How to use Internet Recovery to reinstall macOS

The first approach is to use a feature called Internet Recovery. Newer Macs are able to boot directly from an internet connection, even with no Recovery partition available. Here is how to use MacOS Internet Recovery:

1. Shut down your Mac.
2. Hold down Command-Option/Alt-R and press the Power button. (On some Mac keyboards the Option key will be named Alt).
3. Hold down those keys until you a spinning globe and the message "Starting Internet Recovery. This may take a while".
4. The message will be replaced with a progress bar. Wait for it to fill. Expect it to take a while...
5. Wait for the MacOS Utilities screen to appear.
6. Click Reinstall macOS and follow the installation process.

There are issues with Internet Recovery. It only works with networks using WEP and WPA security. This is most home Wi-Fi networks, but if you're on a proxy network or PPPoE then you will have problems. In these cases it's usually best to find another network rather than create a USB Recovery Stick (our next step). If you have Internet Recovery, then make use of it to reinstall macOS if possible.

Requirements for installing macOS in Recovery Mode

After entering  Internet Recovery Mode and choosing to install or reinstall macOS, your Mac will need to download the installer for the version of macOS that came preloaded on your Mac when you took it out of the box.

If OS X Recovery is used for reinstallation, your Mac must use DHCP on a Wi-Fi or Ethernet network and WPA/WPA2 as a security method on Wi-Fi. You cannot reinstall macOS over a Wi-Fi or Ethernet network that uses the following authentication protocols:

• WEP
• WPA-Enterprise
• Certificate-based authentication / 802.1x
• Proxies (where specific proxy servers must be configured in network preferences)
• Captive Wi-Fi networks (where you click an “Agree” button to access the Internet)
• PPPoE (where there is no router handling the PPPoE connection)

The network requirements listed above also apply to the version of Safari that’s included with macOS’ Internet Recovery and standard Recovery Mode.

If your Internet connection has requirements that are unsupported by macOS Recovery, change the settings to a supported configuration for the duration of the macOS installation.

What to do when Internet Recovery is unavailable

If the recovery partition on your Mac has been damaged and you cannot enter standard Recovery Mode and Internet Recovery is unavailable, you can still start the computer from an external drive with a bootable version of OS X.