After updating my 14.04.5 lts version, I have this message on screen
system-undevd[672]: failed to execute '/bin/systemctl''/bin/systemctl start -- no-block invidia persistenced': no such file or directory
After that, I obtain a black screen. If I make Ctrl+alt+F1 I can have the Console and enter to my session. I am asked if I want to upgrade to Ubuntu 16.04.01 lts
Finally I found the solution: ***sudo apt-get purge nvidia**** thank to this post
