Internet Recovery

Internet Recovery is an option available to macOS users in case the recovery volume becomes corrupted, or if macOS Recovery fails to revive an unbootable Mac. Alternatively referred as "restore", this process can reinstall both the recovery volume and macOS operating system, downloaded from an Apple server.

Starting up Internet Recovery
It is possible to boot directly into Internet Recovery by restarting a computer with the following steps:
 * Macs with Intel processors:
 * Hold down the command, option and R keys during startup to restore with the newest version of macOS available for the affected Mac model.
 * Hold down the command, option, shift and R keys during startup to restore with an older version of macOS closest to the one that the affected Mac model shipped with.
 * Macs with Apple processors: Continue holding down the power button during startup until the startup options appears and then click the gear icon labeled "Options".