This happened to me twice this year already, once the
very first day of the year, the second time
yesterday: Linux Mint 18.3 wouldn’t boot. It entered some emergency
or maintenance mode. The recommendation was to run
journalctl -xb, which didn’t make it clear to me what
was the cause of the trouble.
That first time I finally found a thread in
Ask Ubuntu, of which I ignored most, but
I did try running what was mentioned there as a simple measure
which in hindsight might have sufficed:
that solved the problem for me, although it remains a mystery why
And yesterday, again that was the solution.
Sylvia 18.3 is of course rather old. Current is now Ulyssa 20.1.
I don’t know how relevant this is for that version. But if anything
goes wrong, it is always worth trying this