I want to power off my monitor at system shutdown. Tried the following:

sleep 10; xset dpms force off; poweroff

xset command turn off the monitor, but then poweroff exits from X and turn monitor on again in console mode, I can see various messages as in any usual shutdown, and finally after system poweroff, my monitor goes in stand-by status, with the usual flashing stand-by led.

But I want the monitor off when system has terminated the shutdown process.

So is there a way to launch a command and obtain:

  • poweroff

  • monitor completely turned off

  • You might have a setterm --powersave powerdown command to apply to the console video, but I don't know where you might place this command.
    – meuh
    Jun 3 '20 at 19:26
  • What do you mean by the monitor being off? As long as the monitor's power button is on, it is not completely off.
    – D. SM
    Jun 4 '20 at 0:54
  • I mean: - black screen (off) - and no flashing led as in powersave mode.
    – Joe
    Jun 5 '20 at 8:32
  • I tried setterm in rc.0 init script (slackware), it seems to work: during shutdown the screen is turnef off with no flashing led. The problem is that when shutdow has completed and the PC is off, the monitor turns on and goes in powersave mode with its falshing led again, as usual. Monitor model is Dell U2415: may be there isn't any way to put it really off by operative system command, and the only way to turn it off is by pressyng its power button. If I press the monitor power button and then turn off the pc, It doesn't turn on again when shutdown is completed.
    – Joe
    Jun 5 '20 at 8:32

Based on arch linux wiki: If our monitor supports Display Data Channel Command Interface, we can "hardware control" it by console with ddcutil (as root):

Get infos about monitor DDC/CI capabilities:

# ddcutil capabilities
Feature: D6 (Power mode)
     01: DPM: On,  DPMS: Off
     04: DPM: Off, DPMS: Off
     05: Write only value to turn off display

In my case it's a Dell U2415 monitor, and the above output confirms it supports DCC "power mode" feature. To turn it off in the same way we cand do by pressing power button by hand:

# ddcutil setvcp D6 05

If I try to launch that command followed by poweroff, the screen turns off, and the system is shutted down. After that, the monitor rests turned off, as I wanted.

Note: With ddcutil can be controlled also brigthness, contrast and many other hardware features supported by the monitor.

Hope this helps! Bye

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