Where New file is the configuration file as provided by the package (either shipped with the package, or generated by the maintainer scripts on the fly), and Destination is the location (usually under /etc) where the real configuration file lives, and is potentially modified by the end user.

This script attempts to provide conffile like handling for files that can not be labelled conffiles, are not shipped in a Debian package, but handled by the postinst instead. This script allows one to maintain files in /etc, preserving user changes and in general offering the same facilities while upgrading that dpkg normally provides for "conffiles". Additionally, this script provides facilities for transitioning a file that had not been provided conffile like protection to come under this schema, and attempts to minimize questions asked at install time. Indeed, the transitioning facility is better than the one offered by dpkg while transitioning a file from a non-conffile to conffile status. The second form in the SYNOPSIS above is for purging information about the configuration file when the package is purged; and is critical for allowing smooth reinstallations.