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 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 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 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  tran-
       sition  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 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 lastver-
       sion 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  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 
	       oldconffile newconffile lastversion package -- "$@"

       oldconffile  and  newconffile  are the old and new name of the conffile to rename. lastversion is the last version of the package that con-
       tained 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 oldconf-
       file.dpkg-remove. On configuration, the postinst removes oldconffile.dpkg-remove and renames oldconffile to newconffile if  oldconffile	is
       still available. On abort-upgrade/abort-install, the postrm renames oldconffile.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)