compizshow-desktopunity
The function SHOW DESKTOP when moving mouse to the HOT CORNERS in ubuntu 13.04 worked.
After updating to 13.10, SHOW DESKTOP/HOT CORNERS only works until rebooting or setsid unity, after which it doesn't work.
I thought that something was wrong in the update to 13.10, so I made a clean install of ubuntu 14.04 to find out that the same issue exists.
What can I do to make SHOW DESKTOP/HOT CORNERS work again?
I have already tried to reset compiz and unity, and I did fresh install.
More than likely you used Compiz Config Settings Manager to set up your hot corners. There are other applications, but since you seem to be using Unity I won't go into all of that.
In general, setting up a hot corner is dependent on the particular plugin/feature that you want to activate (in other words you have to choose the hot corner from the plugin's settings).
The same method works for other plugins that support hot corners, including showing the desktop (in general options), activating scale mode (globabally), etc.
Install dconf-editor:
$ sudo apt-get install dconf-tools
Run dconf-editor (don't use sudo as the changes wont affect your account)
Navigate to org -> compiz -> profiles -> unity -> plugins -> core.
Copy the field active-plugins into Gedit, and edit it so unityshell is the last item. Paste it back into dconf.
Restart your computer.
(Tried on 14.04, it works.)
Best Answer
I was able to solve the problem by brute force.
Moving every single option in CompizConfig Settings Manager I did find that when Unity was disabled then Show Desktop works as expected with the HOT CORNERS.
So i click every single checkmark in Ubuntu Unity Plugin to finally find that Show Live Previews of Windows in the Switcher was the one to blame. (After unchecking it hot corners works as expected.