Man page 1 : dpkg-maintscript-helper

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. .

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. .