Comment 0 for bug 1463120

I found this on my main 15.04 desktop but have reproduced it in a VM:
1. Install Ubuntu 15.04 (I included updates and non-free but I doubt that matters).
2. Add a bogus entry to /etc/fstab, eg:
  /dev/sdd1 /mnt/sdd1 ext4 errors=remount-ro 0 0
Note that /mnd/sdd1 exists but /dev/sdd1 does not
3. Reboot

Expected: Failure to mount /dev/sdd1 reported and option to boot without mounting it
Actual: System appears to hang, although it will eventually present a root terminal (with no indication of the cause of the problem). It appears to hang prior to switching graphical mode, with the result that any warnings/errors that are present on all boots but invisible because the screen clears before they're seen become visible for the first time incorrectly suggesting they are the cause of the problem.

Removing (or commenting out) the problematic entries and rebooting allows the system to boot.

HOWEVER: The grub boot menu now appears and any pre-existing menu timeout and default action seems to have been lost; it's now necessary to select a boot option on each boot. This may be a separate bug (or feature?).

My actual case: I have external drives permanently connected via USB, however the USB card appears to have failed hence the drives are not accessible. With no clues (and being unfamiliar to systemd) working out why the system wouldn't boot was a tough job.