ucf 3.0036 (amd64 binary) in ubuntu xenial

 Debian policy mandates that user changes to configuration files must be
 preserved during package upgrades. The easy way to achieve this behavior
 is to make the configuration file a 'conffile', in which case dpkg
 handles the file specially during upgrades, prompting the user as
 needed.
 .
 This is appropriate only if it is possible to distribute a default
 version that will work for most installations, although some system
 administrators may choose to modify it. This implies that the
 default version will be part of the package distribution, and must
 not be modified by the maintainer scripts during installation (or at
 any other time).
 .
 This script attempts to provide conffile-like handling for files that
 may not be labelled conffiles, and 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 with conffile-like protection to come
 under this schema, and attempts to minimize questions asked at
 installation time. Indeed, the transitioning facility is better than the
 one offered by dpkg while transitioning a file from a non-conffile to
 conffile status.