At work, I plug my 11-inch MacBook Air into a 23-inch LCD, which I use as my primary screen, with the Mac’s display as a secondary screen. Frequently, due to some combination of not closing it then unplugging the Mini DisplayPort plug in the proper order, or… something… I will find that when I open up my computer the next day, my desktop background (a.k.a. “wallpaper” for recent Windows switchers) on the MacBook Air is gone, replaced with a far-too-bright light gray generic background. Yuck!
Previously I had resorted to logging out and back in, or even rebooting, to fix this problem, but yesterday I searched and found an answer. It’s really simple! But it does require opening Terminal.
Go into Applications > Utilities and open Terminal. Then at the command prompt, type this (and, of course, hit Return):
killall Dock
That’s it! The Dock will quit and automatically restart, and the desktop will be restored!