configure the Mac to boot not from a local volume but from a server, using NetBoot Īnd more.prepare a volume so that it could be made bootable, by copying boot.efi to the right place.set the two NVRAM variables efi-boot-device and efi-boot-device-data to make any bootable volume the next startup disk.write the information to the volume header which declared that volume as being bootable.This used to be simple, before the advent of SIP, APFS, and Secure Boot in the T2, and came down to a single very complex command bless.
The last piece in the puzzle that is the booting of a Mac is understanding how any given volume is made bootable, and how it can be made the next startup volume.
