All of my icons have disappeared after an update; I tried selecting different icon themes but still no icons are showing up when I log in.

All of my icons have disappeared after an update; I tried selecting different icon themes but still no icons are showing up when I log in.

This is a mime cache issue resolved using
sudo update-mime-database /usr/share/mime
and performed logout and then login, now all icons are back
I add the same ! I was caused by a fail update of linux kernel. My /boot folder was full.
To check that : In a terminal, type
df /boot
if it is full (100%), you can clean it using this tutorial : http://ubuntuhandbook.org/index.php/2016/05/remove-old-kernels-ubuntu-16-04/ Look at "Remove Old Kernels via DPKG".
Et en français : https://www.justegeek.fr/nettoyer-la-partition-boot-des-kernels-non-utilises-sous-ubuntu/ ;)