Thanks pali, I also think it is the source of the problem: # ls /etc/default/mount* /etc/default/mount-opts /etc/default/mount-opts.dpkg-dist And the mount-opts.dpkg-dist seems to be up-to-date. I cannot remember I have ever touched /etc/default/mount-opts, but maybe some third party app did. So I just renamed mount-opts.dpkg-dist to mount-opts.