dpkg-maintscript-helper

       tainer scripts

SYNOPSIS
       dpkg-maintscript-helper command [parameter...] --  maint-script-parame-
       ter...

COMMANDS AND PARAMETERS
       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 auto-
       matically  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-ver-
              sion 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).

              For example, for a conffile removed in version 2.0-1 of a  pack-
              age,  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.

              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.

       package
              The  package  name. When the package is "Multi-Arch: same", this
              parameter must include the architecture qualifier. If  empty  or
              omitted,  the  DPKG_MAINTSCRIPT_PACKAGE environment variable (as
              set by dpkg) will be used.


       This means that if a package is intended to rename or  remove  a  conf-
       file,  it must explicitly do so and dpkg-maintscript-helper can be used
       to implement graceful deletion and moving  of  conffiles  within  main-
       tainer 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  modi-
       fied)  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-conf-
       file.dpkg-remove. On  configuration,  the  postinst  removes  old-conf-
       file.dpkg-remove  and renames old-conffile to new-conffile if old-conf-
       file 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
           dpkg-maintscript-helper symlink_to_dir \
               pathname old-target prior-version package -- "$@"

       pathname  is  the name of the old symlink (the path will be a directory
       at the end of the installation) and old-target the target of the former
       symlink at 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 name of the 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.

       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 path-
       name.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 sym-
       link   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
       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 1.17.5:

           Pre-Depends: dpkg (>= 1.17.5)

Debian Project                    2013-12-11        dpkg-maintscript-helper(1)
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