One addition: On one occasion, pdns.conf.local was overwritten without any questions, probably because it hadn't been manually added before.
However, on a different server, I was asked whether pdns.conf.local should be overwritten. Choosing 'no', a file containing the broken config, named 'pdns.local.ucf-dist' was left in /etc/powerdns/pdns.d. Since all files in this directory are read by PowerDNS, leaving a broken file there (or a file that contains any unwanted configuration; why else would the admin choose not to overwrite pdns.local...) still breaks the installation. No temporary or backup files should be left in /etc/powerdns/pdns.d.
smime.p7s
Description: S/MIME Cryptographic Signature
