3. Binary packages¶
The Debian distribution is based on the Debian package management
dpkg. Thus, all packages in the Debian distribution
must be provided in the
.deb file format.
.deb package contains two sets of files: a set of files to install
on the system when the package is installed, and a set of files that
provide additional metadata about the package or which are executed when
the package is installed or removed. This second set of files is called
control information files. Among those files are the package
maintainer scripts and
control, the binary package control file
that contains the control fields for the
package. Other control information files include the :ref:
`symbols file <s-sharedlibs-symbols>`
`shlibs file <s-sharedlibs-shlibdeps>` used to store shared library
dependency information and the
conffiles file that lists the
package’s configuration files (described in
Section 10.7: Configuration files).
There is unfortunately a collision of terminology here between control
information files and files in the Debian control file format.
Throughout this document, a control file refers to a file in the
Debian control file format. These files are documented in
Control files and their fields. Only files
referred to specifically as control information files are the files
included in the control information file member of the
format used by binary packages. Most control information files are not
in the Debian control file format.
3.1. The package name¶
Every package must have a name that’s unique within the Debian archive.
The package name is included in the control field
format of which is described in Section 5.6.7: Package. The
package name is also included as a part of the file name of the
3.2. The version of a package¶
Every package has a version number recorded in its
file field, described in Section 5.6.12: Version.
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.
If an upstream package has problematic version numbers they should be
converted to a sane form for use in the
3.2.1. Version numbers based on dates¶
In general, Debian packages should use the same version numbers as the
upstream sources. However, upstream version numbers based on some date
formats (sometimes used for development or “snapshot” releases) will not
be ordered correctly by the package management software. For example,
dpkg will consider “96May01” to be greater than “96Dec24”.
To prevent having to use epochs for every new upstream version, the date-based portion of any upstream version number should be given in a way that sorts correctly: four-digit year first, followed by a two-digit numeric month, followed by a two-digit numeric date, possibly with punctuation between the components.
Native Debian packages (i.e., packages which have been written
especially for Debian) whose version numbers include dates should also
follow these rules. If punctuation is desired between the date
components, remember that hyphen (
-) cannot be used in native
package versions. Period (
.) is normally a good choice.
3.3. The maintainer of a package¶
Every package must have a maintainer, except for orphaned packages as described below. 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 maintaining the Debian packaging files, evaluating and responding appropriately to reported bugs, uploading new versions of the package (either directly or through a sponsor), ensuring that the package is placed in the appropriate archive area and included in Debian releases as appropriate for the stability and utility of the package, and requesting removal of the package from the Debian distribution if it is no longer useful or maintainable.
The maintainer must be specified in the
Maintainer control field
with their correct name and a working email address. The email address
given in the
Maintainer control field must accept mail from those
role accounts in Debian used to send automated mails regarding the
package. This includes non-spam mail from the bug-tracking system, all
mail from the Debian archive maintenance software, and other role
accounts or automated processes that are commonly agreed on by the
project.  If one person or team maintains several packages, they
should use the same form of their name and email address in the
Maintainer fields of those packages.
The format of the
Maintainer control field is described in
Section 5.6.2: Maintainer.
If the maintainer of the package is a team of people with a shared email
Uploaders control field must be present and must
contain at least one human with their personal email address. See
Section 5.6.3: Uploaders for the syntax of that field.
An orphaned package is one with no current maintainer. Orphaned packages
should have their
Maintainer control field set to
Debian QA Group <firstname.lastname@example.org>. These packages are considered
maintained by the Debian project as a whole until someone else
volunteers to take over maintenance. 
3.4. The description of a package¶
Every Debian package must have a
Description control field which
contains a synopsis and extended description of the package. Technical
information about the format of the
Description field is in
Section 5.6.13: Description.
The description should describe the package (the program) to a user (system administrator) who has never met it before so that they have enough information to decide whether they want to install it. This description should not just be copied verbatim from the program’s documentation.
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.
The description 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.
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 either (that is what the copyright file is for).
3.4.1. The single line synopsis¶
The single line synopsis should be kept brief - certainly under 80 characters.
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.
3.4.2. The extended description¶
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.
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).
The description field needs to make sense to anyone, even people who have no idea about any of the things the package deals with. 
Every package must specify the dependency information about other packages that are required for the first to work correctly.
For example, a dependency entry must be provided for any shared libraries required by a dynamically-linked executable binary in a package.
Packages are not required to declare any dependencies they have on other
packages which are marked
Essential (see below), and should not do
so unless they depend on a particular version of that package. 
Sometimes, unpacking one package requires that another package be first
unpacked and configured. In this case, the depending package must
specify this dependency in the
Pre-Depends control field.
You should not specify a
Pre-Depends entry for a package before this
has been discussed on the
debian-devel mailing list and a consensus
about doing that has been reached.
The format of the package interrelationship control fields is described in Declaring relationships between packages.
3.6. Virtual packages¶
Sometimes, there are several packages which offer more-or-less the same functionality. In this case, it’s useful to define a virtual package whose name describes that common functionality. (The virtual packages only exist logically, not physically; that’s why they are called virtual.) The packages with this particular function will then provide 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.
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. (See also Section 7.5: Virtual packages - Provides)
The latest version of the authoritative list of virtual package names
can be found in the
debian-policy package. It is also available from
the Debian web mirrors at
The procedure for updating the list is described in the preface to the list.
3.7. Base system¶
base system is a minimum subset of the Debian system that is
installed before everything else on a new system. Only very few packages
are allowed to form part of the base system, in order to keep the
required disk usage very small.
The base system consists of all those packages with priority
important. Many of them will be tagged
3.8. Essential packages¶
Essential is defined as the minimal set of functionality that must be
available and usable on the system at all times, even when packages are
in the “Unpacked” state. Packages are tagged
essential for a system
Essential control field. The format of the
control field is described in Section 5.6.9: Essential.
Since these packages cannot be easily removed (one has to specify an
extra force option to
dpkg to do so), this flag must not be used
unless absolutely necessary. A shared library package must not be tagged
essential; dependencies will prevent its premature removal, and we
need to be able to remove it when it has been superseded.
Since dpkg will not prevent upgrading of other packages while an
essential package is in an unconfigured state, all
packages must supply all of 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.
Maintainers should take great care in adding any programs, interfaces,
or functionality to
essential packages. Packages may assume that
functionality provided by
essential packages is always available
without declaring explicit dependencies, which means that removing
functionality from the Essential set is very difficult and is almost
never done. Any capability added to an
essential package therefore
creates an obligation to support that capability as part of the
Essential set in perpetuity.
You must not tag any packages
essential before this has been
discussed on the
debian-devel mailing list and a consensus about
doing that has been reached.
3.9. Maintainer Scripts¶
The package installation scripts should avoid producing output which is
unnecessary for the user to see and should rely on
dpkg to stave off
boredom on the part of a user installing many packages. This means,
amongst other things, not passing the
--verbose option to
Errors which occur during the execution of an installation script must be checked and the installation must not continue after an error.
Note that in general Section 10.4: Scripts applies to package maintainer scripts, too.
You should not use
dpkg-divert on a file belonging to another
package without consulting the maintainer of that package first. When
adding or removing diversions, package maintainer scripts must provide
--package flag to
dpkg-divert and must not use
All packages which supply an instance of a common command name (or, in
general, filename) should generally use
update-alternatives, so that
they may be installed together. If
update-alternatives is not used,
then each package must use
Conflicts to ensure that other packages
are removed. (In this case, it may be appropriate to specify a conflict
against earlier versions of something that previously did not use
update-alternatives; this is an exception to the usual rule that
versioned conflicts should be avoided.)
3.9.1. Prompting in maintainer scripts¶
Package maintainer scripts may prompt the user if necessary. Prompting
must be done by communicating through a program, such as
which conforms to the Debian Configuration Management Specification,
version 2 or higher.
Packages which are essential, or which are dependencies of essential packages, may fall back on another prompting method if no such interface is available when they are executed.
The Debian Configuration Management Specification is included in the
debconf_specification files in the debian-policy package. It is also
available from the Debian web mirrors at
Packages which use the Debian Configuration Management Specification may
contain the additional control information files
config is an additional maintainer script used for
package configuration, and
templates contains templates used for
user prompting. The
config script might be run before the
preinst script and before the package is unpacked or any of its
dependencies or pre-dependencies are satisfied. Therefore it must work
using only the tools present in essential packages. 
Packages which use the Debian Configuration Management Specification must allow for translation of their user-visible messages by using a gettext-based system such as the one provided by the po-debconf package.
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
/etc/news/server), and shared debconf variables 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
dpkg --purge to remove the package’s
configuration. The answers to configuration questions should be stored
in an appropriate place in
/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
postinst script and prompt the user to hit return to acknowledge the
message. Copyright messages do not count as vitally important (they
/usr/share/doc/package/copyright); neither do instructions
on how to use a program (these should be in on-line documentation, where
all the users can see them).
Any necessary prompting should almost always be confined to the
postinst script. If it is done in the
should be protected with a conditional so that unnecessary prompting
doesn’t happen if a package’s installation fails and the
|||A sample implementation of such a whitelist written for the Mailman mailing list management software is used for mailing lists hosted by alioth.debian.org.|
|||The detailed procedure for gracefully orphaning a package can be found in the Debian Developer’s Reference (see Section 1.4: Related documents).|
|||The blurb that comes with a program in its announcements and/or
Essential is needed in part to avoid unresolvable dependency loops on upgrade. If packages add unnecessary dependencies on packages in this set, the chances that there will be an unresolvable dependency loop caused by forcing these Essential packages to be configured first before they need to be is greatly increased. It also increases the chances that frontends will be unable to calculate an upgrade path, even if one exists.
Also, functionality is rarely ever removed from the Essential set, but packages have been removed from the Essential set when the functionality moved to a different package. So depending on these packages just in case they stop being essential does way more harm than good.
|||Debconf or another tool that implements the Debian Configuration Management Specification will also be installed, and any versioned dependencies on it will be satisfied before preconfiguration begins.|