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

       rm_conffile conffile [prior-version [package]]

       mv_conffile old-conffile new-conffile [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 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 prior-version package -- "$@"

       conffile is the filename of the conffile to remove.

       prior-version defines the latest version of the package whose upgrade should trigger the removal. It is important to  calculate	prior-ver-
       sion  correctly so that conffiles are correctly removed even if the user rebuilt the package with a local version. For example, for a conf-
       file 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.

       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 is the package name. If empty or omitted, the DPKG_MAINTSCRIPT_PACKAGE environment variable (as set by dpkg) will be used.

       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 
	       old-conffile new-conffile prior-version package -- "$@"

       old-conffile and new-conffile are the old and new name of the conffile to rename.

       prior-version defines the latest version of the package whose upgrade should trigger the rename of the conffile (see the notes for rm_conf-
       file  above  concerning	the correct value). 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).

       package is the package name. If empty or omitted, the DPKG_MAINTSCRIPT_PACKAGE environment variable (as set by dpkg) will be used.

       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 old-conf-
       file.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.

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

Debian Project							    2012-05-04						dpkg-maintscript-helper(1)