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)

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. 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 --.

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.

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 
       ⟨git://git.debian.org/git/dpkg/dpkg.git⟩ on 2017-04-25.  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)