Bdtyktl

To turn off monitor in console, the command is the following:

sudo vbetool dpms off

To regain control of the console on pressing Enter key, I suggest

sudo sh -c 'vbetool dpms off; read ans; vbetool dpms on'

Try these commands...

To Turn Off:

xset -display :0.0 dpms force off 

To Turn On:

xset -display :0.0 dpms force on 

If your display turns off and then immediately back on then try the following which adds a delay of 1 second before turning the screen off. This give a chance for all events to be processed by the X server before turning the display off.

sleep 1 && xset -display :0.0 dpms force off 

The xset command mentioned in other answers will turn off all the monitors if you have multiple monitor setup. However if you want turn off only one or some of the monitor you should use xrandr.

First run xrandr -q command, which will list all the monitors and its current display settings. At the start of each monitor details you will find monitor name set by the system. You have to keep track of that.

I have two monitors (one is connected to DVI port and other to VGA port) and when I run the command I see this:

Screen 0: minimum 320 x 200, current 1360 x 768, maximum 2726 x 2726

DFP1 connected 1360x768+0+0 (normal left inverted right x axis y axis) 304mm x 228mm

   1360x768       59.7*+

   ... (more details are shown here, but I have hidden it)



CRT1 connected 1360x768+0+0 (normal left inverted right x axis y axis) 410mm x 230mm

   1360x768       59.8*+   60.0  

   ... (more details are shown here, but I have hidden it)

In this output, DVI port connected monitor is labelled as DFP1 and other one as CRT1. So if I want turn off the secondary monitor(i.e., CRT1) I have run this command:

xrandr --output CRT1 --off

if you want switch on that monitor again then you have run this command:

xrandr --output CRT1 --auto

If you have multiple monitors use this:

Turning off your second monitor:

(Assuming CRT-0 is your left monitor and CRT-1 is your right monitor)
xrandr --output CRT-1 --off

Turning on your second monitor:
xrandr --output CRT-1 --right-of CRT-0 --auto

This way xrandr knows not to duplicate the first screen.

I've just installed Ubuntu Server 18.04.1 (no GUI, X, nor anything graphical), and after breaking my back last night trying to turn off the screen I finally found the magic command:

setterm --blank 1

After execute the command the screen will turn off automatically every minute (if idle).

Enjoy!

I use Ubuntu-MATE 16.04 and had problems with xset dpms .... Screen went briefly off, but came instantly back after 1 second.

What did work (if 'suspend' is okay for you in the sense of: black screens and also not doing any computations & services while you're away...) is:

systemctl suspend

(found this advice here)

Beyond command line, I enjoy using it as a custom shortcut from it (noone needs F1 'help' anyways… :+))