unicorn but my screen didn't go black and my CPUs were still running. I wish my screen could go black and the CPUs could stop working.
If you want to suspend the laptop, then try:
sysctl -w hw.acpi.sleep.state=3
or, use the Fn + Sleep
key combination.
Be aware that a) wakeup might not work, and b) even if it does, not all devices may come back up. On my laptop, external USB devices (mouse, keyboard) and the laptop's PS/2 keyboard don't respond after a wakeup. Pressing the power button (which causes a controlled shut-down) is the only option.
If you just want to turn off the screen, do:
sleep 1; xset s activate
if you're in X; on the console, do:
screenblank -b
Or, even this (if you have working DRMKMS on an Intel GPU):
drvctl -S i915drmkms0