Am running Ubuntu 16.04 and have been having irritating problem with boot.
Often - but not always - when I start up, the boot pauses for 90 seconds with the message "[***] A start job is running for dev-mapper...", switching to list all devices currently listed in /etc/fstab. After 90 seconds boot continues but drops into single-user mode.
Once this happens, I can then boot successfully by selecting recovery mode, and then selecting "Resume normal boot".
After much headscratching I think I have traced the problem to an issue with fsck. Boot runs normal reliably when I set fs_passno 0 for my root filesystem (a 256GB SSD formatted ext4). I tried this after booting into a live USB and attempting fsck on the root filesystem and received the message:
/dev/sdd1 has unsupported feature(s): metadata_csum e2fsck: Get a newer version of e2fsck!
When I downloaded a new version (from E2fsprogs) fsck ran correctly.
So my tentative thinking is that the version of fsck running at boot is incompatible with my root file system.
Any suggestions on how to fix this? I'd rather not just disable fsck permanently, but at the moment it seems to be the only solution.