During packages upgrade this error occurred:
Setting up opendkim (2.11.0~alpha-10+deb9u1) ...
Job for opendkim.service failed because the control process exited with error code.
See "systemctl status opendkim.service" and "journalctl -xe" for details.
invoke-rc.d: initscript opendkim, action "start" failed.
● opendkim.service - OpenDKIM DomainKeys Identified Mail (DKIM) Milter
Loaded: loaded (/lib/systemd/system/opendkim.service; enabled; vendor preset: enabled)
Active: activating (auto-restart) (Result: exit-code) since Fri 2018-07-06 17:47:50 UTC; 6ms ago
Docs: man:opendkim(8)
man:opendkim.conf(5)
man:opendkim-genkey(8)
man:opendkim-genzone(8)
man:opendkim-testadsp(8)
man:opendkim-testkey
http://www.opendkim.org/docs.html
Process: 8365 ExecStart=/usr/sbin/opendkim -x /etc/opendkim.conf (code=exited, status=78)
Jul 06 17:47:50 ... systemd[1]: opendkim.service: U…e.
Jul 06 17:47:50 ... systemd[1]: opendkim.service: F…'.
Hint: Some lines were ellipsized, use -l to show in full.
dpkg: error processing package opendkim (--configure):
subprocess installed post-installation script returned error exit status 1
# journalctl -xe
...
-- Unit opendkim.service has begun starting up.
Jul 06 18:06:14 ... opendkim[26012]: /etc/dkim.key: key data is not secure: /etc/dkim.key is not owned by the executing uid (0)
Jul 06 18:06:14 ... opendkim[26012]: opendkim: /etc/opendkim.conf: /etc/dkim.key is not owned by the executing uid (0)
Jul 06 18:06:14 ... systemd[1]: opendkim.service: Control process exited, code=exited status=78
Jul 06 18:06:14 ... systemd[1]: Failed to start OpenDKIM DomainKeys Identified Mail (DKIM) Milter.
-- Subject: Unit opendkim.service has failed
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- Unit opendkim.service has failed.
...
# ls -al /etc/dkim.key
-rwx------ 1 opendkim opendkim 1675 Aug 6 2017 /etc/dkim.key
Operating system Debian Linux 9
Webmin version 1.883 Usermin version 1.741
Virtualmin version 6.03 Theme version Authentic Theme 19.18
Apparently a new configuration file from the package needed to be accepted in place of the old file.