Recover a frozen MacOS

Sometimes MacOS on my MacBook Pro hangs. Symtoms are:

• Dock does not react
• Apple Button does not react
• Spotlight works, applications can be started via Spotlight
• Apps do not react after they have been started
• I can cycle through applications via cmd + tab

Sometimes it is sufficient to restart Dock or the SystemUIServer by running the following commands:

killall -KILL Dock
killall -KILL SystemUIServer

If this doesn't work restarting the MacBook my help. There are several ways to do this:

1. run sudo shutdown -r now
2. cmd + On/Off Button
3. Hold On/Off Button for more than 6 seconds, then press it again

You can hold the shift key while booting to start in save mode. This will take a while.

Once I encountered a situation where none of the above tricks helped. And if even restarting doesn't help, you immediately get the feeling that something is seriousely worng. Well in the end I figured, that my Bluetooth connection was enabled, but my MagicMouse wasn't in range. For some reason the slowed down the whole system. After I disabled bluetooth, everything was fine again. Lesson learned: diable bluetooth if you don't need it.