I got a computer running Ubuntu 12.04 64bit with UEFI. Today (2013-09-21) I installed all updates that were available without carefully reading through the list (shame on me), since noone touched the computer for some weeks and the list was more than 100 items long...
I remember from another machine, that one of the updates changes the boot system on UEFI machines in order to always use shim, even if restricted boot is disabled.
Well, problem diagnosis is rather straightforward: Something went wrong with the bootloader update, although no error was given, and the Ubuntu entry went missing from the UEFI boot menu, making the computer try to boot in BIOS mode, of course failing. If I run efibootmgr
from a bootable USB it only shows the BIOS boot mode for the HDD...
How do I restore the Ubuntu entry in the UEFI menu to make the machine bootable again?