Someone told me that it's possible to group machines you want to shutdown together, and that you can turn them off using the standard
shutdown command in bash.
How would one go about setting this up?
Assuming you have ssh access set up on all computers in question something like
while read host; do ssh "root@$host" shutdown -h now & done < host-list
should work. If you need it configurable just put the host list into a config-like file.