Bug#1058638: grub-installer: boot fails: $bootdev empty [BIOS/MBR, Vista, 2 disks]: Installing grub on ''
Source: grub-installer
Version: 1.194
Severity: important
Tags: d-i
Whilst helping user "mavaviij" in matrix Debian room I was able to
reproduce in a virtual machine a bug that causes the Debian install to
fail to boot with a blinking cursor after install.
After a lot of code-chasing it appears the problem is that
grub-installer script fails to set its $bootdev variable:
grub-installer: info: Installing grub on ''
(note the empty quotes)
The target system has two 'disks'. The first has Microsoft Windows Vista
with 2 NTFS partitions using msdos label/MBR. The second is empty and intended
for the Debian OS and boot-loader.
The system boots in BIOS/Legacy/CSM mode.
I've not been able to trace back through the code to figure out why the
failure occurs. I have however identifed what may be a clue: the Debian
OS disk sector 0 appears to contain GRUB's g2hdr.img which makes me
wonder if grub-ntldr-img was used - although not sure how that is done
and see no sign of it in the (saved) installer logs.
Reproducer:
Using debian-12.4.0-amd64-netinst.iso
fallocate -l 1000000000 disk1-windows-vista.bin
fallocate -l 2000000000 disk2-debian-12.bin
fdisk disk1-windows-vista.bin
#new: 1, default,512M
#type: 1, 07
#new: 2, default, default
#type: 2, 07
#write
sudo losetup -P --show -f disk1-windows-vista.bin
# /dev/loop0
sudo mount /dev/loop0p1 /mnt/tmp/
# fool os-prober into detecting Vista
sudo mkdir /mnt/tmp/boot
sudo touch /mnt/tmp/bootmgr
echo "W i n d o w s V i s t a " | sudo dd of=/mnt/tmp/boot/bcd
find /mnt/tmp/ -ls; hexdump -C /mnt/tmp/boot/bcd
5 4 drwxrwxrwx 1 root root 4096 Dec 13 14:41 /mnt/tmp/
64 0 drwxrwxrwx 1 root root 0 Dec 13 14:42 /mnt/tmp/boot
65 1 -rwxrwxrwx 1 root root 27 Dec 13 14:32 /mnt/tmp/boot/bcd
67 0 -rwxrwxrwx 1 root root 0 Dec 13 14:41 /mnt/tmp/bootmgr
00000000 57 20 69 20 6e 20 64 20 6f 20 77 20 73 20 20 20 |W i n d o w s |
00000010 56 20 69 20 73 20 74 20 61 20 0a |V i s t a .|
0000001b
sudo umount /mnt/tmp
sudo os-prober
/dev/loop0p1:Windows Vista:Windows:chain
Now create a (libvirt/QEMU) VM guest with the 2 disk images attached and
go through the install procedure choosing the unpartitioned second disk
as the target.
At the question about installing the boot loader to the "primary disk"
answer No, then when the option to select which boot device to use choose
the 2nd disk where Debian is installed.
Save debug logs, restart VM, and even if using the SeaBIOS boot menu via
pressing Esc key, choosing the VirtIO boot device results in blinking
cursor.
Examine disk images and note that disk2 appears to have GRUB's g2hdr.img
in sector 0.
hexdump -C -n 512 disk2-debian-12.bin
00000000 fa b8 00 10 8e d0 bc 00 b0 b8 00 00 8e d8 8e c0 |................|
00000010 fb be 00 7c bf 00 06 b9 00 02 f3 a4 ea 21 06 00 |...|.........!..|
00000020 00 be be 07 38 04 75 0b 83 c6 10 81 fe fe 07 75 |....8.u........u|
00000030 f3 eb 16 b4 02 b0 01 bb 00 7c b2 80 8a 74 01 8b |.........|...t..|
00000040 4c 02 cd 13 ea 00 7c 00 00 eb fe 00 00 00 00 00 |L.....|.........|
00000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001b0 00 00 00 00 00 00 00 00 13 43 3c 32 00 00 00 04 |.........C<2....|
000001c0 01 04 83 fe c2 ff 00 08 00 00 00 90 3b 00 00 00 |............;...|
000001d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa |..............U.|
00000200
NOTE: on an UEFI system doing the reproducer one needs to edit
/usr/lib/os-probes/mounted/20microsoft
and comment out the test for UEFI on lines 11-14 if wanting to manually
test os-prober outside the running installer.
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