In the event of a serious problem with your Mac, you may need to reinstall your Mac operating system. There’s a simple way to do this using your Mac Recovery partition or via Mac Internet Recovery.

Lastly, if your Mac supports Internet Recovery, then you can use this by holding Option-Command-R at startup instead of just Command-R. This will load the same recovery tools from Apple's servers that ...

To restart an Intel Mac in Recovery Mode, hold Command+R when the computer restarts. This article teaches you how to restart ...