Bug#1111240: Debian 13 genericcloud amd64 GRUB terminal_output reproducer and workaround

[zarclac1138 at gmail.com]

Hello,

I would like to add a corroborating reproduction of Debian bug
#1111240, specifically with the Debian 13 (trixie) amd64
*genericcloud* QCOW2 image under QEMU/KVM and libvirt.

Observed on 22 October 2026:

- We used an upstream Debian 13 genericcloud image, checked against
the published SHA512SUMS, with a disposable libvirt guest and
host-side serial logging.
- With the image's original GRUB configuration, the serial log
repeatedly showed "Booting Debian GNU/Linux" (135 occurrences in the
instrumented attempt), but no Linux kernel, systemd, or cloud-init
output was observed. We could not establish a successful kernel
handoff.
- We then made a disposable copy and changed only the GRUB output
setting in /boot/grub/grub.cfg:

    terminal_output gfxterm serial
    ->
    terminal_output serial

- With that change, the guest booted the Linux kernel, started
systemd/networkd, and completed NoCloud cloud-init. The follow-up boot
remained stable during observation; the QMP event capture showed no
reset event.

This strongly corroborates the GRUB terminal-output interaction
described earlier in this bug, and extends the reproduction to the
Debian 13 *genericcloud* image rather than only the *generic* and
*nocloud* variants. It does not, by itself, identify whether GRUB's
terminal handling, the emulated serial device, or their interaction is
the root cause.

The guest's separate IP configuration problem was not diagnosed and is
not part of this report.

We preserved host-side serial and QEMU logs, the image checksum
verification, and the test/cleanup reports. Sanitized logs, the
precise image checksum and libvirt XML can be supplied if useful.

Thanks for investigating this issue.