Apple - OSX Yosemite - Mission Control stopped working

(This irritating bug seems to be biting me more often after updating to 10.10.4)

When this happens and I don't want to have to reboot, I only restart the "Dock" process and the problem is gone. There's probably some GUI way to do it, but I just drop into Terminal and do:

killall Dock

But before that, run killall -s Dock to see what would be killed, to make sure it's only going to directly kill the one "Dock" process.

Once you run killall Dock, Dock will restart in a few seconds and then Mission Control is working again. You can verify that the restart happened by checking the Process ID of "Dock" after the restart.

The GUI way:

1. Open Activity Monitor.
2. In the search field, type in 'Dock'.
3. Select Dock in the results.
4. Click on the black X directly above on the left.
5. When asked if you are sure you want to quit the process, choose Quit.

The Dock process will quit and restart. All your gestures/shortcuts will now work again.

I found that the file responsible ist com.apple.dock.plist which sits in ~/Library/Preferences. In this file exists an entry to enable/disable mission control.

For me this procedure helped to get mission control working again:

• Start terminal and execute the following commands:

• defaults write com.apple.dock mcx-expose-disabled -bool FALSE
  (this enables mission control)

• killall Dock
  (kill and automatically restart the Dock, this is necessary to get it done)