If the bootloader attempts to boot Slot B and fails to receive a "boot success" signal within a defined timeout (e.g., 10 seconds), it automatically reverts to Slot A. This is the "bulletproof vest" of ab multiboot.
Create a rauc.conf file defining your slots:
[system] compatible=my-device[slot.rootfs.0] device=/dev/mmcblk0p2 type=ext4 bootname=A ab multiboot
[slot.rootfs.1] device=/dev/mmcblk0p4 type=ext4 bootname=B
The term gained massive traction with Android 7.0 Nougat’s "Seamless Updates" feature. Google introduced AB partitioning to solve a critical problem: update failures. In a legacy Android device, an update that failed halfway would "brick" the phone. With AB Multiboot, the update writes to the inactive slot (e.g., Slot B). If the update succeeds, the system flips a flag and reboots into Slot B. If it fails, it simply boots back into the still-functional Slot A.
This same principle is now being adapted for Linux desktops, embedded systems, and custom bootloaders. If the bootloader attempts to boot Slot B
True multiboot (e.g., dual-booting two different custom ROMs) is possible on A/B devices without repartitioning, using methods like: