Bug#990966: grub-efi-arm64: breaks upgrades when the efivarfs is mounted read-only

[Steve McIntyre]

Control: reassign -1 shim
Control: clone -1 -2
Control: reassign -2 shim-signed

Cloning and reassigning...
-- 
Steve McIntyre, Cambridge, UK.                                st...@einval.com
Welcome my son, welcome to the machine.