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NAME | SYNOPSIS | COMMANDS AND PARAMETERS | DESCRIPTION | COMMON PARAMETERS | CONFFILE RELATED TASKS | SYMLINK AND DIRECTORY SWITCHES | INTEGRATION IN PACKAGES | SEE ALSO | COLOPHON |
dpkg-maintscript-helper(1) dpkg suite dpkg-maintscript-helper(1)
dpkg-maintscript-helper - works around known dpkg limitations in
maintainer scripts
dpkg-maintscript-helper command [parameter...] -- maint-script-
parameter...
supports command
rm_conffile conffile [prior-version [package]]
mv_conffile old-conffile new-conffile [prior-version [package]]
symlink_to_dir pathname old-target [prior-version [package]]
dir_to_symlink pathname new-target [prior-version [package]]
This program is designed to be run within maintainer scripts to
achieve some tasks that dpkg can't (yet) handle natively either
because of design decisions or due to current limitations.
Many of those tasks require coordinated actions from several
maintainer scripts (preinst, postinst, prerm, postrm). To avoid
mistakes the same call simply needs to be put in all scripts and the
program will automatically adapt its behaviour based on the
environment variable DPKG_MAINTSCRIPT_NAME and on the maintainer
scripts arguments that you have to forward after a double hyphen.
prior-version
Defines the latest version of the package whose upgrade should
trigger the operation. It is important to calculate prior-
version correctly so that the operations are correctly
performed even if the user rebuilt the package with a local
version. If prior-version is empty or omitted, then the
operation is tried on every upgrade (note: it's safer to give
the version and have the operation tried only once).
If the conffile has not been shipped for several versions, and
you are now modifying the maintainer scripts to clean up the
obsolete file, prior-version should be based on the version of
the package that you are now preparing, not the first version
of the package that lacked the conffile. This applies to all
other actions in the same way.
For example, for a conffile removed in version 2.0-1 of a
package, prior-version should be set to 2.0-1~. This will
cause the conffile to be removed even if the user rebuilt the
previous version 1.0-1 as 1.0-1local1. Or a package switching
a path from a symlink (shipped in version 1.0-1) to a
directory (shipped in version 2.0-1), but only performing the
actual switch in the maintainer scripts in version 3.0-1,
should set prior-version to 3.0-1~.
package
The package name. When the package is “Multi-Arch: same” this
parameter must include the architecture qualifier, otherwise
it should not usually include the architecture qualifier (as
it would disallow cross-grades, or switching from being
architecture specific to architecture all or vice versa). If
the parameter is empty or omitted, the
DPKG_MAINTSCRIPT_PACKAGE and DPKG_MAINTSCRIPT_ARCH environment
variables (as set by dpkg) will be used to generate an arch-
qualified package name.
-- All the parameters of the maintainer scripts have to be
forwarded to the program after --.
When upgrading a package, dpkg will not automatically remove a
conffile (a configuration file for which dpkg should preserve user
changes) if it is not present in the newer version. There are two
principal reasons for this; the first is that the conffile could've
been dropped by accident and the next version could restore it, users
wouldn't want their changes thrown away. The second is to allow
packages to transition files from a dpkg-maintained conffile to a
file maintained by the package's maintainer scripts, usually with a
tool like debconf or ucf.
This means that if a package is intended to rename or remove a
conffile, it must explicitly do so and dpkg-maintscript-helper can be
used to implement graceful deletion and moving of conffiles within
maintainer scripts.
Removing a conffile
If a conffile is completely removed, it should be removed from disk,
unless the user has modified it. If there are local modifications,
they should be preserved. If the package upgrades aborts, the newly
obsolete conffile should not disappear.
All of this is implemented by putting the following shell snippet in
the preinst, postinst and postrm maintainer scripts:
dpkg-maintscript-helper rm_conffile \
conffile prior-version package -- "$@"
conffile is the filename of the conffile to remove.
Current implementation: in the preinst, it checks if the conffile was
modified and renames it either to conffile.dpkg-remove (if not
modified) or to conffile.dpkg-backup (if modified). In the postinst,
the latter file is renamed to conffile.dpkg-bak and kept for
reference as it contains user modifications but the former will be
removed. If the package upgrade aborts, the postrm reinstalls the
original conffile. During purge, the postrm will also delete the
.dpkg-bak file kept up to now.
Renaming a conffile
If a conffile is moved from one location to another, you need to make
sure you move across any changes the user has made. This may seem a
simple change to the preinst script at first, however that will
result in the user being prompted by dpkg to approve the conffile
edits even though they are not responsible of them.
Graceful renaming can be implemented by putting the following shell
snippet in the preinst, postinst and postrm maintainer scripts:
dpkg-maintscript-helper mv_conffile \
old-conffile new-conffile prior-version package -- "$@"
old-conffile and new-conffile are the old and new name of the
conffile to rename.
Current implementation: the preinst checks if the conffile has been
modified, if yes it's left on place otherwise it's renamed to old-
conffile.dpkg-remove. On configuration, the postinst removes old-
conffile.dpkg-remove and renames old-conffile to new-conffile if old-
conffile is still available. On abort-upgrade/abort-install, the
postrm renames old-conffile.dpkg-remove back to old-conffile if
required.
When upgrading a package, dpkg will not automatically switch a
symlink to a directory or vice-versa. Downgrades are not supported
and the path will be left as is.
Switching a symlink to directory
If a symlink is switched to a real directory, you need to make sure
before unpacking that the symlink is removed. This may seem a simple
change to the preinst script at first, however that will result in
some problems in case of admin local customization of the symlink or
when downgrading the package.
Graceful renaming can be implemented by putting the following shell
snippet in the preinst, postinst and postrm maintainer scripts:
dpkg-maintscript-helper symlink_to_dir \
pathname old-target prior-version package -- "$@"
pathname is the absolute name of the old symlink (the path will be a
directory at the end of the installation) and old-target is the
target name of the former symlink at pathname. It can either be
absolute or relative to the directory containing pathname.
Current implementation: the preinst checks if the symlink exists and
points to old-target, if not then it's left in place, otherwise it's
renamed to pathname.dpkg-backup. On configuration, the postinst
removes pathname.dpkg-backup if pathname.dpkg-backup is still a
symlink. On abort-upgrade/abort-install, the postrm renames
pathname.dpkg-backup back to pathname if required.
Switching a directory to symlink
If a real directory is switched to a symlink, you need to make sure
before unpacking that the directory is removed. This may seem a
simple change to the preinst script at first, however that will
result in some problems in case the directory contains conffiles,
pathnames owned by other packages, locally created pathnames, or when
downgrading the package.
Graceful switching can be implemented by putting the following shell
snippet in the preinst, postinst and postrm maintainer scripts:
dpkg-maintscript-helper dir_to_symlink \
pathname new-target prior-version package -- "$@"
pathname is the absolute name of the old directory (the path will be
a symlink at the end of the installation) and new-target is the
target of the new symlink at pathname. It can either be absolute or
relative to the directory containing pathname.
Current implementation: the preinst checks if the directory exists,
does not contain conffiles, pathnames owned by other packages, or
locally created pathnames, if not then it's left in place, otherwise
it's renamed to pathname.dpkg-backup, and an empty staging directory
named pathname is created, marked with a file so that dpkg can track
it. On configuration, the postinst finishes the switch if
pathname.dpkg-backup is still a directory and pathname is the staging
directory; it removes the staging directory mark file, moves the
newly created files inside the staging directory to the symlink
target new-target/, replaces the now empty staging directory pathname
with a symlink to new-target, and removes pathname.dpkg-backup. On
abort-upgrade/abort-install, the postrm renames pathname.dpkg-backup
back to pathname if required.
When using a packaging helper, please check if it has native dpkg-
maintscript-helper integration, which might make your life easier.
See for example dh_installdeb(1).
Given that dpkg-maintscript-helper is used in the preinst, using it
unconditionally requires a pre-dependency to ensure that the required
version of dpkg has been unpacked before. The required version
depends on the command used, for rm_conffile and mv_conffile it is
1.15.7.2, for symlink_to_dir and dir_to_symlink it is 1.17.14:
Pre-Depends: dpkg (>= 1.17.14)
But in many cases the operation done by the program is not critical
for the package, and instead of using a pre-dependency we can call
the program only if we know that the required command is supported by
the currently installed dpkg:
if dpkg-maintscript-helper supports command; then
dpkg-maintscript-helper command ...
fi
The command supports will return 0 on success, 1 otherwise. The
supports command will check if the environment variables as set by
dpkg and required by the script are present, and will consider it a
failure in case the environment is not sufficient.
dh_installdeb(1).
This page is part of the dpkg (Debian Package Manager) project.
Information about the project can be found at
⟨https://wiki.debian.org/Teams/Dpkg/⟩. If you have a bug report for
this manual page, see
⟨http://bugs.debian.org/cgi-bin/pkgreport.cgi?src=dpkg⟩. This page
was obtained from the project's upstream Git repository
⟨git://git.debian.org/git/dpkg/dpkg.git⟩ on 2017-07-05. If you dis‐
cover any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
1.18.15-3-ga2ef 1970-01-01 dpkg-maintscript-helper(1)