@mcscx but all drives were mounted. I used a rescue CD, checked all extX devices (again, no problem), removed data from /var (while nothing mounted there), edited fstab and commented out a bunch of things; also disabled the systemd's emergency.service & emergency.target (so I could not get stuck there); then rebooted (with a few wrinkles). now Nikola *does* reboot, but has no network (which probably was the main problem in the first place). for all this, I picked up some hints from here: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=757072