This article explains how to turn off screen in Linux using command line.
In TTY mode
If you have physical access to the machine, run the following command
$ setterm --blank 1
This will turn off the screen after 1 minute wihout activity.
If you only have remote access to the machine (e.g. through SSH), you can do the following
$ setterm -term linux -blank < /dev/tty1
where tty1 should be replaced by the actual tty you want to turn off. Use who command to figure out which tty is the one that is attached to the monitor.
In GUI mode
To be continued…