This morning my work laptop would not boot. I could not even get to single user mode initially and when I got as far as that I could not type anything on the terminal. I suspect some upgrade yesterday caused it.
In the end I had to search for a windows user who could write me a debian-live cd.
Using this, I could, after using some hints shown in
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=746358 get my system to boot (taking about 10 minutes do do so) and just as I started to work it rebooted spontaneously.
In the end after several experiments, I removed systemd and as a result a lot of other packages, reinstalled sysvinit and it booted normally again and now I can work.