dpkg-maintscript-helper(1) — Linux manual page

NAME | SYNOPSIS | COMMANDS AND PARAMETERS | DESCRIPTION | COMMON PARAMETERS | CONFFILE RELATED TASKS | SYMLINK AND DIRECTORY SWITCHES | INTEGRATION IN PACKAGES | ENVIRONMENT | SEE ALSO | COLOPHON

dpkg-maintscript-helper(1)     dpkg suite     dpkg-maintscript-helper(1)

NAME         top

       dpkg-maintscript-helper - works around known dpkg limitations in
       maintainer scripts

SYNOPSIS         top

       dpkg-maintscript-helper command [parameter...] -- maint-script-
       parameter...

COMMANDS AND PARAMETERS         top

       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         top

       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.

COMMON PARAMETERS         top

       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         top

       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.

SYMLINK AND DIRECTORY SWITCHES         top

       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.

INTEGRATION IN PACKAGES         top

       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.

ENVIRONMENT         top

       DPKG_COLORS
              Sets the color mode (since dpkg 1.19.1).  The currently
              accepted values are: auto (default), always and never.

SEE ALSO         top

       dh_installdeb(1).

COLOPHON         top

       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
       ⟨https://salsa.debian.org/dpkg-team/dpkg.git⟩ on 2021-08-27.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2021-06-17.)  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
       man-pages@man7.org

1.19.6-2-g6e42d5               2019-03-25     dpkg-maintscript-helper(1)

Pages that refer to this page: dh_installdeb(1)debhelper(7)