The ubuntu desktop menu bar and taskbar program title bar are gone

origin

The system honey juice is automatically updated, from Ubuntu 16.4 to 18.04, I found this bad news when I turned it on, and the top and left are empty

Solution

Tried a few methods, also reinstalled the desktop, and finally got it like this.
reset compiz settings

dconf reset -f /org/compiz/

After resetting compiz, restart Unity:

setsid unity