You need to be root. So, add
sudo in front.
shutdown -P 0
shutdown -r 0
pm-suspend(aka sleep. Fast wake.)
pm-hibernate(save most power. Slow wake.)
pm-suspend-hybrid(a combination of sleep and hibernate.)
pm-is-supported(test which is supported)
man pm-suspend to see its doc.
Sleep mode, also known as Suspend, Standby, puts your computer to a low power mode. The monitor is turned off, and RAM (memory) chip gets minimal power to sustain its data. Computer can quickly wake.
Hibernation mode saves more energy. It is similar to a complete power off. It saves RAM (memory) content to disk, and powers down spinning hard disk. However, hibernation takes longer time to wake up.