I just updated my Kubuntu installation to vivid (15.04). After updating, the default initialization with systemd fails shortly after showing the kubuntu animation (plymouth). The last log file entry is a SIGRTMIN on plymouthd. I am only able to reach the login screen using upstart (instead of systemd) in the advanced options of GRUB.
tldr;
If you are working on a dual boot system (Windows + Linux), an auto-mounted partition (in Linux) might still be locked by Windows (even if it is not the Windows system partition!).
long version
I had the same problem with my xubuntu 16.04. I have Windows 10 and xubuntu installed on my laptop (dual boot) and divided the hard drive into three (+1) partitions: windows, ubuntu (+swap) and 'exchange'. 'Exchange' is thought as an partition for storing common data between Windows and Linux. It is automatically mounted under Windows and Linux.
Unfortunately, the Windows "hybrid" shut down does not only lock the Windows partition but also the 'exchange' partition. When starting xubuntu after a regular (=hybrid) shutdown of Windows, xubuntu cannot auto-mount the 'exchange' partition.
In order to find out whether this is the case, one should use the command
systemctl --failed
. In my case it returned the information that the mounting of 'exchange' failed.The root cause was a change I did in fstab based on recommendations for solid state drives (SSD). I removed these lines and was able to reach the login screen with systemd:
My opinion is that it is unnecessary to configure RAM disks for temporary folders in fstab. SSD can handle enough erase cycles to be used for temporary folders; where it makes sense systemd will configure a RAM disk itself (see https://wiki.archlinux.org/index.php/Tmpfs#Usage) so there is no need fot the user to tweak fstab.