Ubuntu 16.04 Display Resolution 800x600
Solution 1:
I used the work-around in
Stuck at 800x600 display resolution Ubuntu 14
This increases the resolution to an acceptable level (2560x1440) by editing /etc/default/grub - changing to GRUB_GFXMODE 2560x1440.
However, I feel that the Nvidia driver is not installed properly so this is just a work-around...
Solution 2:
You have to update grub too. After some updates on 16.04 (on Parallels) I've lost my display settings. That helps me:
sudo vim /etc/default/grub
GRUB_GFXMODE=1440x900 # MacBookAir resolution
sudo update-grub