Manual: dpkg-maintscript-helper
dpkg-maintscript-helper(1) dpkg suite dpkg-maintscript-helper(1)
NAME
dpkg-maintscript-helper - works around known dpkg limitations in maintainer scripts
SYNOPSIS
dpkg-maintscript-helper command [parameter...] -- maint-script-parameter...
COMMANDS AND PARAMETERS
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]]
DESCRIPTION
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.
COMMON PARAMETERS
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 --.
CONFFILE RELATED TASKS
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.
SYMLINK AND DIRECTORY SWITCHES
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.
INTEGRATION IN PACKAGES
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.
ENVIRONMENT
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.
SEE ALSO
dh_installdeb(1).
1.23.7 2026-03-31 dpkg-maintscript-helper(1)