When I try to power off terminal and click "Ausschalten" on LDM screen this
doesnt work, I have to push on/off switch for 5 sec.
As a solution I could set acpi=force grub parameter:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi=force"

How can I do this for my terminals?

allready tried in /var/lib/tftpboot/ltsp/amd64/pxelinux.cfg/default:
append ro initrd=initrd.img root=/dev/nbd0 init=/sbin/init-ltsp quiet splash
acpi=force plymouth:force-splash vt.handoff=7 nbdroot=:ltsp_amd64
with no success

Regards Marco