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
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 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
$DPKG_MAINTSCRIPT_PACKAGE (this variable is set by dpkg to the name of
the package acted upon). All the parameters of the maintainer scripts
have to be forwarded to the program after "--".
Current implementation: in the preinst, it checks if the conffile was
modified and renames it either to conffile.dpkg-remove (if not
modified) or to conffile.dpkg-backup (if modified). In the postinst,
the latter file is renamed to conffile.dpkg-bak and kept for reference
as it contains user modifications but the former will be removed. If
the package upgrade aborts, the postrm reinstalls the original
conffile. During purge, the postrm will also delete the .dpkg-bak file
kept up to now.
RENAMING A CONFFILE
If a conffile is moved from one location to another, you need to make
sure you move across any changes the user has made. This may seem a
simple change to the preinst script at first, however that will result
in the user being prompted by dpkg to approve the conffile edits even
though they are not responsible of them.
Graceful renaming can be implemented by putting the following shell
snippet in the preinst, postinst and postrm maintainer scripts:
dpkg-maintscript-helper mv_conffile \
oldconffile newconffile lastversion package -- "$@"
oldconffile and newconffile are the old and new name of the conffile to
rename. lastversion is the last version of the package that 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
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 configured 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.