How to set up serial console boot for headless (no graphical) boot

This document (000019728) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server 15

Situation

KVM Guest should be fully controllable by serial console

Resolution

Add following to the xml configuration file of the kvm guest:
/etc/libviretd/qemu/<name>.xml
<os>
<bios useserial='yes' />

To enable boot menu:
<os>
<bootmenu enable='yes' timeout='3000'/>

Cause

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>;

Additional Information

Booting from ISO works after hit return or press cursor up/down is needed to see boot menu.

Disclaimer

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