After updating grub2 (to 2.02~beta2-36ubuntu3.26) and rebooting, my server does not boot: Booting from Hard Disk 0... error: symbol `grub_calloc' not found. Entering rescue mode... grub rescue> _ I rebooted 3 servers in this way (all running Ubuntu 16.04.6 LTS) and all hung. A lot of other peopl…