That's expected. Devices with A/B
partition scheme don't have a recovery partition. You can only boot in recovery mode with fastboot boot twrp.img
. But to permanently flash recovery to device which can be booted into by proper key combination, you need to unpack both of your boot.img
s (A/B) from device and replace the ramdisk
with the one extracted from twrp.img
. Then repack and flash boot.img
s back to device.
On TWRP this has been previously achieved by flashing a special ZIP file, or one could do manually. Now the official TWRP release includes the option Install Recovery Ramdisk
:
Use magiskboot to allow repacking boot images for installing TWRP
Traditionally boot.img
and recovery.img
had two major components; kernel and ramdisk. On A/B devices, no ramdisk is required for normal boot because system.img
is mounted as rootfs
when processing Device Tree (dtb
) which is appended to kernel image usually. So the ramdisk.cpio
in boot.img
is that of recovery. Since kernel is same for a device (other than build configurations), so only ramdisk needs to be replaced.
Sources: