Ubuntu 16.04 LTS displays blank screen on boot after latest update

After updating the packages on the laptop on November 6, 2016, the laptop was not displaying the login screen to continue further work.

On the other hand, pressing Ctrl+Alt+F1 took me to a terminal prompt from where I could at least login through the command line interface. So, all is not lost.

Being able to get to the command line means that there is an issue with the XServer configuration on the laptop. The last upgrade rolled out updated the nvidia drivers on the laptop. Since my laptop using NVidia Optimus, it could be that the issue was the Xorg configuration.

To confirm, I entered the following command.
$ cd /etc/X11 <enter>
$ cat xorg.conf <enter>

Section “ServerLayout”
Identifier “layout”
Inactive “intel”
Screen 0 “nvidia”
EndSection

Section “Device”
Identifier “intel”
Driver “modesetting”
BusID “PCI:0@0:2:0”
Option “AccelMethod” “None”
EndSection

Section “Screen”
Identifier “intel”
Device “intel”
EndSection

Section “Device”
Identifier “nvidia”
Driver “nvidia”
BusID “PCI:1@0:0:0”
Option “ConstrainCursor” “off”
EndSection

Section “Screen”
Identifier “nvidia”
Device “nvidia”
Option “AllowEmptyInitialConfiguration” “on”
Option “IgnoreDisplayDevices” “CRT”
EndSection

The 3rd line above stated Inactive “intel”. This means that the default became nvidia. To fix it, here is what to do:
$ sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf.backup <enter>
This creates a backup of the current xorg.conf file.

$ sudo vi /etc/X11/xorg.conf <enter>
In the 3rd and 4th lines, change from (shown in Red below):
Section "ServerLayout"
Identifier "layout"
Inactive "intel"
Screen 0 "nvidia"
EndSection

to that shown in Green below:
Section "ServerLayout"
Identifier "layout"
Inactive "nvidia"
Screen 0 "intel"
EndSection

:wq
Save the file.

$ reboot <enter>

And the login screen re-appears.