Add serial console boot for Opensuse 15.5

While it works with UEFI boot using “legacy BIOS” the serial console works after grub has prompted the boot menu. But this might be too late e.g. in special cases like encrypted disk where grub needs to request the password.

KVM Guest has already been changed for serial support as outlined below in /etc/default/grub:

change to:

GRUB_TERMINAL="gfxterm serial"

add following line after theme definition:

GRUB_SERIAL_COMMAND="serial --unit=0 --speed=9600 --parity=no"

add console=ttyS0 to GRUB_CMDLINE_LINUX_DEFAULT

To apply changes run:

update-bootloader --refresh

Accessing console works:

virsh console --safe --force <guest_name>;