IBoot

iBoot
Developer(s)Apple Inc.
Operating systemDarwin, macOS,[1] iPadOS and iOS[2]
Platformx86, ARM
TypeBoot loader
LicenseProprietary software

iBoot is the stage 2 bootloader for all Apple products.[3] It replaces the older EFI-based bootloader on Intel-based Macs. Compared with its predecessor, iBoot improves authentication performed in the boot chain.[2]

For x86-based Macs, the boot process starts by running code stored in secured UEFI boot ROM (stage 1). The boot ROM has two primary responsibilities: to initialize system hardware and to select an operating system to run (the POST and UEFI component). For ARM-based Macs, the boot ROM does not include UEFI.[4]

For iPhones, iPads and ARM-based Macs, the boot process starts by running the device's boot ROM. The boot ROM loads the Low-Level Bootloader (LLB), which is the stage 1 bootloader and loads iBoot. If all goes well, iBoot will then proceed to load the iOS, iPadOS or macOS kernel as well as the rest of the operating system.[5][6] If the iBoot fails to load or fails to verify iOS, iPadOS or macOS, the bootloader jumps to DFU (Device Firmware Update)[7] mode; otherwise it loads the remaining kernel modules.[2] Since Apple A7 and Apple M1, the LLB is stored on NAND flash of iPhone or iPad, or SSD of Apple Silicon Mac.

On x86 Macs, iBoot is located in /System/Library/CoreServices/boot.efi.[8] Once the kernel and all drivers necessary for booting are loaded, the boot loader starts the kernel’s initialization procedure. At this point, enough drivers are loaded for the kernel to find the root device.[9]

  1. ^ "Darwin 9.2 Source Code". Apple Inc. Archived from the original on September 21, 2020. Retrieved January 19, 2020.
  2. ^ a b c Ryan, Peter Y. A.; Naccache, David; Quisquater, Jean-Jacques (2016-03-17). The New Codebreakers: Essays Dedicated to David Kahn on the Occasion of His 85th Birthday. Springer. ISBN 9783662493014.
  3. ^ Hayes, Darren R. (2014-12-17). A Practical Guide to Computer Forensics Investigations. Pearson IT Certification. ISBN 9780132756150.
  4. ^ "boot process for T2, M1, and iOS devices".
  5. ^ Apple Inc. (May 2016). "iOS Security Guide" (PDF). apple.com. Archived (PDF) from the original on February 27, 2016.
  6. ^ "Boot process for a Mac with Apple silicon - Apple Support". Jan 2024.
  7. ^ "iFixit Support: DFU Restore". iFixit. Retrieved 2019-09-29.
  8. ^ "rEFIt - The Intel Mac boot process". refit.sourceforge.net. Retrieved 2017-08-26.
  9. ^ "The Early Boot Process". developer.apple.com. Retrieved 2017-08-26.