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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 [parameters...] -- maint-script-parameters

COMMANDS AND PARAMETERS
       rm_conffile conffile [lastversion [package]]

       mv_conffile oldconffile newconffile [lastversion [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 lim-
       itations.

       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 dash.

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  ver-
       sion.  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-main-
       tained 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 explic-
       itly do so and dpkg-maintscript-helper can be used to implement graceful deletion and mov-
       ing 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 lastversion package -- "$@"

       conffile is the filename of the conffile to remove.  lastversion is the	last  version  of
       the  package  that contained the conffile (or the last version of the package that did not
       take care to remove the obsolete conffile if this was not  immediately  implemented).   If
       lastversion  is empty or omitted, then the operation is tried on every upgrade. package is
       the package name, it's optional as it  will  default  to  $DPKG_MAINTSCRIPT_PACKAGE  (this
       variable  is set by dpkg to the name of the package acted upon). All the parameters of the
       maintainer scripts have to be forwarded to the program after "--".

       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 modi-
       fied). In the postinst, the latter file is renamed to conffile.dpkg-bak and kept for  ref-
       erence  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  pre-
       inst, postinst and postrm maintainer scripts:

	   dpkg-maintscript-helper mv_conffile \
	       oldconffile newconffile lastversion package -- "$@"

       oldconffile  and  newconffile are the old and new name of the conffile to rename. lastver-
       sion is the last version of the package that contained the conffile with the old name.  If
       lastversion  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). package is the  package
       name,  it's optional as it will default to $DPKG_MAINTSCRIPT_PACKAGE (this variable is set
       by dpkg to the name of the package acted upon).	All  the  parameters  of  the  maintainer
       scripts have to be forwarded to the program after "--".

       Current	implementation: the preinst checks if the conffile has been modified, if yes it's
       left on place otherwise it's renamed to	oldconffile.dpkg-remove.  On  configuration,  the
       postinst  removes  oldconffile.dpkg-remove  and renames oldconffile to newconffile if old-
       conffile is still available. On abort-upgrade/abort-install, the postrm	renames  oldconf-
       file.dpkg-remove back to oldconffile 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:

	   Pre-Depends: dpkg (>= 1.15.7.2)

       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

AUTHORS
       Copyright (C) 2010 Raphael Hertzog
       Copyright (C) 2008 Joey Hess
       Copyright (C) 2007 Guillem Jover
       Copyright (C) 2005 Scott James Remnant

       This is free software; see the GNU General Public Licence version 2 or later  for  copying
       conditions. There is NO WARRANTY.

Debian Project				    2010-04-16		       dpkg-maintscript-helper(1)
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