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 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

       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 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

       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

       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).

1.21.1                                             2024-02-23                         dpkg-maintscript-helper(1)