If you have just updated your *buntu desktop and use SSSD for client authentication you may find that you can no longer login.
There seems to be a bug in the update. It may not occur if you have autofs installed:
https://bugs.launchpad.net/ubuntu/+source/sssd/+bug/1695129Login via the terminal (you did set up a local user didn't you ? !!!!)
Ctrl+F1
This gets the sssd service running:
sudo service sssd restart
To fix it:
Edit /etc/init/sssd.conf
-start on (filesystem and net-device-up and starting autofs)
+start on (filesystem and net-device-up)
(Just remove 'and starting autofs')
Their Q&A seems to be a complete mess

HTH
Rgds
John