ucf overwrites diverted configuration file breaking unattended upgrades - upstream fix available

[Oliver O.]

An unattended security upgrade (package dovecot-core) failed, interrupting mailbox service. The cause was ucf replacing a custom configuration file which had been diverted (using dpkg-divert) by a custom configuration package.

Excerpt from /var/log/apt/term.log:
---
Setting up dovecot-core (1:2.2.33.2-1ubuntu4.6) ...
Replacing config file /etc/dovecot/dovecot.conf.custom with new version
ucfr: Attempt from package dovecot-core to take /etc/dovecot/dovecot.conf.custom away from package custom-mail-server
ucfr: Aborting.
dpkg: error processing package dovecot-core (--configure):
 installed dovecot-core package post-installation script subprocess returned error exit status 4
---

The underlying issue has been fixed upstream in ucf version 3.0040: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=477773

Affected versions:
- Ubuntu 18.04.5 LTS - ucf 3.0038
- Ubuntu 20.04.1 LTS - ucf 3.0038+nmu1

[Mathew Hodson (mhodson)]

https://launchpad.net/ubuntu/+source/ucf/3.0040
---

ucf (3.0040) unstable; urgency=medium

  * This is a feature add release, for the most part
  * Bug fix: "Add support for creating files with default SELinux
    context", thanks to Christian Göttsche (Closes: #949314).
  * Bug fix: "please consider merge request #1 adding
    ucf_helper_functions", thanks to Marc Haber (Closes: #930130).
  * Bug fix: "ucf has /bin/bash shebangs but does not depend on bash",
    thanks to James Le Cuirot (Closes: #952448). It actually does not need
    bash, so this was easy to do.
  * Bug fix: "should respect dpkg-divert", thanks to Timothy G Abbott
    (Closes: #477773).
  * Bug fix: "[INTL:nl] Dutch translation of debconf messages", thanks to
    Frans Spiesschaert (Closes: #926661).

 -- Manoj Srivastava <email address hidden> Tue, 19 May 2020 23:47:10 -0700