Comment 42 for bug 2056461

@Kip Thanks for the log. The kernel used there does not have my patch applied that I can tell - unless it is included in the Ubuntu kernel build already - but unlikely given that kernel is dated May 20th:

12:09:49.192706 [ 0.000000] Linux version 6.8.0-35-generic (buildd@lcy02-amd64-020) (x86_64-linux-gnu-gcc-13 (Ubuntu 13.2.0-23ubuntu4) 13.2.0, GNU ld (GNU Binutils for Ubuntu) 2.42) #35-Ubuntu SMP PREEMPT_DYNAMIC Mon May 20 15:51:52 UTC 2024 (Ubuntu 6.8.0-35.35-generic 6.8.4)

In my case I manually boot the image file with QEMU and install patched kernel builds into it (using ssh/scp/rsync), do an `apt update; apt upgrade` to prevent autopkgtest doing that in just the (temporary) overlay image it creates for each run. Then ensure the required GRUB menu entry will be used with 'grub-set-default' [0].

[0] grub-set-default "1>4" is the kind of syntax required; this would select the 5th "menuentry" from the 1st "submenu" (indexes begin at 0). The value is written into `/boot/grub/grubenv` that is read early when GRUB loads the generated grub.cfg at boot-time.

To identify the correct value I do a manual count using this (one-line!) command:

awk '{id=gensub(/.*(gnulinux-[^'"'"']*).*/,"\\1","g")};/menuentry /{prefix="";if(submenu){prefix=submenu ">";}print("ENTRY \"" prefix menu++ "\"",id)} /^submenu/{print("SUBMENU",++submenu,id);menu_saved=menu;menu=0}/^}/ && submenu {--submenu;menu=menu_saved}' /boot/grub/grub.cfg