Ubuntu, Debian, etc

Editar o arquivo /etc/rc.local:

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

# shutdown everyday at 6 am
shutdown -h 06:30 &

exit 0

Isso ajudou?