On 15 February, an update to
compiz was pushed out by Ubuntu that triggered the removal of
unity, and (on my system, at least)
The result: rebooting after doing an
apt-get dist-upgrade leaves you with no desktop environment.
The fix: use
aptitude to trigger a downgrade of the relevant
compiz packages (first you might need to use Ctrl+Alt+F1 to get a terminal session, and you might need to install aptitude too).
Here are the commands I needed:
$ sudo apt-get install aptitude $ sudo aptitude install ubuntu-desktop unity unity-tweak-tool
Reject the first “solution” offered by aptitude, and when it offers to downgrade compiz, accept. Then, if needed:
$ sudo reboot