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NAME | SYNOPSIS | COMMANDS AND PARAMETERS | DESCRIPTION | COMMON PARAMETERS | CONFFILE RELATED TASKS | SYMLINK AND DIRECTORY SWITCHES | INTEGRATION IN PACKAGES | ENVIRONMENT | SEE ALSO | COLOPHON |
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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 behavior based on the
environment variable DPKG_MAINTSCRIPT_NAME and on the maintainer
scripts arguments that you have to forward after a double hyphen.
This program was introduced in dpkg 1.15.7.
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 owning the pathname(s). 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
when running the maintainer scripts) 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
Note: This can be replaced in most cases by the
"remove-on-upgrade" flag in DEBIAN/conffiles (since dpkg 1.20.6),
see deb-conffiles(5).
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 upgrade
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.
Note: The symlinks and directories created during these switches
need to be shipped in the new packages, or dpkg will not be able
to remove them on purge.
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 versioned pre-dependency to ensure
that the required version of dpkg has been unpacked before, unless
we know we are upgrading from a release where the required dpkg
version is going to be satisfied. 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. For example,
if we required support for symlink_to_dir when upgrading from a
release that had a dpkg version earlier than 1.17.14, we would
need to add:
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.
DPKG_ROOT
If set, it will be used as the filesystem root directory.
DPKG_ADMINDIR
If set, it will be used as the dpkg data directory.
DPKG_COLORS
Sets the color mode (since dpkg 1.19.1). The currently
accepted values are: auto (default), always and never.
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
clone https://git.dpkg.org/git/dpkg/dpkg.git⟩ on 2025-08-11. (At
that time, the date of the most recent commit that was found in
the repository was 2025-08-06.) If you discover 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
[email protected]
1.22.19-74-gf1ca0 2025-05-18 dpkg-maintscript-helper(1)
Pages that refer to this page: dh_installdeb(1), debhelper-compat-upgrade-checklist(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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