[Nottingham] Ubuntu 18.04 upgrade causes loss of graphical display

[godfrey at gnnix.co.uk]

Hi all,

  Having to dredge up long lost sys admin memories ( and borrow Windows 
[yuk!] laptop from daughter) because latest upgrade has left my beloved 
machine unable to run in graphical mode. I found various advice pages 
and have installed both lightdm and unity. Trying to start gdm fails and 
I only have terminal session. Cannot spot error message in log files so 
do not know exact cause. Running startx from terminal fails with fatal 
error (not specified what). Then installed lightdm and rebooted - hooray 
graphical screen, but login fails even though I know password was typed 
correctly.
Ho, hum - project for bank holiday is to try and sort it all out.

Godfrey