Long boot after upgrade from 14.10 to 15.04

To identify the problem, run;

systemd-analyze blame

Or for graphical analysis

systemd-analyze plot > plot.svg
eog plot.svg

Use any viewer if you do not use eog ;)

Other distros (Fedora and Arch) have been using systemd for longer, and have IMO better documentation then Ubuntu at the moment.

See https://wiki.archlinux.org/index.php/Improve_boot_performance

Optimization may include disabling services you do not need, for example see

https://harald.hoyer.xyz/2013/11/13/fedora-boot-optimization/

Once you have identified where the boot is hanging or taking too long you can look into solutions.

See also http://manpages.ubuntu.com/manpages/utopic/man1/systemd-bootchart.1.html

I really can not find ubuntu specific information on the ubuntu wiki as of yet.