Your message dated Sat, 17 Oct 2026 04:49:47 +0000
with message-id <[email protected]>
and subject line Bug#1151059: fixed in kmscon 10.0.4-2
has caused the Debian Bug report #1151059,
regarding kmscon often freezes on TTY switch with 'cloud-amd64' kernels
to be marked as done.
This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.
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--
1151059: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1151059
Debian Bug Tracking System
Contact [email protected] with problems
--- Begin Message ---
Package: kmscon
Version: 10.0.4-1
Severity: important
X-Debbugs-Cc: [email protected]
Dear Maintainer,
I am currently testing kmscon in forky inside a QEMU KVM guest.
When forky runs on a linux-image-amd64 kernel, kmscon appears to run and handle
TTY switching fine (with CTRL-ALT-F<number>),
both between instances of itself and to/from instances of [email protected].
Disabling [email protected] and enabling [email protected],
to set kmscon as default for all TTYs, also appears to work well after a reboot.
However, for lightweight VMs, I prefer running linux-image-cloud-amd64. When
running this kernel flavour,
roughly 3 out of 5 times, switching from fbcon to kmscon or between kmscon TTYs
apparently causes the target TTY to freeze.
How this "freeze" appears depends on whether QEMU is running the VM on its
default virtual firmware (= Legacy BIOS)
or OVMF (= UEFI). On the former, a frozen kmscon typically appears as a black
screen, while on OVMF I can at least
see a solid (non-blinking) kmscon cursor in the upper-left corner of QEMU's
virtual screen.
Sometimes (= not always), attempts to switch back to a default non-kmscon
console from a frozen kmscon
(with CTRL-ALT-F<number>) will even cause *all* ttys to freeze (regardless of
whether they run fbcon or kmscon),
forcing me to stop kmsconvt@tty<number>.service via SSH or a serial console.
The same apparent game of chance applies on every boot if I try
'systemctl enable [email protected] && systemctl enable [email protected]'
followed by rebooting the VM (in an attempt to make kmscon the system-wide
default for all new TTYs).
If, on a forky VM with these symptoms, I install and reboot into a build of
linux-image-amd64
(instead of ...cloud-amd64), the problem seems to disappear completely.
Boot the same VM guest back into ...cloud-amd64, and the game of chance returns.
How to reproduce:
1. Boot your functioning Debian forky VM.
It should be able to reach an official package mirror and should be using the
default [email protected] for all TTYs.
Example basic QEMU command *without* OVMF/UEFI:
qemu-system-x86_64 -machine accel=kvm:tcg -cpu host -smp 2 -m 4G -netdev
user,id=natdev0,hostfwd=tcp::2222-:22 -device virtio-net-pci,mac="$(randmac
--qemu)",netdev=natdev0,id=natnic0 -smbios
type=41,designation=onboardlan,instance=1,kind=ethernet,pcidev=natnic0 -drive
file=/path/to/your-vdisk.qcow2,if=virtio,format=qcow2
2.1 If you are using linux-image-amd64, enter command inside guest: apt -y
install linux-image-cloud-amd64.
(otherwise, skip to step 3.)
2.2 Reboot the guest, making sure it boots into the kernel which was just
installed.
3. Enter command inside guest: apt -y install kmscon
4. Enter command inside guest: systemctl start [email protected]
5. Press CTRL-ALT-2 to switch to QEMU's 'compatmonitor0'.
6. Enter command in QEMU's 'compatmonitor0': sendkey ctrl-alt-f2
7. Press CTRL-ALT-1 to switch back to your VM guest screen.
Observe whether you get a working and responsive console, or a frozen one.
8. Press CTRL-ALT-2 to switch to QEMU's 'compatmonitor0'.
9. Enter command in QEMU's 'compatmonitor0': sendkey ctrl-alt-f1.
This should return you to your working, "classic" console on tty1,
either still reponsive or, if kms was also frozen, also frozen.
10. If necessary, repeat steps 5-9 a few times to provoke a frozen kmscon.
Workaround:
Install and boot into linux-image-amd64 instead of linux-image-cloud-amd64.
It will take up more storage space and RAM, but kmscon will apparently run and
switch just fine.
Other troubleshooting info:
When I provoke the issue, kmscon itself outputs the following line once:
Error: video_fbdev: cannot get finfo (9): Bad file descriptor
...followed by repeated lines of the following, until I manage to switch away
or kill it:
Warning: terminal: cannot swap display [fbdev] -22
dmesg does not show any complaints from the kernel side. I know kmscon is a
userland program,
but thought I'd check anyway since switching from/to default fbcon is part of
it.
I have, unsuccessfully, tried playing around with the --no-drm and --no-mouse
options.
The kmscon project's own documentation [1] does not seem to specify what kind
of kernel config
settings/modules it needs, and I lack the knowledge necessary to narrow down
which options it would
need to be set a certain way in order to run and switch properly
(assuming, possibly in error, that the kernel is lacking something).
I am not sure whether I should file this bug against kmscon, linux, qemu, or
another package.
I picked kmscon for now, since that is the package I am having apparent basic
usage issues with.
Please feel free to correct me on that and/or which additional package(s) it
affects.
Severity set to important per explanation in reportbug.
Thank you.
[1] https://github.com/kmscon/kmscon/tree/main#requirements
-- System Information:
Debian Release: forky/sid
APT prefers testing
APT policy: (500, 'testing')
Architecture: amd64 (x86_64)
Kernel: Linux 7.2.9+deb14-cloud-amd64 (SMP w/2 CPU threads; PREEMPT)
Locale: LANG=C.UTF-8, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages kmscon depends on:
ii init-system-helpers 1.69+nmu3
ii libc6 2.43-7
ii libdbus-1-3 1.16.2-8
ii libdrm2 2.4.134-3
ii libegl1 1.7.0-3+b1
ii libfontconfig1 2.17.1-5
ii libfreetype6 2.14.3+dfsg-3
ii libgbm1 26.1.6-1
ii libgles2 1.7.0-3+b1
ii libglib2.0-0t64 2.90.1-2
ii libpango-1.0-0 1.58.2-1
ii libpangoft2-1.0-0 1.58.2-1
ii libtsm4 4.8.0-0.1
ii libudev1 262-1
ii libxkbcommon0 1.13.1-1
ii login 1:4.16.0-2+really2.42.4-1
ii ncurses-term 6.6+20260608-2
ii zlib1g 1:1.3.dfsg+really1.3.2-3
kmscon recommends no packages.
kmscon suggests no packages.
-- no debconf information
--- End Message ---
--- Begin Message ---
Source: kmscon
Source-Version: 10.0.4-2
Done: Boyuan Yang <[email protected]>
We believe that the bug you reported is fixed in the latest version of
kmscon, which is due to be installed in the Debian FTP archive.
A summary of the changes between this version and the previous one is
attached.
Thank you for reporting the bug, which will now be closed. If you
have further comments please address them to [email protected],
and the maintainer will reopen the bug report if appropriate.
Debian distribution maintenance software
pp.
Boyuan Yang <[email protected]> (supplier of updated kmscon package)
(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing [email protected])
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512
Format: 1.8
Date: Sat, 17 Oct 2026 00:12:10 -0400
Source: kmscon
Architecture: source
Version: 10.0.4-2
Distribution: unstable
Urgency: medium
Maintainer: Boyuan Yang <[email protected]>
Changed-By: Boyuan Yang <[email protected]>
Closes: 1151059
Changes:
kmscon (10.0.4-2) unstable; urgency=medium
.
* debian/patches: Add patches to fix frozen or blank VTs with the
fbdev backend after VT switches (Closes: #1151059).
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