with required, important, standard or optional
priorities, or are only likely to be useful if you
already know what they are or have specialized
- requirements.
+ requirements (such as packages containing only detached
+ debugging symbols).
</item>
</taglist>
</p>
(see below), and should not do so unless they depend on a
particular version of that package.<footnote>
<p>
- Essential is defined as the minimal set of functionality
- that must be available and usable on the system even
- when packages are in an unconfigured (but unpacked)
- state. This is needed to avoid unresolvable dependency
- loops on upgrade. If packages add unnecessary
- dependencies on packages in this set, the chances that
- there <strong>will</strong> 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
- <strong>calculate</strong> an upgrade path, even if one
- exists.
+ 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
+ <strong>will</strong> 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
+ <strong>calculate</strong> an upgrade path, even if one
+ exists.
</p>
<p>
- Also, it's pretty unlikely that functionality from
- Essential shall ever be removed (which is one reason why
- care must be taken before adding to the Essential
- packages set), but <em>packages</em> have been removed
- from the Essential set when the functionality moved to a
- different package. So depending on these packages
- <em>just in case</em> they stop being essential does way
- more harm than good.
+ Also, functionality is rarely ever removed from the
+ Essential set, but <em>packages</em> have been removed from
+ the Essential set when the functionality moved to a
+ different package. So depending on these packages <em>just
+ in case</em> they stop being essential does way more harm
+ than good.
</p>
</footnote>
</p>
<heading>Essential packages</heading>
<p>
- Some packages are tagged <tt>essential</tt> for a system
- using the <tt>Essential</tt> control file field.
- The format of the <tt>Essential</tt> control field is
- described in <ref id="f-Essential">.
+ 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 an unconfigured (but unpacked) state.
+ Packages are tagged <tt>essential</tt> for a system using the
+ <tt>Essential</tt> control file field. The format of the
+ <tt>Essential</tt> control field is described in <ref
+ id="f-Essential">.
</p>
<p>
appropriate.
</p>
+ <p>
+ Maintainers should take great care in adding any programs,
+ interfaces, or functionality to <tt>essential</tt> packages.
+ Packages may assume that functionality provided by
+ <tt>essential</tt> 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
+ <tt>essential</tt> package therefore creates an obligation to
+ support that capability as part of the Essential set in
+ perpetuity.
+ </p>
+
<p>
You must not tag any packages <tt>essential</tt> before
this has been discussed on the <tt>debian-devel</tt>
Package maintainer scripts may prompt the user if
necessary. Prompting should be done by communicating
through a program, such as <prgn>debconf</prgn>, which
- conforms to the Debian Configuration management
- specification, version 2 or higher. Prompting the user by
+ conforms to the Debian Configuration Management
+ Specification, version 2 or higher. Prompting the user by
other means, such as by hand<footnote>
From the Jargon file: by hand 2. By extension,
writing code which does something in an explicit or
</p>
<p>
- The Debian Configuration management specification is included
+ The Debian Configuration Management Specification is included
in the <file>debconf_specification</file> files in the
<package>debian-policy</package> package.
It is also available from the Debian web mirrors at
</p>
<p>
- Packages which use the Debian Configuration management
- specification may contain an additional
+ Packages which use the Debian Configuration Management
+ Specification may contain an additional
<prgn>config</prgn> script and a <tt>templates</tt>
file in their control archive<footnote>
The control.tar.gz inside the .deb.
Therefore it must work using only the tools present in
<em>essential</em> packages.<footnote>
<package>Debconf</package> or another tool that
- implements the Debian Configuration management
- specification will also be installed, and any
+ implements the Debian Configuration Management
+ Specification will also be installed, and any
versioned dependencies on it will be satisfied
before preconfiguration begins.
</footnote>
</p>
<p>
- Packages which use the Debian Configuration management
- specification must allow for translation of their messages
- by using a gettext-based system such as the one provided by
- the <package>po-debconf</package> package.
+ 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 <package>po-debconf</package> package.
</p>
<p>
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.
+ they exit with a zero status if everything went well.
</p>
<p>
support <tt>-a</tt> and <tt>-o</tt> as binary logical
operators.</item>
<item><tt>local</tt> to create a scoped variable must be
- supported; however, <tt>local</tt> may or may not preserve
- the variable value from an outer scope and may or may not
- support arguments more complex than simple variables. Only
- uses such as:
+ supported, including listing multiple variables in a single
+ local command and assigning a value to a variable at the
+ same time as localizing it. <tt>local</tt> may or
+ may not preserve the variable value from an outer scope if
+ no assignment is present. Uses such as:
<example compact>
fname () {
- local a
- a=''
- # ... use a ...
+ local a b c=delta d
+ # ... use a, b, c, d ...
}
</example>
- must be supported.
+ must be supported and must set the value of <tt>c</tt> to
+ <tt>delta</tt>.
</item>
</list>
If a shell script requires non-SUSv3 features from the shell
</example>
To view the copyright file for a package you could use this command:
<example>
- dpkg --fsys-tarfile <var>filename</var>.deb | tar xOf - \*/copyright | pager
+ dpkg --fsys-tarfile <var>filename</var>.deb | tar xOf - --wildcards \*/copyright | pager
</example>
</p>
</sect>
supposing that a <prgn>smailwrapper</prgn> package wishes to
install a wrapper around <file>/usr/sbin/smail</file>:
<example>
- if [ install = "$1" ]; then
- dpkg-divert --package smailwrapper --add --rename \
- --divert /usr/sbin/smail.real /usr/sbin/smail
- fi
- </example> Testing <tt>$1</tt> is necessary so that the script
- doesn't try to add the diversion again when
- <prgn>smailwrapper</prgn> is upgraded. The <tt>--package
- smailwrapper</tt> ensures that <prgn>smailwrapper</prgn>'s
- copy of <file>/usr/sbin/smail</file> can bypass the diversion and
- get installed as the true version.
+ dpkg-divert --package smailwrapper --add --rename \
+ --divert /usr/sbin/smail.real /usr/sbin/smail
+ </example> The <tt>--package smailwrapper</tt> ensures that
+ <prgn>smailwrapper</prgn>'s copy of <file>/usr/sbin/smail</file>
+ can bypass the diversion and get installed as the true version.
+ It's safe to add the diversion unconditionally on upgrades since
+ it will be left unchanged if it already exists, but
+ <prgn>dpkg-divert</prgn> will display a message. To suppress that
+ message, make the command conditional on the version from which
+ the package is being upgraded:
+ <example>
+ if [ upgrade != "$1" ] || dpkg --compare-versions "$2" lt 1.0-2; then
+ dpkg-divert --package smailwrapper --add --rename \
+ --divert /usr/sbin/smail.real /usr/sbin/smail
+ fi
+ </example> where <tt>1.0-2</tt> is the version at which the
+ diversion was first added to the package. Running the command
+ during abort-upgrade is pointless but harmless.
</p>
<p>
The postrm has to do the reverse:
<example>
- if [ remove = "$1" ]; then
+ if [ remove = "$1" -o abort-install = "$1" -o disappear = "$1" ]; then
+ dpkg-divert --package smailwrapper --remove --rename \
+ --divert /usr/sbin/smail.real /usr/sbin/smail
+ fi
+ </example> If the diversion was added at a particular version, the
+ postrm should also handle the failure case of upgrading from an
+ older version (unless the older version is so old that direct
+ upgrades are no longer supported):
+ <example>
+ if [ abort-upgrade = "$1" ] && dpkg --compare-versions "$2" lt 1.0-2; then
dpkg-divert --package smailwrapper --remove --rename \
--divert /usr/sbin/smail.real /usr/sbin/smail
fi
- </example>
+ </example> where <tt>1.02-2</tt> is the version at which the
+ diversion was first added to the package. The postrm should not
+ remove the diversion on upgrades both because there's no reason to
+ remove the diversion only to immediately re-add it and since the
+ postrm of the old package is run after unpacking so the removal of
+ the diversion will fail.
</p>
<p>
projects / debian / debian-policy.git / blobdiff