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I'm trying to find out how to power off the backlight in a device I'm using with a built-in screen.

I believe that DPMS works with the screen, but X is not installed, so I can't use xset. I thought the non-X11 alternative was setterm and I've tried (as root) the following:

setterm -powersave powerdown > /dev/tty1

to set the DPMS state when the screen is blanked. However, I get the following error:

setterm: cannot (un)set powersave mode: Invalid argument

I get a similar error on other Ubuntu installs on different hardware and for any variation on the -powersave options listed in man setterm.

Why am I getting this error? Is there another (non-X11) way to send DPMS commands to the hardware?

Background

The device is an O2 Joggler (based on the OpenPeak OpenFrame 7) which has an i386 architecture (Intel Atom). I'm running a slightly modified community-supplied version of 12.04.02 server.

This modified version comes with a driver which provides sysfs screen control, including a writeable psuedo-file to supposedly switch off the backlight, but you can still see it glowing in a darkened room. I'm hoping there will be a way to power it down completely.

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The source of the error turns out to be that the setterm command is picky about what can be redirected and what cannot. You can do this:

setterm -clear all > /dev/tty1

from an SSH session to clear the physical console, but you cannot issue any -powerdown commands in the same way. I don't know why this is.

For the record, issuing setterm -powersave powerdown from the console is accepted, but does not appear to be doing what I want for my hardware - there's no apparent difference to just setting the brightness to zero (there's still a faint light from the screen in a dark room).

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