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 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

       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).

1.22.6                                             2024-07-17                         dpkg-maintscript-helper(1)