To shut down a Ubuntu system on s390x in a controlled way you need to use of the commands reboot, poweroff and shutdown (that all point to systemctl) or halt, since you usually work on Ubuntu systems from remote using a ssh connection. Ubuntu systems running in LPAR can also be stopped using the HMC, as well as Ubuntu systems running on z/VM with a CMS command like force, but all this is usually less graceful than using one of the above Linux commands.

Be careful using a key combination like Ctrl+Alt+Del to shutdown or reboot a remote system, because this key combination may have an effect on your local workstation rather than the remote system.

Just use reboot to reboot the system and halt to halt the system without powering it off ^[13]. To power off the machine, use poweroff or shutdown -h now. The systemd init system provides additional commands that perform the same functions; for example systemctl reboot or systemctl poweroff.