Comment # 52 on bug 1188745 from Stefan Dirsch

(In reply to Stefan Dirsch from comment #51)
> On sle15-sp5 the setup works, i.e. systemctl enable/start
> kexec-load.service,but then
> 
> $ sudo systemctl kexec
> No kexec kernel loaded and autodetection failed.
> Automatic loading works only on systems booted with EFI.

I was legacy booting from an USB stick into an installed system (broken grub
install on harddisk). Now I UEFI-booted from the USB stick into  the installed
system. Now I can run

$ sudo systemctl kexec

[...]
[ OK ] Reached target System Shutdown.
[ OK ] Reached target Late Shutdown Services.
           Starting Reboot via kexec ....

That's it. Linux console switching is dead. Still you can change the Numlock
switch LED. But that's it. It doesn't look like kexec would still work with
SP5, let alone SP6.