The GNU/Hurd does not use SYSV runlevels, so commands like

# shutdown -h now

will not work. Simply use the equivalent shortcuts

# halt
# reboot

to respectively shutdown and reboot Hurd, provided natively, instead of from SYSV runlevels.

GNU Mach does not have APM or ACPI support, so it will just stop with In tight loop: hit ctl-alt-del to reboot, and you can switch off the system.