996

@setchapternewpage off

@iftex
@center @titlefont{Debian GNU/Linux Packaging Guidelines}
@tex
\vskip2pt \hrule height 2pt width \hsize \vskip2pt
@end tex
@sp 0.5
@center @value{DATE}
@end iftex

@ifinfo
@format
START-INFO-DIR-ENTRY
* debian-guidelines: (debian-guidelines).       How to make Debian packages.
END-INFO-DIR-ENTRY
@end format
@end ifinfo

@node Top, Additional Information, (dir), (dir)

@ifinfo
@top Debian GNU/Linux Packaging Guidelines
@end ifinfo

   This file documents the steps that must be taken in the preparation
of a Debian GNU/Linux package.  All submissions to be included in the
distribution proper and all packages to be considered for @file{contrib}
or @file{non-free} availability @emph{must} conform to the guidelines
and standards described in this document or they cannot be included or
made available at the archive with the distribution.

   Please read the Guidelines carefully.  If you have comments or
questions, please contact @code{debian-devel@@pixar.com}.  If you are
planning on going further than just contributing a package (i.e., if
you plan to maintain it for an extended period of time or if you are
generally interested in becoming more involved in the Project), you
should join the @code{debian-devel} mailing list.  For more details,
read @file{info/mailing-lists.txt}, available at any Debian GNU/Linux
archive.

   (This file was last updated on @value{DATE}.  Please check the most
recent @file{dpkg} package at any Debian GNU/Linux archive for a
potentially more up to date copy.)

@menu
* Additional Information::
* Package Copyright::           A few words about the importance of
                                understanding the package copyright.
* Package Content::             Requirements for the package content.
* Source Package::              Creating the source package.
* Binary Package::              Creating the binary package.
* Control Files::               The binary package control files.
@end menu



@node Additional Information, Package Copyright, Top, Top
@unnumbered Additional Information

   These Guidelines are intended to be fairly general.  More specific
information is available about certain aspects of building packages,
such as how to use the features of Init under Debian GNU/Linux.  This
information can be found in the directory @file{project/standards}
at any Debian GNU/Linux archive.   At the time of this writing, the
following documents are available:

@table @file
@item README.etc-skel
A description of @file{/etc/skel} and @file{/usr/doc/examples}.
@item descriptions.txt
How to write an extended (and more useful) @file{DESCRIPTION} field.
@item README.init
How to use the features of Init under Debian GNU/Linux in packages.
@item mailers.txt
How to properly configure packages to use the Debian GNU/Linux mail
system.
@item maintainer-script-args.txt
All the ways that the package maintainer scripts inside a package can
be called by dpkg.
@item dpkg-upgrades+errors.txt
What order things happen in during a package upgrade.
@item virtual-dependencies.txt
How to use ``virtual dependencies'' in packages.
@item virtual-package-names-list.text
The list of virtual package names currently in use, together with the
procedure for getting new virtual package names allocated.
@item dependency-ordering.txt
How to properly order package names in the @file{DEPENDS} field.
@end table

   There are a number of documents that describe more technical
details of dpkg's operation, that will probably only be of minority
interest.  Please read them if you're doing anything complicated.

@table @file
@item auto-deconfiguration.txt
How dpkg can sometimes automatically deconfigure packages in order to
do bulk installations smoothly.
@item dpkg-essential-flag.txt
How to tell dpkg a package is essential and should not be removed.
(This is for the use of base system packages only.)
@item dpkg-disappear-replace.txt
What happens when a package appears to have been completely replaced.
@end table

   In the future, we hope also to make available:

@table @file
@item copyright.txt
How to choose a good copyright notice to attach to new programs.
@item version-ordering.txt
The algorithm with which packages' version numbers are compared.
@end table

   Also, you should download the sample files and the sample package
(GNU Hello) available in @file{standards/samples}.  You may use any
of this material as a starting point for new packages.  The following
sample files, incidentally, are available:

@itemize @bullet
@item debian.README
@item debian.control
@item debian.postinst
@item debian.postrm
@item debian.rules
@end itemize



@node Package Copyright, Package Content, Additional Information, Top
@unnumbered Package Copyright

   Please study the copyright of your submission @emph{carefully}
and @emph{understand it} before proceeding!  If you have doubts or
questions, please ask!

   In order to understand how we classify and distribute certain
packages, it is important to understand the distinction between being
freely available and being freely redistributable.

   Being @dfn{freely available}, quite simply, means that the software
can be made available freely, at least for non-commercial purposes and
in its original, unmodified form.  This includes packages made available
freely that have restrictions on non-commercial use, redistribution of
modifications, etc.  Being freely available, therefore, has nothing to
do with being able to modify and redistribute the software.  It only
means that you can get a copy of the software without having to pay
(and it does not necessarily mean that you can @emph{use} the software
without having to pay---shareware is an example of freely available
software).

   @dfn{freely redistributable}, while generally being freely available,
goes beyond just being freely available.  Freely redistributable means
that that the software, in addition to being able to be made available
freely, must be able to be freely modified and redistributed without
restriction.

   All submissions to be included in the distribution proper @emph{must}
be freely redistributable.

   In addition to the distribution, the Project maintains two separate
archives of software packages with the distribution: the @file{contrib}
archive and the @file{non-free} archive.

   @file{contrib} is an archive of user-contributed packages that are
not maintained by the Project, packages that were once maintained by the
Project but that are no longer actively maintained, and packages that
are maintained by the Project but that are not yet considered ready for
inclusion in the distribution proper (i.e., ALPHA and BETA packages).
As above, all submissions for inclusion in the @file{contrib} archive
@emph{must} be freely redistributable.

   @file{non-free} is an archive of packages with either restrictive or
unclear terms of copying or modification.  If a package has @emph{any}
restrictions on modification or redistribution, it can not be included
in the distribution or @file{contrib} archive.  It can only be included
in the @file{non-free} archive, and then only if it is freely available.

   In summary, in order to be included in the distribution proper or the
@file{contrib} archive, a package must be @emph{freely redistributable}.
Anyone must be able to make copies of it, modify it, redistribute it with
their modifications in place, include it on a CD-ROM, or generally sell
it.  To be included in the @file{non-free} archive, a package may have
restrictions, as long as the package remains @emph{freely available}.  We
must be available to make it available freely at the archive, and anyone
must be able to make copies of it and use it for at least non-commercial,
personal purposes.  Software that will typically be included in
@file{non-free} are software that does not allow commercial distribution,
software that does not allow modification or redistribution of
modifications, commercial ``demos'', and ``shareware''.

   When in doubt, send mail to @file{iwj10@@cus.cam.ac.uk} and
@file{imurdock@@debian.org}.  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''.

   Every package submission @emph{must} be accompanied by verbatim copy
of its copyright (with the exceptions of public domain packages and
those covered by the UCB BSD licence or the GNU GPL or LGPL; in these
cases simply indicate which is appropriate).  This information must be
included in a file installed to the directory @file{/usr/doc/copyright}.
See below for details.



@node Package Content, Source Package, Package Copyright, Top
@unnumbered Package Content

   The following requirements apply equally to both the binary and
source packages.  In either case, when files have been installed,
they must conform to the requirements described in this section.

   The primary rule in Debian GNU/Linux is to follow the Linux @dfn{File
System Standard} (@dfn{FSSTND}).  The location of installed files
@emph{must} comply @emph{fully} with the FSSTND.  The latest version of
this document can be found alongside the Guidelines or at
@file{tsx-11.mit.edu} in @file{/pub/linux/docs/linux-standards/fsstnd}.
Specific questions about following the standard should be addressed to
Daniel Quinlan, the FSSTND coordinator, at @code{quinlan@@yggdrasil.com}.

   In addition to the FSSTND, all Debian GNU/Linux packages must follow
the guidelines below.

@itemize @bullet
@item
Directories should be mode 755 or (for group-writability) mode 2775,
with the exception of special ``system'' directories that need to be
another mode.  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, of course.  Use common sense in assigning
permissions and ownerships to directories, and make sure that what is
done is secure if it is ``non-standard''.

@item
Normal binaries should be mode 755 and owned by @code{root.root}.  If
there is a good reason to use a different mode or ownership, you may do
so, but you must try to be as consistent as possible with the rest of
the system.  If you need to use a different mode or ownership, please
discuss it with @code{imurdock@@debian.org}.

@item
Setuid binaries should normally be mode 4755 (not 4711!) and, of course,
owned by the appropriate user.

@item
Setgid binaries should normally be mode 2755 (not 2711!) and, of course,
owned by the appropriate group.

@item
Library files should generally be mode 644 and owned by
@code{root.root}.  If the package requires different permissions
or ownerships to function correctly, they should be used instead.

@item
Manual pages should be mode 644 and owned by @code{root.root}.  The
@file{nroff} source must be installed.  You should @emph{not} install
a preformatted ``cat page'', and you should only use sections 1 to
9---see the FSSTND for more details.

@item
Info documents should be mode 644, owned by @code{root.root}, and
compressed with @file{gzip -9} when installed.  The package must call
@file{install-info} to update the Info @file{dir} file.  This should
be done in the post-installation script (@file{postinst}), like this:

@smallexample
        install-info --quiet /usr/info/foobar.info
@end smallexample

The entries should be removed by the pre-removal script (@file{prerm}),
like this:

@example
        install-info --quiet --remove /usr/info/foobar.info
@end example

It is also a good idea to specify a section for the Info @file{dir}
entry.  This is done with the @file{--section} switch.  To determine
which section to use, you should use look at @file{/usr/info/dir} on
your system and choose the most relevant (or create a new section if
none of the current sections are relevant).

If @file{install-info} cannot find a description entry in the Info file
you will have to supply one.  See @file{install-info}(8) for details.

@item
If a package contains any shared libraries you will have to invoke
@file{ldconfig} in both the @file{postinst} and @file{prerm} scripts
to correctly update the library links.  See @file{ldconfig}(8) for
details.

@item
Any additional documentation that comes with the package can be
installed at the discretion of the package maintainer.  Text
documentation should be mode 644, owned by @code{root.root}, installed
to @file{/usr/doc}, and compressed with @file{gzip -9} unless it is small.

If a subdirectory of @file{/usr/doc} is warranted, please do create one.
Please do not install DVI, PostScript, or large textual documentation to
@file{/usr/doc}.  However, please do upload such documentation as a
separate package so that it can be made available with the distribution.
If a user has the need for the documentation, they can easily get it
from the archive, CD-ROM, etc., but it should not take up disk space
on the machines of the user who do not need or want it installed.

@item
Create a file named @file{/usr/doc/copyright/<@i{package}>} which gives
details of the authorship and copyright of the package.  If the package
is distributed under the GNU General Public Licence, the GNU Library
General Public Licence or the Regents of the University of California at
Berkeley (BSD) licence, please say so instead of including a copy of the
licence.  The files @file{BSD}, @file{GPL}, and @file{LGPL} will be
available in the @file{/usr/doc/copyright} directory for you to refer
to.  @file{/usr/doc/copyright/<@i{package}>} should not be compressed.

@emph{All} authorship and copyright information from the original source
package must be included in the @file{/usr/doc/copyright/<@i{package}>}
file.

@item
Any example files (for example, sample configuration files) should
be placed in the directory @file{/usr/doc/examples}.  If the file is
normally a hidden file, such as @file{.emacs}, then please call it
@file{dot.emacs}, to avoid confusion.  Again, you may create a
subdirectory if it is needed.

@item
All symbolic links should be relative, not absolute.  Absolute links,
in general, cause problems when a file system is not mounted where it
``normally'' resides (for example, when mounted via NFS).  In certain
cases, however, relative links may also cause similar problems.  I
have generally made links into @file{/etc} and @file{/var} absolute
and all other links relative.  There may be other cases in which
absolute links are necessary.

Therefore, in the Makefile, do not do (even though it is easier):
@smallexample
        install: all
                [...]
                ln -fs /usr/bin/gcc /usr/bin/cc
                [...]
@end smallexample
Instead, do:
@smallexample
                ln -fs gcc /usr/bin/cc
@end smallexample
        or
@smallexample
                ( cd /usr/bin ; ln -fs gcc cc )
@end smallexample

Please do not create hard links in the manual page directories.  In
these cases, you should use relative symbolic links or files that
@file{.so} (roff for `source') others instead.

@item
All command scripts should have a @code{#!} line naming the shell to be
used to interpret them.

@item
In the case of Perl scripts this should be @code{#!/usr/bin/perl} or
sometimes @code{#!/bin/perl}, as follows: if the script is a critical
one that may be called when the @file{/usr} partition is unmounted or
broken it should use @file{/bin/perl}.  Otherwise (especially if the
script is not specifically targetted at Debian) it should use Perl's
standard location, @file{/usr/bin/perl}.

@item
Generally the following compilation parameters should be used:

@display
   CC = gcc
   CFLAGS = -O2 -g -Wall # sane warning options vary between programs
   LDFLAGS = # none (or -N, if appropriate; see below)
   install -s (or strip)
@end display

Note that all installed binaries should be stripped, either by using the
@code{-s} flag to @file{install}, or by calling @file{strip} on the
binaries after they have been copied into the @file{debian-tmp} but
before the tree is made into a package.

Make sure that you do not link with @code{-g}, as this makes a.out
compilers produce huge statically linked binaries.  The @code{-g} flag
is useful on compilation so that you have available a full set of
debugging symbols in your built source tree, in case anyone should file
a bug report involving (for example) a core dump.

@code{-N} should only be used on binaries that are very small (less than
8K with the @code{-N} option, roughly) and are not likely to have
multiple instances in memory.  Do not use @code{-N} on daemons, no
matter how small they are.

It is up to the package maintainer to decide what compilation options
are best for the package.  Certain binaries (such as
computationally-intensive programs) may function better with certain
flags (@code{-O3}, for example); feel free to use them.  Please use good
judgment here.  Don't add flags for the sake of adding flags; only add
flags if there is good reason to do so.

@item
Please check with the base system maintainer (Ian Murdock) before using
users or groups other than @code{root} and others specified in this
document.
@end itemize



@node Source Package, Binary Package, Package Content, Top
@unnumbered Source Package

   The source package should contain a file called @file{debian.rules}
which contains at least the following targets, to be invoked in the top
level directory:

@smallexample
build
binary
clean
@end smallexample

@file{debian.rules} should start with

@example
   #!/usr/bin/make -f
@end example

@noindent and be executable.  It is a good idea to arrange for it not
to fail obscurely when invoked in the wrong directory, for example by
testing for the existence of a file in the source directory.

@itemize @bullet
@item
The @file{build} target should perform all non-interactive configuration
and compilation of the package.  If a package has an interactive
pre-build configuration routine, the source package should be built
@emph{after} this has taken place.

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

@item
The @file{binary} target of @file{debian.rules} should be all that is
necessary for the user to build the binary package.  The binary package
should be created using @file{dpkg} and placed in the parent of the top
level directory.  The next section describes how to construct binary
packages from the @file{binary} target.

@item
The @file{clean} target should undo the effects of the @file{build}
target and the @file{binary} target, except that it should leave alone
any @file{../<@i{package}>-<@i{version}>.deb} file created by a run of
@file{binary}.

@item
Additional targets may exist in @file{debian.rules}.  We recommend using
@file{source} and @file{diff} targets to build the Debianised source
package and the Debianisation context diff, respectively.  These files
should be placed in @file{../foo-<@i{version}>.tar.gz} and
@file{../foo-<@i{version}>.diff.gz}.  The @file{install} target, for
installing into a running system direct from the Debianised source
tree, is no longer required.  The sample @file{debian.rules} provides
@file{source} and @file{diff} targets that should work with little or
no alteration, providing that the package-specific variables at the top
of the script have been properly defined.

@item
If you need to edit a @file{Makefile} where @file{configure} scripts
are used, you should edit the @file{.in} files rather than editing
the @file{Makefile} directly.  This allows the user to reconfigure
the package if necessary.  You should @emph{not} configure the package
and edit the generated @file{Makefile}!  This makes it impossible for
someone else to later reconfigure the package.

@item
Please document your changes to the source package so that future
package maintainers know what has been changed.  To do this, include
a description of your changes in the @file{debian.README} (which, as
described above, should already contain authorship and copyright
information!) and include relevant information such as your name,
electronic mail address, date, etc.

@item
If changes to the source code are made, please use a @file{define}.  If
they are changes required to compile or function under Linux in general,
use @file{LINUX}.  If it is a cosmetic or functional change, use
@file{DEBIAN}.

@item
Create the source package using @file{tar}, and use @file{gzip -9} to
compress it.  Source packages should be named in the form
<@i{package}>-<@i{version}>.tar.gz---for example,
@file{fileutils-3.9-3.tar.gz}.

NB, here @code{<@i{version}>} is the full Debian version number, in the
form @code{<@i{original_version}>-<@i{debian_revision}>} (see below),
but the tarfile should unpack into a directory named
@code{<@i{package}>-<@i{original_version}>} (again, see the section
below on version numbering).

@item
Create the context diff against the original package using @file{diff
-cNr}, and use @file{gzip -9} to compress it.  Context diffs should be
named in the form <@i{package}>-<@i{version}>.diff.gz---for example,
@file{fileutils-3.9-3.diff.gz}.
@end itemize

   Please note that the package and patch filenames do @emph{not} need
to fit in MS-DOS 8+3.  They will be made available under an alternative
8+3 name in the archive by the archive maintainer, using a symlink.



@node Binary Package, Control Files, Source Package, Top
@unnumbered Binary Package

   The @file{binary} target of the source package @file{debian.rules}
file should do the following (see the sample @file{debian.rules}
for an implementation that you are free to modify and use in your own
packages, of course):

@itemize @bullet
@item
Create an empty directory in the top-level directory of the source
package (deleting it first, if necessary), and install the files
belonging to this package in that directory.  For example, the directory
could be called @file{debian-tmp} and would probably contain directories
@file{debian-tmp/usr/bin}, @file{debian-tmp/usr/lib}, etc.
(@file{debian-tmp} is the name traditionally used, and it is used in
the sample @file{debian.rules} file, so we will use that name in the
Guidelines.)

@item
Make sure that all the files under @file{debian-tmp} have the correct
ownerships and permissions (@pxref{Package Content}, for more information
about file locations, ownerships, and permissions.)

@item
Create a subdirectory of @file{debian-tmp} called @file{DEBIAN}.  This
directory contains the package control information, including at the
very least the master information file named @file{control}.  The next
section describes the semantics and syntax of the files required and
allowed here.

@item
Run @file{dpkg} to create the binary package, using something like

@smallexample
    dpkg --build debian-tmp
@end smallexample

This will create a file called @file{debian-tmp.deb}, from the
@file{debian-tmp} directory.  You should rename this file to
@file{../<@i{package}>-<@i{version}>.deb} after it is built.

After the @file{binary} target has done all this, the
@file{<@i{package}>-<@i{version}>.deb} file in the parent directory is
the binary distribution.  This file may be distributed and installed on
any Debian GNU/Linux system with @file{dpkg} in the same manner and
using the same methods as all packages are installed to the system.

@item
If a single source package corresponds to several binary packages, there
should usually be a @file{debian.rules} file with a single @file{binary}
target that builds all the binary packages involved and move all packages
to the parent directory of that containing the source package.

In this case, you should choose binary package names which are meant to
make clear the close relationship between the binary packages and which
source package the binary packages came from (for example, the
@file{texinfo} source package build two binary packages: @file{texidoc}
and @file{texinfo}).  You should place the appropriate binary package
name in the @file{Package} field of the control file (not the source
package name), and you should consider whether the other binary packages
that come from the same source tree should be mentioned in the
@file{Depends}, @file{Recommends} or @file{Suggests} fields.  You
should put the source package name in the @file{Source} field.

You should retain the source package version numbering in the
@file{Version} field---the version number should be the same for the
Debianised source tree and all the binary packages generated from it.
See below for details of version numbers.
@end itemize



@node Control Files,  , Binary Package, Top
@unnumbered Control Files

   Each binary package contains, in addition to the files that comprise
the actual package, a set of text files that control how @file{dpkg}
installs, configures, upgrades, removes, etc. the package.  These files
are called @dfn{control files}.  When creating the package, the control
files should placed in a directory called @file{DEBIAN}, as described
earlier (@pxref{Binary Package}, for further information).

The control information files are:

@table @code
@item control
The master package control information file.
@item conffiles
A list of package configuration files.
@item preinst
The package pre-installation script.
@item postinst
The package post-installation script.
@item prerm
The package pre-removal script.
@item postrm
The package post-removal script.
@end table

   Of these, only @file{control} is required.  The various installation
scripts, and the configuration files list, will only be used if they are
present.

@menu
* control::
* conffiles::
* Installation and Removal Scripts::
* Dependencies and Conflicts::
* Package Classification Fields::
@end menu

@node control, conffiles, Control Files, Control Files
@unnumberedsec control

   The @file{control} file contains a number of fields.  Each field
begins with a field name, such as @file{Package} or @file{Version}
(case insensitive), followed by a colon and optionally some spaces or
tabs (a single space is conventional).  Then comes the body of the
field, which may be several lines long; each continuation line must
start with at least one space or tab.  (These are the same rules as
apply to RFC822 mail headers.)  Blank lines are not permitted in the
control file.

   The required fields in the control file are the following:

@table @code
@item Package
The name of the package.
@item Description
The description of the package.
@item Maintainer
The name and e-mail address of the maintainer of the package.
@item Version
The version number in the format
@code{<@i{original_version}>-<@i{debian_revision}>}.
@end table

   Each field has a particular format and meaning for the package
installation tools.

The value of @file{Package} should be the name of the package.
Package names must start with an alphanumeric, must be at least two
characters, and may contain only alphanumerics and the characters
- + . @@ : = % _ (that is, hyphen, plus, stop, at, colon, equals,
percent and underscore).  They are not case sensitive.

   The @code{Maintainer} field should be in the form

@smallexample
Joe J. Bloggs <jbloggs@@foo.com>
@end smallexample

@noindent Note that this will not be useable as an email address if
the name given contains full stop characters, because of a silly
restriction in the Internet mail standards.  If you want to use this
as an email address in a program you should check for full stops and
change the string to the form @code{jbloggs@@foo.com (Joe J. Bloggs)}
if you find any.

   The @code{Version} field should be the version number of the
package.  For most packages which are not written specifically for
Debian, this should be in the form

@smallexample
Version: <@i{original_version}>-<@i{debian_revision}>
@end smallexample

@noindent where @file{<@i{original_version}>} is the original package
version number in whatever form the original package uses and
@file{<@i{debian_revision}>} indicates which ``debianisation'' this is
(this should usually be a plain number or perhaps a two numbers
separated by a full stop, and should be incremented each time the
package is changed or updated).

    Packages which are written specifically for Debian do not have a
@i{debian_revision}, and their version number should simply be
@i{version} (which should not contain any hyphens, to avoid
confusion).

    There is an ordering imposed on version numbers, described in
@file{version-ordering.txt}.  This ordering is designed to `do the right
thing' in most circumstances; if your package has an version number in
an unusual format you may need to reformat it somewhat to get the
ordering right.  This is important because @file{dpkg} is (for example)
reluctant to downgrade packages.

   The optional fields in the control file are the following:

@table @code
@item Depends
The names of prerequisite packages.
@item Recommends
The names of related, recommended packages.
@item Suggests
The names of related, optional packages.
@item Conflicts
The names of packages which conflict with this package.
@item Provides
The names of virtual packages which this package provides.
@item Priority
The `priority' of the package, as shown and used by @file{dselect}.
@item Section
The `section' of the package, as shown and used by @file{dselect}, and
used as a location for the package in the distribution.
@item Essential
A boolean field used by the base packages.
@end table

@noindent See below for details of the semantics and syntax of these
fields.  Most packages will need at least a @code{Depends} field.

   An example of a @file{control} file would be:

@example
  Package: smail
  Version: 3.1.29.1-13
  Maintainer: Ian Jackson <iwj10@@cus.cam.ac.uk>
  Recommends: pine | mailx | elm | emacs | mail-user-agent
  Suggests: metamail
  Depends: cron, libc5
  Conflicts: sendmail
  Provides: mail-transport-agent
  Description: Electronic mail transport system.
   Smail is the recommended mail transport agent (MTA) for Debian.
   .
   An MTA is the innards of the mail system - it takes messages from
   user-friendly mailer programs and arranges for them to be delivered
   locally or passed on to other systems as required.
   .
   In order to make use of it you must have one or more user level
   mailreader programs such as elm, pine, mailx or Emacs (which has Rmail
   and VM as mailreaders) installed.  If you wish to send messages other
   than just to other users of your system you must also have appropriate
   networking support, in the form of IP or UUCP.
@end example

   In this case, @file{mail-user-agent} is a virtual package
representing any user mailer program; the actual package names
@file{pine} is quoted for the reasons described in
@file{dependency-ordering.txt}, and the others because older versions
of those packages do not have the appropriate @file{Provides} field.

@node conffiles, Installation and Removal Scripts, control, Control Files
@unnumberedsec conffiles

   The contents of @file{conffiles} is simply a list of configuration
files in the package.  When installing the package, @file{dpkg} uses
an intelligent method to update these files.  This will ensure that
package-specific configuration files are not overwritten when a package
is upgraded, unless the user wishes the installation tools to do so.

   Typically, files listed in conffiles are package-specific
configuration files, which (according to the Linux Filesystem Standard)
are stored in @file{/etc}.  For example, the @code{sendmail} package may
contain the file @file{/etc/sendmail.cf}, which we do not wish to
overwrite automatically when the user upgrades the sendmail package.
Only those files listed in @file{DEBIAN/conffiles} will be updated
intelligently when a package is upgraded; all other files in the package
will be overwritten by the upgrade process.

   Configuration files which will be functional as shipped and will
probably need little or no local editing should simply be listed the
@file{conffiles} file; in this case you need read no further.

   For packages whose configuration files will need modification on
most systems there are two sensible approaches.  Which one is chosen
depends on how hard the configuration problem is and how much time the
package maintainer has available.

   One option is for you to ship a minimal `best-effort' file in
@file{/etc}, and list the file in @file{conffiles}.  This will mean that
the user will have to go and edit the file themselves to get the package
to work properly, of course.  The next time they upgrade the package, if
you haven't changed the file version, their old file will be left in
place.  If you have modified your version then the user will get a
prompt asking them which version of the file they want, theirs or yours.
They will then usually have to resolve the discrepancies manually.

   The other option is to be preferred, if you can do it: don't put a
copy of the configuration file in the package at all.  Instead, you
check in the postinst whether the file exists, and if it doesn't you
prompt the user for the information you need to create a good one.  This
is obviously harder work.

  You also have to remember that you will have to keep up with your
package's changes: if you discover a bug in the program which generates
the configuration file, or if the format of the file changes from one
version to the next, you will have to arrange for the postinst script to
do something sensible---usually this will mean editing the installed
configuration file to remove the problem or change the syntax.  You will
have to do this very carefully, since the user may have changed the
file, perhaps to fix the very problem that your script is trying to deal
with---you will have to detect these situations and deal with them
correctly.

  If you do go down this route it's probably a good idea to make the
program that generates the configuration file(s) a separate program in
@file{/usr/sbin}, by convention called @i{package}@code{config}, and
then run that if appropriate from the post-installation script.  The
@i{package}@code{config} program should not unquestioningly overwrite an
existing configuration---if its mode of operation is geared towards
setting up a package for the first time (rather than any arbitrary
reconfiguration later) you should have it check whether the
configuration already exists, and require a @code{--force} flag to
overwrite it.

   @file{conffiles} should almost certainly list all the files contained
in your package in the @file{/etc} directory.  There may also be other
files somewhere that the user is expected to edit, which should also be
included.  Note, however, that the FSSTND specifies that configuration
files must be in @file{/etc}.  No Debian package should contain
configuration files in @file{/usr/etc}, and all programs should refer to
configuration files in @file{/etc}.

@noindent For example, the TCP/IP package might use a conffiles which contains

@example
  /etc/init.d/netbase
  /etc/gateways
  /etc/protocols
  /etc/services
  /etc/hosts.allow
  /etc/hosts.deny
  /etc/rpc
@end example

@noindent and so on; the files

@example
  /etc/hosts
  /etc/inetd.conf
  /etc/host.conf
  /etc/networks
  /etc/resolv.conf
@end example

@noindent might be generated by an interactive configuration program,
and would then not be included in the package or listed in the
@file{conffiles}.

@node Installation and Removal Scripts, Dependencies and Conflicts, conffiles, Control Files
@unnumberedsec Installation and Removal Scripts

   The scripts @file{preinst}, @file{postinst}, @file{prerm}, and
@file{postrm} are optional (Bash or Perl) scripts.  As the names
would indicate, if these scripts exist, they will be executed before
installing the package, after installation, before package removal,
and after removal, respectively.

   They are given arguments which indicate the precise situation and
action being performed---see @file{maintainer-script-args.txt} for
details of exactly when each of the scripts is invoked and what its
arguments are.  Extra arguments and situations may be added later, so
you should not test the number of arguments to your script to determine
the situation, and you should choose the sense of your `if it is this
then do this otherwise do that' tests carefully.

   These scripts can be used to perform any site-specific package
configuration.

   Because the scripts will be exectued by the dpkg front-end, it is
guaranteed that the scripts will be executed interactively.  User input
from the scripts should be read from standard input, not the user's
terminal.  Similarly, output should be sent to standard output.

   If your maintainer scripts need to prompt for passwords and/or do
@i{full-screen} interaction should do these things to and from
@file{/dev/tty}, since @file{dpkg} 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 @code{$|=1} so that the output is printed
immediately rather than being buffered.

   The scripts must be idempotent, and they must clean up after
themselves properly.  Ie, they must do the right thing if run multiple
times, even if previous runs failed halfway through.  This is so that if
any errors occur, or if the @file{dpkg} run is interrupted, the user can
recover by rerunning @file{dpkg}, and/or by upgrading to a new version
and then rerunning the failed operation.

   These scripts should avoid producing output which it is unnecessary
for the user to see and should rely on @file{dpkg} to stave off boredom
on the part of a user installing many packages.  This means, amongst
other things, using the @file{--quiet} option on @file{install-info}.

   Packages should try to minimise the amount of prompting they need to
do, and they should ensure that the user will only every be asked each
question once.  This means that packages should try to use appropriate
shared configuration files (such as @file{/etc/papersize} and
@file{/etc/news/server}), rather than each prompting for their own list
of required pieces of information.

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

   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
@file{postinst} script and prompt the user to hit Return to acknowledge
the message.  Copyright messages do not count as vitally important (they
belong in @file{/usr/doc/copyright}; neither do instructions on how to
use a program (these should be in on line documentation, where all the
users can see them).

   They should return a zero exit status for success, or a nonzero one
for failure.  Note that if a script is a @code{#!/bin/sh} script it
should probably start with @code{set -e}, to avoid continuing after
errors---see @file{bash}(1) for details.  Perl scripts should check for
errors when making calls such as @code{open}, @code{print},
@code{close}, @code{rename} and @code{system}.

   If these scripts exist they should be left in the @file{DEBIAN}
directory with execute permission enabled and should contain an
appropriate @code{#!} line, such as @code{#!/bin/bash} for a
@code{bash} script or @code{#!/bin/perl} for a Perl script (see
above).

@node Dependencies and Conflicts, Package Classification Fields, Installation and Removal Scripts, Control Files
@unnumberedsec Conflicts, Depends, Suggests, Recommends and Provides

   The @file{Depends} field lists packages that are required for this
package to provide a significant amount of functionality.  The package
maintenance software will not allow a package to be installed without
also installing packages listed in its @code{Depends} field, and will
run the @code{postinst} scripts of packages listed in @code{Depends}
fields before those of the packages which depend on them, and run the
@code{prerm} scripts before.

   Packages containing dynamically-linked executable binaries (this
includes almost all C programs) should include a @file{Depends} field
which mentions the shared C library required for the program to run.
For a.out binaries linked against @file{libc.so.4} the relevant package
name is @file{libc}; for ELF binaries linked against @file{libc.so.5}
the relevant package name is @file{libc5}.

   The @code{Recommends} field lists packages that would be found
together with this one in all but unusual installations.  The user-level
package maintenance program @file{dselect} will warn the user if they
select a package without those listed in its @code{Recommends} field.
Note that @code{Recommends} fields don't currently have any implications
for the order in which the maintainer scripts are run.

   The @code{Suggests} field lists packages that are related to this one
and can perhaps enhance its usefulness, but without which installing
this package is perfectly reasonable.  The package maintenance software
will not moan at the user for not selecting @code{Suggests} related
packages, but may use the information in the @code{Suggests} field to
assist the user during package selection.

   The syntax of @code{Depends}, @code{Recommends} and @code{Suggests}
is a list of groups of alternative packages.  Each group is a list of
packages separated by vertical bar (or `pipe') symbols, @code{|}.  The
groups are separated by commas.  Each package is a package name
optionally followed by a version number specification in parentheses.  A
version number may start with a @code{>=}, in which case that version or
any later will match, or @code{<=} for that version or any earlier
version. A version number starting with a @code{>>} or @code{<<} will
respectively match any later or earlier version. If a version number or
a version number starting with @code{=} is specified an exact match is
required. Commas are to be read as `AND', and pipes as `OR', with pipes
binding more tightly.

   Versions of dpkg before 1.0.9 used @code{<} and @code{>} for
@code{<=} and @code{>=} (these are still supported for backward
compatibility), and did not support @code{<<} and @code{>>}.

   The @code{Conflicts} field lists packages that conflict with this
one, for example by containing files with the same names (an example
would be Smail vs. Sendmail).  The package maintenance software will not
allow conflicting packages to be installed.  Two conflicting packages
should each include a @code{Conflicts} line mentioning the other.

   The syntax of @code{Conflicts} is a list of package names (with
optional version numbers), separated by commas (and optional
whitespace).  In the @code{Conflicts} field the comma should be read as
`OR'.

   The @code{Provides} field lists the names of any `virtual packages'
of which this packages is to be considered an instantiation.  Virtual
packages are used to allow packages to refer to a service they require
(such as the availability of @file{/usr/sbin/sendmail}) without having
to know the names of all the relevant packages.  The virtual package
names defined in @code{Provides} fields may be used in other packages'
@code{Depends}, @code{Recommends}, @code{Suggests} and @code{Conflicts}
fields.  For more information about how to use virtual packages and
which virtual package names to use read @file{virtual-dependencies.txt}
and @file{virtual-package-names-list.text}.

   The syntax of @code{Provides} is a list of package names separated by
commas (and optional whitespace).

@node Package Classification Fields,  , Dependencies and Conflicts, Control Files
@unnumberedsec Priority, Section and Essential

   The @code{Priority} and @code{Section} fields are used by
@file{dselect} when displaying the list of packages to the user.  There
is no need to put them into a package, since these are usually set by
the distribution maintainers in the @file{Packages} file.

   However, if a user installs a package which is not part of the
standard distribution, or without downloading and updating from a new
@file{Packages} file, the information about the priority and section of
a package will be absent, and the @file{dselect} package listing will
have the package listed under `unclassified'.  It is permissible for a
package to include @code{Section} or @code{Priority} fields to improve
this; however, if you do this you should make sure you keep the
information up to date so that users are not shown conflicting
information.  The @code{Section} field can also be used by the
distribution maintainers as a suggestion about which section you think
is most appropriate for your package.

  The @code{Essential} field should only appear in packages in the
installation's base system.  If it is set to @code{yes} then @file{dpkg}
will not remove the package even if asked to, and will make certain
minor modifications to its installation procedures.  The only other
legal value is @code{no}, which is equivalent to the absence of the
field.

@bye

@c local variables:
@c kept-new-versions: 100
@c version-control:   t
@c end: