The first update always worked, but a subsequent update would not.
To manually switch an installation to PARTUUID, mount its boot partition and
replace the root= kernel parameter in cmdline.txt, like so:
/tmp/breakglass669384965 # mkdir boot
/tmp/breakglass669384965 # mount /dev/mmcblk0p1 boot
/tmp/breakglass669384965 # cat boot/cmdline.txt
console=ttyAMA0,115200 root=/dev/mmcblk0p2 init=/gokrazy/init elevator=deadline rootwait
/tmp/breakglass669384965 # sed -i 's,root=/dev/mmcblk0p,root=PARTUUID=471cad93-0,g' boot/cmdline.txt
/tmp/breakglass669384965 # cat boot/cmdline.txt
console=ttyAMA0,115200 root=PARTUUID=471cad93-02 init=/gokrazy/init elevator=deadline rootwait
/tmp/breakglass669384965 # umount boot
/tmp/breakglass669384965 # reboot
The PARTUUID= for your installation is printed by gokr-packer:
[…]
2020/05/01 10:05:34 write.go:366: writing MBR (LBAs: vmlinuz=51789, cmdline.txt=119561, PARTUUID=471cad93)
[…]
When calling reboot shortly after /update/*, the kernel should flush its cache,
but if you’re not calling reboot, it would be good to persist the data on disk
nevertheless.
Regular updates hit /boot, /root, then /switch.
bakery only updates /boot, so we need to take care of persisting the active root
partition across /boot updates.
