...
qdel - delete jobs from torque scheduler - list job numbers followed by space between them ( example - qdel 100134 100145 ... )
qdel all - delete all jobs. This can be used during maintenance.
lshw - see the hardware details of machine
halt -p now - poweroff the machine immediately. Or shutdown -h now will so the same thing.
touch /etc/nologin or vi /etc/nologin with text - won't allow users except root log in. This file will be removed automatically after system reboot.
rm /etc/nologin - allow users log in