Bug#769406: Serial console not set up after serial install

[Kevin Otte <nivex@nivex.net>]

I've just run headlong into this 10 years later.

I have a script that creates a VM thusly:
virt-install --name ${vm_name} --memory ${mem_size} \
 --disk "size=${disk_size},pool=${disk_pool},discard=unmap" \
 --machine q35 \
 --location 
http://ftp.us.debian.org/debian/dists/${suite}/main/installer-amd64/ \
 --os-variant name=debiantesting \
 --network network=ovs-net,target=ve0-${vm_name} \
 --graphics none --extra-args="console=ttyS0 netcfg/hostname=${vm_name}" \
 --console pty \
 --initrd-inject preseed.cfg

Under both bookworm and trixie, the install completes successfully over 
the serial console.

In bookworm it seems systemd was being overly smart and starting a getty 
on the serial port when it saw one, as there is no other apparent 
configuration to start it. Under trixie this behavior is no longer 
present, so I get no way to log into the installed system. (I can't be 
certain this is the case as I have not been able to locate a relevant 
changelog entry in systemd.) However, since grub does get configured, I 
can edit the kernel command line manually on boot and append 
"console=ttyS0". systemd sees this kernel argument and starts the getty.

So it seems like the simplest way to fix this in the current environment 
is to have the code that sets up the grub serial arguments also go ahead 
and tack on a matching "console=" to GRUB_CMDLINE_LINUX.