Cannot control grub2 bootloader from serial console on HP DragonHawk Server Systems

This document (7016509) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 12

Situation

Running SUSE Linux Enterprise Server 12 on HP DragonHawk Server and configuring the bootloader to use the serial console via yast2/system/bootloader, the grub2 boot menu is displayed correctly on the serial console but keyboard input is not reliably working.
Allowing the timeout to expire, the system will boot correctly.

Resolution

Run YaST2 bootloader and make sure to UNCHECK both

"Use graphical console" AND "Use serial console"

A text console is picked up automatically then and redirected by the UEFI firmware's vga driver to the serial console.
After that the grub2 menu is accessible from serial console again.

Cause

Additional Information

This can be fixed without the help of YaST2, but it is required to set LOADER_TYPE="none" in /etc/sysconfig/bootloader, otherwise there may be unwanted side effects when YaST2 interferes.

Edit /etc/default/grub and set:

GRUB_TERMINAL=console
GRUB_SERIAL_COMMAND="serial --unit=0 --speed=115200 --stop=1 --parity=no --word=8"

then run:

grub2-mkconfig -o /boot/grub2/grub.cfg

to finally create a new grub2 configuration file.

Disclaimer

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