retitle 925556 Use UUID, not sdX on grub linux lines thanks The problem simply turns out to be: grub lines like linux /boot/vmlinuz-4.9.0-8-amd64 root=/dev/sdb2 ro quiet are simply bound to fail:
When the computer boots, no matter when for the installer, or later, the installed system, /dev/sdX could refer to something different. So let's say there are two items plugged in when the grub.cfg is created. And two items plugged in when the newly installed system is booted. Well there is a 50% chance that the system won't boot. With three items, only a 33% chance the system will boot. https://www.gnu.org/software/grub/manual/grub/html_node/Device-map.html Let's examine a proper linux line: linux /boot/vmlinuz-4.19.0-4-amd64 root=UUID=f19dae4b-fcb8-49eb-b43b-6f99597db52d ro quiet I don't know why in the world your installer is still producing such bad linux lines. Maybe it is because I did the install totally offline and that's not what you test with. Anyway, you need to find out why GRUB_DISABLE_LINUX_UUID=true is somehow apparently sadly in effect. Actually it is only half in effect, as you see UUID entries, just not on the linux line: menuentry 'Debian GNU/Linux' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-ee7dd9c6-9f5b-45bc-bf31-36123bd61588' { load_video insmod gzio if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi insmod part_gpt insmod ext2 set root='hd1,gpt2' if [ x$feature_platform_search_hint = xy ]; then search --no-floppy --fs-uuid --set=root --hint-bios=hd1,gpt2 --hint-efi=hd1,gpt2 --hint-baremetal=ahci1,gpt2 ee7dd9c6-9f5b-45bc-bf31-36123bd61588 else search --no-floppy --fs-uuid --set=root ee7dd9c6-9f5b-45bc-bf31-36123bd61588 fi echo 'Loading Linux 4.9.0-8-amd64 ...' linux /boot/vmlinuz-4.9.0-8-amd64 root=/dev/sdb2 ro quiet echo 'Loading initial ramdisk ...' initrd /boot/initrd.img-4.9.0-8-amd64 } For users reading this bug: use "e" from the grub boot screen to fix e.g., sda2 to sdb2 or sdb2 to sda2, etc. (The only other problem I had was the unrelated Bug#926149: (AMD: Add nomodeset kernel parameter to avoid black screen)) Anyway this week I will delay final installation so I can assist further if needed.