I have had occasional desktop freeze-ups on my ubuntu 16.04 tower.I think it is doing it when Variety is trying to change wallpaper automatically and there is other stuff going on,such as open web pages and music playing(Audacious).When this happens,I can still drag open windows around,even to the other monitor,but can't open any new programs.Is the only solution removing Variety from my machine?The tower is an i7 quad core HP.I have also run into this issue on my HP dual core Elitebook.Maybe there is another wallpaper changer that likes HP hardware better?Am currently trying Cortina on the laptop.Another thought:I did clean installs of Ubuntu 16.04 on both machines a week ago,and left the software updater on the default settings.After this problem occurred,I changed it to notify immediately.Maybe this will solve the problem.

Messages ?.
Try starting from the terminal and see if you get amy messae(s) there.

Removed Variety from both computers,using Cortina instead.Will see if this solves problem next time I do some moderately heavy multitasking.It's only eye candy;no big deal.Thanks.