Live CD not booting into serial terminal even if kernel command line is given properly

[bpisch]

Is this a new report?

Yes

System Info

n/a

Package(s) Affected

n/a

Does a report exist for this bug with the project's home (upstream) and/or another distro?

No

Expected behaviour

After starting Qemu with the Live CD and pressing escape to get to the boot: prompt, the system should provide a console on virtual serial console connected to ttyS0. Expected to work with the following kernel command-line: "linux console=ttyS0,115200n8".

Actual behaviour

After providing kernel command line "linux console=ttyS0,115200n8" and pressing enter Qemu continues to stay in graphical mode, after a while upgrades to the screen resolution from 640x480 graphic mode to something higher, and when switching to the serial console, there is no output at all, even after waiting minutes.

Steps to reproduce

qemu-system-x86_64 -hda disk.qcow2 -cdrom void-musl-base.iso -boot order=d -m 4G -net nic -net user -serial telnet:localhost:1234,server,nowait -display curses
2.
Right after Sea BIOS, Qemu switches into graphical mode, press esc quickly to get to the "boot:" prompt.
3.
Open a telnet connection to localhost 1234
4.
4.1.
Type in the following into the "boot:" prompt:
linux console=ttyS0,115200n8
4.2.
Alternatively, try with these, these also don't work:
linux console=ttyS0,115200n8 debug
linux console=ttyS0,115200n8 single
5.
Observe that even after minutes, serial console stays empty.

[classabbyamp]

have you tried without the speed?

[classabbyamp]

you're probably missing a bunch of kernel arguments that the live images need to boot

I was able to boot and use the serial console with that image using qemu/virt-manager:

# cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz initrd=/boot/initrd root=live:CDLABEL=VOID_LIVE init=/sbin/init ro rd.luks=0 rd.md=0 rd.dm=0 loglevel=4 vconsole.unicode=1 vconsole.keymap=us locale.LANG=en_US.UTF-8  rd.live.overlay.overlayfs=1 console=ttyS0

[bpisch]

Hello,
Thank you for your response. I tried first by adding just "linux console=ttyS0" as your first comment suggested, then I tried to paste in the whole kernel cmdline into the boot: prompt, but unfortunately nothing appears in the telnet serial window, even if I wait for 10 minutes. Host OS is Ubuntu 24.04 Qemu version is 8.2.2. Sorry I'm not able to get any guest OS logs because this host can communicate only via SSH so I have no graphical way of accessing the host machine, only a single bash shell. That's why I would need to boot Void into serial console and not using any conventional ways of access.
Also sorry for opening the issue on the wrong repo, I'm not familiar yet with the repo structure of Void unfortunately.
Thank you for your help in advance!

[bpisch]

Hello,
I have discovered something which might cause this issue. It appears that the bootloader of the CD image (I assume it's isolinux since I'm booting it with Sea Bios) doesn't care about the arguments provided on the "boot:" prompt. I tried to provide various false arguments to intentionally cause the kernel to fail loading, but whatever I do the OS still gets booted and still has no serial console. I tried modifying the init parameter, to provide an invalid rootfs parameter, invalid initrd parameter, even an invalid boot label (also even "poweroff" boots the system instead of turning off) so it appears whatever I do there is still the standard boot happening with standard options.
Do you have any idea what could cause this, and how could I influence the bootloader?
Thank you in advance.

[classabbyamp]

in syslinux, you should just need to press tab to edit the entry and enterv to boot it

[bpisch]

Thank you for your response, in my case unfortunately it doesn't work because the bootloader displays it's menu in "640x480 graphic mode" in Qemu. So that's why I can't directly edit the boot option and that's why I have to press "esc" to get to the boot: prompt. After I'm there and I press tab, I see all boot labels listed out, but whatever I type the system gets booted, even for label "poweroff".
Thank you in advance.

[classabbyamp]

if it doesn't say grub at the top, it's isolinux/syslinux

[bpisch]

Yes most likely syslinux because it doesn't say anything at the top. What I'll try is to somehow rebuild the ISO and hand-craft the isolinux.cfg to include serial port parameter by default.