Shutting down at 6:30 AM?

We're having cooling maintenance carried out on Monday morning at 7:30 (yes AM!). As nobody likes getting up so friggin' early in the morning, here's how I'm going to shut down the servers nicely at 6:30. The command is simply called 'at'.

You envoke it by 'at <time>', e.g.:

# at 6:30

> shutdown -hP [Ctrl-D]

Here is where write the command being carried out .. when you're done, simply exit with a [Ctrl-D]. You wil be greeted by a message like

job 3 at 2012-06-29 6:30

The integer is the job id. You can also be more specific:

# at 6:30 monday

Jobs are executed only once. List your current at jobs with atq:

# atq

3    2012-06-29 6:30 a root

And cancel your at jobs with atrm (using the job id):

# atrm 3

Back to the problem at hand. We have a bunch of compute nodes, named *unray (i.e. bunray, gunray, funray, zunray, punray, wunray, runray,). Since I don't want to manually SSH into every node, I use SSH-keys and a for loop. All nodes mount the same /opt/folder. I put a file containing the command "shutdown -hP now" in /opt/scripts/shutdown.txt. at reads commands from a file via the -f switch. Now it is very easy to make all nodes receive the at command:

for i in b f g z p r w

do

ssh root@$i\unray at -f /opt/scripts/shutdown.txt 6:30am monday

done

Happy at'ing!