dpkg-maintscript-helper(1)



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

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. 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
       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
       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.

SEE ALSO
       dh_installdeb(1).

1.18.24                           2017-05-17        dpkg-maintscript-helper(1)

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